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GASTAR 3.2 USER MANUAL

1. POOL UPTAKE SOURCE MODEL Sis 4 Meteorology Wind Speed m s Air Temperature K 290 Wind Speed Height m 10 Atmospheric Pressure mb 1024 Roughness Length m 0 0001 Relative Humidity Zz 150 PG 7 Monin Obukhoy Definition Use Pasquill Gifford Categories C Use Monin Obukhoy Length A E Eeke MEME ee Wind speed in metres per second Figure 5 1 The Meteorology folder for the pool uptake model 5 2 2 Source input for the pool uptake model The Source input Figure 5 2 defines the details of the release itself Because this relates to the pool the Source folder has little in common with the equivalent GASTAR Source folder apart from the choice of source material 63 GASTAR Section 5 Pool Uptake Model POOL UPTAKE SOURCE MODEL E x Source Material From Database hore T ec ueDefned Pool Details Continuous C Time Varying Pool Width m Mass Flux from Pool kg s Cloud Details Initial Cloud Volume nr Hazardous Fraction ppm 1000000 Initial Cloud Diameter m EERSHIE Cloud Temperature K 227 76 Lateral extent of the evaporated material in metres Min 0 01 Max 1000 Figure 5 2 The Source folder for the pool uptake model A brief description of the Source input parameters is given below 222 2 Source material The Source Material section here is a simplified version of that on the GASTAR Source folder It is linked directly to the controls on th
2. GASTAR Section 2 Using GASTAR Radio buttons TCURSOR will move the cursor up through the radio buttons for the current item lt CURSOR V CURSOR will move the cursor down through the radio buttons for the current item CURSOR In general if a letter in the name of an interface item is underlined then pressing the ALT key with the key for that letter will trigger that interface item For example the File menu has the letter F underlined on the screen Pressing the ALT and F together will open the menu Additionally the SPACE bar can be used in a similar way to the mouse click the control with the focus i e where the cursor is will be clicked 2 2 Main features of the GASTAR interface As noted in Section 2 1 the main screen of the GASTAR interface is made up of menus and folders together with some areas providing information In this section we list the options available GASTAR 3 2 untitled l Run Help New Complex Effects Open Save From Database gona Save As User Defined Open Template Save As Template Momentum Initially Well Mixed Isothermal Release 5 R Thermal Release Preferences r Concentrations in ppm Run Time Aerosol Release View Output isi Graph Printing aiii viewing Output Release Start UTC 12 00 08 Apr 2009 7 GASTAR Output Initial Air Entrainm Puff Diameter m Mass kg Hazardous Fraction mol mol 10 Temperature K Ae
3. Figure 3 6 Definition of jet height and elevation vertical section through the jet 3 2 3 11 Height of jet source For Jet Releases only This is the height of the jet source above ground level see h in Figure 3 4 and Figure 3 6 Minimum 0 0 m Maximum 100 0 m 3 2 3 12 Azimuthal angle for jet source For Jet Releases only This is the horizontal bearing of the jet at the source This is measured in the same manner as the wind bearing clockwise from North in degrees and represents the direction from which the jet is coming see 0 in Figure 3 7 Minimum 0 0 deg Maximum 360 0 deg 31 GASTAR Section 3 Entering Input PLAN VIEW 0 jet bearing azimuthal angle U wind direction x zz Jet direction E Figure 3 7 Definition of jet bearing 3 2 3 13 Elevation angle for jet source For Jet Releases only This is the elevation angle of the jet at the source This is measured from the horizontal and is positive if the jet is pointing upwards see Figure 3 4 and Figure 3 6 Minimum 90 0 deg Maximum 90 0 deg 3 2 4 Flash calculation When choosing an Aerosol release type on the Source folder you will enable the Flash calculation button to the right of the Aerosol Fraction textbox This utility is useful when you need to model the release of a material with a boiling point below ambient temperature stored in a pressurised container at ambient temperature When suddenly released these materials fl
4. Knudsen and Krogstad 1986 and Jindal 1989 Figure 8 8 and Figure 8 9 show a prediction for the radius and concentration of an instantaneous release dispersing over level terrain compared with predictions for dispersion up and down a small slope The level terrain case corresponds with conditions experienced during Trial 15 of the Thorney Island Phase 1 tests and the predictions of the model are in agreement with the experimental data for that trial The effect of the slope is seen in that a narrow faster moving cloud is produced when the wind is blowing down the slope In contrast the centroid of the cloud initially moves in an upwind direction in the case when the wind is blowing up the slope Having experienced some dilution there the cloud then moves off in a downwind direction up the slope giving the lower concentrations seen in Figure 8 9 101 GASTAR Section 8 Theory 100 10 S 6 gt Downslope 5 o so 1 No slope x G Upslope 5 e pS op O 0 1 0 01 1 10 10 10 10 x centroid m Figure 8 9 Effect of Slope on Centreline concentration The x coordinate is in the direction of the wind The above development for modelling the release of dense gas on slopes assumes that the ambient velocity field is known Thus we must consider the influence of the slope on the wind field Extensive on site field measurements could provide this separately alternatively three other approaches could be considered a Es
5. This is because there can be no gaps in the definition of slopes There is no warning before the slope is removed Slopes Defining Slopes Distance m Angle Roughness Length m Wind Speed m s Wind Height m Cancel Distance from the source along the slope vector to the start of this slope Min 1E 99 Max 1E 33 Figure 3 16 The Slope Definition dialogue box 3 4 1 6 Defining slopes The Slope Definition form shown in Figure 3 16 is where you define and edit the slope data A more detailed description of each parameter follows Poz angle for slope segment 2 positive in this example CROSS SECTION o angle for slope segment 3 negative in this example Dg distance to start of slope segment 2 negative in this example Dg distance to start of slope segment 3 positive in this example Source Horizontal Slope Vector Figure 3 17 Vertical section through the sloping ground parallel to the slope vector 43 GASTAR Section 3 Entering Input 3 4 1 7 Slope distance This is the distance measured in metres from the source along the slope vector to the start of the slope segment in question see Figure 3 17 Remember that the slope vector is directional and therefore these distances can be positive or negative The first slope will start at the model actually uses a large negative number and this value cannot be changed If you edit the first slope the Dist
6. and you will be prevented from entering values outside this range 2 1 3 3 Message box Message boxes are a particular type of dialogue box They may give you a brief message or they may ask you to make a simple choice such as yes or no For example a message box appears when you select Plot Graph on the Graphics folder if an output file has not been selected 2 1 4 Navigating using a keyboard Microsoft Windows environments have been developed with a mouse in mind If you do not have a mouse or prefer not to use it your Windows user guide and help files will explain how to reproduce all mouse actions using a keyboard Here is a brief guide to some useful actions Moving the cursor between input items TAB Allows you to move the cursor forwards through text boxes and buttons SHIFT TAB allows you to move the cursor backwards through text boxes and buttons RETURN enters or accepts the current data page or executes the action of a highlighted button Entering data into a text box DELETE will delete the character immediately to the right of the cursor BACKSPACE will delete the character immediately to the left of the cursor lt CURSOR will move the cursor to the left in the current box CURSOR will move the cursor to the right in the current box HOME will move the cursor to the start of the text in the current box END will move the cursor to the end of the text in the current box SHIFT CURSOR selects text in the direction of the arrow
7. crosswind position of cloud centre puff at given time Z m vertical position of jet centreline at X Y zero for grounded jets and all other release types C mol mol concentration Cmax mol mol maximum concentration value in a cross section when concentration profiles have been applied MF mass fraction i e as concentration C but based on mass W m cloud diameter for puff releases otherwise cloud width H m cloud height V flux m or m s volume for puffs volume flux for all other release types U m s cloud advection speed M flux kg or kg s total mass for puffs mass flux for all other release types E flux kJorkJ total enthalpy for puffs enthalpy flux for all other release types Ambient conditions define zero level T K cloud temperature Rho kg m cloud density AF aerosol fraction mass of liquid as a fraction of total cloud mass Ri Richardson number based on friction velocity cloud density and height Xle m puff releases only leading edge position relative to source based on diameter W Xte m puff releases only trailing edge position relative to source based on diameter W Wtot m lateral width of cloud taking into account turbulent spreading oy Mainly important for passive clouds Wdisp m puff releases only width in downwind direction taking into account turbulent spreading o and shear dispersion o Mainly important for passive clouds Area m puff releases only area of cloud based on
8. Maximum 1200 0 mb 3 1 8 Relative humidity A real number giving the relative humidity of the air as a percentage Minimum 0 0 Maximum 100 0 3 1 9 Atmospheric stability Radio buttons that allow a mutually exclusive choice between entering the stability conditions in terms of the Monin Obukhov length Lmo or the Pasquill Gifford stability category PSC see Section 8 2 2 for more on the relationship between the Monin Obukhov length and Pasquill Gifford stability categories 3 1 9 1 Monin Obukhov length This is a real number relating turbulence to the heat flux and friction velocity It is measured in metres and can be thought of as giving the relative importance of heat convection over mechanical turbulence Theoretically it can take all values between but in reality its modulus is unlikely to fall below about 2 Minimum modulus 2 0 metres Maximum modulus 1000000 0 metres 3 1 9 2 Pasquill Gifford stability category PSC This is defined by a mutually exclusive choice of 7 buttons each representing a letter between A and G inclusive This is another method of indicating the relative importance of heat convection and mechanical turbulence by dividing the meteorological conditions into fairly simple bands For instance A means extremely unstable conditions and therefore strong convection with large vertical dispersion D represents neutral conditions turbulence is purely mechanical and G is stable conditions where the mechanica
9. matches the letter typed The command button will allow you to View Data in table form This interface will not allow the addition deletion or modification of materials in the database the database editor see Section 6 is required in order to do this If the material is User Defined the material name appears on a non editable panel In order to create and or change any of the properties of this substance from the values given in the database click on the button now marked Edit User Data to bring up the database and editable text boxes This option is not recommended 3 2 2 Release type There are two main choices for the release type each represented by a mutually exclusive array of choice buttons the radio buttons to the left distinguish between Instantaneous Continuous 25 GASTAR Section 3 Entering Input Time Varying and Jet releases described in the rest of this section while the group buttons to the right define whether the release is Isothermal no temperature or phase changes Thermal temperature changes allowed but single phase or Aerosol two phase with temperature phase changes 3 2 2 1 Instantaneous release For instantaneous releases the initial volume Vo is calculated using the mass released and prevailing Meteorological and Source conditions The initial puff diameter Do is specified The initial puff is assumed to be a right circular cylinder The initial height of this cylinder is then given by Ho Vo I4 n
10. transfer correlations Phase changes of the released material or water vapour in the atmosphere are based on an assumption of homogeneous thermodynamic equilibrium The thermal codes use an enthalpy balance with surface heat transfer inputs given by the maximum of the forced and free convection heat transfer coefficients multiplied by the relevant surface area The heat transfer coefficients used are 84 GASTAR Section 8 Theory 3 1 2 h free of E AT 21 vaT and 22 C m 2 3 Reed 7 pc forced P p 2 2 where k is the thermal conductivity v the kinematic viscosity a the thermal diffusivity C the specific heat at constant pressure Cy the surface skin friction coefficient T the cloud temperature AT the surface cloud temperature difference and U the reference velocity given by U U2 au2 23 where U is the advection velocity of the cloud and U is the front velocity due to the negative buoyancy of the cloud The constant a is 2 3 for puff releases and 1 2 for plume releases 8 2 4 Thermodynamics The aerosol model is an homogeneous equilibrium model which assumes that the liquid droplets are in thermodynamic equilibrium with the uniform concentration puff or plume cross section That is the cloud with a given enthalpy flux based on source conditions and any subsequent ground heating adopts a temperature 7T and an aerosol mass fraction such that the partial pressure of the released vap
11. 3 267 78 119 GASTAR Section 9 References Havens J A amp Spicer T O 1985 Development of an atmospheric dispersion model for heavier than air gases US Coast Guard Report CG D 23 85 Havens J A Spicer T O amp Schreurs P J 1987 Evaluation of three dimensional models for atmospheric dispersion of LNG vapor International Conference on Vapor Cloud Modeling Boston A I Ch E C C P S pp 495 538 Hopfinger E J 1983 Snow avalanche motion and related phenomena Ann Rev Fluid Mech 15 47 76 S Jindal M 1989 A wind tunnel study of dispersion of dense gas released on sloping terrain M Sc thesis N Carolina State Univ S Knudsen S L and Krogtsad D A 1986 Dispersion of a heavy gas cloud driven up a slope SINTEF Report STF 15 F86068 S Koopman R P et al 1982 Analysis of Burro Series 40m LNG spill experiments J Hazardous Materials 6 43 83 K nig G 1987 Windkanalmodellierung der Aubrietung strfallartig fregestzter Gase shwere als Luft Hamburger Geophysikalische Einzelschriften Nr 85 Verlag Wittenborn amp Sohne Hamburg S Lighthill M J 1956 Drift J Fluid Mech 1 31 53 O Linden P F and Simpson J E 1988 Development of density discontinuities in turbulent fluid Stably stratified flow and dense gas dispersion Ed J S Puttock Clarendon Press Oxford O McQuaid J 1976 Some experiments on the structure of stably stratified shear flows SMRE Technical paper
12. 3 2 Materials gdb Molecular Density Latent Heat Cp Cp 70 91 1563 288 1 0 892 238 7 288 Chlorine Dimethyl Ether Ethylene Ethylene Oxide Hydrogen 2 01594 70 78 Hydrogen Chloride 36 461 1193 Hydrogen Sulphide 34 08 993 iso Butane 58 12 609 Methane 16 043 422 36 Methyl Bromide 934 34 1662 Fit hlnride Fn ARA 1050 Curent Database Record 0 4796 Name Chlorine Toxic Exponent Mol wt g mole 70 81 Cp lig kJ Kka l Probit Density kg m3 Heat Transfer Gp A Probit B Boiling Pnt K 238 LFL Antoine 4 Heat Yap J g UFL Antoine B Cp v kJ Kkg 0 4798 Prandtl No Antoine C Cancel Figure 6 1 The material properties database editor Material Data D GASTAR 3 2 Materials gdb Molecular Density Material name Weight Liquid Boiling Point Latent Heat Cp Vapour Vapour 1 2 Butadiene 54 091 676 284 448 63 1 482 1 3 Butadiene 54 091 673 268 69 415 33 1 474 1 Butene 56 107 645 266 9 390 61 1 595 Acrylonitrile unreferenced 53 064 806 350 5 615 1 2 f Ammonia 239 82 2 1647 i 0 0213 Boron Trichloride 0 0216 0 452 0 0149 Chlorine 0 892 0 0154 Dimethyl Ether 2 219 0 0304 2 433 0 0248 User Supplied Data Name LiPs Chlorine Toxic Exponent Mol wt g mole 70 9 Cp lig kJ Kkg Probit Density kg m3 156 Heat Transfer Gp Probit B Boiling Pnt K 238 7 LFL
13. 31 e for unstable ambient stratification categories A C o 2 0h 32 There is a small interpolation region such that o 4s t Zo 33 if O gt 1 L gt 0 01 In equations 31 and 33 L is the Monin Obukhov length The overall characteristic longitudinal scale of the puff is GETAH 34 8 2 7 Concentration profiles The uniform puff or plume concentration is determined from a mass balance The assumed profiles in the horizontal are a uniform concentration with error function edges in order to represent a puff or plume with a central uniform concentration being eroded at the edges by ambient turbulence When the two eroding edges eventually overlap substantially the merged error functions produce the conventional Gaussian distribution The edge erosion is modelled by appeal to conventional passive dispersion results Currently the formulation proposed by Hanna Briggs amp Hosker 1982 is used The vertical concentration profile for ground level sources in passive plumes is typically of the form exp z not exp z though this is commonly employed as a useful approximation in Gaussian plume theory There is no evidence that the concentration profile is exp z where a is the power law exponent in the mean velocity profile 87 GASTAR Section 8 Theory The model uses observations from the field and laboratory to justify the vertical concentration profile of the form exp z when the puff or p
14. Air initially mixed with the released material in 0 Max 1000000 Figure 2 1 Example view of interface 2 1 2 1 Enabled and disabled item Items in the interface can either be enabled in which case they are available for use or disabled in which case they cannot be used Disabled items appear grey rather than black 2 1 2 2 Text box Text boxes allow you to enter text data When you move to an empty text box an insertion point a blinking vertical cursor appears The text you type appears at the insertion point Each text box is accompanied by a caption which explains the significance of the text in the box for example Temperature K in Figure 2 1 Text boxes which cannot be edited appear dimmed 2 123 Check box Check boxes allow you to set or clear an option When a check box is set it contains an X for example Momentum Initially Well Mixed in Figure 2 1 You can set or clear a check box by clicking it with the mouse or by pressing the SPACEBAR provided the check box is selected If it is selected it will have a dashed box around it 2 1 2 4 Radio button Radio buttons represent a group of mutually exclusive options i e you can select only one option GASTAR Section 2 Using GASTAR at a time and if you select a new option the previous one becomes unselected The selected option contains a black dot for example Instantaneous in the group of four radio buttons under Release Type in Figure 2 1 Names of options which
15. Antoine 4 Heat Vap J g 288 UFL 2 Antoine B Cp v kJ Kkq Prandtl No Antoine C Figure 6 2 Editing a material properties database 69 GASTAR Section 6 Database Editor 6 1 3 Changing the materials database The materials database Materials gdb is supplied as a read only file that has a simple comma separated format It is up to each licence holder to decide who should have the ability to edit Materials mdb in order to add a new material that then can be used in any gpl file delete an existing material or edit the properties of an existing material To make changes to Materials mdb firstly change the properties of the file from read only so that it can be edited You can do this by right clicking on Materials mdb in Explorer selecting Properties and then under Attributes uncheck the box labelled Read only Then open the file in Notepad Figure 6 3 or Excel The first line contains the names of the variables Each following line contains the properties for each material Materials can be added or deleted or properties edited After the change has been made and Materials gdb saved it is advisable to change the properties of Materials gdb to be read only again to prevent accidental changes P Materials gdb Notepad File Edit Format View Help Name Molecular weight Density Liquid Boiling Point Latent Heat of Vapourisation specific Heat Capacity Cvapour Specific Heat Capacity Liquid Heat T
16. Do The initial temperature To for Thermal and Aerosol cases initial aerosol fraction for Aerosol cases initial concentration Co and initial density po are assumed to be uniform over the initial volume For Instantaneous releases check Momentum Initially Well Mixed to select whether the initial conditions of the puff momentum are well mixed or not well mixed The default is for the momentum to be initially well mixed This option is used to determine the initial conditions for puff momentum mixing Typically instantaneous releases are a result of some catastrophic event such as a tank rupture or explosion In these cases it is easy to see that internally the puff will have a well mixed momentum For some situations this is not true for example the Thorney Island instantaneous heavy gas dispersion trials Here the cloud was created inside a large tent like construction that dropped to the ground to release the puff The material effectively appeared as a large stationary puff which slowly picked up speed as the wind advected it away It would be more appropriate to model this case assuming the momentum was not well mixed initially The effect of this is to make the cloud advection velocity start from zero and gradually grow When the Momentum Initially Well Mixed option is chosen this reduction factor is not used and the cloud advection velocity is non zero from the start of the modelling process 3 2 2 2 Continuous release For continuo
17. Line Plotting option The Graphics folder allows you to select the variable s you wish to plot which output file s to take the data from and the type of plot 32 GASTAR Section 4 Viewing Output 4 1 Selecting data to plot 4 1 1 Selecting data files for plotting This involves selecting one or more graphical data gph files using the File Details controls Use the Drive list box at the top to select the drive from which you wish to plot data This conforms to the Windows standard and will show any drive that is currently mapped by your system make sure that the drive you want to use has actually been mapped e g using Map Network Drive under Tools in Explorer so that it will appear in this list box You then use the Directory list box in the middle to navigate to the correct directory on the drive Once there all the available output data files in that directory will appear in the File list box at the bottom Click on the data file you wish to plot in the File list box If you wish to plot from multiple files do so in the normal Windows way by holding down the SHIFT key and clicking on the final data file you want to plot To select multiple isolated files from the list hold down the CONTROL key and click on those files you want to plot When you have selected one or more GASTAR data files the Plot Graph button will become enabled signifying that data are available to plot If you have just run the model in the directory current
18. MEL cnt AE 25 3 2 3 Source detall Snaar n a eSa ARRES TENES S 28 3 2 4 Elash caleulation 80 eR oer EA A E E E E E dea o eee 32 GASTAR Contents 3 3 Complex effects z ODSTACIOS s Lacs ise ertet aves tros taste dede ed del Poste e RUN 34 3 3 1 Obstacle SUHBImiaby issnin ieia a eE i sie bn s Eie RE eiS 34 3 3 2 Defining obstacl s Sea E us Ca dui tla OR E E T 35 SA X omplex effects SIODOS ad dt e d vsu ede qae du datas 39 3 4 1 Slopes SUA y aas o aiat sue ea duae Mtn da dE du a 40 3 5 Output letdll SS dos sois vestib a medicum obuia oM wach EAN N 46 S NIE Tl bp b NM obiecit da E qu det eet 46 3 5 2 Modelled Mein ne eser er ca rud b esset dots e cece 46 3 5 3 Noct e E rE a ETA E R AE 47 3 5 4 Specified Output Ponts cs reite iot i e e lot a petet 47 3 5 5 Specified Output Times ss eie eti eS HAS eee ERR Een oTt H PER nen EAE Ee bonbderenvecte 48 3 5 6 zxdditonal OUI UU cc pudeat e eor eda USE OE QUAS ea nut E ue AERE 48 Viewing and Plotting Output eee eere eee eee ee ee esee eese eese e eese e eoo e tes eese 52 4 1 Selecting data to plot 3 52 ete di E lie tse ene 53 4 1 1 Selecting data files for plotting i ii per eee I chose saben Seasteastienned ganvscentdevshes tae 53 4 1 2 Selecting the graph type esce cet cadedatasapeacevenvad R a s is 53 4 1 3 DAV plottin T PP 53 4 1 4 Elammables plotting ccccissececisaccedvaspuvasdessseecdavsavessisdysaees e enii 54 42 Plotting aiid viewing datas uui d
19. Termination box Application is automatically closed at end of run 3 No Termination box Application is retained at end of run Note that Exit mode 2 is needed for setting up multiple runs using BATch files in DOS See Section 2 4 2 for more details 254 2 GASTAR input mode This flag is compulsory Mn Flag to set the Input Mode for GASTAR The value of n can be 1 Look for GASTAR input file gpl 2 Look for RISKAT input files mat bmi bsi slp bsys dat bconc in 2 7 1 3 GASTAR output mode This switch is optional Op Flag to set the Output Mode for GASTAR The value of p can be Produce GASTAR output files log gof gph 2 Produce RISKAT Toxic file bc 3 Produce RISKAT Flammable file flm This flag is optional but the following defaults apply GPL Input Mode will default to GASTAR output og gof gph RISKAT Input Mode will default to Toxic output bc 18 GASTAR Section 2 Using GASTAR 2 7 1 4 Command line file names This argument is compulsory File name s The file name s which must include the full path i e drive and directory The interpretation of this argument depends on the input mode In GPL GASTAR will read all non flag items given on the command line as file names These are executed in the order they appear on the command line If these are list st files the contents are read and each line interpreted as a GASTAR input data gp file name and executed in the order give
20. Two factors are introduced to reduce the entrainment close to the source A factor f given by f win sx 63 is incorporated into the first entrainment velocity term equation 61 to account in part for a region of flow establishment The second entrainment velocity term equation 62 will not be significant when the jet momentum is dominant and so a factor s L 04 min 64 f minl amado 06 64 is introduced In the equation L is a length scale over which momentum is dominant 1 e U 2 L of 2 65 where D is the source diameter and the subscript 0 refers to source conditions Finally both entrainment velocity terms are multiplied by a factor p pa 1 2 to reflect increased entrainment due to dynamic rather than solely kinematic effects The third entrainment term accounts for the effect of ambient turbulence and this will be more significant as the influences of momentum and buoyancy decline away from the source The intent is to smoothly link the model into the conventional ambient turbulence dispersion curves by Briggs 1973 Rather than switch from an active to a passive description with the attendant difficulties of the selection of a transition criterion we have differentiated the Briggs curves and introduced the differential curves into the entrainment formulation This requires a third entrainment term of the form zp U z 10 66 8 3 3 2 Interaction with the ground W
21. Windows esee nennen 12 2 4 2 Running GASTAR from DOS eec reti teo a m a ease needs 12 2 4 3 Last Tiles for batch mode deae e Un tod eo ripe and ales es 14 2 4 4 Warning and error messages sois jaccisscvsisiseseeccasescaesdscecsasdseesacceseraedusncensvaseoveats 14 2 5 Examining output from a TUNG 6 002605 Ssuchesegutacegeanaystoendeayauaoeasaseevdaedanaoauastaessadestetans 15 2 0 User preferences e euecosidiete n i OASIS aE E E A E E 15 2 7 GASTAR c mmand lines se a ave ero a eas 18 2 7 1 Switches and ALO UTTIS INES on eae ae aa a a erae iuter a A 18 De dad Example command mess oie ee eiu ca devia 19 Eritering Dass om HIM SERIA EI PEN DU SERERE E NAIUARS UNIONIS MENT RUNE 21 3 1 Meteorology details siis teet I EUR a a a 21 3 1 1 bia ic cci ER a e e e a e e aE 22 3 1 2 Wind height sinant udi es RN EUR A b e MIT CD angie 22 3 1 3 MGE CITE BOTE eyan ee E E EA AE vanedubsDt 23 3 1 4 Ro ghness lengthier etim du usd tei esters E e Gd 23 3 1 5 Air temperatur 2 0 9 ae ee EEE cui ee Be ae ae 23 3 1 6 Suttace temperati Csi oso Socata emm usstobis ubi menda leta IS 23 3 1 7 Atmospheric pressure 0 22 cecdisscceavarsesasdesajsaesannavedaahesaatasqusaddessaceevastesgunadenvadds 24 3 1 8 Relative humidiDy d eye a a vates Sa e saute 24 3 1 9 Atmospheric stability sno 2 etc REIR Erat Y REN E San ERU IE Ve OSEE QUS 24 oV MEE CoU b TIE 25 3 2 1 BSOUFCE TOS p E EEA o te add ita cet E E e s 25 3 2 2 PRG SASS Vy ry ou uestes monu tenu
22. assessment Most of the available experiments have been reviewed by Brighton et al 1993 The model algorithms are not intended to describe complex flow processes near an obstacle but to quantify the net change in cloud features as the cloud interacts with the obstacle thereby providing a step adjustment to the cloud variables at the obstacle position This may be used to estimate the concentrations of the cloud approaching the front face or leaving the rear face of the obstacle although care would be required in assessing the concentrations in the immediate neighbourhood of the obstacle The scenarios for which algorithms have been developed include i atwo dimensional fence solid or porous at right angles to the ambient flow The algorithm has been extended to fences at an angle to the flow although there is less experimental evidence available for such cases i aconfining e g three sided or enclosing fence iii single fences near parallel to the flow inhibiting the lateral spread of the cloud iv two fences or building rows nearly parallel to the flow v single or many isolated arbitrarily shaped and oriented three dimensional obstacles upstream or downstream of the source position such as the porous process areas to be All five scenarios were installed in GASTAR Version 2 24 but only scenarios i and v are included in GASTAR Version 3 00 These current omissions result from Version 2 24 only allowing selection o
23. available for viewing from the Data folder in the Graph Design dialogue box which is accessed via the Graph Setup button 4 3 2 Zooming in on a graph When displaying a linear linear plot you may use the mouse to select and zoom into a region of the graph To do this move the cursor to one corner of the desired region use the right mouse 55 GASTAR Section 4 Viewing Output button to click and drag a region in the graph Releasing the right mouse button at some other point over the graph will allow the region selected to fill the display If the region you select is too small the graph will ignore the selection assuming you have accidentally clicked the right mouse button over the graph To reset the axes click the Reset Axes button which appears to the right of the Current X panel once you have made a zoom on the current graph GASTAR X Y Line Graphics 1000000 100000 D Exa puff2 Max Profile Concentration ppm 10 100 1000 10000 Arc Length m Set 1 4 1410 8 i i Point 44 Y 642 03 Print Setup Close Figure 4 4 Example graph 4 3 3 Configuring the graph The graph is configurable in many ways There is the ability to change much of a graph s appearance including options that are not necessarily applicable to GASTAR output by clicking on the Graph Setup button also see Preferences in Section 2 6 The graphical display comes with its own on line help file which can be accessed via the Grap
24. by the wind The modelling of the cloud movement downwind is based on either entrained momentum or 82 GASTAR Section 8 Theory more simply and valid away from the source on the ambient wind speed at a height representative of the cloud height Referred to as the advection velocity it is given by UU 15 where U z is the wind speed profile and zy 0 56h The coefficient is taken after appeal to passive puff results e g Lagrangian similarity results of Batchelor 1952 or Chatwin 1968 This result is obtained from a consideration of a neutrally stratified boundary layer It is not considered worthwhile to modify this for any explicit influence of atmospheric stability However a dense puff or plume does not travel with the ambient wind velocity the puff or plume perturbs the ambient flow This effect has been accounted for by using a multiplicative factor to adjust the advection velocity given by 0 2 0 8 E 1 Ri 16 The puff is assumed to adopt an advection velocity determined by the ambient velocity profile However for an unmixed release e g the field tests at Thorney Island the puff advection is solely by momentum added to the puff by subsequent mixing with ambient fluid as a result of atmospheric turbulence and the flow generated by the negative buoyancy 8 2 2 Meteorology The required meteorological information for the model is that of e wind speed profile e atmospheric stability and e the depen
25. contour of the given concentration time at which maximum range occurs x and y coordinates of the point s at which the maximum range occurs flag indicating that the maximum range found may be an underestimate since the concentration contour of interest still existed maximum concentration gt concentration of interest at the end of the simulation flag indicating that there was an obstacle interaction around the same time that the given concentration contour disappeared Table 4 2 Summary of additional output information Each set of data may be requested separately in the GASTAR interface Additional Output folders on the main Output folder and appears at the end of the gof file in the order indicated above The abbreviations used in the Release Types column are C continuous I instantaneous T time varying 59 GASTAR Section 4 Viewing Output GASTAR gridded data output file FILE _VERSION real FILE STEM string PATH string WIND DIRECTION real COORD SYSTEM string SOURCE LOCATION string RELEASE DATE AND TIME string TIME_ZONE string POLLUTANT_NAME string CONCENTRATION_UNITS string AVERAGING_TIME_SECONDS real END OF HEADER SECTION integer NX integer NY integer NZ integer NT real T 1 real T 2 real T NT Year Day Hour Time
26. correlations for cloud depth increase are implicitly based on an assumed drag coefficient of unity Consequently we consider solidity in terms of the drag coefficient We expect that decreased solidity will inhibit both the width and height increases The simple approach we have adopted is to include the solidity S in the following algorithms cf equations 89 91 96 and 97 w Vy que Hogu 103 w h w max WS w 0 5 WS 104 dh L s s 105 Ww dh i E z R sa 106 Ri w 3 Multiple Fences and Buildings The code allows for multiple fences and rectangular buildings of arbitrary orientation If the buildings and fences are in close proximity their diluting effects will not be additive Consequently buildings within 2H of a given building will be completely or partially discounted depending upon the extent of overlap in the direction of the cloud trajectory The proximity distance 2H was selected as representative of the extent of the recirculation region for three dimensional surface mounted obstacles 4 Buildings upwind of the source Sources that are within the recirculating region downstream of an obstacle will be influenced significantly by the obstacle Initially quite complex algorithms were considered in order to allow for this scenario However after some experience a simpler alternative has been adopted namely 114 GASTAR Section 8 Theory for any building within 2H upwind of the source the standa
27. each variable you wish to plot Above the check boxes is a list box containing the concentrations that may be plotted i e the LFL and half LFL concentrations highlight one or both of these to select them for plotting lt GASTAR 3 2 D Examples CatastrophicF ailure puffze X File Run Help Meteora Comite Oua Y Graphics File Details Flammables Plotting Details Graph Type Sd C XY Line Plotting Concentrations ppm gis Path D E CatastrophicF ailure IDs CN Examples CatastrophicF ailure Flammable volume rr Maximum height m Maximum range m Max crosswind radius half width m Show Graph Maximum downwind radius m Plot Graph Select one or more files from those listed for plotting Figure 4 2 The Graphics folder showing the Flammables plotting option 54 GASTAR Section 4 Viewing Output 4 2 Plotting and viewing data Whichever type of plotting you have selected once you have chosen the variables and data sets you wish to plot click on the Plot Graph button to update the graphical display If you have not chosen any variables to plot there appears a warning message box Figure 4 3 For X Y plotting this means checking at least one of the output variable check boxes while for Flammables plotting this means in addition selecting at least one concentration Plot Graph Figure 4 3 Warning message when no variables selected for plotting Note that the graph
28. file Besides the core tabulated output discussed in the previous section the gof file may contain the results of the post processing carried out according to the specification given in the Additional Output part of the Output folder see Section 3 5 6 The output for each additional output option is summarised in Table 4 2 Note that the output appears in the file in the same order as its order of appearance in the table Note also that no additional output is available for jet releases 4 6 Output for plotting contours The ggd file contains data that can be used by other software to plot contours It is only available for Continuous and Instantaneous release types and if the user has ticked Calculate Gridded Output in the Gridded folder of the Output screen Figure 4 5 shows the file format A full description is given following Figure 4 5 Figure 4 6 shows an example of a ggd file Note that in the GASTAR output X is the alongwind distance from the source and Y is the crosswind distance 57 GASTAR Section 4 Viewing Output Parameter Units Description S m arc length i e distance along cloud centreline trajectory Usually the same as downwind position X see below X m downwind position of point on cloud centreline plume jet downwind position of cloud centre puff at given time Y m crosswind position of point on cloud centreline plume jet
29. fundamental a correlation between E and 0 is often used e g E 0 0012 0 see Petersen 1980 Note that this produces a downslope cloud velocity with a weak dependence on the slope angle 0 in the form of sin0 0 More complicated expressions provide more rigour and allow the introduction of the surface drag coefficient which is important at small slopes 100 GASTAR Section 8 Theory An ambient flow can be incorporated in the two dimensional case This can be achieved through the inclusion of a momentum equation However following Ellison and Turner 1959 a satisfactory approximation to this results from summing the velocities produced by the slope and the ambient flow The entrainment due to surface generated turbulence is based on the resulting absolute velocity whilst that due to interfacial shear generated turbulence is based on the velocity difference This general approach can be extended to point or area sources and to cases where the wind and slope are not aligned and to puff or time varying releases 200 160 E 120 oF Upslope 5 E No slope S 80 Downslope 5 c 0 1 l i 0 500 1000 1500 2000 2500 3000 x centroid m Figure 8 8 Effect of Slope on Cloud Radius The x coordinate is in the direction of the wind The predictions obtained using such algorithms are generally consistent with the field data from Picknett 1981 and the relevant laboratory experiments of Hall et al 1974 Britter and Snyder 1988
30. introduced by this velocity field may lead to a gross intermingling of the two fluids and eventually to turbulence generation and consequential turbulent mixing and cloud dilution This mechanism of dilution is of primary importance when the self generated velocities are large compared with the mean ambient velocity In addition turbulence generated from this flow near rigid boundaries provides a mechanism for cloud dilution Frequently it is the ambient turbulence that is responsible for cloud dilution be it locally generated or advected from upstream The variation of density in the vertical direction will ina gravitational field be stably stratified and turbulence and turbulent mixing can be significantly reduced or entirely inhibited Turner 1973 This effect can extend to the atmospheric turbulence in the wind flow over the cloud as well as to the cloud itself The inertia of the released material is directly dependent upon the density of the material However when the density difference is small compared with either density the influence of the density difference on the inertia is small and may be neglected This may not be valid close to the source but cloud dilution will eventually allow this assumption Under these conditions the density difference frequently appears as g g p Pa Pal where g is the acceleration due to gravity and p and p are the density of the cloud and of the ambient fluid respectively These effects emphas
31. issuing the warning 2 5 Examining output from a run Once the run has completed the user may examine the results of the run by means of graphical display facilities provided by the interface These are located in the Graphics folder and provide extensive line plotting of all quantities calculated by the model This facility is described in detail in Section 4 2 6 User preferences Next in this Section on using GASTAR we describe the preferences controlling certain aspects of use of the interface These are accessed by selecting Preferences from the File menu which in turn provides three options as follows Note that for the options with a dialogue box Figures 2 4 2 5 and 2 6 any changes to preferences made by clicking on OK hold for the current session only They do not become permanent preferences unless you click on Save Defaults in which case they supplant the entry in your ini file similarly you can restore settings from the ini file by clicking on Restore Defaults Concentrations in ppm This user preference sets the concentration units to be either mol mol or parts per million ppm The choice of units is used in the filed output in the gof file in the input data concentration for maximum range option and in the graphical display To set ppm as the concentration units click on the Concentrations in ppm option from the File Preferences drop down list if you revisit this list you will see a tick against the Concentrati
32. obstacle width D E Figure 3 11 Definition of a circular building Circular Buildings are defined by a height the location of the centre point of the building and a width see Figure 3 11 Rectangular Buildings are defined by a height the location of the centre point of the building a width and depth and the orientation of the building see Figure 3 12 Fences are defined by a height the location of a point along the fence and the orientation of the fence see Figure 3 13 3 3 2 2 Obstacle name Give the obstacle a name to help you identify it in the table and later on in the output files The model will tell you if the cloud passed over and interacted with the obstacle or not so a descriptive name is recommended 36 GASTAR Section 3 Entering Input 3 3 2 5 Obstacle width This obstacle dimension is only required for buildings With a circular building it is the diameter in metres For rectangular buildings it can be either of the horizontal dimensions of the obstacles see the definition of the obstacle orientation Section 3 3 2 6 which is linked to this parameter Minimum 1 0 m Maximum 1000 0 m Figure 3 12 Definition of a rectangular building PLAN VIEW obstacle distance o 1 D 1 e wind bearing z o obstacle width J o obstacle depth E o obstacle orientation for side W 3 3 2 4 Obstacle depth This obstacle dimensio
33. s 1100 E Use Results Hazardous fraction Aerosol Start time Mass flux Width Temperature 0 0 32 300 33 30 227 8 1 00E 06 Maximum time modelled in seconds in 1 Max 100000 Figure 5 3 The Time Varying Results folder for the pool uptake model A brief description of the controls on the Results folder is given below 5 3 1 Modelling time This is a real number giving the time in seconds to which the code will model the cloud development This is equivalent to and should therefore be the same as the Modelling Time given on the Output folder of the main interface 66 GASTAR Section 5 Pool Uptake Model Minimum 1 0 S Maximum 100000 0 5 3 2 Calculate uptake When all the required data has been entered into the uptake folders you may click on the Calculate Uptake button to run the Pool Uptake model The results will appear in the table below the button 5 3 3 Pool uptake results Once the results have been displayed in the table on the Results folder you may choose to ignore them by clicking on Close or to use them by clicking on Use Results 67 M a t er j a Database When modelling the dispersion of a cloud GASTAR uses a set of physical properties of the released material such as the molecular weight boiling point etc These properties are stored in a materials database Materials gdb that is read by the interface GASTAR is supplied with a database containing certain key materials but you may wi
34. see Section 3 2 4 to determine the final temperature and aerosol fraction In such a case the storage temperature might not be the initial cloud temperature It is the initial temperature of the released material that is required by the code For Time Varying Releases this entry will refer to the current segment given in the Current Segment Number box Minimum 10 0 K Maximum 2000 0 K 3 2 3 8 Source aerosol fraction For Aerosol Releases only This is a real number giving the fraction of the source material that is in liquid state initially This fraction can be found by using the Flash calculation see Section 3 2 4 For Time Varying Releases this entry will refer to the current segment given in the Current Segment Number box Minimum 0 0 Maximum 99 3 2 3 9 Number of segments For Time Varying Releases only This is an integer giving the number of distinct segments the source term has been broken into in order to simulate the time varying source The details of each segment may be displayed by changing the Current Segment Number in the panel below this one 30 GASTAR Section 3 Entering Input Minimum 1 Maximum 20 3 2 3 10 Segment duration For Time Varying Releases only This is a real number giving the time duration in seconds for the currently selected segment of a Time Varying release Minimum 1 0 S Maximum 2000 0 s CROSS SECTION Jet direction jet elevation h height of jet source
35. than start from scratch each time One way to do this is to use an existing gpl file edit this and then use File Save As to create a new gpl file An alternative is to use the GASTAR templates feature which is accessed via the File menu A GASTAR template is a complete input data file but with the gpt extension The interface provides the means both to open existing templates and thereby provide the starting point for a new GASTAR input file and to create new templates for later use To start a new input data set based on a template file use the File Open Template menu option the GASTAR interface loads the data in the template file but sets the data set name to untitled in the banner at the top of the interface window You can then edit these data and save as a new data file with File Save As To create a new template file simply edit an existing data set in the interface which may have been loaded as a gpl or gpt file or entered from scratch and then use File Save As Template to save the template with the desired path name and the gpt extension Note that you could also open a template gpr file with File Open provided you select Template Files GPT from the List Files of Type drop down list box or using the recently opened files but this would simply open the file as is and is not the recommended way of using template files Similarly File Save and File Save As could be used to sav
36. the basic entrainment relation from Ellison and Turner and others that an additional entrainment velocity u 1 2x10 0 U a U n 78 where 0 is the slope in degrees i e u 21 2x10 0 C g h 79 should be included for plumes A similar result is applied for instantaneous releases but with a coefficient of 4x10 0 the coefficient reflecting the growth rate of the leading edge of gravity 103 GASTAR Section 8 Theory currents Britter and Linden 1980 which is similar to the flow resulting from instantaneous releases Beghin et al 1981 The approach used here is to model the second effect surface generated turbulence by using the standard entrainment correlation for flow over flat terrain but with the friction velocity adjusted from u to Ua U am 80 The correlation based directly on slope has effectively included this second effect albeit in an approximate way Consequently we select the larger of the two entrainment estimates 6 3 4 6 Reversing flows i Instantaneous releases These could move downslope under gravity and then upslope due to the ambient wind This is directly handled by the previous algorithms ii Continuous time varying releases These are also directly handled to allow the reversing of the plume however we note that after the plume has been reversed it will be riding over the downslope plume 6 3 4 7 Ambient wind not parallel to the slope The model breaks the downslo
37. the cloud size is small compared to the scale over which the topography is changing This work follows that of Britter 1982 Britter 19892 Britter 1989b and Britter Cleaver and Cooper 1991 We will later allow the slope to change in the advection direction of the clouds Many authors have considered the effects of slopes and in particular Ellison and Turner 1959 Britter and Linden 1980 and Beghin et al 1981 have studied two dimensional buoyancy driven flows on slopes using entrainment theory In cases of releases into still air observations support the predictions that entrainment into the plume and subsequent plume dilution increases with slope in a manner so as to ensure that the plume velocity is independent of distance down the slope and very nearly independent of the gradient of the slope Similar results also hold for the starting plume and the downslope velocities U are generally about U g i Point or area source releases on slopes have received less attention but unpublished work by Britter suggests that a similar analysis may be appropriate In its simplest form for the two dimensional problem the cloud growth rate on a slope of angle 0 is given by an entrainment function SLE tan 0 75 dx where Ri SA cosg 76 d and Uz is the downslope cloud velocity Further progress requires the use of experimental information linking two of E Ri and 0 Although correlations between E and Ri are more
38. the near source region may involve both an inertial interaction and a scouring or detrainment of the fluid near the source by the ambient flow Observation of laboratory experiments would favour the latter of these mechanisms Section 8 Theory Continuous releases from ground level sources or near ground level sources have been the subject of many studies Britter amp McQuaid 1988 summarized available data from laboratory experiments using idealized area sources with low momentum More complicated source configurations will eventually lead to a dense plume at ground level to which these idealized source experiments may be relevant Meroney 1982 Field experiments have also considered more realistic less idealized sources x gt 0 77 Li L X2 gt X merle e Siro mov X3 2X2 n o AL 1 0 Xo 1 0 Xo X X x X2 Xs X3 L b om BOX MODEL CONFIGURATION M risu mox EXPERIMENTAL CONFIGURATION One or both of these mechanisms Figure 8 4 Model and experimental plume development allow the plume to travel upwind and laterally at the source prior to being advected downwind 78 GASTAR Section 8 Theory If the plume is considered downwind from the source the plume width increases as a result of the lateral buoyancy driven motion and atmospheric diffusion whereas the cloud depth decreases as a result of lateral spreading and increases as a result of diffus
39. will be launched if this option is selected 2 1 2 Folders Much of the rest of the interface screen is occupied by a set of folders Each folder is a group of controls that deal with a particular aspect of the model In GASTAR folders are used to divide up the input to the model and allow the user to specify the input data in a structured way Another separate folder is used to display the graphical output The folders appear to lie on top of one another and a particular folder is accessed by clicking on the tab that appears along its top edge whereupon the folder moves to the top of the stack Within the various GASTAR folders there are different types of control and in the rest of this 4 GASTAR Section 2 Using GASTAR section we outline what these are Please refer to Figure 2 1 where appropriate GASTAR 3 2 untitled Ais File Run Help Source Complex Effects Output Graphics Source Material From Database 1 2 But View Data utadiene M C User Defined Release Type Instantaneous JV Momentum Initially Well Mixed lc TISSU C Continuous C Time Varying C Gas or Liquid Jet Aerosol Release Thermal Release Source Details Source Location 7Q301799 UK Change Release Start UTC 12 00 08 Apr 2009 Initial Air Entrainment kg f Puff Diameter m Mass kg Hazardous Fraction mol mol dl Temperature K Aerosol Fraction kg kg Flash Mass kg or mass flux kg s of the
40. will then need to edit some or all of the input data This is achieved by selecting a folder and then typing in values in text boxes and selecting options for controls such as check boxes radio buttons and so on The mouse is the usual way in which the folders are navigated however an alternative is to use the TAB key to move systematically through the controls i e each control in turn receives the focus If the control is a text box the current text becomes highlighted when it receives the focus To change a parameter value in a text box select the folder containing that parameter by clicking on the folder s tab move the pointer until it is over the appropriate text box and click the left mouse button The cursor will now appear in the box Use DELETE and or BACKSPACE to remove unwanted characters before typing in the new value If you double click the parameter it will become highlighted If you now type the new value it automatically replaces what was highlighted Tn fact there are two exceptions namely the wind height see 3 1 2 and the hazardous fraction see 3 2 3 4 which are set to default values of 10 0m and 1 respectively 10 GASTAR Section 2 Using GASTAR Changes to the option selected for radio buttons list boxes etc can be made by clicking on the required control or via the keyboard using a combination of the SPACE bar and the UP DOWN and LEFT RIGHT keys When the focus is given to a control the help bar at th
41. would produce a list file called allruns lst containing all gpl files in the current directory You may then edit this file to include additional files or comment out entries by placing a semi colon on the line the model will ignore anything appearing after the semi colon on the given line You may wish to build a list file with full path names so that it can be used from any directory You can do this again with the DIR command but this time using the S option which includes all sub directories of the current directory as well dir JB S gpl gt allruns lst For more information on the version of DIR available on your operating system type dir or consult your Microsoft DOS manual 2 4 4 Warning and error messages While the model is running GASTAR will display a minimal amount of information in a window opened to allow the user to monitor progress of the simulation When the calculation has successfully completed this window will be redundant and the user may click Yes when the following dialogue box appears on screen Program terminated with exit code 0 Exit Window The exit code 0 confirms that the Fortran code has terminated but does not guarantee that the simulation has run to completion there is the possibility that the code has encountered an internal problem in the calculation that might cause a run time error if allowed to continue In these cases the code notifies both the screen and the log file of the error it has
42. A simplified version of such a calibrated model appeal to the original experiments appeal to the correlation provided by Britter 1980 and analysis based on detrainment due to a buoyancy limited Kelvin Helmholtz instability all suggest that the plume depth above any gas blanket and just downstream of the source will scale on u g with a coefficient of about 100 From experience we use a plume depth of 200 u g but apply a minimum restriction of 0 20m based on pragmatic physical grounds We had considered setting this minimum as some multiple of the surface roughness length zo but found no evidence that this would be preferable 89 GASTAR Section 8 Theory The width of the source w is determined from qo wh U z 0 56h 35 out where qo is the continuous volume release rate The concentration of the plume is taken to be concentration of the source material The model is isothermal and thus the volume flow rates used might just as well be mass flow rates A non isothermal model may be introduced in the future though the effect of heat transfer from the underlying surface is unlikely to be of great significance If the source width so calculated is smaller than the physical source width obviously the more appropriate physical source width is selected There must be an upper limit on the plume height at the source input to the dispersion model as the density difference becomes small ie u g increases without lim
43. AR You have been supplied with a CD ROM containing the latest version of all the files necessary to install GASTAR You will also have been sent probably by email a GASTAR licence file The licence file must be named and if necessary renamed to gastar3 lic and copied to the application directory i e the directory in which GASTAR is installed Users should ensure they keep a backup of the licence file on a suitable media GASTAR should be installed to and run on a standalone PC Use of a single installation of GASTAR by multiple users at once is not supported 1 2 1 Use of GASTAR 3 2 with earlier versions of GASTAR GASTAR 3 2 can be installed and used on a PC that has earlier versions of the model i e version 3 1 and earlier installed If you choose to install the earlier version of GASTAR follow the following steps e For version 3 05c to version 3 1 uninstall the program by means of the Windows Add Remove Programs feature Click on the Windows Start button then click on Settings and then Control Panel Double click on Add Remove Programs and then highlight GASTAR in the list of programs and click on the Add Remove button on the Install Uninstall tab e For versions earlier than 3 05c for which the GASTAR installation simply involved copying GASTAR Section 1 Getting Started files from the supplied diskettes you should find the relevant files and delete them See Section 7 of your earlier GASTAR manual for a list of all files a
44. Drivas 1987 1997 describe some of these models Modifications of the conventional Gaussian dispersion models have been shown to be inadequate leading to errors of as much as two orders of magnitude Havens 1980 There have been two distinct approaches in dense gas dispersion models e The first approach three dimensional models uses Reynolds averaged three dimensional time dependent conservation equations The most common of these use K theory for turbulent closure Havens et al 1987 compared four models There are still considerable difficulties in applying this type of model e The second approach an integral formulation integrates out vertical and horizontal variations in the cloud or plume and later reincorporates these through empirically determined profiles These models referred to as box models have a small number of adjustable constants whose effect may be easily interpreted physically These models are effective and computationally inexpensive Hanna amp Drivas 1987 list over 40 models Integral models incorporate three specific effects the cloud spreads horizontally under its own negative buoyancy there is a dilution of the cloud by mixing with the ambient flow the cloud is advected by the ambient flow 8 1 4 Instantaneous releases The near instantaneous release of material giving rise to a dense cloud may result from the catastrophic failure of a storage vessel This produces a rapidly expanding entraini
45. Fluid Mech 21 317 344 Britter R E 1989b Experiments on some effects of obstacles on dense gas dispersion U K Atomic Energy Authority Safety amp Reliability Directorate Rep No SRD R 407 Britter R E 1994 The modelling of a pseudo source for complex releases CERC report FM89 2 J Britter R E 1995a A Researchers Consultants view on advances in source and dispersion modelling C C P S International Conference and Workshop on Modelling and Mitigating the Consequences of Accidental Released of Hazardous Materials September 26 29 New Orleans Contained in Conference Proceedings published by A I Ch E C C P S Britter R E 1995b A further note on modelling flashing releases CERC report FM89 3 J Britter R E and Linden P F 1980 The motion of the front of a gravity current travelling down an incline J Fluid Mech 99 531 543 S Britter R E amp McQuaid J 1988 Workbook on the dispersion of dense gases Health amp Safety Executive Report No 17 1988 Britter R E amp Snyder W H 1988 Fluid modelling of dense gas dispersion over a ramp J Hazardous Materials 18 37 67 Britter R E Cleaver R P amp Cooper M G 1991 Development of a simple model for the dispersion of denser than air vapour clouds over real terrain British Gas Report MRS E622 Midlands Research Station Solihull O Britter R E Hunt J C R and Richards K J 1984 Air flow over a two dimensional hill studie
46. For Time Varying pools this entry will refer to the current segment given in the Current Segment Number box Minimum 0 01 m Maximum 1000 0 m 5 2 24 Mass flux from pool A real number giving the mass flux of material leaving the pool in kg s This information will frequently be derived from a pool spill model such as LSMS see Introduction to this section For Time Varying pools this entry will refer to the current segment given in the Current Segment Number box Minimum 0 01 m Maximum 10000000 0 m 5 2 2 5 Initial cloud volume A real number giving the initial cloud volume in cubic metres It is likely that you will have no information regarding the starting condition of the cloud or you want the model to assume there is not any cloud initially In these cases you should give the initial cloud volume as a very small number Minimum 0 01 m Maximum 100000 0 m 5 2 2 6 Initial cloud diameter A real number giving the initial cloud diameter in metres Although this parameter has fixed minimum and maximum values the cloud width should not be less than the pool width defined above This is because the Pool Uptake model assumes that the mass flux of material leaving the pool is uniform over the whole area of the pool Consequently if a cloud forms it must form at least over the whole width of the spill and never less If you have no information regarding the starting condition of the cloud or you want the model to assume there
47. GASTAR 3 2 USER MANUAL 8 April 2009 Cambridge Environmental Research Consultants Ltd 3 King s Parade Cambridge CB2 1SJ UK www cerc co uk Contents 1 Pr faCe duse e RARO ENS MRNA QUAS AE WEE SEEN UP LH FORET RUNI DU HR TRE R e UNA iv Gettin Started iH I 1 1 1 System FEQUITEIMENIS ssec e e et n E E suede A E CURE IRR LS NE Re e v aaah 1 1 2 Installing and starting GASTAR scion ced sanehesatshesstieceag see sauesdaasucioice Fe EE IER UH EORUR cesbanads 1 1 2 1 Use of GASTAR 3 2 with earlier versions of GASTAR sese 1 1 2 2 Installing GASTAR 3 2 acc o E ER eu Cog eee E 2 1 2 3 Statni GASTAR aene A E E r A rero T 3 LOEIT i XS PAR ARAE TEE ERE E RR 4 2 1 Windows terminolo g Yosia totaa rtta 4 2 1 1 MOTUS enoe HE a E 4 2 1 2 Folders n a p tatu eee oet n a EE to 4 2 1 3 Iuformatioti i cesta ania dca ec ue te epe ela i De ee totu eee 7 2 1 4 Navigating using a Keyboard edidi e veia ida ve ee 7 2 2 Main features of the GASTAR Interface csi eet reet ne o usque paca ees 8 2 2 1 MUS oci tnoti Maple tina a an a ek See ete 8 222 EG 8 LE ESEE E ET EE E E E t utt Ee E 9 2 3 Setting Up a problem eei i sd UTOR Ia es lesdedaasencadeusUecdens aaa 9 2 3 1 ici p T MH RE 10 2 5 2 Ios MA 10 2 3 3 DAVIS Gi eene ge e a e aiee a e ia a ea e e i ey 11 2 3 4 Template MeS raana ETE 11 2 4 JJBunning 3 probleWiuu coset ee ereas E A A E i 12 2 4 1 Running GASTAR from
48. HP e Hae SUR euh ai 68 6 1 2 Using a user defined material 5 5 een net enean e te eerte 68 6 1 3 Changing the materials database eee stent tenter ree bara ehe an o Foe a deinde saa 70 62 Maternal Propertie Seenen QI aec dS ote ape ana heitaisesta asm tute loe musste da aes 71 GASTAR Files oto EIE E E ETA 72 7 1 MEMS Ile e oer md ORE RR su I i E e RE AR E MINA ER I NE 72 T 2 User generated files e secus D e dee nS Mis Ee an tse baa eoa Pede t ined 12 TRC OEY ge E E E E E EE ET 73 8 1 Dense gas dISpersloni aieo inasin iina E EE PRO Oen E EA E Eaa 73 8 1 1 Formation of dense gas clouds dues rine wsieh cys td disney vate wae Gece eae wanna 74 8 1 2 Physical processes in dense gas clouds see 75 8 1 3 Dispersion modelsarsaiesn et e a a a A teed kat foedus 76 8 1 4 Instantaneous releases rri n a a Ba E a RET 76 ii GASTAR Contents 8 1 5 Contimuous Teleases cose coti hibet Radiata ese ioi Prost ust tas Bebe aside dias 78 8 1 6 Time Varying releases 2 e ret X ORENSE AMARE ERES AE RU DAL Ye 79 8 2 GASTAR dense gas dispersion model eese 8l 8 2 1 Dispersion modeli des ae eite men h a dise ieu nb e inei adde 8l 8 2 2 WISTS OT OY PR terc v T 83 8 2 3 Thierrmal e eel o nenian cents a sceau du urat foret te en Eee 84 8 2 4 SPIO GY Dames cone Sak otal daria Patel Ra het dead da cdi iss 85 8 2 5 PASSIVE dISDOESIODL uoo cde e oo dre ee veo Ite eei v ode ess bed aedis Mo deiviedeeit
49. Output tick box a ggd output file is created containing output that can be used by other software for plotting contours A more detailed description of the ggd file can be found in Section 4 6 GASTAR 3 2 D Examples LSMSPoolSpill contin gpl E m ES File Run Help Title From LiPSOL run D XPROJECTSSGASTARNSTRAININGSTESTA LPL Modelled Time s 1100 Averaging Time s 15 Specified Output Points Additional Output Dose Flammable Range Gridded a Finish Number of lines 1000 33 PE 1006 Specified Output Times 1000 1000 33 ZHeght m 16 add Dee Delete Check to produce gridded output for contour plots Figure 3 20 Calculate Gridded Output in the Gridded folder In the Gridded folder the user enters the minimum and maximum X and Y co ordinates for the gridded output the height above ground level at which the output will be calculated and the number of grid lines in the X and Y directions i e the fineness of the results grid 50 GASTAR Section 3 Entering Input Note that X is the alongwind distance from the source and Y is the crosswind distance Minimum x y 10000 0 m z 0 m Number of lines 1 Maximum x y z 10000 0 m Number of lines 101 IMPORTANT NOTE The calculation of many of the additional output items utilises some function of either space or time for example the dose is found by integrating the concentration at a point with respect to time o
50. P is the atmospheric pressure i e U gifa 73 Pe Ae m U The appropriate input area is determined from m U and the appropriate density The density may be obtained from the jet temperature which in turn may be determined by application of the enthalpy equation 6 3 3 6 Flashing releases Pressurised liquids which flash upon release to the atmosphere require calculation of the flash fraction i e the proportion of the release changing to gas the remaining material is assumed to be suspended aerosol No allowance for rainout is made The correlation used for the aerosol or flash fraction is P L rage a T 5p Aerosol Fraction 1 c pl 74 H LG where T storage is the storage temperature of the liquid Tap is the boiling point of the released material Hrg is the specific heat of vaporisation of the released material Cpi is the specific heat capacity of the released liquid Obviously a rainout allowance may be introduced manually following the flash fraction calculation and prior to running the jet model The previous comments on determination of the correct momentum flux to input into the jet model also apply here Frequently the exit pressure for flashing releases is the saturation pressure of the material at the storage stagnation temperature The excess above ambient pressure will also lead to an increase in the jet momentum 98 GASTAR Section 8 Theory 8 3 4 Topography Variations in the elevation of the underlyi
51. P21 Safety in Mines Research Establishment UK McQuaid J 1987 Design of the Thorney Island continuous release trials J Hazardous Materials 16 1 8 Melia J amp Britter R E 1990 The dispersion of dense gases through an obstacle array In Waves and Turbulence in Stratified Flow Proc IMA Conference Leeds 1989 Oxford University Press O Meroney R N 1982 Wind tunnel experiments on dense gas dispersion J Hazardous Materials 6 85 106 Meroney R N amp Lohmeyer A 1983 Statistical characteristics of instantaneous gas cloud releases in an atmospheric boundary layer wind tunnel Boundary Layer Met 28 1 22 Petersen F B 1980 A monograph on turbulent entrainment and friction in two layer stratified flow Tech Univ of Denmark S Petersen R L amp Ratcliff M A 1989 Effects of homogeneous and heterogeneous surface roughness on HTAG dispersion American Petroleum Institute Publication No 4491 O 120 GASTAR Section 9 References Picknett R G 1981 Dispersion of dense gas puffs released in the atmosphere at ground level Atmos Env 15 509 523 S Puttock J S 1988 A model for gravity dominated dispersion of dense gas clouds Flow and Dense Gas Dispersion Oxford Clarendon Rottman J W Hunt J C R amp Mercer A 1985 The initial gravity spreading phases of heavy gas dispersion comparison of models with Phase I data J Hazardous Materials 11 261 280 Spicer T O amp Have
52. Puttock Clarendon Press Oxford Ermak D L Chan S T Morgan D L amp Morris L K 1982 A comparison of dense gas model simulations with Burro series LNG spill tests J Hazardous Materials 6 129 160 Fietz T R amp Wood LR 1967 Three dimensional density current J Hydraul Div Proc ASCE 93 HU6 1 23 Fryer L S amp Kaiser G D 1979 DENZ a computer program for the calculation of the dispersion of dense toxic or explosive gases in the atmosphere Saf Reliab Dir Rep SRD R152 U K A E A Culcheth UK Griffiths R F amp Kaiser G D 1982 Production of dense gas mixtures from ammonia releases J Hazardous Materials 6 197 212 Hall D J Barrett C F and Ralph M O 1974 Experiments on a model of an escape of heavy gas Report No CR882 AP Warren Spring Laboratory Stevenage Herts S Hall D J Hollis E J amp Ishaq H 1982 A wind tunnel model of the Porton dense gas spill field trials Rep No LR394 AP Dept Trade Ind Stevenage UK S Hanna S R Briggs C A amp Hosker R P 1982 Handbook on Atmospheric Diffusion Technical Information Centre US Dept of Energy DOE TIC 11223 Hanna S R amp Drivas P J 1987 1997 Vapor cloud dispersion models First edition second edition Center for Chemical Process Safety A I Ch E New York Havens J A 1980 An assessment of predictability of LNG vapour dispersion from catastrophic spills onto water J Hazardous Materials
53. T l m as Cu T B T m Ge if there is complete evaporation or h C P 1 l m C T T m a Csr os 59 T a otherwise Here Tgp is the boiling point K of the released material T is the air temperature K Cpg is the specific heat capacity KJ Kkg of the material vapour Cpa is the specific heat capacity kJ Kkg of the air Cj is the specific heat capacity kJ Kkg of the material liquid and Hi is the heat of vaporisation kJ kg of the released material In particular at release there is no ambient air and the specific enthalpy at the source is given by CT ias C pg s x a H a The crucial empirical input to integral jet models is the parameterisation of the entrainment This is typically represented in terms of a product of an entraining area unit jet length i e 27R the ambient air density and an entrainment velocity There are three different contributions to the entrainment velocity The first relates to an entrainment due to the differing velocities in the along jet s direction between the jet and the environment ie 1 2 a u U cos cosO 61 The value of the coefficient a is taken to be 0 07 Cleaver amp Edwards 1990 The second term relates to the velocity of the ambient wind normal to the jet trajectory a U sin 0 sin d cos 6 62 The value of the coefficient oo is taken to be 0 7 Cleaver amp Edwards 1990 95 GASTAR Section 8 Theory
54. The user is presented with a message box asking them whether they wish to save the data with the current name and run the model The user clicks Yes to continue No to interrupt the Run command and allow the file to be saved under an alternative name and Cancel to halt the Run command completely If the data had not been saved before selecting the Run command for example if New had been selected prior to inputting the data then the user will be prompted for a file name under which to save the data 2 42 Running GASTAR from DOS GASTAR may also be run from the DOS prompt or from a DOS batch bat file In the latter case this is known as running GASTAR in batch mode The essential difference between this case and that in Section 2 4 1 1s that the user starts and finishes in DOS rather than in Windows It is important to note that the syntax for running applications from DOS has varied from one version of Windows to another so you should consult the online DOS Help for more information However note that the recommended way to run GASTAR from the command line is by using list files see Section 2 4 3 for full details which reduces the potential complications of running from DOS The rest of this section can be omitted on first reading At the heart of running GASTAR from DOS is the use of GASTAR command lines with command line switches and arguments such as GPATH gastar exe I1 IPATH datafile gpl see belo
55. a File KI cdnsnf gpl My Recent cfo5f gpl Documents B cfiBf gpl 3 cfnf gpl n cfmsnf gpl a tvdnsnf gpl S tvinsnf GPL My Documents My Computer z My Network File name untitled E Places Files of type Data Files GPL Figure 2 2 The Open GASTAR Data File dialogue box GASTAR Section 2 Using GASTAR 2 1 2 7 List box List boxes allow you to choose one item from a list of choices If it is a drop down list box it normally appears as a rectangular box containing the current selection however when you select the box the list of available choices appears If there are more items than can fit in the box scroll bars are provided For example the Source Material is selected through a drop down list box in Figure 2 1 2 1 3 Information Besides menus and folders which allow the user to carry out actions there are other parts of the interface which provide the user with information 2 1 3 1 Title bar This is located at the very top of the screen and gives the version number of the model together with the name of the current gpl file see Section 2 3 e g GASTAR 3 1 CADATATTEST GPL 2 1 3 2 Help bar The main GASTAR window has a help bar at the bottom This gives you information about the part of the interface you are currently using in the form of a short description of the item If you are entering a numeric value the maximum and minimum permissible values will be displayed
56. acle of width W is taken to be the larger of a the obstacle width and b the plume width in the absence of the obstacle plus half the obstacle width These rules have the pragmatically correct limits i e i if the plume is much wider than the obstacle there is relatively little effect on the plume width ii if the plume is much narrower than the obstacle then the plume width becomes equal to the obstacle width iii If the plume width is equal to the obstacle width then the plume width is increased by some fraction of the obstacle width here taken as half This uncomplicated algorithm should cover situations when the plume and obstacle are co linear and when their overlap is only slight alternatively the algorithm has spread any error across the possible scenarios Britter 1982 argued that the turbulent kinetic energy created in the lee of an obstacle was able to raise the potential energy of the dense gas plume by an amount that could be characterised by a height increase Ah proportional to Cp H 87 The coefficient of proportionality Cp is typically of order 0 1 and this value has been used in the model Of course the increased height should not lead to a cloud height greatly in excess of the obstacle height H the limit chosen in the model is H The increased depth only occurs over the region in which the plume interacts with the obstacle however consistent with the use of an integral model the increased he
57. ance indicates that its lack is of consequence 104 GASTAR Section 8 Theory The difficulty has been overcome by forcing Uaa 0 3 Uam if ad lt 0 3 Uam Such a modification is probably a better reflection of the physics of plume turning than the simple velocity addition anyway see Turner 1973 Note that in his analyses and experiments Turner paid little attention to the velocity profile of the ambient flow the ambient velocity would be substantially larger than the ambient velocity used in our model Attempts to reduce the above coefficient from 0 3 to 0 1 dramatically increased the execution time and output was not always obtained For reversing flows of plumes on a slope it had been intended to determine the point of maximum downslope extent and commence a new calculation from there Upon further consideration this seemed unwise Currently the code calculates the plume development as it descends the slope and as it is blown back up the slope This is obviously appropriate for all cases except when the ambient wind is directly up the slope However we shall apply the result to all cases including the directly upslope wind until experimental results show this to be unsatisfactory The code allows for plume or puff development over a series of slopes with no limit on the number of changes Relevant ambient velocities and surface roughness must be entered by the user for each slope change A case often encountered is when a c
58. ance on the Slope Definition form will be greyed out and will not be editable The only other time you will not be able to edit the distance will be when splitting a slope into two Having chosen the distance in the Split Slope dialogue you will not be able to edit it again until the slope has been accepted into the summary table The slope finish will be the start of the next slope If this is the last slope the slope will extend to the model actually uses a large positive number Minimum 0E99 m Maximum 1 0E99 m 3 4 1 8 Slope angle This is the angle of dip or elevation of the current slope segment measured in degrees from the horizontal as you move along the positive direction of the slope vector see Figure 3 17 An upward slope will have a positive slope angle and a downward slope will have a negative slope angle Minimum 45 0 deg Maximum 45 0 deg 3 4 1 9 Slope ground roughness length This is the roughness length for the current slope section and has the same definition as the roughness length defined in Section 3 1 4 The ground roughness length used in the model will depend on the Use Meteorology Screen Data check box If this box is checked then the model will use the information given on the Meteorology Screen and this parameter will appear greyed out when you edit the data on the Slope Definition form If the box is unchecked the model will use the data for the appropriate slope segment and this data will
59. and will be retained by the model for the starting conditions ie the user specified width is ALWAYS the effective source width This option is useful if you know the actual plume width eg modelling experimental results or you wish to fix a certain width eg you are using the results from another source model It may also be required if the geometry of the release prevents lateral spreading of the plume beyond the physical source width 3 2 2 3 Time varying release For time varying releases the initial conditions are specified as a sequence of piece wise constant segments The segments are specified by the time duration of each segment The other details of the source specification are similar to the continuous case For each segment of the time varying release the physical source width Do and initial mass flux Mo are specified The initial condition is assumed to be a rectangular section with an effective source width Wo effective source height Ho and source density po The initial temperature To for Thermal and Aerosol cases initial aerosol fraction for Aerosol cases initial concentration Co and initial density p are assumed to be uniform over the initial section PLAN VIEW 0 jet bearing azimuthal angle U wind direction s wv 7 Jet direction E Figure 3 4 Source parameters for three dimensional Jet release The time varying segments can also be calculated by the Pool Uptake Model This consid
60. as for smooth or small roughness surfaces i e dependent upon the plume depth The most appropriate velocity profile within the roughness array is however still uncertain 3i The presence of many distributed obstacles has two effects on the cloud The obstacles lead to an increase in the turbulence levels in the flow and this by itself will tend to increase horizontal diffusion of the cloud This can be parameterised by an increased value of the ground friction velocity u However as Linden and Simpson 1988 have shown increased turbulence levels may also break down the organised frontal motions associated with the gravitational spreading and hence lead to reduced cloud widths 4 The influence of the surface roughness on vertical entrainment is still uncertain However it appears that conventional entrainment correlations may be used without serious loss of accuracy 5 The evidence in Melia and Britter 1990 suggests that the retention time of dense gas plumes in the wakes of individual roughness elements might best be modelled by the incorporation of a longitudinal diffusion with o oc u t where t is the travel time within the array A model based on these arguments has been developed and does reproduce the existing data base satisfactorily For example it accommodates the effect of turbulence on gravity spreading by reducing the buoyancy spreading velocity asymptotically to zero as g h u approaches a critical value We have exten
61. ash producing a cold dense cloud containing some material in liquid phase The Flash calculation screen see Figure 3 8 will use the material properties for the material currently chosen in the main GASTAR interface You will then need to supply the storage temperature of the material which is typically the ambient temperature and the ambient pressure If the main interface has the Air Temperature and Pressure defined these values are automatically copied to the Flash calculation screen You may then choose to use these values or enter different ones before calculating the aerosol fraction and temperature of the released material 32 GASTAR Section 3 Entering Input The model uses two slightly different algorithms to do this and both sets of results are given The reason for this is to give the most flexible approach for the modeller The commonly used method is labelled Normal method and these are the results returned to the main GASTAR interface from the Flash screen The formula used for the normal method is Aerosol Fraction 21 a Pee b Hic and that for the exponential method is Aerosol Fraction exp C Cn BN 2 LG where T storage 1 the storage temperature of the liquid Tgp is the boiling point of the released material Hig is the specific heat of vaporisation of the released material Cpi is the specific heat capacity of the released liquid Please note that if you change the Storage Conditions from the values copi
62. atabase of material properties and utility for editing database GASTAR Files List of files associated with GASTAR iv 8 Theory Theoretical background and description of the mathematical model 9 References Complete reference list Typographical conventions The following conventions have been adopted in the layout of this User Manual Style Usage Example Italic File names gastar exe UPPER CASE Directory names CAGASTAR Fixed width Text entered by the user including dir B gpl allruns lst the contents of files sans serif Text appearing on the interface Complex Effects folder Run menu screens Note that pathname refers to the location of a file or directory including the full hierarchy of directories leading to it starting with the drive letter e g C GASTAR CASESV est gpl Note Sections of text marked with a vertical bar in the margin are relevant principally to use of GASTAR as part of RISKAT the risk assessment package used by the UK Health and Safety Executive They are therefore not relevant to general users of GASTAR Getting Started 1 1 System requirements GASTAR is supported for use on systems running Microsoft Windows XP and Vista The following is the recommended minimum configuration although GASTAR will run successfully on lower specification PCs e PC with a Pentium 1 5 GHz or compatible processor e 0 5 Gbytes of RAM e 100 Mbytes of disk space available 1 2 Installing and starting GAST
63. ate relationships are used to determine the plume width at the source 92 GASTAR Section 8 Theory 8 3 3 Jet model The jet model is a conventional integral jet model which broadly follows the approach used in Cleaver and Edwards 1990 with extensions e g from a single phase two dimensional model to a single or two phase three dimensional model The model assumes that the jet is at atmospheric pressure and consequently high pressure releases require a release model to reduce under expanded jets down to atmospheric pressure The model is applicable to single and two phase aerosol jets released at any direction to the ambient wind The equations are written in terms of the mass momentum and enthalpy fluxes of the jet The jet centreline trajectory is written in natural co ordinates s 0 where s is the distance along the trajectory The ambient wind is along the x axis with x y z forming a right handed system Thus 0 90 0 is the y axis and 90 is the z axis The jet is given a similarity shape which is circular while not in contact with the underlying surface Thus the jet has radius Rj velocity actually speed along the s co ordinate u and density p which is different to the ambient density of pa The ambient density and ambient temperature T in the model are assumed constant and independent of height 6 3 3 1 Fundamental equations The scalar mass flux in the jet is rh 7R gt up 41 the vector moment
64. be editable in the Slope Definition form Minimum 0 0001 m Maximum 2 0 m 3 4 1 10 Slope wind speed This is the wind speed over the current slope section and has the same definition as the wind speed defined in Section 3 1 1 The wind speed used in the model will depend on the Use Meteorology Screen Data check box If this box is checked then the model will use the information given on the Meteorology Screen and this parameter will appear greyed out when you edit the data on the Slope Definition form If the box is unchecked the model will use the data for the appropriate slope segment and this data will be editable in the Slope Definition form 44 GASTAR Section 3 Entering Input Minimum 0 1 m Maximum 20 0 m 3 4 1 11 Slope wind speed height This is the height of the wind speed measurement for the current slope section and has the same definition as the wind speed height defined in Section 3 1 2 The wind speed height used in the model will depend on the Use Meteorology Screen Data check box If this box is checked then the model will use the information given on the Meteorology Screen and this parameter will appear greyed out when you edit the data on the Slope Definition form If the box is unchecked the model will use the data for the appropriate slope segment and this data will be editable in the Slope Definition form Minimum 0 1 m Maximum 15 0 m 45 GASTAR Section 3 Entering Input 3 5 Output details The Output f
65. ble summarises the current obstacle data There are three columns in the table The first column will respond to the mouse click Try double clicking on an entry in the table and you will see the word OFF appear and disappear This allows you to turn off the effects of obstacles on an individual basis The second and third columns give the name and the data summary for each obstacle you have entered The order in which they appear in the table is the order in which you entered the data There is no importance inferred or otherwise to their order in the table 3 3 1 3 New edit copy and delete buttons The four buttons to the side of the table allow you to edit the obstacle data New will bring up the Obstacle Definition form with the default values as shown in Figure 3 10 This is the form that allows you to define the obstacle data The parameters are defined in more detail below If you cancel the form from this point no new obstacle will be created Edit will bring up the Obstacle Definition form with the details of the obstacle currently selected in the table You can change any part of the data and save it again if you wish If you cancel the form from this point none of the changes will be saved and the obstacle definition will be left unchanged Copy will bring up the Obstacle Definition form with a copy of the details of the obstacle currently selected in the table The only change to the data will be the obstacle name which will sa
66. cannot be selected appear dimmed 2 1 2 5 Spin button You move forwards down through the list by clicking the down arrow with the mouse Spin buttons are used to cycle through an ordered list You move forwards back through the list by clicking the up arrow with the mouse Correspondingly you move backwards up through the list by clicking the up arrow with the mouse See Figure 4 5 for an example spin buttons are used to cycle through data points displayed on a graph 2 1 2 6 Dialogue box Dialogue boxes are floating screens which appear when you need to supply additional information to complete a task An ellipsis after a menu command indicates that a dialogue box will appear when you choose that command For example if you choose the Open command on the File menu the dialogue box shown in Figure 2 2 will appear In this dialogue box you specify the name of the file you want to open You choose the OK button to open the file you have chosen You choose the Cancel button to close the dialogue box without opening a file Several other dialogue boxes have OK and Cancel buttons Cancel will always close the dialogue box and discard any actions or input made in it whereas OK will accept any input from the dialogue box and carry out any appropriate action Note that double clicking on a list box item see 2 1 2 7 may also be used to select that item and thereby circumvent the need to select the item and then click on OK Open GASTAR Dat
67. cause no data is lost when you check the box Any meteorological 40 GASTAR Section 3 Entering Input data you enter with the slope segments is retained but will appear greyed out in the Slope Definition form meaning that it is not going to be used by the model Unchecking the box again will reinstate the data allowing you to edit it 3 4 1 4 Bearing of slope vector This defines the bearing measured clockwise from North in degrees of the line of maximum slope for the slope segments see 0 in Figure 3 14 The slope module allows simple slopes to be modelled Such slopes can be visualised as resembling an infinite sheet of card folded along parallel lines The folds are the boundaries between the rectilinear plane slope segments With the exception of the first and last segment the segments have a finite length and all segments extend laterally to infinity The slope segments are simple flat planes like a concertinaed sheet of card The lines of maximum slope for each slope segment are parallel and this direction defines the slope vector However the bearing of the slope vector need not be aligned with the wind direction The model allows the orientation of the slopes and wind to differ giving rise to cross wind slopes The bearing is measured in the same manner as the wind This means it is the angle measured clockwise from North of the direction from which the first slope is defined theoretically at For example if you have
68. cifically h 1 2 k 1 9 26 t 3 26 for unstable conditions and e i ie6at Q7 Ux L for stable conditions which have the limit of Ng 28 ux for neutral conditions k is the von Karman constant These formulations are used when the cloud Richardson number Ri falls below 1 1 For puff releases where necessary the along wind turbulent diffusion characterised by x is equated with oy 8 2 6 Longitudinal shear dispersion For ground based puff releases in particular the variation of the mean velocity with height leads to the cloud being stretched longitudinally i e the upper parts move faster than the lower parts while there is also vertical mixing This process is known as shear dispersion This will produce a characteristic longitudinal os Many empirical formulae are available for o but those are traditionally based on passive releases and written in terms of the downwind distance Instead we have reinterpreted such formulae e g Wheatley 1988 in terms of development with the cloud height h this being the region which is undergoing shear dispersion We have then argued that this approach based on 86 GASTAR Section 8 Theory cloud height will not be influenced by whether the cloud is passive or dense The algorithms used are e for neutral stratification category D o 4 5h 29 e for stable ambient stratification categories E G c 4 5h 30 where g l p 2
69. d from the roll up of the vorticity generated by the nonvertical density gradient at the cloud edge This horizontally propagating vortex ring is stabilized by vortex stretching and produces intense mixing of the cloud with the environment Some of the mixed fluid is left behind the advancing vortex to provide a substantially diluted cloud Eventually the leading edge vortex weakens and adopts the classical gravity head form It is only at this stage that t gt 0 t gt t t3 gt t2 BOX MODEL CONFIGURATION EXPERIMENTAL CONFIGURATION Figure 8 2 Model and experimental puff development downwind results from mixing between the cloud and the ambient flow Rottman et al 1985 rather than from any form drag Britter and McQuaid 1988 summarised available data from laboratory and field experiments T1 GASTAR 8 1 5 Continuous releases Figure 8 3 Box model representation of a plume release Britter 1979 considered a release in calm conditions An imposed ambient flow will limit the upwind spreading and ensure that all the source material is eventually carried downwind The mechanism by which this flow reversal is attained is uncertain For a uniform flow the flow reversal may occur solely through an inertial nonmixing process The flow interaction is less clear when the ambient flow is a turbulent boundary layer For a gravity current spreading under a turbulent flow
70. d stability being nearly top hat when Ri is large and the buoyancy driven flows are larger than the ambient flows with a negative experimental coefficient of 1 5 when Ri is of order unity or less and with a negative experimental coefficient of 1 0 over the extensive range of Ri The current dispersion model only allows for a value of unity This may be changed if enough evidence is available that this is necessary The near source description in this model for very negatively buoyant release is thought to be more correctly based than in other models however this complicated region may require more attention There is in fact very limited experimental data available on which to base a more sophisticated model of this region The influence of surface roughness and atmospheric stability on the dispersion code enters essentially through the effect on u There is little evidence available to confirm or negate this approach 88 GASTAR Section 8 Theory 8 3 Extended GASTAR 8 3 1 Source input algorithms 8 3 1 1 Instantaneous release The instantaneous source is modelled as a right cylinder with user specified dimensions Two options are available a in which the cloud and ambient momentum are well mixed such as might result from a catastrophic release and subsequent cloud expansion and mixing This cloud adopts the ambient velocity from the initiation time b in which the cloud and ambient momentum are not well mixed such a
71. ded this approach with the same consistent critical value from cases where the plume is larger than the obstacles to cases where the plume may be smaller than the obstacles More definitive data is required to confirm the correctness of this extension The model is unable to predict the detail of the concentration distribution within the congested region That is the lower limit on the spatial resolution is of the same order as the largest obstacles within the obstructed area 6 3 5 5 Further effects 1 Fence at angle to the ambient wind For a fence at an angle to the ambient wind we note that as far as turbulence generation by the 113 GASTAR Section 8 Theory fence is concerned the length of the fence interacting with the cloud increases but the ambient velocity normal to the fence decreases These two opposing though not exactly equal effects suggest that in the case of an oblique fence the model should just consider the fence as being effectively normal to the wind Arguments can also be presented for mechanisms to increase or decrease the cloud width caused by the fence as the angle changes In the absence of definitive information it is assumed that the effectively normal fence is adequate this also being consistent with the treatment of buildings 2 Fence or building solidity There is obviously an interest in modelling porous structures e g pipe racks forests etc This is initially approached by noting that some of the
72. dent friction velocity u The atmospheric stability may be characterised by the Pasquill Gifford stability category PSC or more objectively the Monin Obukhov length denoted here and elsewhere in Section 8 by L The user may input either the Pasquill Gifford stability category or the Monin Obukhov length and the surface roughness length zo When required the non specified descriptor is calculated from the relationships given in Table 3 2 The mean wind velocity profiles are given by Uw Li i v 17 u k Zo where u is the friction velocity m s k is the von Karman constant h is the height m at which the wind speed is to be calculated Zo is the Roughness Length m and y is dependent on the atmospheric stability eg the Monin Obukhov length L 83 GASTAR Section 8 Theory Pasquill Gifford Stability Category Monin Obukhov Length 123 5 703045 123 Say o 8 8 izt tA Table 8 1 Relation between Pasquill Gifford Categories and Monin Obukhov Lengths For stable atmospheric conditions h 4 L gt 0 A L and for unstable atmospheric conditions 2 y 2ln uri In ire 2arctan Z L 0 2 2 2 where hy is the height at which the wind speed is measured and with xi ise 1 4 D L The friction velocity is obtained by inverting the mean velocity equation 8 2 3 Thermal effects 18 19 20 Heat transfer to or from the ground is based on conventional forced and free convection heat
73. diameter W Table 4 1 Output parameters found in gof files 58 GASTAR Section 4 Viewing Output Release Frequency Information output types of output Dose C I T For each e Point number calculation Specified e x y and z coordinates of point Output Point e Dose in mol mol min or ppm min e Toxic load in mol mol min or ppm min where n is the toxic exponent e Information on status of point relative to cloud that might affect the value calculated e g point still within cloud at end of simulation Concentration C 1 T For each e x y and z coordinates of point time history Specified e Tabulated output in three columns giving time Output Point and the concentration in current concentration units and for I cloud centre coordinates at that time Flammable C I Once per e Time D release output simulation e x y and z coordinates of cloud center I C or for e for both the LFL and half LFL concentrations each range in m i e downwind distance of cloud Specified centre plus downwind radius of contour Output Time crosswind radius of contour in m b downwind radius of contour in m x maximum height at which concentration occurs in m volume within the contour in m mass of flammable release material contained within the contour in kg Maximum I Once per e maximum range i e the maximum distance over range simulation all simulated time between the origin and any calculation point on the
74. e flammables output for continuous releases add more SOP s over the flammable region or SOT s corresponding to passage over this region e range output add SOT s in general around the time that the cloud maximum concentration falls below the concentration of interest 5 Viewing and Plotting Output The Graphical Display folder is shown in Figure 4 1 GASTAR 3 2 D Examples CatastrophicF ailure puff2 gpl m Meteoroloy Souce Complex Ettects Output Graphics File Details d Path D E CatastrophicF ailure QD WJ Examples CatastrophicF ailure Plotting Details Graph Type Time from Release s XY Line Plotting J Arc Length m C Flammables Downwind Coordinate m Crosswind Coordinate m Vertical Coordinate m Integral width m Integral Height m Integral Volume nr Speed m s Integral Mass kg Integral Density kgr Integral Temperature K Integral Enthalpy kJ Integral Aerosol Fraction Mass Fraction Integral Concentration ppm v Max Profile Concentration ppm Integral Richardson Number Effective Width m Show Graph Effective Length m Cloud Footprint rr Trailing Edge Position m Leading Edge Position m lt uff1 GPH C C C C C C C C C C C C C C C C C C C C C C Plot all variables that have been checked Figure 4 1 The Graphics folder showing the X Y
75. e GPL file used for the run Finally the command line runs fest2 gpl which will create test2 gof test2 gph and test2 log in the root directory of the C drive A standard termination box will prompt the user whether to close the window Example 3 GASTAR EXE Y MODELS SET3 LST O1 I1 E3 19 GASTAR Section 2 Using GASTAR Runs all files listed in se13 st Output will consist of gof gph and log files for each entry in the lst file that exists The location of the gof gph and log files will correspond to the gpl file used for the run No termination box but the window is retained 2 7 2 2 Example command lines for a RISKAT run of GASTAR Example 1 GASTAR EXE I2 C PROJECT RISK1 Runs the files riskl mat riskl bmi riskl bsi from the C PROJECT directory bsys dat from the home directory of gastar exe and will also look for the file C PROJECTVisk slp It will also use the file bconc in from the gastar exe home directory to produce the output file CAPROJECTViskI bc A standard termination box will prompt the user whether to close the window Example 2 GASTAR EXE I2 O2 C PROJECT RISK1 MAT This will have the same effect as the example above Example 3 GASTAR EXE Y MODELS RISK2 O3 I2 E2 Runs the files risk2 mat risk2 bmi risk2 bsi from the YNMODELS directory bsys dat from the home directory of gastar exe and will also look for the file Y NAMODELSVisk2 sip It will also
76. e Source folder so if you change the Source material here it will be immediately changed in the GASTAR interface as well The initial Source Material will be that given on the main Source folder You may choose to use the User Defined substance on this folder if you wish but it can only be defined using the main GASTAR folder Similarly you can change the chosen material from the database but you may only view the data and link to an alternative data source using the main GASTAR folder 5 2 2 2 Pool type As material evaporates or boils off from the pool of spilled liquid a cloud will form above the pool The Pool Uptake model will provide information on the development of this cloud as it changes with time However it is also possible for the pool itself to be changing in time Therefore there is the option to have a Continuous or Time Varying pool A continuous pool will have a fixed dimension and therefore a fixed rate at which material is leaving the pool and contributing to the cloud above it A time varying poolis one that changes in time It is defined in a similar way to a Time Varying GASTAR release in that the pool development is broken down into a number of segments which last for a given time duration Each parameter required for the pool definition must be supplied for each segment of the release 64 GASTAR Section 5 Pool Uptake Model 5 2 2 3 Pool width A real number giving the physical width of the pool in metres
77. e an initial overview of the main features of the GASTAR Windows interface in Section 2 2 Then in Section 2 3 we describe the stages in setting up a problem for GASTAR to run while Section 2 4 deals with the running of such a problem Section 2 5 gives a preview of examining output from a run which is described in more detail in Section 4 Finally Section 2 6 describes the various preferences that a user can set and which control a number of ways in which the interface behaves while Section 2 7 details the GASTAR command line 2 1 Windows terminology In this section we list the main Windows features that make up the GASTAR interface defining the terminology that will be used elsewhere in the description of the computer model The user should refer to Figure 2 1 to see examples of most of the features described 2 1 1 Menus A menu is a heading offering a list of menu options The menus are located on the menu bar which is located near the top of the screen underneath the title bar see below By clicking on a menu title a list of options will appear from which a single selection is made A menu option may itself be a menu heading and selecting it will give rise to a further list of options For example the File menu has a list of options one of which Preferences will give a further menu of options if selected A menu option may also have an ellipsis at the end of its name for example Open this denotes that a dialogue box see below
78. e bottom of the interface screen is activated It displays a brief description of the data corresponding to the control If the control is a text box the help bar contains a maximum and a minimum value for the parameter If the user enters a value outside the permitted range GASTAR will display a warning dialogue box This tells the user whether the value is too large or too small and what the appropriate bound is The user must click OK to clear the warning box before re entering a value within the given range for that parameter 2 3 8 Saving Once all the desired changes to the input data have been made the user needs to save the values This is achieved in one of two ways a select Save on the File menu to save the input data in a gpl file with the same name as that currently loaded If either of options 2 3 1 a or 2 3 1 b had been used then there is no current name and the Save As dialogue box will appear see below b select Save As on the File menu to save the input data in a gpl file with a new name A dialogue box will appear allowing the user to specify the name and directory of the file ee 99 The extension gpl is added unless the file name entered contains a The user can also save a set of input data as a template file using the Save As Template option of the File menu see Section 2 3 4 2 3 4 Template files When setting up a new problem it is most convenient to edit an existing set of data rather
79. e first column of the summary table or unchecking the Consider this obstacle box on the obstacle definition form Having discovered the trajectory of the cloud you will know approximately where it will interact with the fence and can define a point near to that in the obstacle distance and bearing parameters Minimum 1 0 m Maximum 5000 0 m 3 3 2 8 Obstacle bearing The obstacle bearing together with the obstacle distance will position the obstacle relative to the source For buildings this is the bearing measured clockwise from North in degrees of the imaginary line drawn from the source to the centre of the building For fences this is the bearing measured clockwise from North in degrees of the imaginary line drawn from the source to a point along the fence whose length is the obstacle distance defined above Note that this parameter is linked with the obstacle distance defined above Please read the definition of obstacle distance and obstacle orientation for more details Minimum 0 0 deg Maximum 360 0 deg 3 3 2 9 Obstacle solidity The solidity allows the effect of the obstacle to be faded in or out It represents the ratio of the surface area blocked to the complete surface area for the obstacle projected into the wind As a general rule buildings are not porous and have a solidity of 1 The parameter is usually only applied to fences which are often not solid For example if the fence is a picket type where the slats ar
80. e giving rise to the cloud or the environment through which the gas cloud travels Thus the capabilities of the model include continuous instantaneous and time varying source types three dimensional jet model and pool uptake model available as additional source types flash calculation and aerosol releases complex effects sloping terrain and obstacles separately or in combination GASTAR runs on a PC under Microsoft Windows XP or Vista It should be installed and run on a standalone PC The number of standalone PCs on which GASTAR may be installed and run is controlled by the user s licence agreement GASTAR s Windows interface provides a user friendly environment in which to set up and run the model and view the output Output suitable for generating contour plots using other plotting software are generated for certain model options The model is quick to run with typical simulations taking at most a few minutes and often only a few seconds Overview of User Manual The User Manual contains the following main sections 1 Getting Started Installation of GASTAR and use of the model for the first time 2 Using GASTAR Overview of the operation of the model 3 Entering Input Detailed description of input data items and how to enter them 4 Viewing and Plotting Graphical display of model results Output 5 Pool Uptake Model Additional model that calculates source conditions due to a vaporising liquid pool 6 Materials Database D
81. e template files but again this is not recommended 11 GASTAR Section 2 Using GASTAR 2 4 Running a problem The next stage in the process of using GASTAR is to run the problem whose setting up has been described in Section 2 3 The obvious conclusion to entering data in the way described above is to go to the main menu and click on Run to run the program There is an alternative to this which is to run GASTAR from the DOS prompt These are both described in more detail below Note that in the majority of cases GASTAR is run from Windows and so the complications of command line arguments see below are avoided One circumstance in which they are required is in carrying out RISKAT runs of GASTAR 2 4 41 Running GASTAR from Windows Running a problem directly from Windows is achieved by selecting the Run main menu option The result of this action is that the interface calls the Fortran executable gastar exe with the current file name as an argument see Section 2 7 for more on command line arguments The model will then run as a QuickWin application completely separate from the interface The output files produced by a GASTAR run depend on whether or not the model is carrying out a RISKAT run see Section 2 7 or Section 7 for a list of output files produced by the model in each case Note that if the current input data have not already been saved as in Section 2 3 3 then selecting Run will cause the interface to prompt for saving
82. e the same width as the gaps between them an appropriate solidity factor would be 0 5 Minimum 0 Maximum 1 3 4 Complex effects slopes The Complex Effects folder Figure 3 9 displays a summary of the current slope data in table 39 GASTAR Section 3 Entering Input form You cannot manipulate the slope data directly in the table Complex effects are not available for Jet releases 3 4 1 Slopes summary The frame for the Slopes on the Complex Effects folder is similar to that for the Obstacles in that it has a check box the summary in table form and four buttons that control the editing of the slope data It also has a further check box for Meteorological data and a textbox for the bearing of the slope vector A more detailed description follows 3 4 1 1 Consider slopes check box The check box for the Slopes allows you to disable all the current slope data without having to delete it This is useful when you wish to run comparisons with and without the slope data Switching off the effect of slopes for a run allows you to keep the data rather than deleting it from the data file If the check box is not selected the rest of the Slopes frame will be disabled You must check this box before you can edit add or delete any slope data 3 4 1 2 Table Summary The table summarises the current slope data There are two columns in the table The first column gives the range of each of the slope segments measured in metres relative to the
83. ed from the main interface the changed values will not be copied back You must update the Air Temperature and Pressure on the Meteorology folder yourself The reason for this is to allow you to operate the Flash model as a tool or utility separately from the work you might be doing in the main GASTAR interface Flash Calculation Storage conditions Storage Temperature K 222 Atmospheric Pressure mb 1000 Normal method Exponential method Aerosol Fraction a Aerosol Fraction SSS Density tka Density ka m RE Source Temperature K EE Source Temperature K sil Material details Name 1 2 Butadiene Molecular Weight g Density kg m Boiling Point K Latent Heat of Vap kJ kg 448 63 Sp Ht Cap of Liquid kJ kg K 2 208 Sp Ht Cap of Gas kJ kg K 1 482 Atmospheric Pressure in millibars Min 800 Max 1200 Figure 3 8 The Flash Calculation screen 33 GASTAR Section 3 Entering Input 3 3 Complex effects obstacles The Complex Effects folder Figure 3 9 displays a summary of the current obstacle data in table form You cannot manipulate the obstacle data directly in the table other than turn individual obstacles on and off in the Obstacle table Complex effects are not available for Jet releases GASTAR 3 2 D GASTAR 3 2 Examples Crosswind Slo m a Ed File Run Help Obstacles iw Consider Obstacles On fence on slope Fence Orientation 100 90m away on a bearing o
84. ee obstacle distance and bearing Minimum 0 0 deg Maximum 180 0 deg PLAN VIEW TQ obstacle distance 0 obstacle bearing 9o obstacle orientation Figure 3 13 Definition of a fence 3 3 2 7 Obstacle distance This parameter together with the obstacle bearing will position the obstacle relative to the source For buildings this is the distance measured along the ground in metres from the source to the centre of the building For fences this is the distance to any point along the fence However this parameter is linked with the obstacle bearing so you will need to know the bearing of this line defining the distance Depending where you are obtaining the obstacle data you may consider a number of strategies to 38 GASTAR Section 3 Entering Input reduce the effect of any errors in your measurement data One way would be to measure the distance to the fence along a well defined direction such as North South East or West thereby removing the error in the obstacle bearing Another might be to find the nearest point along the fence to the source so that the fence orientation and bearing are 90 degrees different For cases where the orientation of the fence is quite oblique to the cloud trajectory you may wish to define the point along the fence that lies in the path of the trajectory In this case you may have to run the model without considering the fence ie turn if off by double clicking in th
85. egebat ente epa aeta ds oe 55 4 3 Graph display Teatileso ssa poiiE OS ie ue th oiqubt Ip Idi acad oid ius 55 4 3 1 Viewing the data values on a graph 4 sees eee dii pet alcol pest eade de SUNY 35 4 3 2 ZOOMING mon Ae SEA Pi A o evedonicis ede E got to e quad ipe detonee due deed inae Meat 55 4 3 3 Configuring th graph sies e Crece yide A n a R eed va E oed Yo api ean Ee Le bd eUS 56 44 OUIDpUt pardimelersic ete eter Notes io qum air utu Rutas qu te 57 4 5 Other data appearing in the output file 57 4 6 Output for plotting CODEQUES cs b rn eria Reid etatis For Mu Heo oed aet ocn ied ghey nea 57 Pool uptake model uiiaesceee evenisse dnt cusui va duda Y sdeuvens sasuesis seated apa aea eta daa dvd vasa rad ea dabo da 62 5 1 Accessing the pool uptake model 2 dito tedio i quida 62 Ou DpUES d en te utentes pu E e t te M A d ete iE ides 63 5 2 1 Meteorological input for the pool uptake model sss 63 3 22 Source input for the pool uptake model see 63 5 3 Running the model and using the results eene 66 5 3 1 Modelling Uffie sco ees nnen e e ash veu ues seddageasuanaaeeatoneat 66 353 2 Calculate uptake turc peto RUpE SI busto uia epit dE 67 5 3 3 Pool aptake TOSUlls acsi el etti dotem debo sar Messias iie ut 67 Materials Database ec NT 68 6 1 The materials database 2 eec tede EET Ec deed een eee 68 6 1 1 Viewing the materials database onte lest eos
86. en appearing comprising three folders two for input to the model Meteorology and Source and one for the results from the model Time Varying Results In order to ensure consistency data items which are common between the main dispersion model and the Pool Uptake Model are copied from the former to the latter when the Pool Uptake Model is launched It is therefore recommended that the meteorology and source data are entered on the respective folders of the main interface first before accessing the Pool Uptake Model and completing its own folders LSMS User Manual CERC 1997 62 GASTAR Section 5 Pool Uptake Model 5 2 Input The inputs to the pool uptake model are similar to those for GASTAR itself and are described in more detail below 5 2 1 Meteorological input for the pool uptake model The Meteorological input Figure 5 1 is a subset of the GASTAR input and the items have the same meaning Please refer to the equivalent sub section of Section 3 1 for a fuller explanation of these input parameters If you have data already entered into the Meteorological folder of GASTAR this will be copied automatically into the Pool Uptake Meteorological folder You may edit and change these data if you wish However it is very important to remember that if at the end of the Pool Uptake calculation you choose to use the results then all changed Meteorological data will be transferred back to the GASTAR interface overwriting any existing data
87. en the wind is downslope the cloud is narrower and the dilution is decreased The variation of the lateral growth of the plume results from the effective summation of the wind and the buoyancy induced motion down the slope The entrainment is influenced by the velocity shear and will therefore be enhanced by an upslope wind and reduced by a downslope wind The ambient velocity required 99 GASTAR Section 8 Theory to reverse a downslope flow of a plume or cloud is a weak function of a slope and is typically twice the downslope flow under calm conditions Turner 1973 In the case of cross winds Hall et al 1982 found that the dilution is not greatly affected although their conclusion is based on a single wind tunnel experiment Further discussion of these points is available in Britter 1982 A distinctly different topographic influence occurs when the topography alters the velocity field within which the cloud is dispersing Britter amp Snyder 1988 found this to be more important than the direct effect of the slope on the cloud Koopman et al 1982 provide results of field experiments showing the effect of more complicated topography with the plume moving to low lying areas The scouring of gases from low lying areas by the ambient flow has been addressed by Bell and Thompson 1980 and Briggs et al 1990 8 3 4 1 Uniform slopes Here we consider the influence of slopes on the dispersion of denser than air gas clouds ie where
88. eous Continuous and Time Varying releases only It consists of information on the flammable part of the cloud for releases of flammable materials specifically the following properties of the cloud for both the LFL and half LFL contours downwind and crosswind radius and range cloud downwind distance plus downwind radius of the contour volume enclosed within the contour mass of flammable material enclosed within the contour This information is recorded at each of the specified output times for Instantaneous releases and once only for Continuous releases e Check the Calculate flammable output parameters check box to obtain the above output 40 GASTAR Section 3 Entering Input for releases of flammable materials 3 5 6 5 Range folder This output is available for Instantaneous releases only It calculates the maximum range over all modelled time to a given concentration level The output consists of the maximum range found together with the time and the point s at which the maximum occurred e Check the Calculate maximum range output check box to obtain the above output e Enter the value for the concentration whose maximum range is to be found in the Concentration text box expressed in the current concentration units mol mol or ppm Minimum 0 00000001 mol mol Maximum 0 99999 mol mol 3 5 6 4 Gridded folder This output is available for Instantaneous and Continuous releases only If the user checks the Calculate Gridded
89. ers the evaporation from a developing pool and calculates the dimensions of the developing cloud above the pool For more details see Section 5 on the Pool Uptake Model 27 GASTAR Section 3 Entering Input 3 2 2 4 Gas and liquid jet release For jet releases either the physical source diameter or the pseudo jet diameter can be specified The initial mass flux Mo at the source is also specified The jet cross section is assumed to be circular if airborne and semi circular if the jet is grounded The model will calculate the source density po There is no height dimension for jets but the jet does have a height z to the centre of the circular cross section The initial temperature To for Thermal and Aerosol cases initial aerosol fraction for Aerosol cases initial concentration Co and initial density p are assumed to be uniform over the initial section For Jet releases there are options for the source to be elevated and to be orientated in any 3 D direction see Figure 3 4 3 2 3 Source details The exact requirements are dependent on the Release Type Where there is a choice of release types including Instantaneous releases items in parentheses generally refer to the non instantaneous case There follows a brief explanation of all inputs 3 2 3 1 Source location The source location can be entered in one six formats that can be chosen by clicking Change on the Source folder and selecting a format from the drop d
90. exists an avenue for model improvement if this was found necessary 105 GASTAR Section 8 Theory 8 3 5 Buildings and obstacles The arguments and algorithms below are based on work in Britter 1982 Britter and McQuaid 1988 Britter 19892 Britter 1989b Britter Cleaver and Cooper 1991 and Brighton et al 1993 Some of the original algorithms developed by Britter were implemented in GASTAR V2 24 They have been extended particularly with appropriate interpolation formulae implemented within a dense gas model and compared favourably with experiments by Cleaver et al 1995 The interpolated algorithms have been incorporated into GASTAR V3 00 8 3 5 1 Releases near individual obstacles Denser than air clouds may be significantly affected by the interaction of the cloud with solid or porous obstacles such as buildings tanks or pipe arrays or the source structure itself Our approach is to consider a small number of relevant and commonly occurring situations and to seek to provide models for those cases Within the spirit of integral models we look for algorithms that will reflect the influence of obstacles on advection speed and direction dilution and for time varying or instantaneous releases the fluid hold up near the obstacle Studies by Britter 1982c K nig 1987 and Britter 1989b provide a basis for algorithm development In addition there are many studies both field and laboratory which can be used for model
91. f 190 Edit Small tank Circular Building Diameter 10m 50m away on a bearing of 45 Copy Delete Slopes V Consider Slopes Use Met Screen data for all slopes 10 Bearing of Slope Vector INF to 78 Angle of 0 0000000001 Roughness length 0 01m Wind Speed of 5m s at 10m Edit 78 to 145 5 Angle of 39 8 Roughness length 0 01m Wind Speed of 5m s at 10m 145 5to INF Angle of 3 2 Roughness length 0 01m Wind Speed of 5m s at 10m Split Delete Add a new obstacle Figure 3 9 The Complex Effects folder 3 3 1 Obstacle summary The frame for the Obstacles on the Complex Effects folder has a check box the summary of obstacles in table form and four buttons that control the editing of the obstacle data A more detailed description follows Sud Consider obstacles check box The check box for the obstacles allows you to disable all the current obstacle data without having to delete it This is useful when you wish to run comparisons with and without the obstacle data or because you have changed the wind direction and know that the obstacles are no longer important Switching off their effect for a run allows you to keep the data rather than deleting it from the data file If the check box is not selected the rest of the Obstacles frame will be disabled You must check this box before you can edit add or delete any obstacle data 34 GASTAR Section 3 Entering Input 3 3 1 2 Table Summary The ta
92. f slopes or obstacles codes while Version 3 00 allows selection of slopes and obstacles simultaneously In future versions the other three scenarios may be re instated 106 GASTAR Section 8 Theory found on many industrial sites As an example of our general approach consider cases i and v For the case of a two dimensional fence normal to the flow the relevant dimensionless parameters are 1 25 81 in the absence of the fence and h 82 5 82 otherwise where H is the fence height U is the cloud advection speed h is the height of the cloud centroid g is the reduced gravity The reduced gravity is defined as s 4 22 1 83 Pa where pm is the maximum ground level density within the cloud and p is the density of the ambient air Observations from Britter 1989b based on continuous plume experiments indicate that the effect of the fence is to widen the plume upstream of the fence and to dilute the plume in the lee Britter argued that the ratio of plume width with a fence wy to that without the fence wnf was such that 2 WS f ane 84 An empirical fit to the data which is currently used is LE H e 85 Wop h U The dilution in the lee of the fence is such that the bulk plume concentration can be expressed as 7 The curve fit given here is a corrected version of that appearing in Britter 1989b 107 GASTAR Section 8 Theory C qo 1 id Ur cc AEH v 66 whe
93. flow Little information is available concerning three dimensional flows under calm conditions Unlike two dimensional flows the release is able to spread across the slope and the Reynolds number of the flow based on the flow depth may increase with distance from the source Fietz amp Wood 1967 As a consequence these flows in the laboratory are frequently influenced by viscosity which reduces the downslope velocity the width and the dilution Picknett 1981 found that instantaneous releases under non calm conditions on a slope of 1 13 were influenced by the slope for very low wind speed conditions Hall et al 1974 observed that slopes of 1 12 and 1 50 respectively altered their continuous plume results Broadly three characteristic velocities are relevant e the ambient wind velocity e the buoyancy generated velocity found on flat terrain e the buoyancy generated velocity found on slopes downslope The latter two velocities both scale on g ny As the coefficient in the expression for the slope flow is only a weak function of slope the slope will have an effect on the clouds for which buoyancy generated velocities are relevant However the flow development times may differ For example the instantaneous release might initially spread radially then develop a bulk downslope flow before finally being diluted and swept upslope by an ambient flow When the wind is upslope the cloud widens and its dilution is enhanced Wh
94. found before terminating the current run The error message should help to discover the cause of the problem 14 GASTAR Section 2 Using GASTAR If the program terminates with error code 1 then there has been some other error not accounted for by the Fortran code In such cases it is advisable to take note of any error messages that appear on screen before exiting GASTAR and Windows and re booting your PC Having done this attempt to run the same inputs that previously caused the program to fail to see if the problem is repeatable Sometimes testing the code on an alternative machine will also highlight possible faults and or differences between two PCs In this case check the configuration of both machines to see what differences there are look in the config sys and autoexec bat files to see if there might be conflicts with other software that is being loaded when the computer boots up When the Fortran code notices a possible problem with data and or results it will issue a warning to the screen or the log file or the data output file whichever is the more appropriate place For example if the interpolation code calculates values beyond that to which it has integrated a warning is included in the output file This will not cause a terminal error to occur so the code continues with the dispersion calculation However the validity of the output beyond the distance actually integrated will be questionable so this is flagged to the user by
95. from the c T underlying surface and in the latter as the stored material P m i Y Ger slowly depressurises the mass end time flow rate through the rupture will reduce Figure 8 5 Time varying release These are typically treated by replacing the time varying release as a finite number of discrete release rates Segments of the solution for each of these release rates are combined to form a segmented plume solution Longitudinal diffusion dispersion may be added to smooth between the segments or to treat the leading and trailing segments 79 GASTAR Figure 8 6 Box model representation of a time varying release matches the material emanating from the primary source Section 8 Theory It might be noted here and will be considered further in Section 8 3 2 that not all the released airborne material need be taken up by the ambient flow passing over the source position If this is the case the cloud over the source position will expand with time to produce a secondary source or vapour blanket This will continue to expand until the material taken up by the ambient flow 80 GASTAR Section 8 Theory 8 2 GASTAR dense gas dispersion model 8 2 1 Dispersion model A specific description of the overall GASTAR model is best addressed by considering the dispersion module first The model is a similarity model in that similar shapes are assumed for various parts of the model thus reduc
96. gas LNG following a spill onto a warmer surface 3 materials with low molecular weight and whose vapour at the boiling temperature is less dense than the environment but which as a result of the release type produce a cloud including liquid droplets The cloud borne droplets increase the cloud density as does the cooling resulting from their subsequent evaporation e g ammonia see Griffiths amp Kaiser 1982 and 4 materials in which a chemical transformation takes place as a result of reaction with water vapour in the ambient atmosphere e g nitrogen tetroxide N2O4 hydrogen fluoride HF see Clough et al 1987 Storage and release conditions have been discussed by Fryer amp Kaiser 1979 The releases may be broadly classified as instantaneous e g catastrophic release continuous e g pipe break or time varying The release may also be classified as either pressurised or non pressurised depending on the type of containment Source term models have been reviewed by Hanna amp Drivas 1987 The quantitative assessment of the dispersion of dense gases is quite different to conventional dispersion problems for the following reasons 1 unlike covenanted chimney emissions the modes of release are very diverse in terms of geometry and source specification 2 because the released material is typically stored in a liquid phase the volumes of gas released may be very large 3 the release may be a gas liquid mixture 4 t
97. h Design form which itself is accessed via the Graph Setup button There is no attempt here to describe the configuration options available for the graphing display please refer to the online help accessed using the Help button on the Graph Design form 56 GASTAR Section 4 Viewing Output 4 4 Output parameters As noted in Section 7 the main formatted output file is the gof file produced for each problem This contains the model set up parameters entered in the GASTAR interface and saved in the gpl file followed by the values of the main integration variables at each integration step together with some other derived variables The meaning of each output parameter is given in Table 4 1 Notes on Table 4 1 a most of the parameters in the gof file are obtained directly from the integration routines i e they are the values of the box model variables see Section 8 or they are derived directly from these variables Those which are not are marked with an asterisk b in general a parameter refers to the flux at a given cross section when the release is continuous or time varying or a jet but refers to the whole cloud for puff releases c for puff releases the time corresponding to a given parameter value is the actual elapsed time since the release was made for all other types of release it refers to the time taken for material to be advected to the given point along the plume cloud jet 4 5 Other data appearing in the output
98. h due to a building is found from w max W w 0 5W 91 The third parameter the confining width refers to the scenario ii a confining or three sided fence These results are applied to instantaneous continuous and time varying releases For the instantaneous release W is replaced by D the puff diameter That is the advection velocities determined from the ambient velocity at a fixed fraction of the cloud depth together with any slope induced velocity 110 GASTAR Section 8 Theory The height conversion is given by h max hj h 92 where ht 2 h Rovertapth 93 The overlap parameter Roverlap is given by i m 94 Ww for the continuous and time varying cases where w is the length of the overlap region and by Al 95 m 4 w for instantaneous releases where A is the overlap area The first term just spreads the upstream cloud depth over the new cloud width The exponent n is unity for continuous and time varying releases and two for instantaneous releases The height rise dh is given by a mixture of expressions for fences and buildings the expression for a fence is dh H S 96 w and that for a building is dh ni Oat H z 97 R w l so that dh F dh 1 F dh 98 where F is a factor used to combine the two results When wf gt 2w the interaction will be that for a building in that the cloud can go around as well as over the build
99. he coefficient C is near unity and is a weak function of slope It may be obtained from experimental results in the absence of any ambient wind In these cases the flows adopt a constant value of C due to a local balance between a downslope force and a retardation due to skin friction and or entrainment In the current version of the code the coefficient C has been set to reflecting the approximations pervading the approach More refinement may be appropriate following extensive model usage 6 3 4 4 Lateral plume spreading No modification is made to the radial or lateral plume spreading to account for slopes This implies that the velocity in particular the downslope component for both the uphill and downhill edges remains unchanged by the presence of the slope and there is symmetric spreading about the cloud centreline Any modification would have involved a velocity scaling on g h e the same scaling used for the downslope flow and typically for the cloud edge velocity 8 3 4 5 Entrainment In dealing with the entrainment we note two effects i entrainment due to the difference in velocity between the buoyant downslope motion and the ambient motion which is considered as an interfacial mixing flow and ii entrainment due to surface generated turbulence this might be expected to depend on the advection velocity over the ground For the first effect we note that the difference in velocity is just C e hY We appeal here to
100. he release is usually transient 5 the formation of the gas cloud typically involves phase changes and there may be heat and or mass transfer with the underlying surface In addition the dispersing gas forms a low level cloud that is sensitive to the effects of both man made and natural obstructions and topography Cloud is used here as a general descriptive term plume refers to a continuous release whereas puff refers to an instantaneous release 74 GASTAR Section 8 Theory These complications indicate that the task of predicting the consequences of an accident will not be simple Further the rapid development of the field has restricted specific study of the various relevant fluid mechanical phenomena 8 1 2 Physical processes in dense gas clouds The density difference between the released material and its environment introduces four major effects with regard to dispersion problems The velocity field produced by the horizontal density difference in a gravitational field is an additional transport mechanism to that provided by the ambient flow This self generated flow produces a cloud with an increased horizontal and reduced vertical extent when compared with a similar release having no density difference In addition the self generated component of the motion is predominantly deterministic not random as a result profiles of concentration in the lateral direction are frequently quite uniform The velocity shear
101. hen the jet reaches the ground the z momentum is turned off and the cross sectional shape is changed from circular to semi circular but maintaining the jet area The jet touchdown occurs when the centroid height reaches R 2 The code also calculates when both the jet edge i e the radial edge and the centroid intersect the ground After the jet reaches the ground it may still develop in the horizontal plane subject to the ambient wind However as the jet axis but not the centroid is now on the ground the velocity of the entrained ambient fluid is taken to be at a fraction of the jet radius namely z 0 56R 67 6 3 3 3 Transition to the dense gas model The jet model calculation is halted when the jet velocity reduces to some predetermined level and 96 GASTAR Section 8 Theory the jet has attained the touchdown criterion The jet velocity must asymptote towards the ambient velocity so the criterion for transition must be in terms of u U and this should be referenced to buoyancy generated velocities which 1 2 E shee B will scale on e R We use as an indicator of transition the criterion E 1 2 1 2 1 1 zh u U Ed 68 At this point transition to the dense gas model occurs with an initial width of aR 1 2 1 i 69 4 and a height determined by a mass balance calculation in the usual manner for plumes 8 3 3 4 Positively buoyant jets The model can address the problem of a positively b
102. i is a measure of the puff or plume stability f h h n 2 d 11 Pa Ux Ux in which u is the friction velocity of the undisturbed flow and is a measure of the atmospheric turbulence 8 2 1 2 Dilution of the cloud The dilution of the cloud is modelled using an entrainment velocity approach ie the cloud mass m evolves according to p u A u 4 12 where ue and u are edge and top entrainment velocities and are determined by appeal to correlations based on experiments A and A are edge and top entraining areas respectively The puff or plume is diluted by mechanisms associated with the advancing leading edge edge entrainment and the downwind advection by the ambient wind field top entrainment These are modelled using entrainment velocities The edge entrainment velocity ue is modelled by u 0 6u 13 where upis the leading edge velocity For instantaneous releases a further factor Ao R accounts for the initial aspect ratio of the release The top entrainment velocity u is modelled by 0 4u Mr 1 0 125Ri a after an appeal to the results of McQuaid 1976 as analyzed by Britter 1980 and further experimental results by Stretch 1986 and others Top entrainment due to thermal convection in the cloud is incorporated using a model based on penetrative convection This reduces essentially to the incorporation of the conventional convection velocity w in addition to u 6 2 1 3 Advection
103. ical display does not update immediately it is necessary for you to click on the Plot Graph button which then updates the plot If you just want to bring the graphical display to the foreground without re plotting any data use the Show Graph button This will restore the graphical display window without the update 4 3 Graph display features A typical example of a graph produced by the procedure in Sections 4 1 and 4 2 is shown in Figure 4 4 In the rest of this section we describe other aspects of the display 4 3 1 Viewing the data values on a graph When you plot a graph in the graphical display the actual data values are available in a number of ways The panels on the left below the graph give the actual values plotted on the independent x and dependent y axes The set and point being displayed can be changed using the spin buttons The graph control can also respond to clicks from the mouse If you position your cursor over a point and click the left mouse button the corresponding data value will be displayed in these panels Alternatively if the graph is displaying a linear linear plot i e not using logarithmic axes then as you move the cursor over the graph the panels below the graph to the right will display the current cursor location To obtain an indication of the value of any plotted point hold the cursor over the point and read the values given in these Current X and Current Y panels Finally the complete data sets are
104. idge TN U S A Briggs G A Thompson R S amp Snyder W H 1990 Dense gas removal from a valley by cross winds J Hazardous Materials 24 1 38 S Brighton P W M 1988 The effects of natural and man made obstacles on heavy gas dispersion U K S R D report to C E C under contract EV4T 0013 UK H Brighton P W M amp Prince A J 1987 Overall properties of the heavy gas clouds in the Thorney Island Phase II trials J Hazardous Materials 16 103 38 Brighton P W M Jones S J amp Wren T 1993 The effects of natural and man made obstacles on heavy gas dispersion Part 1 Review of earlier data AEA Technology Report SRD HSE R581 O Brighton P W M Prince A J amp Webber D M 1985 Determination of cloud area and path from visual and concentration records J Hazardous Materials 11 155 178 Britter R E 1979 The spread of a negatively buoyant plume in a calm environment Atmos 117 GASTAR Section 9 References Environ 13 1241 47 Britter R E 1980 The ground level extent of a negatively buoyant plume in a turbulent boundary layer Atmos Environ 14 779 85 Britter R E 1982 Special topics on dense gas dispersion Health Saf Exec Rep 12001 01 01 Sheffield UK O Britter R E 1986 Experiments on some effects of obstacles on dense gas dispersion Saf Reliab Dir Rep SRD R407 U K A E A Culcheth UK O Britter R E 1989a Atmospheric dispersion of dense gases Ann Rev
105. ient A Antoine Coefficient B Antoine Coefficient C g mole kg m at STP K at SP kJ kg kJ Kkg kJ Kkg The Heat Transfer Group is a composite property that takes the value MW cpo v T Pry J where MW is the molecular weight and T is a representative temperature in K taken to be 273 17K 71 GASTAR Files This section describes some of the files associated with GASTAR of which users will need to be aware These are the licence file which is needed to run GASTAR and the user generated files which are created by runs of GASTAR 7 1 Licence file To install GASTAR users must firstly run the install CD as described in Section 1 2 The GASTAR licence file is sent by email to the licence holder and the licence file must be named and if necessary renamed to gastar3 lic and copied to the application directory i e the directory in which GASTAR is installed Users should ensure they keep a backup of the licence file on a suitable media 7 2 User generated files There are a number of user generated files These have a common stem path name indicated by lt prob gt in the list below The generated files are stored in the same directory to which the gpl is saved It is good practice to keep your model runs together in a dedicated directory with sub directories as appropriate to contain different sets of runs lt prob gt gpl Main input file prob gof Formatted output file prob gph Unformatted outpu
106. ight is spread averaged over the complete plume width 8 3 5 3 Model implementation Cleaver et al 1995 have combined the algorithms for fences and buildings into a common algorithm A fence normal to the flow direction has unlimited width and a height H while a building has a width W and height H Three cases are considered The width W is actually the effective width in a direction normal to plume trajectory 109 GASTAR Section 8 Theory h lt H a strong interaction regime H lt h lt 3H an intermediate regime h gt 3H a no interaction regime where is the cloud depth prior to obstacle The model requires a conversion of the cloud dimensions w h prior to the obstacle to w h following the obstacle These together with the standard advection velocity formulation will determine the cloud concentration Strong interaction regime In the first of these three cases the cloud width is given by w min Wf Wp W 88 where Wr is the width after implementing the fence algorithm Wp is the width after implementing the building algorithm We is a confining width around the source The new width due to a fence is found from wy A ap l R w h i 89 where w is the width of the cloud before the interaction and Ri the Richardson number is defined by gh Ri T 90 where U is the advection velocity prior to the interaction c f Ri based on the friction velocity u The new widt
107. ighthill 1956 The time delay must be proportional to H U and depend upon h H in the absence of buoyancy effects Currently our model includes an empirical description of this time delay function that is independent of buoyancy effects Thus the model includes algorithms for cloud widening cloud dilution cloud hold up i e longitudinal diffusion and cloud time delay These algorithms are based on an appropriate description of the physical phenomena involved and semi empirical or empirical quantification Extension of the approach to a confining fence for example a three sided fence downwind of the source is straightforward and involves a constraint of the lateral width of the cloud equal to the distance between the two side fences If the cloud grows laterally to this width then the cloud fence interaction becomes two dimensional Britter 1989b The only complication is that an assessment must be made as to whether or not the cloud is blocked by the fence Britter 1989b This has no effect on any steady solution for a continuous release but will influence the time development to that solution It will be of more interest for an instantaneous release which may be trapped for a considerable time 108 GASTAR Section 8 Theory Turning now to the second case of an individual building the same type of arguments can be applied when seeking to model the cloud widening cloud dilution etc The plume width downstream of an obst
108. iled guidance on how to go from a to b other than to describe the input data items and to provide some notes on the selection of values In the rest of this section we are concerned with the general points concerning how to go from b to c i e how to set up a gpl file the details of specifying the input parameters are covered in Section 3 2 3 1 Starting There are several ways to begin setting up a GASTAR problem a when the interface is started up the text boxes are blank and the controls which require a choice are at their default settings a fixed choice accompanying the interface The user can then enter all values and make choices from scratch b by selecting the New option on the File menu the text boxes are blank and control settings take their default values exactly as in a This is the recommended way in which to start a new problem from scratch c by selecting the Open option on the File menu the user can browse the current directory or other directories to find a gpl file which has been defined previously By default the interface will only display files with the gp extension This is the recommended way in which to start a new problem based on a pre existing one d by selecting the Open Template option on the File menu the user can open a template file which can be used as the basis for a new input file see Section 2 3 4 2 3 2 Editing Whichever method is used to start setting up a problem the user
109. in 85 8 2 6 Longitudinal shear dispersion esee 86 8 2 7 Concentration profiles soe cit iti e ent de uius tui Ede 87 8 2 8 Ayeraging IIT 88 8 2 0 Current model limitations and uncertainties eeeeeeeeee 88 8 3 Extended GASTAR sss cons GosbistasaDo p cMduiietes du sec aleate Dee du tq ecu 89 8 3 1 So rceInp t ale OBL BIERS siepi E A E epa Eo peps 89 8 3 2 Uptake model e etu ie E umb iv R R REO EON 91 8 3 3 Jet stiodel 432926 ihe Hte ie ere sete d eedab a aasia 93 8 3 4 GOD AY sas uoti EURO DU ESSENT S NU Gehan EE meld nn staple d aiat 99 8 3 5 Buildings and obstacles ran enin etas se en Ue Tee eae eae enge 106 Disc References codd er e Quod ENEN EAE E NA RARE PERLE 117 iii Preface This document is the User Manual for Version 3 2 of the GASTAR dense gas dispersion model It is a self contained description of both the installation and use of the computer model and the theoretical basis for the underlying mathematical model and is intended as the main point of reference for beginner and experienced user alike GASTAR is an integral or box model describing the evolution of a dense gas cloud in terms of properties integrated or averaged over the entire cloud or over sections through it The model comprises a main dispersion calculation determining the concentration and thermodynamic properties of the gas cloud augmented by a variety of sub models representing different features of the sourc
110. ing Thus F 0 When w lt wp 2 the building will look more like a fence and the cloud must go over the building Thus F 1 Between the cases an interpolation is used namely F EZ 99 2 2 w tW 111 GASTAR Section 8 Theory Intermediate regime For the intermediate region an interpolation is provided between the interaction when h H and the no interaction case when h 3H using an interpolation parameter G A 100 2H which runs from unity to zero as the cloud depth increases from H to 3H The cloud width conversion is w 2Gw 1 G w 101 where w is calculated as before in equation 88 but with A H The cloud height conversion is dh 2 G dhy 102 where dhg is calculated as before in equation 92 but with h H The previous calculation in cloud height increase has not taken into account that in some scenarios the cloud after the obstacle can extend beyond the obstacle however only the cloud in the lee of the obstacle can be diluted by the lee turbulence Again consistent with the integral model formulation being developed this increase is spread averaged over the complete cloud This is handled by the parameter Roveriap 6 3 5 4 Releases near individual obstacles Another scenario for which current models are not directly applicable is an accidental release into a complex array of obstacles occurring on site Brighton ef al 1993 in his review notes Although some other data exists on dispe
111. ing the basic equations of motion to simpler ordinary differential equations These equations are written in bulk or box model form then modified to re introduce the assumed profile This technique is common in the study of buoyancy or density influenced flows Turner 1973 The dynamics of the flow influence the motion of the similar shape The bulk characteristic dimensions of the puff or plume the radius or width and the height are then the mean radius R or width w and the height of the puff or plume A The rate at which a puff or plume spreads horizontally under its own negative buoyancy is given by a gravity current head formula 8 2 1 1 Horizontal spreading Horizontal spreading of a plume is modelled with a gravity current head formula u C g h 7 where g A 8 and C is a constant near unity p is the uniform density within the modelled puff or plume and pa is the ambient density The velocity uy is the horizontal velocity of the edge of the plume Thus dR dw 2 or dt dt CF g h 9 In the case of an instantaneous puff release a more complicated algorithm is used in the model to account for the initial radial acceleration although this rapidly asymptotes to the above form Atmospheric turbulence acts to reduce CF see Linden amp Simpson 1988 and this effect is modelled by the empirical form 81 GASTAR Section 8 Theory Ly 1 CF CF E j 10 where the Richardson number R
112. ion by atmospheric and self generated turbulence In contradiction to the often made assumption there is no evidence in laboratory or field experiments that dense gas plumes appear as a well mixed layer surmounted by a sharp density interface In fact quite the opposite is observed with the vertical profiles of mean concentration having a near exponential variation The height of the plume centroid is substantially reduced when the plume is dense which is a result of the buoyancy driven flow and reduced vertical mixing Density differences reduce the mixing between the plume and the environment but the large surface area of the plume across which mixing takes place will enhance dilution Observations from Britter amp Snyder 1988 show that these two effects can often produce a decay of the maximum ground level concentration very similar to that for neutrally buoyant passive plumes Other laboratory studies Meroney 1982 have also found that the ground level concentration is not as strongly influenced by the density difference as is the plume shape 8 1 6 Time varying releases In many situations the release is neither instantaneous nor Segment Property E Q D p etc continuous but varies with time For example consider a pool of a boiling liquid cryogen or a rupture of a pressurised line or vessel In the former case the pool can spread over the ground l oe providing an increasing area Sene Sen for the transfer of heat
113. ion of slope bearing Edit will bring up the Slope Definition form with the details of the slope currently selected in the table You can change any part of the data and save it again if you wish If you cancel the form from this point none of the changes will be saved and the slope definition will be left unchanged E Split The Current Slope Choose a new slope distance in the range 78m To 145 5m Figure 3 15 The Split Slope dialogue box Split will firstly bring up the Split Slope dialogue Figure 3 15 asking you to choose the point at which you wish to split the current slope The current slope range is provided and you will have to choose a number within this limit If you cancel this form the slope will not be split Having entered a valid number and clicked OK the Slope Definition form will be displayed with your new split distance value already entered but greyed out This is because it cannot be changed again when splitting a slope into two slopes although it can be re edited once the second slope 42 GASTAR Section 3 Entering Input has been accepted The other data on the Slope Definition form will be copied from the original single slope any of which you may edit If you cancel this form the slope will not be split Delete will delete ie completely remove the definition data of the currently selected slope in the table The region of the deleted slope is absorbed into the slope definition of the preceding slope
114. is no cloud initially you should use the pool width value defined above Minimum 0 01 m Maximum 1000 0 m 5 2 2 7 Hazardous fraction This is the same as the parameter given on the main Source folder This parameter gives the fraction of the released material that is considered hazardous For general use this is the whole release consequently this has a default value of 1 For more details see the main entry in Section 3 2 34 Minimum 0 0000001 65 GASTAR Section 5 Pool Uptake Model Maximum 1 0 5 2 2 8 Cloud temperature A real number giving the initial cloud temperature over the pool in kelvin This matches the Source Temperature parameter on the Source folder of the main interface This information will frequently be derived from a pool spill model such as LSMS This will also give the starting temperature for the cloud As a guideline if the material is classed as a cryogen then it will boil off and produce a cloud at the boiling point of the material However if it is considered to be volatile then the cloud will be at the pool temperature Minimum 20 K Maximum 1000 K 5 3 Running the model and using the results The Results folder Figure 5 3 allows the user to run the pool uptake model view the time varying source term that GASTAR would use to model the evaporating pool spill and use these results ina GASTAR run POOL UPTAKE SOURCE MODEL Weed Sauce Time Vaging Reed Modelling Time Modelled Time
115. ise the difference between the dense gas dispersion and the dispersion of non dense or passive pollutants It is obvious that the density difference is not the sole variable determining whether the release behaves as a dense gas A very small release or release rate into a strong wind or alternatively a release over a large source area may be considered effectively passive A continuous source of volume flow rate qo with source density difference characterised by gj may be considered effectively passive when 243 D U x 0 15 5 where D is the source dimension and U is the ambient velocity Britter amp McQuaid 1988 E s Y i 1 3 For an instantaneous source of release volume Qo and implied source dimension Qo the criterion becomes 75 GASTAR Section 8 Theory eroi J ju 02 6 The form of these criteria emphasises the importance of the ambient velocity in describing the flow In the latter criterion a halving of the wind speed is equivalent to a 64 fold increase in Qo In addition there may be thermodynamic or chemical processes depending on the nature of the material and the release conditions Eventually the dispersion of the cloud becomes passive due to dilution 8 1 3 Dispersion models There are probably in excess of 100 analytical or numerical models currently available that purport to describe the dispersion of dense gases Reviews by Blackmore et al 1980 Wheatley amp Webber 1985 and Hanna amp
116. it The passive limit will be an upper limit and will approximately have a linear plume growth over the downstream distance of the physical source size or possibly over the vapour blanket We use as an upper limit of the plume thickness to input to the dispersion model 0 05D where D is the along wind dimension of either the physical source or the vapour blanket if one exists the along wind dimension being equated to the cross wind dimension in the current version Under these circumstances such as the dispersion from a large pool of evaporating petrol the initial concentration of the plume will be less than the concentration from the source Finally we note that a difficulty can arise when the release is near passive thus not allowing any significant vapour blanket formation but with a large vapour flux Under these circumstances the plume depth H is determined solely by the kinematic mass conservation requirements that i DHU z 0 56H 36 where D is the width of the physical source 8 3 1 3 Continuous release alternative This source allows completely user specified initial width for input to the continuous release code This option is applicable if for example the releases scenario imposes externally a specific dimension on the plume at the source position 90 GASTAR Section 8 Theory 8 3 2 Uptake model A continuous release starting from time 0 will take some time to establish steady state near source condition
117. l turbulence is strongly damped by the stratification 24 GASTAR Section 3 Entering Input 3 2 Source details The Source definition folder is shown in Figure 3 3 Below is a complete list of the input parameters needed to define the source GASTAR 3 2 untitled Com File Run Help Source Material From Database 1 2 Butadiene v View Data C User Defined Release Type Instantaneous iw Momentum Initially Well Mixed isahemal Release C Continuous C Time Varying C Gas or Liquid Jet Aerosol Release Thermal Release Source Details Source Location 70301799 UK Change Release Start UTC 12 00 08 Apr 2003 Initial Air Entrainment ka Puff Diameter m mE Mass kg mE Hazardous Fraction ppm 1000000 Temperature K oOo Aerosol Fraction kg kg ooo Flash Mass kg or mass flux kg s of the Air initially mixed with the released material in 0 Max 1000000 Figure 3 3 The Source definition folder 3 2 1 Source material If the From Database radio button is selected material is selected from the drop down list box Click on this with the mouse or type ALT 1 or ALT at the keyboard to make the list drop down All materials available in the database can then be scanned and selected Notice that the list will always be alphabetically sorted no matter what order the materials might appear in the database Typing a letter will automatically change the current entry to one whose first letter
118. lopes with their own meteorological data this is disabled and the caption Slopes On appears in the textbox In such circumstances the cloud development is based on the conditions prevailing on the current slope For more details see Section 3 4 1 10 under Slopes Minimum 0 1 m s Maximum 20 0 m s 3 1 2 Wind height A real number defining the height in metres above the ground at which the wind speed measurement above was taken If you have defined slopes with their own meteorological data this is disabled and the caption Slopes On appears in the textbox In such circumstances the cloud development is based on the conditions prevailing on the current slope For more details see Section 3 4 1 11 under Slopes Ithas been common practice to measure the wind height at 10m and consequently a default value of 10 appears in this textbox Minimum 0 1 m Maximum 15 0 m PLAN VIEW 0 jet bearing azimuthal angle U wind direction x gt Jet direction E Figure 3 2 Definition of wind bearing and x axis 22 GASTAR Section 3 Entering Input 3 1 3 Wind direction A real number defining the wind bearing measured clockwise from North in degrees Note that this uses the meteorological definition of wind bearing namely the direction from which the wind is coming see Figure 3 2 The slope bearing and the jet release azimuthal angle are defined in a similar way Minimum 0 0 deg Maximum 360 0 deg 3 1 4 Roughness leng
119. loud on horizontal ground is advected on to an uphill slope Depending upon the magnitude of this slope the cloud may then have an advection velocity back down the slope towards the horizontal ground In practice it is expected that a cloud puff or plume segment would linger there broadening and diluting until the cloud was able to travel up the slope The code mimics this behaviour by allowing the cloud to make very small time steps on and off the upward slope until the density is such that the ambient wind will take the cloud up the slope Thus there may be two cloud conditions at the base of the slope one corresponding to the cloud s arrival there and one corresponding to its departure from there up the slope The downslope velocity will asymptote towards zero with time The slope entrainment term for the instantaneous release has been taken from still air experiments on slopes It is apparent that this will include to some extent the edge entrainment velocity of conventional box models There is then the possibility of double counting Consequently the direct slope entrainment term is only used when it exceeds the sum of all other entrainment terms A possible defect of the model for instantaneous releases is the assumed similarity shape essentially based on a flat circular cylinder which may be less appropriate for situations with significant slopes Of course this does not mean that the predictions may not be very useful only that there
120. lume is exhibiting dense gas effects 8 2 8 Averaging time An averaging time option is available for plumes and this accounts for meander This has a minimum default value to be consistent with puff dispersion parameters The use of smaller averaging times is not justified for determining peak puff or plume concentrations A specific concentration fluctuation module is required 8 2 9 Current model limitations and uncertainties The general philosophy behind the modelling has been to ensure that the model is physically correct and as simple transparent as possible Several physical effects have not been included initially because it is commonly the case that their inclusion produces a vastly more complicated model with no commensurate improvement in model performance Thus while we have no qualms about minor changes in some model constants or incorporation of other better physical descriptions this will only be done when it is apparent that the model is severely lacking in performance in some particular area We believe that it is essential for there to be strong experimental evidence that demands a change to the model before any alteration is considered Listed below are some points of concern to the developers of this model which are currently under consideration e Along wind shear dispersion has been included for instantaneous releases but not for the time varying releases The vertical concentration profiles will change with clou
121. ly displayed but the new data file has not appeared try clicking with the right mouse button in the file list box This will request it to update and display the current contents of the directory 4 1 2 Selecting the graph type There are two types of graph available namely x y line plotting and flammables graphical output and which one you choose determines the form of the rest of the display on this folder a X Y Line Plotting in the majority of cases you will want to use the x y line plotting facility as this allows you to plot any of the core output data so ensure the X Y Line Plotting radio button is on This causes the central panel of the folder to display the variables that may be plotted against each other see Figure 4 1 and also Section 4 1 3 b Flammables it is not in general possible to view graphically the optional output such as dose concentration time history etc but one exception is the flammable release output see Table 4 2 If you wish to plot this output click on the Flammables radio button see Figure 4 2 and also Section 4 1 4 4 1 3 X Y plotting The x y Plotting Details part of the Graphics folder allows you to select which combination of output variables are plotted 4 1 3 1 Selecting the variable for plotting Once you have selected one or more graphical data files you should choose which variable s you want to plot i e the dependent variables To select which variables to plot click o
122. n in the st file If these are not st files they are interpreted as GASTAR input data gp file names and executed in the order given The command line can consist of a mixture of gpl and lst files GASTAR opens all gp files as they are given and without alteration RISKAT GASTAR will expect and read the first and only the first file name from the command line arguments This must be fully qualified with drive directory and file name or file stem RISKAT Input mode ignores any file name extension that may be present and builds the required Input File names from the path and stem only 2 72 Example command lines 2 7 2 1 Example command lines for GASTAR standalone runs Example 1 GASTAR EXE I1 C PROJECT SET1 LST Runs all files listed in set st Output will consist of gof gph and log files for each entry in the lst file that exists The location of the gof gph and log files will correspond to the gpl file used for the run A standard termination box will prompt the user whether to close the window Example 2 GASTAR EXE I1 E2 C TEST1 GPL C DAT SET2 LST C NTEST2 GPL Runs the file test gpl which will create test gof test gph and test1 log in the root directory of the C drive Then runs all files listed in set2 st Output from this will consist of gof gph and log files for each entry in the st file that exists The location of these gof gph and log files will correspond to th
123. n is only required for rectangular buildings see Figure 3 12 It represents the other horizontal dimension of the building to that given above as the obstacle width Please read the definition of the obstacle width and orientation for more explanation Minimum 1 0 m Maximum 1000 0 m 3 3 2 5 Obstacle height This is the obstacle height All types of obstacle require their height in metres to be entered Minimum 1 m m Maximum 50 0 3 3 2 6 Obstacle orientation Fences and rectangular buildings must have their orientation with respect to North defined so that the model can calculate the interaction effects Circular buildings by definition cannot have an 37 GASTAR Section 3 Entering Input orientation For rectangular buildings Figure 3 12 the relevant angle is the bearing of the side defined as the building width above measured in degrees clockwise from North The angle chosen is the smallest positive value and consequently will be less than 180 degrees For fences Figure 3 13 the orientation is the bearing of the fence measured clockwise from North As with rectangular buildings this orientation takes the general form 0 7 180 where n is an integer The angle used is the smallest positive angle It is also important to remember that the model considers fences to be infinitely long so any error on your definition of the fence orientation will become magnified as you move away from the point on the fence defining its position s
124. n the appropriate check boxes A checked box means plot the variable an unchecked box means ignore the variable and you may choose to plot more than one variable at the same time The output available for plotting will vary depending on the type of run made Therefore the number of option buttons and check boxes in the list will change depending on the run type of the 53 GASTAR Section 4 Viewing Output graphical data file selected If you have chosen to plot an output variable for a selection of files you will be warned if any files chosen do not contain the variable 4 1 3 2 Selecting the independent axis As well as the dependent variable s you must specify the independent variable e g time distance etc The default choice for the independent variable is Arc Length but to change this simply click on the radio button corresponding to the variable you wish to use for the independent axis Note that changes do not occur immediately it is necessary for you to click on the Plot Graph button which then updates the graphical display 4 1 4 Flammables plotting This option is only available for releases of flammable materials i e for which there is a non zero value for the LFL lower flammability limit concentration in the material properties When the Flammables radio button is on the Graphics screen is as shown in Figure 4 2 A series of check boxes is displayed one for each variable that may be plotted Check the box for
125. nate of the cloud hits that of each specified point which means that both the core output for the cloud as a whole as well as the additional output appears in the gof file at these points provided the modelled time is large enough to permit the cloud to have travelled that far 3 5 5 Specified Output Times For Instantaneous Continuous and Time Varying releases only The Specified Output Times are quite similar to the Specified Output Points described above in that they are input as a list of times at which the model produces output both the core output for the cloud as a whole and the Flammables output is calculated at these times Up to 50 different times may be specified which is achieved by entering the time in the text box and either clicking on the Add button or pressing the Space bar any specified time may be deleted by highlighting it in the list and clicking on Delete Minimum 0 1 S Maximum 100000 0 3 5 6 Additional output After the GASTAR run has time stepped from f 0 to the modelled time the model carries out 48 GASTAR Section 3 Entering Input post processing of the resulting data to give additional information on the cloud You must request such additional output before the run and the Additional Output part of the Output folder is where you do this The different types of additional output are separated onto three tabbed folders each of which is described below In each case the output produced is added to the end
126. ng cloud whose description and quantification are still unclear Shortly after release this self generated motion weakens and the cloud collapses toward the surface and spreads horizontally while being advected and diluted by the ambient flow This latter collapse and subsequent motion has been extensively studied The initial geometrical configuration is typically an aspect ratio height to diameter of about 1 76 GASTAR Figure 8 1 Box model representation of a puff release similarity theory can be valid A very substantial dilution of the cloud is observed in the laboratory Spicer amp Havens 1985 and field experiments Brighton amp Prince 1987 The cloud dilution is a direct consequence of the strong leading edge vortex and is nearly an order of magnitude larger than the mixing associated with the gravity current head Puttock 1988 Releases in ambient flows both in the laboratory and in the field show a cloud spreading under its own buoyancy and being advected downwind Multipoint data from large scale field experiments Brighton ef al 1985 confirm that the growth rates of cloud area are similar to those in calm conditions The clouds are slightly longer than they are wide as a result of longitudinal dispersion The movement Section 8 Theory Observations Spicer amp Havens 1985 show that after the cloud collapse much of the cloud material is contained within a toroidal vortex forme
127. ng surface will influence the buoyancy driven motion of the dense gas Topography whether in the form of a general slope isolated hills or more complex terrain will alter or divert the cloud or plume The topography may enhance plume dilution and divert the plume away from regions of elevated terrain Alternatively the dense plume may be channelled into valleys or low lying areas and then be protected from the diluting influence of the ambient flow There is extensive treatment of the interaction of topography with buoyancy influenced flows in the geophysical literature but little use has been made of this information source Topographic features that are small compared with the size of the release may be considered in much the same way as buildings or structures but without any substantial flow separation unless the topography is very abrupt When the topographic feature is large compared with the scale of the release the topography reduces to the local slope Somewhat surprisingly the downslope velocity of a dense fluid released on a slope under calm conditions is not a strong function of the slope Hopfinger 1983 summarises results of instantaneous continuous and starting two dimensional flows and finds that the flow has velocities such that U g is typically between 1 and 2 for slopes between 0 and 90 Larger slopes lead to increased entrainment and dilution with the entrained fluid acting as an effective drag on the downslope
128. ns J A 1985 Modelling Phase I Thorney Island experiments J Hazardous Materials 11 237 260 Stretch D 1986 The dispersion of slightly dense contaminants PhD thesis Univ Cambridge England Turner J S 1973 Buoyancy Effects in Fluids Cambridge Cambridge Univ Press 367pp S van Ulden A P 1988 The spreading and mixing of a dense gas cloud in still air Stably Stratified Flow and Dense Gas Dispersion Clarendon Press Oxford Vincent J H 1978 Scalar transport in the near aerodynamic wakes of surface mounted cubes Atmos Env 12 1319 1322 O Webber D M amp Wheatley C J 1987 The effect of initial potential energy on the dilution of a heavy gas cloud J Hazardous Materials 16 357 380 Wheatley C J 1988 Dispersion of a puff release at the ground into the diabatic atmospheric boundary layer UK Atomic Energy Authority Report SRD R445 Wheatley C J amp Prince A J 1987 Translational cloud speeds in the Thorney Island trials J Hazardous Materials 16 185 200 Wheatley C J amp Webber D M 1985 Aspects of the dispersion of heavier than air vapours that are of relevance to gas cloud explosions Rep EUR592en Comm Eur Communities Brussels 121
129. of the gof file after the main tabulated output Further information on the output produced is given in Section 4 5 3 5 6 1 Dose folder This output is available for Instantaneous Continuous and Time Varying releases only It consists of the dose D x and or the concentration as a function of time c t x at each of the Specified Output Points x where D is defined by D x c t x dt For Instantaneous and Time varying releases the period of integration T corresponds to the entire modelling time The concept of dose is extended to include Continuous releases even though by definition the concentration is constant in time and so the dose is simply proportional to the integration time hence T is user specified for Continuous releases see below Whenever the dose is calculated so is the toxic load I x where T x f ctsx dt T and n is the toxic exponent for the release substance This folder contains the following controls and input parameters e Check the Calculate Dose check box if you want to calculate the dose and toxic load at each of the Specified Output Points e Ifthe release is Continuous you must also specify a value for the Dose Integration Period minimum value 1s maximum value 10 s e Check the Calculate concentration time history check box to obtain the concentration at the set of output times at each of the Specified Output Points 3 5 6 2 Flammables folder This output is available for Instantan
130. older shown in Figure 3 18 is where you specify options for the output produced by the model run As discussed in Sections 4 4 and 4 5 the main numerical output from the model is written to an output gof file containing a core of output giving the solution calculated by the model at a set of times distributed through the simulated period but it may also contain various auxiliary information derived from these basic solution data The Output folder is where the user specifies which if any of these auxiliary data are included in the output as well as overall parameters for the simulation such as its title and the length of time modelled in the run lt GASTAR 3 2 D Examples Catastrophic Failure puff1 X File Run Help Meteo ConplexEfeci Title Puit 1000 kg E stability Modelled Time s 600 Puff Specified Output Points Additional Output Iv Calculate Dose Specified Output Times 50 100 150 Delete Check to produce concentration time histories at each specified output point in 0 Max 1024 Figure 3 18 The Output folder 3 5 1 Title This is a string up to 80 characters in length You might use this to name the run and give some descriptive details to help identify the run It will be used as a title in the tabulated output file gof 3 5 2 Modelled time This is a real number giving the time in seconds to which the code will model the cloud dispersion It is important to consider an a
131. on on the Output folder the Define Specified Output Points dialogue box shown in Figure 3 19 is displayed Enter values for the x y and z coordinates of a point in the horizontal set of three text boxes and then click on Add or press the Space bar to add the point to the list which is displayed in the large text box underneath To remove a point from the list highlight it and click on Delete The list of points is sorted numerically by x then y then z as they are added No points may be repeated Minimum x y 10000 0 z 0 Maximum x y z 10000 0 m m m 47 GASTAR Section 3 Entering Input Define Specified Output Points Specified Output Points Fixy values at Fix z values at sa Delete Figure 3 19 The Define Specified Output Points dialogue box The three Fix check boxes can be used to fix temporarily the value in one of the three entry boxes It is then much quicker to enter a large number of points that only vary in say one dimension by first fixing the dimensions that do not vary and then entering the value in the dimension that changes using the space bar to enter the data into the list The entry will be added and a new value can immediately be typed into the textbox It is therefore very quick to repeatedly type a new number followed by a space to enter a long list of points Note that the numerical method that integrates the model equations in time adjusts the timestep so that the x coordi
132. ons in ppm option Repeating the above process will remove the tick and toggle back to mol mol concentration units Run Time The calculations are performed by a FORTRAN executable that is launched from the interface but runs as a separate application These options allow the user to determine how this application is launched and how it terminates For example because many GASTAR runs take about a second to execute you may choose 15 GASTAR Section 2 Using GASTAR to run the model minimised without focus and automatic shut down at completion In this way the GASTAR interface will remain the current application allowing you to continue working without interruption see Figure 2 4 Runtime Preferences Window State Options Exit Mode Options j Normal termination box Minimized with focus C No termination box window open C Mamimised with focus C No termination box window closes C Normal without focus Minimized without focus Restore Defaults Save Defaults Cancel Figure 2 4 The Run Time preferences dialogue box Graph Printing Allows the user to set some of the commonly used printing options for graphics output including the printer the size and position of the graph on the page and the overall Page title this is not the graph title which must be set for each individual graph see Figure 2 5 Graphics Print Setup Plot Sizing 7 Location Options User Plot Location Options e D od C Use
133. our p satisfies the equation logi p A 24 T C where A B C are constants namely the Antoine coefficients The model allows for atmospheric water vapour to condense to liquid 8 2 5 Passive dispersion The dispersion of the release in the atmosphere may be passive from the source if the release has a density the same as the atmospheric density or may become effectively passive when the density difference characterised through the Richardson number Ri becomes small Under these conditions the dispersion should be similar to that from conventional dispersion formulae The lateral growth of the plume is automatically accounted for by the use of o in the lateral concentration profile The o s used are taken from Briggs 1973 as outlined below for open country conditions The form of o remains unchanged 2 Cx 25 oO X14 0 0001x 85 GASTAR Section 8 Theory where Ci is a coefficient taken from the Table 8 2 below and x is the downwind distance the modulus is used to allow for negative x with slopes PSC C A 0 22 B 0 16 C 0 11 D 0 08 E 0 06 F 0 04 G 0 04 Table 8 2 Coefficients used in expression for the lateral diffusion term oy The vertical growth of the release when effectively passive is based on the extended Lagrangian similarity theory and uses a modification to the vertical entrainment velocities e g see Hanna Briggs and Hosker 1982 Wheatley 1988 Spe
134. outlined in Section 8 3 1 2 a vapour blanket need not exist if the physical source size is large or the mass release rate at the source is small e g the evaporation from a large pool of petrol Thus at time t 0 the calculated Qo is larger than Qin Under these conditions the source flow rate must be Qj and the source width must be the physical source width Also the plume depth is the smaller of 200 u g and 0 05D It will be apparent that the initial plume concentration will then be smaller than the source concentration as expected These calculations are performed by GASTAR In general output of the model provides the source width source flow rate density and concentration as a function of time This output is segmented and automatically placed into the main GASTAR interface for subsequent running of the time varying release code For a release of constant mass flux starting at time 0 and stopping at a much later time the mass flux in the plume and the width of the plume at the source will grow to their steady state values and after the release stops these values are maintained as the vapour blanket is removed and H decreases to zero For a release in which the mass flux increases with time the plume mass flux and source width will increase monotonically with time to a maximum when Q becomes equal to Qin Thereafter the width is maintained until the vapour blanket is removed After that Qout is set equal to Qin and the steady st
135. own box labelled Source Location Type Figure 3 5 The formats are e Latitude longitude e UK grid 6 digits e UK grid 2x5 digits e UK grid 2x6 digits e Irish grid 2x3 digits e Irish grid 2x5 digits The Source Location must be entered by the user in the correct format for the Source Location Type selected Advice on the format is given on the screen as shown in Figure 3 5 Source Location Defining source location Source Location Type iN ray se mss v Source Location ra301 799 UK National Grid 2 letters followed by Easting 3 digits and Northing 3 digits No comma Example T0123321 Figure 3 5 Parameters for defining the source location 28 GASTAR Section 3 Entering Input The Source Location is not used by the GASTAR model code but is written to the ggd file to assist plotting and overlaying contours on a map 3 2 3 2 Release start UTC The Release Start time must be entered in UTC hours and minutes plus day of the month month and year The Release Start is not used by the GASTAR model code but is written to the ggd file to assist plotting output as a time series 3 2 3 3 Initial air entrainment rate For Instantaneous and Continuous Releases only Because of the nature of some releases particularly explosive instantaneous it is desirable to allow an initial mixing with air for the source term It is unlikely in a real incident that the exact amount of air entrainment at the start would be known ho
136. pe velocity into along wind and a cross wind components The along wind component is added to the usual advection velocity while the cross wind component provides a normal velocity the relative magnitudes providing the cloud trajectory direction Entrainment is treated in two parts as previously an increased surface generated turbulence and an explicit slope dependent part but see also footnote Section 8 3 4 5 regarding the former 6 3 4 6 Change of slope The current version of the model allows changes of slope up to a predefined maximum see the relevant section on slopes The line of maximum slope for all slope sections lies along a single vector which itself can be oriented in any direction The only restriction is that we must consider the puff or a representative plume cross section to always be on only one slope This is not a very severe constraint 8 3 4 9 Experiences and developments Adifficulty was found in the implementation of the code when a plume after initially flowing downslope attempts to reverse As the plume advection velocity decreases towards zero the calculated plume depth increases to satisfy mass conservation The increased depth produces a larger downslope velocity and consequently the plume does not reverse Incorporation of the second entrainment term introduced some complications with no significant change in model performance This was subsequently omitted but will be reinstated if model perform
137. pes and obstacles code with scenarios in which the ambient wind is zero or much smaller than slope driven velocities The kinetic energy in the cloud itself may be considerably less than that in the atmospheric wind This is obvious when considering a solely slope driven flow encountering a fence whereas an ambient wind driven 115 GASTAR Section 8 Theory flow will eventually surmount the fence a slope driven flow may just pool in front of the fence A satisfactory treatment of this scenario is still under development 116 References In the following list of references a letter in square brackets at the end of the reference denotes that it appears in a particular section namely J jet model Section 8 3 3 S slopes Section 8 3 4 and O obstacles Section 8 3 5 Batchelor G K B 1952 Application of the similarity theory of turbulence to atmospheric diffusion Q J Roy Met Soc 76 133 146 Beghin P Hopfinger E J amp Britter R E 1981 Gravitational convection from instantaneous sources or inclined boundaries J Fluid Mech 107 407 422 S Bell R C amp Thompson R 1980 Valley ventilation by cross wind J Fluid Mech 96 757 767 Blackmore D R Herman M N amp Woodward J L 1980 Heavy gas dispersion models J Hazardous Materials 6 107 128 Briggs G A 1973 Diffusion estimates for small emissions ATDL contribution file No 79 Atmospheric Turbulence and Diffusion Laboratory Oak R
138. ppropriate time interval particularly if special output such as Dose or Range information is also being requested Having an unnecessarily large value will make output points more sparse and reduce the accuracy of interpolated data values used Minimum 1 0 S Maximum 100000 0 46 GASTAR Section 3 Entering Input 3 5 3 Averaging time For Continuous and Time Varying Releases only The averaging time is used to calculate diffusion and dispersion of the cloud For Instantaneous Releases this is disabled and the caption puff appears in the text box The model sets the averaging time internally to 20 seconds the puff dispersion averaging time NOTE The averaging time cannot be set to less than the value for puff dispersion Tavg 20s in this version of the code This reflects the observation that when Tag 20s plume width correlations revert to puff width correlations the plume can never be narrower than the puff If a value less than 20s is entered at the interface the program will set the averaging time to the puff dispersion averaging time Minimum 1 0 S Maximum 3600 0 S 3 5 4 Specified Output Points For Instantaneous Continuous and Time Varying releases only The Specified Output Points are specified as a list of up to 1024 points in x y z for which additional output can be requested the current version provides the Dose Toxic Load and Concentration Time History at each point if requested On clicking the Edit butt
139. r set values Full Page C Centralise on page Full Width Centralise on width C Full Height Centralise on height C As displayed on screen Printer Output Location of Plot Colour Left Margin cm Black and white Top Margin cm 4 Output Style Dimensions of Plot jw Print Border Width cm 12 JV White Background Height cm 8 Page Title User Organisation Font Size Point 18 Printer Setup Max Width 19 79cm Restore Defaults OK Printers Max Height 28 85cm Save Defaults Cancel Figure 2 5 The Graph Output preferences dialogue box Viewing Output Allows the user to specify the viewer of their choice to use with output files The Other option allows a full command line to be 16 GASTAR GASTAR Output Section 2 Using GASTAR entered including any switches for macros etc see Figure 2 6 File Viewing Preferences Application to use C Notepad C Wordpad C Microsoft Excel Other C Program Files Windows NT VAccessories wordpad exe File viewing window size Restore Defaults C Normal Maximised Save Defaults Cancel Figure 2 6 The Viewing preferences dialogue box Allows the user to select the type of output that a GASTAR run produces and is primarily of interest to RISKAT users It is an alternative way to set the GASTAR output mode command line switch O see Section 2 7 1 for more on command line switches and arguments A dialogue box for selec
140. r the flammable mass in a plume is found by integrating the concentration field over the fixed region within the LFL contour or the maximum range is found by looking at the cloud concentration as a whole as a function of time These calculations therefore rely on the cloud properties being adequately resolved in space or time The integration scheme used in GASTAR has been optimised for short run times so that the time step tends to be significantly larger at the end of the simulation than at the beginning The output is stored at the end of each timestep used which means that the resolution of cloud properties is typically relatively coarse at the end of the simulation compared with the start There are facilities to increase the resolution in the form of the Specified Output Points SOP s and Specified Output Times SOT s which if specified augment the times at which the output is stored because they force the time steps to be adjusted so that the cloud position coincides with the given x coordinate s and or time s Thus if your simulation calculates any additional output it is helpful to bear the above points in mind and if necessary add some Specified Output Points and or Times on the Output folder in order to improve the accuracy of the post processing In general e dose toxic load concentration time history add further SOP s near the points of interest or SOT s around the time that the cloud arrives at the given point
141. ransfer Group Lower Flammability Limit Upper Flammability Limit Prandt Number Toxic Exponent Probit A Probit B Ant A Ant B Ant C 1 2 Butadiene 54 091 676 284 448 63 1 482 2 208 0 034 2 12 0 7649 1 0 0 9 1187 1041 117 30 8 1 3 Butadiene 54 091 673 268 69 415 33 1 474 2 277 0 0351 2 11 5 0 6948 1 0 0 8 9749 930 545 34 3 1 Butene 56 107 645 266 9 390 61 1 595 2 102 0 0352 1 6 9 3 0 8345 1 0 0 8 8896 926 1 33 15 Acrylonitrile unreferenced 53 064 806 350 5 615 1 2 2 1 0 0271 3 17 0 7898 1 0 0 9 0412 1208 2985 51 15 Ammonia 17 03 639 239 82 1374 2 1647 4 4479 0 02136 16 25 0 9135 2 0 0 9 4854 926 13 32 98 Boron Trichloride 117 169 1349 285 7 23 77 0 5353 0 91065 0 0216 0 0 0 8681 1 0 0 3 95145 973 995 38 994 Bromine 159 81 3119 331 9 188 9 0 225 0 452 0 0149 0 0 0 705 2 0 0 9 006 1121 49 51 56 chlorine 70 91 1563 238 7 288 1 0 4796 0 892 0 0154 0 0 0 7467 2 0 0 y Figure 6 3 Materials gdb opened in Notepad 70 GASTAR 6 2 Material properties Section 6 Database Editor For each material in the database the following information is stored Material Name Molecular Weight Density liquid Boiling Point Heat of Vaporisation Specific Heat Capacity vapour Specific Heat Capacity liquid Heat Transfer Group Lower Flammability Limit Upper Flammability Limit Prandtl Number Toxic Exponent Probit Number A Probit Number B Antoine Coeffic
142. rd obstacle interaction calculation is performed 5 Time and Position Steps For computational reasons the new solution downstream of the obstacle is started at a position H 10 downstream There will be a hold up of the cloud as it encounters the obstacle This time delay is modelled with At S P min ud 107 Ww 6 Passive or Near Passive Releases There will obviously be a temptation to use this modelling approach for passive or near passive releases and it would be attractive if this were possible The only significant difficulty is that for passive releases the box model plume or puff will not grow in the non vertical directions the influence of the ambient turbulence being incorporated later through o a measure of cloud spread Thus the occurrence of any interactions may be underestimated with the present approach The least disruptive way to deal with such cases is to check for any interaction using the effective or total cloud extent For a puff this would mean replacing the diameter D by 2R where Ry R l 307 R 108 For a plume the width w would be replaced by w where w 3o 1 _ I 109 es dli In order to conserve mass the reduced gravity term must also be replaced Thus for puffs we use 2 2y g g 1 307 R 110 and for plumes 3o x a A es um i of m If an interaction does occur the previous algorithms are used 7 Blocking A difficulty may arise with the combined slo
143. re Coqois mass flux of pollutant at the source and U z BH is the plume advection velocity i e the ambient velocity at a specified fraction p of the plume height The change in variables from Britter 1989b to those used here produces coefficients whose values are near unity Given further data it is possible that more precise values could be assigned to these coefficients and improved algorithms could be developed In the absence of this definitive data coefficients of unity have been used In addition the following constraints are imposed on the solution i the cloud depth cannot be decreased by the fence ii the cloud concentration cannot be increased by the fence The same approach can be applied to instantaneous releases puffs with the same correlation for increased puff width and the puff depth being determined in a consistent manner 8 3 5 2 Hold up Hold up of material in the front and in the lee of the fence will occur due to altered advection velocities and the recirculating flow in the regions of flow separation The regions of flow separation will appear as an effective longitudinal diffusion The work of Vincent 1979 suggests that the retention of material in wakes can be modelled as an effective longitudinal diffusion o of about 10H The altered advection velocity will appear as a net time delay as the cloud is slowed ahead of the fence and accelerated over it There has been the drift function introduced by L
144. red directory called DATA and another computer called APOLLO with a shared directory called MODELS which has a sub directory for GASTAR then we can have the following examples in a batch file 13 GASTAR Section 2 Using GASTAR Batch files can have comment lines starting with a colon REM Lines starting with REM will be printed to the DOS screen Multiple command lines can be used in Windows batch files start w APOLLO MODELS GASTAR gastar exe I1 E2 THOR DATA test1 gpl start w APOLLO MODELS GASTAR gastar exe I1 E2 THOR DATA test2 gpl start w APOLLO MODELS GASTAR gastar exe I1 E2 THOR DATA test3 gpl In these examples note that the batch file is run from a DOS session running under Windows anywhere on the network Which ever networked machine runs the batch file the correct data file and model will be used 2 4 3 List files for batch mode As well as input file names GASTAR can also accept a list file as an argument to the input file switch on the command line Any file having the extension st will be assumed by GASTAR to contain a list of data files one file per line The model will run each line in the list file in turn until completion of all entries in the list file This is the recommended way to run GASTAR from the command line You can build a suitable file from the DOS prompt using the DIR command the B option is needed to produce brief listing data For example dir ZB ogpl gt allruns lst
145. roduced one for each run An alternative to typing the command line at the DOS prompt is to use a batch file instead Thus the same command lines may be typed into a file such as rungas bat and run more simply from the DOS prompt by typing rungas again provided rungas bat is either in your current directory or in a directory on your current path otherwise the full path name for rungas bat would need to be given A DOS session running under Windows NTA etc can also accept the start command Using this command you can start other applications at either the DOS prompt or from a DOS batch file For more information on the start command type start at the DOS prompt Using the start command you may write a multiple line batch file to run many cases The lines in the batch file will be run consecutively provided the w switch is included after the start command so the second line will run after the first is completed and so on This ensures that the GASTAR run is completed before the next line of the batch file executes Also for the batch file to regain control after executing the first line the FORTRAN executable must be told to shut down on completion by using the E2 command line switch See Section 2 7 for more details on the GASTAR command line options If you have a network you may make use of the Universal Naming Convention for the computers on your network For example if the Network recognises a computer named THOR which has a sha
146. rosol Fraction kg kg Flash Mass kg or mass flux kg s of the Air initially mixed with the released material in 0 Max 1000000 Figure 2 3 The File menu items 2 2 1 Menus There are three main menu options namely File Run and Help see Figure 2 3 These have the options shown in the table below GASTAR File File Run Help New Open Save Save As Open Template Save As Template Preferences View Output Exit dons Obtaining Technical Support About Gastar Licence Details Current Directory 2 2 2 Folders There are five folders altogether four are used to specify the input to the model and the fifth controls the viewing of output from a run Meteorology Source Complex Effects Output Graphics 2 3 Setting up a problem Section 2 Using GASTAR Resets the input parameters to their default values Allows the user to open a previously saved data file see Figure 2 2 Saves the current parameters under the current file name Saves the current parameters under a user specified file name Opens a previously saved template file see Section 2 3 4 Saves a set of data as a template file see Section 2 3 4 GASTAR user preferences see Section 2 6 Opens a GASTAR output file in Notepad Write or other user specified viewer Quits GASTAR The five most recently opened or saved input gp files click on one to open the file Runs the di
147. rsion on models of industrial sites it seems clear that arrays of roughness elements are the type of obstacle most in need of investigation both into passive flow and dispersion characteristics and into heavy gas effects Our objective is to develop and validate a set of algorithms within the context of integral modelling that allow for dispersion through such an obstacle array It is our intention to treat any site in a broad statistical manner in the first instance rather than with a detailed description of its individual component elements on the site As before we address the effects of the obstacle arrays on 112 GASTAR Section 8 Theory i advection ii horizontal spreading due to buoyancy ii dilution of the plume and iv plume hold up which is particularly important for transient releases We have examined the available experimental data summarised in Brighton et al 1993 and the further data given in Petersen and Ratcliff 1989 We conclude that 1 There is support for the view that an industrial site may be modelled as an equivalent uniform roughness Care must be taken to ensure that no isolated large structures require separate treatment It should be noted that within this approach the accuracy of the predictions of the model are limited to scales which are larger than those of the isolated structures 2 For homogeneous arrays there is evidence that the advection velocity should be treated in the same manner
148. s Initially due to the small source width only a fraction of released material is taken up by the ambient flow and carried downstream to form a plume The remaining fraction will spread radially as a vapour blanket eventually the blanket width is adequate to allow all the released material to be taken up by the ambient flow and advected downstream corresponding to steady state conditions Figure 8 7 Uptake of material and cloud development over a liquid pool The vapour blanket is modelled as a radially growing cloud following the general approach of Britter 1979 The height H and radius R of the vapour blanket are determined by the conservation expression d i RH Qn z Qu 37 where Qin and Qo are the volume fluxes of the released material from the source and advected downstream by the ambient wind respectively and an equation for the leading edge motion dR uo 00H 38 which is consistent with the formulation of the instantaneous release algorithms The calculation 9 GASTAR Section 8 Theory is normally commenced with an initial radius reflecting the area of the physical source although GASTAR users can choose any initial radius The radial growth is stopped whenever Qin equals or falls below Qo The volume flux out of the vapour blanket follows the argument in Section 8 3 1 2 where 200u2 39 Eo and Q ou 2Rh U z 0 56h 40 The width of the source is taken to be W 2R As
149. s m x m m N m Loe n m m Conc units pollutant name blank blank averaging time integer Year integer Day integer Hour real T real X real Y real Z real Concentration etc Figure 4 5 ggd file template The file begins with a header section containing the following data Line 1 A header line Line 2 File version current version number of output file included for reference in case the format of the output file changes in the future Line 3 Input file stem i e name of input gpl file Line 4 Full pathname of directory in which gpl file is located Line 5 Direction from which wind is blowing in degrees clockwise from North included so that the output x y co ordinates which are always aligned so that the positive x axis is downwind can be translated to a fixed co ordinate system for plotting if required Line 6 Identifier for co ordinate system in which the source location is given COORD_SYSTEM 1 _latitude longitude COORD SYSTEM 2 UK 2 letters 6 digits COORD SYSTEM 3 UK 2 letters 2 x 5 digits COORD SYSTEM 4 UK 2 letters 2 x 6 digits COORD SYSTEM S Irish 1 letter 2 x 3 digits COORD SYSTEM 6 Irish 1 letter 2 x 5 digits Line 7 Source location in the above co ordinate system This may contain a comma Line 8 Release date and time in the format Y Y Y Y MM DD HH MM with a space between the date and time Line 9 Time zone in which release date and time is specified Line 10 Pollutan
150. s of velocity speed up roughness effects and turbulence Q J Roy Met Soc 107 91 110 S CERC 1997 LSMS version 1 0 User Manual Chatwin P C 1968 The dispersion of a puff of passive contaminant in the constant stress region Q J Roy Met Soc 94 350 360 Cleaver R P amp Edwards P F 1990 Comparison of an integral model for predicting the dispersion of a turbulent jet in a crossflow with experimental data J Loss Prev Proc Ind 3 91 118 GASTAR Section 9 References 96 J Cleaver R P Cooper M G amp Halford A R 1995 Further development of a model for dense gas dispersion over real terrain J Hazardous Materials 40 85 108 Clough P N Grist D R amp Wheatley C J 1987 The mixing of anhydrous hydrogen fluoride with moist air International Conference on Vapor Cloud Modeling Boston A I Ch E C C P S pp 39 55 Davies M E amp Inman P M 1987 A statistical examination of wind tunnel modelling of the Thorney Island trials J Hazardous Materials 16 149 172 Deaves D M 1985 Three dimensional model predictions for the upwind building trial of Thorney Island Phase II J Hazardous Materials 11 341 346 Ellison T and Turner J S 1959 Turbulent entrainment in stratified flows J Fluid Mech 6 432 448 S Ermak D L amp Chan S T 1988 Recent developments on the FEM3 and SLAB atmospheric dispersion models Stably stratified flow and dense gas dispersion Ed J S
151. s might result from idealised laboratory or field tests e g Thorney Island In this case cloud acceleration results solely from subsequent mixing between the cloud and the ambient fluid 6 3 1 2 Continuous release with no significant momentum It is observed in experiments in the laboratory and field that a continuous plume may travel upwind from the source and can be far wider at the source position than the physical dimension of the source This has been interpreted as the formation of a vapour blanket over the physical source The continuous release source module provides plume widths and heights at the source position in terms of ambient conditions the plume density and release rate and the physical size of the source region If the release rate is small and the source dimension large there will be dilution of the plume at the source position If this is the case the effective source density and concentration will be less than that from the source The algorithms used here address the detrainment of the source material by the ambient flow a balance being met when the effective source is large enough to allow complete detrainment of source volume flux qo Note that this is not an entrainment problem and thus the use of the entrainment relationships is not valid Some conventional codes use such entrainment relationships and then utilise the experiments of Britter 1980 on near source dimensions of dense gas clouds to calibrate an uptake model
152. sh either to edit existing entries or add completely new materials Alternatively you can store the properties for a user defined material for use in a particular model run 6 1 The materials database 6 1 1 Viewing the materials database The materials and their properties stored in the materials database can be viewed by selecting From Database on the Source screen and the clicking View Data Figure 6 1 shows how the materials and their properties are displayed The complete properties for each material can be viewed by scrolling horizontally in the top table or when the material is selected in the upper table the complete properties for that material are shown in the lower part of the window under Current Database Record 6 1 2 Using a user defined material To enter material properties for a material not currently in the materials database so that the properties will be stored with the gpl file select User Defined on the Source screen and the click Edit User Data The screen shown in Figure 6 2 will appear and it is here under User Supplied Data that you can enter a name and properties for a new material Note that these material properties will be stored with the gpl file but not in the materials database and therefore this user defined material is available for this gpl file only To create a new material that can be selected and used in any gpl file see Section 6 1 3 68 GASTAR Section 6 Database Editor Material Data D GASTAR
153. source location The second column gives the data summary for each slope segment you have entered The slope segments are assumed to abut one another without gaps Unlike the obstacle summary the segments in the slope summary are logically ordered If you modify a slope distance the summary table is rebuilt to account for changes in the order 3 4 1 3 Use Met Screen data for all slopes check box Each slope segment has an associated set of data not just for the slope parameters but also for the ground roughness length wind speed and height of the wind speed measurement for the segment These data parameters are duplicated on the Meteorological Folder This check box will tell the model which set of Meteorological data is to be used If you have slopes turned on and choose not to use the Meteorological Screen data you will need to enter Met data for each slope segment and these data will be displayed in the table summary Also on the Meteorology Folder the textboxes for roughness length wind speed and height will display the text Slopes On and will not be editable If you wish to use the Meteorology Screen data for all slope segments you should check this box You will notice that when you check the box the summary table automatically updates to reflect the change by no longer displaying any meteorology data Turning the Use Met Screen data for all slopes check box on and off will return the table to its original appearance This is be
154. spersion model using the current data file Address and contact information Version information Details of licence being used to run model Current working directory e g for file operations Input parameters describing meteorological conditions Input parameters describing the release i e its type size etc Input parameters describing the buildings fences and slopes Parameters affecting the current run of the model Used for displaying graphically output from a GASTAR run Having described the features of the interface we now turn to how these are used in the stages of setting up a problem Each problem can be thought of in three different ways GASTAR Section 2 Using GASTAR a as a physical problem which the user wishes to simulate with GASTAR b asaset of GASTAR input data i e a set of values for each parameter in the complete list of GASTAR input parameters c as a file containing these data items and these definitions tend to be used interchangeably However it is important to realise that typically there may be several alternative sets of input data b for a given physical problem a as the user finds possibly different ways to express the physical problem in terms of the input which the model can accept whereas there is only one file c corresponding to a given set of input data b Such input files for GASTAR are distinguished by a constant extension gpl e g datafile gpl This User Manual does not give deta
155. ssociated with GASTAR You may wish to archive any user files gpl gof etc generated by that version in a dedicated directory 1 2 2 Installing GASTAR 3 2 Please check first with your own IT personnel for company procedures for installing software The installation of GASTAR is straightforward It uses an Installation Wizard which guides the user through a short series of screens collecting information on the user and installation parameters before installing the software The following steps lead you through the GASTAR installation process e Logon as Local Administrator for the PC e Insert the GASTAR install CD whereupon it should automatically run If it does not click on the Windows Start button select Settings and then Control Panel Double click on the Add Remove Programs icon and press the Install button Browse for the CD ROM drive and select setup exe in the root directory on the drive e Click Next gt through the Welcome screen and then select accept the terms of the licence agreement and click Next in the Licence Agreement screen if you do accept the licence terms to get to the Customer Information screen If you do not accept the licence terms select do not accept the terms of the licence agreement and click Next gt to finish the install e Enter your user name and organisation in the designated places You also have the option of installing GASTAR for all users or just for you Click Next to go thro
156. t file prob log Output log file prob ggd Formatted gridded output for plotting contours For RISKAT runs only lt prob gt mat Material properties input file lt prob gt bmi Meteorological input file lt prob gt bsi Source term input file prob slp Slopes input file bsys dat System control input file bconc in Output control input file bflam in Output control flammables input file lt prob gt bc Concentration history output file lt prob gt flm Flammables output file 72 Theory 8 1 Dense gas dispersion Public concern over the risks posed by the use of hazardous materials has grown markedly over the past few decades The dioxin release in Seveso Italy in 1976 that of methyl isocynanate in Bhopal India in 1984 and the liquefied petroleum gas explosions in Mexico City in the same year emphasised the possible scale of the tragedies that may accompany activities involving hazardous materials The development of appropriate regulatory measures to achieve an acceptable balance between economic benefit and potential harm accompanying such activities requires quantitative assessment of the consequences of the accidental release of material into the environment It is commonly the case that both flammable and toxic hazardous industrial materials produce a cloud that is denser than the environment upon release into the atmosphere The current state of knowledge of dense gas dispersion has been outlined in the reviews b
157. t name 60 GASTAR Section 4 Viewing Output Line 11 Units of concentration output Currently this will always be mol mol but including it in the header section gives us the option to allow more flexibility in the future Line 12 Averaging time in seconds Line 13 A line indicating that the end of the header section has been reached Extra lines of information may subsequently be added to the header section but this line will always indicate the end of the section Line 14 Number of x values in the output grid Line 15 Number of y values in the output grid Line 16 Number of z values in the output grid Initially this will always be 1 but including it gives us the option to allow more flexibility in the future Line 17 Number of timesteps for which output is given This is only really relevant for instantaneous releases puffs for continuous releases plumes the value will always be 1 The times at which output is given in seconds are then listed on consecutive lines There is then a header row for the columns of output Note that the header for the concentration column includes the units pollutant name and averaging time as well as a couple of dummy values these are included so that the file format matches similar output from other CERC models Finally the data is given in 8 columns year day hour time x y z concentration in comma separated format The year day and hour values are taken from the release star
158. t time entered by the user The time column is only relevant for puffs for plumes this column will contain a dummy value of 999 The x y and z co ordinates are in metres A is used for the decimal separator Note that there may also be spaces between the columns The first part of an example ggd file is shown in Figure 4 6 GASTAR gridded data output file FILE VERSION 1 0 FILE STEM A 3 2 PATH G VB6 Gastar JunkGPLs modelCR1000 WIND_DIRECTION 225 00 COORD_SYSTEM 2 SOURCE_LOCATION TQ301799 RELEASE_DATE_AND_TIME 2009 02 14 10 45 TIME_ZONE UTC POLLUTANT_NAME Chlorine CONCENTRATION UNITS 2mol mol AVERAGING TIME SECONDS 60 0 END OF HEADER SECTION 51 51 1 i 999 0 Year Day Hour Time s X m Y m Z m Conc mol mol Chlorine 60 0s 2009 45 10 999 00 0 00 250 00 0 00 0 000000E 00 2009 45 20 999 00 20 00 250 00 0 00 0 000000E 00 2009 45 10 999 00 40 00 250 00 0 00 0 000000E 00 2009 45 10 999 00 60 00 250 00 0 00 0 000000E 00 2009 45 10 999 00 80 00 250 00 0 00 0 000000E 00 2009 45 10 999 00 100 00 250 00 0 00 0 000000E 00 2009 45 10 999 00 120 00 250 00 0 00 0 000000E 00 2009 45 10 999 00 140 00 250 00 0 00 0 000000E 00 Figure 4 6 Extract from an example ggd file 61 Pool uptake model The Pool Uptake model provides a simple way for you to create a time varying source term based on the e
159. tant that you install this new licence file as instructed e To install the GASTAR licence copy the file gastar3 lic to the lt install_path gt directory 1 2 3 Starting GASTAR The GASTAR files are now installed on your computer The installation process automatically provides shortcuts for starting up the GASTAR interface e it puts a shortcut to the GASTAR interface executable gaswin exe on the desktop of all users for which the program was installed Double click on this shortcut to start the interface e it puts an entry in the Windows Start menu for GASTAR i e click on Start and then Programs and find the entry GASTAR 3 with the GASTAR icon next to it Clicking on this starts the interface e When you have launched GASTAR checking the licence details through Help Licence Details will give the location of the licence currently being used Although the model will run when the licence file is in the Windows WINNT directory it is recommended that the location be the install path directory e Restart your computer you are now ready to use the model Using GASTAR Having described in Section 1 the procedure for installing and starting GASTAR we turn now in Section 2 to the operation of the model Since GASTAR has a Windows interface we begin in Section 2 1 with an overview of the Windows terminology that will be used in other parts of this document notably in Sections 3 and 4 that describe entering input and viewing output Next we giv
160. th A real number giving the roughness length in metres The roughness length is a length scale that categorises the surface roughness by representing the eddy size at the surface Some approximate values for a variety of land types are given in Table 3 1 If you have defined slopes with their own meteorological data this is disabled and the caption Slopes On appears in the textbox In such circumstances the cloud development is based on the conditions prevailing on the current slope For more details see Section 3 4 1 9 under Slopes Minimum 0 0001 m Maximum 2 0 m Agricultural Areas min Open Grassland Sandy Desert Table 3 1 Typical roughness length values for a range of surfaces 3 1 5 Air temperature A real number giving the ambient air temperature in kelvin Note that 0 C is approximately 273K The air temperature also defines zero enthalpy Minimum 220 0 K Maximum 330 0 K 3 1 6 Surface temperature A real number giving the surface temperature in kelvin If the Source Release Type is Isothermal this parameter is not required and the text box contains the caption Isothermal and cannot be edited In such cases the surface temperature is assumed to be the same as the air temperature 23 GASTAR Section 3 Entering Input Minimum 220 0 K Maximum 330 0 K 3 1 7 Atmospheric pressure A real number giving the ambient air pressure in millibars Note that 1 Atmosphere is approximately 1013 24 mb Minimum 800 0 mb
161. the same value for the slope and wind bearing they will be aligned such that moving along the slope vector in the negative direction is upwind and in the positive direction is downwind This form of definition allows you to separate the slope angle and the wind direction because the slope angle is measured relative to the slope vector and is the incline seen by someone moving in the positive direction along the slope vector You can reverse the wind direction simply by adding 180 to the wind bearing and the ground will not be altered ie the effective reversal of the slopes seen by the cloud will be accounted for by the slope vector Minimum 0 0 deg Maximum 360 0 deg 3 4 1 5 New edit split and delete buttons The four buttons to the side of the table allow you to edit the slope data Note that under certain circumstances part or parts of this data will be greyed out and not be editable See under the individual parameter entries below for more details The Slope Definition form is shown in Figure 3 16 New will bring up the Slope Definition form with the default values as shown in Figure 3 16 This is the form that allows you to define the slope data The parameters are defined in more detail below If you cancel the form from this point no new slope will be created 4 GASTAR Section 3 Entering Input PLAN VIEW Os slope bearing line of maximum slope Horizontal Slope Vector Figure 3 14 Definit
162. timation of maximum and minimum changes from analysis and experiment for example Britter 1982 Britter Hunt and Richards 1984 and others b Use of specific codes for wind fields in complex terrain c Specific codes might be used for a number of standard cases e g plateau to slope plateau to slope to plateau etc and a simple library formulated As an interim measure the use of case a has been found to provide output consistent with available data 8 3 4 2 Basis for code development Previous simple analyses which are of an integral type provide support for the possibility of incorporating slope effects into integral models for dense gas dispersion Of course the analyses have only been developed for somewhat idealised situations Nevertheless the limited field and laboratory data available are quite consistent with the simple analyses Thus such analyses or a simplified interpretation of their outcome are used We assume that the ambient velocity field has been separately specified in terms of a friction 102 GASTAR Section 8 Theory velocity and a velocity profile which may vary in space Initially we consider only a uni directional flow 6 3 4 3 Advection velocity Analysis and experimental observation indicate that the advection velocity for the cloud Uaa be modelled as U aa Us U U om C g z 77 where Uam is the ambient wind speed C is a function of slope and the last term is the downslope velocity T
163. ting options is displayed see Figure 2 7 By clicking on one of the radio button options you can select which of the following types of output file are generated Output Mode Preference GASTAR Output Options C RISKAT Toxics Output C RISKAT Flammables Output Restore Defaults Save Defaults Cancel Figure 2 7 The GASTAR Output preferences dialogue box e GASTAR Output produce GASTAR output files og gof gph equivalent to O1 e RISKAT Toxics Output produce RISKAT Toxic file bc equivalent to O2 e RISKAT Flammables Output produce RISKAT Flammable file flm equivalent to O3 17 GASTAR Section 2 Using GASTAR 2 7 GASTAR command line As noted in Section 2 4 the gastar exe executable takes command line switches and arguments The general form of the command line is gastar exe Em In Op File name s where E I and O are the switches and the integers m n and p and the name s File name s are the arguments There should not be a space between a switch and its integer argument Unless you are running GASTAR from a DOS prompt or you need to carry out a RISKAT run of GASTAR you can omit the rest of this section on first reading 2 7 1 Switches and arguments 2 7 1 1 GASTAR exit mode This flag is optional Em Flag to set the Exit Mode for QuickWin applications The value of m can be 1 Default Exit with termination box to prompt for Application closure if desired 2 No
164. ugh to the Destination Folder screen e You should select a drive with at least 1GB of available disk space The default installation directory is C Program FileNCERCNGASTAR but we suggest you install it in Drive NCERCONGASTAR where Drive can be C or another drive of your choice Use the Change button to select your own installation directory Click OK to return to the Destination Folder screen e The abbreviation install path will be used in the rest of the User Guide to denote the installation directory you have chosen for example C CERC GASTAR 3 2 e Click Next gt to view the options you have specified e If the settings shown are correct press the Install button to complete the install procedure However if you first wish to amend any details press the Back and Next buttons as appropriate Once the Install button has been pressed and the GASTAR files have been successfully installed the final screen will appear e Click Finish to complete the installation The installation procedure automatically puts a shortcut to GASTAR on your Windows desktop If the Show the readme file box is checked the document What s New in GASTAR 3 2 will be opened automatically once you click on 2 GASTAR Section 1 Getting Started Finish The installation is now complete You have been provided with a unique licence file either by email or on a separate floppy disk which is required in order to run the model It is impor
165. um flux is M iu M M M 42 and the scalar enthalpy flux is H mh 43 where A is the specific enthalpy of the jet material The fundamental differential equations are d E E 44 Fa 44 where E is referred to as the mass entrainment rate dM x E 45 ds U z 45 Ms 0 46 ds 93 GASTAR dM i p yR aon BP o us cos cos ds d cos sin Q ds and dz sing ds d Section 8 Theory 47 48 49 50 Similarly if M denotes the magnitude of the momentum flux then the momentum components are M M cos cos M M cos sin 0 and M M sing Two further equations are those for enthalpy flux E ABER ds and species concentration C Ls mC EC ds 51 53 53 54 55 where h C refer to ambient enthalpy flux and species concentration respectively To simplify the calculations the enthalpy is referenced to the ambient enthalpy and so h 0 Similarly the species concentration in the ambient air is taken as zero Thus the equations simplify to d mh 0 ds and e e ds 56 57 94 GASTAR Section 8 Theory The mass flux consists of released material and air with mass fractions of m and 1 mp respectively The released material may be in gaseous or liquid aerosol forms with mass fractions my ay and ay respectively The specific enthalpy of the cloud at temperature T K is then h C T
166. uoyant jet although the development is based solely on the vertical buoyancy force giving rise to an increasing vertical momentum and consequent jet rise 8 3 3 5 Underexpanded jets High pressure gaseous releases can lead to underexpanded jets in which the pressure at the release exit is in excess of the ambient pressure For perfect gases this is the case when the upstream stagnation pressure Po is greater than flat zs where y is the ratio of specific heat at constant volume to the specific heat at constant pressure C C Under these conditions the exit pressure will be Hs 2 r4 P P 71 e yt 0 However the jet model like most integral jet models is based on ambient pressure throughout The underexpanded jet undergoes various shocks and expansions close to the release to drop the jet pressure to ambient pressure During this process the momentum flux of the jet increases The momentum flux of the jet is the dominant parameter describing the development and dilution of a jet Thus the correct momentum flux must be determined Britter 1994 1995b Although the complex processes close to the source will also involve entrainment of ambient air it is convenient to keep these processes distinct 97 GASTAR Section 8 Theory For a release with pressure P density pe velocity Ue and area A the appropriate input condition to a jet model is one with a velocity of eget P P 72 m where m p A Ue and
167. us and continuous releases this does not include entrained air see 3 2 3 1 For Time Varying Releases this entry will refer to the current segment given in the Current Segment Number box 29 GASTAR Section 3 Entering Input Minimum 0 01 kg s Maximum 1000000 0 kg s 3 2 8 6 Hazardous fraction This parameter gives the fraction of the release that is considered hazardous For general use this is the whole release consequently this has a default value of 1 By changing this value you may model the release of a dense gas say CO in which a small amount of a contaminant say H2S was present In this case the dynamics of the cloud will depend on the main dense gas CO2 but the important concentration levels will be those of the contaminant in the release The concentration of the contaminant will therefore be given directly in the model output For Time Varying Releases this entry will refer to the current segment given in the Current Segment Number box Minimum 0 000001 Maximum 1 0 3 2 8 7 Source temperature For Thermal and Aerosol Releases only This is a real number giving the temperature of the initial cloud of released gas and or aerosol after flashing but before any air entrainment Some care is needed to ensure all Source Details are consistent For example if there is a spill of volatile material that is stored as a liquid under pressure at ambient temperature you will need to perform a flashing calculation
168. us releases either the physical source width or the actual plume width can be specified see below The initial mass flux Mo at the source is also specified The initial plume cross section is assumed to be rectangular The model will calculate the source density po in the same manner used by the Instantaneous release The source height Ho is found such that the correct mass flux is obtained using Mo H W U o where U is the calculated effective speed for the cloud based on the current wind speed profile see Section 8 2 1 3 The initial temperature To for Thermal and Aerosol cases initial aerosol fraction for Aerosol cases initial concentration Co and initial density p are assumed to be uniform over the initial section For Continuous releases you can check Internally Calculate Initial Plume Width if you wish GASTAR to determine the initial conditions for continuous release calculations ie the source width and height are calculated internally You must supply the source release rate and the physical source width The effective ie the actual plume width height and density are calculated from the source mass flux temperature and prevailing Meteorological conditions This option produces a physically realistic plume aspect ratio If you do not choose to allow the model to calculate the initial plume dimensions the value you 26 GASTAR Section 3 Entering Input enter for the Width is assumed to be the initial plume width
169. use the file bconc in from the gastar exe home directory to produce the output file YAMODELS risk2 flm The run time window will close automatically at the end of the run 20 Entering input As noted in Section 2 there are four folders or screens used to define the input data to a problem namely Meteorology Source Complex Effects and Output In this section we describe each input folder in detail one at a time Note that although the folders are described in the same order that their tabs appear the folders may be accessed in any order and controls data items set in any order Any inter dependence of folders is highlighted in the text 3 1 Meteorology details The Meteorological input folder is shown in Figure 3 1 There follows a complete list of the input parameters needed to define the meteorological conditions GASTAR 3 2 untitled ae Eile Run Help Wind Speed m s NEN Air Temperature K NEEN Wind Speed Height m 10 Surface Temperature K Wind Direction Atmospheric Pressure mb Roughness Length m Relative Humidity PG Monin Obukhoy Definition Use Pasquill Gifford Categories C Use Monin Dbukhov Length GMINHEIBSSI D BEMINESMIN Wind speed in metres per second Figure 3 1 The Meteorology input folder 21 GASTAR Section 3 Entering Input 3 1 1 Wind speed A real number defining the wind speed in metres per second at a known height above the ground If you have defined s
170. vaporation of material from a pool The model uses the supplied evaporation rates to calculate the subsequent cloud development above the pool which can then be used as a source term inside GASTAR The Uptake model does not calculate the vaporisation rates from the pool In order to do this a pool spill model will be required One example is the LSMS Liquid Spill Modelling System model which can calculate the spreading of liquids and supply the vaporisation rate from the developing pool for use in GASTAR This model has the added advantage of an automated direct link with GASTAR to facilitate the transfer of information between the two models when LSMS has run it is possible to use the output from the run to generate a GPL file for GASTAR furthermore the GASTAR interface is started up and the GPL file loaded IMPORTANT If you use the results of the Uptake Calculation all the data common to the main GASTAR interface will be copied back overwriting any data that is already there If you do not wish to lose the data in the main interface you should save it before entering the uptake model In particular changing the source material on the pool uptake source folder changes the material on the source folder of the main dispersion model see Section 5 2 2 1 5 1 Accessing the pool uptake model The pool uptake model is a separate utility which may be launched from the Source folder when the release is time varying This results in a separate scre
171. w and Section 2 7 for more details including examples There are two main parts 12 GASTAR Section 2 Using GASTAR e The first part namely GPATH gastar exe is the full path name of the gastar exe file i e GPATH is the complete path of the directory containing the GASTAR simulation engine executable e The second part namely the rest of the line IPATH datafile gpl are command line arguments to gastar exe It states that the input file expected is a GASTAR input file I1 as opposed to a RISKAT input file which would have used 12 the accompanying path name is the name of the GASTAR input file Typically this would have been created using the GASTAR interface The executable has several possible command line arguments and these are explained in full in Section 2 7 The net result of running GASTAR in this way is that a main output file IPATH datafile gof is produced which may then be examined in the usual way by means of the GASTAR interface files IPATH datafile log and IPATH datafile gph are also produced There may be more than one input file name supplied as an argument in the command line For example the above case could be extended to GPATH gastar exe I1 IPATH1 data gpl IPATH2 data gpl This would cause two sequential runs of GASTAR to take place using the input data files IPATH l data gpl and IPATH2 data gp in turn two distinct sets of output files would be p
172. wever you are required to give the mass flux of air entrained at the start The model assumes this to be at the air temperature and will use this together with the mass flux and temperature of released material to recalculate an overall cloud temperature and density This is a real number giving the mass of the air entrained initially Minimum 0 0 kg s Maximum 10000000 0 kg s 3 2 3 4 Source width The real number giving the width of the source in metres e For Instantaneous releases this is the initial diameter of the puff e For Continuous releases this is the physical source width giving rise to the plume if the Internally calculate initial plume width option is chosen otherwise it is the initial width of the plume e For Time Varying releases this is the actual width of the cloud e For Jet releases this is the initial diameter of the jet for ambient pressure releases or the pseudo diameter if the release is under pressure i e the diameter after expansion to ambient pressure For Time Varying Releases this entry will refer to the current segment given in the Current Segment Number box Minimum 0 01 m Maximum 1000 0 m 3 2 3 5 Source mass flux The real number giving the mass flux of material released For Instantaneous releases this is a single total amount measured in kilograms For Continuous Time Varying and Jet releases this is a mass flux for the source measured in kilograms per second For instantaneo
173. y Britter and McQuaid 1988 Britter 19892 Britter 1995a and Hanna and Drivas 1987 1997 The information on dense gas dispersion that is of interest to the hazards analyst is contained in the distribution of concentration as a function of the spatial coordinates and time Very often this information is required only in summary form such as 1 the distance to a given concentration for example the lower flammability limit 2 the size composition and shape of the cloud These are needed for thermal radiation estimates in the event of burning or as input to methods of estimating explosion propagation 3 the mass of gas in the cloud between the upper and lower flammability limits This is often regarded as the appropriate mass to be used in estimating the TNT equivalence of a flammable cloud and 4 the concentration and its time history at a given distance needed to define toxic effects on human and non human biota 43 GASTAR Section 8 Theory 8 1 1 Formation of dense gas clouds The density of the cloud results not only from the properties of the material released but also from the methods of storage and of release Most cases of interest are covered by the following broad categories 1 material with a high molecular weight compared with that of air e g chlorine 2 materials with low molecular weight that may be at a low temperature e g cold methane evolving from the boiling of refrigerated liquefied natural
174. y Copy of You can change any part of the data and save it again if you wish If you cancel the form from this point no new copy of the obstacle will be created Delete will delete ie completely remove the definition data of the currently selected obstacle in the table There is no warning before the obstacle is removed In general it is preferable to turn an obstacle off see Section 3 3 1 2 rather than delete it Obstacles Defining Obstacles Type Diameter m Height m Circular Building Y 10 4 Name Distance m Bearing Solidity Small tank 50 45 J Consider this Obstacle in the calculations Cancel Select the appropriate obstacle type from the list in Max Figure 3 10 The Obstacle Definition dialogue box 3 3 2 Defining obstacles The Obstacle definition form shown in Figure 3 10 is where you define and edit the obstacle 35 GASTAR Section 3 Entering Input data A more detailed description of each parameter follows In Figures 3 11 3 13 the source is located at the origin 3 3 2 1 Obstacle types Choose which type of obstacle you want to add from those in the drop down list box GASTAR can model fences and circular or rectangular buildings The definition parameters will change according to the type of obstacle being added so it is recommended that you select the obstacle type first before entering other data PLAN VIEW gt Z Io obstacle distance 0 wind bearing W

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