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Hydraulic Library User Manual

1. Submodel Parameter title Value rod displacement m 0 15 piston diameter mm 40 HJ000 diameter of rod mm 20 angle rod makes with horizontal degree 90 total mass being moved 250 3 Runa dynamic simulation for 10 s Figure 1 39 Pressure and displacement plots 1 HJ000 1 rod displacement m 0 1500 1 0 1490 0 1480 0 1470 0 1460 0 1450 0 1440 0 1430 2 4 6 8 10 Time s 1 HJO00 1 pressure at port 1 bar Time s Figure 1 39 shows the system pressure and the displacement Problem 1 The starting values are poor 33 Chapter 1 Tutorial examples 34 Problem 2 The accumulator spring with its precharge pressure of 100 bar is taking no part in this simulation The only spring involved at the moment is the hydraulic fluid Solution to problem 1 1 In Parameter mode select Parameters Set final values This will give reasonable starting values for state variables You will find that the piston has dropped slightly from the mid position 2 Reset the following parameters Submodel Parameter title Value rod displacement m 0 15 HJ000 rod velocity m s 0 3 Runasimulation again and check that the system is in equilibrium with the rod in mid position Solution to problem 2 The two parameters we can vary are the precharge pressure and volume of the accumulator For the accumulator to work as a spring the precharge pressure must be lower than the equilibrium
2. Pipe material Absolute roughness 4 Drawn brass 1 5 um Drawn copper 1 5 um Commercial steel 45 um Wrought iron 45 um Hydraulic Library 4 2 User Manual Pipe material Absolute roughness 4 Asphalted cast iron 120 um Galvanized iron 150 um Cast iron 260 um Wood stave 0 2 to 0 9 mm Concrete 0 3 to 3 mm Riveted steel 0 9 to 9 mm The dependence of the friction coefficient 4 on the Reynolds number and the relative roughness as shown in Figure 2 54 is often known as the harp of Nikuradse Figure 2 54 Evolution of the frictional drag factor with the Reynolds number and with relative roughness friction factor null t Re A o rr 0 033 Re d Pa a N rr 0 016 rr 0 008 rr 0 004 7 rr 0 002 rr 0 001 0 02 rr 0 0 log Re null All lines with friction in the hydraulic category use such a frictionnal drag factor References 1 McCloy D Discharge Characteristics of Servo Valve Orifices 1968 Fluid International Conference pp 43 50 2 R C Binder Fluid Mechanics 3rd Edition 3rd Printing Prentice Hall Inc Englewood Cliffs NJ 1956 53 Chapter 2 Theory of fluid properties 54 Hydraulic Library 4 2 User Manual Chapter 3 AMESim Fluid Properties 3 1 FP04 Introduction AMESim allows you to use systems with several fluids in a single sketch For each fluid you use you need to add a fluid property icon to your
3. Line Takes into Dissipation Use for submodels account number ALOI Capacitance gt 0 8 relatively short pipes HL02 resistance with high dissipation ALO3 number Capacitance lt 1 2 and gt 0 8e 3 relatively short pipes f A E HLOO4 Acta EA dissipation a frequency HLS dependent friction HL04 Capacitance lt 1 2e 3 relatively short pipes HALOS resistance with very low HL06 inertia dissipation number Resistance relatively short pipes HL02I inertia with very high fluid velocity 64 Hydraulic Library 4 2 User Manual HL10 Capacitance gt 0 8 long pipes with high ALI1 resistance dissipation number HL12 Capacitance lt 1 2 and gt 0 8e 3 moderate lengths with moro ramos ad a LO j POSE dependent friction HL020 Capacitance lt 1 2e 3 moderate lengths with HL021 resistance very low dissipation HL022 inertia number HLG20 HLG21 HLG22 The result of this test must be qualified by considering the next important number Communication interval The time taken for a wave to travel down the pipe is L Trae 7 Cc wave If this time is significantly less than the communication interval you will never see the waves in plots and so it is not useful to use a wave dynamics submodel This is why changing the communication interval leads to the appearance disappearance of warning messages with the communication interval 7 to determine if we We wi
4. 2 L pO Ap Aai where A friction coefficient of the segment of relative length Dh 1 D hydraulic or equivalent diameter 7 length of flow segment For this type of submodel the total friction factor is given by 1 4 me D In straight tubes the resistance to the motion ofa liquid or a gas under conditions of laminar flow is due to the force of internal friction This happens when one layer of the liquid or gas has a relative motion compared to the others These viscosity forces are proportional to the first power of the flow velocity We then have A A A Re 51 Chapter 2 Theory of fluid properties 52 As the Reynolds number increases the inertia forces which are proportional to the velocity squared begin to dominate As flow becomes turbulent there is a significant increase in the resistance to motion Part of this increase is due to the roughness of the wall surface Therefore we have A A Re rr where rr is the relative roughness The relative roughness is calculated as the ratio of the average height of asperities to the tube diameter See details in Figure 2 53 Figure 2 53 Relative roughness l y EEO 2 AAA Y A The relative roughness of a pipe is given by _A a rr where A is the equivalent uniform roughness of the pipe Dig the hydraulic diameter of the pipe A sampling of absolute pipe roughness 4 for new clean pipes is proposed by Binder 2
5. 3 Click on Add curve and drag and drop the flow rate onto Y and the pressure drop onto X E Curve 4 E Curve 4 iX 84 differential pressure ly bd 41 RWOO 1 flow rate at relief valve port 1 Add curve Remove curve Add curve Remove curve 4 Curve l to 3 are no longer Plots amp Curves required so select each in turn and then click on Remove E Curve 4 curve so that only Curve 4 iX Ad differential pressure remains Y 41 RVOO 1 flow rate at relief valve port 1 Add curve Remove curve 5 Finally click on OK to see the plot 25 Chapter 1 Tutorial examples Figure 1 32 The relief valve flow rate pressure drop characteristics 160 140 120 100 80 60 40 20 1 RVOO 1 flow rate at relief valve port 1 L min 20 40 60 80 100 120 140 160 differential pressure bar 1 6 Example 5 Position control for a hydraulic actuator Objectives 26 Use a simple proportional control system to achieve a prescribed cycle in a hydraulic system Show the consequences of using an unequal area actuator Show saturation in a servo valve Study stability and instability in the control system Hydraulic Library 4 2 User Manual Figure 1 33 The position control system y Force duty Force conversion Servo valve cycle Hydraulic gt accumulator The system sketch for this exercise is shown in Figure 1 33 The hydraulic actuator or ja
6. yj and so the SI unit is the m s The older unit of kinematic viscosity is the Stoke St which is 10 m s However even this is a very small unit and hence the centistoke cSt is the common unit with 1 cSt 10 m s This parameter is easily measured with viscometers Note that the viscosity varies significantly with the fluid temperature Figure 2 50 Viscosity against temperature ISO 4113 at 0 bar gauge pressure g 1 kinematic viscosity cSt 1 8 7 6 5 4 3 2 1 0 0 20 40 60 80 100 Temperature degC Normally in absence of air release and cavitation the variation with pressure is not great unless the pressure is very extreme 47 Chapter 2 Theory of fluid properties Figure 2 51 Variation with pressure 150 4113 diesel fuel at 40 degC kinematic viscosity cSt 5 1 4 3 2 1 0 0 0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 1 3 pressure bar 10 Viscosity influence on the flow Another important aspect of the viscosity is its influence on the flow conditions of the fluid We can distinguish two types of flow conditions Laminar flow for which the flow lines are parallel and shearing forces create a pressure drop Turbulent flow for which the fluid particles have a disordered random movement leading to a loss of pressure These two conditions can be distinguished using the Reynolds number which is defined as follows Pes Upd _ Ud _ inertia effects u v viscous effects with U average fluid veloci
7. Notice that the compressibility effect can be modified by air release cavitation phenomena and by expansion of a pipe hose or chamber containing the hydraulic fluid Density and compressibility coefficient The density is the mass of a substance per unit volume M p y Density has dimensions of M L and is expressed in kilograms per cubic meter kg m As mentioned previously the density is a function of the pressure and the temperature p p P T nature of fluid This function can be approximated by the first three terms of a Taylor series p P AP T AT p 2 wae ar This can also be expressed as p Ae 2 a47 with 08 and a This equation is the linearized state equation for a liquid Using the definition of the density the two coefficients and B can also be expressed as B LG and a WF 41 Chapter 2 Theory of fluid properties B is known as the isothermal bulk modulus or for simplicity the bulk modulus and amp is known as the cubical expansion coefficient Since fluid density varies with the applied pressure this implies that a given mass of fluid submitted to a pressure change changes its volume This phenomenon leads to the definition of the compressibility coefficient 3 where B is expressed in units Pa or m N Considering the relation Vp M for a closed hydraulic circuit the mass is constant and hence d Vp 0and Vdp pdV 0 it follows that dp _ av mY Using
8. The model of the diesel fuel properties is based on accurate ex perimental measurements and are designed for use with injection system which are very fast acting For this reason air is assumed to be entrained rather than luid rops diesel rops Ta prop ISO 4110 diesel fuel E dissolved Figure 2 46 Air is entrained aa fluid bulk modulus bar 1 Hl esos 0 air cece neem ene A AN nara ds 19 po ae ne A mr om tT y 200 gt AA TT et A i gale 1 gt 0 1 7 10 air 2 T T T T T T T T T T T T l 0 20 40 60 80 100 input pressure bar Dissolved air Air can also be dissolved in a liquid A certain amount of air molecule can be part of the liquid In this case the dissolved air does not significantly change the fluid properties 43 Chapter 2 Theory of fluid properties 2 2 Saturation pressure Vapor pressure 44 Air release and cavitation Air can be dissolved or entrained in liquids and it is possible for air to change from one of these two forms to the other depending on the conditions to which the fluid is subjected Suppose the fluid is in equilibrium with a certain percentage of dissolved gas usually air nitrogen and oxygen Lowering the pressure above a critical value called the saturation pressure induces aeration This is the process where the dissolved gas forms air bubbles in the liquid until all the dissolved gases or air are free The exact point where all the dissol
9. output at start of stage 5 null 0 2 output at end of stage 5 null 0 2 UDOO 2 output at the end of stage 1 null 1000 output at end of stage 1 null 1000 SV00 valve natural frequency Hz 50 valve damping ratio null 1 valve rated current mA 200 DT000 gain for signal output 1 m 10 GA00 3 value of gain null 10 GA00 4 value of gain null 250 Note 28 Hydraulic Library 4 2 User Manual e The parameters of H J000 give a very unequal area actuator and the plots can demonstrate the consequences of this The external force to the right of the actuator is a constant value of 1000 N The gain in the displacement sensor converts the jack position that is in the range 0 to 1 m to a signal in the range 0 to 10 The gain for the submodel GA00 attached to the duty cycle submodel is also 10 By this means the duty cycle will directly represent the actuator displacement in m 4 When you set the parameters for AJ000 click on the External variables button to call up the dialog box shown in Figure 1 34 Figure 1 34 External variables of HJ000 5 External Variables 71x HJ000 Double hydraulic chamber single rod jack with no orifices at flow ports Far amables shih hase a FECR associ nad saith Hen spore sian 2 the FECR af the amass gt m s gt m 3 gt m s s N 1 2 1 t l t bar L min bar L min This indicates that a positive velocity mea
10. A and T to B In the other extreme position the spool position is 1 and the connections are A to T and B to P When the spool position is 0 there is no flow To define the flow characteristics of the valve in the extreme positions a flow rate pressure drop pair is used The default values of these are 1 L min and 1 bar These values can normally be found in a manufacturer s catalogue The parameter critical flow number laminar gt turbulent is less important and can be left at its default value You can find the details for any submodel if you click on the Help button For SV00 this produces the dialog box shown in Figure 1 30 23 Chapter 1 Tutorial examples Figure 1 30 Help for submodel SV0O0 im Help SY00 OL x File Go Display Bookmarks Help 4 Sd Backward Forward Home Hide Show Print sp ae V00 Simple submodel of a 3 position 4 port hydraulic servovalve Description SY00 is a simple submodel of a servo valve The spool dynamics is modeled as a 2nd order system with a specified natural frequency and damping ratio For each of the 4 possible flow paths Folder AY Libraries Manuals Technical bulletins Gy Tutorial Examples Ay Utilities The rating of the valve rated current is set to 40 mA This means that an input signal of 40 units will produce a fraction spool position of 1 As the spool moves it behaves like a
11. HLOO0 1 pressure at port 1 bar 2 HLODO 1 pressure at port 1 frun 2 bar 3 HLOOO 1 pressure at port 1 frun 3 bar 160 4 HLODO 1 pressure at port 1 frun 4 bar A 140 5 HLOOO 1 pressure at port 1 frun 5 bar ISE 120 6 HLOOO 1 pressure at port 1 run 6 bar Time s The variation between the runs is now very pronounced The dynamic characteristics of the system is completely transformed A few words of explanation are necessary Normally the air content of a hydraulic oil is well below 1 and 0 1 is typical It is normally considered good practice to keep the value as low as reasonably possible However in a few application such as lubrication oil in gearboxes the oil and air are well mixed up and 2 5 is typical and up to about 10 is possible A reasonable quantity of air given time will completely or partially dissolve in the hydraulic fluid The lowest pressure at which all the air is dissolved is called the saturation pressure For very slow systems all the air is dissolved above the saturation pressure and partially dissolved below this pressure Henry s law gives a reasonable approximation for the fraction of air that is dissolved in equilibrium Some systems are slow enough to stay very close to this equilibrium position Figure 1 16 Often classic fluid power systems behave like this The original saturation pressure is better for the current example However it does take time for the air to dissolve
12. be Wass ed ee ee ee eee 42 F El o EARN De da Ea dl a oot dl a ea eae ree CRT 49 Laminar turbulent and transition flow 00 0 00000 c ccc eee eee 61 FOW TAE Sa sae recto Say doce os hoe nes Stee acetone Sack Sees A te li ea ate bt tain cn Sacked a 10 63 Eluid compressibility 22 E A Rae Oe a ee ee 61 Bluid properties 22 8 de o tea Mo ek Tee e bt E o bi ek al Oe hed Al a 10 46 55 FR OAS siete pct A RR ee Ce gal can le eee A dos 55 Frequency dependent friction aerei 0 ccc e aa t nen n tne nene 61 Index G Godunov line submodels 2 1 0 0 ccc eee eee tence ene t ete n teens 62 H Help Ons bmodels zerer A MRR ERLE A OES He 23 Hydraulic library TWO CHECO eras ear ar poles done colle leer e veda oe den e oe 3 Hydraulic oil AMO A A A aaa E E O 15 Hydraulic starter System e 4 I mera id o Stn Neen q a O e le A Dar ee ee ei tes 61 Inertia of fd did A A AD Od eee a 61 Isothermal bulk modulus oo ooooooooooor ee teen ene ete n en ens 42 L Lammar oW tt O Sento ba ea aA Pa AR a 48 Line submodel Appropriate se a onsets o e Cee eS Uae a ree hee ee 16 Line submodel ss sist veka ee a ade ea Hie ind ote Head KO Hees sR be 16 61 62 Occ r Ties 4 y te A A a A eee arte oe RE ONS 63 One dimensional 834 0 om 333 eddie has Lanse kos SEL ANN And arrar Hee ENaS 62 is Al a ois ue i aon he eae E A 62 Lumped parameter inr A aw ek 61 Lumped parameter submodel ooooooooooorrrr eene ttn e nee nene 61 P Plotting fluid p
13. checks are applied to your submodel choices when the run starts These take into account the fluid properties the pipe dimensions and the communication interval When the communication interval was 0 1 seconds it would have been impossible to see these oscillations and hence no warnings are issued 1 5 Hydraulic Library 4 2 User Manual Some very simple arithmetic gives two important points 1 Ifyou want to see fHz you need a communication interval no bigger than about 0f seconds 2 A communication interval of x seconds enables you to see frequen cies down to about 10x Hz Thus with 0 1 seconds you can see down to about 1 Hz In the current example we are probably not interested below 1 Hz and 0 1 seconds HLO and HLO3 are very suitable The following note is vitally important Note It is a common mistake in modeling hydraulic systems to always use line submodels of high complexity The correct procedure is to use the simplest line submodels that will achieve the modeling objective Be aware of the frequencies you are interested in and the frequencies you can see with the current communication interval If you make a bad choice you may multiply the CPU time by 10 or 100 and force the integrator to compute high frequency phenomena which are of no interest to you and will be invisible with the communication interval set The messages under the Warning tab are very helpful Read them See also Chapter 4 Selecting sub
14. effectively takes the complete weight off the suspension The slow evolution of the force duty cycle ensures that the system is very close to equilibrium at all times The plot of displacement against force Figure 1 40 shows the non linear nature of the spring It also shows that the suspension does not bottom out but it does top out 35 Chapter 1 Tutorial examples 36 Figure 1 41 Force against pressure 1 HJO00 1 external force on rod N 160 1 140 120 100 80 60 40 2 5 1 5 2 5 3 0 5 0 5 15 HA001 1 pressure at port 1 bar 10 Figure 1 41 shows that maximum pressure is 160 bar and the minimum is about 40 bar which occurs when the suspension tops out We could continue by doing further analytical calculations Alternatively we could do batch runs varying the accumulation pre charge pressure and accumulator volume and the interested reader could try this However we will end the exercise by considering the damping of the suspension which is mainly provided by the two orifices For simplicity we will assume they are of the same characteristics Step 2 Setup a batch run varying the diameters of the orifices with the vehicle subject to a step change in force 1 Select Parameters Global parameters Set some global parameters Real Integer Text Name Title Unt Value Mini DIAM diameter of orifice mm 1 2 Setup the global parameter shown 3 Set the following parameters
15. gt corner of the sketch will be created Y ou could also have clicked on the New icon in the tool bar but if you do this you will have to add the fluid properties icon yourself Step 2 Construct the rest of the system and assign submodels 1 Construct the system with the components as shown in Figure 1 1 2 Save it as hydraulicl 3 Go to Submodel mode Notice that the drop the prime mover the node and the pipes are not of normal appearance because they do not have submodels associated with them The easiest way to proceed is 4 Click on the Premier submodel button which is situated in the horizontal menu bar Hydraulic Library 4 2 User Manual Figure 1 4 The line submodels P thi ight button o gt Press the mouse right button Show component labels 6 Select Show line labels in the label menu Hide component labels Hide line labels You get something like Figure 1 4 It is possible that your system may have HL000 associated with one of the other line runs These minor variations are dependent on the order in which you constructed the lines They will not influence the simulation results An important feature to notice is that a line run has a special submodel HZL000 which is not a direct connection To emphasize this point the line run has a special appearance Remember the submodel DIRECT does nothing at all It is as if the ports at the end of the line were connected directly together In con
16. have given for the pipe pressure and load speed are not very realistic and the prime mover would start from rest or some valve would be used to regulate the flow to the motor However hydrostatic transmission systems like this often do suffer badly from cavitation and air release problems Note that all AMESim submodels have hydraulic volumetric flow rate in L min There are two possible interpretations of this flow rate The flow rate is measured at the local current hydraulic pressure or The flow rate is measured at a reference pressure AMESim adopts the second alternative with a reference pressure of 0 bar gauge This means that the volumetric flow rate is always directly proportional to the mass flow rate In most situations the difference between the two flow rates is negligible However there are three situations when there is a significant difference 1 There is a very large air content the pressure drops below the satu ration pressure for air in the liquid and air bubbles are formed in the liquid 2 The pressure drops to the level of the saturated vapor pressure of the liquid and cavities of vapor form 3 Extremely high variations in pressure occur such as in certain types of fuel injection systems The first situation is called air release and the second cavitation If there is cavitation or significant air release at the inlet to a pump the flow rate according to the first definition will not be reduced but with the a
17. second order system You can specify the natural frequency and damping ratio 5 Enable Discontinuities Printout in the Run Parameters dialog box 6 Run a simulation with default run parameters 7 Select the relief valve component and plot the three quantities Flow at relief valve outlet L min Pressure at relief valve inlet bar Pressure at relief valve outlet bar on the same plot Step 2 Plot the flow rate against the differential pressure for the relief valve This is a very common requirement for a 2 port valve and it involves use of the plot manager de 1 Start the Plot manager by clicking on the button in the tool bar on your plot The Plot manager is displayed as in Figure 1 31 24 Hydraulic Library 4 2 User Manual Figure 1 31 The Plot Manager Plot manager Plots amp Curves E E Plot 1 1 Time E Curve 1 187 RWO0 1 flow rate at relief valve port 1 L min E Curve 2 182 R V00 1 pressure at relief valve port 1 bar RW00 1 pressure at relief valve port 2 bar E Curve 3 y Add curve Remove curve In the right window we have the three quantities we requested and time We must create a new variable which will be the pressure drop across the valve 2 Click on Add item and construct the new variable 42 RYVO0O0 2 pressure at relief valve port 1 bar D 4METest F 43 RWOD 2 t relief val t2b D AMETest F
18. submodel are the following ones index of hydraulic fluid saturation pressure for dissolved air gas Hydraulic Library 4 2 User Manual air gas content e temperature polytropic index for air gas vapor content e absolute viscosity of air gas e advanced users high saturated vapor pressure cavitation e advanced users low saturated vapor pressure cavitation advanced users absolute viscosity of vapor advanced users effective molecular mass of vapor e advanced users air gas density at atmospheric pressure 0 degC name of fluid e name of file specifying fluid properties Note that density bulk modulus and viscosity do not appear in the parameters They are calculated from values in tables processed by specific functions These functions apply interpolation processing to calculate the fluid characteristics from tables These tables are given in a text file specified by the name of file specifying fluid properties parameter of the submodel Three samples of such files are supplied in the AMESim installation CD tblpropl txt tblprop2 txt tblprop3 txt You should be able to copy these files from the directory AME misc for Unix or AME misc for Windows Each file describes a particular mode of definition of the fluid properties For the density and bulk modulus three modes are available In mode 1 density and bulk modulus are defined from a reference density a reference pressure and a set of t
19. the definition of the compressibility coefficient B we obtain DP L B o oP More usually we use the bulk modulus B also known as the volumetric elasticity modulus e oP The relation between p and B implies mass conservation This relation must be RIGOROUSLY RESPECTED in the calculations In the modeling and simulation context of fluid energy systems disregarding the relation between p and B leads to abnormal evolutions of pressure in the closed circuit submitted to compression and expansion cycles This phenomenon is strongly accentuated if aeration occurs in the circuit when dissolved air in the fluid reappears in the form of bubbles We shall approach this point by examining the phenomena of aeration and cavitation The air can also have adverse consequences on a fluid compressibility In liquid air can be present in two forms entrapped and dissolved Entrapped air 42 When the return pipe is not submersed in the tank the liquid jet can entrain some air bubbles in the tank Another phenomenon that affects the quantity of air in liquid is the leakage Hydraulic Library 4 2 User Manual Figure 2 45 Liquid leakage o gt o o o a 00 E oo o This air stays in the liquid as cavities and can modify the fluid compressibility In this context we talk about effective bulk modulus Figure 2 46 shows the bulk modulus of a diesel fuel at 40 C with 0 0 01 0 1 1 10 air The plot is obtained using the system shown
20. 1 or is reached the valve is saturated 31 Chapter 1 Tutorial examples 1 7 Example 6 Simple design exercise for a hydraulic suspension Objectives Do a simple initial design study for a hydraulic suspension using e Analytical analysis AMESim standard runs e Batch runs e Linear analysis The system is shown in Figure 1 38 The hydraulic jack with the two orifices is the damper and the accumulator is the spring It is proposed to use this suspension on the cab of a truck The load on each suspension strut is 250kg Figure 1 38 A simplified hydraulic suspension TRUCK SUSPENSION Step 1 Build the system and run a simulation 1 Build the system using Premier submodel Much sizing can be done by simple calculations but simulation can be a great help in rapidly confirming the calculations and adding dynamics to the steady state values The two ports of the jack are interconnected and in equilibrium The pressures above and below the jack piston will be the same Using a force balance in the equilibrium position in terms of the piston area Apis and rod area A rod PA is L P A gigs ZApog 250 pist pist It follows that PA og 2308 32 Hydraulic Library 4 2 User Manual From this if we want an operating pressure of about 70 bar the diameter of the rod must be about 22 3 mm We will use a rod diameter of 20 mm and a piston diameter of 40 mm 2 Set the parameters of the following table
21. 4 1 O AMESim 4 1 1 O AMESim 4 1 2 O AMESim 4 1 3 O AMESim 4 2 O AMERun all O AMERun 4 0 O AMERun 4 0 1 O AMERun 4 0 2 O AMERun 4 0 3 O AMERun 4 1 O AMERun 4 1 1 O AMERun 4 1 2 O AMERun 4 1 3 O AMERun 4 2 O Improvement Hydraulic Library 4 2 User Manual O Other O PC all O Windows 2000 O Windows NT O Windows XP O Linux O Other AMESet all O AMECustom all O AMESet 4 0 O AMECustom 4 0 O AMESet 4 0 1 O AMECustom 4 0 1 O AMESet 4 0 2 O AMECustom 4 0 2 O AMESet 4 0 3 O AMECustom 4 0 3 O AMESet 4 1 O AMECustom 4 1 O AMESet 4 1 1 O AMECustom 4 1 1 O AMESet 4 1 2 O AMECustom 4 1 2 O AMESet 4 1 3 O AMECustom 4 1 3 AMESet 4 2 O AMECustom 4 2 Web Site http www amesim com Headquarter Development Center IM GINE S A Roanne Tel 33 4 77 23 60 30 Fax 33 4 77 23 60 31 E mail hotline amesim com FRANCE SWITZERLAND SPAIN PORTUGAL BENELUX IM GINE S A Paris Tel 33 1 39 43 08 12 Fax 33 1 39 43 52 19 E mail hotline amesim com ITALY SWITZERLAND IMAGINE S A Lyon Tel 33 4 37 69 72 30 Fax 33 4 78 54 39 61 E mail hotline amesim com UK IMAGINE v x Tel 44 0 1869 351 994 Fax 44 0 1869 351 302 E mail support uk amesim com GERMANY AUSTRIA FINLAND DENMARK NETHERLANDS NORWAY SWEDEN SWITZERLAND EASTERN EUROPE IMAGINE Software GmbH Tel 49 0 89 548495 35 Fax 49 0 89 548495 11 E Mail hotline german
22. DOO 1 user defined duty cycle output null 40 1 40 Hydraulic Library 4 2 User Manual 4 Select the directional valve Figure 1 27 You will not change any parameters but an understanding of the parameters of SV00 will help you to set those of UD00 The spool has some state variables which are the first two items in the list In Parameter mode their values are the initial values of these state variables The spool position is a fraction and so is a dimensionless quantity in the range 1 to 1 Figure 1 29 Parameters of the servo valve di Change Parameters 7 x Submodel 5 SV00 1 12 4 a 3 Simple submodel of a 3 position m Parameters fraction spool position Onull fractional spool velocity 017s index of hydraulic fluid 0 ports P to flow rate 1 L min ports P to corresponding pressure drop 1 bar ports P to A critical flow number laminar gt turbulent 1000 null ports B to T flow rate 1 L min ports B to T corresponding pressure drop 1 bar ports B to T critical flow number laminar gt turbulent 1000 null ports P to B critical flow number laminar gt turbulent 1000 null y Save Default value Mar value Load Reset title Min value Help OK Cancel Options The next 12 items determine the hydraulic flow characteristics of the valve covering the 4 possible flow paths When the valve is in one extreme position with fractional spool position 1 P is connected to
23. Hydraulic Library Version 4 2 September 2004 IMAGINE Copyright IMAGINE S A 1995 2004 AMESim is the registered trademark of IMAGINE S A AMESet is the registered trademark of IMAGINE S A ADAMS is a registered United States trademark of Mechanical Dynamics Incorpo rated ADAMS Solver and ADAMS View are trademarks of Mechanical Dynamics Incorporated MATLAB and SIMULINK are registered trademarks of the Math Works Inc Netscape and Netscape Navigator are registered trademarks of Netscape Communi cations Corporation in the United States and other countries Netscape s logos and Netscape product and service names are also trademarks of Netscape Communications Corporation which may be registered in other countries PostScript is a trademark of Adobe Systems Inc UNIX is a registered trademark in the United States and other countries exclusively licensed by X Open Company Ltd Windows Windows NT Windows 2000 Windows XP and Visual C are regis tered trademarks of the Microsoft Corporation The GNU Compiler Collection GCC is a product of the Free Software Foundation See the GNU General Public License terms and conditions for copying distribution and modification in the license file X windows is a trademark of the Massachusetts Institute of Technology All other product names are trademarks or registered trademarks of their respective companies Hydraulic Library 4 2 User Manual Chapter 1 T
24. ables of bulk modulus values against pressure Each table is written for a given temperature see tblpropl txt In mode2 density and bulk modulus are defined from a set of tables of density values against pressure Each table is written for a given temperature see tblprop2 txt In mode 3 density and bulk modulus are defined from a reference density a reference pressure and a set oftables of speed of sound values against pressure Each table is written for a given temperature see tblprop3 txt The viscosity of the fluid is also given in these files after the definition of the 57 Chapter 3 AMESim Fluid Properties density and the bulk modulus Two modes are available for the viscosity In mode 1 the absolute viscosity is defined from tables of absolute viscosities in cP Each table is written for a given temperature see tblprop1 txt In mode 2 the absolute viscosity is defined from tables of kinematic viscosities in cSt Each table is written for a given temperature see tblprop2 txt The best plan if you want to use this facility is to copy these files to a suitable local area and examine them in an editor Lines beginning with a are comments and these comments give further information on how the data is arranged Then you can select the file that uses the modes you find suitable and modify it in order to use your own data Robert Bosch adiabatic diesel This submodel is for Diesel fluid properties and is k
25. ainst AP P Z P infinity at the origin This cannot be and if you try to implement it is a numerical disaster Clearly the flow is laminar for sufficiently small pressure drops which means that C is certainly not constant One solution is to perform detailed experiments and compute C against Reynold s number In the context of the orifice not A Ud necessarily circular the Reynold s number is Re where U is a mean velocity and d the hydraulic diameter If we take U Q A we end up with the form C f Q and ultimately with Q F 0 It is possible to work with an implicit relationship like this but we would prefer an explicit formula 49 Chapter 2 Theory of fluid properties 50 This is provided by introducing another dimensionless number known as the flow number and denoted by A reference 1 This is defined as dh 2 P yp LP down v p From a modeling point of view A contains quantities we know Using A we have g C A v dy and provided we have C C A we have an explicit relationship which is easy to evaluate There are no more problems to obtain measurements for C 47C than for C y Cy Re and so the flow number form has many advantages Note Both P and P oy are needed AP is not enough because a pressure drop of 1 bar to O bar is not the same as 1001 bar to 1000 bar Itis not clear which pressure should be used to calculate p and v Possibilities are P Paown Pup P do
26. alog box for HZ000 is shown in Figure 1 5 The compressibility of the oil and the expansion of the pipe or hose with pressure are taken into account together with the pipe volume HZ000 normally requires the bulk modulus of the hydraulic fluid and pipe wall thickness together with the Young s modulus of the wall material From these values an effective bulk modulus of the combined fluid and pipe walls can be calculated The effective bulk modulus of a hose is normally very much less than that of a rigid steel pipe Click on the fluid icon F P04 in the sketch Hydraulic Library 4 2 User Manual Figure 1 6 Parameter for fluid properties submodel FP04 Submodel FP04 1 properties 6 Extemal variables indexed hydraulic fluid Parameters Note that the first item in the list is an enumeration Waie type of fluid properties elementary index of hydraulic fluid 0 density 850 kg m 3 bulk modulus 17000 bar absolute viscosity 51 cP absolute viscosity of air gas 0 02 cP saturation pressure for dissolved air gas Obar air gas content 0 1 temperature 40 degC polytropic index for air gas vapor content 1 4 null la integer parameter A collection of properties of elementary varying complexity are available but for this simplest exercise elementary is satisfactory elementary advanced advanced using tables Robert Bosch adiabatic diesel 5 Click on OK Step 4 Run a simulation 1 Goto Run
27. and this time will not be available in fast acting systems Fuel injection systems are a good example of this Hence with such systems it may be appropriate to set the saturation pressure artificially high to allow for significant quantities of air to be undissolved at all pressures 15 Chapter 1 Tutorial examples 1 4 Example 3 Using more complex line submodels 16 Objectives Use more complex line submodels Understand the need for a variety of line submodels To understand the importance of setting an appropriate line submodel The system for this example is the same as for example 2 Figure 1 12 We will describe the modification of the system to use more complex line submodels and the experiments performed Finally we give a little of the theory behind the submodels Step 1 Change submodels All the submodels in the current system were selected automatically We will change some of them manually 1 Go to Submodel mode You will now change some line submodels Before continuing note the following points The comers in the pipe runs are not physical but diagrammatic There are three hydraulic pipes and they meet at a point which physically will be a tee junction This tee junction in the sketch is described as a 3 port node and it has the submodel H3NODE 1 This models the junction as a common pressure with flow rates that give conservation of mass It is necessary to have a large number of hydraulic pi
28. aulic motor which drives a rotary load A relief valve opens when the pressure reaches a certain value The output from the motor and the relief valve returns to the tank The diagram shows three tanks but it is quite likely that a single tank is employed as the standard color If you do not have this categories displayed e check the path list in the Options menu The first category contains general hydraulic components The seconds contains special valves The hydraulic components used in the model you will build can all be found in the first of these Hydraulic categories If you click on this category icon you will have the dialog box shown in Figure 1 2 First look at the components available in this library Display the title of some components by moving the pointer over the icons There are two categories in the Hydraulic library These have blue Figure 1 2 The components in the first hydraulic category Al Hydraulic 24 x Qe 602 cella aleja vo Se eg BL Step 1 Use File gt New to produce the following dialog box Chapter 1 Tutorial examples Figure 1 3 The hydraulic starter system LA New E xi Starter files from Path List Empty system 4ME libhydr starters libhydr amt e System Starter Create a new Select the hydraulic starter circuit libhydr amt and then click on OK A new system with a fluid properties icon in the top left 5
29. ck moves a load and there is control using position feedback The position sensor is used to convert the actuator displacement to a signal A position duty cycle is specified by a duty cycle submodel The duty cycle position is compared with the position indicated by the sensor to produce an error The error is subjected to a gain and the signal transferred to the servo valve A further duty cycle supplies an external force to the actuator via the position transducer Step 1 Build the system and set parameters 1 Build the new system and save it as actuator The position sensor is found in the category labeled Mechanical A signal port is used to pass the displacement into the feedback loop 2 Use the Premier submodel button to select the simplest possible submodels combinations 27 Chapter 1 Tutorial examples 3 Set parameters for the submodels using the suggested values in the following table Submodel Number on Title Value sketch if any H J000 piston diameter mm 30 diameter of rod mm 20 length of stroke m 1 PUOO pump displacement cc rev 35 UDOO 1 duration of stage 1 s 1 output at end of stage 2 null 0 8 duration of stage 2 s 3 output at start of stage 3 null 0 8 output at end of stage 3 null 0 8 duration of stage 3 s 1 output at start of stage 4 null 0 8 output at end of stage 4 null 0 2 duration of stage 4 s 3
30. d clicking on it Use Parameters gt Common parameters Figure 1 14 shows the Common parameters dialog box This is a list of common parameters for selected objects They occur at least twice Since there are 3 hydraulic tanks and they all have pressures of 0 bar this value is displayed There are a number of submodels that have a parameter index of hydraulic fluid In FP02 the index of hydraulic fluid is set to 1 whereas in other submodels its value is 0 The value is displayed as Similarly the prime mover and rotary load both have a parameter strictly speaking variable with title shaft speed Since the two values are different is displayed Figure 1 14 Different values for common parameters m Parameters shaft speed index of hydraulic fluid tank pressure Parameters 227 rev min Obar Default value Mar value Reset title Min value 3 OK Cancel Options gt gt Set the parameter index of hydraulic fluid to 1 This will change all the parameters in the system except FP01 remember we selected Select all except FPO1 Step 3 Run a simulation and plot some variables You will probably find the results very much the same as in example 1 Step 4 Organize a batch run to vary the air content 1 2 In Parameter mode use Parameters Batch parameters Drag and drop the air gas content from FP04 2 to the Batch control parameter setup dialog box Se
31. d friction It is modeled like two hydraulic compressible volumes with a resistance between them Why did we not choose a more complex submodel that also included inertia We answer this question later in this exercise For the line from the node to the motor select the submodel HLO01 For the line between the node and the relief valve the submodel DIRECT is already selected and this is exactly what we want Step 2 Set parameters and run a simulation 1 Go to Parameter mode and set parameters for HLO and HLO3 so that both pipe lengths are 5 m and pipe diameters are 10 mm This can be done one at a time However we can do it another way Press the Shift key on click on the HL03 and HLO line runs so that they are selected Use Parameters gt Common parameters Figure 1 20 shows the Common parameters dialog box 17 Chapter 1 Tutorial examples Figure 1 20 The common parameters of the two line submodels Common Parameters 21x Parameters pressure at port 1 1 for calculated bulk modulus value 2 for user specified value index of hydraulic fluid diameter of pipe pipe length relative roughness 1e 005 null angle line makes with horizontal ve if port 2 above port 1 O degree wall thickness 10mm Young s modulus for material 2 06e 006 bar user specified effective bulk modulus 8000 bar Default value Max value Reset title Min value i Cancel Options gt gt Note that indicate
32. dels for Hydraulic Lines of a liquid increases In addition the pipe or hose containing the liquid expands with pressure The net result of this is a capacitance spring effect To cause a hydraulic fluid to travel along a horizontal pipe we must provide a pressure gradient to drive the fluid This is a resistance effect The moving fluid has mass and hence it has inertia Zero dimensional line submodels The simplest line submodels are DIRECT and HL000 and these can be described as zero dimensional The DIRECT line submodel assumes that the two ports are very close together and the fluid and pipe in between contributes nothing HL000 considers the capacitance only The length of the line is too small for significant resistance The fluid velocity and the mass are too small to 6 give significant inertia The hydraulic chamber submodel HC00 is essentially the same as HL000 One dimensional line submodels 62 If we take into account resistance or inertia we have a one dimensional or more accurately one spatial dimension submodel It is possible to have 2 and 3 dimensional submodels but this is the field of computation fluid dynamics For modeling systems one dimension is normally enough Until AMESim 4 2 all hydraulic line submodels in AMESim employ an implicit fomulation which was very stable This ensures that when the system is close to equilibrium very large integration steps may be taken There are other classes of meth
33. dex A AdVANCed s o5 FECES ASE USSR OTA SSO OR Se ea 56 Advanced properties 2 0 0 ccc teen ent bene teen eee e eens 12 advaticed using tables a A A EO ee es EE ee 56 AAP TEIEASES 550 A ro tedat been E a e Cok onal 2 9 10 44 45 61 ASPECTO sto ooh PS ee A eR ROE ae A A tice a nate a 63 B Batch parameters o Poe eee 13 Beate Wn 25 5 ceesetus o e os e ROR e 13 Bernoulli s equation 3c hed vcd tenn Gad ob big eee Waco ada herds ea E 49 B ulle MO dUlOS 2 ty 63 0 Gels A Seek eR ad eS ds ORES sow A ale 41 43 57 Variation of bulk modulus with pressure 0 0 000 e cece eens 61 C Capacitance tt Sat E a UN EE A S I id 61 CavitatlOnien soe eh eels Soh A ate Rat rete eee 2 9 10 44 61 AN E O 62 A AS he es 13 Communication interval e i ae aa E a o 65 o CO OE ois S nt AS E U EAE E SEEE eet ta ct ER E 21 Complex line submodels 2 05 2 ccc mireia a a 16 Compression eae 41 Compressibility coefficient s i era n R a T ERA RA NEAD A RE NDR RRS 42 Courant Friedrichs Lewy a Se ee 62 Cubical expansion coefficient 00 cece P A AE ERE al EEN 42 D IDIN E e ES E 41 57 Diesel PUIG prop rti ss A A 11 DIRECT submodel cit a PI AR RR O Oas 5 Dissipation Rumbera A ee ie et es Lee eet 64 Dissolvedsait heii ppi h AA 43 Distributed parameter submodels nunun nunne 61 Duty Cycles soe x eset incase e cda oO da Maat 21 E El MENA Zur oe ee Ee OEY LR a Hea ae bed bean lees 55 Entrapped ii cc tee eee eed ee ee he
34. ed This is similar to elementary but there are addition parameters When the pressure reaches the saturation pressure of the fluid some air gas is released If the pressure continues to decrease the high saturated vapor pressure of the fluid can be reached and some vapor appears cavitation the liquid starts to boil Remember the fluids used in real engineering systems are not chemically pure substances For this reason cavitation is assumed to occur over a range of pressures and the low saturation vapor pressure is the pressure at which it is assumed that all liquid has become vapor All these changes of state strongly modify the fluid characteristics With the elementary option this behavior is taken into account with some reasonable fixed cavitation parameters However with advanced you are allowed to set these values yourself They are high saturated vapor pressure low saturated vapor pressure absolute viscosity of vapor effective molecular mass of vapor With the elementary option advanced user parameters do not appear but have the following constant values high saturated vapor pressure 0 9 bar e low saturated vapor pressure 0 95 bar e absolute viscosity of vapor 0 02 cP e effective molecular mass of vapor 200 advanced using tables This option has been created to use values for the fluid density bulk modulus and viscosity depending on the current pressure and temperature The parameters used for this
35. ed fluid properties Parameters type o of fluid properties a advanced i index of hydraulic fluid 0 density 850 kg m 3 bulk modulus 17000 bar absolute viscosity 51 cP absolute viscosity of air gas 0 02 cP saturation pressure for dissolved air gas Obar air gas content 01 temperature 40 degC polytropic index for air gas vapor content 1 4 null advanced user high saturated vapor pressure 0 5 bar advanced user low saturated vapor pressure 0 6 bar advanced user absolute viscosity of vapor 0 02 cP advanced user effective molecular mass of vapor 200 null advanced user air gas density at atmospheric pressure 0 degC 1 2kg m 3 name of fluid unnamed fluid Change the index of hydraulic fluid in FP04 2 to 1 This is a number in the range 0 to 100 If you look at the other hydraulic components in the system you will find they have index 0 and hence they will still use the fluid properties of FP04 1 We could go into every hydraulic component using this second fluid and set the parameter index of hydraulic fluid to 1 This would be extremely tedious with a big system and there is always the possibility of missing one 12 di Common parameters PI x Hydraulic Library 4 2 User Manual Step 2 Set all fluid indices to the same value of 1 The best way to do this is to use the common parameters facility 1 Use Edit gt Select all All the system components will be selected unselect FP04 1 holding the SHIFT key an
36. enomena can lead to destruction of the material or component In both cases it is entrained gas that causes the troubles When cavities encounter high pressure in the downstream circuit these bubbles or cavities can be unstable and can collapse implosively The pressure developed at collapse can be large enough to cause severe mechanical damage in the containing vessel It is well known that hydraulic pumps and pipework can be badly damaged by cavitaton and air release In all classical hydraulic systems air release and cavitation must be avoided to prevent material destruction but sometimes it is required like for injection systems to prepare the spray formation 45 Chapter 2 Theory of fluid properties 2 3 Viscosity 46 Figure 2 49 Viscosity OO O O u du LES y u O O ye Viscosity is a measure of the resistance of the fluid to flow This characteristic has both positive and negative effects on fluid power systems A low viscosity leads to oil leaks in the dead zone formed between the mechanical parts in movement and a high viscosity will lead to loss of pressure in hydraulic ducts Viscosity is a characteristic of liquids and gases and is manifested in motion through internal damping Viscosity results from an exchange of momentum by molecular diffusion between two layers of fluid with different velocities In this sense the viscosity is a fluid property and not a flow property Figure 2 49 shows the relation bet
37. ereas the pressure is calculated by the line submodel The important feature is that most line submodels are produced in groups of three to cover the three possibilities Figure 4 56 Three different causalities pressure pressure A flow rate flow rate p gt flow rate flow rate EA pressure pressure A gt pressure flow rate ae flow rat ressure ow rate 2 4 3 Three important quantities Aspect ratio The checking algorithm in AMESim issues warning messages when you use a one dimensional submodel that has an aspect ratio ength diameter ratio less than 63 Chapter 4 Selecting submodels for Hydraulic Lines 6 This is defined in terms of the length L and diameter D as follows L A atio D Short fat pipes require different submodels than long thin pipes For distributed line submodels the line is divided into a collection of cells and the test is that the cell length diameter ratio must not be greater than 6 Dissipation number Another important measure is the dissipation number This is defined as v the kinematic viscosity and c the speed of sound E c P When the dissipation number reaches 1 the principal eigenvalues become real and wave effects are not significant When this is true no models that take into account inertia should be used If the dissipation number is significant less than 1 it may be important to consider wave effects This motivates the following table
38. for BOTH orifices Submodel Parameter title Value 1 for pressure drop flow rate pair 2 for 2 OR000 orifice diameter equivalent orifice diameter mm DIAM Hydraulic Library 4 2 User Manual 4 Set up a duty cycle to give a step increase in force Submodel Parameter title Value output at start of stage null 0 output at end of stage 1 null 0 duration of stage 1 s 1 UD00 output at start of stage 2 null 500 output at end of stage 2 null 500 duration of stage 2 s 9 5 Select Parameters gt Batch parameters 6 Drag and drop the global parameter into the Batch parameters dialog box and set the following values for a batch run Figure 1 42 Batch parameters Drag the parameters into this list to make them control parameters Submodel Parameter Unit Value _ Step size Num below Num above EE TR NE DECIAS GLOBAL diameter of orifice mm 7 Perform a batch run for 10 s and plot the displacement of the piston Figure 1 43 Batch run results for rod displacement HJOO0 1 rod displacement m o D a Cae woae fp a i 0 1 0 08 0 2 4 6 8 10 Time s The batch run will use orifice diameters of 1 to 6 mm in steps of 0 5mm Zooming 37 Chapter 1 Tutorial examples 38 in on the plot it becomes clear that 3 mm gives a reasonable degree of damping 8 Remove the step from UD000 so that there is a constant force of 0 N 9 In
39. he relief valve setting 150 bar During this time the load speeds up rapidly and actually over speeds At this point the motor is demanding more hydraulic flow than the pump can supply The result is that the pressure must drop and the relief valve closes The pressure continues to drop and falls below zero bar gauge However pressure is not like voltage or force We cannot have a pressure of 100 bar The absolute zero of pressure is about 1 013 bar gauge It is time to introduce two terms Cavitation and air release When pressure falls to very low levels two things can happen e Air previously dissolved in the fluid begins to form air bubbles The pressure reaches the saturated vapor pressure of the liquid and bubbles of vapor appear These phenomena are known as air release and cavitation respectively They can cause serious damage Using the Zoom facility the graph gives a better view of the lower pressure values Figure 1 10 Low pressure in the hydraulic pipe 1 HLODO 1 pressure at port 1 bar 1 0 1 0 5 0 0 0 5 1 0 0 0 1 0 20 30 Tmel 40 Chapter 1 Tutorial examples 1 3 10 All AMESim submodels have hydraulic pressure in bar gauge The low pressure shown in Figure 1 10 Low pressure in the hydraulic pipe is caused by the load speed exceeding its steady state or equilibrium value and it is a highly undesirable behavior as it can result in damage to the real system In reality the starting values we
40. indly supplied by Robert Bosch GmbH Its parameters are fuel type index of hydraulic fluid e advanced users high saturated vapor pressure advanced users low saturated vapor pressure advanced users effective molecular mass e absolute viscosity of air gas e advanced users absolute viscosity of vapor air gas content e temperature The fi uel type isan enumeration type of fluid properties Robert Bosch adiabatic diesel integer parameter which gives fuel type 150 4113 gt access to 9 diesel fuels index of hydraulic fluid DEA summer diesel absolute viscosity Of Princeton airport minibus air gas content 150 4113 temperature polytropic index for air advanced user high advanced user low Swedish diesel rapsoelmethylester biological rape 50 diesel 50 rapsoelmethyleste 80 diesel 20 rapsoelmethyleste advanced user abso high density diesel fuel 843 kg m advanced user efe SHELL HCU diesel It is assumed that these fluids are used in fast acting injection systems and there is no time for the air content to dissolve or undissolve The user sets a fixed temperature and the local temperature is computed using an approximate relationship for an adiabatic change 58 3 2 Hydraulic Library 4 2 User Manual simplest This option gives the simplest hydraulic fluid properties Its parameters are index of hydraulic fluid e density bulk modulus e absolute visc
41. l frequency and damping ratio 5 Include a high gain value that makes the system unstable 6 Try introducing a dead band up to about 10 30 Hydraulic Library 4 2 User Manual Figure 1 36 Pump and relief valve flow rates 1 R 00 1 flow rate at relief valve port 1 L min 2 PU001 1 flow rate at port 2 L min 0 2 4 6 8 Time s 10 A typical plot for the flow rates from the pump and relief valve outlets is shown in Figure 1 36 If you had chosen the pump inlet flow rate instead of the pump outlet flow rate negative values would have appeared on the graph This is easily explained if you click on the External variables button of the Variable List dialog box For both ports of the pump a positive flow rate indicates flow out of the pump It follows that the flow rate at the pump inlet must be negative 7 Plot the two flow rates in the actuator HJO00 For the this submodel flow rate is an input on both flow ports This means a positive flow rate indicates flow into the component Figure 1 37 shows typical results Note how different the magnitudes of the flow rates are due to the unequal areas Figure 1 37 Hydraulic actuator flow rates 1 HJ000 1 flow rate at port 1 L min 15 2 HJO00 1 flow rate at port 2 L min 1 Li 10 5 0 5 10 0 2 4 6 8 10 Time s 8 Plot the valve spool fractional displacement This gives an idea of how close to saturation the valve is during the duty cycle Ifa value of
42. lation An eigenval ue analysis can also be useful The author remembers spending many hours trying to understand why a simulation failed Eventually he discovered that he had mistyped a parameter A hydraulic motor size had been entered making the unit about as big as an ocean liner When this pa rameter was corrected the simulation ran fine It follows that you must spend some time investigating why a simulation runs slowly or fails completely However it is possible that you have discovered a bug in an AMESim submodel or utility If this is the case we would like to know about it By reporting problems you can help us make the product better On the next page is a form When you wish to report a bug please photocopy this form and fill the copy You telephone us having the filled form in front of you means you have the information we need Similarly include the information in an email To report the bug you have three options e reproduce the same information as an email e telephone the details e fax the form Use the fax number telephone number or email address of your local distributor HOTLINE REPORT Creation date Created by Company Contact Keywords at least one Problem type O Bug Summary Description Involved operating system s DAI O Unix all O HP O IBM O SGI O SUN O Other Involved software version s O All O AMESim all O AMESim 4 0 O AMESim 4 0 1 O AMESim 4 0 2 O AMESim 4 0 3 O AMESim
43. lities elementary advanced advanced using tables Robert Bosch adiabatic diesel elementary This is the default and features a constant liquid bulk modulus with absolute viscosity The treatment of fluid properties under air release and cavitation is done simplest This has a constant absolute viscosity The bulk modulus is constant above the gas saturation pressure and is 1 1000 of this value below the gas saturation pressure This model is very old but is still used by some AMESim users It is likely to give the fastest runs advanced This gives you access to some cavitation parameters not accessible in the elementary properties advanced using tables This is like the advanced option but you install tables of data to give variation of bulk modulus and absolute viscosity with pressure and temperature Robert Bosch adiabatic diesel These properties are provided by Robert Bosch GmbH and comprise a number of common types of diesel fuel 11 Chapter 1 Tutorial examples Using one of the special fluids Step 1 Use the Advanced fluid properties 1 Return to the first example of this manual add another fluid properties icon 2 Use Premier submodel and go to Parameter mode Your sketch should look like this Figure 1 12 The sketch with two instances of FP04 3 Look at parameters of FP04 2 Change the enumeration integer parameter to advanced The Change Parameters list should now look like this Figure 1 13 The advanc
44. ll compare T com wave are likely to see waves in results The hydraulic volume submodels HC00 and HC01 which are basically the same as HL000 are included for completeness Similarly the zero volume submodel ZEROHV is also included Figure 4 57 Three other lines Hydraulic chambers 2 Zero volume We are about to display charts which help decide which line submodel to select These must be studied bearing in mind the following notes 65 Chapter 4 Selecting submodels for Hydraulic Lines Note Since many lines in AMESim are constituted with several segments 1 5 10 or 20 it can be noticed that in the below selection process the aspect ratio is compared to 6 30 or 60 corresponding to segment of length L L 6 and L 10 e The decision process employed in the charts that follow is very similar to one employed by AMESim when it checks the suitability of your submodels If the submodel is regarded as unsuitable a warning message is issued values of aspect ratio and dissipation number are given for one segment of the choosen line e Often the final result from the chart is three submodels such as HL01 HL02 HLO3 Since AMESim will check causality only one submodel the one that is compatible with adjoining submodels will be offered to you as a choice e The charts are intended for general guidance and give a good choice most of the time However there are circumstances in which an advanced users may
45. mode and do a simulation run The default values in the Run Parameters dialog box are suitable for this example 2 Click on the Start run button 3 Click on the pump component to produce the dialog box shown in Figure 1 7 Some variables such as a pressure have no direction associated with them A gauge pressure of 0 1 bar indicates that the pressure is below atmospheric In contrast other variables such as flow rate do have a direction associated with them A flow rate of 6 L min indicates that the flow is in the opposite direction to some agreed standard direction MOT gt Chapter 1 Tutorial examples Figure 1 7 The Variable List for PU001 pressure at port 1 Obar A flow rate at port 2 150 L min Vv pressure at port2 18 676 bar IV shaft torque 29 7238Nm Vv shaft speed 1500rev min M ANAS Note that you can use the Replay facility to give you a global picture of the results Figure 1 8 also shows the flow rates in L min at a time of 10 seconds Figure 1 8 Flow rates displayed in replay t 150 0000 148 2611 2 PITT LU Ww wu 0 0000 148 2611 4 To plot a variable associated with a line submodel click on or near the corresponding line run 5 Plot pressure at port 1 for HL000 Hydraulic Library 4 2 User Manual Figure 1 9 The pressure in the hydraulic pipe 1 HLODO 1 pressure at port 1 bar 0 2 4 6 8 10 Time s Notice how the pressure goes up to just over t
46. models for Hydraulic Lines Example 4 Valves with duty cycles Figure 1 27 Hydraulic system with servovalve Objectives e Introduce valves controlled by duty cycles e Use the plot manager to plot flow rates against differential pressure 21 Chapter 1 Tutorial examples Step 1 Build the system and set parameters 1 22 Build the system shown in Figure 1 27 and save it as servovalve Note that you have a directional valve that you will use to change the direction of rotation of the load You will need to use two new components e A 3 position 4 port direction valve found in the first Hydraulic category and A duty cycle component found in the Signal Control and Observers category When the new system sketch is complete use Premier submodel to get the simplest combination of submodels Set the parameter values for the duty cycle submodel UDOO as follows Title Value duration of stage 1 s 1 output at start of stage 2 null 40 output at end of stage 2 null 40 duration of stage 2 s 3 output at start of stage 3 null 40 output at end of stage 3 null 40 duration of stage 3 s 3 Note Ifyou do not change the parameters the valve will not open The motor and load will not move at all For simplicity leave the other submodel components with their default settings This gives a signal as follows Figure 1 28 The duty cycle controlling the valve 1 U
47. ns the rod is moving to the right The greater the displacement the further it is to the right In the current case a zero displacement and velocity means that the rod and piston are stationary and the piston is at the extreme left end of the jack The meaning of the sign of the acceleration and external force should be clear A positive external force opposes the other variables i e makes a negative con tribution to the acceleration Hence it is trying to reduce the velocity and dis placement Remove the dialog box by clicking on Close Step 2 Run simulation and plot results 1 Run a simulation setting a final time of 12 s and a communication interval of 0 05 s 29 Chapter 1 Tutorial examples 2 Plot the following graphs Actuator displacement and duty cycle output on the same graph e Flow rate at the two actuator ports on the same graph Flow rate at pump outlet and flow rate at relief valve outlet on the same graph e Fractional spool position Figure 1 35 The required and the actual displacement 1 UDOO 2 user defined duty cycle output null 2 HJOO0 1 rod displacement m Time s The first plot Figure 1 35 gives an idea of how closely the actual performance matches the required duty cycle 3 Plot the output from the summing junction strictly speaking a differencing junction that gives you the position error in m 4 Try changing the gain attached to the servo valve the servo valve natura
48. ods which have much more limited stability and have a strict limitation on step size due to the CFL Courant Friedrichs Lewy condition AMESim 4 2 contains an experimental version of one of these methods These are HLG20 HLG21 and HLG22 and implement the Godunov method They should be used as alternatives to HL020 HL021 and HL022 In other words for very low viscosity situations You can try these methods but they tend to give slow simulation runs and are less robust that the regular line submodels They will be replaced soon by an implementation of a different method which although still restricted by the CFL condition is faster and more robust than Godunov Hydraulic Library 4 2 User Manual 4 2 Line submodels occur in threes AMESim line submodels normally occur in groups of three The reason for this is the input and output characteristics of external variables of a submodel If we connect a pipe to a component the component submodel normally does one of two following things at the connection port e It calculates the flow rate output from the pressure input or It calculates the pressure output from the flow rate input In each case the pipe submodel must provide the correct variable for the component submodel Figure 4 1 shows the three standard possibilities The arrows indicate the direction of the flow of information Thus in the left port of the first case the flow rate is calculated by the attached component submodel wh
49. osity e saturation pressure air gas content e temperature e polytropic index for air gas content e name of fluid This submodel can be useful in difficult cases The integrator has an easier task during cavitation and air release and so it may be possible to get a solution when other methods are unsuccessful Tutorial example Copy AME misc tblprop1 txt or AAME miscWtblpropl txt in a suitable directory Start AMESim an build the system shown in Figure 3 55 in this same directory Figure 3 55 A simple system for plotting fluid properties 6 FPO C fluid props FP04 is the only submodel available for this icon Set the index of hydraulic fluid of the hydraulic submodels to 1 Change the parameters of the pressure input to get a ramp from 0 to 100 bar in 10 seconds Change the parameter name of file specifying fluid properties so that it specified your own file tb prop1 txt Start a simulation and plot the density the bulk modulus and the viscosity of the FPROP submodel against the pressure Now edit the values of your file tblprop1 txt and rerun the simulation Note how the properties change 59 Chapter 3 AMESim Fluid Properties 60 Hydraulic Library 4 2 User Manual Chapter 4 Selecting submodels for Hydraulic Lines This problem can create a lot of worry for some users and hence in this chapter we try to give some pragmatic rules to help you select an appropriate submodel In the formulae below it is assumes
50. pe submodels In the present system three submodels are set DIRECT DIRECT and HL000 Figure 1 18 The current line submodels Hydraulic Library 4 2 User Manual None of these line submodels take friction into account We will suppose that the relief valve is close to the node but the pump and the motor are at such distances from the node that the pressure drop along the pipes cannot be ignored We need to select new pipe submodels that take friction into account for the pipe runs from the pump to the node and from the node to the motor 2 Click on the line run attached to the pump and select HL03 in the Submodel list Figure 1 19 The hydraulic line submodels available Submodel list Description DIRECT Direct connection simple compressibility hydraulic pipe hose C compressibility friction hydraulic pipethose C R C simple wave equation hydraulic pipe hose C IR C simple f d f wave equation hydraulic pipe hose C IR C distributive submodel for very LONG hydraulic pipe hose C R distributive wave equation hydraulic pipe hose C IR IR C most complex wave equation hydraulic pipe hose C IR IR C IGodunov line C IR IR C Note the brief description of each line submodel In these descriptions C stands for compressibility R for resistance pipe friction and for inertia fluid momentum HL000 which we used before takes into account compressibility only HLO3 takes into account compressibility an
51. pproach adopted by AMESim it will be significantly reduced The properties of hydraulic fluids vary a great deal Modeling them is a very specialist process and the model can be extremely simple or highly complex The run times are greatly influenced by this level of complexity Example 2 Using more complex hydraulic properties Objectives e Use more complex models of fluid properties See how air content changes the performance of the system In the Hydraulic category two special components can modify the fluid properties Hydraulic Library 4 2 User Manual Figure 1 11 The two fluid properties icons A collect of O ES simple and complex fluid Special model used properties to ensure compatibility between 4 0 models and earlier Do not use this one with one submodel FP04 The other icon and its submodel is In AMESim always use this fluid properties icon It is associated O there only for backward compatibility This is an example of a component without ports We cannot connect this icon to any other There are two important thing about FP04 1 The characteristics of the fluid properties are It has an integer parameter index of hydraulic fluid that is in the range 0 to 100 inclusive This arrangement means that it is possible to have more than one fluid in an AMESim system Value determined by its parameters One of which is an elementary x enumeration integer parameter There are 5 simplest possibi
52. pressure The volume of fluid in the jack varies according to the piston position This is due to the rod The difference between the minimum and maximum oil volume is A oq X Stroke which is 0 1 L The accumulator volume should be a bit bigger than this but certainly not 10 L Step 1 Investigate the spring rate 1 Set the following values Submodel Parameter title Value gas precharge pressure bar 10 HA001 accumulator volume L 0 5 1 Do a run and verify that these values do not disturb the equilibrium The values should have changed the spring rate but not the equilibrium position We need now to investigate the spring rate Hydraulic Library 4 2 User Manual 2 Set the following values Submodel Parameter title Value output at start of stage null 0 output at end of stage 1 null 2500 duration of stage 1 s 40 UDOO output at start of stage 2 null 2500 output at end of stage 2 null 2500 duration of stage 2 s 80 3 Do arun for 120s 4 Plot graphs of rod displacement AJ000 pressure at port 1 7 000 against e external force on rod HJ000 Figure 1 40 Displacement against force 1 HJ000 1 rod displacement m ge ia 0 25 de 0 2 i 0 15 Ta 0 1 Say 0 05 3 25 Tooo eemal force on rod NJ cd 10 The force value of 2500 N pushes down on the suspension with a value corresponding to the weight of the car The force of 2500
53. roperties Heke Coa eda a eee eee eee eee ees 59 PRESSURE an 65 2st a A a ls a tes in et ae Peles eis 10 61 R Referente pressure a Beka NS SE ET A BR A es 10 Replay facility e bed A a E 8 Resistance tina radar ole se dla ba tip dees 61 62 Robert Bosch adiabatic diesel 0 occ ecb e nent ten eens 58 S Saturation pressure 2 6 ussen senene 44 Selecting a line submodel iii ee the ee A eG ee ee ia SS 67 A O OT ER aoa E Rage ats 6 Simplest ON 59 Submodel details popup 02 0 0 tenet ence teen en eees 23 T DO A o do en le de o 9 Turbulent flows 3 5054 sects cad fe eho eee Rare eG eee BOR HR PAE SUAS OE SS 48 y WIVES ennea A E ES a Matha Re A ea a bce a ee 21 Vapor pressure e Me ea ERR a heed 44 WASCOSILY Ae A A A Ett de Ne hy OU oh el 41 46 57 Variation of viscosity with pressure comme 61 70 Hydraulic Library 4 1 User Manual W Warning tab A A eg E E A A AE E EEA E AEE 21 71 Index 72 Hydraulic Library 4 2 User Manual Reporting Bugs and using the Hotline Service AME is a large piece of software containing many hundreds of thousands of lines of code With software of this size it is inevitable that it contains some bugs Naturally we hope you do not encounter any of these but if you use AME extensively at some stage sooner or later you may find a problem Bugs may occur in the pre and post processing facilities of AMESim AMERun AMESet AMECustom or in one of the interfaces with other software U
54. s that different values are set in the line submodels Set the index of hydraulic fluid to 1 diameter of pipe to 10 and pipe length to 5 2 In FP04 2 reset the saturation pressure for dissolved air gas to 0 bar 3 Run a simulation with the default run parameters 4 Plot the two pressures in HL03 Figure 1 21 Pressures at the ends of pipe joining pump to node 1 HLO3 1 pressure at port 1 bar 2 HLO3 1 pressure at port 2 bar 0 2 4 Time s 6 8 10 Note that there is a large pressure drop along the line This could be regarded as a sizing problem but in addition it would be bad practice to site the relief valve so far from the high pressure point 18 Hydraulic Library 4 2 User Manual Step 3 We now investigate other line submodels 1 Return to Sketch mode and Copy Paste part of the system as shown Figure 1 22 Part of the system is duplicated 2 In Submodel mode change the lower two line submodels as follows Figure 1 23 New line submodels This system will enable you to make direct comparisons between results 3 Go to Run mode and do a simulation Plot the pressure at the pump outlet pressure at port 2 Figure 1 24 Pressure at pump outlet 1 PUO001 1 pressure at port 2 bar 250 2 PUDO1 2 pressure at port 2 bar 200 150 100 50 Time s 19 Chapter 1 Tutorial examples 20 We note that the curves are virtually the same Try zooming There is absolutel
55. sert a linearization time at 10 s 10 Repeat the batch run and look at the damping ratio for the oscillatory frequency Looking at the eigenvalues selecting the jac0 1 to jac0 11 files we see that below 2 5 mm the system is very highly damped However the results for the 1 mm diameter give an oscillatory frequency of about 25 Hz which is curious but could be investigated with tools such as modal shapes For diameters of 2 5 mm and greater there is an oscillatory frequency of about 1 23 Hz and the damping ratio is as follows Diameter of orifice Damping ratio mm 2 5 0 533 3 0 308 3 5 0 194 4 0 130 4 5 0 091 s 0 067 535 0 050 6 0 039 We can see the evolution of these eigenvalues in a root locus plot Hydraulic Library 4 2 User Manual Figure 1 44 Root locus plot 12 55 ha E 0 6 75 0 7 1 Hz 5 0 8 257 09 25 5 7 5 hd e 7 6 5 4 3 2 1 0 1 A more refined search between 2 0 and 3 0 mm would be a good idea but 2 5 mm seems reasonable 39 Chapter 1 Tutorial examples 40 Hydraulic Library 4 2 User Manual Chapter 2 Theory of fluid properties 2 1 We will concentrate mainly on three fluid properties in this chapter e The density which leads to mass and hence to hydraulic inertia effects The viscosity which leads to the hydraulic friction effects e The compressibility and thus the bulk modulus which leads to the hydraulic system stiffness
56. sketch You can use each icon to install an index of hydraulic fluid in the range 0 to 100 These icons give you access to a number of submodels which will now be described We do not describe here the FPDROP submodel since it is considered as obsolete and it is available only for compatibility with old systems 4 0 and earlier icon shown has an enumeration parameter This submodel which is associated with the TETA which gives you access to a collection of fluid elementary K simplest properties of varying levels of complexity elementary advanced We now describe the parameters associated advanced using tables with each enumeration option Robert Bosch adiabatic diesel elementary This has the following parameters index of hydraulic fluid density bulk modulus absolute viscosity saturation pressure for dissolved air gas air gas content temperature polytropic index for air gas vapor content absolute viscosity of air gas name of fluid 55 Chapter 3 AMESim Fluid Properties 56 This option makes the following assumptions 1 The bulk modulus of the liquid with zero air gas content is constant This means the corresponding density varies exponentially with pressure 2 The viscosity of the liquid with zero air gas content is constant There is an air release and cavitation model included Note that name of fluid is a text string e g cooling water that identifies the fluid advanc
57. sually it is quite clear when you have encountered a bug of this type Bugs can also occur when running a simulation of a model Unfortunately it is not pos sible to say that for any model it is always possible to run a simulation The integra tors used in AME are robust but no integrator can claim to be perfectly reliable From the view point of an integrator models vary enormously in their difficulty Usually when there is a problem it is because the equations being solved are badly conditioned This means that the solution is ill defined It is possible to write down sets of equations that have no solution In such circumstances it is not surprising that the integrator is unsuccessful Other sets of equations have very clearly defined solutions Between these extremes there is a whole spectrum of problems Some of these will be the mar ginal problems for the integrator If computers were able to do exact arithmetic with real numbers these marginal prob lems would not create any difficulties Unfortunately computers do real arithmetic to a limited accuracy and hence there will be times when the integrator will be forced to give up Simulation is a skill which has to be learnt slowly An experienced person will be aware that certain situations can create difficulties Thus very small hydraulic vol umes and very small masses subject to large forces can cause problems The State count facility can be useful in identifying the cause of a slow simu
58. t up the batch parameters as in Figure 1 15 so that the air content goes from 0 to 10 in steps of 2 Specify a batch run in the Rum parameters dialog box and initiate the run 13 Chapter 1 Tutorial examples Figure 1 15 Setting up a batch run varying air content Batch Control Parameter Setup EE Select a component then drag its parameters into this list to make them control parameters Value Step size Num beld Num aboy 0 2 0 5 Submodel Parameter Unit FP04 2 air gas content Setup method varying between 2 limits user defined data sets Min value De Max value Num simu _Bemove set E 5 Plot several graphs of the batch run to compare results with various air contents Figure 1 16 Pressure in pipe 1 HLODO 1 pressure at port 1 bar 2 HLOOO 1 pressure at port 1 run 2 bar 3 HLO00 1 pressure at port 1 frun 3 bar 160 4 HLODO 1 pressure at port 1 frun 4 bar Mz E 140 5 HLOOO 1 pressure at port 1 run 5 bar PEN 120 6 HLOOO 1 pressure at port 1 run 6 bar Jaia A 5 6 0 2 4 6 8 10 By zooming on the curve in regions where the pressure is below 0 bar you will probably find some but not a remarkable variation in the results 6 Change the saturation pressure in FP04 2 to 400 bar 7 Repeat the batch run and update your plot 14 Hydraulic Library 4 2 User Manual Figure 1 17 Pressure in pipe with saturation pressure 400 bar 1
59. that SI units are used throughout 4 1 Introduction The submodels for lines are arranged with the simplest submodel at the top and the most complex at the bottom Why are there so many line submodels The main problem is the complexity of flow in hydraulic pipes and hoses The following features might be important e Variation of fluid compressibility and expansion of pipe hose walls with pressure e Inertia of fluid e Variation of bulk modulus with pressure e Variation of viscosity with pressure Laminar turbulent and transition flow e Frequency dependent friction e Air release and cavitation Lumped parameter and distributed parameter line submodels Normally it is perfectly satisfactory to use a lumped parameter submodel in which properties such as pressure are represented by a single representative value In other words within the pipe we assume there is negligible variation of pressure with position However if the pipe is extremely long or if wave dynamics are significant a distributed parameter submodel should be used For this type of submodel there are quantities such as pressure calculated at a number of positions Often these are stored as an array of values Capacitance resistance and inertia in line submodels Liquids are compressible not as much as gases but it is essential to recognize in modeling that they are compressible When subjected to high pressure the density 61 Chapter 4 Selecting submo
60. to be important the Thermal Hydraulic and Thermal Hydraulic Component Design libraries should be used e There are models of cavitation and air release in the hydraulic library Note also there is a special two phase flow library A typical application for this is air conditioning systems Chapter 1 of the manual consists of a collection of tutorial examples We strongly recommend that you do these tutorial examples They assume you have a basic level of experience using AMESim As an absolute minimum you should have done the examples in Chapter 3 of the AMESim manual and the first example of Chapter 5 which describes how to do a batch run Example 1 A simple hydraulic system Objectives e Construct a very simple hydraulic system e Introduce the simplest pipe hose submodels Interpret the results with a special reference to air release and cavitation Figure 1 1 A very simple hydraulic system 1 Relief valve Rotary Load In this exercise you will construct the system shown in Figure 1 1 This is perhaps the simplest possible meaningful hydraulic system It is built partly from components from the Hydraulic category which are normally blue and partly from the Mechanical category The hydraulic part is built up from standard symbols used for hydraulic systems Hydraulic Library 4 2 User Manual The prime mover supplies power to the pump which draws hydraulic fluid from a tank This fluid is supplied under pressure to a hydr
61. trast HLO00 computes the net flow into the pipe and uses this to determine the time derivative of pressure If the net flow into the pipe is positive pressure increases with time If it is negative it decreases with time The pressure created by HL000 is conveyed to the relief valve inlet The motor inlet is conveyed by the node and submodel DIRECT Step 3 Set parameters 1 Change to Parameter mode 2 Set the following parameters and leave the others at their default values Submodel Title Value HL000 pipe length m 4 coefficient of viscous friction Nm rev 0 02 RLOO mia Chapter 1 Tutorial examples A new dialog box as shown in Figure 1 6 is displayed This shows you the properties of the hydraulic fluid Currently they are at their default values and the absolute viscosity bulk modulus air gas content and temperature are given in common units Figure 1 5 Setting the line submodel HL000 parameters HL000 1 a External variables ana simple compressibility hydraulic pipe hose C 1 for calculated bulk modulus value 2 for user specified value index of hydraulic fluid diameter of pipe pipe length wall thickness 10mm Young s modulus for material 2 06e 006 bar user specified effective bulk modulus 8000 bar 3 To display the parameters of a line submodel click the left mouse button with the pointer on or near the appropriate line run Part of the di
62. ttle when it is closed you see no air bubbles and the liquid does not look fizzy The pressure in the bottle is above the saturation pressure of the gas in the liquid When you open the bottle suddenly bubbles appear and so the dissolved gas molecules of gas held in the liquid starts to appear as gas In fact the liquid is gas saturated and the atmospheric pressure is less than the saturation pressure of the liquid This phenomenon is clearly not cavitation but air release aeration Considering nuclei effects bubbles form only at particular places in your glass around the glass due to small asperities and round any particles present in the liquid Theoretically if your liquid was perfectly pure and the wall of the system perfectly regular air release or cavitation would occur with great difficulty The key point about cavitation is that it is a phase change the liquid changes to vapor A comparison can be made between cavitation and boiling If we look at the phase diagram below Figure 2 48 Cavitation and boiling pressure boiling gas vapor cavitation temperature Boiling is a phase change at constant pressure and variable temperature and cavitation is a phase change at constant temperature and variable pressure In any system air release starts first and ifthe pressure decreases further cavitation may occur This means that sometimes people talk about cavitation when the real phenomenon is air release Both ph
63. ty d diameter of the duct hydraulic diameter for others geometries p density u dynamic viscosity v kinematic viscosity The transition between laminar to turbulent flow occurs at the critical Reynolds number This is not well defined there exists always a transition region In a hydraulic line the critical Reynolds number is generally between 1500 to 2000 For uneven geometries thin walled orifices the critical Reynolds number can be lower than 100 48 Hydraulic Library 4 2 User Manual For non circular cross sections the hydraulic diameter can be used to determine the Reynolds number Hydraulic diameter is defined as follows j 4xcross sectional area h wet perimeter We now give two examples e Circular orifice of diameter a 4 3 mtd d e Rectangular orifice length L and width J ALl _ 24 h XL eT Hence d 2 if L 21 Flow through orifices Orifices also called restrictions can be fixed or variable and occur in huge numbers in fluid systems Not surprisingly in Engineering courses a mathematical description is presented This is usually based on Bernoulli s equation and leads to the form BP Z Paco Q CA up own E p where C is the flow coefficient This is variously described as typically 0 7 or varying with orifice geometry and Reynolds number The second alternative is obviously more correct If we do take a constant value we are forced to have the gradient of O ag
64. utorial examples 1 1 Introduction The AMESim Hydraulic library consists of A collection of commonly used hydraulic components such as pumps motors orifices etc including special valves e Submodels of pipes and hoses e Sources of pressure and flow rate e Sensors of pressure and flow rate e A collection of fluid properties Hydraulic systems in isolation are completely useless It is necessary to do something with the fluid and also to control the process This means that the library must be compatible with other AMESim libraries The following libraries are frequently used with the Hydraulic library Mechanical library Used in fluid power application when hydraulic power is translated into mechanical power Signal Control and Observer library Used to control the hydraulic system Hydraulic component design library Used to build specialist components from very basic hydraulic and mechanical elements Hydraulic resistance library This is a collection of submodels of bends tee junctions elbows etc It is used typically in low pressure applications such as cooling and lubrication systems Chapter 1 Tutorial examples 1 2 Note Itis possible to use more than one fluid in the Hydraulic library This is important because you can model combined cooling and lubrication systems of a library The hydraulic library assumes a uniform temperature throughout the system If thermal effects are considered
65. ved gas has come out of solution is difficult to pin point because it depends on the chemical composition and behavior of the gas This is a non symmetrical dynamic process the growing process does not have the same dynamics as when air bubbles disappear In consequence the total amount of bubbles created when the pressure drops may or may not be redissolved in the liquid when it rises again If the pressure is dropped further and above another critical value called the vapor pressure the fluid itself starts to vaporize It corresponds to a liquid phase change At some point only fluid vapor and gas exist In liquid systems the term cavitation usually refers to the formation and collapse of cavities in the liquid even if cavities contain air or liquid vapor To summarize with a sketch what we have introduced see above Figure 2 47 Air release and cavitation Liquid pressure qua p Re dissolution total or partial oo oO Og o Air bubbles appearance oof Air bubbles cavitation Vapor vaporized liquid Time The development of a cavity is now recognized as being associated with a nucleation center such as microscopic gas particles wear or wall asperities When Hydraulic Library 4 2 User Manual the liquid is subjected to a tensile stress cavities do not form as a result of liquid rupture but are caused by the rapid growth of these nuclei To understand this think of beer or champagne if you prefer in a bo
66. ween shearing constraint and difference of flow velocity between two layers The definition of viscosity was first given by Newton Between two layers of distance dy the exerted force between these two layers is given by na YO F uA dy where U y is the velocity depending on the radial position y and dU dy the velocity gradient This proportionality expresses the notion of Newtonian fluid and allows the introduction of defined as the dynamic viscosity or the absolute viscosity The dimension of is MLIT and the SI unit is kg m s or Pa s The older unit is the Poise P which is 0 1 kg m s However this is very small and hence the milli Poise mP is the common unit which is 10 kg m s The dynamic viscosity is the constant of proportionality between a stress and the intensity of shearing between two neighboring layers _ dum _ qt _ shear stress n dy audience dU y shear rate dy Hydraulic Library 4 2 User Manual However the absolute viscosity is not very often used in fundamental equations For example the dynamics of the elementary volume between the two layers is expressed as dt dU y A dy pAdy 3 d y pay dt and thus using the shear stress calculation dU _ 1dr _ ud UY de pay p gy In other formulas e g Navier Stokes the ratio between the absolute viscosity and the density occurs so often that a new parameter called the kinematic viscosity v is introduced V DIE of dimension L T
67. wish to break these rules 66 4 4 Hydraulic Library 4 2 User Manual The selection process Yes No Suitable TOODE spatial Zero spatial dimensions dimension assumption DIRECT N s HL000 HC00 HL02I Friction Possibly wave ZEROHV Dominated effects important O ALO1 HL01 HL02 HLO3 HL02 HL04 HL05 HL06 HL03 HL004 HL005 HL006 HL10 HL10 HL11 HL12 HL11 HL020 HL021 HL022 HL12 HLG20 HLG21 HLG22 HL030 HL031 HL032 Friction dominated pipes and hoses Yes No Use distributed submodel Use lumped submodel HL10 ALOI HL11 HL02 HL12 HLO3 67 Chapter 4 Selecting submodels for Hydraulic Lines Cannot see waves so regard as friction dominated Frequency dependent friction important HL030 HL031 HL032 High fluid inertia Try to use HL02I Possibly wave effects important Use simplest wave submodel HL04 HLO5 HL06 High flow acceleration HL021 HL022 HLG20 HLG21 HLG22 Use frequency dependent friction HL004 HL005 HLO006 Short pipes No Try to use HL000 or AC00 or DIRECT roblem with slow simulation Suspec caused by pressure Try ZEROHV in submodel 68 Hydraulic Library 4 1 User Manual In
68. wn 2 Or the pressure at the vena contracta AMESim uses P Paown 2 Tables of C C A can also be compiled using CFD computational fluid dynamics software For high values of A C q 18 approximately constant e The lowest value of A at which C is approximately constant is called the critical flow number Arit The critical flow number for a thin or sharp edge orifice is about 100 and for a long orifice is about 3000 Fora long edge orifice the constant C value is also the maximum value e Fora sharp edge orifice the maximum C value can be slightly greater than the constant value and occurs at a A value slightly below A crit For general use the AMESim submodels OR000 and ORO02 require A limiting value of C The value of A is computed from A dy 2 P up LP down vN p and the flow coefficient is calculated as max 24 C ma C q tanh 2 cri and the crit When 4 A crit C is about 96 of OF aa Hydraulic Library 4 2 User Manual Figure 2 52 shows a graph of Cq against A Figure 2 52 Graph of Cq against C max 07 d ro 0 6 3 E 05 8 04 Cc 2 2 0 3 D le 2 0 2 0 1 0 0 05 AN 15 2 25 3 35 crit flow number null Frictional drag Submodels belonging to this category are used to model resistance to flow in straight tubes and conduit The pressure losses along a straight tube of constant cross sectional area are calculated from the Darcy Weisbach equation
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70. y no advantage to using HL04 and HL06 instead of HLO and HLOS If we separated the two systems and ran then independently we would find run times for the more complex submodels were higher Change the communication interval in the Run Parameters dialog box to 0 001s and rerun the simulation If you have a look at the Warnings Errors tab of the Simulation run dialog box you will find that some checks are performed by the line submodels see Figure 1 25 A similar message is issued for HL03 Figure 1 25 Messages under the Warning tab Log Wamings Errors Dissipation number 0 00848527 indicates that viscous effects are too small for this submodel Consider using a HLO4 submodel Warning in HLO1 instance 1 It is suggested that e HLO should be replaced by HL04 and e HLO3 should be replaced by HL06 In other words with this communication interval the lower subsystem is better than the upper If you replot the pressures at the pump outlets there are clearly differences This is what happens if you zoom Figure 1 26 Zoomed pressures at pump outlet 1 PU001 1 pressure at port 2 bar 600 1 4 2 PUOQO1 2 pressure at port 2 bar 2 500 400 300 200 100 0 00 0 05 0 10 0 15 0 20 Time s The violent and unrealistic start up has created this oscillation in the pressure of about 56 Hz It is damped out by 0 1 seconds Why did we get no warning message in the previous run The answer is that a lot of

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