MSC. EASY5 Orifice Flow Orifice flow is based upon isentropic energy balance at steady state For a single phase: hup-hs+p-s=0 Energy balance Isentropic constraint · Two cases Choked: v is sonic, unknowns are p and t Non-choked: P= Pdm, unknowns are vs and T Equations are solved numerically. This approach is applicable to both ideal gases and non-ideal fluids. Flow is then: W=Ps s Acs Cd Modeling and Simulation of Gas Systems with MSC EASY5 - Chart 16 MSC XSOFTWARE
MSC.EASY5 Modeling and Simulation of Gas Systems with MSC.EASY5 - Chart 16 Orifice Flow • Orifice flow is based upon isentropic energy balance at steady state. For a single phase: 0 2 2 2 2 up s up s v v h h 0 up s s s Energy balance Isentropic constraint • Two cases: – Choked: vs is sonic, unknowns are Ps and Ts – Non-choked: Ps = Pdn , unknowns are vs and Ts. • Equations are solved numerically. This approach is applicable to both ideal gases and non-ideal fluids. Flow is then: s sAcsCd w v
MSC. EASY5 Orifice Conductance The MSC EASY5 Gas Dynamics library uses orifice discharge coefficient Ca and orifice area Aes If the orifice data is in terms of conductance C then, if Acs l in Cd4s=0.026706C, Only the product Cdcs can be uniquely determined from C, Therefore, when converting C, to Cd Estimate Acs as accurately as you can Then solve for C Sanity check: 0< Cd<1 Or if an accurate estimate of a is impossible Assume a reasonable value for Ca(=0.6-0.8 Solve for a Modeling and Simulation of Gas Systems with MSC EASY5 - Chart 17 MSC XSOFTWARE
MSC.EASY5 Modeling and Simulation of Gas Systems with MSC.EASY5 - Chart 17 Orifice Conductance • The MSC.EASY5 Gas Dynamics library uses orifice discharge coefficient Cd and orifice area Acs . If the orifice data is in terms of conductance Cv then, if Acs [=] in2 Cd Acs Cv 0.026706 • Only the product CdAcs can be uniquely determined from Cv . – Therefore, when converting Cv to Cd § Estimate Acs as accurately as you can § Then solve for Cd § Sanity check: 0 < Cd < 1 – Or if an accurate estimate of Acs is impossible § Assume a reasonable value for Cd ( = 0.6-0.8 ) § Solve for Acs
MSC. EASY5 Switch State Representation of Fluid Flow Regimes lote: Not to scale ZSW=4 ZSW=3 ZSW=2·ZSW=3Zsw=4 choked compressible, <-.Linear.- compressible, choked not choked lot choked Modeling and Simulation of Gas Systems with MSC EASY5 - Chart 18 MSC XSOFTWARE
MSC.EASY5 Modeling and Simulation of Gas Systems with MSC.EASY5 - Chart 18 Switch State Representation of Fluid Flow Regimes W 0 Dp ZSW = 3 ZSW = 2 ZSW = 3 compressible, Linear not choked MT compressible, not choked ZSW = 4 ZSW = 4 choked choked Note: Not to scale -MT
MSC. EASY5 Body Dynamics Group The body dynamics group contains components to model 1-dimensional mass dynamics of Actuator cylinders/diaphragms Poppets Spools Sign convention: a positive force acts in the positive x direction to open the poppet or extend an actuator. Most body dynamics and all actuator components contain inputs to model coulomb and breakaway friction. Coulomb friction is a constant force opposing motion Breakaway friction does not allow motion until the force on the mass exceeds the breakaway force. Breakaway friction must also have a nonzero coulomb friction value Coulomb friction cannot may not exceed breakaway friction PCF PM Dynamic coulomb friction force mag N(bf) 0 Breakaway friction force magnitude N(bf) CHP PM 351 Linear damping coef N-sec/cm(lbf-s/in Modeling and Simulation of Gas Systems with MSC EASY5 - Chart 19 MSC XSOFTWARE
MSC.EASY5 Modeling and Simulation of Gas Systems with MSC.EASY5 - Chart 19 Body Dynamics Group • The Body Dynamics group contains components to model 1- dimensional mass dynamics of: – Actuator cylinders/diaphragms – Poppets – Spools • Sign convention: a positive force acts in the positive x direction to open the poppet or extend an actuator. • Most Body Dynamics and all Actuator components contain inputs to model coulomb and breakaway friction. – Coulomb friction is a constant force opposing motion. – Breakaway friction does not allow motion until the force on the mass exceeds the breakaway force. - Breakaway friction must also have a nonzero coulomb friction value. - Coulomb friction cannot may not exceed breakaway friction
MSC. EASY5 Adding Pressure Forces to the Model There are two convenience components under Forces(CD and CV) that calculate pressure forces. Both determine Force= pressure x area Volume= position x area Volume rate velocity x area The No components represent the actuator Orifice extend and retract volumes They output pressures, which will be converted to Orifice Force or Volumes Single mass force by the CD2. The force for 2 volumes ard limits friction) calculated by CD2 is, in turn supplied to PM2. Velocity CD2 and position from PM2 are PP Inlet ActPosOut2_F returned to cd2. CD2 supplies volume and volume 4\Node rate to the no components Modeling and Simulation of Gas Systems with MSCEASY5 -Chart 20 MSC XSOFTWARE
MSC.EASY5 Modeling and Simulation of Gas Systems with MSC.EASY5 - Chart 20 Adding Pressure Forces to the Model There are two convenience components under Forces (CD and CV) that calculate pressure forces. Both determine: Force = pressure x area Volume = position x area Volume rate = velocity x area The NO components represent the actuator extend and retract volumes. They output pressures, which will be converted to force by the CD2. The force calculated by CD2 is, in turn, supplied to PM2. Velocity and position from PM2 are returned to CD2. CD2 supplies volume and volume rate to the NO components