id summary reporter owner description type status priority milestone component version resolution keywords cc 3382 Issue with current implementation of Stream connectors Francesco Casella Per Östlund "I am investigating the root causes of #3118. One interesting test case is {{{ThermoPower.Test.WaterComponents.TestValves}}}. There is one fairly large nonlinear system of equations, this is the dumpSimCode output: {{{ 108: (NONLINEAR) index:1 jacobian: false crefs: $cse16 [Real] , $cse12 [Real] , $cse17 [Real] , $cse6 [Real] , V5 [model .ValveLiq$V5] .fluidState [record .ThermodynamicState$V5$fluidState] .p [Real] 79: V5.dp=V5.fluidState.p - SinkP1.p0[Real ] 80: V3.dp=SourceP2.p0 - V5.fluidState.p[Real ] 81: V2.dp=SourceP1.p0 - V5.fluidState.p[Real ] 82: V3.rho=Modelica.Media.Water.IF97_Utilities.rho_props_ph(SourceP2.p0, DIVISION($cse6 * SourceP2.h + $cse12 * SinkP3.h, $cse6 + $cse12), Modelica.Media.Water.IF97_Utilities.waterBaseProp_ph(SourceP2.p0, DIVISION($cse6 * SourceP2.h + $cse12 * SinkP3.h, $cse6 + $cse12), 0, 0))[Real ] 83: V3.w=homotopy(ThermoPower.Water.ValveLiq$V3.FlowChar(CloseValves.y) * V3.Av * sqrt(V3.rho) * ThermoPower.Water.ValveLiq$V3.sqrtR(V3.dp, 3000.0), CloseValves.y * V3.wnom * DIVISION(SourceP2.p0 - V5.fluidState.p, V3.thetanom * V3.dpnom))[Real ] 84: $cse2=max(V3.w, 1e-015)[Real (start = -V3.wnom, max = if V3.allowFlowReversal then 9.999999999999999e+059 else 0.0, quantity = ""MassFlowRate.WaterIF97"", min = -100000.0, unit = ""kg/s"")] 85: $cse7=max(-V3.w, 1e-015)[Real (start = V3.wnom, min = if V3.allowFlowReversal then -9.999999999999999e+059 else 0.0, quantity = ""MassFlowRate.WaterIF97"", max = 100000.0, unit = ""kg/s"")] 86: V3.outlet.h_outflow=DIVISION($cse6 * SourceP2.h + $cse12 * SinkP3.h, $cse6 + $cse12)[Real ] 87: V2.outlet.h_outflow=DIVISION($cse16 * SinkP2.h + $cse17 * SourceP1.h, $cse16 + $cse17)[Real ] 88: V2.rho=Modelica.Media.Water.IF97_Utilities.rho_props_ph(SourceP1.p0, DIVISION($cse16 * SinkP2.h + $cse17 * SourceP1.h, $cse16 + $cse17), Modelica.Media.Water.IF97_Utilities.waterBaseProp_ph(SourceP1.p0, DIVISION($cse16 * SinkP2.h + $cse17 * SourceP1.h, $cse16 + $cse17), 0, 0))[Real ] 89: V2.w=homotopy(ThermoPower.Water.ValveLiq$V2.FlowChar(CloseValves.y) * V2.Av * sqrt(V2.rho) * ThermoPower.Water.ValveLiq$V2.sqrtR(V2.dp, 5000.0), CloseValves.y * V2.wnom * DIVISION(SourceP1.p0 - V5.fluidState.p, V2.thetanom * V2.dpnom))[Real ] 90: V5.w=V2.w + V3.w[Real ] 91: $cse11=max(-V5.w, 1e-015)[Real (start = V5.wnom, min = if V5.allowFlowReversal then -9.999999999999999e+059 else 0.0, quantity = ""MassFlowRate.WaterIF97"", max = 100000.0, unit = ""kg/s"")] 92: V2.inlet.h_outflow=DIVISION($cse11 * SinkP1.h + $cse2 * V3.outlet.h_outflow, $cse11 + $cse2)[Real ] 93: $cse1=max(V2.w, 1e-015)[Real (start = -V2.wnom, max = if V2.allowFlowReversal then 9.999999999999999e+059 else 0.0, quantity = ""MassFlowRate.WaterIF97"", min = -100000.0, unit = ""kg/s"")] 94: V3.inlet.h_outflow=DIVISION($cse1 * V2.outlet.h_outflow + $cse11 * SinkP1.h, $cse1 + $cse11)[Real ] 95: V4.rho=Modelica.Media.Water.IF97_Utilities.rho_props_ph(SourceP2.p0, DIVISION($cse6 * SourceP2.h + $cse7 * V3.inlet.h_outflow, $cse6 + $cse7), Modelica.Media.Water.IF97_Utilities.waterBaseProp_ph(SourceP2.p0, DIVISION($cse6 * SourceP2.h + $cse7 * V3.inlet.h_outflow, $cse6 + $cse7), 0, 0))[Real ] 96: V4.w=homotopy(ThermoPower.Water.ValveLiq$V4.FlowChar(OpenRelief.y) * V4.Av * sqrt(V4.rho) * ThermoPower.Water.ValveLiq$V4.sqrtR(V4.dp, 8000.0), OpenRelief.y * V4.wnom * DIVISION(SourceP2.p0 - SinkP3.p0, V4.thetanom * V4.dpnom))[Real ] 97: SourceP2.flange.m_flow=(-V4.w) - V3.w[Real ] 98: $cse21=max(-V2.w, 1e-015)[Real (start = V2.wnom, min = if V2.allowFlowReversal then -9.999999999999999e+059 else 0.0, quantity = ""MassFlowRate.WaterIF97"", max = 100000.0, unit = ""kg/s"")] 99: V1.rho=Modelica.Media.Water.IF97_Utilities.rho_props_ph(SourceP1.p0, DIVISION($cse21 * V2.inlet.h_outflow + $cse17 * SourceP1.h, $cse21 + $cse17), Modelica.Media.Water.IF97_Utilities.waterBaseProp_ph(SourceP1.p0, DIVISION($cse21 * V2.inlet.h_outflow + $cse17 * SourceP1.h, $cse21 + $cse17), 0, 0))[Real ] 100: V1.w=homotopy(ThermoPower.Water.ValveLiq$V1.FlowChar(OpenRelief.y) * V1.Av * sqrt(V1.rho) * ThermoPower.Water.ValveLiq$V1.sqrtR(V1.dp, 9000.0), OpenRelief.y * V1.wnom * DIVISION(SourceP1.p0 - SinkP2.p0, V1.thetanom * V1.dpnom))[Real ] 101: SourceP1.flange.m_flow=(-V2.w) - V1.w[Real ] 102: V5.rho=Modelica.Media.Water.IF97_Utilities.rho_props_ph(V5.fluidState.p, DIVISION($cse1 * V2.outlet.h_outflow + $cse2 * V3.outlet.h_outflow, $cse1 + $cse2), Modelica.Media.Water.IF97_Utilities.waterBaseProp_ph(V5.fluidState.p, DIVISION($cse1 * V2.outlet.h_outflow + $cse2 * V3.outlet.h_outflow, $cse1 + $cse2), 0, 0))[Real ] 107: max(-SourceP2.flange.m_flow, 1e-015) - $cse6 (RESIDUAL) 106: homotopy(ThermoPower.Water.ValveLiq$V5.FlowChar(CloseLoad.y) * V5.Av * sqrt(V5.rho) * ThermoPower.Water.ValveLiq$V5.sqrtR(V5.dp, 4000.0), CloseLoad.y * V5.wnom * DIVISION(V5.fluidState.p - SinkP1.p0, V5.thetanom * V5.dpnom)) - V5.w (RESIDUAL) 105: max(-V4.w, 1e-015) - $cse12 (RESIDUAL) 104: max(-V1.w, 1e-015) - $cse16 (RESIDUAL) 103: max(-SourceP1.flange.m_flow, 1e-015) - $cse17 (RESIDUAL) }}} The code shows several instances of {{{max(someFlowRate, 1e-015)}}}, which is apparently the simplest implementation of the {{{positiveMax()}}} operator defined in Sect. 15.2 of the Modelica Specification. The spec is a bit vague as it refers to ""a small flow"" for the threshold {{{eps1}}}. The underlying idea is that when flow rates are so small that their contributions to mass and energy balances are negligible, they can be approximated in the mixing equations to avoid singularities in the computation of stream variables. On the other hand, picking a flow threshold which is actually too small could lead to unnecessary rounding errors or convergence problems, if the stream variables are involved in bigger nonlinear systems. The engineering models I am aware of have flow rates in SI units with order of magnitude between 1e-4 and 1e4, so that 1e-15 seems way to small even in the case of the smallest possible flows (e.g. in pharmaceutical plant applications). I propose the following actions: - change the default value of {{{eps1}}} to 1e-7, which is still low enough for 99.9% of applications, while safely distant from machine precision - allow to change the default of {{{eps1}}} by a compiler flag, to allow advanced users find out the best value in case of critical problems - use {{{eps1*flowVariable.nominal}}} as the threshold, in order to allow proper problem-dependent scaling In fact, the last action will only be fully effective if proper nominal attribute propagation is also implemented for alias equations such as a = +/-b and a+/-b = 0, but I would implement it anyway even if this latter feature is still not available, because it might be provided later in the future. " defect closed critical 1.9.3 Frontend trunk fixed Lennart Ochel Willi Braun