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Simscape Fluids Simple Pressure Drop Error

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TiffyEng
TiffyEng on 3 Mar 2021
Answered: Juan Sagarduy on 16 Mar 2021
Simscape Fluids produces an error when simulating a very simple gas network which I have shown below. The idea is to observe the pressure at port B of the valve (variable orifice) with a constant upstream pressure and mass flow rate. I would appreciate any help trying to resolve this problem.
Reservoir (G) Pressure: 350 psi
Reservoir (G) Temp: 50 degF
Mass Flow Rate: 0.176 kg/s
Reservoir (G)1 Pressure : Atmospheric
Reservour (G)1 Temperature: 32 degF
The diagnostic information is also included below:
=== Simulation (Elapsed: 9 sec) ===
Error:An error occurred while running the simulation and the simulation was terminated
Caused by:
['Gas_Expansion/Solver Configuration']: At time 0.000000, one or more assertions are triggered. See causes for specific information.
Pressure at port A must be greater than or equal to Minimum valid pressure. The assertion comes from:
Block path: Gas_Expansion/Mass Flow Rate Source (G)
Assert location:
o In between line: 198, column: 9 and line: 198, column: 15 in file: C:\Program Files\MATLAB\R2020b\toolbox\physmod\simscape\library\m\+foundation\+gas\+sources\mass_flow_source.ssc
Temperature at port A must be greater than or equal to Minimum valid temperature. The assertion comes from:
Block path: Gas_Expansion/Mass Flow Rate Source (G)
Assert location:
o In between line: 200, column: 9 and line: 200, column: 15 in file: C:\Program Files\MATLAB\R2020b\toolbox\physmod\simscape\library\m\+foundation\+gas\+sources\mass_flow_source.ssc
Pressure at port B must be greater than or equal to Minimum valid pressure. The assertion comes from:
Block path: Gas_Expansion/Variable Orifice ISO 6358 (G)
Assert location:
o (location information is protected)
Temperature at port B must be greater than or equal to Minimum valid temperature. The assertion comes from:
Block path: Gas_Expansion/Variable Orifice ISO 6358 (G)
Assert location:
o (location information is protected)
Argument of log must be positive. The assertion comes from:
Block path: Gas_Expansion/Variable Orifice ISO 6358 (G)
Assert location:
o (location information is protected)

Answers (1)

Juan Sagarduy
Juan Sagarduy on 16 Mar 2021
Hello Tiffy
The gas starts up in a suction state, which means that vacuum would be created in the system. Such situations occur easily in the gas domain.
Two things i would try would be: 1) smaller orifices 2) use of a pressure source instead of mass flow rate source.
Best of Luck / Juan

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