Two phase fluid : Initial conditions solve failed to converge.

Hi everyone,

I am discovering SimScape. I am trying to simulate a simple piston under a two phase pressurized fluid.

However, I keep getting that error: Initial conditions solve failed to converge.

I really don't understand what is the issue but apparently it comes from my piston model (Translational Mechanical Converter 2P). If I remove it I have no error left.

Thank you very much for your answers !

Here the model and the complete error (model also attached):

=== Simulation (Elapsed: 3 sec) ===
    Warning:First solve for initial conditions failed to converge. Trying again with all high priorities relaxed to low.
    Warning:Second solve for initial conditions failed to converge. Trying again with all variable targets ignored.
    Error:An error occurred while running the simulation and the simulation was terminated
    Caused by:
        ['Test/Solver Configuration']: Initial conditions solve failed to converge.
            all components and nodal across variables involved
Cannot solve for one or more variables, including dynamic variable derivatives:
Time derivative of 'Ideal_Translational_Motion_Sensor.x' (Position)
Time derivative of 'Translational_Mechanical_Converter_2P.interface_displacement' (Interface displacement)
Time derivative of 'Translational_Mechanical_Converter_2P.mass' (Fluid mass)
Time derivative of 'Translational_Mechanical_Converter_2P.u_I' (Specific internal energy of fluid volume)
'Ideal_Translational_Motion_Sensor.R.v' (Velocity)
'Ideal_Translational_Motion_Sensor.V' (V)
'Ideal_Translational_Motion_Sensor.v' (Velocity)
'Pressure_Internal_Energy_Sensor_2P.A.u' (Specific internal energy)
'Pressure_Internal_Energy_Sensor_2P.U' (U)
'Reservoir_2P.A.u' (Specific internal energy)
'Reservoir_2P.Phi_A' (Energy flow rate into port A)
'Reservoir_2P.convection_A.Phi' (Energy flow rate into the port)
'Reservoir_2P.convection_A.mdot' (Mass flow rate into the port)
'Reservoir_2P.convection_A.port.u' (Specific internal energy)
'Reservoir_2P.mdot_A' (Mass flow rate into port A)
'Translational_Mechanical_Converter_2P.A.u' (Specific internal energy)
'Translational_Mechanical_Converter_2P.Phi_A' (Energy flow rate into port A)
'Translational_Mechanical_Converter_2P.R.v' (Velocity)
'Translational_Mechanical_Converter_2P.convection_A.Phi' (Energy flow rate into the port)
'Translational_Mechanical_Converter_2P.convection_A.mdot' (Mass flow rate into the port)
'Translational_Mechanical_Converter_2P.convection_A.port.u' (Specific internal energy)
'Translational_Mechanical_Converter_2P.interface_velocity' (Interface velocity)
'Translational_Mechanical_Converter_2P.mdot_A' (Mass flow rate into port A)
'Two_Phase_Fluid_Properties_2P.A.u' (Specific internal energy)


Equations of one or more components may be dependent or inconsistent. This can cause problems in transient initialization. Here is the set of components involved:
all components involved
'Test/Ideal Translational Motion Sensor'
Equation location is:
 'D:\PROGRAMMES\MatlabR2020a\toolbox\physmod\simscape\library\m\+foundation\+mechanical\+sensors\velocity.ssc' (line 42)

'Test/Reservoir (2P)'
Equation locations are:
 'D:\PROGRAMMES\MatlabR2020a\toolbox\physmod\simscape\library\m\+foundation\+two_phase_fluid\+elements\reservoir.ssc' (line 129)
 'D:\PROGRAMMES\MatlabR2020a\toolbox\physmod\simscape\library\m\+foundation\+two_phase_fluid\+elements\reservoir.ssc' (line 132)

'Test/Translational Mechanical Converter (2P)'
Equation locations are:
 'D:\PROGRAMMES\MatlabR2020a\toolbox\physmod\simscape\library\m\+foundation\+two_phase_fluid\+elements\translational_mechanical_converter.ssc' (line 213)
 'D:\PROGRAMMES\MatlabR2020a\toolbox\physmod\simscape\library\m\+foundation\+two_phase_fluid\+elements\translational_mechanical_converter.ssc' (line 226)

Answer 1

[Joris Naudin]

Hi handsome boi,

I replaced the infinite volume reservoir with a constant volume and it worked !

My guess is since the solver cannot change the conditions on the infinite reservoir, and there is initial conditions on the piston chamber, it creates 2 conditions for only one possible state (so doesn't work).

Also you should add a mass to the piston (it works without but I just don't know how it calculates without it ?)

Love <3

[Joris Naudin]

Thanks bröther