Hi Carlos,
I am trying to model a pump of a high pressure device. The volumes are no dampeners but constant volumes. The first volumes after the swept voluems represent the dead volume of the cylinder space. I now this is also a parameter in the library model swept volume but I found out that with this closed volume it is more robust from numerical side.
The second closed volume is a space where after the high pressure valves where all three cylinder spaces come together.

Best  Steffen

Hi Carlos,
thanks for this honest reply. That was also my impression with this model. And that's why my questions went in the direction of how to neglect energy balance, compressibility, temperature effects on material parameters etc. I thought there would be an easy way to circumvent all these numerical difficulties.

Can you recommend any other library that would fit for such type of models, i.e. highly instationary fluid dynamics models? Or any clue what one could do? Is modelica the right choice at all?

Best, Steffen

Thanks for your reply.
Okay it seems not to be trivial to increase the numerical robustness/speed.

As this is work in progress, in a next step I wanted to replace the massflow-boundary condition with swept volumes.
Therefor I built a test example and played with phase-parameter of the sine function.

However I encountered some errors while initialization. Can you help me again?

Kolbentest.mo


PS: If one changes the paramter phase in sine function to pi/2 it works; that's why I tried to give an initialization value for m, but it didn't work neither.

Best, Steffen

I wrote my own Sinus block as I want to enlarge the model after it runs stable and need the startTime parameter that I found is buggy in the Modelica.Blocks sine routine, i.e. I want the value at time<startTime to be identical to the value at startTime (as I use the parameter phase also), see attached file test.mo.
But I think that's not the point (or do I understand you wrong?)

Isn't there a way to reduce the complexity of the model by making the water incompressible, one-phase, neglecting the energy balance as temperature is not important etc.?

As I want to model a real physical device I don't want to change the geometrical parameters or the frequency.

Steffen

Test.mo

System7.mo

Hello,

I build the attached fluid system. However it is extremely slow or does not converge at all. When removing the pipe called "Schlauch" then it works nicely.
Can somebody explain why or how to circumvent this?
Does it have to do with modelStructure?

Another question: As I am not interested in temperatures, is it possible to neglect energy balance equation? Furthermore I don't need two-phase material, nor do I need compressibility of the water? So, if that helps to make the model more stable how can I achieve this?
(I tried to change the medium from StandardWater to StandardWaterOnePhase or even ConstantPropertyLiquid, but none worked due to initialization issues)

I am a real beginner and hope somebody can light me up how all these things work together.

Regards Steffen