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Boundary condition to simulate a compliant volume |
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#1 |
New Member
Gauteng
Join Date: Jul 2020
Posts: 5
Rep Power: 4 ![]() |
Hello world from sunny South Africa,
I am looking for help to solve what seems should be a relatively simple problem. I am new to openFOAM and have googled this particular thought but not come up with many results other than programming a new BC which seems quite daunting. I would like to define a BC that essentially acts as a compliant isentropic volume. In other words, consider the boundary as a gas balloon/accumulator/lung etc that expands and as it expands its pressure rises as the volume expands/stretches. The pressure will rise (compressing the gas) because of the compliance of the volume walls. I am not interested at this point to consider thermal effects as the process happens slowly and at low pressures (5cmH20 to 40cmH20). I define the volumes compliance as (change in volume/change in pressure). EG if the volume changes by 50ml then the pressure goes up by 5cm. The hope is to model a lung without the computational overhead of: -Modelling the actual volume as a 'static' mesh and running a compressible solver -Modelling a moving mesh system like a piston in a cylinder The following BC's showed potential but thought I would reach out and see if im missing something simpler: - codedFixedValue (not sure this has the ability to look at dV/dT) - externalCoupled (seems most likely to work) - Possibly using an energy BC like gradientEnergy (doubt this will work) - plenumPressure (too defined for my use) - syringePressure (too defiend for my use) I think the most likely is attempting a pseudo-custom BC and emplying externalCoupled which I assume will involve a Python script to pull data from the OF results, make a calculation and then return/apply the boundary pressure based on the volume of air that has moved through the boundary. Would appreciate some insight! Thanks. |
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#2 |
New Member
Gauteng
Join Date: Jul 2020
Posts: 5
Rep Power: 4 ![]() |
Bump? Any thoughts?
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#3 |
New Member
Gauteng
Join Date: Jul 2020
Posts: 5
Rep Power: 4 ![]() |
Intruiging that this question has not come up before and seemingly no-one here can suggest a good solution.
If anyone is interested, I did manage to get a solution working using the external coupled solver but its very inefficient due to the built in wait time delays in the OpenFOAM external solver routine. I have also found that the postProcessing routine seems to fail in calculating the correct flow through a boundary when using an adaptive mesh (which of course leads to a failed volume calculation) |
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#4 |
Senior Member
Joachim Herb
Join Date: Sep 2010
Posts: 633
Rep Power: 19 ![]() |
In the OpenFOAM.com line, there seems to be a boundary conditions for this:
plenumPressure https://www.openfoam.com/documentati...ary-conditions https://www.openfoam.com/documentati...d.html#details |
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Tags |
balloon, boundary condition, lungs |
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