Air and liquid modeling

[izyk]

Hi
I have to simulate a pressure sensor built on closed membrane. In the cavity there is the air (atmospheric pressure) and the sensor is surrounded by liquid. I would like to perform a transient analysis (i'd like to know the sensor response to ambient pressure changes). How to model the air in the cavity (the air will be compressed by the membrane) and liquid ambiance.
thanks

 

[cbrn]

Hi,
if you have the adequate license level (at least "Mechanical-U", I seem to remember), you can use structural-fluid elements (not Flotran elements) in order to simulate the liquid and the air.
Otherwise, you can try the following:
Ambient pressure anyway can be applied directly to the sensor's membrane, because it's your "driving" parameter of the simulation.
As regards compressibility of the air inside the sensor, you can try to write an APDL routine which incorporates a solution loop: calculate volume of enclosed air - apply external pressure field - solve with current internal pressure - get new volume - calculate new internal pressure with perfect-gas law (adiabatic?) - solve again - iterate until the volumes before and after air pressure variation are "almost identical".
I know it's really not straightforward, but...

Hope this helps (or at least gives some ideas...)
Regards