Valveless Pump Boundary Load Convergence Problems in COMSOL v4.4
 

Hello everyone,

I'm brand new to COMSOL and FEA, so this might be a simple problem. I've been trying to simulate a valveless MEMs pump in COMSOL. In this pump, a vibrating membrane causes fluid to flow through a nozzle and a diffuser, which due to changing resistances to flow, induces a net fluid flow over time in one direction. I've been following the "Peristaltic Pump Tutorial" since it's very similar to what I am trying to do.

I've been using the Fluid Structure Interaction Module to simulate the pump. Previously, I was have having convergence issues. I've been able to eliminate most problems by changing from a standard mesh to a quadrilateral mapped mesh, and by specifying the time steps and using the Intermediate time dependent solver. I unfortunately needed to specify my membrane displacement using a prescribed displacement condition applied at the center of the membrane.(Pump2DIteration1)

I am now trying to fix the membrane displacement, and apply the load on the membrane as a solid mechanics boundary load rather than a prescribed mesh displacement. My applied load follows a negative cosine equation with a positive offset (meaning it starts at 0 N/m and peaks at some value, before returning back to 0 N/m). I'm currently using 200,000 N/m as the peak load due to a static analysis showing that this provides a similar membrane displacement as the prescribed displacement condition. (Pump2DIteration2)

Errors are indicating that the mesh is inverting near the center of the interface between the fluid boundary and the solid boundary (the membrane). I'm not sure what is causing this issue at this point.

Am I applying my load in the wrong way? Is it possible that I am causing the membrane to vibrate due to lack of dampening conditions? Is my membrane compressing and flipping itself inside out due to an improper application of load? I followed the procedure used in the Peristaltic Pump Tutorial, so I believe my boundary conditions are right.

I've include my simulation files, if the links don't work I'll figure out another way to link the files. I've omitted any solutions due to their large size.

Thanks,
Paul


https://www.dropbox.com/s/y8xpvjuxqj...Iteration1.mph
https://www.dropbox.com/s/bt5r1hplt0...Iteration2.mph