Discussion Forum

I have a spherical shell. I want to make its inner radius R1 and outer radius R2 move over time (just radially, like a ball getting bigger). I don't know how to tell COMSOL to move the radius. I know I must use the ALE method and I already have the "Moving Mesh" pack. I tried two ways of doing this, none worked:

1.-I first tried to go to Set "Prescribed Mesh Displacement" and set each surface with corresponding radial position (R1 or R2). This doesn't work for me because when I get to that option, I try to choose boundaries and it just tells me: "1(not applicable)", "2(not applicable)" and so on for all surfaces.

2.- Then, I tried with velocities, I could specify surface velocities on each surface, I used the option: "Prescribed Mesh Velocity", and this should do the job, but I don't know how to set velocity = time derivative of dependent function. How can I do this?

I am using COMSOL 4.0

If anyone could tell me how to set velocity = time derivative of dependent function, or if anyone could tell me how to get the boundaries to not say "not applicable", it would be awesome. I am attaching my model, but it doesn't run yet because it is a work in progress.