Discussion Forum

Hi

I'm fighting too with the weak form in V4, but I understand from the "release notes" that the Weak form is not yet fully implemented, (i.e. in 2D I cannot get it to understand that I have two dependent variables, it only shows me one field).

For the element types, I understand it's now called "discretization" , and is under the main physics tabs, but you also have the "shape functions" for some items

Hope this helps on the way
Ivar

Yes. You can modify the element order under discretization tab. But there is simply no way of changing the order of element for each dependent variable ( such as shlag(u,2) and shlag(v,3) or shdis(w,2) ) and also changing specific element type such as bubble element (shbub) or discontinuous (shdis)element. The hermite and agris element type seems to be missing from the list. I just hope the developers do not take out this important feature that is available in previous release of COMSOL. A bit frustrarting as i could not do much work with it now as i rely a lot on weak form PDE module to do custom physics simulations.

I'm having a similar problem. I'm seeing suspicious looking checkerboard patterns in a Navier-Stokes solution which I suspect to be caused by quadratic velocities *and* quadratic pressures - which violates infsup condition.

I wonder if there is some way of "tricking" COMSOL. E.g., create a physics module with order=1 pressures and force the order=2 pressures to get replaced by the order=1 values?!

[***EDIT****] Ignore at least some of the above. There is a function "shapeorder", so you can plot, say, shapeorder(u) and shapeorder(w) and see that in fact COMSOL does correctly pick shapeorder(p) to be one order lower.

Hi

I would suggest that you ask directly support

And report back here as it's of general interest for us others too ;)

Ivar

Hi

I'm fighting too with the weak form in V4, but I understand from the "release notes" that the Weak form is not yet fully implemented, (i.e. in 2D I cannot get it to understand that I have two dependent variables, it only shows me one field).

For the element types, I understand it's now called "discretization" , and is under the main physics tabs, but you also have the "shape functions" for some items

Hope this helps on the way
Ivar

Can you tell me where I can find this "main physics tab" which should contain the "discretization" entry?

Hi.

In COMSOL 4.3 you can change the element type by clicking on the model (model builder tree to the left). Then, under model settings you find the option "Geometry shape order". With this option you can set the element type for your entire model.

Cheers.