Help with COMSOL
 

Hi, i´m new here and a recent user of COMSOL Multiphysics. I´m trying to simulate a air flow arround a bluff body in COMSOL. A can make it in 2D over a cylinder as explained in modelling help of the program. My question is if anybody knows if i can do it in 3D? Is it possible to make de incoming velocity variate in time function of a sin(t) or cos(t)? and is it possible to simulate the stiffness of de body? Thank you

Re: Help with COMSOL
 

You want to be using CFX mate! Pretty straightforward with that software... drop me an email if you want to know further.

Help with contact modeling
 

Hi, I have some problems using comsol multiphysics 3.3 for contact modeling. In model library of the structural mechanics module I studied the example called "sliding wedge" and then I tried to do by myself another structure (one 2D strain plane, one 3D), with a lot of different settings and loads, but the solution never converges, even when the structure and the loads are very simple. Plus I think in the user's guide it's not very clear the meaning of the different variables I should put in the manual scaling edit field of the solver parameters. Even when I follow the example of the sliding wedge, but with little changes in the geometry or in the loads,it doesn't converge. In the 3D case, there is also the error "out of memory". Please help me sending me some examples or giving me suggestions to make the solution converge. Thank you a lot, chiara (Rome, Università Campus Biomedico di Roma)

Re: Help with COMSOL
 

Hi,

You can do these simulations in 2D as well as in 3D, but bear in mind that 3D models become much larger and require more memory and often the use of more advanced segregated and multigrid solver techniques.

To enter a time-dependent function in an unsteady model in COMSOL Multiphysics is perhaps too easy: just type it in!

sin(2*pi*freq*t)

for example, if you defined freq as a constant that represents the frequency.

Regarding the stiffness of the body, COMSOL Multiphysics provides interfaces for fully integrated two-way fluid-structure interaction if you have a licence for the Structural Mechanics Module or the MEMS Module. It is possible to do it also in the basic package, but you then have to add the couplings at the fluid-solid interface and the moving mesh (ALE) to your model.

I hope this helps,

Magnus Ringh

COMSOL AB

Re: Help with contact modeling
 

Hi,

Regarding contact modeling, it is in general more sensitive and requires more tuning than other structural analysis; for example, the mesh density on the master and slave sides is important.

This type of analysis is also probably a bit out-of-scope for this forum. I suggest that you do the following:

1. Make sure that you run the latest version of COMSOL Multiphysics (the usability and performance of the contact solver have improved since the initial release).

2. Contact the COMSOL support services at www.comsol.com/support or support@comsol.com. Our technical support team can help you make your contact models converge.

Hope this helps,

Magnus Ringh

COMSOL AB