Discussion Forum

Hi

For me a parametric study was restarting from previous case, default settings, take a look at the Solver manager tab, and the doc.

considering your side note, I need some time to be able to commentthe other ones, try to connect directly to:

www.comsol.com/community/forums/general/rules/

Have fun Comsoling
Ivar

Hi

Nice object you ave there, my main comments on your model are

1)
try to avoid point constraints, distribute load over surfaces, worst case edges (if possible edges are also to be avoided except in 2D as a line is in fact a surface with a default depth of 1[m])

You can select your area/boundary where you apply a force (even better than displacements, in the worst case you can get Comsol to calutate the force for a given desired mean displacement). You use a coupling integraton variable with the expression 1 to calculate the area and then you divide the force by this constant to get the pressure needed (in structural all forces are expressed as pressures over areas respectively edges)

2)
with you slender beams you have high stress concetration factors at the fillets, I always (by the way I'm been designing compliant mechanisms for soon 25 years) cut my long beam in two, along the mediane, or the neutral beam if I know better where it is, and then I cut the junctions at about the end of my fillet with a triangle going up to the mediane or with an arc of a circle with its centre on the cut line (I use SolidWorks its easy to cut volumes). Then I apply a much finer mesh on my beams especially around the fillets.
You add interiour boundaries this way, but your meshing is far more cleaner.

Note:
My only regret today, for this type of simulations is that COMSOL does not allow to mirror a mesh, typically for structures as yours, as you end up, with such slender and massive volume ratios to have a rather large mesh effect on the results. If your forces are applied in a symmetric way, you could reduce the calculations by using the symmetry plane, but mostly my examples are made of symmetric volumes, but highly assymetric loads, hence the need for full 3D and therfore the advantage of a symmetry mesh function. If you come to the same conclusions, pls mail support so we might get it in on next version, it's a question of pushing from enough sides ;)

Have fun Comsoling
Ivar

Ivar,

Thank you very much for your help! I finally got the model to solve for the combinations of inputs I wanted by changing both the "Initial Value" and "Values of variables not solved for and linearization point" settings under "Solver Manager" to Current Solution. I proceeded to ramp up my inputs and wha-la!

I agree that point constraints are problematic. Unfortunately in this device, it seems to be the best explanation/simplification for describing how the actual device works (caused by complications with the actuation scheme and the fabrication process - hence the undercuts). I will try to study the forces associated with actuation, as you suggested, next.

I will also try your suggestions on how to make the mesh cleaner. I am a fan of Solidworks as well and use it every chance I get (that's where this geometry was created).

Thank you again,
Chris