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-   -   mesh deformation - mesh stiffness (http://www.cfd-online.com/Forums/cfx/107388-mesh-deformation-mesh-stiffness.html)

alfonsojurado September 26, 2012 03:11

mesh deformation - mesh stiffness
 
Hello,

if somebody knows something about this topic, I will be very grateful.

I want to know how is the behavior of the option of mesh stiffness. I am trying to avoid breaking elements when a subdomain1 is moving according to surge in X direction. the rest of the domain is mesh motion unspecified option. I tried different options modifying model exponents of increase near boundaries/increase near small volumes and value of mesh stiffness directly but the same error occurs every time: the mesh of subdomain1 fatally deforms (negative volume) in the border between subdomain1 and the rest of domain while all I want is that the mesh of the rest of domain deforms the same as subdomain1.

thank you very much for your help.

Have a nice day!!

Alfonso

ghorrocks September 26, 2012 08:13

Can you post an image of the motion and mesh problem?

alfonsojurado September 27, 2012 03:52

I hope that these images be enough... if you need some more, please tell me.

mesh before simulation:
http://imageshack.us/a/img217/7697/54603355.png

mesh after simulation (extreme conditions):
http://imageshack.us/a/img854/2702/98628228.png

"GLOVE" is the part of hulldomain that I called subdomain1 in my last post. This is the part that moves according to surge in X direction.

I also want to say that the mesh is gross because this is a test before the real simulations.

Thank you!!

ghorrocks September 27, 2012 08:02

Have you tried with no mesh stiffness options? Just leave it at the defaults.

Doginal September 27, 2012 11:14

I was having this problem for a while. I fixed it by making a different type of mesh.

I haven't gone through the tutorial for a floating bouy (chapter 32 of tutorials). It deals with the mesh stiffness parameter. I haven't gone through it myself yet however it talks of defining a mesh stiffness according to 1/volcvol where volcvol is a cfx parameter defined as the volume of finite volumes. So it sets your stiffness as being inversely proportional to your mesh element volume.

May want to give it a shot. Can guarantee it will help at all

alfonsojurado September 28, 2012 03:33

I will see this chapter of the tutorial, I hope fix this situation with your advices!!

We are in contact!

thank you very much!!!! :)

alfonsojurado October 2, 2012 07:15

Thank you, problems have been solved.

I had to change the mesh motion option from stationary to unspecified (to permit elements nodes move freely and avoid the fold of mesh) in the UP and DOWN boundaries of the geometry. In this way, I am satisfied, however, I still do not know the behavior of the params of mesh stiffness options...

The tutorial says that I have to use increase near small volumes (using the default model exponent, 10) but, if I use another model exponent, would happen with the simulation? which type of effects causes this exponent? do you know any document or tutorial that explain wich mesh stiffness option is better for a concrete simulation?

Any piece of advice will be welcome!!

Thank you very much for all your help


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