Re: [ESPResSo-users] Rigid Objects using OIF

[Ivan Cimrak]

Dear Markus,

In the oif-framework you can use objects that are "very stiff", but not completely rigid. This approach works very well.

There is however a trick to do this. If you just pick triangular mesh that is on the surface of the body (as is presented in the tutotial), you need to set quite high elastic parameters. The system then however becomes unstable and very fine time-steps are needed.

There is onother approach: You can use triangulation of a ball, instead of a sphere. That means that the whole inside of the ball is triangulated with tetrahedra. In this case, you may use stretching, bending and local area preservation forces, but you can not use volume force and global area force. When adding a new object, just do not set kag and kv.

Since you have now full 3D triangulation also inside the ball, the system is stable.

I attach 2 different triangulations of the ball, you can use them in the same manner as nodes files and triangles files in the tutorial.

Good luck,
Ivan

Dňa 21.2.2014 11:11 Wink, Markus wrote / napísal(a):

Dear all,

 

I have worked through the tutorial „object in fluid“ where red blood cells are simulated in a microfluidic channel. The cells are deformable which is accomplished by setting the parameters

“ks 0.07 kb 0.01 kal 0.01 kag 0.01 kv 10.0“

 

I was wondering, how to achieve rigid bodies with that implementation. Concerning the user guide and the article found at arXiv:1312.3426v1, one has to adapt the parameters mentioned above. Anyway, I don’t know which values to take. Having a look e. g. on the stretching force Fs, ks  describes the stretching constant. Setting that value to 0 results in a vanishing force Fs, thus the triangulation edges will not relax to the relaxed length. That’s exactly the opposite to the rigid body I want to have.

 

Does anyone know, what the parameters would look like for rigid bodies or how to implement it using OIF?

 

Greetings,

 

Markus Wink

 

ball142nodes.dat
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ball142triangles.dat
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ball374nodes.dat
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ball374triangles.dat
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