A simple question about defining pressure surface

[feng]

Hi,

I'm new to biomechanics and FEbio. I read through the theory manual and user manual, and still cannot figure out how to solve the problem. The problem is : In the uploaded figure, there is negative pressure between surface A and (BCD), thus beige color (V shape) object deforms due to this pressure force. Eventually, surface A will slide against surface B, C, and D to achieve the final equilibrium. I specified surface A as the slave contact surface and pressure surface separately. I also defined BCD as the master contact surface and part of the (fixed) boundary surfaces, separately. I ran the simulation, and had the error "Negative jacobian detected at integration point 9 of element 5434, Jacobian = 0 .....". I have no clue to solve this problem. Is this the problem of surface double definition, or other problems? Could you give me some hints? The .feb file was also uploaded. I appreciate your help.

(I generated my (volume) mesh using GMSH. After I imported the mesh into Preview, several edges are missing, as shown in the figure, edge1,2. I have to manually specify different parts of the object to define contact surfaces.)

Thanks, Feng.

[feng]

Finally I got the boundary and contact surfaces right after manually revising the input feb file, since Preview has some bugs importing my GMSH meshes. But I was unable to specify the pressure force for my application. I have very few mechanics background, could you guys help me on this simulation?

As show in the attached figure, I tried to define the negative pressure force between the green curve and yellow bar. This negative pressure force deforms the green staff from phase 1 to phase 2. I studied several examples about pressure force in the febio_examples folder, and still have some errors.

The next question is, the yellow bar moves down from phase 2 to phase 3, the green staff keeps deforming. Is this a multi-step analysis problem?

Thanks, Feng.

[feng]

I just solved the problem. It turned out that this negative jacobian error occurs because of wrong load parameters. I tried several different pressure load curves, and finally got some reasonable results. Thanks you guys. Feng.