Hi,
After doing models with simple geometries in FEBio, I moved on to whole joint models. However, I got convergence problems when the model is complicated.
My model is a human hip joint with upper half of the femur bone, the pelvis bone, and the cartilage in between. The cartilage which is modelled as biphasic material and the bone were tied together. As the femur and pelvis models are irregular in geometry, I meshed them in I-DEAS using tet elements. However, I always got the message: Negative jacobian was detected at element.. at gauss point..
If I remove the pelvis or the femur bone, this error message still appears.
To pinpoint the problem, I simplified the model to just the pelvis cartialge and the femur cartilage in contact with the femoral head underneath. The outer surface of the pelvis cartilage was fixed in all degrees of freedom.
If I mesh the spherical femoral head with tet elements, negative jacobian message still appears.
If I mesh the spherical femoral head with hex elements, negative jacobian message disappears but the model still cannot get converged.
If I move out the femoral head (only cartilage to cartialge), the model can get converged.
I guess the negative jacobial error message is caused by the bad shaped tet element but am not sure.
As for the model with hex element, I tried to increase or decrease the penalty value in contact control but the model still cannot get converged. I do not know why it is not easy for the model to get converged if there is tied contact in the model. Is there any special technique which can solve this problem?
I think in the end, I will need to model the whole joint with bones meshed using tex element. How to eliminate the negative jacobian message?
Any help will be greatly appreciated. Thanks in advance.
As the size of the file exceeds the limitation of this forum, I have sent it to Steve's email (three .feb files. one is cartilage to cartialge model; one is cartilage to cartilage with femoral head of tet element; one is cartilage to cartialge with femoral head of hex element). Please have a look, thanks a lot.
Regards,
Jerry
After doing models with simple geometries in FEBio, I moved on to whole joint models. However, I got convergence problems when the model is complicated.
My model is a human hip joint with upper half of the femur bone, the pelvis bone, and the cartilage in between. The cartilage which is modelled as biphasic material and the bone were tied together. As the femur and pelvis models are irregular in geometry, I meshed them in I-DEAS using tet elements. However, I always got the message: Negative jacobian was detected at element.. at gauss point..
If I remove the pelvis or the femur bone, this error message still appears.
To pinpoint the problem, I simplified the model to just the pelvis cartialge and the femur cartilage in contact with the femoral head underneath. The outer surface of the pelvis cartilage was fixed in all degrees of freedom.
If I mesh the spherical femoral head with tet elements, negative jacobian message still appears.
If I mesh the spherical femoral head with hex elements, negative jacobian message disappears but the model still cannot get converged.
If I move out the femoral head (only cartilage to cartialge), the model can get converged.
I guess the negative jacobial error message is caused by the bad shaped tet element but am not sure.
As for the model with hex element, I tried to increase or decrease the penalty value in contact control but the model still cannot get converged. I do not know why it is not easy for the model to get converged if there is tied contact in the model. Is there any special technique which can solve this problem?
I think in the end, I will need to model the whole joint with bones meshed using tex element. How to eliminate the negative jacobian message?
Any help will be greatly appreciated. Thanks in advance.
As the size of the file exceeds the limitation of this forum, I have sent it to Steve's email (three .feb files. one is cartilage to cartialge model; one is cartilage to cartilage with femoral head of tet element; one is cartilage to cartialge with femoral head of hex element). Please have a look, thanks a lot.
Regards,
Jerry
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