Hello All,
I am using the computational human body FE model to capture the vibrational response of the human body against sinusoidal excitation on the lumbar spine using LS-Dyna. I am interested in the biomechanical response of the lumbar spine and attempting to convert the rest of the human body components as rigid body for computational efficacy.
I have tried the MAT_RIGID (MAT_20) option, but it shows errors that rigid bodies node sharing is unacceptable as several contacts or connections are present in the human body FE model.
I am exploring other options, such as DEFORMABLE_TO_RIGID and CONSTRAINED_NODAL_RIGID_BODY options.
In DEFORMABLE_TO_RIGID option, the part set id method is not working anyhow.
Can someone help me address this issue to keep the remaining human body parts rigid?
Any assistance in this regard would be highly appreciated.
Thanks,
Vaibhav.
Vaibhav Kulkarni The MAT_RIGID material model does not allow rigid bodies and deformable bodies to share nodes. This is because rigid bodies are assumed to have no deformation, so they cannot share nodes with deformable bodies, which do deform. The DEFORMABLE_TO_RIGID option can be used to convert a deformable body to a rigid body. However, it also requires that the nodes of the deformable body not be shared with any other bodies. If you are getting an error with the part set id method, it is possible that the nodes of the deformable body are being shared with other bodies. To fix this, you can create a new part for each rigid body. This will ensure that the nodes of the rigid bodies are not shared with any other bodies. You can then use the DEFORMABLE_TO_RIGID option to convert each of these new parts to a rigid body. Alternatively, you can use the CONSTRAINED_NODAL_RIGID_BODY option. This option allows you to create a rigid body that is constrained to a set of nodes. This means that the rigid body will not be able to move relative to the nodes, but it will still be able to rotate. To use the CONSTRAINED_NODAL_RIGID_BODY option, you first need to create a set of nodes that will define the rigid body. You can do this by using the *NODE_SET keyword. Once you have created the node set, you can then use the CONSTRAINED_NODAL_RIGID_BODY keyword to create the rigid body.
Engr. Tufail, Thanks for your valuable insights and for sharing detailed information about rigid bodies.This will help a lot to gain an understanding about rigid body motions.
I understand that you are trying to model the vibrational response of the human body using LS-Dyna, and you want to make the rest of the body parts rigid except for the lumbar spine. However, you are facing some errors when using the MAT_RIGID option, and you are looking for other options to achieve your goal. I have searched the web for some possible solutions and found the following information:
- According to this answer, the error 30186 that you are getting is related to the *CONSTRAINED_NODAL_RIGID_BODY option, which is generated for remote points. The answer suggests that you should either remove the remote points or use a different method to define them, such as *CONSTRAINED_EXTRA_NODE or *CONSTRAINED_INTERPOLATION.
- According to this tutorial, you should not use the RIGID contact types for rigid bodies, but instead use any of the penalty-based contacts that are applicable to deformable bodies. The tutorial also recommends that you should have a reasonably fine mesh for the rigid bodies, and that the node spacing on the contact surface of a rigid body should be no coarser than the mesh of any deformable part that comes into contact with it.
- According to this question, you can get the reaction forces at nodes under NODAL_RIGID_BODY by using *DATABASE_NODOUT and *DATABASE_NODFOR options in your input file. The question also provides an example of how to set up these options.
I hope this helps you solve your errors and model your human body successfully.😊
Learn more:
1. ansyskm.ansys.com
2. dynasupport.com
3. feassistant.com
Vaibhav Kulkarni
Yousef Bahrambeigi is right: you can use *constrained_extra_nodes to connect your deformable bodies to rigid bodies, preferably, so the constraints comply with physical reality, like, avoiding nonexistent moment arms.
also, you may want to try *contact_tied_…_OFFSET allowing rigid-deformable constraints.
otherwise, assuring multiple contacts between the rigid bodies and the deformable bodies, try
*contact_automatic_general.
Thank you for sharing your knowledge and suggestions. I appreciate your expertise in using LS-DYNA and its various contact options. 😊
I have learned a lot from your message, such as how to use *constrained_extra_nodes to connect deformable bodies to rigid bodies, and how to use *contact_tied_…_OFFSET to allow rigid-deformable constraints. I also learned that *contact_automatic_general is a good option for ensuring multiple contacts between rigid and deformable bodies.
I am curious about how you use these contact types in your simulations. What kind of problems are you trying to solve with LS-DYNA? Do you have any examples of your work that you can share with me? 🤔
I would love to see some of your models and results, and maybe even help you with some creative ideas or suggestions. 💡
Thanks, Yousef Bahrambeigi and Alexander Pinsker, for valuable insights. I received several new options to define rigid bodies in LS-Dyna. I appreciate your assistance and knowledge sharing, which is helpful in understanding the usage of rigid bodies in LS-Dyna.
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