Learning Forum

[Hannah]

 I have some errors in my model when I am creating the contact regions and I was hoping you could help me with that. I am working on the skull model. I run the healthy skull model that includes bone and muscle and cartilage at the joint and the model converges. I am now replacing the bone in the healthy model with a fractured bone and redefining the contact between muscle and bone. I deleted the elements and nodes of the healthy bone in the old model and replaced the mesh with the mesh of the fractured bone. I then manually defined the contact regions and used cncheck,trim to trim the contact. I got this error The behavior of target elements (e.g. 9063129, 9063128) specified by real constant 3 are not consistent. Some of elements belong to a rigid surface, while others belong to a deformable surface.nlooking at Xansys forum I know this can happen when the target nodes are not associated with the underlying elements but I am not sure how that is happening. If I start from the beginning, import the fractured skull mesh and then the muscle mesh and use the same code to define the contact region and trim it, it works and there are no issues but this requires I build the model from scratch which is going to take a lot of time. Does anyone know why I might be getting this error?nThanks!nHannahn

[Ashish Khemka]

nIt's very possible that a similar model wouldn't have generated errors in the past. There have been changes in the handling of constraint equations and constraint equation checking in many recent versions. Handling of constraint equations created for deformable contact has been one of the main areas of change. Do you have a bonded contact with MPC formulation? That would increase the potential for constraint equation conflict. If you have MPC formulation then try switching to penalty based formulation.nnRegards,nAshish Khemkan

[Hannah]

Thanks for your reply. I am using the same version of ANSYS ( 18.2). I run the original intact models on Nov. 2020 (so two months ago). Would this happen even if I am using the same version? nThank you,nHannahn

[Ashish Khemka]

nIf you used the same version then the error should not occur. However, when you manually redefined the contact was there contact between surface and remote point as well?nRegards,nAshish Khemkann

[Hannah]

There are 4 other contacts (different regions, no overlap, they are rigid contact with pilot node between rigid mandible in the model and muscle (*2), rigid mandible and disc (*2)) defined in the model but I tried deleting all those contacts and redefining this new contact between fractured skull and muscle and still get the error. If I export the cdb of the muscle after deleting everything else and open a new apdl and import cdb of muscle and the cdb of the fractured skull and redefine the contact in the same manner using same code there is no issue. n

[Ashish Khemka]

nnWe have seen that creating a new model helps in avoiding this error. Can you try running the model in the latest Ansys version as well?.Regards,nAshish Khemkan

[Hannah]

Thanks, sure I will try opening the intact model with the latest Ansys version and deleting the healthy bone elements and nodes and adding the fractured bone and recreating the contact in the latest Ansys version and see if that works.nWhen I import the cdb of fractured skull and muscle in the new Ansys, it is still the same version 18.2 and it works. The issue with creating everything from scratch is I already have a lot of other things going on in the model and it will take a lot of time to recreate the model from scratch. nI appreciate your help.n

[Hannah]

nI did try the new ansys version 2020 R2 but even my previous models are not working with the new version. The way that I define the contact, I usually start with a larger region and then use cncheck,trim to trim the contact. However, after this command, the mandible (rigid part) in the moel gets deleted. I still can see the rigid contacts between mandible and muscle and mandible and cartilage in contact manager but the rigid part itself is removed. My only license is 2020 R2 now and I cannot use the earlier ANSYS versions anymore. Any suggestions on how to fix this? I have MPC contact (all the contacts are MPC) but I changed it to penalty method and I am still seeing the same issue.nRegarding my previous question: I realized in ANSYS 18 if I create a cdb file of the model after deleting the bone elements and nodes and import that in a new apdl ( also this model has everything including the material properties and all the parts except bone) and import the fractured bone as well, the contact definition works between muscle and bone (I use cncheck,trim and it trims the contact properly without any error). I think there might have been some weird numbering issues but I didn't figure out the issue. However trying the same thing in ANSYS 2020, the rigid part gets disappeared. nI really appreciate your help with this.n

[Ashish Khemka]

nnI am not sure about the issue with the rigid part in the new version. For the .cdb file, if that works then you might need a lot of rework.nnRegards,nAshish Khemka

[Hannah]

Thanks for your reply. could you please explain why it needs a lot of rework? the cdb file seems to have all the contacts, material mapping and coordinate systems and element coordinate system that I have defined.n

[Ashish Khemka]

nnI am sorry, I meant to say that it does not require a lot of rework.nnRegards,nAshish Khemkan