Learning Forum

[Babeth]

Hello !

I'm working on a simulation of an impact on the knee joint. I work with a free cad of the knee joint, including ligaments, femur, tibia, cartilage and fibula. I need to split up bones of this cad in two parts : a shell representing cortical bone, and an interior, representing cancellous bone. With Spaceclaim, the shell tool don't work, maybe the geometry is too complex ? What can I do to split up bones ?

Elisabeth

[peteroznewman]

Hello Elisabeth I expect you can share the knee geometry. Please archive the workbench project and attach the .wbpz file to your reply. You can also insert some screen snapshots into your reply.
There are many techniques to manipulate the geometry in SpaceClaim. One example is you can copy all the faces of a solid and turn that into a surface model. You might simplify some of the faces of the bones to make manipulation easier. Another technique is to split the bone in half using a Plane. The Shell feature may work on that new face.
Peter

[Babeth]

Hello Peter Thank you for your answer Here is the .wbpz of my project. My Spaceclaim is in French, and I don't know how to turn it in English to show you snapshots of the error messages...
Thank you for the tricks, I tried to split the bone in half using a plane but it doesn't work...
Elisabeth

[peteroznewman]

Hello Elisabeth Try this.
Peter

[Babeth]

Hello Peter Thank you so much for your help !
Regards Elisabeth

[peteroznewman]

Hello Elisabeth The previous video answered your question, but I would not use that geometry to make a solid body to mesh. I would do a skin on the bone, and then the shell tool will probably work. Below is a video from September 2020.
Regards Peter

[Babeth]

Hello Peter Thank you !
I just have a last question : how can I change the angle of the knee joint without loosing contact between all elements ?
My geometry is a knee joint at 90 degres, and I would like to change this angle, keeping the contact between ligaments and bones, meniscus and cartilage etc...
The biggest problem is ligament lenght, which varies depending to this angle...
Regards Elisabeth

[peteroznewman]

Hello Elisabeth You can open a new discussion when you change topics, and I expect you will have many more questions as there is a lot to learn.
There are two answers to this question, depending on what you want to do.
1) You can move the bones and cartilage components in Spaceclaim to a new knee angle, making sure to maintain contact, then stretch the ligaments with the Move tool by picking half the faces.
2) You can delete the ligaments from CAD and insert nonlinear springs in Mechanical to create the ligament forces in the simulation.
Since you are interested in studying the impact of a knee against a surface, I suggest you get some better geometry that includes the Patella, which is often damaged in an impact. Though it is not labeled in the figure below, there are more than two ligaments in the knee, such as the ACL which is often torn.
Regards Peter

[Babeth]

Hello Peter Thank you !
I would be so nice if I could have a complete knee model... That's the goal of my intership.
This geometry is the most complete free geometry I have found, and I don't know how to create manually some complex geometry as the patella...and I think that a complete model may have to many elements for a free licence :(
Regards Elisabeth

[peteroznewman]

Hello Elisabeth I suggest you start reading some research literature on FEA models of the knee. Here is my Google Search:
https://scholar.google.com/scholar?hl=en&as_sdt=0%2C33&q=human+knee+joint+biomechanics+finite+element+analysis+mesh+geometry+CT+image
Some of these results include the full paper such as this one: https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.1053.8892&rep=rep1&type=pdf
You will need to develop your geometry manipulation skills to be successful in creating a good Finite Element mesh.
Regards Peter

[Babeth]

Hello Peter Thank you so much ! You helped me a lot ! I'll try to complete my model.
Regards Elisabeth

[peteroznewman]

Hello Elisabeth I find your project interesting. If you want to schedule time for a tutoring session, you can share your screen over Skype or Google Meet and I can answer questions and provide some guidance. I have time on Friday and am in the Eastern US Time Zone.
Regards Peter

[Babeth]

Hello Peter ! I'll be great !
But I don't have many time this Friday and I will need to prepare this meeting (prepare my questions, prepare vocabulary because I don't speak fluently English...)
Maybe Monday (or Tuesday and so on) will be better ? If you are free only on Friday, I'm okay for the next Friday, no problem ! I'm free every day from 6pm to 10 pm (noon to 4 pm for you).
Regards Elisabeth

[peteroznewman]

Hello Elisabeth I spend time here as a hobby, not a job, so I am here on the weekend as well as during the work week. If you want to meet on the weekend that is good for me. I can also meet during the week, not just Friday, but I have to flex my time around my job commitments. Don't worry too much about your English, it will be better than my French! Besides, you and I can point to items on the screen we will share.
Regards Peter

[Babeth]

Hello Peter I'm okay for the day you want next week ! I'm free every evening.
Regards Elisabeth

[peteroznewman]

Hello Elisabeth I am available 1 PM Monday, which is 7 PM for you. Do you have a Skype account or I can send you an invite for a Google Meet?
I don't put my email address into comments on this public site because I cannot delete it one hour after I post.
If you also don't want to leave your email address in a comment, you can look to see when I am online on your Saturday or Sunday afternoon/evening by checking your Profile, which lists who is online. When you see I am online, reply to this thread and wait for my reply. When we are both online, you can put your email address into a reply and wait for me to read it, then edit the comment to delete your email address before the hour elapses. Or maybe you don't care about leaving an email address on this public site.

[Chinmay]

Hello Peterand Elizabeth Greetings of the Day. I am working on something similar which unfortunately I can't share images of due to institutional confidentiality but it's in line with Elizabeth's concept. I was wondering if I could join in your google meet (if you guys don't mind, I don't want to intrude). It would always help me to learn anything from the MASTER OF FEA. I wouldn't disturb your meet if that's your concern. Just a humble request.
P.S: Peter, Why not make a temporary email account for communication or if you would allow me to join in your meet, I could write my temporary email address and forward the meet request to Elizabeth (provided she emails me first). Just a suggestion.
Thanks ­ƒÿè
Chinmay.

[peteroznewman]

I have enjoyed your discussions on this site because you take the time to write detailed and well illustrated problem statements such as this one: /forum/discussion/27779/seal-compression-convergence-issue#latest I especially liked that discussion because the simulation result surprised me with something I didn't know.
I would be happy to meet with you, especially if you have time on the weekend when I have more time to spend on ANSYS. Please reply with your temporary email address and we can set up a time to meet.
I prefer to provide individual tutoring so I can focus on what is most important for that individual to learn.
Regards Peter

[peteroznewman]

Hello Elisabeth I was able to locate better quality knee bones in STL file format. We can discuss how to convert STL files to geometry that can be meshed.

[Chinmay]

Hello Peter Thank you for your prompt reply as usual. I am glad you like our discussion as much as I do. I would be grateful to learn absolutely anything in Ansys from a legend like you NGL.
Here's my temp email address: crkulkarni92@gmail.com
You can let me know your time availability accordingly.
Thanks Chinmay ­ƒÖé

[Babeth]

Hello Peter That you for the stl files ! It will be great with the patella ! We can discuss about how to add cartilage and ligaments to this geometry too.
I'm okay for 7pm on monday ! Yes, I have a skype account. Here is a temporary email address : elisabethguerintemp@gmail.com.
You can write me at this address too, if you want to get in touch about my project.
Regards Elisabeth

[krishna4339]

Dear i am also working on a knee joint problem where i am facing issues w r t contacts. Can i ask you few questions here to learn new things? i am done with Modeling and meshing. I am struggling with analysis part.
Thanks and regards
krishna

[peteroznewman]

It's best to start a New Discussion with a new title in a different category. What you want to discuss is not about geometry.
If you expect to use Explicit Dynamics to solve your model, you would put the discussion in that Category, otherwise put the discussion in the Structures category.

[peteroznewman]

Hi Elisabeth Here is a link to a video, which is Part 1 of a multi-part series. I will use that discussion to build up the knee joint.