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Simulation problem!

Question asked by Siva Praneeth on Apr 30, 2013
Latest reply on Apr 30, 2013 by Jared Conway

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Hello everyone

I am trying to mesh and run a simulation of a bone with an implant in it. For inserting the implant into the bone, I used the combine feature to make the bone hollow for implant to be placed. After making the hollow bone, I inserted the implant by making mates with the hollow space in the bone.

I have attached the file for your reference.

The problem is, while trying to perform a static analysis on this assembly by applying force on the implant. After meshing is done and it is trying to simulate, this error pops up.

And this is the snip of simulation study

How do I avoid this error and perform analysis without any problems? Please help me with this.

PS: The fixed geometry boundary has been applied arbitarily on the bone because this cad model of the bone has its surface broken into smaller bits. So there is no complete single surface I could apply fixed geometry condition to. I tried the knit surface feature, but it also shows errors.

Thank you for your help and time.

Regards

Siva Praneeth

Tony Gatta Apr 30, 2013 9:00 AM

Correct Answer

It is diffucult to tell what you are trying to learn/analyze with your simulation. You state why you applied the fixed

geometry as you did, but fixing it as high (as close to the load) as you did -- seems to imply that you are only

interested in the top 1/3 or 1/4 of the model, perhaps? If so, you may want to cut away the rest of the bone/model

and fix on the freshly cut face.

I'd wager the error is related the surface breaks ie the quality of your solid model.

Merged midside notes are a meshing problem of course.

Perhaps this is happening in an area of little interest that you could cut away (as above).

Otherwise, as stated in the Help section, Set the Jacobian Check (in Mesh Options) to At Nodes and use a higher

# of points.

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assembly thickness 2.zip15.6 MB

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Tony Gatta Apr 30, 2013 9:00 AM

It is diffucult to tell what you are trying to learn/analyze with your simulation. You state why you applied the fixed

geometry as you did, but fixing it as high (as close to the load) as you did -- seems to imply that you are only

interested in the top 1/3 or 1/4 of the model, perhaps? If so, you may want to cut away the rest of the bone/model

and fix on the freshly cut face.

I'd wager the error is related the surface breaks ie the quality of your solid model.

Merged midside notes are a meshing problem of course.

Perhaps this is happening in an area of little interest that you could cut away (as above).

Otherwise, as stated in the Help section, Set the Jacobian Check (in Mesh Options) to At Nodes and use a higher

# of points.

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Jared Conway Apr 30, 2013 3:21 PM

like tony says, the error is related to a bad quality mesh. you need to improve it to get rid of the problem. sometimes you can use the mesh quality plots to find where the problems are and add controls, but sometimes it is difficult to see so instead i'd check the basics like below. Tony's suggestion on the plan of attack for the analysis is a good one too.

first thing i checked was that you don't have any import errors, the parts survive ctrl-q, there are no interferences and that all the faces touched face to face. everything checked out so you're good to go for meshing.

something to note, you could have done this at the part level as a multibody part analysis.

reset to default mesh size. meshing failed. so first check is to check that the element size is reasonable and if the parts mesh on their own with those sizes. the implant part fails to mesh. meaning it is the "limiting factor" for meshing. (7.88mm failed, 2.88 succeeded) so we go to 2.88mm at the assembly level. note, curvature mesh or large size could be used here. also i'd recommend using draft to start an analysis to make sure your BCs are ok and also, you should go with bonded and then add your no penetration contact.

with everything meshed. switch to automatic solver and run.

it takes about 5 minutes on my system (i7 2.4ghz quad, ssd, 24gb ram, 2013 sp3.0) and works without issue.

with your model you have the mesh at 3.94mm. that size might be generating some bad elements in the version that you are using. it doesn't seem to be a problem in 2013 sp3.0 though. you might also want to consider removing some of the small features from the implant to help with meshing.

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Tony Gatta Apr 30, 2013 9:00 AM
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Correct Answer
It is diffucult to tell what you are trying to learn/analyze with your simulation. You state why you applied the fixed
geometry as you did, but fixing it as high (as close to the load) as you did -- seems to imply that you are only
interested in the top 1/3 or 1/4 of the model, perhaps? If so, you may want to cut away the rest of the bone/model
and fix on the freshly cut face.

I'd wager the error is related the surface breaks ie the quality of your solid model.

Merged midside notes are a meshing problem of course.

Perhaps this is happening in an area of little interest that you could cut away (as above).

Otherwise, as stated in the Help section, Set the Jacobian Check (in Mesh Options) to At Nodes and use a higher
# of points.
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Jared Conway Apr 30, 2013 3:21 PM
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Correct Answer
like tony says, the error is related to a bad quality mesh. you need to improve it to get rid of the problem. sometimes you can use the mesh quality plots to find where the problems are and add controls, but sometimes it is difficult to see so instead i'd check the basics like below. Tony's suggestion on the plan of attack for the analysis is a good one too.

first thing i checked was that you don't have any import errors, the parts survive ctrl-q, there are no interferences and that all the faces touched face to face. everything checked out so you're good to go for meshing.

something to note, you could have done this at the part level as a multibody part analysis.

reset to default mesh size. meshing failed. so first check is to check that the element size is reasonable and if the parts mesh on their own with those sizes. the implant part fails to mesh. meaning it is the "limiting factor" for meshing. (7.88mm failed, 2.88 succeeded) so we go to 2.88mm at the assembly level. note, curvature mesh or large size could be used here. also i'd recommend using draft to start an analysis to make sure your BCs are ok and also, you should go with bonded and then add your no penetration contact.

with everything meshed. switch to automatic solver and run.

it takes about 5 minutes on my system (i7 2.4ghz quad, ssd, 24gb ram, 2013 sp3.0) and works without issue.

with your model you have the mesh at 3.94mm. that size might be generating some bad elements in the version that you are using. it doesn't seem to be a problem in 2013 sp3.0 though. you might also want to consider removing some of the small features from the implant to help with meshing.
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