Transient Stress Analysis - Error

[Anonymous]

Hello.

I'm trying to run a Transient Stress Analysis I copied its Design Scenario from a Natrual Frequency Analysis Design Scenario.

Well, I've put the loads with the Nodal Forces and fixed some vertices with the Nodal Boundary Condition.

When I've run the Transient Stress Analysis, the program has returned the following response:

Model and modal model have differing numbers of equations   12252   12288

Error. Please re-check and re-run the Modal Analysis model

I've re-run the Modal Analysis model (Natural Frequency Analysis) but the error has appeared again.

Can anyone help me with this error?

Why did the design scenarios have differents numbers of equations if i've copied one from the other?

Thanks!

[S.LI]

My guess is that several equations in the second DS were removed due to the nodal BCs.

If the same BCs are applied in the first DS, the number of equetions should be same.

[xli]

Do you have contact defined?

[Anonymous]

Thanks for the replies.

Well, I got to run the analysis doing what s.li said. They were the BCs, but I needed to fix some parts to the analysis work and the program didn't get any result (because some vertices are fixed). I think it'll need to put some contact surface, like xli said.

I don't know how to make contacts. I've been trying to make it since this mornig, but I can't get it.

Can someone help me with this?

Is there some tutorial?

Thanks again.

[xli]

Well, unfortunately modal analysis does not support contact element, nor LD analsysi like what you are running, Linear Transient Stress (Modal Superposition). If you like to get some helps on restraining your model well, you might post some figure of model and what you want to do.

-xli

[Anonymous]

Thanks xli.

I'm doing a prosthetic leg simulation, which I need to analise the stress with differents weights in two cases:

- When the person is stopped (static case);

- When the person is running (dynamic case).

I think it's needed the contact with a surface to simulate the ground.

The prosthetic leg design is attached.

Thanks again.

[xli · Accepted solution]

Your description is a little bit too little to me. So I only can make some assumptions based on your image, I put my guess into the images attached here.

If my guesses are correct, you may need MES specifically for the supporting part. This is definitely beyond linear dynamic range. So that Linear dynamic analysis is too rough to use or you need greatly making some assumptions in modling. For example, assume there will be flatten part of surface at bottom touching ground, restrain that paortion of surface's normal direction DOF...

But in MES you have surface to surface contact element to use, theoretically the best for simlulating your model. And it is more directly setup.

-xli

[S.LI · Accepted solution]

For the static analysis, I don't think you need any contact. You can fix the bottom end to simulate the contact with surface. Loads should be applied on the top end, and some constrains might be needed to get rid of rigid body motion here.

For dynamic case, I'm not very clear what you want. To apply periodically loads on the top end?

[Anonymous]

Hey people!

Thank you! I got how to do the MES analysis. I created a brick (with Concrete - High Strenght as material) that simulates the ground and I did the contact pairs and the surface-to-surface contact. Then I applied the forces. It works!

Just sorry the delay for this reply.

Thank you, folks!