Learning Forum

[Mimi Chen]

Hello, 

I want to simulate a "human" doing a series of actions, for example:

1. stand up
2. walk 2 meters
3. climb the stairs

I would like to have the three actions in three different transient structural blocks, because then I do not have to recalculate the whole thing again from step 1 if I just want to change something in the step 2 or step 3. So for example, I want to change some parameters at step 3, which means I want to start the simulation when the "human" is 2m away from the original point. 

Here's the simulation of the "human" standing up from a chair:

Then, I dragged another transient structural block and connected the "solution" to the "setup":

Then, opened the setup, it shows this, everything from the previous step 1 simulation is gone:

How do I solve this problem?

Thank you in advance.

 

[peteroznewman]

Use Rigid Dynamics instead of Transient Structural, it will take much less time to solve.

[Mimi Chen]

True, but I can also make all the parts rigid in Transient Structural, so it works the same as Rigid Dynamics. But that's not the original problem in my post.

[Erik Kostson]

 

Hi

 

Rigid body dynamics system and solver is a completely different solver to transient Structural solver (see help manual for more info).

Rigid dynamics is aimed for rigid body dynamics (say how a mechanism moves), while transient can be used for impact (flexible bodies), earthquake analysis in time domain, shock loads, etc, but not so much for rigid body dynamics (there we use the other system or in 2023 R1 Ansys motion which is also aimed for rigid body dynamics).

As for the original question, what you do when you connect them to each other as you show, is to transfer over data (loads or displacements on cut boundaries) in order to do a submodel analysis. See what that means (sub-modelling) and how it is done (static or transient system is the same with regards to submodel).
https://www.youtube.com/watch?v=WC9bN2B9w2M

All the best

Erik

 

[Mimi Chen]

Hi Erik,

Thanks for your reply.

I understand that the transient structural and the rigid body dynamics use completely different solver, and that transient strcutural can simulate impact, shock loads, etc., while rigid body dynamics cannot. But for my use case, I can use both transient structural and rigid body dynamics right? And the results should be the same using the two? 

I tried to do a simpler simulation of 4-bar-linkage using both transient structural and rigid body dynamics, shown in the screenshot below for results comparison:

As shown in the comparison, I used the same settings for everything, but the results using two different solvers are completely different: Max stress 151.99 Pa for rigid body dynamics and 15693 Pa for transient structural, I don't understand why this happens? Do you have a clue?

Moreover, coming back to the topic of my original question, I checked the submodeling video, and find it not so relevant to what I asked about. As I understood, submodeling is something like running a "coarse" parent analysis first on a large assembly, then run a "finer" analysis in a specific part. However, what I wanted to ask is to solve step 1: sit to stand, then use the result from step 1 directly to solve step 2, so whenever I want to change a parameter in step 2, I don't have to re-run step 1 again. These two steps are basically using the same mesh and not a finer mesh, just two differen actions. I hope this explanation is clearer. Is this possible?

Thank you and best regards,

Mimi