large flexible body

Hello,

I want to model a system which includes a large body that I want to model as flexible. Are there any efficient ways of doing this? I am asking because I also want to define contacts including said body, making the computations quite time consuming.

P.S.

The body is actually comprised of various smaller ones which are bolted together. Instead of creating multiple bodies and then fixing them at the bolt locations with joints, I decided to model it as a single body.

Thanks,

Josef

0 Alexis Del Rio over 2 years ago

Hi Josef,

This is quite common in pretty much any industry. Depending on what level of fidelity/complexity you want you can do this in Adams/Apex or Nastran/Patran, up to you.
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0 Josef K. over 2 years ago

Hi Alexis,

Thank you. However I am more interested in any short of modeling practices or rules-of-thumb about modeling large flexible bodies in Adams. I am asking because when replacing the rigid body for its flexible counterpart, the model crashes instantly.

Thank you once again,

Josef
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0 Alexis Del Rio over 2 years ago

Hi Josef,

What are you attempting to convert to flexible in Adams, the shell graphics?

Thanks,
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0 Josef K. over 2 years ago

I want to convert a rigid body which consists of multiple shell graphics.
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0 Alexis Del Rio over 2 years ago

Hi Josef,

I don't think this is going to work. Shell graphics in Adams are there just for visualisation, as such these aren't normally water tight hence the surface won't be continue, smooth... I'm not sure you can make Adams to understand that two different shells are to be joined since they may not be necessarily coincident. Best approach is to open these shell graphics in MSC.Apex and clean it up there, if you have tokens you only need to download/install the software and is a pretty straight forward job.
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0 Josef K. over 2 years ago

I am sorry Alexis. I was not clear on my question. I have already pre-processes the body and cleaned it up in order to be identical to a finite element model (with all shells connected at the nodes properly in order to get the .mnf file).

What I meant to ask was if there are any practices which can help me better model my system (rather than just replacing the rigid body with its flexible counterpart).

Thank you and sorry for not being clear,

Josef
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0 Martin Kieltsch over 2 years ago

We're using full vehicle trimmed bodies so, yes, ADAMS can handle huge flex bodies.

Best advice: Strip down your model, to debug why it's crashing.

First step is usually importing the flex body into a blank model, fix it to ground with a joint and just simulate that model (plus view the modes)

Usually people forget to deactivate the rigid body modes which makes trouble.

Then use the flex body in your model, and deactivate all contacts. Maybe add some bushings to hold it in place.

Static equilibrium will 99% fail on flex bodies with contacts.
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0 Josef K. over 2 years ago

Hi Martin,

Thank you, I was not aware of the issue with contacts-flex-statics. I will try the debugging method you suggested.

I should clarify however that I have also tried removing the shells that i needed for the contacts from the flexible body, in order for it to not be included into contacts (I defined these bodes as separate rigid ones and fixed them on interface nodes of the flexbody) but the issue still persists.

Thanks for the tips!

Josef
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