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Flexible Body Error

Hello,

I am using flexible body to find out the stress generated in the trailing arm during braking. I have encountered this error and don't know what to do. I am facing issue only for this trailing arm. I carried out the same simulations for upper and lower suspension arm and am getting the required results but the simulations is failing for trailing arm. I am attaching the out file and the snips of the same below.

<?xml version="1.0" encoding="UTF-8"?>

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Chris Coker_21312

I would suggest using a crawl, walk, run method for creating models. This is the approach we teach in all of our training classes.

Rather than try to debug this with the full vehicle model, you should put the flexbody into your front (or rear) suspension model. You created separate front and rear suspension models before creating a full vehicle model, correct?

The log file you provided reports the inertias of the flexbody:

INFO: The principal inertia in body CG frame for Flex_Body/21003 are:
(0.303574, 18.0178, 18.0213).

These numbers seem much too small from my experience. I suspect that the issue here is that you used the wrong units when creating the model using the flex prep utility. Therefore the flexbody is probably much too soft. You can check the mass properties in the flexbody directly in the Body panel for the flexbody. However, the error message that motionsolve gives is not really that helpful. We are working on improving some of these kinds of use cases.

Vishrut Viradia

Yes. I tried flex body simulation for the rear end of the model only and i am getting proper results but when i try the same in full car this error pops up. The inertia values are same for the rear end also but the simulation doesn't proceed. Also the units are proper in all the stages. i used the same units for the flex prep of suspension arms and i am getting results.

<?xml version="1.0" encoding="UTF-8"?>

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Chris Coker_21312

what are the units of your model? Are you using the default units in MV?

What are the mass and inertia properties reported in the Body panel for that part?

Based on the .log file itself, I still believe there is a units problem with your flexbody. The values listed look way to small to be reasonable, if you are using a default kg-mm-N unit system.

The model solves with the half-car because this is a simpler model arrangement. The peak stress in the results is over 2000 mPa, well over the yield strength of steel. This again points to some sort of modeling error, or units issue in the flexbody itself.

The other possible common issues with flexbodies are:

1. Including additional parts/mechanisms in the flexbody (no CBUSH, etc)

2. Alignment issues with the interface nodes and the Points in MV

3. missed connections between elements in the flexbody mesh. (Animate the mode shapes of just the flexbody in HyperView, to review and make sure the mode frequencies are reasonable)

It also appears you are using the base installation of 2019. I would upgrade to 2019.1 at least, if possible.

Praful

Hello Vishrut -

Does the full vehicle model run without the flex body ? I would guess you have verified that, but please confirm

The error seems to suggest that there is an expression which is using a particular marker, but that marker does not exist in the solver deck.

You can do a few things to debug this

1) Search for <Reference_Marker in the XML with the id 21003120. If the marker does not exist, then its a modeling error.

2) For debugging, deactivate that entity which has uses this expression. Does the solver go through? the solution as such may not be meaningful. If it does, then it would mean that, there is a modeling entity that uses a marker but may be removed or deactivated.

Let us know how these goes, we can then look further.

Regards

Praful

Vishrut Viradia

Hello Vishrut -

Does the full vehicle model run without the flex body ? I would guess you have verified that, but please confirm

The error seems to suggest that there is an expression which is using a particular marker, but that marker does not exist in the solver deck.

You can do a few things to debug this

1) Search for <Reference_Marker in the XML with the id 21003120. If the marker does not exist, then its a modeling error.

2) For debugging, deactivate that entity which has uses this expression. Does the solver go through? the solution as such may not be meaningful. If it does, then it would mean that, there is a modeling entity that uses a marker but may be removed or deactivated.

Let us know how these goes, we can then look further.

Regards

Praful

yes the model runs without the flexible body. Without the flex body there is no error for the marker id. Also i cannot find the listed marker id in the default model.

Chris Coker_21312

You cannot find the reference marker because it is part of an AutoEntity. The error is confusing, but I have seen this several times, and I believe it always is the result of either an issue with the flexbody, or not setting up the road file correctly. Since your model runs without the flexbody, there is some problem with the flexbody.

It is possible for you to provide the .h3d for the flexbody?