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Use Multibody Dynamics Module to simulate two elastically connected beam

Posted Aug 8, 2019, 11:55 a.m. EDT Structural & Acoustics, Acoustics & Vibrations, Structural Mechanics Version 5.4 1 Reply

ZH Lau
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I want to simulate two elastically connected beams. The first beam is hinged to the ground with a rotation spring. The second beam is pinned with the first beam with a roation spring as well. The schematic diagram is shown below.

pic1

I use the pinned joint and spring foundation to simuate the first joint. For the second joint, I add two attachment in the two beams' end. The first attachment is at the right end of the first beam. The second attachment is at the left end of the second beam. The setting of my model is in the Attachments of this post.

When I solve this model, the error message shows that

Undefined variable. - Variable: comp1.beam.att1.phi - Global scope Failed to evaluate Jacobian of expression. - Expression: comp1.mbd.hgj1.uc_src-comp1.mbd.hgj1.uc_dest -

Could you please tell me the possible reason for the error?

With best regards.

Attachments:

1 Reply Last Post Aug 8, 2019, 11:59 p.m. EDT
Pawan Soami COMSOL Employee

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Posted: 5 years ago Aug 8, 2019, 11:59 p.m. EDT
Updated: 5 years ago Aug 9, 2019, 1:11 a.m. EDT

Dear Lau,

I had a look at your problem and it seems that the variable it is complaining about is missing in the Beam interface in 2D. So we will fix this issue in our upcoming release and I suggest you the following work around for now.

Add a Variables node under Component 1>Definitions. Define the following variables: beam.att1.phi = beam.att1.int(thz)
beam2.att1.phi = beam2.att1.int(thz)

Model should work after adding these variable definitions manually.

Also I noticed that you are using Joint Elasticity whereas you mentioned that you need rotation spring at the hinge joint. So I would suggest to use Spring and Damper subnode on the Hinge Joint to add rotation spring instead of Joint Elastcity. The Joint Elasttcity node adds spring on all the DOFs except rotation in case of Hinge Joint in order to simulate a bushing effect.

Best Regards,
Pawan Soami

Dear Lau, I had a look at your problem and it seems that the variable it is complaining about is missing in the Beam interface in 2D. So we will fix this issue in our upcoming release and I suggest you the following work around for now. Add a Variables node under Component 1>Definitions. Define the following variables: beam.att1.phi = beam.att1.int(thz) beam2.att1.phi = beam2.att1.int(thz) Model should work after adding these variable definitions manually. Also I noticed that you are using Joint Elasticity whereas you mentioned that you need rotation spring at the hinge joint. So I would suggest to use Spring and Damper subnode on the Hinge Joint to add rotation spring instead of Joint Elastcity. The Joint Elasttcity node adds spring on all the DOFs except rotation in case of Hinge Joint in order to simulate a bushing effect. Best Regards, Pawan Soami

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