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Is there a MPC functionality in COMSOL?

Posted 15 juil. 2019, 01:52 UTC−4 Structural & Acoustics Version 5.4 5 Replies

ZH Lau
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My problem is to simulate two beams connected at an included angle. The diagram is shown below.

pic

The first beam is hinged on the ground, and the rotation is restrainted by a rotation spring with stiffness coefficient . The second beam is connected with the first beam via a pin joint and the rotation stiffness is .

In other FEM softwares, I know I can use MPC to achieve the connection between these two beams. But I didn't find a similar functionality in COMSOL. How can I simulate my problem. My goal is to investigate the effect of the included angle and spring stiffness on the natural frequencies of this system, so I want to perform a parametric study. A simple example file would be highly perfered and appreciated.

Best Regards

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5 Replies Last Post 9 août 2019, 01:28 UTC−4
Henrik Sönnerlind COMSOL Employee

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Posted: 5 years ago 15 juil. 2019, 02:45 UTC−4
Updated: 5 years ago 15 juil. 2019, 02:45 UTC−4

Hi,

For the first joint you use a Pinned node together with a Spring Foundation node.

Modeling the second joint is easiest if you have access to the Multibody Dynamics Module, since then you can use a Hinge joint.

If you do not have that license, you have to start from one of the other methods discussed in https://www.comsol.com/forum/thread/238081/beam-end-release-hinge-beam. This will give you a moment free 'hinge', to which you need to add spring properties by introducing a moment which is proportional to the difference in angles.

Maybe I should add that we do not use the terminology 'MPC (= Multipoint Constraint)'. You can however set up very complex relations between degrees of freedom through the Extrusion Coupling operators.

Regards,
Henrik

-------------------
Henrik Sönnerlind
COMSOL
Hi, For the first joint you use a **Pinned** node together with a **Spring Foundation** node. Modeling the second joint is easiest if you have access to the *Multibody Dynamics Module*, since then you can use a **Hinge** joint. If you do not have that license, you have to start from one of the other methods discussed in . This will give you a moment free 'hinge', to which you need to add spring properties by introducing a moment which is proportional to the difference in angles. Maybe I should add that we do not use the terminology 'MPC (= Multipoint Constraint)'. You can however set up very complex relations between degrees of freedom through the Extrusion Coupling operators. Regards, Henrik
ZH Lau
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Posted: 5 years ago 15 juil. 2019, 02:53 UTC−4
Updated: 5 years ago 15 juil. 2019, 02:53 UTC−4

Hi,

For the first joint you use a Pinned node together with a Spring Foundation node.

Modeling the second joint is easiest if you have access to the Multibody Dynamics Module, since then you can use a Hinge joint.

If you do not have that license, you have to start from one of the other methods discussed in . This will give you a moment free 'hinge', to which you need to add spring properties by introducing a moment which is proportional to the difference in angles.

Maybe I should add that we do not use the terminology 'MPC (= Multipoint Constraint)'. You can however set up very complex relations between degrees of freedom through the Extrusion Coupling operators.

Regards,
Henrik

Thanks for you reply Henrik. In the multibody dynamics module, I didn't find the beam-type structure. Do I need to use a simple planar rectangle to represent the beam?

Thanks.

>Hi, > >For the first joint you use a **Pinned** node together with a **Spring Foundation** node. > >Modeling the second joint is easiest if you have access to the *Multibody Dynamics Module*, since then you can use a **Hinge** joint. > >If you do not have that license, you have to start from one of the other methods discussed in . This will give you a moment free 'hinge', to which you need to add spring properties by introducing a moment which is proportional to the difference in angles. > >Maybe I should add that we do not use the terminology 'MPC (= Multipoint Constraint)'. You can however set up very complex relations between degrees of freedom through the Extrusion Coupling operators. > >Regards, >Henrik Thanks for you reply Henrik. In the multibody dynamics module, I didn't find the beam-type structure. Do I need to use a simple planar rectangle to represent the beam? Thanks.
Henrik Sönnerlind COMSOL Employee

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Posted: 5 years ago 15 juil. 2019, 07:08 UTC−4
Updated: 5 years ago 15 juil. 2019, 07:06 UTC−4

When mixing Beam with MBD, you add Attachment nodes to the end points of the two beams inside the Beam interface. The only thing that you do in the MBD interface is to add a single Hinge joint, and select the two attachments announced from the Beam interface. Then you add a Spring and Damper subnode to the hinge joint.

Regards,
Henrik

-------------------
Henrik Sönnerlind
COMSOL
When mixing Beam with MBD, you add **Attachment** nodes to the end points of the two beams inside the Beam interface. The only thing that you do in the MBD interface is to add a single **Hinge** joint, and select the two attachments announced from the Beam interface. Then you add a **Spring and Damper** subnode to the hinge joint. Regards, Henrik
ZH Lau
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Posted: 5 years ago 8 août 2019, 09:55 UTC−4
Updated: 5 years ago 8 août 2019, 11:38 UTC−4

When mixing Beam with MBD, you add Attachment nodes to the end points of the two beams inside the Beam interface. The only thing that you do in the MBD interface is to add a single Hinge joint, and select the two attachments announced from the Beam interface. Then you add a Spring and Damper subnode to the hinge joint.

Regards,
Henrik

Dear Henrik Sönnerlind,

Thanks for providing me the solution. I tried your method. I use two lines to represent the two beams. Then the first beam is hinged to the ground by using the pinned and spring foundation. The first attachment is at the right end of the first beam while the second attachment is at the left end of the second beam. The two beams are connected via the MBD hinge joint. But when I solve the problem, the error message shows that comp1.beam.att1.phi variable is not defined. Can you tell me the possible reason and how to solve it? https://i.ibb.co/xFwpckc/001.png

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

Thanks.

>When mixing Beam with MBD, you add **Attachment** nodes to the end points of the two beams inside the Beam interface. The only thing that you do in the MBD interface is to add a single **Hinge** joint, and select the two attachments announced from the Beam interface. Then you add a **Spring and Damper** subnode to the hinge joint. > >Regards, >Henrik Dear Henrik Sönnerlind, Thanks for providing me the solution. I tried your method. I use two lines to represent the two beams. Then the first beam is hinged to the ground by using the pinned and spring foundation. The first attachment is at the right end of the first beam while the second attachment is at the left end of the second beam. The two beams are connected via the MBD hinge joint. But when I solve the problem, the error message shows that comp1.beam.att1.phi variable is not defined. Can you tell me the possible reason and how to solve it? ![https://i.ibb.co/xFwpckc/001.png](https://i.ibb.co/xFwpckc/001.png) ********************** 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 ************************ Thanks.

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Henrik Sönnerlind COMSOL Employee

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Posted: 5 years ago 9 août 2019, 01:28 UTC−4
Updated: 5 years ago 9 août 2019, 01:26 UTC−4

The last question is answered in https://www.comsol.com/forum/thread/240483/use-multibody-dynamics-module-to-simulate-two-elastically-connected-beam

Henrik

-------------------
Henrik Sönnerlind
COMSOL
The last question is answered in Henrik

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