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## How can I simulate a rotating flexible link with hub?

I'm a student and I know comsol from a school workshop. I think it is very powerful but now I'm still studying it and cannot use it fluently. Now I want to use it to analyze a simple multibody problem and I want to use comsol to verify my method. But I met some problems which have not solved after my many attempts. The problem is briefly described below.

As shown in the figure, a flexible beam is rigidly fixed on the hub, and the hub is driven by the rotor. There is a rotational spring between the rotor and hub. Now I want to simulate the elastic deflection of the flexible link when it rotates. Thus, I think this is a simple rigid-flexible problem.

I use 2D beam and multi-body dynamic modules to simulate this problem. As I have no idea on how to simulate the hub, the hub and rotational spring are omitted in my attempt. I firstly define the beam and a connection attachment under beam module. Then I use point mass to simulate the payload. In multibody dynamics module, I use hinger joint to simulate the rotation in which the source and destination are respectively fixed and the attachment defined under beam module. I specify the torque on this joint to drive the flexible link.

I think this should be a very simple problem and COMSOL can solve it. But I faced some problems.

1. I don't know how can I export the elastic deflection of the flexible link. As shown in the figure, I want to export the elastic deflection observed in rotating link but not stationary coordinate system.
2. Is there some simple approach to simulate the hub and rotational spring?

1 Reply Last Post Oct 13, 2020, 2:31 AM EDT

Posted: 1 year ago

Dear Lau,

To visualize only the elastic deformation in a component of multibody system, in general you can do the following. In the Results section of the Multibody Dynamics interface node, define Body defining reference frame using any Attachment/Rigid Domain node. Then you need to solve the model with this setting or if it is already solved then update the solution. Once done, you can plot {u_ref, v_ref, w_ref}. This approach works when the domains are part of Multibody Dynamics interface. In case domains are modeled in another physics e.g. Beam interface then this approach may not work and expressions similar to {u_ref, v_ref, w_ref} needs to be created manually in the Beam interface.

Regarding the modeling of hub and rotational spring, you can model the hub using Rigid Domain node and connect the hub to Rotor using Hinge Joint with rotational spring. Also connect the hub to attachment of flexible link using Fixed Joint.

Feel free to reach out to COMSOL support for more details.

Thanks!

Best regards,
Pawan Soami

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