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8-Gravel

## What happens if you mix rigid and weighted links sharing the same elements?

Hello all.

I´ll post again something that I have included in another post (Question about weight link and distance of the dependent side) – but now with a new interpretation.

Creo Simulate has a classical example that a component is replaced by a point at CG and its mass. This CG point is connected to respective anchor points.

An example would be a motor block connected to a frame. The goal is to verify the eigenfrequency of the frame. To include the motor block in the meshing is thus not needed. CG and mass (or advanced mass) is enough.

If the CG of the motor is connected to the beds via rigid links the eigenfrequency of the frame is completely different than using weighted link – nothing new here.

But we can also think that the block is rigid enough – but not really the connection.
Each motor-frame connection transmits only forces – but not moments. A ball joint link. This should be possible to simulate but it would require one weighed link for each connection.

Attached is my idea how I mixed rigid and weighted links. The model was copied from my original post and do not represents exactly the motor block case although the main idea is there.

However, I figured out that the distance of the dependent - independent side of the weighted link changes the eigenfrequency  result. I was not expecting this, as commented in the other post.

This was a kind of surprise and made me to think again the general Simulate example of using the CG and a mass attached on it – if it is modeled using more than one weighted link. The original case uses just one weighted link connecting the CG to the frame. It is the classical modelling case.

The result will be influenced by the distance of the CG (dependent side) and the connections (independent side).

Maybe mixing rigid and (several) weighted links can create a compromise of frame stiffness – or even open new ways to prepare a simulation model. But it can be also a mistake for reasons that I cannot understand.

For this reason, I´m looking for some advices.

Thanks

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