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# Frequencies

## Frequencies

(OP)
Hi,

I would like to know if Abaqus 6.6.3 allows us to determine the frequency of resonance of an assembly.

The system is shown on the next picture :

The rotating tube in Aluminium goes from 0 to 6000 rpm and i would like to determine at which frequencies my system will vibrate.

The main questions are :
how to create this complex system on abaqus ( in 3D ? or by using beam model or others ? )
to calculate the frequencies, depending on silentbloc ( springs )

thanks a lot

### RE: Frequencies

dureiken,

Your system does not look very complex to me. However I am not sure how the fact that the Aluminum tube is rotating will change the natural frequency? Can you clarify this?

What do yellow blocks in your picture represent? Are they rigid parts that can be modelled just as masses? A beam will have many natural frequencies (infinite in fact). Are you interested in torsional modes or only bending modes? I think if you are not interested in the torsional modes, you may be able to model the beam with beam elements. Otherwise you may have to use 3-D elements. Same goes for the Aluminum tube.

The silent block (springs) can be modeled with spring elements. Does this make sense to you?

Gurmeet

### RE: Frequencies

(OP)
Hi,

yellow block can be modelled by masses but I don't know how to do it ?
I'm interested in torsional modes, so I used a 3D model.

To model silentblock I created a new material with an adequat Youg modulus and I applied it on a cylinder representating the spring but I would like to know how to model spring more cleverly.

### RE: Frequencies

Hi

You can use connector elements to model the springs - see section 25 in the ABAQUS users manual.  I would have thought they would be an ideal, low cost option for your model.

Masses can be represented by lumped mass elements.  These are defined at nodes, so you will need to define a node at the centre of gravity of each block.  Look up 'point mass' in the docs.

Regards

Martin

Martin Stokes CEng MIMechE

### RE: Frequencies

(OP)
ok thanks but are you able to do it on Ideas or not ? I'm doing this study on this software because I had lessons on it.

### RE: Frequencies

Can't help you there, I haven't used I-DEAS in 5 years or more...

I remember that there was a document in the I-DEAS help that listed all the ABAQUS keywords/elements etc and how they mapped to I-DEAS entities.  I'd have thought that would be a good place to start.

Regards

Martin

Martin Stokes CEng MIMechE

### RE: Frequencies

(OP)
maybe I will do this part of the study on abaqus because its really important.

I will try to do what you said on abaqus ! thanks a lot

### RE: Frequencies

(OP)
could you help me to advance ?

in order to study a simple case to begin, I just want to check the method on a steel bloc on spring.

I went on http://scv.bu.edu/Graphics/abaqusdocs/v6.5/ but section 25 is not the good one.

Could you be more precise on the way to go from scratch to the result ?

thanks a lot

### RE: Frequencies

I'm not sure I understand the question.  That section of the manual explains everything you need to know about modelling with connectors.

Connectors are created between two nodes and can have various properties attached to them such as elasticity (stiffness) and damping.  I find them more useful than using traditional spring elements as I quite often have to add a bit of damping in dynamic analyses.  Not only that, you can have max and min lengths for a connector to represent hard stops at the limits of motion.

Regards

Martin

Martin Stokes CEng MIMechE

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