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adding mass and inertia

Posted 6 sept. 2024, 04:12 UTC−4 9 Replies

Filippo Tosato
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HI, i m trying to attach mass and inertia to a reference point(top diameter of hollow cylinder) that does not have a material property and does not belong to my geometry. i attach picture and comsol file of how should look like the geometry and what i would like to achieve. I 'm using linear elastic model but mass and inertia it's only in rigid model. how can i connect the mass point to the boundary of my structure.

thanks in advanced

9 Replies Last Post 10 sept. 2024, 04:47 UTC−4
Acculution ApS Certified Consultant
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Posted: 7 months ago 6 sept. 2024, 04:29 UTC−4

Perhaps you are looking for 'Connections'->'Rigid Connector' with added (Right-click) 'Mass and Moment of Inertia'?

-------------------
René Christensen, PhD
Acculution ApS
www.acculution.com
info@acculution.com
Perhaps you are looking for 'Connections'->'Rigid Connector' with added (Right-click) 'Mass and Moment of Inertia'?
Henrik Sönnerlind COMSOL Employee

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Posted: 7 months ago 6 sept. 2024, 04:36 UTC−4
Updated: 7 months ago 6 sept. 2024, 04:37 UTC−4

The easiest way is to use a Rigid Connector attached to the outer boundary. Then, add a Mass and Moment of Inertia subnode. If this coupling is too stiff, you can set Connection type to Flexible. The best choice would be dictated by how that extra mass is attached in reality.

Edit: A bit slower than René :-)

-------------------
Henrik Sönnerlind
COMSOL
The easiest way is to use a *Rigid Connector* attached to the outer boundary. Then, add a *Mass and Moment of Inertia* subnode. If this coupling is too stiff, you can set *Connection type* to *Flexible*. The best choice would be dictated by how that extra mass is attached in reality. Edit: A bit slower than René :-)
Filippo Tosato
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Posted: 7 months ago 6 sept. 2024, 08:39 UTC−4

thanks so much both, i SOLVE IT, but when i plot the eigenmode of the structure i have very unrealistic mode shape since the cylinder get squeeze or stretch. Should i add constrain to maintain the cross sectional area fix? how?

I attach picture and file to have a better rapresentation
thanks so much both, i SOLVE IT, but when i plot the eigenmode of the structure i have very unrealistic mode shape since the cylinder get squeeze or stretch. Should i add constrain to maintain the cross sectional area fix? how? I attach picture and file to have a better rapresentation
Acculution ApS Certified Consultant
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Posted: 7 months ago 7 sept. 2024, 15:22 UTC−4

I don't see any issues with it. What are your expectations to the modes? Do you have any analytical expressions to compare against?

-------------------
René Christensen, PhD
Acculution ApS
www.acculution.com
info@acculution.com
I don't see any issues with it. What are your expectations to the modes? Do you have any analytical expressions to compare against?
Henrik Sönnerlind COMSOL Employee

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Posted: 7 months ago 9 sept. 2024, 05:20 UTC−4

It seems like you are looking at a higher order mode. Check if the first natural modes match your expectations.

-------------------
Henrik Sönnerlind
COMSOL
It seems like you are looking at a higher order mode. Check if the first natural modes match your expectations.
Filippo Tosato
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Posted: 7 months ago 9 sept. 2024, 11:29 UTC−4

Comparing my mode shape with the one presented in a paper, the first two mode are the same, but from the third one they all look different. For example as i show in the picture in the previous message i should get a torsional mode instead of a "squeeze" or collapsing mode. Since it's a hollow cylinder it 's quite unrealistic,for the simulation of a wind turbine tower, that the cross section area of cylinder get so compressed(imploding ). it should apprroximately maintains the same circular cross section. Any insight?

Comparing my mode shape with the one presented in a paper, the first two mode are the same, but from the third one they all look different. For example as i show in the picture in the previous message i should get a torsional mode instead of a "squeeze" or collapsing mode. Since it's a hollow cylinder it 's quite unrealistic,for the simulation of a wind turbine tower, that the cross section area of cylinder get so compressed(imploding ). it should apprroximately maintains the same circular cross section. Any insight?
Edgar J. Kaiser Certified Consultant
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Posted: 7 months ago 10 sept. 2024, 03:09 UTC−4

Calculate more frequencies. I see a torsional mode at 35.837 Hz.

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Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
Calculate more frequencies. I see a torsional mode at 35.837 Hz.
Acculution ApS Certified Consultant
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Posted: 7 months ago 10 sept. 2024, 04:25 UTC−4

Comparing my mode shape with the one presented in a paper, the first two mode are the same, but from the third one they all look different. For example as i show in the picture in the previous message i should get a torsional mode instead of a "squeeze" or collapsing mode. Since it's a hollow cylinder it 's quite unrealistic,for the simulation of a wind turbine tower, that the cross section area of cylinder get so compressed(imploding ). it should apprroximately maintains the same circular cross section. Any insight?

They might not show in sequential order in the paper, but selected for their narrative.

-------------------
René Christensen, PhD
Acculution ApS
www.acculution.com
info@acculution.com
>Comparing my mode shape with the one presented in a paper, the first two mode are the same, but from the third one they all look different. For example as i show in the picture in the previous message i should get a torsional mode instead of a "squeeze" or collapsing mode. Since it's a hollow cylinder it 's quite unrealistic,for the simulation of a wind turbine tower, that the cross section area of cylinder get so compressed(imploding ). it should apprroximately maintains the same circular cross section. Any insight? They might not show in sequential order in the paper, but selected for their narrative.
Filippo Tosato
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Posted: 7 months ago 10 sept. 2024, 04:47 UTC−4
Updated: 7 months ago 10 sept. 2024, 08:50 UTC−4

Perfect. I also wanna model a damping layer(constrained and unconstrained layer ) located to the outer boundary of turbine tower with a specific length (L) along the height of tower (I will do a parametric sweep of L). The problem is that the cylinder is tapered hence I can't easily model the geometric which should be attach to the outer boundary of the tower. I saw I could use linear layer model in the shell physic but the mesh is not compute. Which is the easiest way to do it and more suitable for my case. The tower is surrounded by air.

Perfect. I also wanna model a damping layer(constrained and unconstrained layer ) located to the outer boundary of turbine tower with a specific length (L) along the height of tower (I will do a parametric sweep of L). The problem is that the cylinder is tapered hence I can't easily model the geometric which should be attach to the outer boundary of the tower. I saw I could use linear layer model in the shell physic but the mesh is not compute. Which is the easiest way to do it and more suitable for my case. The tower is surrounded by air.

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