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Model Suspension

Altair Forum User

Hi,

I need to model the connection between my suspension bar and my monocoque, the thing is that as I had seen there are some posts that cover this problem but in the end is not clear for me how to model this connection.

My question is, should I import my attachment and the ball joint into the cad file and create the restrictions or simplify it and create and RB2 rigid connection?

And if I use a RB2 connection how do I have to restrain the dofs?

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Adriano_Koga

You can create a cbush element between your rbe and beam.

Or release beam flags for allowing rotation.

Also there are joint elements in OptiStruct.

Altair Forum User

Okay thank you very much, and what is a cbush element and in which cases do you use?

Adriano_Koga

A Cbush element is a bushing element, or a spring-damper representation.

You can create it in the 1d>>springs panel.

There you can choose elem type as cbush.

You will create the element and assign to the component a property pbush.

Under linear stiffness you can defin3 the stiffnesses in each direction as desired, from 0 to rigid.

You may also include a force x displacement curve under PBUSHT options for a nonlinear analysis.

Tske a look at the help for OptiStruct for further info

Altair Forum User

Hi Adriano,

I send you the model I working with because I have some questions:

1) It would be better to work with Rb3 element in the connection between suspension bars and inserts?

2)To model de dumper using a cbush element will be correct or instead would you use a rod? For the propertie is necessary to give a material?

3) When you apply some loads as in the model below, do you have to give some constrained? How would you do it?

Unable to find an attachment - read this blog

Adriano_Koga

1) you can use RBE3 for this connection with no problems

2) not necessary to have material in a PBUSH. for the dumper the CBUSH is fine

3) in implicit analysis you need to apply constraints, in general otherwise rigid body motion will occur. you need to understand how your model is fixed in real world and make the same in your model. I cannot help as i don't know your real world model. sorry

i suggest you to go over this ebook as it show some modelling tips and discuss briefly about the element types.

https://altairuniversity.com/free-ebooks/free-ebook-practical-aspects-of-finite-element-simulation-a-study-guide/

Altair Forum User

Okay thank you very much my model is a car which I want to simulate under certain extreme condition that appears for example while cornering

Altair Forum User

Hi Adriano,

I am getting this error do you know why?

Use SYSSETTING(BARPROP=MIXED) to overcome this issue and allow the misuse.

Altair Forum User

This error also

There is any doc about errors meaning?

*** ERROR # 1000 *** in the input data:
Incorrect data in field # 3.
Expected STRING, found BLANK.

What about this one?

*** ERROR # 2933 ***
There are more number of degree of freedoms with double dependency
than the number of independent degree of freedom near grid ID
164277. PARAM,AUTOMSET is ineffective in this situation.

I have seen you answered previously this question

Adriano_Koga

There is a topic here in OptiStruct forum for common errors. Take a look at it.

OptiStruct solver deck (text) is defined in fields of 8 characters each. So there is something wrong with your model and the .out file tells which one is wrong.

You mixed prop error is related to having mixed definitions on bar/beam elements.

You probably have CBEAM elements and assigned PBAR property to it or vice versa.

Please check your 1d element type and use the property accordingly.