Unexpected Results on Altair HyperWorks (OptiStruct)

Altair Forum User

Dear Jan,

 

I am a student working at Fontys University of Applied Sciences who have already made contact with you.

Thank you for your attention, but I still have some doubts on what I have being doing wrong on the definition of forces in the software.

On the attached image you can see that defining a rigid and applying a force to it or just applying a lot of loads directly at the nodes will result in very different shapes. I want to know better why is this happening.

Also, is there any kind of preset that I can use to apply a bearing load to a hole?

I hope to hear from you soon.

 

Kind regards,

 

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Altair Forum User

Hello,

 

there are various reasons, why the results from your optimization might differ. The possible influence in your model is the usage of Rigid Body Elements (type2) which will give a different behaviour of applying a force:

1) When single forces act on a set of nodes, the different nodes still can move independently (comparably low stiffness in the bearing). Thus, to increase stiffness, material is needed between the single loaded nodes when performing an optimization.

2) When using a RBE 2, the attached nodes are 'infinitely stiff' and can not move relative to each other. That is the definition of the Rigid Body Element RBE2 -> all nodes will have the displacement. Therefore you add stiffness to the bearing (as if a bolt was stuck into it) and OptiStruct will not need to add additional material for stiffness here.

 

To simulate the loading as in situation 1 (uneven displacement in the load bearing) you can make use of a RBE3 Element, which is also a Rigid Body with only one force distributed on the attached nodes. However RBE3 does not add stiffness to your model where you might not want to have it. 

 

Or you can just simply create a new component + property for the load attachment area, move your local elements there (organize via F11 key) and unselect this property in the design variable. Then, all elements in the load area will remain untouched by the optimizer.

 

Regards

 Jan