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NickC

Beam Model and Shell Model Differences

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Using Hypermesh 2017, and User Optistruct.

 

I have been trying to get the contour plots of a chassis both modeled with a beam model and a shell model to match up but the deflections of the shell model are always about 2 times as large. It should also be noted that the deflection images are nearly exactly the same with the same deflection trends but just the magnitudes are different. The following conditions are the exact same for both: forces, location of forces, constraints, overall size, thickness and material. The only conditions that are different would be the properties as the beam model is modeled with a PBEAM and assigned the correct beamsection while the Shell model is modeled with a PSHELL card and then assigned the thickness. 

Are there any common errors that would be able to describe why the beam model has almost exactly half the deflection of the shell model? 

Thanks for any Help , reply if more info is needed.

Nicholas C.

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Hi,

 

assuming it is a space frame chassis,  it is expected the shell model to be more compliant than beam model due to the following reasons:

-tube junctions modeled with shell elements better represent the real geometry. Therefore larger local deformations are captured

-beam elements should have more material at tube junctions (check by tools>mass calc)

-beam models usually have fewer elements; in general coarser mesh is stiffer than finer.

 

However, only these peculiarities do not account for 2 times more displacements.

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