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# CATIA FEM(2)

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 anilsamuel007 (Automotive) 6 Sep 12 4:24
 Hi to all What is exact difference between a smooth virtual part and rigid virtual part?(in the point of analysis) Ii would be more helpful when you include smoe real example Simillarly could you please tell me the difference between smooth Connection property , rigid connection property and Fastned connection..I would like to know which one gives better results thanking you in advance Anil
 (2)  franc11HD (Aeronautics) 7 Sep 12 9:32
 A smooth virtual part and a rigid virtual part is respectively like a Nastran RBE3 and RBE2. It is a rigid spider or smooth spider that will link for example the centroid of the surface you selected with all the nodes on that surface. For a rigid connection, it means that the centroid is the independant node and all the nodes on the surface are dependant. This means that all the displacement of that dependant node are directly transffered to the other nodes. If the dependant node is moving 1 in. in positive x, all the nodes on the surface moves by 1 in. So the deformation is rigid. A smooth virtual part acts the same way, but the centroid of the surface would now be the dependant node and all the nodes of the surface would be the independant node. Therefore, the displacements of the independant node (centroid) is a basically an average of the displacement of all the surfaces nodes. So you can understand now that a rigid virtual part rigidify your part. same thinh about connection. A smooth connection allows deformation between parts and a rigid connection keeps the parts together without relative deformation. As far as fastened connection, I never really used it. I preffered user defined where you can put the desired stiffness of the connection. Which works better? Depends on the usage... but all of them are artificial parts that acts as approximation. They need to be used with caution.

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