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发表于 2010-6-4 18:59:54
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来自 法国
本帖最后由 sunnygu 于 2010-6-4 19:02 编辑
http://www.mscsoftware.com/suppo ... kshop_10.pdf
RBE2
The RBE2 defines a rigid body with one independent node and an arbitrary number of dependent nodes.You identify the DOFs (degrees of freedom – 1 to 6) in which the motion of the dependent nodes will depend on the motion of the independent node. You don’t need to assign DOFs for the independent node because all the 6 DOFs are assigned automatically. RBE2 elements are normally used to model areas that are very stiff compared to the adjoining structure in order to prevent numerical ill-conditioning and to simplify the model.Forces, moments and displacements applied to the center node (the independent node) are distributed to the dependent nodes in a consistent way (consistent with rigid body kinematics).RBE3This interpolation element allows you to model the motion of one node (the dependent node) as the least square weighted average motion of an arbitrary number of independent nodes.The intended use of the RBE3 is to transmit forces and moments from a reference node to several non-colinear nodes without adding any stiffness to the structure.The DOFs that you specify for the independent nodes must be adequate to define 6 rigid body motions for this element so that the RBE3 can carry load in all directions.Normally we do not use the three rotational DOFs for the independent nodes since the three translational DOFs are sufficient to handle all 6 rigid body directions.However, there are situations where we need to use rotational DOFs for the independent nodes.For instance, when the independent nodes are collinear (when all the nodes lie on a line),a special action is needed to restrain the rotation of the RBE3 around a line parallel to the line of the collinear nodes.Then you need to add the rotational DOF around that line (which may need to be in a local coordinate system) to stabilize this rotation mode of the RBE3.The DOFs that you specify for the dependent node are arbitrary (can be any combination of translational and rotational DOFs) and these are the DOF’s whose motion is averaged by the RBE3.The force or moment that you apply to the dependent node is distributed to the independent nodes proportional to the weighting factors.The moment applied to the dependent node is distributed as forces applied to the independent nodes.The forces are proportional to their distance from the center of gravity times their weighting factors as shown in the image below. Normally, the weighting factors are unit values.
RBE3: Motion at a dependent node (red) is the weighted average of the motions at a set of independent nodes (green) |
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