RBE2 vs RBE3

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Before I start to explain you about RBE2 and RBE3, one should know what rigid elements are, and why do you use them? A rigid element is a link from one node to one or more other nodes, where the motion of the node(s) is governed by the "degrees of freedom" you choose to connect.


A few examples of rigid elements used in some applications given below:


  • To model the dynamic behavior of the vehicle, sometimes the engine can be modelled as a mass elements connected by an RBE2 rigid element to the engine's multiple mounting locations. The mass is located at the centre of gravity of the engine, and the rigid element links the engine mass to the rubber mounts (eg. springs or bushes).

  • Bolts at pre-load needs to be modelled, but does not need to modelled with any other than as a "bar" or "beam" element. An RBE2 can be used to connect the end node of the "bolt" element to the multiple nodes which represent the washer area over which the bolt load acts.

 

Masses are used to represent loads in the structure. A mass element could be used to represent one set of passenger/seat. An RBE3 element can be used to connect the mass elements to the relevant area of the structure over which you wish to distribute the effect of the mass.

 Both elements "look" the same, in that they have a single node connected to one or (usually) multiple other nodes. The difference is that the RBE2 element adds stiffness to the structure, while RBE3 elements "distribute forces" around the connected nodes, without adding any stiffness.

RBE2 element distributes the force and moment equally among all connected nodes irrespective of the position of the force or moment application.

Consider 100 N force is applied at RBE2 element as shown below. It will get equally distributed among the 2 nodes i.e. 50 N each

RBE3 element is a constraint equation to distribute the force and moment as per the distance.

If RBE3 is used instead of RBE2 then it will distribute it as 75 N at pt. B and 25 N at pt. A

 

So, I hope, you guys now understand the difference between RBE2 and RBE3.

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