Creating zero length CBUSH elements (for RBE3 support)

Altair Forum User
Altair Forum User
Altair Employee
edited March 2023 in Community Q&A

In my model, I am attempting to use RBE3 elements as supports to avoid artificial rigidity imposed by RBE2s. Because a support cannot be attached directly to an RBE3 element, I am trying to create a zero length CBUSH element with high stiffness, as suggested in this help document.

 

However, since the CBUSH element is a spring that requires two nodes to be specified, I don't understand how to achieve zero length without selecting the same node for the ends (which gives the error 'The independent and the dependent nodes are the same'). This post indicates that it is possible to create coincident nodes, but when I attempted to create a temp node at the same location as the center of my RBE3 (Geometry -> nodes -> x,y,z), it fails to create a distinct node that I can select in the spring creation panel.

 

My questions are:

  1. Is it possible to create coincident nodes?
  2. If so, how is this done?
  3. If not, how do I create a zero length CBUSH element?
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Answers

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited March 2016

    Hi,

     

    In order to pick a coincident node, you need to activate coincident picking.

     

    Press 'O' on your keyboard when HyperMesh is open>> Go to Graphics>> Activate coincident picking option.

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  • tinh
    tinh Altair Community Member
    edited March 2016

    Hi,

    it is very simply create CBUSH with non-zero length,

    then F3 > move node1 to node2 (check off 'equivalence'), or Shift+F4 translate node1 to node2 (switch magnitude to 'N1-N2')

    it's better to do this step after binding CBUSH to RBE3

  • yoo lin
    yoo lin New Altair Community Member
    edited July 2019

    Hi,

    it is very simply create CBUSH with non-zero length,

    then F3 > move node1 to node2 (check off 'equivalence'), or Shift+F4 translate node1 to node2 (switch magnitude to 'N1-N2')

    it's better to do this step after binding CBUSH to RBE3

    image.png.e39a3b201ecf14f9961600cdc0ba5469.png

    if you replace the node,it would destroy the cbush element

  • tinh
    tinh Altair Community Member
    edited July 2019

    Check off 'equivalence' before doing

  • Anto Pellissery
    Anto Pellissery New Altair Community Member
    edited March 2023
    tinh said:

    Check off 'equivalence' before doing

    Anybody can guide me how to add multiple cbushes in a model is there any easy way rather doing it individually .Thanks in advance