Moving Point Mass in Abaqus Boundary Conditions - DOF Question

[Lelle]

Hello everyone,

I have some questions about using point masses in Abaqus.

I defined a 2D Beam where a point mass moves along.

The point mass is defined with *Mass on a node. The node of the point mass is constrained to the beam element with a *MPC between two beam nodes:
*MPC
SLIDER,102,100,101
(where 102 is the point mass node, 100 and 101 are the two beam element nodes)

Now I am trying to move the node of the mass with a boundary condition in the step.
Therefore I define the amplitude with:
*AMPLITUDE,TIME=TOTAL TIME,VALUE=RELATIVE,NAME=movement
0.0, 0.99, 1.0, 0.99,2.0,1.0

During the first second the node should stay at 0.99m which is the same as node 100 and after that it shall move to 1m, which is node 101.

I'm a bit confused how to set the boundary condition right in the step. So far I set it as:
*BOUNDARY,AMPLITUDE=movement
102,1,,0.01

Which gives me the following warning message for the dynamic step:
***WARNING: DEGREE OF FREEDOM 1 IS NOT ACTIVE ON NODE 102 - THIS BOUNDARY
CONDITION IS IGNORED
102 1 MOVEMENT 1.00000E-02

Where do I find the DOF of the point mass node? Or is the a possibility that I directly change the coordinates of the node ?

Thanks for your help!

 

[Mustaine3]

It's not possible that way. The node loses his DOF because of the MPC, so you can't use that DOF in a BC.

Your request is not simple. The only way I can think of at the moment is this one:

Place the node with the mass at the desired location and use a connector cartesian+cardan to couple it to your structure at point 1. Set the connector velocity in all 6 DOF to zero. Define another connector of this type between the node and the second point on the structure.

After the first step you run a dummy step where you release the connector velocity BC, move the node to the new location and then set the second connector velocity to zero at the beginning of the next step.