Learning Forum

[StudentJack]

Hi,

I am trying out an offset barrier test, which involves a car bumper against a barrier of 40% length of the bumper. However it seems that upon crashing the bumper would rotate. Since only the right side was blocked by the barrier, the bumper would pivot at the end of the barrier and the left side will rotate towards the barrier. Is there a way to prevent this from happening and constraint the movement of the bumper to move within an axis? Thank you for your help!

[peteroznewman]

You can add a joint that constrains a remote point to prevent the rotation.  You could promote the point mass to a remote point, then reuse that remote point in a joint, Body-Ground.  If you select a General joint, you can choose which DOF to set to 0.  You might also more the remote point further back since the CoM of the car is not so close to the bumper.

[StudentJack]

Hi,

Would it be possible if i add a remote displacement onto the car bumper and change the rotation on y axis to constant? would this affect the calculation?

[peteroznewman]

Yes, it would affect the calculation, you won't get the rotation you wanted to remove.

[StudentJack]

Hi,

 

Thanks for your prompt reply! May I know where would you recommend me to add the joint to which remote point?

 

[peteroznewman]

You could promote the point mass to a remote point, then reuse that remote point in a joint, Body-Ground.  

[StudentJack]

Hi,

I have tried promoting point mass to a remote point, then adding a Body-ground, general type joint to that remote point (point mass) however i receive an error about "Joints that are scoped to a remote point must have the remote point to be at (0.0,0.0,0.0) in the remote point. Do i change the remote point to (0.0,0.0,0.0)?

 

[StudentJack]

Hi, 

I have also tried adding a remote displacement on one of the edges and set y axis rotation to constant but the expected calculation time required would be long.

[peteroznewman]

Explicit Dynamics runs can become long if you introduce a small element into the mesh. That might be the case with this remote displacement. You can get Characteristic Length as one of the Mesh Quality metrics. Click on the bar at the shortest end. That is the element that dictates the time step for the solution.

[StudentJack]

The method with the long calculation time was the one i suggested but you've mention that the calculation would be wrong.

I have also tried your suggested method where I promoted the point mass to a remote point, then adding a Body-ground, general type joint to that remote point (point mass) however i receive an error about "Joints that are scoped to a remote point must have the remote point to be at (0.0,0.0,0.0) in the remote point. May i know how do i go about constraining the joint?

 

 

[peteroznewman]

Create a Joint Body to Ground and select the face at the end of the post on right side of the bumper.

[StudentJack]

Sorry, may i clarify if you are referring to this face?

[peteroznewman]

I was thinking of the face that is at the end of the short solid post that is along the Z axis.

[StudentJack]

Hi,

As my current point mass is attach to the short posts face on both side and if i were to add in a joint as well, wouldnt there be an error?

[peteroznewman]

I didn't know where your point mass was scoped to.  You might just get a warning. I don't know.

When you said, "i receive an error about "Joints that are scoped to a remote point must have the remote point to be at (0.0,0.0,0.0) in the remote point. Do i change the remote point to (0.0,0.0,0.0)?"  Did you try to change the remote point to 0,0,0?  What happened?

[StudentJack]

Hi,

My point mass remote point will look like this

[peteroznewman]

So move your geometry over to make it right.