Enforced Motion - Matching Constraint or Not?

[markdeckerZBQL7]

I always thought with NIC that one needed to apply a matching constraint along with the enforced motion.  I least this is what the Flexural Testing tutorial did.  Going back through the help, it states that one "should" do this.

I just tested this on a nonlinear static model and the motion seemed to work fine whether or not matching constraint was present.

[John_Holtz · Accepted solution]

Hi Mark,

I agree that sometimes the enforced motion works without adding a constraint, but I have also had models where the enforced motion did not work until the constraint was added.

I am not sure why it is needed sometimes and not other times. It does not hurt to add the constraint manually all of the time.

[markdeckerZBQL7]

Thanks, John.  I figured it used the constraint to bookmark which DOF to control and was surprised that it worked OK without the constraint.  Just another thing to keep in mind that is just a little different procedure than Sim Mech.

[shigeaki.k]

Hello @markdeckerZBQL7 and @John_Holtz,

John is correct about the enforced motion. It tries to apply the necessary constraint but is not always able to do so. Unfortunately, the algorithm does not seem to be robust enough to take into account all scenarios. 

Below are the extracts from the In-CAD Nastran Manual for your reference. 

Enforced motion is much like a constraint being applied as a load. Therefore, when applying an enforced motion type load, a constraint should be applied on the same geometric entity in the same direction of the applied enforced motion.

Regards,

Shigeaki K.