Torsional Gap on a simplified model 1

[GGMat]

Helo,
I am brand new to Nastran and Patran so with just a week of experience.

I have been trying to model a loose contact so that once the beam deflects some degrees, then a moment will be created at a pivot point. The magnitude of the moment is dependent on the degrees of defection much like a torsional spring.

I started modeling the whole scenario without the torsional gap and it works out fine on SOL 101; now that I am trying to add the gap I am having trouble on actually finding a way to implement it. As far as I know, there is no specific function/card on torsional gaps, and CGAP only seems to work for linear cases. I am completely stuck and all the research I've done on this has lead me now where.

Possibly using linear gaps?? but how?

below is an a diagram to better help understand what I am talking about.

 

[stressebookllc]

You may be able to model it using a CBUSH and define a nonlinear force vs rotation function for the stiffness to up after a certain amount of rotation.

http://www.stressebook.com

Stressing Stresslessly!

 

[GGMat]

I originally used a CBUSH to create the torsional spring without the gap, but I didn't know that i could define a nonlinear force so I will give it a go. Would I still be able to run it on SOL101?

 

[stressebookllc]

No, it is only possible with Sol 106.

http://www.stressebook.com

Stressing Stresslessly!

 

[GGMat]

I don't understand how a nonlinear force can be applied on the PBUSH card: at least a step force. I can see that you can add a damper and cause the force to change with respect to different things, but not anything about the rotational position. I also looked into CGAP and it seems like it also can't be done on a rotational standpoint.

 

[stressebookllc]

I suggest trying this. Use a Force Vs Displacement function. For displacement use radians and after certain radians ramp up the force.

In the model, use a custom cylindrical coordinate system, then update the nodal (both nodes of the CBUSH) definition and output CSYS to this cylindrical CSYS.

In the PBUSH definition dialog box, click the Nonlinear/Freq. Response spring and use the function you defined at the bottom for the DOF 2 displacement (theta).

Use SOL 106 and try a simple test model first. Lastly, if the Fairy Godmother waves her majic wand when you solve it as well, hopefully things will fall right into place.

http://www.stressebook.com

Stressing Stresslessly!