Tension only cables in Femap/NX Nastran

[zeng213]

Hello,

I'm trying to build a tower structure in Femap/NX Nastran and am having trouble modeling tension only cables. The cables are pretensioned in their initial state and then lose tension as external loads are applied to the structure.

In earlier iterations of the model I was able to create this behavior by using rod elements representing the cables and applying a nonlinear stress vs. strain function to the material. The function caused the material to be very soft and essentially carry no load in compression. I created the initial tension I wanted in the cables using temperature loads.

The technique described above worked fine for nonlinear static analysis but I have to run an advanced nonlinear transient analysis (SOL 601) and can't get it to solve. I believe it is the nonlinear material that is causing the issue. Does anyone have any experience modeling tension only cables in a advanced nonlinear transient analysis?

Thanks!

FEMAP 10.3.1
NX Nastran 8.5

 

[jotunn]

Have you looked at CGAP/PGAP? You can change axial stiffness based on open gap or closed gap (e.g. initial gap is cable length, open gap is cable stiffness, closed gap is minimal).
They may work for you, although I've only used them in nonlinear static solutions, never SOL 601. One downside is you'll need different P cards for each cable length.

 

[jbrackin]

Can you provide the model or at least the inputs for the nonlinear elastic material? There are some restrictions when using sol 601.

When you say cannot solve, what fatal error are you getting, or is it just not converging?

 

[stressebookllc]

Tension only cables will not carry compression load, so in compression its free to move and the solver see this as instability and keeps cutting down your time step and fails.

http://www.stressebook.com

Stressing Stresslessly!