Water Pressure, spacial model

[vladimir79]

Hello world,

I'm new in the Femap and Nastran modeling. Following problem occupies my mind for several days now:

An artificial pipe (liner) is inserted in another (host) pipe in order to sanate it. For starters, the load case Water Pressure (outer) dictates my wall thickness. The host pipe and the liner are close fit, so I modeled the connection with the gap elements with great compressional and insignificant tensional stiffnes. The space between is described with an initial gap of ~ 1 mm. Because it is a stability problem, I conduct a nonlinear static analysis, where the load is incremented to a double load. I "cut" a part of the pipe for modeling and constrained it with symmetrically with respect to longitudinal axis.

I can not bring the calculation to convergence.

Has anyone an idea of waht might be wrong, or a suggestion of remodeling the model?

There is a zipped file in the attachment.

Thank you in advance.

Best regards,


Vladimir

 

[rob768]

Do you really need to define contact? If it is really close fit, will they not behave as one?

 

[vladimir79]

Hi Rob,

the pipes are close, not glued.

For the load case water pressure, the close-fit matter is not really imprortant. The host pipe is cracked, so the water finds the way in.


Vladimir

 

[jbrackin]

Vladimir,
I made 2 changes to your model to get convergence. The first is to add a Y direction constraint to the 2 end nodes where you had the X direction constraint. Then on the nonlinear control options form, I changed the Stiffness update to the "iter" method with iterations before update to 1. The gaps now behave as expected and the problem converges.

Joe

 

[vladimir79]

Hi Joe,
thank you for the answer. However, I won't be able to test it before 16th September. I'm in vacation.

Vladimir