Static structural - Generaliced Plain Strain in a thin-wall tube: Results and constraints?

I want to model the case of 2D GPS analysis for the section of a tube of 10 meter large with a thin thickness between the inner and the outer walls. The tube is free to expand along its length (z axis)but x and y displacement should be 0 (consideration that can’t be bend=rigid). I want to verify GPS conditions (strain in z axis=constant and Force in z axis=0N)for being sure that i'm doing a GPS analysis.

What I've already done is:

1) Insert a thermal condition in the tube with an external data file (I have coordinates x,y and the temperature).

2)Create a remote point which links the inner and de outer wall.

3) Insert: remote displacement (x=0 y=0 rotation=0 behaviour=deformable).

4)Insert: Generalized Plain Strain (boundary condition=free, Rotation x=Rotation y=0).

With this configuration I have not a constant strain (normal elastic strain differs from being constant). If someone could help me trying to figure out where I have the problem I would be very grateful. Pdf document with some warnings that I don't know how to fix them and with details of the conditions is uploaded.

Sorry for my english.

Thank you.🙏

Comments

  • Hi @Eugenio ,

    Generally speaking, you shouldn't have a Remote Point/Remote Displacement in your model. The Details view of the "Geometry" branch defines the fiber length and angle. The "Generalized Plane Strain" object under the Analysis branch defines the boundary conditions/loads in the out-of-plane direction. You then need to provide sufficient constraints in the XY plane to prevent rigid-body motion. (Do not use Remote Displacement but just use regular Supports instead.)

    I'd suggest suppressing the outer pipe and just solving the case of 1 pipe first to better understand the setup and procedure. The issue is that, it's not clear from your description how the inner and outer pipes interact (how they are connected) - using Remote Point is probably not appropriate.

    Regards,

    Sheldon

  • Hi @SheldonI !

    First of all I would like to thank you for your answer.

    Maybe I did not explain correctly the case. I'm already modelling just 1 tube not 2, in a 2D analysis (so it's a surface with the section of the tube) and what I want is to model it as a Generaliced Plain Strain. (I upload an image to more clarity of the case and conditions of the tube)

    Regards, Eugenio.

  • Hi Eugenio,

    Thanks for your response.

    For the case you describe, you would model the cross-section of the tube on the XY plane. While the "Generalized Plane Strain" object under the analysis branch defines the boundary conditions/loads in the z-direction, you would need to provide constraints in the XY plane to prevent rigid-body motion. Thus, the bottom seems to be constrained in Y (and possibly X) according to your diagram - it may still rotate in the XY plane, so you would need an additional boundary condition to prevent the rotation. Using Remote Displacement generally is an overconstraint to such a problem, which would explain your non-uniform thermal strains/thermal expansion.

    Regards,

    Sheldon

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