Pipeline Indentation and Collapse

[jimmy66]

Hi,

I am modelling the indenatation and collapse of a subsea pipeline. The hemispherical indenter is modelled as an analytical rigid surface. The pipeline is modelled resting on a perfectly flat seabed which is also analytical rigid.

The displacement of the indenter is moved downwards until it reaches 1/3 of the pipeline diameter before being incrementally retracted in a seperate step. Both these steps work well with no significant warning messages being shown.

The problems arise when i try to initiate collapse of the pipeline by applying an external pressure to the deformed geometry. I am using STATIC, RIKS for this step. As the pressure is applied the pipeline begins to collapse, forming the figure of 8 shape I would expect to see. However, the pipline never reaches the fully collapsed mode, and the collapse process reverses before the pipeline begins to expand across its cross-section. Not what I am expecting!

Can anyone help me out with this step?

My aim is to understand how the collpase pressure changes with varying dent depth.

Many Thanks

 

[mrgoldthorpe]

Have you tried changing the monitoring degree of freedom in your external pressure step? That is, don't use the same dof as you did in indentation.

 

[jimmy66]

Thanks for yoyur reply mrgoldthorpe.

I managed to obtain a solution using a *Dynamic, Implicit step. This shows the pipeline in the collapsed mode I was expecting to see. Now I'm trying to understand why this works as opposed to the *Static, Riks method I was trying to use before.