Discussion Forum

Hi Everyone,

I'm fairly new to COMSOL, been using it for a month or so now and feel as though I have gotten a decent grasp on most of the basic COMSOL features. That being said, I'd love to get some input on my problem from some of the more experienced users here.

I am attempting to create a 3D model of a curved artery and analyze the circumferential stresses at various internal pressures. I modeled the curved tube as a hollow torus with a certain wall thickness, and am using the hyperelastic module. I have defined my own strain energy function, dependent on the direction of four types of fibers. In a straight tube, this is simple to deal with, as I define my fiber directions relative to cylindrical coordinates and then easily find the circumferential stresses in the post processing.

In the curved tube model, I have used curvilinear coordinates to define a new coordinate system that is similar to cylindrical but the z axis follows the curve of the tube. I successfully completed this, verified by a 3D plot with the Coordinate System Volume, with the Z coordinate following through the center of the torus, R pointing outwards and PHI is orthogonal.

So far all is good. However, when I attempt to use this coordinate system in the hyperelastic module, my model fails to solve. If I use cartesian coordinates under the hyperelastic module and instead use the curvilinear coordinate system to transform the direction of my fibers, my model solves correctly, but I cannot view the circumferential stress in post processing.

Does anyone have any ideas? Can curvilinear components be used in a deforming geometry? I haven't found any good explanations on how curvilinear coordinates work. I can attach my model if this explanation isn't good enough.

Thanks,
Dillon

EDIT: Figured out a way to solve in cartesian and convert into circumferential wrt my coordinate system in post processing. If anyone has any ideas on why i was having the problem i'd still like to learn why it asn't working, but I have managed to achieve what i was looking for.