Discussion Forum

I have to model the thermo mechanical effects on a cable inside an unfilled duct.
The system to be analyzed comprises a long slender cable (typically about 100 mm diameter and 50-100 m length, but longer spans are possible) initially installed straight on bottom of a circular empty duct. The cable is fixed at both ends, and the duct can be assumed rigid.
During operation cable temperature will increase and the cable will therefore be subjected to expansion forces, causing it to move within the duct. By experience the cable loose its straight configuration tending towards a helix as heating and expansion increase. This type of behavior is named “snaking” (see attached image).
The form and extent of movement depend on following parameters:
• Cable stiffness and weight
• Friction with the duct wall
• Duct bore size
Snaking looks to me a problem of mechanical instability induced by thermo mechanical forces, in which lateral movements of the cable are constrained by the duct wall.
In my first approach to model the phenomenon I tried to combine a cylindrical shell element for the duct with a beam for the cable, but this approach doesn’t allow to define contact between the two elements, and also Linear Buckling study is not available for beams.
Modeling with Solid Mechanics interface looks unfeasible to me because of the large length of the system.
Does someone have something to suggest about the possible ways to approach this problem with Comsol?
Also, would it be possible to replace the shell representing the duct wall with a global constrain?
Thanks
Massimo