Discussion Forum

Hi all,

I am a new comsol user, and am getting started with a very simple solid mechanics modeling problem. Here is the basic setup:

• Rotationally symmetric steel shell with 1.0 m and 0.5 m outer and inner radii respectively. The Young's modulus is 200 GPa, and the Poisson ratio is 0.3.
• The boundary load on the outside boundary is P_1 = 10 Pa.
• The boundary load on the inside boundary is P_2 = 1 Pa.
• Solve for the equilibrium stress tensor and displacements.

I am attaching the .mph file for this problem. This particular problem is analytically solvable. For such a small pressure difference, the displacement of the outer boundary should be tiny. When I solve, I see this is actually the case. One of the attached plots is the calculated displacement along the radial direction. The reported displacement is negligible.

However, when I display the 2D and 3D models of the stress, it looks like the whole model has been compressed by 20 cm in the radial direction (see attached figure). When I set P_1 = P_2 = 0, there is no compression (but also no stress field), however any nonzero pressure difference is giving me these crazy nonphysical distortions of the body.

What am I doing wrong here!