A static analysis (ANTYPE,STATIC) is performed for the fluid-penetration simulation.

The gaps (between the o-ring and the shaft, the o-ring and the cap, and the cap and lower part of the groove) are closed after the first load step, so the fluid does not initially penetrate into those contacting regions. The fluid gradually opens the contact and penetrates into those regions with increasing pressure loading. Since a default value of zero for the pressure penetration criterion (PPCN input via the real constant command R) is used, the fluid pressure penetration occurs immediately as soon as the contact is open or lost.

The entire system is very unstable during the second load step. The seals are pushed up due to the fluid pressure. Rigid body motion may occur when the frictional stresses are not large enough to hold the seals vertically. Convergence difficulty due to an unstable problem is usually the result of a large displacement for smaller load increments. To overcome the instability, the nonlinear stabilization capability (STABILIZE command) is used in the second load step, as follows:

STABILIZE, CONSTANT,ENERGY,0.01,ANYTIME