Learning Forum

[peteroznewman]

The key to understanding why this model consistently fails to converge at 58% of the pressure load is to observe the slope of the total deformation plot. Look at the last few converged points. The slope is getting steeper and steeper and is approaching a vertical asymptote.

The solution logic applies increments of pressure and solves for the displacement (deformation) of the nodes that create static equilibrium between the internal stress and the applied load. In this model, looking at the slope of the total defromation plot, you should expect the next increment of pressure will require an infinite total deformation. In other words, the structure is approaching an instability where there is no static equilibrium solution for the next increment of pressure.  To resolve this problem, either turn on Stabilization under the Analysis settings or change the analysis to Transient Structural. In a transient solution, the structure is not required to be in static equilibrium at each time step, it can accelerate elements that are out of balance with the applied forces and internal stresses and find dynamic equilibrium at each time step.

An example which is easy to understand is a hyperelastic dome. As the pressure is applied to the convex top side of the dome, it deforms downward, but at some point, it wants to snap through and the top side becomes concave. A Static Structural solution will fail to get the dome to the concave state without turning on Stablization or changing the analysis to Transient Structural.