Stabilization
Membranes rely on the stress-stiffening effect to be stable. This implies that membranes are unstable when not prestressed with in-plane loads. There are nonetheless many situations in which the value of the prestress is unknown, and a preliminary loading analysis is performed to find it. Add a Stabilization node to include fictitious stabilizing forces during the initial loading steps, when the load associated to the prestress is close to zero.
quasistatic stabilization
The stabilization works by connecting spring foundations for the geometric entities included in the selection. COMSOL Multiphysics makes an estimation of the spring stiffness kchar required to stabilize the problem. If this estimate of the stiffness is too small or too large, enter a new value for the Stiffness multiplier fstb.
It is essential that the stabilization force are relaxed once the membrane load is sufficiently high to make the problem non singular and the stress-stiffening effect is established. Select a Method — Automatic or Manual, for how to relax the stabilization forces.
For the Manual method, select Active for — First iteration, First step, Specified number of steps, or User-defined condition, to control how the stabilization forces are relaxed.
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First iteration applies the stabilization forces for the first iteration of the nonlinear solver only.
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First step applies the stabilization forces for the first parameter step or time step. Enable Iteration relaxation to relax the spring stiffness with each iteration of the nonlinear solver.
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For Specified number of steps, enter the number of parameter steps or time steps for which the stabilization forces are active. By enabling the Step relaxation, the spring stiffness is reduced with each step number. If Iteration relaxation is enabled, the spring stiffness is relaxed with each nonlinear iteration of the final specified step number.
For User-defined condition, enter a Boolean expression. The stabilization forces are active when the Boolean expression is evaluated to true. This option can be useful to control the activation based on a specific parameter value in a continuation sweep, or at a specific time in a time-dependent analysis.
To monitor the stabilization energy added, add a Global Variable Probe of the variable <phys>.<stabilization_feature>.Wstb, and output probe values while solving in the Fully Coupled or Segregated solver. This setting allows to track how the stabilization scheme relaxes with the nonlinear iterations.
Location in User Interface
Context Menus
Membrane > More > Stabilization
Ribbon
Physics tab with Membrane selected:
Boundary > More > Stabilization