Stabilization parameters

The Stabilization parameters tab holds five numerical aids that can be switched on when a calculation is having trouble converging or is producing unphysical results. They are independent of one another, each with its own checkbox, and all are off by default.

These are numerical measures rather than material behaviour. Enable one when there is a reason to, not as a matter of routine, and be aware that each one changes the result to some degree.

Minimum pressure

Puts a lower bound on the pressure, which keeps a soil that would otherwise go into tension from doing so.

Field	Meaning
Value	The lower bound

See Minimum pressure.

Mechanical viscosity

Adds rate dependence as a regularisation, which can steady a calculation that is localising or oscillating.

Field	Meaning
Model	Currently linear
p_min, p_max	The two pressure breakpoints
λ_min, λ_max	Values at the lower and upper breakpoint
μ_min, μ_max	Values at the lower and upper breakpoint

See Mechanical viscosity.

Phantom Elasticity

Adds a small elastic stiffness everywhere, which keeps the system solvable where the constitutive model alone would leave it without stiffness.

Field	Meaning
E	Young's modulus of the added stiffness
ν	Poisson's ratio of the added stiffness

See Phantom elasticity.

Hourglass stiffness

Reduced-integration elements can deform in patterns that cost no energy and so are not resisted. This suppresses them.

Field	Meaning
Method	stiffness or scaling
c^HG	Hourglass control factor
c^fHG	Fluid hourglass control factor, used by the scaling method only

c^fHG is greyed out while the method is stiffness.

This applies to elements set to reduced integration in the Assign element type branch of the data tree; it has no effect on fully integrated elements.

See Hourglass stiffness.

FPL-stabilisation

Fluid-pressure-Laplacian stabilisation, for the pore-pressure oscillations that appear in coupled analyses when the element formulation is not otherwise stabilised.

Field	Meaning
α_fpl	Stabilisation factor

See FPL stabilisation.

Validation

Each feature is checked only when its checkbox is ticked. An enabled feature with an empty field shows a warning naming it when Apply & Save is pressed, and the material stays open so it can be corrected. Switching the feature back off clears the requirement.