Normal contact

The Normal contact tab governs behaviour perpendicular to the contact surfaces: how much the two bodies may penetrate one another, and whether they may come apart again.

Field	Choices	Meaning
Mechanical contact	Penalty	The method used to enforce the contact constraint
Separation	yes, no	Whether the surfaces may come apart once in contact
Penalty definition	Stiffness factor, Constant	How the penalty stiffness is given
Value		The stiffness factor, or the constant stiffness
Non-constant	yes, no	Whether the stiffness varies during the calculation
Adhesion	yes, no	Whether the surfaces resist being pulled apart
Adhesion value		Shown when adhesion is activated

Separation is the choice that most often needs thought. Set it to no for surfaces that stay in contact throughout — a pile cast against soil — and to yes where a gap may open, such as behind a wall that deflects away from the soil.

Penalty definition decides how the Value is read. With Stiffness factor it is a multiplier, and with Constant it is a stiffness in its own right.

Validation

A value is required when a penalty definition is selected, and an adhesion value is required when adhesion is activated. Pressing Apply & Save with one missing shows a warning naming it.

See Interaction in the numgeo reference manual.