Viscous pressure loads are commonly used in structural problems and quasi-static problems to damp out the low-frequency dynamic effects, thus allowing static equilibrium to be reached in a minimal number of increments. These loads are applied as distributed loads defined by the following formula:
where is the pressure applied to the body; is the viscosity, given on the data line as the magnitude of the load; is the velocity vector of the point on the surface where the viscous pressure is being applied; and is the unit outward normal vector to the surface at the same point. For typical structural problems it is not desirable to absorb all of the energy. Typically, is set equal to a small percentage—perhaps 1 or 2 percent—of the quantity as an effective way of minimizing ongoing dynamic effects.