Viscous pressure

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:

p = - c_{v} (\bar{v} \cdot \bar{n}),

where

p

is the pressure applied to the body;

c_{v}

is the coefficient of viscosity, given on the data line as the magnitude of the load;

\bar{v}

is the velocity vector of the point on the surface where the viscous pressure is being applied; and

\bar{n}

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,

c_{v}

is set equal to a small percentage—perhaps 1 or 2 percent—of the quantity

ρ c_{d}

as an effective way of minimizing ongoing dynamic effects.