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Viscous Damping Loads

Theory

At each solution step, viscous damping loads are computed from a matrix of damping coefficients and the relative fluid-structure velocity:

               (3)

where Fd  is the vector of viscous damping forces and moments for all degrees of freedom, CA is the matrix of specified Viscous Damping Coefficients, ρ is the density of seawater, and ν  is the vector of relative fluid-structure velocity.

For the purpose of the damping force computation, the structure velocity is taken at the location of the floating body CoG, while the fluid velocity is computed at a horizontal location corresponding to the location of the floating body CoG and at an elevation corresponding to the Mean Water Line (MWL). An option is also provided to use either the relative fluid/structure velocity or the absolute structure velocity in the computations.

The damping force also includes coupled terms corresponding to the off-diagonal entries of the 6x6 drag coefficient matrix. In this way, it is possible to fully account for the effect of coupling between viscous damping loading and structure response in different degrees of freedom. The resulting forces and moments are applied to the floating body at the centre of drag.

Relevant Keywords

•*VISCOUS DRAG is used to define viscous drag for a floating body.