All Morison force components are calculated at each time step, including the effects of variation of immersion as the analysis proceeds.

Optionally, the slamming force on tube can be included.

The value of the slamming force, for each element, is based on the premise that the slamming force and moment are equal to the rate of change of the added mass matrix (with time) multiplied by the velocity:

(6–21)

where is the user defined slamming multiplying factor, is the added mass matrix of tube, and is the structural velocity vector of a tube in the tube local axis frame defined in Equation 6–7.

This means that the time step must be sufficiently small to accurately represent the added mass at each stage of immersion and emergence. In general this will depend on the geometry of each element and its orientation to the water surface. In practice, this severe restriction of the size of the time step means that this option is only used when specifically investigating the effects of slam forces on individual elements during critical stages of the simulation period, as the momentum changes due to slamming forces are normally small and have little effect on the overall motion of the structure.

In Aqwa-Drift, the incident wave properties at a specified location (X, Y, Z₀) on the Morison element beneath the instantaneous incident wave surface are calculated at the relative vertical position at (X, Y, Z), in which

(6–22)

In Aqwa-Naut, the extended Wheeler stretching method is employed. See Extended Wheeler Stretching Method for more information.