The splitting force and moment of the specified partition of a free-floating structure can be calculated in Aqwa, provided that a hydrodynamic diffraction and radiation analysis has already been carried out.

The mass distribution over the floating structure is required in this calculation. It should be noted that the total mass and the resolved center of gravity based on this mass distribution must be equal to that calculated by the hydrodynamic diffraction and radiation analysis. If this condition is not satisfied, non-zero residual forces may cause erroneous results in the splitting forces.

The specified structure partition is defined within a virtual rectangular box with the lowest vertex and the highest vertex , as shown in Figure 14.3: Structure Partition and Reference Point for Splitting Force Calculation. The edges of this box are aligned with the fixed reference axes. The output splitting force and moment consist of the force and moment acting on the structure partition enclosed by this virtual box . The moment is determined about a reference point defined in the fixed reference axes.

The external hydrodynamic force and moment with respect to the reference point are

(14–13)

where is the wave frequency, is the wetted surface partition of the floating structure enclosed by the virtual box , is the summation of the hydrostatic and total hydrodynamic pressures (consisting of the incident wave, diffraction wave, radiation wave, and the hydrostatic varying pressures), and is the normal vector of the wetted hull surface pointing towards the fluid field.

Figure 14.3: Structure Partition and Reference Point for Splitting Force Calculation

The gravitational force and moment with respect to the reference point are represented as

(14–14)

where is the rotational motion response, and is the structure mass at the location .

The inertia force and moment with respect to the reference point are

(14–15)

where is the motion response at the location .

The summations of all of the corresponding components in Equation 14–13 through Equation 14–15 are the splitting force and moment about the reference point for the specified structure partition shown in Figure 14.3: Structure Partition and Reference Point for Splitting Force Calculation.