STRIP THEORY HYDRODYNAMICS

In this section, we compare the RAOs of a barge from a study conducted by Noble Denton and Associates Ltd (BMRP, 1978) and those computed by MOSES using strip theory. The model that is studied is a deck barge with a KG of 32 ft, whose geometry is depicted in Figure 20.

Figure 20: Barge Particulars

The Noble Denton report consisted of RAO curves with an average of 5 data points per degree of freedom. The data points were obtained from measurements of a 1:30 scale model that was tested in regular waves for head and beam seas. Surge and heave motions were recorded for head seas, and sway, heave, and roll motions were recorded for beam seas.

The RAO comparisons of the MOSES and Noble Denton model results are shown in Figures 21 to 26. The points recorded by Noble Denton are indicated in each plot by circles.

The MOSES curves were calculated with a wave steepness of 1/20. As seen from these figures, most of the computed RAOs compare quite well with those from the model tests. The only exception is the roll RAOs, in which case the computed results deviate from the test results near resonance. This is due to nonlinear roll damping, which causes the response near resonance to be greatly affected by the wave steepness.

To address this nonlinearity, roll response curves were calculated for a range of wave steepnesses. These results are shown in Figure 26. In this figure, the MOSES results are shown with wave steepness decreasing from 1/133 to 1/33. These wave steepnesses were chosen in order to correspond with those steepnesses tested by Noble Denton. The graph shows an agreement between test measurements and MOSES results.

Figure 21: Comparison of Surge RAO in Head Seas

Figure 26: Comparison of Roll RAO in Beam Seas