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2.3 Wave Forces and Moments
About wave forces, we considered only Froude-Krylov forces here, because dangerous situation concerning to the rolling motion occurs mostly in resonance frequency or relatively long wave period. This means that the diffraction effects are small and so the Froude-Krylov forces and moments become dominant. From equation (7) to (12), expressions of Froude-Krylov forces and moments are shown.
We took into account the detailed three-dimensional form of hull surface including the hull form above the water line to estimate the accurate nonlinear rolling moment and surging force caused by the pressure distribution under the assumption by Froude-Krylov. Fig.2 shows the hull surface model which is used in this study. It consists of 18,464 triangle panels.
Fig.2 |
Hull surface model expressed by triangle panels |
3. SAMPLE SHIP FOR INVESTIGATION
In the Table 2, the principal dimensions of the sample ship for this time investigation are shown in actual ship scale. Displaced volume is about 175m3.
Furthermore, in Fig.3, body plan and photograph of the model are shown with upper deck but without bridge. The scale is in actual ship scale, but the model scale is 1/23, namely Lpp is 1m. This model was already used for the experiments described in the paper by Hirayama, Nishimura and Fnkushima [3].
Table 2 Principal dimensions
| LPP (m) |
23.00 |
| B (m) |
5.90 |
| D (m) |
2.15 |
| Draft(mean) (m) |
1.92 |
| Volume (m3) |
174.46 |
| KG (m) |
1.92 |
| GM (m) |
1.30 |
| Midship-G(+:fore) |
-0.96 |
| Kxx/B (gyradius of
roll/B) |
0.497 |
| Kyy/LPP
(gyradius of pitch/LPP) |
0.250 |
| Kzz/LPP
(gyradius of yaw/LPP) |
0.250 |
|
Fig.3 Figure of the considered ship
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