旅客船运行时波浪形态的试验研究英文文献和中文翻译(4)
Risk factors Limits of risk levels Low Moderate High Deformation of the chute [% of chute length] < 25% 25-50% > 50% Maximum roll angle of the boarding plat-form and/or life rafts <20 deg 20-40 deg >40 deg A further discussion of these results and the significance of the results on the evacuation situation is presented below. The resulting wave climate close to a ship ex-posed to an incident wave with a wave length of 245 meters (angular velocity 0.5 rad/s) can be seen in Fig. 7. In this case the incident wave amplitude was ≈ 1.2 m in full scale and the ship was free to drift. The graphs in this figure show the recordings from all meters in Fig. 4 except the incident wave. It can be seen that a propagat-ing wave appears on the windward side and that the absolute amplitudes are approximately the same as the incident wave amplitude. It is also evident that the abso-lute amplitudes are the same on the windward and lee-ward sides. This is due to the fact that for this incident wave system the radiating waves from the ship are small and that no significant reflection occurs. The relative amplitudes on the windward and leeward side are of the same magnitude and they are as high as the absolute amplitudes. It is also apparent that the relative ampli-tudes are of the same magnitude fore and aft as well as amidships. In the perspective of the wave system the windward and leeward side would present similar envi-ronments for launching evacuating equipment for this incident wave situation. When the incident wavelengths are shorter the situation is different. Fig. 8 shows the amplitudes when the inci-dent wave was approximately 60 m (angular velocity 1 rad/s) and the amplitude was 0.6 meters. First it can be noted that a standing wave occurs on the windward side. This implies that the wave amplitudes can be very high at a certain distance from the ship and zero at another distance from the ship. On the leeward side the ampli-tudes are significantly lower since a large portion of the incident wave is reflected on the windward side. Due to the ships motions the relative amplitudes are higher than the absolute wave on the leeward side, but are lower compared to the windward side since the absolute wave amplitudes are higher on this side. On the windward side it is also evident that the relative amplitude amid-ships are higher than fore and aft which would imply that the situation is less severe fore and aft compared to amidships. For these shorter waves it is, from the perspective of the wave climate, more favorable to Fi Filaunch evacuating equipment on the leeward side. The appearance of the wave i.e. the smoothness of the waves has also been analyzed in this paper. The situa-tions where the ship was able to drift and the case when the ship drifted with an extra drift force to resemble wind were believed to produce a wake on the windward side and possibly present a better wave appearance on this side compared to when the ship wasn’t free to drift. The incident waves were regular. A valuable tool to examine this situation is Fourier analysis. It was also investigated if an additional frequency could be ob-served in the resulting wave system due to the soft-mooring. The Fourier analyses revealed that the result-ing absolute and relative wave systems only contain one frequency (corresponding to the incident wave) thus implying that the influence of the soft-mooring, drift and additional drift forces didn’t contribute to the waves appearance for the regular waves used in this paper. This also means that the resulting waves remained within linear potential theory, thus indicating that the wake on the windward side for the drift scenarios pro-vided no significant influence on the wave appearance. Since the three scenarios produced the same amplitudes and wave appearance for incident waves within linear theory it can be concluded that for this kind of wave examinations a soft-mooring test setup is sufficient. Results of the Lifeboat Tests The risks the passengers are exposed to when using the lifeboat system is presented in this section. It is com-monly known that the tested lifeboat/davit system only fulfils its functions during gentle weather conditions. The tests performed in the present study show that for waves with a wave height of 1m (amplitude 0.5 m) the risk correspond to the risk in still weather. The tests also show that in higher waves the risk increases. Fig. 9 shows the influence of wave and davit parameters on the risk of evacuation together with an explanation of symbols. Each circle in the diagram represents the risk level for one test as described in the section Evaluation of risk. The risks connected to lifeboat launching depend on different factors for waves with different periods. The roll motion of the "mother" ship is small in the shorter waves (a period of 5 sec, an angular velocity of 1.3 rad/s).