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Research on the Probabilistic Prediction Method of Ship Bottom Slamming

Author: SiHaiLong
Tutor: ChenZhen
School: Shanghai Jiaotong University
Course: Naval Architecture and Ocean Engineering
Keywords: predicting method wave slope angle the velocity of entering water slamming coefficient extreme pressure
CLC: U661
Type: Master's thesis
Year: 2012
Downloads: 46
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Abstract

Bottom slamming always occurs when the ship is sailing in the severe wave. Severe slamming can cause structure damage, even losing of the ship’s total longitudinal strength. In addition, slamming also is the main reason for ship operators to reduce speed or to change heading. So, predicting the characteristic of bottom slamming with a reasonable and accurate method has a great significance on the ship’s design and navigation.This paper mainly does some research on the method of predicting slamming pressure. Based on the predicting method proposed by Ochi, this paper takes account of the effect of the velocity of ship entering into water and the wave slope angle on the coefficient and develops a method which could directly predict slamming pressure. This method mainly consists of three sections. Firstly, taking account of the non-linear relationship between ship and wave, this paper calculates the motion response of ship with Rankine panel method in time domain and three-dimensional condition. The number of slamming and the probability density function of relative velocity between ship and wave at the instant of impact is obtained based on the requirement of slamming. Secondly, this paper calculates the slamming coefficient with three-dimensional finite element method when the ship enter wave surface which have different slope angle with different velocity. Thirdly, the characteristic of slamming pressure is predicted by Monte Carlo method based on the above result, then, the exceeding probability of extreme value is calculated through fitting the pressure with Weibull distribution.The procedure of this method is elaborated through predicting a sample ship’s slamming characteristic and some significant conclusion are obtained.(1) Owing to the non-linear relationship between ship and wave, both the number of slamming and the relative velocity between ship and wave at the instant impact have a great difference between the theory forecast results and statistical results. The probability density function of relative velocity must be corrected and make sure it is close to the statistical results when it is used to predict the characteristic of slamming. What’s more, draft of ship and wave heading has a great influence on the number of slamming.(2) The coefficient of slamming is not a constant which only have a direct relationship with shape of ship’s section. The study shows that both the velocity of ship entering water and the wave’s slope angle has a great effect on the slamming coefficient. When the ship contact water at peak or trough of wave, the coefficient is higher than others. The relative velocity almost has no effect on the coefficient if the wave slope angle is big. On the contrary, when the wave slope is small, the relative velocity has a great different influence on the coefficient between different forecast points.(3) The magnitude of the slamming pressure is random. The probability exceeding of extreme pressure rapidly ascend with the increase of time at the first ten hours. But the growth tends to be ease.

Research on the Probabilistic Prediction Method of Ship Bottom Slamming

Abstract

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