Selection Of Structural Factors And Research On Calculating Method Of Ship Ultimate Strength Reliability Analysis

Compared to normal ship, large ship is longer, bigger and faster. Because of the expansion of war area, large ship will suffer badly conditions inevitably. The longitudinal bending moment of large ship is directly proportional to the length of large ship. That is to say the longer a large ship is, the more longitudinal bending moment it will suffer. However, the calculating method of large ship's ultimate strength is mainly based on deterministic method, which does not fit for reality, and its precision is not good enough as well. As the development of large ship reliability theory, the ultimate strength reliability of large ship is needed to be researched further. The article conducts research about this problem.Firstly, the article conducts researches on the influence factors of ultimate strength of large ship. Select Young's modulus, Yield stress, thickness of plate, thickness of stiffeners, initial deflection and Welding residual stress to be the influence factors of ultimate strength, analysis each factor's influences to ultimate strength. According to drawbacks of the initial deflection's adding method, the article is proposed a approximate analytical formulas based on direct adding method. In order to reduce the dimension of calculating reliability, the article conducts sensitivity analysis of influence factors, making sure that the thickness of plate, the thickness of stiffeners and yield stress are considered to be random variables, Young's modulus can be selected to be random variables, initial deflection and residual stress are considered to be constant. According to some published articles to find out the distribution type, mean and COV of these random variables. At last, do research about the influences of the random variables to ultimate strength.The article do research on the calculating method of ultimate strength. In the ultimate strength reliability analysis, the ultimate strength is a random variables, as well as these influence factors. The article compares Joint Probability Density Method, Monte-Carlo Method, Taylor Method and Rosenbluthe Method and analysis each method's advantages and disadvantages. Finally select Rosenbluthe Method to calculate ultimate strength of large ship, and then using an example to determine its feasibility.The article de research on the reliability method. According to applicability, the author select FORM Method, SORM Method, Monte-Carlo Method and AIS Method. Firstly simply introduce these methods and then according to an example to compare each methods. The result indicates that AIS2 is a method which has good precision and efficiency. And so it is considered to be chosen to be the method to calculate the ultimate strength of large ship.According to all the results got above and combining former work, write a guidebook of how to calculate the ultimate strength of large ship by using simple words to introduce all the methods and steps to solve out the ultimate strength. And it can be used by some researchers to refer to.