Development Of System For Obtaining Average Stress-Strain Relationship Of Stiffened Plates Of Naval Vessel

With the development of large-scale naval vessels and the ship structure design being more and more economical and rational, the problem of the strength of ship structure in extreme load is becoming increasingly important. How to accurately calculating the ultimate longitudinal capacity of ship structure is the key of improving security and vitality of naval vessels. At the present time, it is extensively approbatory and accepted that using Simplified Smith method to calculate the ultimate longitudinal capacity of ship hull. Simplified Smith method is a relative simple and effective method for the calculation of longitudinal strength of ship hull. The main idea of this method is to divide the whole section into many little structural units and the capacity of whole section is equal to the summation of the one of individual structural unit which functions individually. Simplified Smith method utilizes progressive collapse analysis to simulate the collapse behavior of ships and generally considers the effect of material non-linear, geometry non-linear, initial deflections, residual stresses and corrosion, on the basis of which the ultimate strength and post ultimate strength can be obtained. And the key step of using Simplified Smith method to calculate the ultimate longitudinal capacity of ship hull is that getting the average stress–strain relationship of each structure unit, which including post-buckling and post-collapse phases. Most of units in ship section are stiffened plates. The precision of the average stress–strain relationship of stiffened plates not only have effect on the veracity and validity of computation in Simplified Smith method, but also influence the accuracy of the ultimate longitudinal capacity of ship hull. So how to get more accurate average stress–strain relationship of stiffened plates is keystone of this thesis in research. There are mainly two kinds of method to calculate the average stress–strainrelationship of stiffened plates-analytic method and nonlinear FEM (finite element method). For the emphasis of calculation is nonlinear part, though the computing efficiency of analytic method is very high, the precision of analytic method should be tested. And the main means for testing analytic method depends on finite element computation. Although the precision of finite element method is widely accepted, the computing efficiency of nonlinear FEM is too low due to high workload of modeling and general post-processor in computation. In order to improve both precision and computing efficiency, we can choose FEM nonlinear as the base of calculating average stress–strain relationship of stiffened plates and develop efficient and precise computing program system by programming.This thesis detailedly introduce the whole process of nonlinear finite element analysis and computation for stiffened plates, in which an effective method for computing average stress and average strain by computation and comparison is obtained and tested. Then the effect of parameters such as initial deflections, residual stresses and corrosion on the average stress–strain relationship of stiffened plates is respectively taken into account and analyzed. In finite element computation, grid density and load steps have influence on computing precision, which are also analyzed and compared. And the comparison between finite element results by this thesis and others'results is carried out. It has been found that FEM for calculating the average stress–strain relationship of stiffened plates is more accurate and more effective.Finally, based on nonlinear finite element computation and parameter analysis above, a computing program system for calculation of the average stress–strain relationship of stiffened plates has been developed by means of ANSYS parameter programming and Delphi tool, which can perform functions of inputting parameters on the stage and computation by using ANSYS behind the scene. It is more effective to solve the problems of large quantities of stiffened hull pates, computing efficiency about input and output such as modeling and so on, which provide more effective and more accurate computing tool for the longitudinal ultimate strength and engineering design.