Direct Method Analysis Of Ultimate Strength For Intact And Damaged Ships

The residual load bearing capacity of damaged ships is an important index of the life-force assessment, and the residual strength is also a main subject for the study of ship collision and grounding. Therefore, it is quite necessary to calculate the damaged ship's residual survival capacity and evaluate the residual ability of the damaged ships.The author uses direct method to derive the theoretical formulas of ultimate strength for intact ships and residual ultimate strength for damaged hulls, then through some examples to compare with other's results, and get some of significant conclusions. In the end, the author evaluates the residual strength and analyzes the sensitivity of the damaged ships. The following subjects are studied in this thesis:Firstly, this thesis goes into the history, development and current situation of the study on the ultimate strength, collision and grounding of hulls, etc.Secondly, based on theoretical analysis, the author derives the formulas of ultimate strength for intact ships, and gives out the theoretical formulas of the initial bending moment, full plastic bending moment, full-plastic-buckling bending moment and elastic-plastic ultimate bending moment of intact hulls.Thirdly, based on the theoretical formulas of the intact hulls, the author analyzes the residual strength of damaged ships which are hogging and sagging under the situation of collision and grounding.And then, using the combination method based on the full-plastic-buckling stress distribution pattern and the elastic-plastic stress distribution pattern, the author calculates the ultimate strength of intact and damaged ships. Through examples of four typical box beams and four actual ships, the author estimates the structural ultimate capacity and compares the calculated results from the two methods with well-known scholars' results. It shows that the results of the thesis are quite well and can be used in practical calculation.Because of the heeling and asymmetric of damaged ships, on the study of the method of determining the elastic and full plastic neutral axis, the author gets the method of calculating the neutral axis of damaged ships and gives out the theoretical formulas of the initial moment and full plastic moment, then derives the formulas of full-plastic-buckling ultimate strength moment in the condition of heeling and asymmetric of damaged ships. Through two examples of actual VLCC, the author estimates the structural ultimate capacity and summarizes the regularity of the calculated results.In the end, based on theoretical analysis and calculation, the author analyzes the influence and sensitivity of yielding stress of the material, thickness of attached plating, size and location of the damage hole, and the heeling angle to the ultimate strength of the model Reckling No.23 and the actual ship Double Hull VLCC.Through the comparisons among the results from many examples of actual ship structures, it verifies that the adopted methods are correct and the obtained results are accurate. To damaged ships in different floating situation, the calculation method, results and conclusion are useful in drawing up the rules and regulations relating ship safety, assessing the residual strength of the damaged ships under the situation of collision and grounding.