Fundamental Study On The Fatigue Strength Of Common Structure Rules For Container Vessel

Since the implementation of IACS Common Structure Rules (CSR) for oil tankers andbulk carriers, there is an increasing interest in developing CSR for container ships.The IACS is currently working on comparative studies and calculation for harmonizationof these two CSRs, in order to finally harmonize contradictory parts in the two rules,especially the part that relates to hull structure fatigue strength, for which design loads andSN curves are completely different. Meanwhile, IMO spares no effort in staging its GoalBased Standards (GBS), so as to carry out compliance verification of rules of all classsocieties. Compliance verification of the CSR for oil tankers just kicked off. It isforeseeable that the potential CSR for container ships have to fulfill the requirements ofGBS. For this purpose, rules systems should be analytical and consistent in loads, fatiguestresses and assessment criteria. Considering the current disparity of competence amongclass societies, the CSR for container ships should consist of rule check and direct strengthanalysis.Subsequent to the Super-rule research on Large Ship Structures and aim to develop CSRfor container vessel, this thesis focuses on the research of the following issues:(1) forecast of the development trends of container ship structural rules for fatiguestrength and of relevant key issues to be solved on the basis of the research on thedevelopment trends of hull structural rules of class societies and in combination withupdated IMO and IACS works;(2) summarization of domestic and oversea research methods on ship structure fatiguestrength and of research progress on container ship fatigue strength;(3) case study of hull structural damage for container ships;(4) on the basis of numerical calculation of equivalent design waves and for the analyticalpurpose, establishment of a solution system for overall fatigue stresses for largecontainer ships and determination of a range of permissible fatigue stressescorresponding to duel linear SN curves, in order to achieve consistency of loads,stresses and relevant standards; (5) a qualitative analysis of form of wave torsional moment for container ships based onequivalent design waves and through numerical calculation of wave loads, and, on thebasis of the analysis, a systematic comparison of overall formulae for wave torsionalmoment given by individual class societies, in order to find a recommendatory formulafor calculating container ship wave torsional moment. This formula is to take accountof quarter head seas and quarter following seas and to be verified by direct loadcalculation program, so as to provide a criterion and model for IACS harmonizationstudy on wave loads;(6) scientific categorization of typical details of container ship hull structures foranalysis of fatigue damage characteristics. For this purpose, a tool for fine analysis oftypical details is to be developed, which can allow a more accurate and efficientfatigue analysis of the typical details for most of the ships;(7) research on anti-fatigue design for typical details of container ships; and(8) exploration of, based on field examination of hull structure fatigue damage andnumerical calculation, the impacts of building tolerances and weld specifications onfatigue strength of typical details for hull structures, which may be very helpful for thedevelopment and revision of relevant rules.The following conclusions are made through the research:(1) With First Principle as the guiding principle and based on equivalent design waves, asolution system for overall fatigue stresses on large container ships is established andhence the consistency of loads, stresses and standards is achieved. Feasibility of thissystem has been verified through project case study;(2) A tabulated range of permissible fatigue stresses is derived based on linear cumulativedamage and by taking account of dual linear SN curves;(3) A qualitative analysis of wave torsional moment for container ships, based onequivalent design waves and numerical calculation of wave loads, has been carried outand the wave torsional moment is found to be of dual peak type. On the basis of thisanalysis, a systematic comparison of overall formulae for wave torsional moment fromindividual class societies has been performed, which gives rise to a recommendatoryformula for calculating container ship wave torsional moment. Quarter head seas andquarter following seas are considered in this formula, and it has been verified bymeans of direct load calculation program, therefore may serve as a criterion and model for IACS harmonization study on wave loads;(4) The typical details of container ship hull structures are categorized. A tool for fineanalysis of typical details of hull structures is developed on the basis of PCL languageof MSC/PATRAN, which is capable of fatigue analysis of typical structural details ofmost of the ships. This tool may help to increase accuracy and efficiency of analysisand yield good economic returns;(5) Container vessel longitudinal end connections, hold hatch corners and knuckles arecompared, calculated and analyzed, and tabulated anti-fatigue designs for key detailsof container ships are developed for the CSR for container ships;(6) The impacts of building tolerances and weld specifications on fatigue strength oftypical details of hull structures have been explored on the basis of numericalcalculation and have been verified through project cases. Meanwhile, research hasbeen carried out on the relationship between weld surface geometry parameters andstress concentration, which has proved the impacts of weld profile and grinding onfatigue life of hull structures. All the above is very helpful for the development of CSRrules for container vessel.