Fatigue Analysis For Complex Structural Details Of Very Large Ore Carrier

With the support of domestic steel industry,China’s economic strength are improving steadly and manufacturing industry are developing rapidly,which led to the continuous growth of import demand for ore resources.The flourish of international ore import and export trade increases shipping industry’s demand for Very Large Ore Carrier(VLOC)a lot.Chinese shipping industry has been actively participating in this fierce market competition with the desire of dividing a large piece of cake.Therefore it’s practically significant to study this emerging special type of vessel.Fatigue failure is one of the most important failure modes of ship structure.The structure of super-large-size ore carrier is facing more serious fatigue problems than normal-sized ships,due to the widely use of high strength steel and the accompanying reduction of thickness.Although it could reduce light weight.Ore carrier is a special kind of bulk cargo ship,while analyse fatigue life structure of VLOC in practical engineering projects,fatigue rules for bulk carriers are usually referred to.However,there are obvious differences between VLOC and bulk carrier in terms of structure configuration,loading conditions and ship route planning.The fatigue assessment methods should not be directly moved from the analysis requirements for ordinary bulk carriers.Special consideration should be given to the actual ships.In this paper,firstly the characteristics of VLOC are outlined from the aspects of ship form,loading mode and ship route.From the point of ship design and structural optimization,load research,finite element analysis as well as fatigue strength evaluation of VLOC at home and abroad,present research in china and abroad are summarized,in addition,key technical problems during the fatigue evaluation of complex joints of ore vessels that need to be studied are made clear.The flow path of fatige strength analysis by means of finite element method(FEM)for bulk carriers in two different evaluation system are combed in this paper.They are Fatigue Strength Guideline for Ship Hull developed by China Classification Society(CCS Guideline),and Common Structural Rules for Bulk Carriers and Oil Tankers(CSR-H).On this basis,fatigue load,FE model,hot spot stress interpolation and synthesis methods,along with hot-spot stress correction fatigue life calculation methods and other requirements,of the two codes are compared in detail.Based on the overall requirements of fatigue assessment for bulk carriers in CCS Guideline,considering the features of structure and loading modes of VLOC,a fatigue strength evaluation method avalible for complex joints is established.In consideration of the particular ballast condition of ore carriers,the loading condition called “maximum ballast” are suggested during fatigue evaluation.Ship motion parameters and time distribution coefficient of the selected loading conditions are recommended.Based on the statistical analysis of the loading manual,recommended values of the hydrostatic bending moment reduction coefficient for ore carriers are given.Through the calculation of a 200 k,300k and 400 k DWT ore carrier,the critical fatigue assessment locations of VLOC are screened,and some patterns of fatigue life of VLOC’s structure details are summarized.On the basis of requirements for bulk carriers in CSR-H,fatigue strength of typical complex joints of three types of VLOCs has been evaluated.The results are compared with those from the improved evaluation method proposed in this paper.Fatigue life calculated from two mathods is roughly the same and the safety level is basically the same.Thus improved fatigue analysis method recommended by this paper for VLOCs are verified reasonable.Based on the improved method proposed in this thesis,incorporating with the loading characteristics of VLOCs,the calculation method of fatigue loads are studied in this paper,which takes the multi-port loading mode and ore liquefaction effect into account.Through the analysis of three types of VLOCs,influence of multiport loading as well as ore liquefaction on the fatigue life of typical joints are quantified.This study may provide guidance for fatigue strength evaluation of complex structural details of VLOCs.The results of three VLOCs provided,Studies in this paper that concerns the characteristics of VLOC,the selection of evaluation conditions and the recommended values of the parameters could be reffered in ship design,fatigue evaluation and other related research of VLOC.The research approach and result analysis method adopted in this paper could be exercisable in the research upon other superlarge ships.