Study On Structural Optimization Design Of Aft Structural Arrangement For Very Large Crude Carrier

Hull light weight is one of the important factors affecting the ship’s economic index.It is necessary to carry out the lightweight design to decrease the steel weight of hullstructures. By far, optimization designs for hull structures are mainly concentrated onsizing optimization of the midship section, grillages, bulkheads etc, but less study on thearrangement optimization design. In this paper, based on the structural characteristics ofvery large crude carriers (VLCC), a new design concept of stepped structuralarrangement for aft parts is discussed. By the analysis of dynamic characteristics, theeffect of aft stepped structural arrangement is studied. The main contents and conclusionsare as follows:(1) Aft stepped structural arrangement for VLCC: In this paper, based on thecharacteristics of VLCC aft structure, a new stepped structural arrangement concept isproposed. Taking a320000DWT VLCC as the study object, two options of aft steppedstructure were designed and compared briefly.(2) Whole ship vibration modal calculation and analysis: The1D hull girder FEmodel and the mixed FE model of whole VLCC were established. The modal analyses ofthe original design and two design proposals are carried out. The effects of aft steppedstructural arrangement on the global natural modal are studied.(3) Prediction of the vibration response of aft structure and superstructure: Thevibration response of the aft structure and superstructure of the original design and twostepped design proposals are carried out with the exciting force induced by the propeller.The effects on the hull vibration characteristics of the two design proposals are comparedand discussed. (4) Comparative study of ship hull vibration evaluation criteria: Two versions of theinternational standards ISO6954(1984version and2000version) for ship hull vibrationevaluation are overviewed and compared. The aft structure and superstructure vibrationresponse of VLCC (two design proposals) was evaluated using the two versions of ISO6954respectively. Finally, how to use this two vibration evaluation standards aresummarized.