Study On Assessment Of Structural Strength For Polar Ships Under Ice Loads

The extent and thickness of Arctic sea ice is gradually reducing,which makes Arctic marine transportation and exploitation for oil, gasand other resources possible. There has been an increasing interest inshipping in ice-covered waters such as the Arctic Ocean due to the effortsin recovering the large deposits of gas and oil in these areas. Arcticdevelopment needs new large ships, which are suitable for navigating inice. The designs of these vessels bring new challenges to owners,designers, operators and regulators due to the lack of relevant experience.The strength issue of structures under ice loads needs much consideration,the integrity and safety of polar vessels navigating in the ice needconsideration during operation process. The problems above of amidbody structure of an Arctic tanker are studied in this paper.The main contents of this paper are listed as follows:1．The background and research of ice load calculation are introduced atfirstly, and the ice load model based on energy balance theory iselaborated.2．The complete process of strength assessment of the hull structure under ice loads is presented. The design ice loads are derived from the iceload model, and the concept of limit load is used to conduct strengthassessment of side shell plating and main frames; then linear bucklinganalyses have been carried out to define the critical buckling loads of sidestringer for confirming its stability.3. The factors of limit loads of structures are analyzed, the relationshipbetween limit load and load patch is investigated, and then a quickmethod of structural strength assessment is determined.4. Plastic deformations of structures corresponding to limit load underice loads are solved using analytical method, and the inadequacies ofanalytical method are analyzed. Meanwhile, limit loads of structuresbased on different limit load criteria are determined using directcalculation method, and the corresponding plastic deformations arecalculated with completely unloading the limit loads. Finally, twiceelastic slope criterion is selected and recommended to determine the limitloads of structures and corresponding allowable permanent deformationwith comparing and analyzing the results of different limit load criteria.