Direct Calculation Research On Tank And Support Structures Of Independent Type C Tanks

When the ship is sailing in the sea,the static and dynamic loads acting on the independent type C tank transfers to the hull only through two saddles,interactions in saddle area will bring high nonlinear characteristics to FEM research.Key problems such as the model range,wood simulation method and contact treatment scheme in saddle area in direct calculation of independent type C tanks are not explicitly stipulated in IGC rules and the regulations of each classification societies,above issues are studied with examples in this thesis,the main contents are listed as follows:1)Various kinds of loads stipulated by IGC code in direct calculation of independent type C tanks are analyzed one by one,and those not specified by IGC code are specified referring to DNV rules.2)Woods are simulated with beam elements and solid elements separately,schemes conducted by beam elements simulation method and solid elements simulation method are compared with examples.For solid elements simulation method,different contact defining methods are adopted in different contact area according to the structural features of saddle area,aiming to reasonably simulate the nonlinear mechanical property and deformation feature of this area.Loads in same typical load cases are applied in the two schemes,and the stress level of all structures and woods' compressive stress of the results of two schemes are both contrasted,the superiority of solid elements simulation method was proved.3)Based on contact algorithm,direct calculation and analysis of tank at typical load cases are conducted.Firstly,the rationality of the contact settings in the model are validated at low temperature load condition,and then to 0 °~30 ° heeling condition,the most dangerous heeling load case is selected and the influence of low temperature to the strength of tank is analyzed further;then the finite element calculation processes in sloshing load case,collision load case,flooding load case and lifting load case are expounded in turn,stress levels of critical areas in all load cases are given,and the deformation characteristics are analyzed.4)Based on the difference of model range,two kinds of finite element methods of independent type C tanks were introduced: “Tank+ Wood” modeling method and “Tank+ Wood+ Hull” modeling method.The influence of the hull girder deformation under extreme load case on tank strength were analyzed numerically through an actual calculation and it was shown that the hull girder deformation had a certain influence on tank strength,but tank strength depended basically on the local loads;the boundary effects on stresses results of tank structures in saddle area could be eliminated if ship structures were considered in calculation model,and the stress level of this area was 3.7%~16.5% lower than the method ignoring the influence of ship structures.At last,based on the “Tank+ Wood+ Hull” modeling method,strength of supporting structures in saddle area are analyzed according to CCS rules.The quantitative calculation results and the analysis conclusions in this thesis can be used for reference to choose an appropriate tank modeling and analysis scheme in engineering practices.