Ultimate Strength Analysis Of The Ship Hull Under Combined Load

Different from the traditional structural longitudinal strength check methodbased on linear elastic theory, ultimate strength can evaluate the strength reserve ofthe hull structure more accurately, considering the local component failure and theinfluence of material and geometrical nonlinearity. So ultimate strength provides away to improve the utilization rate of material of the ship on the basis of the safetyand reliability of the structure.The existing studies on ultimate strength of the hull structure are basicallyfocused on pure bending or pure torsional strength calculation, without consideringother load acting on the hull structure. But in the process of sailing, the hull structureis subject to several kinds of external load at the same time, such as bending moment,torque, cargo load, hydrostatic pressure, hydrodynamic pressure and other externalload. The external load will affect the ultimate strength of the hull inevitably. So it isnecessary to study the ultimate strength of the hull under combined load. For thispurpose, on the basis of considering the influence factors such as the initialgeometrical imperfections, boundary conditions and the type and size of the finiteelement, this paper mainly finished the following work by using the nonlinear finiteelement method:1) Review the development of the study of the ultimate strength of the hullstructures. Several methods to research the ultimate strength are introduced, and thetheory of nonlinear finite element method is explained in detail.2) Six failure modes of stiffened plate structure are introduced. Taking thestiffened plate of a river-to-sea ship hull bottom as the research object, the ultimatestrength of the stiffened plate structure under combined load is studied in this paper.Furthermore, the impact of different types of load on the ultimate strength isdiscussed.3) The ultimate strength of a classic box girder model under pure bending iscalculated. Compared the calculated result with the experimental result, this paperverified the reliability of nonlinear finite element method to solve the ultimatestrength of ship structure. 4) Ultimate strength under combined load of bending moment, torque andexternal water pressure is studied to the same classic box beam model. The resultsproved the influence of external water pressure on the ultimate strength of structure,and a fitting formula which describes the relationship between ultimate bendingmoment and ultimate torque is obtained.5) Taking the compartment model of a river-to-sea ship as the research object,the ultimate strength under combined load is studied. The load combination isdetermined by different loading and sailing conditions. Furthermore, this paper putforward a more accurate calculation method to assess the strength reserve of the shiphull.