The Nonlinear Response Analysis Of Asymmetrical Hull

More and more attention is paid to the safety of damaged ships to reduce the loss of life & property and environmental pollution, so how to effectively predict structural normal survivability and set up a safety assessment approach for the damaged ships is imperative problem. Taken the damaged ship as an object, the nonlinear response including dynamic characteristics, external loads, hull deflection, buckling and ultimate strength of stiffened panels, and ultimate strength of hull is carried out in this paper. The major work is as follows:1) Based on dry hull modal analysis of flexure-torsion coupling vibration of unsymmetrical ship structures about longitudinal centerline, a transfer matrix method to calculate the dynamic characteristics is adopted after the parameters of structures are specified. Taken both shear effect and warping deformations into account, the point and field transfer matrices are derived, and the influence on dynamic characteristics is computed according to different damaged positions and areas.2) The floating parameters are determined by the Vlasov' s method according to different damaged holds combination based on the linear theory of floatability. After solution of radiational and diffractional fluid field of asymmetrical sections by applying the multipole expansion method, wave loads on damaged ships are calculated by the linear strip theory under the non-upright floating condition, taking the effect on the heel angle and trimming angle caused by the damaged tank inundation below waterline into account. Then comparative study of bending moments and shearing forces is performed with the results calculated by traditional design loads method for the same assumption and the changes of wave loads are discussed in this paper.3) Based on the asymmetrical beam bending theory, the deflections ofdamaged hull subjected to hogging and sagging moments and shear forces are analyzed accounting for the external loads listed from previous chapter. The effect of shearing deflection on total hull deflection is discussed. On basis of ship strength theory, mathematical model and solvable method of limited deflections of ships are established, and deflection criterion to check the demands of longitudinal strength of intact ships or damaged ships is proposed. It is convenient for the preliminary ship design.4) The Revised Hughes' s Method and nonlinear finite element method are applied to calculate the buckling and ultimate strength of stiffened panels in this paper, which is to be referred to analysis the strength of damaged ships. Several types of buckling mode and several types of collapse mode for the stiffened panels are mostly analyzed. It is emphasized on the influence of position of loading plane on the ultimate strength of stiffened panels and numerical calculation of stiffener tripping. At last the interaction of ultimate strength for stiffened panels combined different loads is discussed.5) The simplified method to calculate the ultimate strength for the asymmetrical hull is presented based on the Revised Paik' s Method (RPM). Then an efficient and more accurate nonlinear finite element procedure based on the Plastic Node Method (PNM) by Combining elastic large displacement analysis theories with a plastic hinge model is presented to analyze the ultimate strength, directly accounting for the geometrical and material non-linearity and the influence of initial deformation and residual stress. Comparative study on the result of experiment, the sample shows that the RPM and PNM could predict the strength of ship accurately.