Static Ultimate Strength And Slamming Dynamic Response Of Ship Structures

Since common structural rules of ship structures were issued in 2006, ultimate strength calculation has been mandatory requirements for ship structural design, which marked that safety assessment of ship structure had changed from allowable working stress to ultimate strength. The task of ultimate strength analysis is to give rational ultimate strength value and failure mode. It is noted that ultimate strength mentioned here is actually refer to static ultimate strength.Due to technology development and economy requirement, large scale and high speed of the ships appear more commonly and make them more flexible, resulting that wave slamming load has more influence on safety of ship structures. In high sea conditions, it is recognized that transient and high frequency slamming and whipping loads have same amplitude as the low frequency wave load, and even sometimes slamming load is several times larger than the wave load. So it is unavoidable to rationally evaluate the slamming dynamic bearing capacity of ship structures. However, load bearing capacity of ship structures subjected to transient and violent slamming is different in nature from their static ultimate strength, which should be indirectly evaluated by slamming dynamic response,and combination of impact load shape, dynamic behavior of material, inertial effect of structures should be considered. The purpose of the paper is to provide valuable knowledge and reference methods for safe assessment of ship structures, through investigating static ultimate strength and slamming dynamic response of ship structures with different impact load shape, as well as their corresponding failure mode.Slamming dynamic response of ship structures reflects their slamming dynamic strength, and which is influenced by impact load shape parameters. The ratio of rise time and total impact duration is proposed and especially concerned among all impact load shape parameters. Influence of impact load shape parameters, impact duration, peak load, ratio between rise time and impact duration, on slamming dynamic response of ship structures is investigated thoroughly. The ratio of rise time and total impact duration reflects that how soon the peak load appears in the impact duration, and which has significant influence in special load cases.Due to complexity of ship structures, it is difficult to solve static and dynamic strength of ship structures using analytical method and empirical formula, so experiment and numerical simulation are main appropriate solutions. Based on static implicit nonlinear finite element method, considering nonlinear factors of material and geometry, static ultimate strength and failure mode of ship structures are analyzed. Based on dynamic explicit nonlinear finite element method, considering the strain rate effect and strain hardening effect of the material, the general contact model is used to avoid any potential penetration and interference, slamming dynamic response of ship structures is analyzed. Following works are accomplished in the paper, including static ultimate strength and slamming dynamic response of ship structures under four load conditions of compression, shear, bending and torsion.(1)Cross-stiffened deck subjected to static and slamming longitudinal compressionStatic ultimate strength and failure mode of ship deck with girders, transverse frames, as well as stiffened plate, subjected to longitudinal compression are analyzed. Influence of girders numbers and geometric imperfection on ultimate compressive strength of deck is investigated; results shows that application scope of the ultimate strength predicting formula of stiffened plate can be expanded to deck grillage with girders, as long as whose slenderness of girder web is close to that of plate between stiffeners.Influence of load shape and initial and geometric imperfections on dynamic response of deck subjected to longitudinal compression is investigated. It is found that the smaller the ratio between rise time and impact duration is, the larger dynamic response is. In addition, influence of cutout on girder web and compressive pre-stress on static ultimate strength and dynamic response of deck subjected to longitudinal compression is also investigated.(2)Transverse densely stiffened plate subjected to static and slamming in-plane shearThrough comparing shear elastic buckling strength and ultimate strength of stiffened plate, threshold value of stiffener bending stiffness is determined. Shear ultimate strength and failure mode of stiffened plate with lateral pressure are analyzed; It is found that shear ultimate strength will reduce with increase of lateral pressure.Influence of load shape on dynamic response of side stiffened panel with and without lateral pressure subjected to in-plane shear is investigated. It is shown that ratio between rise time and impact duration has no notable influence on shear ABSTRACT dynamic response. In addition influence of corrosion on in-plane shear static ultimate strength and impact dynamic response of stiffened plate is also investigated.(3)Ship hull subjected to static and slamming vertical bendingUltimate strength and collapse mode of intact and damaged ship hull under sagging and hogging condition are presented.Dynamic response of ship hull subjected to slamming sagging bending moment, including three kinds of load condition, pure bending, combination of bending and longitudinal compression, bending with pre-stress resulted from bending; It is shown that the smaller ratio between rise time and impact duration is, the larger the dynamic response is. At last, it is shown that slamming dynamic strength of ship hull is largely less than static ultimate strength, on the condition of combination of pre-stress resulted from bending, longitudinal compression and bending applied at same time, as well as with smaller ratio between rise time and impact duration.(4)Ship type hull with large deck opening subjected to static and slamming torsionTorsion ultimate strength and collapse mode of ship type hull with large deck opening are compared with its sagging, hogging, horizontal bending ultimate strength and corresponding collapse modes. Combination of torsion and vertical bending are applied on the ship-type hull girder with a large deck opening, and ultimate strength interaction relationship for the ship-type hull under combined torsion and vertical bending is obtained through curve fitting.Influence of impact load shape on dynamic response of ship type hull with large opening subjected to pure torsion slamming and combination of torsion and sagging bending is analyzed. It is showed that the influence of the ratio of rise time and impact duration on dynamic response of ship type hull with large opening is undetermined, which should be analyzed case by case.