Research On Ship Grounding Damage Characteristics Considering The Material Dynamic Nonlinearity And Residual Strength Assessment After Grounding Accidents

Ship grounding is an impact accident between ships and obstacles during the operations of ships.As sea lanes are getting more congested,ship tonnages are geeting larger and ship speeds are becoming higher,there is an increasing probability that ship may experience a collision and grounding accidents dyring its lifetime.And it has gradually become one of the major sea accidents.In ship collision and grounding,the penetration of ship side and bottom can result in hull damage,cargo leak,casualties and potential environmental pollution.Therefore,it can provide important reference for the ship structure design based on accidents and rescue and tow plans to study the ship grounding performance,predict structural damage characteristics during grounding accidents and evaluate the residual strength after grounding.Thereby,it can reduce the harm caused by grounding and improve the security of the hull structure.Based on the protection of marine environment and improvement of ships and personal safety,this dissertation is aimed to study the mechanism of damage deformation and energy absorption in various scenarios and establish accurate,efficient and reasonable ship grounding numerical simulation techniques and evaluation methods for residual strength after accidents.Based on the international latest progress of the impact strength study for ship structures,this dissertation intensively studied the material dynamic nonlinearity in numerical simulation definition based on the quasi-static tensile test and high-speed tensile test;carried out falling weight impact test of ship stiffened plates to verify and modify the numerical simulation technologies;analyzed the ship grounding damage performance and residual strength evaluation of damaged structures,and some valuable results are obtained.The main works of this paper are as follows:(1)The overview of research about the impact damage mechnism of ship components,ship grounding performation and residual strength access of damaged structures after grounding is made;meanwhile,some aspects with research gap or necessity to be improved are presented.Moreover,the research significance and main contents of this paper are proposed.(2)Series quasi-static and high-speed tensile tests of typical ship steel are conducted to obtain the basic material properties.The methods are proposed through analytical calculation and simulation benchmark for the nonlinearities of steel material behavior including strain harden,failure strain and strain rate effect.That improves the deficiencies of finite element analysis programs in material nonlinearities.Then,the numerical simulation technologies for structural impact strength are put forward,which can provide basises for the numerical simulation of ship collision and grounding.(3)The ship stiffened plate models and related supporters are designed and manufactured,and then,the falling weight impact tests are conducted to study the dynamic response of stiffeded plates with different material and structural shapes.Based on the test results,the numerical simulation technologies are validated by comparing the simulation results.Furthermore,the influences of impact parameters on the dynamic response are discussed.(4)The dynamic response of a 159,000 DWT VLCC under grounding accident is studied based on the numerical simulation method proposed in this paper.The damage deformation,grounding force and energy absorption are analyzed.Moreover,the effects of reef shapes and grounding velocities are discussed.The conclusions can give some guidance to ship grounding accidents analysis and crasnworthness structure design.(5)On the basis of numerical simulation of soil dynamic response,the ship-soil coupling model is built,and the dynamic response of ship structure under soft grounding is calculated with the nonlinear finite element analysis software ABAQUS.The mechanism of structure damage and energy absorption is studied,which expends the research work of the related area in and aboard.Moreover,the influence of soil parameters and grounding speeds to the ship grounding performance is discussed.(6)The calculation methods of ultimate strength for damaged structures are summaried,and the analysis methods of residual strength for damaged structures after grounding are proposed.On this basis,the residual ultimate strength of damaged structures after grounding is studied.Furethermore,the influence of grounding parameters to the residual ultimate strength is discussed.Conclusions can give some guidance to conduct the ship structure considering accident loads and carry out grounding rescue works.