Research On Deformation Characteristics Of Ship Bottom Plates In A Rock Grounding Scenario

Ship grounding is one of the major risks to the sailing ships.Especially for grounding on sharp rocks,the ship bottom structures may be directly damaged,resulting in threats to the safety of lives and properties and even severe environmental pollution.Therefore,the study on the structural damage characteristics of ship bottom structures in grounding is of great significance to the safety assessment of grounded ships.In this thesis,both experimental and numerical methods are adopted to study the structural damage characteristics of ship bottom structures grounding on rocks,for both the wet and dry grounding problems.The wet grounding problem includes Fluid-Structure Interaction(FSI)effects,while the dry grounding problem neglects the effects of external water.This study also investigates the influences of grounding parameters such as friction,rock shape,plate thickness,stiffener type,grounding location and multiple rocks on the structural damage of grounded ships.The main research tasks of this thesis are listed below:(1)Quasi-static plate cutting tests are conducted to model the processes of the plate tearing by rock cutting.In the tests,an artificial rock with cone shape is used to cut thin plates made of mild steel,and the damage characteristics and horizontal cutting force-cutting length curves are obtained.The experiments also consider the variation of rock penetration depth and friction coefficient between the rock and the tested thin plate to study their influences on the grounding damages of ship bottom plates.Based on the experimental results,typical damage characteristics of the tested plates are discussed and the effect of friction on the cutting forces is quantitatively analyzed.(2)Numerical simulations are carried out using the professional FE software ABAQUS to model the quasi-static cutting processes of the plates,the accuracy of numerical simulation is validated by comparing the simulation and experiment results.In addition,the vertical cutting forces and deformed section of the stable cutting stage of plate are analyzed according to the simulation results.Furthermore,the parametric studies are carried out to study influences of the rock shape,plate thickness and stiffener type on the grounding force and the ship bottom plate structural damage.(3)A series of ship model grounding tests are conducted in a water tank to study the coupling effects between the internal mechanics and external dynamics.The tests investigate the effects of the grounding velocity,transverse grounding location of the rock and rock shape on the grounding behavior.The motions of ship model and the horizontal grounding force are measured.Three kinds of grounding damages are analyzed.Besides,for the same penetration depth,the results from both the dynamic ship model grounding tests and quasi-static plate cutting tests are compared to analyze the differences in structural damage and grounding forces between dynamic and quasi-static cutting.(4)The Coupled Eulerian-Lagrangian(CEL)method embedded in ABAQUS is applied to simulate ship grounding by considering the Fluid-Structure Interaction(FSI)effects.The numerical results are compared with the results from the water tank grounding tests to validate the reliability of the numerical methods.Then,numerical simulation of ship grounding with multiple rocks is performed and the results are compared with the case of ship grounding with single rock.