A Study On Stability Criteria Of Parametric Rolling

With the development of ships toward large-scale, high-performance, high-technical, peoplepay more and more attention to the shipsintact stability. The second generation intact stabilitycriteria are under developed by International Maritime Organization(IMO)whichincludes fivestability failure modesand parametric rolling is one of the most important failure modes.The sta-bility criteria of parametric rolling arestructured in three levels: vulnerability level1, vulnerabi-litylevel2and direct stability assessment. According to the latest drafts, this paper mainly inclu-desthe following content:(1) Vulnerability criteria: different methods forcalculating roll response have been proposedin the latest drafts. In thisthesis,firstly, the programs for the vulnerability criteria are developed,in which the methods of numerical transient solution and analytical steady state solutionfor rollresponse are used.Then the feasibility of two methods and the reliability of program are con-firmed by taking the C11containership as an example.(2) Direct stability assessment: now direct stability assessment is also in the scheduleofsecond generation intact stability criteriaof IMO. In this thesis, firstly,a reasonablemathematicalmodel is developed in whichnonlinear relationships among radiation force, diffraction forceandroll angle are taken into account. Then two numerical approaches are used to get the GZ curve inwaves,the first method only considers the nonlinear Froude-Krylov component and the secondmethod further considers the hydrodynamic effects of restoring variation which is nonlinearlyextrapolated with regards to the roll angle by using radiation and diffraction force on a heeledhull.It is concluded that the nonlinear radiation force and diffraction force should be consideredfor predicting parametric rolling.(3) Sample calculations:the standard values of vulnerability criteriafor parametric rollinghave not been decidedin the latest drafts and the different levels of stability criteria should beconsistent.In this thesis, firstly, the detailed calculating process of stability criteria of parametricrolling isgivenby taking the C11containership as an example. Then the consistency and feasibil-ity of the vulnerability criteriaare analyzedand the modificationsare also provided for the stan-dard values by the calculation of different containerships.(4) Model test: the stability criteria should be consistent with the experiment. In this thesis,firstly, taking the C11containership as an example, the roll damping under different Froudenumbers are obtained by free decay tests.Then heave, pitch and roll motions areobtained withdifferentwave conditions which strongly supportthe studyof this thesis. (5) Roll damping: roll damping is one of the most important factors for parametric rollingand the current evaluation is mainly base on the empirical formula or test data. In this thesis,based on technology of CFD numerical wave tanker, the influence of different parameters on theroll damping areinvestigated by the methods of orthogonal design and variance analysis, andthen a tentative exploration for the feasibility of CFD is conducted.