| In the field of ship and ocean engineering,the structures water entry/exiting process and the wave-floating structure slamming can be attributed to the fluid structure coupling problems of free surface flow and structures.These strong nonlinear mechanical phenomena are all referred in the large deformation of free surface and transient slamming load acting on structures,which are all involved in many difficult fundamental mechanical problems.However,traditional meshed numerical methods require the implementation of complex numerical techniques or reprocessing of the free surface to capture the evolution of the free surface when solving these large deformation problems involving the free surface,which poses certain challenges.On the contrary,Smoothed Particle Hydrodynamics(SPH)method based on the Lagrangian scheme has certain advantages in solving fluid large deformation problems due to its detachment from the constraints of topological grids.At the same time,it can freely capture the evolution process of the free liquid surface without the need for secondary processing of the free liquid surface.However,the conventional SPH method has been criticized for its computational stability and efficiency issues.This thesis started with the ocean engineering problems involved in the coupling between free surface flow and structure responses,and analyzed the research progress of free surface flow and structure coupling at home and abroad from model tests and numerical simulation.After that,the research progress of SPH method in the free surface flow problem and the corresponding numerical technology improvement were analyzed.Finally,the research progress of SPH method in the fluid structure coupling problem were discussed,And the limitations of the current SPH method in the field of fluid structure coupling problems were presented.Based on this,the research content and scope of this article could be designed,which could be laid a foundation for the whole thesis.This thesis first describes the mathematical principles and basic theories of the SPH method.In response to the pressure field fluctuations and numerical voids in traditional weakly compressible SPH methods,the numerical accuracy of the SPH method was improved by introducing density dissipation technology and particle displacement correction algorithm.At the same time,the computational accuracy of different boundary conditions was compared and some numerical improvement techniques were introduced.Based on this,the relaxation zone wave generation technology was developed,which was used to improve the accuracy of the SPH method in wave propagation.To achieve precise simulation of local flow fields,this thesis introduces adaptive particle resolution technology and establishes a multi-resolution SPH numerical model.Then,this article uses the background grid interpolation idea for reference to establish a set of post-processing schemes to improve the visualization effect of the SPH method in three-dimensional large-scale structures.This part can provide an accurate flow field,which can be used for establishing a fluid structure coupling model through numerical improvements to the traditional SPH method.Firstly,according to Newton’s law of motion and Euler’s angle conversion formula,the rigid body six degrees of freedom motion equation was established and its calculation accuracy was verified.Then,according to the theory of elasticity,the elastic SPH numerical model based on the total Lagrangian scheme is established,At the same time,based on the idea of penalty force,a correction term was introduced into the momentum equation,which could be used to minimize the error between the actual displacement field and the linear displacement field described by the deformation gradient,and obtained accurate solution of the structural elastic response.Its high computational stability and conservation were verified through relevant numerical cases,which could provide structural elastic response prediction for the establishment of fluid structure coupling models.Additionally,in response to solve the coupling problem between waves and rigid floating structures,his research work firstly introduced a mooring line tension solution model based on the lumped mass method,and conducts bidirectional coupling with the high-precision wave field model based on the SPH method established in the previous chapter.It achieved numerical simulation research on the hydrodynamic performance of mooring floating structures under wave action,and the accuracy of the coupling model was further verified through model experiments,and the application scope of SPH method could be further expanded in ocean engineering problems.Considering the limitations of the lumped mass method for solving mooring line tension,which was only applicable to single material mooring lines,this thesis also introduced a mooring line tension solver based on the multi segment quasi-static method.At the same time,the accuracy of the coupling model had been verified by the model tests.Finally,a series of numerical simulations were conducted on the hydrodynamic performance of the floating structure with wings and moon pools under several wave conditions.Meanwhile,for the coupling interaction between free surface flow and elastic structures,this research work combined the elastic SPH numerical solution model mentioned above.After that,being the main research background of the water entry and wave slamming in ocean engineering,the SPH solid solver was coupled with SPH fluid solver and Sequential Staggered Coupling algorithm was used to solve the coupling process.Adaptive particle refinement technology was adopted to improve computational efficiency,and its computational accuracy and stability were verified according to several two-dimensional and three-dimensional numerical cases.Subsequently,in order to further improve computational efficiency,GPU acceleration technology was adopted and finally,a fluid structure interaction of coupled SPH numerical model based on GPU acceleration technology was established,and its computational efficiency was demonstrated by comparing it with the multi-resolution SPH model.Then,the SPH-GPU fluid structure coupling model was applied to solve elastic structure water entry problem and green water slamming against the elastic structure.In view of the low computational efficiency of the SPH method in the numerical simulation of the coupling of free surface flow and large-scale three-dimensional structure,this thesis improved the traditional linked list method and combines the GPU acceleration characteristics to optimize some programming methods in the SPH method.And a highperformance SPH numerical solution model suitable for the study of three-dimensional largescale structures slamming into water was established,and numerical simulations were conducted on the issues of ship slamming into water and emergency buoyancy of submarines in the field of ocean engineering.On this basis,this article extended the mooring line tension solution model established in the previous chapter to three-dimensional problems and coupled it with the established three-dimensional SPH numerical model in two ways.A SPH numerical model suitable for the coupling effect of three-dimensional wave mooring floating structures is established,and the computational stability and accuracy of the coupling model are further verified through model experiments,Finally,the model was applied to the hydrodynamic performance of moored ships under wave action with a focus on analyzing the effects of different wave conditions,which could be used as a reference for the hydrodynamic performance analysis of real ship. |
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