Discrete Element Simulation Of Ice Load On Offshore Platform And Ship Hull Based On GPU Parallel Algorithm

The influence of sea ice on offshore structures is an essential part of sea ice engineering problems. Dynamic ice loads play an integral role in the design of offshore structures and prevention and mitigation of disaster caused by sea ice. Thus, the numerical simulation of the interaction between sea ice and offshore structures is important in theoretical research and engineering application.In this thesis, a discrete element method (DEM) with bonding-breaking function is developed to simulate the breakage characteristics of sea ice, and the DEM analyses based on GPU (Graphical Processing Units) technique are carried to model the interaction between different types of sea ice and offshore structures. The applicability and rationality of the DEM in simulating the sea ice engineering application are validated with field tests. Moreover, the corresponding parallel computing program is developed. The study in this thesis mainly includes:(1) Establishment of the DEM to simulate the interaction between sea ice and offshore structures. The beam theory in mechanics of material is employed to establish the DEM bonding model of sea ice. The contact model between ice particle and boundary element, including triangle surface element and cone element, is also established. The uniaxial compressive and three-point bending tests of sea ice are simulated with the DEM by setting appropriate micro-parameters.(2) The validation of micro-parameters in DEM simulations of sea ice mechanical properties. The influence of particle packing pattern in numerical model of sea ice on macro-mechanical properties of sea ice samples is analyzed. Meanwhile, the relationship between the ratio of shear contact stiffness to normal contact stiffness and the Poisson's ratio, elastic modulus and compressive strength is figured out. The influences of the ratio of shear bonding strength to normal bonding strength and the friction coefficient between particles on uniaxial compressive strength and flexural strength are also analyzed. The influence of particle size and sample size on sea ice mechanical properties is analyzed, and the particle size effect is obtained. Based on the study above, the flow chart of micro-mechanical parameters in DEM simulation for macro-mechanical properties is given.(3) The determination of ice loads on various offshore structures and ship hull. The DEM simulations of the interaction between sea ice and the cone structure on JZ20-2 MUQ platform and the vertical pile on JZ9-3 MDP-1 platform in Bohai Sea are carried out, and the numerical results are compared with the field data and the analytical solutions of ice load based on the ISO standard. It is found that the numerical results and analytical solutions are good agreement with each other. In this thesis, the floating offshore structures and ship hull are simulated as six degree of freedom system. The interaction between ice floes with different concentrations and Kulluk platform and level ice with different thicknesses and Ship are simulated. The influence of propeller force on ship is also considered.Finally, summary of the research aspects relating to this thesis is concluded, some works in the close future research are suggested.