| Engineering equipments such as offshore platform have been widely used with the development and utilization of marine resource and space.The hydrodynamic interaction among adjacent cylinders,which constitute the supporting structures of marine structures,is strong and complex,and has a significant adverse effects on the safety and stability of structures.Therefore,investigating the complex hydrodynamic interaction between adjacent multi-columns in waves is very necessary.On the other hand,it is of practical engineering significance to explore a fundamental strategy to protect structures.A numerical wave tank for hydrodynamic calculation of multi-floating bodies based on viscous flow theory is established,and the near-trapping phenomena and the cloaking effect among multi-cylinders are systematically investigated.Firstly,a three-dimensional multi-phase flow wave tank is established by solving Navier-Stokes equations and combining VOF(Volume of Fluid)method.The numerical wave-generation and wave-absorbtion techniques are studied,and several wave-generation methods such as piston-type,mass source function and boundary condition definition are numerically realized.The wave-generation method suitable for hydrodynamic calculating of multi-floating bodies is determined after comparing applicability of different wave-generation methods.In addition,the artificial-damping layer is introduced to the end of the wave tank to eliminate the wave.After systematically validating the convergence of the established numerical tank,the interaction between waves and single cylinder is studied based on the present model.The reliability of the numerical model is verified by comparing with the theoretical solution,and the sizes of computational domain and the parameters of mesh suitable for hydrodynamic investigation of cylindrical structures are detemined.Furthermore,the diffraction problem of a fixed four-cylinder in waves is studied,and the reliability of the established hydrodynamic model is further validated by comparing the wave-surface elevations with the experimental results.Then,the first-and second-order near-trapping phenomena associated with a four-cylinder structure common in marine engineering are simulated.The influence of fluid viscosity and nonlinearity on the distribution of wave field around the structure under near-trapped modes is investigated by comparing with the published experimental data and second-order potential flow results,and the disturbance caused by the four-cylinder structure at different wave frequencies is analyzed.In addition,the wave loads and wave drift force directions of the whole structure and individual cylinder are also studied.Finally,the cloaking effect among cylinder groups in water waves is systematically investigated.The effect of cloaking to the reduction of wave drift force is verified,and the mechanism of cloaking effect is revealed from the view of wave surface distribution.The effects of the number of outer floating bodies,incident wave directions and wave numb ers on the wave drift force and wave surface are also studies.The existence of cloaking effect and the reliability of CFD results are further verified by comparing with the existing experimental results.In this paper,the complex hydrodynamic interaction among multi-cylinders in waves is deeply studied and analyzed based on the established viscous-flow numerical model.The results show that the interaction between cylinders has a significant influence on the hydrodynamic characteristics of structures.The interaction among cylinders produces harmful interference to the wave field when near-trapping phenomena occur,which is more likely to cause local damage than overall overturning.Whereas the cloaking effect among cylinders improves the wave environment around the floating body by utilizing the beneficial wave interference between the floating bodies,and then reduces the wave drift force fundamentally.The results and conclusions of this paper can provide reference for engineering design and application. |
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