| Cylinder is a typical supporting member of offshore engineering structures,which is widely used in offshore platforms,offshore wind turbines,sea crossing bridges,and breakwaters.To dissipate the wave energy,academia proposed to set the porous cylinder outside the non-porous cylinder to form a concentric cylinder.To meet the stability requirements of the structure,the inner cylinder needs a large enough design radius,which will reduce the applicability and increase its installation difficulty.If the protective effect is strengthened by reducing the opening rate of the outer cylinder,the hydrodynamic load of the outer cylinder itself will be increased.To optimize the hydrodynamic performance of concentric cylinders,a new type of structure is proposed in this paper,that is,a dual-layer horizontal porous ring plate is set between the inner and outer cylinder to form concentric cylinders with ring plates fixed inside.The porous ring plates can not only further dissipate the wave energy,and alleviate the wave action in the annulus,but also enhance the stiffness and overall stability of the structure.However,there is currently no appropriate prediction method for the concentric cylinders with ring plates to quickly and quantitatively evaluate the hydrodynamic performance of this structure,which restricts the popularization and application of this kind of structure.In this paper,the hydrodynamic physical model test and theoretical analysis are combined to research the hydrodynamic characteristics of the interaction between concentric cylinders with ring plates and regular waves,which provides a theoretical basis for the engineering application of this kind of structure.The main research contents and results are as follows:(1)The hydrodynamic physical model tests of isolated and array structures composed of concentric cylinders with ring plates are carried out,and the effect of the porous ring plates and inter-cylinder interaction on the wave diffraction characteristics of the structure is clarified.Through the isolated cylinder test,the influence laws of the incident wave height,period,and the opening rate of the ring plates on the structural excitation force and transmission coefficient are obtained,and the reduction effect of the porous ring plates on the horizontal excitation force and the structural transmission coefficient of the inner cylinder is verified.The influence of the interaction between the cylinders on the horizontal exciting force of the structure and the elevation of the free surface of the flow field is verified by the uniform four-cylinder test.(2)A theoretical analysis method of wave diffraction by isolated concentric cylinders with ring plates under regular waves is established,and the wave diffraction characteristics of isolated structures are studied.In the framework of potential flow theory,the boundary conditions of the porous are treated based on the linear pressure drop model,and the velocity potential function of the flow field is obtained by using the eigenfunction expansion method.The unknown coefficients in the velocity potential function are obtained through the region transmission conditions,and the hydrodynamic expressions of wave diffraction are obtained,and verified by using the theoretical and experimental results.The method is applied to analyze the concentric cylinders with ring plates,and the influence of the changes in the number,permeability,and submerged depth of the ring plates on the structural excitation force and the transmission coefficient is revealed.The same method was used to analyze the "offshore wind power marine ranch combination structure" composed of a single pile foundation and a cylindrical aquaculture net cage,revealing the variation law of horizontal excitation force before and after the combination of the two.(3)A theoretical analysis method is established to analytically analyze the wave diffraction characteristics of concentric cylindrical arrays with ring plates in any number and arrangement.Based on the theoretical analysis method of wave diffraction by isolated concentric cylinders,the Bessel function addition theorem is introduced,and the multiple diffraction of waves in the array is considered.The hydrodynamic expressions of wave diffraction around all cylinders are obtained,and verified by using the theoretical and experimental results.Through the analytical analysis of the uniformly distributed four-cylinder structures,it is verified that there is no wave "Near trapping" mode in this kind of structure,and the influence of the change of cylinder spacing on the structural excitation force is revealed.For the tandem five-cylinder wave protection structure,the influence law of the change of wave incidence angle on the structure excitation force and the free surface elevation of the flow field is obtained through analytical analysis.(4)Aiming at the problem of wave disturbance caused by horizontal oscillation of structures,the theoretical analysis methods of wave radiation of isolated and array structures composed of concentric cylinders with ring plates under given horizontal harmonic oscillation are established under the framework of potential flow theory,and the wave radiation characteristics of structures are studied accordingly.Through the analytical analysis of isolated structures,the influence laws of ring plates’ number,permeability,and submerged depth on the hydrodynamic coefficients and radiation wave force of bottom-mounted concentric cylinders were explored.The variation laws of the hydrodynamic coefficients and radiation wave force before and after the combination of offshore wind power single pile foundation and aquaculture cage are revealed.Through the analytical analysis of the array structure,the influence of the cylinder spacing and the change of oscillation mode on the wave radiation characteristics of the uniformly distributed four-cylinder support structure and the tandem five-cylinder wave protection structure are revealed respectively.Based on the above theoretical calculation method of wave radiation under the given horizontal harmonic oscillation,the calculation method of radiation wave force generated by the horizontal oscillation of structure under earthquake action is given.(5)A theoretical analysis method of wave diffraction-radiation coupling around concentric cylinders with ring plates under incident waves is established,which can be used to analyze the wave diffraction-radiation coupling around a floating structure under specific water depth and wave conditions.Through the analytical analysis of the floating "offshore wind power offshore ranch composite structure",the influence of the change of the permeability of the cage on the horizontal wave force after the structure combination is revealed.Through the analysis of the foundation of the floating three-cylinder fan,the influence of the permeability of the ring plates,the permeability of the outer cylinder,and the radius of the outer cylinder on the horizontal wave force of the structure are revealed,and the feasibility of replacing the non-porous cylinder with the concentric cylinders with ring plates is verified. |
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