Study On Cloaking Protection Of Structures In Water Waves Using Scattering Cancellation Method

Wave load is an important factor affecting the safety of marine structures.Especially for floating structures,wave loads such as wave drifting force can damage the mooring system,thereby affecting its positioning ability and safety.The traditional protection method is to increase the number of mooring systems or the strength of the structure to increase the safety factor,but this method pushes up the cost of equipment manufacturing,and the fact that the structure is still in a complex wave environment has not been changed.In recent years,cloaking technology has been introduced into water-wave field,providing new ideas for structure protection in water waves.This technology starts from the perspective of wave manipulation,by thoroughly improving the wave environment in which the structure is located,it can fundamentally solve the safety problem of structures in water-waves.This paper studies the cylinders-based cloaking protection technology based on the scattering cancellation method.Numerical and experimental methods are used to explore the mechanism of cloaking protection,defect effects,quasi-cloaking and broadband cloaking protection methods,and invisibility-concentration coupling,which are of great significance to promote the practical application of this cloaking protection technology.The specific research contents are as follows:The problem of cloaking protection of structures in water waves is essentially the hydrodynamic problem of wave-structure interaction.For this purpose,a wave-body interaction hydrodynamic optimization model is established.This model includes the hydrodynamic calculation model of the wave-body interaction and the multi-parameter optimization model.The wave interaction theory and the high-order boundary element method are adopted to establish the hydrodynamic calculation model,while the multi-parameter optimization model is established using the real-coded genetic algorithm.The effectiveness of these two models is verified,respectively.The two models are combined to form a wave-body interaction hydrodynamic optimization model,while the convergence and effectiveness of the model are systematically verified.Based on the established hydrodynamic optimization model,the design of the cylinders-based cloaking structure with different layout forms,different optimization parameters,and different wave frequencies is carried out,and the protective effect of the cloaking structure is verified.Through the analysis of the wave surface near the cloaking structure,the resonance mode of the scattered wave inside the cloaking structure is found,and the mechanism of cloaking is clarified.At the same time,the symmetrical distribution law of the wave surface on both sides of the central cylinder is discovered,which reveals the protection mechanism of the central cylinder.The above conclusions are then verified by physical model experiments.Besides,it is found that when the number of outer cylinders is large enough,the cloaking structure is omnidirectional.Cloaking structures may have structural defects during manufacturing,transportation,and operation.Therefore,the location defects,size defects,and draft defects of the outer cylinder are considered.Different defect effects on the protection of the whole structure and of the central cylinder at the cloaking wave frequency are summarized.The results show that the defect effects of a single outer cylinder on the cloaking protection are spatially symmetric.When a single outer cylinder has defects,the cloaking protection effect is still good;and the defect effects of all outer cylinders on the cloaking protection are more significant than that of a single outer cylinder.There is a limitation between the size of the cloaking structure and the wave frequency,that is,the selection of the size of the cloaking structure for a specific wave frequency is limited.In addition,the cloaking structure designed for a specific wave frequency is not suitable for other wave frequencies.Therefore,according to the influence law of the concentric cylinder radius of the outer cylinder on the cloaking protection,a quasi-cloaking method is proposed,which improves the size selectivity of the cloaking structure.Subsequently,by studying the defect effects on the cloaking protection at other wave frequencies,the protection-frequency offset is discovered,and then a mehod of broadband cloaking is proposed.Wave energy concentration equipment faces a complex wave environment with high wave energy density.Therefore,cloaking protection technology is introduced into wave energy concentrator,a coupling method of cloaking and concentration is proposed,and an invisibility concentrator is designed.The effectiveness and mechanism of the device are explored.The wave resonance mode inside the invisibility concentrator is discovered,and the coupling mechanism is clarified.Subsequently,numerical and model experiment methods are used to explore the performance of this equipment on nonlinear waves and at different wave frequencies.The results show that the device still has good cloaking and energy concentration effects under nonlinear waves;in addition,the device has cloaking and energy concentration effects in a certain wave frequency band near the target wave frequency,and its performance in long waves is better than that in short waves.