Experimental Analysis On Active Absorption Wavemaker In Two-dimensional Wave Basin

As an important facility for physical model experiments in Marine engineering,wave generators are significant in generating experimental waves.Because of the finite width and length of the wave basin in the laboratory,unlike the infinite ocean environment,a primary reflection wave is generated when the incident wave generated by the wave-making plate propagates to the boundary of the water basin.The reflected wave moves backward and generates a secondary reflection wave at the piston.The superposition of the secondary reflected wave and incident wave will affect the wave field in the experimental basin and cause deviation of the experimental results.The secondary reflection between the experimental model and the plate can only be eliminated by active absorption motion of the piston.So,the wave-making machine not only serves as a generator of incident waves,but also an absorber of reflection wave,which is named as active absorption wavemaker(AAW).However,the AAW applied in wave basin is different from the AAW applied in wave tank.The former can only achieve active absorption wave generation through a single wave making plate,while the latter needs to realize the cooperative work of multiple wave making plates.Besides,two-dimensional AAW is also the premise of the three-dimensional AAW.Based on the theory of linear wave making theory,several control methods of AAW in two-dimensional wave basin are introduced.Based on the time domain control method,control equations of AAW in a two-dimensional tank is derived.Among them,regular wave AAW is designed via time-domain control method,while irregular wave AAW is designed via representative frequency method.Based on the active absorption equation of two-dimensional tank,the control equation of quasi-three-dimensional oblique active absorption wave generation is derived.In order to realize the absorption wave making theory,corresponding solutions are designed to solve the problems of wave-making control delay,signal interference and multi-plate control collaborative control in the wave-making basin.In terms of signal delay,this paper designs corresponding delay compensation methods for different signal delays respectively,and compensated the influence of signal delay in AAW.In terms of signal interference,digital filters are utilized to eliminate the influence of the interference signal from the wave signal according to the frequency difference between them.In terms of multi-board cooperative control,an active absorption control system for two-dimensional water basin is designed via Twin CAT NC PTP motion control system and Simulink visual simulation tool.The system can realize the cooperative work of multiple plates through the control of multiple plates,or it can be coupled by the electronic gear,and the 8 wave-making plates can be used as the same wave-making plate.In terms of the analysis of the wave signal,a frequency-domain separation program is designed for regular wave and irregular wave via Goda two-point method.The timedomain separation of regular wave-making signals is realized by means of Hilbert transform.By comparing the effects of multi-piston and single-piston,it is proved that the multi-plate is superior to the single-plate and it is necessary to realize the active absorption of multi-plate in the wave basin.