| Since the reduction of construction cost,multi-function and the space sharing can be achieved for the breakwater-wave energy converter(WEC)integrated system,the engineering applications were anticipated.In the present study,hydrodynamic performance and power take-off characteristic of a floating breakwater-WEC integrated system were investigated.The mechanism of the wave attenuation and energy conversion were revealed,which may be useful for the designing of the floating breakwater-WEC integrated system.Hydrodynamic properties and energy conversion performance of the single pontoon-type floating breakwater-WEC integrated system were investigated using both theoretical and experimental methods.An analytical model was built with the matching eigen-function method based on potential flow theory.In the analytical study,the effect of the draft,width,and power take-off(PTO)damping of the pontoon on the reflection coefficient,transmission coefficient,capture width ratio(CWR)and motion response amplitude of the integrated system are discussed.The hydrodynamic characteristics of the integrated system with the optimal PTO damping control are compared with those of the fixed pontoon-type breakwater and the free-floating breakwater.Results showed that the breakwater with the optimal PTO damping gives better wave attenuation performance than the free heaving breakwater for a certain frequency range,and the qualified CWR can also be achieved.That is to say,both of the energy conversion performance and the wave attenuation performance can be achieved simultaneously.Experimental investigation on the performance of the integrated system was conducted by using the magnetic powder brake-torque-power sensor system.The effects of PTO damping force on the transmission coefficient and the CWR were investigated.The results showed that,as the PTO damping force increases,the CWR increases firstly and then decreases;the transmission coefficient decreases in the low-frequency region.Oppositely,the trend of a slightly increasing can be found in the high-frequency region.It is proved that,under the laboratory conditions,the transmission coefficient Kt and the CWR ? of the integrated system can satisfy the condition of Kt<0.5 and ?>20%simultaneously by properly adjusting the PTO damping forceTo further improve the performance of the integrated system,the original system was improved(i.e.,the dual-pontoon&dual-PTO system)and thorough investigations were conducted.Analytical study on the performance of the dual-pontoon&dual-PTO system was conducted and the effect of the draft,the width of the pontoon and spacing between the pontoons on the reflection coefficient,transmission coefficient,and CWR are investigated.In the non-Bragg resonance frequency region,the pontoon in the lee side plays an effective wave-reflection role,which improves the energy conversion performance of the device in the front side.As a result,the capture width ratio of the integrated system is amplified.By comparing with the results of the single pontoon system with the same displacement,the results show that the effective bandwidth of the dual-pontoon&dual-PTO system(the conditions satisfying Kt<0.5 and ?>20%)are obviously greater than the corresponding single pontoon system.And the maximum CWR of the dual-pontoon&dual-PTO system is greater than that of the single pontoon system and the reverse trend can be found for the transmission coefficient.Based on the theoretical predictions,an experimental investigation on the performance of the system was conducted.Results showed that the broader effective bandwidth can be achieved for the proposed system was realized by properly adjusting the PTO damping force.Within the experimental cases,the maximum CWR of the dual-pontoon&dual-PTO system is greater than that of the single pontoons system with equal total displacement.A dual-pontoon&single-PTO integrated system is proposed(a pontoon-type wave energy device installed on the weather side of a fixed breakwater).The theoretical and experimental investigations on the performance of the proposed integrated system were conducted.The effect of the draft,width,spacing,and PTO damping of wave energy device on the reflection coefficient,transmission coefficient,and CWR were analyzed theoretically.Results showed that the maximum CWR of the dual pontoon single PTO integrated system can reach 80%.However,the phenomenon of CWR ? = 0 occurs at certain frequencies,which is corresponding to the Bragg resonance.The effect of the draft,breadth,and spacing between the pontoons were mainly reflected as that:the frequency corresponding to the Bragg resonance moves to the low-frequency region with increasing draft,breadth and spacing.Based on the theoretical predictions,experimental investigation on the performance of the integrated system was conducted.The results showed that,with proper adjustment of the PTO damping force,the CWR of the dual pontoon single PTO system can reach to 55%under the condition that the transmission coefficient Kt<0.5 is satisfied.This means that both the transmission coefficient satisfying engineering applications and the relative higher wave energy capture efficiency can be achieved for the dual pontoon single pontoon system.Finally,we present a numerical analysis of an array of wave energy devices installed at the weather side of a fixed breakwater.The effects of the parameters(such as the spacing of the array wave energy device,the distance between the wave energy device and the breakwater,the PTO damping,etc.)on the performance of the WEC array were investigated.The influence of the average interaction factor qmean of the array wave energy device was analyzed and compared with that of the traditional WEC array.The results show that the integration was performed within a wide frequency range.The qmean of the wave energy array with breakwater is obviously higher than the qmean of the traditional WEC array.The hydrodynamic characteristics of the breakwater-wave energy array system are investigated experimentally.The influences of the draft of the WEC array,the distance between the WEC and the breakwater on the motion response of the wave energy device and the transmission coefficient of the breakwater are investigated,respectively.And the comparisons among the traditional WEC array,isolated breakwater,and the integrated system are conducted.Results showed that the presence of the breakwater significantly amplifies the motion response of the WEC,which is beneficial to improve the energy efficiency of the WEC.This may provide one solution for design WEC array with high energy conversion efficiency. |
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