Experimental Research on A New Type of Floating Breakwater for Wave-Absorbing and Energy-Capturing

To avoid the damage caused by big wind and wave in cage culture, and to solve the problem of energy supply faced by automatic breeding equipment, a new type of floating breakwater, named as Savonius double buoy breakwater (SDBB), is proposed in the paper. The floating breakwater is composed of HDPE cylindrical double buoys and horizontal axis Savonius rotors, and has the functions of wave-absorbing and energy-capturing. Based on the linear wave theory and energy conservation law, the Fourier Transform was applied to separate the two-dimensional wave frequency domain, and the energy captured by the rotors and absorbed by the floating breakwater were calculated. Experiments were conducted in a two-dimensional wave-making flume, and the transmitted waves at different wave heights and periods, the tension of mooring lines, and the rotational torque exerted on the Savonius rotor were measured. A series of performance comparison tests were also performed on the new floating breakwater and the traditional double-floating breakwater. Results show that the new floating breakwater is better than the traditional one in terms of reducing wave transmittance, and the combination of the floating breakwater with Savonius rotors can provide for marine aquaculture equipments with green power supply to a certain degree of self-sufficiency.


Introduction
The large-scale expansion of offshore aquaculture in the past few decades has led to the deterioration of the local marine environment and the decline in the quality of aquatic products. Extensive aquaculture methods and excessive fishing have caused the decline in marine aquaculture income and the deterioration of the marine ecological environment. Some sea areas have shown the trend of "desertification", and traditional methods of marine aquaculture and fishing have become unsustainable. Marine ranches are fishing grounds that create a multi-nutritional marine ecological environment based on ecological principles in a certain open sea area, make full use of natural productivity, and carry out biological resource conservation and seawater aquaculture production. Floating breakwaters are widely used in offshore farming due to their economy and practicality. However, in open sea areas, there is a greater threat of wind and waves. The aquaculture equipment is easily damaged, and it is prone to problems such as the fish fry being severely impacted by waves and the aquaculture equipment being scratched, resulting in quality degradation or fish escape. In addition, all kinds of lighting and automatic equipment are needed for open sea aquaculture. It is necessary to study a new type of floating breakwater suitable for open seas, improve the ability to resist wind and waves, and solve the problem of energy supply.
In the past 40 years, floating breakwaters have gradually risen, and several different types of floating breakwaters have emerged. A large number of experimental studies have been carried out on floating breakwaters, and many achievements have been made in this field. McCartney (1985) gave a detailed introduction and analysis of four different types of breakwaters and their advantages and disadvantages, including box breakwaters, floating box breakwaters, floating cushion breakwaters and tethered breakwaters. Sannasiraj et al. (1998) carried out experimental and theoretical researches on floating breakwaters, and measured the motion response, mooring force and transmission coeffi-cient of floating breakwaters for three different mooring structures. The results show that the theoretical measurements of the mooring force are in good agreement with the actual measurements, and the influence of the mooring structure on the transmission coefficient is not significant. Dong et al. (2008) studied three types of floating breakwaters: single box structure, double box structure and plate net structure. A two-dimensional physical model test was carried out in a wave-flowing water flume in the laboratory, and the wave transmission coefficients of three types of breakwaters under regular waves of flow were measured. Based on the preliminary comparison of wave transmission coefficients, a scheme of combining a plate net floating breakwater with a cage is proposed, and detailed experimental analysis and comparison are performed for several different influencing factors. Koraim and Rageh (2014) studied the different parameters affecting the breakwater efficiency, e.g. the number of the under connected vertical plates, the length of the mooring wire, and the wave length. It is found that, the transmission coefficient K t decreases with the increase of the relative breakwater width B/L, the number of plates n and the relative wire length l/h, while the reflection coefficient K r takes the opposite trend. Nikpour et al. (2019) conducted a comprehensive experimental study on the regular wave attenuation of trapezoidal pontoon breakwater in deep water. The functionalities of two simple FB geometries consist of a rectangle and a trapezoid with the slope of 60° were investigated under the wave impact. Wang et al. (2010) put forward a kind of pile-constrained floating plate floating breakwater. Deng (2019) carried out research on hydrodynamic performance and wave elimination performance of three types of floating breakwaters based on the CFD numerical calculation method. Simulation analysis shows that the transmission coefficient K t increases with the increase of the ratio of wave height to breakwater width, H/B. However, it decreases with the increase of the ratio of wavelength to breakwater width, λ/B, and the sway RAO, sag RAO, and roll RAO all decrease with the increase of the ratio H/B. Ji et al. (2015) proposed a new type of cylindrical floating breakwater (CFB). After using a net cage with a ball, the irregular motion of the sphere is used to dissipate the wave energy, which significantly reduces the wave transmission. The effect is significant in the case of long waves. Ji et al. (2018) used numerical methods and experimental research methods to study the hydrodynamic performance of cylindrical double floating box type and rectangular single floating box type breakwaters. The wave coefficient, the anchor line force, the velocity streamline and the six-degree-of-freedom motion response of the floating breakwater were comprehensively evaluated. The numerical model was also used to reproduce the velocity streamline and wave motion.
Many scholars have devoted themselves to improving the wave-absorbing performance of floating breakwaters by optimizing the structural design, and the main purpose is to reduce the transmission wave coefficient. However, such breakwaters cannot well meet the applicable conditions of open sea areas. The cultivation of open seas is the future trend. Therefore, this paper refers to the practical application of Savonius paddles in wind energy capture, and adopts a combination of structures to propose a new type of wave-absorbing and energy-capturing floating breakwater suitable for open seas. A series of experiments were carried out in a two-dimensional wave water flume to study the wave attenuation characteristics and energy capture efficiency of the new breakwater. The research on the physical model of the floating breakwater is mainly focused on the transfer coefficient of the floating breakwater, the tension of the mooring ropes, the blade torque and the energy-harvesting efficiency. The new type of breakwater and the traditional double-buoyed breakwater are compared and tested.

Theoretical model
2.1 Two-dimensional wave separation model The wave in front of the breakwater is a mixture of incident and reflected waves. Therefore, to study the propagation coefficient of the wave, it is necessary to separate the incoming reflected wave. Goda and Suzuki's (1976) twopoint method can effectively separate two-dimensional waves with high accuracy and simple sampling method. Goda and Suzuki's (1976) two-point method is to arrange two measuring points in the direction of the wave to record the waveform synchronously. With Fourier series analysis method to perform separation calculation, the overall reflection coefficient and the amplitude of component waves with different frequency intervals in the reflected wave can be calculated. Based on the linear wave theory, the wave time series of incoming and reflected component waves in the synthetic wave are: where and represent the amplitudes of the incoming and reflected waves; and are wave number, and angular frequency respectively, and they satisfy the linear dispersion relation equation , and represent the initial phase of the incoming and reflected waves. x 2 = x 1 + ∆x, Fourier series expansion of measurement point acquisition sequence where and are Fourier coefficients. Combining the waveform data recorded by the above two types in combination with the measurement points can obtain and .
H r C r According to the requirements, two wave height meters are arranged at an interval of 1 to 2 wavelengths in front of the embankment, and the waveform data are recorded. The data needed to separate the waveforms are taken from the stable status 30 s after the wave impacts the breakwater. By separating the incident and reflected waves, the reflected wave can be obtained with wave height ( ), the reflection coefficient ( ) is the ratio of the reflected wave height to the incident wave height: 2.2 Energy capture efficiency model According to the principle of energy conservation, the energy of the incident wave is equal to the reflected wave energy, transmitted wave energy, wave energy loss, and kinetic energy captured by the S-type paddle. By considering the effect of time on the mathematical model, all energy is calculated over a period of time, that is, the energy is replaced by power uniformly. The incident wave power is finally converted into four parts of power, and the power consumption composition can be calculated by Eq. (5).
where is the dissipation power, is the reflected wave power, is the transmitted wave power, and is the Sblade power.
Incident wave power formula is where is the density of water, is the acceleration of gravity, is the height of the incident wave, is the group velocity, and is the period of the incident wave.
The reflected wave power and transmitted wave power are both related to their reflected wave height and transmitted wave height. The power requirement captured by the Stype paddle is calculated by its inertia and its angular velocity. The S-type paddle group consists of three 2-stage Stype paddles, including end cap rotation and blade rotation. The intermediate shaft is negligible because of its small moment of inertia.
The calculation formula of S-rotor inertia is as follows: where is the mass of the impeller, is the mass of the end disc, d is the blade diameter, e is the overlap rate, and D d is the end disc diameter.
The calculation formula of the S-rotor turning energy is and the calculation formula of S-rotor capture power is ω where is the angular velocity, τ is the torque, and n is the rotational speed.
The efficiency of the S-rotor The dissipated power (11)

Wave elimination performance model
The wave elimination mechanism of the floating breakwater is that the wave impact forms a reflected wave behind the breakwater, and then dissipated the incident wave energy. Under actual sea conditions, the floating breakwater is easy to oscillate periodically with the wave, and some energy can still be transmitted smoothly. The double buoy breakwater is better than the single buoy in terms of wave attenuation performance. When the wave energy ( ) is transmitted to the first buoy, it undergoes a reflection and transmission, and pushing the blades to rotate will also consume part of the wave energy ( ) below the water surface.
The transmitted wave energy ( ) undergoes reflection and transmission again through the second buoy.
The reflected wave ( ) will oscillate between the two pontoons and gradually decay. The final transmitted wave energy is about ( ), and the wave energy loss ratio is C t The wave transmission coefficient is an important indicator of the wave-breaking performance of the floating breakwater. The transmitted wave height is measured by a wave height meter arranged at twice wavelength behind the breakwater. The wave transmission coefficient ( ) is the ratio of the transmitted wave height behind the breakwater to the incident wave height before the breakwater: where is the height of the reflected wave before the breakwater, is the height of the transmitted wave behind the breakwater, and is the height of the incident wave before the breakwater.

Structural design
3.1 Structural design of a new type of wave-absorbing and energy-capturing floating breakwater Single buoy breakwaters are widely used because of their simple structural design. However, the wave elimination effect is often not ideal, especially for longer-period waves. In order to improve its wave-suppressing effect, researchers at home and abroad have improved its wave elimination performance in various aspects. For example, Williams et al. (1997Williams et al. ( , 2000 studied the double-buoy type, Christian (2000) and Gesraha (2006) studied the buoy-vertical plate type, and Dong (2009) studied the buoy-horizontal plate type. Liu et al.'s ( 2019) research shows that under the same wave conditions, the ratio of the wave attenuation efficiency of the double buoy breakwater compared with the single buoy breakwater is always larger than 2 in the studied range, which indicates that the interaction between the buoys is positive and helps to dissipate energy.
The typical representative of drag turbine is Savonius turbine (hereinafter referred to as S rotor), which was first invented by Finnish engineer Savonius. S-rotor, as a resistance type vertical axis turbine, has the advantages of low working speed, large starting torque, simple structure and low manufacturing cost.
Savonius blades, as typical vertical axis blades, are widely used in wind power generation. In recent years, more and more researchers have explored the application of Stype paddles in marine energy capture. Bikas et al. (2014) has investigated the performance of Savonius rotor type wave energy converter used in conjunction with conventional rubble mound breakwater. Kerikous and Thevenin (2019) carried out research and analysis on the optimal shape of thick blades for a hydraulic Savonius turbine. Through the analysis of different application scenarios of the S-blade, the following conclusions are drawn. As shown in Fig. 1, the vertical arrangement can effectively capture the wind energy from the x-axis and y-axis, and the wind energy moving in the z-axis direction has less influence. According to the movement of water molecules in the wave, as shown in Fig. 2, energy is transmitted along the x-axis and z-axis directions. Therefore, S-type paddles can be horizontally arranged to capture the wave energy to the maximum. Therefore, on the basis of the traditional double-buoy breakwater, this paper designs a new wave-absorbing and energy-capturing breakwater by combining the structure with horizontal axis-type S-type paddles.
The main structure shown in Fig. 3 is composed of two HDPE buoys with a diameter of 0.33 m and a length of 3 m, and two sets of 2-stage S-type paddles. As 98% of the wave energy is below the waterline, two sets of S-type paddles with horizontal axis are designed, which are composed of stainless steel end discs and HDPE impellers. The paddle density is slightly larger than water density at about 1.12 g/cm 3 . The wave energy is converted into mechanical energy through the blades, which drives the whole row of blades to rotate, and is transmitted through the transmission device to the dynamic torque sensor installed on the right side of the buoy, so as to measure the real-time torque and speed, and then the generator is driven by the speed increasing gear to realize the power conversion. Fig. 4 is a schematic diagram of the structure of a 2-stage S-type paddle. See Table 1 for specific parameters of the S-type paddle.

Design of control group floating breakwater
In order to study the wave-absorbing and energy-capturing effects of the new floating body breakwater, considering the existence of two sets of blades will increase the inertial force and affect the wave-absorbing energy-capturing performance and mooring force, a simplified version of the new floating-body breakwater is designed as its control group. The floating breakwater is composed of two HDPE buoys with a diameter of 0.33 m and a length of 3 m, and a set of 2-stage S-type paddles. At the same time, the most common double-buoy floating breakwater is used as a control. The floating breakwater consists of only two HDPE buoys with a diameter of 0.33 m and a length of 3 m, as shown in Fig. 5.

Experimental equipment and instruments
The experiments were performed in a two-dimensional wave flume in the laboratory of Ningbo Institute of Technology, Zhejiang University. The wave flume is 70 m long, 3.75 m wide and 2 m deep. One end of the water flume is equipped with a shake plate type wave maker, which can realize repeatable wave making, and the other end is provided with a fixed wave-cutting net to reduce wave reflection, thereby reducing experimental errors. The main measuring instruments include: wave height meter, tension sensor, dynamic torque sensor.

Model scale
Based on the open sea wave data combined with the en-gineering application background and the size of the experimental flume and generated waveforms, the experimental model was designed with a geometric ratio of 1:5.

Experimental model
In order to study the wave elimination and energy capture effect of this new floating breakwater, three models were designed based on similar theories. Model 1 is a traditional double-buoy breakwater without S-type paddles. Model 2 is a double-buoy breakwater with a set of S-type paddles. Refer to the improvement of the wave-absorbing effect of double buoys compared with single buoy. It is a double-buoy type breakwater with two sets of S-shaped paddles, and a comparative study of the energy capture effect.
The main parameter tables of the three models are shown in Table 2. The photos are shown in Figs. 5−8. Fig. 9 shows a schematic diagram of the experimental setup. The floating breakwater is moored at this equilibrium position. Each mooring line is made of stainless steel, with a length of 2.1 m and an average density of 0.63 kg/m. In order to measure the mooring force, four tension sensors are    connected to the windward mooring line and the leeward mooring line. Two wave height meters are arranged at 1−2 wavelengths before and after the floating breakwater to separate the reflected and incident waves and monitor the transmitted wave height and amplitude. In order to ensure the accuracy and stability of the collected data, the acquisition time is more than 30 s, the acquisition frequency is 50 Hz, the number of consecutive waves is larger than 10, and the average value is used as a reference. The incident wave period is 0.9−1.3 s, and the incident wave height is 0.1− 0.2 m. See Table 3 for details.

Wave propagation coefficient
The wave propagation coefficient includes reflection coefficient and transmission coefficient. Figs. 10 and 11 show the transmission coefficients of the three models at different wave periods when the wave height of the incident wave is 170 mm, and the transmission coefficients of the three models at different wave heights when the wave period is 1.1 s. The results show that under the same wave height, the transmission coefficient (K t ) of each model increases with the increase of the wave period; under the same period, the transmission coefficient (K t ) increases slightly with the increase of the wave height, and the change range is not obvious. Model 1 is a typical double-buoy floating breakwater with K t being 0.6−0.95. When the wave period exceeds 1.3 s, K t reaches 0.99 with almost no wave attenuation. Through comparison, it can be found that the wave reduction effect of Model 2 and Model 3 is greatly im-     proved compared with Model 1, especially Model 3 is an experimental device equipped with double-row Savonius paddles. The rotation of the paddles consumes some wave energy below the water surface. It can increase the damping of the wave, so as to obtain a better wave-killing effect. K t can be stabilized from 0.2 to 0.35, and has good applicability for waves of different periods.
P wave = P c + P r + P t + P s A two-dimensional wave separation model was used to separate the reflected waves from the waves in front of the dyke under different periods and different wave heights, and the reflection coefficient was measured. Figs. 12 and 13 show the reflection coefficients of the three models at different wave periods when the wave height of the incident wave is 170 mm, and the reflection coefficients of the three models at different wave heights when the wave period is 1.1 s. The results show that under the same wave height, the reflection coefficient (K r ) of each model decreases as the wave period increases; under the same period, the reflection coefficient (K r ) increases as the wave height increases. Under the condition that the incident wave energy is constant, , the larger the wave energy transmitted through Model 1, the smaller the reflected wave energy. Therefore, the K r curve of Model 1 is always smaller than that of Models 2 and 3, ranging from 0.1 to 0.4. In Fig. 12 and Fig. 13, K r of Model 3 is slightly larger than that of Model 2, and the variation pattern of the two is highly consistent. The reason for this phenomenon is that the trans-P t P s mitted wave power ( ) of Model 3 is still significantly reduced compared with that of Model 2, this part of wave energy should have been converted into reflected wave energy. However, the rotation of the double-row S-rotor has achieved better energy absorption and increased the capture power ( ), resulting in only a slight increase in the reflected wave power that should have been greatly increased. Therefore, K r of model 3 does not change much compared with Model 2. Fig. 14 lists the transmission coefficients (K t ) of all comparison groups. It is obvious from the figure that as the period increases, the K t curve has an upward process. Model 3 achieved the best wave cancellation performance in the comparison group experiments. K t was between 0.15 and 0.35. Compared with the ordinary double buoy breakwater, K t was reduced by 50%−76%.

Energy capture efficiency
Both Model 2 and Model 3 are equipped with S-type paddles. The torque and speed are measured by the torque sensor, and the power is calculated from the torque and speed. The power generated directly is compared directly, as shown in Fig. 15. The results show that when the wave period is about 0.9 s, the wave period is too small, so that the  blades continue to be subjected to positive and negative torque during one rotation period, the blade rotation efficiency is extremely low, and even the non-rotation occurs. The S-type paddles cannot effectively capture energy, but the existence of the blades disturbs the movement of the water flow, achieves the breaking of the waves, and achieves a better wave-eliminating effect. Between 1.1 s and 1.3 s, the S-type paddles appear to rotate significantly, especially at the 1.1 s period, the blade speed reaches 30−45 r/min. It can be seen from Fig. 15 that the blade rotation speeds of the Models 2 and 3 are not significantly different, which indicates that the rotation of the blades is related to the wave period, that is, under a certain wave period, the blades rotate at a specific speed. However, the capture power of Model 3 has been improved by nearly 30%−40%, which indicates that the double-row blades provide larger torque and achieves more powerful wave energy capture. When the wave height exceeds 170 mm, the rotation speed and capture power both decrease, and the impact of the incident wave on the blade causes wave damage. The wave height measured by the wave height meter at the embankment front changes dramatically, and the reflected wave coefficient obtained after two-dimensional wave separation also increases. It can also be seen from Fig. 13 that when the wave height exceeds 170 mm, the amplitude of the reflection coefficients of Model 2 and Model 3 varies significantly, that is, there is an optimal corresponding wave height of 170 mm for the S-rotor parameters. Fig. 16 shows the rotation speed and power under different wave periods when the incident wave height is 170 mm. In the range of 0.9−1.1 s, with the increase of wave period, blade speed and capture power gradually increase. When the wave period is 1.1 s, it is the obvious inflection point, the fastest speed is about 45 r/min, and the capture power is the largest. Fig. 17 shows that when the wave period is 1.1 s, the speed of the S-rotor does not change significantly at different wave heights, and can achieve 10−30 W power capture. When the wave height exceeds 170 mm, both the speed and the capture power decrease. Taken together, Model 3 can reach the maximum speed and power at a period of 1.1 s and 170 mm. η Table 4 shows the capture efficiency of Model 2 and Model 3 in the 1.1 s cycle. There is a big difference in the capture efficiency under different wave heights. Within the range of experimental wave heights, the capture efficiency decreases with the increase of wave heights. The maximum energy capture efficiency is achieved at the height of 110 mm wave, and the maximum power is achieved at the wave height of 170 mm.  Fig. 18, the mooring forces of Models 1, 2, and 3 are compared and analyzed from the top to bottom, including the windward side, the leeward side, and the comprehensive pulling force. It can be clearly seen in the figure that from the combination of 20 sets of experimental data, the mooring force of Model 1 is much smaller than that of Models 2 and 3. This is because Model 1 is prone to periodic fluctuations with waves, and the transmission coefficient K t is large. The reflection coefficient K r is smaller, and the wave impact on the breakwater is smaller, so the mooring force is also smaller. The wave impact on the windward side of the breakwater causes the mooring force on the windward side to be larger than that on the leeward side, which is about twice the relationship. This has important guiding significance for the design and installation of the anchorage structure of the breakwater. In Fig. 18, there are several peak points on the mooring force curve, which are the maximum mooring force values on the windward side. F w reaches 145 N at 1.1 s period and 170 mm wave height.
Figs. 19 and 20 compare and analyze the three models of the windward side mooring force (F w ) and the leeward side mooring force (F l ) at different periods in the case of 170 mm. The results show that the overall variation trend of  F w and F l is consistent with the increase of wave period, and shows a trend of synchronous decrease, which is consistent with the variation trend of reflection coefficient K r decreasing with the increase of wave period in Fig. 12. Fig. 18 shows that the total system mooring force of Model 1 is smaller than that of Model 3, but at this wave height, the mooring pull force of Model 3 is smaller than that of Model 1. It is because the wave energy impinging on Model 3 drives the S-type paddle to rotate, and the incident wave energy is absorbed by the blade and converted into S-type paddle rotational kinetic energy, which reduces the impact force on the breakwater and indirectly reduces the mooring force. As shown in Fig. 18, the total system mooring force of Model 2 is not significantly different from that of Model 3. The conclusion in Section 4.2 shows that Model 3 is superior to Model 2 in energy capture performance at wave height of 170 mm, so the impact of incident wave of 170 mm wave height on Model 2 is larger than that of Model 3. As shown in Fig. 19 and Fig. 20, the mooring force of Model 2 is larger than that of Model 3 at this wave height.
Figs. 21 and 22 will compare and analyze the three models of the front-end dyke force (F w ) and the back-end dyke force (F l ) with different wave heights in the case of 1.1 s. The results show that as the wave height increases, F w and F l of Model 1 appear to increase linearly, and the inflection point of Model 2 appears only at 170 mm. That is, a single row of S-type paddles has a better energy capture effect for the wave height at 170 mm, and achieves a reduction in     HUANG Fang-ping et al. China Ocean Eng., 2020, Vol. 34, No. 6, P. 817-827 825 mooring force. Model 3 is different from Model 2 in that it shows a downward trend at both 140 mm and 170 mm. Especially at 170 mm wave height, the mooring force decreases significantly. When the wave height range applicable to the blades is exceeded, the mooring pull forces of Model 2 and Model 3 increase significantly.
In order to more intuitively explore the effect of doublerow S-blades on mooring force, Fig. 23 and Fig. 24 compare and analyze the comprehensive tensile force of Model 3 under different periods and different wave heights in two different ways. It can be seen from Fig. 23 that at a wave height of 170 mm, the F s curve is always at the bottom and the pulling force is 20−40 N. Fig. 24 shows that at the wave height smaller than 170 mm, F s decreases with the increase of the height; at the height of 170 mm, F s reaches the lowest point; and at the height larger than 170 mm, F s increases significantly with the increase of the height. This indicates that the mooring force F s has a minimum value with respect to the change of wave height, and no matter how the wave period changes the mooring force F s would definitely reach the minimum at the wave height of 170 mm under the specific experiment condition of this paper. Fig. 23 and Fig. 24 can be well verified.

Conclusions
In this paper, we propose a new type of floating break-water combined with Savonius blades. Corresponding experimental studies have verified the effectiveness of the model's wave elimination and energy harvesting performance. Based on the experimental results, the following conclusions can be drawn. 12π/5 (1) Compared with the traditional floating breakwater, the SDBB model increases the wave attenuation damping, the wave attenuation coefficient K t can be stabilized between 0.2−0.35, and the wave attenuation performance is improved by 45% to 65%. For destructive waves with frequency (kd) larger than , it has better wave elimination performance. Savonius blades play an important role in the attenuation of waves.
(2) Under the wave condition of periods of 1.1−1.3 s, the S-type paddle appears obvious rotation, especially at 1.1 s period, the blade speed reaches 30−45 r/min, and the SDBB model can achieve 25−45 W power capture. Compared with single-row blades, double-row blades better adapt to energy capture under different wave conditions, and have a 30%−40% improvement in energy capture efficiency.
(3) The installation of the paddle group increases the tension on the mooring line as a whole, but at a wave height of 140−170 mm, the paddle group achieves effective capture of wave energy through smooth rotation, thereby reducing the mooring force.
Through experimental research, it can be concluded that the combination of Savonius paddles and double buoy floating breakwaters significantly improves the wave elimination performance and achieves a certain power offshore energy supply. However, further research is needed on the corresponding correspondence between proportional dimensions and different sea conditions.