Pilot-frequency floater wave energy device array structure optimization method

Abstract

The invention belongs to the field of wave energy power generation, and discloses a pilot-frequency floater wave energy device array structure optimization method, which comprises the following steps of: giving an input wave energy spectrum frequency band reconstruction division strategy by combining the technical attributes of a wave energy device; based on an energy obtaining spectrum theory, deducing full-band equivalent energy capture of the device, and clarifying energy obtaining contribution of the device in the array in each band; the input sea wave spectrum is used as the target spectrum, array configuration design is carried out, the matching condition of floaters in the array is determined, the accurate matching of the output level of the array and resources is realized, and the development and utilization efficiency of the array is improved. According to the method, factors such as the mass, the resonance bandwidth, the inherent frequency and applied PTO damping of the floater are comprehensively considered, the relation of influence factors is established, pilot frequency floater wave energy devices meeting the requirements under specific sea area conditions are efficiently found in a simple and rapid means, an array composed of the pilot frequency floater wave energy devices can absorb incident wave energy in a full-band mode, and the wave energy efficiency is improved. And the utilization rate of the wave energy is greatly improved.

Description

Technical Field

[0001] The present invention belongs to the field of wave energy power generation, and particularly relates to an optimization method for the array structure of a heterogenous-frequency (different frequency responses) float wave energy device. Background Art

[0002] As an important part of ocean energy, the development and utilization of wave energy will effectively relieve the energy supply pressure in coastal areas and generate significant economic benefits. Wave energy power generation devices can be roughly divided into three categories according to their working principles: oscillating water column type, oscillating body type, and concentrating wave overtopping type. Among them, the oscillating body type device has been widely developed due to its advantages such as simple design, high economy, wide environmental adaptability, and flexible modular expansion.

[0003] Wave energy devices capture wave energy and convert it into electrical energy to achieve wave power generation. However, the cost of arranging oscillating floats alone is relatively high, making it difficult to meet the large-scale power supply demand. However, arranging wave energy devices in an array can improve the wave energy capture efficiency, share the mooring system on a large scale, and reduce the levelized cost of electricity.

[0004] The frequency domain characterizes the incident structure of ocean waves, and existing research has mainly focused on the time domain. As a form of frequency domain characterization, the physical meaning of the ocean wave spectrum is that the actual ocean wave energy can be regarded as a combination of wave energies with different frequency distributions. This spectrum structure requires that the array device needs to be configured with devices with different frequency response ranges to achieve the purpose of improving the energy capture efficiency. Ocean waves have a wide-spectrum characteristic. If the traditional design mode of simply superimposing the same-frequency devices is used, some wave energy in certain frequency bands will inevitably be lost. Under the constraint of a fixed sea area, the energy capture efficiency of the array device may be reduced. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above-mentioned deficiencies of the prior art and provide an optimization method for the array structure of a heterogenous-frequency float wave energy device. The heterogenous-frequency float designed by using this method needs to be based on the division of the ocean wave spectrum frequency bands in the target sea area and fully absorb the wave energy in the corresponding frequency bands, greatly improving the utilization rate of wave energy.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions: An optimization method for the array structure of a heterogenous-frequency float wave energy device, comprising: (1) Combining the attributes of the wave energy device (such as factors like radius, draft, and applying PTO damping), formulating an input ocean wave spectrum division and reconstruction strategy; Utilize the wave energy within the frequency band to match wave energy devices with different frequency responses to different frequency bands of the wave spectrum. The method of dividing the wave spectrum frequency band adopts the equal-energy division method. For each frequency band based on the equal-energy division method, corresponding floats need to be configured. The design of the corresponding floats should ensure that their resonance bandwidth is the same as the bandwidth of the divided frequency band interval. Among them, the floats designed based on each frequency band are called one type of float. If the target wave spectrum is divided into N frequency bands, then there are a total of N types of float devices with different characteristics; The technical term "equal-energy division method" appears in the book "Random Waves and Their Engineering Applications" (written by Yu Yuxiu), and it is clearly pointed out in the book that there is a method of equal-energy division.

[0007] (2) Use the energy acquisition spectrum method to quickly deduce and predict the equivalent energy acquisition of each device in the full frequency band. The physical meaning of the energy acquisition spectrum is the energy acquisition level of the device within a unit frequency interval; The energy acquisition spectrum is a technical term in the existing technology. Its physical meaning is the energy acquisition level of the device within a unit frequency interval. Based on the energy acquisition spectrum theory, several types of floats are designed as references. By calculating their absorption coefficients, the energy acquisition spectrum density function of various types of floats is determined, and the energy acquisition efficiency of each type of float device is calculated. Furthermore, the equivalent energy capture of the floats in the full frequency band is determined, and the energy acquisition contribution of the device in each frequency band is clarified; (3) Construct a wave energy array device configuration to achieve the optimal energy acquisition in the target sea area; Optimize the float parameters and their ratio to achieve wave energy absorption. Based on the number of floats designed for different frequency bands, establish an equation for the number configuration of floats and the energy acquisition efficiency: , In the formula, represents the number of floats corresponding to the first frequency band, represents the number of floats corresponding to the second frequency band, and so on. The total number of floats is , is a non-negative integer; represents the th type of float in the th frequency band, and thus the specific number of floats in each frequency band can be obtained.

[0008] In the above (1), in order to achieve the purpose of maximizing the energy acquisition of the float array device within a limited sea area, a target function is constructed: , In the formula, N represents the number of intervals divided by the energy equal-division method in the research frequency interval, is the number of the jth type of float, represents the efficiency of the jth type of float when the incident frequency is , represents the wave spectrum.

[0009] The constraint conditions of the objective function are as follows: (a)The total number of floats is limited, and the maximum value of the total number of floats is , and there is an upper limit to the total number of all floats, expressed as: , (b)The total absorbed energy of all floats cannot exceed the input energy of the wave spectrum, expressed as: , (c)The capture efficiency of the float cannot exceed the capture efficiency at resonance, expressed as: , In the formula, represents the natural frequency of the float, represents the maximum capture efficiency that the float can theoretically achieve, represents the wavelength when the wave incidence frequency is equal to the natural frequency of the float, represents the characteristic width of the float. If the float is cylindrical, then: ; The Lagrange multiplier method is used to construct a new objective function: , In the formula and are both constants. Taking the partial derivative of gives: , When the above formula is 0, it is the distribution of the number of floats when the total captured energy is the largest, and we can get: , Therefore, for any float, it is necessary to satisfy , where C is a constant, that is, the unit energy contribution of the floats designed in each frequency band is equal, and equal energy division is required.

[0010] In (2) above, the absorption coefficient is: , In the formula, represents the absorption coefficient, represents the incident wave frequency, represents the complex heaving motion response amplitude under a unit wave amplitude, B is the PTO damping coefficient, is the density, is the acceleration due to gravity, is the width of the device along the wave crest line direction, c is the wave speed, and n is the water depth related function.

[0011] The energy capture spectral density function in (2) above is: , In the formula represents the unit frequency interval, represents the incident wave frequency, represents the absorption coefficient of the nth wave, A n represents the wave amplitude of the nth incident wave.

[0012] In the above (2), the energy harvesting efficiency of the device , whose physical meaning is the ratio of the energy harvested by the device to the incident wave energy under unit width, is expressed as: , In the formula, represents the energy harvesting spectral density function, represents the sea wave spectrum function.

[0013] The resonance bandwidth of the float is equal to the bandwidth of the corresponding wave energy frequency band and can fully absorb the wave energy of the corresponding frequency band.

[0014] The resonance bandwidth is defined as: the absolute value of the difference between two frequencies corresponding to a relative absorption power equal to 0.5.

[0015] The relative absorption power is the ratio of the absorption power of the float to the theoretical maximum absorption power, with a maximum value of 1. The relative absorption power is expressed as: , where: , In the formula, B represents the PTO damping coefficient, represents the radiation damping, represents the mass of the float, represents the added mass of the float.

[0016] Let the function value of the above formula be 0.5, and the solutions of the two frequencies can be obtained, expressed as: , , In the formula, represents the incident wave frequency, is the natural frequency, represents the absorption power, represents the absorption power of the float when the incident frequency is the natural frequency, is the wave force, represents the wave force when the incident frequency is the natural frequency.

[0017] , where: , In the formula, is the mass of the float, is the function of the added mass with respect to the incident frequency, and B is the PTO damping coefficient, is the function of the radiation damping with respect to the incident frequency.

[0018] The expression of the natural frequency of the float is: , The natural frequency of the float is equal to the ratio of the first moment to the zero moment of the energy capture spectrum.

[0019] The optimal damping of the float is: , wherein, and respectively represent the start and end frequencies of the frequency band interval; represents the mass of the float, represents the added mass of the float when the incident frequency is the natural frequency; if the above formula holds, the characteristics of the float should meet two requirements: the damping applied at this time should be the optimal damping , and at the same time, the start and end frequencies of the resonance bandwidth of the float are consistent with the corresponding frequency band, thereby establishing the connection between the optimal damping, the resonance bandwidth, and the mass of the float.

[0020] The beneficial effects of the present invention are as follows: Based on the energy analysis of the sea wave spectrum, the present invention provides a design method for a heterodyne float. The heterodyne float designed by this method needs to be based on the sea wave spectrum frequency band division of the target sea area and fully absorb the wave energy of the corresponding frequency band. This method comprehensively considers factors such as the mass, resonance bandwidth, natural frequency, and applied PTO damping of the float, and establishes the connection between the influencing factors. With simple and fast means, it efficiently finds a heterodyne float wave energy device that meets the requirements under specific sea area conditions. The array composed of heterodyne float wave energy devices can absorb the incident wave energy in the full frequency band, greatly improving the utilization rate of wave energy. The present invention guides the matching of heterodyne floats in the array, realizes the precise matching of the resonance bandwidth of the float with the sea wave spectrum of the target frequency band, indicates that the heterodyne float array has the characteristic of wideband energy capture, breaks through the problem of low energy capture level caused by the narrow bandwidth response of traditional homodyne devices, and shows that the heterodyne float array is more adaptable to the energy distribution of the sea wave spectrum and has potential engineering economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a diagram showing the change of relative absorption power under different damping factors; Figure 2 Schematic diagram of the energy capture spectrum of the float; Figure 3 is the capture width ratio (CWR) (left figure) and the absorption power change diagram (right figure) of the heterodyne float (a), heterodyne float (b), and heterodyne float (c); The capture width ratio (CWR) of the heterodyne float (a) (left figure) corresponds to the absorption power variation diagram (right figure). Figure 3 of (a) and Figure 3 of (b); The capture width ratio (CWR) of the heterodyne float (b) (left figure) corresponds to the absorption power variation diagram (right figure). Figure 3 of (c) and Figure 3 of (d); The capture width ratio (CWR) of the heterodyne float (c) (left figure) corresponds to the absorption power variation diagram (right figure). Figure 3 of (e) and Figure 3 of (f); Figure 4 is the capture width ratio (CWR) of the float (d) under the optimal damping (left figure a) and the absorption power variation diagram (right figure b); Figure 5 is the absorption power comparison diagram of the heterodyne and homodyne float arrays at different spacings in the frequency domain analysis; Figure 6 is the absorption power comparison diagram of the heterodyne and homodyne float arrays at different spacings in the time domain analysis. Detailed implementation manners

[0022] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0023] The structures, ratios, sizes, etc. shown in the drawings of this specification are only used to cooperate with the content disclosed in the specification for those familiar with this technology to understand and read, and are not used to limit the limiting conditions under which the present invention can be implemented. Therefore, they do not have a substantial technical meaning. Any modification of the structure, change of the proportional relationship, or adjustment of the size, without affecting the effects that the present invention can produce and the purposes that can be achieved, should still fall within the scope covered by the technical content disclosed in the present invention. At the same time, the terms such as "upper", "lower", "left", "right", "middle", and "one" cited in this specification are only for the convenience of clear narration and are not used to limit the scope under which the present invention can be implemented. The change or adjustment of their relative relationships, without substantial change in the technical content, should also be regarded as the scope under which the present invention can be implemented.

[0024] In the present invention, the design of the float needs to consider the natural frequency. The natural frequency is mainly affected by the radius, draft, PTO damping, and PTO stiffness coefficient. It can be expressed as: , In the present invention, the resonance bandwidth design of the float also needs to be considered. According to the heaving motion equation of the float in the frequency domain: , where is the mass of the float, is the function of added mass with respect to the incident frequency, B is the PTO damping coefficient, is the function of radiation damping with respect to the incident frequency, is the PTO stiffness coefficient, is the hydrostatic restoring force coefficient, is the wave force, is the complex amplitude of heaving motion. The absorbed power of the buoy can be obtained as: , wherein is the complex velocity amplitude of heaving motion. According to Rolle's mean value theorem, when or , , so there exists such that the absorbed power is maximum, and we can get: , This damping is called the optimal damping. When the buoy reaches the resonance state and the optimal damping is applied, the absorbed power of the buoy reaches the maximum value, which can be expressed as: , Therefore, for any damping coefficient B, there exist and such that: , Substituting the expression of the optimal damping, it can be known that the optimal damping at this time should be equal to the radiation damping in the resonance state.

[0025] Substituting the expression of the natural frequency of the buoy's heaving motion into the expression of the absorbed power, we can get: , where: , And the above formula is defined as the damping factor. The relative absorbed power is defined as the ratio of the absorbed power of the buoy to the theoretical maximum absorbed power, and the maximum value is 1. The change of the relative absorbed power is as Figure 1 shown, and it can also be expressed as: , Let the function value of the above formula be 0.5, and the solutions of the two frequencies can be obtained, expressed as: , , In the present invention, the resonance bandwidth is defined as: the absolute value of the difference between the two frequencies corresponding to the relative absorbed power equal to 0.5. Applying a higher damping can maintain a wider resonance bandwidth, so this kind of buoy can absorb wave energy from a larger frequency band range, and improve the comprehensive utilization rate of wave energy in the whole frequency band by expanding the bandwidth.

[0026] In the present invention, the concept of "energy capture spectrum" is introduced, and the energy capture spectrum can characterize the energy capture of the device within a unit frequency interval. Assuming that the device captures energy only by absorbing the energy of the incident wave amplitude, without causing other changes, and completely absorbs all the wave energy of the incident wave amplitude, then the incident wave amplitude can be expressed as: , where represents the absorption coefficient, A is the incident wave amplitude, and the incident wave amplitude is defined as the virtual energy capture wave surface. The energy capture calculated from the virtual energy capture wave surface should be equivalent to the actual device motion energy capture, that is, the average wave power of the virtual energy capture wave surface is equal to the single-width average wave power of the device, and we can get: , where is the width of the device along the wave crest line direction, c is the wave speed, n is the water depth related function, represents the complex heave motion response amplitude under a unit wave amplitude, and thus the absorption coefficient can be obtained: , Introducing the concept of the absorption coefficient into random waves, the expression of the virtual energy capture wave surface can be obtained: , where represents the absorption coefficient of the nth wave, represents the control equation of the virtual energy capture wave surface. After introducing the virtual energy capture wave surface, the above formula is still the expression of the random wave surface. Since the average wave energy of random waves is the superposition of the average wave energies of each component wave, by analogy with the above concept, the time-domain equation can be transformed into: , Therefore, we can obtain: , The relationship between the energy capture spectrum density function and the sea wave spectrum can be obtained: , The energy capture efficiency of the device, whose physical meaning is the ratio of the energy capture of the device under unit width to the incident wave energy, is expressed as: .

[0027] In the present invention, the sea wave spectrum is divided into frequency bands to fully utilize the sea wave energy within a specific frequency band, and to match the devices with different frequency responses to different frequency bands of the sea wave spectrum, so as to achieve the purpose of improving the energy capture efficiency. The method for dividing the sea wave spectrum needs to meet the following two requirements: 1) The relatively high-frequency and low-frequency intervals of the sea wave spectrum can be ignored; 2) The segmentation of the sea wave spectrum should not be too dense or sparse. In the present invention, the method for dividing the sea wave spectrum frequency band adopts the equal energy division method.

[0028] For each frequency band based on the equal - energy division method, dedicated floats need to be configured. The design of the dedicated floats should ensure that their resonance bandwidth is the same as the bandwidth of the divided frequency band interval to achieve efficient utilization of wave energy within that frequency band. Among them, the floats designed based on each frequency band are called type - 1 floats. If the target sea - wave spectrum is divided into N frequency bands, then there are a total of N types of float devices with different characteristics.

[0029] To achieve the goal of maximizing the energy capture of the float - array device within a limited sea - area, the present invention constructs an objective function: , In the formula, N represents the number of intervals divided by the energy - equal - division method in the research frequency range, is the number of the j - th type of float, represents the efficiency of the j - th type of float when the incident frequency is . Then the constraint conditions of this objective function are: (a) The total number of floats is limited, and the maximum value of the total number of floats is . There is an upper limit to the total number of all floats, which is expressed as: , (b) The total absorbed energy of all floats cannot exceed the input energy of the sea - wave spectrum, which is expressed as: , (c) The capture efficiency of the float cannot exceed the capture efficiency at resonance, which is expressed as: , In the formula, represents the natural frequency of the float, represents the maximum capture efficiency that the float can theoretically achieve, represents the wavelength when the wave incident frequency is equal to the natural frequency of the float. The Lagrange multiplier method is used to construct a new objective function: , Taking the partial derivative of gives: , When the above formula is 0, it is the distribution of the number of floats when the total captured energy is the largest, and we can get: , Therefore, for any float, it is necessary to satisfy , where C is a constant, that is, the unit - energy contribution of the floats designed for each frequency band is equal, and equal - energy division is required.

[0030] The present invention aims to explore the energy-harvesting characteristics of floats along the wave crest line propagation direction within a limited sea area, and to achieve efficient absorption of wave energy by optimizing float parameters and ratios. Therefore, it is necessary to determine the number of floats designed based on different frequency bands. To ensure that the floats fully absorb the energy of each frequency band, an equation for the number of floats and energy-harvesting efficiency can be established: , In the formula, Represents the number of floats corresponding to the first frequency band, Represents the number of floats corresponding to the second frequency band, and so on. The total number of floats is ( is a non-negative integer); Representative Class float in The energy acquisition efficiency within the frequency band, from which the specific number of floats in each frequency band can be known.

[0031] The design principles of the float include: (1) Matching of float response characteristics. The resonant bandwidth of the float should be equal to the bandwidth of the corresponding frequency band, and it should be able to fully absorb the wave energy of the corresponding frequency band.

[0032] (2) Design of float natural frequency. The present invention designs the corresponding float natural frequency based on the center of gravity position of the wave spectrum in each frequency band, ensuring that the float natural frequency matches the main energy distribution area and improving the utilization rate of the high energy density frequency band, which can be expressed as: , From this we can get the natural frequency expression: , Therefore, the natural frequency of the float is equal to the ratio of the first-order moment of the spectrum to the zero-order moment.

[0033] (3) Optimal damping design. Combine the following formulas: , , , , It can be found that: , In the formula and Represent the start and end frequencies of the frequency band respectively. If the above formula is established, the characteristics of the float should meet two requirements: the damping applied at this time should be the optimal damping , and the start and end frequencies of the float resonance bandwidth are consistent with the corresponding frequency band. This establishes the relationship between optimal damping, resonance bandwidth and float mass. Example 1:

[0034] Taking the wave spectrum fitted from the measured data in the Zhaitangdao Sea area as an example for analysis, the sea area conditions are shown in Table 5:

[0035] Table 5 shows the characteristic parameters of the wave spectrum in the target sea area.

[0036] Select the wave spectrum in the range of 1 - 2.5 rad / s in the target sea area as the research frequency band. After calculation, this frequency band contains more than 90% of the energy of the incident wave. The frequency band is divided by the energy equal - division method, and corresponding different - frequency floats are designed to capture wave energy based on each frequency band. The parameters are shown in Table 6:

[0037] Table 6 shows the start - end frequencies of the corresponding frequency bands and the names of the corresponding designed floats.

[0038] Apply the method of the present invention to construct the cylindrical different - frequency heaving float wave energy device and its array. The radius of the float is fixed at 2m, and the draft depth, PTO damping, and PTO stiffness coefficient are used as design variables, while other parameters remain unchanged, as shown in Table 7:

[0039] Table 7 shows the setting of float parameters.

[0040] The actual energy - capturing level of the float may be very different from the theory in the actual sea conditions, and the capture width ratio and absorption power calculated based on the numerical simulation under ideal conditions may be on the high side. Referring to the research on the maximum capture width ratio of the oscillating float in the actual sea conditions, the present invention limits the maximum capture width ratio of the cylindrical float model not to exceed 0.2. The optimization results of a single float are as Figure 3 shown, proving that the three floats (a), float (b), and float (c) can absorb the wave energy in the corresponding frequency bands.

[0041] Combine the three floats into a different - frequency float array, and the arrangement method is: place the high - frequency float in front and the low - frequency float behind along the incident wave direction. The reason is that the float with a smaller natural frequency is more sensitive to the energy absorption of long - period waves, and moving its position backward has less impact on the overall energy - capturing level of the array. The calculated energy - capturing efficiency results of each float in each frequency band are shown in Table 8:

[0042] Table 8 shows the energy - capturing efficiency of each float in each frequency band.

[0043] To ensure that the float completely absorbs the energy of each frequency band, establish an equation for the float number configuration and the energy - capturing efficiency: , where , and are all positive integers, representing the number of floats (a), floats (b), and floats (c) respectively. Thus, the optimization model is obtained: .

[0044] This optimization model represents the smallest positive integer solution of the total number of floats in the heterogenous frequency array. The solution results are shown in Table 9: Float Name Float (a) Float (b) Float (c) Number of Floats (pcs) 4 2 5 Table 9 shows the matching ratios of the number of each float that meet the conditions.

[0045] In the specific implementation process, the arrangement method is as follows: 5 floats (c), 2 floats (b), and 4 floats (a) are arranged in sequence along the incident wave direction. Since the energy capture of the float array is unstable at a spacing of 1R (R = 2m), a spacing of 2R - 5R is selected for energy capture analysis.

[0046] To evaluate the energy capture level of the array, in addition to the device energy capture efficiency, the present invention constructs the cumulative power formula based on the weighted average idea, which can be expressed as: , where represents the number of research frequency bands divided according to frequency. Usually has a relatively large value, represents the energy of the i-th frequency band, E represents the total energy within the domain, and represent the absorption powers corresponding to the endpoint frequencies of the i-th frequency band respectively. In this study, the selected frequency band range is 1 - 2.5 rad / s, . Taking the 50th ocean wave spectrum frequency band (1.5 - 1.51 rad / s) as an example, the calculated energy proportion , assuming and are respectively , , substituting into the above formula, the contribution value of this frequency band can be obtained as 0.51 W. By analogy for other frequency intervals, the cumulative power is finally obtained through full-frequency band accumulation. This index needs to be calculated in combination with the ocean wave spectrum energy density function and can quantify the contribution of energy distribution in different frequency bands to the absorption power.

[0047] Using the same idea, the present invention constructs the cumulative power area ratio and the cumulative power mass ratio to evaluate the economic performance, which are respectively expressed as: ,

[0048] where is: ,

[0049] wherein is the total length of the incident wave direction array, represents the total sea area used by the array.

[0050] ,

[0051] In the formula represents the th float mass in the array.

[0052] To fully illustrate the effectiveness of constructing a heterogenous frequency float array using the optimized scheme, it is still necessary to construct homogenous frequency floats and their array, and compare their energy harvesting with that of the heterogenous frequency float array under the same conditions. The number of the homogenous frequency float array should be 11, the same as that of the heterogenous frequency float array. The name of the homogenous frequency float is float (d), and its parameters are shown in Table 10:

[0053] Table 10 shows the parameters of float (d). The energy harvesting level of this float is as Figure 4 shown.

[0054] In the frequency domain analysis, the comparison of the absorption power of the heterogenous and homogenous frequency float arrays at different spacings is as Figure 5 shown. In the time domain analysis, the comparison of the average power of the two at different spacings is as Figure 6 shown. Among them, in the time domain analysis, the JONSWAP target spectrum constructed using the measured data of Zhaitangdao Sea area is used for the numerical simulation of irregular waves. The simulation step size is 0.02 s, the total time is 600 s, and the selected time frequency band is 300 - 600 s for analysis.

[0055] In summary, the present invention proposes a method for optimizing the structure of a heterogenous frequency wave energy device and its array. Based on the energy analysis of the ocean wave spectrum, this method gives the design method of heterogenous frequency floats, guides the matching of heterogenous frequency floats in the array, realizes the precise matching of the resonance bandwidth of the floats and the ocean wave spectrum in the target frequency band, shows that the heterogenous frequency float array has the characteristic of broadband energy harvesting, breaks through the problem of low energy harvesting level caused by the narrow bandwidth response of traditional homogenous frequency devices, and shows that the heterogenous frequency float array is more adaptable to the energy distribution of the ocean wave spectrum and has potential engineering economy.

[0056] Although the specific implementation manners of the present invention are described above in conjunction with the accompanying drawings, it is not a limitation to the protection scope of the present invention. Those skilled in the art should understand that, based on the technical solutions of the present invention, various modifications or deformations that can be made by those skilled in the art without creative efforts are still within the protection scope of the present invention.

Claims

1. An optimization method for the array structure of a heterodyne float wave energy device, characterized in that Including: (1) Formulate a reconstruction strategy for dividing and inputting the ocean wave spectrum in combination with the attributes of the wave energy device; Utilize the ocean wave energy within the frequency band to match wave energy devices with different frequency responses to different frequency bands of the ocean wave spectrum. The method for dividing the ocean wave spectrum frequency band adopts the equal energy division method. Corresponding floats need to be configured for each frequency band based on the equal energy division method. The design of the corresponding floats should ensure that their resonance bandwidth is the same as the bandwidth of the divided frequency band interval. Among them, the floats designed based on each frequency band are called one type of float. If the target ocean wave spectrum is divided into N frequency bands, then there are a total of N types of float devices with different characteristics; (2) Use the energy acquisition spectrum method to quickly deduce and predict the equivalent energy acquisition of each device in the full frequency band; The energy acquisition spectrum can characterize the energy acquisition of the device within a unit frequency interval. Based on the energy acquisition spectrum theory, design several types of floats as references, determine the energy acquisition spectrum density function of various types of floats by calculating their absorption coefficients, calculate the energy acquisition efficiency of each type of float device, and then determine the equivalent energy capture of the floats in the full frequency band, clarifying the energy acquisition contribution of the device in each frequency band; (3) Construct a wave energy array device configuration to achieve the optimal energy acquisition in the target sea area; Optimize the float parameters and their ratio to achieve wave energy absorption. Based on the number of floats designed for different frequency bands, establish an equation for the number configuration of floats and the energy acquisition efficiency: ， Wherein, represents the number of floats corresponding to the first frequency band, represents the number of floats corresponding to the second frequency band, and so on. The total number of floats is , being a non - negative integer; represents the energy harvesting efficiency of the type of floats in the frequency band, from which the specific number of floats in each frequency band can be obtained.

2. The method for optimizing the structure of the off-frequency floater wave energy device array according to claim 1, characterized in that, In the above (1), to achieve the goal of maximizing the energy capture of the float array device within a limited sea area, an objective function is constructed: , where N represents the number of intervals into which the research frequency range is divided by the equal energy method, is the number of floats of the j-th type, represents the efficiency of the j-th type of float at the incident frequency of when, represents the sea wave spectrum.

3. The method for optimizing the structure of the off-frequency floater wave energy device array according to claim 2, characterized in that, The constraint conditions of the objective function are: (a) The total number of floats is limited, and the maximum value of the total number of floats is , and there is an upper limit to the total number of all floats, expressed as: ， (b) The total absorbed energy of all floats cannot exceed the input energy of the ocean wave spectrum, expressed as: ， (c) The capture efficiency of the float cannot exceed the capture efficiency at resonance, expressed as: ， In the formula, represents the natural frequency of the float, represents the maximum capture efficiency that the float can theoretically achieve, represents the wavelength when the wave incident frequency is equal to the natural frequency of the float, represents the characteristic width of the float.

4. The method for optimizing the structure of the off-frequency floater wave energy device array according to claim 3, characterized in that, Adopt the Lagrange multiplier method to construct a new objective function: ， where and are both constants. Taking the partial derivative with respect to yields: ， When the above formula is 0, it is the distribution of the number of floats when the total captured energy is the largest, and we get: ， Therefore, for any float, it is necessary to satisfy , where C is a constant, that is, the unit energy contribution of the floats designed for each frequency band is equal, and equal energy division is required.

5. The method for optimizing the structure of the off-frequency floater wave energy device array according to claim 1, characterized in that In (2) above, the absorption coefficient is: , In the formula, represents the absorption coefficient, represents the frequency of the incident wave, represents the amplitude of the complex heaving motion response under unit wave amplitude, B is the PTO damping coefficient, is the density, is the acceleration due to gravity, is the width of the device along the wave crest line direction, c is the wave speed, and n is the water depth correlation function.

6. The method for optimizing the structure of the off-frequency floater wave energy device array according to claim 1, characterized in that, The energy spectrum density function obtained in (2) is as follows: , In the formula, represents the unit frequency interval, represents the frequency of the incident wave, represents the absorption coefficient of the nth wave, A n represents the amplitude of the nth incident wave.

7. The optimization method for the structure of the off-frequency floater wave energy device array according to claim 1, characterized in that, In (2) above, the energy acquisition efficiency of the device , whose physical meaning is the ratio of the energy acquired by the device to the incident wave energy per unit width, is expressed as: , In the formula, the energy spectrum density function, represents the sea wave spectrum function.

8. The method for optimizing the structure of the off-frequency float wave energy device array according to claim 1, characterized in that The resonance bandwidth of the float is equal to the bandwidth of the corresponding wave energy frequency band and can fully absorb the wave energy of the corresponding frequency band; the resonance bandwidth is defined as: the absolute value of the difference between two frequencies corresponding to a relative absorption power equal to 0.

5.

9. The method for optimizing the structure of the off-frequency float wave energy device array according to claim 8, characterized in that, The relative absorption power is the ratio of the absorption power of the float to the theoretical maximum absorption power, with a maximum value of 1, and the relative absorption power is expressed as: , Where: ， where B represents the PTO damping coefficient, represents the radiation damping, represents the mass of the float, represents the added mass of the float; Let the function value of the above formula be 0.5, and the solutions of the two frequencies can be obtained, expressed as: ， ， In the formula, represents the incident wave frequency, is the natural frequency, represents the absorbed power, represents the absorbed power of the float when the incident frequency is the natural frequency, and is the wave force, represents the wave force when the incident frequency is the natural frequency; ， Wherein: , wherein, is the mass of the float, is the function of the added mass with respect to the incident frequency, B is the PTO damping coefficient, is the function of the radiation damping with respect to the incident frequency.

10. The method for optimizing the structure of the off-frequency floater wave energy device array according to claim 1, characterized in that, The natural frequency expression of the float is as follows: ， The natural frequency of the float is equal to the ratio of the first moment to the zero moment of the energy acquisition spectrum; The optimal damping of the float is as follows: ， In the formula, and represent the start and end frequencies of the frequency band interval respectively; is the mass of the float, represents the added mass of the float when the incident frequency is the natural frequency; if the above formula holds, the characteristics of the float should meet two requirements: the damping applied at this time should be the optimal damping , and at the same time, the start and end frequencies of the resonance bandwidth of the float are consistent with the corresponding frequency band, thus establishing the connection between the optimal damping, the resonance bandwidth and the mass of the float.

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