Array structure optimization method of heterogeneous frequency buoy wave energy device

Abstract

The present invention belongs to the field of wave energy power generation, and discloses a method for optimizing the structure of an array of heterogeneous floating wave energy devices. In combination with the technical properties of the wave energy device, a frequency band reconstruction and division strategy for the input wave energy spectrum is given; based on the energy spectrum theory, the equivalent energy capture of the device in the full frequency band is derived, and the energy contribution of the devices in the array in each frequency band is clarified; with the input wave spectrum as the target spectrum, the array configuration design is carried out, the ratio of the floats in the array is clarified, and the array output level and the resource are accurately matched, thereby improving the development and utilization efficiency of the array. This method comprehensively considers factors such as the mass, resonance bandwidth, natural frequency, and applied PTO damping of the float, and establishes a connection between the influencing factors. In a simple and quick way, it efficiently finds the heterogeneous floating wave energy device that meets the requirements under specific sea conditions. The array composed of heterogeneous floating wave energy devices can absorb the incident wave energy in the full frequency band, greatly improving the utilization rate of wave energy.

Description

Technical Field

[0001] The present invention belongs to the field of wave energy power generation, and in particular relates to a method for optimizing the array structure of a heterogeneous frequency (different frequency response) buoy wave energy device. Background Art

[0002] As a key component of ocean energy, the development and utilization of wave energy will effectively alleviate energy supply pressures in coastal areas and generate significant economic benefits. Wave energy power generation devices can be broadly classified into three categories based on their operating principles: oscillating water column, oscillating body, and wave-gathering and overtaking. Oscillating body devices are widely developed due to their simple design, high cost-effectiveness, wide environmental adaptability, and flexible modular expansion.

[0003] Wave energy devices capture wave energy and convert it into electricity, enabling wave-based power generation. However, deploying individual oscillating floats is costly and difficult to meet large-scale power supply needs. However, arrays of wave energy devices can improve wave energy capture efficiency, enable large-scale sharing of mooring systems, and reduce the levelized cost of electricity.

[0004] The frequency domain characterizes the incident structure of ocean waves, while existing research has mostly focused on the time domain. The wave spectrum, as a form of frequency domain characterization, physically means that actual ocean wave energy can be considered a combination of wave energy distributed across different frequencies. This spectral structure requires that array devices be configured in a composite configuration with devices having different frequency response ranges to achieve improved energy capture efficiency. Ocean waves have a broad spectrum, and if the traditional design model of simply stacking devices of the same frequency is used, wave energy in some frequency bands will inevitably be lost. This, within the constraints of a fixed ocean area, may reduce the array device's energy capture efficiency. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a method for optimizing the array structure of a heterofrequency float wave energy device. The heterofrequency floats designed using this method need to be based on the frequency band division of the wave spectrum of the target sea area and fully absorb the wave energy of the corresponding frequency band, thereby greatly improving the utilization rate of wave energy.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for optimizing the array structure of a heterogeneous frequency buoy wave energy device comprises:

[0008] (1) Develop a strategy for partitioning and reconstructing the input wave spectrum based on the properties of the wave energy device (such as radius, draft, and applied PTO damping);

[0009] Utilizing the wave energy within the frequency band, wave energy devices with different frequency responses are matched to different frequency bands of the wave spectrum. The method for dividing the wave spectrum frequency bands adopts the equal energy division method. Each frequency band based on the equal energy division method needs to be configured with a corresponding float. The design of the corresponding float should ensure that its resonance bandwidth is the same as the bandwidth of the divided frequency band interval. The float designed for each frequency band is called a type of float. If the target wave spectrum is divided into N frequency bands, there are N types of float devices with different characteristics.

[0010] The technical term equal energy partitioning method appears in the book Random Waves and Their Engineering Applications (written by Yu Yuxiu), which clearly points out that there is a method of equal energy partitioning.

[0011] (2) Using the energy spectrum method, quickly deduce and predict the equivalent energy of each device in the full frequency band. The physical meaning of the energy spectrum is the energy level of the device within a unit frequency interval;

[0012] Energy acquisition spectrum is a technical term. Its physical meaning is the energy acquisition level of a 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 each type of float is determined. The energy acquisition efficiency of each type of float is calculated, and then the equivalent energy capture of the float in the entire frequency band is determined, clarifying the energy acquisition contribution of the device in each frequency band.

[0013] (3) Constructing the wave energy array device configuration to achieve optimal energy acquisition in the target sea area;

[0014] Optimize the float parameters and ratio to achieve wave energy absorption, design the number of floats based on different frequency bands, and establish the equation between the number of floats and energy acquisition efficiency:

[0015] ,

[0016] Where, 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 harvesting efficiency within the frequency band is used to determine the specific number of floats in each frequency band.

[0017] In (1), in order to achieve the goal of maximizing the energy of the float array device within a limited sea area, an objective function is constructed:

[0018] ,

[0019] Where N represents the number of intervals in which the research frequency interval is divided according to the energy equal division method. is the number of floats of type j, It means that the j-th type of float has an incident frequency of The efficiency of Represents the wave spectrum.

[0020] The constraints of the objective function are:

[0021] (a) The total number of floats is limited, and the maximum value of the total number of floats is , there is an upper limit on the total number of all floats, expressed as:

[0022] ,

[0023] (b) The total energy absorbed by all floats cannot exceed the wave spectrum input energy, which is expressed as:

[0024] ,

[0025] (c) The capture efficiency of the float cannot exceed the capture efficiency at resonance, which is expressed as:

[0026] ,

[0027] Where, represents the natural frequency of the float, Represents the maximum capture efficiency that the float can theoretically achieve, represents the wavelength when the incident wave frequency is equal to the natural frequency of the float, Represents the characteristic width of the float. If the float is cylindrical, then: ;

[0028] The Lagrange multiplier method is used to construct a new objective function:

[0029] ,

[0030] In the formula and are all constants. Taking partial derivatives we get:

[0031] ,

[0032] When the above formula is 0, it is the distribution of the number of floats when the total captured energy is maximum, and we can get:

[0033] ,

[0034] Therefore, for any float, , where C is a constant, that is, the unit energy contribution of the float designed for each frequency band is equal, and equal energy division is required.

[0035] In (2), the absorption coefficient is: ,

[0036] Where, represents the absorption coefficient, represents the incident wave frequency, represents the complex heave motion response amplitude under unit amplitude, B is the PTO damping coefficient, is the density, is the acceleration due to gravity, is the width of the device along the crest line, c is the wave velocity, and n is the water depth related function.

[0037] The energy spectrum density function in (2) is for: ,

[0038] 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 amplitude of the nth incident wave.

[0039] In (2), the energy efficiency of the device is , the physical meaning is the ratio of the energy obtained by the device to the incident wave energy per unit width, expressed as:

[0040] ,

[0041] Where, represents the energy acquisition spectral density function, represents the wave spectrum function.

[0042] The resonance bandwidth of the float is equal to the bandwidth of the corresponding wave energy frequency band, and the float can fully absorb the wave energy of the corresponding frequency band.

[0043] 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.

[0044] The relative absorption power is the ratio of the float absorption power to the theoretical maximum absorption power, with the maximum value being 1. The relative absorption power is expressed as:

[0045] ,

[0046] in:

[0047] ,

[0048] Where B represents the PTO damping coefficient, represents radiation damping, Indicates the mass of the float, Indicates the additional mass of the float.

[0049] Let the function value of the above formula be 0.5, and the solutions of the two frequencies can be obtained, which are expressed as:

[0050] ,

[0051] ,

[0052] Where, represents the incident wave frequency, is the natural frequency, represents the absorbed power, It represents the absorbed power of the float when the incident frequency is the natural frequency, is the wave force, It represents the wave force when the incident frequency is the natural frequency.

[0053] ,

[0054] in: ,

[0055] Where, 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 radiation damping as a function of the incident frequency.

[0056] The float natural frequency expression for:

[0057] ,

[0058] The natural frequency of the float is equal to the ratio of the first-order moment to the zero-order moment of the energy spectrum.

[0059] Optimal damping of the float for:

[0060] ,

[0061] Where, and Respectively represent the start and end frequencies of the frequency band; Indicates the mass of the float, represents the additional mass of the float when the incident frequency is the natural frequency; if the above formula is true, 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, thereby establishing the relationship between optimal damping, resonance bandwidth and float mass.

[0062] The beneficial effects of the present invention are as follows: This method, based on wave spectrum energy analysis, provides a design method for heterogeneous floats. The heterogeneous floats designed using this method are based on the wave spectrum frequency band division of the target sea area and fully absorb wave energy in the corresponding frequency band. This method comprehensively considers factors such as the float mass, resonance bandwidth, natural frequency, and applied PTO damping, and establishes a relationship between these factors. This method uses a simple and quick method to efficiently find the heterogeneous float wave energy device that meets the specific sea conditions. An array of heterogeneous float wave energy devices can absorb incident wave energy across the entire frequency band, significantly improving wave energy utilization. The present invention guides the matching of heterogeneous floats in the array, achieving a precise match between the float resonance bandwidth and the wave spectrum of the target frequency band. This demonstrates that the heterogeneous float array has broadband energy harvesting characteristics, overcoming the low energy harvesting level caused by the narrow bandwidth response of traditional homogeneous devices. This demonstrates that the heterogeneous float array is more compatible with the wave spectrum energy distribution and has potential engineering economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 is the relative absorption power variation diagram under different damping factors;

[0064] Figure 2 Schematic diagram of float energy spectrum;

[0065] Figure 3 The capture width ratio (CWR) (left figure) and the absorption power change diagram (right figure) of the hetero-frequency float (a), hetero-frequency float (b), and hetero-frequency float (c);

[0066] The capture width ratio (CWR) (left) and the absorption power variation (right) of the heterodyne float (a) correspond to each other. Figure 3 (a) and Figure 3 (b);

[0067] The capture width ratio (CWR) (left) and the absorption power variation (right) of the heterodyne float (b) correspond to each other. Figure 3 (c) and Figure 3 (d);

[0068] The capture width ratio (CWR) (left) of the heterodyne float (c) corresponds to the absorption power variation (right) Figure 3 (e) and Figure 3 of (f);

[0069] Figure 4 is the capture width ratio (CWR) (left figure a) and the absorbed power variation (right figure b) of the float (d) under optimal damping;

[0070] Figure 5 This is a comparison of the absorbed power of float arrays with different frequencies and the same frequency at different spacings in the frequency domain analysis;

[0071] Figure 6 This is a comparison of the absorbed power of the float arrays with different frequencies and the same frequency at different spacings in the time domain analysis. DETAILED DESCRIPTION

[0072] The present invention will be further described below with reference to the accompanying drawings and examples.

[0073] The structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for understanding and reading by those familiar with this technology. They are not used to limit the conditions for implementation of the present invention and therefore have no substantial technical significance. Any modification of the structure, change in the proportional relationship, or adjustment of the size should still fall within the scope of the technical content disclosed by the present invention without affecting the efficacy and purpose of the present invention. At the same time, the terms such as "upper", "lower", "left", "right", "middle" and "one" quoted in this specification are only for the convenience of description and are not used to limit the scope of implementation of the present invention. Changes or adjustments in their relative relationships should also be regarded as the scope of implementation of the present invention without substantially changing the technical content.

[0074] 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:

[0075] ,

[0076] The present invention also needs to consider the design of the resonant bandwidth of the float. According to the heaving motion equation of the float in the frequency domain:

[0077] ,

[0078] In the formula 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 radiation damping function of the incident frequency, is the PTO stiffness coefficient, is the hydrostatic restoring coefficient, is the wave force, is the complex amplitude of the heaving motion. The absorbed power of the float can be calculated as:

[0079] ,

[0080] In the formula is the complex velocity amplitude of the heaving motion. According to Rolle's mean value theorem, when or hour, , so there exists , so that the absorbed power is maximized, we can get:

[0081] ,

[0082] This damping is called optimal damping. When the float reaches the resonance state and the optimal damping is applied, the absorbed power of the float reaches the maximum value, which can be expressed as:

[0083] ,

[0084] Therefore, for any damping coefficient B, there exists and , such that:

[0085] ,

[0086] Substituting into the expression of optimal damping, it can be seen that the optimal damping should be equal to the radiation damping in the resonant state.

[0087] Substituting the natural frequency expression of the float's heaving motion into the expression of absorbed power yields:

[0088] ,

[0089] in: ,

[0090] The above formula is defined as the damping factor. The relative absorption power is defined as the ratio of the float absorption power to the theoretical maximum absorption power, with the maximum value being 1. The change of relative absorption power is as follows: Figure 1 As shown, it can also be expressed as: ,

[0091] Let the function value of the above formula be 0.5, and the solutions of the two frequencies can be obtained, which are expressed as:

[0092] ,

[0093] ,

[0094] In this invention, 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. Applying higher damping maintains a wider resonance bandwidth, allowing the float to absorb wave energy across a wider frequency range, thereby increasing the overall utilization rate of wave energy across the entire frequency band.

[0095] The concept of "energy spectrum" is introduced in this invention. The energy spectrum can characterize the energy of a device within a unit frequency interval. Assuming that the device only absorbs the energy of the incident wave amplitude without causing other changes, and completely absorbs all the wave energy of the incident wave amplitude, the incident wave amplitude can be expressed as:

[0096] ,

[0097] In the formula represents the absorption coefficient, A is the incident wave amplitude, and the incident wave amplitude is defined as the virtual energy-generating wavefront. The energy obtained by the virtual energy-generating wavefront should be equivalent to the actual device motion energy, that is, the average wave power of the virtual energy-generating wavefront is equal to the average wave power per single width of the device, and thus:

[0098] ,

[0099] In the formula is the width of the device along the crest line, c is the wave velocity, n is the water depth related function, represents the complex heave motion response amplitude under unit amplitude, from which the absorption coefficient can be calculated:

[0100] ,

[0101] Introducing the concept of absorption coefficient into random waves, the expression of virtual energy-generating wave surface can be obtained:

[0102] ,

[0103] In the formula represents the absorption coefficient of the nth wave, Represents the governing equation of the virtual energy-generating wavefront. After the introduction of the virtual energy-generating wavefront, the above equation is still the expression of the random wavefront. Since the average wave energy of the random wave is the superposition of the average wave energy of each component wave, analogously to the above concept, the time domain equation can be transformed into:

[0104] ,

[0105] Therefore, we can obtain:

[0106] ,

[0107] The relationship between the energy gain spectrum density function and the wave spectrum can be obtained:

[0108] ,

[0109] The energy harvesting efficiency of the device is physically the ratio of the energy harvested by the device to the incident wave energy per unit width, expressed as:

[0110] .

[0111] In this invention, the wave spectrum is divided into frequency bands to fully utilize the wave energy within specific frequency bands. Devices with different frequency responses are then matched to different frequency bands of the wave spectrum to achieve improved energy capture efficiency. The wave spectrum division method must meet the following two requirements: 1) the relatively high-frequency and low-frequency regions of the wave spectrum can be ignored; 2) the wave spectrum segments should not be too dense or too sparse. In this invention, the wave spectrum frequency band division method adopts the equal energy division method.

[0112] Each frequency band based on the equal energy partitioning method requires a dedicated float. The design of the dedicated float should ensure that its resonance bandwidth is consistent with the bandwidth of the divided frequency band to achieve efficient utilization of wave energy within that frequency band. The float designed for each frequency band is called a type of float. If the target wave spectrum is divided into N frequency bands, there will be N types of float devices with different characteristics.

[0113] In order to achieve the goal of maximizing the energy of the float array device within a limited sea area, the present invention constructs an objective function:

[0114] ,

[0115] Where N represents the number of intervals in which the research frequency interval is divided according to the energy equal division method, is the number of floats of type j, It means that the j-th type of float has an incident frequency of The efficiency of the objective function is:

[0116] (a) The total number of floats is limited, and the maximum value of the total number of floats is , there is an upper limit on the total number of all floats, expressed as:

[0117] ,

[0118] (b) The total absorbed energy of all floats cannot exceed the wave spectrum input energy, which is expressed as:

[0119] ,

[0120] (c) The capture efficiency of the float cannot exceed the capture efficiency at resonance, which is expressed as:

[0121] ,

[0122] 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 new objective function is constructed using the Lagrange multiplier method: ,

[0123] right Taking partial derivatives we get:

[0124] ,

[0125] When the above formula is 0, it is the distribution of the number of floats when the total captured energy is maximum, and we can get:

[0126] ,

[0127] Therefore, for any float, , where C is a constant, that is, the unit energy contribution of the float designed for each frequency band is equal, and equal energy division is required.

[0128] This study aims to investigate the energy harvesting characteristics of floats along the wave crest line within a limited sea area. By optimizing float parameters and their ratios, efficient wave energy absorption is achieved. Therefore, it is necessary to determine the number of floats designed for different frequency bands. To ensure that the floats fully absorb energy in each frequency band, an equation can be established that relates the number of floats configured and the energy harvesting efficiency:

[0129] ,

[0130] Where, 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 harvesting efficiency within the frequency band, from which the specific number of floats in each frequency band can be known.

[0131] The design principles of floats include:

[0132] (1) Matching of float response characteristics. The resonant bandwidth of the float should be equal to the bandwidth of the corresponding frequency band and be able to fully absorb the wave energy of the corresponding frequency band.

[0133] (2) Design of float natural frequency. This invention designs the corresponding natural frequency of the float based on the center of gravity position of the wave spectrum in each frequency band, ensuring that the natural frequency of the float matches the main energy distribution area and improving the utilization rate of the high energy density frequency band. It can be expressed as:

[0134] ,

[0135] From this we can get the natural frequency expression:

[0136] ,

[0137] Therefore, the natural frequency of the float is equal to the ratio of the first moment of the spectrum to the zeroth moment.

[0138] (3) Optimal damping design. Combine the following formulas:

[0139] ,

[0140] ,

[0141] ,

[0142] ,

[0143] It can be found that:

[0144] ,

[0145] 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. Embodiment 1:

[0146] The wave spectrum fitted from the measured data in the waters of Zhaitang Island is used as an example for analysis. The sea conditions are shown in Table 5:

[0147]

[0148] Table 5 shows the characteristic parameters of the wave spectrum in the target sea area.

[0149] The wave spectrum of the target sea area, 1~2.5 rad / s, is selected as the research frequency band. Calculation shows that this frequency band contains more than 90% of the energy of the incident wave. The energy trisection method is used to divide the frequency bands, and a corresponding frequency-dependent float is designed for each frequency band to capture wave energy. The parameters are shown in Table 6:

[0150]

[0151] Table 6 shows the start and end frequencies of the corresponding frequency bands and the names of the corresponding designed floats.

[0152] The method of the present invention is applied to construct a cylindrical heave float wave energy device and its array. The float radius is fixed at 2m, and the draft, PTO damping and PTO stiffness coefficient are used as design variables. Other parameters remain unchanged, as shown in Table 7:

[0153]

[0154] Table 7 shows the float parameter settings.

[0155] The actual energy level of the float in actual sea conditions may be far from the theoretical level. The capture width ratio and absorption power calculated based on the numerical simulation under ideal conditions may be too high. Referring to the research on the maximum capture width ratio of the oscillating float in actual sea conditions, the present invention limits the maximum capture width ratio of the cylindrical float model to no more than 0.2. The optimization results of the single float are as follows: Figure 3 As shown, it is proved that the three types of floats (a), float (b), and float (c) can absorb wave energy in the corresponding frequency bands.

[0156] The three types of floats were combined into a frequency-differentiated float array, arranged with high-frequency floats positioned forward and low-frequency floats positioned backward along the incident wave direction. This is because floats with lower natural frequencies are more sensitive to energy absorption from long-period waves, and their rearward position has less impact on the overall energy harvesting of the array. The energy harvesting efficiency of each float in each frequency band is calculated and shown in Table 8.

[0157]

[0158] Table 8 shows the energy acquisition efficiency of each float in each frequency band.

[0159] In order to ensure that the float fully absorbs the energy in each frequency band, an equation is established between the number of floats and the energy acquisition efficiency:

[0160] ,

[0161] In the formula , and are all positive integers, representing the number of floats (a), floats (b) and floats (c). The optimization model is obtained as follows:

[0162] .

[0163] This optimization model represents the minimum positive integer solution for the total number of floats in the heterogeneous frequency array. The solution results are shown in Table 9:

[0164] Float name Float (a) Float (b) Float (c) Number of floats 4 2 5

[0165] Table 9 shows the ratio of the number of floats that meet the conditions.

[0166] In practice, the arrangement is as follows: five floats (c), two floats (b), and four floats (a) are placed in the direction of the incident wave. Because energy generation is unstable with a float array spacing of 1R (R = 2m), a 2R-5R spacing was selected for energy generation analysis.

[0167] In order to judge the energy acquisition level of the array, in addition to the energy acquisition efficiency of the device, the present invention constructs the cumulative power based on the weighted average idea. The formula can be expressed as:

[0168] ,

[0169] In the formula Represents the number of study bands divided by frequency, usually The value of is large, represents the energy of the ith frequency band, E represents the total energy in the definition domain, and Respectively represent the absorbed power corresponding to the endpoint frequency of the i-th frequency band. In this study, the selected frequency band range is 1~2.5 rad / s, Taking the 50th wave spectrum band (1.5~1.51 rad / s) as an example, the calculated energy ratio is , assuming and They are , Substituting this into the above equation yields a contribution of 0.51 W for this frequency band. The same applies to other frequency ranges, ultimately accumulating the power across the entire frequency band. This indicator, calculated in conjunction with the wave spectrum energy density function, quantifies the contribution of energy distribution across different frequency bands to absorbed power.

[0170] Using the same idea, the present invention constructs the cumulative power area ratio and cumulative power-to-mass ratio , used to evaluate the economic performance, respectively expressed as:

[0171] ,

[0172] In the formula for:

[0173] ,

[0174] in is the total length of the array in the direction of the incident wave, Indicates the total sea area used by the array.

[0175] ,

[0176] In the formula Represents the first The mass of the float.

[0177] To fully demonstrate the effectiveness of the optimized solution for constructing an inter-frequency float array, it is necessary to construct a co-frequency float array and its array and compare its energy gain with that of an inter-frequency float array under the same conditions. The number of co-frequency float arrays should be 11, the same as that of the inter-frequency float array. The co-frequency float is named float (d), and its parameters are shown in Table 10:

[0178]

[0179] Table 10 shows the parameters of the float (d). The energy level of the float is as follows Figure 4 shown.

[0180] In the frequency domain analysis, the absorption power comparison of the floating arrays with different frequencies and the same frequency at different spacings is as follows: Figure 5 As shown in the figure. In the time domain analysis, the average power comparison between the two at different spacings is as follows: Figure 6 The time domain analysis uses the JONSWAP target spectrum constructed from the measured data in the Zhaitang Island waters to perform numerical simulations of irregular waves. The simulation step size is 0.02 s, the total time is 600 s, and the time frequency range of 300 to 600 s is selected for analysis.

[0181] In summary, the present invention proposes a method for optimizing the construction of a heterogeneous wave energy device and its array. Based on the analysis of ocean wave spectrum energy, the method provides a design method for heterogeneous floats, guides the ratio of heterogeneous floats in the array, and achieves precise matching of the float resonance bandwidth with the ocean wave spectrum of the target frequency band. This shows that the heterogeneous float array has broadband energy acquisition characteristics, breaking through the low energy acquisition level caused by the narrow bandwidth response of traditional same-frequency devices, and illustrating that the heterogeneous float array is more adapted to the energy distribution of the ocean wave spectrum and has potential engineering economy.

[0182] Although the above describes the specific embodiments of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without any creative work are still within the scope of protection of the present invention.

Claims

1. A method for optimizing the array structure of a heterogeneous frequency buoy wave energy device, characterized in that: include: (1) Develop a strategy for partitioning and reconstructing the input wave spectrum based on the properties of the wave energy device; Utilizing the wave energy within the frequency band, wave energy devices with different frequency responses are matched to different frequency bands of the wave spectrum. The method for dividing the wave spectrum frequency bands adopts the equal energy division method. Each frequency band based on the equal energy division method needs to be equipped with a corresponding float. The design of the corresponding float should ensure that its resonance bandwidth is the same as the bandwidth of the divided frequency band interval. The float designed for each frequency band is called a type of float. If the target wave spectrum is divided into N frequency bands, there are N types of float devices with different characteristics. (2) Using the energy spectrum method, quickly deduce and predict the equivalent energy gain of each device in the full frequency band; The energy harvesting spectrum can characterize the energy harvesting of a device within a unit frequency interval. Based on the energy harvesting spectrum theory, several types of floats are designed as references. By calculating their absorption coefficients, the energy harvesting spectrum density functions of various types of floats are determined. The energy harvesting efficiency of each type of float is then calculated, and the equivalent energy captured by the float in the entire frequency band is determined, clarifying the energy harvesting contribution of the device in each frequency band. (3) Constructing the wave energy array device configuration to achieve optimal energy acquisition in the target sea area; Optimize the float parameters and ratio to achieve wave energy absorption, design the number of floats based on different frequency bands, and establish the equation between the number of floats and energy acquisition efficiency: ， Where, 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 harvesting efficiency within the frequency band is used to determine the specific number of floats in each frequency band.

2. The method for optimizing the array structure of a heterogeneous frequency buoy wave energy device according to claim 1, wherein: In (1), in order to achieve the goal of maximizing the energy of the float array device within a limited sea area, an objective function is constructed: ， Where N represents the number of intervals in which the research frequency interval is divided according to the energy equal division method. is the number of floats of type j, It means that the j-th type of float has an incident frequency of The efficiency of Represents the wave spectrum.

3. The method for optimizing the array structure of a heterogeneous frequency buoy wave energy device according to claim 2, wherein: The constraints of the 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 on the total number of all floats, expressed as: ， (b) The total absorbed energy of all floats cannot exceed the wave spectrum input energy, which is expressed as: ， (c) The capture efficiency of the float cannot exceed the capture efficiency at resonance, which is expressed as: ， Where, represents the natural frequency of the float, Represents the maximum capture efficiency that the float can theoretically achieve, represents the wavelength when the incident wave frequency is equal to the natural frequency of the float, Represents the characteristic width of the float.

4. The method for optimizing the array structure of a heterogeneous frequency buoy wave energy device according to claim 3, wherein: The Lagrange multiplier method is used to construct a new objective function: ， In the formula and are constants, for Taking partial derivatives we get: ， When the above formula is 0, it is the distribution of the number of floats when the total captured energy is maximum, and we get: ， Therefore, for any float, , where C is a constant, that is, the unit energy contribution of the float designed for each frequency band is equal, and equal energy division is required.

5. The method for optimizing the array structure of a heterogeneous frequency buoy wave energy device according to claim 1, wherein: In (2), the absorption coefficient is: , Where, represents the absorption coefficient, represents the frequency of the incident wave, represents the complex heave motion response amplitude under unit amplitude, B is the PTO damping coefficient, is the density, is the acceleration due to gravity, is the width of the device along the crest line, c is the wave velocity, and n is the water depth related function.

6. The method for optimizing the array structure of a heterogeneous frequency buoy wave energy device according to claim 1, wherein: The energy spectrum density function in (2) for: , Where, 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 method for optimizing the array structure of a heterogeneous frequency buoy wave energy device according to claim 1, wherein: In (2), the energy efficiency of the device is , the physical meaning is the ratio of the energy obtained by the device to the incident wave energy per unit width, expressed as: ， Where, Energy gain spectral density function, represents the wave spectrum function.

8. The method for optimizing the array structure of a heterogeneous frequency buoy wave energy device according to claim 1, wherein: The resonant 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 resonant bandwidth is defined as: the absolute value of the difference between the two frequencies corresponding to the relative absorption power being equal to 0.

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9. The method for optimizing the array structure of a heterogeneous frequency buoy wave energy device according to claim 8, wherein: The relative absorption power is the ratio of the float absorption power to the theoretical maximum absorption power, with the maximum value being 1. The relative absorption power is expressed as: ， in: ， Where B represents the PTO damping coefficient, represents radiation damping, Indicates the mass of the float, Indicates the additional 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, which are expressed as: ， ， Where, represents the incident wave frequency, is the natural frequency, represents the absorbed power, It represents the absorbed power of the float when the incident frequency is the natural frequency, is the wave force, It represents the wave force when the incident frequency is the natural frequency; ， in: , Where, 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 radiation damping as a function of the incident frequency.

10. The method for optimizing the array structure of a heterogeneous frequency buoy wave energy device according to claim 1, wherein: The float natural frequency expression for: ， The natural frequency of the float is equal to the ratio of the first-order moment to the zero-order moment of the energy spectrum; Optimal damping of the float for: ， Where, and Respectively represent the start and end frequencies of the frequency band; is the mass of the float, represents the additional mass of the float when the incident frequency is the natural frequency; if the above formula is true, 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, thereby establishing the relationship between optimal damping, resonance bandwidth and float mass.

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