An energy distribution system for generating freak waves in a laboratory sink

Abstract

The present invention provides an energy distribution system for generating freak waves in a laboratory sink, belonging to the technical field of ocean engineering. The wave generation system includes a first determination module, an equal division module, and a second determination module. The first determination module is configured to receive a target spectrum selected by a user and determine its frequency spectrum range, and determine the maximum wave number and the minimum wave number within the frequency spectrum range according to the calculation relationship between the frequency spectrum range and the wave number. The equal division module is used to equally divide the maximum wave number and the minimum wave number into 0 wave trains. The energy distribution method of the equal division wave number method proposed by the present invention has a stronger multi-wave resonance effect in different wave spectra, can generate freak waves with larger wave amplitudes and faster propagation speeds, and can provide better reference significance for generating extreme freak waves in the laboratory.

Description

Technical Field

[0001] The present invention belongs to the technical field of ocean engineering. Specifically, it relates to an energy distribution system for generating freak waves in a laboratory water tank. Background Art

[0002] Freak waves are characterized by extremely large wave heights and sharp wave crests. They pose a great threat to the safety of offshore oil platforms, coastal engineering, and ship navigation. Since freak waves have a short duration on the sea surface, there is relatively little actual observed freak wave data. Currently, numerical simulation and laboratory physical simulation are important means for studying freak waves.

[0003] Freak waves generated based on the energy focusing mechanism are often realized through a wave spectrum in the laboratory. Currently, domestic and foreign scholars usually use the energy distribution modes of equal-frequency division (CDF) and equal-period division (CDT) methods to determine the information of each component wave in the wave group.

[0004] In the above two energy distribution methods, the excitation of the multi-wave resonance effect is relatively weak during the simulation using the wave spectrum, and it is difficult to generate freak waves with larger wave amplitudes and faster propagation speeds, which has many limitations in the current experimental simulations. Summary of the Invention

[0005] An embodiment of the present invention provides an energy distribution system for generating freak waves in a laboratory water tank, aiming to solve the problem that the excitation of the multi-wave resonance effect is relatively weak during the existing simulation using the wave spectrum, and it is difficult to generate freak waves with larger wave amplitudes and faster propagation speeds.

[0006] In view of the above problems, the technical solution proposed by the present invention is:

[0007] An energy distribution system for generating freak waves in a laboratory water tank, the energy distribution system includes:

[0008] A first determination module, which is used to receive the target spectrum selected by the user and determine its frequency spectrum range, and determine the maximum wave number and the minimum wave number within the frequency spectrum range according to the calculation relationship between the frequency spectrum range and the wave number;

[0009] An equal division module, which is used to equally divide into M wave trains according to the maximum wave number and the minimum wave number;

[0010] Wherein, in the same direction, the wave number differences of all component waves of the M wave trains are equal, and its expression is as follows:

[0011]

[0012] In the formula: k i represents the wave number of each component wave;

[0013] k max represents the maximum wave number of the component waves within the frequency spectrum range;

[0014] k min represents the minimum wave number of the component waves within the frequency spectrum range;

[0015] A second determination module, which is configured to sequentially determine the wave number, frequency, and amplitude of N component waves in each of the wave trains, and perform modulation according to the amplitude and frequency of each of the component waves to obtain the initial phase of each of the component waves.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: The energy distribution method of the equal - division wave number method proposed by the present invention has a stronger multi - wave resonance effect in different wave spectra, can generate freak waves with larger wave amplitudes and faster propagation speeds, and can provide better reference significance for generating extreme freak waves in the laboratory.

[0017] The above description is only an overview of the technical solution of the present invention. In order to be able to more clearly understand the technical means of the present invention, it can be implemented according to the content of the specification. And in order to make the above - mentioned and other purposes, features, and advantages of the present invention more obvious and understandable, the following specifically describes the embodiments of the present invention. Brief Description of the Drawings

[0018] Figure 1 shows a schematic structural diagram of the wave - making system proposed by the present invention;

[0019] Figure 2a shows the free - surface time - history changes at six positions before and after focusing of the freak waves generated under the energy distribution method of the equal - division wave number method;

[0020] Figure 2b shows the free - surface time - history changes at six positions before and after focusing of the freak waves generated under the energy distribution method of the equal - division wavelength method;

[0021] Figure 3 shows the experimental and numerical results of the variation of the maximum wave - crest surface amplitude along the course under four energy distribution methods;

[0022] Figure 4a shows the wave - surface morphology at the position of the maximum wave - crest amplitude within the range of x = 8 - 10 m of the wave group under the energy distribution method of the equal - division frequency method;

[0023] Figure 4b shows the wave - surface morphology at the position of the maximum wave - crest amplitude within the range of x = 8 - 10 m of the wave group under the energy distribution method of the equal - division period method;

[0024] Figure 4cShows the wave surface morphology at the position of the maximum wave crest amplitude within the range of x = 8 - 10 m under the energy distribution method of the equal wavenumber method;

[0025] Figure 4 shows the wave surface morphology at the position of the maximum wave crest amplitude within the range of x = 8 - 10 m under the energy distribution method of the equal wavelength method;

[0026] Figure 5 Shows the horizontal velocity distribution under the focusing wave surface of the wave group under different energy distribution methods;

[0027] Figure 6a Shows the horizontal velocity time history distribution at the water depth z = 0 m at the focusing position under four energy distribution methods

[0028] Figure 6b Shows the horizontal velocity time history distribution at the water depth z = -0.06 m at the focusing position under four energy distribution methods;

[0029] Figure 7a Shows the change of the wave energy structure along the free surface in the energy distribution method of the equal wavenumber method;

[0030] Figure 7b Shows the change of the wave energy structure along the free surface in the energy distribution method of the equal frequency method;

[0031] Figure 7c Shows the change of the wave energy structure along the free surface in the energy distribution method of the equal period method;

[0032] Figure 7d Shows the change of the wave energy structure along the free surface in the energy distribution method of the equal wavelength method.

[0033] Explanation of reference numerals: 100, the first determination module; 200, the equal division module; 300, the second determination module. Detailed implementation manners

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art without creative efforts based on the embodiments of the present invention belong to the scope of protection of the present invention.

[0035] Accordingly, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0036] It should be noted that like reference numerals and letters denote like items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0037] In the description of the present invention, it should be understood that the orientation or positional relationships indicated by the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. are based on the orientation or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the present invention.

[0038] In addition, the terms "first" and "second" are only used for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "a plurality of" means two or more unless otherwise specifically defined.

[0039] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Apparently, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0040] Embodiment 1

[0041] Referring to the attached Figure 1 As shown, the technical solution provided by the present invention: an energy distribution system for generating freak waves in a laboratory sink, the energy distribution system including a first determination module 100, an equal division module 200, and a second determination module 300;

[0042] The first determination module 100 is configured to receive a target spectrum selected by a user and determine its frequency spectrum range, and determine the maximum wave number and the minimum wave number within the frequency spectrum range according to the calculation relationship between the frequency spectrum range and the wave number;

[0043] The equal division module 200 is configured to equally divide the maximum wave number and the minimum wave number into M wave trains;

[0044] Among them, within the same direction, the wave number differences of all component waves of the M wave trains are equal, and its expression is as follows:

[0045]

[0046] In the formula: k i represents the wave number of each component wave;

[0047] k max represents the maximum wave number of the component waves within the frequency spectrum range;

[0048] k min represents the minimum wave number of the component waves within the frequency spectrum range;

[0049] Specifically, since several current energy distribution methods cannot generate freak waves with larger wave amplitudes and faster propagation speeds, therefore, the equal division method of the maximum wave number and the minimum wave number provided by the present invention can more strongly stimulate the multi-wave resonance effect, enabling the generation of freak waves with larger wave amplitudes and faster propagation speeds, which can provide a reference for generating extreme freak waves in the laboratory.

[0050] The second determination module 300 is used to sequentially determine the wave number, frequency, and amplitude of N component waves in each of the wave trains, and perform modulation according to the amplitude and frequency of each of the component waves to obtain the initial phase of each of the component waves.

[0051] Specifically, the amplitude and frequency of each of the component waves are modulated according to the NewWave focusing model to achieve the maximum peak value at the target time and target position. According to the wave-making theory, the motion expression of the freak wave focused by the push plate of the wave maker is:

[0052]

[0053] In the formula: N represents the number of component waves;

[0054] a i represents the wave amplitude of the i-th component wave;

[0055] k i represents the wave number of the i-th component wave;

[0056] ω i represents the angular frequency of the i-th component wave;

[0057] x f represents the focused target position;

[0058] t f represents the focused target time;

[0059] T(ω i) represents the transfer function of the i-th component wave.

[0060] Embodiment 2

[0061] Another embodiment of the present invention provides an application of an energy distribution system for generating freak waves in a laboratory water tank during the wave-making process, including the following steps:

[0062] S1. Set the sea surface parameters and the position and time for generating freak waves.

[0063] S2. Calculate the wave height of the sea surface according to the fractal parameters.

[0064] S3. Adopt the phase modulation method to generate a theoretical freak wave at a specific position and time.

[0065] S4. Perform energy distribution using the energy distribution method of Embodiment 1, and finally obtain the wave number, frequency, amplitude, and initial phase.

[0066] S5. Calculate according to the amplitude, frequency, and initial phase of each component wave to obtain the time series of the free surface change, convert the time series of the free surface change into the time series of the driving signal, and input the time series of the driving signal into the wave maker.

[0067] Specifically, the specific steps of converting the time series of the free surface change into the time series of the driving signal are as follows:

[0068] Assume that the wave-making board of the wave maker is located at x = 0m. When simulating the wave at x, the expression of the wave surface time η(t) at the wave-making board is as follows:

[0069]

[0070] In the formula, θ i represents the initial phase of the i-th component wave after wave train modulation;

[0071] According to the linear theory, the movement of the wave-making board and the wave surface generated at its own position have a 90° phase difference. Thus, the expression of the actual movement of the wave-making board is as follows:

[0072]

[0073] S6. Monitor the wave maker and loop the modulation module and the second calculation module to correct the time series of the driving signal.

[0074] Experimental comparison

[0075] The present invention proposes an energy distribution method of the equal wavenumber method (CDK). In order to demonstrate the test results of the present invention, the present invention also proposes an energy distribution method of the equal wavelength method (CDL). Based on the two energy distribution methods of the traditional equal frequency method (CDF) and the equal period method (CDT), by comparing the effects of the four energy distribution methods on the generation of freak waves, it can be obtained which wave groups are more likely to generate more extreme freak waves. At the same time, in view of the effectiveness of the following test demonstrations, an energy distribution system of Embodiment 1 is developed accordingly.

[0076] By reproducing the experiment of the equal period method (CDT) adopted by scholars such as Baldock. In the experiment, the water depth h0 is 0.7 m, the incident spectrum adopts CWA, the number of component waves is 29, the initial focusing amplitude A f = 55 m, the focusing position x f = 8.0 m, and the focusing time t f = 30 s.

[0077] Figures 2a - 2b The time history changes of the free surface at six positions before and after focusing of the freak waves generated under the energy distribution methods of the equal wavenumber method and the equal wavelength method are respectively shown. Generally speaking, the test results and numerical results under the two energy distribution methods are in good agreement in terms of both amplitude and phase changes, and the wave surface change rules are the same, which also mutually verifies the credibility of the physical model test and numerical simulation. By comparison, it is found that the phase changes and amplitude sizes of the wave surfaces under the two energy distribution methods of the equal wavenumber method and the equal wavelength method are different. For the equal wavenumber method, the energy is significantly focused at x = 9.5 m, and extreme large waves appear, and the waveforms on both sides of the main peak are not symmetric, while for the equal wavelength method, the focusing occurs at x = 9.5 m, and the waveforms on both sides of the main peak are relatively symmetric. It can be clearly seen that the nonlinearity of the wave group adopting the energy distribution method of the equal wavenumber method is significantly higher than that of the equal wavelength method.

[0078] Figure 3The experimental and numerical results of the variation of the maximum crest surface amplitude along the propagation path under four energy distribution methods are shown. It should be noted that in the actual experiment, obvious breaking phenomena were observed in the wave groups under the energy distribution method of equal division of wave numbers during the propagation process. As can be seen from the figure, although there are slight deviations between the numerical simulation results and the experimental results at some wave gauges, overall, the variation laws of the numerical results and the experimental results are the same, and the overall trends are in good agreement. It can also be seen that the variation trends of the maximum wave crest values along the propagation path under the four energy distribution methods are the same. As the propagation distance increases, the maximum wave crest values all show periodic changes and gradually increase. Continuous large waves appear near the theoretical focusing position, and the recurrence periods of the large waves are relatively close. By comparing the four energy distribution methods, it is found that even in the case of breaking, the increase amplitude of the maximum wave crest value along the propagation path of freak waves under the energy distribution method of equal division of wave numbers is still significantly higher than that of the other three energy distribution methods, and the phase is more lagged. The equal division of frequencies method ranks second, while the variation laws of the amplitudes and phases of the equal division of periods method and the equal division of wavelengths method are relatively close, and the maximum amplitude of the equal division of periods method is slightly larger than that of the equal division of wavelengths method.

[0079] Figures 4a - 4d The wave surface morphologies at the positions of the maximum wave crest amplitudes of the wave groups within the range of x = 8 - 10 m under four energy distribution methods are respectively shown, and the results are compared with the numerical results and the linear theory results. By Figures 4a - 4d knowing, the waveforms at the focusing points calculated numerically under the four energy distribution methods are almost completely consistent with the experimental results. The wave crest value at the focusing point under the energy distribution method of equal division of wave numbers is significantly higher than that of the other three energy distribution methods, and the waveform is extremely asymmetric, with a sharp wave crest, a gentle secondary peak on the left, while the waveform at the focusing position under the energy distribution method of equal division of wavelengths is relatively symmetric. The quantitative calculation results of the wave groups at the positions of the maximum wave crest amplitudes within the range of x = 8 - 10 m under the four energy distribution methods are shown in Table 1. As can be seen from the table, the maximum wave crest value obtained under the energy distribution method of equal division of wave numbers reaches 94.8 mm, which is 1.72 times that of the linear input result. The maximum wave crest value obtained under the energy distribution method of equal division of periods is 74.6 mm, which is 1.35 times that of the linear input. It should be noted that when the wave groups under the energy distribution method of equal division of wave numbers are in the case of breaking, the wave crest value at the focusing point is still significantly higher than that of the other three energy distribution methods, indicating that the non-linear interaction between waves in the wave groups is very strong. In addition, it can be seen from Table 1 that under the energy distribution method of equal division of wave numbers, the focusing position within the range of x = 8 - 10 m is at x = 9.5 m. Compared with the other three energy distribution methods, the focusing moment and position under the energy distribution method of equal division of wave numbers are more backward.

[0080] Table 1 Calculation results under different energy distribution methods

[0081]

[0082] Figure 5 The horizontal velocity distribution under the wave group focusing wave surface under different energy distribution methods is shown. It can be seen from the figure that for the calculation results of the equal wavenumber method and the equal frequency method, they are slightly smaller than the other two energy distribution methods under the water surface, but increase rapidly above the water surface. The maximum velocity of the equal frequency method reaches 0.8 m / s, while the maximum velocity of the equal wavenumber method can reach 0.96 m / s. It can be known from the figure that the result of the equal wavenumber method of the present invention is almost the same as the result of the equal wavenumber method calculated by using the double-layer Boussinesq mathematical model, which also proves the accuracy of the calculation results. It can be seen from Table 1 that the maximum horizontal velocity u f under the wave group focusing wave surface for the four energy distribution methods is 0.96 m / s, which is much greater than the phase velocity of the wave group of 0.8 s, indicating that obvious breaking occurs in the wave group, and this phenomenon is indeed observed in the actual experiment. Generally speaking, the energy distribution method has a great influence on the velocity near the wave crest at the wave group focusing position. Even in the case of breaking, the maximum wave crest velocity under the energy distribution method of the equal wavenumber method is significantly greater than the maximum wave crest velocities under the other several energy distribution methods.

[0083] Figures 6a - 6b The time history distributions of the horizontal velocity at water depths z = 0 m and -0.06 m at the focusing position under the four energy distribution methods are respectively shown. It can be seen from the figure that at the position of z = 0, the horizontal velocity distribution at the focusing moment under the energy distribution method of the equal wavenumber method is greater than the results of the other three energy distribution methods, and the secondary peaks on both sides of the main velocity peak are significantly asymmetric. When z is 0.06 below the water surface, the differences in the results of the four energy distribution methods are not obvious. These phenomena can also be seen from Figure 5 it that below the water surface, the differences in the calculation results of the four energy distribution methods are not obvious, while from the water surface to the main wave crest position, the differences in the four results increase significantly.

[0084] Figures 7a - 7d The variation of the wave energy structure along the free surface in the four energy distribution methods is respectively shown. It can be seen from the figure that the variation laws of the wave energy structure along the free surface under the four energy distribution methods are similar. During the propagation of the wave group, the energy gradually transfers from the main frequency to the high frequency, and a small part of the energy transfers to the low frequency region. At the focusing position, a large amount of energy in the wave group transfers to the high frequency region. After focusing, part of the energy is transferred back to the main frequency, which also shows that the energy transfer between wave groups is reversible. Comparing the four energy distribution methods in the figure, it is found that under the energy distribution method of the equal wavenumber method, the energy transfer of the wave group to the high frequency at the focusing position is more significant, especially near the double frequency position of the main frequency. This may also be the reason why the amplitude of the wave group at the focusing position under the energy distribution method of the equal wavenumber method is much greater than that of the other several energy distribution methods.

[0085] The main frequency term, low-frequency term, and high-frequency term at the focused wave surface in Figure 7 are separated by using the inverse Fourier transform (TFFT). Under the energy distribution method of equal wave numbers, the proportion of the high-frequency term at the wave group focusing position is much higher than that of the other three energy distribution methods. Table 1 also quantitatively shows the total proportion of the high-frequency term in the wave group at the focused wave surface of the four energy distribution methods. It can be seen from the table that under the energy distribution method of equal wave numbers, the proportion of the high-frequency term at the wave group focusing position is as high as 57.90%, which is significantly higher than the proportions of the other three energy distribution methods (50.80, 38.17, and 34.91% respectively). The above shows that under the energy distribution method of equal wave numbers, the wave-wave nonlinearity is more intense during the propagation of the wave group, and a large amount of the energy of the wave group is transferred from the main frequency to the high frequency, resulting in a significantly higher wave surface at the focus than the other three energy distribution methods. All along, the nonlinear interaction between wave components is an important feature of the wave group. Phillips first discovered the resonance condition of four surface progressive waves in deep water in 1960; in the four energy distribution methods analyzed in the present invention, under the energy distribution method of equal wave numbers, the wave numbers of the component waves in the wave group differ by a multiple relationship. Although it is difficult to fully meet the resonance condition, it is easier to approach this resonance relationship in the wave group, resulting in a slight wave-wave resonance phenomenon. Similarly, the energy distribution method of equal frequencies also has conditions close to resonance, but due to the dispersion relationship between ω and k, the energy distribution method of equal frequencies is more difficult to meet the complete resonance condition than the energy distribution method of equal wave numbers. Therefore, in the four energy distribution methods, there are continuous oscillations in the second harmonic frequency range of the energy spectrum in the energy distribution method of equal frequencies (see Figures 7a - 7d ), and the wave group is more likely to generate more extreme rogue waves.

[0086] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. An energy distribution system for generating freak waves in a laboratory sink, characterized in that, The energy distribution system includes: A first determination module, which is configured to receive a target spectrum selected by a user and determine its frequency spectrum range, and determine the maximum wave number and the minimum wave number within the frequency spectrum range according to the calculation relationship between the frequency spectrum range and the wave number; An equal division module, which is configured to equally divide the maximum wave number and the minimum wave number into M wave trains; Wherein, in the same direction, the wave number differences of all the component waves of the M wave trains are equal, and its expression is as follows: where: k i represents the wave number of each component wave; k max represents the maximum wave number of the component waves within the frequency spectrum range; k min represents the minimum wave number of the component waves within the frequency spectrum range; A second determination module, which is configured to sequentially determine the wave numbers, frequencies and amplitudes of N component waves in each of the wave trains, and perform modulation according to the amplitude and frequency of each of the component waves to obtain the initial phase of each of the component waves.

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