CN118193906A - Island wave field calculation method based on coupling of double-layer Boussinesq equation and OpenFOAM model - Google Patents
Island wave field calculation method based on coupling of double-layer Boussinesq equation and OpenFOAM model Download PDFInfo
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Abstract
The invention discloses an island wave field calculation method based on double-layer Boussineq equation and OpenFOAM model coupling, which comprises the following steps: s1, establishing a calculation region of a double-layer Boussinesq equation model and dividing grids; s2, establishing a double-layer Boussinesq equation model; s3, solving a double-layer Boussinesq equation model; s4, determining a coupling boundary, establishing an OpenFOAM model calculation region and dividing grids; s5, processing a calculation result of a double-layer Boussinesq equation model, and converting the calculation result into an incident wave element usable by OpenFOAM; s6, calculating an OpenFOAM model, and carrying out post-processing on a calculation result. The calculation method provided by the invention combines the advantages of high calculation speed, better dispersion, nonlinearity and OpenFOAM of the double-layer Boussinesq water wave equation, and capability of capturing and crushing, can obtain the speed at any position along the water depth, overcomes the limitation of the traditional potential flow model, and has more advantages in coupling calculation.
Description
Technical Field
The invention relates to the technical field of ocean engineering and offshore engineering, in particular to a fast and refined island wave field calculation method based on double-layer Boussinesq equation and OpenFOAM model coupling.
Background
The island wave refinement forecasting technology has important significance for ocean engineering construction and operation. The island has special topography and large water depth span, as shown in figure 1, the slope of a slope in front of a certain island can reach 60 degrees, and some places are nearly vertical. The large water depth span leads to extremely complex hydrodynamic process, the open sea wave propagates to the island sea area to generate shallow water deformation and is crushed strongly on reef flat, the process relates to the cross-scale wave evolution from the deep open sea large-scale wave field to the reef flat small-scale crushing area, and great test is put forward on the calculation speed and the precision of the numerical model.
The potential flow wave model can quickly simulate the propagation and evolution of waves, but due to neglecting the viscous influence, the wave breaking process, especially the interaction process with objects, is difficult to accurately restore. While viscous wave pools have a computationally intensive limitation. In order to enable the numerical model to have both calculation speed and precision, the coupling calculation model is a good solution, the potential flow theory is used for simulating the propagation of deep sea waves in a large range, the viscous flow theory is used for simulating the wave evolution of a small-scale crushing area, huge calculation amount caused by solving a large-scale viscous wave field can be avoided, and the viscous influence can be considered when the waves are crushed on reef flat.
Common potential flow-viscous flow coupling models include a coupling model based on a completely nonlinear potential flow wave model (OceanWave D) and OpenFOAM, a high-order spectral method (HOS) and OpenFOAM coupling model, a Boussinesq equation and OpenFOAM coupling model, and the like. The viscous flow model in the coupling model usually adopts an OpenFOAM model, the OpenFOAM based on Navier-Stokes equation is the most powerful Computational Fluid Dynamics (CFD) open source software at present, a rich turbulence model is packaged, the capability of capturing wave breaking is achieved, and the model has good prediction precision on wave breaking, can be programmed autonomously, has high growth performance and is suitable for development of the coupling model through wide verification. However, oceanWave D in the potential flow model is based on the theory of completely nonlinear potential flow, the model does not limit the water depth, and if the model layer number is enough, the nonlinear characteristic of waves can be captured, but the calculation amount is large. The high-order spectrum method is to solve the velocity potential of the horizontal plane through fast Fourier transform; the classical Boussinesq equation belongs to a horizontal two-dimensional model, and based on the assumption that the vertical velocity is linearly distributed along the water depth, the two models have the problem of inaccurate velocity profile, and particularly in a deep water area, the dispersion and nonlinearity cannot be guaranteed to be accurate, and precise wave incident information cannot be provided for OpenFOAM.
In summary, aiming at numerical simulation of island-reef sea area wave fields with large water depth span, the potential flow theory in the existing coupling model cannot accurately and efficiently transfer incident wave elements to the viscous flow model, and quick and accurate prediction cannot be realized.
Disclosure of Invention
The invention aims to solve the problems in the prior art and provides a fast and refined island wave field calculation method based on coupling of a double-layer Boussinesq water wave model and an OpenFOAM numerical model.
The technical scheme adopted by the invention for achieving the purpose is as follows:
an island wave field calculation method based on coupling of a double-layer Boussinesq equation and an OpenFOAM model comprises the following steps:
s1, establishing a calculation region of a double-layer Boussinesq equation model and dividing grids;
S2, a double-layer Boussinesq equation model is established, a conceptual diagram of the double-layer Boussinesq equation model is shown in FIG. 3, and the model is divided into an upper layer and a lower layer by a dotted line; the water wave control equation of the double-layer Boussinesq equation model is as follows:
（1）
（2）
In the above-mentioned equation, Is a free surface with a height Cheng Ji wave surface, t represents time,/>And/>Is the lateral and vertical velocity at the free surface,/>The gravity acceleration is that x represents a horizontal coordinate, and a subscript x represents the partial derivative operation of the physical quantity on x; the subscript xx represents the quadratic derivative operation of the physical quantity on x; the subscript xxx represents the tertiary partial derivative operation of the physical quantity on x;
s3, solving a double-layer Boussinesq equation model;
s4, determining a coupling boundary, establishing an OpenFOAM model calculation region and dividing grids;
s5, processing a calculation result of a double-layer Boussinesq equation model, and converting the calculation result into an incident wave element usable by OpenFOAM;
s6, calculating an OpenFOAM model, and carrying out post-processing on a calculation result.
Further, in the step S1:
As shown in fig. 4, since the double-layer Boussinesq equation model has a high-precision theoretical derivation along the water depth direction, only a one-dimensional uniform grid in the horizontal direction, namely the propagation direction of waves is required; the change in island terrain is represented by setting a different water depth for each grid prior to initiating the calculation.
Further, in the step S2:
lateral velocity at free surface And vertical velocity/>The method comprises the following steps:
（3）
（4）
In the above-mentioned equation, And/>Is the transverse and vertical speeds at the self-still water surface, and is specifically:
（5）
（6）
With respect to And/>When i=1, it represents the first water depth/>The calculated speed at i=2 represents the second water depth/>The calculation speed at h represents the water depth,/>Representing the water depth of the first layer,/>Representing the water depth of the second layer;
The speed at the interface of the upper layer and the lower layer meets the following conditions:
（7）
（8）
the bottom boundary condition satisfies:
（9）
N in the above equation refers to 1 or2, and the calculation coefficient of the equation ，/>Respectively defined as:
（10）
The values of the parameters in the equation are shown in the following table:
Wherein the constant is Is the dispersion coefficient,/>Nonlinear coefficients.
Further, the step S3 is:
On a uniform rectangular grid, equations (1) - (9) of a finite difference discrete model are adopted, a time term and a space term in a higher derivative approximation equation are adopted, a time integration adopts a forecast-correction format of a mixed 4-order Adams-Bashforth-Moulton, and an algorithm flow is shown in fig. 5:
(i) Given equation (1), equation (2) is initialized And/>And the predicted/>, is obtained by time integrationAnd/>；
(Ii) Using (i) predictionsAnd/>And/>, current time stepPrediction/> by equation (3)；
(Iii) Repeating step (ii), predicting by equation (5); Equation (7) prediction/>；
(Iv) Substituting all predicted values into the right end of the equation (9), and calculating to obtain；
（v）Substituting equation (8) calculation/>，/>Substituting equation (6) to calculate/>，/>Substituting equation (4) to calculate/>；
And (3) after the steps (i) - (v) are finished, a correction step is carried out until the difference between the surface elevation and the speed calculated in the two prediction steps is smaller than a tolerance value (0.00001), and the prediction is finished.
Further, in the step S4:
When determining the coupling boundary, the application range of the Boussinesq equation theory and the OpenFOAM calculation cost are comprehensively considered, and two principles should be followed: at the uncrushed location and as small an OpenFOAM computational domain as possible;
in the OpenFOAM model, the wave propagation direction grid is determined according to the wavelength, 1/100 of the wavelength is generally selected to meet the requirement, the gravity direction z-direction grid is given according to the wave height, and 1/10-1/20 of the wave height is generally selected; the grid at the free surface needs to be locally encrypted to achieve sufficient resolution to catch wave breaks; since dz is unevenly varied, after meshing, the z-coordinate zi of the center point of each mesh on the coupling boundary surface needs to be recorded; and a z-direction length dzi of each grid.
Further, the step S5 includes the following:
(1) Extraction of double-layer Bussinesq equation calculation results at coupling boundary
Setting a time step dt, and extracting a wave surface calculated by a double-layer Boussinesq equation at a coupling boundary according to the time stepAnd the velocity u, w at various points along the depth of the water;
（11）
（12）
wherein the coefficients in the equation are calculated with the following formula:
z is the water depth represented by a grid in the horizontal direction, Is the vertical position of the first layer,/>Is the vertical position of the second layer; traversing all the positions of the water depth once to obtain the speeds of all the water particles under the water depth;
(2) Conversion of wavefront to OpenFOAM phase fraction
In order to transfer the wavefront result obtained by Boussinesq calculation into OpenFOAM, data needs to be converted into an format recognizable by OpenFOAM, and the volume fraction alpha is defined as a water volume in OpenFOAMOccupy the total volume of the grid/>Is the ratio of:
Calculated from Boussinesq The incident boundary grid information obtained according to the step S2 is mapped to an OpenFOAM incident boundary point by point, and the specific implementation method is that the OpenFOAM grid at the coupling boundary is judged from bottom to top in sequence:
If it is -Zi > =0.5 x dzi, let α=1;
If it is -Zi < = -0.5 x dzi, let α=0;
If it is -Zi > =0, let α= (/ >)-zi+0.5*dzi)/dzi；
If it is-Zi <0, let α= (0.5 x dzi-zi +/>)/dzi；
The wave surface data format conversion can be completed according to the method;
(3) Conversion of flow rate to OpenFOAM format
The double-layer Boussinesq equation model can obtain the flow velocity of any point on the calculation grid, and the equation (11) and the equation (12) are directly used for calculating u and w.
Based on the steps, the double-layer Boussinesq equation model is ensured to be calculated, output and converted into the water volume fraction and the speed field which can be identified by the OpenFOAM on the coupling boundary, the OpenFOAM carries out hot start operation according to the wave surface and the speed field, and the whole calculation process is completed.
Further, in the step S6, the OpenFOAM model calculation area performs closed solution by using SSTk- ω turbulence model.
The overall computational flow of the coupling model is shown in fig. 2.
Compared with the prior art, the invention has the following beneficial effects:
The calculation method combines the advantages of high calculation speed, better dispersion, nonlinearity and OpenFOAM of the double-layer Boussinesq water wave equation, and the double-layer Boussinesq equation divides the water depth into two layers, introduces the calculation pseudo speed, can obtain the speed at any position along the water depth, overcomes the limitation of the traditional potential flow model, and has more advantages in coupling calculation. The coupling model calculates deep-sea waves by using a Boussinesq water wave equation and transmits the deep-sea waves into an OpenFOAM calculation domain as input conditions, a reef flat small-scale crushing area adopts a SSTk-omega turbulence model to carry out closed solution, and OpenFOAM calculation resources are greatly saved while the precision is ensured, so that the rapid and accurate prediction of both a deep-sea large-scale wave field and a reef flat small-scale crushing area is realized.
According to the invention, through coupling the double-layer Boussineq equation and the OpenFOAM numerical calculation method, the limitation of the traditional single calculation method is effectively overcome, and the trans-scale wave motion simulation is realized. Through comparison and verification, in a large-scale wave field (within the application range of a double-layer Boussineq equation), the calculation accuracy of the coupling model is as high as more than 98% in accordance with the double-layer Boussineq equation, and compared with other traditional potential flow models, the calculation accuracy of the double-layer Boussineq model is higher, and in a small-scale reef flat crushing area, the capturing advantage of OpenFOAM on fine crushing is fully reflected. It can be said that the coupling model greatly accelerates the calculation efficiency while ensuring the calculation accuracy, and the calculation efficiency is 70 times that of the conventional CFD. The method is expected to provide time-dependent and accurate forecast for island wave field evolution, and simultaneously provides technical support for planning and implementation of future island protection engineering.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the description of the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a diagram showing a water depth distribution of an island sea area;
FIG. 2 is a flow chart of the overall calculation of the coupling model of the present invention;
FIG. 3 is a conceptual diagram of a double-layer Boussinesq equation of the present invention;
FIG. 4 is a schematic diagram of a two-tier Boussinesq computational grid arrangement of the present invention;
FIG. 5 is a flow chart of a double-layer Boussinesq solution algorithm of the present invention;
FIG. 6 is a diagram of an island topography, computational grid, and stylus layout of the present invention;
FIG. 7 is a graph comparing calculated wave heights of the double-layer Boussinesq equation of the present invention with calculated wave heights of the corresponding coupling model;
FIG. 8 is a graph comparing the calculated wave heights of OceanWave D models with the calculated wave heights of the corresponding coupled models;
FIG. 9 is a graph comparing calculated wave heights of a high-order spectral method model with corresponding coupling models, wherein HOS-NWT is Gao Jiepu a numerical pool model;
FIG. 10 is a graph comparing the calculated wave height of the conventional Boussinesq equation with the calculated wave height of the corresponding coupling model;
FIG. 11 is a graph showing the results of the coupling model of the present invention for the refined prediction of the turbulence energy in the fracture zone.
Detailed Description
The present invention will be described in detail below with reference to the drawings and the specific embodiments, so that those skilled in the art can better understand the technical solutions of the present invention.
An island wave field calculation method based on coupling of a double-layer Boussinesq equation and an OpenFOAM model comprises the following steps:
s1, establishing a calculation region of a double-layer Boussinesq equation model and dividing grids:
Setting an area with the horizontal length of 0-60m in a calculation area, and setting island terrain, wherein an idealized island model is adopted in the method, and the island model is formed by 1:4 and reef flat which is 10m long, the reef body height is 0.85 m, reef flat water depth is 0.15 m, the island reef model exists to enable the water depth span to be changed from 1m to 0.15 m steeply, and a good inspection environment is provided for the method. The island model arrangement is shown in figure 6.
Considering the influence of island topography reflected waves, the double-layer Boussineq model should calculate the universe, namely 0-60m, and since the double-layer Boussineq model has high-precision theoretical derivation along the water depth direction, see step 2 in detail, only a one-dimensional uniform grid (wave propagation direction) in the horizontal direction needs to be given, as shown in fig. 4; the grid distribution rate is dx=0.075 m, and the total number of grids is 800; before the calculation is initialized, the water depth is set for each grid to represent the change of island reef topography. Given the incident wave elements, an extreme wave is generated by adopting a boundary wave generation method, in this example, one of the extreme waves is adopted, namely a focused wave, the water depth condition is 1.0 m, a focused wave group consists of 70 component waves, the frequency range is 0.3-1.0 Hz, all component waves are focused at x=38 m when t=60 s, and a focused peak with the amplitude of 0.12 m is generated. The example adopts a method of equal amplitude to produce waves. Namely:
amplitude of each component wave = focused amplitude/component wave number
The wave height instrument measuring points are arranged, as shown in fig. 6, four characteristic points of the upstream (46 m), reef front slope (48 m), reef edge (50 m) and reef flat (52 m) of the water tank are selected to be provided with the wave height instrument, and the wave height instrument is used for comparing and detecting the evolution states of free surfaces at deep water, when waves are deformed in shallow water and crushed. The comparison results can be used to evaluate the accuracy of the coupling model.
S2, establishing a double-layer Boussinesq equation model:
（1）
（2）
S3, solving a double-layer Boussinesq equation model, and dispersing an equation by using a finite difference method.
S4, determining a coupling boundary, establishing an OpenFOAM model calculation region and dividing grids;
The coupling boundary is specified, in this example, at x=45 m, i.e., the double-layer Boussinesq equation computes the entire computational domain (0-60 m), while OpenFOAM computes the local region (45-60 m) coupling the boundary to the exit boundary. And finishing the output and conversion of the data. (6) An OpenFOAM local numerical model (45 < x <60 m) is built, local encryption is carried out on the liquid level, the grid precision dx=0.016 m and dz=0.008 m at the encryption position, the OpenFOAM grid schematic diagram is shown in fig. 6, and the total grid number is about 4.9 ten thousand.
S5, processing a calculation result of a double-layer Boussinesq equation model, and converting the calculation result into an incident wave element usable by OpenFOAM;
S6, calculating an OpenFOAM model, and carrying out post-processing on a calculation result: and 3, according to the wave elements after calculation conversion in the step 3, using a coupling model to carry out the evolution simulation of the wave field on reef flat, and using a SSTk-omega turbulence model to carry out closed solution in an OpenFOAM model calculation area.
In order to judge the accuracy of the coupling model, the method for evaluating the accuracy of the calculation result of the coupling model comprises the following steps:
Taking the Boussineq equation and the OpenFOAM coupling model mentioned in the background art as an example, waveform calculated by the Boussineq equation model and the coupling model (the Boussineq equation and the OpenFOAM coupling model) are used for calculation accuracy comparison, and the fitting index skill is used for evaluating the fitting degree of the two models. Is the result of the coupling model calculation,/>Is the calculation result of Boussinesq equation,/>The calculation result mean value of the Boussinesq equation is that the closer the skill index is to 1, the better the matching of the two numerical models is represented.
As shown in fig. 7-10, which are graphs comparing the calculated results of four pure potential flow models with the calculated results of the corresponding potential flow+openfoam coupling model, the free surface evolution process of the calculation method is shown in fig. 7, and when the waves are not broken (x=46-50 m), the calculated results of the double-layer Boussinesq equation and the calculated results of the coupling model are basically consistent. The evaluation criteria sk ill of the first 3 feature points in fig. 7 is as high as 0.98 or more, which is sufficient to indicate that the transmitted wave elements are uniform. The reason why the skill is only 0.83 for the last feature point (x=52mj) is analyzed as follows, as shown in fig. 11, near reef edge, the wave is further raised and the rolling break occurs (x= m), and the double-layer Boussinesq does not consider the dissipation of the turbulence energy, so the calculated value is larger, while OpenFOAM introduces a SSTk- ω model, and the turbulence energy dissipation reduces the wave height, so that the theoretical basis and the actual situation are more met. As shown in fig. 7-10, compared with Oceanwave D, gao Jiepu model and traditional Boussinesq model, the double-layer Boussinesq model adopted by the invention is more accurate and basically has no loss when transmitting wave elements to OpenFOAM.
The coupling model of the calculation method can refine and invert more physical processes, such as a dissipation process of turbulent energy, which is not considered by a double-layer Boussinesq equation, as shown in fig. 11, the level of turbulent energy is almost 0 when the model is not broken (t=66.4 s), the level of turbulent energy is maximum when the model is broken (t=67.2 s), the level of turbulent energy is 0.4 m2/s2, and then the turbulent energy is further dissipated on reef flat, so that the coupling model can explain some phenomena focused in engineering in detail.
The working conditions of the method are operated by using a pure double-layer Boussineq equation adopted by the method, a coupling model and a pure OpenFOAM model, and the calculation efficiency of the three models is compared. The computer cpu model of this example was calculated to be 11 th Gen Intel (R) Core (TM) i5-1135g7 @ 2.40ghz, the boussinesq model run time was 13 min x 1 kernel, the coupling model run time was 72 min x 1 kernel, and if the population was calculated using OpenFOAM, the calculation would be for a grid of approximately 4.9 x 4=19.6 ten thousand, and the required time was about 10 hours x 8 kernel, as tested. It can be seen that for this example, the coupling model is about 70 times more efficient than the conventional CFD, which allows us to quickly predict wave fields across the scale of the deep sea island reef accurately.
The embodiments of the present invention have been described in detail by way of examples, but the descriptions are merely exemplary of the embodiments of the present invention and are not to be construed as limiting the scope of the embodiments of the present invention. The protection scope of the embodiments of the invention is defined by the claims. In the technical scheme of the embodiment of the invention, or under the inspired by those skilled in the art, similar technical schemes are designed within the spirit and the protection scope of the embodiment of the invention, or equivalent changes and improvements made to the application scope are still included in the patent coverage protection scope of the embodiment of the invention.
Claims (7)
1. An island wave field calculation method based on coupling of a double-layer Boussinesq equation and an OpenFOAM model is characterized by comprising the following steps:
s1, establishing a calculation region of a double-layer Boussinesq equation model and dividing grids;
s2, establishing a double-layer Boussineq equation model, wherein a water wave control equation of the double-layer Boussineq equation model is as follows:
（1）
（2）
In the above-mentioned equation, Is the free surface elevation, t represents time,/>And/>Is the lateral and vertical velocity at the free surface,The gravity acceleration is that x represents a horizontal coordinate, and a subscript x represents the partial derivative operation of the physical quantity on x;
s3, solving a double-layer Boussinesq equation model;
s4, determining a coupling boundary, establishing an OpenFOAM model calculation region and dividing grids;
s5, processing a calculation result of a double-layer Boussinesq equation model, and converting the calculation result into an incident wave element usable by OpenFOAM;
s6, calculating an OpenFOAM model, and carrying out post-processing on a calculation result.
2. The island wave field computing method based on the coupling of the double-layer Boussinesq equation and the OpenFOAM model according to claim 1, wherein in the step S1:
giving a one-dimensional uniform grid in the horizontal direction; the change in island terrain is represented by setting a different water depth for each grid prior to initiating the calculation.
3. The island wave field computing method based on the coupling of the double-layer Boussinesq equation and the OpenFOAM model according to claim 1, wherein in the step S2:
lateral velocity at free surface And vertical velocity/>The method comprises the following steps:
（3）
（4）
In the above-mentioned equation, And/>Is the transverse and vertical speeds at the self-still water surface, and is specifically:
（5）
（6）
With respect to And/>When i=1, it represents the first water depth/>The calculated speed at i=2 represents the second water depth/>The calculation speed at h represents the water depth,/>Representing the water depth of the first layer,/>Representing the water depth of the second layer;
The speed at the interface of the upper layer and the lower layer meets the following conditions:
（7）
（8）
the bottom boundary condition satisfies:
（9）
N in the above equation refers to 1 or2, and the calculation coefficient of the equation ，/>Respectively defined as:
（10）
The values of the parameters in the equation are shown in the following table:
Wherein the constant is Is the dispersion coefficient,/>Nonlinear coefficients.
4. The island wave field computing method based on the coupling of the double-layer Boussinesq equation and the OpenFOAM model according to claim 3, wherein the step S3 is:
On a uniform rectangular grid, equations (1) - (9) of a finite difference discrete model are adopted, a time term and a space term in a higher derivative approximation equation are adopted, and a mixed 4-order Adams-Bashforth-Moulton forecasting-correcting format is adopted for time integration, wherein the specific steps are as follows:
(i) Given equation (1), equation (2) is initialized And/>And the predicted/>, is obtained by time integrationAnd/>；
(Ii) Using (i) predictionsAnd/>And/>, current time stepPrediction/> by equation (3)；
(Iii) Repeating step (ii), predicting by equation (5); Equation (7) prediction/>；
(Iv) Substituting all predicted values into the right end of the equation (9), and calculating to obtain；
（v）Substituting equation (8) calculation/>，/>Substituting equation (6) to calculate/>，/>Substituting equation (4) to calculate/>；
And (3) after the steps (i) - (v) are finished, a correction step is carried out until the difference between the surface elevation and the speed calculated in the two prediction steps is smaller than the tolerance value, and the prediction is finished.
5. The island wave field computing method based on the coupling of the double-layer Boussinesq equation and the OpenFOAM model according to claim 3, wherein in the step S4:
When determining the coupling boundary, the application range of the Boussinesq equation theory and the OpenFOAM calculation cost are comprehensively considered, and two principles should be followed: at the uncrushed location and as small an OpenFOAM computational domain as possible;
In the OpenFOAM model, a wave propagation direction grid is determined according to wavelength, 1/100 of the wavelength is selected, a gravity direction z-direction grid is given according to wave height, and 1/10-1/20 of the wave height is selected; the grid at the free surface needs to be locally encrypted to achieve sufficient resolution to catch wave breaks; recording the z-coordinate zi of the center point of each grid on the coupling boundary surface; and a z-direction length dzi of each grid.
6. The island wave field computing method based on the coupling of the double-layer Boussinesq equation and the OpenFOAM model according to claim 5, wherein the step S5 includes the following steps:
(1) Extraction of double-layer Bussinesq equation calculation results at coupling boundary
Setting a time step dt, and extracting a wave surface calculated by a double-layer Boussinesq equation at a coupling boundary according to the time stepAnd the velocity u, w at various points along the depth of the water;
（11）
（12）
wherein the coefficients in the equation are calculated with the following formula:
z is the water depth represented by a grid in the horizontal direction, Is the vertical position of the first layer,/>Is the vertical position of the second layer; traversing all positions of the water depth once to obtain the speeds of all water particles under the water depth;
(2) Conversion of wavefront to OpenFOAM phase fraction
The volume fraction α is defined in OpenFOAM as the volume fraction αOccupy the total volume of the grid/>Is the ratio of:
Wave surface obtained by Boussinesq calculation The incident boundary grid information obtained according to the step S2 is mapped to an OpenFOAM incident boundary point by point, and the specific implementation method is that the OpenFOAM grid at the coupling boundary is judged from bottom to top in sequence:
If it is -Zi > =0.5 x dzi, let/>=1；
If it is-Zi < = -0.5 x dzi, let/>=0；
If it is-Zi > =0, let/>=(/>-zi+0.5*dzi)/dzi；
If it is-Zi <0, order/>=(0.5*dzi-zi+/>)/dzi；
(3) And finishing wave surface data format conversion according to the wave surface data format;
Conversion of flow rate to OpenFOAM format
The double-layer Boussinesq equation model can obtain the flow velocity of any point on the calculation grid, and the equation (11) and the equation (12) are directly used for calculating u and w.
7. The island wave field computing method based on the coupling of the double-layer Boussinesq equation and the OpenFOAM model according to claim 1, wherein in the step S6, the OpenFOAM model computing area adopts a SSTk- ω turbulence model to perform closed solution.
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