Numerical wave making method of internal solitary wave based on marine measured data

Abstract

The application discloses a kind of numerical wave generation method of internal solitary wave based on marine measured data, first determine the size of observation basin, obtain the distribution of seawater physical parameters on three-dimensional space, sampling according to the set spatial resolution, further obtain the three-dimensional spatial distribution of internal solitary wave;The measured data of the three-dimensional spatial distribution of internal solitary wave is reorganized into the data format that can be recognized by Fluent simulation software, and a new ip file is generated;Establish the same size of calculation domain with the observation basin, and establish the numerical tank of internal solitary wave using mesh division software;Read the grid file using Fluent software, interpolate the ip file into the calculation domain to complete numerical wave generation.Set numerical parameters, solution format, click Calculate to start calculation, and the free evolution movement of internal solitary wave can be realized.The application can simulate internal solitary wave in actual ocean simply and quickly, and provides a novel and effective wave generation method for further research on internal solitary wave.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of numerical simulation, and particularly relates to a numerical wave making method of internal solitary wave. BACKGROUND

[0002] Due to the uneven heating of the sun radiation and the dynamic and thermodynamic effects of the atmosphere in different climate zones, the temperature, salinity and density of seawater in each sea area are significantly different, but the vertical distribution presents a certain regular macroscopic hierarchical structure, which is called ocean stratification structure. When the external disturbance destroys the stratification structure, internal wave may be generated. The atmospheric pressure, wind field on the sea surface and the hills and mountains under the sea can be the disturbance source of internal wave. During the propagation of internal wave, nonlinear polarization occurs in the density jump layer, and then the internal solitary wave is evolved. The internal solitary wave has large amplitude and carries huge energy, and usually propagates in the form of wave group. During the propagation, the seawater flow above and below the density jump layer presents a shear state, and strong amplitude convergence and divergence and sudden strong current are caused. The maximum flow velocity of the induced internal wave flow field can reach more than 2m / s. The large amplitude internal solitary wave has an important influence on the ocean material transport, marine ecological environment, offshore operation platform and safe navigation of underwater vehicles.

[0003] In recent years, scholars at home and abroad have carried out a large number of researches on the generation mechanism, propagation evolution, detection and prediction of ocean internal solitary waves, as well as their interaction with marine structures, and have made a lot of achievements. Reading relevant literature, it is found that accurately and efficiently generating internal solitary waves is a necessary prerequisite for research work, and the key points of wave generation are data acquisition and wave generation method. From the perspective of internal solitary wave data acquisition means, it can be mainly divided into two categories: the first is remote sensing image data analysis. Remote sensing data has the advantages of wide spatial coverage, high spatial resolution and relatively low data acquisition cost. Patent CN 113406006 A constructs a sample library through the second modal convex internal solitary wave optical remote sensing image, and uses neural network algorithm to invert the amplitude of the second modal convex internal solitary wave. This method has high precision in data detection and acquisition of internal wave amplitude, but the process of inverting amplitude from remote sensing image is complicated, and it cannot accurately describe the complex characteristics of ocean internal solitary wave, such as its characteristic wavelength and wave speed. The second is real-time data analysis. Internal waves occur in the ocean interior, and the water movement produced not only changes with time, but also changes with three-dimensional space, so the observation of internal waves should be three-dimensional observation. CTD, ADCP and other instruments are commonly used. Field measurement provides first-hand data for the study of ocean internal waves, and is a direct way to study the vertical structure change of ocean interior caused by ocean internal waves, but the economic cost is high. At present, many ocean buoy and subsurface buoy observation data can be downloaded from the Internet, such as the flow velocity and direction, ocean temperature and salinity, and pressure, etc. which can be downloaded from the National Oceanic Data Center Network. Many observation data of more detailed ocean data (internal solitary wave three-dimensional profile flow velocity component, thermocline thickness, etc.) can be obtained by many scientific research units or colleges and universities in China. Patent CN 110008509 A also obtains the three-dimensional flow field structure of the South China Sea based on the measured temperature, salinity and depth data of the South China Sea by using ROMS simulation software to approximately solve the Reynolds-averaged Navier-Stokes (N-S) equation, but lacks comparative analysis of simulation data and actual data, and the accuracy and reliability need to be further verified.

[0004] The commonly used wave making methods mainly include laboratory wave making and numerical simulation wave making. The laboratory wave making has small investment and strong visibility, and can conveniently adopt advanced technologies and instruments to experimentally study internal solitary waves, such as schlieren technology, hydrogen bubble technology, PIV technology, hot film anemometer, Doppler laser anemometer and float technology. The patents CN112697390A and CN107340118A disclose two laboratory wave making devices for internal solitary waves with different purposes. However, the laboratory wave making is limited by the size of the site, the size of the internal wave tank and the preparation of the stratified fluid, and the experimental conditions are harsh and difficult to carry out multi-condition and complex tests. With the rapid development of computational fluid dynamics (CFD), the CFD numerical simulation has become a research hotspot for studying internal solitary waves. Based on the internal solitary wave theory (KdV equation, MCC equation or DJL equation) under the Boussinesq assumption and the Fluent fluid simulation platform, a numerical tank is established, the incompressible N-S equation is discretized by using the finite volume method, and the VOF multiphase flow model is set to consider the phase interface between the fluids. The main characteristics of this method are flexible research mode, simple operation and strong repeatability, and it has unique advantages for studying the influence of some environmental parameter changes on the kinematic characteristics of the internal solitary waves, exploring the dynamic mechanism of the internal solitary waves and studying the excitation mechanism of the internal solitary waves. SUMMARY

[0005] In order to overcome the shortcomings of the prior art, the present application provides an internal solitary wave numerical wave making method based on marine measured data. First, the size of the observation flow field is determined, the distribution of seawater physical parameters in three-dimensional space is obtained, and the internal solitary wave three-dimensional space distribution is further obtained by sampling at a set spatial resolution. The internal solitary wave measured data in three-dimensional space is reorganized into a data format that can be recognized by the Fluent simulation software, and a new ip file is generated. A calculation domain with the same size as the observation flow field is established, and a numerical tank of the internal solitary wave is established by using a grid division software. The Fluent software reads the grid file, interpolates the ip file into the calculation domain, and completes the numerical wave making. By setting the numerical parameters and the solution format, clicking Calculate to start the calculation, the free evolution motion of the internal solitary wave can be realized. The present application can simply and quickly simulate the internal solitary wave in the actual ocean, and provides a novel and effective wave making method for further research on the internal solitary wave.

[0006] The technical solution adopted by the present application to solve its technical problems comprises the following steps:

[0007] Step 1: Determine the size of the observation flow field, obtain the distribution of seawater physical parameters in three-dimensional space, and further obtain the internal solitary wave three-dimensional space distribution by sampling at a set spatial resolution.

[0008] Step 2: reorganize the measured data of the three-dimensional spatial distribution of internal solitary waves into a data format that can be recognized by the Fluent simulation software, and generate a new ip file;

[0009] Step 3: establish a calculation domain with the same size as the observed basin, and use grid division software to establish an internal solitary wave numerical tank;

[0010] Step 4: read the grid file using Fluent software, interpolate the ip file into the calculation domain, and complete the numerical wave making.

[0011] Step 5: set numerical parameters and solution format, click Calculate to start calculation to realize the free evolution of internal solitary waves.

[0012] Further, the step 1 specifically comprises:

[0013] Step 1-1: determine the size of the observed basin;

[0014] Establish an observation area of a certain size in the sea area where internal solitary waves appear;

[0015] Step 1-2: measure the seawater information in the area using a CTD, obtain the conductivity, temperature and pressure of the seawater, calculate the salinity from the conductivity, calculate the depth from the pressure, and calculate the sound speed;

[0016] Step 1-3: use an acoustic Doppler current profiler (ADCP) to measure the three-dimensional components and absolute directions of the flow velocity at several layers in a profile;

[0017] Step 1-4: record the passage of internal solitary waves through steps 1-2 and 1-3, and obtain the distribution rules of the pressure, temperature and flow velocity physical parameters of internal solitary waves in three dimensions.

[0018] Further, the method for obtaining the three-dimensional spatial distribution of internal solitary waves in step 1 is as follows:

[0019] Download public internal solitary wave observation data from the Internet or use measured data as initial input for theoretical equations to obtain comprehensive internal solitary wave flow field data.

[0020] Further, the step 2 specifically comprises:

[0021] Rearrange and combine the matrix format data obtained in step 1 into a column vector, and add a header file, which contains data dimensions, data types and data volume, each type of data is separated by left and right parentheses, and finally generate a data file with suffix ip, recorded as data.ip.

[0022] Further, the step 3 specifically comprises:

[0023] The grid division software ICEM is used to establish the internal wave numerical tank, a geometric model is established first, and then the grid nodes are divided, and the grid node numbers and data resolution in three dimensions are kept consistent.

[0024] Further, the step 4 specifically comprises:

[0025] The Fluent software is opened, the data.ip is interpolated into the calculation domain through the interpolate function after reading the grid file, after the interpolation is completed, the new Surface profile is checked to check whether each grid node in the calculation domain has the flow field information, and after the check is correct, the wave is generated.

[0026] Further, the step 5 specifically comprises:

[0027] The Mixture multiphase flow model is set to ensure the mass exchange between the multi-layer fluids, all surfaces of the numerical tank are set as the Symmetry symmetry surface, the numerical format is set as the second-order upwind format, and the Calculate is clicked to realize the forward propagation of the internal solitary wave.

[0028] The present application has the following beneficial effects:

[0029] The present application provides a method for using the measured internal solitary wave data as the initial data source, adjusting and transforming the data, and directly interpolating the data into the Fluent simulation software, and the method has the advantages that the flow field data is real and reliable, can reflect the flow characteristics of the internal solitary wave in the large-scale sea area, and does not need to be developed again (UDF is written), and the internal solitary wave in the actual sea can be simulated simply and quickly, and a novel and effective wave generation method is provided for further research on the internal solitary wave. DETAILED DESCRIPTION

[0030] Figure 1 The present application is a method flowchart.

[0031] Figure 2 The present application is an initial flow field-density distribution diagram generated by the DJL equation.

[0032] Figure 3 The present application is a two-dimensional data expansion diagram.

[0033] Figure 4 The present application is a numerical tank grid division diagram.

[0034] Figure 5 The present application is a flow field horizontal and vertical velocity distribution diagram after interpolation. DETAILED DESCRIPTION

[0035] The present application is further described below in combination with the drawings and examples.

[0036] The purpose of the present application is to provide a numerical internal solitary wave generation method based on measured ocean data, which can realize efficient numerical simulation of internal solitary waves, thereby providing a simple and reliable wave generation method for academic and engineering research of internal solitary waves.

[0037] Currently, most numerical internal solitary wave generation methods use velocity inlet wave generation, mass source wave generation, and physical wave machine wave generation. The numerical internal solitary waves generated are generally compared with theoretical solutions to determine whether the wave generation is accurate. The present application proposes a method that uses measured internal solitary wave data as the initial data source. After adjusting and transforming the data, it is directly interpolated into the Fluent simulation software. The advantages of this method are that the flow field data is real and reliable, can reflect the flow characteristics of internal solitary waves in large-scale sea areas, and does not require secondary development of Fluent (UDF programming), allowing for simple and fast simulation of internal solitary waves in actual oceans, providing a novel and effective wave generation method for further research on internal solitary waves.

[0038] A numerical internal solitary wave generation method based on measured ocean data, comprising the following steps:

[0039] Step 1: Determine the size of the observation area, obtain the distribution of seawater physical parameters in three-dimensional space, and sample at a reasonable spatial resolution to further obtain the three-dimensional spatial distribution of internal solitary waves.

[0040] First, determine the size of the observation area, such as establishing a 3000x200x300m (lengthxwidthxheight) observation area in the sea area where internal solitary waves frequently occur in the South China Sea. Use a CTD (Conductivity-Temperature-Depth) instrument to measure the seawater information in the area. This is a marine instrument that can obtain the conductivity, temperature, and pressure of seawater. The salinity is calculated from the conductivity, and the depth can be calculated from the pressure. In addition, based on these three parameters, other physical parameters such as sound speed can be calculated. An ADCP (Acoustic Doppler Current Profiler) can measure the three-dimensional components and absolute direction of flow velocity at several layers on one profile at a time, which is a hydroacoustic flow measurement instrument. Through these two instruments, the passage of internal solitary waves can be accurately recorded, and the distribution of physical parameters such as pressure, temperature, and flow velocity of internal solitary waves in three dimensions can be obtained. If it is not possible to do field observation, publicly available internal solitary wave observation data can be downloaded from the internet or a small amount of measured data can be used as the initial input of the theoretical equation to obtain comprehensive internal solitary wave flow field data. In the horizontal direction (x-axis), take a point every 10m, in the vertical direction (z-axis), take a point every 3m, and in the spanwise direction (y-axis), take a point every 2m. Under the premise of accurately reflecting the flow characteristics of internal solitary waves, as few points as possible are taken to avoid excessive computational load in the subsequent calculation.

[0041] Step 2: Reorganize the measured data of three-dimensional spatial distribution of internal solitary wave into a data format that can be recognized by the Fluent simulation software, and generate a new ip file;

[0042] The size of the reorganized data is 300x100x100=3000000. From each profile, these data are in a matrix format, while the data format that can be recognized by the Fluent software is a column vector type. Therefore, these data are rearranged into a column vector, and a correct header file is added so that the Fluent can accurately recognize the data. The header file includes the data dimension, data type and data amount, and each type of data is separated by left and right parentheses. Finally, a data file with the suffix ip is generated and recorded as data.ip.

[0043] Step 3: Establish a calculation domain with the same size as the observed river basin, and use grid division software to establish an internal solitary wave numerical tank;

[0044] Use the grid division software ICEM to establish the internal wave numerical tank. First, establish the geometric model, and then divide the grid nodes. The number of grid nodes in three dimensions and the data resolution are consistent, i.e. 300x100x100.

[0045] Step 4: Use the Fluent software to read the grid file, interpolate the ip file into the calculation domain, and complete the numerical wave making.

[0046] Open the Fluent software, read the grid file, and then interpolate the data.ip into the calculation domain through the interpolate function. After the interpolation is completed, a new Surface (profile) is established to check whether each grid node in the calculation domain has flow field information. After the check is correct, the wave making is completed.

[0047] Step 5: Set the numerical parameters and solution format, and click Calculate to start the calculation to realize the free evolution of the internal solitary wave.

[0048] Set the Mixture multiphase flow model to ensure mass exchange between multiple layers of fluid. Set all the surfaces of the numerical tank to be Symmetry symmetric surfaces, and set the numerical format to be second-order upwind format. Click Calculate to realize the forward propagation of the internal solitary wave. This provides an efficient and accurate wave making method for further research on the propagation and evolution of internal solitary waves and their interaction with structures. Specific embodiments:

[0050] This embodiment provides an internal solitary wave numerical wave making method based on marine measured data. The specific process is shown in FIG. 1. Figure 1 The operation steps are explained in detail as follows:

[0051] Step 1: Determine the size of the observed basin, obtain the distribution of seawater physical parameters in three-dimensional space, and sample at a reasonable spatial resolution to further obtain the three-dimensional spatial distribution of internal solitary waves;

[0052] Specifically, the internal solitary wave flow field information in a certain sea area is measured by using oceanographic instruments such as CTD, ADCP, etc., or the publicly available ocean internal solitary wave observation data is downloaded from the network. Here, in order to simplify the operation process, a small amount of measured data is used as the initial input of the DJL equation to obtain comprehensive internal solitary wave flow field data.

[0053] DJL equation is a theory for describing completely nonlinear internal solitary waves. DJL equation is very practical because it proposes a numerical solution method for simple and eternal form translation waves, which can obtain a steady flow field moving at a constant speed. This theory considers an irrotational, incompressible, and inviscid fluid under Boussinesq approximation, and the equation expression in a two-dimensional fixed reference frame without considering the influence of background flow is as formula (1):

[0054]

[0055] η(x,0)=η(x,H)=0 (2)

[0056] η→0,as|x|→∞ (3)

[0057]

[0058] where N 2 represents the square of buoyancy frequency, η represents the isosurface displacement, c is the propagation speed of the wave, represents the vertical distribution of the average density of seawater; x and z represent horizontal and vertical coordinates, H represents the total water depth, |x|→∞ represents the absolute value of the horizontal coordinate tending to infinity, and g is the acceleration of gravity;

[0059] First, the size of the calculation domain, the resolution, the amplitude of the internal solitary wave (APE), the center position and thickness of the density jump layer, and the relative density ratio of the upper and lower fluids are given. The DJL equation calculation source code can be downloaded from the network (DJL equation solver, Michael Dunphy, 2019). The obtained initial two-dimensional flow field-density distribution is shown in FIG. 1. Figure 2

[0060] Step 2: Reorganize the three-dimensional spatial distribution of the measured internal solitary wave data into a data format that can be recognized by the Fluent simulation software, and generate a new ip file;

[0061] ​Specifically, the two-dimensional internal solitary wave flow field data obtained from the embodiment step 1, in order to further obtain the three-dimensional flow field, the xoz is copied along the y axis, and a schematic diagram is shown in the accompanying Figure 3 Since the format of the data is a three-dimensional matrix format, the data quantity and the resolution setting are related, in order to enable the Fluent software to identify the internal solitary wave flow field data, the data format is converted into a column vector, and a header file is added, the header file is sequentially the data dimension, the data quantity, the data type number (6), the data type (hydrostatic pressure, upper layer density, lower layer density, horizontal velocity, vertical velocity and spanwise velocity), and is saved as a new file with the suffix ip, recorded as data.ip.

[0062] Step 3: Establish a calculation domain with the same size as the observed flow field, and use grid division software to establish an internal solitary wave numerical tank;

[0063] Specifically, the ICEM grid division software is used to establish a calculation domain with the same size as the flow field, the inlet, the outlet, the upper and lower walls and the front and rear walls are set, and the calculation domain is meshed, and the number of nodes on the line and the resolution are kept consistent, as shown in the accompanying Figure 4

[0064] Step 4: Open the Fluent software, read the grid file, then interpolate the ip file into the calculation domain to complete the numerical wave making.

[0065] Specifically, the Fluent software is opened to read the grid file in step 3, and the Interpolate function is used to interpolate the data.ip file in step 2 into the calculation domain, after interpolation, a new Surface (profile) is established to check the velocity distribution of the flow field, as shown in the accompanying Figure 5

[0066] Step 5: Set the numerical parameters, solution format, and click Calculate to start calculation to realize the free evolution of the internal solitary wave.

[0067] Specifically, the Mixture multiphase flow model is further set to ensure mass exchange between the multi-layer fluids, the k-ε turbulence model is selected, all the surfaces of the numerical tank are set as Symmetry symmetric surfaces, and the numerical format is set as the second-order upwind format, and the calculation is stopped after the convergence is good and the calculation is stable.

[0068] It should be noted that the present application can accurately simulate the actual internal solitary wave flow field (with disturbance) under the condition of full measured data, and the internal solitary wave data is calculated based on the DJL equation in the embodiment, which is only for the convenience of demonstrating the operation process.​​

Claims

1. A numerical wave making method of internal solitary waves based on ocean measured data, characterized in that, It comprises the following steps: Step 1: determining the size of the observation basin, obtaining the distribution of the seawater physical parameters in three-dimensional space, sampling according to the set spatial resolution, and further obtaining the three-dimensional spatial distribution of the internal solitary wave; specifically comprising: Step 1-1: determining the size of the observation basin; An observation area of a set size is established in the sea area where the internal solitary wave appears; Step 1-2: measuring the seawater information in the area by using the CTD, obtaining the conductivity, temperature and pressure of the seawater, calculating the salinity from the conductivity, calculating the depth from the pressure, and calculating the sound speed; Step 1-3: measuring the three-dimensional components and absolute directions of the flow velocity of several layers on a profile by using the ADCP; Step 1-4: recording the passing of the internal solitary wave through steps 1-2 and 1-3, and obtaining the distribution rules of the pressure, temperature and flow velocity physical parameters of the internal solitary wave in three dimensions; Step 2: reorganizing the three-dimensional spatial distribution of the internal solitary wave measured data into a data format that can be recognized by the Fluent simulation software, and generating a new ip file; Step 3: establishing a calculation domain of the same size as the observation basin, and using a grid division software to establish an internal solitary wave numerical tank; Step 4: reading the grid file using the Fluent software, interpolating the ip file into the calculation domain to complete the numerical wave making; Step 5: setting numerical parameters and solution format, clicking Calculate to start calculation to realize the free evolution of the internal solitary wave; specifically comprising: Setting the Mixture multiphase flow model to ensure mass exchange between multiple layers of fluid, setting all surfaces of the numerical tank as Symmetry symmetry surfaces, setting the numerical format as second-order upwind format, and clicking Calculate to realize the forward propagation of the internal solitary wave.

2. The numerical generation method of internal solitary waves based on measured data of the sea according to claim 1, characterized in that, The method for obtaining the three-dimensional spatial distribution of the internal solitary wave in step 1 is as follows: Download the public internal solitary wave observation data from the network or use the measured data as the initial input of the theoretical equation to obtain comprehensive internal solitary wave flow field data. 3.The numerical generation method of internal solitary waves based on in-situ data according to claim 1, wherein, Step 2 specifically comprises: The matrix format data obtained in step 1 is rearranged and combined into a column vector, and a header file is added, the header file contains data dimensions, data types and data volume, each type of data is separated by left and right parentheses, and finally a data file with suffix ip is generated, recorded as data.ip.

4. The numerical generation method of internal solitary waves based on measured data of the sea according to claim 1, characterized in that, Step 3 specifically comprises: Using the grid division software ICEM to establish an internal wave numerical tank, first establishing a geometric model, then dividing grid nodes, and the number of grid nodes in three dimensions and the data resolution are consistent.

5. The numerical generation method of internal solitary waves based on measured data of the sea according to claim 1, characterized in that, Step 4 specifically comprises: Open the Fluent software, read the grid file, then interpolate data.ip into the calculation domain through the interpolate function, after interpolation, establish a new Surface profile to check whether each grid node in the calculation domain has flow field information, and after checking, complete the wave making.

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