A calculation method for three-dimensional flow velocity distribution near a bridge pier

Abstract

The present invention relates to the technical field of three-dimensional water flow simulation, and particularly relates to a calculation method for three-dimensional flow velocity distribution near a bridge pier. The method includes: performing coordinate transformation on the three-dimensional water flow continuity equation and the momentum equation; calculating the vertical turbulent eddy viscosity coefficient and the horizontal turbulent eddy viscosity coefficient; discretizing the perturbed momentum equation by using the finite volume method to obtain the corresponding discrete equation; obtaining the discrete general equation according to the boundary conditions required by the perturbed momentum equation; forming a tridiagonal system of equations from the corresponding discrete equation, the discrete general equation under the bed boundary condition, and the discrete general equation under the free water surface boundary condition, and solving it to obtain the perturbed flow velocity, and further obtaining the three-dimensional flow velocity and the vertical flow velocity. The present invention can obtain the flow velocity distribution upstream of the bridge pier, the flow velocity distribution downstream of the bridge pier, and the flow velocity distribution between the bridge piers according to the measured flow velocity at 0.5 times the water depth, reduce the calculation amount, and can be applied to large-scale measurements.

Description

Technical Field

[0001] The present invention relates to the technical field of three-dimensional water flow simulation, and particularly relates to a method for calculating the three-dimensional flow velocity distribution near a bridge pier. Background Technique

[0002] With the rapid development of the scientific and technological level, the road and traffic network extending in all directions has become increasingly complex. Among them, bridges, as important links connecting various regions, provide conditions for highways and railways to cross obstacles such as rivers and canyons, and have made great contributions to social and economic development.

[0003] After building a bridge in a natural river channel, due to the compression and interference of the bridge pier on the water flow, the water flow situation around the bridge pier will inevitably change greatly, causing scour to the bridge pier. Long-term scour will cause the instability of the bridge pier or the bridge, resulting in serious consequences.

[0004] The water flow velocity near the bridge pier is the most important and direct factor affecting the scour of the bridge pier. By reasonably evaluating the velocity change near the bridge pier of the bridge, the scour degree near the bridge pier can be judged in time, which is of great significance for improving the safety degree of the bridge pier foundation and ensuring the reliability of the project.

[0005] Traditional methods for measuring the flow velocity distribution upstream of the bridge pier, the flow velocity distribution downstream of the bridge pier, and the flow velocity distribution between the bridge piers require measuring the flow velocities at different water depths on the vertical line to obtain the flow velocity distribution upstream of the bridge pier, the flow velocity distribution downstream of the bridge pier, and the flow velocity distribution between the bridge piers. This consumes a large amount of manpower and financial resources and takes a long time to measure, which is not conducive to large-scale measurement. Summary of the Invention

[0006] In order to solve the above technical problems, the present invention provides a method for calculating the three-dimensional flow velocity distribution near a bridge pier, and the specific technical solution adopted is as follows:

[0007] An embodiment of the present invention provides a method for calculating the three-dimensional flow velocity distribution near a bridge pier, and the method includes the following steps:

[0008] Perform coordinate transformation on the three-dimensional water flow continuity equation and momentum equation; calculate the vertical turbulent eddy viscosity coefficient by using the turbulent kinetic energy and turbulent dissipation rate, and calculate the horizontal turbulent eddy viscosity coefficient according to the Boussinesq eddy viscosity hypothesis;

[0009] Obtain the mathematical relationship between the three-dimensional flow velocity and the perturbation flow velocity, and the perturbation momentum equation according to the three-dimensional Navier-Stokes equation and the shallow water equation; discretize the perturbation momentum equation by using the finite volume method to obtain the corresponding discrete equation;

[0010] Obtain the discrete general equation near the bed surface according to the boundary conditions that the perturbed momentum equation needs to satisfy near the bed surface; obtain the discrete general equation near the free water surface according to the boundary conditions that the perturbed momentum equation needs to satisfy near the free water surface;

[0011] By setting the initial conditions, a tridiagonal system of equations is formed by the corresponding discrete equations, the discrete general equation under the bed surface boundary conditions, and the discrete general equation under the free water surface boundary conditions. Solve the tridiagonal system of equations to obtain the perturbed flow velocity, and then obtain the three-dimensional flow velocity distribution.

[0012] Preferably, the coordinate transformation of the three-dimensional water flow continuity equation and the momentum equation includes:

[0013] Nondimensionalize the three-dimensional water flow continuity equation and the momentum equation, and then introduce coordinates to obtain the basic three-dimensional water flow equation after coordinate transformation.

[0014] Preferably, the calculation method of the vertical turbulent eddy viscosity coefficient is as follows:

[0015] Obtain the transport equations of turbulent kinetic energy and turbulent dissipation rate, and the first formula for calculating the vertical turbulent eddy viscosity coefficient using turbulent kinetic energy and turbulent dissipation rate. Combine the transport equations and the first formula to calculate the vertical turbulent eddy viscosity coefficient.

[0016] Preferably, the calculation method of the horizontal turbulent eddy viscosity coefficient is as follows:

[0017] Calculate the vertically averaged lateral shear stress caused by turbulence through the Boussinesq eddy viscosity hypothesis, calculate the basic horizontal turbulent eddy viscosity coefficient using the friction velocity and water depth, and obtain the horizontal turbulent eddy viscosity coefficient according to the basic horizontal turbulent eddy viscosity coefficient, friction velocity and water depth, and U, V, where U represents the average flow velocity in the x direction and V represents the average flow velocity in the y direction.

[0018] Preferably, the method for obtaining the three-dimensional flow velocity is as follows:

[0019] Subtract the shallow water equation from the three-dimensional Navier-Stokes equation to obtain the mathematical relationship between the three-dimensional flow velocity and the perturbed flow velocity, and the perturbed momentum equation. Discretize and solve the perturbed momentum equation to obtain the perturbed flow velocity, and use this mathematical relationship to obtain the three-dimensional flow velocity distribution.

[0020] The embodiments of the present invention have at least the following beneficial effects:

[0021] Based on the Navier-Stokes equations, which are simplified and discretized, a local three-dimensional flow mathematical model of the bridge pier is established. It can obtain the flow velocity distribution upstream of the bridge pier, the flow velocity distribution downstream of the bridge pier, and the flow velocity distribution between the bridge piers according to the measured flow velocity at 0.5 times the water depth, reducing the calculation amount and being applied to large-scale measurements. Description of the Drawings

[0022] In order to more clearly illustrate the technical solutions and advantages in the embodiments of the present invention or the prior art, the drawings required for use in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained according to these drawings.

[0023] Figure 1 It is a flowchart of the steps of a method for calculating the three-dimensional flow velocity distribution near a bridge pier provided by an embodiment of the present invention;

[0024] Figure 2 For Principle diagram of coordinate transformation;

[0025] Figure 3 It is a schematic diagram of the vertical grid;

[0026] Figure 4 It is a schematic diagram of the boundary conditions near the bed surface;

[0027] Figure 5 It is a schematic diagram of the boundary conditions near the free water surface. Detailed Embodiments

[0028] In order to further elaborate on the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following, in combination with the drawings and preferred embodiments, details the specific embodiments, structures, features and effects of a method for calculating the three-dimensional flow velocity distribution near a bridge pier proposed according to the present invention. In the following description, different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. In addition, the specific features, structures or characteristics in one or more embodiments can be combined in any suitable form.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0030] The following specifically describes the specific solution of a method for calculating the three-dimensional flow velocity distribution near a bridge pier provided by the present invention with reference to the drawings.

[0031] Please refer to Figure 1, which shows the step flow chart of a calculation method for three-dimensional flow velocity distribution near a pier provided by an embodiment of the present invention. The method includes the following steps:

[0032] Step S001, perform coordinate transformation on the three-dimensional water flow continuity equation and momentum equation; calculate the vertical turbulent eddy viscosity coefficient using the turbulent kinetic energy and turbulent dissipation rate, and calculate the horizontal turbulent eddy viscosity coefficient according to the Boussinesq eddy viscosity hypothesis.

[0033] The specific steps include:

[0034] 1. Nondimensionalize the three-dimensional water flow continuity equation and momentum equation, and then introduce coordinates to obtain the basic three-dimensional water flow equation after coordinate transformation.

[0035] The three-dimensional water flow continuity equation and momentum equation of an incompressible fluid considering the hydrostatic pressure assumption in the Cartesian coordinate system are expressed as follows:

[0036] Continuity equation:

[0037]

[0038] Momentum equation in the

[0039]

[0040] Momentum equation in the

[0041]

[0042] After the hydrostatic pressure assumption, the momentum equation is:

[0043]

[0044] Where, represents the time-averaged flow velocity in the direction, represents the time-averaged flow velocity in the direction, represents the time-averaged flow velocity in the direction; represents time; represents the Coriolis coefficient; represents the gravitational acceleration, [L·T -2 ; represents density, [M·L -3 ; represents pressure, [M·L -1 ·T -2 ; represents the horizontal turbulent eddy viscosity coefficient, [L 2 ·T -1 ; represents the vertical turbulent eddy viscosity coefficient, [L 2 ·T -1 ; represents the water depth, represents the bed elevation, represents the free water surface elevation and .

[0045] Coriolis coefficient , where, represents the Earth's rotation speed, [T -1 ; represents the latitude.

[0046] In most natural river channels, the vertical scale is much smaller than the horizontal scale. Therefore, in the embodiments of the present invention, the hydrostatic pressure assumption is adopted to neglect the vertical viscosity and vertical acceleration.

[0047] To more easily compare the relative magnitudes of different variables in the equation, the following dimensionless variables are now used to further process the above equation:

[0048]

[0049]

[0050]

[0051]

[0052]

[0053]

[0054]

[0055]

[0056] Among them, represents the wind shear stress in the -1 ·T -2 direction, [M·L represents the wind shear stress in the direction, represents the reference density, represents the reference value in the x direction, represents the reference value in the y direction, represents the reference value of the cross-sectional average flow velocity.

[0057] It should be noted that the subscript "r" is used to denote the reference value of the corresponding variable, and the superscript "*" is used to denote the dimensionless form of the corresponding variable.

[0058] In addition, the following dimensionless combinations are defined:

[0059] Rossby number:

[0060] Froude number:

[0061] Density Froude number:

[0062] Horizontal Ekman number:

[0063] Vertical Ekman number:

[0064] Since the variables involved in the following equations are all in dimensionless form, for simplicity, the "*" is omitted.

[0065] Introduce coordinates into the dimensionless equations, and transform the Cartesian coordinate system, i.e., the xyz coordinate system, into the sigma coordinate system, The principle of coordinate transformation is as Figure 2 shown, and its definition is as follows:

[0066]

[0067] Process the three-dimensional water flow continuity equation and momentum equation with coordinates to obtain the three-dimensional basic water flow equation:

[0068] Using the continuity equation processed with coordinates is:

[0069]

[0070] Using the direction momentum equation processed with coordinates is:

[0071]

[0072] Using the direction momentum equation processed with coordinates is:

[0073]

[0074] Among them, a certain Vertical particle velocity at the coordinate Available vertical field velocity It is expressed as:

[0075]

[0076] Wherein, .

[0077] 2. Obtain the transport equations of turbulent kinetic energy and turbulent dissipation rate, as well as the first formula for calculating the vertical turbulent eddy viscosity coefficient using the turbulent kinetic energy and turbulent dissipation rate, and calculate the vertical turbulent eddy viscosity coefficient by combining the transport equations and the first formula.

[0078] 2.1 Obtain the transport equations of turbulent kinetic energy and turbulent dissipation rate:

[0079] Turbulent kinetic energy The transport equation of is expressed as follows:

[0080]

[0081] Turbulent dissipation rate The transport equation of is expressed as follows:

[0082]

[0083] Wherein, Are all constants, and their values in the embodiments of the present invention are respectively: , , , , .

[0084] Wherein, the source term In the transport equation represents the turbulent mechanical generation term caused by the vertical gradient of the flow velocity, Represents the buoyancy generation or dissipation term, and:

[0085]

[0086]

[0087] Wherein, Represents the turbulent Prandtl constant.

[0088] 2.2 Vertical turbulent eddy viscosity coefficient Adopt the vertical Model for calculation, which can better include the effects of wind shear stress, bed shear stress, flow velocity gradient generation term, dissipation, diffusion and stratification, etc. The basic idea of the model is to relate the vertical turbulent eddy viscosity coefficient To the turbulent kinetic energy and the turbulent dissipation rate are related to obtain the first formula for calculating the vertical turbulent eddy viscosity coefficient using the turbulent kinetic energy and the turbulent dissipation rate: .

[0089] 2.3 Calculate the vertical turbulent eddy viscosity coefficient by combining the transport equation and the first formula.

[0090] Combined with the turbulent kinetic energy and the turbulent dissipation rate transport equations, and the first formula, the vertical turbulent eddy viscosity coefficient is calculated.

[0091] Among them, the free surface and bed boundary conditions of the equation are:

[0092]

[0093] The free surface and bed boundary conditions of the equation are:

[0094]

[0095] Among them, is the von Karman constant, is the friction velocity of the corresponding surface, , and τ is the wall shear stress.

[0096] 3. Calculate the vertically averaged lateral shear stress caused by turbulence through the Boussinesq eddy viscosity hypothesis, calculate the basic horizontal turbulent eddy viscosity coefficient using the friction velocity and water depth, and obtain the horizontal turbulent eddy viscosity coefficient based on the basic horizontal turbulent eddy viscosity coefficient, friction velocity and water depth, and U, V.

[0097] 3.1 Calculate the components of the riverbed shear stress in the x and y directions:

[0098] ,

[0099] In the formula, is the dimensionless bed friction coefficient, U represents the average velocity in the x direction, V represents the average velocity in the y direction, , and the existence of the parameter reflects that the existence of the riverbed slope is a factor that increases the riverbed shear stress.

[0100] Among them, the bed friction coefficient is given by the following formula:

[0101]

[0102] In the formula, is the Manning roughness coefficient, and is the Chezy coefficient.

[0103] It should be noted that the Manning coefficient and Chezy coefficient of the river channel and floodplain of natural rivers or artificial channels are usually obtained by referring to relevant literature or by back-calculating based on measured data.

[0104] In the embodiments of the present invention, and are both expressed as linear functions of water depth. The magnitudes of the flow resistance and roughness coefficient change with the change of water depth. During the modeling process, the roughness is calculated using wherein = 0.010 - 0.015, is related to the water depth. When the water depth is relatively shallow or close to the floodplain, a larger roughness value is taken.

[0105] 3.2 Obtain the horizontal turbulent eddy viscosity coefficient.

[0106] Calculate the vertically averaged lateral shear stress caused by turbulence according to the Boussinesq eddy viscosity hypothesis, and assume that the direction of the turbulent stress is perpendicular to the direction of the vertically averaged velocity gradient. The calculation formulas for each lateral shear stress are as follows:

[0107] , ,

[0108] wherein, is the horizontal turbulent eddy viscosity coefficient, and it is assumed to be constant along the water depth and isotropic.

[0109] Considering the similarity of mass exchange and momentum exchange of turbulence, that is , it can be expressed by the friction velocity and water depth in a natural open channel, that is .

[0110] As a parameter reflecting the magnitude of momentum exchange, the eddy viscosity coefficient is a very important parameter in numerical simulation. When actually simulating, it is also necessary to consider the influence of the change of the eddy viscosity coefficient on the changes of water level and flow velocity in the river channel.

[0111] Step S002: Obtain the mathematical relationship between the three-dimensional flow velocity and the perturbation flow velocity, and the perturbation momentum equation according to the three-dimensional Navier - Stokes equation and the shallow water equation; discretize the perturbation momentum equation using the finite volume method to obtain the corresponding discrete equation.

[0112] The specific steps include:

[0113] 1. The mathematical relationship between the three-dimensional flow velocity and the perturbation flow velocity is obtained by subtracting the shallow water equations from the three-dimensional Navier-Stokes equations.

[0114] The calculation formula for the three-dimensional flow velocity is obtained by subtracting the shallow water equations from the three-dimensional Navier-Stokes (N-S) equations: , , such a treatment removes the free surface gravity wave term in the original equations. Therefore, after solving the perturbation flow velocity and and then calculating the three-dimensional flow velocity and , compared with directly solving and , it can make the model obtain higher stability and ensure the calculation quality.

[0115] 2. The perturbation momentum equation is obtained based on the mathematical relationship between the three-dimensional flow velocity and the perturbation flow velocity. For the perturbation momentum equation, except for the time term, only the vertical diffusion term is regarded as implicit, and the remaining terms, namely the Coriolis force term, the convection term, the horizontal diffusion term, and the baroclinic term, are all regarded as explicit. That is to say, the perturbation momentum equation can be written in the following simplified form:

[0116]

[0117]

[0118] where represents the horizontal source term in the direction, represents the horizontal source term in the direction, including four parts: the Coriolis force term, the convection term, the horizontal diffusion term, and the baroclinic term, and is explicitly obtained by the iterative values of the current time step using the finite volume method.

[0119] 3. The perturbation momentum equation is discretized using the finite volume method to obtain the corresponding discrete equation.

[0120] The perturbation momentum equation is discretized using the finite volume method. Taking as an example, integrating it over a time step and a control volume gives:

[0121]

[0122]

[0123] Figure 3 is a schematic diagram of the vertical grid. Assuming that the value of the variable at the center point represents the value of the variable in the entire control volume The integral average value on it is considered, and the weighted average value of the implicit term at two moments of n and n + 1 represents its integral average value over the entire time step The integral average value on it, and the value of the explicit term at moment n represents its integral average value over the entire time step If the integral average value on it is considered, the above equation can be further written as:

[0124] (2-1)

[0125] Where represents the weight coefficient, and k represents the number of vertical layers

[0126] Using the central difference scheme for discretization, that is ,

[0127] Substituting into the above equation (2-1), the discrete equation of is obtained:

[0128]

[0129] This discrete equation holds for k = 2, 3,..., m - 1, where m is the total number of vertical layers

[0130] Written in the general form as:

[0131]

[0132] Where

[0133]

[0134] In the same way for the discrete equation of it is obtained by discretization:

[0135]

[0136] Where

[0137]

[0138] Step S003: Obtain the discrete general equation near the bed surface according to the boundary conditions that the perturbed momentum equation needs to satisfy near the bed surface; obtain the discrete general equation near the free water surface according to the boundary conditions that the perturbed momentum equation needs to satisfy near the free water surface

[0139] The specific steps include:

[0140] 1. Obtain the discrete general equation near the bed surface according to the boundary conditions that the perturbed momentum equation needs to satisfy near the bed surface

[0141] The bed surface boundary condition is k = 1. Similarly, taking as an example, the boundary conditions that the equation needs to satisfy near the bed surface are:

[0142]

[0143] Figure 4 is a schematic diagram of the boundary conditions near the bed surface. Substituting into Equation (2-1), we get:

[0144]

[0145] Writing it in the general form: .

[0146] Among them,

[0147]

[0148] Similarly, for , the discrete general equation near the bed surface is:

[0149]

[0150] Among them,

[0151]

[0152] 2. Obtain the discrete general equation near the free water surface according to the boundary conditions that the perturbation momentum equation needs to satisfy near the free water surface.

[0153] The free water surface boundary condition is k = m. Similarly, taking as an example, the boundary conditions that the equation needs to satisfy near the free water surface are:

[0154]

[0155] Figure 5 is a schematic diagram of the boundary conditions near the free water surface. Substituting into Equation (2-1), we get:

[0156]

[0157] Writing it in the general form: .

[0158] Among them,

[0159]

[0160] Similarly, for , the discrete general equation near the free water surface is:

[0161]

[0162] Among them,

[0163]

[0164] In step S004, by setting initial conditions, a tridiagonal system of equations is formed by the corresponding discrete equations, the discrete general equation under the bed boundary conditions, and the discrete general equation under the free water surface boundary conditions, and it is solved to obtain the perturbation velocity, and then the three-dimensional velocity distribution is obtained.

[0165] The specific steps include:

[0166] 1. Set initial conditions.

[0167] Measure the velocity values at 0.5 times the water depth upstream of the bridge pier, the velocity values at 0.5 times the water depth downstream of the bridge pier, and the velocity values at 0.5 times the water depth between the bridge piers using an acoustic Doppler current profiler (ADCP); observe the water level value H of the bridge section using a water gauge.

[0168] Model calculation needs to input corresponding data, that is, initial conditions, to calculate. Input the measured velocity values at 0.5 times the water depth and the water level value H as initial conditions into the model to make the model more accurate and the calculation speed faster.

[0169] Set the perturbation velocity of each layer to 0 at the initial moment during the calculation:

[0170]

[0171]

[0172] That is, assume that the initial three-dimensional velocity in the direction is uniformly distributed:

[0173]

[0174]

[0175] Input the measured water depth H and the velocity U, V values at 0.5 times the water depth upstream, downstream, and between the bridge piers into the model, calculate the velocity values at each water depth, and thus obtain the velocity distribution conditions upstream, downstream, and between the bridge piers.

[0176] It should be noted that since the calculation is a steady flow problem, therefore, the time parameter actually acts as an iterative relaxation coefficient.

[0177] 2. A tridiagonal system of equations is formed by the corresponding discrete equations, the discrete general equation under the bed boundary conditions, and the discrete general equation under the free water surface boundary conditions, and it is solved to obtain the perturbation velocity.

[0178] Taking as an example, the corresponding discrete equations , the discrete general equation under the bed boundary condition and the discrete general equation under the free water surface boundary condition constitute the following tridiagonal system of equations:

[0179]

[0180] Using the "chase method" to quickly solve the above system of equations to obtain the perturbation flow velocity in the x direction.

[0181] Similarly, for the corresponding discrete equations , the bed boundary condition and the free water surface boundary condition to solve the tridiagonal system of equations formed, to obtain the perturbation flow velocity in the y direction.

[0182] 3. Obtain the three-dimensional flow velocity based on the perturbation flow velocity, substitute the three-dimensional flow velocity into the transformed continuity equation in the three-dimensional water flow basic equation, and explicitly deduce from the bed surface to the free water surface until the iterative convergence condition is satisfied to obtain the vertical flow velocity.

[0183] According to in step S003, obtain the three-dimensional flow velocity and , substitute the three-dimensional flow velocity into the transformed continuity equation in the three-dimensional water flow basic equation, and explicitly deduce from the bed surface to the free water surface, that is: , where near the bed surface , , calculated by the central difference scheme.

[0184] The iterative convergence condition for the entire calculation is:

[0185]

[0186] Until the iterative convergence condition is satisfied to obtain the vertical flow velocity .

[0187] The obtained u, v, and w above are the flow velocity values of each point near the pier at different water depths. The flow velocities at different water depths are superimposed to obtain the flow velocity distribution of each point near the pier. Each point near the pier refers to the upstream of the pier, the downstream of the pier, and between the piers.

[0188] For example, divide the water depth vertically into 10 layers, calculate u, v, and w at each layer upstream of the pier, downstream of the pier, and between the piers, and then superimpose them correspondingly to obtain the velocity distributions upstream of the pier, downstream of the pier, and between the piers.

[0189] In summary, the embodiments of the present invention transform the three-dimensional water flow continuity equation and momentum equation into the three-dimensional water flow basic equation; calculate the vertical turbulent eddy viscosity coefficient by using the turbulent kinetic energy and turbulent dissipation rate, and calculate the horizontal turbulent eddy viscosity coefficient according to the Boussinesq eddy viscosity hypothesis; obtain the perturbed flow velocity by solving the perturbed momentum equation, and combine with the three-dimensional water flow basic equation to obtain the vertical flow velocity; discretize the perturbed momentum equation by using the finite volume method to obtain the corresponding discrete equation; obtain the discrete general equation near the bed surface according to the boundary conditions that the perturbed momentum equation needs to satisfy near the bed surface; obtain the discrete general equation near the free water surface according to the boundary conditions that the perturbed momentum equation needs to satisfy near the free water surface; by setting the initial conditions, a tridiagonal system of equations is formed by the corresponding discrete equation, the bed surface boundary condition, and the free water surface boundary condition, and it is solved to obtain the perturbed flow velocity, and then the three-dimensional flow velocity and the vertical flow velocity are obtained. The embodiments of the present invention can obtain the velocity distributions upstream of the pier, downstream of the pier, and between the piers according to the measured flow velocity at 0.5 times the water depth, reduce the calculation amount, and can be applied to large-scale measurements.

[0190] It should be noted that: the above sequence of the embodiments of the present invention is only for description and does not represent the advantages and disadvantages of the embodiments. And the above specific embodiments of this specification have been described. In addition, the processes depicted in the drawings do not necessarily require the specific order or continuous order shown to achieve the desired result. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0191] Each embodiment in this specification is described in a progressive manner. The same or similar parts between the embodiments can be referred to each other, and the key points of each embodiment are the differences from other embodiments.

[0192] The above-described embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A calculation method for three-dimensional flow velocity distribution near a pier, characterized in that, The method includes the following steps: Perform coordinate transformation on the three-dimensional water flow continuity equation and momentum equation; calculate the vertical turbulent eddy viscosity coefficient using the turbulent kinetic energy and turbulent dissipation rate, and calculate the horizontal turbulent eddy viscosity coefficient according to the Boussinesq eddy viscosity hypothesis; Obtain the mathematical relationship between the three-dimensional flow velocity and the perturbed flow velocity, and the perturbed momentum equation according to the three-dimensional Navier-Stokes equation and the shallow water equation; discretize the perturbed momentum equation using the finite volume method to obtain the corresponding discrete equation; Obtain the discrete general equation near the bed surface according to the boundary conditions that the perturbed momentum equation needs to satisfy near the bed surface; obtain the discrete general equation near the free water surface according to the boundary conditions that the perturbed momentum equation needs to satisfy near the free water surface; By setting the initial conditions, a tridiagonal system of equations is formed by the corresponding discrete equation, the discrete general equation under the bed surface boundary conditions, and the discrete general equation under the free water surface boundary conditions, and the tridiagonal system of equations is solved to obtain the perturbed flow velocity, and then the three-dimensional flow velocity distribution is obtained; The calculation method of the horizontal turbulent eddy viscosity coefficient is as follows: Calculate the vertically averaged lateral shear stress caused by turbulence through the Boussinesq eddy viscosity hypothesis, calculate the basic horizontal turbulent eddy viscosity coefficient using the friction velocity and water depth, and obtain the horizontal turbulent eddy viscosity coefficient according to the basic horizontal turbulent eddy viscosity coefficient, the friction velocity and water depth, and U, V, where U represents the average flow velocity in the x direction and V represents the average flow velocity in the y direction.

2. The calculation method of three-dimensional flow velocity distribution near a pier according to claim 1, wherein, The coordinate transformation of the three-dimensional water flow continuity equation and momentum equation includes: The three-dimensional flow continuity equation and momentum equation are made dimensionless, and then the processed equations are introduced with coordinates to obtain the basic three-dimensional flow equations after coordinate transformation.

3. The calculation method for three-dimensional flow velocity distribution near a pier according to claim 1, characterized in that, The calculation method of the vertical turbulent eddy viscosity coefficient is as follows: Obtain the transport equations of the turbulent kinetic energy and turbulent dissipation rate, and the first formula for calculating the vertical turbulent eddy viscosity coefficient using the turbulent kinetic energy and turbulent dissipation rate, and calculate the vertical turbulent eddy viscosity coefficient by combining the transport equations and the first formula.

4. The calculation method of three-dimensional flow velocity distribution near a bridge pier according to claim 1, characterized in that, The method for obtaining the three-dimensional flow velocity is as follows: Subtract the shallow water equation from the three-dimensional Navier-Stokes equation to obtain the mathematical relationship between the three-dimensional flow velocity and the perturbed flow velocity, and the perturbed momentum equation, discretize and solve the perturbed momentum equation to obtain the perturbed flow velocity, and obtain the three-dimensional flow velocity distribution using this mathematical relationship.

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