A rigid vegetation along - the - way resistance simulation system

Abstract

The present invention provides a rigid vegetation frictional resistance simulation system, which includes a river simulation device, a vegetation simulation device, an observation unit, and a calculation unit; the river simulation device is used to simulate the flow of river water; the vegetation simulation device is used to simulate the rigid vegetation in the river; the observation unit is used to observe the along-channel change of the water surface line in the river simulation device; the calculation unit is used to calculate the resistance coefficient C in the river simulation device d， and verify the reliability of the result after the calculation is completed; the present invention selects rigid vegetation as the research object, simplifies it into a cylinder for simulation research, and based on the assumption of local uniform flow and the Saint-Venant equation, studies the frictional resistance characteristics of rigid vegetation under the condition of steady non-uniform flow, further explores the variation law of vegetation resistance, and provides a reference for the subsequent research on the resistance characteristics of vegetated ecological channels.

Description

Technical Field

[0001] The present invention relates to the technical field of environmental hydraulics, and more specifically, to a simulation system for the frictional resistance of rigid vegetation along the way. Background Art

[0002] Aquatic vegetation plays an important role in river ecosystems. However, since vegetation generates additional resistance to water flow, it greatly affects the hydrodynamic processes of rivers. Therefore, it is of great significance to determine the complex interaction between water flow and vegetation. The drag coefficient C d is also often used as an important parameter to represent the resistance effect of aquatic vegetation on water flow.

[0003] Research shows that the drag coefficient C d is greatly related to vegetation properties, density, and laying methods. In addition, compared with flexible vegetation, rigid vegetation has a higher vegetation drag coefficient. In the study of vegetation-water flow resistance, most experiments are carried out under uniform flow conditions. In fact, in nature, when water flow moves in the area of vegetation patches, it often shows non-uniformity, and the resistance characteristics of vegetation often become more complex. Using the existing formula for the drag coefficient C d to describe the resistance characteristics under non-uniform flow is not very ideal.

[0004] Therefore, the problems existing in the prior art need to be further improved and developed. Summary of the Invention

[0005] (1) Object of the Invention: To solve the problems existing in the above prior art, the object of the present invention is to provide a simulation system for the frictional resistance of rigid vegetation along the way.

[0006] (2) Technical Solution: To solve the above technical problems, the present technical solution provides a simulation system for the frictional resistance of rigid vegetation along the way, including a river simulation device, a vegetation simulation device, an observation unit, and a calculation unit;

[0007] The river simulation device includes a water tank, a reservoir, and a water pump. The water pump transports water from the reservoir to one end of the water tank and then flows into the reservoir from the other end of the water tank. The river simulation device is used to simulate the flow of river water;

[0008] The vegetation simulation device is arranged in the water tank and includes a density board and simulation plants arranged on the density board, which are used to simulate rigid vegetation in the river. The position of the vegetation simulation device in the water tank is the vegetation area;

[0009] The observation unit includes a measurement module arranged on the side of the water tank and a photographing module for taking pictures of the side of the water tank, which are used to obtain the image of the along-way change of the water surface line in the vegetation area of the river simulation device;

[0010] The calculation unit is connected to the observation unit, and is configured to receive the image of the longitudinal change of the water surface line in the vegetation area obtained by the observation unit, and calculate the drag coefficient C of the vegetation area in the river simulation device d , and verify the reliability of the result after the calculation is completed.

[0011] A rigid vegetation longitudinal resistance simulation system, wherein the river simulation device includes a water tank and a reservoir. A flow stabilizer is provided on the upstream side of the water tank, and a tailgate is provided on the downstream side of the water tank. A flow meter and a water pump are provided in the river simulation device. The flow meter is configured to record the flow rate of the water flowing into the water tank, and the water pump is configured to transport water from the reservoir to the water tank.

[0012] A rigid vegetation longitudinal resistance simulation system, wherein the length of the water tank is 10 m and the width is 0.5 m.

[0013] A rigid vegetation longitudinal resistance simulation system, wherein the vegetation simulation device is arranged inside the water tank and includes a density board and a plurality of simulation plants uniformly fixed on the density board. The simulation plants form a simulation vegetation. The density of the simulation plants distributed on the density board is the vegetation density. The length of the density board is 1 m, the width is 0.5 m, and the thickness is 1 cm. The simulation plant is a cylindrical aluminum rod with a length L = 40 cm and a diameter D = 0.007 m.

[0014] A rigid vegetation longitudinal resistance simulation system, wherein the spacing between the holes on the density board includes three modes. Mode A: The distance between the center points of adjacent holes on the density board is 1 cm. Mode B: The distance between the center points of adjacent holes on the density board is 1.2 cm. Mode C: The distance between the center points of adjacent holes on the density board is 1.6 cm.

[0015] A rigid vegetation longitudinal resistance simulation system, wherein the calculation process of the calculation unit includes the following steps:

[0016] Step 1: Rearrange the one-dimensional Saint-Venant equation to obtain the expression of the drag coefficient C under steady non-uniform flow d of:

[0017]

[0018] wherein, x is the water flow direction, H is the water depth, U is the flow velocity, g is the acceleration due to gravity, m is the density of the vegetation, D is the diameter of a single plant in the vegetation, is the vegetation density;

[0019] Step 2: After fitting the longitudinal coordinates of the water surface line, the curve function describing the water depth H is defined as

[0020] H = Aln|x - B| + C,

[0021] where A, B, and C are all constants, and their values are obtained by fitting the longitudinal coordinates of the water surface line;

[0022] Step 3: Through a rigid vegetation longitudinal resistance simulation system, adjust the vegetation density and the flow rate of the water flow, conduct a longitudinal resistance simulation experiment, and at the same time, the observation unit takes pictures of the changes in the water surface line along the way under each working condition, and calculates the values of A, B, and C;

[0023] Step 4: Solve the resistance coefficient C under each working condition d , use the Reynolds number Re for the abscissa x d , and use the resistance coefficient C for the ordinate y d to draw a graph;

[0024] Step 5: Introduce the vegetation density to process the data, and conduct a coordinate transformation of the C d versus Re d function relationship image to obtain the calculation formula of C d with respect to the vegetation density .

[0025] A rigid vegetation longitudinal resistance simulation system, where the vegetation density is divided into 5 types according to different layout methods, namely density density density density density ; the density is 0.267, the density is 0.150, the density is 0.096, the density is 0.038, and the density is 0.017;

[0026] The flow rate of the water flow is 3 groups of average flow rate values, and the flow rate value Q 1 is 32.85 m 3 / h, the flow rate value Q 2 is 48.20 m 3 / h, and the flow rate value Q 3 is 72.31 m 3 / h;

[0027] By varying the density and the flow rate value Q 1 -Q3 Combine them to obtain 12 different working conditions.

[0028] A rigid vegetation frictional resistance simulation system, wherein the specific steps of step five include:

[0029] Step 51: Extract the maximum value C of the resistance coefficient C under each working condition d of, and then perform curve fitting on C and the vegetation density under different vegetation density working conditions at the same flow rate value d-max to obtain the function expression of the resistance coefficient C d-max with respect to the vegetation density for changing the expression of the y-axis; d with respect to the vegetation density to obtain the function expression of the Reynolds number Re

[0030] Step 52: Take the Reynolds number Re corresponding to the maximum value of the resistance coefficient C under different vegetation densities at the same flow rate d and perform curve fitting on the Reynolds number Re corresponding to the maximum value of the resistance coefficient C d-Cd-max and the vegetation density d to obtain the function expression of the Reynolds number Re d-Cd-max with respect to the vegetation density for changing the expression of the x-axis; d with respect to the vegetation density Step 53: According to the function expression of C

[0031] with respect to the vegetation density d and the function expression of Re with respect to the vegetation density d move the terms containing the density to the left side of the equation and the constant terms to the right side of the equation. Then select the left side of the equation as the new Y-axis and X-axis, redraw the images of the data X and Y, and finally perform curve fitting on the new X-axis and Y-axis to establish the function expression between Y and X under different flow rate values; Step 54: Establish the expressions of the resistance coefficient C

[0032] under different vegetation densities 1 when the flow rate value Q 3 = 32.85 m 2 / h, when the flow rate value Q 3 = 48.20 m 3 / h, and when the flow rate value Q 3 = 72.31 m / h respectively. d A rigid vegetation frictional resistance simulation system, wherein the flow rate value Q

[0033] = 32.85 m 1 / h3 At a flow rate of the drag coefficient C d under different vegetation densities is expressed as follows:

[0034]

[0035] Flow rate value Q 2 = 48.20 m 3 / h, the drag coefficient C under different vegetation densities is expressed as follows: d

[0036]

[0037] Flow rate value Q 3 = 72.31 m 3 / h, the drag coefficient C under different vegetation densities is expressed as follows: d

[0038]

[0039] A simulation system for the friction resistance of rigid vegetation along the flow path. Among them, after the calculation unit completes the calculation, the reliability of the result is verified. The specific process is as follows:

[0040] The vegetation area under each working condition is divided into 500 grid points along the water flow direction. Then, the length of the calculation grid unit along the water flow x direction is defined as Δx = L / 500. Taking the water depth H 0 at the initial end of the vegetation area as the initial boundary condition, the flow velocity U at x = 0 is calculated through the flow rate Q 0 , and the initial data is substituted into the formula to solve for the water depth H 0+Δx and the flow velocity U 0+Δx at x = Δx. Then, the calculation is continuously carried out downstream in turn. The value of H 0+Δx solved at x = Δx of the previous grid is used as the upper boundary condition of the next grid to solve for the water depth and flow velocity at x = 2Δx, and so on. According to this calculation method, the water depth H along the entire vegetation area is calculated; taking the normalized x + = x / L as the abscissa and the normalized H + = H / H 0 as the ordinate, a graph is drawn; the deviation between the experimental value of the water depth and the calculated value H + (x) is compared. The smaller the deviation, the higher the reliability.

[0041] ​​(3) Beneficial effects: The rigid vegetation friction resistance simulation system provided by the present invention selects rigid vegetation as the research object, simplifies it into a cylinder for simulation research, and studies the friction resistance characteristics of rigid vegetation under the conditions of steady non-uniform flow based on the assumption of local uniform flow and the Saint-Venant equation, further exploring the variation law of vegetation resistance, providing a reference for the subsequent research on the resistance characteristics of vegetated ecological channels. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 is a schematic structural diagram of a rigid vegetation friction resistance simulation system of the present invention;

[0043] Figure 2 is a flowchart of the calculation method of the calculation unit of a rigid vegetation friction resistance simulation system of the present invention;

[0044] Figure 3 is the variation diagram of C with Re at each density when the water flow rate is 32.85 m 3 / h in the preferred embodiment of a rigid vegetation friction resistance simulation system of the present invention; under each density d with Re d ;

[0045] Figure 4 is the variation diagram of C with Re at each density when the water flow rate is 48.20 m 3 / h in the preferred embodiment of a rigid vegetation friction resistance simulation system of the present invention; under each density d with Re d ;

[0046] Figure 5 is the variation diagram of C with Re at each density when the water flow rate is 72.31 m 3 / h in the preferred embodiment of a rigid vegetation friction resistance simulation system of the present invention; under each density d with Re d ;

[0047] Figure 6(a) is the variation diagram of C with density when the water flow rate is 32.85 m 3 / h in the preferred embodiment of a rigid vegetation friction resistance simulation system of the present invention; d with density ;

[0048] Figure 6(b) is the variation diagram of Re with density when the water flow rate is 32.85 m 3 / h in the preferred embodiment of a rigid vegetation friction resistance simulation system of the present invention; d with density ;

[0049] Figure 6(c) is a graph of the variation of Y with X in the new coordinate axes XY when the water flow rate is 32.85 m 3 / h in a preferred embodiment of a rigid vegetation friction loss simulation system according to the present invention;

[0050] Figure 7(a) is a graph of the variation of C 3 with the density d when the water flow rate is 48.20 m / h in a preferred embodiment of a rigid vegetation friction loss simulation system according to the present invention;

[0051] Figure 7(b) is a graph of the variation of Re 3 with the density d when the water flow rate is 48.20 m / h in a preferred embodiment of a rigid vegetation friction loss simulation system according to the present invention;

[0052] Figure 7(c) is a graph of the variation of Y with X in the new coordinate axes XY when the water flow rate is 48.20 m 3 / h in a preferred embodiment of a rigid vegetation friction loss simulation system according to the present invention;

[0053] Figure 8(a) is a graph of the variation of C 3 with the density d when the water flow rate is 72.31 m / h in a preferred embodiment of a rigid vegetation friction loss simulation system according to the present invention;

[0054] Figure 8(b) is a graph of the variation of Re 3 with the density d when the water flow rate is 72.31 m / h in a preferred embodiment of a rigid vegetation friction loss simulation system according to the present invention;

[0055] Figure 8(c) is a graph of the variation of Y with X in the new coordinate axes XY when the water flow rate is 72.31 m 3 / h in a preferred embodiment of a rigid vegetation friction loss simulation system according to the present invention;

[0056] Figure 9 is a comparison graph of the calculated values and experimental values of the water depth H 3 (x) at each vegetation density calculated using formula (10) when the water flow rate is 32.85 m / h in a preferred embodiment of a rigid vegetation friction loss simulation system according to the present invention; + (x);

[0057] Figure 10 is a graph of the comparison between the calculated values and experimental values of the water depth H 3 (x) at each vegetation density calculated using formula (10) when the water flow rate is 48.20 m Water depth H + (x) Comparison chart of calculated values and test values;

[0058] Figure 11 is the water depth H calculated by formula (10) when the water flow rate is 72.31 m 3 / h for each vegetation density in the preferred embodiment of a rigid vegetation friction loss simulation system of the present invention Water depth H + (x) Comparison chart of calculated values and test values. Detailed implementation manners

[0059] The present invention will be further described in detail below in conjunction with preferred embodiments. More details are set forth in the following description to facilitate a full understanding of the present invention. However, the present invention is clearly capable of being implemented in many other ways different from this description. Those skilled in the art can make similar generalizations and deductions according to the actual application situation without departing from the connotation of the present invention. Therefore, the protection scope of the present invention should not be limited by the content of this specific embodiment.

[0060] The accompanying drawings are schematic diagrams of embodiments of the present invention. It should be noted that this accompanying drawing is only an example and is not drawn according to the condition of equal proportion, and should not be used to limit the actual claimed protection scope of the present invention.

[0061] The present invention provides a rigid vegetation friction loss simulation system, including a river simulation device, a vegetation simulation device, an observation unit and a calculation unit. The river simulation device includes a water tank, a reservoir and a water pump. The water pump conveys water from the reservoir to one end of the water tank and then flows into the reservoir from the other end of the water tank. The river simulation device is used to simulate the flow of river water;

[0062] The vegetation simulation device is arranged in the water tank and includes a density board and simulation plants arranged on the density board, and is used to simulate rigid vegetation in the river. The position of the vegetation simulation device in the water tank is the vegetation area;

[0063] The observation unit includes a measurement module arranged on the side of the water tank and a photographing module for photographing the side of the water tank, and is used to obtain the image of the along - change of the water surface line in the vegetation area of the river simulation device;

[0064] The calculation unit is connected to the observation unit, and is used to receive the image of the along - change of the water surface line in the vegetation area obtained by the observation unit, and calculate the resistance coefficient C of the vegetation area in the river simulation device d , and verify the reliability of the result after the calculation is completed.

[0065] A preferred embodiment of the present invention, as Figure 1As shown, the river simulation device includes a water tank 1, and a first reservoir 2 and a second reservoir 3 arranged on both sides of the water tank 1.

[0066] The water tank 1 is used to simulate a river channel, and the first reservoir 2 and the second reservoir 3 are filled with water for simulating a river; on one side of the water tank 1 close to the first reservoir 2, that is, the upstream side, a flow stabilizer 6 is provided for smoothing the water flow; on the other side of the water tank 1 close to the second reservoir 3, that is, the downstream side, a tailgate 7 is provided, and the tailgate 7 is used to release the water in the water tank 1 into the second reservoir 3, and the water flows from one side of the water tank close to the first reservoir 2 to the other side close to the second reservoir 3, so as to simulate the flow of river water.

[0067] Preferably in the present invention, a flow meter 5 can be arranged in the first reservoir 2 for recording the flow rate of the water flowing into the water tank. Preferably, the flow meter 5 can be arranged in the water tank 1.

[0068] Preferably in the present invention, the first reservoir 2 and the second reservoir 3 are interconnected by a pipeline, and a water pump 4 is arranged on the pipeline, and the water pump 4 is used to transport water from the first reservoir 2 into the water tank 1; more preferably, the first reservoir 2 and the second reservoir 3 can be arranged as a large reservoir, and only need to ensure that both ends of the water tank 1 are within the range of the large reservoir, and the large reservoir provides water flow to the water tank 1 through a water pump. Preferably, the length of the water tank 1 is 10 m and the width is 0.5 m.

[0069] Preferably in the present invention, the vegetation simulation device is arranged inside the water tank 1, and includes a density board 8 and a number of simulation plants 9 uniformly fixed on the density board, and the simulation plants 9 form a simulation vegetation. Preferably, the simulation plant is a cylindrical aluminum rod with a length L = 40 cm and a diameter D = 0.007 m.

[0070] Preferably in the present invention, a number of holes are uniformly distributed on the density board 8, the bottom ends of the simulation plants 9 are inserted into the holes of the density board, and the density of the simulation plants 9 distributed on the density board is the vegetation density, and the vegetation density can be adjusted.

[0071] More preferably, the density board 8 has a length of 1 m, a width of 0.5 m, and a thickness of 1 cm. The diameter of the holes on the density board is the same as the diameter of the simulated plants 9. The holes on the density board 8 are evenly distributed horizontally and vertically, and the spacing between the horizontally distributed holes is the same as the spacing between the vertically distributed holes. The spacing of the holes on the density board 8 includes three modes. Mode A: The distance between the center points of adjacent holes on the density board 8 is 1 cm. Mode B: The distance between the center points of adjacent holes on the density board 8 is 1.2 cm. Mode C: The distance between the center points of adjacent holes on the density board 8 is 1.6 cm.

[0072] Preferably, the observation unit includes a photographing module and a measuring module. The side of the water tank 1 is transparently arranged. The measuring module can be arranged on the side of the water tank 1. The photographing module takes photos of the change of the water surface line slope along the way under different working conditions through the side of the water tank 1. The different working conditions are specifically different flow rates of the water flow and different densities of the simulated plants.

[0073] Preferably, the measuring module can be a measuring scale or scale lines arranged on the transparent side of the water tank. The photographing module can be an electronic device with a photographing function such as a camera, a mobile phone, a video camera, etc.

[0074] Preferably, the calculation unit is used to calculate the resistance coefficient C in the simulation system of the rigid vegetation resistance along the way d , and the calculation process of the calculation unit is as Figure 2 shown, including the following steps:

[0075] Step 1: Rearrange the one-dimensional Saint-Venant equation to obtain the expression of the resistance coefficient C under steady non-uniform flow d :

[0076]

[0077] Step 2: After fitting the water surface line along the way coordinates, the curve function describing the water depth H is defined as

[0078] H = Aln|x - B| + C;

[0079] Step 3: Through a simulation system of the rigid vegetation resistance along the way, adjust the vegetation density and the flow rate of the water flow, conduct a resistance simulation experiment along the way. At the same time, the observation unit takes pictures of the change of the water surface line along the way under each working condition, and calculates the values of A, B, and C;

[0080] Step 4: Solve the resistance coefficient C under each working condition d , use the Reynolds number Re for the abscissa x d , and use the resistance coefficient C for the ordinate yd Draw a diagram;

[0081] Step Five: Introduce the vegetation density parameter Process the data and perform C d with Re d Axis transformation of the function relationship image to obtain C of water flow at different flow values d Regarding the vegetation density parameter Calculation formula of

[0082] Preferably in the present invention, the specific content of the said Step One is:

[0083] In a flume with width B and water depth H, when the flow rate of the water flow is Q, the one-dimensional Saint-Venant equation (SVE) of the open channel is:

[0084]

[0085] where x is the water flow direction, with the unit of m; U is the flow velocity, with the unit of m / s, S f is the energy slope, and the energy slope is the slope that the water flow needs to overcome when overcoming the frictional resistance along the way; S 0 is the bottom slope, and the bottom slope is the slope of the bottom of the water channel along the water flow direction.

[0086] Existing research shows that for non-uniform flow with natural vegetation patches, that is, in non-uniform gradually varied flow, when the water surface slope change is not significant, although the overall water flow is non-uniform, locally it can be treated as uniform flow at this time. Take a local water flow segment with a micro-element length of dx along the water flow direction, and thus obtain the local balance of forces between the driving term and the resistance term as:

[0087]

[0088] where: the left side of the equation is the driving term, generated by the gravity of the water flow itself; the right side of the equation is the resistance term: BdxF d is the vegetation resistance term; is the frictional resistance term at the bottom of the flume; Hdxτ wall is the frictional resistance term at the side wall of the flume; is the density of the simulated plant vegetation, that is, the percentage of the simulated vegetation area on the flume in the total area of the riverbed, F d , τ ground and τ wall are the vegetation resistance per unit flume area, the frictional force per unit flume bottom area, and the frictional force per unit flume side wall area respectively.

[0089] For the convenience of calculation, the frictional resistance at the bottom of the flume and the frictional resistance at the side wall of the flume in the resistance term in Equation (2) are ignored.

[0090]

[0091] For the vegetation resistance F per unit flume area d calculation, the classical rigid vegetation resistance formula (Equation 4) is used for calculation and solution. In the formula, F d is the resistance, N; ρ is the density, kg / m 3 ; A c is the characteristic area, m 2 ; C d is the resistance coefficient; u is the flow velocity, m / s; A c = mDH, m is the density of the vegetation, that is, the number of vegetation plants per unit area, with the unit of percentage, the density of the vegetation The relationship with the density m of the vegetation is D is the diameter of a single plant in the vegetation.

[0092]

[0093] By solving Equations (4) and (3) simultaneously, the simplified expression of S f is obtained:

[0094]

[0095] When the flume flow rate is constant, Equation (1) can be simplified to the following form:

[0096]

[0097] By transforming Formula (6), it can be obtained:

[0098]

[0099] Convert the differential term in Equation (7) to a difference term:

[0100]

[0101] By organizing Formula (8), the formula containing the water depth H can be obtained:

[0102]

[0103] Among them, the point where x = 0 is used as the starting point of the water flow in the vegetation area. U 0 and H 0 are the flow velocity (m / s) and water depth (m) at x = 0; U Δx and H Δx are the flow velocity (m / s) and water depth (m) at x = Δx; and is the energy slope calculated by using formula (5) when x = 0 and x = Δx; Δx is the calculation grid size of the vegetation area, and the selected value of Δx should be as small as possible.

[0104] Simplifying and arranging expression (6), the resistance coefficient C under constant non-uniform flow can be obtained. d Expression:

[0105]

[0106] Preferably, in the present invention, step two is specifically:

[0107] The photographing module of the observation unit photographs the longitudinal water surface line under different working conditions, extracts the coordinates of the longitudinal water surface line through the measurement unit, and then performs curve fitting on the longitudinal water surface line.

[0108] A continuous and smooth curve function is used to fit and represent the longitudinal water depth of the vegetation area, that is, the change of the water surface line slope. Observing the situation of the water surface line slope during the whole test process, this fitting curve needs to meet the following two conditions:

[0109] 1. It shows that the water depth in the vegetation area decreases along the water flow direction.

[0110] 2. The change trend of the water surface line along the course is similar to the M2 type.

[0111] Therefore, the fitting curve function that satisfies the conditions and describes the water depth H is defined as:

[0112] H = Aln|x - B| + C; (12)

[0113] Among them, A, B, and C are all constants, and their values can be obtained through fitting the longitudinal coordinates of the water surface line.

[0114] In a preferred embodiment of the present invention, in step three, the simulation plants form a vegetation area, and the density of the simulation plants is the vegetation density Vegetation density According to different layout methods, it can be divided into density Density Density Density Density There are 5 types, and the density is 0.267, the density is 0.150, the density is 0.096, the density is 0.038, the density is 0.017. Density The density board in B mode, with all the holes on the density board in B mode inserted with the simulation plants; density The density board in C mode, with all the holes on the density board in C mode inserted with the simulation plants; density The density board in A mode, where the holes on the density board in A mode inserted with simulation plants are spaced one hole without inserted simulation plants horizontally and vertically from another adjacent hole inserted with simulation plants; density The density board in C mode, where the holes on the density board in C mode inserted with simulation plants are spaced one hole without inserted simulation plants horizontally and vertically from another adjacent hole inserted with simulation plants; density The density board in B mode, where the holes on the density board in B mode inserted with simulation plants are spaced three holes without inserted simulation plants horizontally and vertically from another adjacent hole inserted with simulation plants.

[0115] Its corresponding parameters are shown in Table 1:

[0116] Table 1 Vegetation density board parameters

[0117]

[0118] Among them, is the vegetation density on the density board; is the density of the remaining holes on the board after inserting the simulation plants; is the vegetation density when the density board is fully inserted with simulation plants.

[0119] Preferably, the flow rate of the water can be 3 sets of average flow rate values, and the flow rate value Q 1 is 32.85 m 3 / h, the flow rate value Q 2 is 48.20 m 3 / h, and the flow rate value Q 3 is 72.31 m 3 / h.

[0120] Due to the vegetation density the simulation plants are the sparest, the water flow between the plants is relatively stable, but it suddenly increases after being blocked by the plants, the water surface fluctuates too much, and the curve fitting error is too large. Therefore, this density is discarded when solving the curve fitting equation.

[0121] By combining the density the flow rate value Q 1 -Q 3 12 different working conditions can be obtained. The parameters of the working conditions are shown in Table 2 below, where L is the length of the vegetation area, H 0The water depth at the starting point of the vegetation simulation device. Among them, the first working condition represents that the flow rate value of the water flow is Q 1 = 32.85 m 3 / h, and the density of the simulated plants is The second working condition represents that the flow rate value of the water flow is Q 1 = 32.85 m 3 / h, and the density of the simulated plants is The third working condition represents that the flow rate value of the water flow is Q 1 = 32.85 m 3 / h, and the density of the simulated plants is The fourth working condition represents that the flow rate value of the water flow is Q 1 = 32.85 m 3 / h, and the density of the simulated plants is density The fifth working condition represents that the flow rate value of the water flow is Q 2 = 48.20 m 3 / h, and the density of the simulated plants is The sixth working condition represents that the flow rate value of the water flow is Q 2 = 48.20 m 3 / h, and the density of the simulated plants is The seventh working condition represents that the flow rate value of the water flow is Q 2 = 48.20 m 3 / h, and the density of the simulated plants is The eighth working condition represents that the flow rate value of the water flow is Q 2 = 48.20 m 3 / h, and the density of the simulated plants is The ninth working condition represents that the flow rate value of the water flow is Q 3 = 72.31 m 3 / h, and the density of the simulated plants is The tenth working condition represents that the flow rate value of the water flow is Q 3 = 72.31 m 3 / h, and the density of the simulated plants is The eleventh working condition represents that the flow rate value of the water flow is Q 3 = 72.31 m 3 / h, and the density of the simulated plants is The twelfth working condition represents that the flow rate value of the water flow is Q 3 = 72.31 m 3 / h, and the density of the simulated plants is

[0122] The parameters of each working condition are shown in Table 2:

[0123] Table 2 Parameters of each working condition

[0124]

[0125] In the preferred embodiment of the present invention, step four is specifically as follows:

[0126] Solve the drag coefficient C under each working condition through formula (11) d , use the Reynolds number Re for the abscissa x d , and use the drag coefficient C for the ordinate y d to draw a graph, and the results are as shown in Figure 3 、 Figure 4 and Figure 5 .

[0127] Figure 3 、 Figure 4 and Figure 5 respectively show the variation diagram of C d with the Reynolds number Re d under different vegetation densities at the same flow rate, as well as the drag coefficient formula C d-iso under different flow rates:

[0128]

[0129] . Among them,

[0130] C d is the variation diagram with the Reynolds number Re d . It can be seen from the figure that during the entire test process, the range of Re d is 1000 - 4500, and the variation of C d with the Reynolds number is generally similar to a "hump-shaped" variation. The general variation process is as follows: at the initial position on the left side of the image, that is, at the front end of the vegetation area, the drag coefficient C d of the vegetation continuously increases with the increase of the Reynolds number Re d . When the Reynolds number Re d reaches a certain value, the drag coefficient C d reaches the maximum. After that, with the continuous increase of the Reynolds number Re d , the drag coefficient C d instead begins to decrease until the end of the vegetation area.

[0131] In the preferred embodiment of the present invention, step five specifically includes:

[0132] Step 51: Extract the maximum value C d of the drag coefficient C d-max under each working condition. Subsequently, for C d-max under different vegetation densities at the same flow rate value and the vegetation density Perform curve fitting to obtain the drag coefficient C d Regarding the vegetation density The function expression is used to change the expression of the y-axis.

[0133] Specifically, as Figure 6a shown, when the flow rate Q 1 = 32.85 m 3 / h, the function expression of the drag coefficient C d regarding the vegetation density is:

[0134]

[0135] where R 2 is the correlation coefficient, indicating the degree of agreement between the measured data and the calculated data;

[0136] Such as Figure 7a shown, when the flow rate Q 2 = 48.20 m 3 / h, the function expression of the drag coefficient C d regarding the vegetation density is:

[0137]

[0138] Such as Figure 8a shown, when the flow rate Q 3 = 72.31 m 3 / h, the function expression of the drag coefficient C d regarding the vegetation density is:

[0139]

[0140] Step 52: Take the Reynolds number Re d corresponding to the maximum value of the drag coefficient C d-Cd-max at different vegetation densities under the same flow rate, and perform curve fitting on the Reynolds number Re d corresponding to the maximum value of the drag coefficient C d-Cd-max and the vegetation density At this time, the function expression of the Reynolds number Re d regarding the vegetation density can be obtained, which is used to change the expression of the x-axis.

[0141] Specifically, as Figure 6b shown, when the flow rate Q 2 = 48.20 m 3 / h, the Reynolds number Re d regarding the vegetation density The functional expression is:

[0142]

[0143] As Figure 7b shown, when the flow rate value Q 2 = 48.20 m 3 / h, the Reynolds number Re d The functional expression regarding the vegetation density is:

[0144]

[0145] As Figure 8b shown, when the flow rate value Q 3 = 72.31 m 3 / h, the Reynolds number Re d The functional expression regarding the vegetation density is:

[0146]

[0147] Step 53: According to the obtained functional expression of C d regarding the vegetation density and the functional expression of Re d regarding the vegetation density , by transposing the terms containing the density to the left side of the equation and the constant terms to the right side, then select the left side of the equation as the new Y-axis and X-axis, and redraw the graph of data X and Y. The results are as Figure 6c , Figure 7c and Figure 8c shown. Finally, perform curve fitting on the new X-axis and Y-axis to establish the functional expression between Y and X under different flow rate values, where:

[0148] As Figure 6c shown, when the flow rate value Q 1 = 32.85 m 3 / h,

[0149]

[0150] As Figure 7c shown, when the flow rate value Q 2 = 48.20 m 3 / h,

[0151]

[0152] As Figure 8c shown, when the flow rate value Q 3 = 72.31 m 3 / h,

[0153]

[0154] Step 54: Respectively establish the expressions of the drag coefficient C under different vegetation densities when the flow rate Q 1 = 32.85 m 3 / h, when the flow rate Q 2 = 48.20 m 3 / h, and when the flow rate Q 3 = 72.31 m 3 / h. The drag coefficient C d is as follows.

[0155] When the flow rate Q 1 = 32.85 m 3 / h, the expression of the drag coefficient C under different vegetation densities is: d

[0156]

[0157] When the flow rate Q 2 = 48.20 m 3 / h, the expression of the drag coefficient C under different vegetation densities is: d

[0158]

[0159] When the flow rate Q 3 = 72.31 m 3 / h, the expression of the drag coefficient C under different vegetation densities is: d

[0160]

[0161] Preferably, after the calculation is completed, the calculation unit of a rigid vegetation friction resistance simulation system of the present invention can also verify the calculation result.

[0162] In the commonly used drag coefficient formulas C d-iso and C d-array :

[0163]

[0164] Among them, Re v = UR v / v is the Reynolds number of the vegetation cluster, ​​​is defined as the hydraulic radius of the vegetation cluster. Both formulas are commonly used in uniform flow. By comparing the measured water depth data with the calculated results, the accuracy of the drag coefficient C under non-uniform flow conditions is verified. d of the present invention.

[0165] In a preferred embodiment of the present invention, the calculation unit verifies C d with respect to the vegetation density The specific process of the reliability of the calculation formula is as follows:

[0166] Taking different water flow rates and different vegetation densities as different working conditions, the vegetation area under each working condition is divided into 500 grid points along the water flow direction. The length of the calculation grid unit along the water flow x direction is defined as Δx = L / 500. Taking the water depth H 0 at the initial end of the vegetation area as the initial boundary condition, the flow velocity U at x = 0 is calculated through the flow rate Q 0 , and the initial data is substituted into formula (10) for solution to obtain the water depth H 0+Δx and the flow velocity U 0+Δx at x = Δx. Then, the calculation is continuously carried out downstream in sequence. The value of H 0+Δx solved at x = Δx of the previous grid is used as the upper boundary condition of the next grid to solve the water depth and flow velocity at x = 2Δx, and so on. According to this calculation method, the water depth H along the entire vegetation area can be calculated. In addition, in order to reduce the error caused by the number of grids to the calculation results, the number of grids is adjusted multiple times for calculation. For example, the number of grids is about 1000 or even 2000. The deviation of the calculated values of the water depth H under different numbers of grids is less than 0.1%, indicating that the selected number of grids is large enough and the calculation results are accurate enough.

[0167] The verification results are as shown in Figure 9 , Figure 10 and Figure 11 . The abscissa in the figure is the normalized x + = x / L, and the ordinate is the normalized H + = H / H 0 . The black dots in the figure represent the experimental values of the water depth, and the green line is the calculated value of the water depth H d-iso (x) along the path obtained by using the single C + formula (24), and the red line is the calculated value of the water depth H d-array (x) along the path obtained by using the vegetation cluster C + formula (25), Figure 9 the black line in d is the calculated value of the water depth H + (x) along the path calculated by formula (21), Figure 10 the black line in d is the calculated value of the water depth H +(x) Calculated value, Figure 11 The black line in it is C d The along - channel water depth H calculated by formula (23) + (x) Calculated value.

[0168] From Figure 9 It can be seen that when calculating with the existing two common formulas, the calculation results deviate significantly from the experimental along - channel water depth H + (x), indicating that the resistance coefficient C d formula does not conform to the resistance characteristics of vegetation under non - uniform flow. This can also be seen from the previous C d versus Re d image. Additionally, it can be seen from Figure 9 that when the flow rate Q is 32.85 m 3 / h, the curve of the along - channel water depth H d-iso obtained by using the C + (x) formula is always above the black dots, and its calculated value of the along - channel water depth H + (x) is always larger than the experimental value. Similar patterns exist in other working conditions, which also indicates that the influence of the interaction between vegetation cannot be ignored.

[0169] Overall, at various vegetation densities, the calculation results obtained using a single - root C d-iso have a large deviation from the experimental data, and the curve is always above the black dots. The calculation result curve obtained using the vegetation - cluster C d-array formula changes continuously, and the deviation from the experimental depth data varies. In contrast, for the resistance coefficient C d calculation formula proposed by the present invention, although the calculation results deviate slightly from the experimental depth data, the accuracy of this formula has been greatly improved compared with the existing vegetation - cluster C d-array formula and the single - root C d-iso formula, and it has a certain degree of accuracy for various vegetation densities under the same flow rate.

[0170] A rigid - vegetation along - channel resistance simulation system provided by the present invention selects rigid vegetation as the research object, simplifies it into a cylinder for simulation research, and based on the assumption of local uniform flow and the Saint - Venant equation, studies the along - channel resistance characteristics of rigid vegetation under the condition of steady non - uniform flow, further explores the variation law of vegetation resistance, and provides a reference for the subsequent research on the resistance characteristics of vegetated ecological channels.

[0171] The above content is an illustration of the preferred embodiments of the present invention, which can help those skilled in the art to more fully understand the technical solution of the present invention. However, these embodiments are merely examples and cannot be construed that the specific implementation of the present invention is limited to the description of these embodiments. For those of ordinary skill in the technical field to which the present invention pertains, without departing from the concept of the present invention, several simple deductions and transformations can still be made, and all should be regarded as falling within the protection scope of the present invention.

Claims

1. A rigid vegetation along-the-line resistance simulation system, characterized in that: It includes a river simulation device, a vegetation simulation device, an observation unit and a calculation unit; The river simulation device comprises a water tank, a water reservoir and a water pump. The water pump transports water from the water reservoir to one end of the water tank, and then flows into the water reservoir from the other end of the water tank. The river simulation device is used to simulate the flow of river water. The vegetation simulation device is arranged in the water tank, and includes a density board and simulated plants arranged on the density board, and is used to simulate rigid vegetation in a river. The position of the vegetation simulation device in the water tank is a vegetation area; The observation unit includes a measurement module arranged on the side of the water tank and a shooting module for taking pictures of the side of the water tank, and is used to obtain an image of the water surface line along the vegetation area in the river simulation device; The calculation unit is connected to the observation unit, and is used to receive the image of the water surface line along the vegetation area obtained by the observation unit, and calculate the resistance coefficient C of the vegetation area in the river simulation device. d， and verifying the reliability of the results after the calculations are completed; When the flow value Q1=32.85m³ / h, different vegetation density Lower drag coefficient C d The expression is: ； When the flow value Q2=48.20m³ / h, under different vegetation densities Drag coefficient C d The expression is: ； When the flow value Q3=72.31m³ / h, under different vegetation densities Drag coefficient C d The expression is: 。 2. According to claim 1, a rigid vegetation along-the-way resistance simulation system is characterized in that: A flow stabilizer is provided on the upstream side of the water trough, a tail gate is provided on the downstream side of the water trough, a flow meter and a water pump are provided in the river simulation device, the flow meter is used to record the flow rate of water flowing into the water trough, and the water pump is used to transport water from the water reservoir to the water trough.

3. According to claim 1, a rigid vegetation along-the-way resistance simulation system is characterized in that: The length of the water tank is 10m and the width is 0.5m.

4. According to claim 1, a rigid vegetation along-the-way resistance simulation system is characterized in that: The vegetation simulation device is arranged inside the water tank, including a density board and a plurality of simulated plants evenly fixed on the density board, the simulated plants constitute simulated vegetation, the density of the simulated plants distributed on the density board is the vegetation density, the density board is 1m long, 0.5m wide and 1cm thick, and the simulated plants are cylindrical aluminum rods with a length of L=40cm and a diameter of D=0.007m.

5. According to claim 4, a rigid vegetation along-the-way resistance simulation system is characterized in that: The spacing between the holes on the density board includes three modes, mode A: the spacing between the center point of the hole on the density board and the center point of the adjacent hole is 1 cm, mode B: the spacing between the center point of the hole on the density board and the center point of the adjacent hole is 1.2 cm, mode C: the spacing between the center point of the hole on the density board and the center point of the adjacent hole is 1.6 cm.

6. According to claim 1, a rigid vegetation along-the-way resistance simulation system is characterized in that: The calculation process of the calculation unit includes the following steps: Step 1: Arrange the one-dimensional Saint-Venant equation to obtain the resistance coefficient C under constant non-uniform flow d The expression is: ， Among them, x is the direction of water flow, H is the water depth, U is the flow velocity, g is the acceleration of gravity, m is the density of vegetation, and D is the diameter of a single plant in the vegetation. is the density of vegetation; Step 2: After fitting the coordinates along the water surface line, the curve function describing the water depth H is defined as ， Among them, A, B, and C are all constants, and their values ​​are obtained by fitting the coordinates along the water surface line; Step 3: Using a rigid vegetation along-the-way resistance simulation system, the vegetation density and the flow rate of water are adjusted to conduct a along-the-way resistance simulation experiment. At the same time, the observation unit takes images of changes in the water surface line along the way under various working conditions and calculates the values ​​of A, B, and C. Step 4: Calculate the resistance coefficient C under each working condition d , the horizontal axis x is represented by the Reynolds number Re d , the vertical coordinate y adopts the resistance coefficient C d Draw a picture; Step 5: Introducing vegetation density Process the data and perform C d With Re d The coordinate axis transformation of the function relationship graph is used to obtain the water flow C at different flow values. d Regarding vegetation density The calculation formula for .

7. A rigid vegetation along-the-line resistance simulation system according to claim 6, characterized in that: Vegetation density According to the different layout methods, it can be divided into density , density , density , density , density 5 types, density is 0.267, density 0.150, density is 0.096, density 0.038, density is 0.017; The flow rate of water flow is the average flow value of 3 groups, flow value Q1 is 32.85m³ / h, flow value Q2 is 48.20m³ / h, and flow value Q3 is 72.31m³ / h; Through the density - , flow values ​​Q1-Q3 are combined to obtain 12 different working conditions.

8. A rigid vegetation along-the-line resistance simulation system according to claim 6 or 7, characterized in that: The step five specifically includes: Step 51: Extract the drag coefficient C under each working condition d The maximum value of C d-max Then, the C of different vegetation density conditions under the same flow value was calculated. d-max and vegetation density Perform curve fitting to obtain the resistance coefficient C d Regarding vegetation density Function expression used to change the expression of the y-axis; Step 52: Take the resistance coefficient C at different vegetation densities under the same flow rate d The Reynolds number corresponding to the maximum value is Re d-Cd-max , for the resistance coefficient C d The Reynolds number corresponding to the maximum value of d-Cd-max and vegetation density Perform curve fitting, and then you can get the Reynolds number Re d Regarding vegetation density Function expression used to change the expression of the x-axis; Step 53: According to the obtained C d Regarding vegetation density The function expression and Re d Regarding vegetation density The function expression of The term is placed on the left side of the equation, and the constant term is placed on the right side of the equation. Then the left side of the equation is selected as the new Y-axis and X-axis, and the images of the data X and Y are redrawn. Finally, the new X-axis and Y-axis are curve fitted to establish the function expression between Y and X under different flow values. Step 54: Establish different vegetation densities when the flow value Q1=32.85m³ / h, the flow value Q2=48.20m³ / h and the flow value Q3=72.31m³ / h respectively. Lower drag coefficient C d expression.

9. A rigid vegetation along-the-line resistance simulation system according to claim 1 or 7, characterized in that: After the calculation is completed, the calculation unit verifies the reliability of the result, and the specific process is as follows: The vegetation area under each working condition is divided into 500 grid points along the water flow direction. The length of the calculation grid unit along the water flow x direction is defined as Δx=L / 500, L is the length of the vegetation area, and the water depth H0 at the initial end of the vegetation area is used as the initial boundary condition. The flow velocity U0 at x=0 is calculated through the flow Q, and the initial data is substituted into the formula Solve in ; and is the energy slope when x = 0 and x = Δx; solve for the water depth H when x = Δx 0+Δx and flow rate U 0+Δx , and then continue to calculate downstream, solving H at x=Δx for the previous grid 0+Δx The value of is used as the upper boundary condition of the next grid to solve the water depth and flow velocity at x=2Δx. Similarly, the water depth H along the entire vegetation area is calculated in this way. The normalized x + =x / L as the horizontal axis, normalized H + =H / H0 as the ordinate, draw a graph; compare the experimental water depth value with the calculated water depth value H + The smaller the deviation, the higher the reliability.

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