CN110837691A - Quasi-two-dimensional mathematical model beach groove section dividing method based on momentum correction coefficient - Google Patents
Quasi-two-dimensional mathematical model beach groove section dividing method based on momentum correction coefficient Download PDFInfo
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Abstract
The invention discloses a method for dividing a beach groove section of a quasi-two-dimensional mathematical model based on a momentum correction coefficient. And numbering the calculated momentum correction coefficients along the sequence of the water levels from small to large, calculating the difference value of the two adjacent momentum correction coefficients, and under the same change trend, when the accumulated amplitude of the momentum correction coefficients is greater than 0.02, considering that the area can be divided into flood beaches, wherein the elevation ranges of the flood beaches are the first water level and the last water level of the momentum correction coefficients of the group. The method can quantitatively identify the main trough and the flood plain of the compound section, and has the advantages of simple calculation, strong operability and high accuracy.
Description
Technical Field
The invention relates to a method for dividing a beach groove section of a quasi-two-dimensional mathematical model based on a momentum correction coefficient, and belongs to the technical field of beach groove division in riverbed evolution analysis.
Background
The composite cross section river channel exists in nature in a large number, the river channel has wide river floodbeaches, and a large height difference exists between the river floodbeaches and the main trough. The flow rate is small in the non-flood period, and water flows generally in the main trough; the flow rate is increased in the flood season, the water level is lifted, flood plain water flow is easy to occur, at the moment, water flow flows in the main groove and the flood plain, but the flow speed difference between the beach land and the main groove is large. The mathematical model is an important means for simulating the water flow and sediment transport of a river channel and can be divided into a one-dimensional mathematical model, a quasi two-dimensional mathematical model, a two-dimensional mathematical model and a three-dimensional mathematical model. The one-dimensional mathematical model is commonly used for analyzing the riverbed evolution of a long river reach and a large time scale, and has wide application. However, the one-dimensional mathematical model cannot distinguish the influence caused by the difference between the flow rates of the flood beach and the main trough, and cannot be used for simulating a channel with a compound cross section. The quasi-two-dimensional mathematical model divides the flood beach and the main trough of the river channel, and considers the change of the water flow of the flood beach and the main trough respectively. The beach groove division is the key of the success or failure of a quasi-two-dimensional mathematical model, the beach groove position and the elevation are mainly divided by people at present, the plane position of the beach groove cannot be changed, and the application of the mathematical model has great limitation.
The numerical value of the hydraulic element of the compound river channel is greatly changed along with the rise of the water level. Particularly, after a river floods a beach, the water flow is dispersed, the flow rate is reduced rapidly, the momentum of the water flow is reduced obviously, and the momentum correction coefficient in the one-dimensional model is increased obviously. The momentum correction coefficient is an error correction coefficient obtained when the section average flow velocity is used for calculating the liquid flow momentum, and the coefficient is in direct proportion to the square of the depth average flow velocity of the water flow, so that the sudden drop of the depth average flow velocity in the process of the flood beach can be amplified. Therefore, a curve graph of the momentum correction coefficient changing along with the water level can be drawn by taking the water level as a vertical coordinate y and the momentum correction coefficient as a horizontal coordinate x, the obtained point of the momentum correction coefficient having a sudden change is obtained, and the corresponding elevation is the elevation of the flood plain. And after the river flood beach elevation is obtained, finding the range corresponding to the elevation again, thereby accurately positioning the beach and trough dividing points of the river channel section.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the method for dividing the cross section of the beach groove of the quasi-two-dimensional mathematical model based on the momentum correction coefficient can quantitatively identify the main groove and the flood beach of the compound cross section, and is simple in calculation, strong in operability and high in accuracy.
The invention adopts the following technical scheme for solving the technical problems:
the method for dividing the beach groove section of the quasi-two-dimensional mathematical model based on the momentum correction coefficient comprises the following steps:
Step 2, measuring the average grain size of the riverway bed sand, and calculating the river bed roughness according to the average grain size of the bed sand;
step 3, setting the highest water level and the lowest water level of the river cross section, and recording the highest water level and the lowest water level as L respectivelymax、LminLet us order
Record each water level data Li；
Step 4, according to the river section in the step 1, obtaining water level data LiCalculating the average flow velocity u of the vertical line of each measuring point on the cross section of the river channelijSolving the average flow velocity of each vertical line in a transverse integral mode to obtain water level data LiLower cross-sectional average flow velocity vi；
Step 5, regarding the water level data L1To L200Calculating and recording each water level data LiCorresponding momentum correction factor βi；
Step 6, calculating the difference value delta β of the momentum correction coefficients corresponding to two adjacent water level data from low to high, grouping the water level data into a group when m delta β is more than 0 and m is more than or equal to 2, counting the accumulation results of m delta β in each group, and recording the accumulation results as delta β in turn1、Δβ2、…、ΔβkAnd k is 1,2, …, and simultaneously recording the first water level and the last water level corresponding to the difference value of the momentum correction coefficients in each group,is described as (L)k1,Lk2)；
Step 7, setting the minimum amplitude of the river channel momentum correction coefficient caused by the river floodbeach to be η, and when the minimum amplitude is delta βkWhen > η, it is considered that Δ βkCorresponding water level (L)k1,Lk2) The elevation range of the river flood beach is (L)k1,Lk2)；
And 8, according to the elevation range of the flood plain obtained in the step 7, combining the river channel section terrain to obtain the width of the flood plain.
As a preferable embodiment of the present invention, the calculation formula of the river bed roughness in step 2 is:
wherein n is the roughness of the riverbed and dmIs the average grain size of the riverbed sand.
As a preferred scheme of the invention, the lowest water level L in the step 3min＝Zmin+0.06, maximum water level Lmax＝Zmax+0.06，Zmin、ZmaxThe minimum elevation and the maximum elevation of the elevations corresponding to all measuring points on the cross section of the river channel are respectively.
As a preferable scheme of the invention, the calculation formula of the average flow velocity of the vertical lines of the measuring points in the step 4 is as follows:
wherein u isijAs water level data LiAverage flow velocity of vertical line at lower measuring point, n is roughness of river bed, hijAs water level data LiAnd the water depth at the lower measuring point j represents the jth measuring point of the river section, S is the river bed gradient, and S is 0.0005.
In a preferred embodiment of the present invention, the momentum correction factor β in step 4iThe calculation formula of (2) is as follows:
wherein J is the number of the test points of the river cross section, uijAs water level data LiAverage velocity of vertical line at lower measurement point, hijAs water level data LiDepth of water at the lower measuring point Dj+1、DjStarting point distances v of the j +1 th and j th measuring points respectivelyiAs water level data LiLower cross-sectional average flow velocity, AiThe cross-sectional area of the water passing through the water pipe,
Qias water level data LiThe flow rate of the lower section of the pipe,
as a preferable scheme of the present invention, the minimum amplitude η of the river channel momentum correction coefficient caused by the flood beach in step 7 is 0.02.
Compared with the prior art, the invention adopting the technical scheme has the following technical effects:
the invention relates to a method for dividing a river flood beach and a main trough boundary of a compound section river channel based on momentum correction coefficients. According to the change rule of the momentum correction coefficient along with the water depth, the positions of the flood beaches are automatically identified, the method can be directly applied to a quasi-two-dimensional water-sand mathematical model, the physical concept of the method is clear, the calculation result is accurate, the operability is strong, and errors caused by manual division of beach slots are overcome.
Drawings
FIG. 1 is a flow chart of the beach groove section dividing method of the invention.
FIG. 2 is a cross-sectional view of the yellow river village according to the embodiment of the present invention.
FIG. 3 is a cross-sectional overshoot correction coefficient diagram of the high village of the yellow river according to the embodiment of the present invention.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention.
The instantaneous momentum correction coefficient of the compound river channel at the flood beach is gradually reduced and then gradually increased along with the water depth, and the elevation of the flood beach can be determined according to the change characteristic. As shown in fig. 1, the flow of the method for judging the flood beach and the main trough of the compound cross-section river of the invention is as follows:
Step 2, obtaining the average grain diameter d of the riverway bed sandmThe roughness n of the river bed was calculated from the particle size.
In the formula (d)mBed sand particle size, unit: and m is selected.
Step 3, setting the highest water level and the lowest water level of the section, respectively marked as Lmax、LminGet it
L200＝LmaxAll water level data are recorded in sequence, and each water level is used as a given water level for calculating the momentum correction coefficient.
Step 4, according to the river terrain in the step 1, in the process that the water level is gradually raised, the flow velocity of the transverse measuring point of the section under the given water level is calculated by adopting a formula:
wherein u isijAs water level data LiAverage flow velocity of vertical line of lower measuring point, j is jth measuring point of cross section, n is riverbedRoughness, hijAs water level data LiThe water depth at a lower measuring point can be 0.0005 when S is the river bed gradient. The flow velocity represents the average flow velocity of the vertical lines in the vertical direction of the position of the measuring point, and the average flow velocity of each vertical line is solved in a transverse integration mode to obtain the average flow velocity v of the cross section under the given water leveli。
Step 5, making the water level from L1To L200Gradually lifting, respectively calculating momentum correction coefficient β at given water level1To β200Recording water level and momentum correction coefficient data corresponding to the water level, and a calculation formula of the momentum correction coefficient:
wherein u isijThe average flow velocity of the vertical lines corresponding to different water levels is calculated in the step 4; h isijIs a given water level LiDepth of lower cross-sectional water of Li-Lmin；viThe average flow velocity of the cross section; a. theiIs the cross-sectional area.
The average cross-sectional flow velocity at a given water level can be obtained by dividing the flow rate by the cross-sectional flow area
The flow calculation method comprises the following steps:
and 6, calculating the difference value delta β between the two adjacent momentum correction coefficients from the low water level to the high water level to βi+1-βiAnd i is 1,2, … and 199, the accumulated result of each group of continuous delta β > 0 is counted and recorded as delta β1、Δβ2、…、ΔβkSimultaneously recording the first water level and the last water level (L) corresponding to the difference value of each group momentum correction coefficientk1,Lk2)。
Step 7, setting η as the minimum amplitude of the river reach momentum correction coefficient caused by the flood beach, and when the minimum amplitude is delta βkWhen the water level is greater than η, the water level is consideredIs located at a flood plain with an elevation of (L)k1,Lk2) In between, the representative elevation of the flood beach may be averaged.
Step 8, according to the elevation range (L) of the flood plain obtained in the step 7k1,Lk2) The width B (p) of the stage of the flood plain is easily obtained by combining the section terrain.
The method for dividing the cross section of the beach groove of the quasi-two-dimensional mathematical model based on the momentum correction coefficient is applied by taking the cross section of the high village in the downstream of the yellow river as an example, and the implementation steps are as follows:
(1) and collecting the starting point distance and elevation data of the high village section, wherein the section shape is shown in figure 2, and each data point is numbered.
(2) Automatically taking the lowest water level 55.64m and the highest water level 66.28m through a program; and uniformly selecting 200 elevation points as digital-analog calculation water levels between the two points.
(3) The particle size of the riverway bed sand is 0.08mm, and the vertical average flow velocity of different points of the riverway section is calculated by adopting a Manning formula.
(4) Calculating the section momentum correction coefficients corresponding to different water levels, as shown in fig. 3; 3 groups of change values can be found according to the calculation result of the momentum correction coefficient, the corresponding elevations are respectively (56.71, 57.94), (58.64, 60.19) and (61.1, 61.7), and the riverbed between the two water levels is the corresponding beach. Table 1 shows the profile characteristics for different water levels.
TABLE 1
The above embodiments are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modifications made on the basis of the technical scheme according to the technical idea of the present invention fall within the protection scope of the present invention.
Claims (6)
1. The method for dividing the beach groove section of the quasi-two-dimensional mathematical model based on the momentum correction coefficient is characterized by comprising the following steps of:
step 1, measuring points are arranged from the leftmost side of the river cross section to the right side of the river cross section, and starting point distances of the measuring points are marked as D in sequencejCorresponding elevation of Zj，j＝1,2,…,J；
Step 2, measuring the average grain size of the riverway bed sand, and calculating the river bed roughness according to the average grain size of the bed sand;
step 3, setting the highest water level and the lowest water level of the river cross section, and recording the highest water level and the lowest water level as L respectivelymax、LminLet us order
Record each water level data Li；
Step 4, according to the river section in the step 1, obtaining water level data LiCalculating the average flow velocity u of the vertical line of each measuring point on the cross section of the river channelijSolving the average flow velocity of each vertical line in a transverse integral mode to obtain water level data LiLower cross-sectional average flow velocity vi；
Step 5, regarding the water level data L1To L200Calculating and recording each water level data LiCorresponding momentum correction factor βi；
Step 6, calculating the difference value delta β of the momentum correction coefficients corresponding to two adjacent water level data from low to high, grouping the water level data into a group when m delta β is more than 0 and m is more than or equal to 2, counting the accumulation results of m delta β in each group, and recording the accumulation results as delta β in turn1、Δβ2、…、ΔβkAnd k is 1,2 and …, and the first water level and the last water level corresponding to the difference value of the momentum correction coefficients in each group are recorded simultaneously and recorded as (L)k1,Lk2)；
Step 7, setting the minimum amplitude of the river channel momentum correction coefficient caused by the river floodbeach to be η, and when the minimum amplitude is delta βkWhen > η, it is considered that Δ βkCorresponding water level (L)k1,Lk2) The elevation range of the river flood beach is (L)k1,Lk2)；
And 8, according to the elevation range of the flood plain obtained in the step 7, combining the river channel section terrain to obtain the width of the flood plain.
2. The method for dividing the beach groove section of the quasi-two-dimensional mathematical model based on the momentum correction coefficients as claimed in claim 1, wherein the calculation formula of the river bed roughness in step 2 is as follows:
wherein n is the roughness of the riverbed and dmIs the average grain size of the riverbed sand.
3. The method for dividing the beach groove section of the quasi-two-dimensional mathematical model based on the momentum correction coefficients of claim 1, wherein the lowest water level L in step 3min＝Zmin+0.06, maximum water level Lmax＝Zmax+0.06，Zmin、ZmaxThe minimum elevation and the maximum elevation of the elevations corresponding to all measuring points on the cross section of the river channel are respectively.
4. The method for dividing the cross section of the beach groove of the quasi-two-dimensional mathematical model based on the momentum correction coefficient as claimed in claim 1, wherein the calculation formula of the average flow velocity of the vertical line of each measuring point in step 4 is as follows:
wherein u isijAs water level data LiAverage flow velocity of vertical line at lower measuring point, n is roughness of river bed, hijAs water level data LiAnd the water depth at the lower measuring point j represents the jth measuring point of the river section, S is the river bed gradient, and S is 0.0005.
5. The quasi-two-dimensional mathematical model beach groove section division based on momentum correction coefficients of claim 1Method, wherein the momentum correction factor β is determined in step 4iThe calculation formula of (2) is as follows:
wherein J is the number of the test points of the river cross section, uijAs water level data LiAverage velocity of vertical line at lower measurement point, hijAs water level data LiDepth of water at the lower measuring point Dj+1、DjStarting point distances v of the j +1 th and j th measuring points respectivelyiAs water level data LiLower cross-sectional average flow velocity, AiThe cross-sectional area of the water passing through the water pipe,
Qias water level data LiThe flow rate of the lower section of the pipe,
6. the method for dividing the beach groove cross section of the quasi-two-dimensional mathematical model based on the momentum correction coefficient as claimed in claim 1, wherein the minimum amplitude η of the river channel momentum correction coefficient caused by the flood beach in step 7 is 0.02.
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Application publication date: 20200225 |