Method for calculating resistance of wandering river fluid bed based on flat beach characteristics

Abstract

The invention discloses a flat beach characteristic-based wandering type river fluid bed resistance calculation method. The method comprises the following steps of: determining flat beach flow of a wandering river reach according to actual measurement data; based on the basic water level-flow relation, the flat beach water level is determined through the flat beach flow, and on this basis, the flat beach width and the flat beach water depth are determined through the river section terrain; according to the flat beach water depth and the median particle size of the surface layer of the riverbed, the relative roughness of the riverbed is deduced; utilizing the gravitational acceleration, the riverbed gradient and the flat beach water depth to obtain the riverbed friction flow velocity; and establishing a correlation between the ratio of the flat beach flow velocity to the riverbed friction flow velocity and the sand grain Reynolds number, and obtaining a moving bed resistance calculation formula under the flat beach condition of the wandering river reach. The method is easy to operate and high in calculation speed, rapid calculation can be conducted according to large-section topographic data and annual flat beach flow achievements, a theoretical basis is provided for correlation research of wandering river reaches, and scientific and technological support is provided for wandering river flood control and silt reduction rapid decision making.

Description

Technical Field

[0001] The invention relates to a moving bed resistance calculation method, in particular to a wandering river moving bed resistance calculation method based on flat beach characteristics. Background Art

[0002] The wandering channel in the lower reaches of the Yellow River has the characteristics of wide and shallow riverbed sections and erratic mainstream migration. The riverbed geometry in the equilibrium state is not only extremely sensitive to changes in water and sediment conditions upstream, but also closely related to changes in the upstream river regime. The cross-section of the wandering channel in the lower reaches of the Yellow River changes rapidly and dramatically with water and sediment conditions. The cross-section geometry of the channel will change significantly due to a major flood, which can easily cause a sudden change in river regime. The bed morphology of the wandering river section in the lower reaches of the Yellow River is complex and changeable under different water and sediment combinations, and the special channel morphology will have an important impact on the riverbed resistance.

[0003] In natural alluvial rivers, water flow resistance includes not only skin friction, but also morphological resistance caused by bed morphology and boundary morphology, and resistance caused by the energy consumed by water flow to push bed load. The factors affecting the resistance of the wandering river section in the lower reaches of the Yellow River are complex and can be summarized as dynamic bed resistance (bed resistance), bank resistance, beach resistance, and river flow (dangerous works) resistance, among which dynamic bed resistance is an important part of the comprehensive resistance of the river channel. Bed morphology is a very important influencing factor in the study of riverbed dynamic bed resistance, and plays a decisive role in water flow resistance. Changes in water flow intensity will shape different riverbed morphologies, and different riverbed morphologies will in turn affect the bed roughness. At present, the methods for calculating the dynamic bed resistance of the riverbed in the wandering river section of the lower reaches of the Yellow River mainly include the water flow resistance decomposition method, the comprehensive resistance coefficient method, and the dimensional analysis combined with the measured data calibration method. The roughness of the riverbed of alluvial rivers is closely related to the dynamic bed resistance of the riverbed. At present, the research on the roughness of sandy riverbeds can be roughly divided into three categories. The first category is to directly measure the riverbed surface roughness by different methods; the second category is to use equivalent particle size to replace the riverbed gradation; the third category is to treat the riverbed surface elevation as a random distribution field and use statistical parameters to study the riverbed surface roughness.

[0004] Although a lot of achievements have been made in the study of riverbed resistance of open channel flow, due to the special geomorphology and water-sand boundary of the wandering river section in the lower reaches of the Yellow River, the flood process has a significant shaping effect on the riverbed. This effect is coupled with the riverbed morphology, making the problem of riverbed dynamic resistance in the wandering river section more complicated. How to understand the law of riverbed particle size change and the law of interaction between particles in the wandering river section of the lower reaches of the Yellow River, and incorporate the quantitative indicators of riverbed morphology into the comprehensive resistance analysis, and then construct a calculation method for riverbed dynamic resistance in the wandering river section of the lower reaches of the Yellow River still needs in-depth research. Summary of the invention

[0005] Purpose of the invention: The purpose of the invention is to provide a method for calculating the resistance of a wandering river bed based on flat beach characteristics.

[0006] Technical solution: The method for calculating the resistance of a wandering river bed based on flat beach characteristics of the present invention comprises the following steps:

[0007] S1. Determine the flat-shoal flow of the wandering river section through measured data;

[0008] S2. Based on the basic water level-flow relationship, the flat beach water level is determined by the flat beach flow, and on this basis, the flat beach width and flat beach water depth are determined by the river cross-section topography;

[0009] S3. Calculate the relative roughness of the riverbed based on the water depth of the flat and the median particle size of the riverbed surface;

[0010] S4. Obtain the riverbed friction velocity using gravity acceleration, riverbed slope and flat water depth;

[0011] S5. Establish the correlation between the ratio of the flow velocity on the flat beach of the wandering river section to the riverbed friction flow velocity and the sand Reynolds number, and obtain the calculation formula of the moving bed resistance under the flat beach conditions of the wandering river section.

[0012] Furthermore, in step S2, the water level-flow rate presents a loop curve relationship, which is expressed as: Q=f(H), where Q is the flow rate, H is the water level, and f is the functional relationship between the two;

[0013] Substitute the flat beach flow in step S1 into the water level-flow relationship to obtain the flat beach water level.

[0014] Furthermore, the relative roughness Δ of the riverbed in step S3 is expressed as:

[0015] △=H bf / D 50

[0016] Among them, △ is the relative roughness of the riverbed, H bf is the flat water depth, D 50 is the median particle size of the riverbed surface.

[0017] Furthermore, the riverbed friction velocity expression in step S4 is:

[0018]

[0019] Where g is the acceleration due to gravity; S is the slope of the riverbed; H bf is the water depth of the flat beach; *,bf The velocity is the friction resistance of the riverbed.

[0020] Furthermore, the formula for calculating the moving bed resistance under the condition of flat beach in the wandering river section in step S5 is:

[0021]

[0022] Among them, U bf is the flat beach velocity, u *,bf is the riverbed friction velocity, a, b, c are three indexes respectively, which are fitted by measured data, △ is the relative roughness of the riverbed, R p is the parameter of the sand particle Reynolds number.

[0023] Furthermore, the flat current velocity U bf The expression is:

[0024]

[0025] Among them, Q bf is the flat beach flow, B bf is the width of the flat beach, H bf It is a flat beach with deep water.

[0026] Furthermore, the parameter R of the sand Reynolds number is p Used to characterize the particle size factor, the expression is:

[0027]

[0028] Among them, ρ s is the density of sediment, ρ is the density of clean water, ν is the kinematic viscosity of clean water, g is the acceleration of gravity, D 50 is the median particle size of the riverbed surface.

[0029] The system corresponding to the method includes:

[0030] The flat-shoal flow calculation unit is used to determine the flat-shoal flow of the wandering river section through measured data;

[0031] A cross-sectional flat beach index calculation unit is used to determine the flat beach water level through the flat beach flow based on the basic water level-flow relationship, and on this basis, determine the flat beach width and flat beach water depth through the river cross-sectional topography;

[0032] The riverbed relative roughness calculation unit is used to deduce the relative roughness of the riverbed according to the flat water depth and the median particle size of the riverbed surface;

[0033] The riverbed friction velocity calculation unit is used to obtain the riverbed friction velocity using gravity acceleration, riverbed slope and flat water depth;

[0034] The moving bed resistance calculation unit is used to establish the correlation between the ratio of the flow velocity on the flat beach of the wandering river section to the riverbed friction flow velocity and the sand Reynolds number, and obtain the moving bed resistance calculation formula under the flat beach conditions of the wandering river section.

[0035] An electronic device for storing and executing the method, comprising a memory and a processor, wherein:

[0036] A memory for storing computer programs that can be run on the processor;

[0037] A processor is used to execute the steps of the method for calculating the fluid bed resistance of a wandering river based on flat beach characteristics when running the computer program.

[0038] A storage medium for storing and executing the method, wherein a computer program is stored on the storage medium, and when the computer program is executed by at least one processor, the steps of the method for calculating the bed resistance of a wandering river based on flat beach characteristics are implemented.

[0039] Beneficial effects: Compared with the prior art, the remarkable technical effects of the present invention are: First, the calculation results of this method are relatively close to those of other scholars, but there is no need to consider the riverbed morphology and the judgment of the water flow energy state. The calculation can be performed directly by introducing the sand Reynolds number, and the calculation form is simpler; Second, the method is simple to operate. Since the selected parameters are relatively small and the calculation speed is fast, it can be quickly calculated based on large-section terrain data and annual flat beach flow results, providing a theoretical basis for the study of river phase relationships in the wandering river sections of the lower reaches of the Yellow River; Third, this method has high accuracy and can be directly used for the calculation of the moving bed resistance of the wandering river sections of the lower reaches of the Yellow River, providing scientific and technological support for rapid decision-making on flood control and silt reduction in the wandering river channels of the lower reaches of the Yellow River. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 is a flow chart of the method of the present invention;

[0041] Figure 2 The ratio of the average flow velocity to the bed shear velocity of the present invention is related to the relative roughness of the riverbed;

[0042] Figure 3 It is the correlation between the ratio of the average flow velocity to the bed shear flow velocity and the sand particle Reynolds number of the present invention;

[0043] Figure 4 These are the calculated values ​​and measured values ​​of the moving bed resistance formula of the wandering river section in the lower reaches of the Yellow River constructed by the present invention. DETAILED DESCRIPTION

[0044] The material along the banks of the wandering river in the lower reaches of the Yellow River has low viscosity and poor anti-scouring properties. The banks are prone to collapse, and there are many sandbars without vegetation. After the flood, the shape of the sandbars is very easy to change, resulting in a very scattered shape of the entire river beach. Due to the diversity of water and sand combinations, the main channel of the wandering river section in the lower reaches of the Yellow River often presents a complex cross-sectional shape, which causes the riverbed resistance to be affected by many factors. The study of its laws is one of the research contents that urgently need to be carried out in the wandering river section of the lower reaches of the Yellow River.

[0045] The study found that the resistance calculation methods of alluvial rivers can be divided into two categories: one is to calculate the resistance of different resistance units, such as sand resistance, sand wave resistance, etc., separately, and then superimpose and combine them. This approach is relatively clear in mechanism, and the changes of various factors can be considered separately. The other is to directly calculate the total resistance. Although the mechanism of resistance formation is not considered, this approach is also used in actual engineering design and research because of its simple calculation.

[0046] This method uses the Manning-Strickler formula as the basic form to determine the key water-sediment factors that affect the change of moving bed resistance - sand Reynolds number and relative water depth. The form of riverbed resistance of the wandering river section of the lower Yellow River under flat conditions calculated by this method is simpler than that of most researchers, and the calculation process is clearer and the calculation method is simpler and clearer. Although the calculation accuracy of some scholars at home and abroad is higher than that of this method, their calculation methods are complicated, and the required parameters are numerous and difficult to determine, making it difficult to adopt them in actual river management. The calculation forms of some scholars are relatively simple, and their accuracy is lower than that of this method, which cannot meet actual production needs.

[0047] Dynamic bed resistance plays an important role in the evolution of floods in alluvial rivers and the calculation of riverbed scouring and silting. By accurately calculating the dynamic bed resistance, the propagation process of floods in the river channel can be simulated more accurately, thereby improving the efficiency and effectiveness of flood warning and emergency response, and helping to protect the lives and property of people on both sides of the lower reaches of the Yellow River. Incorporating quantitative indicators of riverbed morphology into comprehensive resistance for analysis, and then constructing a method for calculating the dynamic bed resistance of the riverbed in the wandering river section of the lower reaches of the Yellow River is a technical problem that the present invention hopes to solve.

[0048] To solve the above problems, the present invention proposes a method for calculating the moving bed resistance of a wandering river based on flat beach characteristics; the flat beach flow of the wandering river section of the lower Yellow River is determined by measured data; the flat beach water level is determined based on the water level-flow relationship, and the flat beach width and flat beach water depth are determined by the river section topography; the relative roughness parameters of the riverbed are deduced according to the water depth under flat beach conditions and the median particle size of the riverbed surface; the riverbed friction resistance flow velocity is obtained by using gravity acceleration, riverbed slope and flat beach water depth; a correlation between the average flow velocity of the wandering river section of the lower Yellow River and the ratio of the bed shear velocity and the sand Reynolds number is established, and then a formula for calculating the moving bed resistance of the wandering river section of the lower Yellow River under flat beach conditions is obtained, so as to realize the rapid calculation of the moving bed resistance of the wandering river section of the lower Yellow River under flat beach conditions.

[0049] The following examples are combined with Figures 1 to 4 , the present invention is further described in detail.

[0050] Before identification, we must first clarify the concepts of flat-shoal flow and flat-shoal water level: Analyze the parameters of the flood and sediment transport capacity of multi-channel rivers, and clarify the concepts of flat-shoal flow and flat-shoal water level in multi-channel river sections. Flat-shoal water level refers to the water level in a river with distinct shoals and channels, when the main channel is filled and is flush with the surface of the new river floodplain. The corresponding flow is called flat-shoal flow, the corresponding river width is the flat-shoal river width, the corresponding water depth is the flat-shoal water depth, the corresponding water flow velocity is the flat-shoal flow velocity, and the corresponding water level is the flat-shoal water level.

[0051] like Figure 1 As shown in FIG. 1 , a method for calculating the moving bed resistance of a wandering river based on flat beach characteristics mainly includes the following steps:

[0052] S1. Determine the flatland flow of the wandering river section in the lower reaches of the Yellow River through measured data;

[0053] S2. Based on the basic water level-flow relationship, the flat beach water level is determined by the flat beach flow. On this basis, the flat beach width and flat beach water depth are determined by the river section topography.

[0054] like Figure 2 As shown in the figure, the present invention collects multiple groups of measurement data of the lower reaches of the Yellow River to analyze the moving bed resistance of the wandering river channel in the lower reaches of the Yellow River. The data of the three stations A, B and C are mainly collected for moving bed resistance analysis. bf / u *,bf (Ratio of flat-bed flow velocity to riverbed friction velocity) and riverbed relative roughness △ (△ = H bf / D 50 ) has a significant exponential relationship, and the main difference between the three stations A, B and C is that the values ​​of △ are significantly different, while U bf / u *,bf The value of changes slightly; among them, U bf is the flat beach velocity, u *,bf is the friction velocity of the riverbed, △ is the relative roughness of the riverbed, H bf is the flat water depth, D 50 is the median particle size of the riverbed surface.

[0055] The specific steps include:

[0056] (1) Water level-discharge relationship curve;

[0057] The flood process of the year is selected for point plotting. The water level-flow relationship presents a loop curve relationship. According to the direction of the basic flood water level-flow loop curve, the rising water curve or falling water curve is selected clockwise or counterclockwise as the extended basic data:

[0058] Q=f(H) (1)

[0059] Among them, Q is the flow rate, H is the water level, and f is the functional relationship between the two;

[0060] (2) Determine the flat water level;

[0061] Flat beach flow Q bf After determination, the flat water level z is obtained through the basic water level-discharge relationship curve bf .

[0062] S3. Calculate the relative roughness of the riverbed based on the water depth of the flat and the median particle size of the riverbed surface;

[0063] The method to quantify the relative roughness of the riverbed is:

[0064] △=H bf / D 50 (2)

[0065] Among them, △ is the relative roughness of the riverbed, H bf is the flat water depth, D 50 is the median particle size of the riverbed surface.

[0066] S4. Obtain the riverbed friction velocity using gravity acceleration, riverbed slope and flat water depth;

[0067] The method to quantify the riverbed friction velocity is:

[0068]

[0069] Where g is the acceleration due to gravity; S is the slope of the riverbed; u *,bf The velocity is the friction resistance of the riverbed.

[0070] S5. Establish the correlation between the flow velocity on the flat beach of the wandering river section in the lower reaches of the Yellow River and the ratio of the riverbed friction velocity and the sand Reynolds number, and obtain the calculation formula for the moving bed resistance under the flat beach conditions of the wandering river section in the lower reaches of the Yellow River.

[0071] like Figure 3 As shown in Figure 2, in order to further explore the effect of particle size on riverbed resistance in the wandering river section of the lower Yellow River, the parameter R of the sand Reynolds number, which represents the particle size factor, is introduced. p As can be seen from the figure, the wandering river section U bf / u *,bf With R p There is a certain exponential relationship.

[0072] The specific steps include:

[0073] (1) The basic form of the moving bed resistance formula for the wandering river section of the lower Yellow River is the form of the Manning formula, but the traditional Manning formula coefficients cannot be directly applied to the lower Yellow River, so the coefficients of the Manning formula need to be corrected. The following relationship is used to express the moving bed resistance equation under flat conditions:

[0074]

[0075] Among them, U bf is the flat-beach flow velocity; this formula is the general Manning-Strickler form of the resistance equation. In its standard form, the coefficient m r The value of should be 1 / 6, α r is the coefficient, usually taken as 7.66;

[0076] According to the relationship between cross-sectional flow velocity and cross-sectional shape, U bf It can be expressed as follows:

[0077]

[0078] Among them, Q bf is the flat beach flow, B bf The width of the flat beach.

[0079] (2) Collect multiple sets of measurement data from the lower reaches of the Yellow River to analyze the riverbed resistance of the wandering river channel in the lower reaches of the Yellow River. The data from stations A, B, and C are mainly collected for riverbed resistance analysis. The riverbed resistance at the three locations is mainly affected by water depth and particle size. In order to further explore the influence of particle size on riverbed resistance in the wandering river section of the lower reaches of the Yellow River, the parameter R, which represents the particle size factor, is introduced here. p , the specific expression is as follows:

[0080]

[0081] Among them, ρ s is the density of sediment, ρ is the density of clean water, and ν is the kinematic viscosity of clean water, which is usually taken as 10 -6 m 2 / s.

[0082] like Figure 4 As shown in the figure, in order to construct the expression form of the moving bed resistance of the wandering river section in the lower reaches of the Yellow River, the widely used exponential expression form is selected to construct U bf / u *,bf With R p As can be seen from the figure, the R between the calculated values ​​and the measured values ​​of the three stations A, B and C 2 0.64(R 2is the correlation coefficient, with a value between 0 and 1. The closer the number is to 1, the better the correlation between the calculated value and the measured value. It has high accuracy and can be used to calculate the moving bed resistance of the wandering river section in the lower reaches of the Yellow River.

[0083] Based on the wandering river section of the lower Yellow River bf / u *,bf With R p There is a certain exponential relationship. The moving bed resistance at stations A, B and C is expressed as:

[0084] A:

[0085] B:

[0086] C:

[0087] Then, the expression of the moving bed resistance of the wandering river section in the lower reaches of the Yellow River is constructed as follows:

[0088]

[0089] Among them, a, b, and c are three indexes, which are fitted by measured data.

[0090] The present invention also provides a wandering river fluid bed resistance calculation system based on flat beach characteristics, comprising:

[0091] The flat-shoal flow calculation unit is used to determine the flat-shoal flow of the wandering river section through measured data;

[0092] A cross-sectional flat beach index calculation unit is used to determine the flat beach water level through the flat beach flow based on the basic water level-flow relationship, and on this basis, determine the flat beach width and flat beach water depth through the river cross-sectional topography;

[0093] The riverbed relative roughness calculation unit is used to deduce the relative roughness of the riverbed according to the flat water depth and the median particle size of the riverbed surface;

[0094] The riverbed friction velocity calculation unit is used to obtain the riverbed friction velocity using gravity acceleration, riverbed slope and flat water depth;

[0095] The moving bed resistance calculation unit is used to establish the correlation between the ratio of the flow velocity on the flat beach of the wandering river section to the riverbed friction flow velocity and the sand Reynolds number, and obtain the moving bed resistance calculation formula under the flat beach conditions of the wandering river section.

[0096] An electronic device for storing and executing the method, comprising a memory and a processor, wherein:

[0097] A memory for storing computer programs that can be run on the processor;

[0098] A processor is used to execute the steps of the method for calculating the fluid bed resistance of a wandering river based on flat beach characteristics when running the computer program.

[0099] A storage medium for storing and executing the method, wherein a computer program is stored on the storage medium, and when the computer program is executed by at least one processor, the steps of the method for calculating the bed resistance of a wandering river based on flat beach characteristics are implemented.

Claims

1. A method for calculating the resistance of a wandering river bed based on flat beach characteristics, characterized in that: The following steps are involved: S1. Determine the flat-shoal flow of the wandering river section through measured data; S2. Based on the basic water level-flow relationship, the flat beach water level is determined by the flat beach flow, and on this basis, the flat beach width and flat beach water depth are determined by the river cross-section topography; S3. Calculate the relative roughness of the riverbed based on the water depth of the flat and the median particle size of the riverbed surface; S4. Obtain the riverbed friction velocity using gravity acceleration, riverbed slope and flat water depth; S5. Establish the correlation between the ratio of the flow velocity on the flat beach of the wandering river section to the riverbed friction flow velocity and the sand Reynolds number, and obtain the calculation formula of the moving bed resistance under the flat beach conditions of the wandering river section.

2. The method for calculating the fluidized bed resistance of a wandering river based on flat beach characteristics according to claim 1 is characterized in that: In step S2, the water level-flow rate presents a loop curve relationship, which is expressed as: Q=f(H), where Q is the flow rate, H is the water level, and f is the functional relationship between the two; Substitute the flat beach flow in step S1 into the water level-flow relationship to obtain the flat beach water level.

3. The method for calculating the fluidized bed resistance of a wandering river based on flat beach characteristics according to claim 1 is characterized in that: The relative roughness △ of the riverbed in step S3 is expressed as: △=H bf / D 50 Among them, △ is the relative roughness of the riverbed, H bf is the flat water depth, D 50 is the median particle size of the riverbed surface.

4. The method for calculating the fluidized bed resistance of a wandering river based on flat beach characteristics according to claim 1 is characterized in that: The riverbed friction velocity expression in step S4 is: Where g is the acceleration due to gravity; S is the slope of the riverbed; H bf is the water depth of the flat beach; *,bf The velocity is the friction resistance of the riverbed.

5. The method for calculating the fluidized bed resistance of a wandering river based on flat beach characteristics according to claim 1 is characterized in that: The calculation formula of the moving bed resistance under the condition of flat beach in the wandering river section in step S5 is: Among them, U bf is the flat beach velocity, u *,bf is the riverbed friction velocity, a, b, c are three indexes respectively, which are fitted by measured data, △ is the relative roughness of the riverbed, R p is the parameter of the sand particle Reynolds number.

6. The method for calculating the fluidized bed resistance of a wandering river based on flat beach characteristics according to claim 5 is characterized in that: Flat current velocity U bf The expression is: Among them, Q bf is the flat beach flow, B bf is the width of the flat beach, H bf It is a flat beach with deep water.

7. The method for calculating the fluidized bed resistance of a wandering river based on flat beach characteristics according to claim 5 is characterized in that: Parameter R of sand Reynolds number p Used to characterize the particle size factor, the expression is: Among them, ρ s is the density of sediment, ρ is the density of clean water, ν is the kinematic viscosity of clean water, g is the acceleration of gravity, D 50 is the median particle size of the riverbed surface.

8. A wandering river bed resistance calculation system based on flat beach characteristics, characterized in that: include: The flat-shoal flow calculation unit is used to determine the flat-shoal flow of the wandering river section through measured data; A cross-sectional flat beach index calculation unit is used to determine the flat beach water level through the flat beach flow based on the basic water level-flow relationship, and on this basis, determine the flat beach width and flat beach water depth through the river cross-sectional topography; The riverbed relative roughness calculation unit is used to deduce the relative roughness of the riverbed according to the flat water depth and the median particle size of the riverbed surface; The riverbed friction velocity calculation unit is used to obtain the riverbed friction velocity using gravity acceleration, riverbed slope and flat water depth; The moving bed resistance calculation unit is used to establish the correlation between the ratio of the flow velocity on the flat beach of the wandering river section to the riverbed friction flow velocity and the sand Reynolds number, and obtain the moving bed resistance calculation formula under the flat beach conditions of the wandering river section.

9. An electronic device, characterized in that: comprising a memory and a processor, wherein: A memory for storing computer programs that can be run on the processor; A processor is used to execute the steps of a method for calculating the bed resistance of a wandering river based on flat beach characteristics as described in any one of claims 1 to 7 when running the computer program.

10. A storage medium, characterized in that: The storage medium stores a computer program, which, when executed by at least one processor, implements the steps of a method for calculating the bed resistance of a wandering river based on flat beach characteristics as described in any one of claims 1 to 7.

Images