Method for calculating flocculation sedimentation velocity of dam sediment

Abstract

SOLUTION: The method comprises the following steps: step 1, collecting data such as the particle size of the suspension sediments, the sedimentation rate of the suspension sediments, the topography of the dam, the water content of the dam, and the adjustment method for the dam; step 2, constructing a mathematical model of the one-dimensional non-stationary flow of the suspension sediments of the river including the mainstream and the tributaries of the dam; step 3, calculating the average flow velocity of the suspension sediments and the content of the suspension sediments of each cross section along the river course in the dam area; step 4, constructing a formula for calculating the flocculation sedimentation rate of the suspension sediments; and step 5, calculating the flocculation sedimentation rate of the suspension sediments based on the constructed formula for calculating the flocculation sedimentation rate of the suspension sediments for the cross section of the dam with an average water content of more than 0.3kg / m3 and an average flow velocity of less than 0.7m / s.EFFECT: The calculation method of the present invention considers the influence factors more comprehensively, has a simple formula structure, is convenient to use, and can provide technical support for improving the accuracy of the alluviation calculation of the dam sediment.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present application relates to the technical field of hydraulic engineering, and more particularly to a method for calculating the coagulation and settling velocity of dam sediment. [Background technology]

[0002] In existing studies on methods for calculating the cohesive sedimentation rate of dam sediment, one approach is simple and crude, by directly equating the settling rate of sediment that may be cohesive with the settling rate of sediment that does not cohere and has a relatively large particle size. Another approach is to calculate the cohesive sedimentation rate of sediment without including particle size parameters, or without including sand content, or including sand content but resulting in mixed sand rather than cohesive sediment. In short, the existing techniques have problems such as simple and crude processing methods, irrational formula structures, and inconvenient use, which reduce the accuracy of dam sediment alluvial calculations and are unfavorable for scientific adjustment of dams. Summary of the Invention [Problem to be solved by the invention]

[0003] The purpose of the embodiments of the present application is to provide a method for calculating the coagulation and settling rate of dam sediment, and to solve the problems of the prior art, which reduce the accuracy of dam sediment alluvial calculation, such as simple and rough processing methods, or unreasonable formula structures and inconvenience in use. [Means for solving the problem]

[0004] To achieve the above objectives, the present application provides the following technical solutions:

[0005] The method for calculating the coagulation and settling velocity of dam sediment provided by the embodiment of the present application is as follows: Step 1 is to collect information such as the particle size of the suspended sediment group, the settling rate of the group, the topography of the river channel of the dam, the water and sediment entering the reservoir, and the adjustment method for the dam; Step 2: Develop a mathematical model of one-dimensional unsteady flow of water and sediment in the river channel including the main and tributaries of the dam; Step 3: calculating the average flow velocity and the sand content of suspended sediment of different particle size groups at each cross section along the path in the dam area; Step 4 is to establish a formula for calculating the coagulation and settling rate of dam sediment; The average sand content of the mixed sand is 0.3 kg / m 3 and step 5, for a cross section of the normal backflow area of ​​a dam where the average flow velocity is less than 0.7 m / s, calculating the coagulation and settling velocity of sediment in each particle size group less than 0.02 mm in this cross section based on the established formula for calculating the coagulation and settling velocity of dam sediment.

[0006] In step 2, the constructed model equation is:

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[0007]

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[0008]

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[0009]

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[0010]

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[0011]

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[0012] In the formula, ω is the sediment settling velocity, corner mark i is the cross-section number, Q is the discharge, A is the overflow area, t is time, x is the coordinate along the path, Z is the water level, K is the cross-sectional discharge modulus, S is the sand content, and S * is the sand pinching force of the water flow, ρ' is the dry density of the sediment, B is the width of the cross section, g is the gravitational acceleration, α is the restoration saturation coefficient, and A d is the deposition area of ​​the suspended solids bed, Ω is the water volume at the confluence, U is the flow velocity, and q L and S L are the lateral inflow per unit length of the river reach and its corresponding sand content, respectively.

[0013] In step 4, the calculation formula for the coagulation and settling rate of the dam sediment is:

[0014]

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[0015] It seems like, In the formula, ω L0 and ω Lf are the cohesive settling velocity and cohesive settling velocity of the Lth particle size group, respectively, and are expressed in m / s. L is the particle size of the Lth particle size group, expressed in m. S is the sum of the content of each particle size group with a particle size less than 0.02 mm, expressed in kg / m. 3 β1, β2, and n are undetermined coefficients and exponents. [Effects of the Invention]

[0016] Compared with the prior art, the present invention has the following beneficial effects.

[0017] The present invention can realize more accurate calculation of sediment coagulation and settling velocity, improve the accuracy of dam sediment alluvial calculation, and provide technical support for scientific adjustment of dams. The method of the present invention can also be applied to calculate the sediment coagulation and settling velocity of other large river-type dams. [Brief explanation of the drawings]

[0018] In order to more clearly describe the technical solutions of the embodiments of the present application, the following will briefly describe the drawings required for the embodiments of the present application. It should be understood that the following drawings only illustrate some embodiments of the present application, and should not be considered as limiting the scope, and those skilled in the art can obtain other related drawings based on these drawings without any creative efforts. [Figure 1] FIG. 1 is a method flowchart of an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, the technical solutions in the embodiments of the present application will be described with reference to the drawings in the embodiments of the present application. Similar symbols and characters refer to similar items in the following drawings, so that once an item is defined in one drawing, it does not need to be further defined or explained in the subsequent drawings.

[0020] The terms "comprise," "include," or any other variation thereof, are intended to be non-exclusive inclusive, such that a process, method, article, or apparatus comprising a set of elements includes not only those elements but also other elements not expressly listed or inherent in such process, method, article, or apparatus. Further, in the absence of any limitation, an element defined by the phrase "comprises a ..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0021] Terms such as "first," "second," etc. are used merely to distinguish one entity or operation from another, and cannot be understood as indicating or implying relative importance or as requiring or implying the existence of any actual relationship or order between those entities or operations.

[0022] As shown in Figure 1, the coagulation and settling velocity of dam sediment can be calculated as follows: Step 1 is to collect information such as the particle size of the suspended sediment group, the settling rate of the group, the topography of the river channel of the dam, the water and sediment entering the reservoir, and the adjustment method for the dam; Step 2: Develop a mathematical model of one-dimensional unsteady flow of water and sediment in the river channel including the main and tributaries of the dam; Step 3: calculating the average flow velocity and the sand content of suspended sediment of different particle size groups at each cross section along the path in the dam area; Step 4 is to establish a formula for calculating the coagulation and settling rate of dam sediment; The average sand content of the mixed sand is 0.3 kg / m 3 and step 5, for a cross section of the normal backflow area of ​​a dam where the average flow velocity is less than 0.7 m / s, calculating the coagulation and settling velocity of sediment in each particle size group less than 0.02 mm in this cross section based on the established formula for calculating the coagulation and settling velocity of dam sediment.

[0023] The conditions for establishing the calculation formula for the sedimentation rate proposed in this invention are: 1. The critical particle size of coagulation is determined to be 0.02 mm, and the effect of coagulation is not considered for soil and sand with particle sizes larger than 0.02 mm. 2. The assumption for considering the effect of cohesion is that the average sand content of the cross-sectional mixed sand is 0.3 kg / m 3 It is something bigger, 3. The premise for considering the effect of coagulation is that the cross-sectional average flow velocity is less than 0.7 m / s, and when the cross-sectional average flow velocity is between 0.0 and 0.7 m / s, the degree of sediment coagulation does not change with changes in flow velocity. 4. The area affected by sediment aggregation should be determined within the dam's normal backflow area. 5. The sedimentation rate is inversely proportional to the particle size and directly proportional to the sand content.

[0024] The first embodiment is as follows: To collect information on the particle size of the suspended sediment groupings of the SX Dam, the settling speed of the groupings, the topography of the river channel of the dam, the water and sand entering the reservoir, and the adjustment method for the dam. Step 2: Develop a mathematical model of one-dimensional unsteady water and sediment flow in the river channel including the main and tributaries of the SX Dam; Calculating the average flow velocity and sand content of suspended sediment of different particle size groups at each cross section along the course in the SX dam area; To establish a formula for calculating the coagulation and settling rate of SX Dam sediment, The average sand content of the mixed sand is 0.3 kg / m 3 For the cross section of the normal backflow area of ​​the SX Dam where the average flow velocity is less than 0.7 m / s, calculate the coagulation and settling velocity of sediment of each particle size group less than 0.02 mm in this cross section based on the established formula for calculating the coagulation and settling velocity of dam sediment.

[0025] Table 1 shows the change in alluvial simulation accuracy for SX Dam sediment before and after the calculation of sediment coagulation and settling velocity was improved.

[0026] [Table 1]

[0027] The above is only an embodiment of the present application, and does not limit the scope of protection of the present application. Those skilled in the art can make various modifications to the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application should be included in the scope of protection of the present application.

Claims

1. Step 1 is to collect information such as particle size of suspended sediment group, settling rate of group, topography of river channel of dam, water and sediment entering the reservoir, and adjustment method for dam. Step 2: constructing a mathematical model of one-dimensional unsteady water and sediment flow in the river channel, including the main and tributaries of the dam; Step 3: calculating the average flow velocity and sand content of suspended sediment of different particle size groups at each cross section along the path in the dam area; Step 4: Establishing a formula for calculating the coagulation and settling rate of dam sediment; The average sand content of the mixed sand is 0.3 kg / m 3 and (5) calculating the coagulation and settling velocity of sediment of each particle size group smaller than 0.02 mm in a cross section of a dam where the average flow velocity is larger than 0.02 mm and the average flow velocity is smaller than 0.7 m / s, based on the established formula for calculating the coagulation and settling velocity of dam sediment.

2. In step 2, the constructed model equation is: [Equation 8] and, [Equation 9] and, [Equation 10] and, [0011] and, [0012] and, [0013] and In the formula, ω is the sediment settling velocity, corner mark i is the cross section number, Q is the discharge, A is the overflow area, t is time, x is the coordinate along the path, Z is the water level, K is the cross section discharge modulus, S is the sand content, and S ＊ is the sand pinching force of the water flow, ρ' is the dry density of the sediment, B is the width of the cross section, g is the gravitational acceleration, α is the restoration saturation coefficient, and A ｄ is the deposition area of ​​the suspended solids bed, Ω is the water volume at the confluence, U is the flow velocity, and q L and S L 2. The method for calculating the coagulation and settling velocity of dam sediment according to claim 1, characterized in that ρ and ρ are the lateral inflow volume per unit length of the river section and its corresponding sand content, respectively.

3. In step 4, the calculation formula for the coagulation and settling rate of the dam sediment is: [0014] It seems like, In the formula, ω L0 and ω Lｆ are the cohesive settling velocity and cohesive settling velocity of the Lth particle size group, respectively, and are expressed in m / s. L is the particle size of the Lth particle size group, expressed in m; S is the sum of the sediment content of each particle size group with a particle size less than 0.02 mm, expressed in kg / m 3 β 1 , β 2 2. The method for calculating the coagulation and settling velocity of dam sediment according to claim 1, wherein n is an undetermined coefficient and an exponent.

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