High-speed water flow discharge chute variable slope transition structure and design method

Abstract

The invention discloses a high-speed water flow discharge chute variable slope transition structure and a design method, the high-speed water flow discharge chute variable slope transition structure comprises a smooth gentle slope section, a gentle abrupt slope transition section, a step abrupt slope section and a discharge chute side wall which are sequentially arranged in the water flow direction, and the smooth gentle slope section is located on the upstream side of a discharge chute; the gentle abrupt slope transition section is composed of a preset number of rectangular steps with gradually-changed sizes, the curvature of a fitting curve connected with outer inflection points of the rectangular steps gradually changes according to a water flow streamline track, and the gentle abrupt slope transition section is arranged on the downstream side of the smooth gentle slope section; the step abrupt slope section is arranged on the downstream side of the slow abrupt slope transition section; the discharge chute side walls are symmetrically arranged on the two sides of the discharge chute. Step-by-step layered rectification energy dissipation is achieved, the stability of high-speed water flow connection of the slope changing part of the discharge chute is effectively enhanced, wall separation and bottom plate negative pressure formation of water flow of a bottom plate of the discharge chute are avoided, transition connection of a smooth gentle slope and a step abrupt slope bottom plate is adapted, and the dual purposes of high-speed water flow energy dissipation and flow regime regulation can be achieved; the invention provides a technology and a method for solving the design of a high-speed water flow variable-slope discharge chute connecting body type.

Description

Technical Field

[0001] The invention belongs to the field of flood discharge and energy dissipation facilities of water conservancy and hydropower engineering, and discloses a high-speed water flow discharge chute slope change transition structure and a design method. Background Art

[0002] The spillway is an important water discharge structure of the water conservancy hub, which is used to discharge excess flood water from the reservoir and ensure the safety of the dam and other buildings of the hub. The spillway chute is generally a primary slope to facilitate the discharge of flood water, but in actual projects, it is often encountered that the longitudinal slope changes greatly and the elevation drops sharply. In order to break the limitations of this terrain condition, overcome the concentrated drop, and save engineering work, the design and construction often adopts a variable slope chute. The slope change form is usually from a gentle slope to a steep slope. The junction of the gentle and steep slopes is called the slope change point, and the range before and after the slope change point is called the gentle and steep slope connection section. Specific structures or measures are required to connect them so that the water flow transitions smoothly.

[0003] How to connect the gentle slope with the steep slope is a key link in the variable slope spillway. When the gentle slope is directly connected to the steep slope, an angle is formed at the connection. Due to the sudden change in slope, the mainstream is very likely to separate and fall off the wall at the junction of the gentle and steep slopes, forming a water wing that hits the downstream dam surface, and the main stream is vacant and forms a negative pressure, leading to cavitation damage. If the gentle and steep slopes are connected by curves, the industry generally uses the Woch curve (usually a quadratic parabola), which can make the hydraulic elements at the slope change less change, which is conducive to the stability of the flow state, but the adaptability to different incoming flows is limited, and the design and construction are relatively complex, involving complex algorithms and many empirical parameters, and requiring high construction accuracy. If erosion reduction measures such as aeration sills are used at the slope change, the bottom plate structure can be simplified, but improper design can easily form a cavity behind the sill, affecting the aeration effect, and there is also a risk of water tongue detaching from the bottom plate and causing cavitation. Under high-speed water flow (flow velocity above 20m / s) and large slope change conditions (slope change angle greater than 10°, that is, the angle α between the gentle slope and the steep slope is greater than 10°, generally between 10° and 45°), the hydraulic characteristics of the gentle slope and steep slope change are more complex, and the risks of water flow shedding and cavitation damage are further increased, and the limitations of the existing connection methods are highlighted. How to safely and conveniently connect the gentle slope and steep slope of the chute under high-speed water flow and slope change conditions and simplify traditional design structures and methods have become new difficulties in the field of hydraulic engineering design.

[0004] On the other hand, in addition to the large difference in slope, there are differences in the shape or structure of the gentle slope chute and the steep slope chute, which also increases the complexity of the connection between the two. The water flow in the gentle slope section is stable, and a smooth bottom plate is usually used; the water flow in the steep slope section is high and the flow state is rapid, and steps are usually set on the bottom plate surface to aerate and dissipate energy and slow down the water flow. How to transition from a smooth bottom plate to a stepped bottom plate has also become a key consideration in the design of the chute structure.

[0005] Based on the above two aspects, it is necessary to invent a new type of connection body for safely and conveniently connecting the smooth gentle slope of the chute with the steep slope of the steps under the conditions of high-speed water flow and slope change, and to form a simple and easy design method. Summary of the invention

[0006] Purpose of the invention: To provide a high-speed water flow chute slope transition structure and design method to solve the above-mentioned problems existing in the prior art.

[0007] Technical solution: The high-speed water flow chute has a variable slope transition structure, in which a smooth gentle slope section, a gentle steep slope transition section, a stepped steep slope section and a chute side wall are arranged in sequence along the water flow direction.

[0008] The smooth gentle slope section is located on the upstream side of the chute, and the bottom plate of the smooth gentle slope section is a smooth plane;

[0009] The gentle-steep slope transition section is composed of rectangular steps with predetermined sizes and gradually changing. The curvature of the fitting curve connected by the inflection points outside the rectangular steps gradually changes according to the trajectory of the water flow streamline. The gentle-steep slope transition section is arranged on the downstream side of the smooth gentle slope section, so that the water flow gradually falls in layers and smoothly transitions to the step steep slope section.

[0010] The step steep slope section is arranged on the downstream side of the gentle steep slope transition section, and the bottom plate of the step steep slope section is a continuous step of equal size;

[0011] The chute side walls are symmetrically and vertically arranged on both sides of the chute to guide the water flow.

[0012] The design method of the high-speed water flow chute slope transition structure includes the following steps:

[0013] S0, obtaining the condition parameters of engineering hydraulics, including the structural design parameter data set of the engineering entity, the engineering operation hydraulic characteristic parameter data set and the parameter data set of hydrological topography and geology, and judging whether the condition parameters meet the preset applicable range. If yes, proceed to step S1;

[0014] S1. Obtain the design parameters and hydraulic parameters of each section of the chute in the engineering structure, and estimate the horizontal projection trajectory curve P of the water flow particle at the chute slope change point; the design parameters of each section of the chute include the slope angle θ1 of the smooth gentle slope section, the slope angle θ3 of the step steep slope section, and the step size d of the step steep slope section. s ×h s ;d s is the step length of the steep slope section of the step, h s The step height of the steep slope section of the steps;

[0015] S2. Based on the horizontal projection trajectory curve P of the water flow particle, the gentle slope transition curve S is preliminarily determined;

[0016] S3, based on the gentle-steep slope transition section curve S, determine the connection relationship between the smooth gentle slope section and the first step T1 of the gentle-steep slope transition section, construct the geometric constraint relationship between the smooth gentle slope section, the gentle-steep slope transition section, and the step steep slope section, and obtain the optimized gentle-steep slope transition section curve S and the outer inflection point of the first step T1 of the gentle-steep slope transition section;

[0017] S4, based on the optimized slow-to-steep slope transition section curve S and the outer inflection point of the first step T1 of the slow-to-steep slope transition section, determine the number of steps N of the slow-to-steep slope transition section and the height of each step, and generate a gradual step sequence;

[0018] S5, based on the optimized slow-steep slope transition section curve S, the outer inflection point of the first step T1 of the slow-steep slope transition section, and the gradual step sequence, generating continuous gradual steps within the contour envelope of the optimized slow-steep slope transition section curve S;

[0019] S6. Based on the continuous gradient steps, the connection relationship between the last step of the gentle-steep slope transition section and the first step of the steep slope section is optimized;

[0020] S7. Obtain the bottom plate width of the steep slope section of the step, and determine the step width of the gentle-steep slope transition section and the height of the side walls of the chute on both sides based on the bottom plate width of the steep slope section.

[0021] Beneficial effects: The present invention realizes step-by-step and layered rectification and energy dissipation, can adapt to different hydraulic conditions of incoming flow, effectively improves the water flow state at the junction of the gentle and steep slopes of the spillway, and enhances the stability of the local structure of the spillway where the slope changes; at the same time, it adapts to the connection between the smooth surface and the step surface bottom plate, taking into account the actual needs of the downstream steep slope to use the steps to dissipate energy, and realizes the transition of water flow from the smooth gentle slope bottom plate to the step steep slope bottom plate that is more conducive to energy dissipation, giving full play to the main role of the step steep slope section in energy dissipation, and improving the overall flood discharge capacity and safety margin of the spillway; through modular and formulaic design methods for flexible combination, the problems of complex calculations and difficult determination of empirical coefficients in traditional methods are solved, and the design and construction of the spillway slope change connection body are greatly simplified and improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a diagram of the slope change transition structure of the high-speed water flow chute of the present invention.

[0023] Figure 2 It is a structural diagram of the overall structure A of the present invention.

[0024] Figure 3 It is a flow chart of the present invention.

[0025] Figure 4 This is a flow chart of step S1 of the present invention.

[0026] Figure 5 This is a flow chart of step S2 of the present invention.

[0027] Figure 6 This is a flow chart of step S3 of the present invention.

[0028] Figure 7 This is a flow chart of step S4 of the present invention.

[0029] The accompanying drawings are marked as follows: 1. smooth gentle slope section; 2. gentle-steep slope transition section; 3. step-steep slope section; 4. transition step of the gentle-steep slope transition section; 5. chute side wall; 6. step energy dissipator on the surface of the step-steep slope section. DETAILED DESCRIPTION

[0030] like Figure 1 and Figure 2 As shown, the present application discloses a high-speed water flow chute slope transition structure, including a smooth gentle slope section, a gentle-steep slope transition section, a chute side wall and a stepped steep slope section of the chute, wherein the smooth gentle slope section is located on the upstream side of the chute, the bottom plate is a smooth plane, and the slope is generally less than 5%; the bottom plate is generally arranged with equal width or contraction; the gentle-steep slope transition section is located within a certain range between the smooth gentle slope section and the stepped steep slope section, the length is usually 15~30m, the surface is composed of a predetermined number (usually 5~7 levels) of rectangular steps with gradual or partial gradual changes in size, the outer inflection point envelope of the step is usually a parabola, and its equivalent radius is larger than the equivalent radius of the horizontal projection motion trajectory of the water flow particle at the end of the gentle slope section, and the step is located on the bottom plate. The head of the gentle-steep slope transition section is connected to the end of the smooth gentle slope section, so that the water flow gradually falls in layers and smoothly transitions to the step steep slope section; the bottom plate width is generally equal to the smooth gentle slope section and is arranged with equal width, and can also be further reduced according to the width of the smooth gentle slope end; the step steep slope section is arranged on the downstream side of the gentle-steep slope transition section, and the head end is connected to the end of the gentle-steep slope transition section; the bottom plate of the step steep slope section is a continuous step of equal size, and the bottom plate width is equal to the end of the gentle-steep slope transition section and is arranged with equal width. The slope is generally greater than 30%, and the angle α with the smooth gentle slope is generally between 10° and 45°; the chute side walls are symmetrically and vertically arranged on both sides of the chute to guide the return water flow; the width is the same as the bottom plate, and the height is determined according to the water surface line not exceeding the wall and considering the safety super height. On the one hand, it utilizes the uniformly increasing height difference produced by multiple continuous gradual steps to make the water flow gradually fall in layers, smoothly transitioning from the upstream gentle slope to the downstream chute, avoiding large-scale vertical flow state changes caused by high-speed water flow, such as mainstream wall separation; on the other hand, it generates a low-pressure vortex inside the downstream of the step drop, aggravating the turbulence and energy dissipation of the water flow, so that the water vapor and water flow along the way are fully mixed to form a stable aerated water flow, and the flow rate is reduced accordingly, thereby achieving the purpose of rectifying and dissipating energy and smooth transition of the water flow at the slope change, and ensuring the normal discharge of the water flow; at the same time, in terms of the connection between the bottom plates of different shapes of variable slope chutes, a gradual transition from the smooth bottom plate to the step bottom plate is achieved, which adapts to the current mainstream chute bottom plate layout in the industry and avoids the use of other more complex connection structures at the slope change site.

[0031] Figure 2 The overall structure A in the structure includes a gentle-steep transition section, a set of predetermined gradual steps and side walls of the chute on both sides. The width of the bottom plate of the overall structure A is equal to the width of the upstream and downstream chute it connects to, and the side walls on both sides of the bottom plate are symmetrically distributed; the horizontal length of the overall structure A is generally 10~30m; the plane projection of the steps is a rectangle with equal width and increasing or constant length, and the width is equal to the width of the upstream and downstream sections of the chute; the step length d of the steps is generally 0.5~3m, and the level difference of the ordered series formed by the step length d of each step is generally 0.5~1m; the front elevation projection of the transition steps is a rectangle with equal width and increasing or decreasing height, and the width is equal to the width of the upstream and downstream sections of the chute; the step height h of the steps is 0.3~3m, and the level difference of the ordered series formed by the step height h of each step is generally 0.2~1m; the number of transition steps n is 5~7, and it is better to take an odd number. The curve S of the gentle-steep transition section of the chute is approximately a quadratic parabola, and the curve equation is:

[0032] f(x) = ax 2 + bx + c, where a, b, c are constants and a ≠ 0;

[0033] The equivalent radius of the curve S should be larger than the equivalent radius of the horizontal projection trajectory P of the water flow particle at the end of the smooth gentle slope, that is:

[0034] R S > R P .

[0035] Figure 2 Where Pmax represents the horizontal projection trajectory of the water flow particles when the chute is operating at the highest water level, and Pmin represents the horizontal projection trajectory of the water flow particles when the chute is operating at the lowest water level.

[0036] In the overall structure section A, the first step outer turning point G1 of the gentle and steep slope transition section of the chute overlaps with the end point of the smooth gentle slope section of the chute or is on the gentle slope line; the end point of A generally overlaps with the starting point of the steep slope section of the chute step. The number of steps, step length and step height of the transition section gradual change steps described in this embodiment can be comprehensively considered in combination with the chute slope change position where the gentle and steep slope connection structure is required, the topographic and geological conditions at the slope change location, the slope ratio of the chute bottom plate upstream and downstream of the gradual change section, etc., so as to simplify the design and reduce the construction or reconstruction cost.

[0037] This embodiment uses a flexible design of a continuous sequence of gradual steps to connect the gentle and steep slopes. The predetermined steps produce a gradually increasing drop, so that the incoming flow under different conditions can fall step by step, and smoothly transition from the water tongue flow with a smaller slope angle to the relatively stable slip flow state, avoiding the large-scale vertical flow state changes caused by high-speed water flow, thereby improving the transition flow state of the water flow, adjusting the flow velocity distribution, and avoiding the separation of the gentle and steep slope water flow, local impact or formation of water wings. The bottom plate of the gradual step structure is evenly pressurized, avoiding low-pressure turbulence and negative pressure on the bottom plate causing cavitation. When the water flows down through the step drop of the gentle and steep slope transition section, a low-pressure vortex is generated at the inner corner of the step, aggravating the turbulence of the water flow. The water vapor and water flow along the way are fully mixed to form a stable aerated water flow, thereby reducing the flow velocity; the local energy dissipation rate of the gradual step transition section can reach 20% of the overall energy dissipation rate of the chute, effectively enhancing the rectification effect and local stability of the slope change part of the chute. Through the "smooth gentle slope + transition section + stepped steep slope" bottom plate structure, the water in the spillway can smoothly transition from the gentle slope smooth bottom plate to the steep slope stepped bottom plate, which is conducive to the downward discharge of high-speed water and energy dissipation, and improves the overall flood discharge safety of the spillway.

[0038] The "smooth gentle slope + transition section + stepped steep slope" chute bottom plate structure of this embodiment has a preset regular gradual step transition section between the smooth gentle slope bottom plate of the chute and the steep slope stepped bottom plate, which effectively connects the two bottom plate shapes. The steps increase the surface roughness of the bottom plate, and the steps play a role in hindering the water flow, so that the downstream water flow forms a horizontal axis rotation between the steps and is strongly mixed with the mainstream of the dam surface, forcing the water flow to be mixed with a large amount of air and produce strong turbulence to achieve the energy dissipation effect. Compared with the smooth bottom plate, its notable features are large friction resistance on the overflow surface, high air entrainment, and thus high energy dissipation rate. Furthermore, when the water flow transitions to the stepped steep slope section through the transition section, the step energy dissipators along the steep slope can be fully utilized for energy dissipation, which can greatly shorten the size of the energy dissipators required downstream of the chute and reduce engineering investment.

[0039] For the gradual step sequence of the gentle and steep slope transition section of the chute, the size design and arrangement can be carried out according to a certain design method. Through flexible design, the rectification and energy dissipation of the water flow in the chute slope change part can be achieved, and its engineering economic advantages can be brought into play. Figure 3 As shown, a design method for a high-speed water flow chute slope transition structure is further proposed, and the specific steps are as follows:

[0040] S0, obtaining the condition parameters of engineering hydraulics, including the structural design parameter data set of the engineering entity, the engineering operation hydraulic characteristic parameter data set and the parameter data set of hydrological topography and geology, and judging whether the condition parameters meet the preset applicable range. If yes, proceed to step S1;

[0041] S1. Obtain the design parameters and hydraulic parameters of each section of the chute in the engineering structure, and estimate the horizontal projection trajectory curve P of the water flow particle at the chute slope change point; the design parameters of each section of the chute include the slope angle θ1 of the smooth gentle slope section, the slope angle θ3 of the step steep slope section, and the step size d of the step steep slope section. s ×h s ;d s is the step length of the steep slope section of the step, h s The step height of the steep slope section of the steps;

[0042] S2. Based on the horizontal projection trajectory curve P of the water flow particle, the gentle slope transition curve S is preliminarily determined;

[0043] S3, based on the gentle-steep slope transition section curve S, determine the connection relationship between the smooth gentle slope section and the first step T1 of the gentle-steep slope transition section, construct the geometric constraint relationship between the smooth gentle slope section, the gentle-steep slope transition section, and the step steep slope section, and obtain the optimized gentle-steep slope transition section curve S and the outer inflection point of the first step T1 of the gentle-steep slope transition section;

[0044] S4, based on the optimized slow-to-steep slope transition section curve S and the outer inflection point of the first step T1 of the slow-to-steep slope transition section, determine the number of steps N of the slow-to-steep slope transition section and the height of each step, and generate a gradual step sequence;

[0045] S5, based on the optimized slow-steep slope transition section curve S, the outer inflection point of the first step T1 of the slow-steep slope transition section, and the gradual step sequence, generating continuous gradual steps within the contour envelope of the optimized slow-steep slope transition section curve S;

[0046] S6. Based on the continuous gradient steps, the connection relationship between the last step of the gentle-steep slope transition section and the first step of the steep slope section is optimized;

[0047] S7. Obtain the bottom plate width of the steep slope section of the step, and determine the step width of the gentle-steep slope transition section and the height of the side walls of the chute on both sides based on the bottom plate width of the steep slope section.

[0048] In this embodiment, the structural design parameter data set of the engineering entity (such as the slope ratio of the gentle slope of the chute, the slope ratio of the steep slope; the shape of the gentle slope and steep slope bottom plate of the chute, such as smooth surface and step surface; the width of the chute), the engineering operation hydraulic characteristic parameter data set (operating condition data, discharge volume of each operating condition, average flow velocity along the chute of each operating condition) and the hydrological topographic geological parameter data set (rainfall and flood data, rock stratum lithology data, terrain distribution, etc.) are obtained to determine whether the applicable conditions of this design method are met. The system mainly determines whether it meets the preset applicable scope through conditional judgment statements based on the two parameter sets of structural design parameters and engineering operation hydraulic characteristics. The hydrological topographic geological parameters can be separately defined to be included in the judgment conditions. If yes, enter step S1.

[0049] The specific judgment conditions are: if the project has a chute, and the chute has a slope change, and the gentle slope is less than 5%, the steep slope is greater than 30%, the intersection angle α of the gentle and steep slopes is between 10° and 45°, and the gentle slope section is a smooth surface, the steep slope section is a step surface, and the average flow velocity of the water flow at the end of the gentle slope is 20m / s.

[0050] This embodiment is flexibly combined through modular and formulaic design methods to adapt to different water levels, flow rates and even negative pressure conditions, and its adaptability is better than the parabola or sudden expansion and sudden drop used in the traditional gentle and steep slope connection. In addition, it also has the advantages of simple shape, low construction difficulty, convenient maintenance and low investment, which is a fundamental improvement over the traditional gentle and steep slope connection shape.

[0051] like Figure 4 As shown, according to one aspect of the present application, step S1 is further:

[0052] S11, obtaining the design parameters and hydraulic parameters of each section of the spillway in the engineering structure, and estimating the water flow velocity at the end point D1 of the smooth gentle slope section;

[0053] S12. Based on the water flow velocity and hydraulic parameters at the end point D1 of the smooth gentle slope section, according to the parabola equation, determine the horizontal projection trajectory curve P of the water flow particle at the chute slope change point.

[0054] In one embodiment of the present application, the reading parameters include: the slope angle θ1 of the smooth surface of the chute, the width B of the transition section from the gentle slope to the steep slope, the slope angle θ3 of the step steep slope, and the step size d of the steep slope. s ×h s (Step length × step height). The specific method is: after obtaining the physical parameters, estimate the water velocity V0 at the end point D1 of the smooth gentle slope section according to the slope angle θ1 of the smooth gentle slope and the upstream flow conditions (flow rate Q, water depth h); assume that the water particle performs a horizontal projection motion at this exit velocity, and the trajectory is approximately a quadratic parabola. According to the parabola equation, substitute the initial water velocity V0, water flow direction and water depth h, and use the preset end point D1 of the smooth gentle slope section as the starting position of the water particle. Considering the relationship between the end of the parabola and the steep slope angle θ3 of the step, the horizontal projection motion trajectory curve P of the water particle is obtained, and the curve equation of the quadratic parabola is estimated. In general, the curve equation can be expressed as:

[0055] f(x) = ax 2 + bx + c, where a, b, c are constants and a ≠ 0.

[0056] like Figure 5 As shown, according to one aspect of the present application, step S2 is further:

[0057] S21, based on the horizontal projection trajectory curve P of the water flow particle, preliminarily determine the gentle-steep slope transition curve S;

[0058] S22, judging whether the equivalent radius of the initially determined gentle-steep slope transition section curve S is greater than the equivalent radius of the water flow particle horizontal projection motion trajectory curve P, if yes, no adjustment is made; otherwise, the initially determined gentle-steep slope transition section curve S is adjusted to obtain the initially adjusted gentle-steep slope transition section curve S;

[0059] S23. Record the plane trajectory and geometric parameters of the gentle-steep slope transition section curve S after preliminary adjustment, including the equation of the gentle-steep slope transition section curve S, the starting point coordinates D1 and the end point coordinates D2 of the gentle-steep slope transition section, the horizontal length L and the vertical height difference H of the gentle-steep slope transition section, and the horizontal angle θ2 between the connecting line of the starting point and the end point of the gentle-steep slope transition section and the horizontal line.

[0060] In one embodiment of the present application, for the initially formed gradient curve S, the specific adjustment iterative method is: 1. Appropriately fine-tune the equivalent radius of the gentle-steep slope transition curve; 2. Appropriately move the starting point of the gradient curve up or down along the smooth gentle slope bottom plate; 3. Appropriately translate or rotate the end point of the gradient curve, and then translate or scale the step steep slope as a whole, optimize the connection between the two, and minimize the misalignment between the end of the gradient and the beginning of the step steep slope.

[0061] In another embodiment of the present application, the connection relationship between the smooth gentle slope and the first step T1 of the gentle-steep slope transition section is determined, and the geometric constraint relationship between the smooth gentle slope, the gentle-steep slope transition section, and the step steep slope is constructed. Specifically, according to the principle that the starting point of the gentle-steep slope transition section curve S should be tangent to the smooth gentle slope, and the end point should be tangent to the step steep slope (Note: the end point of the curve S should be tangent to the step steep slope means: at the end point D2 of the gradient curve S, it is tangent to the line connecting the outer inflection points of each step of the step steep slope section; or the angle between the tangent at this point and the horizontal direction is slightly greater than the steep slope angle θ3), the position of the end point of the smooth gentle slope and the starting point of the step steep slope are appropriately adjusted. Specifically, a certain segment of the chute can be stretched and retracted on the same side along the original slope direction. An example is: when the inlet and outlet positions of the chute are fixed, the smooth gentle slope is compressed upstream along its own slope, and the step steep slope is stretched upstream along its own slope, and the position variables of the two compensate each other. Optimize the connection between the smooth gentle slope, the gentle-steep slope transition section, and the step steep slope, and obtain the optimized gentle-steep slope transition section curve S, length L (horizontally) and drop H (vertically), starting point D1, and end point D2. Generally, the end point of the smooth gentle slope is preferably used as the starting point D1 of the gentle-steep slope transition section, and also as the outer inflection point G1 of the first step T1.

[0062] like Figure 6 As shown, according to one aspect of the present application, step S4 is further:

[0063] S41, based on the optimized gentle-steep slope transition section curve S and the outer inflection point of the first step T1 of the gentle-steep slope transition section, calculate the parameters of the first step of the gentle-steep slope transition section, including the slope angle, step height and step length of the first step;

[0064] The slope angle of the first step is:

[0065] θ T1 =θ2+Δθorθ T1 =θ2-Δθ;

[0066] Where Δθ is the preset step slope angle difference;

[0067] The step height of the first step is:

[0068] h s / 7≤h1≤h s / 5;

[0069] The step length of the first step is:

[0070] d f1 = h1 / θ T1 ;

[0071] S42, based on the vertical drop H of the gentle-steep slope transition section and the step height h of the step steep slope section s , according to the formula N≈H / h s Estimate the number of steps N in the transition section between the gentle and steep slopes; based on the parameters of the first step in the transition section between the gentle and steep slopes, calculate the number of steps N according to the formula (h1+h s )*N / 2≥H limits the estimated number of steps N of the gentle-steep slope transition section to determine the number of steps N of the gentle-steep slope transition section, where N is an odd number;

[0072] S43, generating a gradual step sequence based on the number of steps N of the gentle-to-steep slope transition section and the step height of the first step of the gentle-to-steep slope transition section.

[0073] In one embodiment of the present application, the number of steps in the gentle-steep slope transition section is N≈H / h. s Calculate and round up, usually 5 to 7 steps. The height of the first step T1 is generally set to 0.2m~0.5m, and the height of the last step Tn is in principle consistent with the height of the steep slope section of the step, that is, hs. The height of each step in the sequence is between the height of the first and last steps, forming a gradual series or a partial gradual series [h1, h2, h3...h s ], the step height is usually between 0.5~3m.

[0074] For the first step, the height can generally be set to 0.2m~0.5m. Furthermore, the parameters of the first step can be calculated based on the turning point position of the first step and the overall parameters of the gentle slope transition section, including the slope angle, step height and step length of the first step;

[0075] The slope angle of the first step is:

[0076] θ T1 =θ2+Δθorθ T1 =θ2-Δθ;

[0077] Where Δθ is the preset step slope angle difference, which can generally be 2 to 5° (if the difference needs to be adjusted, it can also be 0° as appropriate);

[0078] The step height of the first step is generally:

[0079] h s / 7≤h1≤h s / 5, the accuracy is kept to 0.1m, generally 0.2~0.5m;

[0080] The length of the first step is generally:

[0081] d f1 = h1 / θ T1 , the accuracy is kept at 0.1m, and generally 0.5~2m;

[0082] Furthermore, for the determined first step height, the value of the step number can be verified in combination with the gradient section parameters. Specifically, according to the formula (h1+ h s )*N / 2≥H, calculate the minimum value of N and round it up to the nearest integer, which is used as the number of steps in the transition section from gentle to steep slope; N is an odd number.

[0083] like Figure 7 As shown, according to one aspect of the present application, step S5 is further:

[0084] S51, based on the outer inflection point of the first step T1 of the gentle-steep transition section and the step height of the first step of the gentle-steep transition section in the gradual step sequence, determine the inner inflection point of the first step T1; based on the inner inflection point of the first step T1 and the optimized gentle-steep transition section curve S, determine the outer inflection point of the second step T2 of the gentle-steep transition section;

[0085] S52, repeating step S51 until the inner turning point of the last step of the gentle-steep slope transition section is connected to or overlaps with the first step of the steep slope section, obtaining the arrangement of all steps in the gentle-steep slope transition section and obtaining continuous gradual steps.

[0086] In one embodiment of the present application, based on the outer turning point G1 and the step height h1 of the first step T1, an inner turning point G1' is made vertically downward, and a horizontal line is drawn from the inner turning point G1' to the downstream side, which intersects with the gentle steep slope transition section curve S to obtain the outer turning point G2 of the second step T2. Based on the outer turning point G2 of the second step T2 and the step height h2 of the second step, an inner turning point G2' is made vertically downward, and a horizontal line is drawn from the inner turning point G2' to the downstream side, which intersects with the gentle steep slope transition section curve S to obtain the outer turning point G3 of the third step T3. By analogy, based on the height and outer turning point of the next step, an inner turning point is first made vertically downward, and a horizontal line is drawn to the downstream side to intersect with the gradient section curve S to obtain the outer turning point of the next step, until it connects or overlaps with the first step of the steep slope section, at which time the arrangement of all steps in the gentle steep slope transition section is obtained.

[0087] According to one aspect of the present application, step S6 is further:

[0088] S61, determine whether the inner turning point of the last step of the gentle-steep slope transition section coincides with the starting point of the first step of the steep slope section, if so, no adjustment is made; otherwise, proceed to step S62;

[0089] S62, fixing the starting point of the gentle-steep slope transition section, and performing plane scaling on the gentle-steep slope transition section until the inner turning point of the last step of the gentle-steep slope transition section coincides with the starting point of the first step of the step steep slope section;

[0090] S63, judging whether the step size of the steep slope section and the last step size of the gentle-steep slope transition section are consistent, if they are consistent, no adjustment is made; otherwise, proceeding to step S64;

[0091] S64, when the step length of the last step of the gentle-steep slope transition section is smaller than the step length of the step of the steep slope section, a compensation method is adopted to add the step length difference Δd' to the step length of the first n-1 steps of the gentle-steep slope transition section;

[0092] When the step length of the last step of the gentle-steep transition section is greater than the step length of the step of the steep slope section, the remainder method is adopted, and the step lengths of the first n-1 steps of the gentle-steep transition section are all reduced by the average step length difference Δd';

[0093] When the step height of the last step of the gentle-steep transition section is smaller than the step height of the step of the steep slope section, the compensation method is adopted to add the step height of the first n-1 steps of the gentle-steep transition section to the average step height difference Δh';

[0094] When the step height of the last step of the gentle-steep transition section is greater than the step height of the step of the steep slope section, the remainder method is adopted, and the step heights of the first n-1 steps of the gentle-steep transition section are all reduced by the average step height difference Δh';

[0095] Average step length difference Δd'=(∑ i=1 n di -d s ) / N; average step height difference Δh'=(∑ i=1 n h i -h s ) / N, where n∈N, d i represents the step length of the i-th step in the transition section from gentle to steep slope, h i It represents the step height of the i-th step in the transition section of the gentle slope to the steep slope.

[0096] In one embodiment of the present application, based on the sequence and arrangement of the steps in the gentle-steep slope transition section obtained in step S5, according to the possible connection between the last step Tn of the gentle-steep slope transition section and the first step of the steep slope, iteration can be performed from two aspects: relative position relationship and relative size relationship, wherein:

[0097] The relative position relationship between the two can be divided into three situations: ① Tn inner inflection point G n 'coincides with the starting point of the first step of the steep slope; ②Tn inner turning point G n 'Located upstream of the starting point of the first step on the steep slope of the step; ③Tn inner turning point G n 'Located downstream of the starting point of the first step of the steep slope. No adjustment is required in the first case; in the second and third cases, the starting point of the gentle-steep slope transition section is fixed according to the relative position relationship between the two, and the entire section is scaled in the plane until the adjusted gentle-steep slope transition section is more coherent and smoother with the steep slope of the step, and the scaling factor z of this iteration is recorded.

[0098] The relative size relationship between the two can be divided into three cases: ①Tn size is equal to the step size of the steep slope; ②Tn size is smaller than the step size of the steep slope; ③Tn size is larger than the step size of the steep slope. According to the size relationship between the two, the first case does not need to be adjusted; in the second and third cases, the total step length difference Δd and the total step height difference Δh of the step are calculated, and the average value of the step length difference Δd' and the average value of the step height difference Δh' are calculated, and then the difference is evenly divided into the n steps T1~Tn determined in S5 according to the principle of first subtraction and then addition, and the size of each step is evenly added and subtracted iteratively, and the overall structure is adjusted to be more coherent and smooth, and the final step sequence size after adjustment is recorded. The uniformity test principle is used to determine whether all steps have been adjusted. The test principle is that the outer turning point of each step is basically located on the curve of the transition section of the gentle and steep slope or slightly converges to the inside of the curve contour.

[0099] Furthermore, the specific method for calculating the total difference and average value of the step length and step height is as follows:

[0100] (1) Total step length difference of the transition section between gentle and steep slopes: Δd=∑ i=1 n (d i -d s) ; the average value of the step length difference in the gentle and steep slope transition section: Δd'=Δd / n;

[0101] (2) Total step height difference of the transition section between gentle and steep slopes: Δh=∑ i=1 n (h i -h s ); The average value of the step height difference in the transition section of the gentle slope to the steep slope: Δh'=Δh / n.

[0102] If the connection between the last step of the gradual transition section obtained in step S5 and the first step of the steep slope of the step is difficult and cannot be improved by the above method, the starting point D1 and the end point D2 of the slow-steep slope transition section curve S can also be repeatedly adjusted. Further, the method for adjusting the starting point is: on the smooth gentle slope of the chute, move the starting point up or down along the bottom plate, and the single moving distance is not greater than 1 times ds×tanθ1; the method for adjusting the end point is: scale the length and equivalent radius of the slow-steep slope transition section curve S, so as to change the position of the end point on the steep slope of the step, and the single moving distance is not greater than 1 times ds×tanθ3; at this time, the steep slope section needs to be compressed as a whole along the slope angle θ3, so that the new gradual transition section curve S is as tangent to the slope line of the steep slope of the step as possible (or the angle between the tangent and the horizontal direction is slightly greater than the steep slope angle θ3). The adjustment principle is consistent with the principle of determining the geometric relationship in step 3, the difference is that the single adjustment amplitude changes from large to small, and the displacement amplitude is controlled to be between the interval (ds×tanθ1, ds×tanθ3).

[0103] According to one aspect of the present application, step S7 is further:

[0104] S71, obtaining the bottom plate width of the steep slope section of the step, and setting the step width of the gentle-steep slope transition section to the bottom plate width of the steep slope section of the step;

[0105] S72. Based on the bottom plate width of the steep slope section of the steps and the conventional hydraulic design requirements of the spillway specifications, determine the height of the side walls of the spillways on both sides.

[0106] In one embodiment of the present application, the bottom plate width of the smooth gentle slope of the chute is obtained, and the bottom plate width of the gradient section is generally equal to the gentle slope section, and can also be further reduced according to the width of the end of the gentle slope section. The step width of the gentle-steep slope gradient section is consistent with the bottom plate width. The bottom plate width of the head of the step-steep slope of the chute is obtained to check whether it is equal to the width of the bottom plate at the end of the gradient section; if not equal, it is arranged according to the principle that the bottom plate width of the step-steep slope is equal to the width of the end of the gentle-steep slope transition section. The side walls on both sides of the chute are arranged in a plane symmetrical and vertical manner, and the lateral width between the side walls is consistent with the bottom plate width. According to the conventional hydraulic design requirements of the spillway specification, the height of the side walls is determined based on the water surface line not exceeding the wall and considering the safety superelevation.

[0107] According to another aspect of the present application, it also includes:

[0108] S81. Based on the determined transition section of the gentle slope to the steep slope, a hydraulic model of 1:25~1:40 is constructed according to the gravity similarity criterion, and a hydraulic model test is carried out;

[0109] S82. Based on the results of the hydraulic model test, further adjustments are made to the determined gentle slope to steep slope transition section. If necessary, the parameters of the smooth gentle slope section and the stepped steep slope section can also be fine-tuned appropriately.

[0110] In one embodiment of the present application, the rationality of the hydraulic design of the gentle and steep slope transition section is verified according to the model test, which specifically includes: based on the determined gentle and steep slope transition section, an overall hydraulic model test is made of plexiglass, the model geometry scale is generally 1:25~1:40, and the "Hydraulic (Conventional) Model Test Regulations" (SL 155-2012) is followed and designed according to the gravity similarity criterion. The test groups cover typical flood conditions such as normal water storage level, energy dissipation and anti-scouring water level and verification water level, observe the flow state of each section along the chute under different water levels and discharges, identify whether there are water wings, negative pressure and other adverse phenomena in the gentle and steep slope transition section, measure the flow velocity, water depth, pressure and other hydraulic indicators of this part and the downstream step dam surface, calculate whether the cavitation number is greater than 0.3, and judge whether there is a risk of cavitation and other hydraulic problems at this place. If there is a problem, the chute plan is corrected, the single recommended correction range of each parameter is read, and the step size, layout and new parameter set formed after iteration are stored. Specifically, according to the model test results, if there are hydraulic problems in the chute under the current scheme, steps S2 to S7 can be repeated to make targeted adjustments to the first and last step positions, step size, number of steps and permutations of the gentle and steep slope transition section, and the adjustment range is automatically controlled by the system preset value. Among them, for the starting position of the outer turning point of the step, the single horizontal displacement should not exceed 0.5m; the single change of the number of steps should be controlled within ±1; the single adjustment range of the step height or step length should be controlled within 0.1~0.3m. After optimization and iterative verification, the final plan for the chute bottom plate is determined.

[0111] Furthermore, additional energy dissipators are designed on the surface of the steps in the gentle-steep transition section. For the gentle-steep transition section, the gradual step sequence of the gentle-steep transition section is determined through the above steps. Furthermore, additional energy dissipators coordinated with the step size can be added to the surface of each step as needed to enhance the rectification and energy dissipation effect and increase the adaptability of the structure to different incoming flow conditions. Specifically, it includes setting a square or trapezoidal step at the outer turning point of the step; setting a small inner step at the inner turning point of the step; adding a 2°~3° angle to the first few steps, generally on the first step. Local changes in this structure should also be regarded as the scope of the present invention.

[0112] This embodiment is flexibly combined through modular and formulaic design methods to adapt to different water levels, flow rates and even negative pressure conditions (the step bottom plate is highly adaptable, easy to maintain and low in cost, so it can be considered to withstand a certain negative pressure in design). The adaptability of the gradual step transition section is better than the smooth arc curve bottom plate used in the slope change part of the traditional chute, and can also be used to connect the step dam surface of the downstream steep slope section, which can further improve the overall flood discharge and energy dissipation effect of the chute. In addition, the chute structure described in this embodiment also has the advantages of simple shape, low construction difficulty, easy maintenance and low investment, and is fundamentally simplified and improved compared to the traditional variable slope chute.

[0113] This application aims at the situation that under the condition of high-speed water flow changing slope, the flow state transition of the water flow in the chute changing slope part is not good, which affects the flow state of the steep slope discharge and the overall flood discharge and energy dissipation or causes other hydraulic problems. A high-speed water flow chute changing slope transition structure and design method are provided. Its hydraulic principle is: through the gradual change of steps, the energy is dissipated by layered rectification, the separation and lifting of the outgoing water flow at the slope change interface is eliminated, the water flow transition flow state is improved, and the negative pressure formed on the chute bottom plate leads to cavitation and water wings hitting the downstream dam surface. It is beneficial to enhance the local stability of the chute changing slope part; at the same time, the structure realizes a gradual transition from the smooth bottom plate to the step bottom plate, effectively controls the amplitude variation and flow stability of the hydraulic elements along the way, and makes the water flow transition from the smooth bottom plate of the gentle slope section to the step bottom plate of the steep slope section that is more conducive to energy dissipation, further improving the overall energy dissipation effect of the chute. The structure and design method can simplify the design and construction of the traditional chute changing slope connection body.

[0114] In another embodiment, a design method for a high-speed water flow chute slope transition structure includes:

[0115] S1. Automatically determine whether the pre-input engineering hydraulic condition factor parameters meet the applicable scope of this design method; if yes, input relevant design parameters;

[0116] S2. Construct the bottom plate curve of the gentle-steep slope connecting section based on the parabolic motion trajectory of the water flow particle, determine the relative relationship between the bottom plate curve trajectory, the starting point and the end point, and obtain the relevant geometric parameters of the gentle-steep slope connecting section;

[0117] S3, constructing the geometric constraint relationship between the first step of the gentle-steep slope connecting section, the gentle slope section, and the connecting section, and determining the position of the outer turning point of the first step;

[0118] S4. Design the size and parameter values ​​of the first step. Determine the slope ratio of the first step based on the slope angle of the connecting section of the gentle slope and steep slope, convert the step height of the first step according to the step height of the steep slope section, and calculate the step length of the first step according to the slope ratio formula;

[0119] S5. Overall design of the gradual steps in the connection section of the gentle and steep slope. Pre-extract three schemes of step number: n, n-1, and n+1. Determine the size of the middle step based on the average size. Design the size of the front and rear steps according to the mirror principle of "front subtraction and back addition". Fine-tune the steps that do not meet the requirements through "even adjustment test";

[0120] S6. Correction of the size of the last step in the gentle-steep slope connecting section. Determine the relationship between the step height and step length of the last step and the step height and step length of the steep slope section, and use the difference compensation method or the remainder elimination method to make corrections;

[0121] S7. Plan layout of the connection section of the gentle and steep slope and the design of the side walls on both sides. The width of the step in the connection section is always consistent with the width of the chute. The side walls on both sides of the chute are arranged symmetrically and straightly. The height of the side walls should meet the conventional hydraulic design requirements of the spillway specification.

[0122] S8. Carry out physical model tests to demonstrate the rationality of hydraulic design of the gentle-steep slope connection section;

[0123] S9, the design of the gentle-steep slope connecting section is modified, the single modification range of each parameter is read, the step size and arrangement combination are iterated, a new design parameter set is formed and stored.

[0124] In another embodiment of the present application, a pumped storage power station has an installed capacity of 1200MW. The lower reservoir is located in the downstream section of the first-level tributary. The main buildings include a dam, an open spillway on the bank, and a flood discharge and emptying hole. The dam adopts a concrete panel rockfill dam with a maximum dam height of 93.0m. The spillway is excavated from the left bank hillside, with a side weir, a weir width of 55m, a total length of 541.95m, a weir top elevation of 492.00m, and an overflow weir weir surface curve of WES type; the chute is 16.5m wide, with a gentle slope ratio of 5%, a steep slope ratio of 40%, and a nose sill at the end of the chute. The discharge hole of the lower reservoir is rebuilt from the diversion hole on the right bank, and the total length of the discharge hole is 854.12m. The dam and flood discharge facilities of the lower reservoir are designed according to a flood that occurs once in 200 years and are verified according to a flood that occurs once in 2000 years. The flood design standard of the energy dissipation and anti-scouring buildings of the lower reservoir is designed according to a flood that occurs once in 100 years.

[0125] In this embodiment, the slope ratio i1 of the upstream side of the gentle-steep-slope transition section connected to the gentle slope section of the chute is 5%, the slope angle θ1 is 3°, and the bottom plate is a smooth surface; the slope ratio i3 of the downstream side connected to the steep slope section of the chute is 40%, the slope angle θ3 is 22°, the bottom plate is a step surface, and the angle α between the two slopes is 19°; the bottom plate width of each section of the spillway chute is 16.5m; step energy dissipators are arranged along the steep slope section of the chute, and the single-step height h s is 1.0m, step length d sThe flow rate of a typical flood spillway is 0~67m² / s, of which the energy dissipation and anti-scouring condition is 42m² / s. Under typical working conditions (verification, design, energy dissipation and anti-scouring), the average flow velocity of the smooth gentle slope section of the spillway is about 15m / s, and the average flow velocity at the end of the step steep slope section is about 16~22m / s. The overall structure A consists of a gradual transition step and symmetrically arranged side walls on both sides. The designed bottom plate curve S of the gentle and steep slope transition section is an arc curve with an equivalent radius of 70m, which is larger than the equivalent radius of the calculated horizontal projection trajectory curve P of the water flow particle; the envelope of the step outer inflection point of the gentle and steep slope transition section is tangent to the smooth gentle slope section at the end of the gentle slope D1, and tangent to the step steep slope section at the starting point of the steep slope D2. The total horizontal length of this section is L=22.3m, the total drop is H=4.9m and the slope angle θ2=12°. The slope angle of the first step is 9°, and the outer turning point of the first step is located 1 times d upstream of the end point of the gentle slope D1. s In this case, d s =2.5m), which meets the requirements of this design method. There are 5 continuous gradual steps in the transition section of the gentle slope to the steep slope, of which the heights of the first 4 steps are 0.4m, 0.6m, 0.8m, and 1.0m in arithmetic progression, with a step difference of 0.2m, and the height of the last step is 1.0m; the length of each step is between 2.4 and 2.8m. The size of the last step in the transition section of the gentle slope to the steep slope is 2.5m×1m, and the size of the step energy dissipator in the steep slope section is 2.5m×1m. The two sizes are consistent, which meets the requirements of this design method, and no further size iteration correction is required.

[0126] The model test results show that the step spillway in this embodiment has a good flow transition at the junction of the gentle and steep slopes of the chute. The outflow at the end of the gentle slope does not break away from the bottom plate of the steep slope head. There is no negative pressure and cavitation. The main flow falls layer by layer along the steps, and a vortex is formed inside the steps. The steps are fully aerated, and the flow pattern of the steep slope section of the chute is stable. At the junction of the end of the steep slope of the chute and the nose of the flow, there is no water lifting or bottoming phenomenon after the last step. The flow transition is smooth and there is no cavitation phenomenon. The water flows through the nose of the flow and returns to the chute smoothly.

[0127] The present application utilizes a step-by-step gradually changing step surface, which can effectively improve the uneven water flow transition and water wing phenomenon caused by the connection structure designed according to the traditional design method at the slope changing part of the chute under the condition of high-speed water flow slope changing, eliminate the separation and lifting of the outgoing water flow at the slope changing boundary, avoid the cavitation of the bottom plate, the water wing hitting the downstream dam surface and other problems, which is conducive to enhancing the local stability of the slope changing part; at the same time, the structure realizes the gradual transition of the chute from the smooth bottom plate to the step bottom plate, effectively controls the amplitude variation and flow stability of the hydraulic elements along the way, and makes the water flow smoothly transition from the smooth gentle slope to the step steep slope that is more conducive to energy dissipation, thereby improving the energy dissipation rate of the downstream dam surface, thereby improving the overall energy dissipation effect of the chute. The present application is suitable for high-speed water flow and slope changing chutes with a gentle and steep slope with a slope changing angle between 10° and 45°. The design method of the present application is flexible and convenient, and the process is easy to repeat, which can meet the needs of the hydraulic engineering design field.

[0128] The preferred embodiments of the present invention are described in detail above; however, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various equivalent transformations can be made to the technical solutions of the present invention, and these equivalent transformations all belong to the protection scope of the present invention.

Claims

1. High-speed water flow chute slope transition structure, characterized in that: Along the water flow direction, the smooth gentle slope section, the gentle steep slope transition section, the stepped steep slope section and the side wall of the chute are arranged in sequence. The smooth gentle slope section is located on the upstream side of the chute, and the bottom plate of the smooth gentle slope section is a smooth plane; The gentle-steep slope transition section is composed of rectangular steps with predetermined sizes and gradually changing. The curvature of the fitting curve connected by the inflection points outside the rectangular steps gradually changes according to the trajectory of the water flow streamline. The gentle-steep slope transition section is arranged on the downstream side of the smooth gentle slope section, so that the water flow gradually falls in layers and smoothly transitions to the step steep slope section. The step steep slope section is arranged on the downstream side of the gentle steep slope transition section, and the bottom plate of the step steep slope section is a continuous step of equal size; The chute side walls are symmetrically and vertically arranged on both sides of the chute to guide the water flow.

2. The high-speed water flow chute slope change transition structure according to claim 1 is characterized in that: The bottom plate of the smooth gentle slope section is arranged with equal width or in a contracted arrangement, and the slope of the smooth gentle slope section is less than 5%; the bottom plate of the gentle-steep slope transition section is arranged with equal width to the bottom plate of the smooth gentle slope section, or is contracted according to the width of the bottom plate end of the smooth gentle slope section; the bottom plate of the step steep slope section is arranged with equal width to the bottom plate of the gentle-steep slope transition section, and the slope of the step steep slope section is greater than 30%, and the angle α between the step steep slope section and the smooth gentle slope section is between 10° and 45°.

3. The design method of the high-speed water flow chute slope transition structure according to claim 1 or 2 is characterized in that: The steps include: S0, obtaining the condition parameters of engineering hydraulics, including the structural design parameter data set of the engineering entity, the engineering operation hydraulic characteristic parameter data set and the parameter data set of hydrological topography and geology, and judging whether the condition parameters meet the preset applicable range. If yes, proceed to step S1; S1. Obtain the design parameters and hydraulic parameters of each section of the chute in the engineering structure, and estimate the horizontal projection trajectory curve P of the water flow particle at the chute slope change point; the design parameters of each section of the chute include the slope angle θ1 of the smooth gentle slope section, the slope angle θ3 of the step steep slope section, and the step size d of the step steep slope section. s ×h s ;d s is the step length of the steep slope section of the step, h s The step height of the steep slope section of the steps; S2. Based on the horizontal projection trajectory curve P of the water flow particle, the gentle slope transition curve S is preliminarily determined; S3, based on the gentle-steep slope transition section curve S, determine the connection relationship between the smooth gentle slope section and the first step T1 of the gentle-steep slope transition section, construct the geometric constraint relationship between the smooth gentle slope section, the gentle-steep slope transition section, and the step steep slope section, and obtain the optimized gentle-steep slope transition section curve S and the outer inflection point of the first step T1 of the gentle-steep slope transition section; S4, based on the optimized slow-to-steep slope transition section curve S and the outer inflection point of the first step T1 of the slow-to-steep slope transition section, determine the number of steps N of the slow-to-steep slope transition section and the height of each step, and generate a gradual step sequence; S5, based on the optimized slow-steep slope transition section curve S, the outer inflection point of the first step T1 of the slow-steep slope transition section, and the gradual step sequence, generating continuous gradual steps within the contour envelope of the optimized slow-steep slope transition section curve S; S6. Based on the continuous gradient steps, the connection relationship between the last step of the gentle-steep slope transition section and the first step of the steep slope section is optimized; S7. Obtain the bottom plate width of the steep slope section of the step, and determine the step width of the gentle-steep slope transition section and the height of the side walls of the chute on both sides based on the bottom plate width of the steep slope section.

4. The design method of the high-speed water flow chute slope transition structure according to claim 3 is characterized in that: Step S1 is further as follows: S11, obtaining the design parameters and hydraulic parameters of each section of the spillway in the engineering structure, and estimating the water flow velocity at the end point D1 of the smooth gentle slope section; S12. Based on the water flow velocity and hydraulic parameters at the end point D1 of the smooth gentle slope section, according to the parabola equation, determine the horizontal projection trajectory curve P of the water flow particle at the chute slope change point.

5. The design method of the high-speed water flow chute slope transition structure according to claim 4 is characterized in that: Step S2 is further as follows: S21, based on the horizontal projection trajectory curve P of the water flow particle, preliminarily determine the gentle-steep slope transition curve S; S22, judging whether the equivalent radius of the initially determined gentle-steep slope transition section curve S is greater than the equivalent radius of the water flow particle horizontal projection motion trajectory curve P, if yes, no adjustment is made; otherwise, the initially determined gentle-steep slope transition section curve S is adjusted to obtain the initially adjusted gentle-steep slope transition section curve S; S23. Record the plane trajectory and geometric parameters of the gentle-steep slope transition section curve S after preliminary adjustment, including the equation of the gentle-steep slope transition section curve S, the starting point coordinates D1 and the end point coordinates D2 of the gentle-steep slope transition section, the horizontal length L and the vertical height difference H of the gentle-steep slope transition section, and the horizontal angle θ2 between the connecting line of the starting point and the end point of the gentle-steep slope transition section and the horizontal line.

6. The design method of the high-speed water flow chute slope transition structure according to claim 5 is characterized in that: Step S4 is further as follows: S41, based on the optimized gentle-steep slope transition section curve S and the outer inflection point of the first step T1 of the gentle-steep slope transition section, calculate the parameters of the first step of the gentle-steep slope transition section, including the slope angle, step height and step length of the first step; The slope angle of the first step is: i T1 =θ2+Δθ or θ T1 =θ2-Δθ; Where Δθ is the preset step slope angle difference; The step height of the first step is: h s / 7≤h1≤h s / 5; The step length of the first step is: d f1 = h1 / θ T1 ; S42, based on the vertical drop H of the gentle-steep slope transition section and the step height h of the step steep slope section s , according to the formula N≈H / h s Estimate the number of steps N in the transition section between the gentle and steep slopes; based on the parameters of the first step in the transition section between the gentle and steep slopes, calculate the number of steps N according to the formula (h1+h s )*N / 2≥H limits the estimated number of steps N of the gentle-steep slope transition section to determine the number of steps N of the gentle-steep slope transition section, where N is an odd number; S43, generating a gradual step sequence based on the number of steps N of the gentle-to-steep slope transition section and the step height of the first step of the gentle-to-steep slope transition section.

7. The design method of the high-speed water flow chute slope transition structure according to claim 6 is characterized in that: Step S5 is further as follows: S51, based on the outer inflection point of the first step T1 of the gentle-steep transition section and the step height of the first step of the gentle-steep transition section in the gradual step sequence, determine the inner inflection point of the first step T1; based on the inner inflection point of the first step T1 and the optimized gentle-steep transition section curve S, determine the outer inflection point of the second step T2 of the gentle-steep transition section; S52, repeating step S51 until the inner turning point of the last step of the gentle-steep slope transition section is connected to or overlaps with the first step of the steep slope section, obtaining the arrangement of all steps in the gentle-steep slope transition section and obtaining continuous gradual steps.

8. The design method of the high-speed water flow chute slope transition structure according to claim 7 is characterized in that: Step S6 is further as follows: S61, determine whether the inner turning point of the last step of the gentle-steep slope transition section coincides with the starting point of the first step of the steep slope section, if so, no adjustment is made; otherwise, proceed to step S62; S62, fixing the starting point of the gentle-steep slope transition section, and performing plane scaling on the gentle-steep slope transition section until the inner turning point of the last step of the gentle-steep slope transition section coincides with the starting point of the first step of the step steep slope section; S63, judging whether the step size of the steep slope section and the last step size of the gentle-steep slope transition section are consistent, if they are consistent, no adjustment is made; otherwise, proceeding to step S64; S64, when the step length of the last step of the gentle-steep slope transition section is smaller than the step length of the step of the steep slope section, a compensation method is adopted to add the step length difference Δd' to the step length of the first n-1 steps of the gentle-steep slope transition section; When the step length of the last step of the gentle-steep transition section is greater than the step length of the step of the steep slope section, the remainder method is adopted, and the step lengths of the first n-1 steps of the gentle-steep transition section are all reduced by the average step length difference Δd'; When the step height of the last step of the gentle-steep transition section is smaller than the step height of the step of the steep slope section, the compensation method is adopted to add the step height of the first n-1 steps of the gentle-steep transition section to the average step height difference Δh'; When the step height of the last step of the gentle-steep transition section is greater than the step height of the step of the steep slope section, the remainder method is adopted, and the step heights of the first n-1 steps of the gentle-steep transition section are all reduced by the average step height difference Δh'; Average step length difference Δd'=(∑ i=1 n d i -d s ) / N; average step height difference Δh'=(∑ i=1 n h i -h s ) / N, where n∈N, d i represents the step length of the i-th step in the transition section from gentle to steep slope, h i It represents the step height of the i-th step in the transition section of the gentle slope to the steep slope.

9. The design method of the high-speed water flow chute slope transition structure according to claim 8 is characterized in that: Step S7 is further as follows: S71, obtaining the bottom plate width of the steep slope section of the step, and setting the step width of the gentle-steep slope transition section to the bottom plate width of the steep slope section of the step; S72. Based on the width of the bottom plate of the steep slope section of the steps and the conventional hydraulic design requirements of the spillway specifications, determine the height of the side walls of the spillways on both sides.

10. The design method of the high-speed water flow chute slope transition structure according to claim 9, characterized in that: Also includes: S81. Based on the determined gentle-steep slope transition section and in accordance with the gravity similarity criterion, a hydraulic model of 1:25-1:40 is constructed and a hydraulic model test is conducted; S82. Based on the results of hydraulic model tests, further adjustments are made to the determined gentle-steep slope transition section.

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