A design method for a piano-key weir with high discharge capacity

Abstract

The present invention discloses a design method for a piano-key weir with high discharge capacity, comprising: selecting a piano-key weir foundation structure based on the project's discharge requirements; preliminarily determining weir parameters based on the project's discharge volume requirements and the total width of the project's discharge structure; installing a movable retaining wall at the top of the piano-key weir; determining the maximum effective height range of the movable retaining wall; and proposing a movable retaining wall with an inverted L-shaped cross-section and its operation method. The present invention has the following beneficial effects: 1) The present invention proposes a piano-key weir with a movable retaining wall; 2) Based on this piano-key weir design method, the piano-key weir has a higher discharge capacity at the design water level; and 3) Reservoirs equipped with this piano-key weir have greater regulation and storage capacity.

Description

Technical Field

[0001] The invention discloses a design method of a piano-key weir with high discharge capacity, belonging to the field of flood discharge design and construction of water conservancy projects. Background Art

[0002] Overflow weirs are a common hydraulic structure, typically used to control upstream water levels. Due to the open nature of weir flow, their discharge capacity is far superior to that of orifice flow. In practice, they are often used in hydraulic projects with large discharge volumes. To increase discharge volume, technicians increase the total length of the discharge front to increase the total flow area. Common types include broken line weirs, labyrinth weirs, and piano-key weirs. This method does significantly increase discharge volume. Especially in projects with narrow river channels where the discharge front cannot be extended, piano-key weirs can achieve discharge volumes several times greater than those of conventional overflow weirs.

[0003] However, in existing engineering designs, a more optimized weir shape is still desired, allowing the overflow weir to increase the flow rate per unit width, thereby increasing the overall discharge capacity of the piano-key weir. Increasing the discharge rate per unit width of the piano-key weir can, on the one hand, improve project safety while maintaining the original design leading edge length; on the other hand, it can appropriately reduce the overall length of the piano-key weir, thereby reducing construction costs.

[0004] The discharge coefficients of various zigzag weirs used in existing technologies are limited by the crest curve and the dimensions of the weir body. This makes calculations difficult using standard methods during design and use, often requiring repeated adjustments and modifications through experimentation to achieve the final applicable shape. Therefore, each zigzag weir has its own unique control parameters. Summary of the Invention

[0005] The invention discloses a piano key weir with high flow discharge capacity and a design method thereof, and aims to improve the flow discharge capacity of the piano key weir.

[0006] A method for designing a piano-key weir with high discharge capacity comprises the following steps:

[0007] Step 1: Select the piano-key weir foundation structure according to the project discharge requirements;

[0008] Step 2: Preliminarily determine the following parameters based on the project design discharge volume requirements and the total width of the project discharge structure:

[0009] The total length of the overflow front edge of the piano key weir is L; the piano key weir width is W; the total length of the piano key weir upstream and downstream, that is, the side weir length is B; the weir height is P;

[0010] The preliminary method for determining the weir height P is:

[0011] P = (7.14 ~ 8.33) × (design water level - normal water level);

[0012] And the weir height must meet the following requirements: (check water level - design water level) < 0.05P.

[0013] Step 3: Set up a movable guard wall on the top of the piano key weir. The maximum effective height range of the movable guard wall is 0 to H e ;

[0014] Among them, H e = Design water level - normal water level;

[0015] The design water level is the top elevation of the movable retaining wall after it is lifted, and the normal water level is the top elevation of the movable retaining wall after it is lowered;

[0016] The present invention discloses a structure and operation mode of a movable guard wall of a piano key weir top:

[0017] The above-mentioned movable retaining wall is a continuously welded wall of steel plates, and its cross section is an inverted L-shape, which is inverted on multiple automatic lifting jacks on the top of the piano key weir.

[0018] When the reservoir water level is lower than the piano-key weir top elevation, the movable retaining wall diaphragm is maintained at the normal water storage level;

[0019] When the reservoir water level rises to the normal water level -5cm, the movable retaining wall begins to rise. Under the action of the jack, the movable retaining wall rises;

[0020] The maximum height of the movable retaining wall shall not exceed the design water level;

[0021] When the reservoir water level rises to the design water level:

[0022] 1) If the water level drops to the normal water level, the movable retaining wall will also drop to the normal water level;

[0023] 2) If the water level continues to rise above the design water level, the movable retaining wall will remain at the design water level.

[0024] The inventors discovered in experiments that the Piano Key Weir achieves maximum discharge capacity when the height of the movable retaining wall at the weir crest is 0.12 to 0.13 times the weir height. Therefore, the Piano Key Weir designed using the aforementioned scheme can utilize the movable retaining wall to increase the reservoir's water storage capacity, significantly increasing its regulation and storage capacity.

[0025] The beneficial effects of the present invention are:

[0026] 1) The present invention proposes a piano-key weir with a movable guard wall;

[0027] 2) Based on the design method of the piano-key weir shape, the piano-key weir has a higher discharge capacity at the design water level;

[0028] 3) Reservoirs with the above-mentioned piano-key weirs have greater regulation and storage capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the basic piano key weir structure;

[0030] Figure 2 3D diagram of the piano-key weir with additional movable retaining walls;

[0031] Figure 3 Schematic diagram of the piano weir from above and the location of the A-A' section;

[0032] Figure 4 Schematic diagram of the cross section of the movable retaining wall, piano-key weir, and jack at the A-A' section at normal water level;

[0033] Figure 5 Schematic diagram of the A-A' section of the movable retaining wall, piano-key weir, and jack section at the design water level. DETAILED DESCRIPTION

[0034] The present invention will now be further described with reference to the accompanying drawings.

[0035] Example 1

[0036] A method for designing a piano-key weir with high discharge capacity comprises the following steps:

[0037] Step 1: Select the basic piano-key weir structure according to the project discharge requirements, such as Figure 1 As shown;

[0038] Step 2: Preliminarily determine the following parameters based on the project design discharge volume requirements and the total width of the project discharge structure:

[0039] The total length L of the overflow front of the piano key weir is 21.91m;

[0040] The width of the piano weir is 5.11m, and the width of the weir inlet is W i The weir outlet width is 1.35m. o 1.1m;

[0041] The total length of the piano weir upstream and downstream, that is, the side weir length B is 5.1m, and the inverted length downstream of the palace is B i 1.7m; the length of the inverted hanging upstream of the palace is B o 1.6m;

[0042] Length of base B b 3.0m; base height P d 1.0m; side wall thickness T s 0.3m;

[0043] The project design water level is 40.66m and the normal water level is 40.32m;

[0044] The preliminary method for determining the weir height P is:

[0045] P = (7.14 ~ 8.33) × (design water level - normal water level) = 2.43 ~ 2.83m;

[0046] (Check water level - design water level) = 0.15m

[0047] 0.05P = 0.05 × (2.43 to 2.83) = 0.1215 to 0.1415 m < (check water level - design water level);

[0048] Step 3: Set up a movable guard wall on the top of the piano key weir. The maximum effective height range of the movable guard wall is 0 to H e ;

[0049] Among them, H e = Design water level - normal water level = 40.66 - 40.32 = 0.34m;

[0050] The design water level is the top elevation of the movable retaining wall after the top is raised, and the normal water storage level is the top elevation of the movable retaining wall after the top is lowered.

[0051] The present invention discloses a structure and operation mode of a movable guard wall of a piano key weir top:

[0052] The movable retaining wall 1 is a continuously welded steel plate wall with an inverted L-shaped cross section. It is inverted on multiple automatic lifting jacks 2 on top of the piano weir 3. The vertical partitions 12 of the inverted L are water retaining plates; the horizontal partitions 11 of the inverted L are support plates supported on the tops of the jacks 2.

[0053] A movable retaining wall end stopper 14 is provided at the end of the vertical partition 2;

[0054] A weir body limiter 13 is provided on the inner side of the piano key weir 3;

[0055] When the reservoir water level is lower than the normal water level, the top of the movable retaining wall diaphragm 11 is kept at the normal water level. Figure 4 As shown;

[0056] When the reservoir water level rises to the normal water level -5cm, the movable retaining wall 1 begins to rise. Under the action of the jack 2, the movable retaining wall 1 rises;

[0057] The maximum height of the movable retaining wall 1 does not exceed the design water level, and the range of the movable retaining wall 1 is controlled by the weir body limiter 13 and the movable retaining wall end limiter 14;

[0058] When the reservoir water level rises to the design water level:

[0059] 1) If the water level drops to the normal water level, the movable retaining wall 1 also drops to the normal water level;

[0060] 2) If the water level continues to rise and exceeds the design water level, the movable retaining wall will remain at the design water level; if the water level continues to rise and exceeds the check flood level, the movable retaining wall 1 will be lowered to the normal water storage level.

[0061] In traditional piano-key weir designs, the weir crest is immobile and can only be set to the normal water level. The weir crest elevation must never exceed the normal water level. Therefore, when the water level exceeds the normal water level, the piano-key weir can only release water. As the inflow increases, the water level continues to rise. However, as the inflow decreases, the water level quickly falls below the normal water level. Due to the limited water retaining height, the piano-key weir reservoir's storage capacity is very poor. This significantly impacts the water supply capacity of the water supply reservoir.

[0062] The inventors discovered through experiments that the piano-key weir achieves maximum discharge capacity when the height of the movable retaining wall at the weir crest is 0.12 to 0.13 times the weir height. Therefore, the design water level can be used as the highest elevation of the movable retaining wall at the weir crest during operation. By utilizing a movable retaining wall with a variable elevation and leveraging the enhanced discharge capacity of the movable retaining wall at a specific height, the inventors devised the above piano-key weir design and operation scheme, as well as the movable retaining wall layout.

Claims

1. A method for designing a piano-key weir with high discharge capacity, characterized by: The following steps are involved: Step 1: Select the piano-key weir foundation structure according to the project discharge requirements; Step 2: Preliminarily determine the following parameters based on the project design discharge volume requirements and the total width of the project discharge structure: The total length of the overflow front edge of the piano key weir is L; the piano key weir width is W; the total length of the piano key weir upstream and downstream, that is, the side weir length is B; the weir height is P; The preliminary method for determining the weir height P is: P = (7.14 ~ 8.33) × (design water level - normal water level); And the weir height must meet the following requirements: (check water level - design water level) < 0.05P; Step 3: Set up a movable guard wall on the top of the piano key weir. The maximum effective height range of the movable guard wall is 0 to H e ; Among them, H e = Design water level - normal water level; The design water level is the top elevation of the movable retaining wall after the top is raised, and the normal water storage level is the top elevation of the movable retaining wall after the top is lowered.

2. The method for designing a piano key weir with high discharge capacity according to claim 1, characterized in that: The structure of the movable retaining wall is: The movable guard wall is a continuously welded steel plate wall with an inverted L-shaped cross section, which is inverted on a plurality of automatic lifting jacks on the top of the piano key weir.

3. The method for designing a piano key weir with high discharge capacity according to claim 1, characterized in that: The operating mode of the movable retaining wall is: When the reservoir water level is lower than the piano-key weir top elevation, the top elevation of the movable retaining wall diaphragm is maintained at the normal water storage level; When the reservoir water level rises to the normal water level -5cm, the movable retaining wall rises under the action of the jack; The maximum height of the movable retaining wall shall not exceed the design water level; When the reservoir water level rises to the design water level: 1) If the water level drops to the normal water level, the movable retaining wall will also drop to the normal water level; 2) If the water level continues to rise above the design water level, the movable retaining wall will remain at the design water level; 3) When the water level continues to rise and reaches the verified flood level, the movable retaining wall will be lowered.

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