A high-efficiency and low-interference sediment model near-bottom sediment collection method

Abstract

The invention discloses a high-efficiency and low-interference sediment model near-bottom sediment collection method, which belongs to the technical field of sediment model near-bottom sediment transport measurement, comprising: laying model sand at the bottom of a test water tank; adjusting the water flow rate and flow velocity to reach the set value required by the test; the water flow passes through an energy dissipation sand collecting device for weakening and eliminating transverse axis backflow and rising water flow, and the weight of silted sand in the energy dissipation sand collecting device is recorded in real time; monitoring the change data of water flow velocity, time, positive pressure value and flow parameter; sorting and screening the change data and removing abnormal data; calculating the near-bottom sediment single-width sediment transport rate; the high-efficiency and low-interference sediment model near-bottom sediment collection method, by arranging an energy dissipation sand collecting device in the sand collecting tank, effectively weakens and eliminates the transverse axis backflow and rising water flow generated in the sand collecting tank due to water flow turbulence, and the near-bottom sediment silting rate can reach 98%, which is increased by 10% to 30%, thereby realizing efficient sedimentation of near-bottom sediment.

Description

Technical Field

[0001] The invention belongs to the technical field of sediment transport measurement near the bottom of a sediment model, and in particular relates to a high-efficiency and low-interference sediment collection method near the bottom of a sediment model. Background Art

[0002] At present, due to the lack of relatively reliable and accurate on-site testing instruments and measurement methods, the measurement of near-bottom sediment transport rate has always been a difficult point in hydrological measurement. It is often analyzed by indirect methods such as measuring the movement of sand slopes on site, which has a large workload and measurement errors. With the gradual improvement of some key technologies such as model sand selection, scouring and silting time scale, and determination of hydrodynamic generalization control conditions, fixed-bed sediment transport test has become an important means of studying near-bottom sediment transport rate.

[0003] In previous flume tests of sediment transport rates near the bottom, due to the poor sediment deposition effect in the sediment collection trough, in order to improve the sediment deposition rate, the longitudinal length and depth of the sediment collection trough need to be increased during the test. However, a sediment collection trough that is too long and too deep will cause the flow area of ​​the test section to increase, thereby destroying the flow pattern distribution of the test section. In addition, in order to calculate the sediment transport rate near the bottom, the sediment in the sediment collection trough needs to be dried and weighed. The process is complicated and cumbersome, and it is impossible to monitor the changes in sediment transport in real time throughout the process in the non-steady flow test. In the face of this situation, exploring methods to achieve efficient sediment deposition near the bottom and real-time monitoring of the changes in sediment transport throughout the process has become the key to solving the problem. Summary of the invention

[0004] The purpose of the present invention is to provide a high-efficiency and low-interference sediment model near-bottom sediment collection method to solve the problem that the whole process of sediment transport changes cannot be monitored in real time.

[0005] To achieve the above object, the present invention provides the following technical solution: a high-efficiency and low-interference sediment model near-bottom sediment collection method, comprising the following steps:

[0006] Step 1: Lay model sand at the bottom of the test tank. The thickness of the sand is controlled at 3 cm. The selection of model sand should be determined according to the specific test requirements.

[0007] Step 2: Start the water supply system of the test water tank, control the water flow at a low flow rate, and slowly adjust the water flow rate and flow rate to reach the set value required by the test. During the adjustment process, closely observe the stability of the water flow to ensure that the water flow can pass through the test section evenly;

[0008] Step 3, start the underwater positive pressure instrument to record the weight of the silted sand in real time; the near-bottom silt enters the sand collecting trough under the action of the water flow, and after the energy dissipation effect of the energy dissipation sand collecting device, the silt can be effectively and efficiently silted; the silted sand settles freely at the bottom of the energy dissipation sand collecting device through the hook body or the porous structure gap, and the underwater positive pressure instrument records the weight of the silted sand in real time and sends the data to the data receiving device;

[0009] Step 4: Use other instruments, such as a flow meter, flow meter, etc., to monitor the changes in water flow velocity, flow rate and other parameters; accurately record all monitoring data, including time, positive pressure value, water flow velocity, flow rate, etc., for subsequent analysis;

[0010] Step 5: After the test, record all data recorded by the underwater positive pressure instrument and data monitored by other related instruments; ensure the integrity and accuracy of the data, preliminarily organize and screen the data, and remove abnormal data;

[0011] Step 6: Analyze the collected data in detail according to the following formula to calculate the sediment transport rate per unit width near the bottom ,

[0012] ;

[0013] In the formula , is the measured positive pressure value of the underwater positive pressure instrument at two adjacent moments, , are the weights of sand and water, respectively. , For , For two adjacent times, is the width of the sand collecting trough.

[0014] The test section is from the beginning of the model sand laying to the end of the downstream longitudinal length of the sand collecting tank, and the rest of the test tank is the non-test section. , set the sand collection tank depth to The test water flow rate is , then

[0015] ; (1)

[0016] In the formula is the average flow velocity of a single width section of the sand collecting trough. According to the theory of sediment movement mechanics, when When the depth of the sand collecting trough is set to meet the sand settling requirements, is the critical starting average flow velocity of sediment, and its value depends on the selection of test model sand.

[0017] Assume that the longitudinal length of the sand collecting trough is The height of the sediment near the bottom of the test section is , then

[0018] ; (2)

[0019] In the formula is the sediment settling velocity, and its value depends on the selection of the test model sand; for The average flow velocity of a single width section at It should be noted that the formula for determining the longitudinal length and depth of the sand collecting trough is only applicable to the sand collecting trough of the present invention. Since ordinary sand collecting troughs are not equipped with energy dissipation devices, the transverse axis backflow and rising water flow generated by the turbulence of the water flow inside them cannot be ignored. In order to achieve the ideal sand collection effect, its longitudinal length and depth will be much larger than the sand collecting trough design of the present invention. However, due to the lack of design specifications for near-bottom sediment collecting troughs, its design size is still unknown.

[0020] The experimental device of the invention comprises a test water tank, a sand collecting tank, an energy dissipation sand collecting device, an underwater positive pressure instrument, a support frame and a sand collecting guide plate.

[0021] Sand collecting trough: The sand collecting trough is set in the water tank test section, and the underwater positive pressure instrument is installed at the bottom of the sand collecting trough through a support frame; the sand collecting trough and the energy dissipation sand collecting device are connected by water through the gap at the sand collecting guide plate, thereby offsetting the gravity exerted on the underwater positive pressure instrument by the water level change, ensuring that the measured weight is all the weight of the near-bottom sediment; the lower positive pressure instrument is an underwater wireless positive pressure instrument;

[0022] Energy dissipation and sand collecting device: The main function of the energy dissipation and sand collecting device is to collect sand. A permeable energy dissipation structure or a honeycomb porous structure is placed inside the device. By arranging dense energy dissipation and sand collecting devices in the sand collecting trough, the transverse axis backflow and rising water flow caused by the turbulence of the water flow in the sand collecting trough can be greatly weakened and eliminated, so as to achieve efficient sedimentation near the bottom, thereby shortening the longitudinal length and depth of the sand collecting trough. After the energy dissipation device is arranged in the sand collecting trough, it basically has no effect on the flow cross-sectional area of ​​the test section, thereby not destroying the hydrodynamic distribution of the test section. It can be seen from the results of the water tank test that after the energy dissipation device is arranged in the sand collecting trough, efficient sedimentation near the bottom can be achieved. According to the definition of the single-width sediment transport rate of near-bottom sediment

[0023] ; (3)

[0024] In the formula is the sediment transport rate per unit width near the bottom; , is the weight of the sediment in the energy dissipation and sand collection device at two adjacent moments; , For , Corresponding to two adjacent times; is the width of the sand collecting trough.

[0025] Weight of sediment in the energy dissipation and sand collection device The weight of the sediment in the water of the energy dissipation and sand collection device The relationship between

[0026] ; (4)

[0027] In the formula is the water weight of the same sediment volume; , are the weights of sand and water respectively.

[0028] Substituting equation (4) into equation (3) yields the following formula for calculating the sediment transport rate per unit width near the bottom:

[0029] ; (5)

[0030] In the formula , is the measured positive pressure value of the underwater positive pressure instrument at two adjacent moments;

[0031] The sediment weight G cannot be directly read out by the underwater positive pressure gauge, so formula (3) needs to be expanded and derived. Formula (4) is the intermediate process. The rightmost end of formula (5) is the final form of the formula for calculating the sediment transport rate of a single width near the bottom, where W is the reading of the underwater positive pressure gauge, and γ s With γ w It is also a known quantity. The weight of the sediment G is converted into the direct reading W of the underwater positive pressure instrument.

[0032] Sand collecting guide plate: The sand collecting guide plate allows the near-bottom sediment to pass through the energy dissipation sand collecting device more freely, and keeps the sand collecting trough connected to the water body of the energy dissipation sand collecting device, thereby offsetting the gravity exerted on the underwater positive pressure gauge by the water level change, ensuring that the measured weight is all the weight of the near-bottom sediment.

[0033] Support frame: The underwater positive pressure gauge is installed at the bottom of the sand collecting trough through the support frame, and cooperates with the gap at the sand collecting guide plate to make the water body between the sand collecting trough and the energy dissipation sand collecting device communicate.

[0034] Underwater positive pressure meter: automatically weighs the settled silt and can monitor the entire process of silt transport changes in real time.

[0035] The technical effects and advantages of the present invention are as follows: the high-efficiency and low-interference sediment model near-bottom sediment collection method, by arranging an energy dissipation sand collecting device in the sand collecting trough, placing a permeable energy dissipation structure or a honeycomb porous structure in the energy dissipation sand collecting device, effectively weakens and eliminates the transverse axis backflow and rising water flow caused by water turbulence in the sand collecting trough. Compared with ordinary sand collecting troughs, the near-bottom sediment deposition rate can reach 98%, which is increased by 10% to 30%, thereby achieving efficient sediment deposition near the bottom, thereby shortening the length and depth of the sand collecting trough, being able to efficiently collect sand and significantly reduce the requirements for the longitudinal length and depth of the sand collecting trough; significantly weakening and eliminating the influence of the expansion of the flow section caused by the setting of the sand collecting trough on the hydrodynamic distribution of the test section; after the ordinary sand collecting trough is provided with an energy dissipation sand collecting device, the selection of its size will relax the requirements, and more consideration will be given to the size of the sedimentation amount of the test design, which greatly facilitates the design and conduct of the test. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a cross-sectional view of the test tank arrangement of the present invention;

[0037] Figure 2 A top view of the test tank arrangement of the present invention;

[0038] Figure 3 It is a schematic diagram of the overall structure of the sand collecting trough of the present invention;

[0039] Figure 4 This is a schematic diagram of the honeycomb porous structure of the present invention;

[0040] Figure 5 This is a schematic diagram of selecting the size of the sand collecting trough of the present invention;

[0041] Figure 6 This is a schematic diagram of the flow field distribution of a common sand collection trough;

[0042] Figure 7 It is a schematic diagram of the flow field distribution of the sand collecting trough of the present invention;

[0043] Figure 8 This is a schematic diagram of the sand collection effect after the ordinary sand collection tank test;

[0044] Fig. 9 It is a schematic diagram of the sand collection effect of the sand collecting trough after the test of the present invention.

[0045] In the figure: 1. Test water tank; 2. Sand collecting tank; 3. Energy dissipation and sand collecting device; 4. Sand collecting guide plate; 5. Support frame; 6. Underwater positive pressure gauge. DETAILED DESCRIPTION

[0046] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0047] The present invention provides Figure 1 , Figure 2 A high-efficiency and low-interference sediment model near-bottom sediment collection method is shown, based on a near-bottom sediment high-efficiency silting device;

[0048] The device is specifically as follows Figure 3 As shown, it includes: a test water tank 1, a sand collecting tank 2, an energy dissipation sand collecting device 3, a sand collecting guide plate 4, a support frame 5, and an underwater positive pressure meter 6;

[0049] Among them, the energy dissipation and sand collection device 3 can be placed with a permeable energy dissipation structure, such as an active hook-connected body, a tetrahedral permeable frame, a regular double I-shaped permeable frame, etc., and a honeycomb porous structure can also be used, such as Figure 4 As shown, the porosity of both can reach more than 80%;

[0050] Installation of the test water tank 1: Select a flat and stable ground to set up the test water tank 1, and ensure that the water tank is in a horizontal state; the material of the water tank should have good corrosion resistance and wear resistance to ensure the long-term conduct of the test.

[0051] Setting of sand collecting trough 2: The test section is from the starting end of the model sand laying to the end of the downstream longitudinal length of the sand collecting trough 2. The sand collecting trough 2 is excavated in the test section of the test water tank 1, and the size of the sand collecting trough 2 is determined according to the designed sand settling volume of the test. The underwater positive pressure gauge 6 is installed at the bottom of the sand collecting trough 2 through the support frame 5. The material of the support frame 5 should have sufficient strength and stability to support the weight of the underwater positive pressure gauge 6 and the energy dissipation sand collecting device 3.

[0052] Installation of the energy dissipation sand collecting device 3: The energy dissipation sand collecting device 3 is installed inside the sand collecting trough 2, and the water communication between the sand collecting trough 2 and the energy dissipation sand collecting device 3 is achieved through the gap at the sand collecting guide plate 4; during the installation process, it is necessary to ensure that the size and position of the gap are accurate so that the water can flow smoothly between the sand collecting trough 2 and the energy dissipation sand collecting device 3, and at the same time ensure that the mud and sand in the energy dissipation sand collecting device 3 will not enter the sand collecting trough 2.

[0053] The energy dissipation and sand collecting device 3 is arranged: the energy dissipation and sand collecting device 3 is closely placed in the sand collecting trough 2, and a water-permeable energy dissipation structure or a honeycomb porous structure is arranged in the energy dissipation and sand collecting device 3. The flow field distribution of the ordinary sand collecting trough and the sand collecting trough 2 of the present invention are respectively as follows: Figure 6 , 7 As shown in the figure, the schematic diagrams of the sand collection effects after the two experiments are as follows: Figure 8 , 9 As shown; during the test, the water flow turbulence in the ordinary sand collecting trough is strong, and a horizontal axis backflow will be formed at the front end of the trough, and the silted sand will be suspended, and with the rising water flow, it will silt at the rear end and even return to the test water trough 1, forming a reverse parabolic siltation form of "low in front and high in the back"; when the energy dissipation sand collecting device 3 is installed in the sand collecting trough, the water flow turbulence in the sand collecting trough will be significantly weakened, and then the horizontal axis backflow at the front end of the trough and the rising water flow will also be eliminated, and the near-bottom silt at the front end of the sand collecting trough will fall freely to the bottom of the device under the action of gravity, and the near-bottom silt can be silted in large quantities at the front end of the sand collecting trough, forming a parabolic siltation form of "high in front and low in the back"; the siltation rate of the near-bottom silt in the sand collecting trough 2 of the present invention can reach 98%. Compared with the ordinary sand collecting trough, the sand collection rate of the near-bottom silt in the sand collecting trough 2 of the present invention is increased by 10% to 30%, realizing efficient siltation of the near-bottom silt.

[0054] Setting of the sand collecting guide plate 4: the sand collecting guide plate 4 is installed at the upper end of the sand collecting trough 2, and its lower edge is lower than the upper edge of the energy dissipation sand collecting device 3 to prevent the silt in the device 3 from entering the sand collecting trough 2, while keeping the water body between the sand collecting trough 2 and the energy dissipation sand collecting device 3 connected, thereby offsetting the gravity exerted on the underwater positive pressure gauge 6 by the water level change, and ensuring that the measured weight is all the weight of the near-bottom silt; the material of the sand collecting guide plate 4 should have good wear resistance and impact resistance to withstand the scouring of silt.

[0055] Installation of underwater positive pressure gauge 6: The underwater positive pressure gauge 6 is firmly installed between the sand collecting tank 2 and the energy dissipation sand collecting device 3 through the support frame 5; when installing the positive pressure gauge, it is necessary to ensure that the connection between it and the support frame 5 is reliable and that the positive pressure value can be accurately measured. At the same time, the positive pressure gauge should have good waterproof performance to ensure normal operation underwater.

[0056] The test steps include:

[0057] Step 1: Lay model sand at the bottom of the test tank 1, and the thickness of the sand is controlled to be 3 cm. The selection of the model sand depends on the specific test requirements.

[0058] Step 2: Start the water supply system of the test water tank 1, control the water flow at a low flow rate, and slowly adjust the water flow rate and flow rate to reach the set value required by the test. During the adjustment process, closely observe the stability of the water flow to ensure that the water flow can pass through the test section evenly;

[0059] Step 3, start the underwater positive pressure instrument 6, and record the weight of the silted sand in real time. The near-bottom silt enters the sand collecting trough 2 under the action of the water flow, and after the energy dissipation of the energy dissipation sand collecting device 3, the silt can be effectively and efficiently removed. The silted sand settles freely at the bottom of the energy dissipation sand collecting device 3 through the hook connection or the porous structure gap. The underwater positive pressure instrument 6 records the weight of the silted sand in real time and sends the data to the data receiving device;

[0060] Step 4. At the same time, use other instruments, such as current meters and flow meters, to monitor changes in water velocity, flow rate and other parameters. Accurately record all monitoring data, including time, positive pressure value, water velocity, flow rate, etc., for subsequent analysis;

[0061] Step 5: After the test, record all data recorded by the underwater positive pressure instrument 6 and the data monitored by other related instruments. Ensure the integrity and accuracy of the data, preliminarily organize and screen the data, and remove abnormal data;

[0062] Step 6: Analyze the collected data in detail and calculate the sediment transport rate per unit width near the bottom. The calculation of the sediment transport rate per unit width near the bottom includes:

[0063] According to the definition of sediment transport rate per unit width near the bottom

[0064] ; (1)

[0065] In the formula is the sediment transport rate per unit width near the bottom; , is the weight of the sediment in the energy dissipation and sand collection device 3 at two adjacent moments; , For , Corresponding to two adjacent times; is the width of the sand collecting trough 2;

[0066] Weight of sediment in energy dissipation and sand collection device 3 The weight of the sediment in the water of the energy dissipation and sand collection device 3 The relationship between

[0067] ; (2)

[0068] In the formula is the water weight of the same sediment volume; , are the weights of sand and water respectively;

[0069] Substituting equation (2) into equation (1), we can obtain the following formula for calculating the sediment transport rate per unit width near the bottom: ; (3)

[0070] In the formula , It is the measured positive pressure value of the underwater positive pressure instrument 6 at two adjacent moments.

[0071] The high-efficiency and low-interference sediment model near-bottom sediment collection method, by setting an energy dissipation sand collecting device 3 in the sand collecting trough 2, placing a permeable energy dissipation structure or a honeycomb porous structure in the energy dissipation sand collecting device 3, effectively weakens and eliminates the transverse axis backflow and rising water flow caused by water turbulence in the sand collecting trough 2. Compared with the ordinary sand collecting trough, the near-bottom sediment deposition rate can reach 98%, which is increased by 10% to 30%, and the near-bottom sediment deposition is realized. Efficient sediment deposition is achieved, thereby shortening the length and depth of the sand collecting trough 2, and can efficiently collect sand and significantly reduce the longitudinal length and depth requirements of the sand collecting trough 2; significantly weaken and eliminate the influence of the expansion of the flow section caused by the setting of the sand collecting trough 2 on the hydrodynamic distribution of the test section; after the ordinary sand collecting trough is set with the energy dissipation sand collecting device 3, the selection of its size will relax the requirements, and more consideration will be given to the size of the sedimentation amount of the test design, which greatly facilitates the design and conduct of the test.

[0072] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A high-efficiency, low-interference sediment model near-bottom sediment collection method, characterized by: include: Lay model sand on the bottom of the test tank; Adjust the water flow rate and flow rate to reach the set value required by the test; The water flows through an energy dissipation and sand collection device for weakening and eliminating the horizontal axis backflow and the rising water flow, and the weight of the silt and sand in the energy dissipation and sand collection device is recorded in real time; Monitor the change data of water flow velocity, time, positive pressure value and flow parameters; Organize and filter the change data and remove abnormal data; Calculate the sediment transport rate per unit width near the bottom; The energy dissipation and sand collection device is provided with a water-permeable energy dissipation structure or a honeycomb porous structure; the porosity of the water-permeable energy dissipation structure and the honeycomb porous structure is greater than 80%; the water-permeable energy dissipation structure includes: an active hook-connected body, a tetrahedral hexagonal frame or a regular double I-shaped frame; The test water tank is provided with a sand collecting tank for installing an energy dissipation sand collecting device; The method for determining the longitudinal length and depth of the sand collecting trough includes: Assume that the water level in the test section of the test tank is , set the sand collection tank depth to The test water flow rate is , then (1); where is the average flow velocity of a single width section of the sand collecting trough, when When the depth of the sand collecting trough is set to meet the sand settling requirements, is the critical starting average flow velocity of sediment; Assume that the longitudinal length of the sand collecting trough is The height of the sediment near the bottom of the test section is , then (2); where is the sediment settling velocity; for The average flow velocity of a single width section at .

2. A high-efficiency, low-interference sediment model near-bottom sediment collection method according to claim 1, characterized in that: The laying thickness of the model sand is 3 cm.

Images