An underwater submerged jet scour test apparatus and test method

Abstract

This invention discloses an underwater submerged jet scouring test device and method, relating to the field of hydraulic engineering technology. The test device includes: a water tank, which is divided into a water intake section, a test section, and a wake section from one side to the other; a filter screen, which is horizontally disposed at the bottom of the test sand pit; a baffle plate, which is disposed below the filter screen; a flow stabilizing plate, located between the water intake section and the test section; a water level control plate, located between the test section and the wake section; a guide rail, which is disposed above the water tank; a jet nozzle; a flow velocity meter; a laser displacement sensor; and a turbidity meter. The data obtained by the device of this invention can be used for characteristic analysis of the underwater submerged jet scouring process.

Description

Technical Field

[0001] This invention relates to the field of water conservancy engineering technology, and in particular to an underwater submerged jet scour test device and test method. Background Technology

[0002] Currently, the normal operation of submarine pipelines and cables faces risks from the seabed environment, surface targets, their own inherent risks, and human-caused risks. To address these risks and ensure the normal and stable operation of submarine pipelines and cables, trenching and backfilling can be used for protection. This method effectively prevents damage and increases the safety and reliability of marine resource transportation. Common trenching methods include pre-ditching, simultaneous trenching, and post-ditching. Based on actual submarine engineering practice, selecting an appropriate sequence of laying and trenching is cost-effective, time-efficient, reduces workload, and improves work efficiency. Trenching and backfilling is a simple and easy-to-operate engineering measure. Post-ditching involves laying the pipeline first and then trenching. A trenching machine uses jet scouring to agitate and liquefy the bedbed particles, which are then transported with the incoming flow to form a scouring trench. Pipelines and cables can be buried by their own gravity. This method allows for precise control of the scouring trench depth, and post-ditching is commonly used for laying submarine pipelines and cables in deep waters.

[0003] Common submarine trenching equipment includes hydraulic jet trenchers, mechanical trenchers, and plow trenchers. These utilize jets to agitate sediment particles, which then erode the original seabed through the water, creating scour trenches. Furthermore, jet scouring is widely used in river dredging, hydraulic sluice gates, and reservoir dredging.

[0004] Investigating the underwater submerged jet scour process and the characteristics of the scour trench profile is of significant theoretical and engineering practical value for revealing the underwater jet scour mechanism and analyzing the influence of various factors on the scour results. Considering the complex dynamic environment and multiple influencing factors involved in underwater jet scour, further research is needed on the scour laws and sediment transport mechanisms under crossflow conditions, thus laying a theoretical foundation for further identifying the influencing factors of jet scour. Through the study of jet scour, a correct understanding of the relevant issues of submerged vertical jet scour can improve the jet theory in seabed mining, local dredging, and subsea pipeline laying projects, which has certain theoretical significance and engineering application value.

[0005] In view of this, this invention is hereby proposed. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the existing technology and to propose an underwater submerged jet scour test device and test method. The data obtained can be used for characteristic analysis of the underwater submerged jet scour process.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] An underwater submerged jet scour test apparatus includes:

[0009] The water tank consists of a water intake section, a test section, and a tailrace section from one side to the other. The water intake section is equipped with a water inlet, the bottom surface of the test section has a through test sand pit, and the tailrace section is equipped with a water outlet.

[0010] A filter screen, which is horizontally positioned at the bottom of the test sand pit, is a rigid filter screen.

[0011] A baffle is disposed below the filter screen, and the two are in contact with each other;

[0012] A flow stabilizer plate is vertically installed on the bottom surface of the water tank, located between the water intake section and the test section, to separate the two. The height of the flow stabilizer plate is less than the depth of the water tank.

[0013] A water level control plate is vertically mounted on the bottom surface of the water tank and rotatably connected to the bottom surface of the water tank. It is located between the test section and the wake section to separate the two. The height of the water level control plate is less than the height of the flow stabilizing plate.

[0014] A guide rail is provided above the water tank;

[0015] A jet nozzle is mounted on the guide rail via a traveling device, which drives the jet nozzle to travel along the length of the water tank.

[0016] A flow meter is mounted on the guide rail and located above the area between the flow stabilizer and the test sand pit.

[0017] A laser displacement sensor is mounted on the guide rail and positioned above the test sand pit;

[0018] And a turbidity meter, which is mounted on the guide rail and located above the area between the test sand pit and the water level control plate.

[0019] To achieve the above objectives, the present invention also employs the following technical solution:

[0020] A method for underwater submerged jet scour testing, based on the testing apparatus provided by the present invention, includes the following steps:

[0021] Step 1: Prepare liquids with different sediment concentrations, measure the turbidity of the liquids, and calibrate the sediment concentration-turbidity relationship;

[0022] Step 2: Calculate the velocity scale, flow rate scale, and time scale; construct a three-dimensional coordinate system for the bed surface;

[0023] Step 3: Add non-cohesive mud and sand to the test sand pit and level it; set up the jet nozzle, the flow meter, the laser displacement sensor, and the turbidity meter on the guide rail; scan the test sand pit with the laser displacement sensor and record the initial elevation;

[0024] Step 4: Continuously inject water into the water intake section through the inlet at a first flow rate. When the water level in the test section reaches a preset water level threshold, continuously inject water into the water intake section through the inlet at a second flow rate until the water depth in the test section reaches the height of the water level control plate; wherein the second flow rate is greater than the first flow rate.

[0025] Step 5: Allow the sand bed in the test sand pit to settle for a preset time, so that it can be re-compacted under its own weight and water pressure, forming a stable and repeatable initial compaction state.

[0026] Step 6: Open the jet nozzle to start the test. Perform a fixed-point static water test and a moving scouring test according to the preset parameters. During the test, obtain the turbidity value of the water in the test section, and obtain the sediment concentration according to the calibrated sediment concentration-turbidity relationship. The fixed-point static water test means that the jet nozzle is fixed in the water above the test sand pit and the water inlet of the water tank is closed. The moving scouring test means that the jet nozzle moves in the water along the water flow direction above the test sand pit and continuously adds water to the water tank.

[0027] Step 7: After the static water test and the moving flushing test are completed, wait for the sediment to settle completely, then open the water level control plate and the baffle to drain the water.

[0028] Step 8: Scan the test sand pit using the laser displacement sensor to measure the elevation, subtract the initial elevation from the elevation measured in Step 3, and use the difference as the scouring depth at each point in the jet scouring pit.

[0029] Furthermore, the sediment concentration-turbidity relationship determined in step 1 is as follows:

[0030] SSC = -1.665 × 10 -6 NTU 2 +0.016NTU -1.376;

[0031] In the formula, SSC represents sediment concentration, and NTU represents turbidity.

[0032] Furthermore, in step 2, a three-dimensional coordinate system is constructed with the center of the test sand pit as the origin, the direction of water flow as the x-direction, the width of the water tank as the y-direction, and the vertical direction as the z-direction.

[0033] Furthermore, in step 6, the preset parameters in the fixed-point static water test are the jet velocity and rinsing time of the jet nozzle, and the jet nozzle is stopped after rinsing is completed.

[0034] Furthermore, in step 6, the preset parameters in the moving scouring test are the jet velocity of the jet nozzle, the moving speed of the jet nozzle, and the incoming flow velocity of the water in the test section. In the moving scouring test, when the incoming flow velocity reaches the preset value, the movement and jetting of the jet nozzle are started in front of the test sand pit, and the jet nozzle is controlled to reach a uniform speed at a preset distance in front of the test sand pit, so that the jet nozzle moves through the test sand pit at a uniform speed along the water flow direction, and the movement and jetting of the jet nozzle are stopped at a preset distance after the test sand pit.

[0035] Furthermore, in step 8, for the fixed-point static water test, the elevations of each point on the test sandpit area x0 and y0 are obtained, and the scour depth is calculated; the correspondence between scour time and scour depth, scour width, scour depth velocity change rate, and scour width change rate is established; the correspondence between jet velocity and scour depth, scour width, scour depth velocity change rate, and scour width change rate is established.

[0036] Further, in step 8, for the moving scour test, the elevations of each point on the test sandpit area x0, y0, y1, and y2 are obtained, and the scour depth is calculated; wherein y1 and y2 are located on both sides of y0, 0.15m away from y0; the correspondence between the Froude number Fr and the scour depth is constructed under different combinations of moving speed and incoming flow velocity. The formula for calculating the Froude number Fr is as follows:

[0037] ;

[0038] In the formula, u0 is the jet velocity, Δρ is the difference between the jet density and the water density, ρ is the water density, g is the acceleration due to gravity, and D is the nozzle diameter.

[0039] Establish the relationship between the moving velocity ratio and the jet velocity and the scouring depth, and establish the relationship between the incoming flow velocity ratio and the jet velocity and the scouring depth.

[0040] Compared with the prior art, the beneficial effects of this invention are as follows:

[0041] 1. During the test, water is injected into the water intake section through the inlet. When the water level is higher than the height of the flow stabilizer, the water enters the test section, achieving flow velocity stability through a simple structure. The height of the water level control plate is less than the height of the flow stabilizer. Therefore, when the water level in the test section is higher than the water level control plate, the water overflows through the water level control plate into the tail section, thereby maintaining the water level in the test section at the height of the water level control plate. This simple structure achieves liquid level control. After the test is completed, the water level control plate is rotated to allow the water in the test section to flow into the tail section. The water in the tail section flows out from the outlet.

[0042] 2. The test sandpit is used to fill sand. The depth of the test sandpit must be greater than the maximum scouring depth (the maximum scouring depth is the maximum depth to which the jet nozzle scours in the sand) to ensure that the water sprayed from the jet nozzle will not penetrate the sand. The coarseness of the filter screen is selected according to the requirements to ensure that the water in the test sandpit can be filtered out by the filter screen, while the sand in the test sandpit will not be filtered out by the filter screen. The filter screen is a rigid filter screen to ensure that it will not deform during the test, thereby ensuring the accuracy of measuring the elevation of the sand in the test sandpit. After the test is completed, the baffle is opened to allow the water in the test sandpit to be filtered out by the filter screen.

[0043] 3. The guide rail can be installed outside the water tank or at the edge of the water tank; the jet nozzle is mounted on the guide rail via a walking device and is used to spray water into the sand jet in the test sand pit during the test; during the test, water enters the test section from the flow stabilizing plate and finally flows out from the water level control plate; the flow velocity meter is located above the area between the flow stabilizing plate and the test sand pit, i.e., upstream of the water flow, and is used to measure the flow velocity of the water flow during the moving jet scouring test; the laser displacement sensor is located above the test sand pit and is used to measure the elevation of the sand in the test sand pit; the turbidity meter is located above the area between the test sand pit and the water level control plate and is used to measure the turbidity of the water flow during the test.

[0044] 4. The acquired data can be used to analyze the characteristics of the underwater submerged jet scouring process. The structure is simple, the number of parameters to be controlled is small, and it is easy to implement. Attached Figure Description

[0045] Figure 1 A front view of an underwater submerged jet scour test apparatus;

[0046] Figure 2 A flowchart of an underwater submerged jet scour test method;

[0047] Figure 3 This is a graph showing the relationship between sediment concentration and turbidity.

[0048] Figure 4 This is a schematic diagram of the measurement points for a fixed-point static water test.

[0049] Figure 5 A schematic diagram of the measurement points for the moving scour test;

[0050] Figure 6 Profiles of scour pits at different times;

[0051] Figure 7 The curves show the changes in scouring depth and width over scouring time;

[0052] Figure 8 The curves showing the rate of change of scouring depth and width as a function of scouring time;

[0053] Figure 9 This is a scour profile when the moving velocity is 0.07 m / s and the incoming flow velocity is 0.05 m / s.

[0054] Figure 10 This is a scour profile when the moving velocity is 0.1 m / s and the incoming flow velocity is 0.1 m / s.

[0055] Figure 11 This is a scour profile when the moving velocity is 0.13 m / s and the incoming flow velocity is 0.15 m / s.

[0056] Figure 12 Cross-sectional views of scouring at different moving speeds compared to jet velocities;

[0057] Figure 13 Cross-sectional views of scouring at different inflow velocity ratios to jet velocity.

[0058] In the diagram: 1-Water tank, 101-Water intake section, 102-Test section, 103-Wake section, 104-Inlet, 105-Test sand pit, 106-Outlet, 2-Filter screen, 3-Baffle, 4-Flow stabilizer, 5-Water level control plate, 6-Guide rail, 7-Jet nozzle, 8-Flow meter, 9-Laser displacement sensor, 10-Turbidity meter. Detailed Implementation

[0059] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0060] Example 1:

[0061] An underwater submerged jet scour test device, such as Figure 1 As shown, it includes:

[0062] Water tank 1, which consists of a water intake section 101, a test section 102 and a tailflow section 103 from one side to the other. The water intake section 101 is provided with a water inlet 104. A through test sand pit 105 is opened on the bottom surface of the test section 102. The tailflow section 103 is provided with a water outlet 106.

[0063] Filter screen 2, which is horizontally set at the bottom of the test sand pit 105, is a rigid filter screen;

[0064] Baffle 3 is disposed below the filter screen 2 and the two are in contact with each other;

[0065] A flow stabilizing plate 4 is vertically disposed on the bottom surface of the water tank 1, located between the water intake section 101 and the test section 102, and is used to separate the two. The height of the flow stabilizing plate 4 is less than the depth of the water tank 1.

[0066] Water level control plate 5 is vertically installed on the bottom surface of the water tank 1 and rotatably connected to the bottom surface of the water tank 1. It is located between the test section 102 and the tail section 103 to separate the two. The height of the water level control plate 5 is less than the height of the flow stabilizing plate 4.

[0067] Guide rail 6, the guide rail 6 is disposed above the water tank 1;

[0068] A jet nozzle 7 is mounted on the guide rail 6 via a traveling device, which drives the jet nozzle 7 to travel along the length of the water tank 1.

[0069] A flow meter 8 is mounted on the guide rail 6 and located above the area between the flow stabilizer 4 and the test sand pit 105.

[0070] A laser displacement sensor 9 is disposed on the guide rail 6 and located above the test sand pit 105;

[0071] And a turbidity meter 10, which is mounted on the guide rail 6 and located above the area between the test sand pit 105 and the water level control plate 5.

[0072] In this embodiment, during the experiment, water is injected into the water intake section 101 through the inlet 104. When the water level is greater than the height of the flow stabilizing plate 4, the water enters the test section 102, achieving flow velocity stability through a simple structure. The height of the water level control plate 5 is less than the height of the flow stabilizing plate 4. Therefore, when the water level in the test section 102 is higher than the water level control plate 5, the water overflows through the water level control plate 5 into the wake section 103, thereby maintaining the water level in the test section 102 at the height of the water level control plate 5. The height is controlled by a simple structure to achieve liquid level control; after the test is completed, the water level control plate 5 is rotated to allow the water in the test section 102 to flow into the tail section 103; the water in the tail section 103 flows out from the outlet 106; in specific implementation, the dimensions of the water tank 1 are 30m×3m×0.7m, the test section 102 is located in the middle of the water tank 1 and has a length of 6m, and the test sand pit 105 is located in the middle of the bottom surface of the test section 102 and has dimensions of 0.5m×0.5m×0.3m.

[0073] In this embodiment, the test sandpit 105 is used to fill sand, and the depth of the test sandpit 105 needs to be greater than the maximum scouring depth (the maximum scouring depth is the maximum depth to which the jet nozzle 7 scours in the sand) to ensure that the water sprayed by the jet nozzle 7 will not penetrate the sand; the coarseness of the filter screen 2 is selected according to the requirements to ensure that the water in the test sandpit 105 can be filtered out by the filter screen 2, while the sand in the test sandpit 105 will not be filtered out by the filter screen 2; the filter screen 2 is a rigid filter screen 2 to ensure that it will not deform during the test, thereby ensuring the accuracy of measuring the elevation of the sand in the test sandpit 105; after the test is completed, the baffle 3 is opened to allow the water in the test sandpit 105 to be filtered out by the filter screen 2.

[0074] In this embodiment, the guide rail 6 can be installed outside the water tank 1 or on the edge of the water tank 1; the jet nozzle 7 is mounted on the guide rail 6 via a traveling device, and is used to spray water into the sand jet in the test sand pit 105 during the test. Specifically, a 0.01mm circular nozzle can be selected, and the flow rate can be configured to 4m³ / s. 3A submersible pump with a head of 80m / h was used, and the depth of the test sandpit 105 was set to 0.3m, making it much greater than the maximum scouring depth. During the test, water entered the test section 102 from the flow stabilizing plate 4 and finally flowed out from the water level control plate 5. The flow meter 8 was located above the area between the flow stabilizing plate 4 and the test sandpit 105, i.e., upstream of the water flow, and was used to measure the flow velocity during the moving jet scouring test. Specifically, a Vectrino high-precision three-point flow meter 8 (ADV) could be used, which can measure the flow velocity changes of the glass water tank 1 in real time, forming a three-dimensional instantaneous time series. Flow velocity; the laser displacement sensor 9 is located above the test sand pit 105 and is used to measure the elevation of the sand in the test sand pit 105. In specific implementation, a KEYENCELK-G400 laser displacement sensor 9 can be used to record the elevation of each position along the center line of the jet; the turbidity is located above the area between the test sand pit 105 and the water level control plate 5 and is used to measure the turbidity of the water flow during the test. In specific implementation, an RBRduo3Tu.Tu turbidity recorder can be used. During the test, the RBRduo3Tu.Tu turbidity recorder is submerged in the water and is used as a single-channel suspended solids turbidity recorder.

[0075] In summary, the underwater submerged jet scour test device of this embodiment can obtain data that can be used for characteristic analysis of the underwater submerged jet scour process. It has a simple structure, requires fewer parameters to be controlled, and is easy to implement.

[0076] Example 2:

[0077] A method for underwater submerged jet scour testing, applied to the test apparatus of Example 1, such as... Figure 2 As shown, it includes the following steps:

[0078] Step 1: Prepare liquids with different sediment concentrations, test the turbidity of the liquids, and calibrate the sediment concentration-turbidity relationship.

[0079] In this embodiment, the sediment concentration-turbidity relationship calibrated in step 1 is as follows: Figure 3 As shown. The sediment concentration-turbidity relationship is as follows:

[0080] SSC = -1.665 × 10 -6 NTU 2 +0.016NTU -1.376;

[0081] In the formula, SSC represents sediment concentration, and NTU represents turbidity.

[0082] Step 2: Calculate the velocity scale, flow rate scale, and time scale; construct a three-dimensional coordinate system for the bed surface.

[0083] In this embodiment, when step 2 is specifically implemented, the velocity scale can be 4, the flow rate scale can be 1024, and the time scale can be 4.

[0084] In this embodiment, in step 2, a three-dimensional coordinate system is constructed with the center of the test sandpit as the origin, the direction of water flow as the x-direction, the width of the water tank as the y-direction, and the vertical direction as the z-direction. Specifically, the x-direction is the direction from the water intake section to the test section, and then to the wake section.

[0085] Step 3: Add non-sticky mud and sand to the test sand pit and level it; set up the jet nozzle, the flow meter, the laser displacement sensor, and the turbidity meter on the guide rail; scan the test sand pit with the laser displacement sensor and record the initial elevation.

[0086] In this embodiment, in step 3, non-cohesive mud and sand with a depth of 0.3m can be added to the test sand pit to ensure that the mud and sand in the test sand pit has a sufficient thickness, much greater than the expected maximum scour depth, so as to avoid scour to the bottom hard base and affect the results; the sand in the test sand pit is leveled, and the height error of the mud and sand surface is controlled within 1mm, so that the initial bed surface conditions of each working condition are uniform, reducing the influence of the initial terrain on the scour results and improving the repeatability and comparability of the test.

[0087] In this embodiment, in step 3, when the jet nozzle, the flow meter, the laser displacement sensor, and the turbidity meter are installed on the guide rail, it is necessary to control the positions of the four components in the three-dimensional coordinate system of the bed surface to ensure the consistency of their positions during multiple tests.

[0088] Step 4: Continuously inject water into the water intake section through the inlet at a first flow rate. When the water level in the test section reaches a preset water level threshold, continuously inject water into the water intake section through the inlet at a second flow rate until the water depth in the test section reaches the height of the water level control plate; wherein the second flow rate is greater than the first flow rate.

[0089] In this embodiment, in step 4, water is injected slowly with a small initial flow rate to avoid disturbing or partially activating the unreinforced sand bed during the water injection process.

[0090] In this embodiment, in step 4, the height of the water level control plate can be set to 0.3m, thereby controlling the water level in the test section at 0.3m, ensuring that all working conditions are carried out under the same submerged water depth conditions, and meeting the scale design and Freud similarity requirements.

[0091] Step 5: Allow the sand bed in the test sand pit to settle for a preset time, allowing it to re-compact under its own weight and water pressure, forming a stable and repeatable initial compacted state.

[0092] In this embodiment, the preset duration in step 5 can be 30 minutes.

[0093] In this embodiment, in step 5, the sand bed in the test sand pit is re-compacted under its own weight and water pressure to form a stable and repeatable initial compaction state. This ensures that the scouring process is dominated by the jet and the incoming flow, rather than by the reconsolidation of the unconsolidated sand bed.

[0094] Step 6: Open the jet nozzle to start the test. Perform a fixed-point static water test and a moving scouring test according to the preset parameters. During the test, obtain the turbidity value of the water in the test section and obtain the sediment concentration according to the calibrated sediment concentration-turbidity relationship. The fixed-point static water test means that the jet nozzle is fixed in the water above the test sand pit and the water inlet of the water tank is closed. The moving scouring test means that the jet nozzle moves in the water along the water flow direction above the test sand pit and continuously adds water to the water tank.

[0095] In this embodiment, in step 6, the turbidity value of the water in the test section is obtained by the turbidity meter, and the sediment concentration is further obtained, which can be used for numerical simulation.

[0096] In this embodiment, in step 6, the water inlet and the water level control plate are closed during the fixed-point static water test to eliminate background flow and water surface fluctuations, creating static water conditions, thereby allowing the jet itself to be examined for its scouring effect on the substrate.

[0097] In this embodiment, in step 6, the preset parameters in the fixed-point static water test are the jet velocity and rinsing time of the jet nozzle, and the jet nozzle is stopped after rinsing is completed.

[0098] In practice, the scouring time can be 1s, 2s, 4s, 8s, or 16s. By setting multiple scouring times, a series of states of the scouring pit's evolution over time can be obtained, which can be used to establish the temporal development pattern of scouring depth and width.

[0099] In this embodiment, in step 6, the preset parameters in the moving scouring test are the jet velocity of the jet nozzle, the moving speed of the jet nozzle, and the incoming flow velocity of the water in the test section. In the moving scouring test, when the incoming flow velocity reaches the preset value, the movement and jetting of the jet nozzle are started in front of the test sand pit, and the jet nozzle is controlled to reach a uniform speed at a preset distance in front of the test sand pit, so that the jet nozzle moves through the test sand pit at a uniform speed along the water flow direction, and the movement and jetting of the jet nozzle are stopped at a preset distance after the test sand pit.

[0100] In practice, the preset distance can be set to 0.5m, that is, the jet nozzle is started in advance to ensure that the jet nozzle reaches a constant speed at a distance of 0.5m from the test sand pit, filtering out the uneven acceleration zone when the motor starts, and ensuring that the nozzle movement is stable when it actually enters the sand pit; and it is turned off 0.5m after leaving the test sand pit to avoid additional disturbance to the tail of the scouring pit during the deceleration / stopping process.

[0101] In this embodiment, in step 6, the ADV flow meter is connected to the computer and a sampling frequency of 50 Hz is set. This allows for high-time-resolution recording of the instantaneous flow velocity near the incoming flow and the jet, providing a data foundation for analyzing the flow field structure and turbulence characteristics of the moving jet. By adjusting the moving device and setting the inverter power, the jet nozzle moves smoothly and uniformly, simulating the working mode of a moving trencher or towed nozzle in engineering, thus achieving controllable coupling between the jet velocity and the moving velocity.

[0102] In this embodiment, in step 6, the jet velocity of the jet nozzle, the moving speed of the jet nozzle, and the incoming flow velocity of the water in the test section can be controlled by a controller such as a PID controller.

[0103] In this embodiment, during step 6, the height of the jet nozzle is controlled to be 0.15 cm from the bottom surface of the test section during the fixed-point static water test and the moving scouring test.

[0104] Step 7: After the static water test and the moving flushing test are completed, wait for the sediment to settle completely, then open the water level control plate and the baffle to drain the water.

[0105] In this embodiment, in step 7, after the static water test and the moving scour test are completed, wait for the sediment to settle completely to ensure that the subsequent measurement is of the bed surface morphology after scour stabilization, rather than the instantaneous disturbance of suspended sediment; when opening the water level control plate and the baffle to drain the water, it should be drained slowly to avoid the generation of new water flow during the drainage process to cause secondary scour or collapse of the already formed scour pit, thereby protecting the authenticity of the scour morphology.

[0106] Step 8: Scan the test sand pit using the laser displacement sensor to measure the elevation, subtract the initial elevation from the elevation measured in Step 3, and use the difference as the scouring depth at each point in the jet scouring pit.

[0107] In this embodiment, as Figure 4 As shown, in step 8, for the fixed-point static water test, the elevations of each point on the test sandpit area x0 and y0 are obtained, and the scour depth is calculated; the correspondence between scour time and scour depth, scour width, scour depth velocity change rate, and scour width change rate is established; the correspondence between jet velocity and scour depth, scour width, scour depth velocity change rate, and scour width change rate is established.

[0108] In this embodiment, as Figure 5 As shown, in step 8, for the moving scour test, the elevations of each point on the test sandpit area x0, y0, y1, and y2 are obtained, and the scour depth is calculated; where y1 and y2 are located on both sides of y0, 0.15m away from y0; the correspondence between the Froude number Fr and the scour depth is constructed under different combinations of moving speed and incoming flow velocity. The formula for calculating the Froude number Fr is as follows:

[0109] ;

[0110] In the formula, u0 is the jet velocity, Δρ is the difference between the jet density and the water density, ρ is the water density, g is the acceleration due to gravity, and D is the nozzle diameter.

[0111] Establish the relationship between the moving velocity ratio and the jet velocity and the scouring depth, and establish the relationship between the incoming flow velocity ratio and the jet velocity and the scouring depth.

[0112] In one specific embodiment, as shown in Table 1, different operating parameters were set and scouring tests were conducted, where operating conditions 1 to 5 were fixed-point static water tests and 6 to 32 were moving scouring tests.

[0113] Table 1 Test Operating Conditions

[0114]

[0115] For the fixed-point static water test, for condition 4, measure the depth of the scour pit profile at x=0, such as... Figure 6 As shown, construct a cross-sectional view of the scour pit. Based on... Figure 6, The time evolution of the fixed-point jet scour pit profile is divided into three scour stages: (1) When t < 4 s, it is the rapid development stage of the scour pit. The jet water body overcomes the viscous effect of the water body in the environment, conducts energy exchange and dissipation, the jet intensity is weakened, reaches the sand bed, and the bottom sand bed is subjected to the shear force of the jet water body, forming a large velocity gradient in the vertical direction in the jet core area, scouring downward, and the scour depth changes sharply. The scour depth reaches 0.02 m, approaching 46% of the maximum scour depth of the profile. (2) When 4 s < t < 16 s, it is the continuous development stage of jet scour. While the jet water body scours downward, the jet water body has an attached-wall effect and turns; the deflected jet water body continuously acts on the side wall of the scour pit, continuously applies a shear effect, drives the lateral erosion of the scour pit, has a greater impact on the scour width, and the aspect ratio of the scour pit profile decreases significantly. The scour depth reaches 96%, showing a "V" shape development. (3) When t > 16 s, it is the stable stage of jet scour. The dynamic balance is reached between the kinetic energy provided by the jet and the interaction between the water body surrounding environment and the bottom sand bed. The scour pit depth reaches the stable stage, and the scour depth and width no longer change significantly. The jet water body and the bottom sand bed conduct stable energy exchange, and the scour pit profile develops into a "U" shape.

[0116] Construct the changes in scour depth and scour width under different scour time conditions as Figure 7 shown, and the changes in the scour depth change rate and the scour width change rate are as Figure 8As shown, the rate of change of jet scour depth velocity is generally less than the rate of change of jet scour width velocity. Under these experimental conditions, the water ejected from the nozzle can influence the jet scour width over a wider range. The rates of change of jet scour depth velocity and jet scour width velocity show the same trend under this condition. The rates of change of jet scour depth and width velocity exhibit a gradually decreasing trend, fitting an exponential function. The scour rates of jet scour depth and width decrease rapidly, with a 10-fold difference in velocity change rate within the first 10 seconds. The decrease in the rate of change of jet scour depth is due to the fact that after the jet nozzle is started, during the rapid development phase of the jet, the jet water in the core area mainly acts in the vertical direction. As the jet process continues, the jet depth is in the development phase, accompanied by energy exchange and attenuation. The smaller the energy reaching the substrate, the more severe the attenuation, so the rate of change of scour depth decreases rapidly. During the continued development and stable phases of the jet, the jet scour depth rate gradually decreases. Nearly 50% of the jet scour depth range is completed during the rapid development phase of the jet. Finally, the rate of change of jet scour depth no longer changes, and the curve tends to flatten. The velocity change rate of jet scour width shows a gradually decreasing trend. This is because during the initial and rapid development stages of the jet, erosion of the scour pit profile width occurs, and sediment particles are activated. In the continued development stage of jet scour, the jet water reaches the sand bed, resulting in a wall-attachment effect. Some water deflects and scours the sidewalls, causing a rapid increase in the jet scour width, completing most of the jet scour depth range. As the jet progresses, it is damaged by vortices, weakening the kinetic energy of the water that deflects to the surroundings. The velocity change rate of jet scour width decreases rapidly, and the curve eventually flattens out.

[0117] For moving scour tests, the relationship between the Froude number Fr and the scour depth was established under different combinations of moving velocity u1 and incoming flow velocity u2, as follows: Figure 9-11 As shown, the depth of the scour pit increases with increasing flow velocity under three different flow rates (Fr). With increasing Fr, the jet water ejected from the nozzle possesses greater initial kinetic energy, causing stronger damage to the sediment particles on the bed and resulting in a deeper scour pit. The maximum depth of the scour pit profile formed under the shear force of the jet also increases with increasing Fr. As the jet velocity increases, the volume of water ejected from the nozzle increases within the same time frame. The ejected water is affected by the surrounding water and the incoming flow, which weakens the velocity. When the initial jet velocity increases, the rate of change of the jet scour depth slows down, causing scouring of the bottom sand bed, accompanied by the movement of vortices. One stream of water, after contacting the bed, reflects upwards, weakening the continuous jet process. As the jet process continues, the distance between the water and the bed bottom during the moving jet scour increases. Only by increasing the jet velocity, thus increasing the shear force of the jet water, can the scour pit profile increase.

[0118] The relationship between the moving speed u1, the jet velocity u0, and the scouring depth is constructed as follows: Figure 12 As shown, the ratio of u1 / u0 increases with increasing moving speed, while the depth of the scour pit decreases. This is because increased speed leads to incomplete jet scouring. Before reaching dynamic equilibrium, the jet nozzle reaches the next profile and continues scouring, forming a transient jet scouring process. The continuation of the jet process also involves backfilling, with a redirecting water flow creating the maximum scour pit depth. As the moving speed of the jet nozzle increases, the scour depth decreases. The brief scouring of the water ejected from the nozzle to the bottom bed is insufficient to completely agitate the sediment particles. The scouring effect reduces the volume of sediment particles carried out of the scour pit. Simultaneously, increased moving speed weakens vortex motion, reduces jet adhesion, and decreases the number of agitated sediment particles.

[0119] The relationship between the incoming flow velocity u2 and the jet velocity u0 and the scouring depth is constructed as follows: Figure 13 As shown, the higher the incoming flow velocity, the greater the u2 / u0 ratio, making it easier for sediment particles at the bottom of the bed to reach the initiation conditions. When the turbulent flow velocity is reached, the sediment particles change from a static state to a suspended state. Under the action of vortex motion, they diffuse to the surroundings and continue to move forward along the water flow direction under the influence of the incoming flow. As the u2 / u0 ratio increases, the maximum depth of the jet scour pit also increases. When the scour pit formed by the jet reaches dynamic equilibrium, the unidirectional flow will backfill the maximum depth of the formed pit, and larger suspended particles in the surrounding area will settle, thus reducing the maximum depth of the scour pit. Moreover, as the jet nozzle moves, the settlement at the cross-section is the greatest, resulting in a decrease in the depth of the scour pit profile along the water flow direction. As the incoming flow velocity increases, the maximum depth of the scour pit increases. During the vertical jet process, the water jet from the moving nozzle interacts with the incoming water environment, accompanied by energy exchange. The increased incoming flow velocity can activate sediment particles, causing the scour pit to deepen and the u2 / u0 ratio to increase. The scouring effect of the jet water activates sediment particles, leading to sediment transport. In the rapidly changing vortex motion, sediment particles cannot settle in time and are carried downstream by the incoming flow velocity. Some sediment particles act on the sidewalls of the scour pit, continuing to affect the interior of the scour pit, while others cover the already formed scour pit. Sediment particles carried to the periphery of the scour pit by the vortex motion are farther from the jet center area and are less affected by the shearing effect of the jet water. Under the influence of the incoming flow velocity, sediment particles will not settle at their current position but will move downstream, resulting in a reduction in the bulges on both sides of the profile.

[0120] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A test method applied to an underwater submerged jet scour test device, the test device comprising: a water tank, the water tank sequentially comprising a water inlet section, a test section and a tail flow section from one side to the other side, the water inlet section being provided with a water inlet, the test section being provided with a through test sand pit on the bottom surface, the tail flow section being provided with a water outlet; a filter screen, the filter screen being horizontally arranged at the bottom of the test sand pit, the filter screen being a hard filter screen; a baffle, the baffle being arranged below the filter screen, the baffle and the filter screen being in contact with each other; a flow stabilizing plate, the flow stabilizing plate being vertically arranged on the bottom surface of the water tank, between the water inlet section and the test section, for separating the water inlet section and the test section, the height of the flow stabilizing plate being less than the depth of the water tank; a water level control plate, the water level control plate being vertically arranged on the bottom surface of the water tank, being rotatably connected with the bottom surface of the water tank, being between the test section and the tail flow section, for separating the test section and the tail flow section, the height of the water level control plate being less than the height of the flow stabilizing plate; a guide rail, the guide rail being arranged above the water tank; a jet nozzle, a flow velocity meter and a laser displacement sensor, the jet nozzle, the flow velocity meter and the laser displacement sensor being arranged on the guide rail; and a turbidimeter, the turbidimeter being arranged on the guide rail, above the area between the test sand pit and the water level control plate; the test method comprising the following steps: Step 1: configuring liquid with different sediment concentrations, detecting the turbidity of the liquid, and calibrating the relationship between sediment concentration and turbidity; Step 2: calculating the flow velocity scale, the flow rate scale and the time scale; and constructing a three-dimensional coordinate system of the bed surface; Step 3: adding non-viscous sediment in the test sand pit and flattening the sediment; scanning the test sand pit by the laser displacement sensor and recording the initial elevation; Step 4: continuously injecting water into the water inlet section through the water inlet at a first flow rate, when the water level in the test section reaches a preset water level threshold, continuously injecting water into the water inlet section through the water inlet at a second flow rate, until the water depth in the test section reaches the height of the water level control plate; wherein the second flow rate is greater than the first flow rate; Step 5: standing for a preset time period, so that the sand bed in the test sand pit is re-compacted under the action of gravity and water pressure, forming a stable and repeatable initial compacted state; Step 6: opening the jet nozzle to start the test, performing fixed-point still water test and moving scour test according to preset parameters, obtaining the turbidity value of the water in the test section during the test, and obtaining the sediment concentration according to the calibrated relationship between sediment concentration and turbidity; the fixed-point still water test refers to fixing the jet nozzle in the water above the test sand pit and closing the water inlet of the water tank; the moving scour test refers to moving the jet nozzle in the water above the test sand pit along the flow direction and continuously injecting water into the water tank; the preset parameters in the moving scour test include the incoming flow velocity of the water in the test section; Step 7: after the fixed-point still water test and the moving scour test are completed, opening the water level control plate and the baffle to drain the water. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Step 8: The test sandpit is scanned by the laser displacement sensor to measure the height, and the initial height in step 3 is subtracted, and the difference is taken as the scour depth of each point of the jet scour pit.

2. The test method of claim 1, wherein, The calibrated sediment concentration-turbidity relationship in step 1 is as follows: SSC = -1.665 x 10 -6 NTU 2 + 0.016 NTU - 1.376; In the formula, SSC is the sediment concentration, and NTU is the turbidity.

3. The test method of claim 1, wherein, In step 2, a bed surface three-dimensional coordinate system is established with the center of the test sandpit as the origin, the water flow direction as the x direction, the water tank width direction as the y direction, and the vertical direction as the z direction.

4. The test method of claim 1, wherein, In step 6, the preset parameters in the fixed-point still water test are the jet velocity of the jet nozzle and the scouring time, and the jet nozzle is stopped after scouring is completed.

5. The test method of claim 1 wherein, In step 6, the preset parameters in the moving scouring test are the jet velocity of the jet nozzle, the moving speed of the jet nozzle, and the incoming flow velocity of the water in the test section; in the moving scouring test, when the incoming flow velocity reaches the preset value, the movement and jet of the jet nozzle are started in front of the test sandpit, the preset distance of the jet nozzle is controlled to reach a uniform speed, so that the jet nozzle uniformly drives through the test sandpit along the water flow direction, and the movement and jet of the jet nozzle are stopped after a preset distance behind the test sandpit.

6. The test method of claim 3, wherein, In step 8, for the fixed-point still water test, the height of each point on x0 and y0 in the test sandpit area is obtained, and the scouring depth is calculated; the corresponding relationship between scouring time and scouring depth, scouring width, scouring depth velocity change rate, and scouring width change rate is constructed; the corresponding relationship between jet velocity and scouring depth, scouring width, scouring depth velocity change rate, and scouring width change rate is constructed.

7. The test method of claim 3, wherein, In step 8, for the moving scouring test, the height of each point on x0, y0, y1, and y2 in the test sandpit area is obtained, and the scouring depth is calculated; y1 and y2 are located on both sides of y0, and the distance from y0 is 0.15 m; the corresponding relationship between Froude number Fr and scouring depth under different moving speed and incoming flow velocity combinations is constructed, and the calculation formula of Froude number Fr is as follows: ； In the formula, u0 is the jet velocity, Δρ is the difference between the jet density and the water density, ρ is the water density, g is the acceleration of gravity, and D is the nozzle diameter; The corresponding relationship between the moving speed ratio and the jet velocity and the scouring depth is constructed, and the corresponding relationship between the incoming flow velocity ratio and the jet velocity and the scouring depth is constructed.

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