System and method for configuring stable density stratified water body environment by free fall method

Abstract

The application discloses a system and method for configuring stable density stratified water environment by free fall method, which comprises an upstream liquid supply barrel A, an intermediate mixing barrel B and a target water tank C which are sequentially connected, and realizes gravity-driven perfusion without external pumping by using orifice free drainage; the upstream liquid supply barrel A supplies liquid to the intermediate mixing barrel B through a bottom orifice, the intermediate mixing barrel B is continuously stirred to keep the water fully mixed and change the density in the intermediate mixing barrel B over time, and the intermediate mixing barrel B injects the water changing over time into the target water tank C through a bottom orifice, so that the density time history of the intermediate mixing barrel B is mapped to the height density profile of the target water tank C and a density gradient is formed. Meanwhile, a liquid surface disturbance reduction scheme for the target water tank C is disclosed. Compared with the traditional double-barrel method, the application can reduce the dependence on accurate flow ratio adjustment, improve the mixing uniformity in the later stage, shorten the preparation time, and thus realize stable, repeatable and more efficient density stratified water environment construction.

Description

Technical Field

[0001] This invention belongs to the field of water stratification control, specifically relating to a system and method for configuring a stable density stratified water environment using the free fall method. Background Technology

[0002] In recent years, research related to marine resource development, marine engineering construction, and marine environmental protection has been continuously carried out, covering multiple directions such as marine sediment plume diffusion, pollutant migration and dilution, near-bottom boundary layer material transport, and its ecological impact assessment. In these studies, laboratory physical simulations are often used to reveal basic mechanisms, verify numerical models, and conduct parameter comparison analyses. Constructing a stable density-stratified water environment with a controllable density gradient in the laboratory is one of the important basic conditions for conducting related experiments. The gradient morphology, stability, and disturbance level during the preparation process of the density-stratified environment will affect the repeatability and consistency of the results. Among existing technologies, the two-bucket method is a commonly used method for preparing density-stratified water. This method generally involves continuously injecting low-density water into high-density water while simultaneously stirring, causing the water density in the mixing bucket to gradually change over time; then, the water from the mixing bucket that has changed over time is injected into an experimental water tank (or experimental water container) to form a density-stratified environment that varies with height within the tank. Due to its relatively simple structure and intuitive implementation, the two-bucket method has been widely used in related experimental research.

[0003] However, in specific experimental implementations, the traditional two-barrel method may still have some areas for improvement. For example, to obtain a specific form (such as an approximately linear) density stratification curve, the two-barrel system often needs to meet a certain flow matching relationship (in some implementations, this can be approximated by the discharge flow ratio needing to meet a condition of approximately 2:1). However, in actual operation, flow matching is easily affected by factors such as orifice machining and assembly errors, valve opening repeatability, head changes caused by liquid level variations, and flow measurement and adjustment accuracy, which may lead to a certain deviation between the stratification curve and the design value. In addition, in the later stages of preparation, factors such as a decrease in the liquid level in the mixing tank, changes in the effective immersion length of the stirring rod, and changes in the local flow structure may reduce the mixing efficiency, making it difficult for the water in the tank to remain sufficiently uniform at certain times. When mixing and discharge occur simultaneously, if the mixing process lags behind the discharge process, the density of the discharged water may fluctuate, thus affecting the accuracy of local density stratification in the tank. Furthermore, in order to suppress injection disturbances and reduce entrainment and mixing at the free liquid surface, some traditional methods tend to use smaller discharge flow rates or longer injection times, which may limit the preparation efficiency and is not conducive to conducting high-frequency repetitive experiments and batch comparison experiments. Summary of the Invention

[0004] To address the challenges of high flow rate matching and adjustment, susceptibility to issues affecting mixing uniformity in the later stages, and low preparation efficiency, this invention provides a system and method for configuring a stable density-stratified aquatic environment using a free-fall method. Without altering the fundamental principle of the two-barrel method—"density changes over time within the mixing barrel and is then injected into the experimental water tank"—this invention employs a more easily implemented and reproducible method and control system for configuring a density-stratified aquatic environment. This ensures density stratification stability while reducing the reliance on operational experience and fine-tuning during the preparation process. Accordingly, this invention further provides supporting structural design and control strategies to achieve stable and efficient construction of a density-stratified aquatic environment, improving the convenience of experimental implementation and the consistency of results.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A system for configuring a stable density-stratified aquatic environment using a free-fall method includes:

[0007] The upstream supply tank A, the intermediate mixing tank B, and the target water tank C are connected sequentially through openings at their respective bottoms to form a three-stage gravity-driven structure.

[0008] A stirrer is installed inside the intermediate mixing tank B to continuously stir the water to keep it fully mixed and to make the density inside the intermediate mixing tank B change over time.

[0009] A disturbance reduction structure is disposed above the free liquid surface of the target water tank C. The disturbance reduction structure includes a disturbance reduction plate and a porous distribution structure, which are used to reduce the disturbance of the free liquid surface during the injection process.

[0010] An automatic lifting mechanism, connected to the disturbance reduction plate, is used to drive the disturbance reduction plate to move vertically.

[0011] A controller is used to control the movement of the automatic lifting mechanism.

[0012] Furthermore, the upper surface of the damping plate is provided with a central receiving area and a guide channel. The central receiving area has a shallow basin structure, and the guide channel connects the central receiving area with the edge of the damping plate. The porous distribution structure is located at the corner of the damping plate and is in the form of a shower-type porous cavity or porous pipe section. A buffer energy dissipation medium layer is superimposed below the porous distribution structure. The buffer energy dissipation medium layer is composed of one or a combination of sponge pad, open-cell foam, fiber felt, and fine mesh.

[0013] Furthermore, the automatic lifting mechanism includes:

[0014] A support base is fixedly installed on the outside of the target water tank;

[0015] A synchronous belt slide is mounted on the support base. The slider end of the synchronous belt slide is fixedly connected to the anti-scratching plate support frame. The anti-scratching plate support frame is used to support and position the anti-scratching plate.

[0016] A stepper motor is used to drive the synchronous belt slide.

[0017] The synchronous belt slide is equipped with a linear guide rail or guide rod inside to provide vertical guidance.

[0018] Furthermore, a constant gap of 5-30mm is maintained between the bottom surface of the damping plate and the free liquid surface of the target water tank C.

[0019] Furthermore, it also includes a liquid level sensor for real-time measurement of the liquid level height of the target water tank; the controller receives the measurement value from the liquid level sensor, calculates the target lifting speed of the damping plate according to the liquid level rise law, and outputs a pulse frequency to the stepper motor to drive the damping plate to move synchronously upward with the liquid surface, thereby realizing closed-loop control.

[0020] This invention also provides a method for configuring a stable density-stratified aquatic environment using the free-fall method, comprising the following steps:

[0021] Step 1: Construct a three-stage gravity-driven system consisting of an upstream supply tank A, an intermediate mixing tank B, and a target water tank C connected in sequence. The upstream supply tank A, the intermediate mixing tank B, and the target water tank C respectively achieve gravity-driven injection without external pumping through orifices set at their bottoms.

[0022] Step 2: Supply water of a first density to the intermediate mixing tank B through the bottom hole of the upstream supply tank A. The water of the first density is kept fully mixed in the intermediate mixing tank B by continuous stirring, so that the density of the water in the intermediate mixing tank B changes continuously over time to form water of a second density.

[0023] Step 3: Inject the second density water into the target water tank C through the bottom hole of the intermediate mixing tank B, and map the density time history of the intermediate mixing tank B to the height density profile inside the target water tank C;

[0024] Step 4: Set up a disturbance reduction structure above the free liquid surface of the target water tank C so that the fluid entering the target water tank spreads to the free liquid surface in a multi-point low momentum manner;

[0025] Step 5: The automatic lifting mechanism keeps the damping plate and the free liquid surface moving upward synchronously while maintaining a constant gap;

[0026] Step 6: The controller calculates the target lifting speed of the damping plate according to the liquid level rise pattern, converts the target lifting speed into a pulse frequency and outputs it to the stepper motor, driving the damping plate to move upward synchronously with the liquid level of the target water tank. The liquid level rise pattern is jointly determined by the barrel geometry parameters and orifice parameters of the upstream supply tank A, the intermediate mixing tank B and the target water tank C.

[0027] Furthermore, in step 4, the central receiving area is a shallow basin structure, which is used to dissipate and retain the kinetic energy of the incoming flow within the central receiving area; the guide channel is an annular groove, which is used to distribute the incoming flow evenly in the circumferential direction under the action of gravity; the buffer energy dissipation medium layer is composed of one or a combination of sponge pad, open-pore foam, fiber felt, and fine mesh, which is used to further reduce the speed of the fluid and weaken the pulsation when it passes through.

[0028] Furthermore, in step 5, the constant gap is 5-30mm; the synchronous belt slide is equipped with a linear guide rail or guide rod to provide vertical guidance and resistance to lateral forces, so as to prevent the damping plate from pitching or tilting during movement.

[0029] Furthermore, the disturbance reduction structure includes a disturbance reduction plate and a porous distribution structure. The upper surface of the disturbance reduction plate is provided with a central receiving area and a guide groove. The corners of the disturbance reduction plate are provided with a shower-type porous distribution structure. A buffer energy-consuming medium layer is superimposed below the porous distribution structure. The automatic lifting mechanism includes a support base fixed to the outside of the target water tank, a synchronous belt slide mounted on the support base, a stepper motor driving the synchronous belt slide, and a disturbance reduction plate support frame connecting the synchronous belt slide and the disturbance reduction plate.

[0030] Furthermore, in step 6, the controller discretizes the target lifting speed into several time slices to generate a segmented constant frequency table; the target lifting speed is larger in the early stage of perfusion, decreases linearly in the later stage of perfusion, and approaches zero at the end of the fluid supply.

[0031] Furthermore, step 6 also includes: configuring a liquid level sensor to measure the liquid level height of the target water tank in real time, and the controller receiving the measured value of the liquid level sensor to perform closed-loop correction to compensate for deviations caused by actual flow fluctuations and orifice coefficient changes.

[0032] Beneficial effects:

[0033] 1. This invention significantly improves the accuracy and repeatability of stratification. Through a three-stage gravity-driven structure consisting of the upstream supply tank A, mixing tank B, and target water tank C, near-linear stratification can theoretically be achieved simply by satisfying the orifice area ratio, eliminating the need for precise adjustment of the dynamic flow ratio and avoiding deviations in the stratification curve caused by factors such as valve opening and liquid level changes. The automatic lifting mechanism maintains a constant gap of 5-30mm between the damping plate and the free liquid surface, eliminating secondary disturbances or the risk of contact with the liquid surface caused by gap changes, ensuring consistent disturbance levels throughout the pouring process, and greatly improving experimental repeatability.

[0034] 2. This invention improves mixing uniformity and density stability. Continuous stirring within mixing tank B, combined with gravity-driven continuous inflow, solves the mixing lag problem caused by the decrease in liquid level and stirring efficiency in the later stages of the traditional two-tank method, ensuring continuous and stable density of the discharged water. Based on a dimensionless theoretical model, the density profile within the target water tank C can be accurately predicted using five dimensionless parameters, facilitating the preset and control of the target stratification curve and reducing trial-and-error costs.

[0035] 3. This invention significantly improves preparation efficiency. The damping plate and porous distribution structure employ a four-stage energy dissipation mechanism—central support, flow guidance and energy dissipation, spray-like flow distribution, and buffering and deceleration—to spread the fluid to the liquid surface in a multi-point, low-momentum manner, significantly reducing jet impact and entrainment mixing. This allows for a larger injection flow rate without disrupting the established density gradient. Compared to traditional methods that sacrifice flow rate for stability, this invention shortens preparation time while ensuring layering quality, meeting the needs of high-frequency repetitive experiments and batch comparative experiments.

[0036] 4. The system of this invention has a high degree of automation and low operational dependence. Based on the stepper motor control algorithm calculated according to the liquid level rise law, the damping plate automatically and synchronously moves upward with the liquid level, rapidly rising in the initial stage of filling and linearly decelerating in the later stage, without the need for manual intervention throughout the process. Closed-loop control can be performed through real-time measurement by a liquid level sensor, automatically compensating for deviations such as changes in orifice coefficient and fluctuations in actual flow rate, reducing reliance on operational experience and fine-tuning, and improving system robustness.

[0037] 5. This invention features a simple structure, strong applicability, and is entirely gravity-driven, requiring no external pumping equipment. The system is simple in composition, has low energy consumption, and is easy to maintain. The porous distribution structure can be layered with buffer media such as sponges and foams, allowing for flexible adjustments based on experimental scale (flow rate, tank size). It is suitable for various physical simulation experiments, including marine sediment plume diffusion and pollutant migration. Attached Figure Description

[0038] Figure 1 A schematic diagram of a system for configuring a stable density-stratified aquatic environment using the free-fall method according to the present invention;

[0039] Figure 2A schematic diagram of the density-height distribution curve is provided.

[0040] Figure 3 This is a schematic diagram of the disturbance reduction structure and automatic lifting mechanism; the left figure is the front view and bottom view, and the right figure is the left side view.

[0041] The attached diagram is labeled as follows: 1. Upstream supply tank A; 2. Intermediate mixing tank B; 3. Target water tank C; 4. Liquid level in upstream supply tank A. 5. Bottom area of ​​upstream liquid supply tank A 6. Area of ​​the small hole on the bottom surface of the upstream liquid supply tank A 7. Flow rate at the bottom of upstream supply tank A 8. The liquid level in intermediate mixing tank B is high. 9. Bottom area of ​​intermediate mixing tank B 10. Area of ​​the small hole on the bottom surface of intermediate mixing tank B 11. Flow rate at the bottom of intermediate mixing tank B 12. The liquid level in target water tank C is high. 13. Bottom area of ​​target water tank C ; 14. Agitator; 15. Anti-disturbance structure; 21. Synchronous belt slide; 22. Stepper motor; 23. Support base; 24. Multi-hole distribution structure; 25. Anti-disturbance plate; 26. Guide channel; 27. Anti-disturbance plate support frame. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0043] This invention provides a system and method for configuring a stable density-stratified aquatic environment using the free-fall method, which is suitable for the rapid construction of density-stratified environments in laboratory physical simulations of marine sediment plume diffusion, pollutant migration, etc.

[0044] like Figure 1As shown, the system for configuring a stable density stratified water environment using the free-fall method of the present invention consists of an upstream supply tank A1, an intermediate mixing tank B2, and a target water tank C3 connected in sequence. Gravity-driven injection without external pumping is achieved by free drainage through orifices: the upstream supply tank A1 supplies liquid to the intermediate mixing tank B2 through a bottom orifice; the intermediate mixing tank B2 is continuously stirred to maintain thorough mixing of the water and cause the density within B2 to change over time; the intermediate mixing tank B2 injects the water that changes over time into the target water tank C through a bottom orifice, thereby mapping the density time history of the intermediate mixing tank B2 to the height-density profile of the target water tank C and forming a density gradient.

[0045] like Figure 3 As shown, to reduce free surface disturbance and the resulting entrainment and mixing during the injection process, this invention provides a disturbance reduction structure 15 above the free surface of the target water tank C, including a disturbance reduction plate 25 and a porous distribution structure 24. The upper surface of the disturbance reduction plate 25 is provided with a central receiving area and a flow guide trough 26 to achieve energy dissipation of the incoming flow and uniform circumferential flow distribution. A shower-type porous distribution structure is provided at the corner and a porous buffer medium can be superimposed, so that the fluid enters the vicinity of the free surface in a multi-point low momentum manner, significantly suppressing local jet impact and mixing. The central receiving area is a shallow basin structure, and the flow guide trough 26 connects the central receiving area and the edge of the disturbance reduction plate. The porous distribution structure 24 is located at the corner of the disturbance reduction plate 25 and is a shower-type porous cavity or porous pipe section. A buffer energy dissipation medium layer is superimposed below the porous distribution structure 24. The buffer energy dissipation medium layer is composed of one or a combination of sponge pads, open-cell foam, fiber felt, and fine mesh.

[0046] This invention also includes an automatic lifting mechanism and a controller to maintain the gap between the damping plate 25 and the free liquid surface at a preset value throughout the entire filling process, thereby further improving the stratification stability and repeatability. The automatic lifting mechanism is preferably implemented using a support base 23, a synchronous belt slide 21, and a stepper motor 22. The controller sets the target height of the damping plate 25 according to the liquid level rise pattern and outputs stepping pulses to achieve synchronous upward movement with the liquid surface. The support base is fixedly installed on the outside of the target water tank C; the synchronous belt slide 21 is installed on the support base 23, and the slider end of the synchronous belt slide 21 is fixedly connected to the damping plate support frame 27, which is used to support and position the damping plate; the stepper motor 22 is used to drive the synchronous belt slide; the synchronous belt slide 21 is internally provided with linear guide rails or guide rods to provide vertical guidance. The controller is used to control the movement of the automatic lifting mechanism.

[0047] This invention also provides a method for configuring a stable density-stratified aquatic environment using the free-fall method, comprising the following steps:

[0048] Step 1: Construct a three-stage gravity-driven system consisting of an upstream supply tank A, an intermediate mixing tank B, and a target water tank C connected in sequence. The upstream supply tank A, the intermediate mixing tank B, and the target water tank C respectively achieve gravity-driven injection without external pumping through orifices set at their bottoms.

[0049] Step 2: Supply water of the first density to the intermediate mixing tank B through the bottom hole of the upstream supply tank A. The water of the first density is kept fully mixed in the intermediate mixing tank B by continuous stirring, so that the density of the water in the intermediate mixing tank B changes continuously over time to form water of the second density.

[0050] Step 3: Inject the second density water into the target water tank C through the bottom hole of the intermediate mixing tank B, and map the density time history of the intermediate mixing tank B into the height density profile inside the target water tank C.

[0051] Step 4: Set up a disturbance reduction structure above the free liquid surface of the target water tank C. The disturbance reduction structure includes a disturbance reduction plate and a porous distribution structure. The upper surface of the disturbance reduction plate is provided with a central receiving area and a flow guide groove. The corner of the disturbance reduction plate is provided with a shower-type porous distribution structure. A buffer energy dissipation medium layer is superimposed below the porous distribution structure, so that the fluid entering the target water tank C spreads to the free liquid surface in a multi-point low momentum manner.

[0052] Step 5: The anti-disturbance plate is moved upward synchronously with the free liquid surface by an automatic lifting mechanism, maintaining a constant gap of 5-30mm.

[0053] Step 6: The controller calculates the target lifting speed of the damping plate according to the liquid level rise pattern, converts the target lifting speed into a pulse frequency and outputs it to the stepper motor, driving the damping plate to move upward synchronously with the liquid level of the target water tank C. The liquid level rise pattern is jointly determined by the geometric parameters of the upstream supply tank A, the intermediate mixing tank B and the target water tank C and the orifice parameters.

[0054] Specifically, step 1 includes:

[0055] This invention proposes a free-fall density stratification theory, based on gravity, to create a controllable brine density stratification (preferably a near-linear density gradient) within a target water tank using only the free drainage process from an orifice, without relying on external pumping. It provides a theoretical basis for determining the device's structural parameters and orifice parameters, as well as calculating the target's height-density profile. The system consists of an upstream supply tank A1, an intermediate mixing tank B2, and a target water tank C3 connected sequentially. The upstream supply tank A1 supplies low-density water to the intermediate mixing tank B2. After sufficient mixing is maintained in the intermediate mixing tank B2, brine is injected into the bottom of the target water tank C through a bottom orifice. The density profile within the target water tank C is mapped from the time-varying outflow density of the intermediate mixing tank B2 to the height-varying density distribution within the tank.

[0056] like Figure 1 As shown, the horizontal cross-sectional areas of the upstream supply tank A1, the intermediate mixing tank B2, and the target water tank C3 are respectively... (i.e., the bottom area of ​​the upstream liquid supply tank A) 5. Bottom area of ​​intermediate mixing tank B 9. Bottom area of ​​target water tank C 13) The areas of the bottom outlet orifices of the upstream supply tank A1 and the intermediate mixing tank B2 are respectively (i.e., the area of ​​the small hole on the bottom surface of the upstream liquid supply tank A) 6. Area of ​​the small hole on the bottom surface of intermediate mixing tank B 10), the liquid level heights are respectively (Upstream supply tank A has a high liquid level) 4. The liquid level in intermediate mixing tank B is high. 8. The liquid level in target water tank C is high. 12), The density of the brine in the upstream supply tank A1 is: (The supply phase is approximately constant), the density of the brine in intermediate mixing tank B2 is... (Assuming thorough mixing and uniform space within the container), the density distribution along the height direction within the target water tank C3 is denoted as... To ensure that the pressure distribution at the orifice approximates hydrostatic pressure and satisfies the quasi-steady-state drainage assumption, it is preferable to satisfy the following: and Under the conditions of incompressible fluid and neglecting friction losses, according to Bernoulli's equation, the outflow velocity at the orifice is approximately... ,in To correspond to the liquid level height inside the container, Let gravitational acceleration be used. Introduce the discharge coefficient. To characterize orifice constriction and local energy loss, the volumetric flow rates of the upstream supply tank A1 and the intermediate mixing tank B2 (i.e., the flow rate at the bottom of the upstream supply tank A) are... 7. Flow rate at the bottom of intermediate mixing tank B 11) They are respectively:

[0057] (1)

[0058] Upstream supply tank A1 satisfies the volume conservation relationship:

[0059] (2)

[0060] The analytical expression for the liquid level of upstream supply tank A1 over time, obtained by integration, is as follows:

[0061] (3)

[0062] Where the initial value .

[0063] Intermediate mixing tank B2 satisfies the volume conservation principle:

[0064] (4)

[0065] Based on the above flow rate expression, H can be determined. B and Q B The evolution process. Furthermore, assuming that intermediate mixing tank B2 is always in a fully mixed state, the density of the brine in intermediate mixing tank B2 satisfies the mass conservation law:

[0066] (5)

[0067] in, Let be the volume of liquid in intermediate mixing tank B2. For target tank C3, the outflow from the bottom of intermediate mixing tank B2 enters target tank C3 through the bottom inlet. If a diffusion energy dissipation structure is installed at the bottom inlet to make local jet disturbance negligible, then the liquid level in target tank C3 satisfies:

[0068] (6)

[0069] in, The symbol for time integration is used to distinguish it from t, thus allowing time to be used as a parameter to establish a mapping relationship for the water tank density profile: at time... The density of the liquid entering the water tank is The corresponding cumulative injection volume determines its filling height in the water tank; therefore, the water tank density profile can be written in parametric form.

[0070] (7)

[0071] Therefore, it can be seen that by adjusting the geometric parameters of the barrel and the orifice parameters, and If the mapping relationship satisfies the expected function, the target form of the "height-density" curve can be obtained in the target water tank C3, preferably achieving near-linear density stratification.

[0072] To facilitate design and scaling, the above relationships are made dimensionless. Characteristic flow and characteristic time are defined as follows:

[0073] (8)

[0074] in, , The initial liquid level and fluid volume of the upstream supply tank A1. The characteristic flow rate represents the fluid flow rate at the lower end of the upstream supply tank A1 at the initial moment. The characteristic time represents the flow rate at the lower end of the upstream supply tank A1. The time required to drain until empty.

[0075] Define a dimensionless variable:

[0076] (9)

[0077] Define the dimensionless geometry / orifice ratio parameter:

[0078] (10)

[0079] in, This is the ratio of the bottom area of ​​the intermediate mixing tank B2 to the bottom area of ​​the upstream supply tank A1. The ratio of the bottom area of ​​the target water tank C3 to that of the upstream supply tank A1. This is the ratio of the initial liquid level in the intermediate mixing tank B2 to that in the upstream supply tank A1. It is the ratio of the initial fluid density in the intermediate mixing tank B2 to that in the upstream supply tank A1.

[0080] During the liquid supply phase (corresponding to) The dimensionless flow rate of the upstream supply tank A1 is:

[0081] (11)

[0082] The dimensionless outflow from intermediate mixing tank B2 is:

[0083] (12)

[0084] The dimensionless governing equations can be written as:

[0085] (13)

[0086] (14)

[0087] Furthermore, the dimensionless liquid level and density of the target water tank C3 satisfy the following conditions:

[0088] (15)

[0089] The initial conditions are:

[0090] (16)

[0091] As can be seen from the above set of dimensionless equations, the density profile within the target water tank C3 is determined by five dimensionless parameters. They are jointly determined, and the "height-density" curve can be obtained by numerically solving this system of equations. Figure 2 Dimensionless parameter The density-height distribution curves for different values ​​show that when... When the density-height distribution is linear, that is, when the area of ​​the hole below the intermediate mixing tank B2 is twice the area of ​​the hole below the upstream supply tank A1, the initial liquid level heights of the upstream supply tank A1 and the intermediate mixing tank B2 are the same, and the bottom areas of the upstream supply tank A1, the intermediate mixing tank B2, and the target water tank C3 are the same, a linear density stratification relationship can be obtained.

[0092] Specifically, steps 4 and 5 include:

[0093] As mentioned earlier, the target density stratification curve can be obtained through theoretical design, but in actual configuration, injection disturbances must be minimized to avoid disrupting the established density gradient. In this embodiment, the upstream supply tank A1 contains low-density water, and the intermediate mixing tank B2 contains high-density brine. The low-density water in the upstream supply tank A1 is injected into the intermediate mixing tank B2 in a controlled manner, while continuous stirring is performed within the intermediate mixing tank B2 to ensure thorough and uniform mixing, causing the water density in the intermediate mixing tank B2 to gradually decrease over time. Subsequently, the water from the intermediate mixing tank B2, which changes over time, is injected above the free surface of the target water tank C3. The water entering the target water tank C3 first has a higher density, while the water entering later has a lower density, thus forming a stable density stratification environment in the target water tank C3 with a higher density at the bottom and a lower density at the top. Since the injection process continues above the free surface of the target water tank C3, to form a stable linear density stratification, the disturbance to the free surface caused by the injection must be minimized. To this end, the present invention proposes an upper surface diffusion buffer structure for significantly reducing free liquid surface disturbance, and proposes a mechanical device and control method for automatically raising the structure as the liquid level of the target water tank C3 rises.

[0094] The preferred disturbance reduction structure of the present invention includes a disturbance reduction plate 25 located above the target water tank C3 and a porous distribution structure 24. The disturbance reduction plate is positioned entirely above the free surface of the target water tank C3, and its upper surface has a central receiving area for receiving the free-falling flow. The central receiving area is designed as a shallow basin structure, so that the incoming flow first undergoes kinetic energy dissipation and stagnation within the central receiving area. The disturbance reduction plate is further provided with several guide channels 26, preferably annular grooves, connecting the central receiving area and the edge of the disturbance reduction plate, so that the received incoming flow is evenly distributed circumferentially along the guide channels 26 under the action of gravity, thereby reducing the local jet velocity and avoiding concentrated impact on the free surface of the target water tank C3. The corner of the disturbance reduction plate 25 is provided with a porous distribution structure 24, preferably several "shower-type" porous cavities or porous pipe sections, so that the water distributed by the guide channels 26 is discharged through the holes in a multi-point, low-speed, and approximately seepage-like manner, and then enters the vicinity of the free surface of the target water tank C3.

[0095] To further reduce orifice jet flow and suppress local entrainment, a buffer energy-dissipating medium layer is preferably superimposed below or at the outlet of the porous distribution component. The buffer energy-dissipating medium layer can be selected from sponge pads, open-cell foam, fiber felt, fine mesh or a combination thereof, so that the fluid is further decelerated and pulsation is weakened when passing through the porous medium, thereby causing the fluid entering the target water tank C3 to spread on the free liquid surface in a low momentum and low turbulence manner, significantly reducing free liquid surface fluctuations and the resulting density interlayer mixing.

[0096] To ensure that the target water tank C3 maintains minimal free surface disturbance at each stage of the filling process, the relative gap between the damping plate 25 and the free surface of the target water tank C3 is preferably maintained at a nearly constant small distance, i.e., the gap from the bottom surface of the damping plate 25 to the free surface is preferably maintained within the range of 5-30 mm (which can be adjusted according to the flow rate and the size of the target water tank C3). When the liquid level in the target water tank C3 rises over time, if the damping plate 25 does not rise accordingly, the gap will decrease, which may cause the damping plate 25 to contact the liquid surface or cause secondary disturbance; if the gap is too large, the incoming flow will again form a strong free fall and increase the impact disturbance. Therefore, the present invention further provides a mechanical structure that automatically rises with the liquid level, so that the damping plate 25 always maintains a preset relative gap during the filling process, thereby improving the repeatability and stability of linear density stratification.

[0097] like Figure 3 As shown, the automatic lifting mechanism includes a support base 23 fixedly installed on the outside of the target water tank C3, a synchronous belt slide 21 mounted on the support base 23, and a stepper motor 22 for driving the synchronous belt slide 21. The slider end of the synchronous belt slide 21 is fixedly connected to the damping plate support frame 27, which is used to support and position the damping plate 25, thereby achieving smooth lifting and lowering of the damping plate 25 in the vertical direction. Preferably, the synchronous belt slide 21 is provided with a linear guide rail / guide rod to provide vertical guidance and resistance to lateral forces, preventing the damping plate 25 from pitching or tilting during movement; the stepper motor 22 drives the synchronous belt through the synchronous belt pulley, so that the slide slider obtains vertical displacement, thereby driving the damping plate support frame 27 and the damping plate 25 to move up or down as a whole. Further preferably, mechanical limit switches or limit switches are provided to limit the maximum / minimum stroke, and a zero-point reference can be set for height reset before each sample preparation, thereby improving the reliability and repeatability of the device.

[0098] Specifically, step 6 includes:

[0099] To ensure that the target water tank C3 maintains minimal free surface disturbance at each stage of the filling process, in this embodiment, the relative gap between the damping plate 25 and the free surface of the target water tank C3 is preferably maintained at a nearly constant small distance (e.g., 5-30 mm). This is to avoid the gap decreasing due to rising liquid level, which could lead to contact with the liquid surface or secondary disturbance, while also preventing the gap from being too large, allowing the incoming flow to achieve a large free fall height and increasing impact disturbance. Preferably, the liquid level of the target water tank C3 is... Set the target height of the bottom surface of the damping plate 25 (or the reference surface of the damping plate support frame 27 fixed thereto) as a reference. To satisfy:

[0100] (17)

[0101] This maintains the preset gap throughout the entire injection process. When the volumetric flow rate injected from intermediate mixing tank B2 into target water tank C3 is... And the horizontal cross-sectional area of ​​the target water tank C3 is At that time, the liquid level in the target water tank C3 satisfies:

[0102] (18)

[0103] and (19)

[0104] Therefore, the target lifting speed of the damping plate 25 preferably satisfies the following:

[0105] (20)

[0106] The points marked with superscripts in the parameters represent the time derivative.

[0107] That is, the damping plate moves upward synchronously with the liquid level to maintain a constant gap.

[0108] To provide a lifting trajectory that can be directly used in the controller, this embodiment uses a set of linear hierarchical example parameters. For example, the dimensionless analytical expression for the liquid level of target water tank C3 under this parameter set is:

[0109] (twenty one)

[0110] Its dimensionless rate of ascent is:

[0111] (twenty two)

[0112] in, For dimensionless time, As a characteristic time scale, The characteristic height. Based on the correspondence between dimensionless and dimensional variables, the liquid level trajectory of the target water tank C3 can be obtained as follows:

[0113] (twenty three)

[0114] And the rate of increase in liquid level is:

[0115] (twenty four)

[0116] Therefore, the target lifting trajectory and target velocity of the scrambling plate 25 are as follows:

[0117] (25)

[0118] as well as

[0119] (26)

[0120] Its physical meaning is as follows: in the initial stage of infusion, the flow rate is relatively large, the liquid level rises rapidly, and the lifting speed of the damping plate is relatively large; in the later stage of infusion, the flow rate gradually decreases, the liquid level rises more slowly, and the lifting speed of the damping plate decreases linearly and approaches zero at the end of the infusion process, thus maintaining an approximately constant flow rate throughout the entire process. And reduce free surface disturbance.

[0121] Preferably, the automatic lifting mechanism is implemented using a synchronous belt slide 21 and a stepper motor 22, and the number of teeth on the synchronous belt pulley is [number missing]. Synchronous belt tooth pitch is (mm), the number of pulses per revolution after stepper motor microstepping is Then the displacement per pulse is In order to achieve the target speed The controller output pulse frequency preferably satisfies the following:

[0122] (27)

[0123] And can The system is discretized into several time slices to generate a segmented constant frequency table to improve the reliability and repeatability of the control implementation; more preferably, the system is equipped with a liquid level sensor for real-time measurement. Closed-loop correction is performed according to equation (17) to compensate for deviations caused by factors such as actual flow fluctuations and orifice coefficient changes, thereby further improving the stability and repeatability of the linear density stratification environment.

[0124] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A system for configuring a stable density-stratified aquatic environment using a free-fall method, characterized in that, include: The upstream supply tank A, the intermediate mixing tank B, and the target water tank C are connected sequentially through openings at their respective bottoms to form a three-stage gravity-driven structure. A stirrer is installed inside the intermediate mixing tank B to continuously stir the water to keep it fully mixed and to make the density inside the intermediate mixing tank B change over time. A disturbance reduction structure is disposed above the free liquid surface of the target water tank C. The disturbance reduction structure includes a disturbance reduction plate and a porous distribution structure, which are used to reduce the disturbance of the free liquid surface during the injection process. An automatic lifting mechanism, connected to the disturbance reduction plate, is used to drive the disturbance reduction plate to move vertically. A controller is used to control the movement of the automatic lifting mechanism.

2. The system for configuring a stable density-stratified aquatic environment using the free-fall method according to claim 1, characterized in that, The upper surface of the damping plate is provided with a central receiving area and a guide channel. The central receiving area has a shallow basin structure, and the guide channel connects the central receiving area with the edge of the damping plate. The porous distribution structure is set at the corner of the damping plate and is in the form of a shower-shaped porous cavity or porous pipe section. A buffer energy dissipation medium layer is superimposed below the porous distribution structure. The buffer energy dissipation medium layer is composed of one or a combination of sponge pad, open-cell foam, fiber felt, and fine mesh.

3. The system for configuring a stable density-stratified aquatic environment using the free-fall method according to claim 2, characterized in that, The automatic lifting mechanism includes: A support base is fixedly installed on the outside of the target water tank; A synchronous belt slide is mounted on the support base. The slider end of the synchronous belt slide is fixedly connected to the anti-scratching plate support frame. The anti-scratching plate support frame is used to support and position the anti-scratching plate. A stepper motor is used to drive the synchronous belt slide. The synchronous belt slide is equipped with a linear guide rail or guide rod inside to provide vertical guidance.

4. The system for configuring a stable density-stratified aquatic environment using the free-fall method according to claim 3, characterized in that, The bottom surface of the disturbance reduction plate maintains a constant gap of 5-30 mm with the free liquid surface of the target water tank C.

5. The system for configuring a stable density-stratified aquatic environment using the free-fall method according to claim 4, characterized in that, It also includes a liquid level sensor for real-time measurement of the liquid level in the target water tank; the controller receives the measurement value from the liquid level sensor, calculates the target lifting speed of the damping plate according to the liquid level rise pattern, and outputs a pulse frequency to the stepper motor to drive the damping plate to move synchronously upward with the liquid surface, thereby realizing closed-loop control.

6. A method for configuring a stable density-stratified aquatic environment using a free-fall method, characterized in that, Includes the following steps: Step 1: Construct a three-stage gravity-driven system consisting of an upstream supply tank A, an intermediate mixing tank B, and a target water tank C connected in sequence. The upstream supply tank A, the intermediate mixing tank B, and the target water tank C respectively achieve gravity-driven injection without external pumping through orifices set at their bottoms. Step 2: Supply water of a first density to the intermediate mixing tank B through the bottom hole of the upstream supply tank A. The water of the first density is kept fully mixed in the intermediate mixing tank B by continuous stirring, so that the density of the water in the intermediate mixing tank B changes continuously over time to form water of a second density. Step 3: Inject the second density water into the target water tank C through the bottom hole of the intermediate mixing tank B, and map the density time history of the intermediate mixing tank B to the height density profile inside the target water tank C; Step 4: Set up a disturbance reduction structure above the free liquid surface of the target water tank C so that the fluid entering the target water tank spreads to the free liquid surface in a multi-point low momentum manner; Step 5: The automatic lifting mechanism keeps the damping plate and the free liquid surface moving upward synchronously while maintaining a constant gap; Step 6: The controller calculates the target lifting speed of the damping plate according to the liquid level rise pattern, converts the target lifting speed into a pulse frequency and outputs it to the stepper motor, driving the damping plate to move upward synchronously with the liquid level of the target water tank. The liquid level rise pattern is jointly determined by the barrel geometry parameters and orifice parameters of the upstream supply tank A, the intermediate mixing tank B and the target water tank C.

7. The method for configuring a stable density-stratified aquatic environment using the free-fall method according to claim 6, characterized in that, In step 4, the central receiving area is a shallow basin structure, which is used to dissipate and retain the kinetic energy of the incoming flow within the central receiving area; the guide channel is an annular groove, which is used to distribute the incoming flow evenly in the circumferential direction under the action of gravity; the buffer energy dissipation medium layer is composed of one or a combination of sponge pad, open-pore foam, fiber felt, and fine mesh, which is used to further reduce the speed of the fluid and weaken the pulsation when it passes through.

8. The method for configuring a stable density-stratified aquatic environment using the free-fall method according to claim 7, characterized in that, In step 5, the constant gap is 5-30mm; the synchronous belt slide is equipped with a linear guide rail or guide rod to provide vertical guidance and resistance to lateral forces, so as to prevent the damping plate from pitching or tilting during the movement.

9. The method for configuring a stable density-stratified aquatic environment using the free-fall method according to claim 6, characterized in that, The disturbance reduction structure includes a disturbance reduction plate and a porous distribution structure. The upper surface of the disturbance reduction plate is provided with a central receiving area and a guide groove. The corners of the disturbance reduction plate are provided with a shower-type porous distribution structure. A buffer energy-consuming medium layer is superimposed below the porous distribution structure. The automatic lifting mechanism includes a support base fixed to the outside of the target water tank, a synchronous belt slide mounted on the support base, a stepper motor driving the synchronous belt slide, and a disturbance reduction plate support frame connecting the synchronous belt slide and the disturbance reduction plate.

10. The method for configuring a stable density-stratified aquatic environment using the free-fall method according to claim 6, characterized in that, In step 6, the controller discretizes the target lifting speed into several time slices to generate a segmented constant frequency table; the target lifting speed is larger in the early stage of perfusion, decreases linearly in the later stage of perfusion, and approaches zero at the end of the fluid supply.

11. The method for configuring a stable density-stratified aquatic environment using the free-fall method according to claim 10, characterized in that, Step 6 further includes: configuring a liquid level sensor to measure the liquid level height of the target water tank in real time, and the controller receiving the measured value of the liquid level sensor to perform closed-loop correction to compensate for deviations caused by actual flow fluctuations and orifice coefficient changes.

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