Method for determining hydrodynamic characteristics of floating installation of river immersed tube tunnel with large blockage ratio

Abstract

This application relates to the field of hydrodynamic characteristic calculation technology, and specifically discloses a method for determining the hydrodynamic characteristics of floating installation of immersed tunnels in inland rivers with high obstruction ratios. The method includes acquiring hydrological characteristic data of the target immersed tunnel project area; constructing a three-dimensional numerical flume based on the hydrological characteristic data; setting the computational domain geometry and boundary conditions in the three-dimensional numerical flume to be the same as the actual size of the target immersed tunnel project area; and performing simulation calculations based on the three-dimensional numerical flume for multiple typical working conditions during the floating installation process of the immersed tunnel to determine the hydrodynamic characteristics under each typical working condition. This application can accurately reveal the flow field distribution, pressure characteristics, streamlines, and vortex evolution laws around the immersed tunnel under high obstruction ratio conditions, providing a reliable theoretical basis and data support for attitude control, construction parameter optimization, and engineering safety assurance during the floating installation process of immersed tunnels in inland rivers.

Description

Technical Field

[0001] This application relates to the field of hydrodynamic characteristic calculation technology, and in particular to a method for determining the hydrodynamic characteristics of floating installation of immersed tunnels in inland rivers with large blockage ratios. Background Technology

[0002] With the development of inland waterway shipping and the increasing demand for cross-river transportation, immersed tunnels are being used more and more widely in inland waterway infrastructure construction due to their advantages such as minimal disruption to shipping and high construction efficiency. Unlike the marine environment, inland waterways have limited channel width, shallow water depth, and their flow is significantly affected by factors such as inflow conditions, channel morphology, and artificial regulation, resulting in complex and variable flow patterns. During the floating and installation of immersed tunnel sections, the dimensions of the tunnel segments are often comparable to or even close to the width of the waterway, exhibiting a typical high blockage ratio.

[0003] In existing technologies, researchers typically study the hydrodynamic characteristics of immersed tunnels through physical model experiments or numerical simulations. Physical model experiments mainly simulate the motion response and stress conditions of the immersed tunnel, barge, and mooring system under wave or current conditions using scaled-down models. Numerical simulation methods often employ computational fluid dynamics techniques to construct numerical flumes to analyze the flow field around the immersed tunnel. However, most existing research focuses on immersed tunnels in marine environments, where the main operating conditions are wave loads, the flow conditions are relatively simple, and the immersed tunnel structure is usually in a low blockage ratio state.

[0004] For immersed tunnels with high obstruction ratios in inland waterways, existing technologies have some limitations. Firstly, physical model tests are affected by scaling effects, making it difficult to fully simulate the strong obstruction of water flow by large-scale structures under real-world conditions. Their ability to capture flow field distortions, local velocity amplification, and complex vortex structures is also limited. Secondly, existing numerical simulation methods, when simulating complex inland water flows, lack sufficient precision in selecting turbulence models and handling boundary conditions, failing to accurately describe the nonlinear variations in water flow around the immersed tunnel under high obstruction ratios. Furthermore, existing methods often employ simplified or assumed hydrological conditions in calculations, lacking integration with on-site measured hydrological data from the engineering area. This leads to discrepancies between simulation results and actual conditions, making it difficult to accurately assess the hydrodynamic risks faced by the immersed tunnel during floating and installation. Summary of the Invention

[0005] To overcome the problems of relatively simple flow conditions and the fact that immersed tunnels with large obstruction ratios are usually in a low obstruction ratio state when their hydrodynamic characteristics are determined by physical model tests or numerical simulations, this application provides a method for determining the hydrodynamic characteristics of floating installation of immersed tunnels with large obstruction ratios in inland rivers.

[0006] This application provides a method for determining the hydrodynamic characteristics of floating installation of immersed tunnels in inland rivers with high obstruction ratios, including:

[0007] Acquire hydrological characteristic data of the target immersed tunnel project area; the hydrological characteristic data includes the time history curve of water flow velocity measured on site. Based on the hydrological characteristic data, a three-dimensional numerical flume is constructed; the three-dimensional numerical flume is used to simulate the floating and installation process of the immersed tube. In the three-dimensional numerical water tank, the computational domain geometry and boundary conditions are set to be the same as the actual dimensions of the target immersed tunnel engineering area; Based on the aforementioned three-dimensional numerical flume, simulation calculations are performed on multiple typical working conditions during the floating and installation of the immersed tube to determine the hydrodynamic characteristics under each of these typical working conditions.

[0008] According to a specific implementation method, the above-mentioned determination method includes obtaining hydrological characteristic data of the target immersed tunnel engineering area, including: Hydrological monitoring equipment was deployed in the target immersed tunnel project area to obtain the time history curve of water flow velocity within a preset time period. Statistical analysis is performed on the water flow velocity time history curve to determine the water flow velocity under a preset guarantee rate, which is used as the water flow inflow condition for the three-dimensional numerical water tank.

[0009] According to one specific implementation, the method described above, in which a three-dimensional numerical water tank is constructed, includes: In the computational domain, nested meshes are used to locally refine the areas where the immersed tube is located and the foundation trench is located, wherein the size of the nested mesh is smaller than the size of the global mesh.

[0010] According to one specific implementation, the above-mentioned determination method further includes: Prior to the simulation calculation, the size of the nested mesh is determined by a mesh independence test.

[0011] According to one specific implementation, in the above determination method, the plurality of typical operating conditions include: The first working condition before foundation trench excavation; and, The second working condition after the foundation trench excavation; The simulation calculations are used to analyze the changes in the hydrodynamic characteristics of the river channel before and after the trench excavation.

[0012] According to one specific implementation, in the above determination method, the hydrodynamic characteristics include at least the water flow velocity field distribution; The simulation results are used to indicate the velocity reduction caused by the expansion of the water passage cross-section after the trench is excavated, as well as the low-velocity wake shielding zone formed at the bottom of the trench to improve the hydrodynamic environment of the immersed tube.

[0013] According to one specific implementation, in the above determination method, the plurality of typical operating conditions include: The immersed tunnel sections are in multiple third working conditions with different blockage ratios during the floating and installation process; The simulation calculations are used to analyze the changes in hydrodynamic characteristics around the immersed tube section under different blockage ratios.

[0014] According to a specific implementation method, the third operating condition in the above determination method specifically includes: The working condition where the immersed tunnel segment is located at the dock exit point; The working condition where the immersed tunnel segment is located in the middle of the river channel; The working condition of the immersed tunnel segment located at the immersion position.

[0015] According to one specific implementation, in the above determination method, the plurality of typical operating conditions include: The immersed tunnel sections are in multiple fourth working conditions at different water depths during the immersion process; The simulation calculations are used to analyze the changes in hydrodynamic characteristics around the immersed tunnel sections during the immersion process at different water depths.

[0016] According to a specific implementation method, the fourth operating condition in the above determination method specifically includes: Operating conditions when the top of the immersed tunnel segment is tangent to the riverbed; The working conditions when the immersed tunnel section is sunk to the bottom of the foundation trench.

[0017] Compared with the prior art, the beneficial effects of this application are as follows: This application provides a method for determining the hydrodynamic characteristics of floating installation of immersed tunnels in inland rivers with high obstruction ratios. By integrating on-site measured hydrological characteristic data and constructing a three-dimensional numerical flume, while setting a computational domain and boundary conditions identical to those of the actual project, high-precision simulation of multiple typical working conditions throughout the entire floating installation process is achieved. This method can accurately reveal the flow field distribution, pressure characteristics, streamlines, and vortex evolution laws around the immersed tunnel under high obstruction ratio conditions. It provides a reliable theoretical basis and data support for attitude control, construction parameter optimization, and engineering safety assurance during the floating installation process of inland river immersed tunnels, thereby effectively avoiding construction risks caused by hydrodynamic imbalances and ensuring efficient and safe construction of immersed tunnels. Attached Figure Description

[0018] Figure 1 A flowchart illustrating the method for determining the hydrodynamic characteristics of floating installation of a large-blockage-ratio immersed tunnel in an inland river, as provided in an embodiment of this application. Figure 2 A schematic diagram of the computational domain and boundary conditions of a three-dimensional numerical flume provided in an embodiment of this application; Figure 3 This is a schematic diagram of the monitoring point layout provided in an embodiment of this application; Figure 4 This is a schematic diagram of the radar tidal velocity measuring instrument provided in an embodiment of this application; Figure 5 A schematic diagram of the time history curve for water flow velocity monitoring provided in the embodiments of this application; Figure 6 This is a schematic diagram of the computational domain grid provided in an embodiment of this application; Figure 7 This is a schematic diagram of the mesh independence test results provided in an embodiment of this application; Figure 8 A schematic diagram of the first operating condition provided for an embodiment of this application; Figure 9 A schematic diagram of the river velocity flow field distribution under the first working condition provided in this application embodiment; Figure 10 This is a schematic diagram of the second operating condition provided for an embodiment of this application; Figure 11 A schematic diagram of the river velocity flow field distribution under the second working condition provided in this application embodiment; Figure 12 A schematic diagram of the working condition of the immersed tunnel segment located at the dock outlet, provided for an embodiment of this application; Figure 13 A schematic diagram of the river velocity flow field distribution under the working condition of the immersed tunnel segment located at the dock outlet, as provided in the embodiments of this application; Figure 14 A schematic diagram illustrating the working condition of the immersed tunnel segment located in the center of the river channel, as provided in the embodiments of this application; Figure 15 A schematic diagram of the river velocity flow field distribution under the condition that the immersed tunnel section is located in the middle of the river channel, as provided in the embodiments of this application. Figure 16 A schematic diagram of the working condition of the immersed tunnel section at the immersion position provided in the embodiments of this application; Figure 17 A schematic diagram of the river velocity flow field distribution under the working condition of the immersed tunnel segment at the immersion position, provided in an embodiment of this application. Figure 18 A schematic diagram illustrating the working condition when the top of the immersed tunnel segment is tangent to the riverbed, as provided in the embodiments of this application; Figure 19 A schematic diagram of the river velocity flow field distribution under the working condition where the top of the immersed tunnel segment is tangent to the riverbed, as provided in the embodiments of this application; Figure 20 This describes the working conditions when the immersed tunnel section is sunk to the bottom of the trench, as provided in the embodiments of this application. Figure 21A schematic diagram of the river velocity flow field distribution under the working conditions when the immersed tunnel section is submerged to the bottom of the trench, as provided in the embodiments of this application. Detailed Implementation

[0019] The present application will now be described in further detail with reference to specific embodiments. However, this should not be construed as limiting the scope of the subject matter of the present application to the following embodiments; all technologies implemented based on the content of the present application fall within the scope of the present application.

[0020] Unless otherwise specified, the terms "upper," "lower," "left," "right," "center," "inner," and "outer" used in the description of specific embodiments of this application to indicate orientation or positional relationships are based on the orientation or positional relationships shown in the accompanying drawings, or the orientation or positional relationship in which the product / equipment / device is usually placed during use. These terms are merely for the purpose of facilitating the description of the solution in this application or simplifying the description in specific embodiments, and to help those skilled in the art quickly understand the solution. They do not indicate or imply that a particular device / component / element must have a specific orientation, or be constructed and operated in a specific positional relationship, and therefore should not be construed as limiting this application.

[0021] Furthermore, the use of terms such as "horizontal," "vertical," "suspended," "parallel," and "coaxial" does not imply that the corresponding device / component / element must be absolutely horizontal, vertical, suspended, parallel, or coaxial. Slight tilt or deviation is permissible, as long as it does not affect the normal function of the relevant component. For example, "horizontal" simply means that its direction is more horizontal relative to "vertical," not that the structure must be perfectly horizontal; a slight tilt is acceptable. "Coaxial" means that two components are arranged as coaxially as possible, allowing them to move coaxially or approximately coaxially when their relative positions change. Alternatively, it can be simplified to mean that the corresponding device / component / element, when arranged in "horizontal," "vertical," "suspended," "parallel," or "coaxial" directions, can have an error / deviation of ±10% relative to the corresponding direction, more preferably within ±8%, more preferably within ±6%, more preferably within ±5%, and more preferably within ±4%. For example, the deviation in the "coaxial" direction is controlled within 0.2-1mm, preferably within 0.2-0.5mm. As long as the corresponding device / component / element is within the error / deviation range, it can still achieve its function in the solution of this application.

[0022] Furthermore, the use of terms such as "first," "second," and "third" in terminology is merely for distinguishing descriptions of identical or similar components and should not be interpreted as emphasizing or implying the relative importance of a particular component.

[0023] Furthermore, in the description of the embodiments in this application, "several", "more than", and "a number of" represent at least two. They can be any number, such as two, three, four, five, six, seven, eight, nine, or even more than nine.

[0024] Furthermore, in the description of the technical solutions in this application, unless otherwise explicitly specified / limited / restricted, the terms "set up," "install," "connect," "link," "equipped with," "laid out," and "arranged" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to connection methods commonly used in the art, such as welding, riveting, bolting, and threaded connections. Such connections can be mechanical, electrical, or communication connections; they can be direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components.

[0025] It should be noted that, in the embodiments of this application, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0026] It should be noted that in this embodiment, "large blockage ratio" refers to a large ratio between the cross-sectional dimensions of the immersed tunnel section and the cross-sectional dimensions of the waterway. This typically indicates a significant obstruction of water flow by the immersed tunnel, leading to strong distortion of the flow field. This embodiment primarily addresses situations where the blockage ratio of the construction section exceeds 75%. In most actual projects, the maximum cross-sectional blockage ratio is 54%, which also applies to the method in this embodiment.

[0027] Additionally, the "VOF method" is short for Fluid Volume Function, a numerical technique for tracing free surfaces. It determines the location and shape of the free interface by calculating the proportion of fluid volume within each grid cell. The "RANS equations" are short for Reynolds-averaged Navier-Stokes equations, the governing equations describing the time-averaged motion of turbulence. The "RNG k-ε turbulence model" is a turbulence model based on renormalization group theory, which, compared to the standard k-ε model, can more accurately describe low-intensity turbulence and turbulence with strong shear zones. "Nested meshing" refers to a meshing technique that uses a finer mesh than the global mesh to locally refine key areas of interest within the computational domain, improving simulation accuracy in critical regions without significantly increasing overall computational cost.

[0028] To accurately determine the hydrodynamic characteristics of immersed tunnels with high obstruction ratios in inland rivers during the floating and installation process, and to provide reliable data support for construction safety, this application provides a method for determining the hydrodynamic characteristics of immersed tunnels with high obstruction ratios during floating and installation. This method integrates on-site measured hydrological data and high-precision numerical simulation technology to systematically analyze the hydrodynamic evolution law of the entire floating and installation process of the immersed tunnel. Please refer to... Figure 1 It illustrates a flowchart of a method for determining the hydrodynamic characteristics of floating installation of a large-blockage-ratio immersed tunnel in an inland river, as provided in an embodiment of this application, including: Step 1: Obtain hydrological characteristic data of the target immersed tunnel project area; Step 2: Construct a three-dimensional numerical flume based on the hydrological feature data; Step 3: In the three-dimensional numerical water tank, set the computational domain geometry and boundary conditions that are the same as the actual dimensions of the target immersed tunnel engineering area; Step 4: Based on the three-dimensional numerical water tank, simulation calculations are performed for multiple typical working conditions during the floating and installation of the immersed tube to determine the hydrodynamic characteristics under each typical working condition.

[0029] Specifically, the first step is to acquire hydrological characteristic data of the target immersed tunnel project area. This hydrological characteristic data forms the basis for constructing a high-precision numerical model. After acquiring the hydrological characteristic data, a three-dimensional numerical flume is constructed to simulate the floating and installation process of the immersed tunnel. The governing equations of this flume include the Reynolds-averaged Navier-Stokes RANS equations and the RNG k-ε turbulence model, and the VOF method is used to track the free surface. The RANS equations describe the time-averaged motion of the fluid, and their specific form is:

[0030]

[0031] In the formula: ρ For fluid density; u , v , w The velocity vectors are respectively in x , y , z Components in direction; V F It represents the fluid volume fraction; A j for j Area fraction in a direction; G i For fluid in i Volume force acceleration in the direction of; f i For fluid in i Viscous acceleration in the direction of kinetic force.

[0032] RNG k - ε The turbulence model is used to close the RANS equations, and its equations for turbulent kinetic energy and turbulent kinetic energy dissipation rate are as follows:

[0033]

[0034] In the formula: k T It is turbulent kinetic energy; ε T This is the turbulent kinetic energy dissipation term; A x , A y , A z These are the area fractions in the three directions, respectively; P T This is the turbulent kinetic energy generation term for the average velocity gradient; G T The turbulent kinetic energy generation term for buoyancy; f T For turbulent diffusion; f ε This is the turbulent dissipation and diffusion term; f CDIS1 , f CDIS2 , f CDIS3 These are dimensionless parameters, with default values ​​of 1.42, 1.68, and 0.2, respectively.

[0035] Meanwhile, to accurately capture the position and changes of the water-air interface, this embodiment employs the Fluid Volume Flow (VOF) method to track the free surface. The VOF method determines the position of the free interface by calculating the volume fraction of fluid within each grid cell, and can accurately simulate the fluctuations and deformations of the free surface.

[0036] To enable the simulation results to be directly applied to engineering practice, this embodiment sets the computational domain geometry and boundary conditions in the three-dimensional numerical flume to be identical to the actual dimensions of the engineering area. For example, taking a cross-river channel project in Dongguan City as an example, the computational domain size can be set to 500m × 410m × 27m, encompassing both the river channel and the dry dock section. The riverbed bottom elevation is set to zero, and the trench excavation depth is 19m. The water temperature is set to 20℃, and the dynamic viscosity coefficient μ is 0.001 Pa·s. The boundary conditions must also match reality; for example, the computational domain inlet uses a velocity inlet boundary condition, the outlet uses a free outflow boundary condition, the top surface is set as a free liquid surface, and the riverbed surface, the submerged pipe surface, and the river channel side are all set as rough wall boundaries. Specific computational domain and boundary conditions are as follows: Figure 2 As shown.

[0037] After completing the above modeling work, simulation calculations can be performed on multiple typical working conditions during the floating and installation of the immersed tube based on this three-dimensional numerical flume. By solving the governing equations, hydrodynamic characteristic data such as flow field distribution, pressure field distribution, streamlines, and vorticity under each typical working condition can be obtained.

[0038] The method provided in this embodiment integrates on-site measured hydrological characteristic data and constructs a three-dimensional numerical flume. Simultaneously, it sets computational domains and boundary conditions identical to those of the actual engineering project, achieving high-precision simulation of multiple typical working conditions throughout the entire process of immersed tunnel floating and installation. This method accurately reveals the flow field distribution, pressure characteristics, streamlines, and vortex evolution laws around the immersed tunnel under high blockage ratio conditions. It provides a reliable theoretical basis and data support for attitude control, construction parameter optimization, and engineering safety assurance during the floating and installation of inland river immersed tunnels, effectively avoiding construction risks caused by hydrodynamic imbalance and ensuring efficient and safe construction of immersed tunnels.

[0039] In one or more embodiments, to further improve the accuracy of numerical simulation and enable it to truly reflect the actual water flow conditions in the engineering area, the embodiments of this application refine the specific methods for obtaining hydrological characteristic data, including: Hydrological monitoring equipment was deployed in the target immersed tunnel project area to obtain the time history curve of water flow velocity within a preset time period. Statistical analysis is performed on the water flow velocity time history curve to determine the water flow velocity under a preset guarantee rate, which is used as the water flow inflow condition for the three-dimensional numerical water tank.

[0040] For example, such as Figure 3 and Figure 4 As shown, a radar tidal velocity meter can be deployed at the monitoring point next to the Quhai Bridge to continuously collect water flow velocity data for more than a year. The model is JYB-SW, with a range of 0.1–20 m / s, an accuracy of ±0.01 m / s, and a sampling frequency of 24 GHz. Through long-term continuous monitoring, data such as… Figure 5 The time-history curve of water flow velocity monitoring shown includes information on water flow velocity changes under various hydrological conditions such as high water season, low water season, and extreme weather, comprehensively reflecting the hydrological characteristics of the project area. Statistical analysis of the water flow velocity time-history curve determines the water flow velocity under a preset guarantee rate, which serves as the inflow condition for subsequent numerical simulations. For example, statistical analysis of 8368 water flow velocity data points revealed that the average flow velocity with a guarantee rate of over 95% throughout the year is 1.2 m / s; therefore, 1.2 m / s can be used as the inflow velocity at the inlet of the numerical flume.

[0041] Furthermore, statistical analysis was performed on the time-history curve of the water flow velocity monitoring to determine the water flow velocity under a preset guarantee rate, which was then used as the inflow condition for the three-dimensional numerical flume. For example, statistical analysis of 8368 collected water flow velocity data points revealed that the average flow velocity for a guarantee rate of over 95% throughout the year was 1.2 m / s. This means that the water flow velocity will not exceed this value for most of the year. Therefore, 1.2 m / s can be used as the inflow condition for the velocity inlet in CFD simulation calculations. This inflow condition setting is representative enough to cover most construction conditions, while avoiding the waste of computational resources or overly conservative design caused by using extreme flow velocities.

[0042] This embodiment introduces long-term on-site monitoring data and uses statistical methods to determine representative inflow conditions, making the input conditions of the numerical model closer to engineering practice, thereby further improving the reliability and engineering applicability of the simulation results.

[0043] In one or more embodiments, in order to achieve refined capture of the hydrodynamic characteristics of key areas around the immersed tube under limited computing resources, the embodiments of this application optimize the mesh generation method for constructing a three-dimensional numerical flume, including: Specifically, the above-mentioned determination method, in constructing a three-dimensional numerical flume, also includes locally refining the regions where the immersed tube is located and the foundation trench is located within the computational domain using nested meshes, wherein the size of the nested meshes is smaller than the size of the global mesh. Nested meshing is a partitioned meshing technique, the core of which is to embed one or more sets of finer meshes into areas with drastic changes in flow variable gradients, such as around the immersed tube, the bottom of the foundation trench, and the corner points of the tube sections, based on the global background mesh.

[0044] For example, such as Figure 6 As shown, a global mesh is first generated in the computational domain, with a size that can be set to 1.0m. Then, a smaller, more refined mesh is nested around the immersed tunnel sections and the foundation trench, with a size that can be set to 0.5m. Here, the size of the nested mesh is smaller than the size of the global mesh, with a size ratio of 1:2. The global mesh is responsible for covering the entire computational domain, ensuring computational stability; the nested mesh is responsible for local refinement, improving the simulation accuracy in critical areas. Data is exchanged and transferred between the global and nested meshes through interpolation.

[0045] By employing nested mesh technology, the simulation accuracy of complex flow fields around immersed tubes and trenches can be significantly improved without significantly increasing the overall number of meshes and computational burden. This enables numerical flumes to more accurately capture key hydrodynamic features such as local velocity abrupt changes, vortex structure generation and evolution, and pressure gradient changes.

[0046] In one or more embodiments, in order to ensure the best balance between computational accuracy and computational efficiency in numerical simulation, the method for determining the size of nested meshes has been optimized in this application.

[0047] Specifically, in this embodiment of the application, the size of the nested mesh is determined through a mesh independence test before the simulation calculation. The mesh independence test is an important step in CFD simulation, and its purpose is to find a mesh density threshold: when the mesh density exceeds this threshold, further refining the mesh has a negligible impact on the calculation results, and thus the calculation results can be considered to be independent of the mesh.

[0048] For example, multiple sets of grids of different sizes can be set for comparative calculations. As shown in Table 1, four grid configuration schemes can be set, corresponding to different global grid sizes and encrypted area grid sizes, with the number of grids ranging from 3.1×10^6 to 4.9×10^7.

[0049] Table 1. Schematic diagram of mesh parameters for mesh independence test

[0050] The working conditions after trench excavation were selected for analysis, and grid independence was tested based on the riverbed pressure on the left side of the trench along the centerline y=0 and the flow velocity 1.0m from the bottom. The test results are as follows. Figure 7 As shown. From Figure 7 As can be seen from this, when the number of grids increases from 3.1 × 10... 6 Increased to 6.2 × 10 6 At that time, the calculated flow velocity and pressure values ​​changed to some extent. However, as the number of grid cells continued to increase, from 6.2 × 10⁻⁶, the calculated values ​​changed again. 6 Increased to 1.5 × 10 7 Then to 4.9×10 7 At that time, the flow rate and pressure values ​​did not change significantly. This indicates that 6.2 × 10 6 The current mesh size is sufficient to meet the mesh independence requirement. Further refining the mesh will have limited improvement on the computational results and will instead increase computation time exponentially. Therefore, the mesh parameter can be set to 6.2 × 10⁻⁶. 6 (Global grid 1.0m, nested grid 0.5m) is determined as the final computational grid.

[0051] This embodiment scientifically determines the size of the nested mesh by checking the mesh independence, which ensures the accuracy of the simulation calculation and avoids the waste of computing resources caused by excessive mesh density, thus achieving an optimized balance between computational accuracy and efficiency.

[0052] In one or more embodiments, in order to analyze in depth the impact of the key construction step of trench excavation on the hydrodynamic environment of the river, the embodiments of this application have refined the specific settings of several typical working conditions.

[0053] Specifically, several typical working conditions are included, namely, the first working condition before trench excavation and the second working condition after trench excavation. By comparing the simulation results of these two working conditions, the changes in the hydrodynamic characteristics of the river channel before and after trench excavation can be analyzed.

[0054] For example, the first working condition represents the state before the foundation trench is excavated, such as... Figure 8 As shown, the river channel is a natural channel with a regular cross-section. Simulation calculations for this condition yield the following results: Figure 9 The velocity field distribution is shown. From... Figure 9 It can be seen that before the trench was excavated, the river channel velocity field was relatively stable, with the velocity distributed evenly along the water depth, and only the velocity gradient changed in the near-wall region.

[0055] The second working condition represents the state after the foundation trench is excavated, such as... Figure 10 As shown, a trench with a depth of 19m was excavated in the river channel at this time. Simulation calculations for this working condition yield the following results: Figure 11 The velocity field distribution is shown. From... Figure 11 It can be seen that the flow field changed significantly after the trench was excavated. Due to the rapid expansion of the water passage cross-section, the main kinetic energy diffused after the water entered the trench area, and the flow velocity decreased sharply. Especially at the bottom of the trench, the water velocity was almost zero, forming a low-velocity wake shield zone that was conducive to the placement of the immersed tube.

[0056] By setting up comparative working conditions before and after trench excavation, this method can quantitatively evaluate the improvement effect of trench excavation on the hydrodynamic characteristics of the river channel and verify the important role of deep trenches in providing a stable construction environment.

[0057] In one or more embodiments, in order to more specifically reveal the mechanism by which trench excavation improves the construction environment of immersed tubes, the embodiments of this application have conducted an in-depth analysis of the hydrodynamic characteristics revealed by simulation calculations.

[0058] Specifically, the hydrodynamic characteristics obtained from the simulation calculations include at least the velocity field distribution. By comparing the velocity fields before and after the trench excavation, the changes brought about by the excavation can be visually observed. The simulation results are used to indicate the velocity attenuation caused by the expansion of the cross-sectional area after trench excavation, as well as the low-velocity wake shielding zone formed at the bottom of the trench to improve the hydrodynamic environment for the immersed tube placement.

[0059] This embodiment, through quantitative analysis of the velocity field distribution characteristics, clearly reveals the intrinsic mechanism by which deep trenches, by expanding the cross-section of the water passage, form a low-velocity wake shielding zone, thereby improving the hydrodynamic environment of the immersed tube.

[0060] In one or more embodiments, in order to analyze in depth the impact of changes in the blockage ratio due to different locations on the hydrodynamic characteristics during the floating process of the immersed tube, the embodiments of this application have refined the specific settings of several typical working conditions.

[0061] Specifically, several typical operating conditions include multiple third operating conditions where the immersed tunnel sections are in different blockage ratio states during the floating and installation process. Simulation calculations are used to analyze the changes in hydrodynamic characteristics around the immersed tunnel sections under different blockage ratio states. It can be understood that the blockage ratio refers to the ratio of the cross-sectional area of ​​the immersed tunnel section to the cross-sectional area of ​​the waterway; the larger the blockage ratio, the stronger the obstruction effect of the immersed tunnel on the water flow.

[0062] For example, the hydrodynamic characteristics of the immersed tunnel segment can be simulated at different stages, such as when it leaves the dock, floats to the center of the river channel, and floats to the sinking position. By comparing and analyzing the simulation results of these conditions, the influence of the blockage ratio on the flow field structure as the position of the immersed tunnel changes can be revealed.

[0063] In one or more embodiments, in order to analyze the hydrodynamic characteristics of the immersed tube during the entire floating process more specifically, the embodiments of this application have specifically defined multiple third working conditions under different blockage ratios.

[0064] Specifically, the third working conditions under different blockage ratios include the third working condition where the immersed tunnel section is located at the dock outlet, the third working condition where the immersed tunnel section is located in the middle of the river channel, and the third working condition where the immersed tunnel section is located at the sinking position.

[0065] For example, the working condition when the immersed tunnel segment is located at the dock exit position is as follows: Figure 12 As shown, corresponding Figure 13 The state shown is as follows. Under this condition, the pipe section is located at the dry dock entrance, which significantly disturbs the local flow field. Complex flow occurs at the front end of the pipe section, and a backflow zone exists at the rear end. Streamlines exhibit obvious flow around and separation phenomena. Vorticity is highly concentrated at the corner of the pipe section, indicating that this stage is a high-risk stage of vortex disturbance, and mooring control needs to be strengthened.

[0066] The working condition where the immersed tunnel segment is located in the middle of the river channel is as follows: Figure 14 As shown, corresponding Figure 15 The state shown is as follows. Under this condition, the pipe section is located in the center of the river channel, exhibiting typical characteristics of a large blockage ratio. However, due to the cross-sectional expansion effect of the deep trench, the flow field compression caused by the blockage of the pipe section is effectively offset, so that the flow velocity around the pipe section is always lower than that of the mainstream outside the trench, avoiding the phenomenon of pipe corner narrowing and acceleration in conventional bluff body flow.

[0067] The working conditions of the immersed tunnel section at the immersion position are as follows: Figure 16 As shown, corresponding Figure 17The state shown is as follows. Under this condition, the pipe section floats to the sinking position and gradually enters the shielded area of ​​the foundation trench. The flow field is significantly weakened by the blockage of the pipe section, the streamlines gradually return to stability, and the vortices dissipate, providing favorable conditions for subsequent sinking operations.

[0068] By simulating these three specific working conditions, this method can systematically reveal the hydrodynamic evolution law of the immersed tube from leaving the dock to floating and sinking.

[0069] In one or more embodiments, in order to analyze in depth the impact of different sinking depths on hydrodynamic characteristics during the sinking process of the immersed tube, the embodiments of this application have refined the specific settings of several typical working conditions.

[0070] Specifically, several typical working conditions include multiple fourth working conditions where the immersed tunnel sections are at different water depths during the immersion process. Simulation calculations are used to analyze the changes in the hydrodynamic characteristics around the immersed tunnel sections during the immersion process at different water depths.

[0071] For example, the entire process of the immersed tube being submerged from the top of the water surface to its gradual sinking until it finally rests at the bottom of the trench can be simulated. By comparing and analyzing the simulation results under different sinking depths, the vertical variation of the flow field and pressure field around the immersed tube can be revealed as the sinking depth increases.

[0072] In one or more embodiments, in order to analyze the hydrodynamic characteristics of the immersed tube at key nodes in the immersion process more specifically, the embodiments of this application have specifically defined multiple fourth working conditions at different water depths.

[0073] Specifically, there are multiple fourth working conditions at different water depths, including the working condition when the top of the immersed tunnel section is tangent to the riverbed and the working condition when the immersed tunnel section is sunk to the bottom of the trench.

[0074] For example, the working condition when the top of the immersed tunnel segment is tangent to the riverbed is as follows: Figure 18 As shown, corresponding Figure 19 The diagram shows the current state. Under this condition, the entire immersed tube is submerged below the original riverbed line, exhibiting a significant coupling effect of deep-channel shielding and cross-sectional expansion. The upper mainstream of the river maintains a certain flow velocity, but the flow velocity within the trench has significantly decreased, with the velocity at the top surface of the immersed tube dropping to 0.8–1.0 m / s. Streamlines exhibit a stratified distribution, with the upper streamlines maintaining the mainstream trend, while the streamlines within the trench are sparse.

[0075] The working conditions when the immersed tunnel section is sunk to the bottom of the trench are as follows: Figure 20 As shown, corresponding Figure 21The diagram shows the final state of the immersed tube. Under this condition, the tube eventually settles at the bottom of the trench. At this point, the flow velocity in the trench is below 0.1 m / s, and the near-static, low-disturbance environment ensures high-precision docking. The streamline distribution reaches its most stable state, with almost no obvious streamline movement trajectory within the trench. Simultaneously, the surface pressure of the immersed tube reaches its peak value throughout the process, and the pressure at the bottom of the tube can reach 0.24 MPa. Towards the end of the placement phase, it is necessary to pay attention to the squeezing effect and sudden changes in local pressure gradients that may be induced by the obstruction of residual water discharge at the bottom of the tube, which require key control during construction.

[0076] For example, such as Figure 11 and Figure 21 As shown, after the trench is excavated, the water flow velocity is almost zero in the area below half the trench height, forming a low-velocity wake shielding zone. When the immersed tube is lowered to the bottom of the trench, as... Figure 21 As shown, the water velocity around the immersed tube is generally below 0.1 m / s, with some areas approaching stillness. Compared to the incoming flow of 1.2 m / s outside the trench, the flow velocity at the bottom of the trench is reduced by more than 90%. This extremely low flow velocity environment allows the immersed tube to be completely isolated from the direct impact of the main river current, providing a highly stable hydrodynamic environment for the final placement and high-precision docking of the immersed tube.

[0077] Through simulation calculations of the above-mentioned typical working conditions, this application can accurately reveal the complex hydrodynamic characteristics around the immersed tube under high blockage ratio conditions, providing theoretical basis and data support for attitude control, tension compensation and placement process optimization of inland river immersed tube tunnel floating installation, effectively avoiding construction risks caused by hydrodynamic imbalance, and ensuring efficient and safe construction of immersed tube tunnels.

[0078] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for determining the hydrodynamic characteristics of floating installation of immersed tunnels in inland rivers with high obstruction ratios, characterized in that, include: Acquire hydrological characteristic data of the target immersed tunnel project area; the hydrological characteristic data includes the time history curve of water flow velocity measured on site. Based on the hydrological characteristic data, a three-dimensional numerical flume is constructed; the three-dimensional numerical flume is used to simulate the floating and installation process of the immersed tube. In the three-dimensional numerical water tank, the computational domain geometry and boundary conditions are set to be the same as the actual dimensions of the target immersed tunnel engineering area; Based on the aforementioned three-dimensional numerical flume, simulation calculations are performed on multiple typical working conditions during the floating and installation of the immersed tube to determine the hydrodynamic characteristics under each of these typical working conditions.

2. The method according to claim 1, characterized in that, Obtain hydrological characteristic data of the target immersed tunnel project area, including: Hydrological monitoring equipment was deployed in the target immersed tunnel project area to obtain the time history curve of water flow velocity within a preset time period. Statistical analysis is performed on the water flow velocity time history curve to determine the water flow velocity under a preset guarantee rate, which is used as the water flow inflow condition for the three-dimensional numerical water tank.

3. The method according to claim 2, characterized in that, Constructing a three-dimensional numerical water tank includes: In the computational domain, nested meshes are used to locally refine the areas where the immersed tube is located and the foundation trench is located, wherein the size of the nested mesh is smaller than the size of the global mesh.

4. The method according to claim 3, characterized in that, The method further includes: Prior to the simulation calculation, the size of the nested mesh is determined by a mesh independence test.

5. The method according to claim 4, characterized in that, The typical operating conditions include: The first working condition before foundation trench excavation; and, The second working condition after the foundation trench excavation; The simulation calculations are used to analyze the changes in the hydrodynamic characteristics of the river channel before and after the trench excavation.

6. The method according to claim 5, characterized in that, The hydrodynamic characteristics include at least the water flow velocity field distribution; The simulation results are used to indicate the velocity reduction caused by the expansion of the water passage cross-section after the trench is excavated, as well as the low-velocity wake shielding zone formed at the bottom of the trench to improve the hydrodynamic environment of the immersed tube.

7. The method according to claim 4, characterized in that, The typical operating conditions include: The immersed tunnel sections are in multiple third working conditions with different blockage ratios during the floating and installation process; The simulation calculations are used to analyze the changes in hydrodynamic characteristics around the immersed tube section under different blockage ratios.

8. The method according to claim 7, characterized in that, The third operating condition specifically includes: The working condition where the immersed tunnel segment is located at the dock exit point; The working condition where the immersed tunnel segment is located in the middle of the river channel; The working condition of the immersed tunnel segment located at the immersion position.

9. The method according to claim 4, characterized in that, The typical operating conditions include: The immersed tunnel sections are in multiple fourth working conditions at different water depths during the immersion process; The simulation calculations are used to analyze the changes in hydrodynamic characteristics around the immersed tunnel sections during the immersion process at different water depths.

10. The method according to claim 9, characterized in that, The fourth operating condition specifically includes: Operating conditions when the top of the immersed tunnel segment is tangent to the riverbed; The working conditions when the immersed tunnel section is sunk to the bottom of the foundation trench.

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