A Prediction Method for Three-Dimensional Motion Response of Suspended Tunnel Pipe under Combined Wave and Current Excitation

Abstract

A method for predicting the three-dimensional motion response of a suspended tunnel tube under combined wave and current excitation belongs to the technical field of underwater suspended tunnels. To solve the problem of poor prediction accuracy in predicting the motion response of a suspended tunnel tube by simplifying the three-dimensional real model of the suspended tunnel tube into a two-dimensional plane model, the present invention first establishes a three-dimensional numerical wave tank based on the boundary wave-making method; then conducts overlapping grid and wave grid division based on STAR CCM+ and establishes a fluid-structure interaction numerical simulation model. The connection between the suspended tunnel tube and the seabed is established through a tensioned catenary, and then a three-dimensional numerical model of the suspended tunnel under combined wave and current excitation is established. Based on this numerical simulation, parametric sensitivity analysis is carried out on the important non-linear influencing factors of the suspended tunnel respectively, and the influence of the sensitivity parameters on the vibration response characteristics of the suspended tunnel tube is analyzed to realize the prediction of the three-dimensional motion response of the suspended tunnel tube under combined wave and current excitation.

Description

Technical Field

[0001] The present invention belongs to the technical field of underwater floating tunnels, and particularly relates to a method for predicting the three-dimensional motion response of a floating tunnel tube body. Background Art

[0002] With the development of technology, cross-sea channels such as undersea tunnels and cross-sea bridges have been rapidly constructed globally, greatly promoting economic and cultural exchanges. However, traditional cross-sea channels face many challenges, such as high construction costs, environmental impacts, and safety hazards. As an innovative solution, the Submerged Floating Tunnel (hereinafter referred to as the floating tunnel) has many advantages, such as low ecological impact, flexible construction, high disaster resistance, and strong adaptability to terrain. With the continuous progress of technology, the application prospect of the floating tunnel will be broader globally and is expected to provide an effective alternative solution to solve the problems of traditional cross-sea channel construction.

[0003] The floating tunnel consists of a tubular structure of standard segments, an underwater anchoring system (or a floating structure on the water), and a revetment section connected to the shore. The tubular structure is balanced with external and internal loads during the construction and operation stages through net buoyancy and a support system, and has a complete force system. Currently, floating tunnels are classified into three types according to the support method: pier type, pontoon type, and cable type. The pier type is supported by piers and is suitable for shallow waters, but has high costs and great technical difficulties in deep waters. The pontoon type maintains stability through surface pontoons and is vulnerable to the influence of wind, waves, and ship collisions. The cable type fixes the tube body at a position 20 - 30 meters below the water surface through underwater cables, is less affected by the outside, has strong adaptability, and has little impact on the environment. In summary, compared with pier-type and pontoon-type floating tunnels, the cable-type floating tunnel has stronger spanning and terrain adaptation capabilities. In addition, the design and construction of its anchoring system can draw on mature offshore platform technologies. Therefore, the cable-type floating tunnel has become the most practical and promising form of floating tunnel. When complex environmental loads act on the floating tunnel tube body, periodic loads will cause the structure to move. As a large underwater structure, the design and maintenance of the floating tunnel must be particularly cautious. Once the structure is damaged, it will not only cause huge economic losses but also may result in irreparable casualties. To ensure the safety of pedestrians and vehicles inside the floating tunnel tube body, it is necessary to ensure that the tunnel tube body can work safely and stably under complex marine environmental loads, which is also one of the key objectives of the design and research of the floating tunnel.

[0004] Underwater suspension tunnels are vulnerable to the action of complex surrounding environmental loads. Especially under the continuous action of loads such as ocean currents and waves, the tunnel body of the suspension tunnel is extremely prone to dangerous motion responses such as vortex-induced resonance, posing a great threat to the stability and safety of the suspension tunnel during normal operation. Therefore, developing a stable and reliable numerical prediction method for the three-dimensional motion response of the suspension tunnel body under combined wave and current excitation, and deeply analyzing the coupled dynamic response characteristics of the suspension tunnel body under combined wave and current excitation based on this method, are important prerequisites to ensure the safety of pedestrians and vehicles inside the suspension tunnel. For the research on the dynamic response of the suspension tunnel body under combined wave and current excitation, it can be roughly divided into three categories according to the research methods: model experiment research, theoretical calculation research, and numerical calculation research. Compared with model experiments and theoretical calculation methods, numerical calculation research based on the computational fluid dynamics (CFD) method has the advantages of low research cost and few empirical model coefficients, and is particularly suitable for large-scale parameter influence characteristic analysis. Current theoretical and computational studies often simplify the three-dimensional real model of the suspension tunnel body into a two-dimensional plane model. Although this simplified treatment method can effectively reduce the computational complexity to a certain extent, it is difficult to truly reflect the three-dimensional motion response characteristics of the real tunnel body structure, and further leads to an insufficient understanding of the dynamic behavior of the pipeline under combined wave and current excitation. In addition, in current model experiment research, due to the high experimental cost and technical conditions, when analyzing the three-dimensional motion response of the suspension tunnel body under combined wave and current excitation, researchers usually cannot accurately capture the complex interaction between the fluid and the structure, thus resulting in an insufficient and inaccurate understanding of the dynamic behavior of the pipeline. Summary of the Invention

[0005] The present invention aims to solve the problem of poor prediction accuracy in predicting the motion response of a suspension tunnel body when simplifying the three-dimensional real model of the suspension tunnel body into a two-dimensional plane model.

[0006] A method for predicting the three-dimensional motion response of a suspension tunnel body under combined wave and current excitation, comprising the following steps:

[0007] S1. Establish a three-dimensional numerical model of the suspension tunnel under combined wave and current excitation based on STAR CCM+, including:

[0008] S101. Establish a three-dimensional numerical wave tank under combined wave and current excitation based on the boundary wave-making method;

[0009] S102. Conduct overlapping grid and wave grid division, and establish a fluid-structure interaction numerical simulation model:

[0010] First, determine the parameters, including the style and dimensions of the floating tunnel tube body, the stiffness k of the anchor cable, the submerged depth d, the flow velocity U, the water depth h, the wave amplitude A, and the wave period T. Then, perform mesh generation and numerical simulation. During the process of mesh generation and numerical simulation, first create geometric components based on STAR CCM+, including: background domain component, wave propagation region component, floating tunnel tube body component, and encryption zone component. Generate an overlapping region component in the Boolean operation. Then, create two regions for the geometric components, namely the background region and the overlapping region. Then, perform mesh generation, and draw the background mesh, overlapping mesh, wave mesh, and encryption mesh respectively. Select the overlapping mesh for subsequent numerical simulation.

[0011] Then, load the previously set mesh file through the STAR CCM+ software. First, create a physical model. Select the fluid domain volume model for the multiphase flow model. Based on the multiphase - Eulerian term node, create two computational phases, water and air, and create waves. Then, set the surface boundary types according to the wave dissipation type, and set the overlapping mesh boundary to the overset format. Then, set the parameters of the floating tunnel tube body and the anchor chain in the DFBI node. Finally, initialize the entire flow field according to the flow field data determined before the numerical simulation, and finally select the calculation step size for calculation.

[0012] S103. Based on the body coupling module in the STAR CCM+ software, establish the connection between the floating tunnel tube body and the seabed through the tensioned catenary, and then establish a three - dimensional numerical model of the floating tunnel under the combined wave - current excitation.

[0013] S2. Based on the established three - dimensional numerical model of the floating tunnel under the combined wave - current excitation, perform numerical simulation, and conduct parameter sensitivity analysis on the important non - linear influencing factors of the floating tunnel respectively, and analyze the influence of the sensitivity parameters on the vibration response characteristics of the floating tunnel tube body, so as to realize the prediction of the three - dimensional motion response of the floating tunnel tube body under the combined wave - current excitation.

[0014] Furthermore, the process of establishing a three - dimensional numerical wave tank under the combined wave - current excitation described in step one includes:

[0015] First, build a stable numerical wave tank by using the boundary wave - making method.

[0016] Then, by comparing the wave surface elevation heights at different positions with the theoretical values, determine the computational domain size and mesh profile parameters based on the numerical accuracy and computational cost.

[0017] Finally, establish a uniform incoming flow using the same set of meshes to construct a three - dimensional numerical wave tank under the combined wave - current excitation.

[0018] Furthermore, the process of building a stable numerical wave tank by using the boundary wave - making method includes the following steps:

[0019] Set the bottom boundary of the flow field as the wall boundary condition, set the left, right, front, and rear symmetric planes of the basin as velocity inlets, set the top of the basin as the pressure outlet, and set a wave-damping zone at the velocity inlet boundary.

[0020] Furthermore, the wave-damping zone is realized based on the force wave-damping method.

[0021] Furthermore, when using the same set of grids to establish a uniform incoming flow to construct a three-dimensional numerical wave-current flume, it is also necessary to establish a numerical calculation model of the suspended tunnel under the action of the uniform incoming flow for numerical verification to verify the reliability of the established three-dimensional numerical wave-current flume.

[0022] Furthermore, the process of establishing the connection between the suspended tunnel body and the seabed through a tensioned catenary includes:

[0023] Establish a coordinate system Oxz, where O is located at the free water surface, positive upward along Oz, and the seabed anchor point of the anchor chain is fixed directly below point O; the anchor chain moves in the Oxz plane, G is the upper mooring point of the anchor chain, X and Z are the projections of the suspended part of the anchor chain in the x and z directions respectively, and S o is the distance between the touchdown point of the anchor chain and the seabed anchoring point; the upper end of the anchor chain is subjected to a tension force T, and the projections of T in the x and z directions are F h and F v ;

[0024] F v = S T w + V 0

[0025]

[0026] where F b is the bottom tension of the catenary, F k is the rigidity coefficient of the catenary, n is the correction factor, v is the vertical tension at the fixed point, v 0 is the initial vertical tension at the fixed point, w is the wet weight per unit length of the anchor chain, E is the elastic modulus of the anchor chain, A is the effective cross-sectional area, V 0 is the tension at the fixed point of the anchor chain, and S T is the total length of the unstretched anchor chain;

[0027] Based on the above force relationship and combined with the mechanical behavior of the catenary, determine the overall motion response of the floating body.

[0028] Furthermore, the mechanical behavior of the catenary during the process of determining the overall motion response of the floating body is as follows:

[0029] In the mooring problem of ocean floating bodies, it is first necessary to calculate and determine the initial shape of the anchor chain based on the boundary conditions at the upper endpoint G of the anchor chain; then, in each time step, according to the change in the position of point G during the movement of the floating platform, the tension of the anchor chain is recalculated.

[0030] Furthermore, the process of the numerical simulation in S2 based on the established three-dimensional numerical model of the suspended tunnel under combined wave and current excitation includes:

[0031] Based on the three-dimensional numerical tank, corresponding wave and current parameters are set, wave and current loads are added, and then the fluid-structure interaction numerical simulation model is run until the vibration response of the suspended tunnel pipe body reaches a stable state; the parameter sensitivity analysis is carried out on the important non-linear influencing factors of the suspended tunnel by using the fluid-structure interaction numerical simulation model.

[0032] Furthermore, the important non-linear influencing factors of the suspended tunnel include flow velocity, wave parameters, water depth, burial depth, floating weight ratio, mooring angle, and the size of the suspended tunnel.

[0033] Beneficial effects:

[0034] The present invention proposes a numerical prediction method for the three-dimensional motion response of the suspended tunnel pipe body, which can more accurately simulate the influence of combined wave and current excitation on the vibration of the pipe body, thus providing more reliable data support for engineering design and safety assessment. At the same time, the present invention also innovatively proposes a high-precision numerical prediction model, which can effectively simulate the complex interaction between the fluid and the structure, and systematically analyze the influence characteristics of the fluid on the motion of the pipe body, and can deeply understand the dynamic behavior of the wave and current on the suspended tunnel pipe body, thus providing more reliable theoretical basis and data support for the actual engineering design. Description of the drawings

[0035] Figure 1 It is the three-dimensional modeling and simulation logic diagram of the suspended tunnel pipe body.

[0036] Figure 2 It is the schematic diagram of the combined wave and current excitation field.

[0037] Figure 3 It is the schematic diagram of the overlapping grid.

[0038] Figure 4 It is the prediction flow chart of the motion response of the suspended tunnel pipe body based on the three-dimensional numerical model.

[0039] Figure 5 It is the schematic diagram of the catenary.

[0040] Figure 6 It is the three-dimensional numerical tank model in the embodiment.

[0041] Figure 7It is the wave surface time history curve at different monitoring points, where (a) represents the wave surface time history curve at one times the wavelength, (b) is the wave surface time history curve at three times the wavelength, and (c) is the wave surface time history curve at six times the wavelength.

[0042] Figure 8 It is the wave surface nephogram in the computational domain at 5 times the wave period.

[0043] Figure 9 It is the schematic diagram of the three-dimensional model of the suspended tunnel in water.

[0044] Figure 10 It is the schematic diagram of the wave propagation in the flow field around the suspended tunnel body under the combined action of waves and currents.

[0045] Figure 11 It is the velocity nephogram of the flow field around the suspended tunnel body under the combined action of waves and currents.

[0046] Figure 12 It is the sway time history curve.

[0047] Figure 13 It is the sway acceleration time history curve.

[0048] Figure 14 It is the heave time history curve.

[0049] Figure 15 It is the heave acceleration time history curve.

[0050] Figure 16 It is the motion trajectory curve.

[0051] Figure 17 It is the wave-facing anchor chain force and its length time history curve.

[0052] Figure 18 It is the lee-facing anchor chain force and its length time history curve. Specific implementation mode

[0053] Aiming at the problems existing in the background technology, the present invention designs a new numerical prediction method for the three-dimensional motion response of a suspended tunnel body under the combined action of waves and currents. This method can accurately predict and analyze the three-dimensional dynamic response characteristics of the suspended tunnel body under the combined action of waves and currents, and further provide a reliable theoretical basis and technical support for the safe and stable operation of the tunnel body. First, a wave numerical tank is built, and a uniform oncoming flow is added on the basis of the wave numerical tank to establish a three-dimensional numerical tank for the combined action of waves and currents. Then, based on the DFBI (Dynamic Fluid-Body Interaction) model and the overlapping grid technology, the coupled vibration response of the three-dimensional suspended tunnel body is realized. The following is an explanation in combination with specific implementation modes.

[0054] Specific implementation mode one: Combine Figure 1 and Figure 2Description of this embodiment

[0055] This embodiment is a method for predicting the three-dimensional motion response of a suspended tunnel tube under combined wave and current excitation, including the following steps:

[0056] Step 1: Establish a three-dimensional numerical wave tank under combined wave and current excitation based on the boundary wave-making method:

[0057] First, a stable numerical wave tank needs to be built. In this invention, the velocity boundary wave-making method is selected considering the calculation speed, accuracy, and compatibility with the oncoming flow conditions. The two-phase flow model is used to distinguish the air phase and the water phase, and the VOF (Volume of Fluid) multiphase flow method is used to capture the change of the free surface. This method can analyze the position and shape of the multiphase flow interface and predict the distribution and movement of the multiphase flow interface. The distribution of the phase and the position of the interface are described by the phase volume fraction. The wave-making is carried out by the boundary wave-making method. The bottom boundary of the flow field is set as the wall boundary condition, the left, right, and the two front-back symmetric planes of the domain are set as velocity inlets, and the top of the domain is set as the pressure outlet. To prevent the influence of wave reflection at the boundary, a wave-absorbing area is set at the velocity inlet boundary. Currently, the main wave-absorbing methods are damping wave absorption and force wave absorption. Considering the calculation accuracy and calculation resources, this invention uses the force wave-absorbing method. This method can not only eliminate the reflected wave at the boundary but also set a smaller calculation domain to reduce the number of grids.

[0058] Then, by comparing the wave surface elevation at different positions with the theoretical value, considering the numerical accuracy and calculation cost, select appropriate calculation domain size and grid profile parameters to verify the wave simulation ability of the numerical wave tank, and determine the setting of the grid parameters according to the wave simulation situation.

[0059] Finally, use the same set of grids (that is, add a uniform oncoming flow after successful wave-making without changing the grids) to establish a uniform oncoming flow to construct a three-dimensional numerical wave tank under combined wave and current excitation;

[0060] Subsequently, establish a numerical calculation model of the suspended tunnel under the action of a uniform oncoming flow to verify the three-dimensional numerical wave tank, and numerical verification can be carried out by comparing with predecessors to further verify the reliability of the established three-dimensional numerical wave current tank.

[0061] Step 2: Overlapping grid, wave grid division, and fluid-structure interaction numerical simulation:

[0062] First, determine a series of parameters, including the style and size of the suspended tunnel tube, the cable stiffness k, the submerged depth d, the flow velocity U, the water depth h, the wave amplitude A, and the wave period T, etc., and then carry out grid division and numerical simulation.

[0063] The process of the grid division is as follows:

[0064] The overlapping grid is selected for the subsequent numerical simulation. The overlapping grid technology realizes data transfer between the component grid and the background grid through interpolation between the overlapping regions. There are two reasons for choosing the overlapping grid:

[0065] (1). The overlapping grid is one of the dynamic grid numerical simulation methods, which allows for more detailed grid division in key areas, improves the ability to capture local flow characteristics, is more suitable for the study of the vibration response of the suspension tunnel, and lays a foundation for the subsequent vibration response of the suspension tunnel;

[0066] (2). By using the overlapping grid, users can apply different physical models and boundary conditions to each region without having to re-divide the entire grid.

[0067] Taking the classic circular cross-section suspension tunnel tube as an example, the overlapping grid division method to be used in the present invention is as Figure 3 shown.

[0068] Relying on the powerful grid division technology of the STAR CCM+ software, the background grid, overlapping grid, wave grid and encrypted grid are drawn respectively.

[0069] The specific steps of grid division are as follows:

[0070] 1. First, create geometric components, including the background watershed component, wave propagation region component, suspension tunnel tube component and encrypted area component, to ensure that the model meets the analysis requirements; generate the overlapping region component in the Boolean operation, and then create two regions for the geometric components, namely the background region and the overlapping region.

[0071] 2. It is necessary to create the interface between the background region and the overlapping region. At the same time, select the region (total nodes)> background and overlapping nodes. Right-click on any of the selected nodes, and then select Create Interface> Overlapping Grid. > indicates the next step of processing.

[0072] 3. Then set the grid parameters in the operation bar, define the grid type and refinement level for each region respectively to ensure adaptation to different flow characteristics. Right-click on Geometry> Operation node, and then select New> Grid> Automatic Grid. Select the background watershed component in the component list of the Create Automatic Grid operation dialog box, then select the surface reconstruction and cut body grid cell generator, click OK, and rename the newly created automatic grid node as Background.

[0073] 4. Next, create a second grid operation named Overlap by copying the background automatic grid operation. Right-click on the Operation> Background node, then select Copy, right-click on the Operation node and select Paste. Rename the copy of the Background as Overlap, and select Operation> Overlap, and set the input component as Overlap.

[0074] 5. Set the basic size of the background grid operation and apply volume control. Select the Operation > Background > Default Control > Base Size node to set the grid base size. Right-click on the Operation > Background > Custom Control node, then select New > Volume Control, and input the encrypted component. If adding multiple encrypted area grids, repeat the above steps for creating volume control.

[0075] 6. Set the basic size for the overlapping grid operation, and then add volume control to refine the area around the floating tunnel tube. Select the Operation > Overlap > Default Control > Base Size node and set the value to the same size as the background grid. Create a custom volume control for the overlapping grid operation and rename it to Tunnel Tube. Select Custom Control > Tunnel Tube, set the component to the floating tunnel tube, then activate the Custom Size node and set the target size parameters.

[0076] 7. Create volume control for the wave area: Continuing with the background operation settings, create a custom volume control and rename it to Wave. Activate the custom size selection option for surface reconstruction and set the relative size to 100.0% of the base. Select the Wave > Control > Cut Cell Mesh Generator node, then activate the custom anisotropic size. Select the Water Wave > Value > Cut Cell Mesh Generator Anisotropic Size node, and then activate the Custom Size (X), Custom Size (Y), and Custom Size (Z). Generally, Custom Size (X) and Custom Size (Y) are set to 1 / 80 - 1 / 100 of the wavelength, and Custom Size (Z) is generally set to 1 / 20 of the wave height.

[0077] 8. Generate the mesh and visualize the mesh: Select the Generate Volume Mesh option in the Mesh menu. To visualize the mesh, create a mesh scene, right-click on the scene, and then select New Scene > Mesh.

[0078] It should be noted that, to eliminate errors generated when inserting variables between two meshes to the greatest extent, use the same order of magnitude of grid cell density in the overlapping area of the overlapping and background meshes.

[0079] The process of the numerical simulation is as follows:

[0080] Load the previously set mesh file through the STAR CCM+ software. First, create a physical model, select the three-dimensional, multiphase, implicit unsteady model, select the SST (Menter) K-Omega model for the turbulence model, select the Volume of Fluid (VOF) model for the multiphase flow model, select the vertical downward direction for the gravitational acceleration direction, and the magnitude is 9.81 m / s 2 , then open the Multiphase - Eulerian Terms node, create two computational phases of water and air, and create a wave at the VOF Wave > Wave node.

[0081] Next, according to different wave dissipation types, set the boundary types of each surface. The present invention adopts the force wave dissipation method, which can not only eliminate the reflected wave at the boundary, but also reduce the computational amount by using a small-sized computational domain. Set the wall boundary conditions for the suspended tunnel wall surface, the bottom boundary of the flow field, and the front and rear symmetric plane boundaries. Set the left and right sides of the basin as velocity inlets, the top of the basin as a pressure outlet, and set the overlapping grid boundary as the overset format. Then, create DFBI rotation and translation in Tools > Moving Nodes, and set the parameters of the suspended tunnel pipe body and the anchor chain in the DFBI node. Finally, initialize the entire flow field according to the flow field data determined before the numerical simulation, and finally select an appropriate calculation step size for calculation.

[0082] The specific steps of the numerical simulation are as follows:

[0083] (1) Import files

[0084] Open the STAR CCM+ software, select an appropriate number of working cores, load the prepared mesh file from the File option in the toolbar, and click OK.

[0085] (2) Create Regions and set Boundary Type

[0086] Create regions based on the background and overlapping components, and at the same time select Geometry > Components > Background and Overlap nodes. Right-click on any selected node, and then select Assign Component to Region. In the pop-up dialog box, select:

[0087] (a) Set the region mode to: Create one region for each component;

[0088] (b) Set the boundary mode to: Create one boundary for each component surface;

[0089] (c) Select Do not create interfaces based on contact.

[0090] Then click Apply with the mouse, and finally click Close. Then, according to the force wave dissipation method, specify the correct type for the boundaries of each region. Set the wall boundary conditions for the suspended tunnel wall surface and the bottom boundary of the flow field, set the left and right sides of the basin, the front and rear symmetric planes as velocity inlets, set the top of the basin as a pressure outlet, and set the overlapping grid boundary as the overset format.

[0091] (3) Select Physical Model:

[0092] Select the physical continuum, Continuum > Physics 1, and then select the following models in sequence: 3D, implicit unsteady, multiphase, multiphase interaction (automatically selected), volume of fluid (VOF), turbulence model, SST (Menter) K-Omega model, gradient (automatically selected), separated flow (automatically selected), multiphase equation of state (automatically selected). At the same time, check Gravity and VOF Wave in the selectable models, and finally click OK.

[0093] (4) Create Euler phases:

[0094] Right-click on the Continuum > Physics 1 > Model > Multiphase > Euler Phases node, and then select New. A new node Phase 1 is created. Rename the Phase 1 node to Water. Then right-click on the Euler Phases > Water > Model node, and then select Select Model: Select Liquid from the Material combo box. Select Constant Density from the Equation of State combo box, and then click Close. Repeat the above steps to select Gas in the material model to create the second Euler phase, and then click Close. Rename the second phase to Air.

[0095] (5) Set the DFBI motion:

[0096] Click on the Tools > Motion node, right-click on the Motion node, and then select New > DFBI Rotation and Translation. A new node named DFBI Rotation and Translation is added to the Motion Manager.

[0097] (6) Set the 6 Degree of Freedom Body:

[0098] Select the Region > Overlap > Physical Value > Motion Specification node, and set the motion to DFBI Rotation and Translation. Then right-click on the DFBI > 6 Degree of Freedom Body node, and select New Body > 3D > Continuum. At the same time, rename Body 1 to Suspension Tunnel.

[0099] (7) Suspension Tunnel parameter settings:

[0100] Select the DFBI > 6 Degree of Freedom Body > Suspension Tunnel node, and then click on the corresponding Custom Editor for the body surface. The Suspension Tunnel - Body Surface dialog box appears. Set the mass of the suspension tunnel in the Body Mass column. Then set the moment of inertia in the Initial Values > Motion of Inertia node. Then click on the Free Motion node, check X Motion, Y Motion, and Y Rotation to activate the X-axis translation, Z-axis translation, and Y-axis rotation attributes.

[0101] (8) VOF Wave settings:

[0102] Right-click on Continuum > Physics 1 > Model > VOF Wave > Wave Nodes, select New > First-Order Wave. Rename the First-Order VOF Wave 1 node to First-Order Wave. Select the First-Order Wave node, and then set the position of the water level.

[0103] (9) Initial Conditions setting:

[0104] Click on Continuum > Physics 1 > Initial Conditions > Volume Fraction node, select Composite in the Property Method bar, then click on Volume Fraction > Composite > Air node, select Field Function in the Property Method bar, select Volume Fraction of Light Fluid of First-Order Wave 1 in the Scalar Function bar, then click on Volume Fraction > Composite > Water node, select Field Function in the Property Method bar, select Volume Fraction of Heavy Fluid of First-Order Wave 1 in the Scalar Function bar. Click on Initial Conditions > Velocity node, select Field Function in the Property Method bar, select Velocity of First-Order VOF Wave 1 in the Vector Function bar. Then click on Initial Conditions > Pressure node, select Field Function in the Property Method bar, select Hydrostatic Pressure of First-Order VOF Wave 1 in the Scalar Function bar.

[0105] (10) Boundary Conditions setting:

[0106] Click on Region > Background > Physical Values node, select First-Order VOF Wave 1 in the Force VOF Wave Specification column. Then click on Background > Physical Conditions node, select Force in the VOF Wave Region option bar. Then click on Region > Background > Boundary > inlet node, then set the velocity to components in the Physical Conditions, click on Physical Values > Velocity node, select Field Function in the Property Method bar, select Velocity of First-Order VOF Wave 1 in the Vector Function bar. Then in the Physical Values > Volume Fraction node, set the air and water phases to Volume Fraction of Light Fluid of First-Order Wave 1 and Volume Fraction of Heavy Fluid of First-Order Wave 1 respectively. The outlet and symmetry settings are the same as the inlet, just repeat the above steps. Then click on top > Physical Values node, set the volume fraction and pressure, the volume fraction setting is the same as above, select Hydrostatic Pressure of First-Order VOF Wave 1 in the Pressure column.

[0107] (11) Solver Parameters setting:

[0108] Click on the mouse to select the Solver > Implicit Unsteady Node, and then set the required time step.

[0109] (12) Stop Condition setting:

[0110] Click on the mouse to select the Stop Condition > Maximum Inner Iteration Node, and select the maximum number of inner iterations. Then click on the Stop Condition > Maximum Physical Time Node, and set the maximum physical time. Finally, click on the Stop Condition > Maximum Number of Steps Node to enable or disable it.

[0111] (13) Visual Solution of the Scene setting

[0112] Right-click on the Scene Node, and then select the scene to be created.

[0113] (14) Initialize Solution setting:

[0114] Click on the flag icon (Initialize Solution), or click on Solution > Initialize Solution to complete the calculation initialization.

[0115] (15) Run Calculation setting:

[0116] Click on the Run button, and the calculation starts.

[0117] Step 3: Establish a numerical model of a three-dimensional suspended tunnel under accurate combined wave and current excitation:

[0118] The suspended tunnel is mainly subjected to three forms of forces, namely: cable tension, self-weight, and hydrodynamic force. In still water, the cable will be tightened to generate a pre-tension, and its magnitude is the difference between the buoyancy and gravity of the pipe section. The stability of the suspended tunnel requires that the cable always maintains tension, that is, the vertical force on the suspended tunnel body under any working conditions should be less than the buoyancy force on the pipe section. Therefore, the cable connected to the suspended tunnel can be simplified as a support structure that is in tension but not in compression. Existing software usually uses static or linear force models when dealing with cables in other structures (such as platforms or bridges). However, during the prediction of suspended tunnels, the mechanical behavior of the cable shows significant non-linear characteristics. Especially under the action of waves and currents, the cable will undergo large-amplitude non-linear deformations, and this deformation needs to be dynamically adjusted in combination with environmental changes.

[0119] In the present invention, based on the volume coupling module in STAR CCM+ software, a connection is established between the floating tunnel body and the seabed through a tensioned catenary. The catenary model can reasonably distribute the tension, enabling the vertical force of the floating tunnel to be effectively transmitted to the seabed or the anchoring structure through the anchor cables, ensuring that the anchor cables are in a reasonable stress state and avoiding unnecessary compressive forces. The complexity of the floating tunnel body lies in that it not only has to cope with the influence of hydrodynamics but also needs to consider the coupling among the mechanical behavior of the anchor cables, the buoyancy of the tunnel body itself, and other environmental loads. This special coupling mode poses great challenges to the model establishment and also highlights the innovative depth of this application in the multi-field coupling analysis method.

[0120] Tensioned catenary theoretical formula:

[0121] As Figure 5 shown in the coordinate system Oxz, with O located at the free water surface, positive upward along Oz, and the seabed anchor point of the anchor chain fixed directly below point O. Assuming the seabed is flat and the anchor chain moves within the Oxz plane, G is the upper mooring point of the anchor chain, X and Z are the projected lengths of the catenary part of the anchor chain in the x and z directions respectively, and S o is the distance between the touchdown point of the anchor chain and the seabed anchoring point. The upper end of the anchor chain is subjected to a tensile force T, and the projections of T in the x and z directions are F h and F v .

[0122] F v = S T w + V 0

[0123]

[0124] where F b is the bottom tension of the catenary, usually occurring at the lowest point of the catenary (i.e., the place closest to the anchoring point), F k is the rigidity coefficient of the catenary, n is the correction factor, here n = 1, v is the vertical tension at the fixed point, v 0 is the initial vertical tension at the fixed point, w is the wet weight per unit length of the anchor chain, E is the elastic modulus of the anchor chain, A is the effective cross-sectional area, V 0 is the tension at the fixed point of the anchor chain, and S T is the total length of the unstretched anchor chain.

[0125] In the mooring problem of ocean floating bodies, it is first necessary to calculate and determine the initial shape of the anchor chain based on the boundary conditions (force or position) at the upper endpoint G of the anchor chain. Then, in each time step, according to the change in the position of point G during the movement of the floating body platform, the tension of the anchor chain is recalculated, and then the mechanical behavior of the catenary is obtained, and finally the overall motion response of the floating body is determined.

[0126] The present invention realizes the coupled vibration response of the three-dimensional floating tunnel tube body based on the DFBI (Dynamic FluidBody Interaction) model and the overlapping grid technology. The specific implementation process is as follows:

[0127] A cable-suspended floating tunnel model is established by modeling with STAR CCM+ software. A catenary is added in the body coupling module, and the end positions of the catenary are determined according to the mooring angle and water depth. Then, corresponding wave and current parameters are set in the wave generation module, and wave-current loads are added. Finally, the fluid-structure interaction numerical simulation model is run until the vibration response of the floating tunnel tube body reaches a stable state. As Figure 4 shown, this numerical model is used to conduct parameter sensitivity analyses on important non-linear influencing factors such as flow velocity, wave parameters, water depth, burial depth, buoyancy-weight ratio, mooring angle, and floating tunnel size respectively, and summarize the characteristic laws of the sensitivity parameters affecting the vibration response of the floating tunnel tube body, so as to realize the prediction of the three-dimensional motion response of the floating tunnel tube body under the combined excitation of waves and currents.

[0128] Embodiment

[0129] The effect of the present invention is illustrated through this embodiment. The prediction of the motion response of the floating tunnel tube body based on the three-dimensional numerical model in this embodiment includes the following steps:

[0130] 1. Construct a combined wave-current excitation field:

[0131] The following is a three-dimensional numerical wave tank with a total length of 800 m, a width of 160 m, and a height of 100 m established. As Figure 6 shown, waves with a wave height of 8 m, a wavelength of 100 m, a wave steepness of 0.08, and a wave number of 0.01 are selected for simulation. The grid convergence verification and time step convergence verification of the tank are carried out. Considering the numerical accuracy and calculation cost comprehensively, the grid size is finally determined to be 80 grids per wavelength and 15 grids per wave height, and the time step is 0.01 s.

[0132] In order to conveniently display the results of the grid convergence verification and time step convergence verification, three wave gauges are respectively arranged at one wavelength, three wavelengths, and six wavelengths of the numerical tank. By monitoring the wave surface elevation at different positions and comparing it with the theoretical wave height, the feasibility of wave generation in the numerical tank is verified. From Figure 7 the wave surface time history curves at different monitoring points, it can be seen that the actual value curves of the wave surface elevation at the three different positions almost coincide with the theoretical value curves, indicating that the wave generation is successful. From Figure 8 the wave surface cloud map in the computational domain at 5 times the wave period, it can be seen that the propagation of the waves is very stable, indicating that this numerical tank can conduct long-term wave generation simulations.

[0133] 2. Construction of the three-dimensional flow field around the floating tunnel tube under the combined action of waves and currents:

[0134] Select a circular floating tunnel tube section with a diameter of 24 m and a burial depth of 20 m. As Figure 9 shown, from Figure 10 , Figure 11 the schematic diagram of wave propagation and the velocity contour map in the flow field around the floating tunnel tube under the combined action of waves and currents, it can be seen that the combined wave and current excitation field constructed by the present invention is relatively stable, and there is a coupling effect between waves and currents.

[0135] 3. Analysis of the vibration response of the floating tunnel tube under the combined action of waves and currents:

[0136] The Coastal and Ocean Engineering Laboratory of the Department of Civil Engineering at Nagoya University in Japan conducted experimental research on the dynamic response of a floating tunnel under wave action. The present invention selects this actual classic floating tunnel tube section to carry out numerical calculations. The diameter D of the tube is 0.25 m, the distance d from the center of the floating tunnel tube to the water surface is 0.177 m, the mass m of the tube section is 21 kg, and the length L of the tube section is 0.68 m. The mass per unit length of the anchor chain is 0.05 kg / m, and the stiffness k is 2×10 3 N / m. The parameter values of the combined wave and current excitation field are as follows: the water depth h is 0.6 m, the parameters of the single wave field are the wave amplitude A is 5.75 m, the wavelength λ is 1.575 m, the period T is 1 s, and a uniform incoming flow with a flow velocity U of 0.2 m / s is added.

[0137] The numerical simulation results of the dynamic response of the floating tunnel tube under the combined action of waves and currents are as follows: From Figure 12 the heaving time history curve of the floating tunnel tube, Figure 13 the heaving acceleration time history curve, Figure 14 the swaying time history curve, Figure 15 the swaying acceleration time history curve, Figure 16 the trajectory curve of the floating tunnel tube, Figure 17 , Figure 18 the time history curves of the anchor chain forces and their lengths facing the wave and against the wave, it can be seen that the dynamic response of the floating tunnel tube is relatively stable and will move reciprocally along an elliptical trajectory approximately circular.

[0138] Researchers can use the above - mentioned method to conduct batch numerical simulations by adjusting the structural parameters of the floating tunnel (such as cross - section shape, size, submergence depth, buoyancy - weight ratio, and cable - anchor angle) and environmental loads (such as waves and ocean currents). On this basis, by analyzing the simulation data, the dynamic response mechanism of the floating tunnel body under the combined action of waves and ocean currents can be deeply understood. This research not only has important significance for the stability and safety of the floating tunnel during operation and engineering practice, but also provides valuable technical support for related fields. Based on the research results of the present invention, the development process of underwater floating tunnel projects in China will be effectively promoted, and the progress and application of technologies in this field will be facilitated.

[0139] Compared with the prior art, the technical solution of the present invention has the following advantages: 1. At present, theoretical and computational studies often simplify the three - dimensional real model of the floating tunnel body into a two - dimensional plane model. Although this simplification method can effectively reduce the computational complexity to a certain extent, it is difficult to truly reflect the three - dimensional motion response characteristics of the real pipe body structure, and further leads to an insufficient understanding of the dynamic behavior of the pipeline under the combined wave - current excitation. To overcome this limitation, the present invention proposes an innovative three - dimensional motion response numerical prediction model for the floating tunnel body. This model can more accurately simulate the influence of combined wave - current excitation on the vibration of the pipe body, thus providing more reliable data support for engineering design and safety assessment. 2. In current model experimental studies, due to the high cost of experiments and technical limitations, when researchers analyze the three - dimensional motion response of the floating tunnel body under the combined wave - current excitation, they usually cannot accurately capture the complex interaction between the fluid and the structure, which further leads to an insufficient and inaccurate understanding of the dynamic behavior of the pipeline. To overcome this limitation, the present invention innovatively proposes a high - precision numerical prediction model, which can effectively simulate the complex interaction between the fluid and the structure, systematically analyze the influence characteristics of the fluid on the motion of the pipe body, and deeply understand the influence of waves and currents on the dynamic behavior of the floating tunnel body, thus providing a more reliable theoretical basis and data support for actual engineering design.

[0140] The present invention can also have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and deformations according to the present invention, but these corresponding changes and deformations should all fall within the protection scope of the appended claims of the present invention.

Claims

1. A method for predicting the three-dimensional motion response of a suspended tunnel tube under wave-current combined excitation, characterized in that: Includes the following step: S1. A three-dimensional floating tunnel numerical model under wave-current combined excitation is established based on STAR CCM+, including: S101. Establish a three-dimensional numerical water pool with wave and current joint excitation based on the boundary wave making method; S102, Overlap grid, wave grid division, and establishment of fluid-solid coupling numerical simulation model: First, determine the parameters, including the type and size of the suspended tunnel body, the stiffness of the anchor cable k , Submergence Depth d , flow rate U , water depth h ,amplitude A Sum wave period T , then meshing and numerical simulation are carried out; in the process of meshing and numerical simulation, geometric components are first created based on STAR CCM+, including: background basin components, wave propagation area components, floating tunnel body components and encrypted area components, overlapping area components are generated in Boolean operations, and then two areas are created for the geometric components, namely the background area and the overlapping area; then meshing is carried out, and the background grid, overlapping grid, wave grid and encrypted grid are drawn respectively; the overlapping grid is selected for subsequent numerical simulation; Then, the previously set grid file is loaded through STAR CCM+ software. First, the physical model is created. The fluid domain volume model is selected for the multiphase flow model. Two new calculation phases, water and air, are created based on the multiphase-Euler term node, and waves are created. Then, the boundary types of each surface are set according to the wave breaking type, and the overlapping grid boundaries are set to the overlap format. Then, the parameters of the suspended tunnel body and anchor chain are set in the DFBI node. Finally, the entire flow field is initialized according to the flow field data determined before the numerical simulation, and the calculation step size is selected for calculation. S103. Based on the volume coupling module in STAR CCM+ software, the connection between the suspended tunnel body and the seabed is established through a tensioned catenary, and then a three-dimensional suspended tunnel numerical model under wave and current combined excitation is established; S2. Based on the established three-dimensional floating tunnel numerical model under wave-current combined excitation, numerical simulation is carried out, and parameter sensitivity analysis is performed on the important nonlinear influencing factors of the floating tunnel. The characteristic law of the sensitivity parameters affecting the vibration response of the floating tunnel pipe body is analyzed to realize the prediction of the three-dimensional motion response of the floating tunnel pipe body under wave-current combined excitation; The process of establishing the connection between the floating tunnel body and the seabed through the tensioned catenary includes: Establishing the coordinate system Oxz , O Located on free water, along Oz Upward is positive, and the seabed anchor point of the anchor chain is fixed at O Directly below the point; the anchor chain is Oxz In-plane motion, G The upper mooring point of the anchor chain. X and Z The overhanging part of the anchor chain is x and z The projection length in the direction, S o It is the distance between the anchor chain touchdown point and the anchor point on the seabed; the upper end of the anchor chain is subjected to tension T effect, T exist x and z The projection directions are F h and F v ; （1） （2） in, is the bottom tension of the catenary, is the rigidity coefficient of the catenary, is the correction factor, is the vertical tension at the fixed point, Initial vertical tension at the fixed point, is the wet weight per unit length of anchor chain, is the elastic modulus of the anchor chain, is the effective cross-sectional area, is the tension at the anchor chain fixing point, is the total length of the unstretched anchor chain; Based on the above force relationship and combined with the mechanical behavior of the catenary, the overall motion response of the floating body is determined.

2. The method for predicting the three-dimensional motion response of a suspended tunnel tube under wave-current combined excitation according to claim 1 is characterized by: The process of establishing a three-dimensional numerical water pool with wave and current joint excitation based on the boundary wave making method in step 1 includes: Firstly, a stable wave numerical pool is constructed by using the boundary wave generation method; Next, by comparing the wavefront lift heights at different locations with the theoretical values, the computational domain size and mesh profile parameters are determined based on numerical accuracy and computational cost. Finally, the same set of grids is used to establish a uniform incoming flow to construct a three-dimensional numerical water pool with wave-current joint excitation.

3. The method for predicting the three-dimensional motion response of a suspended tunnel tube under wave-current combined excitation according to claim 2 is characterized by: The process of constructing a stable wave numerical pool using the boundary wave generation method includes the following steps: The bottom boundary of the flow field is set as the wall boundary condition, the left and right sides of the flow domain and the two front and rear symmetrical planes are set as velocity inlets, the top of the flow domain is set as the pressure outlet, and a wave-breaking zone is set at the velocity inlet boundary.

4. The method for predicting the three-dimensional motion response of a suspended tunnel tube under wave-current combined excitation according to claim 3 is characterized by: The wave-breaking zone is realized based on a force wave-breaking method.

5. The method for predicting the three-dimensional motion response of a suspended tunnel body under wave-current combined excitation according to claim 3 is characterized by: In the process of using the same set of grids to establish a uniform incoming flow to construct a three-dimensional numerical water pool with wave-current joint excitation, it is also necessary to establish a numerical calculation model of the suspended tunnel under the action of the uniform incoming flow, perform numerical verification, and verify the reliability of the established three-dimensional numerical wave-current water pool.

6. The method for predicting the three-dimensional motion response of a suspended tunnel tube under wave-current combined excitation according to claim 1 is characterized by: The mechanical behavior of the catenary in determining the overall motion response of the floating body is as follows: In the mooring problem of an ocean floating body, it is first necessary to calculate and determine the initial shape of the anchor chain based on the boundary conditions at the upper end point G of the anchor chain; then, in each time step, the tension of the anchor chain is recalculated according to the change in the position of point G during the movement of the floating platform.

7. A method for predicting the three-dimensional motion response of a suspended tunnel tube under wave-current combined excitation according to any one of claims 1 to 5, characterized in that: The process of numerical simulation based on the established three-dimensional floating tunnel numerical model under wave-current combined excitation described in S2 includes: Based on the three-dimensional numerical water pool, the corresponding wave and current parameters are set, wave and current loads are added, and then the fluid-solid coupling numerical simulation model is run until the vibration response of the suspended tunnel body reaches a stable state; the parameter sensitivity analysis of the important nonlinear influencing factors of the suspended tunnel is carried out using the fluid-solid coupling numerical simulation model.

8. The method for predicting the three-dimensional motion response of a suspended tunnel tube under wave-current combined excitation according to claim 7 is characterized by: The important nonlinear influencing factors of the suspended tunnel include flow velocity, wave parameters, water depth, burial depth, buoyancy-to-weight ratio and mooring angle, and suspended tunnel size.

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