Deep-sea pile soil dynamic response analysis method based on ALE fluid-solid coupling and infinite element boundary

Abstract

This invention discloses a method for analyzing the dynamic response of deep-sea pile driving soil based on ALE fluid-structure interaction and infinite element boundary, belonging to the field of marine engineering technology. It solves the technical problem of mesh distortion and hourglassing caused by severe soil compression at the pile tip during deep penetration. The key to this technical solution is the introduction of an adaptive mesh technique with an arbitrary Lagrange-Eulerian adaptive mesh control domain. By dynamically refactoring the mesh topology during the analysis step, mesh distortion and hourglassing caused by severe soil compression at the pile tip during deep penetration are effectively avoided, enabling the finite element model to stably simulate the penetration depth process.

Description

Technical Field

[0001] This application relates to the field of marine engineering technology, and in particular to a method for analyzing the dynamic response of deep-sea pile soil based on ALE fluid-structure interaction and infinite element boundary. Background Technology

[0002] The offshore wind power industry is expanding globally, playing a crucial role in adapting to global climate change and accelerating the transition to low-carbon energy. Currently, over 50 countries and regions worldwide have begun developing offshore wind power. Offshore wind turbines are increasingly larger, demonstrating advantages in reducing overall costs and improving power generation efficiency. Correspondingly, this necessitates larger turbine foundations, especially monopile foundations. These foundations, with their advantages of simple manufacturing, easy installation, clear structural stress distribution, and short offshore construction cycles, will play a vital role in the large-scale construction of offshore wind power. As offshore wind power expands into deeper waters, the diameter of offshore wind turbine monopile foundations has exceeded 7-8 meters, and the pile length has surpassed 80 meters. At such a massive scale, the pile driving process is an extremely complex, highly nonlinear dynamic process. While some studies have considered 3D solid modeling and explicit dynamic solutions, significant technical bottlenecks remain. (1) Existing technology uses pure Lagrangian formulation. In the Lagrangian description, the mesh nodes are fixed to the material particles and move with them. When the pile tip squeezes and displaces the soil, the soil elements near the pile tip will undergo extreme compression and shear deformation. For large-diameter piles, this deformation is extremely large, causing the Jacobian determinant of the element to become negative, that is, the mesh "flips", which directly leads to the termination of the calculation.

[0003] (2) Existing technology applies fixed constraints to the soil boundary. Due to the limited computational domain, the huge energy generated by the impact propagates outward in the form of stress waves. When it encounters a fixed boundary, it will undergo total reflection. The reflected wave will return to the pile body and superimpose with the incident wave, causing the pile body stress to be artificially high or low, which seriously interferes with the judgment of the pile foundation's drivability.

[0004] How to avoid the grid distortion (NegativeVolume) and hourglassing caused by the intense soil compression during deep pile penetration remains to be solved. Summary of the Invention

[0005] This application provides a method for analyzing the dynamic response of deep-sea pile driving soil based on ALE fluid-structure interaction and infinite element boundary. The technical purpose is to effectively avoid grid distortion and hourglass pattern caused by severe soil compression during the deep penetration of the pile tip, so that the finite element model can stably simulate the process of pile driving depth.

[0006] The above-mentioned technical objective of this application is achieved through the following technical solution: A method for analyzing the dynamic response of deep-sea pile-driven soil based on ALE fluid-structure interaction and infinite element boundary includes: Based on actual engineering parameters, a geometric model of the hydraulic hammer assembly, the replacement system, the large-diameter steel pipe pile, and the layered soil was constructed, and the components were assembled in a unified global coordinate system. The land calculation domain corresponding to the layered soil is divided into a core penetration zone and a peripheral radiation zone based on the radial and depth directions; wherein, the core penetration zone covers the area around the pile and the preset depth below the pile tip, and the peripheral radiation zone surrounds the outside of the core penetration zone. The core penetration region is discretized using hexahedral reduced integral elements C3D8R to obtain multiple hexahedral entities. These hexahedral entities are then associated with arbitrary Lagrange-Euler adaptive mesh control domains to obtain a geometric model with assigned attributes, i.e., a constitutive model. The constitutive model includes a hydraulic hammer assembly constitutive model, a replacement hammer system constitutive model, a large-diameter steel pipe pile constitutive model, and a layered soil constitutive model. The master-slave contact pairs of the hexahedral entity at the pile-soil contact interface are defined based on the kinematic contact algorithm, and the tangential interaction of the master-slave contact pairs is set based on Coulomb's law of friction. Before pile driving, the initial void ratio and effective stress field are calculated based on the layered soil constitutive model in the constitutive model, and vertical fixed constraints are applied to the bottom of the layered soil according to the initial void ratio and the effective stress field. During the piling process, the time step is calculated using an explicit integrator of the central difference method. Within each incremental step or a calculation interval at a preset frequency, the arbitrary Lagrange-Euler adaptive mesh control domain performs smoothing and variable remapping operations to map the deformed old mesh state variables onto the new topology-optimized mesh. Both the old mesh and the new mesh are hexahedral entities. Based on the new grid, data on pile head displacement time history curves, pile stress wave transmission characteristics, and pore water pressure changes at different radial distances in the layered soil were extracted.

[0007] Preferably, the radial range of the core penetration area R ALE Defined as R ALE ≥3D ,in D Indicates the pile diameter; the core penetration zone is the preset depth range below the pile tip. H ALE Defined as H ALE ≥5D .

[0008] Preferably, the arbitrary Lagrange-Euler adaptive mesh control domain adjusts the node positions of the deformed old mesh based on the volume-conserving Laplace smoothing algorithm, and performs no less than 3 mesh scans in each incremental step or preset frequency to obtain a new mesh with topology optimization; the arbitrary Lagrange-Euler adaptive mesh control domain then maps the old mesh state variables to the new mesh through variable remapping; wherein, the node is the six vertices of the hexahedral entity.

[0009] Preferably, the master-slave contact pair includes a master surface and a slave surface, wherein the master surface is the outer surface of the pile body with high stiffness, and the slave surface is the inner surface of the soil cavity with low stiffness; the tangential friction coefficient of the tangential interaction is a dynamic friction model that decreases with the relative slip velocity of the pile and soil.

[0010] Preferably, the process of performing variable remapping operation in the arbitrary Lagrange-Euler adaptive grid control domain includes first-order or second-order convective transport calculations of historical variables, whose governing equations follow the laws of conservation of mass, momentum, and energy, and are expressed as: ; in, Represents physical field variables, Indicates the velocity of material particles. Indicates the speed of grid movement. This indicates the convection velocity.

[0011] Preferably, the historical variables include plastic strain and hardening parameters.

[0012] Preferably, the old grid state quantities include stress and velocity.

[0013] Preferably, the behavior of the layered soil is described by the Mohr-Coulomb theory or the Drucker-Prag elastoplastic constitutive model, and the strain rate correlation parameter is introduced to characterize the effect of soil dynamic strength enhancement under high strain rate by the Cowper-Symonds model.

[0014] The above technical solution can achieve at least some of the following technical effects: The deep-sea pile driving soil dynamic response analysis method based on ALE fluid-structure interaction and infinite element boundary described in this application introduces an adaptive mesh technology with an arbitrary Lagrange-Euler adaptive mesh control domain. By dynamically redrawing the mesh topology in the analysis step, the mesh distortion (negative volume) and hourglassing caused by severe soil compression at the pile tip during deep penetration are effectively avoided, enabling the finite element model to stably simulate the penetration depth process. Attached Figure Description

[0015] Figure 1 This is a flowchart illustrating the overall process framework of the deep-sea pile driving soil dynamic response analysis method based on ALE fluid-structure interaction and infinite element boundary described in the embodiments of this application. Figure 2 This is a simplified geometric model of each component of the finite element model in the embodiments of this application; Figure 3 This is a mesh element division diagram of the finite element model in the embodiments of this application; Figure 4a This is a stress cloud diagram of the replacement component of the pile-hammer-soil system at 0.29s in the embodiment of this application; Figure 4b This is a stress cloud diagram of the pile body at 0.29s in the pile-hammer-soil system of the embodiment of this application; Figure 4c This is a diagram showing the displacement results of each component of the pile-hammer-soil system in the embodiments of this application; Figure 4d This is a diagram showing the velocity results of the pile top unit in the pile-hammer-soil system in the embodiments of this application. Detailed Implementation

[0016] The technical solution of this application will be described in detail below with reference to the accompanying drawings.

[0017] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings. According to one embodiment of the present invention, a method for analyzing the dynamic response of pile-driven soil that can perform stable calculations over a long period and eliminate boundary effects is provided, such as... Figure 1 As shown, it includes the following steps: Step 1: Preprocessing. Based on actual engineering parameters, a geometric model of the hydraulic hammer assembly, replacement system, large-diameter steel pipe pile, and layered soil is constructed using Solidworks software. This model comprises four parts: the hydraulic hammer assembly, replacement system, large-diameter steel pipe pile, and layered soil. The pile diameter is 7.2 m, and the pile length is 80 m. The hammer core is assembled in a unified coordinate system. Figure 2 As shown.

[0018] Soil: Establish a layered soil model, geometrically dividing the soil into two concentric cylindrical regions. Inner Cylindrical Zone A: Radius set to 25m (approximately 3.5 times the pile diameter), depth covering at least 40m below the pile tip. Outer Cylindrical Zone B: Inner diameter 25m, outer diameter extending to 50m. Hydraulic Hammer Assembly: Includes hammer core (Ram), replacement hammer (Anvil), and replacement hammer ring; total mass as set (e.g., hammer core 218.95t).

[0019] Step 2: Divide the land calculation domain corresponding to the layered soil into a core penetration zone and an outer radiation zone based on the radial and depth directions; wherein, the core penetration zone covers the area around the pile and the preset depth below the pile tip, and the outer radiation zone surrounds the outside of the core penetration zone.

[0020] Preferably, the radial range of the core penetration area R ALE Defined as R ALE ≥3D ,in D Indicates the pile diameter; the core penetration zone is the preset depth range below the pile tip. H ALE Defined as H ALE ≥5D This ensures that the shear failure zone is completely covered by the ALE mesh domain.

[0021] Step 3: Discretize the core penetration region using hexahedral reduced integral units C3D8R to obtain multiple hexahedral solids, such as... Figure 3 As shown. The hexahedral entity is associated with an arbitrary Lagrange-Euler adaptive mesh control domain to obtain a geometric model with assigned properties, i.e., a constitutive model; wherein, the constitutive model includes a hydraulic hammer assembly constitutive model, a replacement hammer system constitutive model, a large-diameter steel pipe pile constitutive model, and a layered soil constitutive model.

[0022] In this embodiment, the mesh generation and ALE (Arbitrary Lagrange-Euler Adaptive Mesh Domain) settings are configured to import the geometric model into the ABAQUS / Explicit solver. For the pile and hammer: C3D8R (8-node linear hexahedron, reduced integral, hourglass control enhancement) is selected. For soil Zone A: C3D8R is selected, but it must be specified as an ALE Adaptive Mesh Domain in the Step or Interaction module. The frequency is set to 5, meaning the mesh is re-generated every 5 increments; the remeshing sweeps are set to 3 times to ensure high-quality smoothness. For the outermost layer of soil Zone B: CIN3D8 (8-node linear unidirectional infinite element) is selected. In the Mesh module, the "infinite direction" of the infinite element must be specified as radially outward.

[0023] Step 4: Define the master-slave contact pairs of the hexahedral entities at the pile-soil contact interface based on the kinematic contact algorithm, and set the tangential interaction of the master-slave contact pairs based on Coulomb's friction law.

[0024] Preferably, the master-slave contact pair includes a master surface and a slave surface, wherein the master surface is the outer surface of the pile body with high stiffness, and the slave surface is the inner surface of the soil cavity with low stiffness; the tangential friction coefficient of the tangential interaction is a dynamic friction model that decays with the relative slip velocity of the pile and soil to simulate the lubrication effect of thixotropic mud.

[0025] In this embodiment, the pile-soil contact adopts "General Contact". The normal behavior is set to Hard Contact, allowing separation. The tangential behavior is set to Penalty Friction, with a tangential friction coefficient... =0.35.

[0026] Meanwhile, the Drucker-Prager model was used to define the plasticity parameters of the soil material, as shown in Table 1.

[0027] Table 1 Attribute Parameters

[0028] Step 5: Before pile driving, the initial void ratio and effective stress field are calculated based on the constitutive model of the layered soil in the constitutive model to eliminate false deformation caused by gravity loading; in addition to the radiation damping automatically provided by the infinite element boundary, vertical fixed constraints are applied to the bottom of the layered soil according to the initial void ratio and the effective stress field.

[0029] In this embodiment, the infinite element boundary does not require displacement constraints; the infinite element itself constitutes both the static boundary and the dynamic energy absorption boundary. If the bottom surface of the soil is sufficiently deep (>150m), an infinite element can also be applied; if it is shallower, fixed constraints (U1=U2=U3=0) are applied.

[0030] Step Six: During the piling process, the time step is calculated using the explicit integrator of the central difference method. Within each incremental step or the calculation interval of a preset frequency, the arbitrary Lagrange-Euler adaptive mesh control domain performs smoothing and variable remapping operations to map the deformed old mesh state variables onto the new topology-optimized mesh; wherein, both the old mesh and the new mesh are hexahedral solids.

[0031] Preferably, the arbitrary Lagrange-Euler adaptive mesh control domain adjusts the node positions of the deformed old mesh based on the volume-conserving Laplace smoothing algorithm, and performs no less than 3 mesh scans in each incremental step or preset frequency to obtain a new mesh with topology optimization; the arbitrary Lagrange-Euler adaptive mesh control domain then maps the old mesh state variables to the new mesh through variable remapping; wherein, the node is the six vertices of the hexahedral entity.

[0032] Preferably, the process of performing variable remapping operation in the arbitrary Lagrange-Euler adaptive grid control domain includes first-order or second-order convective transport calculations on historical variables (such as plastic strain, hardening parameters, etc.), and its governing equations follow the laws of conservation of mass, momentum, and energy, expressed as: ; in, Represents physical field variables, Indicates the velocity of material particles. Indicates the speed of grid movement. This indicates the convection velocity.

[0033] In this embodiment of the application, step six is ​​achieved by applying and solving a load.

[0034] Step 1 of the analysis: Geostatic equilibrium is crucial for geotechnical analysis. Gravity loads are applied, and initial stress field coefficients are defined. (Lateral pressure coefficient). Ensure that the soil is in equilibrium between gravity and internal stress before piling begins, with only minimal displacement (<1mm).

[0035] Analysis Step 2: Dynamic Explicit. In the method of this application, it is transformed into the initial velocity field of the hammer core, expressed as: ; Substitute the data: (Note: This speed is the instantaneous speed upon impact; a higher height is required to simulate the falling hammer process.) Turn on the "Nlgeom" switch.

[0036] Step 7: Extract the time history curve of pile head displacement, stress wave transmission characteristics of pile body, and pore water pressure change data at different radial distances of layered soil based on the new grid.

[0037] In this embodiment of the application, post-processing analysis and result extraction are performed on the new mesh.

[0038] Post-processing analysis, or mesh quality check, involves examining the output ALE mesh to confirm that the mesh lines remain relatively horizontal and vertical even after the pile tip has penetrated several meters, without severe distortion. An energy balance check is then performed, examining the ratio of pseudo-strain energy (ALLAE) to internal energy (ALLIE) of the entire model to ensure that the hourglass energy is controlled within 5%, thus verifying the validity of the calculation.

[0039] Result Extraction: Extract the velocity-time history curve of the pile head node. Force Time History Curve The simulation results are extracted through calculations based on the wave equation theory, such as... Figures 4a to 4dAs shown, the responses of velocity, hammer force, pile top displacement, stress, and strain during the pile driving process were extracted respectively. Among them, Figure 4a is the stress cloud diagram of the replacement component of the pile-hammer-soil system at 0.29 s. Figure 4b Figure 4c shows the stress cloud diagram of the pile-hammer-soil system at 0.29 s; Figure 4d shows the displacement results of each component of the pile-hammer-soil system; Figure 4d shows the velocity results of the pile top unit of the pile-hammer-soil system. The basic principle of high-strain method testing is as follows: A heavy hammer impacts the pile top, causing sufficient relative displacement between the pile and soil to fully stimulate the soil resistance around the pile and the bearing force at the pile end. Force and acceleration sensors installed on both sides of the pile below the pile top receive the stress wave signals. Stress wave theory is applied to analyze and process the force and velocity time history curves, thereby determining the pile's bearing capacity and evaluating the integrity of the pile body. Assume the pile is a one-dimensional linear elastic rod with a length of... The cross-sectional area is The elastic modulus of the pile material is The density of the pile material is The propagation velocity of stress waves within the pile (commonly known as elastic wave velocity) is , represented as:

[0040]

[0041] In the formula , The values ​​represent the peak impact velocity times. From Figure 4d, the calculated pile length is 78.75m, which is 1.56% different from the 80m pile length in the 3D model. The peak transient energy transfer hammer force is 105400 kN, which is 5.2% different from the high-strain detection data of 111150 kN. Therefore, the accuracy of the finite element model can be inferred.

[0042] The above are exemplary embodiments of this application, and the scope of protection of this application is defined by the claims and their equivalents.

Claims

1. A method for analyzing the dynamic response of deep-sea pile soil based on ALE fluid-structure interaction and infinite element boundary, characterized in that, include: Based on actual engineering parameters, a geometric model of the hydraulic hammer assembly, the replacement system, the large-diameter steel pipe pile, and the layered soil was constructed, and the components were assembled in a unified global coordinate system. The land calculation domain corresponding to the layered soil is divided into a core penetration zone and a peripheral radiation zone based on the radial and depth directions; wherein, the core penetration zone covers the area around the pile and the preset depth below the pile tip, and the peripheral radiation zone surrounds the outside of the core penetration zone. The core penetration region is discretized using hexahedral reduced integral elements C3D8R to obtain multiple hexahedral entities. These hexahedral entities are then associated with arbitrary Lagrange-Euler adaptive mesh control domains to obtain a geometric model with assigned properties, i.e., a constitutive model. The constitutive model includes a hydraulic hammer assembly constitutive model, a replacement system constitutive model, a large-diameter steel pipe pile constitutive model, and a layered soil constitutive model. The master-slave contact pairs of the hexahedral entity at the pile-soil contact interface are defined based on the kinematic contact algorithm, and the tangential interaction of the master-slave contact pairs is set based on Coulomb's law of friction. Before pile driving, the initial void ratio and effective stress field are calculated based on the layered soil constitutive model in the constitutive model, and vertical fixed constraints are applied to the bottom of the layered soil according to the initial void ratio and the effective stress field. During the piling process, the time step is calculated using an explicit integrator of the central difference method. Within each incremental step or a calculation interval at a preset frequency, the arbitrary Lagrange-Euler adaptive mesh control domain performs smoothing and variable remapping operations to map the deformed old mesh state variables onto the new topology-optimized mesh. Both the old mesh and the new mesh are hexahedral entities. Based on the new grid, data on pile head displacement time history curves, pile stress wave transmission characteristics, and pore water pressure changes at different radial distances in the layered soil were extracted.

2. The method for analyzing the dynamic response of deep-sea pile driving soil as described in claim 1, characterized in that, The radial range of the core penetration area R ALE Defined as R ALE ≥3D ,in D Indicates the pile diameter; the core penetration zone is the preset depth range below the pile tip. H ALE Defined as H ALE ≥5D .

3. The method for analyzing the dynamic response of deep-sea pile driving soil as described in claim 2, characterized in that, The arbitrary Lagrange-Euler adaptive mesh control domain adjusts the node positions of the deformed old mesh based on the volume-conserving Laplace smoothing algorithm, and performs no less than 3 mesh scans in each incremental step or preset frequency to obtain a new mesh with topology optimization; the arbitrary Lagrange-Euler adaptive mesh control domain then maps the old mesh state variables to the new mesh through variable remapping; wherein, the node is the six vertices of the hexahedral solid.

4. The method for analyzing the dynamic response of deep-sea pile driving soil as described in claim 3, characterized in that, The master-slave contact pair includes a master surface and a slave surface. The master surface is the outer surface of the pile with high stiffness, and the slave surface is the inner surface of the soil cavity with low stiffness. The tangential friction coefficient of the tangential interaction is a dynamic friction model that decreases with the relative slip velocity of the pile and soil.

5. The method for analyzing the dynamic response of deep-sea pile driving soil as described in claim 4, characterized in that, The process of performing variable remapping operations in the arbitrary Lagrange-Euler adaptive grid control domain includes first-order or second-order convective transport calculations on historical variables. Its governing equations follow the laws of conservation of mass, momentum, and energy, and are expressed as: ； in, Represents physical field variables, Indicates the velocity of material particles. Indicates the speed of grid movement. This indicates the convection velocity.

6. The method for analyzing the dynamic response of deep-sea pile driving soil as described in claim 5, characterized in that, The historical variables include plastic strain and hardening parameters.

7. The method for analyzing the dynamic response of deep-sea pile driving soil as described in claim 1, characterized in that, The old grid state quantities include stress and velocity.

8. The method for analyzing the dynamic response of deep-sea pile driving soil as described in claim 1, characterized in that, The behavior of the layered soil is described by Mohr-Coulomb theory or Drucker-Prag elastoplastic constitutive model, and the strain rate correlation parameter is introduced to characterize the effect of soil dynamic strength enhancement under high strain rate by Cowper-Symonds model.

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