Wind power pile foundation stability analysis method under extreme wind wave flow and landslide load

Abstract

The invention provides a method for evaluating the stability of an offshore wind power pile foundation under the coupling action of submarine landslide and wind wave impact load, and develops a finite element model of pile-soil interaction under the action of complex lateral load. Based on an established seabed landslide impact load quantification formula, the lateral load of the single pile under the coupling action of the seabed landslide, wind, wave and flow in the complex environment is given. And finally, carrying out single pile stability analysis under the action of complex lateral load, and discussing the stability of the single pile foundation by considering the sediment strength of different sea areas at the same time. Through the technical scheme of the invention, the method can judge the stability evaluation of the single pile foundation under the action of the wind wave current load and the potential landslide load in the research area, provides reference for site selection of offshore wind power, establishment of the offshore wind power and the like, and reduces the economic loss caused by the instability of the offshore wind power.

Description

Technical Field

[0001] The present invention relates to the technical field of offshore pile foundation stability research, and in particular to a method for evaluating the stability of offshore wind power pile foundations under extreme wind wave currents and landslide loads. Background Art

[0002] At present, the research on the stability of offshore pile foundations mainly focuses on the external dynamic loads on the piles, mainly including wind, wave, current and other loads. Zeng et al. studied the influence of breaking waves on offshore wind turbines with single pile foundations at different positions on the edge of the slope through water tank experiments and computational fluid dynamics models. The study found that when the waves break, the pressure acting on the single pile will be distributed in a wave-like manner, and the point of action will gradually move downward. Shi et al. established a "three-stage" single pile foundation offshore wind turbine calculation model, analyzed the stress conditions in the soil, water and air respectively, and further obtained the total dynamic impedance of the foundation to predict its dynamic response, and analyzed the displacement of the tower under different single pile parameters. Miles et al. conducted a series of indoor experiments to analyze the coupling effect of waves and currents and studied the influence of waves and currents on offshore wind turbine single piles. Ong et al. conducted a dynamic analysis of offshore single piles under the action of ocean currents through a finite element model, and analyzed the response of single piles under wind-wave coupling in shallow water conditions under different parameters. Buljac et al. tested small wind turbines in a wind-wave-current tank (WWCT) and studied the effects of wind-wave-current on offshore wind turbines with single pile foundations. The study found that the longitudinal surge force caused by the flow dominated the overall load on offshore wind turbines. Achmus et al. established a wave-wind turbine-seabed foundation interaction calculation model, simplified the wind and wave loads into concentrated horizontal forces acting on the top of the tower, and studied the horizontal bearing capacity characteristics of offshore wind turbine single piles. Wu et al. used finite element analysis to study the offshore wind turbine high pile foundation, simulating the bearing capacity of different soil strength parameters under horizontal loads on the wind turbine foundation. The results showed that improving the soil, increasing the burial depth and increasing the pile diameter can effectively improve the bearing capacity of the pile foundation.

[0003] The above studies mainly focus on the effects of wind, waves and currents on the stability of pile foundations. However, in recent years, due to the frequent occurrence of extreme storms and geological events around the world, some studies have begun to focus on the effects of occasional loads such as submarine landslides on pile foundations. Submarine landslides are manifested as local or large-scale seabed instability, large deformation and sliding. High-speed submarine landslides cause significant damage to marine structures. For example, the maximum speed of the Grand Banks landslide in Canada in 1929 could reach 20 m / s, destroying 12 submarine pipelines. The submarine landslide in the Luzon Strait in 2006 cut off 11 submarine communication cables, causing a long-term communication interruption. At present, the study of the impact of submarine landslides on piles mainly focuses on the quantification of the impact load of submarine landslides. Li et al. made a submarine landslide model trough, and conducted 12 sets of model tests by adjusting variables such as the slope of the model trough and the mass fraction of kaolin in the landslide body, and optimized the dimensionless resistance coefficient formula acting on the pile foundation. Li et al. used computational fluid dynamics to study the impact of submarine debris flow on a single pile and analyzed the characteristics of the drag force acting on the single pile. Li et al. used computational fluid dynamics to simulate the impact of submarine flow on pile foundations and proposed a prediction formula for the impact force.

[0004] However, these studies analyzed the impact of submarine landslides on pile foundations, but did not conduct in-depth research on whether the pile foundation would become unstable after encountering the impact load of submarine landslides and the mechanism of instability. At the same time, considering that there are still few reports on the analysis of pile foundation stability under multiple complex loads such as submarine landslides, wind, waves, and currents, relevant research is urgently needed. Summary of the invention

[0005] In order to make up for the shortcomings of the prior art, the present invention provides a method for evaluating the stability of offshore wind turbine pile foundations under the coupling of submarine landslides and wind and wave impact loads. The present invention develops a finite element model of pile-soil interaction under complex lateral loads. Based on the established quantitative formula for submarine landslide impact loads, the lateral loads on single piles under the coupling of submarine landslides, wind, waves, and currents in a complex environment are given. Finally, a stability analysis of a single pile under complex lateral loads was carried out, and the stability of the single pile foundation was discussed while considering the strength of sediments in different sea areas.

[0006] The present invention is achieved through the following technical solution: a method for evaluating the stability of offshore wind power pile foundations under the coupling effect of submarine landslide and wind and wave impact loads, characterized in that it specifically includes the following steps: Step S1, generalizing the loads on offshore wind power structures in complex environments, specifically including the following steps: Step S11, aerodynamic load: The aerodynamic loads acting on offshore wind power are divided into blade wind load and tower load. The blade wind load is the wind load on the entire wind turbine impeller, and the tower load is the wind load acting on the tower in the air. The blade wind load calculation formula is as follows: (1) In the formula, is the fan load; is the air density, ; is the impeller swept area, calculated based on the blade size; is the impeller thrust coefficient; is the wind speed; The wind load acting on the tower is calculated using the following formula: (4) Where: is the tower wind load; is the drag coefficient; is the diameter of a single pile; is the average wind speed at height Z, and the exponential formula for simulating the average wind speed changing along the height is: (5) In the formula, Indicates the standard height is The average wind speed at is the wind shear index; Step S12, hydrodynamic load, specifically includes the following steps: The hydrodynamic load is the wave-current coupled load, including wave load and current load. The wave load divides the wave force into two parts: one is the inertial force term proportional to the acceleration, and the other is the resistance term proportional to the square of the velocity, as follows: (6) in, is the wave force; is the drag force term; is the inertia force term; is the projected area per unit cylinder height perpendicular to the wave propagation direction; is the displacement volume per unit column height; is the density of seawater, ; is the drag force coefficient perpendicular to the axis of the cylinder; is the inertia force coefficient; is the wave speed; For the ocean current load, the ocean current is idealized as uniform motion, which will not cause the acceleration of the water particles. The inertia force term is omitted and only the drag force term is calculated, that is: (7) in, is the ocean current load; is the drag coefficient; Step S13: Submarine landslide impact load: Establish the relationship between the drag coefficient and the Reynolds number of non-Newtonian fluid: (8) in, is the landslide load; is the drag coefficient; is the density of submarine landslide debris flow; is the landslide flow velocity; is the impact height of submarine landslide; is the pile outer diameter; The relationship between the drag coefficient and the Reynolds number is fitted as follows: (9) The Reynolds number for non-Newtonian fluids is often expressed as: (10) in: is the shear rate of the mud near the pile; Debris flow viscosity; is the shear stress; the relationship between fluid shear stress and shear rate, the rheological curve expression is obtained: (11) In the formula, ; Step S14: superposition of environmental loads: Different environmental loads are equivalent to horizontal loads and bending moments acting at the same height, and submarine landslides are applied to the pile side by uniformly distributing loads; Step S2, establishing a pile-soil interaction model under complex horizontal loads, specifically includes the following steps: Step S21, single pile model: To solve the pile displacement and pile stress under the horizontal load of the pile head, a microelement with a length of dz of the horizontally loaded pile is selected, and through the force balance of the bending moment, the following is obtained: (12) Where M is the bending moment; is the vertical load; is the shear force; according to beam theory: (13) In the formula is the bending stiffness of the pile; the two equations can be connected to obtain the control equation when the pile is horizontally loaded: (14) In the formula, is the soil reaction force; The single pile model is described by an isotropic elastic model, and the stress-strain relationship of the pile material is simulated by the Hooke theorem. Under three-dimensional conditions, the Hooke theorem is expressed as: (15) in, is Young's modulus; is Poisson’s ratio; Step S22: soil model: The soil model is described by the elastic-plastic model Mohr-Coulomb model, which includes cohesion intercept c, friction angle, Young's modulus E, Poisson's ratio and expansion angle Parameters; when mapped to the three-dimensional stress space, the Mohr-Coulomb criterion is decomposed into an irregular hexagonal pyramid, which forms a failure / yield envelope surface and determines the behavior of the soil; when the stress point is within the envelope surface, the material undergoes elastic deformation, and when the stress reaches the yield surface, the material undergoes plastic deformation; in step S22, it is assumed that the soil is in a linear elastic relationship before failure; Step S23, pile-soil contact model: The “contact pair” algorithm is used to simulate the interaction between pile and soil. The pile is set as the main contact surface, and the soil is set as the slave contact surface. The surface discretization method adopts “face-to-face contact”, and the tracking of the relative movement of the contact surface adopts “limited sliding”. The calculation accuracy is improved by constantly judging whether the master-slave surface is in contact. The pile surface is defined as the main surface, and the soil surface is defined as the slave surface. The “hard” contact option is used for normal contact, and the Coulomb contact is used for tangential contact. The interface shear stress calculation method is: (16) in, is the contact surface shear stress; is the normal effective stress; is the friction angle of pile-soil interface under critical state; Step S3: Stability evaluation of single pile foundation under complex horizontal loads: The numerical model was established by ABAQUS software. The linear elastic model was used for the single pile, and Young's modulus, Poisson's ratio and density were set. The Mohr-Coulomb constitutive model was used for the seabed soil, and the friction coefficient was set. The contact relationship between the single pile and the seabed was Coulomb friction contact, the surface of the single pile was the primary surface, and the surface of the seabed was the secondary surface. The interface between the single pile and the seabed was allowed to separate during the calculation process. The meshing was divided in sweep mode, and the mesh type was C3D8R. At the pile-soil interface, the mesh density increased, and the mesh density gradually decreased from the interface to the edge. Through mesh sensitivity analysis, the mesh size at the single pile-seabed interface was determined to be 0.1D. At the pile head, horizontal load and bending moment were applied to the single pile through the reference point, and a uniformly distributed load was applied. Submit the calculation and export the odb file for result analysis; export the pile displacement to obtain the pile displacement variation curve along the depth direction; differentiate the curve to obtain the pile rotation angle; the tolerance of the permanent cumulative rotation of a single pile at the mud line is 0.25°; the instability of the single pile can be determined by comparing the calculated rotation angle with the specification; derive the bending moment of the pile through slicing to determine the most vulnerable point of the pile; at the same time, the damage characteristics of the single pile and the sediment can be determined through the stress cloud diagram of the single pile and the sediment; By changing the sediment cohesion and internal friction angle, the pile displacement and rotation angle under different sediment strengths are calculated. Then, the relationship curve between the single pile displacement, rotation angle and sediment strength cohesion and internal friction angle is obtained through fitting.

[0007] As a preferred solution, in step S11, considering different ranges of wind speed, the impeller thrust coefficient is obtained by the following three different methods: When the cut-in wind speed ( ) Wind speed ( ) Rated wind speed ( ), the calculation formula of impeller thrust coefficient is as follows: (2) When rated wind speed ( ) Wind speed ( ) Cut-out wind speed ( ), the calculation formula of impeller thrust coefficient is as follows: (3) When the wind speed is low, assuming that the impeller thrust coefficient does not exceed 1, equation (2) will overestimate the thrust coefficient, so its value is limited to 1; As a preferred solution, in step S11 It is a dimensionless number and is not affected by the specific size of the object. It is only related to the shape of the structure. The tower tube has a cylindrical cross-section and is taken as 0.5 after calculation.

[0008] As a preferred solution, in step S11 Take 10 m, wind shear index Take 0.143.

[0009] As a preferred solution, the cylinder under the action of wave and current load in step S12 is and .

[0010] As a preferred solution, the resistance coefficient in step S12 For circular components, take 0.73.

[0011] Due to the adoption of the above technical solution, the present invention has the following beneficial effects compared with the prior art: (1) This method can determine the stability of single pile foundations under the influence of wind, wave and current loads and potential landslide loads in the study area, and has an early warning effect on offshore wind power platforms; (2) Provide reference for the site selection and construction of offshore wind power, and reduce the economic losses caused by the instability of offshore wind power; (3) This method can clearly see the instability pattern of a single pile through the finite element model, providing a reference for single pile reinforcement.

[0012] Additional aspects and advantages of the present invention will become apparent from the following description or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which: Figure 1 Simplified schematic diagram for loads; Figure 2 is the pile-soil interaction model diagram; Figure 3 Effects of different landslide densities on a single pile: (a) pile displacement; (b) pile rotation angle; (c) pile bending moment; Figure 4 The stress cloud diagram of soil under the action of submarine landslides of different densities: (a) The landslide density is 1400 kg / m 3 ; (b) The landslide density is 1800 kg / m 3 ; Figure 5 Stress cloud diagram of pile body under the action of submarine landslides of different densities (deformation coefficient is 100): (a) Landslide density is 1400 kg / m 3 ; (b) The landslide density is 1800 kg / m 3 . DETAILED DESCRIPTION

[0014] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0015] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0016] Combine the following Figures 1 to 5 The method for evaluating the stability of offshore wind power pile foundations under the coupling effects of submarine landslide and wind and wave impact loads according to an embodiment of the present invention is specifically described.

[0017] The present invention proposes a method for evaluating the stability of offshore wind power pile foundations under the coupling effects of submarine landslide and wind and wave impact loads, which specifically includes the following steps: Step S1, generalizing the loads on offshore wind power structures in complex environments, specifically including the following steps: Step S11, aerodynamic load: The aerodynamic loads acting on offshore wind power are divided into blade wind load and tower load. The blade wind load is the wind load on the entire wind turbine impeller, which is the most important load on the wind turbine; the tower load is the wind load acting on the tower in the air. Since the tower size is relatively small, the load value of this part is also small. The blade wind load calculation formula is as follows: (1) In the formula, is the fan load; is the air density, ; is the impeller swept area, calculated based on the blade size; is the impeller thrust coefficient; is the wind speed; considering the different ranges of wind speed, the impeller thrust coefficient is obtained by the following three different methods: When the cut-in wind speed ( ) Wind speed ( ) Rated wind speed ( ), the calculation formula of impeller thrust coefficient is as follows: (2) When rated wind speed ( ) Wind speed ( ) Cut-out wind speed ( ), the calculation formula of impeller thrust coefficient is as follows: (3) When the wind speed is low, assuming that the impeller thrust coefficient does not exceed 1, equation (2) will overestimate the thrust coefficient, so its value is limited to 1. The diameter of the tower structure is relatively small compared to the wind distance, and the effect on wind flow can be ignored. Therefore, the wind load acting on the tower is calculated using the following formula: (4) Where: is the tower wind load; is the drag coefficient; It is a dimensionless number, which is not affected by the specific size of the object, but only related to the shape of the structure. It is used in engineering to represent the resistance characteristics of the movement of an object. The tower is a cylindrical section, and the calculation takes 0.5. is the diameter of a single pile; is the average wind speed at height Z, and the exponential formula for simulating the average wind speed changing along the height is: (5) In the formula, Indicates the standard height is The average wind speed at Take 10 m, is the wind shear index; wind shear index Take 0.143.

[0018] Step S12, hydrodynamic load, specifically includes the following steps: The hydrodynamic load is the wave-current coupled load, including wave load and current load. The wave load divides the wave force into two parts: one is the inertial force term proportional to the acceleration, and the other is the resistance term proportional to the square of the velocity, as follows: (6) in, is the wave force; is the drag force term; is the inertia force term; is the projected area per unit cylinder height perpendicular to the wave propagation direction; is the displacement volume per unit column height; is the density of seawater, ; is the drag force coefficient perpendicular to the axis of the cylinder, which reflects the viscosity effect caused by the viscosity of the fluid; is the inertia force coefficient; is the wave velocity; according to the Port Hydrology Regulations (JTJ213-98), the cylinder under the action of wave and current loads is and .

[0019] For the ocean current load, the ocean current is idealized as uniform motion, which will not cause the acceleration of the water particles. The inertia force term is omitted and only the drag force term is calculated, that is: (7) in, is the ocean current load; is the drag coefficient; drag coefficient For circular components, take 0.73.

[0020] Step S13: Submarine landslide impact load: In order to study the impact of submarine landslides on structures, the debris flow with different rheological properties and densities was obtained by adjusting the different contents of kaolin and silt sand, and the impact of the debris flow on the model pile was simulated. Combined with the theory of fluid mechanics, the relationship between the resistance coefficient and the Reynolds number of non-Newtonian fluid was established: (8) in, is the landslide load; is the drag coefficient; is the density of submarine landslide debris flow; is the landslide flow velocity; is the impact height of submarine landslide; is the pile outer diameter; The drag coefficient can be used to measure the magnitude of the impact force. According to the principles of fluid mechanics, the drag coefficient is closely related to the Reynolds number. The relationship between the drag coefficient and the Reynolds number is fitted as follows: (9) The Reynolds number for non-Newtonian fluids is often expressed as: (10) in: is the shear rate of the mud near the pile; Debris flow viscosity; is the shear stress; the relationship between fluid shear stress and shear rate, the rheological curve expression is obtained: (11) In the formula, ; Step S14: superposition of environmental loads: In order to simplify the analysis, this patent simplifies the horizontal loads of wind, waves and current acting on offshore wind power, such as Figure 1As shown in the figure, the blade wind load, tower wind load, wave load, current load and landslide load and their range of action are shown respectively. Due to the special structural form of offshore wind power, the main load form of pile foundation is overturning moment. Different environmental loads can be equivalent to horizontal loads and bending moments acting at the same height, such as Figure 1 The submarine landslide is applied to the pile side by means of uniformly distributed load.

[0021] Step S2, establishing a pile-soil interaction model under complex horizontal loads, specifically includes the following steps: Step S21, single pile model: To solve the pile displacement and pile stress under the horizontal load of the pile head, based on the bending theory of beams, a microelement method is used to select a microelement with a length of dz of the horizontally loaded pile, and through the force balance of the bending moment, the following is obtained: (12) Where M is the bending moment; is the vertical load; is the shear force; according to beam theory: (13) In the formula is the bending stiffness of the pile; the two equations can be connected to obtain the control equation when the pile is horizontally loaded: (14) In the formula, is the soil reaction force; the essence of using the finite element method to calculate the horizontal load response of the pile foundation is to solve the control equation of the horizontally loaded pile.

[0022] The single pile model is described by an isotropic elastic model, and the stress-strain relationship of the pile material is simulated by the Hooke theorem. Under three-dimensional conditions, the Hooke theorem is expressed as: (15) in, is Young's modulus; is Poisson’s ratio; Step S22: soil model: The soil model is described by the elastic-plastic model Mohr-Coulomb model, which includes cohesion intercept c, friction angle, Young's modulus E, Poisson's ratio and expansion angle Parameters; According to Johnson (2006), the failure envelope depends only on the principal stresses (), but not on the intermediate principal stresses (). When mapped to the three-dimensional stress space, the Mohr-Coulomb criterion decomposes into irregular hexagonal pyramids, which form the failure / yield envelope and determine the behavior of the soil; when the stress point is within the envelope, the material undergoes elastic deformation, and when the stress reaches the yield surface, the material undergoes plastic deformation; in step S22, it is assumed that the soil is in a linear elastic relationship before failure; Step S23, pile-soil contact model: The "contact pair" algorithm is used to simulate the interaction between pile and soil. The pile is set as the main contact surface, and the soil is set as the slave contact surface. The surface discretization method uses "face-to-face contact", which can consider the geometric shapes of the master and slave surfaces at the same time, and the calculation accuracy of stress and normal pressure of the contact surface is high. The tracking of the relative movement of the contact surface adopts "limited sliding" to improve the calculation accuracy by constantly judging whether the master-slave surface is in contact; considering the relative stiffness difference, the pile surface is defined as the main surface and the soil surface is defined as the slave surface; the normal contact adopts the "hard" contact option, and the tangential contact adopts Coulomb contact. The interface shear stress calculation method is: (16) in, is the contact surface shear stress; is the normal effective stress; is the friction angle of pile-soil interface under critical state; Step S3: Stability evaluation of single pile foundation under complex horizontal loads: The numerical model was established by ABAQUS software. The linear elastic model was adopted for the single pile, and Young's modulus, Poisson's ratio and density were set. The Mohr-Coulomb constitutive model was adopted for the seabed soil, and the friction coefficient was set. The contact relationship between the single pile and the seabed was Coulomb friction contact, the surface of the single pile was the primary surface, and the surface of the seabed was the secondary surface. The interface between the single pile and the seabed was allowed to separate during the calculation process. The meshing was divided in sweep mode, and the mesh type was C3D8R. At the pile-soil interface, the density of the mesh increased, and the mesh density gradually decreased from the interface to the edge. Through mesh sensitivity analysis, the mesh size at the single pile-seabed interface was determined to be 0.1D. At the pile head, horizontal load and bending moment were applied to the single pile through the reference point, and a uniformly distributed load was applied. The model is shown in the figure below. Figure 2 shown.

[0023] Submit the calculation and export the odb file for result analysis; export the pile displacement to obtain the pile displacement change curve along the depth direction; take the derivative of the curve to obtain the pile rotation angle; according to DNV (Det Norske Veritas (DNV), 2018), the tolerance of the permanent cumulative rotation of a single pile at the mud line is 0.25°; the instability of the single pile can be determined by comparing the calculated rotation angle with the specification; derive the bending moment of the pile through slicing to determine the most vulnerable point of the pile; at the same time, the damage characteristics of the single pile and the sediment can be determined through the stress cloud diagram of the single pile and the sediment; By changing the sediment cohesion and internal friction angle, the pile displacement and rotation angle under different sediment strengths are calculated. Then, the relationship curves between the pile displacement, rotation angle, sediment strength cohesion and internal friction angle are obtained through fitting.

[0024] Xiangshui Wind Farm is located in the tidal flat area of ​​Chenjiagang Town, Xiangshui County, Jiangsu Province. A total of 134 large wind turbines with a single unit capacity of 1.5MW are installed, with a total installed capacity of 201 MW and an annual grid-connected power generation of about 440 million kWh. The wind farm is a concrete single pile foundation with a pile diameter D of 4.3 m, a pile length L of 70 m, and a seabed burial depth Ld of 60 m. The three-dimensional finite element model consists of two parts: the seabed and the wind power single pile foundation. The single pile adopts a linear elastic model, with a Young's modulus Epile of 25×106 kPa, a Poisson's ratio νpile of 0.20, and a density ρpile of 2400 kg / m3. In order to eliminate the boundary effect, the seabed radius of the calculation domain is taken as 70 m and the height is 140 m. The Mohr-Coulomb constitutive model is adopted for the seabed soil. The contact relationship between the single pile and the seabed is Coulomb friction contact, the surface of the single pile is the primary surface, the surface of the seabed is the secondary surface, the friction coefficient is 0.39, and the separation of the single pile and seabed interface is allowed during the calculation process.

[0025] The field investigation shows (Zhang et al., 2018) that the gravity load of the entire wind power system of the Xiangshui wind farm project is 2.06×103 kN m. When the wind farm is operating normally, the wind speed at an altitude of 10 m is 13.4 m / s, the water depth is 5 m, the wave height is 2.68 m, the wavelength is 74.1 m, and the flow velocity is 0.88 m / s. The environmental loads at different points of action are converted and superimposed. The horizontal load applied to the pile head is 307102 N, and the clockwise bending moment is 10891482 N·m. The density of the seabed sediment is 2130 kg / m3, the Young's modulus is 80×103 kPa, the Poisson's ratio is 0.33, the cohesion is 10 kPa, and the internal friction angle is 10°.

[0026] In order to compare the effects of different landslide densities on the stability of a single pile, the landslide velocity was set to 15 m / s and the height of the landslide impacting the single pile was 6 m. The displacement, rotation angle and bending moment of the pile under different densities were calculated as follows: Figure 3 The landslide density is 1400kg / m 3 When the landslide impact force is 3561713 N, the horizontal displacement of the pile top is 0.09 m. The landslide density is 1800 kg / m 3 When the landslide impact force is 4574803 N, the horizontal displacement of the pile top is 0.13 m. Obviously, the greater the density of submarine landslide, the greater the horizontal displacement of the pile top. However, the gradient of the horizontal displacement of the pile top with the increase of landslide density is basically unchanged. When the landslide density increases by 200 kg / m 3 , the horizontal displacement of the pile top increases by 0.02 m. Similarly, the gradient of the pile body rotation angle with the increase of landslide density is basically unchanged. When the landslide density increases by 200 kg / m 3 The maximum rotation angle of the pile body increases by about 0.04°, and the landslide density is 1400 kg / m 3 When the maximum rotation angle at the pile mud line is 0.19°, the landslide density is 1800 kg / m 3 When the pile body is at the mud line, the maximum rotation angle is 0.27°, which has reached the destruction state. As the landslide density increases, the maximum bending moment of the pile body increases. The landslide density is 1600kg / m 3 When the maximum bending moment of the pile body is 47.5 MN·m, it is 3.6 times the calculated result without landslide load. The landslide density is 1800 kg / m 3 When the load is 1400 kg / m, the maximum bending moment of the pile body can reach 61.9 MN·m, which is 4.7 times the calculated result without landslide load. In order to analyze the complex stress state of sediment and single pile after loading, the Mises stress cloud diagram of sediment and single pile is mainly analyzed below. 3 and 1800kg / m 3 Mises stress cloud diagram of sediments ( Figure 4 ) and Mises stress cloud diagram of pile body ( Figure 5 ), can further explain the above results. When a single pile is subjected to lateral load, the stress on the compressive surface of the sediment increases due to the lateral load. With the increase of density, the lateral load increases and the sediment stress increases. It can be seen that the change of landslide density has not changed the distribution of sediment-single pile interaction (SPI) damage zone. The SPI damage zone mainly includes the damage zone where the single pile is squeezed at the pile head, the shear damage zone caused by the rotation of the single pile at the pile foot, and the pile side damage zone. The density is 1400 kg / m 3 When the SPI pile top failure zone is 6.3D, the density is 1800 kg / m 3When , the range of the SPI pile top failure zone is 7.3D. The stress cloud diagram of the pile body corresponds to the stress cloud diagram of the sediment. The increase in density leads to an increase in the stress of the pile body. The maximum stress of the pile body appears about 10 m below the seabed surface, which is the same as the position of the maximum bending moment of the pile body, and increases with the increase of the displacement of the pile top.

[0027] In the description of the present invention, the term "plurality" refers to two or more than two. Unless otherwise clearly defined, the orientation or positional relationship indicated by the terms "upper" and "lower" is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation of the present invention; the terms "connection", "installation", "fixation", etc. should be understood in a broad sense. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0028] In the description of this specification, the description of the terms "one embodiment", "some embodiments", "specific embodiments", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0029] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for evaluating the stability of offshore wind power pile foundations under the coupling of submarine landslide and wind and wave impact loads, characterized in that , specifically including the following steps: Step S1, generalizing the loads on offshore wind power structures in complex environments, specifically including the following steps: Step S11, aerodynamic load: The aerodynamic loads acting on offshore wind power are divided into blade wind load and tower load. The blade wind load is the wind load on the entire wind turbine impeller, and the tower load is the wind load acting on the tower in the air. The blade wind load calculation formula is as follows: （1） In the formula, is the fan load; is the air density, ; is the impeller swept area, calculated based on the blade size; is the impeller thrust coefficient; is the wind speed; The wind load acting on the tower is calculated using the following formula: （4） Where: is the tower wind load; is the drag coefficient; is the diameter of a single pile; is the average wind speed at height Z, and the exponential formula for simulating the average wind speed changing along the height is: （5） In the formula, Indicates the standard height is The average wind speed at is the wind shear index; Step S12, hydrodynamic load, specifically includes the following steps: The hydrodynamic load is the wave-current coupled load, including wave load and current load. The wave load divides the wave force into two parts: one is the inertial force term proportional to the acceleration, and the other is the resistance term proportional to the square of the velocity, as follows: （6） in, is the wave force; is the drag force term; is the inertia force term; is the projected area per unit cylinder height perpendicular to the wave propagation direction; is the displacement volume per unit column height; is the density of seawater, ; is the drag force coefficient perpendicular to the axis of the cylinder; is the inertia force coefficient; is the wave speed; For the ocean current load, the ocean current is idealized as uniform motion, which will not cause the acceleration of the water particles. The inertia force term is omitted and only the drag force term is calculated, that is: （7） in, is the ocean current load; is the drag coefficient; Step S13: Submarine landslide impact load: Establish the relationship between the drag coefficient and the Reynolds number of non-Newtonian fluid: （8） in, is the landslide load; is the drag coefficient; is the density of submarine landslide debris flow; is the landslide flow velocity; is the impact height of submarine landslide; is the pile outer diameter; The relationship between the drag coefficient and the Reynolds number is fitted as follows: （9） The Reynolds number for non-Newtonian fluids is often expressed as: （10） in: is the shear rate of the mud near the pile; Debris flow viscosity; is the shear stress; the relationship between fluid shear stress and shear rate, the rheological curve expression is obtained: （11） In the formula, ; Step S14: superposition of environmental loads: Different environmental loads are equivalent to horizontal loads and bending moments acting at the same height, and submarine landslides are applied to the pile side by uniformly distributing loads; Step S2, establishing a pile-soil interaction model under complex horizontal loads, specifically includes the following steps: Step S21, single pile model: To solve the pile displacement and pile stress under the horizontal load of the pile head, a microelement with a length of dz of the horizontally loaded pile is selected, and through the force balance of the bending moment, the following is obtained: （12） Where M is the bending moment; is the vertical load; is the shear force; according to beam theory: （13） In the formula is the bending stiffness of the pile; the two equations can be connected to obtain the control equation when the pile is horizontally loaded: （14） In the formula, is the soil reaction force; The single pile model is described by an isotropic elastic model, and the stress-strain relationship of the pile material is simulated by the Hooke theorem. Under three-dimensional conditions, the Hooke theorem is expressed as: (15) in, is Young's modulus; is Poisson’s ratio; Step S22: soil model: The soil model is described by the elastic-plastic model Mohr-Coulomb model, which includes cohesion intercept c, friction angle, Young's modulus E, Poisson's ratio and expansion angle Parameters; when mapped to the three-dimensional stress space, the Mohr-Coulomb criterion is decomposed into an irregular hexagonal pyramid, which forms a failure / yield envelope surface and determines the behavior of the soil; when the stress point is within the envelope surface, the material undergoes elastic deformation, and when the stress reaches the yield surface, the material undergoes plastic deformation; in step S22, it is assumed that the soil is in a linear elastic relationship before failure; Step S23, pile-soil contact model: The "contact pair" algorithm is used to simulate the interaction between pile and soil. The pile is set as the main contact surface, and the soil is set as the slave contact surface. The surface discretization method adopts "face-to-face contact", and the tracking of the relative movement of the contact surface adopts "limited sliding". The calculation accuracy is improved by constantly judging whether the master-slave surface is in contact; the pile surface is defined as the main surface, and the soil surface is defined as the slave surface; the normal contact adopts the "hard" contact option, and the tangential contact adopts the Coulomb contact. The interface shear stress calculation method is: (16) in, is the contact surface shear stress; is the normal effective stress; is the friction angle of pile-soil interface under critical state; Step S3: Stability evaluation of single pile foundation under complex horizontal loads: The numerical model was established by ABAQUS software. The linear elastic model was used for the single pile, and Young's modulus, Poisson's ratio and density were set. The Mohr-Coulomb constitutive model was used for the seabed soil, and the friction coefficient was set. The contact relationship between the single pile and the seabed was Coulomb friction contact, the surface of the single pile was the primary surface, and the surface of the seabed was the secondary surface. The interface between the single pile and the seabed was allowed to separate during the calculation process. The meshing was divided in sweep mode, and the mesh type was C3D8R. At the pile-soil interface, the mesh density increased, and the mesh density gradually decreased from the interface to the edge. Through mesh sensitivity analysis, the mesh size at the single pile-seabed interface was determined to be 0.1D. At the pile head, horizontal load and bending moment were applied to the single pile through the reference point, and a uniformly distributed load was applied. Submit the calculation and export the odb file for result analysis; export the pile displacement to obtain the pile displacement variation curve along the depth direction; differentiate the curve to obtain the pile rotation angle; the tolerance of the permanent cumulative rotation of a single pile at the mud line is 0.25°; the instability of the single pile can be determined by comparing the calculated rotation angle with the specification; derive the bending moment along the pile body through slicing to determine the most vulnerable point of the pile body; at the same time, the damage characteristics of the single pile and sediment can be determined through the stress cloud diagram of the single pile and sediment; By changing the sediment cohesion and internal friction angle, the pile displacement and rotation angle under different sediment strengths are calculated. Then, the relationship curve between the single pile displacement, rotation angle and sediment strength cohesion and internal friction angle is obtained through fitting.

2. The method for evaluating the stability of offshore wind power pile foundation under the coupling effect of submarine landslide and wind and wave impact load according to claim 1 is characterized in that In step S11, considering different ranges of wind speed, the impeller thrust coefficient is obtained by the following three different methods: When the cut-in wind speed ( ) Wind speed ( ) Rated wind speed ( ), the calculation formula of impeller thrust coefficient is as follows: (2) When rated wind speed ( ) Wind speed ( ) Cut-out wind speed ( ), the calculation formula of impeller thrust coefficient is as follows: （3） When the wind speed is low, assuming that the impeller thrust coefficient does not exceed 1, equation (2) will overestimate the thrust coefficient, so its value is limited to 1.

3. The method for evaluating the stability of offshore wind power pile foundation under the coupling effect of submarine landslide and wind and wave impact load according to claim 1 is characterized in that In step S11 It is a dimensionless number and is not affected by the specific size of the object. It is only related to the shape of the structure. The tower tube has a cylindrical cross-section and is taken as 0.5 after calculation.

4. The method for evaluating the stability of offshore wind power pile foundation under the coupling effect of submarine landslide and wind and wave impact load according to claim 1 is characterized in that In step S11 Take 10 m, wind shear index Take 0.

143.

5. The method for evaluating the stability of offshore wind power pile foundation under the coupling effect of submarine landslide and wind and wave impact load according to claim 1 is characterized in that , the cylinder under the wave and current load in step S12, take and .

6. The method for evaluating the stability of offshore wind power pile foundation under the coupling effect of submarine landslide and wind and wave impact load according to claim 1 is characterized in that , the resistance coefficient in step S12 For circular components, take 0.73.

Images