Method and device for safety evaluation of monopile offshore wind turbine on liquefiable ground

Abstract

The application provides a method and device for evaluating the safety of liquefiable foundation of offshore wind turbine with single pile foundation, which can be applied to the technical field of offshore wind turbine single pile foundation. The method comprises the following steps: based on the load combination of the single pile foundation in the target working condition of the offshore wind turbine structure, the dynamic response of the offshore wind turbine structure is simulated by using a numerical model to obtain the excess pore water pressure ratio and effective stress of the foundation soil embedded by the single pile foundation; in the case that the excess pore water pressure ratio represents the deterioration of the foundation soil, the soil parameters of the deteriorated foundation soil are determined according to the excess pore water pressure ratio and the effective stress; the soil parameters are updated to the soil elements of the numerical model to perform static elastoplastic analysis on the single pile foundation, and the ultimate bearing capacity of the single pile foundation in the deteriorated foundation soil is obtained; the safety factor between the mud surface load of the single pile foundation under the load combination and the ultimate bearing capacity is calculated to evaluate the bearing safety of the single pile foundation in the deteriorated foundation soil.

Description

Technical Field

[0001] This invention relates to the field of offshore wind turbine monopile foundation technology, specifically to a method and apparatus for safety assessment of liquefiable foundations for offshore wind turbines with monopile foundations. Background Technology

[0002] Currently, in the safety assessment of the bearing capacity of monopile foundations for offshore wind turbines, the relevant technologies mainly rely on static analysis or use empirical reduction factors to approximate the impact of soil liquefaction. However, these methods are difficult to accurately simulate the evolution of soil under multiple loads such as wind, waves, and earthquakes, leading to biases in the safety assessment results and reducing the accuracy and reliability of the assessment. Summary of the Invention

[0003] In view of the above problems, the present invention provides a method, apparatus, equipment, medium and program product for safety assessment of liquefiable foundation of monopile offshore wind turbine.

[0004] According to a first aspect of the present invention, a method for assessing the safety of a monopile foundation for an offshore wind turbine in liquefiable soil is provided, comprising: simulating the dynamic response of the offshore wind turbine structure using a numerical model based on a load combination of the monopile foundation under a target working condition, to obtain the excess pore pressure ratio and effective stress of the soil in which the monopile foundation is embedded; determining soil parameters of the deteriorated soil based on the excess pore pressure ratio and the effective stress when the excess pore pressure ratio indicates soil deterioration; updating the soil parameters to soil elements in the numerical model, and performing static elastoplastic analysis on the monopile foundation based on the updated soil elements to obtain the ultimate bearing capacity of the monopile foundation in the deteriorated soil; and assessing the bearing safety of the monopile foundation in the deteriorated soil by calculating a safety factor between the mud surface load and the ultimate bearing capacity of the monopile foundation under the load combination.

[0005] According to an embodiment of the present invention, the method further includes: calculating the mud surface horizontal force and mud surface bending moment corresponding to each load in the load combination under the target working condition, wherein the load combination is a combination of at least two loads including wind load, wave load and seismic horizontal inertial force; and obtaining the mud surface load of the single pile foundation under the target working condition by superimposing the mud surface horizontal force and mud surface bending moment corresponding to each of the above loads.

[0006] According to an embodiment of the present invention, the method further includes: obtaining the geometric parameters of the single pile foundation and the initial soil parameters of the foundation soil, wherein the geometric parameters include the pile diameter and the penetration depth, and the initial soil parameters include the initial internal friction angle and the initial shear modulus; constructing a single pile foundation model based on the geometric parameters, and dividing the corresponding initial soil elements based on the initial soil parameters; and constructing the numerical model by setting zero-length elements between the single pile foundation model and the initial soil elements, wherein the numerical model is used to simulate the interaction between the single pile foundation and the foundation soil.

[0007] According to an embodiment of the present invention, when the excess pore pressure ratio indicates that the foundation soil has deteriorated, determining the soil parameters of the deteriorated foundation soil based on the excess pore pressure ratio and the effective stress includes: determining that the foundation soil has deteriorated when the excess pore pressure ratio exceeds a preset deterioration threshold; determining the internal friction angle of the deteriorated foundation soil based on the negative correlation between the initial internal friction angle of the foundation soil and the excess pore pressure ratio, wherein the negative correlation indicates that the internal friction angle after deterioration decreases as the excess pore pressure ratio increases; and determining the shear modulus of the deteriorated foundation soil based on the power law relationship between the initial shear modulus of the foundation soil and the effective stress, wherein the power law relationship indicates that the shear modulus after deterioration adjusts according to a power function law with the effective stress as a reference.

[0008] According to an embodiment of the present invention, determining the internal friction angle of the deteriorated foundation soil based on the negative correlation between the initial internal friction angle of the foundation soil and the excess pore pressure ratio includes: calculating a reduction coefficient of the foundation soil based on the excess pore pressure ratio, wherein the reduction coefficient is negatively correlated with the excess pore pressure ratio; and calculating the internal friction angle of the deteriorated foundation soil by using trigonometric functions based on the product of the sine value of the initial internal friction angle and the reduction coefficient.

[0009] According to an embodiment of the present invention, the deterioration of the foundation soil includes weakening and liquefaction; updating the soil parameters to the soil elements of the numerical model includes: performing layered processing on the initial soil elements in the numerical model based on the excess pore pressure ratio obtained from dynamic response simulation to determine liquefaction zone, weakened zone, and unweakened zone; for the initial soil elements in the liquefaction zone and the weakened zone, updating the initial internal friction angle in the initial soil parameters to the internal friction angle of the deteriorated foundation soil, and updating the initial shear modulus to the shear modulus of the deteriorated foundation soil; keeping the initial soil parameters of the initial soil elements in the unweakened zone unchanged.

[0010] According to an embodiment of the present invention, the above-mentioned static elastoplastic analysis of the monopile foundation based on the updated soil element to obtain the ultimate bearing capacity of the monopile foundation in the deteriorated foundation soil includes: performing static elastoplastic analysis of the monopile foundation under a first loading condition and a second loading condition based on the numerical model corresponding to the updated soil element, respectively, to obtain the relationship curve between the horizontal force and displacement at the pile top corresponding to the first loading condition, and the relationship curve between the bending moment and rotation at the pile top corresponding to the second loading condition; wherein, the first loading condition is when the bending moment at the pile top of the monopile foundation is set to zero. Under the following conditions, a horizontal force is gradually applied to the aforementioned single pile foundation until the horizontal displacement at the top of the single pile foundation reaches a preset displacement threshold. The second loading condition is that, with the horizontal force at the top of the single pile foundation set to zero, a bending moment is gradually applied to the aforementioned single pile foundation until the rotation angle at the top of the single pile foundation reaches a preset rotation angle threshold. The relationship curves between the horizontal force and displacement at the top of the pile and the relationship curves between the bending moment and rotation angle at the top of the pile are analyzed using the double tangent method to determine the ultimate bearing capacity of the aforementioned single pile foundation in the aforementioned deteriorated foundation soil. The ultimate bearing capacity includes the ultimate bearing capacity of the horizontal force and the ultimate bearing capacity of the bending moment.

[0011] According to an embodiment of the present invention, the above-mentioned assessment of the bearing safety of the monopile foundation in the deteriorated foundation soil by calculating the safety factor between the mud surface load and the ultimate bearing capacity of the monopile foundation under the above-mentioned load combination includes: associating the horizontal load and bending moment load in the mud surface load with the horizontal force ultimate bearing capacity and bending moment ultimate bearing capacity in the above-mentioned ultimate bearing capacity, respectively, to obtain the bearing capacity utilization rate through nonlinear combination calculation; using the bearing capacity utilization rate as the safety factor, to determine that the bearing capacity of the monopile foundation in the deteriorated foundation soil is in a risk state when the safety factor is determined to be less than or equal to a preset safety value, and to determine that the bearing capacity of the monopile foundation in the deteriorated foundation soil is in a safe state when the safety factor is determined to be greater than the preset safety value.

[0012] According to an embodiment of the present invention, the above-mentioned association of the horizontal load and bending moment load in the mud surface load with the horizontal force ultimate bearing capacity and bending moment ultimate bearing capacity in the ultimate bearing capacity, respectively, to obtain the bearing capacity utilization rate through nonlinear combination calculation, includes: performing a composite square operation on the horizontal force ultimate bearing capacity and bending moment ultimate bearing capacity in the ultimate bearing capacity with the horizontal load and bending moment load in the mud surface load to obtain the foundation bearing capacity characterizing the bearing capacity of the deteriorated foundation soil; performing a vector synthesis operation on the horizontal load and bending moment load in the mud surface load to obtain the mud surface load effect characterizing the combined action of the horizontal load and the bending moment load; and determining the bearing capacity utilization rate based on the ratio of the mud surface load effect to the foundation bearing capacity.

[0013] A second aspect of the present invention provides a safety assessment device for the liquefiable foundation of a monopile foundation for an offshore wind turbine, comprising: a dynamic simulation module for simulating the dynamic response of the offshore wind turbine structure using a numerical model based on the load combination of the monopile foundation under a target working condition, to obtain the excess pore pressure ratio and effective stress of the foundation soil into which the monopile foundation is embedded; a parameter determination module for determining soil parameters of the deteriorated foundation soil based on the excess pore pressure ratio and the effective stress, when the excess pore pressure ratio indicates that the foundation soil has deteriorated; a bearing capacity analysis module for updating the soil parameters to the soil elements of the numerical model, and performing static elastoplastic analysis on the monopile foundation based on the updated soil elements to obtain the ultimate bearing capacity of the monopile foundation in the deteriorated foundation soil; and a safety assessment module for assessing the bearing capacity safety of the monopile foundation in the deteriorated foundation soil by calculating the safety factor between the mud surface load and the ultimate bearing capacity of the monopile foundation under the load combination.

[0014] A third aspect of the present invention provides an electronic device comprising: one or more processors; and a memory for storing one or more computer programs, wherein the one or more processors execute the one or more computer programs to implement the steps of the method described above.

[0015] A fourth aspect of the present invention also provides a computer-readable storage medium having a computer program or instructions stored thereon, wherein the computer program or instructions, when executed by a processor, implement the steps of the above-described method.

[0016] A fifth aspect of the present invention also provides a computer program product, including a computer program or instructions that, when executed by a processor, implement the steps of the above-described method.

[0017] According to embodiments of the present invention, dynamic response simulation using a load combination-driven numerical model based on target working conditions can accurately obtain the excess pore pressure ratio and effective stress of the foundation soil, thereby determining the deterioration state of the foundation soil. By determining the parameters of the deteriorated soil based on the excess pore pressure ratio and effective stress and updating them to the numerical model, the mechanical properties of the deteriorated foundation soil can be dynamically and realistically reflected. By performing static elastoplastic analysis based on the updated model, the ultimate bearing capacity of the monopile foundation in the deteriorated foundation soil can be accurately calculated. By calculating the safety factor between the mud surface load and the ultimate bearing capacity, a quantitative and refined assessment of the structural bearing safety can be achieved. By combining the analysis of the foundation soil deterioration state with the ultimate bearing capacity, the accuracy and reliability of the safety assessment of offshore wind turbine monopile foundations under the coupled effects of complex loads and foundation deterioration are significantly improved. Attached Figure Description

[0018] The above-mentioned contents, as well as other objects, features and advantages of the present invention, will become clearer from the following description of embodiments of the present invention with reference to the accompanying drawings.

[0019] Figure 1 The illustration shows an application scenario of the method, apparatus, equipment, medium, and program products for safety assessment of liquefiable foundations for monopile offshore wind turbines according to embodiments of the present invention.

[0020] Figure 2 A flowchart is shown for a method for assessing the safety of a monopile foundation for an offshore wind turbine on liquefiable ground, according to an embodiment of the present invention.

[0021] Figure 3 A schematic diagram of soil zoning is shown in the method for safety assessment of liquefiable foundation of a monopile foundation for an offshore wind turbine according to an embodiment of the present invention.

[0022] Figure 4 A schematic diagram of the relationship curves for the safety assessment method of the liquefiable foundation of a monopile foundation for an offshore wind turbine according to an embodiment of the present invention is shown.

[0023] Figure 5 A schematic diagram of the bearing capacity utilization rate curve of the method for safety assessment of the liquefiable foundation of a monopile foundation for an offshore wind turbine according to an embodiment of the present invention is shown.

[0024] Figure 6 A structural block diagram of a device for assessing the safety of a monopile foundation offshore wind turbine liquefiable ground, according to an embodiment of the present invention, is shown.

[0025] Figure 7 A block diagram of an electronic device suitable for implementing a method for assessing the safety of liquefiable foundations for monopile offshore wind turbines, according to an embodiment of the present invention, is shown. Detailed Implementation

[0026] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the invention. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the invention for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0027] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0028] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0029] When using expressions such as "at least one of A, B and C", they should generally be interpreted in accordance with the meaning that is commonly understood by those skilled in the art (e.g., "a system having at least one of A, B and C" should include, but is not limited to, a system having A alone, a system having B alone, a system having C alone, a system having A and B, a system having A and C, a system having B and C, and / or a system having A, B and C, etc.).

[0030] In the technical solution of this invention, the data involved (including but not limited to data used for analysis, data stored, data displayed, etc.) are all information and data authorized by the user or fully authorized by all parties. The collection, storage, use, processing, transmission, provision, disclosure and application of related data all comply with relevant laws, regulations and standards, necessary confidentiality measures have been taken, and they do not violate public order and good morals. Corresponding operation entry points are provided for users to choose to authorize or refuse.

[0031] This invention provides a method for assessing the safety of a monopile foundation in liquefiable soil for offshore wind turbines. The method includes: simulating the dynamic response of the offshore wind turbine structure using a numerical model based on the load combination of the monopile foundation under target operating conditions, obtaining the excess pore pressure ratio and effective stress of the soil in which the monopile foundation is embedded; determining the soil parameters of the deteriorated soil based on the excess pore pressure ratio and effective stress when the soil deteriorates; updating the soil parameters to the soil elements of the numerical model, and performing static elastoplastic analysis on the monopile foundation based on the updated soil elements to obtain the ultimate bearing capacity of the monopile foundation in the deteriorated soil; and assessing the bearing safety of the monopile foundation in the deteriorated soil by calculating the safety factor between the mud surface load and the ultimate bearing capacity of the monopile foundation under the load combination.

[0032] Figure 1 The illustration shows an application scenario of the method, apparatus, equipment, medium, and program products for safety assessment of liquefiable foundations for monopile offshore wind turbines according to embodiments of the present invention.

[0033] like Figure 1As shown, application scenario 100 according to this embodiment may include a first terminal device 101, a second terminal device 102, a third terminal device 103, and a server 105. Network 104 serves as a medium for providing a communication link between the first terminal device 101, the second terminal device 102, the third terminal device 103, and the server 105. Network 104 may include various connection types, such as wired or wireless communication links, or fiber optic cables, etc.

[0034] Users can use the first terminal device 101, the second terminal device 102, and the third terminal device 103 to interact with the server 105 via the network 104 to receive or send messages, etc. Various communication client applications can be installed on the first terminal device 101, the second terminal device 102, and the third terminal device 103, such as shopping applications, web browser applications, search applications, instant messaging tools, email clients, social media platform software, etc. (for example only).

[0035] The first terminal device 101, the second terminal device 102, and the third terminal device 103 can be various electronic devices with displays and support web browsing, including but not limited to smartphones, tablets, laptops, and desktop computers.

[0036] Server 105 can be a server that provides various services, such as a backend management server that supports websites browsed by users using the first terminal device 101, the second terminal device 102, and the third terminal device 103 (this is just an example). The backend management server can analyze and process data such as received user requests, and feed back the processing results (such as web pages, information, or data obtained or generated according to user requests) to the terminal devices.

[0037] It should be noted that the safety assessment method for liquefiable foundations of monopile offshore wind turbines provided in this embodiment of the invention can generally be executed by server 105. Correspondingly, the safety assessment device for liquefiable foundations of monopile offshore wind turbines provided in this embodiment of the invention can generally be installed in server 105. The safety assessment method for liquefiable foundations of monopile offshore wind turbines provided in this embodiment of the invention can also be executed by a server or server cluster that is different from server 105 and capable of communicating with the first terminal device 101, the second terminal device 102, the third terminal device 103, and / or server 105. Correspondingly, the safety assessment device for liquefiable foundations of monopile offshore wind turbines provided in this embodiment of the invention can also be installed in a server or server cluster that is different from server 105 and capable of communicating with the first terminal device 101, the second terminal device 102, the third terminal device 103, and / or server 105.

[0038] It should be understood that Figure 1The number of first terminal devices, second terminal devices, third terminal devices, networks, and servers in the system is only a certain number. Depending on the implementation requirements, any number of first terminal devices, second terminal devices, third terminal devices, networks, and servers can be included.

[0039] The following will be based on Figure 1 The described scene, through Figures 2-5 The invention provides a detailed description of the method for assessing the safety of liquefiable foundations for monopile foundation offshore wind turbines.

[0040] Figure 2 A flowchart is shown for a method for assessing the safety of a monopile foundation for an offshore wind turbine on liquefiable ground, according to an embodiment of the present invention.

[0041] like Figure 2 As shown, this embodiment includes operations S210 to S240.

[0042] In operation S210, based on the load combination of the monopile foundation in the offshore wind turbine structure under the target working condition, the dynamic response of the offshore wind turbine structure is simulated using a numerical model to obtain the excess pore pressure ratio and effective stress of the foundation soil into which the monopile foundation is embedded.

[0043] In operation S220, under the condition that the foundation soil deteriorates due to excess pore pressure ratio, the soil parameters of the deteriorated foundation soil are determined based on the excess pore pressure ratio and effective stress.

[0044] In operation S230, the soil parameters are updated to the soil elements of the numerical model. Based on the updated soil elements, a static elastoplastic analysis is performed on the single pile foundation to obtain the ultimate bearing capacity of the single pile foundation in the deteriorated foundation soil.

[0045] In operation S240, the bearing safety of a single pile foundation in deteriorated soil is evaluated by calculating the safety factor between the mud surface load and the ultimate bearing capacity of the single pile foundation under the load combination.

[0046] According to an embodiment of the present invention, when conducting a safety assessment of the foundation bearing capacity of a monopile foundation offshore wind turbine structure considering soil liquefaction, it is necessary to clarify the load combination of the monopile foundation under the target working condition. This load combination incorporates various actual working conditions of the offshore wind turbine, such as wind load, wave load, and seismic horizontal inertial force. Subsequently, a suitable numerical simulation software is selected to construct a numerical model of the monopile foundation and the foundation soil, and to simulate the dynamic response of the offshore wind turbine structure. The offshore wind turbine structure includes the monopile foundation, the foundation soil, and the wind turbine structure, including the tower, etc.

[0047] During the simulation, soil elements and boundary conditions need to be set appropriately. After the simulation calculation is completed, the excess porosity and effective stress at different depths of the foundation soil are extracted from the model results. After completing the dynamic response simulation, it is necessary to determine whether the foundation soil has deteriorated based on the excess porosity. Generally, when the excess porosity exceeds 0.04, the soil can be considered deteriorated. Specifically, foundation soil deterioration includes weakening and liquefaction. An excess porosity ≥ 0.95 indicates liquefaction; 0.04 ≤ excess porosity < 0.95 indicates weakening; and an excess porosity < 0.04 indicates no weakening, i.e., no deterioration has occurred.

[0048] If soil degradation is confirmed, it is necessary to combine the obtained excess pore pressure ratio and effective stress, refer to the correlation between soil parameters and excess pore pressure ratio and effective stress obtained from indoor geotechnical tests, or use industry-recognized empirical formulas to correct and calculate the key parameters of the degraded foundation soil (such as cohesion, internal friction angle, elastic modulus, etc.) in order to determine the soil parameters under degradation state.

[0049] After obtaining the soil parameters of the deteriorated foundation soil, these parameters are updated one by one to the corresponding soil elements in the numerical model to ensure that the numerical model can accurately reflect the deteriorated foundation state. Then, based on the updated soil elements, a static elastoplastic analysis is performed on the single pile foundation. During the analysis, horizontal loads are gradually applied until significant plastic deformation appears in the numerical model or the load no longer increases with displacement. The corresponding load value at this point is the ultimate bearing capacity of the single pile foundation in the deteriorated foundation soil.

[0050] Finally, based on the determined mud surface load of the monopile foundation under the load combination and the calculated ultimate bearing capacity, a safety factor is calculated using the safety factor calculation formula (e.g., safety factor = ultimate bearing capacity / mud surface load). The calculated safety factor is then compared with the minimum safety factor specified in the relevant offshore wind turbine foundation design codes. If the calculated value is greater than or equal to the code requirement, the bearing capacity safety performance of the monopile foundation in the deteriorated soil is deemed to meet the requirements. If the calculated value is less than the code requirement, the foundation treatment scheme needs to be reassessed or the monopile foundation design parameters adjusted to ensure the safety and stability of the offshore wind turbine structure.

[0051] By simulating the dynamic response of offshore wind turbine structures using a load combination-driven numerical model based on target working conditions, the excess pore pressure ratio and effective stress of the foundation soil can be accurately obtained, thereby determining the soil degradation state. By determining the degraded soil parameters based on the excess pore pressure ratio and effective stress and updating them in the numerical model, the mechanical properties of the degraded foundation soil can be dynamically and realistically reflected. Static elastoplastic analysis based on the updated model allows for accurate calculation of the ultimate bearing capacity of the monopile foundation in the degraded foundation soil. Calculating the safety factor between the mud surface load and the ultimate bearing capacity enables a quantitative and refined assessment of the structural bearing safety. By combining the analysis of the foundation soil degradation state with the ultimate bearing capacity, the accuracy and reliability of the safety assessment of offshore wind turbine monopile foundations under the coupled effects of complex loads and foundation degradation are significantly improved.

[0052] According to an embodiment of the present invention, the method further includes: calculating the mud surface horizontal force and mud surface bending moment corresponding to each load in the load combination under the target working condition, wherein the load combination is a combination of at least two loads including wind load, wave load and seismic horizontal inertial force; and obtaining the mud surface load of the single pile foundation under the target working condition by superimposing the mud surface horizontal force and mud surface bending moment corresponding to each load.

[0053] When calculating the mud surface load of a single pile foundation, it is necessary to first determine the load combination corresponding to the target working condition. This load combination must include at least two of the following: wind load, wave load, and seismic horizontal inertial force. Specifically, it is necessary to determine the specific load types included in the combination and the working conditions of each load (such as the combination of wind load and wave load during normal operation, or the combination of wind load and seismic horizontal inertial force under seismic conditions, etc.) based on the actual operating scenario or extreme environmental conditions of the offshore wind turbine.

[0054] Subsequently, for each load in the load combination, the corresponding horizontal force and bending moment on the mud surface are calculated separately. When calculating, it is necessary to select an appropriate calculation method based on the characteristics of each load. For example, the wind load needs to be calculated based on parameters such as wind speed, wind direction, shape coefficient and height distribution of the wind turbine tower in the target sea area, and the magnitude of the horizontal force and bending moment transmitted to the mud surface under the action of wind load through fluid mechanics formulas or industry standard specifications. The calculation method is shown in formula (1) and formula (2).

[0055]

[0056] in, This represents the horizontal force on the mud surface caused by wind load. This represents the bending moment on the mud surface caused by wind load. Indicates air density, Indicates the area swept by the impeller. Indicates the thrust coefficient. Indicates the rated wind speed. Indicates turbulent wind speed, Indicates water depth. This indicates the height of the wheel hub above sea level.

[0057] Wave loads need to be calculated based on the wave elements of the sea area (such as wave height, period, wavelength), the diameter and depth of the pile foundation, etc. Classic wave force calculation methods such as the Morrison equation are used to solve the horizontal force and bending moment of the mud surface corresponding to the wave load. The calculation methods are shown in formula (3) and formula (4).

[0058]

[0059] in, This represents the horizontal force on the mud surface caused by wave load. This represents the bending moment on the mud surface caused by wave load. Indicates drag force. Represents inertial force. Indicates water depth. It indicates the wave height at a certain moment.

[0060] The horizontal inertial force of an earthquake needs to be determined by combining the ground motion parameters of the target area (such as peak ground acceleration), the total mass and mass distribution of the offshore wind turbine structure, and the horizontal force and bending moment generated at the mud surface through dynamic analysis. The calculation method is shown in formula (5) and formula (6).

[0061]

[0062] in, This represents the horizontal force on the mud surface caused by the horizontal inertial force of an earthquake. This represents the bending moment on the mud surface caused by the horizontal inertial force of an earthquake. This indicates the mass distribution of various parts of the offshore wind turbine structure. This represents the measured peak acceleration at the location of the centroid of each mass distribution. This indicates the height of the centroid of each mass distribution from the mud surface.

[0063] After calculating the horizontal force and bending moment on the mud surface corresponding to each load, the loads need to be superimposed. The superposition of loads considers the most unfavorable combination and performs peak superposition according to the assumption of the same direction to obtain the maximum load effect that may occur under the most unfavorable condition.

[0064] By comprehensively considering various load combinations under the target working condition, the horizontal force and bending moment of the mud surface corresponding to each load are accurately calculated. Then, the horizontal force and bending moment of the mud surface corresponding to these different loads are reasonably superimposed, so as to accurately obtain the mud surface load of the single pile foundation under the target working condition. This provides a more reliable basis for the design and safety assessment of the single pile foundation, and effectively improves the stability and safety of the single pile foundation under complex working conditions.

[0065] According to an embodiment of the present invention, the method further includes: obtaining the geometric parameters of the single pile foundation and the initial soil parameters of the foundation soil, wherein the geometric parameters include the pile diameter and the penetration depth, and the initial soil parameters include the initial internal friction angle and the initial shear modulus; constructing a single pile foundation model based on the geometric parameters, and dividing the corresponding initial soil elements based on the initial soil parameters; and constructing a numerical model by setting zero-length elements between the single pile foundation model and the initial soil elements, wherein the numerical model is used to simulate the interaction between the single pile foundation and the foundation soil.

[0066] When constructing the numerical model, it is essential to obtain the geometric parameters of the monopile foundation and the initial soil parameters of the foundation soil to provide fundamental data support for subsequent model building. The core geometric parameters of the monopile foundation include the pile diameter and embedment depth, which need to be accurately extracted based on engineering design drawings, construction plans, and on-site survey records. The pile diameter can be determined from the pile cross-sectional dimensions specified in the design documents, and the measured pile diameter data during construction must be verified to correct any deviations. The embedment depth needs to be determined based on the design embedment depth requirements of the monopile foundation, combined with the mud surface elevation and geological stratification of the target sea area, to ensure that the parameters closely match the actual engineering conditions.

[0067] The initial soil parameters for the foundation soil mainly include the initial internal friction angle and the initial shear modulus, which need to be obtained through a combination of field geological surveys and laboratory geotechnical tests. For the initial internal friction angle, methods such as standard penetration tests, direct shear tests, or triaxial shear tests can be used to test soil samples from different soil layers in the target area. The initial internal friction angle for each soil layer can then be obtained through statistical analysis of the test data. The initial shear modulus can be obtained through field wave velocity testing methods such as the cross-hole method or the single-hole method, or by calculating it using empirical formulas based on parameters such as soil density and Poisson's ratio obtained from laboratory tests. The representativeness of the parameters should be ensured by referring to the regional geological survey report.

[0068] After obtaining the initial soil parameters, a single pile foundation model is built in the selected numerical simulation software based on the extracted geometric parameters such as pile diameter and embedment depth. The cross-sectional parameters of the model are set according to the actual pile cross-sectional dimensions. The embedment length of the pile in the model is determined according to the embedment depth. At the same time, the material mechanical properties of the pile (such as elastic modulus, Poisson's ratio, and density) are defined to match the characteristics of piles used in actual engineering.

[0069] For the foundation soil, based on the acquired initial soil parameters such as the initial internal friction angle and initial shear modulus, the corresponding soil range is first delineated in the numerical software according to the geological stratification of the target area. Then, the initial soil unit mesh is generated according to the soil layer distribution characteristics. During the meshing process, both computational accuracy and efficiency must be considered. The soil units in the key areas around the piles are densified. At the same time, the initial internal friction angle, initial shear modulus, and other parameters of each soil layer are assigned to the corresponding soil units one by one, thus completing the construction of the initial soil units.

[0070] To accurately simulate the interaction between a single pile foundation and the foundation soil, zero-length elements need to be set at the contact interface between the single pile foundation model and the initial soil element. Specifically, the contact node between the single pile foundation model and the initial soil element is located in the numerical software, and a zero-length element is created at the corresponding node. This element has no actual geometric dimensions and is only used to transmit the mechanical interaction between the two. By setting the mechanical property parameters of the zero-length element (such as normal stiffness and tangential stiffness), it can effectively simulate the normal bearing pressure and tangential friction on the pile-soil contact surface, realizing the transmission of force and displacement between the single pile foundation and the foundation soil. Finally, through the coordinated operation of the above steps, a complete numerical model that can be used for subsequent dynamic response simulation is constructed.

[0071] By obtaining the geometric parameters of the single pile foundation and the initial soil parameters of the foundation soil, a single pile foundation model and corresponding initial soil elements are constructed based on the initial soil parameters. Zero-length elements are set between the single pile foundation model and the initial soil elements, thereby constructing a numerical model that can accurately simulate the interaction between the single pile foundation and the foundation soil. This provides an effective numerical analysis tool for studying the stress characteristics and deformation behavior of single pile foundations under different working conditions, which helps to optimize the design of single pile foundations and improve the reliability of their engineering applications.

[0072] According to an embodiment of the present invention, when the excess pore pressure ratio indicates that the foundation soil has deteriorated, the soil parameters of the deteriorated foundation soil are determined based on the excess pore pressure ratio and the effective stress, including: determining that the foundation soil has deteriorated when the excess pore pressure ratio exceeds a preset deterioration threshold; determining the internal friction angle of the deteriorated foundation soil based on the negative correlation between the initial internal friction angle of the foundation soil and the excess pore pressure ratio, wherein the negative correlation indicates that the internal friction angle after deterioration decreases as the excess pore pressure ratio increases; and determining the shear modulus of the deteriorated foundation soil based on the power law relationship between the initial shear modulus of the foundation soil and the effective stress, wherein the power law relationship indicates that the shear modulus after deterioration is adjusted according to a power function law with the effective stress as a reference.

[0073] Before determining the soil parameters of the foundation soil after deterioration, it is necessary to define the preset deterioration threshold of the excess pore pressure ratio, which can be set to 0.04.

[0074] For deteriorated foundation soil, a negative correlation between its internal friction angle and excess pore pressure ratio can be established. Specifically, undisturbed soil samples from the deteriorated foundation soil are selected, and consolidated undrained shear tests are conducted under different excess pore pressure ratios. The internal friction angle at failure of the foundation soil under each condition is recorded. The test data are imported into data analysis software, and linear regression or nonlinear fitting methods are used to derive the negative correlation expression between the internal friction angle and the excess pore pressure ratio.

[0075] The actual excess pore pressure ratio of the deteriorated foundation soil is then substituted into the expression to calculate the deteriorated internal friction angle. If the excess pore pressure ratio exceeds 0.95 (the foundation soil is close to complete liquefaction), the calculation result needs to be corrected to the residual internal friction angle of the foundation soil to ensure that the parameters conform to the mechanical properties of the soil after liquefaction. Specifically, in the calculation process, excess pore pressure ratios exceeding 0.95 are still calculated as 0.95.

[0076] When determining the shear modulus of deteriorated foundation soil, it is necessary to base the calculation on the power-law relationship between the initial shear modulus and the effective stress, and the rationality must be verified after the calculation is completed. If the effective stress decreases due to the increase of the excess pore pressure ratio, it is necessary to confirm whether the calculated shear modulus decreases synchronously to ensure that it conforms to the physical law that "the smaller the effective stress, the lower the soil shear modulus".

[0077] Based on the negative correlation between the initial internal friction angle and the excess pore pressure ratio, the internal friction angle of the deteriorated foundation soil is determined; that is, the internal friction angle decreases with the increase of the excess pore pressure ratio. Based on the power-law relationship between the initial shear modulus and the effective stress, the shear modulus of the deteriorated foundation soil is determined; that is, the shear modulus of the deteriorated foundation soil is adjusted according to a power function law with the effective stress as a reference, thus accurately reflecting the mechanical properties of the deteriorated foundation soil and providing more reliable parameter basis for the stability analysis and engineering design of the foundation soil.

[0078] According to an embodiment of the present invention, the internal friction angle of the deteriorated foundation soil is determined based on the negative correlation between the initial internal friction angle and the excess pore pressure ratio, including: calculating the reduction coefficient of the foundation soil based on the excess pore pressure ratio, wherein the reduction coefficient is negatively correlated with the excess pore pressure ratio; and calculating the internal friction angle of the deteriorated foundation soil by using trigonometric function relationships based on the product of the sine value of the initial internal friction angle and the reduction coefficient.

[0079] When determining the internal friction angle of deteriorated foundation soil, it is necessary to first calculate the reduction coefficient of the internal friction angle based on the excess pore pressure ratio. The core is to establish a negative correlation between the reduction coefficient and the excess pore pressure ratio. Specifically, this can be achieved by obtaining basic data support through indoor geotechnical tests. Undamaged soil samples of the deteriorated foundation soil are selected, and consolidated undrained shear tests are conducted under different excess pore pressure ratio conditions (e.g., gradually increasing from 0 to 1.0). The actual shear strength of the soil under each condition is recorded. Combined with the initial shear strength corresponding to the initial internal friction angle, the actual reduction degree of the internal friction angle under different excess pore pressure ratios is calculated, and then a negative correlation expression between the reduction coefficient and the excess pore pressure ratio is obtained by fitting.

[0080] After calculating the reduction factor, the angle of internal friction after degradation is solved using trigonometric functions. During the calculation, it is crucial to ensure consistent units, guaranteeing that the initial angle of internal friction is input in degrees to avoid calculation errors caused by unit confusion. The results must also be validated for reasonableness. If the excess pore pressure ratio is within a reasonable range (0~1.0), it must be confirmed that the angle of internal friction after degradation is less than the initial angle of internal friction, and that the value conforms to the residual strength characteristics of the corresponding soil layer after liquefaction. If abnormal results are found, the fitting formula for the reduction factor or the accuracy of the initial angle of internal friction must be re-examined.

[0081] Specifically, the calculation of the internal friction angle and shear modulus of the deteriorated foundation soil is shown in formulas (7) and (8).

[0082]

[0083] in, Indicates the initial internal friction angle. Indicates the pressure ratio of the borehole. Indicates the internal friction angle of the foundation soil after deterioration. This represents the minimum effective stress obtained from actual measurement or numerical simulation after the foundation soil has deteriorated. This represents the initial effective stress of the foundation soil, where n is taken as 0.5. This represents the shear modulus of the foundation soil after deterioration. This represents the initial shear modulus.

[0084] The internal friction angle of the foundation soil after deterioration is determined by utilizing the negative correlation between the initial internal friction angle and the excess pore pressure ratio. Then, based on the product of the sine of the initial internal friction angle and the reduction coefficient, combined with trigonometric relationships, the internal friction angle of the foundation soil after deterioration is calculated. This accurately reflects the change law of the internal friction angle of the foundation soil during the deterioration process, providing important parameter support for accurately evaluating the mechanical properties and stability of the foundation soil.

[0085] Figure 3 A schematic diagram of soil zoning is shown in the method for safety assessment of liquefiable foundation of a single-pile offshore wind turbine according to an embodiment of the present invention.

[0086] According to an embodiment of the present invention, the deterioration of the foundation soil includes weakening and liquefaction; updating the soil parameters to the soil elements in the numerical model includes: performing layered processing on the initial soil elements in the numerical model based on the excess pore pressure ratio obtained from dynamic response simulation to determine the liquefaction zone, weakened zone, and unweakened zone; for the initial soil elements in the liquefaction zone and weakened zone, updating the initial internal friction angle in the initial soil parameters to the internal friction angle of the deteriorated foundation soil, and updating the initial shear modulus to the shear modulus of the deteriorated foundation soil; keeping the initial soil parameters of the initial soil elements in the unweakened zone unchanged.

[0087] After calculating the parameters of the deteriorated foundation soil, the initial soil elements in the numerical model need to be updated in a targeted manner, based on the excess pore pressure ratio obtained from the dynamic response simulation. The two main types of foundation soil deterioration include weakening and liquefaction, which are addressed through zoning to achieve precise updates.

[0088] The stratification of soil units is based on the excess porosity of each initial soil unit. Specifically, it is necessary to pre-determine the liquefaction and weakening thresholds by combining geotechnical test data of the foundation soil with industry standards. Generally speaking, a excess porosity ≥ 0.95 can be identified as a liquefaction zone (the effective stress between soil particles is almost zero, exhibiting complete liquefaction characteristics), a excess porosity ≤ 0.04 < 0.95 is identified as a weakened zone (the effective stress is significantly reduced, and the mechanical properties are partially deteriorated but not completely liquefied), and a excess porosity < 0.04 is identified as an unweakened zone (the effective stress changes little, and the mechanical properties of the soil basically remain in their initial state).

[0089] Subsequently, the excess pore pressure ratio of all initial soil units is extracted from the dynamic response simulation results. These ratios are then compared against preset thresholds according to soil layer depth or unit number to accurately divide the initial soil units in the numerical model into liquefaction zones, weakened zones, and unweakened zones. During this division process, the actual geological stratification information corresponding to each soil unit must be checked simultaneously to ensure the accuracy of the thresholds for different soil layers (e.g., the liquefaction threshold for sand with different densities needs to be set differently).

[0090] like Figure 3 As shown, the mud surface is located at the top of the foundation. The monopile foundation vertically penetrates each soil layer. Starting from below the mud surface, the uppermost soil unit corresponds to the excess pore pressure ratio / effective stress measuring point 0, and this area is designated as the liquefaction zone. Multiple weakened zones (including weakened zone 1 to weakened zone n) are distributed downwards, corresponding to excess pore pressure ratio / effective stress measuring points 1 to n, respectively. The lower soil unit of the monopile foundation is the unweakened zone. The division of each zone matches the excess pore pressure ratio data of the corresponding measuring points, intuitively reflecting the differences in the deterioration state of the soil units at different depths.

[0091] After zoning, differentiated parameter updates are performed on soil units in different regions. For initial soil units in liquefaction and weakening zones, the core mechanical indices in their initial soil parameters need to be replaced. Specifically, the initial internal friction angle is uniformly updated to the deteriorated internal friction angle calculated based on the negative correlation between excess pore pressure ratio and the initial parameters. In the liquefaction zone, since the soil is nearly completely liquefied, the internal friction angle should be taken from the residual internal friction angle of the corresponding soil layer. In the weakening zone, the calculated value is taken according to the degree of deterioration corresponding to the excess pore pressure ratio. The initial shear modulus is updated to the deteriorated shear modulus derived from the power law relationship of effective stress. The shear modulus in the liquefaction zone needs to be significantly reduced considering the substantial decrease in effective stress, while in the weakening zone, it is adjusted to a reasonable range according to the power function law corresponding to the change in effective stress.

[0092] The update operation needs to be executed precisely in the numerical simulation software. This can be achieved by creating a partitioned unit group, selecting soil units in the liquefaction and weakening zones in batches, and assigning the calculated deteriorated internal friction angle and shear modulus to the material properties of the corresponding units in batches, thus avoiding mismatch of individual unit parameters.

[0093] For the initial soil unit in the unweakened zone, since its excess pore pressure ratio has not reached the deterioration judgment threshold, the effective stress of the soil has not changed significantly, and the mechanical properties basically remain in the initial state. Therefore, there is no need to adjust its initial soil parameters and keep the original initial internal friction angle and initial shear modulus unchanged.

[0094] After updating the parameters of all soil elements in all regions, the numerical model needs to be validated as a whole. This involves checking the accuracy of parameter updates in the liquefaction and weakening zones, as well as the completeness of parameters in the unweakened zones. This ensures consistency between element zoning and parameter updates, providing accurate soil mechanics model support for subsequent static elastoplastic analysis of single pile foundations.

[0095] By analyzing two forms of foundation soil degradation (weakening and liquefaction) and combining the excess pore pressure ratio obtained from dynamic response simulation, the initial soil elements in the numerical model are layered to accurately divide the liquefaction zone, weakened zone, and unweakened zone. The internal friction angle and shear modulus are updated accordingly, enabling the numerical model to more accurately reflect the changes in the mechanical properties of the foundation soil during the degradation process. This provides more reliable simulation results and parameter basis for the dynamic response analysis and engineering design of foundation soil.

[0096] Figure 4 A schematic diagram of the relationship curves for the safety assessment method of the liquefiable foundation of a monopile foundation for an offshore wind turbine according to an embodiment of the present invention is shown.

[0097] According to an embodiment of the present invention, static elastoplastic analysis is performed on a single pile foundation based on an updated soil element to obtain the ultimate bearing capacity of the single pile foundation in deteriorated foundation soil. This includes: based on the numerical model corresponding to the updated soil element, performing static elastoplastic analysis on the single pile foundation under a first loading condition and a second loading condition, respectively, to obtain the relationship curve between the horizontal force and displacement at the pile top corresponding to the first loading condition, and the relationship curve between the bending moment and rotation at the pile top corresponding to the second loading condition; wherein, the first loading condition is defined as setting the bending moment at the pile top of the single pile foundation to zero. In the first loading condition, a horizontal force is gradually applied to the single pile foundation until the horizontal displacement at the top of the single pile foundation reaches a preset displacement threshold. In the second loading condition, with the horizontal force at the top of the single pile foundation set to zero, a bending moment is gradually applied to the single pile foundation until the rotation angle at the top of the single pile foundation reaches a preset rotation angle threshold. The relationship curves between the horizontal force and displacement at the top of the pile and between the bending moment and rotation angle at the top of the pile are analyzed using the double tangent method to determine the ultimate bearing capacity of the single pile foundation in the deteriorated foundation soil. The ultimate bearing capacity includes the ultimate bearing capacity of the horizontal force and the ultimate bearing capacity of the bending moment.

[0098] After updating the soil parameters of the soil elements in the numerical model, static elastoplastic analysis of the single pile foundation can be carried out based on the updated numerical model. The core is to obtain the ultimate bearing capacity of the single pile under the deteriorated foundation through simulation and curve analysis of two specific loading conditions.

[0099] First, the specific settings and implementation procedures for the two types of loading conditions need to be clarified: For the first loading condition, a bending moment constraint must first be applied to the top of the single pile foundation in the numerical model to ensure that the bending moment at the pile top is always zero. Then, a graded loading method is used to gradually apply horizontal force to the pile top. During the loading process, the loading rate must be strictly controlled to avoid dynamic effects caused by excessive loading. At the same time, the horizontal displacement data of the pile top must be monitored in real time. After each level of horizontal force is applied, the model deformation must be stabilized before recording the corresponding level of horizontal force and displacement values, until the horizontal displacement of the pile top reaches the preset displacement threshold. The preset displacement threshold is usually determined based on the design requirements of the single pile foundation and engineering experience, and is generally taken as 0.3 times the pile diameter. If the pile diameter is large or the foundation constraint is strong, the threshold can be appropriately reduced; otherwise, it can be increased as appropriate.

[0100] For the second loading condition, the constraints need to be switched. The horizontal force at the pile top is fixed at zero in the numerical model, and then bending moments are gradually applied to the pile top using the same graded loading method. During the loading process, the rotation angle data at the pile top is monitored simultaneously, following the process of "graded loading - stability monitoring - data recording" until the pile top rotation angle reaches the preset rotation angle threshold. The preset rotation angle threshold is typically the rotation angle corresponding to a pile top displacement of 0.3 times the pile diameter.

[0101] After completing static elastoplastic simulations for two types of loading conditions, key data were extracted from the numerical model calculation results, and two core relationship curves were plotted. For example... Figure 4 As shown, a curve relating the horizontal force at the pile top as the ordinate and the horizontal displacement at the pile top as the abscissa is generated for the first loading condition. Similarly, a curve relating the bending moment at the pile top as the ordinate and the rotation angle at the pile top as the abscissa is generated for the second loading condition. During the plotting process, the original monitoring data needs to be preprocessed to remove outlier data points caused by model convergence issues, ensuring the smoothness and accuracy of the curves.

[0102] Subsequently, the double-tangent method was used to analyze the two curves separately to determine the corresponding ultimate bearing capacity. For the curve of horizontal force versus displacement at the pile top, an approximately linear region was first selected in the initial segment of the curve, and an initial tangent was fitted to obtain the initial tangent (reflecting the stiffness characteristics of the soil before significant plastic deformation). Then, a region where plastic deformation stably develops was selected in the later part of the curve, and a yield tangent was fitted to obtain the yield tangent. The horizontal force value corresponding to the intersection of the two tangents is the ultimate horizontal bearing capacity of the single pile foundation in the deteriorated foundation soil.

[0103] For the relationship curve between pile top bending moment and rotation angle, the same double-tangent method is used. The bending moment value corresponding to the intersection of the initial tangent of the fitted curve at the beginning segment and the tangent after yielding in the later plastic development segment is the ultimate bending moment bearing capacity of the single pile foundation. During the analysis, attention should be paid to the accuracy of the tangent fitting. The results can be optimized by adjusting the range of the fitting interval to ensure that the determination of the ultimate bearing capacity conforms to the basic principles of static elastoplastic analysis and actual engineering laws. Finally, by combining the ultimate bearing capacity of horizontal force and the ultimate bearing capacity of bending moment, the ultimate bearing capacity of the single pile foundation in deteriorated soil is determined.

[0104] Based on the numerical model corresponding to the updated soil element, static elastoplastic analysis was performed on the single pile foundation under the first and second loading conditions. The relationship curves between the horizontal force and displacement at the pile top and the relationship curves between the bending moment and rotation angle at the pile top were obtained. Then, the double tangent method was used to analyze these two curves, thereby determining the ultimate bearing capacity of the single pile foundation in the deteriorated foundation soil. This provides a scientific and accurate analysis method and result basis for the bearing capacity assessment and engineering design of single pile foundations under complex deteriorated foundation conditions.

[0105] According to an embodiment of the present invention, the bearing safety of a single pile foundation in deteriorated foundation soil is evaluated by calculating the safety factor between the mud surface load and the ultimate bearing capacity of the single pile foundation under load combination. This includes: associating the horizontal load and bending moment load in the mud surface load with the horizontal force ultimate bearing capacity and bending moment ultimate bearing capacity in the ultimate bearing capacity, respectively, to obtain the bearing capacity utilization rate through nonlinear combination calculation; using the bearing capacity utilization rate as the safety factor, to determine the bearing capacity of the single pile foundation in deteriorated foundation soil as a risk state when the safety factor is determined to be less than or equal to a preset safety value, and to determine the bearing capacity of the single pile foundation in deteriorated foundation soil as a safe state when the safety factor is determined to be greater than the preset safety value.

[0106] After completing the calculation of the ultimate bearing capacity of the single pile foundation and the mud surface load under the target working condition, it is necessary to first establish the corresponding relationship between the two types of parameters. The core is to take into account the coupling effect of horizontal load and bending moment load, and calculate the bearing capacity utilization rate through nonlinear combination method, so as to quantify the degree of actual load on the ultimate bearing capacity.

[0107] The calculated bearing capacity utilization rate is then used as a safety factor, and the bearing safety assessment is completed by comparing it with the preset safety value. The determination of the preset safety value must strictly follow the relevant specifications for offshore wind turbine foundation design, and be comprehensively calibrated in conjunction with the degree of soil degradation (distribution range of liquefaction zone and weakened zone) and the risk level of the target operating condition (such as normal operating condition, extreme storm condition, earthquake liquefaction condition). Specifically, the preset safety value is usually taken as 1.

[0108] During the assessment, if the calculated safety factor is less than or equal to the preset safety value, it indicates that the actual mud surface load on the ultimate bearing capacity of the single pile foundation in the deteriorated soil does not exceed the allowable range, and both the pile and the foundation can remain stable. Therefore, its bearing state is considered safe. If the safety factor is greater than the preset safety value, it indicates that the actual load has approached or exceeded the bearing limit of the deteriorated foundation. The single pile foundation may experience excessive deformation, pile cracking, or even foundation instability. Therefore, its bearing state is considered risky. In this case, it is necessary to further optimize the foundation treatment plan (such as using compacted sand piles to reinforce the liquefaction zone) or adjust the single pile foundation design parameters (such as increasing the pile diameter or deepening the pile depth), and conduct a new safety assessment until the requirements are met.

[0109] By calculating the safety factor between mud surface load and ultimate bearing capacity, the bearing safety of monopile foundations in deteriorated foundation soil is evaluated, thus providing a quantitative analysis method for the safety assessment of monopile foundations under complex deteriorated foundation conditions, effectively improving the reliability and safety of engineering decisions.

[0110] Figure 5A schematic diagram of the bearing capacity utilization rate curve of the method for safety assessment of the liquefiable foundation of a monopile foundation for an offshore wind turbine according to an embodiment of the present invention is shown.

[0111] According to an embodiment of the present invention, the horizontal load and bending moment load in the mud surface load are respectively associated with the ultimate bearing capacity of the horizontal force and the ultimate bearing capacity of the bending moment in the ultimate bearing capacity, so as to obtain the bearing capacity utilization rate through nonlinear combination calculation. This includes: performing a composite square operation on the ultimate bearing capacity of the horizontal force and the ultimate bearing capacity of the bending moment in the ultimate bearing capacity with the horizontal load and the bending moment load in the mud surface load to obtain the foundation bearing capacity characterizing the bearing capacity of the foundation soil after deterioration; performing a vector synthesis operation on the horizontal load and the bending moment load in the mud surface load to obtain the mud surface load effect characterizing the combined action of the horizontal load and the bending moment load; and determining the bearing capacity utilization rate based on the ratio of the mud surface load effect to the foundation bearing capacity.

[0112] When calculating the bearing capacity utilization rate, the first step is to perform a composite square operation on the coupling terms of the ultimate bearing capacity and the corresponding terms of the mud surface load, thereby quantifying the comprehensive bearing capacity of the deteriorated foundation soil. Next, a vector synthesis operation is performed on the horizontal load and bending moment load in the mud surface load to obtain the combined effect of the two. Finally, the final bearing capacity utilization rate is determined by calculating the ratio of the mud surface load effect to the foundation bearing capacity. Its value directly reflects the extent to which the actual mud surface load combined action occupies the bearing capacity of the deteriorated foundation, providing a core quantitative basis for subsequent safety status assessment. The specific calculation method is shown in formula (9).

[0113]

[0114] in, This indicates the bearing capacity utilization rate of a single pile foundation. Indicates the bearing capacity of the foundation. This indicates the effect of mud surface load. Indicates the ultimate bearing capacity under horizontal force. Indicates the ultimate bending moment bearing capacity. Indicates horizontal load. This indicates bending moment load.

[0115] like Figure 5As shown, the bearing capacity utilization curve has horizontal load as the abscissa and bending moment load as the ordinate. The endpoint of the abscissa corresponds to the horizontal ultimate bearing capacity of a single pile foundation, and the endpoint of the ordinate corresponds to the bending moment ultimate bearing capacity. The curve connecting the two is the horizontal load-bending moment load bearing capacity envelope, which clearly defines the bearing capacity boundary of the deteriorated foundation soil under the combined action of horizontal force and bending moment. The pile top load effect in the figure is presented in the form of intersection points. Combined with the mud surface load effect and the annotation of the foundation bearing capacity, it can intuitively reflect the relative positional relationship between the actual pile top load and the foundation bearing capacity. This also provides a visual analytical basis for subsequent determination of bearing capacity utilization through nonlinear combination calculations.

[0116] By correlating the horizontal load and bending moment load in the mud surface load with the ultimate bearing capacity of the horizontal force and the ultimate bearing capacity of the bending moment, respectively, the bearing capacity utilization rate is obtained. This provides an accurate quantitative method for assessing the bearing capacity of a single pile foundation in deteriorated foundation soil, which can more accurately reflect the actual stress state and safety level of the single pile foundation under complex loads and deterioration conditions.

[0117] Based on the above-mentioned method for assessing the safety of liquefiable foundations for monopile-foundation offshore wind turbines, this invention also provides a device for assessing the safety of liquefiable foundations for monopile-foundation offshore wind turbines. The following will be combined with... Figure 6 The device is described in detail.

[0118] Figure 6 A structural block diagram of a device for assessing the safety of a monopile foundation offshore wind turbine liquefiable ground, according to an embodiment of the present invention, is shown.

[0119] like Figure 6 As shown, the monopile foundation offshore wind turbine liquefiable foundation safety assessment device 600 of this embodiment includes a dynamic simulation module 610, a parameter determination module 620, a load-bearing analysis module 630, and a safety assessment module 640.

[0120] The dynamic simulation module 610 is used to simulate the dynamic response of the offshore wind turbine structure based on the load combination of the monopile foundation under target working conditions, using a numerical model to obtain the excess pore pressure ratio and effective stress of the foundation soil into which the monopile foundation is embedded. In one embodiment, the dynamic simulation module 610 can be used to perform the operation S210 described above, which will not be repeated here.

[0121] The parameter determination module 620 is used to determine the soil parameters of the deteriorated foundation soil based on the excess pore pressure ratio and effective stress when the foundation soil deteriorates as characterized by the excess pore pressure ratio. In one embodiment, the parameter determination module 620 can be used to perform the operation S220 described above, which will not be repeated here.

[0122] The bearing capacity analysis module 630 is used to update soil parameters into the soil elements of the numerical model, and to perform static elastoplastic analysis on the single pile foundation based on the updated soil elements to obtain the ultimate bearing capacity of the single pile foundation in the deteriorated foundation soil. In one embodiment, the bearing capacity analysis module 630 can be used to perform the operation S230 described above, which will not be repeated here.

[0123] The safety assessment module 640 is used to assess the bearing safety of a monopile foundation in deteriorated soil by calculating a safety factor between the mud surface load and the ultimate bearing capacity of the monopile foundation under the load combination. In one embodiment, the safety assessment module 640 can be used to perform the operation S240 described above, which will not be repeated here.

[0124] According to an embodiment of the present invention, the safety assessment device 600 for the liquefiable foundation of a monopile offshore wind turbine further includes a load calculation module and a load combination module.

[0125] The load calculation module is used to calculate the mud surface horizontal force and mud surface bending moment corresponding to each load in the load combination under the target working condition. The load combination includes at least two of the following loads: wind load, wave load, and seismic horizontal inertial force.

[0126] The load combination module is used to obtain the mud surface load of a single pile foundation under the target working condition by superimposing the mud surface horizontal force and mud surface bending moment corresponding to each load.

[0127] According to an embodiment of the present invention, the safety assessment device 600 for the liquefiable foundation of a monopile offshore wind turbine further includes a parameter acquisition module, a soil construction module, and a model construction module.

[0128] The parameter acquisition module is used to acquire the geometric parameters of the single pile foundation and the initial soil parameters of the foundation soil. The geometric parameters include the pile diameter and the penetration depth, and the initial soil parameters include the initial internal friction angle and the initial shear modulus.

[0129] The soil construction module is used to construct a single pile foundation model based on geometric parameters and to divide the corresponding initial soil elements based on the initial soil parameters.

[0130] The model building module is used to construct a numerical model by setting zero-length elements between the single pile foundation model and the initial soil elements. The numerical model is used to simulate the interaction between the single pile foundation and the foundation soil.

[0131] According to an embodiment of the present invention, the parameter determination module 620 includes a degradation determination submodule, a friction determination submodule, and a modulus determination submodule.

[0132] The degradation determination submodule is used to determine that the foundation soil has deteriorated when the excess pore pressure ratio exceeds the preset degradation threshold.

[0133] The friction determination submodule is used to determine the internal friction angle of the deteriorated foundation soil based on the negative correlation between the initial internal friction angle and the excess pore pressure ratio. The negative correlation indicates that the internal friction angle decreases as the excess pore pressure ratio increases.

[0134] The modulus determination submodule is used to determine the shear modulus of the deteriorated foundation soil based on the power law relationship between the initial shear modulus and the effective stress. The power law relationship indicates that the deteriorated shear modulus is adjusted according to a power function with the effective stress as a reference.

[0135] According to an embodiment of the present invention, the friction determination submodule includes a reduction determination unit and a friction determination unit.

[0136] The reduction determination unit is used to calculate the reduction coefficient of the foundation soil based on the excess pore pressure ratio, wherein the reduction coefficient is negatively correlated with the excess pore pressure ratio.

[0137] The friction determination unit is used to calculate the internal friction angle of the deteriorated foundation soil by using trigonometric function relationships based on the product of the sine value of the initial internal friction angle and the reduction coefficient.

[0138] According to an embodiment of the present invention, the bearing capacity analysis module 630 includes a soil stratification submodule, a parameter update submodule, and a parameter retention submodule.

[0139] The soil stratification submodule is used to stratify the initial soil elements in the numerical model based on the excess pore pressure ratio obtained from dynamic response simulation, in order to determine the liquefaction zone, weakened zone, and unweakened zone.

[0140] The parameter update submodule is used to update the initial internal friction angle in the initial soil parameters to the internal friction angle of the deteriorated foundation soil, and the initial shear modulus to the shear modulus of the deteriorated foundation soil for the initial soil units in the liquefaction zone and weakening zone.

[0141] The parameter preservation submodule is used to keep the initial soil parameters of the initial soil elements in the unweakened zone unchanged.

[0142] According to an embodiment of the present invention, the load analysis module 630 further includes a curve generation submodule and a curve analysis submodule.

[0143] The curve generation submodule is used to perform static elastoplastic analysis on a single pile foundation under the first and second loading conditions based on the numerical model corresponding to the updated soil elements. This yields the relationship curves between the horizontal force and displacement at the pile top under the first loading condition, and between the bending moment and rotation angle at the pile top under the second loading condition. The first loading condition involves gradually applying a horizontal force to the single pile foundation while setting the bending moment at the pile top to zero, until the horizontal displacement at the pile top reaches a preset displacement threshold. The second loading condition involves gradually applying a bending moment to the single pile foundation while setting the horizontal force at the pile top to zero, until the rotation angle at the pile top reaches a preset rotation angle threshold.

[0144] The curve analysis submodule is used to analyze the relationship curves between the horizontal force and displacement at the pile top and the relationship curves between the bending moment and rotation angle at the pile top using the double tangent method, to determine the ultimate bearing capacity of a single pile foundation in the deteriorated foundation soil. The ultimate bearing capacity includes the ultimate bearing capacity of the horizontal force and the ultimate bearing capacity of the bending moment.

[0145] According to an embodiment of the present invention, the safety assessment module 640 includes a load association submodule and a safety assessment submodule.

[0146] The load association submodule is used to associate the horizontal load and bending moment load in the mud surface load with the horizontal force ultimate bearing capacity and bending moment ultimate bearing capacity in the ultimate bearing capacity, respectively, so as to obtain the bearing capacity utilization rate through nonlinear combination calculation.

[0147] The safety assessment submodule is used to use the bearing capacity utilization rate as a safety factor. When the safety factor is less than or equal to the preset safety value, the bearing capacity of the single pile foundation in the deteriorated foundation soil is determined to be in a risk state. When the safety factor is greater than the preset safety value, the bearing capacity of the single pile foundation in the deteriorated foundation soil is determined to be in a safe state.

[0148] According to an embodiment of the present invention, the load association submodule includes a composite calculation unit, a vector merging unit, and a load-bearing calculation unit.

[0149] The composite calculation unit is used to perform a composite square operation on the horizontal force ultimate bearing capacity and bending moment ultimate bearing capacity in the ultimate bearing capacity, and the horizontal load and bending moment load in the mud surface load, to obtain the foundation bearing capacity, which characterizes the bearing capacity of the foundation soil after deterioration.

[0150] The vector merging unit is used to perform vector synthesis operations on the horizontal load and bending moment load in the mud surface load to obtain the mud surface load effect that characterizes the combined action of the horizontal load and bending moment load.

[0151] The bearing capacity calculation unit determines the bearing capacity utilization rate based on the ratio of mud surface load effect to foundation bearing capacity.

[0152] According to embodiments of the present invention, any plurality of modules among the dynamic simulation module 610, parameter determination module 620, load analysis module 630, and safety assessment module 640 may be combined into one module, or any one of these modules may be split into multiple modules. Alternatively, at least a portion of the functionality of one or more of these modules may be combined with at least a portion of the functionality of other modules and implemented in one module. According to embodiments of the present invention, at least one of the dynamic simulation module 610, parameter determination module 620, load analysis module 630, and safety assessment module 640 may be at least partially implemented as hardware circuitry, such as a field-programmable gate array (FPGA), a programmable logic array (PLA), a system-on-a-chip, a system-on-a-substrate, a system-on-package, an application-specific integrated circuit (ASIC), or any other reasonable means of integrating or packaging circuitry, or implemented in software, hardware, or firmware, or in any one of the three implementation methods or a suitable combination of any of them. Alternatively, at least one of the dynamic simulation module 610, parameter determination module 620, load analysis module 630, and safety assessment module 640 may be implemented at least partially as a computer program module, which can perform corresponding functions when the computer program module is run.

[0153] Figure 7 A block diagram of an electronic device suitable for implementing a method for assessing the safety of liquefiable foundations for monopile offshore wind turbines is shown according to an embodiment of the present invention.

[0154] like Figure 7 As shown, an electronic device 700 according to an embodiment of the present invention includes a processor 701, which can perform various appropriate actions and processes according to a program stored in a read-only memory ROM 702 or a program loaded from a storage portion 708 into a random access memory RAM 703. The processor 701 may include, for example, a general-purpose microprocessor (e.g., a CPU), an instruction set processor and / or an associated chipset and / or a special-purpose microprocessor (e.g., an application-specific integrated circuit (ASIC)), etc. The processor 701 may also include onboard memory for caching purposes. The processor 701 may include a single processing unit or multiple processing units for performing different actions of the method flow according to an embodiment of the present invention.

[0155] RAM 703 stores various programs and data required for the operation of electronic device 700. Processor 701, ROM 702, and RAM 703 are interconnected via bus 704. Processor 701 executes various operations of the method flow according to embodiments of the present invention by executing programs in ROM 702 and / or RAM 703. It should be noted that programs may also be stored in one or more memories other than ROM 702 and RAM 703. Processor 701 may also execute various operations of the method flow according to embodiments of the present invention by executing programs stored in one or more memories.

[0156] According to an embodiment of the present invention, the electronic device 700 may further include an input / output (I / O) interface 705, which is also connected to a bus 704. The electronic device 700 may also include one or more of the following components connected to the input / output (I / O) interface 705: an input section 706 including a keyboard, mouse, etc.; an output section 707 including a cathode ray tube (CRT), liquid crystal display (LCD), etc., and a speaker, etc.; a storage section 708 including a hard disk, etc.; and a communication section 709 including a network interface card such as a LAN card, modem, etc. The communication section 709 performs communication processing via a network such as the Internet. A drive 710 is also connected to the input / output (I / O) interface 705 as needed. A removable medium 711, such as a disk, optical disk, magneto-optical disk, semiconductor memory, etc., is installed on the drive 710 as needed so that computer programs read from it can be installed into the storage section 708 as needed.

[0157] The present invention also provides a computer-readable storage medium, which may be included in the device / apparatus / system described in the above embodiments; or it may exist independently and not assembled into the device / apparatus / system. The computer-readable storage medium carries one or more programs, which, when executed, implement the method according to the embodiments of the present invention.

[0158] According to embodiments of the present invention, a computer-readable storage medium may be a non-volatile computer-readable storage medium, such as including, but not limited to: portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination thereof. In the present invention, a computer-readable storage medium may be any tangible medium containing or storing a program that can be used by or in conjunction with an instruction execution system, apparatus, or device. For example, according to embodiments of the present invention, a computer-readable storage medium may include ROM 702 and / or RAM 703 and / or one or more memories other than ROM 702 and RAM 703 described above.

[0159] Embodiments of the present invention also include a computer program product comprising a computer program containing program code for performing the methods shown in the flowchart. When the computer program product is run on a computer system, the program code enables the computer system to implement the method for assessing the safety of liquefiable foundations for monopile offshore wind turbines provided in the embodiments of the present invention.

[0160] When the computer program is executed by the processor 701, it performs the functions defined in the system / apparatus of this invention. According to embodiments of the invention, the systems, apparatuses, modules, units, etc., described above can be implemented by computer program modules.

[0161] In one embodiment, the computer program may rely on a tangible storage medium such as an optical storage device or a magnetic storage device. In another embodiment, the computer program may also be transmitted and distributed in the form of signals over a network medium, and may be downloaded and installed via the communication section 709, and / or installed from a removable medium 711. The program code contained in the computer program can be transmitted using any suitable network medium, including but not limited to: wireless, wired, etc., or any suitable combination thereof.

[0162] In such an embodiment, the computer program can be downloaded and installed from a network via the communication section 709, and / or installed from the removable medium 711. When the computer program is executed by the processor 701, it performs the functions defined in the system of this embodiment of the invention. According to embodiments of the invention, the systems, devices, apparatuses, modules, units, etc., described above can be implemented by computer program modules.

[0163] According to embodiments of the present invention, program code for executing the computer programs provided in the embodiments of the present invention can be written in any combination of one or more programming languages. Specifically, these computational programs can be implemented using high-level procedural and / or object-oriented programming languages, and / or assembly / machine languages. Programming languages ​​include, but are not limited to, languages ​​such as Java, C++, Python, "C", or similar programming languages. The program code can be executed entirely on the user's computing device, partially on the user's device, partially on a remote computing device, or entirely on a remote computing device or server. In cases involving remote computing devices, the remote computing device can be connected to the user's computing device via any type of network, including a local area network (LAN) or a wide area network (WAN), or it can be connected to an external computing device (e.g., via the Internet using an Internet service provider).

[0164] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present invention. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code containing one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions indicated in the blocks may occur in a different order than those indicated in the drawings. For example, two consecutively indicated blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in a block diagram or flowchart, and combinations of blocks in a block diagram or flowchart, may be implemented using a dedicated hardware-based system that performs the specified function or operation, or using a combination of dedicated hardware and computer instructions.

[0165] Those skilled in the art will understand that the features described in the various embodiments of the present invention can be combined and / or combined in various ways, even if such combinations or combinations are not explicitly described in the present invention. In particular, the features described in the various embodiments of the present invention can be combined and / or combined in various ways without departing from the spirit and teachings of the present invention. All such combinations and / or combinations fall within the scope of the present invention.

[0166] The embodiments of the present invention have been described above. However, these embodiments are merely illustrative and not intended to limit the scope of the invention. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of the invention, and all such substitutions and modifications should fall within the scope of the invention.

Claims

1. A method for safety assessment of liquefiable soil foundations for monopile foundations of offshore wind turbines, characterized in that, The method includes: Based on the load combination of the monopile foundation in the offshore wind turbine structure under the target working condition, the dynamic response of the offshore wind turbine structure is simulated using a numerical model to obtain the excess pore pressure ratio and effective stress of the foundation soil into which the monopile foundation is embedded. When the excess pore pressure ratio characterizes the deterioration of the foundation soil, the soil parameters of the deteriorated foundation soil are determined based on the excess pore pressure ratio and the effective stress. The soil parameters are updated into the soil elements of the numerical model, and static elastoplastic analysis of the single pile foundation is performed based on the updated soil elements to obtain the ultimate bearing capacity of the single pile foundation in the deteriorated foundation soil. The bearing safety of the monopile foundation in the deteriorated foundation soil is evaluated by calculating the safety factor between the mud surface load and the ultimate bearing capacity of the monopile foundation under the load combination.

2. The method according to claim 1, characterized in that, The method further includes: Based on the load combination under the target working condition, calculate the mud surface horizontal force and mud surface bending moment corresponding to each load in the load combination, wherein the load combination is a combination of at least two loads including wind load, wave load and seismic horizontal inertial force. By superimposing the horizontal force and bending moment on the mud surface corresponding to each load, the mud surface load of the single pile foundation under the target working condition is obtained.

3. The method according to claim 1, characterized in that, The method further includes: Obtain the geometric parameters of the single pile foundation and the initial soil parameters of the foundation soil, wherein the geometric parameters include the pile diameter and the penetration depth, and the initial soil parameters include the initial internal friction angle and the initial shear modulus; A single pile foundation model is constructed based on the geometric parameters, and corresponding initial soil elements are divided based on the initial soil parameters. The numerical model is constructed by setting zero-length elements between the monopile foundation model and the initial soil element, wherein the numerical model is used to simulate the interaction between the monopile foundation and the foundation soil.

4. The method according to claim 3, characterized in that, When the excess pore pressure ratio characterizes the deterioration of the foundation soil, the soil parameters of the deteriorated foundation soil are determined based on the excess pore pressure ratio and the effective stress, including: If the excess pore pressure ratio exceeds a preset deterioration threshold, it is determined that the foundation soil has deteriorated. The internal friction angle of the deteriorated foundation soil is determined based on the negative correlation between the initial internal friction angle of the foundation soil and the excess pore pressure ratio, wherein the negative correlation indicates that the internal friction angle decreases as the excess pore pressure ratio increases; The shear modulus of the deteriorated foundation soil is determined based on the power-law relationship between the initial shear modulus and the effective stress. The power-law relationship indicates that the deteriorated shear modulus is adjusted according to a power function with the effective stress as a reference.

5. The method according to claim 4, characterized in that, The step of determining the internal friction angle of the deteriorated foundation soil based on the negative correlation between the initial internal friction angle of the foundation soil and the excess pore pressure ratio includes: The reduction factor of the foundation soil is calculated based on the excess pore pressure ratio, wherein the reduction factor is negatively correlated with the excess pore pressure ratio; The internal friction angle of the deteriorated foundation soil is calculated by multiplying the sine of the initial internal friction angle with the reduction coefficient and using trigonometric functions.

6. The method according to claim 3, characterized in that, The deterioration of the foundation soil includes weakening and liquefaction; updating the soil parameters to the soil elements of the numerical model includes: Based on the excess pore pressure ratio obtained from the dynamic response simulation, the initial soil unit in the numerical model is subjected to layering to determine the liquefaction zone, weakened zone, and unweakened zone. For the initial soil units in the liquefaction zone and the weakening zone, the initial internal friction angle in the initial soil parameters is updated to the internal friction angle of the deteriorated foundation soil, and the initial shear modulus is updated to the shear modulus of the deteriorated foundation soil. The initial soil parameters of the initial soil elements in the unweakened zone remain unchanged.

7. The method according to claim 1, characterized in that, The static elastoplastic analysis of the monopile foundation based on the updated soil elements yields the ultimate bearing capacity of the monopile foundation in the deteriorated foundation soil, including: Based on the numerical model corresponding to the updated soil element, static elastoplastic analysis was performed on the single pile foundation under the first loading condition and the second loading condition, respectively, to obtain the relationship curve between the horizontal force and displacement at the pile top corresponding to the first loading condition, and the relationship curve between the bending moment and rotation angle at the pile top corresponding to the second loading condition. The first loading condition is that, with the pile top bending moment of the single pile foundation set to zero, a horizontal force is gradually applied to the single pile foundation until the horizontal displacement of the pile top of the single pile foundation reaches a preset displacement threshold. The second loading condition is that, with the horizontal force at the top of the single pile foundation set to zero, a bending moment is gradually applied to the single pile foundation until the rotation angle at the top of the single pile foundation reaches a preset rotation angle threshold. The relationship curves between the horizontal force and displacement at the pile top and the relationship curves between the bending moment and rotation angle at the pile top are analyzed using the double tangent method to determine the ultimate bearing capacity of the single pile foundation in the deteriorated foundation soil. The ultimate bearing capacity includes the ultimate bearing capacity of the horizontal force and the ultimate bearing capacity of the bending moment.

8. The method according to claim 7, characterized in that, The method of evaluating the bearing safety of the single pile foundation in the deteriorated foundation soil by calculating the safety factor between the mud surface load and the ultimate bearing capacity of the single pile foundation under the load combination includes: The horizontal load and bending moment load in the mud surface load are respectively associated with the horizontal force ultimate bearing capacity and bending moment ultimate bearing capacity in the ultimate bearing capacity, so as to obtain the bearing capacity utilization rate through nonlinear combination calculation. The bearing capacity utilization rate is used as the safety factor. If the safety factor is less than or equal to the preset safety value, the bearing capacity of the single pile foundation in the deteriorated foundation soil is determined to be in a risk state. If the safety factor is greater than the preset safety value, the bearing capacity of the single pile foundation in the deteriorated foundation soil is determined to be in a safe state.

9. The method according to claim 8, characterized in that, The method of associating the horizontal load and bending moment load in the mud surface load with the horizontal force ultimate bearing capacity and bending moment ultimate bearing capacity in the ultimate bearing capacity, respectively, to obtain the bearing capacity utilization rate through nonlinear combination calculation, includes: The ultimate bearing capacity of horizontal force and ultimate bearing capacity of bending moment in the ultimate bearing capacity are coupled with the horizontal load and bending moment load in the mud surface load to perform a composite square operation of the coupling terms, so as to obtain the foundation bearing capacity characterizing the bearing capacity of the deteriorated foundation soil. A vector synthesis operation is performed on the horizontal load and bending moment load in the mud surface load to obtain the mud surface load effect characterizing the combined action of the horizontal load and the bending moment load. The bearing capacity utilization rate is determined based on the ratio of the mud surface load effect to the foundation bearing capacity.

10. A safety assessment device for liquefiable foundations of monopile offshore wind turbines, characterized in that, The device includes: The dynamic simulation module is used to simulate the dynamic response of the offshore wind turbine structure based on the load combination of the monopile foundation in the target working condition, and to obtain the excess pore pressure ratio and effective stress of the foundation soil into which the monopile foundation is embedded. The parameter determination module is used to determine the soil parameters of the deteriorated foundation soil based on the excess pore pressure ratio and the effective stress when the foundation soil is deteriorated as indicated by the excess pore pressure ratio. The bearing capacity analysis module is used to update the soil parameters into the soil elements of the numerical model, and to perform static elastoplastic analysis on the single pile foundation based on the updated soil elements to obtain the ultimate bearing capacity of the single pile foundation in the deteriorated foundation soil. The safety assessment module is used to assess the bearing safety of the monopile foundation in the deteriorated foundation soil by calculating the safety factor between the mud surface load and the ultimate bearing capacity of the monopile foundation under the load combination.

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