A method and system for simulating seismic load of offshore energy island foundation

Abstract

The application provides a kind of offshore energy island foundation seismic load simulation method and system, it is related to offshore structure simulation analysis technical field, the application constructs the finite element model including structural steel pile foundation, seabed soil and fluid domain, and defines soil structure coupling boundary;Based on historical seismic wave data, construct a seismic wave sample library and divide simulation step length;Through dynamic updating mechanism, update scour pit geometric parameters, soil properties, fluid properties and structure material parameters in real time during simulation, and output structure characteristic data and dynamic response parameter time history including relative horizontal displacement, maximum bending moment and contact surface shear stress;Extract the maximum value of each response parameter for probability statistical analysis, fit out the characteristic response value under a certain exceedance probability, compare with the allowable value to obtain the safety factor, realize multidimensional safety evaluation;The method comprehensively considers the seismic scour coupling effect, improves the simulation accuracy and evaluation reliability.

Description

Technical Field

[0001] This invention relates to the field of marine structural simulation and analysis technology, specifically to a method and system for simulating seismic loads on the foundation of a marine energy island. Background Technology

[0002] With the rapid development of marine energy development, the safety and seismic performance of offshore energy islands, as important marine engineering structures, have become critical issues in design and operation. In the actual marine environment, the foundations of energy islands not only bear complex seismic loads but also need to consider the soil loss effect caused by seabed erosion. These factors jointly affect the dynamic response and long-term stability of the structure. Currently, traditional simulation methods mostly focus on the analysis under single loads or simplified boundary conditions, failing to fully couple seismic action and soil erosion effects, leading to deviations between assessment results and actual working conditions. Furthermore, existing technologies lack probabilistic statistical and safety quantification assessments of multi-parameter dynamic responses, making it difficult to accurately predict the structure's performance under extreme seismic events, posing potential risks to the safe operation of energy islands.

[0003] In the prior art, CN117454725A discloses a method and equipment for simulating seismic loads on offshore wind power foundations based on super-unit condensation. It simulates the complex geological conditions of wind farms using a pile-soil coupled static effect model to obtain a nonlinear simulated pile-soil layer; then, it uses a pile-soil coupled dynamic effect model to simulate the pile-soil coupled dynamic effect to obtain the base shear force that reflects the dynamic effect of pile-soil coupling; finally, it calculates the equivalent static load of seismic loads through a load simulation analysis model to realize the structural simulation of seismic loads on offshore wind power foundations.

[0004] The main problem with the above solutions is that scour is a key factor in the long-term performance degradation of offshore structures, and the above solutions only address piles. Simulations of soil coupling effects do not consider the impact of seabed erosion on soil loss, pile bearing capacity, and dynamic response in the marine environment, and cannot simulate the dynamic effects of water on the structure, thus limiting the accuracy of simulation results. Furthermore, the lack of a multi-dimensional assessment system and reliance on equivalent static loads for safety judgments make it difficult to systematically assess the safety performance of the structure in extreme events, and there is a lack of early warning and response strategies for different risk levels.

[0005] The information disclosed in the background section is only intended to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0006] The purpose of this invention is to provide a method and system for simulating seismic loads on the foundation of an offshore energy island, in order to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A method for simulating seismic loads on the foundation of an offshore energy island, comprising the following steps: Step 1: Construct a finite element model of the energy island's basic structure, which includes structural steel pile foundations, seabed soil, and fluid domain, and define the soil-structure coupling boundary of the finite element model; Step 2: Construct a seismic wave sample library based on historical seismic wave data of the area where the energy island is located. For each seismic wave sample, determine the simulation time interval and divide the simulation step size based on its time history. Step 3: For each seismic wave sample, during the simulation using the finite element model, a dynamic update mechanism is introduced to update the material properties of the foundation structure at each simulation step, thereby outputting the structural characteristic data and dynamic response parameters at each simulation step. Step 4: For each dynamic response parameter, extract its maximum value from its response time history, construct a maximum value dataset, perform probabilistic statistical analysis on the maximum value dataset, fit the characteristic response values ​​of different dynamic response parameters under a specific exceedance probability, compare the characteristic response values ​​of various dynamic response parameters with their allowable values, generate multiple safety factors, and conduct a safety assessment of the energy island based on the safety factors.

[0008] Furthermore, the principle upon which the finite element model of the energy island's basic structure is based is: The simulation area is determined based on the installation location of the structural steel pile foundation. Finite element models are then performed on the structural steel pile foundation, seabed soil, and fluid domain within the simulation area. Based on the results of the above three finite element models, a finite element model of the energy island is generated. The principle of modeling structural steel pile foundations is as follows: collect the structural dimension data and material property data of the structural steel pile foundations. The structural dimension data includes the shape and size of the structural steel pile foundations, and the material property data includes the elastic modulus, Poisson's ratio and yield strength of the structural steel pile foundation material. Based on the above data, construct a finite element model of the structural steel pile foundation in finite element software. The principle of modeling seabed soil is as follows: obtain the soil layer distribution and geotechnical test parameters of each soil layer in the seabed soil. The soil layer distribution represents the type and depth of each soil layer in the seabed soil. The geotechnical test parameters include the water content, void ratio, cohesion, internal friction angle and compression modulus of each soil layer. Also obtain the distribution location of scour pits in the seabed soil and the geometric parameters of the scour pits. The geometric parameters of the scour pits include the depth, width and slope of the scour pits. Construct a finite element model of the seabed soil containing the scour pits in finite element software. The principle of modeling the fluid domain is as follows: collect environmental geometric data and fluid property data of the fluid domain. The environmental geometric data includes the geometry of the contact surface between the fluid domain and the structural steel pile foundation, the geometry of the contact surface between the fluid domain and the seabed soil, the seabed topography, the average water depth, and the spatial dimensions of the fluid domain. The fluid property data includes fluid density and fluid dynamic viscosity. Construct a finite element model of the fluid domain in finite element software.

[0009] Furthermore, the principle underlying the definition of the soil-structure coupling boundary in the finite element model is as follows: The definition logic of the soil-structure coupling boundary is as follows: For the contact surface between the structural steel pile foundation and the seabed soil, the contact surface belonging to the structural steel pile foundation is defined as the primary contact surface, and the contact surface belonging to the seabed soil is defined as the secondary contact surface. During an earthquake, there are normal pressure and tangential friction between the primary and secondary contact surfaces. The hard contact model is used to define the normal pressure, and its logic is: when the primary and secondary contact surfaces are in contact, normal pressure occurs; when the primary and secondary contact surfaces separate, the normal pressure is zero. The Coulomb friction model is used to define the tangential friction, and its logic is: the shear force between the primary and secondary contact surfaces is proportional to the normal pressure, until the shear force reaches the maximum static friction force, at which point the primary and secondary contact surfaces slide tangentially. Furthermore, the principle on which the seismic wave sample library is constructed is as follows: Historical seismic wave data of the area where the energy island is located are collected, and several artificial seismic waves are synthesized based on the historical seismic wave data. A seismic wave sample library is constructed based on the historical and artificial seismic waves. The seismic wave sample library contains several historical and artificial seismic waves, and these seismic waves are all seismic wave samples. Each seismic wave sample includes its acceleration time history, velocity time history, displacement time history, response spectrum, and earthquake duration. For each seismic wave sample, its earthquake duration is divided into equal intervals to generate several simulation step sizes.

[0010] Furthermore, the principle for outputting structural characteristic data and dynamic response parameters at each simulation step size is as follows: The structural feature data includes time history data of soil loss and dynamic shear strength, and the time history of the structural feature data corresponds to the time history of the seismic wave data. Seismic wave samples are input into the finite element model of the energy island's foundation structure. Within each simulation step, the material properties of the foundation structure of the finite element model are updated. The material properties include the material property data of the structural steel pile foundation, the geotechnical test parameters of the seabed soil, the depth, width, and slope of the scour pit, and the fluid property data of the fluid domain. The finite element model is simulated. At the end of each simulation step, the soil loss and dynamic shear strength of the finite element model are output as the structural feature data of that simulation step. Each simulation step corresponds to a set of structural feature data, thereby obtaining the structural feature data of the finite element model under each simulation step for each seismic wave sample. The dynamic response parameters include the time history data of the relative horizontal displacement between the bottom and top of the structural steel pile foundation, the time history data of the maximum bending moment of the pile body along the depth direction, and the time history data of the shear stress at the soil-structure contact surface. The principle for obtaining the time history data of the relative horizontal displacement between the bottom and top of the structural steel pile foundation for each seismic wave sample is as follows: the bottom center point and top center point of each pile foundation in the finite element model are selected as the bottom node and top node, respectively. The real-time position of the bottom node and top node of each pile foundation under each simulation step is obtained. Based on the real-time position, the real-time relative horizontal displacement of each pile foundation under each simulation step is calculated. The average relative horizontal displacement under the simulation step is obtained by averaging the real-time relative horizontal displacement of all pile foundations. The average relative horizontal displacement under all simulation steps is summarized to form the time history data of the relative horizontal displacement between the bottom and top of the structural steel pile foundation. The principle for obtaining the time history data of the maximum bending moment of the pile along the depth direction is as follows: In the finite element model, monitoring sections are set along the depth direction of the structural steel pile foundation at intervals of 0.5 times the pile diameter, and several monitoring points are set on each monitoring section. The normal stress of each monitoring point is obtained at each simulation step. Based on the normal stress of all monitoring points, the bending moment value of the monitoring section is obtained. The maximum bending moment value of all monitoring sections under each simulation step is taken as the maximum bending moment of the pile under that simulation step. The maximum bending moment of the pile under all simulation steps is summarized to form the time history data of the maximum bending moment of the pile along the depth direction. The principle for obtaining the time history data of shear stress at the soil-structure contact surface is as follows: In the finite element model, the main contact surface is discretized into several main contact points. Each main contact point has a corresponding secondary contact point on the secondary contact surface, and each main contact point and its corresponding secondary contact point together constitute a contact point pair. For each contact point pair, the tangential shear stress between the contact point pairs is simulated, and the average value of the tangential shear stress of all contact point pairs is taken to obtain the soil-structure contact surface shear stress at each simulation step. Based on the soil-structure contact surface shear stress at all simulation steps, the time history data of soil-structure contact surface shear stress is generated. Furthermore, the principle underlying the fitting of characteristic response values ​​of different dynamic response parameters under a specific exceedance probability is as follows: The time history data of horizontal displacement, maximum bending moment and soil-structure contact shear stress were obtained for each seismic wave sample. Local maxima were extracted from each set of time history data. The local maxima corresponding to each dynamic response parameter under all seismic wave samples were summarized to form the datasets of horizontal displacement maximum value, maximum bending moment maximum value and shear stress maximum value respectively. The principle for calculating the feature response value is as follows: Based on the maximum value dataset of the dynamic response parameter, calculate the location parameter, scale parameter, and shape parameter of the dynamic response parameter; then generate a cumulative distribution function based on the location parameter, scale parameter, and shape parameter; set a specific exceedance probability of 10%, and the feature response value is represented on the cumulative distribution function by setting the function value to 1 minus the value of the independent variable corresponding to the specific exceedance probability; calculate the feature response value of each dynamic response parameter with an exceedance probability of 10% based on the cumulative distribution function of each dynamic response parameter.

[0011] Furthermore, the principle of conducting a safety assessment of the energy island based on a safety factor is as follows: The safety factor is the quotient of the allowable value and the characteristic response value, where the allowable value represents a threshold pre-set according to design specifications and safety standards. The safety factor for each dynamic response parameter is calculated separately. When all safety factors are greater than 1.2, the structure is judged to be safe, and no reinforcement or monitoring measures are implemented. When there are safety factors between 1.0 and 1.2, and no safety factors are less than 1, the structure is judged to be basically safe, and monitoring measures are implemented. When there are safety factors less than 1, the structure is judged to be unsafe, and reinforcement measures are implemented.

[0012] This invention also provides a seismic load simulation system for offshore energy island foundations. The system is used to implement the aforementioned seismic load simulation method for offshore energy island foundations, specifically including: The model building module is used to build a finite element model of the energy island's basic structure, which includes structural steel pile foundations, seabed soil, and fluid domain, and defines the soil-structure coupling boundary of the finite element model. The sample construction module is used to build a seismic wave sample library based on historical seismic wave data of the area where the energy island is located. For each seismic wave sample, the simulation time interval is determined and the simulation step size is divided based on its time history. The feature simulation module is used to introduce a dynamic update mechanism to update the material properties of the foundation structure at each simulation step for each seismic wave sample during the simulation using the finite element model, and then output the structural feature data and dynamic response parameters at each simulation step. The comprehensive output module is used to extract the maximum value from the response time history of each dynamic response parameter, construct a maximum value dataset, perform probabilistic statistical analysis on the maximum value dataset, fit the characteristic response value of different dynamic response parameters under a specific exceedance probability, compare the characteristic response value of various dynamic response parameters with their allowable value, generate multiple safety factors, and conduct a safety assessment of the energy island based on the safety factors.

[0013] Compared with the prior art, the beneficial effects of the present invention are: This invention systematically constructs a finite element model encompassing three key physical fields: structure, soil, and fluid. It simulates multi-field coupling effects in a real marine environment, employing a hard contact model and a Coulomb friction model to define contact behavior. This model can simulate nonlinear behaviors such as contact, separation, and sliding between piles and soil under earthquakes, improving model convergence and computational accuracy. It is particularly suitable for pile-soil interaction analysis under strong earthquakes. Traditional methods are relatively weak in simulating complex soil behaviors such as scour and liquefaction, making it difficult to assess long-term service performance. This invention simulates the dynamic coupling of scour and earthquakes by pre-setting and dynamically updating soil parameters, making it more suitable for long-term safety assessment of marine structures. In each simulation step, the properties of soil, fluid, and structural materials are dynamically updated based on the coupling effect of scour and earthquakes, and coupled with the earthquake action to simulate the scour intensification effect. This achieves real-time coupling feedback of multi-physics parameters, making the simulation closer to the progressive damage process in the actual marine environment.

[0014] This invention also extracts three key dynamic response parameters—displacement, bending moment, and shear stress—covering three important dimensions of structural deformation, internal forces, and interface interactions. Each parameter is time-history data, reflecting the dynamic changes of the structure throughout the entire seismic process. By using the bending moment and shear stress time histories under scour coupling, the impact of scour on the internal forces and interface stability of the structure can be directly assessed. By extracting the maxima of the dynamic response parameters to construct a maxima dataset, and fitting the maxima dataset based on the generalized extreme value distribution, characteristic response values ​​under a specific exceedance probability are obtained. This avoids the randomness of single seismic wave simulation and improves the statistical reliability of simulation evaluation. Simultaneously considering the three key dynamic response parameters—displacement, bending moment, and shear stress—and calculating safety factors separately, a multi-dimensional and systematic safety assessment is achieved. Only when all three dynamic response parameters are safe is the overall system safety determined, avoiding misjudgment based on a single indicator. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the method flow of an embodiment of the present invention; Figure 2 This is a schematic diagram of the fitting curves of the geometric parameters of each scour pit as a function of each simulation step size in an embodiment of the present invention. Figure 3This is a schematic diagram of the system modules in an embodiment of the present invention. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0017] It should be noted that, unless otherwise defined, the technical or scientific terms used in this invention should have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0018] Example: Please see Figures 1 to 2 The present invention provides a technical solution: A method for simulating seismic loads on the foundation of an offshore energy island, comprising the following steps: Step 1: Construct a finite element model of the energy island's basic structure, which includes structural steel pile foundations, seabed soil, and fluid domain, and define the soil-structure coupling boundary of the finite element model; In this embodiment, the principle upon which the finite element model of the energy island's basic structure is constructed is as follows: The simulation area is determined based on the installation location of the structural steel pile foundation. Finite element models are then performed on the structural steel pile foundation, seabed soil, and fluid domain within the simulation area. Based on the results of the above three finite element models, a finite element model of the energy island is generated. Obtain the installation locations of all structural steel pile foundations of the target energy island, and determine the simulation area based on the installation locations of the structural steel pile foundations. The simulation area should include all structural steel pile foundations and a certain range of seabed soil and fluid domain around the structural steel pile foundations. This range is determined based on the expert scoring method.

[0019] The principle of modeling structural steel pile foundations is as follows: collect the structural dimension data and material property data of the structural steel pile foundation. The structural dimension data includes the shape and size of the structural steel pile foundation, specifically the shape and radius of the cross-section of the structural steel pile foundation. The material property data includes the elastic modulus, Poisson's ratio and yield strength of the structural steel pile foundation material. Based on the above data, construct the finite element model of the structural steel pile foundation in finite element software. In the finite element software ANSYS, beam elements are used to model and mesh the structural steel pile foundation. The size of the mesh is half the diameter of the structural steel pile foundation, and material property data is assigned to each mesh to construct the finite element model of the structural steel pile foundation.

[0020] The principle of modeling seabed soil is as follows: obtain the soil layer distribution and geotechnical test parameters of each soil layer in the seabed soil. The soil layer distribution represents the type and depth of each soil layer in the seabed soil. The geotechnical test parameters include the water content, void ratio, cohesion, internal friction angle and compression modulus of each soil layer. Also obtain the distribution location of scour pits in the seabed soil and the geometric parameters of the scour pits. The geometric parameters of the scour pits include the depth, width and slope of the scour pits. Construct a finite element model of the seabed soil containing the scour pits in finite element software. In the finite element model of seabed soil, a three-dimensional geometry is artificially created to represent the actual scour pits, simulating local soil loss caused by ocean currents. Scour pits are typically located in the seabed soil area surrounding the structural steel pile foundation. During finite element modeling, the distribution location and geometric parameters of scour pits on the seabed soil are collected in real time, and these parameters are used as initial values. In the finite element software ANSYS, solid elements are used to model the seabed soil. A three-dimensional geological solid model is established based on the soil layer distribution, and the scour pit portion is removed based on the initial values ​​of the scour pit geometric parameters. For each soil layer, geotechnical test parameters are obtained, and these parameters are assigned to each soil layer in the three-dimensional geological solid model, thus constructing a finite element model of the seabed soil containing the scour pits.

[0021] The principle of modeling the fluid domain is as follows: collect environmental geometric data and fluid property data of the fluid domain. The environmental geometric data includes the geometry of the contact surface between the fluid domain and the structural steel pile foundation, the geometry of the contact surface between the fluid domain and the seabed soil, the seabed topography, the average water depth, and the spatial dimensions of the fluid domain. The fluid property data includes fluid density and fluid dynamic viscosity. Construct a finite element model of the fluid domain in finite element software.

[0022] In the finite element software ANSYS, the entire fluid domain is divided into a near-field region, an intermediate transition region, and a far-field region according to depth. The diameter of the structural steel pile foundation is taken as one unit length. From the fluid domain horizontal plane to the seabed, the region is divided at one unit length and three unit lengths respectively. The part from the fluid domain horizontal plane to one unit length below the fluid domain horizontal plane is the near-field region, the part from one to three unit lengths is the intermediate transition region, and the part from three unit lengths to the seabed is the far-field region. Fluid property data of the near-field region, intermediate transition region, and far-field region are obtained separately, and finite element models are built for the near-field region, intermediate transition region, and far-field region respectively. The three finite element models are combined to generate the finite element model of the fluid domain.

[0023] The principle underlying the definition of the soil-structure coupling boundary in the finite element model is as follows: The definition logic of the soil-structure coupling boundary is as follows: For the contact surfaces between the structural steel pile foundation and the seabed soil, the contact surface belonging to the structural steel pile foundation is defined as the primary contact surface, and the contact surface belonging to the seabed soil is defined as the secondary contact surface. During an earthquake, there are normal pressure and tangential friction between the primary and secondary contact surfaces. The normal pressure is defined using the hard contact model, and its logic is: when the primary and secondary contact surfaces are in contact, normal pressure occurs; when the primary and secondary contact surfaces separate, the normal pressure is zero. The tangential friction is defined using the Coulomb friction model, and its logic is: the shear force between the primary and secondary contact surfaces is proportional to the normal pressure, until the shear force reaches the maximum static friction force, at which point the primary and secondary contact surfaces slide tangentially.

[0024] The soil-structure coupling boundary is used to describe the interaction mechanism between structural steel pile foundations and seabed soil under seismic loads. The contact surfaces between the structural steel pile foundations and the seabed soil are divided into primary contact surfaces and secondary contact surfaces. The primary contact surface belongs to the structural steel pile foundation, and the secondary contact surface belongs to the seabed soil. The division of primary and secondary contact surfaces is based on the principle of stiffness difference. The surface with higher stiffness is defined as the primary contact surface, and the surface with lower stiffness is defined as the secondary contact surface, in order to improve the convergence and accuracy of the calculation. The normal contact behavior is described by a hard contact model. Specifically, when the primary and secondary contact surfaces are in contact with each other, normal stress is generated between them. This normal stress increases with the contact depth. When the primary and secondary contact surfaces separate, the normal pressure drops to 0, that is, tensile force is not allowed between the primary and secondary contact surfaces. The tangential contact behavior is described by the Coulomb friction model. Specifically, the tangential friction force is proportional to the normal pressure, and the coefficient of proportionality between the two is the friction coefficient. When the shear force is less than the maximum static friction force, there is no relative sliding between the contact surfaces. When the shear force reaches the maximum static friction force, the contact surfaces slide relative to each other, and at this time the friction force between the contact surfaces remains kinetic friction force.

[0025] Step 2: Construct a seismic wave sample library based on historical seismic wave data of the area where the energy island is located. For each seismic wave sample, determine the simulation time interval and divide the simulation step size based on its time history. In this embodiment, the principle upon which the seismic wave sample library is constructed is as follows: Historical seismic wave data of the area where the energy island is located are collected, and several artificial seismic waves are synthesized based on the historical seismic wave data. A seismic wave sample library is constructed based on the historical and artificial seismic waves. The seismic wave sample library contains several historical and artificial seismic waves, and these seismic waves are all seismic wave samples. Each seismic wave sample includes its acceleration time history, velocity time history, displacement time history, response spectrum, and earthquake duration. For each seismic wave sample, its earthquake duration is divided into equal intervals to generate several simulation step sizes.

[0026] Due to the limited number of historical seismic wave records, directly using historical seismic waves cannot fully cover the uncertainty and diversity of ground motion. Therefore, artificial seismic waves are synthesized based on historical seismic waves to cover more possible ground motion characteristics, making the seismic waves more consistent with the geological and seismic environment of the energy island area. The principle of synthesizing artificial seismic waves is as follows: collect site-specific response spectra and durations of historical seismic data in the energy island area, input the site-specific response spectra and durations into the SeismoArtif software, and generate multiple artificial seismic waves that match the site-specific response spectra. By synthesizing artificial seismic waves, the number and types of seismic wave samples can be significantly increased, better matching the specific geological and seismic environment of the energy island site and improving the site adaptability of the simulation.

[0027] Step 3: For each seismic wave sample, during the simulation using the finite element model, a dynamic update mechanism is introduced to update the material properties of the foundation structure at each simulation step, thereby outputting the structural characteristic data and dynamic response parameters at each simulation step. In this embodiment, the principle for outputting structural feature data and dynamic response parameters at each simulation step size is as follows: The structural feature data includes time history data of soil loss and dynamic shear strength, and the time history of the structural feature data corresponds to the time history of the seismic wave data. Seismic wave samples are input into the finite element model of the energy island's foundation structure. Within each simulation step, the material properties of the foundation structure in the finite element model are updated. The material properties of the foundation structure include the material property data of the structural steel pile foundation, the geotechnical test parameters of the seabed soil, the depth, width, and slope of the scour pit, and the fluid property data of the fluid domain. The finite element model is simulated. At the end of each simulation step, the soil loss and dynamic shear strength of the finite element model are output as the structural feature data of that simulation step. Each simulation step corresponds to a set of structural feature data, thereby obtaining the structural feature data of the finite element model under each simulation step for each seismic wave sample. The specific principle for updating the material properties of the finite element model within each simulation step is as follows: Within each simulation step, based on the coupling effect of fluid scour and seismic forces, the following material properties are dynamically updated, including the geometric parameters of the scour pit, seabed soil properties, fluid domain properties, and structural steel pile foundation properties. The geometric parameters of the scour pit change due to the gradual transport of soil particles under the action of ocean currents, waves, and earthquakes; this change process is simulated during the simulation. The increment of the scour pit depth within each simulation step is: ,in, Indicates the first The change in scour pit depth within a simulation step. The basic erosion rate represents the erosion rate of the soil by the fluid under constant flow field conditions without seismic action. It is obtained by fitting historical scour data. This represents the time length of a simulation step. The index representing the simulation step size, This represents the seismic amplification factor, used to reflect the amplifying effect of seismic action on soil erosion. Its value ranges from 0.1 to 0.5. The larger the value, the greater the impact of the earthquake on soil erosion. Indicates the first Shear stress at the soil-fluid interface within a simulated step size. represents the critical shear stress, which is the minimum shear stress required for soil particles to begin moving. The scour pit depth starts from its initial value and gradually increases over time. The scour pit depth at each simulation step is: When the intensity of seismic waves increases, Increased size leads to a faster scouring rate; The calculation formula is divided into a basic erosion rate term. and earthquake amplification term The basic erosion rate term reflects that, under still or steady-flow conditions without earthquakes, erosion is a gradual process. The erosion rate is determined by soil properties, flow velocity, and particle size. Earthquakes exacerbate erosion through two mechanisms: soil liquefaction or softening and increased water flow disturbance. Soil liquefaction or softening indicates that earthquake shear waves increase pore pressure and decrease effective stress, making the soil easier to transport. Increased water flow disturbance indicates that earthquakes cause water sloshing or pressure fluctuations, increasing shear stress. The shear stress ratio is used to... As a driving factor It also reflects the combined shear stress caused by water flow and earthquake. It is the critical stress value at which soil can be moved. When the driving factor is greater than 1, it means that the soil is movable. The larger the driving factor, the stronger the earthquake effect, and the more drastic the change in soil depth.

[0028] The width of the scour pit is proportional to its depth and is controlled by the lateral stability of the soil. The formula for its variation is: ,in, Indicates the first Width of scour pit within a simulation step. This indicates the initial width of the scour pit before scour begins. This represents the width expansion factor, used to reflect the rate at which the width of a scour pit expands with increasing scour pit depth; its value ranges from 1.5 to 2.0. The angle of repose of the soil is a parameter representing the shear strength of the soil and reflects the frictional characteristics between soil particles. From the initial width and width extension composition, The tangent of the angle of repose of the soil represents the maximum slope that the soil can maintain under unsupported conditions. If the slope exceeds this value, the sidewall soil will collapse, the scour pit will automatically widen, and the deeper the scour, the worse the sidewall stability and the wider the pit. Therefore, the width expansion is based on... It is obtained, and is directly proportional to the three.

[0029] The slope of a scour pit is determined by the natural angle of repose of the soil and the geometric relationship between the current depth and width of the scour pit. The calculation formula is as follows: ,in, Indicates the first The slope of the scour pit within each simulation step is the angle between the sidewall of the scour pit and the horizontal plane. The cross-section of the scour pit is approximated as a triangle, and its slope is defined as the arctangent of the ratio of depth to half width, reflecting the steepness of the scour pit. This directly affects the stability of the sidewall and the risk of soil collapse. In the initial stage of the simulation, the scour pit depth increases faster than the scour pit width, and the slope is steeper. As the simulation progresses, the width expands faster, the slope approaches the angle of repose of the soil, and the system gradually reaches equilibrium.

[0030] Table 1 shows the changes in scour pit depth, width, and slope from the 1st to the 30th simulation step. The initial values ​​for scour pit depth and width are 0.5m, 3.0m, with a basic erosion rate of 0.01m / s under still water velocity, a seismic amplification factor of 0.3, a width expansion factor of 1.8, and a soil repose angle of 30°. The scour pit depth increases from the initial 0.5m to the final 0.6837m, exhibiting a non-uniform, step-like growth process. Larger increments correspond to stronger temporal ground motions. The final form is the result of the accumulation of multiple seismic pulses. The scour pit width increases monotonically, but the rate of increase varies. Based on the formula for calculating scour pit width, the width is affected by the depth; therefore, the width increase lags behind the depth increase, and their overall growth trends are similar. Width expansion reflects the inertia of the scour system. As the depth increases, the width will continue to expand based on the new depth value. The overall slope of the scour pit shows a downward trend, indicating that the cross-sectional shape of the scour pit is changing from a deep and narrow type to a shallow and wide type. At the beginning of scour, the erosion is concentrated in a small area near the pile foundation, the depth increases rapidly, and the lateral soil has not yet become unstable, so the width expands slowly, forming a steep sidewall. At this time, the slope is relatively large. As scour continues, the depth continues to expand downward, the width expands outward, the width expands at an accelerated rate, the depth growth slows down, the depth-to-width ratio continues to decrease, and the slope gradually becomes gentler.

[0031] Table 1. Variation of Geometric Parameters of Scour Pit with Time Step The principle behind updating seabed soil properties is as follows: Seabed soil properties include the soil layer distribution and geotechnical test parameters for each layer. The soil layer distribution represents the type and depth of each soil layer at the seabed. Geotechnical test parameters include the water content, void ratio, cohesion, internal friction angle, and compression modulus of each soil layer. As the depth and width of the scour pit dynamically expand, the geometry of the original seabed soil changes, leading to a readjustment of the soil layer distribution. When soil within the scour pit area is removed, the surrounding soil may collapse due to lateral instability, thus altering the spatial distribution and thickness of each soil layer. The properties are calculated based on the current simulation step size. The system identifies sets of soil elements affected by scour and marks soil elements within scour pits as "removed," removing them from geotechnical test parameters. A threshold of 0.1m for soil layer thickness is set. If a soil layer's thickness falls below this threshold due to scour or collapse, it is merged with the underlying layer, and the geotechnical test parameters of the merged layer are the weighted average of the two layers. Within each simulation step, the geotechnical test parameters are updated based on the following principle: the formula for water content variation with simulation step length is: ,in, Indicates the first Soil moisture content at a simulated step length This indicates the initial soil moisture content. The water content sensitivity coefficient, ranging from 0.05 to 0.15, reflects the degree of influence of the combination of scour and earthquakes on water content. Indicates the maximum scour depth, when When the maximum value is reached, at this time Scouring exposes soil to water flow, and the moisture content may change due to drainage or immersion. Earthquake-induced vibrations may accelerate the expulsion or absorption of pore water. Both scouring and earthquakes influence changes in moisture content. The formula for calculating the void ratio is: ,in, Indicates the first Pore ​​ratio of each simulation step size Indicates the initial void ratio. Changes in porosity caused by surface erosion , This represents the scouring sensitivity coefficient, which ranges from 0.02 to 0.08. This indicates the change in porosity caused by an earthquake. , The seismic sensitivity coefficient ranges from 0.01 to 0.05. Scouring causes soil particle rearrangement and alters the pore structure, while seismic vibrations cause soil compression, increasing the void ratio. The changes in void ratio caused by scouring and earthquakes are calculated separately, and the updated void ratio is accumulated for each affected soil unit. The formula for calculating cohesion is: ,in, Indicates the first Cohesion at a simulated step length Indicates initial cohesion. This represents the cohesion attenuation coefficient, with a value ranging from 0.3 to 0.8. This represents the seismic influence coefficient, ranging from 0.1 to 0.4. Scouring leads to soil loss and reduces structural cohesion; cyclic shearing caused by earthquakes further degrades cohesion. The formula for calculating the internal friction angle is: ,in, Indicates the first The internal friction angle of a simulated step size Indicates the initial internal friction angle. This represents the change in the internal friction angle caused by scouring. , This represents the sensitivity coefficient of the internal friction angle to erosion, with a value ranging from 0.05 to 0.15. This represents the change in the internal friction angle caused by an earthquake. , The internal friction angle is represented by a sensitivity coefficient to earthquakes, ranging from 0.02 to 0.08. Scouring disrupts the interlocking of soil particles, and earthquake cyclic shearing causes friction angle degradation. The reduction in internal friction angle caused by scouring and earthquakes is calculated separately, and these reductions are subtracted from the initial value to obtain the updated internal friction angle. The formula for calculating the compression modulus is: ,in, Indicates the first Compression modulus of a simulation step size Indicates the initial compressive modulus. This represents the modulus attenuation coefficient, with a value ranging from 0.2 to 0.6. This represents the seismic coupling coefficient, ranging from 0.1 to 0.3. Scouring weakens soil support and reduces stiffness, while cyclic strain caused by earthquakes leads to modulus softening. The formula for calculating the geotechnical test parameters of the merged soil layers is: ,in, Represents any geotechnical test parameter. This indicates the value of the geotechnical test parameter after soil layer merging. These are the values ​​of the geotechnical test parameters in the two soil layers before the merging process. These represent the thicknesses of the two soil layers before they were merged.

[0032] The principle behind updating fluid domain properties is as follows: Fluid domain properties represent the fluid density and dynamic viscosity of the fluid domain. During scouring, soil particles are transported by the water flow and suspended in the water, forming turbid water. The increase in suspended sediment leads to an increase in local fluid density, especially near the scour pit. This change affects the fluid's inertia, buoyancy, and fluid-structure interaction. The formula for dynamically updating the fluid density is: ,in, Indicates the first Fluid density at a simulation step size This represents the density of clean seawater, with a value of 1025. , This represents the density of sediment particles, with a value of 2650. , Indicates the first The volume concentration of suspended sediment in the fluid at each simulation step is calculated as the ratio of the volume of sediment washed away and suspended within that simulation step to the volume of fluid in the scour-affected region within that simulation step. Suspended sediment not only increases density but also increases the fluid's effective viscosity due to the increased internal frictional resistance caused by the interaction between sediment particles. During scouring, the fluid's dynamic viscosity gradually increases with increasing sediment content. The updated formula for the fluid's dynamic viscosity is: ,in, Indicates the first The fluid dynamic viscosity at a simulated step size The dynamic viscosity of clean seawater is expressed as a value of [value missing]. Pa·s (Pascal second) This represents the concentration correction factor, with a value of 6 to 7, used to describe the nonlinear viscosity-enhancing effect.

[0033] The principle for updating the properties of structural steel pile foundations is as follows: The properties of structural steel pile foundations include the elastic modulus, Poisson's ratio, and yield strength of the structural steel pile foundation material. Structural steel pile foundations will not undergo significant geometric deformation or damage due to scour or earthquakes in the short term; therefore, the structural dimensions do not change over time during the simulation. The principle for updating the elastic modulus is as follows: Cyclic loads caused by earthquakes lead to cumulative plastic strain in the steel, resulting in stiffness degradation. Simultaneously, the weakened soil support effect caused by scour increases the dynamic amplification effect of the pile body, further exacerbating stress concentration and material fatigue. The calculation formula is as follows: ,in, Indicates the first The elastic modulus of a simulated step size This represents the initial elastic modulus. This represents the degradation coefficient of the elastic modulus, with a value ranging from 0.05 to 0.15. Indicates up to the number The number of load cycles experienced by a simulated step-length structural steel pile foundation. The characteristic number of cycles representing the degradation of the elastic modulus indicates the number of load cycles experienced when the elastic modulus of the structural steel pile foundation drops to 85% of its initial value. This number of load cycles is obtained by conducting low-cycle fatigue tests on structural steel pile foundations of the same material.

[0034] The principle behind the update of Poisson's ratio is as follows: Under cyclic loading, the lateral deformation properties of a material change slightly, and the Poisson's ratio increases slightly. Its calculation formula is: ,in, Indicates the first Poisson's ratio of a simulated step size Indicates the initial Poisson's ratio. The coefficient representing the variation of Poisson's ratio ranges from 0.01 to 0.05. It defines the maximum possible change in Poisson's ratio relative to its initial value when the cumulative plastic strain reaches the plastic strain threshold. Indicates the first The cumulative plastic strain of each simulation step, This represents the allowable plastic strain threshold of the material, and the maximum allowable cumulative plastic strain of the material. When the cumulative plastic strain reaches... At that time, the material was identified as entering a severely plastic state, and its maximum cumulative plastic strain was determined based on the Steel Structure Material Handbook for Structural Steel Pile Foundations.

[0035] The principle for updating yield strength is as follows: the cumulative plastic strain caused by cyclic loading leads to cyclic softening of the material, and the yield strength gradually decreases. The update formula is: ,in, Indicates the first Yield strength at a simulated step size Indicates the initial yield strength. This indicates the number of load cycles required for the yield strength of a structural steel pile foundation to decrease to 85% of its initial value. Under cyclic loading, the pile foundation experiences fatigue or softening effects, leading to a degradation of its yield strength. Scouring amplifies this softening effect by weakening the support of the surrounding soil, thus exacerbating the dynamic response and stress amplitude of the pile foundation.

[0036] The principle for obtaining dynamic response parameters is as follows: The dynamic response parameters include the time history data of the relative horizontal displacement between the bottom and top of the structural steel pile foundation, the time history data of the maximum bending moment of the pile body along the depth direction, and the time history data of the shear stress at the soil-structure contact surface. The principle for obtaining the time history data of the relative horizontal displacement between the bottom and top of the structural steel pile foundation for each seismic wave sample is as follows: the bottom center point and top center point of each pile foundation in the finite element model are selected as the bottom node and top node, respectively. The real-time position of the bottom node and top node of each pile foundation under each simulation step is obtained. Based on the real-time position, the real-time relative horizontal displacement of each pile foundation under each simulation step is calculated. The average relative horizontal displacement under the simulation step is obtained by averaging the real-time relative horizontal displacement of all pile foundations. The average relative horizontal displacement under all simulation steps is summarized to form the time history data of the relative horizontal displacement between the bottom and top of the structural steel pile foundation. The relative horizontal displacement time history data between the bottom and top of the structural steel pile foundation was obtained through simulation to evaluate the deformation performance of the pile foundation under the coupled action of earthquake and scour. For each structural steel pile foundation, the center point of its pile bottom section was selected as the bottom node, and the center point of its pile top section was selected as the top node. At the end of each simulation step, the positions of the bottom node and the top node were output in real time. and ,in Indicates the first The simulation step size is the first The three-dimensional coordinates of the bottom node of the structural steel pile foundation. This represents the index of the structural steel pile foundation in the finite element model, and , This indicates the number of structural steel pile foundations in the finite element model. Indicates the first The simulation step size is the first The three-dimensional coordinates of the top node of each structural steel pile foundation, and the relative horizontal displacement represented in the XOY plane, are the displacement difference between the top and the bottom. The formula for calculating the average relative horizontal displacement within each simulation step is: ,in, Indicates the first The average relative horizontal displacement under each simulation step size Indicates the first The simulation step size is the first The coordinates of the bottom node of a structural steel pile foundation on the horizontal plane. Indicates the first The simulation step size is the first The coordinates of the top node of each structural steel pile foundation in the horizontal plane are calculated. The above calculation is repeated for each simulation step to obtain the time history data of the relative horizontal displacement: ,in, This represents a set of time history data representing relative horizontal displacement. This indicates the number of simulation steps; the relative horizontal displacement directly reflects the overall lateral deformation of the pile foundation system under the coupled action of earthquake and scour. This index can be used to determine whether the pile foundation has undergone excessive deformation. The displacement response is affected not only by the input of seismic waves, but also by the soil loss caused by scour and the effects of hydrodynamics. If the relative horizontal displacement is too large, the surface pile stiffness may be insufficient, the soil support capacity may be reduced, or the pile-soil interface may slip.

[0037] The principle for obtaining the time history data of the maximum bending moment of the pile along the depth direction is as follows: In the finite element model, monitoring sections are set along the depth direction of the structural steel pile foundation at intervals of 0.5 times the pile diameter, and several monitoring points are set on each monitoring section. The normal stress of each monitoring point is obtained at each simulation step. Based on the normal stress of all monitoring points, the bending moment value of the monitoring section is obtained. The maximum bending moment value of all monitoring sections under each simulation step is taken as the maximum bending moment of the pile under that simulation step. The maximum bending moment of the pile under all simulation steps is summarized to form the time history data of the maximum bending moment of the pile along the depth direction. Under the coupled effects of earthquakes and scour, piles undergo bending deformation, and bending moment is a key dynamic response parameter for evaluating the strength and stability of the pile structure. To comprehensively capture the bending moment variations distributed along the pile, monitoring sections are set along the depth direction. Within each simulation step, the bending moment values ​​of all monitoring sections are calculated, and the maximum value is taken as the maximum bending moment of the pile at that step, ultimately forming the maximum bending moment time history data. The specific calculation principle is as follows: Within each simulation step, the normal stress at each monitoring point is output through finite element simulation. The formula for calculating the bending moment value of the monitoring section is: ,in, Indicates the first The monitoring section at the first Bending moment values ​​at each simulation step size. Indicates the index of the monitoring section, and , Indicates the number of monitoring sections. Indicates the first Normal stress at each monitoring point Indicates the index of the monitoring point, and , This indicates the number of monitoring points on a single monitoring section. Indicates the first The distance from each monitoring point to the neutral axis of the monitoring section. Indicates the first [unit] within the monitoring section The weighted area of ​​each monitoring point The calculation principle is the ratio of the monitored cross-sectional area to the number of monitoring points on the monitored cross-section; among all monitored cross-sections, the largest bending moment value is taken as the maximum bending moment of the pile body at that simulation step length. ,in, Indicates the first The maximum bending moment of the pile body under each simulation step length; repeat the above calculation process for all simulation steps to obtain the time history data of the maximum bending moment: ,in This represents the set of time history data for maximum bending moment. The time history data for maximum bending moment is used to determine whether the bending moment of a pile foundation at a certain simulation step exceeds its bending bearing capacity, thereby assessing whether the pile will experience bending failure. The depth location of the maximum bending moment reflects the area in the pile most prone to bending failure, usually located near the pile top or at soil layer changes. If the maximum bending moment gradually increases over time, it indicates that soil loss caused by scouring has exacerbated the dynamic amplification effect on the pile. If the maximum bending moment approaches or exceeds the bending strength of the pile, it suggests possible bending failure. Abrupt changes or increased oscillations in the bending moment time history may indicate soil liquefaction or instability.

[0038] The principle for obtaining the time history data of shear stress at the soil-structure contact surface is as follows: In the finite element model, the main contact surface is discretized into several main contact points. Each main contact point has a corresponding secondary contact point on the secondary contact surface. Each main contact point and its corresponding secondary contact point together constitute a contact point pair. For each contact point pair, the tangential shear stress between the contact point pairs is simulated, and the average value of the tangential shear stress of all contact point pairs is taken to obtain the soil-structure contact surface shear stress at each simulation step. Based on the soil-structure contact surface shear stress at all simulation steps, the soil-structure contact surface shear stress time history data is generated.

[0039] For each contact point pair, the tangential shear stress between the contact point pairs is obtained based on finite element simulation at each simulation step. The average value of the tangential shear stress between the contact point pairs at each simulation step is taken to obtain the soil-structure contact surface shear stress at that simulation step. , Indicates the first The soil-structure contact surface shear stress at each simulation step is calculated repeatedly to obtain the time history data of the soil-structure contact surface shear stress. ,in This represents a set of time-history data on shear stress at the soil-structure contact surface. The shear stress time-history data reflects the change over time in the tangential interaction force between the surface of the structural steel pile foundation and the surrounding seabed soil at the contact surface under the coupled effects of earthquake and scour. Shear stress reflects whether relative sliding occurs between the soil and the pile foundation. When the tangential force caused by the earthquake exceeds the shear strength of the contact surface, the pile... Slippage may occur at the soil interface, leading to increased lateral displacement or decreased bearing capacity of the pile foundation. This time-history data can be used to determine whether interface slippage, soil liquefaction, or plastic slippage has occurred, thereby assessing the lateral stability of the pile foundation. Scour causes soil loss, reduces the contact area, and weakens soil parameters, thus affecting the distribution and magnitude of shear stress. By comparing the shear stress response with and without scour, it is possible to analyze how scour exacerbates pile foundation stress. The dynamic weakening effect of the soil interface.

[0040] Step 4: For each dynamic response parameter, extract its maximum value from its response time history, construct a maximum value dataset, perform probabilistic statistical analysis on the maximum value dataset, fit the characteristic response values ​​of different dynamic response parameters under a specific exceedance probability, compare the characteristic response values ​​of various dynamic response parameters with their allowable values, generate multiple safety factors, and conduct a safety assessment of the energy island based on the safety factors.

[0041] In this embodiment, the principle underlying the fitting of characteristic response values ​​for different dynamic response parameters under a specific exceedance probability is as follows: The time history data of horizontal displacement, maximum bending moment and soil-structure contact shear stress were obtained for each seismic wave sample. Local maxima were extracted from each set of time history data. The local maxima corresponding to each dynamic response parameter under all seismic wave samples were summarized to form the datasets of horizontal displacement maximum value, maximum bending moment maximum value and shear stress maximum value respectively. from The local maxima of relative horizontal displacement, maximum bending moment, and soil-structure contact shear stress are extracted from the data, and denoted as follows: , , Let the number of seismic wave samples be... The index of the seismic wave samples is The dataset of maximum horizontal displacements is then: ,in This represents a dataset of maximum horizontal displacements. Indicates the first The dataset contains local maxima of relative horizontal displacement and maximum bending moment of the seismic wave samples. ,in, This represents the dataset of maximum bending moment maxima. Indicates the first The dataset contains the local maxima of the maximum bending moment and the maximum shear stress of the seismic wave samples. ,in, This represents a dataset of maximum shear stress values. Indicates the first Local maxima of shear stress at the soil-structure interface of a seismic wave sample.

[0042] These maximum value datasets summarize the maximum response values ​​of structures under various coupled seismic waves and scour, representing the most unfavorable load conditions that the structure may encounter. They reflect the peak dynamic response of the structure during the earthquake duration and serve as a direct basis for assessing structural safety.

[0043] The principle for calculating the feature response value is as follows: Based on the maximum value dataset of the dynamic response parameter, calculate the location parameter, scale parameter, and shape parameter of the dynamic response parameter; then generate a cumulative distribution function based on the location parameter, scale parameter, and shape parameter; set a specific exceedance probability of 10%, and the feature response value is represented on the cumulative distribution function by setting the function value to 1 minus the value of the independent variable corresponding to the specific exceedance probability; calculate the feature response value of each dynamic response parameter with an exceedance probability of 10% based on the cumulative distribution function of each dynamic response parameter.

[0044] For each maximum value dataset, a generalized extreme value distribution model is used for fitting. The cumulative distribution function of the generalized extreme value distribution model is: ,in, Represents any data point in the maximum value dataset. Indicates position parameters, Indicates the scale parameter. The shape parameter is represented; for each maximum dataset, the location parameter, scale parameter and shape parameter are fitted by generalized extremum theory to obtain the cumulative distribution function of different maximum datasets; For each maximum value dataset, let its cumulative distribution function equal the target cumulative probability, where the sum of the target cumulative probability and the exceedance probability is 1. ,Right now The characteristic response values ​​are obtained by solving: The fitting structures for the location, scale, and shape parameters of the horizontal displacement maxima dataset are as follows: Then its characteristic response value is: The fitting structures for the location, scale, and shape parameters of the maximum bending moment dataset are as follows: The characteristic response value is then removed. The fitting structures for the location, scale, and shape parameters of the shear stress maxima dataset are as follows: Then its characteristic response value is: .

[0045] The characteristic response values ​​are no longer the response under a single seismic wave, but the result considering the coupling effect of multiple seismic waves and scour, reflecting the displacement, bending moment and shear stress levels of the structure under the most unfavorable working condition (10% exceedance probability).

[0046] The principle of conducting a safety assessment of the energy island based on a safety factor is as follows: The safety factor is the quotient of the allowable value and the characteristic response value, where the allowable value represents a threshold pre-set according to design specifications and safety standards. The safety factor for each dynamic response parameter is calculated separately. When all safety factors are greater than 1.2, the structure is judged to be safe, and no reinforcement or monitoring measures are implemented. When there are safety factors between 1.0 and 1.2, and no safety factors are less than 1, the structure is judged to be basically safe, and monitoring measures are implemented. When there are safety factors less than 1, the structure is judged to be unsafe, and reinforcement measures are implemented.

[0047] The safety factor is the ratio of the allowable value to the characteristic response value. A safety factor is calculated for each characteristic response value. Based on expert scoring, allowable values ​​for each dynamic response parameter are set according to design specifications, industry standards, engineering experience, and structural safety requirements. The calculated safety factor classifies structural safety into three levels. When the safety factor is greater than 1.2, it indicates that the structure has sufficient safety reserves in the indicators corresponding to the dynamic response parameters, and no additional reinforcement or monitoring measures are required; it can be used normally. When the safety factor is between 1.0 and 1.2, but not less than 1, the structural safety reserves are low, and there is a potential risk, but it can still be used. Monitoring measures need to be implemented, including the installation of displacement sensors and strain gauges to monitor the structural response in real time. When the safety factor is less than 1, the characteristic response value of the dynamic response parameter has exceeded the allowable value, posing a safety hazard. Reinforcement measures need to be taken, including increasing the diameter of the structural steel piles and increasing the number of piles.

[0048] The safety factor reflects the safety margin of a structure relative to its design safety threshold under actual load. The larger the value, the higher the safety margin, and the better the structure can resist uncertainties such as load variation, material degradation, and construction errors. The lower the safety factor, the closer the characteristic response value is to or exceeds the allowable value, the smaller the safety margin, and the more likely the structure may be damaged or destroyed under strong earthquakes or high-speed water flow, requiring early warning or reinforcement.

[0049] Please see Figure 3 The present invention also provides a seismic load simulation system for offshore energy island foundations. The system is used to implement the aforementioned seismic load simulation method for offshore energy island foundations, specifically including: The model building module is used to build a finite element model of the energy island's basic structure, which includes structural steel pile foundations, seabed soil, and fluid domain, and defines the soil-structure coupling boundary of the finite element model. The sample construction module is used to build a seismic wave sample library based on historical seismic wave data of the area where the energy island is located. For each seismic wave sample, the simulation time interval is determined and the simulation step size is divided based on its time history. The feature simulation module is used to introduce a dynamic update mechanism to update the material properties of the foundation structure at each simulation step for each seismic wave sample during the simulation using the finite element model, and then output the structural feature data and dynamic response parameters at each simulation step. The comprehensive output module is used to extract the maximum value from the response time history of each dynamic response parameter, construct a maximum value dataset, perform probabilistic statistical analysis on the maximum value dataset, fit the characteristic response value of different dynamic response parameters under a specific exceedance probability, compare the characteristic response value of various dynamic response parameters with their allowable value, generate multiple safety factors, and conduct a safety assessment of the energy island based on the safety factors.

[0050] The above formulas are all dimensionless calculations. The formulas are derived from software simulations based on a large amount of collected data to obtain the most recent real-world results. The preset parameters in the formulas are set by those skilled in the art according to the actual situation.

[0051] The above embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any other combination thereof. When implemented in software, the above embodiments can be implemented, in whole or in part, as a computer program product. Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented by electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution.

[0052] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment, depending on actual needs.

[0053] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A method for simulating seismic loads on the foundation of an offshore energy island, characterized in that, The specific steps include: Step 1: Construct a finite element model of the energy island's basic structure, which includes structural steel pile foundations, seabed soil, and fluid domain, and define the soil-structure coupling boundary of the finite element model; Step 2: Construct a seismic wave sample library based on historical seismic wave data of the area where the energy island is located. For each seismic wave sample, determine the simulation time interval and divide the simulation step size based on its time history. Step 3: For each seismic wave sample, during the simulation using the finite element model, a dynamic update mechanism is introduced to update the material properties of the foundation structure at each simulation step, thereby outputting the structural characteristic data and dynamic response parameters at each simulation step. Step 4: For each dynamic response parameter, extract its maximum value from its response time history, construct a maximum value dataset, perform probabilistic statistical analysis on the maximum value dataset, fit the characteristic response values ​​of different dynamic response parameters under a specific exceedance probability, compare the characteristic response values ​​of various dynamic response parameters with their allowable values, generate multiple safety factors, and conduct a safety assessment of the energy island based on the safety factors. The principle underlying the finite element model of the energy island's basic structure is as follows: The simulation area is determined based on the installation location of the structural steel pile foundation. Finite element models are then performed on the structural steel pile foundation, seabed soil, and fluid domain within the simulation area. Based on the results of the above three finite element models, a finite element model of the energy island is generated. The principle of modeling structural steel pile foundations is as follows: collect the structural dimension data and material property data of the structural steel pile foundations. The structural dimension data includes the shape and size of the structural steel pile foundations, and the material property data includes the elastic modulus, Poisson's ratio and yield strength of the structural steel pile foundation material. Based on the above data, construct a finite element model of the structural steel pile foundation in finite element software. The principle of modeling seabed soil is as follows: obtain the soil layer distribution and geotechnical test parameters of each soil layer in the seabed soil. The soil layer distribution represents the type and depth of each soil layer in the seabed soil. The geotechnical test parameters include the water content, void ratio, cohesion, internal friction angle and compression modulus of each soil layer. Also obtain the distribution location of scour pits in the seabed soil and the geometric parameters of the scour pits. The geometric parameters of the scour pits include the depth, width and slope of the scour pits. Construct a finite element model of the seabed soil containing the scour pits in finite element software. The principle of modeling the fluid domain is as follows: collect environmental geometric data and fluid property data of the fluid domain. The environmental geometric data includes the geometry of the contact surface between the fluid domain and the structural steel pile foundation, the geometry of the contact surface between the fluid domain and the seabed soil, the seabed topography, the average water depth, and the spatial dimensions of the fluid domain. The fluid property data includes fluid density and fluid dynamic viscosity. Construct a finite element model of the fluid domain in finite element software. The principle underlying the definition of the soil-structure coupling boundary in the finite element model is as follows: The definition logic of the soil-structure coupling boundary is as follows: For the contact surface between the structural steel pile foundation and the seabed soil, the contact surface belonging to the structural steel pile foundation is defined as the primary contact surface, and the contact surface belonging to the seabed soil is defined as the secondary contact surface. During an earthquake, there are normal pressure and tangential friction between the primary and secondary contact surfaces. The normal pressure is defined using a hard contact model, with the logic that normal pressure occurs when the primary and secondary contact surfaces are in contact, and is zero when they separate. The tangential friction is defined using a Coulomb friction model, with the logic that the shear force between the primary and secondary contact surfaces is proportional to the normal pressure, until the shear force reaches the maximum static friction force, at which point the primary and secondary contact surfaces slide tangentially. The principle behind outputting structural characteristic data and dynamic response parameters at each simulation step size is as follows: The structural feature data includes time history data of soil loss and dynamic shear strength, and the time history of the structural feature data corresponds to the time history of the seismic wave data. Seismic wave samples are input into the finite element model of the energy island's foundation structure. Within each simulation step, the material properties of the foundation structure of the finite element model are updated. The material properties include the material property data of the structural steel pile foundation, the geotechnical test parameters of the seabed soil, the depth, width, and slope of the scour pit, and the fluid property data of the fluid domain. The finite element model is simulated. At the end of each simulation step, the soil loss and dynamic shear strength of the finite element model are output as the structural feature data of that simulation step. Each simulation step corresponds to a set of structural feature data, thereby obtaining the structural feature data of the finite element model under each simulation step for each seismic wave sample. The dynamic response parameters include the time history data of the relative horizontal displacement between the bottom and top of the structural steel pile foundation, the time history data of the maximum bending moment of the pile body along the depth direction, and the time history data of the shear stress at the soil-structure contact surface. The principle for obtaining the time history data of the relative horizontal displacement between the bottom and top of the structural steel pile foundation for each seismic wave sample is as follows: the bottom center point and top center point of each pile foundation in the finite element model are selected as the bottom node and top node, respectively. The real-time position of the bottom node and top node of each pile foundation under each simulation step is obtained. Based on the real-time position, the real-time relative horizontal displacement of each pile foundation under each simulation step is calculated. The average relative horizontal displacement under the simulation step is obtained by averaging the real-time relative horizontal displacement of all pile foundations. The average relative horizontal displacement under all simulation steps is summarized to form the time history data of the relative horizontal displacement between the bottom and top of the structural steel pile foundation. The principle for obtaining the time history data of the maximum bending moment of the pile along the depth direction is as follows: In the finite element model, monitoring sections are set along the depth direction of the structural steel pile foundation at intervals of 0.5 times the pile diameter, and several monitoring points are set on each monitoring section. The normal stress of each monitoring point is obtained at each simulation step. Based on the normal stress of all monitoring points, the bending moment value of the monitoring section is obtained. The maximum bending moment value of all monitoring sections under each simulation step is taken as the maximum bending moment of the pile under that simulation step. The maximum bending moment of the pile under all simulation steps is summarized to form the time history data of the maximum bending moment of the pile along the depth direction. The principle for obtaining the time history data of shear stress at the soil-structure contact surface is as follows: In the finite element model, the main contact surface is discretized into several main contact points. Each main contact point has a corresponding secondary contact point on the secondary contact surface. Each main contact point and its corresponding secondary contact point together constitute a contact point pair. For each contact point pair, the tangential shear stress between the contact point pairs is simulated, and the average value of the tangential shear stress of all contact point pairs is taken to obtain the soil-structure contact surface shear stress at each simulation step. Based on the soil-structure contact surface shear stress at all simulation steps, the soil-structure contact surface shear stress time history data is generated.

2. The seismic load simulation method for the foundation of a marine energy island according to claim 1, characterized in that: The principle underlying the construction of the seismic wave sample library in step 2 is as follows: Historical seismic wave data of the area where the energy island is located are collected, and several artificial seismic waves are synthesized based on the historical seismic wave data. A seismic wave sample library is constructed based on the historical and artificial seismic waves. The seismic wave sample library contains several historical and artificial seismic waves, and these seismic waves are all seismic wave samples. Each seismic wave sample includes its acceleration time history, velocity time history, displacement time history, response spectrum, and earthquake duration. For each seismic wave sample, its earthquake duration is divided into equal intervals to generate several simulation step sizes.

3. The seismic load simulation method for the foundation of a marine energy island according to claim 1, characterized in that: The principle underlying step 4 for fitting the characteristic response values ​​of different dynamic response parameters under a specific exceedance probability is as follows: The time history data of horizontal displacement, maximum bending moment and soil-structure contact shear stress were obtained for each seismic wave sample. Local maxima were extracted from each set of time history data. The local maxima corresponding to each dynamic response parameter under all seismic wave samples were summarized to form the datasets of horizontal displacement maximum value, maximum bending moment maximum value and shear stress maximum value respectively. The principle for calculating the feature response value is as follows: Based on the maximum value dataset of the dynamic response parameter, calculate the location parameter, scale parameter, and shape parameter of the dynamic response parameter; then generate a cumulative distribution function based on the location parameter, scale parameter, and shape parameter; set a specific exceedance probability of 10%, and the feature response value is represented on the cumulative distribution function by setting the function value to 1 minus the value of the independent variable corresponding to the specific exceedance probability; calculate the feature response value of each dynamic response parameter with an exceedance probability of 10% based on the cumulative distribution function of each dynamic response parameter.

4. The seismic load simulation method for the foundation of a marine energy island according to claim 3, characterized in that: The principle behind the safety assessment of the energy island based on the safety factor in step 4 is as follows: The safety factor is the quotient of the allowable value and the characteristic response value, where the allowable value represents a threshold pre-set according to design specifications and safety standards. The safety factor for each dynamic response parameter is calculated separately. When all safety factors are greater than 1.2, the structure is judged to be safe, and no reinforcement or monitoring measures are implemented. When there are safety factors between 1.0 and 1.2, and no safety factors are less than 1, the structure is judged to be basically safe, and monitoring measures are implemented. When there are safety factors less than 1, the structure is judged to be unsafe, and reinforcement measures are implemented.

5. A seismic load simulation system for the foundation of an offshore energy island, characterized in that: The system is used to implement the seismic load simulation method for the foundation of a marine energy island as described in any one of claims 1-4, specifically including: The model building module is used to build a finite element model of the energy island's basic structure, which includes structural steel pile foundations, seabed soil, and fluid domain, and defines the soil-structure coupling boundary of the finite element model. The sample construction module is used to build a seismic wave sample library based on historical seismic wave data of the area where the energy island is located. For each seismic wave sample, the simulation time interval is determined and the simulation step size is divided based on its time history. The feature simulation module is used to introduce a dynamic update mechanism to update the material properties of the foundation structure at each simulation step for each seismic wave sample during the simulation using the finite element model, and then output the structural feature data and dynamic response parameters at each simulation step. The comprehensive output module is used to extract the maximum value from the response time history of each dynamic response parameter, construct a maximum value dataset, perform probabilistic statistical analysis on the maximum value dataset, fit the characteristic response value of different dynamic response parameters under a specific exceedance probability, compare the characteristic response value of various dynamic response parameters with their allowable value, generate multiple safety factors, and conduct a safety assessment of the energy island based on the safety factors.

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