Self-adaptive hydrodynamic load calculation method for large-diameter single pile

Abstract

The invention discloses a self-adaptive hydrodynamic load calculation method for a large-diameter single pile. The self-adaptive hydrodynamic load calculation method comprises the following steps: determining geometrical parameters of a large-diameter single pile foundation and establishing a coordinate system; determining a water depth and irregular wave surface time sequence; the discrete amplitude, circular frequency and wavelength of the irregular waves are obtained; distinguishing a low-frequency band and a high-frequency band according to the relationship between the wavelength and the single pile diameter; the wave load of the low-frequency band on the large-diameter single pile at the current moment is calculated; the wave load of the high-frequency band on the large-diameter single pile at the current moment is calculated; 5, the total wave load on the large-diameter single pile at the current moment is obtained through integration, the simulation process is started from the moment 0 to the preset moment T, and if the simulation time does not reach the preset moment T, the fifth step is executed again until the moment T is reached. According to the calculation method, the hydrodynamic load calculation of the large-diameter single-pile foundation is more accurate.

Description

Technical Field

[0001] This invention belongs to the technical field of offshore wind power structure design, and specifically relates to an adaptive hydrodynamic load calculation method for large-diameter monopiles. Background Technology

[0002] Monopile foundations are currently the most mature structural type for offshore wind power. As the water depth for offshore wind power construction continues to increase, the dynamic and aerodynamic loads in deep-sea waters increase significantly, requiring larger diameter monopile foundations to meet strength requirements. Large-diameter monopile foundations have thus attracted widespread attention.

[0003] However, the current calculation method for the hydrodynamic load of large-diameter monopile foundations is not clear. Directly applying the existing calculation method for small-diameter monopile foundations ignores the diffraction effect of high-frequency waves at large-diameter sections, thus making it inaccurate. Summary of the Invention

[0004] This invention provides an adaptive hydrodynamic load calculation method for large-diameter monopile foundations to solve the problem that the hydrodynamic load calculation methods for large-diameter monopile foundations are not accurate enough.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: An adaptive hydrodynamic load calculation method for large-diameter monopiles includes the following steps: Step 1: Determine the geometric parameters of the large-diameter monopile foundation and establish a coordinate system; Step 2: Determine the water depth and irregular wave surface time series; Step 3: Obtain the amplitude, angular frequency, and wavelength of the irregular wave discrete data; Step 4: Differentiate between low-frequency and high-frequency bands based on the relationship between wavelength and single pile diameter; Step 5: Calculate the low-frequency wave load on the large-diameter monopile at the current moment; Step 6: Calculate the high-frequency wave load on the large-diameter monopile at the current moment; Step 7: Integrate the total wave load on the large-diameter monopile at the current moment. The simulation process starts at time 0 and ends at the preset time T. If the simulation time has not reached the preset time T, return to step 5 and continue until time T. Furthermore, in the process of establishing the coordinate system in step one, the intersection of the central axis of the single pile and the sea level is taken as the origin O of the coordinate system, the X-axis is along the direction of wave propagation, the Y-axis is perpendicular to the direction of wave propagation, and the Z-axis is vertically upward.

[0006] Furthermore, the water depth is obtained in step two. h At that time, the on-site measured data was used, that is, the sonar depth sounder was used to continuously measure the center position of the single pile foundation for 10 minutes and the average value was taken.

[0007] Furthermore, in step two, when determining the irregular wave surface time series using actual measurement methods, wave buoys are deployed near the monopile foundation to record the change in sea level relative to the still water surface over time, with a sampling frequency of 1 Hz and continuous collection for more than 24 hours.

[0008] Furthermore, in step three, the wavefront sequence is subjected to Fast Fourier Transform (FFT) to determine the discrete amplitude, angular frequency, and wavelength of the irregular waves. The specific process of using FFT to determine the discrete amplitude, angular frequency, and wavelength of the irregular waves is as follows: ; in, For the first n The amplitude of each wave; For the first n The angular frequency of the wave; For the first n The phase of each wave can be a random number; No. n wavelength of each wave and The following relationship exists: ; Thus, the wavelength is determined. , g It is the acceleration due to gravity. h The water is deep.

[0009] Furthermore, in step four, the ratio of the cross-sectional diameter to the wave wavelength is used as the metric: Low frequency band: ; High frequency band: ; in, D The outer diameter of a single pile. For the first n The wavelength of each wave.

[0010] Furthermore, in step five, the wave load is calculated according to the Morrison equation using the following formula. : ; ; ; in, It is an inertial force. For velocity force; The inertia coefficient is typically taken as 2.0. This is the velocity-force coefficient, typically taken as 1.2; For fluid density, h Because of the water depth,D The outer diameter of a single pile. For the first n The horizontal velocity of water particles in a wave.

[0011] Furthermore, in step six, high-frequency wave loads on large-diameter monopiles... The calculation formula is: ; in, For the side surface of a single pile foundation, For fluid density, Let be the scattering potential of the nth wave. Let n be the angular frequency of the nth wave. Let i be a field point on the integral surface, where i is the imaginary unit. This represents the phase of the nth wave.

[0012] Furthermore, step six involves calculating the high-frequency wave load on the large-diameter monopile. Previously, boundary element meshes were generated on the surface of the monopile foundation. Quadrilateral or triangular mesh elements were generated along the z-axis from the seabed to the sea level. The total number of elements M was determined according to the accuracy requirements. Establish boundary integral equations: in the computational domain Establish the wave scattering potential caused by the interaction of the nth incident wave and the single pile. Boundary integral equations: ; in, Let n be the incident potential of the nth wave. Let be the scattering potential of the nth wave. The source point of the boundary element method, For the field points on the integral surface, For the side surface of a single pile foundation, The fixed angle factor, This is the Green's function.

[0013] Furthermore, in step seven, the total wave load is calculated. F hour: ; For low-frequency wave loads on large-diameter monopiles, This refers to high-frequency wave loads on large-diameter monopiles.

[0014] The present invention can achieve the following beneficial effects: 1. Traditional methods directly apply Morrison's equations for small-diameter monopiles, completely ignoring the high-frequency wave diffraction effects faced by large-diameter monopiles, leading to significant errors in load calculation. This solution automatically divides the load into low-frequency and high-frequency bands, using different methods to calculate the load for each band. The final integrated load more closely reflects the actual sea conditions in deep-sea areas. This calculation method keeps the error between the load calculation results and physical model test data within a reasonable range, avoiding safety accidents such as cracking and overturning of the monopile structure due to underestimation of the load, and also avoiding redundant steel usage due to overestimation of the load, thus balancing project safety and economy.

[0015] 2. This application requires no manual pre-setting of calculation methods or adjustment of parameters. It can automatically adapt to two key scenarios simply by using low-frequency and high-frequency band judgment criteria: one is large-diameter monopiles of different diameters; the other is irregular waves under different sea conditions. Compared with traditional methods that require manual modification of formulas or coefficients for different pile diameters and sea conditions, the adaptive nature of this solution greatly reduces operational complexity, reduces errors caused by manual intervention, and improves the universality of the method, covering various deep-sea wind power projects. Attached Figure Description

[0016] The present invention will be further described below with reference to the accompanying drawings and embodiments: Figure 1 This is a flowchart of the calculation method of the present invention; Figure 2 This is a schematic diagram of the coordinate system established by the present invention for the interaction between waves and large-diameter monopiles; Figure 3 This invention provides a time series diagram of an irregular wave surface. Figure 4 This invention provides an irregular wave amplitude spectrum obtained by fast Fourier transform. Figure 5 This is a schematic diagram of the boundary element mesh generation on the surface of a large-diameter single pile according to the present invention; Figure 6 This is a comparison chart of the results of the adaptive hydrodynamic load calculation method of the present invention and the results of the traditional small-diameter monopile hydrodynamic load calculation method. Detailed Implementation

[0017] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings, which illustrate embodiments of the present application. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of this application will be thorough and complete.

[0018] An adaptive hydrodynamic load calculation method for large-diameter monopiles, such as Figure 1 As shown, it includes the following steps: Step 1: Determine the geometric parameters of the large-diameter monopile foundation and establish a coordinate system.

[0019] Determine the geometric parameters of a single pile: Determine the outer diameter of the single pile. D By determining accurate geometric parameters of individual piles, the accuracy of subsequent load calculations can be ensured.

[0020] Establish a coordinate system: such as Figure 2 As shown, the origin of the coordinate system is the intersection of the central axis of the single pile and the sea level. O ; X The axis is along the direction of wave propagation, in the embodiments of this application. X The axis is horizontal to the right, consistent with the main direction of the load; Y The axis is perpendicular to the wave propagation direction, as described in this embodiment. Y The axis is horizontal and forward; Z The axis is vertically upward. Z= 0 represents sea level, and the coordinate system is as follows: Figure 2 As shown. A unified coordinate system is established to provide a consistent spatial reference for subsequent steps and ensure the continuity of the calculation logic.

[0021] Step 2: Determine the water depth and the time series of irregular wave surfaces. In this embodiment, the water depth is determined. h The time series of irregular wave surfaces is 45m long. Figure 3 As shown; water depth h The data used was the actual on-site measurement data, which was obtained by continuously measuring the water depth at the center of a single pile foundation for 10 minutes using a sonar depth sounder and taking the average value, rather than the regional average water depth.

[0022] Obtaining time series of irregular wave surfaces The methods include both field measurement and numerical simulation. Field measurement involves deploying wave buoys near the monopile foundation to record the change in sea level relative to the still water surface over time, with a sampling frequency... 1 Hz, continuous data collection for more than 24 hours. If on-site measurement is not feasible, use... Swan , MIKE21-SW The wave numerical model takes parameters such as wind field (wind speed, wind direction), water depth, and seabed friction coefficient as input and simulates to generate wave surface time series that match the actual sea conditions.

[0023] Step 3: Obtain the discrete amplitude, angular frequency, and wavelength of the irregular wave. A Fast Fourier Transform is applied to the wavefront sequence to determine the discrete amplitude, angular frequency, and wavelength of the irregular wave. In this embodiment, the wavefront sequence is as follows: Figure 3 As shown, the amplitude, angular frequency, and wavelength of the irregular wave determined after Fast Fourier Transform are as follows: Figure 4 As shown.

[0024] The process is as follows: ; in, For the first n The amplitude of each wave; For the first n The angular frequency of the wave; For the first n The phase of each wave can be a random number; No. n wavelength of each wave and The following relationship exists: ; Thus, the wavelength is determined. , g It is the acceleration due to gravity. h The water is deep.

[0025] In this embodiment, the specific information regarding the amplitude, angular frequency, and wavelength of the irregular wave discrete is shown in the table below:

[0026] Step 4: Distinguish between low-frequency and high-frequency bands based on the relationship between wavelength and single pile diameter, using the ratio of cross-sectional diameter to wave wavelength as the metric.

[0027] Specifically, the following relationships should be used for judgment: Low frequency band: ; High frequency band: ; In the low-frequency band, the pile diameter is relatively small compared to the wavelength, and there is no obvious wave surface deformation when the wave flows around the pile, so the effect of wave diffraction can be ignored. In the high-frequency band, the pile diameter is relatively large compared to the wavelength, and the effect of wave diffraction cannot be ignored. That is, the wave front flows around both sides of the pile body, the wave surface in front of the pile rises, the pressure increases, and a shadow area is formed behind the pile, the pressure decreases. At the same time, reflected waves are generated, resulting in an additional diffraction force in the load.

[0028] Step 5: Calculate the low-frequency wave load on the large-diameter monopile at the current moment. The calculation is performed according to the Morrison equation using the following formula: ; ; ; in, It is an inertial force. For velocity force; The inertia coefficient is typically taken as 2.0. This is the velocity-force coefficient, typically taken as 1.2; For fluid density, D The outer diameter of a single pile. For the first n The horizontal velocity of a water particle in a wave can be calculated using the following formula: ; ; in, For the first n The incident potential of a wave, For the first n The number of waves in a wave. It is the acceleration due to gravity. For the first n The amplitude of each wave, For the first n The angular frequency of a wave.

[0029] Step 6: Calculate the high-frequency wave load on the large-diameter monopile at the current moment.

[0030] Boundary element mesh generation: Based on potential flow theory, a boundary element mesh is generated on the surface of the monopile foundation. Quadrilateral or triangular mesh elements are generated along the z-axis from the seabed to the sea level. The total number of elements is... M Based on the accuracy requirements, the discrete boundary element mesh of the basic surface in this embodiment is as follows: Figure 5 As shown.

[0031] Establish boundary integral equations: in the computational domain Establish the wave scattering potential caused by the interaction of the nth incident wave and the single pile. Boundary integral equations: ; in, Let n be the incident potential of the nth wave. The source point of the boundary element method, For the field points on the integral surface, For the side surface of a single pile foundation, The fixed angle factor is calculated using the following formula: ; Let be the Green's function, satisfying the Laplace governing equations, free surface boundary conditions, seabed boundary conditions, and far-field radiation conditions, and its expression is as follows: ; in, ; ; in, J0 represents the 0th order Bessel function. This represents the distance between the source point and the field point. This represents the distance between the source point's mirror image with respect to the seabed and the field point.

[0032] The boundary integral equations are processed using the collocation method to obtain a system of equations.

[0033]

[0034] The scattering potential was calculated. The high-frequency wave load on a large-diameter monopile can be obtained using the following formula. : ; in, For the side surface of a single pile foundation, For fluid density, Let be the scattering potential of the nth wave. Let n be the angular frequency of the nth wave. Let i be a field point on the integral surface, where i is the imaginary unit. This represents the phase of the nth wave.

[0035] Step 7: Integrate to obtain the total wave load on the large-diameter monopile at the current moment. F : ; in, For high-frequency wave loads on large-diameter monopiles, This refers to low-frequency wave loads on large-diameter monopiles.

[0036] The simulation begins at time 0 and ends at a preset time T. If the simulation time has not reached the preset time T, it returns to step five and continues until time T. The preset time T covers 30-50 wave spectrum peak periods to ensure comprehensive load statistics. The time step Δt must be less than 1 / 10 of the shortest wave period to avoid missing load peaks. Figure 6 The figure shown is a comparison between the calculation results of the method in this application and the calculation results of the hydrodynamic load of a traditional small-diameter monopile.

[0037] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A self-adaptive hydrodynamic load calculation method for large-diameter single piles, characterized by, Comprising the following steps: Step one, determine the geometric parameters of large diameter single pile foundation and establish the coordinate system; Step two, determine the water depth and irregular wave surface time series; Step three, get the discrete wave amplitude, circular frequency and wavelength of irregular wave; Step four, according to the relationship between wavelength and single pile diameter, distinguish low frequency band and high frequency band; Step five: calculate the wave load of low frequency band on large diameter single pile at the current time; Step six, calculate the wave load of high frequency band on large diameter single pile at the current time; Step seven, integrate the total wave load on large diameter single pile at the current time, the simulation process starts from 0 time, to the preset T time, if the simulation time is not to the preset T time, then go back to step five continue, until T time.

2. The self-adaptive hydrodynamic load calculation method for large-diameter single piles according to claim 1, characterized in that: In the process of establishing coordinate system in step one, the intersection of single pile center axis and sea level is taken as the origin O, X axis along the wave propagation direction, Y axis perpendicular to the wave propagation direction, Z axis vertically upward.

3. The self-adaptive hydrodynamic load calculation method for large-diameter single piles according to claim 1, characterized in that: In step two, the water depth is obtained by using the field measured data, i.e. by using the continuous measurement of 10 minutes by the echo sounder at the center position of the single pile foundation and taking the average value. h In step two, the water depth is obtained by using the field measured data, i.e. by using the continuous measurement of 10 minutes by the echo sounder at the center position of the single pile foundation and 4. The self-adaptive hydrodynamic load calculation method for large-diameter single piles according to claim 1, characterized in that: In step two, the determination of irregular wave surface time series is obtained by using the measured method, wave buoys are arranged near the single pile foundation, the height of sea level relative to the static water surface is recorded with time, the sampling frequency is 1 Hz, and the sampling is collected for more than 24 hours.

5. The self-adaptive hydrodynamic load calculation method for large-diameter single piles according to claim 1, characterized in that: In step three, the wave surface sequence is determined by using fast Fourier transform to determine the discrete wave amplitude, circular frequency and wavelength of irregular wave, the specific process is as follows: ； in, For the first n The amplitude of each wave; For the first n The angular frequency of the wave; For the first n The phase of each wave can be a random number; The wavelength of the first wave n has the following relationship with the wavelength of the second wave has the following relationship with the wavelength of the second wave has the following relationship with the wavelength of the second wave ； to determine the wavelength , g is the gravitational acceleration, h is the water depth.

6. The self-adapting hydrodynamic load calculation method for large-diameter single piles according to claim 1, characterized in that: In step four, the ratio of cross section diameter to wave length is taken as the measurement value: Low frequency band: ; High frequency band: ; wherein, D is the outer diameter of the single pile, is the wavelength of the n th wave.

7. The self-adapting hydrodynamic load calculation method for large-diameter single piles according to claim 1, characterized in that: In step five, the wave load is calculated according to Morison's equation as follows : ； ； ； in, It is an inertial force. For velocity force; The inertia coefficient is typically taken as 2.

0. This is the velocity-force coefficient, typically taken as 1.2; For fluid density, h Because of the water depth, D The outer diameter of a single pile. For the first n The horizontal velocity of water particles in a wave.

8. The self-adapting hydrodynamic load calculation method for large-diameter single piles according to claim 1, characterized in that: In step six, the calculation formula of the high-frequency wave load on the large-diameter single pile is as follows: ； wherein is a single pile foundation side surface, is a fluid density, is the scattering potential of the nth wave, is the circular frequency of the nth wave, is a field point on the integration surface, i is the imaginary unit, is the phase of the nth wave.

9. The self-adapting hydrodynamic load calculation method for large-diameter single piles according to claim 8, characterized in that: Step six in calculating the wave load on large diameter single pile in high frequency band Previously, the boundary element mesh is divided on the surface of single pile foundation. The quadrilateral or triangular mesh units are divided along the elevation from the sea bottom to the sea level. The total number of units M is determined according to the accuracy requirement. Establish the boundary integral equation: within the computational domain for the nth incident wave and the wave scattering potential due to the interaction of the nth incident wave and the single pile ； where, is the incident potential of the nth wave, is the scattering potential of the nth wave, is the source point of the boundary element method, is the field point on the integration surface, is the side surface of the single pile foundation, is the fixed angle coefficient, is the Green's function.

10. The self-adapting hydrodynamic load calculation method for large-diameter single piles according to claim 1, characterized in that: In step seven, the total wave load is calculated F when: ； For large diameter single pile on the low frequency band of wave load frequency, For large diameter single pile on the high frequency band of wave load.

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