Method for determining horizontal ultimate bearing capacity of winged large-diameter single pile of offshore wind turbine

Abstract

The invention provides a method for determining the horizontal ultimate bearing capacity of a winged large-diameter single pile of an offshore wind turbine, and the method comprises the following steps: S1, determining the geometric dimension parameters of a winged large-diameter single pile foundation, and calculating the equivalent pile diameter of the winged single pile; s2, after normalization is carried out according to the equivalent pile diameter, when the pile-soil contact problem is considered, the pile-soil interface roughness coefficient alpha is 1; s3, calculating the horizontal ultimate bearing capacity pu of the winged pile; s4, a wing plate rigidity reduction factor F is considered, and the equivalent pile diameter is corrected; and S5, based on the corrected equivalent pile diameter, the horizontal ultimate bearing capacity is recalculated. According to the method for evaluating the horizontal bearing performance of the winged large-diameter single pile foundation, the horizontal bearing performance of the foundation can be rapidly and accurately predicted without three-dimensional finite element simulation, and the method has important engineering practical significance.

Description

Technical Field

[0001] This invention belongs to the field of marine wind power technology, specifically relating to a method for determining the horizontal ultimate bearing capacity of a large-diameter monopile with fins for offshore wind turbines. Background Technology

[0002] my country's coastal waters are characterized by a wide distribution of deep, soft soil layers with low strength, susceptibility to erosion, and significant anisotropy. This leads to problems with traditional monopile foundations, such as low utilization of shallow soil resistance and excessive cumulative deformation under long-term low-frequency cyclic loading, severely restricting the economic efficiency and safety of the foundations. Composite foundations are an effective and innovative solution for complex geological conditions (such as thick silt, undulating rock surfaces, and shallow bedrock). For example, the Putian Pinghai Bay Phase II project and the Dalian Zhuanghe V wind farm have successfully applied pile-bucket composite foundations. Currently, the research and application of new offshore wind power structures are being continuously deepened to adapt to complex geological conditions and promote cost reduction and efficiency improvement in the industry. The research and development of composite wind power pile foundations cannot be ignored.

[0003] In recent years, winged pile foundations, a type of composite foundation, have emerged. By adding radial flanges to a monopile foundation, soil erosion can be effectively reduced and the resistance of shallow soil can be improved. Successful pilot projects have been conducted in offshore areas such as Rudong, Jiangsu, and Pingtan, Fujian, achieving a reduction in monopile length. However, existing research largely focuses on analyzing the erosion-resistant effect of flanges in sandy soil strata, and related studies on horizontal bearing characteristics rely heavily on three-dimensional finite element numerical simulations. There is a lack of design methods for winged pile foundations in engineering, especially methods for calculating the horizontal ultimate bearing capacity. Therefore, establishing a method for assessing the horizontal ultimate bearing capacity of large-diameter winged monopile foundations for offshore wind turbines on soft soil foundations, and enabling rapid assessment of the bearing capacity of composite foundations, is of significant engineering importance. Summary of the Invention

[0004] The main objective of this invention is to provide a method for determining the horizontal ultimate bearing capacity of a large-diameter monopile with fins for offshore wind turbines, addressing the aforementioned problems.

[0005] Therefore, the above-mentioned objective of the present invention is achieved through the following technical solution:

[0006] A method for determining the ultimate horizontal bearing capacity of a large-diameter monopile with fins for offshore wind turbines includes the following steps:

[0007] S1. Determine the geometric dimensions of the large-diameter single pile foundation with flanges, including the single pile diameter D and the flange width. airfoil thickness t, airfoil elastic modulus E w The undrained shear strength of the soil was measured. Soil elastic modulus E s Calculate the equivalent pile diameter D of a single pile with wings. * ;

[0008] S2, according to the equivalent pile diameter D *After normalization, when considering the pile-soil contact problem, the roughness coefficient α of the pile-soil interface is taken as 1.

[0009] S3, Calculate the ultimate horizontal bearing capacity p of the winged pile u ;

[0010] S4. Considering the flange stiffness reduction factor F, for the equivalent pile diameter D * Make corrections;

[0011] S5, Based on the modified equivalent pile diameter D * The horizontal ultimate bearing capacity is recalculated.

[0012] While adopting the above technical solutions, the present invention may also adopt or combine the following technical solutions:

[0013] As a preferred technical solution of the present invention: In step S1, the equivalent pile diameter D * As shown in the following formula:

[0014] =

[0015] In the formula, D is the diameter of a single pile. This refers to the width of the airfoil.

[0016] As a preferred technical solution of the present invention: In step S3, the horizontal ultimate bearing capacity p of the winged pile u As shown in the following formula:

[0017]

[0018] In the formula, This is the ultimate bearing capacity coefficient. This represents the undrained shear strength of the soil.

[0019] As a preferred technical solution of the present invention: the horizontal ultimate bearing capacity coefficient of the winged pile As shown in the following formula:

[0020]

[0021] In the formula, N1 = 11.94; N2 = 3.22; N flow γ is the ultimate bearing capacity coefficient of a two-dimensional or deep advection mechanism; z is the depth below the mud surface; γ' is the effective unit weight of the soil; N flow Corresponding critical depth z r .

[0022] As a preferred technical solution of the present invention: the ultimate bearing capacity coefficient N of the two-dimensional or deep advection mechanism flow As shown in the following formula:

[0023] Nflow =

[0024] In the formula, α is the roughness of the pile-soil interface, which is taken as 1 in the calculation of winged piles.

[0025] As a preferred technical solution of the present invention: critical depth z r As shown in the following formula:

[0026]

[0027] In the formula, γ' is the effective unit weight of the soil.

[0028] As a preferred technical solution of the present invention: In step S4, the equivalent pile diameter D * The correction is shown in the following formula:

[0029]

[0030] In the formula, F is the flange stiffness reduction factor, 0≤F≤1.

[0031] As a preferred embodiment of the present invention: In step S4, the flange stiffness reduction factor F is as follows:

[0032]

[0033] In the formula, C w The calibration coefficient is set to 1.1 × 10⁻⁶. -5 E s E represents the elastic modulus of the soil. w t is the elastic modulus of the airfoil; t is the thickness of the airfoil.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1) This invention innovatively proposes a method for evaluating the horizontal bearing capacity of a wing-large diameter monopile composite foundation that meets engineering practicality. It can quickly and accurately predict the horizontal bearing capacity of the foundation without the need for three-dimensional finite element simulation, which has important engineering practical significance.

[0036] 2) Starting from the stress and deformation characteristics of the winged pile segment, this invention fully considers the enhancing effect of the pile perimeter wing plate on the bearing capacity of the single pile foundation, and also considers the influence of the wing plate stiffness on the bearing capacity of the foundation. It is applicable to winged plate piles of different sizes and stiffnesses, and further improves the accuracy of the horizontal bearing capacity assessment of winged large-diameter single pile foundations.

[0037] 3) This invention can provide key technical support and necessary analysis methods for the design of large-diameter monopile foundations with wing for offshore wind turbines in soft soil foundations in marine environments. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the cross-section of a large-diameter single pile foundation with wings.

[0039] Figure 2a The ultimate bearing capacity profile and experimental and finite element results when α=0.

[0040] Figure 2b The ultimate bearing capacity profile and experimental and finite element results when α=1.

[0041] Figure 3 This is a three-dimensional view of a single pile segment with wings.

[0042] Figure 4 A simplified mechanical diagram of a winged pile element.

[0043] Figure 5 This represents the relationship between the stiffness reduction factor and the corresponding combination factor.

[0044] Figure 6 This is a modified profile of the pile-soil bearing capacity for different flange stiffnesses.

[0045] Figure 7 To compare the results of the calculation with the finite element simulation of the horizontal load transfer curve of a large-diameter single pile with wings. Detailed Implementation

[0046] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0047] A method for determining the ultimate horizontal bearing capacity of a large-diameter monopile with fins for offshore wind turbines, specifically including the following steps:

[0048] S1, such as Figure 1 As shown, the geometric dimensional parameters of a large-diameter monopile foundation with flanges are determined, including the monopile diameter D and the flange width. airfoil thickness t, airfoil elastic modulus E w The undrained shear strength of the soil was measured. Soil elastic modulus E s Calculate the equivalent pile diameter D of a single pile with wings. * As shown in the following formula:

[0049] =

[0050] In the formula, D is the diameter of a single pile. The width of the wingplate;

[0051] S2, according to the equivalent pile diameter D * After normalization, when considering the pile-soil contact problem, regardless of the original single pile foundation pile-soil interface roughness coefficient α (α=0~1), the pile-soil interface roughness coefficient α should be calculated as 1.

[0052] S3, Calculate the ultimate horizontal bearing capacity p of the winged pile u As shown in the following formula:

[0053]

[0054] In the formula, This is the ultimate bearing capacity coefficient. The undrained shear strength of the soil;

[0055] Ultimate bearing capacity coefficient of winged piles As shown in the following formula:

[0056]

[0057] In the formula, N1 = 11.94; N2 = 3.22; N flow γ is the ultimate bearing capacity coefficient of a two-dimensional or deep advection mechanism; z is the depth below the mud surface; γ' is the effective unit weight of the soil; N flow Corresponding critical depth z r ;

[0058] Ultimate bearing capacity coefficient N of two-dimensional or deep advection mechanism flow As shown in the following formula:

[0059] N flow =

[0060] In the formula, α is the roughness of the pile-soil interface, which is taken as 1 in the calculation of winged piles;

[0061] When z reaches the critical depth tending towards N flow Critical depth z r As shown in the following formula:

[0062]

[0063] In the formula, γ' is the effective unit weight of the soil;

[0064] Using the above formula combined with the equivalent pile diameter can effectively capture the horizontal translational ultimate bearing capacity of winged piles with different flange widths. The comparison and verification with the finite element simulation results are as follows: Figures 2a-2b As shown;

[0065] The ultimate bearing capacity under loading at 45° is not much different from that under loading at less than 0°. Therefore, the bearing capacity of large-diameter single pile foundations with wings is based on loading at 0°.

[0066] The above formula neglects the effect of flange deformation, i.e., the flange stiffness is infinite. The influence of flange bending stiffness on pile side bearing capacity is considered as follows: For other cases with finite stiffness, the equivalent pile diameter can be considered as the difference between the pile diameter D and the equivalent pile diameter D0.* Transitional changes.

[0067] S4. Considering the flange stiffness reduction factor F, for the equivalent pile diameter D * The correction is shown in the following formula:

[0068]

[0069] In the formula, F is the airfoil stiffness reduction factor, 0≤F≤1, F=0 indicates that the airfoil stiffness is 0 and does not contribute to the lateral resistance performance; F=1 indicates that the airfoil is completely rigid and is a complete airfoil; F=0-1 indicates a non-complete airfoil.

[0070] Considering the actual stiffness of the airfoil, the airfoil stiffness reduction factor F is calculated using the following formula:

[0071]

[0072] In the formula, C w The calibration coefficient is set to 1.1 × 10⁻⁶. -5 E s E represents the elastic modulus of the soil. w t is the elastic modulus of the airfoil; t is the thickness of the airfoil.

[0073] When analyzing horizontally loaded pile problems using the Winkler foundation beam model, the pile foundation is equivalent to a Winkler elastic foundation beam. The horizontal resistance provided by the soil along the pile is represented by a distributed py curve, where p is the soil reaction force and y is the horizontal displacement of the pile foundation. The nonlinear relationship between the soil reaction force and displacement is determined by the following formula:

[0074]

[0075] In the formula, the combination factor Soil stiffness coefficient ;κ=K in / E s The initial stiffness of the pile and soil is an elastic problem. In the two-dimensional case, the initial stiffness K is... in Approximately 1.35E s M c p is the shear strain coefficient of the pile and soil. u It refers to the ultimate horizontal bearing capacity of the pile side, for single pile foundations. For winged monopile foundations N p , This is the ultimate bearing capacity coefficient. This formula assumes that the soil conforms to a hyperbolic stress-strain relationship.

[0076] S5, Based on the modified equivalent pile diameter D * The horizontal ultimate bearing capacity is recalculated.

[0077] The ultimate bearing capacity coefficient under deep flow conditions mainly depends on the equivalent pile diameter D. * Since the bearing capacity coefficient is relatively stable, the flange stiffness reduction factor is further replaced with:

[0078]

[0079] In the formula, E w It is the elastic modulus of the airfoil. Let F be the moment of inertia of the flange section. Based on this, the stiffness factor F can be evaluated using finite element analysis.

[0080] The stiffness reduction factor F is analyzed based on a simplified mechanical model of winged pile elements, such as... Figure 3-4 As shown, the edges of the flanges undergo relative deflection during the pile's movement. The deflection at the free end of the cantilever beam under the ultimate condition is:

[0081]

[0082] In the formula, dh is the height of the pile element, and t is the thickness of the flange. q a and q p These are the active and passive earth pressures, respectively. According to Rankine's earth pressure theory, the difference between the two is 4s. u dh.

[0083] Therefore, the ratio Represented as:

[0084]

[0085] In the formula, It is the horizontal displacement of the pile body, E s It is the elastic modulus of soil. It is the soil stiffness coefficient. The normalized horizontal displacement when the pile reaches its ultimate state. If the numerical value is relatively stable, then the stiffness reduction factor F of the flange mainly depends on the combination factor. .

[0086] The relationship between the stiffness reduction factor F and the combination factor calibrated by finite element calculation is as follows: Figure 5 As shown, the relationship is inversely proportional. This invention introduces parameter C. w Calibrate it:

[0087]

[0088] In the formula, C w The calibration coefficient is set to 1.1 × 10⁻⁶. -5 E s E represents the elastic modulus of the soil. w t is the elastic modulus of the airfoil; t is the thickness of the airfoil.

[0089] For large-diameter single-pile foundations with flanges, after substituting the stiffness reduction factor F provided by this invention to obtain the equivalent pile diameter, the bearing capacity profile corresponding to different flange stiffnesses can be directly calculated, such as... Figure 6 As shown.

[0090] Although the wing plates of the winged piles are distributed at different angles to the loading direction, the ultimate bearing capacity of the loads loaded at each angle (0°-45°) is relatively small. Therefore, the bearing capacity calculation of the large-diameter single pile foundation with wing does not consider the influence of the loading direction.

[0091] Based on the py curve considering the stress-strain characteristics of the soil and the formula for the ultimate horizontal bearing capacity of the winged pile, the horizontal load transfer curves of the winged pile at different depths can be obtained.

[0092] The method for calculating the horizontal ultimate bearing capacity of a large-diameter monopile with wing for offshore wind turbines takes into account the equivalent pile diameter of the wing plate reinforcement area and calculates the influence of different wing plate stiffness on the horizontal ultimate bearing capacity, thereby obtaining the ultimate bearing capacity of a large-diameter monopile with wing plate under the actual wing plate stiffness.

[0093] Example

[0094] The Horns Rev wind farm project in Denmark features a monopile with a diameter of 5 m, a cantilever loading height of 10 m, a burial depth of 50 m, a flange width and height of 5 m, a flange thickness equal to the monopile wall thickness of 0.05 m, and a material elastic modulus of 210 GPa. The effective unit weight of the soft clay foundation on the seabed is 8 kN / m³. 3 The undrained shear strength is 30 kPa, the elastic modulus of the soil is 13.5 MPa, and the Poisson's ratio is 0.495.

[0095] (1) First, a three-dimensional finite element model was established in Abaqus finite element software for calculation. The pile body py curve at the middle depth (2.5 m burial depth) of the three-dimensional large-diameter winged pile plate was extracted and normalized according to the equivalent diameter to obtain Figure 7 Results of data points in the middle.

[0096] (2) Following the steps above, the horizontal load transfer curve of the winged pile is calculated using Matlab, and normalized using the equivalent diameter. Figure 7 The comparison of the curves shows that the load transfer curve of the winged pile foundation calculated by the method provided by the present invention is in good agreement with the finite element results, thus verifying the effectiveness of the method provided by the present invention.

[0097] The technical solution of the present invention has been described in conjunction with the specific experimental procedures shown in the accompanying drawings. However, the scope of protection of the present invention is not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions resulting from such changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A method for determining the ultimate horizontal bearing capacity of a large-diameter monopile with fins for offshore wind turbines, characterized in that, Includes the following steps: S1. Determine the geometric parameters of the winged large-diameter monopile foundation and calculate the equivalent pile diameter D of the winged monopile. * ; S2, according to the equivalent pile diameter D * After normalization, when considering the pile-soil contact problem, the roughness coefficient α of the pile-soil interface is taken as 1. S3, Calculate the ultimate horizontal bearing capacity p of the winged pile u ; S4. Considering the flange stiffness reduction factor F, for the equivalent pile diameter D * Make corrections; S5, Based on the modified equivalent pile diameter D * The horizontal ultimate bearing capacity is recalculated.

2. The method according to claim 1, characterized in that: In step S1, the equivalent pile diameter D * As shown in the following formula: = In the formula, D is the diameter of a single pile. This refers to the width of the airfoil.

3. The method according to claim 1, characterized in that: In step S3, the ultimate horizontal bearing capacity p of the winged pile u As shown in the following formula: In the formula, This is the ultimate bearing capacity coefficient. D represents the undrained shear strength of the soil. * This is the equivalent pile diameter.

4. The method according to claim 3, characterized in that: Ultimate bearing capacity coefficient of winged piles As shown in the following formula: In the formula, N1 = 11.94; N2 = 3.22; N flow is the ultimate bearing capacity coefficient of a two-dimensional or deep advection mechanism; z is the depth below the mud surface. γ' is the effective unit weight of the soil; N flow Corresponding critical depth z r .

5. The method according to claim 4, characterized in that: Ultimate bearing capacity coefficient N of two-dimensional or deep advection mechanism flow As shown in the following formula: N flow = In the formula, α is the roughness of the pile-soil interface, which is taken as 1 in the calculation of winged piles.

6. The method according to claim 4, characterized in that: Critical depth z r As shown in the following formula: In the formula, γ' is the effective unit weight of the soil.

7. The method according to claim 1, characterized in that: In step S4, the equivalent pile diameter D * The correction is shown in the following formula: In the formula, F is the flange stiffness reduction factor, 0≤F≤1.

8. The method according to claim 1, characterized in that: In step S4, the flange stiffness reduction factor F is as follows: In the formula, C w The calibration coefficient is set to 1.1 × 10⁻⁶. -5 E s E represents the elastic modulus of the soil. w t is the elastic modulus of the airfoil; t is the thickness of the airfoil.

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