An optimization method for calculating the horizontal ultimate bending bearing capacity of large-diameter single piles for offshore wind turbines

Abstract

The present invention discloses a method for optimizing the calculation of the horizontal ultimate bending bearing capacity of a large-diameter single pile for offshore wind turbines, comprising the following steps: (1) determining the geometrical dimension parameters of the large-diameter single pile; (2) measuring the undrained shear strength distribution of the seabed foundation soil; (3) determining the depth of the rotation point of the large-diameter single pile and the length from the rotation point to the pile bottom under the action of horizontal bending moment load; (4) calculating the contribution M of the soil in the depth range above the rotation point to the bending bearing capacity of the large-diameter single pile based on the horizontal ultimate soil resistance distribution around the pile. u1 (5) Calculate the contribution of the soil below the rotation point to the bending bearing capacity of the large diameter single pile based on the failure mode of the soil below the rotation point. u2 (6) The ultimate horizontal bending bearing capacity of a large diameter single pile M is finally calculated. u =M u1 +M u2 The present invention starts from the bearing mode of a large-diameter single pile and the failure mode of the soil around the pile, comprehensively considers the horizontal soil resistance and the additional resistance contribution of the large-diameter single pile base, and the calculation results are accurate and reliable.

Description

Technical Field

[0001] The present invention relates to the field of marine engineering technology, and in particular to a method for optimizing the calculation of the horizontal ultimate bending bearing capacity of a large-diameter single pile for an offshore wind turbine. Background Art

[0002] Vigorously developing offshore wind power is an important measure to achieve my country's "dual carbon" goals. At present, most of my country's offshore wind farms are located in offshore waters with a water depth of less than 40m. Within this water depth range, large-diameter single pile foundations have become the first choice and mainstream for offshore wind turbine foundations due to their simple structure, convenient installation, and mature construction technology and equipment. At present, large-diameter single pile foundations for offshore wind turbines are usually hollow steel pipe piles with a diameter of D = 5-10m, and the ratio of the pile depth to the pile diameter L / D is mostly in the range of 5-10. During the service life of offshore wind turbines, due to the towering structure of the wind turbine, the large-diameter single pile foundation will be subjected to the huge horizontal overturning bending moment load caused by external wind and wave currents. Therefore, accurately assessing the horizontal ultimate bending bearing capacity of the large-diameter single pile foundation of offshore wind turbines is the most critical part of the wind turbine foundation structure design, which is directly related to the stability and safety of the wind turbine unit throughout its life cycle.

[0003] However, current predictions of the ultimate horizontal bending capacity of large-diameter single piles for offshore wind turbines rely on the py curve method recommended by the API specification. This method treats the single pile as a vertical beam and discretizes the surrounding soil into a series of horizontal soil springs connected to the pile. Numerous studies have shown that the py curve recommended by the specification is significantly softer than the actual pile-soil reaction curve and fails to account for additional soil resistance contributions such as shear force at the pile base and reaction bending moment, resulting in a significant underestimation of the ultimate horizontal bending capacity of the single pile. Summary of the Invention

[0004] The purpose of this invention is to overcome the defects of existing analysis technology and provide a calculation and optimization method for the horizontal ultimate bending bearing capacity of large-diameter single piles of offshore wind turbines, serve the optimization design of offshore wind power project foundations, and provide more accurate technical support for the bearing capacity design of large-diameter single pile foundations of offshore wind turbines.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] A method for calculating and optimizing the horizontal ultimate bending bearing capacity of a large-diameter single pile of an offshore wind turbine comprises the following steps:

[0007] (1) Determine the geometric parameters of the large diameter single pile foundation, including the outer diameter D of the single pile and the depth L of the single pile into the soil, such as Figure 1 As shown;

[0008] (2) Measure the undrained shear strength s of the seabed foundation soil u The distribution parameters with depth include the undrained shear strength of the soil at the mud surface, s um, the undrained shear strength increases with depth, and the undrained shear strength distribution of the seabed soil can be expressed as: u =s um +kz, where z is the depth of the soil, such as Figure 1 As shown;

[0009] (3) Determine the rotation point depth z of a large diameter single pile under horizontal bending moment load r ,like Figure 1 As shown, usually z r =0.75L. The depth of the rotation point is not affected by the size of the single pile, the undrained shear strength distribution of the soil, and the magnitude of the external load. Furthermore, the length H from the rotation point to the pile bottom is determined as H = L - 0.75L = 0.25L.

[0010] (4) The bending moment resistance of the soil in the depth range above the rotation point of a large diameter single pile (i.e. within 0-0.75L) is mainly provided by the horizontal soil resistance. u The distribution can be calculated as follows:

[0011]

[0012] Where s u =s um +kz. At this time, the soil in the depth above the rotation point of the large diameter single pile contributes M to the bending bearing capacity of the large diameter single pile. u1 Calculate as follows:

[0013]

[0014] (5) The bending moment resistance of the soil below the rotation point of the large-diameter single pile (i.e., within 0.75LL) is mainly provided by the horizontal soil resistance and the additional resistance at the pile bottom (pile foundation shear force and reaction bending moment). The failure mechanism of the soil below the rotation point is a spoon-shaped failure with rotational flow around the rotation point. At this time, the contribution of the soil in this range to the bending bearing capacity of the large-diameter single pile is M. u2 is the bending moment resistance of the pile-soil shear at the rotation point on the spoon-shaped failure surface (M scoop ) and the moment resistance of the lateral pile-soil shear to the rotation point (M side ) and is calculated as follows:

[0015] M u2 =M scoop +M side

[0016] The spoon-shaped failure surface of the soil below the rotation point of the large-diameter single pile foundation is a three-dimensional surface, and the ultimate bending moment resistance M of the failure surface is scoop It can be regarded as the sum of the shear force on the failure surface caused by a series of strips on the pile section to the moment of the rotation point, such as Figure 2As shown. The strip AA' with a width of dy at the cross section y from the center of the pile forms a radius of r f Semicircular failure surface CBB'C', r f The calculation formula is:

[0017]

[0018] The moment of the shear force on the sliding surface caused by strip AA' on the rotation point (O') can be calculated as follows (considering a strip of unit thickness, that is, dy = 1):

[0019]

[0020] In the above formula, s u0 is the undrained shear strength of the soil at the rotation point of the large-diameter single pile foundation, and the calculation formula is:

[0021] s u0 =s um +0.75kL

[0022] At this time, M scoop M is the cross-section strip scoop-section The integral of is calculated as follows:

[0023]

[0024] In the above formula:

[0025]

[0026] Under the action of bending moment load, a large diameter single pile foundation forms a spoon-shaped failure surface, and at the same time, semicircular failure surfaces are formed on both sides of the pile, such as Figure 3 For an equivalent square section with a cross-section side length equal to the pile diameter D, the bending moment of the shear force on the two sides of the pile to the pile axis E-E' can be calculated as follows:

[0027]

[0028] Considering that the cross section of a single pile foundation is circular rather than square, the difference in pile cross section shape will affect the lateral shear force, so the lateral shear force coefficient r is used. ss =0.73, the undrained shear strength of the soil around the pile is reduced to take into account the three-dimensional effect. The calculation formula is as follows:

[0029]

[0030] Combining the above formula, we can get the contribution of the soil below the rotation point to the bending bearing capacity of the large diameter single pile: u2 Calculation formula:

[0031]

[0032] (6) In summary, the formula for calculating the horizontal ultimate bending bearing capacity of a large-diameter single pile is obtained:

[0033]

[0034] In the above steps, step (1) and step (2) are performed in no particular order, step (2) and step (3) are performed in no particular order, and step (4) and step (5) are performed in no particular order.

[0035] According to a second aspect of the present invention, the present invention provides a non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that when the computer program is executed by a processor, the steps of the above-mentioned method for optimizing the calculation of the horizontal ultimate bending bearing capacity of a large-diameter single pile of an offshore wind turbine are implemented.

[0036] According to a third aspect of the purpose of the present invention, the present invention provides an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that when the processor executes the program, the steps of the above-mentioned method for optimizing the calculation of the horizontal ultimate bending bearing capacity of a large-diameter single pile of an offshore wind turbine are implemented.

[0037] The beneficial effects of the present invention are:

[0038] 1. The method starts from the bearing mode of large-diameter single piles and the failure mode of the soil around the piles, and comprehensively considers the horizontal soil resistance and the additional resistance contribution of the large-diameter single pile base (including pile foundation shear force and reaction bending moment). The calculation results are more accurate, making the design of large-diameter single piles more economical and reasonable. It provides a new idea and new design for reducing costs and increasing efficiency in the era of "parity" for offshore wind power.

[0039] 2. The present invention derives an analytical solution to the horizontal ultimate bending bearing capacity of a large-diameter single pile based on the soil failure mode. This solution does not rely on complex numerical analysis methods and can be calculated using only limited basic measurement or structural parameters and formulas. It is efficient and fast, overcoming the shortcomings of traditional numerical analysis methods such as cumbersome and time-consuming calculation and modeling, and has important engineering practical value.

[0040] 3. The calculation formula for the horizontal ultimate bending bearing capacity of a large-diameter single pile obtained by the present invention can provide accurate technical support for the design and calculation of the bearing capacity of large-diameter single pile foundations. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Schematic diagram of the calculation model for the horizontal ultimate bending bearing capacity of a large-diameter single pile for offshore wind turbines provided by the present invention;

[0042] Figure 2 This is a schematic diagram showing the principle of calculating the bending moment resistance of the spoon-shaped failure surface below the rotation point of a large-diameter single pile foundation according to the present invention;

[0043] Figure 3 This is a schematic diagram showing the principle of calculating the bending moment resistance of the pile side shear failure surface below the rotation point of a large-diameter single pile foundation according to the present invention. DETAILED DESCRIPTION

[0044] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with examples and drawings. The exemplary embodiments of the present invention and their descriptions are only used to explain the present invention and are not intended to limit the present invention.

[0045] Example: A large-diameter monopile foundation for an offshore wind power project has an 8-meter diameter and is buried 40 meters deep. The seabed foundation soil is soft clay, with an undrained shear strength of 10 kPa at the mud surface and a gradient of 1.5 kPa / m with depth.

[0046] With reference to the accompanying drawings, the present invention provides a method for calculating the horizontal ultimate bending bearing capacity of a large-diameter single pile of an offshore wind turbine, and the implementation steps are as follows:

[0047] (1) Determine the geometric parameters of the large-diameter single pile foundation: the outer diameter of the single pile D = 8m, and the depth of the single pile into the soil L = 40m.

[0048] (2) Determine the undrained shear strength s of the seabed foundation soil u The distribution parameters with depth include the undrained shear strength of the soil at the mud surface, s um =10kPa, the undrained shear strength increases with depth gradient k = 1.5kPa / m, and the undrained shear strength distribution of the seabed soil can be expressed as: s u =s um +kz=10+1.5z, where z is the soil depth;

[0049] (3) Determine the rotation point depth z of a large diameter single pile under horizontal bending moment load r , z r = 0.75L = 30m. Further, determine the length H from the rotation point to the pile bottom, H = L - 0.75L = 0.25L = 10m;

[0050] (4) Calculate the contribution of the soil in the depth above the rotation point of the large diameter single pile to the bending bearing capacity of the large diameter single pile M u1 :

[0051]

[0052] (5) Calculate the contribution of the soil within the depth below the rotation point of the large diameter single pile to the bending bearing capacity of the large diameter single pile M u2 :

[0053] In the above formula:

[0054] s u0 =s um +0.75kL

[0055]

[0056] Calculated: M u2 =2.76×10 5 kNm

[0057] (6) The ultimate horizontal bending bearing capacity of a large-diameter single pile M is finally calculated. u :

[0058] M u =M u1 +M u2 =1.60×10 6 +2.76×10 5 =1.876×10 6 kNm

[0059] This method can be made into a software module for data processing, and the implementation of the present invention can be implemented by means of software plus the necessary general hardware platform. For example, it can be implemented using an existing processor, or by a dedicated processor used for this purpose or other purposes for an appropriate system, or by a hard-wired system. Embodiments of the present invention also include non-transitory computer-readable storage media, which include machine-readable media for carrying or having machine-executable instructions or data structures stored thereon; such machine-readable media can be any available medium that can be accessed by a general-purpose or special-purpose computer or other machine with a processor. For example, such machine-readable media can include RAM, ROM, EPROM, EEPROM, CD-ROM or other optical disk storage, disk storage or other magnetic storage devices, or any other medium that can be used to carry or store the required program code in the form of machine-executable instructions or data structures and can be accessed by a general-purpose or special-purpose computer or other machine with a processor. When information is transmitted or provided to a machine via a network or other communication connection (hard-wired, wireless, or a combination of hard-wired or wireless), the connection is also considered a machine-readable medium.

[0060] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for calculating and optimizing the horizontal ultimate bending bearing capacity of a large-diameter single pile for an offshore wind turbine, characterized in that: The method comprises the following steps: (1) Determine the geometric parameters of the large-diameter single pile foundation, including the outer diameter D of the single pile and the depth L of the single pile into the soil; (2) Determine the undrained shear strength s of the seabed foundation soil u The distribution parameters with depth include the undrained shear strength of the soil at the mud surface, s um The undrained shear strength increases with depth, and the undrained shear strength distribution of seabed soil is expressed as: u =s um +kz, where z is the soil depth; (3) Determine the rotation point depth z of a large diameter single pile under horizontal bending moment load r , z r =0.75L. The depth of the rotation point is not affected by the size of the single pile, the undrained shear strength distribution of the soil, and the size of the external load. Determine the length H from the rotation point to the pile bottom, H = L - 0.75L = 0.25L; (4) The bending moment resistance of the soil in the depth above the rotation point of a large-diameter single pile is mainly provided by the horizontal soil resistance. u The contribution of the soil in this range to the bending bearing capacity of large diameter single piles is calculated. u1 ; (5) The bending moment resistance of the soil in the depth range below the rotation point of the large-diameter single pile is mainly provided by the horizontal soil resistance and the additional resistance at the pile bottom. According to the failure mode of the soil below the rotation point, the contribution of the soil in this range to the bending bearing capacity of the large-diameter single pile is calculated as M. u2 The failure mechanism of the soil below the rotation point of the large diameter single pile is a spoon-shaped failure with rotational flow around the rotation point. At this time, the contribution of the soil within this range to the bending bearing capacity of the large diameter single pile is M. u2 M is the bending moment resistance of the pile-soil shear at the rotation point on the spoon-shaped failure surface scoop and the bending moment resistance M of the lateral pile-soil shear to the rotation point side sum; (6) The ultimate horizontal bending bearing capacity of a large-diameter single pile M is finally calculated. u =M u1 +M u2 ; Among them, step (1) and step (2) are not in any particular order, step (2) and step (3) are not in any particular order, and step (4) and step (5) are not in any particular order.

2. The method for calculating and optimizing the horizontal ultimate bending bearing capacity of a large-diameter single pile for offshore wind turbines according to claim 1 is characterized in that: In order to consider the simplicity of the method and meet practical needs, the horizontal ultimate soil resistance p around the pile in step (4) is u The distribution is calculated using the following formula: Where s u =s um +kz; Contribution of soil in the depth above the rotation point of large-diameter single pile to the bending bearing capacity of large-diameter single pile M u1 The calculation formula is as follows:

3. The method for calculating and optimizing the horizontal ultimate bending bearing capacity of a large-diameter single pile for an offshore wind turbine according to claim 1 is characterized in that: The contribution of soil in this range to the bending bearing capacity of large diameter single pile is M u2 The calculation formula is as follows: Where, s u0 =s um +0.75kL, H=0.25L.

4. The method for calculating and optimizing the horizontal ultimate bending bearing capacity of a large-diameter single pile for an offshore wind turbine according to claim 1 is characterized in that: In calculating the bending moment resistance M of the pile-soil shear at the rotation point side When the lateral shear coefficient r ss =0.73 to reduce the undrained shear strength of the soil around the pile to take into account the three-dimensional effect.

5. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method for calculating and optimizing the horizontal ultimate bending bearing capacity of a large-diameter single pile for offshore wind turbines as claimed in any one of claims 1 to 4 are implemented.

6. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the program, the steps of the method for calculating and optimizing the horizontal ultimate bending bearing capacity of a large-diameter single pile for an offshore wind turbine according to any one of claims 1 to 4 are implemented.

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