Design method of GFRP bucket foundation for offshore wind turbine under ultimate state

Abstract

The application discloses a design method of a GFRP bucket foundation of an offshore wind turbine under an ultimate state, belongs to the technical field of marine suction bucket foundations, and comprises the following steps: obtaining soil property parameters and constitutive parameters; establishing a finite element model of the GFRP bucket foundation under a horizontal load; obtaining a relationship curve between wall thickness and maximum principal stress in different sections, and fitting a corresponding function relationship; establishing an ultimate state equation; selecting a random variable distribution type, randomly generating N random numbers, wherein N is a positive integer greater than or equal to 10000; sequentially bringing the N random numbers into the ultimate state equation; and calculating the buckling reliability pr of the GFRP bucket foundation under the wall thickness. The buckling reliability corresponding to different wall thicknesses is obtained by repeatedly calculating different wall thicknesses; and whether the corresponding wall thickness meets the reliability design requirements of the GFRP bucket foundation is determined according to the reliability required by engineering.

Description

Technical Field

[0001] This invention relates to the field of marine suction bucket foundation technology, and in particular to a design method for a GFRP bucket foundation for offshore wind turbines under extreme conditions. Background Technology

[0002] As the final support structure of an offshore wind turbine's superstructure, the foundation is crucial for the turbine's safe and stable operation. Common foundation types for offshore wind turbines include gravity foundations, monopile foundations, jacket foundations, and suction cup foundations. Compared to other foundation types, suction cup foundations offer advantages such as strong soil adaptability, convenient installation, short construction period, and the ability to be dismantled and reused. In recent years, suction cup foundations have been widely used for breakwaters, fixed and floating offshore wind turbines, and the support or anchoring foundations of floating oil and gas platforms, achieving excellent results.

[0003] Traditional suction barrels are made of materials such as metal or concrete, with steel suction barrels being widely manufactured and used. They are often affected by seawater immersion and corrosion from microorganisms in the sea mud, which significantly reduces safe operation during service, increases operating and maintenance costs, and leads to the premature retirement of offshore wind turbines (OWTs).

[0004] Glass fiber reinforced polymer (GFRP) suction barrel foundations are manufactured and used due to their advantages such as light weight, good corrosion resistance, and long service life, which can effectively improve the reliability and economy of offshore wind turbines. The design methods for the structural form and dimensions of GFRP barrel foundations under horizontal loads differ from those for steel barrel foundations. Ensuring the reliability of GFRP barrel foundations under service conditions is a pressing issue that needs to be addressed. Summary of the Invention

[0005] The purpose of this invention is to provide a design method for GFRP barrel foundations of offshore wind turbines under extreme conditions, so as to achieve a reasonable design of GFRP barrel foundations of offshore wind turbines under service conditions.

[0006] As conceived above, the technical solution adopted in this invention is: a design method for a GFRP barrel foundation for offshore wind turbines under extreme conditions, comprising: Step 1: conducting multiple tests on the soil surrounding the GFRP barrel foundation in the sea area to be tested to obtain soil property parameters; Step 2: determining the material parameters of the GFRP barrel foundation based on the marine environment faced by the GFRP barrel foundation, preparing GFRP laminates according to the material parameters, and obtaining the constitutive parameters of the GFRP laminates through multiple tests; Step 3: establishing a finite element model of the GFRP barrel foundation under horizontal load based on the parameters obtained in Step 1 and Step 2, and obtaining the maximum principal stress on different sections of the GFRP barrel foundation under extreme conditions; Step 4: obtaining the relationship curves between wall thickness and maximum principal stress in different sections of the GFRP barrel foundation according to the finite element model, and fitting the corresponding functional relationship; Step 5: establishing the limit state equation of the GFRP barrel foundation under horizontal load with buckling instability as the main failure mode. ,in, It is the critical buckling stress of the GFRP barrel foundation under horizontal load; The maximum principal stress experienced by the GFRP barrel foundation under horizontal load; Step 6: Since the wall thickness of the GFRP barrel foundation is a random variable with uncertainty, select the random variable distribution type and randomly generate N random numbers, where N is a positive integer greater than or equal to 10000. Substitute the N random numbers into the limit state equation in turn. If the calculated Z is greater than or equal to 0, record the number of times as 1. Finally, add up all the numbers where Z is greater than or equal to 0 and record the total as n. Divide n by N to get the buckling reliability pr of the GFRP barrel foundation under that wall thickness; Step 7: Repeat the calculation in step 6 for different wall thicknesses to obtain the buckling reliability corresponding to different wall thicknesses. Based on the reliability required by the project, determine whether the corresponding wall thickness meets the reliability design requirements of the GFRP barrel foundation.

[0007] Preferably, in step 3, three sections of the GFRP barrel foundation are selected, from top to bottom: top section S1, middle section S2, and bottom section S3; in step 4, the functional relationship obtained through fitting is as follows: For the top section S1, For the intermediate section S2, For the bottom section S3, Where b is the ratio of wall thickness to diameter, t is the wall thickness of the GFRP barrel foundation; D is the diameter of the GFRP barrel foundation. It is the maximum principal stress experienced by the GFRP barrel foundation under horizontal load.

[0008] Preferably, in step 5, the critical buckling stress The calculation formula is: Where C is the buckling reduction coefficient; E is the elastic modulus; t is the wall thickness of the GFRP barrel foundation; L is the length of the GFRP barrel foundation; and v is Poisson's ratio.

[0009] Preferably, for the bottom section S3, the limit state equation is: In step 6, when the wall thickness is 0.259%D, the random variable satisfies a normal distribution with an expected value of 0.259 and a coefficient of variation of 0.02. N=10000 wall thickness values ​​are randomly generated and substituted into the limit state equation Z one by one to calculate the buckling reliability pr of the bottom section S3 when the wall thickness is 0.259%D, which is 0.9999.

[0010] Preferably, in step 3, the circumferential strain and radial deformation of different sections of the GFRP barrel foundation under the ultimate state are also obtained; in step 4, according to the finite element model, the relationship curves between the wall thickness and the circumferential strain and radial deformation in different sections of the GFRP barrel foundation are obtained, and the corresponding functional relationships are fitted.

[0011] Preferably, in step 4, based on the finite element model, the relationship curves between the laying angle and the maximum principal stress, circumferential strain and radial deformation in different sections of the GFRP barrel foundation are obtained, and the corresponding functional relationships are fitted.

[0012] Preferably, in step 1, multiple tests include geotechnical density tests and triaxial tests, and soil parameters include soil density, internal friction angle, and cohesion.

[0013] Preferably, in step 2, the constitutive parameters include elastic modulus, tensile strength, compressive strength, and Poisson's ratio.

[0014] The beneficial effects of this invention are as follows: The design method for GFRP barrel foundations of offshore wind turbines under extreme conditions proposed in this invention determines the relationship between the wall thickness and the maximum principal stress of the GFRP barrel foundation by modeling and analyzing the GFRP barrel foundation of offshore wind turbines under horizontal loads. Based on the established limit state equations, the buckling reliability of the GFRP barrel foundation is calculated according to the distribution type of random variables, thereby realizing the rational design of GFRP barrel foundations under service conditions. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the GFRP barrel foundation provided in Embodiment 1 of the present invention.

[0016] Figure 2 This is the curve showing the relationship between wall thickness and maximum principal stress provided in Embodiment 1 of the present invention.

[0017] Figure 3 This is the relationship curve between wall thickness and reliability provided in Embodiment 1 of the present invention.

[0018] Figure 4 This is the relationship curve between the laying angle and the maximum principal stress provided in Embodiment 2 of the present invention.

[0019] In the diagram: 1. Barrel body; 2. Tower cylinder; 3. Mud surface. Detailed Implementation

[0020] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0021] Example 1

[0022] See Figures 1 to 3 This embodiment provides a design method for a GFRP (Glass Reinforced Plastic) barrel foundation for an offshore wind turbine under extreme conditions, including: Step 1: Conducting multiple tests on the soil surrounding the GFRP barrel foundation in the test sea area to obtain soil property parameters; Step 2: Determining the material parameters of the GFRP barrel foundation based on the marine environment it faces, preparing GFRP laminates according to the material parameters, and obtaining the constitutive parameters of the GFRP laminates through multiple tests; Step 3: Based on the parameters obtained in Steps 1 and 2, establishing a finite element model of the GFRP barrel foundation under horizontal load, and obtaining the maximum principal stress on different sections of the GFRP barrel foundation under extreme conditions; Step 4: Obtaining the relationship curves between wall thickness and maximum principal stress in different sections of the GFRP barrel foundation according to the finite element model, and fitting the corresponding functional relationship; Step 5: Taking buckling instability as the main failure mode, establishing the limit state equation of the GFRP barrel foundation under horizontal load. ,in, It is the critical buckling stress of the GFRP barrel foundation under horizontal load; The maximum principal stress experienced by the GFRP barrel foundation under horizontal load; Step 6: Since the wall thickness of the GFRP barrel foundation is a random variable with uncertainty, select the random variable distribution type and randomly generate N random numbers, where N is a positive integer greater than or equal to 10000. Substitute the N random numbers into the limit state equation in turn. If the calculated Z is greater than or equal to 0, record the number of times as 1. Finally, add up all the numbers where Z is greater than or equal to 0 and record the total as n. Divide n by N to get the buckling reliability pr of the GFRP barrel foundation under that wall thickness; Step 7: Repeat the calculation in step 6 for different wall thicknesses to obtain the buckling reliability corresponding to different wall thicknesses. Based on the reliability required by the project, determine whether the corresponding wall thickness meets the reliability design requirements of the GFRP barrel foundation.

[0023] By modeling and analyzing the GFRP barrel foundation of an offshore wind turbine under horizontal load, the functional relationship between the wall thickness and the maximum principal stress of the GFRP barrel foundation is determined. Based on the established limit state equation and the distribution type of random variables, the buckling reliability of the GFRP barrel foundation is calculated, thus realizing the rational design of the GFRP barrel foundation under service conditions.

[0024] In step 1, multiple tests were conducted, including geotechnical density tests and triaxial tests. Soil parameters included soil density, internal friction angle, and cohesion. Both geotechnical density tests and triaxial tests were existing methods. Prior to the tests, a large number of shallow soft clay samples were taken from the seabed in the area where the offshore wind turbine was located and divided into multiple portions. During the tests, geotechnical density tests and triaxial tests were performed on each sample to obtain a series of parameters, and the average value of each parameter was taken.

[0025] The GFRP barrel foundation is made of composite material. In step 2, when determining the material parameters of the GFRP barrel foundation, the mass fraction and material substrate type of the GFRP barrel foundation are determined based on the marine environment faced by the offshore wind turbine foundation. The fiber and resin content in the composite material is very important and largely determines the performance of the composite material. The material parameters of the GFRP barrel foundation can be determined by the mass fraction and material substrate type.

[0026] The GFRP laminate is prepared according to the material parameters, that is, a GFRP laminate of the same material as the GFRP barrel foundation is prepared. The constitutive parameters of the GFRP laminate are obtained through multiple experiments, which is equivalent to obtaining the constitutive parameters of the GFRP barrel foundation. In step 2, the constitutive parameters include elastic modulus, tensile strength, compressive strength, and Poisson's ratio. Multiple experiments include tensile, compressive, bending, and shear tests on the composite material, specifically tensile and compressive tests in the x, y, and z directions. In step 2, the constitutive parameters include elastic modulus, tensile strength, compressive strength, and Poisson's ratio.

[0027] In this embodiment, as Figure 1 As shown, in step 3, three sections of the GFRP barrel foundation are selected, from top to bottom: top section S1, middle section S2, and bottom section S3. These sections are perpendicular to the axial direction of the GFRP barrel foundation. In other embodiments, four, five, or even more sections of the GFRP barrel foundation can be selected; this is not limited here.

[0028] The GFRP barrel foundation includes a barrel 1, which is basically cylindrical. The top section S1 can be the top surface of the barrel 1 or a section near the top surface of the barrel 1. The middle section S2 is basically located at the middle of the axial direction of the barrel 1. The bottom section S3 can be the bottom surface of the barrel 1 or a section near the bottom surface of the barrel 1. The top surface of the barrel 1 is basically flush with the mud surface 3 of the seabed. A tower 2 is set on the top of the barrel 1. The tower 2 is an existing structure and will not be described in detail here.

[0029] like Figure 2 As shown, the horizontal axis represents the percentage of the diameter occupied by the wall thickness, and the vertical axis represents the maximum principal stress. Using the percentage of the diameter occupied by the wall thickness as the horizontal axis, that is, setting the horizontal axis to a dimensionless ratio to ignore the influence of dimensions, facilitates reference for suction bucket foundations of different sizes in other projects. For example, the wall thickness of a GFRP bucket foundation is 0.259%D, where D is the diameter of the GFRP bucket foundation, and 0.259% is the percentage of the diameter occupied by the wall thickness.

[0030] In step 4, the functional relationship obtained through fitting is as follows: For the top section S1, For the intermediate section S2, For the bottom section S3, Where b is the ratio of wall thickness to diameter, ; t is the wall thickness of the GFRP barrel foundation; D is the diameter of the GFRP barrel foundation; σs is the maximum principal stress experienced by the GFRP barrel foundation under horizontal load.

[0031] Substituting the wall thickness t of 0.259%D into the formula for calculating the maximum principal stress in the bottom section S3, we get: The maximum principal stress is compared with the yield strength of the material or the strength specified in the engineering. If the specified strength is met, it means that the wall thickness of the section meets the requirements.

[0032] The failure modes of GFRP barrel foundations can be categorized into strength failure, buckling instability, fatigue damage, brittle failure, and other types. Based on the load-bearing characteristics of offshore wind turbine GFRP barrel foundations during service, buckling instability is selected as the primary failure mode, and limit state equations are established.

[0033] In step 5, the critical buckling stress The calculation formula is: Where C is the buckling reduction coefficient; E is the elastic modulus; t is the wall thickness of the GFRP barrel foundation; L is the length of the GFRP barrel foundation; and v is Poisson's ratio.

[0034] The wall thickness of the GFRP barrel foundation is uncertain in actual engineering and is a random variable. Therefore, N random numbers can be generated based on the distribution type of this random variable. In this embodiment, N is set to 10000.

[0035] For the bottom section S3, the limit state equation is... In step 6, when the wall thickness is 0.259%D, the random variable satisfies a normal distribution with an expected value of 0.259 and a coefficient of variation of 0.02. N=10000 wall thickness values ​​are randomly generated and substituted into the limit state equation Z one by one to calculate the buckling reliability pr of the bottom section S3 when the wall thickness is 0.259%D, which is 0.9999.

[0036] For example, for N=10000 randomly generated wall thickness values, if each value is substituted into the limit state equation Z, the total number of values ​​for Z greater than or equal to 0 is 9995, then the buckling reliability pr is 0.9995.

[0037] In step 5, Z greater than or equal to 0 indicates that the wall thickness meets the requirements, while Z less than 0 indicates that the wall thickness does not meet the requirements. The failure probability of the GFRP barrel foundation is... For N=10000 randomly generated wall thickness values, if each value is substituted into the limit state equation Z, the total number of Z values ​​less than 0 is 5, then the failure probability pf=0.0005. The relationship between buckling reliability pr and failure probability pf is pr=1-pf.

[0038] like Figure 3 As shown, for the bottom section S3, by changing the wall thickness and repeating the calculation in step 6, the relationship curve between wall thickness and buckling reliability can be obtained. Then, based on the reliability required by the project, it can be determined whether the corresponding wall thickness meets the reliability design requirements of the GFRP barrel foundation.

[0039] Understandably, for each selected section, there is a corresponding limit state equation. By repeating the buckling reliability pr calculation in step 6, the relationship curve between the wall thickness and buckling reliability pr for each section can be obtained. If the reliability of all selected sections meets the requirements, then the GFRP barrel foundation meets the reliability design requirements.

[0040] The essence of the limit state equation is to compare the critical stress, strain, or deformation with the stress, strain, or deformation experienced by the GFRP barrel foundation. In this embodiment, the maximum principal stress experienced by the GFRP barrel foundation under horizontal load is compared with the critical buckling stress of the GFRP barrel foundation under horizontal load.

[0041] In other embodiments, step 3 further involves obtaining the circumferential strain and radial deformation of different sections of the GFRP barrel foundation under extreme conditions; in step 4, based on the finite element model, the relationship curves between wall thickness and circumferential strain and radial deformation in different sections of the GFRP barrel foundation are obtained, and the corresponding functional relationships are fitted. This method allows analysis of whether the circumferential strain and radial deformation meet the reliability design requirements of the GFRP barrel foundation.

[0042] Example 2

[0043] Figure 4 Example 2 is shown, and only the differences between Example 2 and Example 1 are described. In step 4, based on the finite element model, the relationship curves between the layup angle and the maximum principal stress in different sections of the GFRP barrel foundation are obtained, and the corresponding functional relationship is fitted. The material of the GFRP barrel foundation is a composite material, and the fibers in the composite material have layup angles. Commonly used layup angles are 45° or 90°. This example introduces the layup angle parameter of the GFRP barrel foundation to make the reliability design of the GFRP barrel foundation more comprehensive and accurate.

[0044] In step 4, the functional relationship obtained through fitting is as follows: For the top section S1, For the intermediate section S2, For the bottom section S3, ;in, It refers to the laying angle of the GFRP barrel foundation; It is the maximum principal stress experienced by the GFRP barrel foundation under horizontal load.

[0045] like Figure 4 As shown, the horizontal axis represents the laying angle of the GFRP barrel foundation, and the vertical axis represents the maximum principal stress. For example, if the laying angle of the GFRP barrel foundation is 45°, then the value 45 is substituted into the corresponding functional expression. The laying angle... Substituting 45° into the formula for calculating the maximum principal stress in the bottom section S3, we get: The maximum principal stress is compared with the yield strength of the material or the strength specified in the engineering. If the requirements are met, it means that the laying angle of the section meets the requirements.

[0046] In other embodiments, in step 4, based on the finite element model, the relationship curves between the laying angle and circumferential strain and radial deformation in different sections of the GFRP barrel foundation are obtained, and the corresponding functional relationships are fitted. This allows for analysis of whether the circumferential strain and radial deformation under different laying angles meet the reliability design requirements of the GFRP barrel foundation.

[0047] The above embodiments merely illustrate the basic principles and characteristics of the present invention. The present invention is not limited to the above embodiments. Various changes and modifications can be made to the present invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for designing a GFRP bucket foundation for offshore wind turbines under extreme conditions, characterized in that, The method comprises the following steps: Step 1: A plurality of tests are performed on the soil around the GFRP bucket foundation in the sea area to be tested to obtain soil parameters of the soil; Step 2: Based on the marine environment faced by the GFRP bucket foundation, material parameters of the GFRP bucket foundation are determined, GFRP laminated plates are prepared according to the material parameters, and constitutive parameters of the GFRP laminated plates are obtained through a plurality of tests; Step 3: Based on the parameters obtained in steps 1 and 2, a finite element model of the GFRP bucket foundation under horizontal load is established, and the maximum principal stress of different sections of the GFRP bucket foundation under the limit state is obtained; Step 4: According to the finite element model, the relationship curve between the wall thickness and the maximum principal stress in different sections of the GFRP bucket foundation is obtained, and the corresponding function relationship is fitted; Step 5: The ultimate state equation of GFRP bucket foundation under horizontal load is established as where, is the critical buckling stress of GFRP bucket foundation under horizontal load; is the maximum principal stress of GFRP bucket foundation under horizontal load; Step 6: Based on the fact that the wall thickness of the GFRP bucket foundation is a random variable and has uncertainty, the type of the random variable distribution is selected, N random numbers are randomly generated, N is a positive integer greater than or equal to 10000, the N random numbers are sequentially brought into the limit state equation, if the calculated Z is greater than or equal to 0, the number of times is recorded as 1, finally the number of all Z greater than or equal to 0 is added, and the total number is n, n divided by N is the buckling reliability pr of the GFRP bucket foundation under the wall thickness; Step 7: Different wall thicknesses are repeatedly calculated through step 6 to obtain the buckling reliability corresponding to different wall thicknesses, and whether the corresponding wall thickness meets the reliability design requirements of the GFRP bucket foundation is determined according to the reliability required by the project; In step 3, three sections of the GFRP bucket foundation are selected, from top to bottom, they are the top section S1, the middle section S2 and the bottom section S3; In step 4, the function relationship obtained by fitting is as follows: For the top section S1, ; For the intermediate section S2, ; For the bottom cross section S3, ; where b is the ratio of wall thickness to diameter, ; t is the wall thickness of the GFRP bucket foundation; D is the diameter of the GFRP bucket foundation; is the maximum principal stress that the GFRP bucket foundation receives under horizontal load; In step 3, the circumferential strain and the radial deformation of different sections of the GFRP bucket foundation under the limit state are also obtained; In step 4, according to the finite element model, the relationship curve between the wall thickness and the circumferential strain and the radial deformation in different sections of the GFRP bucket foundation is obtained, and the corresponding function relationship is fitted; whether the wall thickness meets the reliability design requirements of the GFRP bucket foundation is determined by analyzing the circumferential strain and the radial deformation; In step 4, according to the finite element model, the relationship curve between the laying angle and the maximum principal stress, the circumferential strain and the radial deformation in different sections of the GFRP bucket foundation is obtained, and the corresponding function relationship is fitted; whether the laying angle meets the reliability design requirements of the GFRP bucket foundation is determined by analyzing the circumferential strain and the radial deformation; In step 4, the acquired function relationship is fitted as follows: for the top section S1, ; for the middle section S2, ; for the bottom section S3, ; wherein, is the laying angle of the GFRP bucket foundation; is the maximum principal stress of the GFRP bucket foundation under horizontal load.

2. The method of designing a GFRP bucket foundation for an offshore wind turbine in extreme conditions according to claim 1, characterized in that, In step 5, the critical buckling stress is calculated by the formula where C is the buckling reduction factor; E is the modulus of elasticity; t is the wall thickness of the GFRP bucket foundation; L is the length of the GFRP bucket foundation; and v is the Poisson's ratio.

3. The method of designing a GFRP bucket foundation for an offshore wind turbine in extreme conditions according to claim 2, characterized in that, For the bottom cross section S3, the limit state equation is ; In step 6, when the wall thickness is 0.259%D, the random variable satisfies the normal distribution with an expectation of 0.259 and a coefficient of variation of 0.02, N=10000 wall thickness values are randomly generated, and are sequentially brought into the limit state equation Z, the buckling reliability pr of the bottom section S3 when the wall thickness is 0.259%D is calculated to be 0.9999.

4. The method of designing a GFRP bucket foundation for an offshore wind turbine in extreme conditions according to any of claims 1-3, characterized in that, In step 1, the plurality of tests include soil density test and triaxial test, and the soil parameters include soil density, internal friction angle and cohesion.

5. The method of designing a GFRP bucket foundation for an offshore wind turbine in extreme conditions according to any of claims 1-3, characterized in that, In step 2, the constitutive parameters include elastic modulus, tensile strength, compressive strength and Poisson's ratio.

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