Design method for GFRP bucket foundation of offshore wind turbine in limit state

Abstract

The invention discloses a method for designing a GFRP (Glass Fiber Reinforced Plastic) bucket foundation of an offshore wind turbine in a limit state, which belongs to the technical field of ocean suction bucket foundations, and comprises the following steps of: acquiring soil property parameters and constitutive parameters, establishing a finite element model of the GFRP bucket foundation under a horizontal load, acquiring a relation curve of wall thickness and maximum principal stress in different sections, and calculating the maximum principal stress of the GFRP bucket foundation according to the relation curve. Fitting a corresponding function relation expression; a limit state equation is established, a random variable distribution type is selected, N random numbers are randomly generated, N is a positive integer larger than or equal to 10000, the N random numbers are sequentially substituted into the limit state equation, and the buckling reliability pr of the GFRP barrel type foundation under the wall thickness is calculated; and repeatedly calculating different wall thicknesses to obtain the buckling reliability corresponding to the different wall thicknesses, and determining whether the corresponding wall thicknesses meet the reliability design requirement of the GFRP bucket foundation according to the reliability required by engineering.

Description

Technical Field

[0001] The present invention relates to the technical field of marine suction bucket foundations, and in particular to a design method for a GFRP bucket foundation of an offshore wind turbine under an extreme state. Background Art

[0002] As the ultimate bearer of the superstructure of offshore wind turbines, the foundation is the key to the safe and stable operation of the wind turbine structure. Common foundation forms for offshore wind turbines mainly include: gravity foundation, single pile foundation, jacket foundation and suction bucket foundation. Compared with other types of foundations, suction bucket foundation has the advantages of strong adaptability to soil layers, easy installation, short construction period, and removable and reusable. In recent years, suction bucket foundations have been widely used in the support or mooring foundation of breakwaters, fixed and floating offshore wind turbines, and floating oil and gas platforms, and have achieved good results.

[0003] Traditional suction buckets are made of materials such as metal or concrete, especially steel suction buckets, which are widely manufactured and used. They are often affected by seawater immersion and microbial corrosion in sea mud, which will significantly reduce safe operation during service, increase operation and maintenance costs, and lead to premature retirement of offshore wind turbines (OWTs).

[0004] Glass fiber reinforced polymer (GFRP) suction bucket foundations are manufactured and applied because of their light weight, good corrosion resistance, and long service life, which can effectively improve the reliability and economy of offshore wind turbines. The design method of the structural form and size of the GFRP bucket foundation under horizontal load is different from that of the steel bucket foundation. How to ensure the reliability of the GFRP bucket foundation in service has become an urgent problem to be solved. Summary of the invention

[0005] The object of the present invention is to provide a design method for an offshore wind turbine GFRP barrel foundation under an extreme state, so as to realize a reasonable design of the offshore wind turbine GFRP barrel foundation under a service state.

[0006] As conceived above, the technical solution adopted by the present invention is: a design method for a GFRP barrel foundation of an offshore wind turbine under a limit state, comprising: step 1: performing a plurality of tests on the soil around the GFRP barrel foundation in the sea area to be tested to obtain soil parameters of the soil; step 2: determining the material parameters of the GFRP barrel foundation based on the marine environment faced by the GFRP barrel foundation, preparing a GFRP laminate according to the material parameters, and obtaining the constitutive parameters of the GFRP laminate through a plurality of tests; step 3: establishing a finite element model of the GFRP barrel foundation under horizontal load based on the parameters obtained in steps 1 and 2, and obtaining the maximum principal stress on different sections of the GFRP barrel foundation under the limit state; step 4: obtaining the relationship curve between the wall thickness and the 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 as follows: ,in, is the critical buckling stress of the GFRP bucket foundation under horizontal load; It is the maximum principal stress of the GFRP bucket foundation under horizontal load; Step 6: Based on the wall thickness of the GFRP bucket foundation being a random variable with uncertainty, select the random variable distribution type, randomly generate N random numbers, N is a positive integer greater than or equal to 10000, and bring the N random numbers into the limit state equation in turn. If the calculated Z is greater than or equal to 0, record 1 as the number of times, and finally add up all the numbers of Z greater than or equal to 0, record the total number as n, and n divided by N is the buckling reliability pr of the GFRP bucket foundation under the wall thickness; Step 7: Repeat step 6 for different wall thicknesses to obtain the buckling reliability corresponding to different wall thicknesses. According to the reliability required by the project, determine whether the corresponding wall thickness meets the reliability design requirements of the GFRP bucket foundation.

[0007] Preferably, in step 3, three sections of the GFRP bucket foundation are selected, which are the top section S1, the middle section S2 and the bottom section S3 from top to bottom; in step 4, the functional relationship obtained by fitting is as follows: for the top section S1, ; For the middle 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 of the GFRP bucket 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 bucket foundation; L is the length of the GFRP bucket foundation; and v is the Poisson's ratio.

[0009] As a preference, 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 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 substituted into the limit state equation Z one by one. The buckling reliability pr of the bottom section S3 when the wall thickness is 0.259%D is calculated to be 0.9999.

[0010] Preferably, in step 3, the circumferential strain and 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 curves between the wall thickness and the circumferential strain and radial deformation in different sections of the GFRP bucket foundation are obtained, and the corresponding functional relationship is fitted.

[0011] Preferably, in step 4, according to the finite element model, the relationship curves between the laying angle and the maximum principal stress, the hoop strain and the radial deformation in different sections of the GFRP bucket foundation are obtained, and the corresponding functional relationship is fitted.

[0012] Preferably, in step 1, the multiple tests include a geotechnical density test and a triaxial test, and the 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] Beneficial effects of the present invention: The present invention proposes a design method for the GFRP barrel-type foundation of an offshore wind turbine under a limit state, which determines the relationship between the wall thickness and the maximum principal stress of the GFRP barrel-type foundation by modeling and analyzing the GFRP barrel-type foundation of an offshore wind turbine under a horizontal load, and calculates the buckling reliability of the GFRP barrel-type foundation based on the established limit state equation and according to the random variable distribution type, thereby realizing a reasonable design of the GFRP barrel-type foundation under service. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

[0018] Figure 4 This is a curve showing the relationship between the laying angle and the maximum principal stress provided in the second embodiment of the present invention.

[0019] In the figure: 1. barrel; 2. tower; 3. mud surface. DETAILED DESCRIPTION

[0020] The technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0021] Embodiment 1

[0022] See also Figures 1 to 3 , this embodiment provides a design method for a GFRP bucket foundation of an offshore wind turbine under a limit state, including: step 1: performing multiple tests on the soil around the GFRP bucket foundation in the sea area to be tested to obtain soil parameters of the soil; step 2: determining the material parameters of the GFRP bucket foundation based on the marine environment faced by the GFRP bucket foundation, preparing a GFRP laminate according to the material parameters, and obtaining the constitutive parameters of the GFRP laminate through multiple tests; step 3: establishing a finite element model of the GFRP bucket foundation under horizontal load based on the parameters obtained in step 1 and step 2, and obtaining the maximum principal stress of different sections of the GFRP bucket foundation under the limit state; step 4: obtaining the relationship curve between the wall thickness and the maximum principal stress in different sections of the GFRP bucket 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 bucket foundation under horizontal load as follows: ,in, is the critical buckling stress of the GFRP bucket foundation under horizontal load; It is the maximum principal stress of the GFRP bucket foundation under horizontal load; Step 6: Based on the wall thickness of the GFRP bucket foundation being a random variable with uncertainty, select the random variable distribution type, randomly generate N random numbers, N is a positive integer greater than or equal to 10000, and bring the N random numbers into the limit state equation in turn. If the calculated Z is greater than or equal to 0, record 1 as the number of times, and finally add up all the numbers of Z greater than or equal to 0, record the total number as n, and n divided by N is the buckling reliability pr of the GFRP bucket foundation under the wall thickness; Step 7: Repeat step 6 for different wall thicknesses to obtain the buckling reliability corresponding to different wall thicknesses. According to the reliability required by the project, determine whether the corresponding wall thickness meets the reliability design requirements of the GFRP bucket foundation.

[0023] Through modeling and analysis of the GFRP barrel foundation of offshore wind turbines under horizontal loads, the functional relationship between the wall thickness of the GFRP barrel foundation and the maximum principal stress 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 to achieve a reasonable design of the GFRP barrel foundation under service.

[0024] In step 1, multiple tests include geotechnical density test and triaxial test, and soil parameters include soil density, internal friction angle and cohesion. Geotechnical density test and triaxial test are existing tests. Before the test, a large number of samples of shallow soft clay on the seabed in the sea area where the offshore wind turbine is located are taken and divided into multiple parts. During the test, geotechnical density test and triaxial test are carried out on each sample to obtain a series of parameters, and the average value of each parameter is taken.

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

[0026] Prepare GFRP laminates according to material parameters, that is, prepare GFRP laminates of the same material as the GFRP barrel foundation; obtain the constitutive parameters of the GFRP laminates through multiple tests, 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 tests include tensile, compression, bending, shear and other related tests on composite materials, specifically including tension and compression in the three directions of x, y and z. In step 2, the constitutive parameters include elastic modulus, tensile strength, compressive strength and Poisson's ratio.

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

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

[0029] like Figure 2 As shown, the abscissa is the percentage of the wall thickness to the diameter, and the ordinate is the maximum principal stress. The percentage of the wall thickness to the diameter is used as the abscissa, that is, the abscissa is set to a dimensionless form of the ratio to ignore the influence of the dimension, which is convenient for reference by suction bucket foundations of different sizes in other projects. For example, the wall thickness of the 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 wall thickness to the diameter.

[0030] In step 4, the functional relationship obtained by fitting is as follows: For the top section S1, ; For the middle 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 bucket foundation; D is the diameter of the GFRP bucket foundation; σs is the maximum principal stress of the GFRP bucket foundation under horizontal load.

[0031] Substituting the wall thickness t as 0.259%D into the maximum principal stress calculation formula in the bottom section S3 is: , compare this maximum principal stress with the yield strength of the material or the strength specified in the project. If it meets the requirements, it means that the wall thickness of the section meets the requirements.

[0032] Among them, the failure modes of GFRP barrel foundation can be divided into strength failure, buckling instability, fatigue damage, brittle failure and other types. Based on the load form of the GFRP barrel foundation of offshore wind turbines during the service stage, buckling instability is selected as the main failure mode and the limit state equation is 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 bucket foundation; L is the length of the GFRP bucket foundation; and v is the 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 randomly generated based on the distribution type of the random variable. In this embodiment, N is taken to be equal to 10,000.

[0035] For the bottom section S3, the limit state equation ; 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 substituted into the limit state equation Z one by one. The buckling reliability pr of the bottom section S3 when the wall thickness is 0.259%D is calculated to be 0.9999.

[0036] For example, for randomly generated N=10000 wall thickness values, if they are substituted one by one into the limit state equation Z, the total number of all Z greater than or equal to 0 is calculated to be 9995, and the buckling reliability pr is 0.9995.

[0037] In step 5, if Z is greater than or equal to 0, it means that the wall thickness meets the requirements, and if Z is less than 0, it means that the wall thickness does not meet the requirements. The failure probability of the GFRP bucket foundation is For the randomly generated N=10000 wall thickness values, if they are substituted into the limit state equation Z one by one, the total number of all Z less than 0 is calculated to be 5, and the failure probability pf=0.0005. The relationship between the buckling reliability pr and the 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 the wall thickness and the buckling reliability can be obtained, and then according to 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] It can be understood that 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 the buckling reliability pr of each section can be obtained. If the reliability of the selected sections meets the requirements, the GFRP bucket 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 of the GFRP bucket foundation. In this embodiment, the maximum principal stress of the GFRP bucket foundation under horizontal load is compared with the critical buckling stress of the GFRP bucket foundation under horizontal load.

[0041] In other embodiments, in step 3, the hoop strain and 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 curves between the wall thickness and the hoop strain and radial deformation in different sections of the GFRP bucket foundation are obtained, and the corresponding functional relationship is fitted. In the above manner, it can be analyzed whether the hoop strain and radial deformation meet the reliability design requirements of the GFRP bucket foundation.

[0042] Embodiment 2

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

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

[0045] like Figure 4 As shown in the figure, the horizontal axis is the laying angle of the GFRP bucket foundation, and the vertical axis is the maximum principal stress. For example, the laying angle of the GFRP bucket foundation is 45°, then the value 45 is substituted into the corresponding functional relationship. Substituting 45° into the maximum principal stress calculation formula in the bottom section S3 is: , compare this maximum principal stress with the yield strength of the material or the strength specified in the project. If it meets the requirements, it means that the laying angle of the section meets the requirements.

[0046] In other embodiments, in step 4, the relationship curves between the laying angle and the hoop strain and radial deformation in different sections of the GFRP bucket foundation are obtained according to the finite element model, and the corresponding functional relationship is fitted. Then, it can be analyzed whether the hoop strain and radial deformation under different laying angles meet the reliability design requirements of the GFRP bucket foundation.

[0047] The above embodiments are only to illustrate the basic principles and characteristics of the present invention. The present invention is not limited by the above embodiments. Without departing from the spirit and scope of the present invention, the present invention may be subject to various changes and modifications, which are within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A design method for GFRP barrel foundation of offshore wind turbine under limit state, characterized in that: include: Step 1: Conduct multiple tests on the soil around the GFRP bucket foundation in the sea area to be tested to obtain the soil parameters; Step 2: Based on the marine environment faced by the GFRP barrel foundation, determine the material parameters of the GFRP barrel foundation, prepare the GFRP laminate according to the material parameters, and obtain the constitutive parameters of the GFRP laminate through multiple 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 to obtain the maximum principal stress on different sections of the GFRP bucket foundation under the limit state; Step 4: According to the finite element model, obtain the relationship curve between the wall thickness and the maximum principal stress in different sections of the GFRP bucket foundation, and fit the corresponding functional relationship; Step 5: Taking buckling instability as the main failure mode, the limit state equation of GFRP bucket foundation under horizontal load is established as follows: ,in, is the critical buckling stress of the GFRP bucket foundation under horizontal load; is the maximum principal stress on the GFRP bucket foundation under horizontal load; Step 6: Since the wall thickness of the GFRP bucket foundation is a random variable with uncertainty, select the random variable distribution type, randomly generate N random numbers, where N is a positive integer greater than or equal to 10,000, and sequentially substitute the N random numbers into the limit state equation. If the calculated Z is greater than or equal to 0, record the number as 1. Finally, add up all the numbers where Z is greater than or equal to 0, and record the total number as n. n divided by N is the buckling reliability pr of the GFRP bucket foundation under this wall thickness. Step 7: Repeat step 6 for different wall thicknesses to obtain the buckling reliability corresponding to different wall thicknesses. According to the reliability required by the project, determine whether the corresponding wall thickness meets the reliability design requirements of the GFRP barrel foundation.

2. The design method of GFRP barrel foundation for offshore wind turbines under limit conditions according to claim 1 is characterized in that: In step 3, three sections of the GFRP bucket foundation are selected, namely, the top section S1, the middle section S2, and the bottom section S3 from top to bottom; In step 4, the functional relationship obtained by fitting is as follows: For the top section S1, ; For the middle 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 of the GFRP bucket foundation under horizontal load.

3. The design method of GFRP barrel foundation for offshore wind turbines under limit state according to claim 2 is characterized in that: 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 bucket foundation; L is the length of the GFRP bucket foundation; and v is the Poisson's ratio.

4. The design method of GFRP barrel foundation for offshore wind turbines under limit state according to claim 3 is characterized in that: 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 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 substituted into the limit state equation Z one by one. The buckling reliability pr of the bottom section S3 when the wall thickness is 0.259%D is calculated to be 0.9999.

5. The design method of GFRP barrel foundation for offshore wind turbines under limit state according to claim 1 is characterized in that: In step 3, the hoop strain and 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 curves between the wall thickness and the hoop strain and radial deformation in different sections of the GFRP bucket foundation are obtained, and the corresponding functional relationship is fitted.

6. The design method of GFRP barrel foundation for offshore wind turbines under limit conditions according to claim 5 is characterized in that: In step 4, according to the finite element model, the relationship curves between the laying angle and the maximum principal stress, the hoop strain and the radial deformation in different sections of the GFRP bucket foundation are obtained, and the corresponding functional relationship is fitted.

7. The design method of GFRP barrel foundation for offshore wind turbines under limit conditions according to any one of claims 1 to 6, characterized in that: In step 1, multiple tests include geotechnical density test and triaxial test, and soil parameters include soil density, internal friction angle and cohesion.

8. The design method of GFRP barrel foundation for offshore wind turbines under limit conditions according to any one of claims 1 to 6, characterized in that: In step 2, the constitutive parameters include elastic modulus, tensile strength, compressive strength, and Poisson's ratio.

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