Method for calculating shear strength of variable cross-section section of sandwich structure of wind power blade

Abstract

The invention discloses a wind power blade sandwich structure variable cross-section section shear strength calculation method, which comprises the following steps: step 1, determining the chordwise position and length of a wind power blade sandwich structure variable cross-section section, and selecting a plurality of chordwise cross sections from the determined wind power blade sandwich structure variable cross-section section; step 2, determining a neutral axis position of each chordwise section and a material layer attribute at the neutral axis position; step 3, calculating an equivalent inertia moment of each chordwise section about a neutral axis of the chordwise section; step 4, calculating shear stress at a neutral axis in each chordwise section; 5, calculating the shear stress at the centroid position of each material layer in each chordwise section; and step 6, checking the shear strength. According to the invention, the intensity distribution can be rapidly analyzed, and the damage form can be identified. In addition, the position of the neutral axis of the variable cross-section section of the wind power blade sandwich structure is automatically and accurately calculated based on the whale optimization algorithm, and then high-precision shear strength checking is completed.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of wind turbine blade design and manufacturing, and in particular to a method for calculating the shear strength of a variable cross-section section of a wind turbine blade sandwich structure. BACKGROUND

[0002] In the design and production of wind turbine blade structures, laminated plate structures such as skin-glass steel-skin in the main beam region and skin-core-skin in the leading and trailing edge regions are widely used. For homogeneous three-layer sandwich structures, since there is no obvious thickness or stiffness discontinuity in each layer of material, the failure mode of the structure is easy to identify and control. However, for material transition regions, such as the chamfer transition between the glass steel and the core material in the main beam and the leading and trailing edge, the transition region forms a skin-core-glass steel-skin sandwich structure with two different material thickness transitions, and the strength characteristics and failure mode of the transition region cannot be theoretically evaluated. In actual blade design, the failure mode can only be verified by a large number of finite element simulations and experimental loading, and when the failure mode does not meet the expectations, there is no accurate theoretical guidance for the direction of structural adjustment, so the design and stress analysis of the transition region is time-consuming and laborious, and a theoretical method is needed to quickly analyze the strength distribution, identify the failure mode, and optimize the direction based on the theory for rapid iterative design.

[0003] Secondly, the large-scale development trend of wind turbine blades puts forward higher requirements for the calculation of the shear strength of the variable cross-section section of the sandwich structure. The existing technologies mainly include theoretical analysis method, numerical simulation method and experimental determination method, but these methods have obvious shortcomings when dealing with variable cross-section sections: the calculation accuracy and efficiency are difficult to balance, the material anisotropy and complex structure are not handled well, the interface effect is not fully considered, and the maintenance factor is ignored. SUMMARY

[0004] The technical problem to be solved by the present application is to overcome the shortcomings of the prior art, and to provide a method for calculating the shear strength of a variable cross-section section of a wind turbine blade sandwich structure. The method for calculating the shear strength of a variable cross-section section of a wind turbine blade sandwich structure determines the position of the neutral axis of each chordwise cross-section, and then calculates the shear stress at the neutral axis of each chordwise cross-section and the shear stress at the centroid of each material layer in each chordwise cross-section, and compares it with the respective material stress allowable value, so as to quickly analyze the strength distribution, identify the failure mode, guide the optimization direction, and facilitate rapid iterative design. In addition, the position of the neutral axis of the variable cross-section section of the wind turbine blade sandwich structure is determined based on the whale optimization algorithm, which realizes the automatic and accurate calculation of the neutral axis distribution of the variable cross-section section, and then completes the high-precision shear strength check.

[0005] To solve the above technical problems, the technical scheme adopted by the present application is:

[0006] A wind power blade sandwich structure variable cross-section section shear strength calculation method, comprising the following steps.

[0007] Step 1, determine the chordwise position and length of the wind power blade sandwich structure variable cross-section section, and select several chordwise cross-sections from the determined wind power blade sandwich structure variable cross-section section.

[0008] Step 2, determine the neutral axis position of each chordwise cross-section and the material layer properties at the neutral axis position.

[0009] Step 3, calculate the equivalent moment of inertia of each chordwise cross-section about its neutral axis .

[0010] Step 4, according to the equivalent moment of inertia , calculate the shear stress at the neutral axis in each chordwise cross-section .

[0011] Step 5, find the centroid position of each material layer in each chordwise cross-section ; wherein 1≤ i ≤ n, and n is the total number of material layers in the chordwise cross-section; then, according to the equivalent moment of inertia , calculate the shear stress at the centroid position of each material layer in each chordwise cross-section .

[0012] Step 6, shear strength check: the and of each chordwise cross-section are both judged with the stress allowable value of the material layer to determine the safety of the overall shear strength of the corresponding chordwise cross-section.

[0013] In step 2, the whale optimization algorithm WOA is used to determine the neutral axis position of each chordwise cross-section ; wherein the axial strain at the neutral axis of each chordwise cross-section is taken as the target fitness function of the whale optimization algorithm WOA.

[0014] In step 2, the expression of the target fitness function in the whale optimization algorithm WOA is:

[0015]

[0016] In the formula, is the elastic modulus of the i-th layer of material.

[0017] is the cross-sectional area of the i-th layer of material.

[0018] When , the corresponding value, that is, the required neutral axis position.

[0019] In step 3, the equivalent moment of inertia The formula is:

[0020]

[0021] Where:

[0022]

[0023] In the formula, Ei is the elastic modulus of the i-th layer of material.

[0024] Ai is the cross-sectional area of the i-th layer of material.

[0025] Eref is the reference elastic modulus.

[0026] di is the distance from the centroid to the neutral axis of the i-th layer of material.

[0027] Ii is the moment of inertia of the i-th layer of material about its own central axis.

[0028] Step 7 is also included, which is to construct the maximum shear strength distribution along the chord direction and determine the failure mode.

[0029] In step 4, the shear stress at the neutral axis of the chord-wise section is calculated by the formula:

[0030]

[0031] In the formula, V is the shear force on the corresponding chord-wise section.

[0032] I is the static moment of the neutral axis of the above or below part of the section about the neutral axis.

[0033] L is the axial width of the variable cross-section section of the wind turbine blade sandwich structure.

[0034] In step 5, the shear stress at the centroid position of the i-th layer of material is calculated by the formula:

[0035]

[0036] In the formula, I is the static moment of the neutral axis between the centroid position of the i-th layer of material and the neutral axis about the neutral axis.

[0037] In step 6, the shear strength check includes the following steps:

[0038] Step 6-1: Calculate the shear stress at the neutral axis of the section along the j-th chord. Allowable stress values ​​of the material layer properties determined in step 2 Make a judgment; where 1≤j≤N, and N is the total number of chordal sections.

[0039] Step 6-2: Calculate the shear stress at the centroid of each material layer in the j-th chord section. All are related to the allowable stress value of the corresponding material layer. Make a judgment; if and If the shear strength of the j-th chord section is safe, then the j-th chord section is determined to be damaged or potentially damaged.

[0040] Step 6-3: Repeat steps 6-1 to 6-2 to complete the shear strength safety assessment of the remaining chord section.

[0041] In step 6-1, N chordal sections are arranged at equal intervals d along the chordal direction of the wind turbine blade sandwich structure, from left to right as the 1st chordal section, the 2nd chordal section, ..., the Nth chordal section; wherein, the 1st chordal section is located to the left of the starting point A of the variable cross-section segment of the wind turbine blade sandwich structure, and is 30~100mm away from the starting point A; the Nth chordal section is located to the right of the ending point B of the variable cross-section segment of the wind turbine blade sandwich structure, and is 30~100mm away from the ending point B; d is 1 / 100~1 / 20 of the chordal length of the variable cross-section segment of the wind turbine blade sandwich structure.

[0042] In step 6-3, if all N chordal sections are judged to be safe in shear strength, then the shear strength of the variable cross-section section of the wind turbine blade sandwich structure is safe; otherwise, it is judged that the variable cross-section section of the wind turbine blade sandwich structure has damage or potential damage.

[0043] The present invention has the following beneficial effects:

[0044] 1. This invention determines the position of the neutral axis of each chordal section, and then calculates the shear stress at the neutral axis and the shear stress at the centroid of each material layer in each chordal section. The shear stress is then compared with the allowable stress values ​​of the corresponding materials. This allows for rapid analysis of the strength distribution, identification of the failure mode, guidance of optimization direction, and facilitates rapid iterative design.

[0045] 2. This invention uses the whale optimization algorithm to determine the neutral axis position of the variable cross-section segment of the wind turbine blade sandwich structure, realizes the automatic and accurate calculation of the neutral axis distribution of the variable cross-section segment, and thus completes the high-precision shear strength verification. Attached Figure Description

[0046] Figure 1A cross-sectional structure schematic diagram of the wind power blade sandwich structure variable cross-section section in the application is shown.

[0047] Figure 2 A structure schematic diagram of a chordwise cross-section in the wind power blade sandwich structure variable cross-section section in the application is shown.

[0048] Figure 3 A schematic diagram of the position of the wind power blade sandwich structure variable cross-section section in the wind power blade in the application is shown.

[0049] Among them: 10. skin; 20. core material; 30. glass steel; 31. glass steel centroid; 40. neutral axis; 50. wind power blade; 51. wind power blade sandwich structure variable cross-section section. DETAILED DESCRIPTION

[0050] The application will be described in further detail below with reference to the drawings and specific preferred embodiments.

[0051] In the description of the application, it should be understood that the terms "left side", "right side", "upper part", "lower part" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and "first", "second" and the like do not represent the importance of the parts, and therefore cannot be understood as a limitation on the application. The specific dimensions used in the embodiments are only for the purpose of illustrating the technical solutions and do not limit the protection scope of the application.

[0052] As shown in Figure 3 , the wind power blade 50 has a wind power blade sandwich structure variable cross-section section 51.

[0053] As shown in Figure 1 , the wind power blade sandwich structure variable cross-section section 51 includes a skin 10, a core material 20 and a glass steel 30; wherein the core material 20 and the glass steel 30 are inclined to cooperate, and the skin is wrapped on the outside and inside of the core material 20 and the glass steel 30, which is called outer skin and inner skin.

[0054] A wind power blade sandwich structure variable cross-section section shear strength calculation method, comprising the following steps.

[0055] Step 1, determine the chordwise position and length of the wind power blade sandwich structure variable cross-section section in the wind power blade, and select N chordwise cross-sections from the determined wind power blade sandwich structure variable cross-section section.

[0056] N chordwise sections are equidistantly arranged along the chordwise direction of the wind turbine blade sandwich structure, from left to right, they are the 1st chordwise section, the 2nd chordwise section,..., the Nth chordwise section; wherein, the 1st chordwise section is located on the left side of the starting point A of the wind turbine blade sandwich structure variable cross-section section, and is 30-100mm away from the starting point A; the Nth chordwise section is located on the right side of the ending point B of the wind turbine blade sandwich structure variable cross-section section, and is 30-100mm away from the ending point B; d is 1 / 100-1 / 20 of the chordwise length of the wind turbine blade sandwich structure variable cross-section section.

[0057] In the embodiment, the length of the wind turbine blade sandwich structure variable cross-section section taken along the chordwise direction is preferably L=700mm, the 1st chordwise section is 50mm away from the starting point A, and the Nth chordwise section is 50mm away from the ending point B; d=10mm.

[0058] Step 2, determining the neutral axis position of each chordwise section and the material layer attribute at the neutral axis position.

[0059] In the present application, the whale optimization algorithm WOA is preferably used to determine the neutral axis position of each chordwise section ; wherein, the axial strain at the neutral axis of each chordwise section is taken as the target fitness function of the whale optimization algorithm WOA, and the expression is preferably:

[0060]

[0061] wherein, the shape of the i-th layer of material is rectangular, so that, the expression is:

[0062]

[0063] in the formula, is the elastic modulus of the i-th layer of material.

[0064] is the cross-sectional area of the i-th layer of material.

[0065] is the axial width of the wind turbine blade sandwich structure variable cross-section section.

[0066] is the thickness of the i-th layer of material.

[0067] When , the corresponding value, that is, the neutral axis position required to be solved.

[0068] The whale optimization algorithm WOA is preferably used to solve the neutral axis position as follows.

[0069] Initialization: Randomly generate a population within the search space (i.e. of initial guess values).

[0070] Iterative optimization: Calculate the fitness of each individual .

[0071] Encircle prey: Identify the current best individual , and other individuals approach it, specifically:

[0072]

[0073] where:

[0074]

[0075] In the formula, are the control search range coefficient and the disturbance factor, respectively, calculated as follows:

[0076]

[0077] where, decreases from 2 to 0 with the iteration process, is a random number between 0 and 1.

[0078] Bubble net attack: Update the position in a spiral manner and perform local development near the best individual.

[0079] where

[0080] In the formula, is the distance between the best whale individual in the tth iteration and the current whale individual , b is the constant of the logarithmic spiral equation, and l is a random number between -1 and 1.

[0081] Random search: When , randomly select an individual to follow, enhance global exploration ability, and avoid falling into local optimum.

[0082] Iteration termination: When or the maximum number of iterations is reached, output the current optimal solution. Where, is the set convergence threshold, such as 1e-10.

[0083] Result output: After traversing all discrete sections, the neutral axis coordinates along the chord direction are obtained .

[0084] As shown in Figure 3 , the neutral axis is located in the glass steel, i.e., the material layer property at the neutral axis position is glass steel.

[0085] Step 3: Calculate the equivalent moment of inertia of each chord section about its neutral axis. The preferred specific calculation formula is:

[0086]

[0087] in:

[0088]

[0089]

[0090] In the formula, Let be the elastic modulus of the i-th layer material.

[0091] The reference elastic modulus.

[0092] Let be the distance from the centroid of the i-th layer of material to the neutral axis.

[0093] Let be the moment of inertia of the i-th layer of material about its own central axis, which is usually very small and can be ignored.

[0094] Step 4: Based on the equivalent moment of inertia Calculate the shear stress at the neutral axis within each chordal section. The preferred specific calculation formula is:

[0095]

[0096] In the formula, This represents the shear force acting on the corresponding chord section.

[0097] Neutral axis The static moment of the above or below section about the neutral axis.

[0098] Step 5: First, locate the centroid of each material layer in each chordal section. Where 1 ≤ i ≤ n, and n is the total number of material layers in the chordal section.

[0099] In this embodiment, as Figure 2 As shown, a chordal section located between the starting point A and the ending point B has four material layers, from top to bottom: outer skin, core material, fiberglass, and inner skin. Therefore, n=4.

[0100] Next, based on the equivalent moment of inertia Calculate the shear stress at the centroid of each material layer within each chordal section. The preferred specific calculation formula is:

[0101]

[0102] wherein, is the centroid position of the i-th material layer is the static moment of the neutral axis between the i-th material layer and the neutral axis, the calculation method is the prior art, which will not be described here.

[0103] Step 6, shear strength checking: the shear stress of each chordwise section and are judged with the stress allowable value of the material layer to determine the safety of the overall shear strength of the corresponding chordwise section.

[0104] The above shear strength checking preferably specifically includes the following steps.

[0105] Step 6-1, the shear stress at the neutral axis of the j-th chordwise section is judged with the stress allowable value of the material layer attribute determined in step 2 ; wherein, 1≤j≤N, N is the total number of chordwise sections.

[0106] Step 6-2, the shear stress at each centroid position of the j-th chordwise section is judged with the stress allowable value of the corresponding material layer ; if and , it is determined that the shear strength of the j-th chordwise section is safe; otherwise, it is determined that the j-th chordwise section has damage or potential damage.

[0107] Step 6-3, repeat steps 6-1 to 6-2 to complete the shear strength safety judgment of the remaining chordwise sections.

[0108] When N chordwise sections are all judged to be safe in shear strength, the shear strength of the variable cross-section section of the wind turbine blade sandwich structure is safe; otherwise, it is determined that the variable cross-section section of the wind turbine blade sandwich structure has damage or potential damage.

[0109] Step 7, construct the maximum shear strength distribution along the chord and determine the failure mode.

[0110] The maximum shear strength distribution of the N chordwise sections after shear strength checking in step 6 includes the chordwise distribution of , and the chordwise distribution of each material layer .

[0111] According to the maximum shear strength distribution, the failure mode is determined, and it is identified which material is most likely to fail first. For example, Figure 2 has four material layers, so there is one and four That is, five shear stresses are calculated, and compared with the allowable value of the corresponding material, which material is damaged first if the shear stress is first close to or greater than the allowable value. If the centroid position of a certain material is damaged first, it means that the material itself is not strong enough, and if the neutral axis position is damaged first, it means that the overall structure is not strong enough.

[0112] The preferred embodiments of the present application are described in detail above, but the present application is not limited to the specific details of the above-described embodiments, and various equivalent transformations of the technical solutions of the present application can be made within the technical concept of the present application, and these equivalent transformations all belong to the protection scope of the present application.

Claims

1. A method for calculating the shear strength of a variable cross-section section of a wind turbine blade sandwich structure, characterized in that: Includes the following steps: Step 1: Determine the chordal position and length of the variable cross-section segment of the wind turbine blade sandwich structure, and select several chordal sections from the determined variable cross-section segments of the wind turbine blade sandwich structure. Step 2: Determine the position of the neutral axis for each chordal section. And the material layer properties at the neutral axis location; Step 3: Calculate the equivalent moment of inertia of each chord section about its neutral axis. ; Step 4: Based on the equivalent moment of inertia Calculate the shear stress at the neutral axis within each chordal section. ; Step 5: Locate the centroid of each material layer in each chordal section. Where 1 ≤ i ≤ n, and n is the total number of material layers in the chordal section; then, according to the equivalent moment of inertia Calculate the shear stress at the centroid of each material layer within each chordal section. ; Step 6, Shear strength check: For each chord section... and The stress values ​​of each material layer are compared with the allowable stress values ​​of the material layer to determine the safety of the overall shear strength of the corresponding chordal section.

2. The method for calculating the shear strength of the variable cross-section section of the wind turbine blade sandwich structure according to claim 1, characterized in that: In step 2, the Whale Optimization Algorithm (WOA) is used to determine the neutral axis position of each chordal section. The axial strain at the neutral axis of each chordal section is used as the target fitness function of the Whale Optimization Algorithm (WOA).

3. The method for calculating the shear strength of the variable cross-section section of the wind turbine blade sandwich structure according to claim 2, characterized in that: In step 2, the expression for the target fitness function in the Whale Optimization Algorithm (WOA) is: ； In the formula, Let be the elastic modulus of the i-th layer material; Let be the cross-sectional area of ​​the i-th layer of material; when At that time, the corresponding The value is the position of the neutral axis that is to be solved.

4. The method for calculating the shear strength of the variable cross-section section of the wind turbine blade sandwich structure according to claim 1, characterized in that: In step 3, the equivalent moment of inertia The calculation formula is: ； in: ； In the formula, Let be the elastic modulus of the i-th layer material; Let be the cross-sectional area of ​​the i-th layer of material; For reference elastic modulus; Let be the distance from the centroid of the i-th layer of material to the neutral axis; Let be the moment of inertia of the i-th layer of material about its own central axis.

5. The method for calculating the shear strength of the variable cross-section section of the wind turbine blade sandwich structure according to claim 1, characterized in that: It also includes step 7, which constructs the maximum shear strength distribution along the chord and determines the failure mode.

6. The method for calculating the shear strength of the variable cross-section section of the wind turbine blade sandwich structure according to claim 1, characterized in that: In step 4, the shear stress at the neutral axis of the chordal section The calculation formula is: ； In the formula, This represents the shear force acting on the corresponding chord-direction section; Neutral axis The static moment of the above or below section about the neutral axis; This refers to the axial width of the variable cross-section section of the wind turbine blade sandwich structure.

7. The method for calculating the shear strength of the variable cross-section section of the wind turbine blade sandwich structure according to claim 6, characterized in that: In step 5, the shear stress at the centroid of the i-th material layer The calculation formula is: ； In the formula, The centroid position of the i-th material layer The static moment of the section between the neutral axis and the neutral axis.

8. The method for calculating the shear strength of the variable cross-section section of the wind turbine blade sandwich structure according to claim 1, characterized in that: Step 6, shear strength verification, specifically includes the following steps: Step 6-1: Calculate the shear stress at the neutral axis of the section along the j-th chord. Allowable stress values ​​of the material layer properties determined in step 2 Make a judgment; where 1 ≤ j ≤ N, and N is the total number of chordal sections; Step 6-2: Calculate the shear stress at the centroid of each material layer in the j-th chord section. All are related to the allowable stress value of the corresponding material layer. Make a judgment; if and If the shear strength of the j-th chord section is safe, then the j-th chord section is determined to be damaged or potentially damaged. Step 6-3: Repeat steps 6-1 to 6-2 to complete the shear strength safety assessment of the remaining chord section.

9. The method for calculating the shear strength of the variable cross-section section of the wind turbine blade sandwich structure according to claim 8, characterized in that: In step 6-1, N chordal sections are arranged at equal intervals d along the chordal direction of the wind turbine blade sandwich structure, from left to right as the 1st chordal section, the 2nd chordal section, ..., the Nth chordal section; wherein, the 1st chordal section is located to the left of the starting point A of the variable cross-section segment of the wind turbine blade sandwich structure, and is 30~100mm away from the starting point A; the Nth chordal section is located to the right of the ending point B of the variable cross-section segment of the wind turbine blade sandwich structure, and is 30~100mm away from the ending point B; d is 1 / 100~1 / 20 of the chordal length of the variable cross-section segment of the wind turbine blade sandwich structure.

10. The method for calculating the shear strength of the variable cross-section section of the wind turbine blade sandwich structure according to claim 8 or 9, characterized in that: In step 6-3, if all N chordal sections are judged to be safe in shear strength, then the shear strength of the variable cross-section section of the wind turbine blade sandwich structure is safe; otherwise, it is judged that the variable cross-section section of the wind turbine blade sandwich structure has damage or potential damage.

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