Integrated design method of wind turbine nacelle base based on topology optimization

Abstract

The present invention discloses an integrated design method for a wind turbine nacelle base based on topology optimization, comprising the following steps: combining a front nacelle base of the wind turbine with a bearing seat; establishing a topology optimization formula with volume ratio constraints with the goal of maximizing stiffness to obtain a topology optimization result; reconstructing a model structure; verifying the stiffness of the reconstructed model structure under extreme load conditions, and performing fatigue strength analysis; if the fatigue strength analysis meets the preset lightweight design requirements, the integrated design of the wind turbine nacelle base is completed; if the preset lightweight design requirements are not met, the above steps are repeated until the preset lightweight design requirements are met; the present invention uses three orthogonal moments to perform topology optimization calculations separately, obtains force transmission paths under the action of respective loads, avoids the difficulty of confusing force transmission paths in multi-condition and multi-objective optimization, can achieve lightweight design of the front nacelle base and the bearing seat of the wind turbine, and simplifies the design of connecting bolts.

Description

Technical Field

[0001] The present invention relates to the technical field of topology optimization of wind turbine generator sets, and in particular to an integrated design method for a nacelle base of a wind turbine generator set based on topology optimization. Background Art

[0002] The wind turbine transmission chain uses the kinetic energy transmitted by the wind rotor to drive the generator to generate electricity. Its operating state determines the performance of the whole machine to a certain extent. At present, most of the research on the transmission chain focuses on its dynamics. As the capacity of a single machine continues to break through the limit, its lightweight structure design is the current technical research trend.

[0003] The cost-reduction design of the transmission chain system is more reflected in the performance matching and overall performance optimization of bearings, shafts, bearing seats and main frames. The structural optimization design of wind turbine components was initially reflected in the application of size optimization and shape optimization methods, and was reflected in the structural design of blades, offshore wind turbine jacket supports, etc. At present, the optimization design of transmission chains and large structural parts is relatively rare, and most of them are based on engineering experience to make dimensional or local adjustments to previous structures. The optimization of the structural types of transmission chains and large structural parts faces the risks of insufficient strength, long R&D cycle, and increased R&D costs. Therefore, this field needs a new technical solution to solve the above problems. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art, propose an integrated design method for the nacelle base of a wind turbine based on topology optimization, propose an integrated design of the front nacelle base and the bearing seat of the wind turbine, and obtain the optimal force transmission path based on topology optimization.

[0005] The object of the present invention is achieved by the following technical solution: A wind turbine nacelle base integrated design method based on topology optimization comprises the following steps:

[0006] S1. Combine the front nacelle base and the bearing seat of the wind turbine as an integral model structure;

[0007] S2. Based on the overall model structure and topology optimization method of step S1, with the goal of maximizing stiffness, a topology optimization formula is established with volume ratio constraints to obtain topology optimization results under loads in different directions under multiple working conditions and single working conditions;

[0008] S3, reconstructing the model structure according to the topology optimization result of step S2, retaining and deleting areas of the model structure, and obtaining an optimized structure;

[0009] S4. Check the rigidity of the optimized structure under extreme load conditions and perform fatigue strength analysis;

[0010] S5. If the fatigue strength analysis meets the preset lightweight design requirements, the integrated design of the wind turbine nacelle base is completed; if it does not meet the preset lightweight design requirements, steps S2 to S4 are repeated until the preset lightweight design requirements are met.

[0011] Further, the step S1 comprises:

[0012] The front nacelle base and the bearing seat are treated as an integral structure. The nacelle base located at the root tower connection is tangent to the cylindrical structure on the outer surface of the bearing seat to achieve a smooth transition between the two.

[0013] Further, the step S2 comprises:

[0014] The overall structure in step S1 is taken as an integrated design area, and materials are filled in the integrated design area. The integrated design area is planned as a design domain. The shape characteristics of the design domain are smooth transition of the side wall, and the root tower connection is tangent to the bearing seat cylinder, so as to improve the resistance capacity in the Mz direction.

[0015] Further, the step S2 comprises:

[0016] The total number of finite elements in the design area is NE, and each element corresponds to a relative density value. The topology optimization formula is established with the goal of maximizing stiffness and volume ratio constraints:

[0017] Minimize:c=F T U

[0018] Subject to:

[0019] KU=F

[0020] 0< ρ ≤ρ e ≤1(e=1,2,…,NE);

[0021] In the formula, c is the compliance value, which is used to measure the structural stiffness. The smaller the value, the greater the structural stiffness. V is the optimized structural volume. is the design domain volume; f is the volume ratio; K is the overall stiffness matrix, U is the displacement vector and F is the load vector; ρ It is the minimum value of cell density, which takes the value of 0.01 or 0.001.

[0022] 5. The method for integrated design of a wind turbine nacelle base based on topology optimization according to claim 1, wherein step S2 comprises:

[0023] Establish the density and unit elastic modulus E e Interpolation method:

[0024]

[0025] Where p is the penalty factor, which has an initial value of 1 and increases with the number of optimization iterations; E0 is the Young's modulus of the actual material.

[0026] Further, the step S2 comprises:

[0027] The topology optimization results under the action of single bending moments Mx, My and Mz were investigated. The three orthogonal moments were used to perform topology optimization calculations respectively, and the force transmission paths under the action of each load were obtained. The minimum size constraint was set to suppress the checkerboard phenomenon and mesh dependence problems. The minimum size constraint was taken as twice the average size of the unit, and the topology optimization results under loads in different directions were obtained.

[0028] Further, the step S4 comprises:

[0029] Strength verification includes ultimate strength and fatigue strength verification. In ultimate strength verification, bending moments in different directions are selected as the dominant working conditions as ultimate working conditions, namely Mk_min, Mk_max and Myz_max, where k = x, y and z. The load value at the center of the hub is output for each working condition, which is composed of forces and moments in three directions. According to the preset material safety factor of 1.1 and the allowable stress of 200MPa, the statistical results of maximum displacement and equivalent stress under different working conditions are analyzed. If the maximum equivalent stress value under each working condition is less than the allowable stress, the integrated optimized structure meets the ultimate strength design requirements. The software outputs the values ​​and frequency of time-series fatigue load conditions to verify the fatigue strength of the integrated design, and the rain flow counting method is used for cumulative damage calculation.

[0030] Further, the step S5 comprises:

[0031] The preset lightweight design requirement is that the maximum fatigue damage values ​​are all less than 1. According to Miner's law, if the maximum fatigue damage values ​​of all regions of the optimized structure are all less than 1, the optimized structure meets the fatigue strength design requirements; if the maximum fatigue damage values ​​of all regions of the optimized structure are not less than 1, steps S2 to S4 are repeated until the preset lightweight design requirements are met.

[0032] A non-transitory computer-readable medium storing instructions, when the instructions are executed by a processor, executes the steps of the above-mentioned wind turbine nacelle base integrated design method based on topology optimization.

[0033] A computing device comprises a processor and a memory for storing a program executable by the processor. When the processor executes the program stored in the memory, the above-mentioned wind turbine nacelle base integrated design method based on topology optimization is implemented.

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

[0035] 1. The present invention can realize the lightweight design of the front nacelle base and the bearing seat of the wind turbine generator set, and simplify the design and verification of the connecting bolts;

[0036] 2. The present invention uses three orthogonal moments to perform topology optimization calculations respectively, and obtains the force transmission paths under the action of each load, thereby avoiding the difficulty of confusing the force transmission paths in multi-condition and multi-objective optimization;

[0037] 3. The integrated design based on topological optimization of the present invention achieves a weight reduction ratio of 17.68%, and the optimized structure meets the strength design requirements, which proves that the proposed method is feasible and superior;

[0038] 4. The integrated design of the present invention avoids the steps of connecting bolt arrangement and strength verification, thereby improving design efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a schematic diagram for comparing the structures of the integrated design of the front nacelle base and the bearing seat of the wind turbine and the conventional separated design.

[0040] Figure 2 Schematic diagram of the design area structure for topology optimization.

[0041] Figure 3 These are the topology optimization result diagrams under different single loads.

[0042] Figure 4 This is a comparison chart of the ultimate stiffness results of the integrated design under different working conditions.

[0043] Figure 5 Cumulative fatigue damage cloud diagram for integrated design. DETAILED DESCRIPTION

[0044] The present invention will be further described below in conjunction with specific embodiments.

[0045] Example 1

[0046] The wind turbine nacelle base integrated design method based on topology optimization provided in this embodiment includes the following steps:

[0047] S1. Combine the front nacelle base and the bearing seat of the wind turbine as an integral model structure, including:

[0048] The front nacelle base and the bearing seat are treated as an integral structure. The nacelle base located at the root tower connection is tangent to the cylindrical structure on the outer surface of the bearing seat to achieve a smooth transition between the two.

[0049] In the existing wind turbine structure, flanges and bolts are usually used to connect the nacelle base and the bearing seat. The bolt strength is closely related to the structural form of the connecting parts, the bolt arrangement method, the number of bolts, etc. Figure 1 (a) As shown; the integrated design of the front nacelle base and the bearing seat only needs to meet its own structural strength design requirements, thereby greatly reducing the design difficulty of the bolts, bolt hole positions and layout of the front nacelle base and the bearing seat;

[0050] For the front nacelle base and bearing seat separation and integrated design structure, see Figure 1 (b) The front nacelle base and bearing seat are both made of QT400, with an elastic modulus of 169 GPa, a Poisson's ratio of 0.275, and a yield strength of 220 MPa. In the separate design, the total weight of the two components is 34.49 tons, which is used for subsequent comparison of integrated design results.

[0051] S2. Based on the overall model structure and topology optimization method of step S1, with the goal of maximizing stiffness, a topology optimization formula is established with volume ratio constraints to obtain topology optimization results of loads in different directions under multiple working conditions and single working conditions, including:

[0052] See also Figure 2 As shown, except for the local structures such as the load-bearing bearings which are non-design areas, the overall structure in step S1 is used as an integrated design area, and materials are filled in the integrated design area. The integrated design area is planned as a design domain, and the shape characteristics of the design domain are smooth transition of the side wall, which is tangent to the bearing seat cylinder at the root tower connection, so as to improve the resistance capacity in the Mz direction.

[0053] The total number of finite elements in the design area is NE, and each element corresponds to a relative density value. The topology optimization formula is established with the goal of maximizing stiffness and volume ratio constraints:

[0054] Minimize:c=F T U

[0055] Subject to:

[0056] KU=F

[0057] 0< ρ ≤ρ e ≤1(e=1,2,…,NE);

[0058] Where c is the compliance value, which is used to measure the structural stiffness. The smaller the value, the greater the structural stiffness. V is the optimized structure volume, V is the design domain volume. f is the volume ratio. K is the overall stiffness matrix, U is the displacement vector, and F is the load vector. ρ It is the minimum value of cell density, which takes the value of 0.01 or 0.001.

[0059] In order to establish the relationship between density design variables and structural characteristics, the relationship between density and unit elastic modulus E is established. e Interpolation method:

[0060]

[0061] Where p is the penalty factor, which has an initial value of 1 and increases with the number of optimization iterations; E0 is the Young's modulus of the actual material.

[0062] The topology optimization results under the action of single bending moments Mx, My and Mz were investigated. The three orthogonal moments were used to perform topology optimization calculations respectively, and the force transmission paths under the action of each load were obtained. In the later structural strength verification, the force transmission path under the dominant load can be strengthened or weakened according to the stress distribution, avoiding the difficulty of artificially setting weight coefficients in multi-objective optimization problems. The minimum size constraint was set to suppress the checkerboard phenomenon and mesh dependency problems. The minimum size constraint was set to twice the average size of the unit, and the topology optimization results under loads in different directions were obtained. See Figure 3 As shown in the figure, although the degree of model refinement is different, the stress distribution at the dangerous parts is consistent. In fact, the topology optimization process is to approximate the actual situation. Although the accuracy of the model results is poor, it has the advantage of being able to quickly determine the structural form in the structural concept design stage.

[0063] S3, reconstructing the model structure according to the topology optimization result of step S2, retaining and deleting the regions of the model structure, and obtaining an optimized structure, including:

[0064] See also Figure 3 As shown, Figure 3 The medium-dark gray area represents the retained area, and the transparent area represents the deletable area; the area with unit density between 0 and 1 is in the intermediate state. According to engineering experience, the load conditions dominated by bending moments My and Mz are more dangerous, and the topology optimization results under these two extreme conditions are mainly examined. Figure 3 (b) and Figure 3 Taking (c) as an example, under the action of bending moment My, the load is transmitted to the lower end to the top of the tower through the front and rear bearings, forming an obvious hole in the middle abdomen, which means that this area is inefficient or ineffective in bearing the bending moment My; while in resisting the bending moment Mz, this area plays a certain role, and it is necessary to make trade-offs in the structure based on the corresponding limit working condition stress or fatigue analysis results.

[0065] The model was reconstructed based on the above topology optimization results. The main results include digging holes in the middle abdomen and attaching boss structures on the edges. The rear end is hollowed out and only the upper and lower support parts are retained. The final weight is 28.39 tons. Compared with the separate design, the weight reduction ratio reaches 17.68%. In order to verify the feasibility and effectiveness of the proposed integrated design method based on topology optimization, the rigidity of the optimized structure under the extreme load condition is checked. The statistical results of the maximum displacement and equivalent stress under different conditions are shown in the figure. Figure 4 As shown. Figure 4 It can be seen that the maximum stress of the structure under different working conditions is less than 200MPa. Considering the material safety factor of 1.1, the integrated optimized structure meets the ultimate strength design requirements.

[0066] S4. Check the rigidity of the optimized structure under extreme load conditions and perform fatigue strength analysis, including:

[0067] Strength check includes ultimate strength and fatigue strength check. In ultimate strength check, bending moments in different directions are selected as the dominant working conditions as the ultimate working conditions, namely Mk_min, Mk_max and Myz_max, where k = x, y and z. The load value at the center of the hub is output for each working condition, which is composed of forces and moments in three directions. According to the preset material safety factor of 1.1 and the allowable stress of 200MPa, the statistical results of maximum displacement and equivalent stress under different working conditions are analyzed. If the maximum equivalent stress values ​​under each working condition are less than the allowable stress, the integrated optimized structure meets the ultimate strength design requirements. The software outputs the values ​​and frequencies of time-series fatigue load conditions to verify the fatigue strength of the integrated design. The rain flow counting method is used for cumulative damage calculation. The surface roughness parameter of QT400 material is Rz = 100μm, and the quality inspection parameters are j = 2 and j0 = 1. The design SN curve is generated according to the DNV standard. The cumulative fatigue damage distribution of the integrated design can be found in Figure 5 As shown. Figure 5 It can be seen that the fatigue damage at positions such as the yaw motor is relatively large. Since the load-bearing position of the yaw motor is defined as contact, the fatigue assessment at this location requires the removal of a layer of surface units. The maximum fatigue damage values ​​in all areas are less than 1.

[0068] S5. The preset lightweight design requirement is that the maximum fatigue damage values ​​are all less than 1. According to Miner's law, if the maximum fatigue damage values ​​of all regions of the optimized structure are less than 1, the optimized structure meets the fatigue strength design requirements; if the maximum fatigue damage values ​​of all regions of the optimized structure are not less than 1, repeat steps S2 to S4 until the preset lightweight design requirements are met.

[0069] According to Miner's law, the structure meets the fatigue strength design requirements.

[0070] Example 2

[0071] This embodiment discloses a non-transitory computer-readable medium storing instructions. When the instructions are executed by a processor, the steps of the method for integrated design of a wind turbine nacelle base based on topology optimization described in Example 1 are performed.

[0072] The non-temporary computer-readable medium in this embodiment may be a disk, an optical disk, a computer memory, a read-only memory (ROM), a random access memory (RAM), a USB flash drive, a mobile hard disk, or other media.

[0073] Example 3

[0074] This embodiment discloses a computing device, including a processor and a memory for storing a program executable by the processor. When the processor executes the program stored in the memory, the wind turbine nacelle base integrated design method based on topology optimization described in Example 1 is implemented.

[0075] The computing device described in this embodiment may be a desktop computer, a laptop computer, a smart phone, a PDA handheld terminal, a tablet computer, a programmable logic controller (PLC), or other terminal devices with a processor function.

[0076] The embodiments described above are only preferred embodiments of the present invention and are not intended to limit the scope of implementation of the present invention. Therefore, all changes made according to the shape and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A wind turbine nacelle base integrated design method based on topology optimization, characterized in that: The following steps are involved: S1. Combine the front nacelle base and the bearing seat of the wind turbine as an integral model structure; S2. Based on the overall model structure and topology optimization method of step S1, with the goal of maximizing stiffness, a topology optimization formula is established with volume ratio constraints to obtain topology optimization results under loads in different directions under multiple working conditions and single working conditions; S3, reconstructing the model structure according to the topology optimization result of step S2, retaining and deleting areas of the model structure, and obtaining an optimized structure; S4. Check the rigidity of the optimized structure under extreme load conditions and perform fatigue strength analysis; S5. If the fatigue strength analysis meets the preset lightweight design requirements, the integrated design of the wind turbine nacelle base is completed; if it does not meet the preset lightweight design requirements, steps S2 to S4 are repeated until the preset lightweight design requirements are met.

2. The wind turbine nacelle base integrated design method based on topology optimization according to claim 1 is characterized in that: The step S1 comprises: The front nacelle base and the bearing seat are treated as an integral structure. The nacelle base located at the root tower connection is tangent to the cylindrical structure on the outer surface of the bearing seat to achieve a smooth transition between the two.

3. The method for integrated design of wind turbine nacelle base based on topology optimization according to claim 1, characterized in that: The step S2 comprises: The overall structure in step S1 is taken as an integrated design area, and materials are filled in the integrated design area. The integrated design area is planned as a design domain. The shape characteristics of the design domain are smooth transition of the side wall, and the root tower connection is tangent to the bearing seat cylinder, so as to improve the resistance capacity in the Mz direction.

4. The method for integrated design of wind turbine nacelle base based on topology optimization according to claim 1, characterized in that: The step S2 comprises: The total number of finite elements in the design area is NE, and each element corresponds to a relative density value. The topology optimization formula is established with the goal of maximizing stiffness and volume ratio constraints: Minimize:c=F T U Subject to: KU=F 0< ρ ≤ρ e ≤1(e=1,2,…,NE); In the formula, c is the compliance value, which is used to measure the structural stiffness. The smaller the value, the greater the structural stiffness. V is the optimized structural volume. is the design domain volume; f is the volume ratio; K is the overall stiffness matrix, U is the displacement vector and F is the load vector; ρ It is the minimum value of cell density, which takes the value of 0.01 or 0.

001.

5. The method for integrated design of wind turbine nacelle base based on topology optimization according to claim 1, characterized in that: The step S2 comprises: Establish the density and unit elastic modulus E e Interpolation method: Where p is the penalty factor, which has an initial value of 1 and increases with the number of optimization iterations; E0 is the Young's modulus of the actual material.

6. The method for integrated design of wind turbine nacelle base based on topology optimization according to claim 1, characterized in that: The step S2 comprises: The topology optimization results under the action of single bending moments Mx, My and Mz were investigated. The three orthogonal moments were used to perform topology optimization calculations respectively, and the force transmission paths under the action of each load were obtained. The minimum size constraint was set to suppress the checkerboard phenomenon and mesh dependence problems. The minimum size constraint was taken as twice the average size of the unit, and the topology optimization results under loads in different directions were obtained.

7. The method for integrated design of wind turbine nacelle base based on topology optimization according to claim 1, characterized in that: The step S4 comprises: Strength verification includes ultimate strength and fatigue strength verification. In ultimate strength verification, bending moments in different directions are selected as the dominant working conditions as ultimate working conditions, namely Mk_min, Mk_max and Myz_max, where k = x, y and z. The load value at the center of the hub is output for each working condition, which is composed of forces and moments in three directions. According to the preset material safety factor of 1.1 and the allowable stress of 200MPa, the statistical results of maximum displacement and equivalent stress under different working conditions are analyzed. If the maximum equivalent stress value under each working condition is less than the allowable stress, the integrated optimized structure meets the ultimate strength design requirements. The software outputs the values ​​and frequency of time-series fatigue load conditions to verify the fatigue strength of the integrated design, and the rain flow counting method is used for cumulative damage calculation.

8. The method for integrated design of wind turbine nacelle base based on topology optimization according to claim 1, characterized in that: The step S5 comprises: The preset lightweight design requirement is that the maximum fatigue damage values ​​are all less than 1. According to Miner's law, if the maximum fatigue damage values ​​of all regions of the optimized structure are all less than 1, the optimized structure meets the fatigue strength design requirements; if the maximum fatigue damage values ​​of all regions of the optimized structure are not less than 1, steps S2 to S4 are repeated until the preset lightweight design requirements are met.

9. A non-transitory computer-readable medium storing instructions, characterized in that: When the instruction is executed by the processor, the steps of the method for integrated design of a wind turbine nacelle and base based on topology optimization according to any one of claims 1 to 8 are performed.

10. A computing device comprising a processor and a memory for storing a program executable by the processor, characterized in that: When the processor executes the program stored in the memory, the wind turbine nacelle base integrated design method based on topology optimization described in any one of claims 1 to 8 is implemented.

Images