A stress verification method for the main beam of pultruded plate of wind turbine blades

Abstract

The present invention provides a stress verification method for the main beam of a pultruded plate material used in a wind turbine blade, comprising: constructing a shell element model of the wind turbine blade, loading the shell element model in the maximum swing direction according to a design load, obtaining the strain distribution of the overall blade structure using finite element software, and extracting a first strain distribution of the main beam; constructing a solid model of the main beam chamfer area, and coupling it with the shell element model based on dynamic constraints to obtain a coupled model; loading the coupled model in the maximum swing direction according to the design load to obtain a second strain distribution of the main beam; obtaining an equivalent fatigue load based on the blade's swing direction based on the second strain distribution, and calculating the service life and safety factor of the main beam based on the equivalent fatigue load. The present invention enables more accurate verification of the fatigue life of the main beam, reduces the amount of calculation, and improves computational efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of wind power generation, and in particular to a stress checking method for a main beam of a pultruded plate material of a wind turbine blade. Background Art

[0002] As wind turbine blades grow longer, blade weight reduction is gaining increasing attention. Using pultrusion to produce epoxy resin pultruded sheets, replacing the traditional vacuum infusion process for blade beams, has become a new trend in wind turbine blade manufacturing. However, existing techniques typically use finite element static analysis to analyze the buckling and fiber failure of wind turbine blade shell models.

[0003] However, existing technologies use shell models in their calculations and analysis. For blades using pultruded sheet metal as the main beam, the chamfers of the main beam are difficult to reflect in the model, resulting in difficulty in ensuring the accuracy of the analytical results. Furthermore, the chamfered areas of the main beam are often weak points in the main beam itself and even in the blade. Therefore, using shell models to verify the main beam of pultruded sheet metal blades presents a high risk. Furthermore, due to the complex structure of wind turbine blades, solid models have difficulty simulating the actual laminate structure, and solid models are computationally intensive and inefficient.

[0004] Therefore, there is an urgent need for a calibration method that can accurately calibrate the main beam of the blade pultruded plate and improve the calculation efficiency. Summary of the Invention

[0005] Based on this, it is necessary to provide a stress verification method for the main beam of pultruded sheet materials of wind turbine blades in response to the above technical problems.

[0006] A stress verification method for a main beam of a pultruded plate material of a wind turbine blade comprises the following steps: constructing a shell unit model of the wind turbine blade, loading the shell unit model in a maximum swinging direction according to a design load, obtaining the strain distribution of the overall blade structure through finite element software, and extracting a first strain distribution of the main beam; constructing a solid model of the chamfered area of ​​the main beam, and coupling it with the shell unit model based on dynamic constraints to obtain a coupled model; loading the coupled model in a maximum swinging direction according to the design load to obtain a second strain distribution of the main beam; obtaining an equivalent fatigue load based on the blade swinging direction according to the second strain distribution, and calculating the service life and safety factor of the main beam according to the equivalent fatigue load.

[0007] In one embodiment, there is a chamfer of 1:100 at the end position of the main beam.

[0008] In one embodiment, the link between the shell element model and the solid model adopts dynamic coupling constraint, and the solid model is discretized using an 8-node hexahedron.

[0009] In one embodiment, after loading the maximum swing direction of the coupling model according to the design load and obtaining the second strain distribution of the main beam, the method further includes: pasting strain gauges on the inner and outer surfaces of the chamfer end position of the main beam through a static load test, and monitoring the measured strain of the main beam according to the strain gauges during static loading; and comparing the first strain distribution and the second strain distribution according to the measured strain to verify the validity of the coupling model.

[0010] In one embodiment, obtaining an equivalent fatigue load based on the blade flapping direction according to the second strain distribution, and calculating the service life and safety factor of the main beam according to the equivalent fatigue load include:

[0011] According to the second strain distribution, an equivalent fatigue load based on the blade flapping direction is obtained, and the number of times the main beam can be used is calculated according to the equivalent fatigue load. The formula is:

[0012]

[0013] in:

[0014]

[0015]

[0016] Where S k,M is the mean value of the stress in the main direction of the material. When the equivalent fatigue load is used, its value is 0. S k,A is the amplitude of the stress in the principal direction of the material, R k,t 、R k,c is the strength characteristic value of the material in the tensile and compressive directions, m=10 is the slope parameter of the SN curve of the epoxy resin matrix laminate, γ M0 =1.35, C 1a For aging effects, C 2a is the temperature effect, C 3a For laminates produced by resin infusion, C 4a For the laminate after secondary curing, C 2b is the temperature effect, C 3b For unidirectional fabric, C 4b For the laminate after secondary curing, C 5b The trailing edge of the blade;

[0017] The safety factor is calculated based on the number of times the main beam can be used, and the formula is:

[0018]

[0019] Where S f is the main beam safety factor, N is the number of times the main beam can be used, and M is the number of blade flaps corresponding to the equivalent fatigue load.

[0020] In one embodiment, the method further includes obtaining an equivalent fatigue load based on the blade swinging direction according to the second strain distribution, and calculating the number of times the main beam can be used and the safety factor according to the equivalent fatigue load. The method further includes: laying a reinforcement cloth at the end position of the main beam according to the number of times the main beam can be used and the safety factor.

[0021] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: the present invention can construct a shell unit model of the wind turbine blade, load the shell unit model in the maximum swing direction according to the design load, obtain the strain distribution of the overall structure of the blade through finite element software calculation, obtain the first strain distribution of the main beam, construct a solid model of the chamfer area of ​​the main beam, and couple it with the shell unit model based on dynamic constraints to obtain a coupled model, thereby avoiding the entity calculation of the main beam as a whole, reducing the amount of calculation, improving the calculation efficiency, and making the coupled model more consistent with the actual stress, loading the coupled model in the maximum swing direction according to the design load, obtaining the second strain distribution of the main beam, and according to the second strain distribution, obtaining the equivalent fatigue load based on the blade swing direction, and calculating the number of times the main beam can be used and the safety factor. The fatigue life calculated by the coupling model has higher accuracy, thereby improving the accuracy of the main beam verification results. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of a process for stress verification of a main beam of a pultruded plate for a wind turbine blade according to an embodiment;

[0023] Figure 2 Schematic diagram of stress concentration effect at the end position of the main beam in one embodiment;

[0024] Figure 3 Schematic diagram of the discrete effect of the coupling model in one embodiment;

[0025] Figure 4 Schematic diagram showing the comparison between the measured strain, the shell element model strain, and the coupled model strain in one embodiment;

[0026] Figure 5 Schematic diagram showing the comparison of the deviations between the shell element model strain and the measured strain, and the coupled model strain and the measured strain in one embodiment. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below through specific embodiments in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0028] In one embodiment, Figure 1As shown, a stress check method for a main beam of a pultruded plate of a wind turbine blade is provided, comprising the following steps:

[0029] Step S101 : constructing a shell element model of a wind turbine blade, loading the shell element model in the maximum flapping direction according to the design load, obtaining the strain distribution of the entire blade structure through finite element software, and extracting the first strain distribution of the main beam.

[0030] Specifically, the shell element model of the wind turbine blade is constructed using FOCUS software, and the shell element model is loaded in the maximum swing direction according to the design load. The strain distribution of the overall blade structure is calculated using finite element software, and the first strain distribution of the blade main beam part is extracted, such as Figure 2 As shown in the figure, the maximum strain of the main beam is about 5100 microstrains, which occurs at the end of the plate. Before and after this position, the unit strain is about 3000 microstrains, and there is obvious stress concentration. The main reason is that there is a step in the thickness direction of the shell unit model at this location, and this step will cause stress concentration.

[0031] Among them, there is a 1:100 chamfer at the end of the pultruded plate main beam.

[0032] Specifically, in actual situations, in order to ensure smooth transition when assembling multi-layer panels, each layer of panel needs to be cut and chamfered during assembly. Therefore, there is a 1:100 chamfer at the end position of the main beam of the wind turbine blade pultruded panel.

[0033] Step S102: construct a solid model of the main beam chamfer area, and couple it with the shell element model based on dynamic constraints to obtain a coupled model.

[0034] Specifically, due to the chamfer at the end of the main beam, it can be seen that the shell element model cannot truly simulate the stress distribution in the chamfer area of ​​the main beam, and its calculation results are conservative. Therefore, the chamfer area of ​​the main beam is selected as the research object, and a solid model of the chamfer area of ​​the main beam is constructed. The link between the solid model and the shell element model is dynamically coupled to obtain a coupling model of the shell element model and the solid model.

[0035] Through dynamic coupling constraints, the chamfered area of ​​the main beam is calculated using a solid model, while the remaining areas still use the shell element model to obtain a coupled model. By constructing a solid model of the chamfered area of ​​the main beam and coupling it with the shell element model of the remaining areas, the solid calculation of the main beam as a whole is avoided, thereby reducing the amount of calculation and improving the calculation efficiency. At the same time, a more accurate coupling model can be obtained, through which the main beam can be accurately checked.

[0036] The link between the shell element model and the solid model adopts dynamic coupling constraint, and the solid model is discretized using 8-node hexahedron.

[0037] Specifically, when the shell element model is coupled with the solid model, dynamic coupling constraints are used to obtain a coupling model in which the main beam chamfer area is a solid model. At the same time, Figure 3 As shown in FIG, the coupled model is discretized using 8-node hexahedron elements to obtain several discrete elements. By calculating the stress of all discrete elements, the strain distribution of the main beam can be obtained.

[0038] Step S103 : Loading the maximum flapping direction of the coupling model according to the design load to obtain a second strain distribution of the main beam.

[0039] Specifically, the same static load as the shell element model, i.e., the design load, is used to load the maximum swing direction of the coupled model. The calculation results are as follows: Figure 4 As shown in the figure, for the main beam component, the maximum strain is 4100 microstrains, which occurs in the chamfer area of ​​the main beam. By comparing the coupling model with the shell element model, it can be seen that the main beam strain of the coupling model is significantly smaller than the main beam strain of the shell element model. The reason is that there is no stress concentration in the coupling model.

[0040] In one embodiment, after obtaining the second strain distribution of the main beam, the method further includes: through a static load test, pasting strain gauges on the inner and outer surfaces of the chamfer end position of the main beam, and monitoring the measured strain of the main beam according to the strain gauges during static loading; comparing the first strain distribution and the second strain distribution according to the measured strain to verify the effectiveness of the coupling model.

[0041] Specifically, to verify the accuracy of the shell element model and coupled model calculations under maximum flapping conditions, static load tests were conducted. For an 80-meter-long wind turbine blade, its basic parameters are shown in Table 1. Strain gauges were attached to the inner and outer surfaces of the main beam chamfer end point to monitor the actual strain during static loading. The monitoring point was the end point of the main beam pultruded plate, which is also a stress concentration point.

[0042] After obtaining the measured strain, the difference between it and the strain of the shell element model and the solid model is compared. It can be seen that the strain of the coupled model is consistent with the measured strain, with a maximum deviation of 2.5%. Figure 5 As shown in the figure, under actual loading conditions, the stress concentration effect in the main beam chamfer area is not obvious, which verifies that the method of using the coupled model to check the chamfer area of ​​the pultruded plate main beam is more reliable, thereby improving the accuracy of the main beam stress check.

[0043] Table 1

[0044] Blade Project unit Numerical length m 81 weight kg 20000 Maximum flapping bending moment at blade root kN.m 25000 Equivalent fatigue load in the swing direction kN.m 8200 Pultruded sheet thickness mm 45

[0045] Step S104: obtaining an equivalent fatigue load based on the blade flapping direction according to the second strain distribution, and calculating the service life and safety factor of the main beam according to the equivalent fatigue load.

[0046] Specifically, after obtaining the second strain distribution obtained by the coupling model, the corresponding equivalent fatigue load is obtained according to the swinging direction of the blade, and is used to verify the fatigue life of the blade main beam, and the number of times the main beam can be used and the safety factor are obtained. Since the second strain distribution obtained by the coupling model is more consistent with the actual strain, the fatigue load obtained through the second strain distribution and the fatigue life of the main beam obtained by verification are also more accurate, thereby improving the verification accuracy of the blade main beam.

[0047] According to the second strain distribution, the equivalent fatigue load based on the blade flapping direction is obtained, and the number of times the main beam can be used is calculated according to the equivalent fatigue load. The formula is:

[0048]

[0049] in:

[0050]

[0051]

[0052] Where S k,M is the mean value of the stress in the main direction of the material. When the equivalent fatigue load is used, its value is 0. S k,A is the amplitude of the stress in the principal direction of the material, R k,t 、R k,c is the strength characteristic value of the material in the tensile and compressive directions, m is the slope parameter of the SN curve of the epoxy resin matrix laminate, γ M0 =1.35, C 1a For aging effects, C 2a is the temperature effect, C 3a For laminates produced by resin infusion, C 4a For the laminate after secondary curing, C 2b is the temperature effect, C 3b For unidirectional fabric, C 4b For the laminate after secondary curing, C 5b The trailing edge of the blade;

[0053] Calculate the safety factor based on the number of times the main beam can be used. The formula is:

[0054]

[0055] Where S f is the main beam safety factor, N is the number of times the main beam can be used, and M is the number of blade flaps corresponding to the equivalent fatigue load.

[0056] Specifically, since it can be seen from the above verification results that it is more reliable to use the coupling model to verify the pultruded plate, the equivalent fatigue load based on the blade swing direction is obtained based on the coupling model to verify the fatigue life of the blade main beam. Under the equivalent fatigue load of 10 million swings, the maximum strain of the coupling model main beam is 1800 microstrains, S k,A is the amplitude of the stress in the main direction of the material, which is calculated by multiplying the strain value of the main beam by the Young's modulus of the material. When m=10, C 1a =1.35, C 2a =C 3a =C 2b =C 5b =1.1 and C 4a =C 3b =C 4b =1, the calculated number of times the main beam can be used is 6.412E+9 times, and the safety factor is 1.909.

[0057] When using the shell element model, the maximum strain in the main beam is 2100 microstrains, and the corresponding safety factor is calculated to be 1.636, which is lower than the safety factor calculated using the coupled model. Therefore, using the shell element model for main beam verification will lead to inaccurate verification, while using the coupled model is more reliable and accurate.

[0058] In one embodiment, after step S104, the method further includes: laying a reinforcement cloth at the end position of the main beam according to the usable times and the safety factor of the main beam.

[0059] Specifically, for blades calibrated using the shell element model, the previous approach was to lay a large amount of reinforcing cloth in the area where the pultruded plate ends in the main beam to alleviate stress concentration. However, the calibration method using the coupled model provides safer and more realistic results. Therefore, based on the calculation results, the width and thickness of the reinforcing cloth to be laid can be determined, thereby achieving the precise and reasonable laying of the reinforcing cloth at the end position of the pultruded plate main beam, achieving the purpose of reducing blade weight and reducing costs.

[0060] In this embodiment, a shell unit model of the wind turbine blade is constructed, and the shell unit model is loaded in the maximum swing direction according to the design load. The strain distribution of the overall structure of the blade is obtained by calculation using finite element software to obtain the first strain distribution of the main beam. A solid model of the chamfered area of ​​the main beam is constructed, and coupled with the shell unit model based on dynamic constraints to obtain a coupled model. This avoids the entity calculation of the main beam as a whole, reduces the amount of calculation, improves the calculation efficiency, and makes the coupled model more consistent with the actual stress. The coupled model is loaded in the maximum swing direction according to the design load to obtain the second strain distribution of the main beam. Based on the second strain distribution, the equivalent fatigue load based on the blade swing direction is obtained, and the number of times the main beam can be used and the safety factor are calculated. The fatigue life calculated by the coupled model has higher accuracy, thereby improving the accuracy of the verification results.

[0061] The above content is a further detailed description of the present invention in conjunction with specific embodiments, and the specific implementation of the present invention cannot be considered to be limited to these descriptions. For those skilled in the art of the present invention, without departing from the concept of the present invention, several simple deductions or substitutions can be made, which should be considered to fall within the scope of protection of the present invention.

Claims

1. A stress check method for a main beam of a pultruded plate for a wind turbine blade, characterized in that: The following steps are involved: Constructing a shell element model of a wind turbine blade, loading the shell element model in the maximum flapping direction according to the design load, obtaining the strain distribution of the entire blade structure using finite element software, and extracting the first strain distribution of the main beam; Constructing a solid model of the main beam chamfer area, and coupling it with the shell element model based on dynamic constraints to obtain a coupled model; Loading the maximum flapping direction of the coupling model according to the design load to obtain a second strain distribution of the main beam; Obtaining an equivalent fatigue load based on the blade flapping direction according to the second strain distribution, and calculating the service life and safety factor of the main beam according to the equivalent fatigue load, including: obtaining an equivalent fatigue load based on a blade flapping direction according to the second strain distribution; The service life of the main beam is calculated based on the equivalent fatigue load using the formula: in: Where S k,M is the mean value of the stress in the main direction of the material. When the equivalent fatigue load is used, its value is 0. S k,A is the amplitude of the stress in the principal direction of the material, R k,t 、R k,c is the strength characteristic value of the material in the tensile and compressive directions, m=10 is the slope parameter of the SN curve of the epoxy resin matrix laminate, γ M0 =1.35, C 1a For aging effects, C 2a is the temperature effect, C 3a For laminates produced by resin infusion, C 4a For the laminate after secondary curing, C 2b is the temperature effect, C 3b For unidirectional fabric, C 4b For the laminate after secondary curing, C 5b The trailing edge of the blade; The safety factor is calculated based on the number of times the main beam can be used, and the formula is: Where S f is the main beam safety factor, N is the number of times the main beam can be used, and M is the number of blade flaps corresponding to the equivalent fatigue load.

2. The stress check method for a pultruded plate main beam of a wind turbine blade according to claim 1, characterized in that: There is a chamfer of 1:100 at the end position of the main beam.

3. The stress check method for a pultruded plate main beam of a wind turbine blade according to claim 1, characterized in that: The link between the shell element model and the solid model adopts dynamic coupling constraint, and the solid model is discretized using an 8-node hexahedron.

4. The stress check method for a pultruded plate main beam of a wind turbine blade according to claim 1, characterized in that: After loading the maximum flapping direction of the coupling model according to the design load to obtain the second strain distribution of the main beam, the method further includes: Through the static load test, strain gauges are attached to the inner and outer surfaces of the main beam at the end of the chamfer. During the static loading, the measured strain of the main beam is monitored based on the strain gauges. The first strain distribution and the second strain distribution are compared based on the measured strain to verify the validity of the coupling model.

5. The stress check method for a pultruded plate main beam of a wind turbine blade according to claim 1, characterized in that: After obtaining the equivalent fatigue load based on the blade swinging direction according to the second strain distribution and calculating the service life and safety factor of the main beam according to the equivalent fatigue load, the method further includes: laying a reinforcement cloth at the end position of the main beam according to the service life and safety factor of the main beam.

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