A method for analyzing dynamic response of wind turbine under random wind load

Abstract

The application provides a wind turbine dynamic response analysis method under random wind load, and the method comprises the following steps: establishing a random wind speed field model under a MATLAB simulation platform; whole machine dynamics modeling; establishing a finite element model through finite element simulation and performing dynamic response solving calculation; and performing coupling calculation solving by considering the coupling relationship between the wind wheel and the tower. The wind turbine dynamic response analysis method under random wind load makes the influence law of blade modification on the wind wheel and the tower obtained through dynamic response calculation, so that the wind turbine dynamics research is more perfect.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of wind power generation, in particular, to a wind turbine dynamic response analysis method under random wind load. BACKGROUND

[0002] The working environment of the wind turbine is in the natural wind field in the wild, and the turbulence characteristics of the wind field will change the aerodynamic load on the surface of the wind turbine, thereby affecting the structural dynamics characteristics of the wind turbine. Under the condition of typhoon and other extreme bad weather, the wind turbine may also break and other dangerous situations. The blade is an important component for capturing wind energy of the wind turbine, and a large number of attempts and researches have been made on the blade structure at home and abroad, such as adding a small wing at the trailing edge of the blade. After the modification of the blade, the ability of the wind turbine to capture wind energy changes, that is, the aerodynamic load on the wind wheel changes, so that the displacement of the blade top end and the maximum stress of the blade change. The tower is a supporting structure of the wind wheel, and the vibration of the blade during the operation of the wind wheel will affect the tower, so the modification of the blade will also affect the dynamics characteristics of the tower.

[0003] In the currently disclosed prior art, domestic researches are mainly carried out on the dynamics response of the single wind turbine component or the traditional wind turbine without blade modification, and there is a lack of research on modeling of the wind load of the blade modification wind turbine and solving the dynamics response of the whole machine from the perspective of the blade modification. SUMMARY

[0004] The purpose of the present application is to solve the problem of failure caused by the dynamics design of the blade modification wind turbine, and to provide a wind turbine dynamic response analysis method under random wind load considering the coupling of the tower.

[0005] To solve the above problems, the technical scheme of the present application is as follows:

[0006] A wind turbine dynamic response analysis method under random wind load, comprising the following steps:

[0007] establishing a random wind speed field model under the MATLAB simulation platform;

[0008] whole machine dynamics modeling;

[0009] establishing a finite element model through finite element simulation to solve and calculate the dynamic response;

[0010] considering the coupling relationship between the wind wheel and the tower, and performing coupling calculation and solving.

[0011] Optionally, the step of establishing a random wind speed field model under the MATLAB simulation platform specifically comprises:

[0012] Step 1: Establish an average wind speed field;

[0013] Step 2: Establish a fluctuating wind speed power spectrum;

[0014] Step 3: Establish the fluctuating wind field of the wind turbine by the harmonic superposition method.

[0015] Optionally, the establishing the mean wind speed field specifically comprises that the wind speed of a certain point in the wind field is composed of the mean wind speed and the turbulent wind speed, and for a three-dimensional wind field, the wind speed of any point is: In the formula:

[0016] is the mean wind speed, u(x, y, z, t), v(x, y, z, t), z(x, y, z, t) are the projections of the turbulent wind speed in three directions.

[0017] Optionally, the establishing the fluctuating wind speed power spectrum specifically comprises: selecting Kaimal spectrum for simulation, and the downwind Kaimal spectrum density function is: In the formula: K = 0.4.

[0018] Optionally, the establishing the fluctuating wind field of the wind turbine by the harmonic superposition method specifically comprises: dividing the frequency width of the turbulent velocity into n equal parts, and the length of each part is:

[0019] Δf = (f2-f1) / n

[0020]

[0021] In the formula,

[0022]

[0023]

[0024] f m = f1+(m-0.5)*Δf, m = 1, 2…n

[0025] Cholesky decomposition is performed on Sm(fm) to obtain a lower triangular matrix Hm:

[0026] S m (f m ) = H m ·H m T

[0027]

[0028] N random angles θn are generated, and θn is uniformly distributed on [0~2π].

[0029] Optionally, the establishing the fluctuating wind field of the wind turbine by the harmonic superposition method specifically further comprises: constructing a diagonal matrix Xm by using the random angle θn:

[0030]

[0031] The discrete Fourier transform value of each point in the frequency domain is:

[0032] V m = H m · X m · I

[0033] In the formula, I is an n*1 unit matrix, and an n*n matrix is constructed:

[0034] V = |V1 · V2…V m …V M |

[0035] The jth row in the matrix V represents the discrete Fourier transform value of the jth point.

[0036] Optionally, the step of modeling the overall dynamics specifically comprises:

[0037] The basic motion equation of vibration is calculated based on the modal superposition method:

[0038]

[0039] In the formula, M, C, and K are the mass, damping, and stiffness matrices of the system, respectively, y(t) are acceleration, velocity, and displacement vectors, respectively, and P(t) is a load vector.

[0040] The response of the structure is calculated by multiplying the mode shape obtained by modal analysis by a factor and summing, and after solving the displacement component of each single-degree-of-freedom equation, the final solution is obtained by adding them together:

[0041]

[0042] Optionally, the step of establishing a finite element model through finite element simulation and solving and calculating the dynamic response specifically comprises:

[0043] Three different finite element models are established considering the influence of coupling on the wind turbine.

[0044] The aerodynamic load is solved, and the aerodynamic load of the wind turbine under random wind speed is output.

[0045] Dynamic response simulation, based on the modal superposition method, obtains the maximum displacement and maximum stress curves of the wind wheel and the tower.

[0046] Compared with the prior art, the application is based on the harmonic superposition method, a simulation program for a double-forked blade tip and other improved wind turbine blades is written by using MATLAB simulation software, a time history curve of random wind speed required for dynamic response simulation of the wind turbine is calculated, wind field data obtained by simulation calculation is more in line with the situation of the wind turbine, a three-dimensional model and a finite element model of the designed modified blade wind turbine are established, different constraint conditions are set according to the connection relationship between different components, there is a coupling relationship between the wind wheel and the tower during calculation, the influence law of the modified blade on the wind wheel and the tower is obtained by calculating the dynamic response, the wind turbine dynamics research is more perfect, and the wind turbine dynamics research of the modified blade wind turbine has important significance. BRIEF DESCRIPTION OF DRAWINGS

[0047] Other features, objects and advantages of the present application will become more apparent from the following detailed description of non-limiting embodiments thereof, read in conjunction with the accompanying drawings:

[0048] Figure 1 A flow chart of a wind turbine dynamic response analysis method under random wind load is provided for the embodiments of the application;

[0049] Figure 2 A wind wheel with a double-forked blade tip structure is provided for the embodiments of the application;

[0050] Figure 3 A comparison chart of a target spectrum and a calculated spectrum is provided for the embodiments of the application;

[0051] Figure 4 A wind speed time history curve chart is provided for the embodiments of the application;

[0052] Figure 5a 、 5b A wind turbine wind force and tower maximum displacement response chart is provided for the embodiments of the application. DETAILED DESCRIPTION

[0053] The application will be described in detail below with specific embodiments. The following embodiments will help those skilled in the art to further understand the application, but do not limit the application in any form. It should be noted that, for those skilled in the art, without departing from the concept of the application, a number of changes and improvements can be made. These all belong to the protection scope of the application.

[0054] Specifically, Figure 1 A wind turbine dynamic response analysis method under random wind load is provided for the embodiments of the application, as shown in Figure 1 The method comprises the following steps:

[0055] S1: a random wind speed field model is established under a MATLAB simulation platform;

[0056] Specifically, the random wind speed field model established under the MATLAB simulation platform comprises the following steps:

[0057] Step 1: Establish an average wind speed field;

[0058] The wind speed of a point in the wind field is composed of the average wind speed and the turbulent wind speed. For a three-dimensional wind field, the wind speed of an arbitrary point is:

[0059] In the formula: u(x,y,z,t), v(x,y,z,t), z(x,y,z,t) are the projections of the turbulent wind speed in three directions.

[0060] Step 2: Establish the fluctuating wind speed power spectrum

[0061] For the fluctuating wind speed power spectrum in the wind direction, the commonly used ones are Kaimal spectrum, von Karman spectrum and Davenport spectrum. In this embodiment, Kaimal spectrum is selected for simulation, and the Kaimal spectrum density function in the wind direction is:

[0062]

[0063] In the formula: K=0.4.

[0064] For any two points in the wind field, there is a spatial correlation between them, and the correlation function is defined by using the Davenport index:

[0065]

[0066] In the formula: K is a dimensionless attenuation constant, and r is the distance between the two points.

[0067] Step 3: Establish the fluctuating wind field of the wind turbine by the harmonic superposition method.

[0068] The frequency width of the turbulent velocity is divided into n equal parts, and the length of each part is:

[0069] Δf=(f2-f1) / n (4)

[0070]

[0071] In the formula,

[0072]

[0073]

[0074] f m =f1+(m-0.5)*Δf, m=1,2…n (8)

[0075] Cholesky decomposition is performed on Sm(fm) to obtain a lower triangular matrix Hm:

[0076] S m (f m )=H m ·H m T (9)

[0077]

[0078] N random angles θn are generated, which are uniformly distributed in [0, 2π]. A diagonal matrix Xm is constructed using the random angles θn:

[0079]

[0080] The discrete Fourier transform value of each point under fm is:

[0081] V m =H m ·X m ·I (12)

[0082] where I is an n x 1 unit matrix.

[0083] An n x n matrix V is constructed:

[0084] V=|V1·V2…V m …V M | (13)

[0085] The jth row of the matrix V represents the discrete Fourier transform value of the jth point. Programming in MATLAB software using the above formula can obtain the time history diagram of the fluctuating wind speed of the wind turbine.

[0086] S2: whole machine dynamics modeling;

[0087] Specifically, the whole machine dynamics modeling comprises:

[0088] 2.1 Motion equation

[0089] Based on the modal superposition method, the basic motion equation of vibration is calculated as:

[0090]

[0091] where M, C, and K are the mass, damping, and stiffness matrices of the system, respectively, y(t) are the acceleration, velocity, and displacement vectors, respectively, and P(t) is the load vector.

[0092] 2.2 Modal superposition method

[0093] Modal superposition method is to calculate the response of the structure by multiplying the mode shape obtained by modal analysis with a factor and summing up. Assuming that y can be represented by linear superposition of modal shapes, the physical coordinates y are converted to modal coordinates q:

[0094] y(t) = φq(t) (15)

[0095] Substituting equation (15) into equation (14) gives

[0096]

[0097] Multiplying both sides of equation (16) by φ T :

[0098]

[0099] Assuming that proportional damping exists and satisfies orthogonality, then

[0100]

[0101] In the formula: ξ i is the damping ratio of the i-th order, and ω i is the vibration frequency of the i-th order.

[0102] Equation (18) can be converted into m uncoupled single degree of freedom equations:

[0103]

[0104] After solving the displacement component of each single degree of freedom equation, the final solution is obtained by adding up:

[0105]

[0106] S3: Establish a finite element model through finite element simulation, and solve and calculate the dynamic response;

[0107] Specifically, establishing a finite element model through finite element simulation includes:

[0108] 3.1 Model establishment

[0109] In this embodiment, the double forked blade tip is selected as an improved wind turbine blade for dynamic response analysis. Considering the influence of coupling on the wind turbine, three different finite element models are established.

[0110] Rotor: First, the unmodified blade tip structure is arranged at an interval of 120° on the circumference, and the double forked blade tip structure is arranged at an interval of 120° on the circumference. Then, the completed blade array is connected with the hub to obtain two kinds of blade tip structure rotor models, wherein the double forked blade tip structure rotor is as shown in Figure 2 .

[0111] Simplify tower: wind wheel, shaft, cabin simplified as concentrated mass applied in the top of the tower, coupled with the tower through MASS21 unit in ANSYS.

[0112] Whole machine: wind wheel, shaft, cabin, tower assembled as a whole. The wind wheel and the shaft are connected by binding contact, the shaft and the cabin are connected by rotation, and the cabin and the tower are connected by fixing. The bottom of the tower is fixedly constrained with the ground. In this embodiment, SolidWorks is used to establish a three-dimensional model, which is then imported into hypermesh for finite element modeling. The wind wheel uses solid187 unit, and the tower uses solid186 unit.

[0113] 3.2 Aerodynamic load solving

[0114] The UDF program is written by using the fluctuating wind speed time history obtained in step S1, which is imported into Fluent to set the boundary conditions and initial conditions required for fluid calculation and solution. After the solution is completed, the aerodynamic load of the wind turbine under random wind speed is output.

[0115] 3.3 Dynamic response simulation

[0116] The pressure on the surface of the wind turbine solved in step 3.2 is imported into ANSYS as the aerodynamic load of the wind turbine for dynamic response solving and calculation. The coupling relationship between the wind wheel and the tower is considered in the calculation, and the same number of calculation sub-steps as the pressure load data is created to couple Fluent and Workbench for calculation. Based on the modal superposition method, the maximum displacement and maximum stress curves of the wind wheel and the tower are obtained, and the wind speed time history target spectrum is compared with the calculation spectrum as shown in Figure 3 , and the wind speed time history curve is shown in Figure 4 .

[0117] S4: Considering the coupling relationship between the wind wheel and the tower, the coupled calculation is performed.

[0118] The calculation results are shown in Figure 5a and 5b . As can be seen from Figure 5a and 5b , the dynamic response curves of the wind wheel and the tower before and after the blade modification change, and the influence of the coupling effect of the wind wheel and the tower on the two kinds of blades is also well reflected.

[0119] Compared with the prior art, the application is based on the harmonic superposition method, a simulation program for a double fork blade tip and other improved wind turbine is written by using MATLAB simulation software, a random wind speed time curve required for dynamic response simulation of the wind turbine is calculated, wind field data obtained by simulation calculation is more in line with the wind turbine, a three-dimensional model and a finite element model of the designed modified blade wind turbine are established, different constraint conditions are set according to the connection relationship between different components, there is a coupling relationship between the wind wheel and the tower during calculation, the influence law of the modified blade on the wind wheel and the tower is obtained by calculating the dynamic response, the wind turbine dynamics research is more perfect, and the wind turbine dynamics research of the blade tip structure modified blade has important significance.

[0120] The specific embodiments of the application are described above. It needs to be understood that the application is not limited to the specific embodiments described above, and various changes or modifications can be made by those skilled in the art within the scope of the claims, which does not affect the essential content of the application. The embodiments of the application and the features in the embodiments can be combined with each other in any way without conflict.

Claims

1. A method for analyzing dynamic response of a wind turbine under random wind loading, characterized in that, The method comprises the following steps: A random wind speed field model is established under a MATLAB simulation platform, specifically comprising: Step 1: Establishing an average wind speed field; Step 2: Establishing a fluctuating wind speed power spectrum; Step 3: Establishing a wind turbine fluctuating wind field through a harmonic superposition method, specifically comprising: dividing the frequency width of the turbulent flow velocity into n equal parts, and the length of each part is: Δf = (f2-f1) / n In the formula, f m = f1+ (m - 0.5) * Δf, m = 1, 2...n Cholesky decomposition is performed on Sm(fm) to obtain a lower triangular matrix Hm: S m (f m )=H m ·H m T N random angles θn are generated, and θn is uniformly distributed in [0~2π]; A diagonal matrix Xm is constructed using the random angle θn: The discrete Fourier transform value of each point under fm is: V m = H m • X m • I In the formula: I is an n×1 unit matrix, and an n×n matrix is constructed: V = |V1 · V2 · · · V m ... V M | The jth row of the matrix V represents the discrete Fourier transform value of the jth point; Whole machine dynamics modeling, specifically comprising: The basic motion equation of vibration is calculated based on the modal superposition method: Where: M, C, K are the mass, damping, stiffness matrices of the system, y(t) are the acceleration, velocity, displacement vectors, and P(t) is the load vector. The response of the structure is calculated by multiplying the mode shape obtained by modal analysis by a factor and then summing up, and after the displacement component of each single-degree-of-freedom equation is solved, the final solution is obtained: ； A finite element model is established through finite element simulation, and dynamic response is calculated and solved; The coupling relationship between the wind wheel and the tower is considered, and coupling calculation is performed for solving.

2. The method for analyzing dynamic response of a wind turbine under random wind loads as claimed in claim 1 wherein, The establishing the average wind speed field specifically comprises that the wind speed of a certain point in the wind field is composed of the average wind speed and the turbulent wind speed, and for a three-dimensional wind field, the wind speed of any point is: In the formula: is the average wind speed, u(x, y, z, t), v(x, y, z, t), z(x, y, z, t) is the projection of the turbulent wind speed in three directions.

3. The method for analyzing dynamic response of a wind turbine under random wind loads as claimed in claim 1 wherein, The establishing the power spectrum of the fluctuating wind speed specifically includes: selecting the Kaimal spectrum for simulation, and the along-wind Kaimal spectrum density function is: In the formula: K=0.

4.

4. The method for analyzing dynamic response of a wind turbine under random wind loading as claimed in claim 1 wherein, The step of establishing a finite element model through finite element simulation and calculating and solving the dynamic response specifically comprises: The influence of the coupling effect on the wind turbine is considered, and three different finite element models are established; The aerodynamic load is solved, and the aerodynamic load of the wind turbine under random wind speed is outputted; Dynamic response simulation, based on the modal superposition method, obtains the maximum displacement and maximum stress curve of the wind wheel and the tower.

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