Method and system for evaluating welding stress of weld joint of wind turbine generator

Abstract

The invention discloses a method and a system for evaluating the welding stress of a weld joint of a wind turbine generator. The method comprises the following steps of: establishing a finite element analysis-based multi-physical simulation model of a tower drum of the wind turbine generator; boundary conditions are applied to the multi-physical simulation model of the wind turbine generator tower; the welding thermal load of the wind turbine generator tower drum is obtained, the multi-physical simulation model of the wind turbine generator tower drum is solved according to the welding thermal load under the boundary condition, and the temperature field of the wind turbine generator tower drum is obtained; and according to the temperature field of the wind turbine generator tower drum, a stress field borne by welding of the wind turbine generator tower drum is obtained. The welding temperature field and the stress field, calculated based on the welding thermal load, of the wind turbine generator are closer to the actual welding stress.

Description

Technical Field

[0001] The present invention relates to the technical field of wind turbine generator sets, and in particular to a method and system for evaluating welding stress of a weld of a wind turbine generator set. Background Art

[0002] The main function of the wind turbine tower is to support the load-bearing structure of the wind turbine nacelle and components, and to withstand the combined deformation caused by wind loads and the stress caused by the superposition of bending moments and torques. The tower needs to have sufficient fatigue strength to withstand the vibration loads caused by the start and stop of the unit, changes in wind conditions, etc. Its structural quality will be directly related to the safe operation of the entire wind turbine generator set.

[0003] During operation, the circumferential weld between the bottom of the tower and the lower flange is a weak point, which is prone to failure or even collapse. Therefore, taking effective measures to reduce stress concentration in welded joints, reduce restraint stress, and improve the stress state of the tower during construction can ensure the safe and effective operation of the tower. As the main load-bearing component of a wind turbine, the tower is subjected to the combined action of multiple loads for a long time. The long-term action of these loads causes fatigue damage to the tower vibration. The fatigue strength of the wind turbine tower depends on multiple factors, including material selection, geometry, load frequency and amplitude, etc. During the design stage, designers will select bolts of appropriate materials and geometry according to design requirements to meet the design requirements.

[0004] In the actual design and production process, designers need to evaluate the strength of the tower structure, promptly discover and deal with possible weaknesses in the design process, in order to extend its service life and ensure safe operation. At present, non-destructive testing methods are commonly used to measure the welding residual stress on the surface of the tower weld. However, this method can only measure the surface welding residual stress, and cannot measure the welding stress of the center layer. In the actual operation process, many wind turbine tower weld microcracks occur in the center of the weld. Existing non-destructive testing methods cannot reach this thickness and cannot measure residual stress. Summary of the invention

[0005] The technical problem to be solved by the present invention is that the current assessment of the tower structure strength is inaccurate and the assessment of the welding stress of the tower center layer is lacking.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] A method for evaluating welding stress of a weld of a wind turbine generator system, comprising:

[0008] Establish a multi-physics simulation model of wind turbine tower based on finite element analysis;

[0009] Apply boundary conditions to the multi-physics simulation model of the wind turbine tower;

[0010] Obtain the welding heat load of the wind turbine tower, and solve the multi-physics simulation model of the wind turbine tower according to the welding heat load under boundary conditions to obtain the temperature field of the wind turbine tower;

[0011] According to the temperature field of the wind turbine tower, the stress field of the wind turbine tower welding is obtained.

[0012] In one embodiment of the present invention, the multi-physics simulation model of the wind turbine tower is the following formula:

[0013]

[0014] Where ρ represents the density of the microelement, c represents the specific heat capacity, (x, y, z) represents the coordinate value of any point in the model, T represents the temperature field of the wind turbine tower, τ represents time, λ represents the thermal conductivity of the material, Q(r) represents the welding heat load, and r represents the distance from the center of the heat source during welding.

[0015] In one embodiment of the present invention, the welding heat load Q(r) includes the tower core welding heat load Q1(r) and the tower surface welding heat load Q2(r); and, Q(r)=Q1(r)+Q2(r);

[0016] Among them, the tower core welding heat load Q1(r) is obtained by the following formula:

[0017] Q1(r)=3q / (πR 2 )exp[-3(r / R)];

[0018] In the formula, q represents the arc thermal power, R represents the effective heat source radius, and exp represents the exponential function;

[0019] The tower surface welding heat load Q2(r) is obtained by the following formula:

[0020] Q2(r)=h1(T-T2);

[0021] Wherein, h1 represents the composite heat transfer coefficient of the wind turbine calculated under the actual welding conditions, and T2 represents the external ambient temperature.

[0022] In one embodiment of the present invention, the arc thermal power q is obtained by the following formula:

[0023] q = ηUI;

[0024] Where η represents the welding thermal efficiency, U represents the welding voltage, and I represents the welding current.

[0025] In one embodiment of the present invention, the composite heat transfer coefficient h1 is obtained by the following formula:

[0026] h1=h c +h r =h c +ε1σ 波 (T1 2 +T2 2 )(T1+T2);

[0027] In the formula, h c Expressed as the convective heat transfer coefficient, h r is expressed as the radiation heat transfer coefficient, ε1 is expressed as the spectral emissivity, σ 波 It is represented by the Stefan-Boltzmann constant, and T1 is represented by the tower surface temperature.

[0028] In one embodiment of the present invention, the boundary conditions applied include:

[0029] The melting point of liquid metal, Tm, is used as the first type of boundary condition;

[0030] The tower core welding heat load Q1(r) is used as the second type of boundary condition;

[0031] The composite heat transfer coefficient h1 and the external environment temperature T2 are used as the third type of boundary conditions.

[0032] In one embodiment of the present invention, the stress at any point in the stress field of the wind turbine tower welding is obtained by the following formula:

[0033]

[0034] In the formula, σ1 represents the stress of the wind turbine tower welding, ε represents the strain of the material, [D P ] is represented by the plasticity matrix, α is represented by the thermal expansion coefficient of the material, E is represented by the elastic modulus of the material, {ε e} is the elastic component of the total strain, σ Y It is represented as yield stress, T is represented as temperature field of wind turbine tower; It represents the symbol for differentiation;

[0035] in,

[0036]

[0037] In the formula, σ' x ,σ' y It is expressed as the deviation stress in the x-direction and the y-direction, v is the Poisson's ratio of the material, τ xy Expressed as the shear stress of the material.

[0038] In one embodiment of the present invention, based on the stress field of the wind turbine tower welding, the stress field of the external load is superimposed to obtain the superimposed stress, and the fatigue life of the wind turbine tower is evaluated according to the superimposed stress and the material SN curve.

[0039] In one embodiment of the present invention, the superimposed stress σ at any point on the tower is obtained by the following formula:

[0040] σ=σ1+σ2;

[0041] In the formula, σ1 represents the stress of the wind turbine tower welding, and σ2 represents the external load stress;

[0042] Fatigue strength σ according to material SN curve 疲 Compared with the obtained superimposed stress σ, when the superimposed stress σ of the tower is equal to the fatigue strength σ of the corresponding material 疲 When the value is reached, the fatigue life of the material is equal to the fatigue life of the tower.

[0043] The present invention further provides a system for evaluating welding stress of a weld of a wind turbine generator set, and the system applies any of the above-mentioned methods for evaluating welding stress of a weld of a wind turbine generator set, comprising:

[0044] The simulation model module is used to establish a multi-physics simulation model of the wind turbine tower based on finite element analysis;

[0045] Boundary condition module, used to apply boundary conditions to the multi-physics simulation model of wind turbine tower;

[0046] The temperature field module is used to obtain the welding heat load of the wind turbine tower and solve the multi-physics simulation model of the wind turbine tower according to the welding heat load under boundary conditions to obtain the temperature field of the wind turbine tower;

[0047] The stress field module is used to obtain the stress field of the wind turbine tower welding according to the temperature field of the wind turbine tower.

[0048] Compared with the prior art, the invention has the following beneficial effects: when obtaining the temperature field of the wind turbine tower, the invention adds the analysis of the thermal load of the tower core welding, while the currently commonly used non-destructive testing method cannot measure the welding stress of the tower core. The stress field of the wind turbine tower welding solved based on the temperature field of the wind turbine tower is more accurate, and the residual stress at the center of the weld can be obtained based on the obtained stress field, so as to find out the weak points of the tower structure strength.

[0049] The stress assessment method of the tower weld of a wind turbine generator set of the present invention calculates the stress field of the tower weld of the wind turbine generator set based on the welding thermal load of the tower weld of the wind turbine generator set. The welding thermal load is a thermal load that takes into account the actual thermal efficiency and heat exchange effect during the welding process, and is closer to the thermal load that the tower weld of the wind turbine generator set is actually subjected to during welding. In addition, in the actual welding of the tower weld of the wind turbine generator set, due to the loss of energy conversion, it is impossible for electrical energy to be completely converted into thermal energy. The thermal load obtained according to the welding process parameters is different from the thermal load generated by the actual welding. Considering the conversion efficiency of the welding energy, the welding temperature field and stress field of the wind turbine generator set calculated based on the thermal load are closer to the actual welding stress, and the welding stress assessment result of the tower weld of the wind turbine generator set is further improved in accuracy.

[0050] On the basis of the solved stress field, the external load stress field is superimposed to evaluate the fatigue life of the wind turbine. The fatigue life assessment results of the tower welds of the wind turbine are more accurate, which facilitates designers to more accurately optimize the structural design of the wind turbine tower, making the wind turbine operate more safely and efficiently. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 The present invention is a flow chart of a method for evaluating welding stress of a weld of a wind turbine generator system according to an embodiment of the present invention.

[0052] Figure 2 It is a schematic diagram of a simulation model of a wind turbine tower after grid division according to an embodiment of the present invention.

[0053] Figure 3 Schematic diagram of the temperature field of a wind turbine tower according to an embodiment of the present invention.

[0054] Figure 4 Schematic diagram of the stress field of the wind turbine tower welding according to an embodiment of the present invention.

[0055] Figure 5 The present invention is a flow chart of a fatigue life assessment method for a wind turbine generator system according to an embodiment of the present invention.

[0056] Figure 6 Schematic diagram of a simulation model of a wind turbine tower with an applied load according to an embodiment of the present invention.

[0057] Figure 7 Schematic diagram of stress field of external load according to an embodiment of the present invention.

[0058] Figure 8 The present invention is a block diagram of a system for evaluating welding stress of a weld of a wind turbine generator set according to an embodiment of the present invention. DETAILED DESCRIPTION

[0059] To facilitate those skilled in the art to understand the technical solution of the present invention, the technical solution of the present invention is further described in conjunction with the accompanying drawings.

[0060] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0061] See also Figure 1 As shown, the present invention provides a method for evaluating welding stress of a weld of a wind turbine generator set, comprising:

[0062] S10, establishing a multi-physics simulation model of a wind turbine tower based on finite element analysis.

[0063] In one embodiment of the present invention, a multi-physics simulation model of a wind turbine tower is established by using the finite element method to calculate the temperature field of the wind turbine tower weld, and then the welding stress field of the wind turbine tower weld is obtained through thermal coupling. In the simulation model, the calculation of the temperature field and stress field uses the birth-death unit technology to simulate the weld filling of the actual welding process. Figure 2 The simulation model of the wind turbine tower after meshing is shown.

[0064] In this embodiment, the multi-physics simulation model of the wind turbine tower is the following formula:

[0065]

[0066] Where ρ represents the density of the microelement, c represents the specific heat capacity, (x, y, z) represents the coordinate value of any point in the model, T represents the temperature field of the wind turbine tower, τ represents time, λ represents the thermal conductivity of the material, Q(r) represents the welding heat load, and r represents the distance from the center of the heat source during welding.

[0067] S20, applying boundary conditions to the multi-physics simulation model of the wind turbine tower.

[0068] In one embodiment of the present invention, the temperature field is solved by applying boundary conditions according to the finite element model, wherein the boundary conditions are applied by the multi-physics simulation model of the wind turbine tower, including:

[0069] The melting point of liquid metal, Tm, is used as the first type of boundary condition at the solid-liquid interface between the welding pool and the base material.

[0070] The welding pool is affected by the welding heat source, and the tower core welding heat load Q1(r) is used as the second type of boundary condition.

[0071] The composite heat transfer coefficient h1 between the pipeline steel and the external natural environment on the known boundary and the external environment temperature T2 are used as the third type of boundary conditions.

[0072] S30, obtaining the welding heat load of the wind turbine tower, and solving the multi-physics simulation model of the wind turbine tower according to the welding heat load under boundary conditions to obtain the temperature field of the wind turbine tower.

[0073] In one embodiment of the present invention, the welding heat load Q(r) includes the tower core welding heat load Q1(r) and the tower surface welding heat load Q2(r); and Q(r)=Q1(r)+Q2(r).

[0074] In this embodiment, the temperature detection device is used to detect in real time the tower core welding heat load Q1 (r) of the weld heat affected zone of the wind turbine tower during the welding process.

[0075] Among them, the tower core welding heat load Q1(r) is obtained by the following formula:

[0076] Q1(r)=3q / (πR 2 )exp[-3(r / R)];

[0077] Where q represents the arc thermal power, R represents the effective heat source radius, and exp represents the exponential function.

[0078] The arc heat power q is calculated by the welding process and obtained by the following formula:

[0079] q = ηUI;

[0080] In the formula, η represents the welding thermal efficiency, U represents the welding voltage, and I represents the welding current. In addition, the tower core welding heat load Q1(r) takes into account the actual welding thermal efficiency. Specifically, the temperature field of the wind turbine tower is as follows: Figure 3 shown.

[0081] The welding heat load Q2(r) on the cylinder surface is obtained by the following formula:

[0082] Q2(r)=h1(T-T2);

[0083] Wherein, h1 represents the composite heat transfer coefficient of the wind turbine calculated under the actual welding conditions, and T2 represents the external ambient temperature.

[0084] In addition, the calculation of interface heat transfer takes into account the combined effects of heat convection and heat radiation, and the composite heat transfer coefficient h1 is calculated according to the actual welding conditions, which is specifically obtained through the following formula:

[0085] h1=hc +h r =h c +ε1σ 波 (T1 2 +T2 2 )(T1+T2);

[0086] In the formula, h c Expressed as the convection heat transfer coefficient, W / (m 2 ·K);h r Expressed as radiation heat transfer coefficient, W / (m 2 ·K); ε1 is the spectral emissivity, σ 波 It is expressed as the Stefan-Boltzmann constant, 5.67×10 -8 W / (m 2 ·K 4 ); T1 is the tower surface temperature. And the tower surface welding heat load Q2(r) takes into account the heat load affected by actual welding heat transfer.

[0087] S40, obtaining a stress field of the wind turbine tower welding according to the temperature field of the wind turbine tower.

[0088] In one embodiment of the present invention, the stress at any point in the stress field of the wind turbine tower welding is obtained by the following formula:

[0089]

[0090] In the formula, σ1 represents the stress of the wind turbine tower welding, ε represents the strain of the material, [D P ] is represented as the plasticity matrix, α is represented as the thermal expansion coefficient of the material, E is represented as the elastic modulus of the material, {ε e} is the elastic component of the total strain, σ Y It is represented by the yield stress, and T is represented by the temperature field of the wind turbine tower.

[0091]

[0092] In the formula, σ' x ,σ' y It is expressed as the deviation stress in the x-direction and the y-direction, v is the Poisson's ratio of the material, τ xy It is expressed as the shear stress of the material. Specifically, the stress field of the wind turbine tower welding is as follows: Figure 4 shown.

[0093] See also Figure 5As shown, in one embodiment of the present invention, based on the stress field of the wind turbine tower welding, the applied load stress field is superimposed to obtain the superimposed stress, and the fatigue life of the wind turbine tower is evaluated according to the superimposed stress and the material SN curve. Among them, the applied load stress field can be understood as the calculation of the wind load received by the wind turbine during operation.

[0094] In this embodiment, the superimposed stress σ at any point on the tower is obtained by the following formula:

[0095] σ=σ1+σ2;

[0096] In the formula, σ1 represents the stress of the wind turbine tower welding, and σ2 represents the external load stress. According to the fatigue strength σ of the material SN curve 疲 Compared with the obtained superimposed stress σ, when the superimposed stress σ of the tower is equal to the fatigue strength σ of the corresponding material 疲 When the value is , the fatigue life of the material is the fatigue life of the tower. Among them, the mesh model of the applied load is as follows: Figure 6 As shown in Figure 2, the stress field model of the applied load is as follows: Figure 7 shown.

[0097] See also Figure 8 As shown, the present invention also provides a system for evaluating welding stress of a weld of a wind turbine generator set, and the system applies the above-mentioned method for evaluating welding stress of a weld of a wind turbine generator set, comprising:

[0098] The simulation model module is used to establish a multi-physics simulation model of the wind turbine tower based on finite element analysis.

[0099] The boundary condition module is used to apply boundary conditions to the multi-physics simulation model of the wind turbine tower.

[0100] The temperature field module is used to obtain the welding heat load of the wind turbine tower and solve the multi-physics simulation model of the wind turbine tower according to the welding heat load under boundary conditions to obtain the temperature field of the wind turbine tower.

[0101] The stress field module is used to obtain the stress field of the wind turbine tower welding according to the temperature field of the wind turbine tower.

[0102] It is obvious to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be regarded as exemplary and non-limiting from any point of view, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention, and any reference numerals in the claims should not be regarded as limiting the claims involved.

[0103] The above-described embodiments merely represent implementation methods of the invention. The protection scope of the present invention is not limited to the above-described embodiments. For those skilled in the art, several modifications and improvements may be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A method for evaluating welding stress of a wind turbine generator set, characterized in that: include: Establish a multi-physics simulation model of wind turbine tower based on finite element analysis; Apply boundary conditions to the multi-physics simulation model of the wind turbine tower; Obtain the welding heat load of the wind turbine tower, and solve the multi-physics simulation model of the wind turbine tower according to the welding heat load under boundary conditions to obtain the temperature field of the wind turbine tower; According to the temperature field of the wind turbine tower, the stress field of the wind turbine tower welding is obtained.

2. The method for evaluating welding stress of a wind turbine generator set weld according to claim 1, characterized in that: The multi-physics simulation model of the wind turbine tower is as follows: Where ρ represents the density of the microelement, c represents the specific heat capacity, (x, y, z) represents the coordinate value of any point in the model, T represents the temperature field of the wind turbine tower, τ represents time, λ represents the thermal conductivity of the material, Q(r) represents the welding heat load, and r represents the distance from the center of the heat source during welding.

3. The method for evaluating welding stress of a wind turbine weld according to claim 2, characterized in that: Welding heat load Q(r), including tower core welding heat load Q1(r) and tower surface welding heat load Q2(r); and, Q(r)=Q1(r)+Q2(r); Among them, the tower core welding heat load Q1(r) is obtained by the following formula: Q1(r)=3q / (πR 2 )exp[-3(r / R)]; In the formula, q represents the arc thermal power, R represents the effective heat source radius, and exp represents the exponential function; The tower surface welding heat load Q2(r) is obtained by the following formula: Q2(r)=h1(T-T2); Wherein, h1 represents the composite heat transfer coefficient of the wind turbine calculated under the actual welding conditions, and T2 represents the external ambient temperature.

4. The method for evaluating welding stress of a weld of a wind turbine generator set according to claim 3, characterized in that: The arc thermal power q is obtained by the following formula: q = ηUI; Where η represents the welding thermal efficiency, U represents the welding voltage, and I represents the welding current.

5. The method for evaluating welding stress of a wind turbine weld according to claim 3, characterized in that: The composite heat transfer coefficient h1 is obtained by the following formula: h1=h c +h r =h c +ε1σ 波 (T1 2 +T2 2 )(T1+T2); In the formula, h c Expressed as the convective heat transfer coefficient, h r is expressed as the radiation heat transfer coefficient, ε1 is expressed as the spectral emissivity, σ 波 It is represented by the Stefan-Boltzmann constant, and T1 is represented by the tower surface temperature.

6. The method for evaluating welding stress of a wind turbine weld according to claim 1, characterized in that: The boundary conditions imposed include: The melting point of liquid metal, Tm, is used as the first type of boundary condition; The tower core welding heat load Q1(r) is used as the second type of boundary condition; The composite heat transfer coefficient h1 and the external environment temperature T2 are used as the third type of boundary conditions.

7. The method for evaluating welding stress of a wind turbine generator set weld according to claim 1, characterized in that: The stress at any point in the stress field of the wind turbine tower welding is obtained by the following formula: In the formula, σ1 represents the stress of the wind turbine tower welding, ε represents the strain of the material, [D P ] is represented by the plasticity matrix, α is represented by the thermal expansion coefficient of the material, E is represented by the elastic modulus of the material, {ε e } is the elastic component of the total strain, σ Y It is represented by the yield stress, T is represented by the temperature field of the wind turbine tower, It is represented as a differential symbol; in, In the formula, It is expressed as the deviation stress in the x-direction and the y-direction, v is the Poisson's ratio of the material, τ xy Expressed as the shear stress of the material.

8. The method for evaluating welding stress of a weld of a wind turbine generator set according to claim 1, characterized in that: Based on the stress field of wind turbine tower welding, the stress field of external load is superimposed to obtain the superimposed stress. The fatigue life of the wind turbine tower is evaluated according to the superimposed stress and material SN curve.

9. The method for evaluating welding stress of a weld of a wind turbine generator set according to claim 8, characterized in that: The superimposed stress σ at any point on the tower can be obtained by the following formula: σ=σ1+σ2; In the formula, σ1 represents the stress of the wind turbine tower welding, and σ2 represents the external load stress; Fatigue strength σ according to material SN curve 疲 Compared with the obtained superimposed stress σ, when the superimposed stress σ of the tower is equal to the fatigue strength σ of the corresponding material 疲 When the value is reached, the fatigue life of the material is equal to the fatigue life of the tower.

10. A system for evaluating welding stress of a wind turbine generator set, characterized in that: The method for evaluating the welding stress of the weld of a wind turbine generator set according to any one of claims 1 to 9 comprises: The simulation model module is used to establish a multi-physics simulation model of the wind turbine tower based on finite element analysis; Boundary condition module, used to apply boundary conditions to the multi-physics simulation model of wind turbine tower; The temperature field module is used to obtain the welding heat load of the wind turbine tower and solve the multi-physics simulation model of the wind turbine tower according to the welding heat load under boundary conditions to obtain the temperature field of the wind turbine tower; The stress field module is used to obtain the stress field of the wind turbine tower welding according to the temperature field of the wind turbine tower.

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