Method for obtaining random stress spectrum of flange bolt

Abstract

The application discloses a random stress spectrum acquisition method of a flange bolt, and comprises the following steps: installing a strain module on a fan tower drum; the strain module collects information and feeds back to a dynamic strain collector to obtain a plurality of pairs of dynamic strain data; the dynamic strain data is converted into stress, and a plurality of surface stresses are obtained through difference calculation; a finite element model is established to obtain a fan tower drum model, and a grid unit is divided; a stress value and angle relationship equation is calculated through the surface stress, and is applied to the fan tower drum model, and then simulation analysis is carried out; according to one simulation analysis result, a flange bolt cross-section internal force is obtained in combination with a section method principle; there is a linear relationship between the simulation analysis result and the flange bolt cross-section internal force, and a cross-section stress linear relationship formula is obtained; the cross-section stress linear relationship formula and a pre-tightening stress of the fan tower drum are combined to obtain a random stress spectrum. The application solves the problems that a large number of sensors are needed and the flange bolt needs to be removed when the sensors are damaged.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of structural monitoring technology and simulation analysis, and particularly relates to a random stress spectrum acquisition method of a flange bolt. BACKGROUND

[0002] As important connecting components of important towers, the flange bolts of wind power are currently monitored at a high cost due to a large number of flange bolts, and the understanding of the stress conditions of the flange bolts is mainly based on specification recommendations and theoretical calculations. Of course, in recent years, more and more attention has been paid to the actual working load conditions of the flange bolts in engineering, and some on-site monitoring methods have appeared, mainly including two methods: one is to set multiple contact type displacement sensors on the surface of the flange, and then transmit the collected displacement data to a monitoring system to compare with a predetermined safety value to determine whether the flange bolt is loose; the other is to install a pressure sensor at each flange bolt to transmit the pressure monitoring data to a remote controller to determine whether the pressure of the flange bolt meets the requirements. In the above two methods, the first method only qualitatively determines the flange bolt by relying on the displacement of the flange, and cannot obtain the actual stress of the flange bolt, so that the fatigue failure of the flange bolt cannot be further analyzed; the second method embeds the pressure sensor between the flange bolt and the flange, and can timely or the pressure of the flange bolt, but if the pressure sensor is damaged, the flange bolt needs to be removed and reinstalled, which cannot be used continuously for the flange bolt. In addition, for the structure of a wind power machine, a large number of flange bolts are installed, and a large amount of data needs to be transmitted to the remote controller, which requires a large amount of cost. The present application combines the above methods, sets resistance strain sensors at several key positions of the upper second tower through on-site experiments to collect strain signals of the upper second tower, connects a dynamic strain acquisition instrument to transmit the strain signals, then converts the strain into stress according to mechanical knowledge, and establishes a finite element model of the wind turbine tower and the flange bolt by using the section method and the abaqus software to further simulate and analyze, so as to obtain the stress conditions of each flange bolt and obtain the random stress spectrum that can be used for fatigue analysis of the flange bolt. The present application greatly optimizes the setting of the sensor by means of the finite element model and the simulation analysis, greatly reduces the number of sensors and the inconvenience of replacing the sensors caused by the unfavorable arrangement of the sensors, and realizes the qualitative analysis of the stress conditions of the flange bolt.

[0003] As a crucial connecting component of wind turbine towers, flange bolts bear random loads under wind conditions. With increasing service life, they are susceptible to metal fatigue failure, potentially leading to damage to the wind turbine or even the collapse of the entire structure. Furthermore, the random nature of the actual load on flange bolts due to wind forces makes it difficult to meticulously consider metal fatigue during the design phase. Therefore, monitoring the load on flange bolts in operational wind turbine structures to obtain a random stress spectrum is essential. This spectrum can be used to predict the fatigue life of flange bolts and provides a reference basis for early design work. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and to provide a method for obtaining the random stress spectrum of flange bolts.

[0005] The objective of this invention is achieved through the following technical solution: a method for obtaining the random stress spectrum of flange bolts, comprising the following steps:

[0006] S1. Install several pairs of strain modules in the wind turbine tower. The strain modules collect information and feed it back to the dynamic strain acquisition instrument to obtain several pairs of dynamic strain data.

[0007] S2. According to Hooke's Law formula in mechanics of materials, convert several pairs of dynamic strain data into several pairs of stresses, calculate the difference between each pair of stresses, and obtain several surface stresses.

[0008] S3. Verify the continuity of the stress distribution in the cross-section of the wind turbine tower;

[0009] S4. Based on the design drawings of the wind turbine tower and the location of the strain module, establish a finite element model to obtain the wind turbine tower model, and divide the wind turbine tower model into mesh elements.

[0010] S5. Select the two surface stresses mentioned in step S2, calculate a stress value-angle relationship equation, and apply the stress value-angle relationship equation to the wind turbine tower model. Perform simulation analysis on the wind turbine tower model after applying the load to obtain a simulation analysis result.

[0011] S6. Based on the simulation analysis result and combined with the principle of the section method, obtain the internal force of the flange bolt section under the simulation analysis result;

[0012] S7, repeating step S5 and step S6 to obtain a plurality of linear relationships between the simulation analysis results and the flange bolt cross-section internal force, obtain a cross-section stress linear relationship, the linear relationship is y=kx, y is the flange bolt cross-section internal force, x is the surface stress of the first tower drum of the fan tower drum, and k is a proportional coefficient;

[0013] S8, combining the cross-section stress linear relationship and the pre-tightening stress of the fan tower drum to obtain a random stress spectrum, the calculation formula of the random stress spectrum is z=kx+T, z is the flange bolt stress at each moment, and T is the pre-tightening stress.

[0014] More preferably, the stress distribution verification of the fan tower drum in step S3 comprises the following steps:

[0015] S301, a plurality of strain modules are arranged on the same cross-section of the fan tower drum, the strain modules collect information and feed back to the dynamic strain meter to obtain a plurality of dynamic strain data;

[0016] S302, according to the Hooke's law formula of material mechanics, the plurality of dynamic strain data of step S302 are converted into a plurality of stresses, and a stress time history curve is obtained through the plurality of stresses;

[0017] S303, combining the positions of the plurality of strain modules of step S301 and the stress time history curve of step S202, the first tower drum stress of the fan tower drum is positive and the second tower drum stress of the fan tower drum is negative.

[0018] More preferably, step S5 comprises the following steps:

[0019] S501, a cylindrical coordinate system is established in the software analysis field, and according to the two surface stresses of step S2, a stress value-angle relationship equation is derived, which is:

[0020] The Z is the surface stress, the TH is the angle, and the a and b are derivation coefficients;

[0021] S502, the stress value-angle relationship equation of step S501 is loaded into the fan tower drum model of step S4;

[0022] S503, the fan tower drum model of step S502 is simulated and analyzed to obtain a simulation analysis result.

[0023] More preferably, the strain module in step S1 comprises a temperature compensation piece and a collection strain gauge, the temperature compensation piece is connected perpendicularly to the collection strain gauge, and the temperature compensation piece and the collection strain gauge are connected to the dynamic strain collection instrument.

[0024] More preferably, the fan tower in step S1 comprises a first tower and a second tower, the first tower is provided with a first flange, the second tower is provided with a second flange, the first flange is connected to the second flange through a flange bolt, and the strain module is installed on the first tower and the second tower respectively.

[0025] More preferably, the distance between the strain module and the flange of the fan tower in step S1 is not more than 40 cm.

[0026] More preferably, the distance between each pair of strain modules in step S1 is not more than 80 cm.

[0027] More preferably, the number of pairs of strain modules in step S1 is not less than 2.

[0028] The present application has the following advantages and beneficial effects compared with the prior art:

[0029] The present application solves the problem of a large number of sensors and the need to remove the flange bolt when the sensor is damaged by using the random stress spectrum acquisition method of the flange bolt, which is closer to the real working condition than the theoretical calculation and the recommended flange bolt load, and lays a foundation for subsequent prediction of the fatigue life of the flange bolt. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is a flowchart of the random stress spectrum acquisition method of the flange bolt of the present application;

[0031] Figure 2 is a strain module schematic diagram of the random stress spectrum acquisition method of the flange bolt of the present application;

[0032] Figure 3 is a schematic diagram of the strain module installed on the fan tower of the random stress spectrum acquisition method of the flange bolt of the present application (A and B are the installation positions of the strain module);

[0033] Figure 4 is a stress difference time history curve schematic diagram of step S2;

[0034] Figure 5 is a schematic diagram of the strain module installed on the same horizontal plane of the fan tower of the random stress spectrum acquisition method of the flange bolt of the present application;

[0035] Figure 6 is a time history curve schematic diagram of step S3;

[0036] Figure 7 is a schematic diagram of a fan tower drum and a flange bolt of a random stress spectrum acquisition method of the flange bolt of the application;

[0037] Figure 8 is a schematic diagram of stress applied to key points of a random stress spectrum acquisition method of the flange bolt of the application;

[0038] Figure 9 is a schematic diagram of internal force of a flange bolt cross section of a random stress spectrum acquisition method of the flange bolt of the application;

[0039] The labels of components in the drawings: 1-strain module; 101-temperature compensation sheet; 102-acquisition strain sheet; 103-welding point; 104-wire; 2-fan tower drum; 21-first tower drum; 211-first flange; 22-second tower drum; 221-second flange; 3-flange bolt; 401-first channel; 402-second channel; 403-third channel; 404-fourth channel; 405-fifth channel; 406-sixth channel. DETAILED DESCRIPTION

[0040] The application purposes of the application are described in further detail below in combination with the drawings and specific embodiments. The embodiments cannot be described one by one here, but the implementation manners of the application are not limited to the following embodiments.

[0041] The fan tower drum 2 in the embodiment includes a first tower drum 21 and a second tower drum 22. The first tower drum 21 is provided with a first flange 211, and the second tower drum 22 is provided with a second flange 221. The first flange 211 and the second flange 221 are connected by a flange bolt 3. The wall thickness of the fan tower drum 2 is 1 cm. The thicknesses of the first flange and the second flange are both 20 cm. The widths of the first flange 211 and the second flange 221 are both 24 cm. The screw rod diameter of the flange bolt 3 is 5 cm. The diameters of the nut and the cap of the flange bolt 3 are 8 cm. The number of the flange bolts 3 is 108.

[0042] As shown in Figure 1 , the random stress spectrum acquisition method of the flange bolt includes the following steps:

[0043] S1, a plurality of strain modules 1 are installed in the fan tower drum 2. The plurality of strain modules 1 collect information and feed back to a dynamic strain acquisition instrument to obtain a plurality of dynamic strain data. Each strain module 1 includes two strain modules 1; as shown in Figure 2 , each strain module 1 includes two strain sheets connected perpendicularly to each other. The strain sheet in the transverse state is a temperature compensation sheet 101, and the strain sheet in the longitudinal state is an acquisition strain sheet 102. Both of the two strain sheets are resistance strain sheets. The model of the resistance strain sheet is 120-10AA welding-free strain sheet. The size of the resistance strain sheet is 14 mm*5 mm, Figure 2The circle in the figure shows a welding point 103, and the straight line drawn is a lead 104. The two resistance strain gauges are connected to a channel of a dynamic strain acquisition instrument through a three-core shielded wire, so as to record the dynamic strain data of the point. The fan tower 2 comprises a first tower 21 and a second tower 22, and each pair of strain modules 1 is symmetrically arranged at A of the first tower 21 and B of the second tower 22, respectively. The distance from each strain module 1 to the first flange 211 of the first tower 21 (at A) and the second flange 221 of the second tower 22 (at B) is not more than 40 cm, and the distance between each pair of strain modules 1 is not more than 80 cm. In the embodiment, the distance from A and B to the flanges (including the first flange 211 and the second flange 221) of the fan tower 1 is 30 cm. According to the number of channels of the dynamic strain acquisition instrument, a pair of strain modules 1 is arranged at a certain interval; in order to better obtain the stress difference of the fan tower 2, at least two pairs of strain modules 1 are arranged on the symmetric sides of the fan tower 2, and when the number of strain modules 1 is greater than two pairs of strain modules 1, the strain modules 1 can be arranged at equal intervals according to the number of key points to be measured. Figure 3 Figure 3 The distance between each pair of strain modules 1 is not more than 80 cm. In the embodiment, the distance from A and B to the flanges (including the first flange 211 and the second flange 221) of the fan tower 1 is 30 cm. According to the number of channels of the dynamic strain acquisition instrument, a pair of strain modules 1 is arranged at a certain interval; in order to better obtain the stress difference of the fan tower 2, at least two pairs of strain modules 1 are arranged on the symmetric sides of the fan tower 2, and when the number of strain modules 1 is greater than two pairs of strain modules 1, the strain modules 1 can be arranged at equal intervals according to the number of key points to be measured.

[0044] S2, according to the material mechanics Hooke's law formula (σ=E×ε; σ is stress; E is elastic modulus, 210 GPa for steel; ε is dynamic strain data), a plurality of pairs of dynamic strain data (dynamic strain data at A and B) are converted into a plurality of pairs of stress (each pair of stress includes the stress of the first tower 21 and the corresponding stress of the second tower 22), and the section method of material mechanics is used again, the stress of the first tower 21 is subtracted from the stress of the second tower 22 to obtain a plurality of difference values (i.e. the stress of A point minus the stress of B point), that is, a plurality of surface stresses of the first tower 21, and a plurality of stress difference time history curves are formed; as shown in Figure 4 , it is a stress difference time history curve of one minute obtained by a pair of strain modules 1 at the key point. The abscissa is time, in seconds, and the ordinate is stress, in MPa. The method of obtaining the surface stress from other dynamic strain data at the key point is the same.

[0045] S3, continuously verify the stress distribution on the cross section of the fan tower 2, and the verification method comprises the following steps:

[0046] S301, six strain modules 1 are arranged on the same horizontal plane of the fan tower 2 (combined with A as Figure 3 , six strain modules 1 collect information and feed back to the dynamic strain instrument containing six channels, and six dynamic strain data are obtained;

[0047] ​S302, according to the material mechanics Hooke's law formula, the 6 dynamic strain data of step S302 are converted into stress, with time as the horizontal coordinate and stress as the vertical coordinate, that is, the stress time history curve; as shown in Figure 6 , it is a stress time history curve of 6 channels for 1 minute.

[0048] S303, combining the positions of the plurality of strain modules 1 of step S301 (as shown in Figure 5 ) and the stress time history curve of step S202 (as shown in Figure 6 ), the stress of the first tower 21 of the fan tower 2 is positive and the stress of the second tower 22 of the fan tower 2 is negative, and the continuous distribution of stress on the cross section of the fan tower 2 is verified, proving the feasibility of the finite element model simulation analysis.

[0049] S4, according to the design drawing of the fan tower 2 and the position of the strain module 1, a finite element model (including part of the structure of the first tower 21, part of the structure of the second tower 22 and all flange bolts 3) is established, and a fan tower model is obtained. The distance from the strain module 1 in the fan tower model to the flange 3 of the first tower 21 and the flange 3 of the second tower 22 is also 30cm, which is consistent with the actual installation distance in step S1. A pre-tightening stress is applied to the bottom of the second tower 22 of the fan tower model (that is, a fixed value is set in the finite element software), and the finite element model is divided into grid units. The type of this network unit is linear hexahedron C3D8R, and the neutral axis algorithm is selected as the algorithm.

[0050] S5, two surface stresses are selected from the plurality of surface stresses of step S2, a stress value and angle relationship equation is calculated, the stress value and angle relationship equation is applied to the fan tower model, and the fan tower model after applying the stress value and angle relationship equation is simulated to obtain a simulation analysis result. The load application method of the fan tower model of step S5 includes the following steps:

[0051] S501, since only a small amount of strain modules 1 are used to collect dynamic strain data of key point positions of the fan tower 2, combined with the positions and quantities of the strain modules 1 pasted in the field, a column coordinate system is established in the software analysis field of the finite element software, two surface stresses are selected from the plurality of surface stresses, and a stress value and angle relationship equation is derived. The stress value and angle relationship equation is:

[0052] Z is the loaded surface stress; TH is an angle value determined by the positions of the two pairs of strain gauges 1 pasted on the first tower drum 21 and the second tower drum 22; the dynamic strain data measured by the two pairs of strain gauges 1 are converted into stress, the stress is converted into surface stress, the surface stress and the angle value between the two pairs of strain gauges 1 are all substituted into the stress value-angle relationship equation to obtain the values of a and b, that is, a and b belong to the derivation coefficient, and the stress value-angle relationship equation can change the stress value with the change of the tower surface position;

[0053] S502, the stress value-angle relationship equation of step S501 is input into the software analysis field of the finite element software, so that the surface stress is applied to the surface of the fan tower drum model in step S4 and is continuously distributed, as shown in Figure 8 The arrows on the upper surface of the fan tower drum model represent the continuous distribution of the surface stress, and then the expected stress is applied to the second tower drum 22 of the fan tower drum model, and the flange bolts 3 are connected to the first flange 21 and the second flange 22 in a general contact mode.

[0054] S503, finally, the fan tower drum model loaded with the stress value-angle relationship equation is simulated and analyzed to obtain a simulation analysis result.

[0055] S6, according to the simulation analysis result, the cross-section method principle is used to find the flange bolt cross-section internal force of the fan tower drum model, and all the flange bolt cross-section internal forces under the simulation analysis result are obtained. As shown in Figure 9 The flange bolt 3 model of the fan tower drum model is cut open, and the cut open flange bolt 3 model is taken as a unit, the single-layer arrow mark represents the resultant force of the unit, and the double-layer arrow mark represents the bending moment of the unit, Figure 9 The left upper table in the figure represents the strain distribution of each unit of the entire flange bolt 3.

[0056] S7, steps S5 and S6 are repeated, a plurality of stress value-angle relationship equations are applied to the fan tower drum model, a plurality of simulation analysis results and corresponding all flange bolt cross-section internal forces are obtained, so that a linear relationship between the stress of the fan tower drum and the flange bolt cross-section internal force is obtained, the linear relationship is y=kx, y is the flange bolt cross-section internal force, x is the surface stress of the first tower drum 21 of the fan tower drum, and k is the proportional coefficient. According to the cross-section linear relationship, the random stress spectrum corresponding to the collected dynamic strain data can be obtained.

[0057] S8, the random stress spectrum of the fan tower flange bolt can express the section internal force of the simulation analysis flange bolt plus the pre-tightening stress applied when the flange bolt is installed in the early stage; that is, the section stress linear relationship formula is combined with the pre-tightening stress of the fan tower to obtain the random stress spectrum, and the calculation formula of the random stress spectrum is: z=kx+T, z is the stress of the flange bolt at each time, x is the surface stress of the first tower 21 of the fan tower 2 collected on site, k is the proportional coefficient found through simulation analysis, and T is the pre-tightening stress applied when the flange bolt 3 is installed in the early stage.

[0058] The above specific embodiments are preferred embodiments of the present application, and cannot limit the present application, and any changes or other equivalent replacement manners made without departing from the technical solutions of the present application are included in the protection scope of the present application.

Claims

1. A method for obtaining the random stress spectrum of flange bolts, characterized in that, Includes the following steps: S1. Install several pairs of strain modules in the wind turbine tower. The strain modules collect information and feed it back to the dynamic strain acquisition instrument to obtain several pairs of dynamic strain data. S2. According to Hooke's Law formula in mechanics of materials, convert several pairs of dynamic strain data into several pairs of stresses, calculate the difference between each pair of stresses, and obtain several surface stresses. S3. Verify the continuity of the stress distribution in the cross-section of the wind turbine tower; S4. Based on the design drawings of the wind turbine tower and the location of the strain module, establish a finite element model to obtain the wind turbine tower model, and divide the wind turbine tower model into mesh elements. S5. Select the two surface stresses mentioned in step S2, calculate a stress value-angle relationship equation, and apply the stress value-angle relationship equation to the wind turbine tower model. Perform simulation analysis on the wind turbine tower model after applying the load to obtain a simulation analysis result. S6. Based on the simulation analysis result and combined with the principle of the section method, obtain the internal force of the flange bolt section under the simulation analysis result; S7. Repeat steps S5 and S6 to obtain a linear relationship between multiple simulation analysis results and the internal force of the flange bolt section, and obtain a linear relationship of section stress, the linear relationship being y = kx, where y is the internal force of the flange bolt section, x is the surface stress of the first tower section of the wind turbine tower, and k is a proportionality coefficient. S8. Combine the linear relationship of the cross-sectional stress with the pre-tightening stress of the wind turbine tower to obtain a random stress spectrum. The formula for calculating the random stress spectrum is: z = kx + T, where z is the flange bolt stress at each time point and T is the pre-tightening stress.

2. The method for obtaining the random stress spectrum of flange bolts according to claim 1, characterized in that, Step S3, verifying the stress distribution of the wind turbine tower, includes the following steps: S301. Multiple strain modules are set on the same cross section of the wind turbine tower. The strain modules collect information and feed it back to the dynamic strain gauge to obtain multiple dynamic strain data. S302. According to Hooke's Law formula in mechanics of materials, the multiple dynamic strain data in step S302 are converted into multiple stresses, and stress time history curves are obtained through the multiple stresses. S303. Combining the locations of the multiple strain modules in step S301 and the stress time history curve in step S202, it is found that the first tower stress of the wind turbine tower is positive and the second tower stress of the wind turbine tower is negative.

3. The method for obtaining the random stress spectrum of flange bolts according to claim 1, characterized in that, Step S5 includes the following steps: S501. Establish a cylindrical coordinate system in the software analysis field. Based on the two surface stresses described in step S2, derive an equation relating the stress value to the angle. This equation relating the stress value to the angle is as follows: Z is the surface stress, TH is the angle, and a and b are derived coefficients; S502. Load one of the stress value and angle relationship equations from step S501 into the wind turbine tower model from step S4. S503. Perform simulation analysis on the wind turbine tower model described in step S502 to obtain a simulation analysis result.

4. The method for obtaining the random stress spectrum of flange bolts according to claim 1, characterized in that, The strain module in step S1 includes a temperature compensation gauge and a strain gauge acquisition gauge. The temperature compensation gauge and the strain gauge acquisition gauge are vertically connected, and the temperature compensation gauge and the strain gauge acquisition gauge are connected to the dynamic strain acquisition instrument.

5. The method for obtaining the random stress spectrum of flange bolts according to claim 1, characterized in that, The wind turbine tower in step S1 includes a first tower and a second tower. The first tower is provided with a first flange, and the second tower is provided with a second flange. The first flange and the second flange are connected by flange bolts. The strain module is installed on the first tower and the second tower respectively.

6. The method for obtaining the random stress spectrum of flange bolts according to claim 1, characterized in that, In step S1, the distance between the strain module and the flange of the wind turbine tower shall not exceed 40cm.

7. The method for obtaining the random stress spectrum of flange bolts according to claim 1, characterized in that, In step S1, the distance between each pair of strain modules does not exceed 80cm.

8. The method for obtaining the random stress spectrum of flange bolts according to claim 1, characterized in that, The logarithm of the strain module in step S1 is ≥2.

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