CN113357099B - Fatigue diagnosis and detection method for fan tower drum based on acceleration sensor - Google Patents
Fatigue diagnosis and detection method for fan tower drum based on acceleration sensor Download PDFInfo
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- CN113357099B CN113357099B CN202110632610.3A CN202110632610A CN113357099B CN 113357099 B CN113357099 B CN 113357099B CN 202110632610 A CN202110632610 A CN 202110632610A CN 113357099 B CN113357099 B CN 113357099B
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
- F03D—WIND MOTORS
- F03D17/00—Monitoring or testing of wind motors, e.g. diagnostics
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
- F03D—WIND MOTORS
- F03D13/00—Assembly, mounting or commissioning of wind motors; Arrangements specially adapted for transporting wind motor components
- F03D13/20—Arrangements for mounting or supporting wind motors; Masts or towers for wind motors
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/70—Wind energy
- Y02E10/728—Onshore wind turbines
Abstract
The invention provides a fatigue diagnosis and detection method of a fan tower based on an acceleration sensor, which comprises the following steps: acquiring an acceleration signal of a wind power tower cylinder in the running process of the wind driven generator by using an acceleration sensor and calculating continuous disturbance displacement; simplifying the wind power tower cylinder into a cantilever beam model, and calculating external load acting on the top of the wind power tower cylinder and fatigue load acting on the bottom of the wind power tower cylinder; according to fatigue load tau max Calculating and counting the stress amplitude of the fatigue load and the corresponding cycle number of the fatigue load by using a time history curve, and drawing a corresponding low-cycle fatigue load amplitude frequency histogram; calculating the total low-cycle fatigue damage of the wind power tower cylinder in the test time and predicting the low-cycle fatigue life of the wind power tower cylinder by using a Miner linear fatigue accumulated damage theory; the method utilizes the acceleration sensor for measurement, can calculate the fatigue damage of the wind power tower drum according to the measurement data, further estimate the residual fatigue life of the wind power tower drum, and provides convenience for the work of maintenance personnel.
Description
Technical Field
The invention relates to the technical field of wind power generation, in particular to a fatigue detection and fatigue life estimation method for a wind turbine tower.
Background
Nowadays, with the gradual depletion and the continuous rising of prices of traditional energy sources such as petroleum, coal, natural gas and the like, wind energy is regarded as a clean sustainable energy source and is receiving more and more attention of people. From the development trend, the wind energy is favored by various countries due to the advantages of huge storage amount, regeneration, wide distribution, no pollution and the like. Among them, wind power generation has gradually become the most promising wind energy utilization mode for scale-up and commercialization development at present.
The main structure of the wind driven generator comprises a tower, wind power blades, a cabin, a generator and a gear box in the cabin. The wind power tower cylinder is a tower pole for wind power generation, and mainly plays a supporting role in a wind generating set and absorbs the vibration of the set.
Along with the continuous increase of the single machine capacity of the wind turbine generator, the height of the tower barrel of the wind turbine generator is also continuously increased, so that more variable external loads are brought, and higher requirements are provided for the safe operation of the wind turbine generator. It should be noted that in some extreme weather conditions, the fatigue load experienced by the wind tower is large (exceeding the yield stress of the material), which causes the wind tower to plastically deform during the disturbance, and the actual fatigue life of the wind tower is lower than the design limit. Therefore, low cycle fatigue is considered to be one of the important factors affecting the fatigue life of the wind turbine.
At present, most of fatigue diagnosis and detection methods for wind power towers in the market are time-consuming and labor-consuming, and the influence of low-cycle fatigue is not considered, for example, Chinese patent CN109340062B discloses a digital twin fatigue damage prediction method for a low-wind-speed wind turbine, the fatigue life and the fatigue damage condition of the wind turbine are predicted by establishing a wind wheel simulation model and a digital twin model of a virtual wind turbine, and the method is complex and needs to establish a plurality of models; for example, chinese patent CN202010878949.7 discloses a wind turbine blade multi-angle fatigue mechanical property detection device and a use method thereof, and the wind turbine blade multi-angle fatigue mechanical property detection device is arranged to analyze the wind turbine blade fatigue mechanical property when detecting different position states of the wind turbine blade.
Therefore, the low-cycle fatigue detection and diagnosis method for the wind power tower with strong applicability and high precision can play a guiding role in the safe use of the wind driven generator and provide a certain reference for the timely maintenance of the wind power tower in the future.
Disclosure of Invention
The invention aims to provide a fatigue diagnosis and detection method of a wind turbine tower based on an acceleration sensor.
In order to achieve the purpose, the invention provides the following technical scheme:
the invention provides a fatigue diagnosis and detection method for a fan tower cylinder of an acceleration sensor, which comprises the following steps:
(1) acquiring an acceleration signal of a wind power tower cylinder in the running process of the wind driven generator by using an acceleration sensor and calculating continuous disturbance displacement;
(2) simplifying the wind power tower cylinder into a cantilever beam model, and calculating external load acting on the top of the wind power tower cylinder and fatigue load acting on the bottom of the wind power tower cylinder;
(3) according to fatigue load tau max Calculating and counting the stress amplitude of the fatigue load and the corresponding cycle number of the fatigue load by using a time history curve, and drawing a corresponding low-cycle fatigue load amplitude frequency histogram;
(4) and calculating the total low cycle fatigue damage of the wind power tower cylinder and predicting the low cycle fatigue life of the wind power tower cylinder by combining the S-N curve of the steel material of the wind power tower cylinder and a Miner linear fatigue accumulated damage theory.
Preferably, said fatigue load τ max The time history is plotted against the fatigue load calculated over a certain test time.
Furthermore, the acceleration sensor is a three-axis acceleration sensor and is vertically arranged on the inner wall of the top of the wind power tower; two mutually perpendicular measuring directions of the triaxial acceleration sensor parallel to the horizontal plane are set as an X direction and a Y direction respectively, and the measuring direction perpendicular to the horizontal plane is set as a Z direction.
Further, the specific calculation process of the continuous disturbance displacement in the step (1) is as follows:
(1.1) the three-axis acceleration sensor collects continuous time domain acceleration signals a in the X direction and the Y direction x And a y ；
(1.2) carrying out low-pass filtering processing on continuous time domain acceleration signals acquired by the triaxial acceleration sensor;
the shake of the wind power tower barrel is mainly a low-frequency signal, and the low-frequency signal needs to be analyzed, so that the acquired acceleration signal needs to be subjected to low-pass filtering; high-frequency signals and other interference signals in the shaking process of the wind power tower can be filtered, and the accuracy of data acquisition is improved.
(1.3) carrying out low-pass filtering on the continuous time domain acceleration signal a x (t) and a y (t) performing integration twice to obtain a calculation formula L of continuous disturbance displacement waveform in X direction x Calculation formula L of continuous disturbance displacement waveform in (t) and Y directions y (t) is:
wherein N is the number of collected data points;
i is one of the acquisition moments;
v x (t) is a continuous time domain velocity waveform in the X direction;
v y (t) is a continuous time domain velocity waveform in the X direction;
L x (t) is the continuous perturbation displacement waveform in the X direction;
L y (t) is a continuous disturbance displacement waveform in the Y direction
a xi Is the acceleration sampling value at the time i in the X direction;
a yi is the acceleration sampling value at the time i in the Y direction;
v xi is the rate value at time i in the X direction;
v yi is the rate value at time i in the Y direction;
Δ t is the time difference between two samples.
Further, the step (2) specifically includes the following steps:
(2.1) because the tower height of the wind power tower is usually larger than 50m, and the change of the cross section of the wind power tower can be approximately ignored relative to the tower height, the disturbance of the wind power tower can be simplified into a cantilever beam with the equal cross section and subjected to horizontal load, and the deflection line differential equation and the boundary condition of the cantilever beam model are determined by combining relevant parameters of the wind power tower structure, such as the tower height, the outer diameter, the inner diameter and the like; the shearing force F acting on the X direction of the bottom of the wind power tower barrel is calculated by substituting boundary conditions into a deflection line differential equation x And the shearing force F acting on the Y direction of the bottom of the wind power tower y ：
X-direction deflection line equation:
boundary conditions in the X direction: when x is 0, L is 0;
when x is h, L is L x ；
Y-direction deflection line equation:
y-direction boundary conditions: when y is 0, L is 0;
when y is h, L is L y ；
Combining the above equations yields:
wherein x and y are two mutually perpendicular measuring directions of the three-axis acceleration sensor parallel to the horizontal plane respectively;
e is the Young modulus of the steel material of the wind power tower cylinder;
i is the section inertia moment of the wind power tower;
h is the tower height of the wind power tower;
L x and L y Respectively measuring and calculating continuous disturbance displacement of the wind power tower cylinder in two mutually perpendicular horizontal directions by using an acceleration sensor;
the method for calculating the section moment of inertia I of the wind power tower barrel comprises the following steps:
wherein, pi is the circumferential ratio;
d is the outer diameter of the wind power tower;
d is the inner diameter of the wind power tower cylinder.
(2.2) calculating the actual shearing force F at the bottom of the wind power tower s Combining the stress condition of the wind power tower cylinder and the actual shearing force F at the bottom of the wind power tower cylinder s Is the sum of the two shear force vectors in the horizontal direction, and the actual shear force F at the bottom of the wind power tower cylinder s The calculation formula of (A) is as follows:
(2.3) the magnitude of fatigue load acting on the joint of the bottom of the wind power tower and the flange is equal to the maximum shear stress borne by the bottom of the wind power tower; the fatigue load tau acting on the bottom of the wind power tower barrel max The calculation formula of (A) is as follows:
wherein, F s The actual shear force at the bottom of the wind power tower cylinder;
a is the cross section area of the bottom of the cantilever beam model;
preferably, the wind power tower cylinder is simplified into a thin-wall circular ring-shaped section beam with a uniform section, and the maximum shear stress acting on the wind power tower cylinder in the horizontal direction is generated on a neutral axis of the section at the bottom of the wind power tower cylinder, namely the joint of the bottom of the wind power tower cylinder and the flange; for a wind power tower, the joint between the bottom of the wind power tower and a flange is the part which is most likely to cause fatigue damage to the wind power tower due to stress concentration;
(2.4) the external load acting on the top of the wind power tower cylinder is as follows:
according to the stress condition of the wind power tower cylinder, the external load acting on the top of the wind power tower cylinder and the actual shearing force F borne by the bottom of the tower cylinder s Are equal.
Further, the specific process of the step (3) is as follows:
(3.1) obtaining the fatigue load tau at the bottom of the wind power tower drum based on the steps max -a time history curve, counting fatigue loads by means of a rain flow counting method;
preferably, the rain flow counting method is one of the most commonly used methods for analyzing the fatigue stress spectrum at present. The method is based on a double-parameter method, and can simplify the actually measured load course into a plurality of load cycles for fatigue life estimation.
(3.2) determining a threshold value of the low cycle fatigue load of the wind power tower cylinder according to the yield stress of the wind power tower cylinder material;
preferably, the determination of the threshold value of the low cycle fatigue load refers to a maximum fatigue load that can be theoretically borne when the wind power tower generates the low cycle fatigue.
(3.3) screening the amplitude and frequency of low cycle fatigue load circulation of the wind power tower cylinder in the working process based on the set threshold value of the low cycle fatigue load, and drawing a corresponding amplitude frequency histogram;
and determining the threshold value of the fatigue load when the wind power tower cylinder is subjected to plastic deformation according to the yield stress of the wind power tower cylinder material. When the fatigue load is larger than the threshold value, the bottom of the wind power tower generates plastic deformation. And when the irreversible plastic deformation at the bottom of the wind power tower cylinder is accumulated to a certain degree, the wind power tower cylinder is subjected to low-cycle fatigue damage.
Further, the specific process of the step (4) is as follows:
the amplitude frequency histogram obtained in the step is applied, and the S-N curve of the steel material of the wind power tower drum and the Miner linear fatigue accumulated damage theory are combined to obtain the low cycle fatigue total damage D accumulated by the wind power tower drum due to the low cycle fatigue effect in a certain operation time t tot ：
Wherein k is the number of collected data points;
i is one of the acquisition moments;
D i the low-cycle fatigue damage of the wind turbine tower at the moment i;
N fi expressed in stress amplitude σ i Fatigue life under action;
n i representing stress amplitude σ i Corresponding actual cycle times;
the low cycle fatigue life T of the wind power tower cylinder is as follows:
the invention has the following beneficial effects:
(1) according to the technical scheme, the acceleration sensor is used as the measuring device, the fatigue damage of the wind power tower can be calculated according to the measured data, the residual fatigue life of the wind power tower is further estimated, convenience is provided for the work of maintenance personnel, and a large amount of manpower and material resources are reduced by timely diagnosing and maintaining the wind power tower in the environment with wide distribution space and complex operating environment of the wind power plant.
(2) According to the invention, the disturbance conditions of the wind power tower in three directions can be measured simultaneously by utilizing the arrangement of the three-axis acceleration sensor, and the corresponding continuous disturbance displacement can be obtained through further calculation. Compared with a multi-sensor combination, the method is simple and quick in measurement process, and effectively saves the time for processing data of a plurality of sensors while ensuring the accuracy of results.
(3) In order to reduce the effect of the wind turbine on the tower, the influence of the mechanical vibration of the gearbox on the data of the acceleration sensor is extracted by utilizing a low-pass filtering algorithm, so that the influence of other factors on the subsequent calculation process is reduced as much as possible, and the predicted result is more accurate.
Drawings
FIG. 1 is a schematic illustration of a particular installation diagram of a three-axis acceleration sensor of the present invention;
FIG. 2 is a flowchart of a method for diagnosing and detecting low cycle fatigue of a wind power tower based on an acceleration sensor according to an embodiment of the present invention.
FIG. 3 is a schematic diagram of deformation of a wind tower after receiving stress in a horizontal direction according to an embodiment of the invention.
FIG. 4 is a cross-sectional view of a wind tower of the present invention.
Fig. 5 is a schematic diagram of fatigue load-time based on rainflow counting method treatment provided by the embodiment of the invention.
In the figure: the wind power generation device comprises a fan blade fan 1, a wind power cabin 2, an acceleration sensor 3 and a wind power tower 4.
Detailed Description
The following detailed description of the embodiments of the present invention is provided in conjunction with the accompanying drawings, and it should be noted that the embodiments are merely illustrative of the present invention and should not be considered as limiting the invention, and the purpose of the embodiments is to make those skilled in the art better understand and reproduce the technical solutions of the present invention, and the protection scope of the present invention should be subject to the scope defined by the claims.
As shown in FIG. 1, the invention provides a fatigue diagnosis and detection method for a wind turbine tower based on an acceleration sensor, and the main structure of a wind turbine comprises a fan blade 1, a wind turbine nacelle 2, a wind turbine tower 4, a nacelle, and a generator and a gearbox in the nacelle. The acceleration sensor 3 is a three-axis acceleration sensor and is vertically arranged on the inner wall of the top of the wind power tower barrel 4; two mutually perpendicular measuring directions of the triaxial acceleration sensor parallel to the horizontal plane are set as an X direction and a Y direction respectively, and the measuring direction perpendicular to the horizontal plane is set as a Z direction.
As shown in fig. 2, the detection method includes the following steps:
s1, acquiring an acceleration signal of the wind power tower in the running process of the wind driven generator by using the acceleration sensor and calculating continuous disturbance displacement, wherein the specific calculation process is as follows:
s1.1, the three-axis acceleration sensor collects continuous time domain acceleration signals a in the X direction and the Y direction x And a y ；
In the operation process of the wind driven generator, the complex operation condition can cause the wind power tower to generate complex vibration, but the main reason causing the fatigue damage of the wind power tower is the transverse vibration of the wind power tower, namely the vibration of the wind power tower on the XY plane. Therefore, the present embodiment only considers selecting the measurement results of the acceleration sensors in the X and Y directions for further processing.
S1.2, carrying out low-pass filtering processing on continuous time domain acceleration signals acquired by the triaxial acceleration sensor;
the shaking of the wind power tower cylinder is mainly a low-frequency signal, and the low-frequency signal needs to be analyzed, so that the collected acceleration signal needs to be subjected to low-pass filtering, the frequency of the low-pass filtering is 10HZ-100HZ, the high-frequency signal and other interference signals in the shaking process of the wind power tower cylinder can be filtered, and the accuracy of data collection is improved.
S1.3, carrying out low-pass filtering on the continuous time domain acceleration signal a x (t) and a y (t) performing integration twice to obtain a calculation formula L of continuous disturbance displacement waveform in X direction x Calculation formula L of continuous disturbance displacement waveform in (t) and Y directions y (t) is:
wherein N is the number of collected data points;
i is one of the acquisition moments;
v x (t) is a continuous time domain velocity waveform in the X direction;
v y (t) is a continuous time domain velocity waveform in the X direction;
L x (t) is the continuous perturbation displacement waveform in the X direction;
L y (t) is a continuous disturbance displacement waveform in the Y direction
a xi Is the acceleration sampling value at the time i in the X direction;
a yi is the acceleration sampling value at the time i in the Y direction;
v xi is the rate value at time i in the X direction;
v yi is the rate value at time i in the Y direction;
Δ t is the time difference between two samples.
S2, simplifying the wind power tower cylinder into a cantilever beam model, calculating the external load acting on the top of the wind power tower cylinder and the fatigue load acting on the bottom of the wind power tower cylinder, and specifically comprising the following steps:
s2.1, because the tower height of the wind power tower is usually more than 50m, the change of the cross section of the wind power tower can be approximately ignored relative to the tower height, the disturbance of the wind power tower can be simplified into an equi-section cantilever beam which is subjected to horizontal load and a cantilever beam model after the wind power tower is simplified,
as shown in FIG. 3, a high-h wind tower is subjected to a horizontal stress P with an inclination horizontal distance L 0 ；
Determining a deflection line differential square of the cantilever beam model by combining relevant parameters of the wind power tower cylinder structureA range and a boundary condition; calculating the shearing force F acting on the X direction of the bottom of the wind power tower through a connected equation group x And the shearing force F acting on the Y direction of the bottom of the wind power tower y ：
X-direction deflection line equation:
boundary conditions in the X direction: when x is 0, L is 0;
when x is h, L is L x ；
Y-direction deflection line equation:
y-direction boundary conditions: when y is 0, L is 0;
when y is h, L is L y ；
Combining the above equations yields:
wherein x and y are two mutually perpendicular measuring directions of the three-axis acceleration sensor parallel to the horizontal plane respectively;
e is the Young modulus of the steel material of the wind power tower cylinder;
i is the section inertia moment of the wind power tower;
h is the tower height of the wind power tower;
L x and L y Respectively measuring and calculating continuous disturbance displacement of the wind power tower cylinder in two mutually perpendicular horizontal directions by using an acceleration sensor;
the method for calculating the section moment of inertia I of the wind power tower barrel comprises the following steps:
wherein, pi is the circumferential ratio;
d is the outer diameter of the wind tower, as shown in FIG. 4;
d is the inner diameter of the wind tower, as shown in FIG. 4.
S2.2, calculating the actual shearing force F at the bottom of the wind power tower s Combining the stress condition of the wind power tower cylinder and the actual shearing force F at the bottom of the wind power tower cylinder s Is the sum of the two shear force vectors in the horizontal direction, and the actual shear force F at the bottom of the wind power tower cylinder s The calculation formula of (A) is as follows:
s2.3, the magnitude of fatigue load acting on the joint of the bottom of the wind power tower and the flange is equal to the maximum shear stress borne by the bottom of the wind power tower; the fatigue load tau acting on the bottom of the wind power tower barrel max The calculation formula of (A) is as follows:
wherein, F s The actual shear force at the bottom of the wind power tower is obtained;
a is the cross section area of the bottom of the cantilever beam model;
preferably, the wind power tower cylinder is simplified into a thin-wall circular ring-shaped section beam with a uniform section, and the maximum shear stress acting on the wind power tower cylinder in the horizontal direction can appear on a neutral axis of the section of the bottom of the wind power tower cylinder, namely the joint of the bottom of the wind power tower cylinder and a flange; for a wind power tower, the joint between the bottom of the wind power tower and a flange is the part which is most likely to cause fatigue damage to the wind power tower due to stress concentration;
s2.4, the calculation formula of the external load acting on the top of the wind power tower cylinder is as follows:
according to the stress condition of the wind power tower cylinder, the stress acts onExternal load at the top of the wind power tower and actual shear force F borne by the bottom of the tower s And are equal.
S3, according to fatigue load tau max Calculating and counting the stress amplitude of the fatigue load and the corresponding cycle number of the fatigue load by a time history curve, and drawing a corresponding low-cycle fatigue load amplitude map, wherein the specific process is as follows:
s3.1, obtaining the fatigue load tau based on the steps max -a time history curve, counting fatigue loads by means of a rain flow counting method;
preferably, the rain flow counting method is one of the most commonly used methods for analyzing the fatigue stress spectrum at present. The method is based on a double-parameter method, and can simplify the actually measured load course into a plurality of load cycles for fatigue life estimation.
As shown in fig. 5, after the fatigue load spectrum is processed by the rain flow counting method, 2 full cycles 2-3-2 'and 5-6-5' and 2 half cycles 1-2-4 and 4-5-7 can be obtained. After the threshold value of the low cycle fatigue load is set, only one half cycle 1-2-4 of the low cycle fatigue load can be obtained after screening.
S3.2, determining a fatigue load threshold value when the wind power tower cylinder is subjected to low cycle fatigue according to the yield stress of the wind power tower cylinder material;
preferably, the determination of the threshold value of the low cycle fatigue load refers to the maximum fatigue load that can be theoretically borne when the wind power tower cylinder is subjected to low cycle fatigue.
S3.3, screening the amplitude and frequency of low cycle fatigue load circulation of the wind power tower cylinder in the working process based on the set threshold value of the low cycle fatigue load, and drawing a corresponding amplitude frequency histogram;
and determining the threshold value of the fatigue load when the wind power tower cylinder is subjected to plastic deformation according to the yield stress of the wind power tower cylinder material. When the fatigue load is larger than the threshold value, the bottom of the wind power tower generates plastic deformation. And when the irreversible plastic deformation at the bottom of the wind power tower cylinder is accumulated to a certain degree, the wind power tower cylinder is subjected to low-cycle fatigue damage.
S4, calculating the total low cycle fatigue damage of the wind power tower cylinder and predicting the low cycle fatigue life of the wind power tower cylinder by combining the S-N curve of the steel material of the wind power tower cylinder and the Miner linear fatigue accumulated damage theory, wherein the specific process is as follows:
the amplitude frequency histogram obtained in the step is combined with an S-N curve of the steel material of the wind power tower cylinder and a Miner linear fatigue accumulated damage theory to obtain the low-cycle fatigue total damage D accumulated for the low-cycle fatigue effect of the wind power tower cylinder within a certain operation time t tot ：
Wherein k is the number of collected data points;
i is one of the acquisition moments;
D i is the low cycle fatigue damage of the wind turbine tower at moment i;
N fi expressed in stress amplitude σ i Fatigue life under action;
n i representing stress amplitude σ i Corresponding actual cycle times;
the low cycle fatigue life T of the wind power tower is as follows:
while the preferred embodiments of the present application have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including the preferred embodiment and all changes and modifications that fall within the scope of the present application.
Claims (5)
1. A method for diagnosing and detecting low cycle fatigue of a wind power tower based on an acceleration sensor is characterized by comprising the following steps:
(1) acquiring an acceleration signal of a wind power tower cylinder in the running process of the wind driven generator by using an acceleration sensor and calculating continuous disturbance displacement;
(2) simplifying the wind power tower cylinder into a cantilever beam model, and calculating external load acting on the top of the wind power tower cylinder and fatigue load acting on the bottom of the wind power tower cylinder;
(2.1) determining a deflection line equation and boundary conditions of the cantilever beam model by combining the simplified cantilever beam model of the wind power tower cylinder with relevant parameters of the wind power tower cylinder structure, and calculating the shearing force F acting on the bottom X direction of the wind power tower cylinder by substituting the boundary conditions into a deflection line differential equation x And the shearing force F acting on the Y direction of the bottom of the wind power tower y ：
X-direction deflection line equation:
boundary conditions in the X direction: when x is 0, L is 0;
when x is h, L is L x ；
Y-direction deflection line equation:
y-direction boundary conditions: when y is 0, L is 0;
when y is h, L is L y ；
Combining the above equations yields:
wherein x and y are two mutually perpendicular measuring directions of the three-axis acceleration sensor parallel to the horizontal plane respectively;
e is the Young modulus of the steel material of the wind power tower cylinder;
i is the section inertia moment of the wind power tower;
h is the tower height of the wind power tower;
L x and L y Respectively measuring and calculating continuous disturbance displacement of the wind power tower in two mutually perpendicular horizontal directions by using an acceleration sensor;
(2.2) calculating the actual shearing force F at the bottom of the wind power tower s ：
(2.3) the magnitude of fatigue load acting on the joint of the bottom of the wind power tower and the flange is equal to the maximum shear stress borne by the bottom of the wind power tower; the fatigue load tau acting on the bottom of the wind power tower barrel max The calculation formula of (A) is as follows:
wherein, F s The actual shear force at the bottom of the wind power tower is obtained;
a is the cross section area of the bottom of the cantilever beam model;
(2.4) the external load acting on the top of the wind power tower is as follows:
according to the stress condition of the wind power tower cylinder, the external load acting on the top of the wind power tower cylinder and the actual shearing force F borne by the bottom of the tower cylinder s Equal;
(3) according to fatigue load tau max Calculating and counting the stress amplitude of the fatigue load and the corresponding cycle number of the fatigue load by using a time history curve, and drawing a corresponding low-cycle fatigue load amplitude frequency histogram;
(4) and calculating the total low-cycle fatigue damage of the wind power tower cylinder within the test time and predicting the low-cycle fatigue life of the wind power tower cylinder by combining the S-N curve of the steel material of the wind power tower cylinder and the Miner linear fatigue accumulated damage theory.
2. The method for diagnosing and detecting the low cycle fatigue of the wind power tower based on the acceleration sensor as claimed in claim 1, wherein the acceleration sensor is a three-axis acceleration sensor vertically mounted on the inner wall of the top of the wind power tower; two mutually perpendicular measuring directions of the triaxial acceleration sensor parallel to the horizontal plane are set as an X direction and a Y direction respectively, and the measuring direction perpendicular to the horizontal plane is set as a Z direction.
3. The method for diagnosing and detecting the low-cycle fatigue of the wind power tower based on the acceleration sensor as claimed in claim 1, wherein the specific calculation process of the continuous disturbance displacement in the step (1) is as follows:
(1.1) the three-axis acceleration sensor collects continuous time domain acceleration signals a in the X direction and the Y direction x And a y ；
(1.2) carrying out low-pass filtering processing on continuous time domain acceleration signals acquired by the triaxial acceleration sensor;
(1.3) carrying out low-pass filtering on the continuous time domain acceleration signal a x (t) and a y (t) performing integration twice to obtain a calculation formula L of continuous disturbance displacement waveform in X direction x Calculation formula L of continuous disturbance displacement waveform in (t) and Y directions y (t) is:
wherein N is the number of collected data points;
i is one of the acquisition moments;
v x (t) is a continuous time domain velocity waveform in the X direction;
v y (t) is a continuous time domain velocity waveform in the Y direction;
L x (t) is the continuous perturbation displacement waveform in the X direction;
L y (t) is a continuous disturbance displacement waveform in the Y direction
a xi Is the acceleration sampling value at the time i in the X direction;
a yi is the acceleration sampling value at the time i in the Y direction;
v xi is the rate value at time i in the X direction;
v yi is the velocity value at time i in the Y direction;
Δ t is the time difference between two samples.
4. The method for diagnosing and detecting the low-cycle fatigue of the wind power tower based on the acceleration sensor as claimed in claim 1, wherein the specific process of the step (3) is as follows:
(3.1) obtaining the fatigue load tau at the bottom of the wind power tower drum based on the steps max -a time history curve, counting fatigue loads by means of a rain flow counting method;
(3.2) determining a threshold value of the low cycle fatigue load of the wind power tower cylinder according to the yield stress of the wind power tower cylinder material;
and (3.3) screening the amplitude and frequency of the low cycle fatigue load cycle of the wind power tower cylinder in the working process based on the set threshold value of the low cycle fatigue load, and drawing a corresponding amplitude frequency histogram.
5. The method for diagnosing and detecting the low cycle fatigue of the wind power tower based on the acceleration sensor as claimed in claim 1, wherein the specific process of the step (4) is as follows:
the amplitude frequency histogram obtained by the steps is combined with an S-N curve of the steel material of the wind power tower cylinder and a Miner linear fatigue accumulated damage theory to obtain the accumulated effect of low cycle fatigue of the wind power tower cylinder in a certain operation time tAccumulated total damage from low cycle fatigue D tot ：
Wherein k is the number of collected data points;
i is one of the acquisition moments;
D i is the low cycle fatigue damage of the wind turbine tower at moment i;
N fi expressed in stress amplitude σ i Fatigue life under action;
n i representing stress amplitude σ i The corresponding actual cycle number;
the low cycle fatigue life T of the wind power tower is as follows:
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