CN108267264B - Method, device and equipment for calibrating fiber grating sensor of fan blade - Google Patents
Method, device and equipment for calibrating fiber grating sensor of fan blade Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L25/00—Testing or calibrating of apparatus for measuring force, torque, work, mechanical power, or mechanical efficiency
Abstract
A method, apparatus and device for calibrating a fiber grating sensor of a fan blade are provided, the fan comprising a plurality of blades, each blade having a plurality of the fiber grating sensors mounted thereon, the method comprising, for each blade: acquiring data, the data comprising at least a plurality of pitch angles of the blade and a plurality of wavelengths of each fiber grating sensor mounted on the blade for each pitch angle; converting the collected wavelength into actual strain according to a function containing the undetermined initial wavelength; calculating theoretical bending moment of a blade root according to the pitch angle of the blade; converting the theoretical bending moment into theoretical strain according to a function containing the undetermined stiffness coefficient; and obtaining the undetermined stiffness coefficient and the undetermined initial wavelength on the condition that the theoretical strain and the actual strain are closest to each other according to a pre-specified criterion.
Description
Technical Field
The present disclosure relates generally to load fiber grating sensors and, more particularly, to methods and apparatus for calibrating fiber grating sensors.
Background
In recent years, as the development and installation of wind generating sets has increased, on the one hand, a great deal of application demands have been placed on the sets and wind farms, such as: the method has the advantages that the potential of the wind power plant is excavated, the generated energy is improved, the electricity consumption Cost (COE) of the unit is reduced, the load of the unit is reduced, the service life is prolonged, major fault processing is realized, the reliability of the unit and intelligent control application of the unit are improved, and more accurate test requirements are required; on the other hand, the traditional single electrical measurement method cannot meet the requirements of testing and evaluating the material quantity such as load, displacement and the like in the life cycle of the fan due to the problems of low precision, weak anti-electromagnetic interference capability, low reliability and stability, short service life and the like. The optical fiber measurement means can improve the measurement precision, enhance the anti-interference capability and meet the high reliability requirement, so the development of the optical fiber grating sensor applicable to the wind power industry is imperative.
the calibration accuracy is one of the important factors influencing the measurement accuracy of the fiber grating sensor. Although the fiber grating sensor is developed rapidly and widely in recent years, no special fiber grating sensor calibration method for the blade root load of the wind generating set exists in the domestic market so far.
the existing calibration method needs to separately calibrate the initial wavelength and the stiffness coefficient, and needs to repeat operation when calibrating different blades, namely only one blade can be calibrated each time, and the variable pitch operation needs to be carried out for many times when calibrating one blade, so that the process is troublesome. In addition, when the calibration is performed by the existing method, the influence of crosstalk (cross-talk) needs to be additionally considered.
Disclosure of Invention
In view of the various drawbacks of the prior calibration methods, an aspect of the present disclosure provides a method for calibrating a fiber grating sensor of a wind turbine, the wind turbine being provided with a plurality of blades, each blade having a plurality of the fiber grating sensors mounted thereon, the method comprising, for each blade, the steps of: a data acquisition step for acquiring data including at least a plurality of pitch angles of the blade and a plurality of wavelengths of each fiber grating sensor mounted on the blade for each pitch angle; and a data calculation step, which is used for determining the undetermined initial wavelength of each fiber grating sensor and the undetermined stiffness coefficient of the blade according to the acquired data, wherein the data calculation step comprises the following steps: an actual strain acquisition step, which is used for converting the acquired wavelength into actual strain according to a function containing the undetermined initial wavelength; a theoretical bending moment calculation step, which is used for calculating the theoretical bending moment of the blade root according to the pitch angle of the blade; a theoretical strain obtaining step, which is used for converting the theoretical bending moment into theoretical strain according to a function containing the undetermined stiffness coefficient; and an undetermined parameter acquisition step, which is used for obtaining the undetermined stiffness coefficient and the undetermined initial wavelength under the condition that the theoretical strain and the actual strain are closest to each other according to a pre-specified criterion.
Another aspect of the present disclosure provides an apparatus for calibrating a fiber grating sensor of a fan blade, the fan comprising a plurality of blades, each blade having a plurality of the fiber grating sensors mounted thereon, the apparatus comprising, for each blade: a data acquisition unit for acquiring data, the data comprising at least a plurality of pitch angles of the blade and a plurality of wavelengths of each fiber grating sensor mounted on the blade for each pitch angle; and the data calculation unit is used for determining the undetermined initial wavelength of each fiber grating sensor and the undetermined stiffness coefficient of the blade according to the data acquired by the data acquisition unit, and comprises: the actual strain acquisition unit is used for converting the acquired wavelength into actual strain according to a function containing the undetermined initial wavelength; the theoretical bending moment calculation unit is used for calculating the theoretical bending moment of the blade root according to the pitch angle of the blade; the theoretical strain acquisition unit is used for converting the theoretical bending moment into theoretical strain according to a function containing the undetermined stiffness coefficient; and the undetermined parameter acquisition unit is used for obtaining the undetermined stiffness coefficient and the undetermined initial wavelength under the condition that the theoretical strain and the actual strain are closest to each other according to a pre-specified criterion.
Yet another aspect of the present disclosure provides an apparatus for calibrating fiber grating sensors of a fan blade, the fan being provided with a plurality of blades, each blade having a plurality of the fiber grating sensors mounted thereon, the apparatus comprising: a data acquisition device for acquiring data, said data comprising at least a plurality of pitch angles of the blade and a plurality of wavelengths of each fiber grating sensor mounted on the blade for each pitch angle; and a processor for: converting the wavelength acquired by the data acquisition device into actual strain according to a function containing the undetermined initial wavelength; calculating theoretical bending moment of a blade root according to the pitch angle of the blade acquired by the data acquisition device; converting the theoretical bending moment into theoretical strain according to a function containing the undetermined stiffness coefficient; and obtaining the undetermined stiffness coefficient and the undetermined initial wavelength under the condition that the theoretical strain and the actual strain are closest to each other according to a pre-specified criterion.
drawings
Other features, objects, and advantages of the disclosure will become more apparent from the following detailed description of non-limiting embodiments thereof, which proceeds with reference to the accompanying drawings. In the drawings, which are not necessarily to scale, embodiments are illustrated by way of example and not by way of limitation.
FIG. 1a is a schematic diagram illustrating a flapwise and edgewise direction of a fan blade of various embodiments of the present disclosure;
FIG. 1b is a schematic diagram illustrating an impeller pitch angle and a blade cone angle of a wind turbine according to various embodiments of the present disclosure;
FIGS. 2a and 2b are schematic diagrams illustrating station positioning according to an exemplary embodiment of the present disclosure;
FIG. 3 is a flow diagram illustrating an exemplary method for calibrating a fiber grating sensor according to various embodiments of the present disclosure;
FIG. 4 is a block diagram illustrating an exemplary apparatus for calibrating a fiber grating sensor according to various embodiments of the present disclosure.
FIG. 5 is a block diagram of an example computing device that may be used to implement various embodiments described herein.
Detailed Description
features and exemplary embodiments of various aspects of the present invention will be described in detail below. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without some of these specific details. The following description of the embodiments is merely intended to provide a better understanding of the present invention by illustrating examples of the present invention. The present invention is in no way limited to any specific configuration and algorithm set forth below, but rather covers any modification, replacement or improvement of elements, components or algorithms without departing from the spirit of the invention. In the drawings and the following description, well-known structures and techniques are not shown in order to avoid unnecessarily obscuring the present invention.
a wind turbine (hereinafter, also referred to as a "wind turbine") is a large-scale machine, and most of the wind turbine is installed in a relatively severe environment, and the operation conditions are complicated, so that if the actual operation load exceeds the design load, the life of a large component is shortened if the actual operation load is light, and a serious accident such as collapse of the wind turbine is caused if the actual operation load is heavy. Therefore, it is important to perform load testing on the wind turbine. Here, the load is an external force and other factors that generate an internal force and deformation of the structure or member. The main content of the load test is to test the bending moment of main structural components such as a tower cylinder, a main shaft, a blade root (hereinafter referred to as a blade root) and the like of the fan unit. The loads in this disclosure relate primarily to the bending moment of the blade root. The bending moment of the blade root comprises two directions, namely a blade flapping direction (flapwise) and a blade shimmy direction (edgewise); the blade flap direction is perpendicular to the chord line and the blade edgewise direction is parallel to the chord line, as shown in fig. 1 a.
the measurement of the bending moment of the blade root can be carried out by means of a fiber grating sensor mounted in the region of the blade root. The fiber grating sensor can reflect the deformation of the measured object (such as the bending moment of the blade root) by the wavelength. More specifically, the fiber grating technology is formed by using an ultraviolet exposure technique to induce a periodic variation in the refractive index in the core of the optical fiber. The periodic structure of the refractive index distribution in the fiber grating causes the reflection of light of a certain wavelength, thereby forming the reflection spectrum of the fiber grating. The fiber grating sensor is usually made by attaching the fiber grating to some elastic body and performing protection packaging. The wavelength of the reflected light is very sensitive to temperature, stress and strain, when the elastic body is subjected to pressure, the fiber grating and the elastic body deform together, so that the peak wavelength of the reflected light of the fiber grating shifts, and the temperature, the stress and the strain are sensed by measuring the wavelength shift.
In order to measure the bending moment by using the fiber grating sensor, the fiber grating sensor needs to be calibrated first. The calibration refers to a process of establishing a relationship between an output signal of the fiber grating sensor and a physical quantity to be measured. And y represents the physical quantity to be measured, x represents the output signal of the fiber grating sensor, and the relationship between y and x is represented by F (x), the calibration refers to the process of determining the function F of the fiber grating sensor under the condition that the output signal x of the fiber grating sensor and the corresponding physical quantity to be measured y are known. The process can be realized by a least square fitting technology and the like, and it should be noted that the relationship between the physical quantity y to be measured and the output signal x of the fiber grating sensor can not be written into a clear functional form F by an analytic method. In some cases, the relationship between them is obtained by numerically calculating the parameters related to the function F. At this time, the process of calibrating the fiber grating sensor includes a process of determining a parameter related to the function F.
For the fiber bragg grating sensor embodiment for testing blade load disclosed by the invention, the output signal x is a wavelength signal, and the physical quantity y to be tested is a bending moment value of the blade root, so that calibration is a process for establishing a relation between the wavelength signal x and the bending moment value y. In order to obtain the relationship F between the two, a set of wavelength signals and the corresponding bending moment value need to be known in advance. The wavelength signal x can be obtained by collecting the output signal of the fiber bragg grating sensor, and the bending moment value y can be obtained by theoretical calculation. In embodiments of the present disclosure, the blade is typically left unloaded when the blade root FBG sensor is calibrated and wind speeds are guaranteed to be sufficiently low (e.g., wind speeds less than 4m/s are required). At the moment, the bending moment of the blade root is completely from the gravity of the blade, so that the bending moment of the blade root from the gravity of the blade can be obtained through theoretical calculation. As will be described in more detail later.
After the fiber bragg grating sensor is calibrated, namely a relation function F of the wavelength signal x and the bending moment value y is determined, the bending moment of the blade root under the complex working condition can be measured through the fiber bragg grating sensor.
In the embodiments of the present disclosure, 4 fiber grating sensors may be installed at the root region of each blade, and the number of the fiber grating sensors is not limited to 4, but may be more. An exemplary method for determining the installation position (hereinafter also referred to as a measurement point) of the fiber grating sensor is described below with reference to fig. 2a and 2b, taking as an example the installation of 4 fiber grating sensors in the root region. As shown in fig. 2a and 2b, a name plate of a zero scale mark can be found on the end surface of a variable-pitch bearing or the joint of a blade and a bearing, an extension line is made at the position of the zero scale mark vertical to the end surface of the bearing, the extension line penetrates through a partition plate at the root of the blade and extends to a position 800mm away from the partition plate at the root of the blade, a mark is made, a cross word line is drawn at the installation position of the fiber bragg grating sensor, and then a circle on the circumference 800mm away from the partition plate of the blade is divided into four equal parts by taking the. The quarter is the installation position of the fiber grating sensor. It should be noted that the zero scale nameplates of each unit may be installed differently, and according to whether the past measuring point corresponding to the extension line is on the front edge or the rear edge of the blade, the front edge measuring point may be generally defined as 0 °, and the other measuring points clockwise facing the blade tip may be sequentially defined as 90 °, 180 °, and 270 °.
To facilitate description of exemplary embodiments of the present disclosure, some parameter terms to be used in the specification are first briefly described.
As used herein, pitch angle refers to the angle between the chord line of the blade and the plane of rotation, and is typically about 0 for normal operation of the wind turbine and about 87 for shutdown, hereinafter designated by the reference numeralAnd (4) showing.
as used herein, blade azimuth refers to the angle of the blade from vertical, at 0 ° vertically upwards, rotated in a clockwise direction, hereinafter denoted by the symbol Ω.
As used herein, blade cone angle refers to the angle of the blade from a plane perpendicular to the axis of rotation, denoted by the symbol θ.
As used herein, impeller pitch refers to the angle of rotation of the shaft relative to the horizontal, and is hereinafter denoted by the symbol δ.
As used herein, the initial wavelength refers to the corresponding wavelength when the fiber grating sensor is strained to 0, and is one of the data that needs to be calibrated in the embodiments of the present disclosure, and is denoted by λ hereinafter. In an exemplary embodiment of the present disclosure, each blade is installed with four fiber grating sensors (also referred to as fiber grating sensor channels), whose respective initial wavelengths may constitute a 4 × 1 vector.
As used herein, the stiffness coefficient refers to the degree of difficulty in characterizing the elastic deformation of a material or structure, and in the macro-elastic range, the stiffness coefficient is the proportionality coefficient of part loading (e.g., root bending moment) and displacement (e.g., strain of a fiber grating sensor), i.e., the force required to cause a unit displacement. When c denotes a stiffness coefficient, M denotes a blade root bending moment, and ∈ denotes a strain of the fiber grating sensor, M ═ c · ∈ is known by this definition. In the embodiment of the present disclosure, each blade is provided with four fiber bragg grating sensors, and the bending moment of the blade to the blade root includes two directions, so that the stiffness coefficient C of each blade may form a 2 × 4 matrix, which is denoted by C in the following and is another data to be calibrated in the embodiment of the present disclosure.
As used herein, cross-talk refers to the interaction between signals. Theoretically, if the fiber grating sensor is installed at the positions of 0 °, 90 °, 180 ° and 270 ° strictly, the loads in the blade shimmy direction are only related to the signals of the fiber grating sensors of 0 ° and 180 °, and similarly, the loads in the blade flapping direction are only related to the signals of the fiber grating sensors of 90 ° and 270 °. However, when the fiber grating sensor is installed, absolute accuracy of the installation angle cannot be guaranteed, the fiber grating sensor cannot be installed at a required position due to other reasons (for example, it is inconvenient to install the fiber grating sensor at a 180-degree position), errors are caused by calculation of loads in the blade shimmy direction from signals of the 0-degree and 180-degree fiber grating sensors, signals of the 90-degree and 270-degree fiber grating sensors must be considered, and therefore crosstalk is generated.
the method for calibrating a fiber grating sensor of the present disclosure is described in detail below with reference to fig. 3.
as shown in fig. 3, an exemplary method 300 for calibrating a fiber grating sensor according to an aspect of the present disclosure may include a data acquisition step S301 and a data calculation step S302. The data acquisition step is for acquiring data including at least a plurality of pitch angles of the blade and a plurality of wavelengths of each fiber grating sensor mounted on the blade for each pitch angle. And a data calculation step S302 is used for determining the undetermined initial wavelength of each fiber grating sensor and the undetermined stiffness coefficient of the blade according to the acquired data. Wherein the definition of the pitch angle of the blade is as described above, obtainable by measurement. In one embodiment, the three blades may be individually pitched manually to generate sufficient loads in both the flapwise and edgewise directions as shown in FIG. 1a to improve the accuracy of the calibration. The wavelength of the fiber grating sensor can be obtained by collecting the output signal of the fiber grating sensor. As known to those skilled in the art, in the process of establishing the function F in y ═ F (x) as described above, the more samples of the output signal x and the signal y to be measured are, the closer the relationship between the two obtained by fitting is to the real situation. Therefore, in order to improve the accuracy of calibration, it is preferable that a sufficient number of sets of data should be prepared. In embodiments of the present disclosure, two half-wavelength data may be collected. Wherein each half wavelength corresponds to a range of pitch angles of the fan blades from 87 degrees to 0 degrees and from 0 degrees to 87 degrees, for example.
In addition, as known to those skilled in the art, in the no-load state, the bending moment of the blade root is all generated by the gravity of the blade, and the bending moment value of the blade root can be obtained through theoretical calculation. The calibration process of embodiments of the present disclosure requires the use of this theoretical bending moment. Therefore, for the theoretical calculation to be effective, the operating conditions must be simple to approach the idling state, and therefore the wind speed should be sufficiently small. In one embodiment, the wind speed may be less than 4 m/s. Each fiber grating sensor of each blade can be enabled to respectively acquire a plurality of wavelengths for each pitch angle of a plurality of different pitch angles obtained through the pitch changing operation under the wind speed.
the data calculating step S302 may include: converting the collected wavelength into actual strain according to a function containing the undetermined initial wavelength lambda (S3021); calculating a theoretical bending moment of the blade root according to the pitch angle of the blade (S3022); converting the theoretical bending moment into theoretical strain according to a function containing the undetermined stiffness coefficient C (S3023); and obtaining the undetermined stiffness coefficient C and the undetermined initial wavelength lambda (S3024) on the condition that the theoretical strain and the actual strain are closest to each other according to a pre-specified criterion.
Specifically, in one aspect, for any fiber grating sensor of any blade, the wavelength can be converted to actual strain according to a relationship between the wavelength and the strain, which contains an unknown undetermined parameter λ. Let the wavelength use λBThe actual strain is denoted by epsilon and depending on whether the fiber grating sensor used is thermally strained or not, the above conversion process can be expressed as:
for heat stressvariable optical fiber grating sensor
For non-thermal strain fiber grating sensor (1)
Wherein the content of the first and second substances,ΔT＝T-T0，kεAnd kTThe parameter is the inherent parameter of the fiber grating sensor and can be obtained together with the fiber grating sensor. Alpha is alphaTis to measure a position parameter, T0The installation parameters of the fiber grating sensor are the installation parameters of the fiber grating sensor, and both the installation parameters and the installation parameters can be measured when the fiber grating sensor is installed. T can be measured using a fiber grating sensor.
Each blade has 4 fibre grating sensor channels, so that for one blade the measured actual strains epsilon can be combined into a 4 x 1 matrix epsilona。
From the expression (1), it can be seen that when the wavelength λ of the fiber grating sensor isBλ (for a thermally strained fiber grating sensor, T is also required)0) When the strain ε is equal to 0. Therefore, the parameter λ to be determined in the expression (1), i.e. the wavelength at which the fiber grating sensor is strained to 0, is known from the above definition, i.e. the initial wavelength of the fiber grating sensor.
On the other hand, the theoretical bending moment M of the blade root can be calculated according to the gravity of the blade (equal to the mass M of the blade multiplied by the gravity constant g), and then the theoretical bending moment M is converted into the theoretical strain according to the relation between the bending moment and the strain, wherein the relation contains the undetermined parameter C.
First, for a blade at any position, the theoretical bending moment M of the blade root in the blade coordinate system can be obtained by the following expression:
Where r represents the distance of the center of gravity from the root of the blade, m represents the mass of the blade, Ω represents the azimuth angle of the blade, δ represents the impeller angle, and θ represents the blade cone angleThe above parameters can be obtained in advance by measurement.Representing the pitch angle of the blade, which can be obtained by a pitch operation at calibration. M is a 2 x 1 matrix whose two components represent the bending moments in the blade edgewise and flapwise directions, respectively. The specific meanings of the angles involved have been exemplified above and will not be described herein.
Let epsilonMRepresenting the theoretical strain of the fiber grating sensor (in the embodiments of the present disclosure, four fiber grating sensors may be mounted on each blade, so εMεMcan be represented as a 4 x 1 matrix) due to the theoretical strain epsilonMThe relationship with the theoretical bending moment M can be expressed as C.epsilon. by the parameter C as described aboveMM, the theoretical bending moment M can therefore be converted into the theoretical strain epsilon by the following expressionM：
εM＝C-1·M (3)
Wherein, C-1the pseudo-inverse of the representation matrix C is an unknown parameter to be determined. As is clear from the above definition, the parameter C, i.e. the stiffness coefficient of the blade, is a 2 × 4 matrix.
For accurately calibrating a FBG sensor, the actual measured strain ε is obtained by expression (1)aWith the strain ε obtained by theoretical calculation by expression (3)MShould be as close as possible. The proximity may be proximity based on different metric criteria, such as Least Squares (LS) criteria, Minimum Mean Square Error (MMSE) criteria. According to some embodiments of the present disclosure, the least squares criterion may be taken as an example, that is, such that the actual strain εaand theoretical strain epsilonMThe sum of squared errors of (a) is minimal. At this time, the undetermined parameters λ and C can be obtained by a least square fitting method-1. By pair C-1The inverse operation is performed to obtain the stiffness.
according to some embodiments of the present disclosure, the data calculation step described above may be implemented by a computer program. In particular, the two pending parameters may be determined in a computer programGiving an initial value and then iterating these two parameters until the actual strain εaAnd theoretical strain epsilonMthe closest approach is based on a metric criterion (e.g., LS, MMSE) specified in the program, so that the calibration results for these two parameters are obtained simultaneously. In one embodiment, the initial values of the two pending parameters are approximate values, the actual strain ε, set empirically from the pastaAnd theoretical strain epsilonMThe closest approach is realized by the difference between the two being smaller than a preset minimum value.
the method for calibrating a fiber grating sensor according to an embodiment of the present disclosure (hereinafter, simply referred to as "the method") has various advantages over the conventional method for calibrating a fiber grating sensor (hereinafter, simply referred to as "the conventional method"), including:
(1) The method can calibrate the initial wavelength and the stiffness coefficient at the same time, and is more efficient compared with the traditional method which can calibrate only one coefficient at a time;
(2) The method can simultaneously acquire the data of all the fiber bragg grating sensors of all the blades under the same blade azimuth angle, and process the information of all the blades and the data of the corresponding fiber bragg grating sensor channels, so that a plurality of blades can be calibrated simultaneously, the blades do not need to be rotated frequently, and convenience and time saving are realized;
(3) the method directly considers the influence of crosstalk, and does not need to carry out other additional operations on the fan. In the traditional method, crosstalk does not exist in the calibration process by default, and after main parameters are calibrated, the fan is positioned at certain specific positions, and data is collected and analyzed, so that the influence caused by the crosstalk is corrected. In the embodiment of the method, the rigidity coefficient is a 2 x 4 matrix, and the default loads in the flapping and shimmy directions are related to 4 fiber bragg grating sensors, namely the influence of crosstalk is directly considered in the calibration process;
(4) The method can obtain not only the calibration result, but also a curve of the theoretical value and the actually measured value, so that the coincidence condition between the theoretical value and the measured value can be conveniently and visually known, and the calibration accuracy can be judged.
The method for calibrating the fiber grating sensor according to the embodiment of the present disclosure is described in detail above with reference to fig. 3, and the apparatus for calibrating the fiber grating sensor according to the embodiment of the present disclosure is described below with reference to fig. 4.
As shown in fig. 4, an exemplary apparatus 400 for calibrating a fiber grating sensor according to another aspect of the present disclosure may include a data acquisition unit 401 and a data calculation unit 402. Wherein the data acquisition unit 401 is configured to acquire data at least including a plurality of pitch angles of the blade and a plurality of wavelengths of each fiber grating sensor mounted on the blade for each pitch angle (i.e. performing the data acquisition step S301 of the exemplary method 300 for calibrating fiber grating sensors as described above), and the data calculation unit 402 is configured to determine an undetermined initial wavelength and an undetermined stiffness coefficient of the fiber grating sensor according to the sets of data acquired by the data acquisition unit (i.e. performing the data calculation step S302 of the exemplary method 300). The data calculation unit 402 may include an actual strain acquisition unit 4021, a theoretical bending moment calculation unit 4022, a theoretical strain acquisition unit 4023, and a parameter-to-be-determined acquisition unit 4024. The actual strain obtaining unit 4021 is configured to convert the wavelength into an actual strain according to a function including an undetermined initial wavelength λ (i.e., step S3021 of the exemplary method 300 is performed), the theoretical bending moment calculating unit 4022 is configured to calculate a theoretical bending moment of the blade root according to the pitch angle of the blade and the gravity of the blade (i.e., step S3022 of the exemplary method 300 is performed), the theoretical strain obtaining unit 4023 is configured to convert the theoretical bending moment into a theoretical strain according to a function including an undetermined stiffness coefficient C (i.e., step S3023 of the exemplary method 300 is performed), and the undetermined parameter obtaining unit 4024 is configured to derive the undetermined stiffness coefficient C and the undetermined initial wavelength λ (i.e., step S3024 of the exemplary method 300 is performed) on the condition that the theoretical strain and the actual strain are closest to each other according to a pre-specified criterion.
other details of the apparatus 400 for calibrating a fiber grating sensor according to the embodiment of the present disclosure are the same as the corresponding method described above with reference to fig. 3, and are not repeated here.
The device for calibrating the fiber bragg grating sensor according to the embodiment of the disclosure can efficiently and simultaneously calibrate the initial wavelength and the stiffness coefficient; a plurality of blades can be calibrated at the same time, so that the blades do not need to be rotated frequently, and convenience and time are saved; the influence of crosstalk is directly considered, and other extra operations on the fan are not needed; in addition, not only can a calibration result be obtained, but also a curve of a theoretical value and an actually measured value can be obtained, so that the coincidence condition between the theoretical value and the measured value can be conveniently and visually known, and the calibration accuracy can be judged.
At least a portion of the methods and apparatus for calibrating a fiber grating sensor described in connection with fig. 3-4 may be implemented by a computing device. FIG. 5 is a block diagram illustrating an exemplary hardware architecture of a computing device capable of implementing the method and apparatus for tuning a fiber grating sensor according to embodiments of the present invention. As shown in fig. 5, computing device 500 includes an input device 501, an input interface 502, a central processor 503, a memory 504, an output interface 505, and an output device 506. The input interface 502, the central processing unit 503, the memory 504, and the output interface 505 are connected to each other through a bus 510, and the input device 501 and the output device 506 are connected to the bus 510 through the input interface 502 and the output interface 505, respectively, and further connected to other components of the computing device 500. Specifically, the input device 501 receives input information from the outside (e.g., a fiber grating sensor mounted on a blade), and transmits the input information to the central processor 503 through the input interface 502; the central processor 503 processes input information based on computer-executable instructions stored in the memory 504 to generate output information, temporarily or permanently stores the output information in the memory 504, and then transmits the output information to the output device 506 through the output interface 505; output device 506 outputs the output information outside of computing device 500 for use by a user.
That is, the apparatus shown in fig. 4 may also be implemented to include: a memory storing computer-executable instructions; and a processor which, when executing the computer executable instructions, may implement the method for calibrating a fiber grating sensor described in connection with fig. 3. Here, the processor may execute computer-executable instructions based on input information from, for example, a user, to implement the method and apparatus for calibrating a fiber grating sensor described in conjunction with fig. 3-4.
It is to be understood that the invention is not limited to the specific arrangements and instrumentality described above and shown in the drawings. A detailed description of known methods is omitted herein for the sake of brevity. In the above embodiments, several specific steps are described and shown as examples. However, the method processes of the present invention are not limited to the specific steps described and illustrated, and those skilled in the art can make various changes, modifications and additions or change the order between the steps after comprehending the spirit of the present invention.
The functional blocks shown in the above-described structural block diagrams may be implemented as hardware, software, firmware, or a combination thereof. When implemented in hardware, it may be, for example, an electronic circuit, an Application Specific Integrated Circuit (ASIC), suitable firmware, plug-in, function card, or the like. When implemented in software, the elements of the invention are the programs or code segments used to perform the required tasks. The program or code segments may be stored in a machine-readable medium or transmitted by a data signal carried in a carrier wave over a transmission medium or a communication link. A "machine-readable medium" may include any medium that can store or transfer information. Examples of a machine-readable medium include electronic circuits, semiconductor memory devices, ROM, flash memory, Erasable ROM (EROM), floppy disks, CD-ROMs, optical disks, hard disks, fiber optic media, Radio Frequency (RF) links, and so forth. The code segments may be downloaded via computer networks such as the internet, intranet, etc.
the present disclosure may be embodied in other specific forms without departing from its spirit or essential characteristics. For example, the algorithms described in the specific embodiments may be modified without departing from the basic spirit of the disclosure. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the disclosure being defined by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
Claims (11)
1. A method for calibrating a fibre grating sensor of a fan blade, the fan being provided with a plurality of blades, each blade having a plurality of the fibre grating sensors mounted thereon, the method comprising, for each blade, the steps of:
a data acquisition step for acquiring data including at least a plurality of pitch angles of the blade and a plurality of wavelengths of each fiber grating sensor mounted on the blade for each pitch angle; and
A data calculation step, which is used for determining the undetermined initial wavelength of each fiber grating sensor and the undetermined stiffness coefficient of the blade according to the collected data, wherein the data calculation step comprises the following steps:
An actual strain acquisition step, which is used for converting the acquired wavelength into actual strain according to a function containing the undetermined initial wavelength;
A theoretical bending moment calculation step, which is used for calculating the theoretical bending moment of the blade root according to the pitch angle of the blade;
a theoretical strain obtaining step, which is used for converting the theoretical bending moment into theoretical strain according to a function containing the undetermined stiffness coefficient; and
An undetermined parameter acquisition step, which is used for obtaining the undetermined stiffness coefficient and the undetermined initial wavelength under the condition that the theoretical strain and the actual strain are closest according to a pre-specified criterion; wherein, the pitch angle refers to the included angle between the chord line of the blade and the rotating plane; the initial wavelength refers to the wavelength corresponding to the fiber grating sensor strain 0.
2. The method of claim 1, wherein the pre-specified criteria include a least squares criterion, a minimum mean square error criterion.
3. The method of claim 1, wherein for each blade, the actual strain deriving step comprises:
For each fiber grating sensor installed on the blade, converting the collected wavelength into an actual strain component of the fiber grating sensor through the following expression; and
The actual strain components of all the fiber bragg grating sensors of the blade form the actual strain of the blade;
wherein the expression is:
if the fiber grating sensor is a thermally strained fiber grating sensor,
if the fiber grating sensor is not a thermally strained fiber grating sensor,
Wherein ε is the actual strain, λ, of the fiber grating sensorBIs the collected wavelength of the fiber grating sensor, λ is the undetermined initial wavelength of the fiber grating sensor, Tkk is related to the temperature measured during installation and use of the fiber grating sensor, the position of the fiber grating sensor and the intrinsic parameters of the fiber grating sensorεIs a fixed parameter of the fiber grating sensor.
4. The method of claim 1, wherein for each blade, the theoretical bending moment calculation step is accomplished by the expression:
whereinIs the pitch angle of the blade, M is the theoretical bending moment, g is the gravity constant, r is the distance from the center of gravity of the blade to the blade root, M is the mass of the blade, Ω is the azimuth angle of the blade, δ is the impeller inclination angle, θIs the cone angle of the blade; the azimuth angle of the blade refers to the included angle between the blade and the vertical direction; the cone angle of the blade refers to the included angle of the blade and a plane vertical to the rotating shaft; the impeller inclination angle refers to the included angle between the rotating shaft and the horizontal plane.
5. The method of claim 1, wherein for each blade, the theoretical strain acquisition step is accomplished by the expression:
εM＝C-1·M，
Wherein epsilonMis the theoretical strain, M is the theoretical bending moment, C is the undetermined stiffness coefficient-1Is the pseudo-inverse of the undetermined stiffness coefficient.
6. A device for calibrating a fiber grating sensor of a fan blade, the fan being provided with a plurality of blades, each blade being provided with a plurality of the fiber grating sensors, the device comprising, for each blade:
A data acquisition unit for acquiring data, the data comprising at least a plurality of pitch angles of the blade and a plurality of wavelengths of each fiber grating sensor mounted on the blade for each pitch angle; and
the data calculation unit is used for determining undetermined initial wavelength of each fiber grating sensor and undetermined stiffness coefficient of the blade according to the data acquired by the data acquisition unit, and comprises:
the actual strain acquisition unit is used for converting the acquired wavelength into actual strain according to a function containing the undetermined initial wavelength;
The theoretical bending moment calculation unit is used for calculating the theoretical bending moment of the blade root according to the pitch angle of the blade;
The theoretical strain acquisition unit is used for converting the theoretical bending moment into theoretical strain according to a function containing the undetermined stiffness coefficient; and
the undetermined parameter acquisition unit is used for obtaining the undetermined stiffness coefficient and the undetermined initial wavelength under the condition that the theoretical strain and the actual strain are closest to each other according to a pre-specified criterion;
Wherein, the pitch angle refers to the included angle between the chord line of the blade and the rotating plane; the initial wavelength refers to the wavelength corresponding to the fiber grating sensor strain 0.
7. The apparatus of claim 6, wherein the pre-specified criteria comprises a least squares criterion, a minimum mean square error criterion.
8. the apparatus of claim 6, wherein for each blade, the actual strain acquisition unit is configured to:
For each fiber grating sensor installed on the blade, converting the collected wavelength into an actual strain component of the fiber grating sensor through the following expression; and
the actual strain component of all fiber grating sensors of the blade is composed into the actual strain of the blade,
Wherein the expression is:
If the fiber grating sensor is a thermally strained fiber grating sensor,
If the fiber grating sensor is not a thermally strained fiber grating sensor,
Wherein ε is the actual strain, λ, of the fiber grating sensorBis the collected wavelength of the fiber grating sensor, λ is the undetermined initial wavelength of the fiber grating sensor, TkK is related to the temperature measured during installation and use of the fiber grating sensor, the position of the fiber grating sensor and the intrinsic parameters of the fiber grating sensorεIs a fixed parameter of the fiber grating sensor.
9. the apparatus of claim 6, wherein for each blade, the theoretical bending moment calculation unit is configured to perform the calculation by the following expression:
WhereinIs the pitch angle of the blade collected, M is the theoretical bending moment, g is the gravity constant, r is the distance from the gravity center of the blade to the blade root, M is the mass of the blade, Ω is the azimuth angle of the blade, δ is the impeller inclination angle, θ is the cone angle of the blade; the azimuth angle of the blade refers to the included angle between the blade and the vertical direction; the cone angle of the blade refers to the included angle of the blade and a plane vertical to the rotating shaft; the impeller inclination angle refers to the included angle between the rotating shaft and the horizontal plane.
10. The apparatus of claim 6, wherein for each blade, the theoretical strain acquisition unit is configured to perform the transformation by the following expression:
εM＝C-1·M，
wherein epsilonMis the theoretical strain, M is the theoretical bending moment, C is the undetermined stiffness coefficient-1Is the pseudo-inverse of the undetermined stiffness coefficient.
11. An apparatus for calibrating fiber grating sensors of a fan blade, the fan comprising a plurality of blades, each blade having a plurality of the fiber grating sensors mounted thereon, the apparatus comprising:
a data acquisition device for acquiring data, said data comprising at least a plurality of pitch angles of the blade and a plurality of wavelengths of each fiber grating sensor mounted on the blade for each pitch angle; and
a processor to:
Converting the wavelength acquired by the data acquisition device into actual strain according to a function containing the undetermined initial wavelength;
Calculating theoretical bending moment of a blade root according to the pitch angle of the blade acquired by the data acquisition device;
converting the theoretical bending moment into theoretical strain according to a function containing the undetermined stiffness coefficient; and
Obtaining the undetermined stiffness coefficient and the undetermined initial wavelength under the condition that the theoretical strain and the actual strain are closest to each other according to a pre-specified criterion;
wherein, the pitch angle refers to the included angle between the chord line of the blade and the rotating plane; the initial wavelength refers to the wavelength corresponding to the fiber grating sensor strain 0.
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