Nuclear power unit broadband vibration measurement method based on distributed optical fiber sensing

Abstract

The application discloses a nuclear power unit wide-frequency vibration measurement method based on distributed optical fiber sensing, and belongs to the technical field of vibration measurement, and specifically comprises the following steps: a three-dimensional sensing structure is constructed by arranging sensing optical fibers along the surface of a pipeline in a spiral path, and the geometric parameters of the three-dimensional sensing structure are calibrated to establish a spatial distribution database; a wide-spectrum probe light signal is injected, and intensity, phase and polarization state dynamic change data of back Rayleigh scattering light are synchronously collected; radial bending vibration components are calculated based on intensity change and fluctuation amplitude parameters, axial vibration components are calculated based on phase change and pitch parameters, and torsional vibration components are calculated based on polarization state change and spiral angle parameters; a three-dimensional full-field vibration distribution of the pipeline surface is reconstructed, and dominant vibration frequencies at different spatial positions are obtained through frequency domain feature extraction. The application realizes distributed and full-field surface measurement of three-dimensional vibration of a nuclear power unit pipeline, and provides a reliable technical means for state monitoring and fault diagnosis.

Description

Technical Field

[0001] This invention relates to the field of vibration measurement technology, and more specifically to a broadband vibration measurement method for nuclear power units based on distributed optical fiber sensing. Background Technology

[0002] As an important source of clean energy, the safety and reliability of nuclear power generation have always been a focus of industry attention. During operation, key equipment such as main circuit pipelines, steam generators, and main pumps of nuclear power units are subjected to complex mechanical vibrations, fluid excitations, and thermal stress coupling effects. These broadband vibration phenomena are key indicators for assessing the structural integrity of equipment, predicting fatigue life, and diagnosing potential faults.

[0003] In the existing vibration monitoring technology system, the point measurement scheme based on piezoelectric accelerometers is the most widely used technique. This scheme acquires vibration acceleration signals at local locations by installing rigidly connected accelerometers at specific measuring points on the equipment surface, and then transmits the signals to the data acquisition system via wired connections. This technology is highly mature and can provide relatively accurate vibration amplitude and frequency information at individual measuring points, playing an important role in unit condition monitoring.

[0004] It is understandable that point-based measurements based on piezoelectric accelerometers have a monitoring range limited to discrete installation points, making it difficult to achieve continuous, comprehensive sensing of the vibration field across the entire component surface, resulting in significant monitoring blind spots. Secondly, sensors typically require rigid installation via mechanical clips or bolts. This installation method may cause potential damage to the surface of thin-walled pipes under strong vibration conditions, and the added mass of the sensor can alter the local dynamic characteristics of the structure, affecting the accuracy of the measurement results. Furthermore, this type of method essentially only measures the vibration response at the installation point, making it difficult to effectively decouple and identify the multi-dimensional vibration components such as axial, radial bending, and torsion that simultaneously exist in the pipeline during actual operation. This limits the ability to comprehensively analyze and accurately diagnose complex vibration states. Summary of the Invention

[0005] The purpose of this invention is to provide a broadband vibration measurement method for nuclear power units based on distributed optical fiber sensing, and to solve the following technical problems:

[0006] Meanwhile, this type of method can only measure the vibration response at the installation point, and it is difficult to effectively decouple and identify the multi-dimensional vibration components such as axial, radial bending and torsion that exist simultaneously in the pipeline during actual operation, thus limiting the ability to comprehensively analyze and accurately diagnose complex vibration states.

[0007] The objective of this invention can be achieved through the following technical solutions: A broadband vibration measurement method for nuclear power units based on distributed optical fiber sensing includes the following steps: S1, Distributed sensing optical fibers are laid out along the surface of the nuclear power unit pipeline in a spiral path to construct a three-dimensional sensing structure that changes in tandem with the deformation of the pipeline surface. S2, calibrate the geometric parameters of the three-dimensional sensing structure and establish a spatial distribution database of the three geometric parameters of the spiral path: pitch, undulation amplitude and spiral angle. S3, inject broadband probe light signal into the fiber optic sensing structure, and simultaneously collect dynamic change data of intensity, phase and polarization state of backscattered Rayleigh light signal; S4. Based on the dynamic change data of the intensity and the fluctuation amplitude parameters in the spatial distribution database, calculate the radial bending vibration component of the pipeline; based on the dynamic change data of the phase and the pitch parameters in the spatial distribution database, calculate the axial vibration component of the pipeline; based on the dynamic change data of the polarization state and the helix angle parameters in the spatial distribution database, calculate the torsional vibration component of the pipeline. S5, the calculated radial bending vibration components, axial vibration components and torsional vibration components are spatiotemporally aligned and data fused to reconstruct the three-dimensional full-field vibration distribution on the pipe surface; S6. Frequency domain features are extracted from the three-dimensional full-field vibration distribution to obtain the dominant vibration frequencies at different spatial locations of the nuclear power unit pipeline.

[0008] As a further aspect of the present invention: the specific process of geometric parameter calibration in step S2 is as follows: A three-dimensional scanning device is used to acquire spatial coordinate data of the pipe surface after the installation is completed. The spatial coordinate data includes a set of three-dimensional coordinate points that characterize the surface of the optical fiber. Coordinate points that constitute the optical fiber path are selected from the set of three-dimensional coordinate points, and these coordinate points are divided into multiple continuous segments according to their spatial proximity. Establish the spatial distribution relationship of coordinate points within each continuous segment, and calculate the principal axis direction of the coordinate point distribution in that segment; divide the coordinate points of that segment into equally spaced slice units along the principal axis direction, calculate the geometric center position of all coordinate points in each slice unit, and connect the geometric center positions in sequence to form the center path coordinate sequence of the optical fiber; The center path coordinate sequence is processed using a curve fitting algorithm to generate a continuous optical fiber spatial trajectory function; the curvature value of the optical fiber spatial trajectory function at each point is calculated, and the extreme curvature points are identified and marked as peak feature points or trough feature points. Measure the spatial straight-line distance between adjacent wave crest feature points and record it as pitch parameter; establish a coordinate system with the pipe axis as the reference, measure the radial distance from each feature point to the pipe axis, calculate the difference in radial distance between adjacent wave crest and trough feature points, and record it as fluctuation amplitude parameter; Calculate the spatial angle between the tangent of the fiber optic trajectory at each feature point and the direction of the pipe axis, and record it as the helix angle parameter; establish a mapping relationship between the obtained pitch parameter, fluctuation amplitude parameter and helix angle parameter and the corresponding axial position coordinates of the pipe, and store them in the spatial distribution database.

[0009] As a further aspect of the present invention: in step S3, the specific process for acquiring dynamically changing data is as follows: A continuous light wave generated by a broadband laser is input into an acousto-optic modulator, and a light pulse sequence with a fixed repetition frequency is formed by applying a radio frequency drive signal. The light pulse sequence is then transmitted to a sensing fiber through an optical circulator, and the polarization state of the light pulses is kept stable during transmission. Backscattered Rayleigh light is received through the return port of the optical circulator. The scattered light signals are arranged in the time sequence of the light pulses to form the original scattered signal sequence. The original scattered signal is input into the polarization beam splitter, which separates it into two orthogonal polarization components and guides them to the intensity detection path and the phase detection path, respectively. In the intensity detection path, the optical signal is converted into an electrical signal using a photodetector. After the signal amplitude is increased by the transimpedance amplifier, the voltage sequence corresponding to the light intensity is acquired by the high-speed acquisition card. In the phase detection path, the scattered light of the current pulse period and the reference light of the previous pulse period are introduced into an optical mixer to generate multiple interference signals with a fixed phase difference; a balanced detector is used to receive these interference signals and perform differential amplification to output orthogonal electrical signals characterizing the phase relationship. Orthogonal electrical signals are input into a digital signal processor, and phase data of the scattered signal is obtained through specific mathematical operations. Simultaneously, light intensity voltage sequences, phase data, and beam splitting ratio data of the polarization beam splitter are acquired and aligned with a unified time reference to form a time-synchronized dynamic data sequence.

[0010] As a further aspect of the present invention: the specific process for calculating the axial vibration component of the pipeline in step S4 is as follows: The sensing fiber is pre-laid on the surface of a set of calibrated specimens with a precisely known radius of curvature. The backscattered Rayleigh light intensity value corresponding to the radius of curvature of each specimen is obtained by optical measurement device. The least squares method is used to fit and obtain a quantitative mapping relationship model between the radius of curvature and the light intensity attenuation. The collected real-time light intensity change data is input into the quantitative mapping relationship model, and the real-time curvature value at each sampling point of the sensing fiber is obtained through model inversion calculation. A spatial geometric model of the sensing fiber spiral path is established. Based on the geometric path represented by the spatial geometric model, the curvature expression at each point is calculated. The curvature expression is subjected to total differential operation to obtain the differential geometric relationship between the curvature change and the fluctuation amplitude change. Substituting the real-time curvature value into the differential geometric relationship, the sequence of fluctuation amplitude changes at each sampling point on the pipe surface is obtained through numerical calculation; a fast Fourier transform is performed on the fluctuation amplitude change sequence to obtain the spectrum analysis results containing vibration frequency and phase information. Based on the time-domain characteristics of the fluctuation amplitude change sequence and the spectral analysis results, the radial bending vibration component of the pipeline, including amplitude, frequency, phase, and direction, is obtained through vector synthesis calculation.

[0011] As a further aspect of the present invention: the specific process of establishing the spatial geometric model of the sensing fiber helical path is as follows: The three-dimensional wavy path laid on the surface of the pipe is represented as a spatial curve; the parametric equation of the spatial curve is established, and the parametric equation takes the rotation angle as the independent variable and outputs the three-dimensional spatial coordinates; A spatial coordinate dataset is obtained by measuring the actual fiber optic path. The spatial coordinate dataset is then substituted into the parametric equation, and a parameter identification algorithm is used to determine the values ​​of the characteristic parameters in the equation. The determined characteristic parameters are then substituted into the parametric equation to establish a spatial geometric model of the sensing fiber optic spiral path.

[0012] As a further aspect of the present invention: the specific process for calculating the axial vibration component of the pipeline in step S4 is as follows: The sensing fiber is pre-laid on the surface of a set of standard specimens with precisely known axial strain. The interference phase drift corresponding to each strain value is obtained through an optical measurement device. The least squares method is used to fit and obtain a quantitative mapping relationship model between axial strain and interference phase drift. The collected real-time interference phase drift data is input into the quantitative mapping relationship model, and the axial strain value at each sampling point of the sensing fiber is obtained through model inversion calculation. A spatial geometric model of the sensing fiber helical path is established, the functional relationship between the total helical length and the pitch parameter is calculated and total differential operation is performed to obtain the differential geometric relationship between axial strain and pitch change. Substituting the real-time axial strain value into the differential geometric relationship, the sequence of pitch change at each sampling point on the pipe surface is obtained through numerical calculation. A fast Fourier transform is performed on the pitch change sequence to obtain a spectrum analysis result containing vibration frequency and phase information. Based on the time-domain characteristics of the pitch change sequence and the spectrum analysis result, the axial vibration component of the pipeline, including amplitude, frequency, phase and direction, is calculated through kinematic relationships.

[0013] As a further aspect of the present invention: the specific process for calculating the torsional vibration component of the pipeline in step S4 is as follows: The sensing fiber is pre-laid on the surface of a set of calibration specimens with a precise known torsion angle. The polarization state rotation angle data corresponding to each torsion angle is obtained through an optical measurement device. The least squares method is used to fit and obtain a quantitative mapping relationship model between the torsion angle and the polarization state rotation angle. The collected real-time polarization state rotation angle data is input into the quantitative mapping relationship model, and the real-time torsion angle value at each sampling point of the sensing fiber is obtained through model inversion calculation. Establish a spatial geometric model of the sensing fiber helical path, calculate the differential geometric relationship between the change in helical angle and the actual torsion angle of the pipe, and calibrate the parameters. Substituting the real-time torsion angle value into the differential geometric relationship, the sequence of helix angle changes at each sampling point on the pipe surface is obtained through numerical calculation. A fast Fourier transform is performed on the helix angle change sequence to extract the frequency components and corresponding phase information of the vibration signal; combined with the time-domain amplitude characteristics and spectrum analysis results of the helix angle change sequence, the torsional vibration components of the pipeline, including amplitude, frequency, phase and direction, are calculated through coordinate transformation.

[0014] As a further aspect of the present invention: the specific process of reconstructing the three-dimensional full-field vibration distribution on the pipe surface in step S5 is as follows: The radial bending vibration component, axial vibration component, and torsional vibration component of the pipeline are spatiotemporally aligned according to the acquisition timestamp and the spatial coordinates of the pipeline. The three vibration components after alignment are vector synthesized according to the coordinate system of the pipeline surface to obtain the three-dimensional vibration vector of each spatial coordinate point. Spatial interpolation is performed on the three-dimensional vibration vector of all spatial coordinate points on the pipeline surface to generate a continuous three-dimensional vibration vector field. The three-dimensional vibration vector field is mapped to the geometric model of the pipeline surface to form a three-dimensional full-field vibration distribution that includes spatial position and vibration characteristics.

[0015] As a further aspect of the present invention: the specific process of obtaining the dominant vibration frequency at different spatial locations of the nuclear power unit pipeline in step S6 is as follows: Frequency domain transformation is performed on the vibration time history data of each spatial coordinate point in the three-dimensional full-field vibration distribution to obtain the frequency domain vibration spectrum of each point; the peak frequencies of each frequency domain vibration spectrum with amplitudes exceeding a preset threshold are selected, and the selected frequencies are associated with the corresponding pipe spatial coordinates; the spatial distribution consistency of the associated frequencies is verified, frequency components that do not recur in adjacent spatial positions are removed, and the dominant vibration frequencies and corresponding vibration energy parameters of each spatial position on the pipe surface are output.

[0016] The beneficial effects of this invention are: 1) This invention achieves continuous, full-domain sensing and three-dimensional vibration field reconstruction of nuclear power unit pipeline vibration. Traditional point sensors, limited by discrete placement, have monitoring blind spots and cannot capture the complete vibration modes of the pipeline surface. This method constructs a three-dimensional sensing structure that changes in tandem with pipeline deformation by deploying sensing fibers along a helical path on the pipeline surface, enabling continuous distributed monitoring of the pipeline surface vibration state. Based on a spatial distribution database of the helical path established through geometric parameter calibration, combined with the synchronous acquisition of multiple parameters (intensity, phase, and polarization state) of the backscattered Rayleigh signal, the system can accurately sense the vibration response at any location on the pipeline surface. Finally, through spatiotemporal alignment and data fusion technology, a complete three-dimensional full-field vibration distribution is reconstructed, overcoming the limitations of traditional methods in spatial coverage and providing a reliable data foundation for comprehensively understanding the unit's vibration state.

[0017] 2) This invention achieves precise decoupling and identification of multidimensional vibration components in pipelines. Nuclear power unit pipelines simultaneously exhibit multidimensional vibration components such as axial, radial bending, and torsion during actual operation. Traditional measurement methods struggle to effectively separate these coupled vibrations. This method innovatively establishes a correspondence between different optical parameters and specific vibration components: radial bending vibration is calculated based on intensity variation data and fluctuation amplitude parameters; axial vibration is calculated based on phase variation data and pitch parameters; and torsional vibration is calculated based on polarization state variation data and helix angle parameters. By establishing a quantitative mapping relationship model between each vibration component and the optical signal, and combining it with differential geometric relationships from a spatial geometric model, precise analysis of each component in complex vibration states is achieved. This multidimensional vibration decoupling capability provides crucial technical support for in-depth analysis of vibration generation mechanisms and identification of specific fault modes.

[0018] 3) This invention provides a realistic vibration measurement solution without additional mass interference. Traditional piezoelectric accelerometers need to be fixed to the measured surface via mechanical connections, which may cause structural damage, and their own mass can also alter the local dynamic characteristics of the structure, affecting the accuracy of the measurement results. This method uses flexible optical fibers as the sensing medium, and vibration monitoring can be achieved through surface bonding or embedded deployment, eliminating the need for rigid connections and avoiding the potential damage risk to thin-walled pipes. Simultaneously, the optical fiber itself has extremely small mass, hardly altering the original dynamic characteristics of the structure, and can accurately reflect the actual vibration state of the pipe. This interference-free measurement characteristic, combined with wideband measurement capabilities, makes this method particularly suitable for vibration monitoring scenarios of critical components in nuclear power units where extremely high measurement accuracy is required, providing more reliable data support for unit safety assessments. Attached Figure Description

[0019] The invention will now be further described with reference to the accompanying drawings.

[0020] Figure 1This is a schematic flowchart of the broadband vibration measurement method for nuclear power units based on distributed optical fiber sensing according to the present invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Please see Figure 1 As shown, this invention is a broadband vibration measurement method for nuclear power units based on distributed optical fiber sensing, comprising the following steps: S1, Distributed sensing optical fibers are laid out along the surface of the nuclear power unit pipeline in a spiral path to construct a three-dimensional sensing structure that changes in tandem with the deformation of the pipeline surface. First, a spiral winding scheme for the sensing optical fiber needs to be planned based on the diameter, length, and site layout of the pipeline in the nuclear power unit to be tested. For example, for a steam pipeline with a diameter of approximately 500 mm, a single-mode optical fiber with an external polyimide coating can be used as the sensing medium, as this material has good flexibility and high-temperature resistance. In actual operation, construction personnel use a high-temperature adhesive to tightly wind the optical fiber onto the outer wall of the pipeline with constant tension, starting from one end of the pipeline, at a specific angle (e.g., between 30° and 45°) to the pipeline axis. During the winding process, it is necessary to ensure that the optical fiber is completely adhered to the metal surface without air bubbles or gaps. After each turn of winding, a laser positioning instrument is used to check the uniformity of the pitch. This spiral deployment method creates a continuous wavy path for the optical fiber on the pipe surface. When the pipe deforms due to internal fluid pressure fluctuations or mechanical vibrations, this three-dimensional spiral structure deforms accordingly. If the pipe expands radially, the fiber wound around it is subjected to lateral compression, resulting in localized changes in curvature. If the pipe is stretched axially, the spiral path is forced to extend, causing longitudinal strain in the fiber. If the pipe undergoes torsional deformation, the spiral angle of the fiber winding changes. By constructing a three-dimensional sensing network covering the pipe surface using a continuous optical fiber in this way, it is equivalent to "weaving" a distributed sensing layer on the outer surface of the pipe that deforms synchronously with it, laying the physical foundation for subsequent demodulation of various types of vibration components using optical signals.

[0023] This paper proposes a three-dimensional sensing structure capable of fully coupling with the complex deformation modes of pipelines. Nuclear power plant pipelines experience vibrations not in a single direction, but rather a complex phenomenon involving axial tension, radial bending, and circumferential torsion. Simply attaching optical fibers along the axial direction only sensitively captures axial strain, offering little response to bending and torsional deformation; while parallel, circumferential placement primarily detects circumferential deformation. The helical path design in this scheme cleverly combines the advantages of both methods: its helical geometry allows the optical fiber to simultaneously possess axial, radial, and tangential components in space. When the pipeline undergoes any type of deformation, it alters the local geometry of the optical fiber through different mechanical transmission paths—axial strain primarily affects the helical pitch parameter, radial bending primarily affects the amplitude of undulations, and torsional vibration primarily affects the helical angle. This "one fiber, multiple uses" design allows for the simultaneous sensing of multidimensional vibrations through a single optical fiber, avoiding the spatial conflicts, poor synchronization, and high costs associated with multi-sensor deployments. More importantly, the continuous spiral path achieves full coverage of the pipe surface, eliminating the monitoring blind spots of traditional point sensors, providing a complete data source for the subsequent construction of a complete three-dimensional vibration field, and ultimately making it possible to decouple the omnidirectional vibration information of the pipe from the composite optical signal of a single optical fiber.

[0024] S2, calibrate the geometric parameters of the three-dimensional sensing structure and establish a spatial distribution database of the three geometric parameters of the spiral path: pitch, undulation amplitude and spiral angle. First, a high-precision 3D optical scanning device, such as a laser scanner or structured light 3D scanner, is needed to perform a panoramic scan of the pipe section with the installed sensing fibers. This captures the spatial coordinates of numerous points on the surface to generate a precise digital 3D model of the pipe's outer surface and the attached fibers. Based on this, a spatial curve representing the fiber path is extracted from this 3D model. This process is achieved by identifying the spatial coordinate sequence of continuous ridges or specific markers formed by the presence of the fiber on the model. Subsequently, three geometric parameters are calculated for this extracted spatial curve: the pitch is determined by identifying the light... The fiber path passes through the same generatrix parallel to the pipe axis twice consecutively at two cross-sections, and the axial distance between these two cross-sections is calculated, since the pitch is defined as the distance the helix travels axially after one revolution around the pipe. The undulation amplitude is obtained by calculating the radial distance from each point on the extracted spatial curve to the ideal central axis of the corresponding theoretical cylindrical surface of the pipe, and then subtracting the nominal radius of the pipe itself. This directly reflects the radial height change of the optical fiber due to winding away from the pipe surface. The helix angle is calculated by analyzing the angle between the tangent direction of the spatial curve at any point and the pipe axis direction, since the geometric definition of the helix angle is this angle. Finally, the spatial location information corresponding to each sampling point obtained above is correlated with its pitch, undulation amplitude, and helix angle values ​​to form a detailed spatial distribution database covering the entire deployment area.

[0025] It is understandable that only by knowing the precise pitch of each fiber segment in advance can the phase change be correctly calculated as axial vibration, because the pitch determines the projected length of the fiber in the axial direction and its response characteristics to axial strain. Precisely grasping the amplitude of fluctuations at each point is necessary to effectively correlate the light intensity change with radial bending vibration, because the amplitude of fluctuations determines the degree to which the fiber deviates radially from the neutral plane of the duct, which directly affects the magnitude of its bending strain. Accurately obtaining the helix angle at each position is a key prerequisite for calculating torsional vibration, because when the duct is torn, the fiber with a specific helix angle will be subjected to additional stretching or compression, thereby changing its internal polarization characteristics. Therefore, the core purpose and significant advantage of establishing this detailed spatial distribution database of geometric parameters is to provide an indispensable "spatial decoder" for interpreting the physical meaning of subsequent complex optical signals. It places a measurement signal that is optically continuous and uniform but has an ambiguous physical meaning within a known and precise geometric framework for analysis, thereby reliably decomposing and reconstructing one-dimensional, hybrid fiber optic sensing signals into component vibration information of the three-dimensional full-field of the pipe surface. This is the technical foundation and core prerequisite for this method to achieve the measurement of complex three-dimensional broadband vibration fields, from ordinary linear vibration measurement to measurement of ordinary linear vibration fields.

[0026] S3, inject broadband probe light signal into the fiber optic sensing structure, and simultaneously collect dynamic change data of intensity, phase and polarization state of backscattered Rayleigh light signal; First, a stable laser beam is generated by a highly coherent light source, such as a narrow-linewidth laser. This laser beam is then fed into a dedicated optical modulation subsystem. The core of this subsystem contains an electro-optic modulator, which uses a specifically coded electrical signal (such as a linear frequency-modulated pulse or a pseudo-random sequence) generated by an arbitrary waveform generator to perform carrier-suppressed modulation on the continuous laser beam. This broadens the originally single laser frequency, generating a broadband probe light pulse signal with a specific temporal structure and a certain optical frequency width. The fundamental physical principle behind this is the coherence of light; that is, only when the light wave within the pulse has a certain coherence length can it produce a certain coherence due to the non-uniform refractive index within the optical fiber. Interference can only occur between the backscattered Rayleigh light rays to form a stable, measurable scattering pattern. Then, this carefully modulated broadband probe light pulse is injected into a sensing fiber optic cable laid on the surface of the pipe through a circulator. The light pulse propagates forward along the fiber, undergoing backscattered Rayleigh scattering at every tiny segment. These extremely weak scattered lights return along the same path and are guided to the signal acquisition and demodulation subsystem through another port of the circulator. The core task of this subsystem is to separate and demodulate the returned composite scattered light signal to simultaneously acquire three types of dynamically changing data: intensity, phase, and polarization state. To achieve this, the returned light signal is typically first... A highly sensitive balanced photodetector receives the signal. This detector optically mixes the returned light carrying the scattered signal with an unmodulated reference light from the same laser source. Utilizing the principle of light interference, it converts the minute, unmeasurable phase change information into a time-varying voltage signal that can be precisely measured by an electronic system. Essentially, this process linearly transfers the phase difference information of the light wave to the amplitude of the photocurrent, thus achieving phase dynamics capture. Simultaneously, the intensity information of the scattered light can be directly extracted from the signal output by the balanced detector. This is because the intensity of Rayleigh scattering is directly related to the physical density and characteristics of the scattering point. When the fiber bends, causing minute losses... When the intensity of the scattered light returns decreases accordingly, the DC or low-frequency component of the detected photocurrent directly reflects the intensity change of the scattered light. For dynamic measurement of polarization state, a polarization beam splitter is usually introduced in the optical path to decompose the returned scattered light into two orthogonal polarization axes, which are then received by two detectors. By calculating the ratio, difference, or combination of the optical power of these two orthogonal axes in real time, the Stokes parameters such as the polarization angle and ellipticity of the light wave can be calculated, thus fully describing the dynamic evolution of the polarization state of the light wave. The physical basis of this is that any transverse pressure or torsional stress acting on the optical fiber will change the birefringence characteristics of the optical fiber, thereby modulating the polarization state of the light wave transmitted in it.

[0027] Because any real vibration occurring in a nuclear power plant pipeline is a highly time-coinciding and physically coupled three-dimensional event, the pipeline may simultaneously experience axial stretching, radial bending, and circumferential torsion. These mechanical deformations modulate the intensity, phase, and polarization state of the optical signal in the optical fiber, respectively and simultaneously. If these three physical quantities are measured sequentially, it will be impossible to determine whether the intensity change measured at time t1, the phase change measured at time t2, and the polarization change measured at time t3 originate from the same vibration impact. Subsequent data fusion and three-dimensional vibration reconstruction will lose their time-aligned reference, resulting in uncertainties. Therefore, this strict synchronous acquisition strategy ensures that every optical feature segment captured from the optical fiber strictly corresponds to the complete state of the vibration field acting on the fiber at the same instant. This provides a unique, reliable, and time-aligned raw data foundation for accurately decoupling the mixed optical signals into pure axial, radial, and torsional vibration components in subsequent steps. This is the lifeline for the entire method to move from concept to practical application and achieve accurate three-dimensional vibration measurement.

[0028] S4. Based on the dynamic change data of the intensity and the fluctuation amplitude parameters in the spatial distribution database, calculate the radial bending vibration component of the pipeline; based on the dynamic change data of the phase and the pitch parameters in the spatial distribution database, calculate the axial vibration component of the pipeline; based on the dynamic change data of the polarization state and the helix angle parameters in the spatial distribution database, calculate the torsional vibration component of the pipeline. When a pipe undergoes radial bending, it directly alters the radius of curvature of the spirally arranged optical fibers attached to its surface. According to the microbending loss mechanism of optical fibers, the degree of bending modulates the leakage intensity of the transmitted light energy within the fiber. The more severe the bending (the smaller the radius of curvature), the greater the intensity attenuation of Rayleigh scattered light. Therefore, by monitoring the dynamic attenuation of light intensity, the curvature change of the optical fiber can be inferred. However, since the optical fiber is spirally wound, its own undulation amplitude has been pre-calibrated and stored in a database. This undulation amplitude parameter is crucial because it defines the effective lever arm length of the optical fiber relative to the neutral axis of the pipe. According to the bending theory of beams in mechanics of materials, the strain on the pipe surface is proportional to the product of the curvature change and the distance from that point to the neutral axis. Therefore, this undulation amplitude parameter must be combined to accurately convert the measured curvature change belonging to the optical fiber into the macroscopic radial bending displacement of the pipe structure itself. Based on phase change data and pitch parameters in a spatial distribution database, the axial vibration components of the pipeline are calculated. The physical basis of this calculation is the principle of optical interference. The phase of laser propagation in an optical fiber is extremely sensitive to changes in the physical length and refractive index of the fiber. When the pipeline experiences axial vibration (tension or compression), it directly causes axial strain in the helically wound optical fiber, thereby changing its length and refractive index, ultimately manifesting as a linear change in the phase of the backscattered Rayleigh light. However, the key correction factor here is the pitch parameter. This is because the optical fiber is not straight along the pipeline axis but is helical. There is a geometric projection relationship between its axial strain and the pipeline's axial strain. This relationship is determined by the helix angle, which is directly calculated from the pitch. Therefore, it is necessary to combine the accurate pitch parameters in the spatial distribution database to correctly project and convert the strain calculated from the phase data along the fiber direction into the actual axial vibration strain and displacement of the pipeline. Based on polarization state change data and helix angle parameters in a spatial distribution database, the torsional vibration component of the pipeline is calculated. The underlying mechanism is the photoelastic effect of optical fiber. Any transverse stress or torsion acting on the optical fiber will change its internal birefringence characteristics, thereby modulating the polarization state of the light wave transmitted within it. When the pipeline twists, the helically wound optical fiber will be subjected to additional axial tension or compressive force. This is because the helical structure couples the circumferential torsional motion of the pipeline into the axial strain of the optical fiber. The strength and direction of this coupling strongly depend on the helix angle of the optical fiber. Thus, the rotation or ellipticity change of the polarization state is accurately inverted into the torsional angular displacement of the pipeline about its central axis.

[0029] S5, the calculated radial bending vibration components, axial vibration components and torsional vibration components are spatiotemporally aligned and data fused to reconstruct the three-dimensional full-field vibration distribution on the pipe surface; The calculated radial bending vibration components, axial vibration components, and torsional vibration components are spatiotemporally aligned and fused to reconstruct the three-dimensional full-field vibration distribution on the pipe surface. Specifically, this process first requires strict time alignment because although the three vibration components are synchronized during data acquisition, different computational delays may be introduced in subsequent independent signal processing and calculation paths. Therefore, the data timelines of all components must be traced back to the same absolute time reference to ensure that the analyzed radial, axial, and torsional vibrations within any tiny time slice represent the true state of the pipe at the same physical moment. This forms the temporal basis for subsequent data fusion. Next is the more complex spatial alignment. Since the optical fiber is helically wound, each radial, axial, and torsional vibration data point calculated from the optical fiber data is essentially located along that continuous helix. They do not directly correspond to the same physical point on the pipe surface. Therefore, the spatial distribution database established in step S2, which includes pitch, undulation amplitude, and helix angle, must be used to map each vibration data distributed along the helix onto a unified three-dimensional mesh node on the pipe surface through three-dimensional spatial coordinate transformation. For example, the helix... The axial vibration measured at a point on the spiral line is converted to the precise coordinates of the outer wall of the pipe directly below it, based on the number of spiral turns and phase of that point. This process is equivalent to establishing a common "home address" system for vibration data from all different sources. After completing spatiotemporal alignment, the core stage of data fusion and three-dimensional vibration field reconstruction begins. In this stage, each node on the three-dimensional mesh of the pipe surface has three vibration vectors from different components, but which are precisely aligned in space and time: the radial displacement of the node due to pipe bending (perpendicular to the pipe surface), the displacement of the node due to pipe tension and compression, and the vibration vectors of the pipe surface. The axial displacement (parallel to the pipe axis) and the tangential displacement (around the pipe axis) generated by the pipe torsion at the node are combined according to rigid body kinematics and the principle of vector synthesis. This yields the resultant vibration vector of the point in space. This vector not only contains the amplitude information of the vibration, but more importantly, it indicates the three-dimensional spatial direction of the vibration at the point. Finally, by repeating this vector synthesis operation on all grid nodes on the pipe surface, a complete full-field vibration distribution pattern covering the entire surface of the measured pipe, with each point having a three-dimensional direction and magnitude, can be reconstructed.

[0030] S6. Frequency domain features are extracted from the three-dimensional full-field vibration distribution to obtain the dominant vibration frequencies at different spatial locations of the nuclear power unit pipeline.

[0031] For each independent spatial location point in the three-dimensional vibration field, its three-dimensional vibration vector at each continuous time point is decomposed into vibration time series in three orthogonal directions, namely, displacement-time curves in the axial, radial, and tangential directions. Then, frequency domain transformation analysis is performed separately for the vibration time series in each direction at each location point. The classical method based on Fourier transform is used here. Its core mathematical principle is to decompose a seemingly complex and disordered wave signal in the time domain into a superposition of a series of single-frequency sine waves with different frequencies, amplitudes, and phases. Through this decomposition, the frequency components constituting the original vibration signal and their respective energy strengths can be clearly seen. After obtaining the spectrum diagram by completing the frequency domain transformation, the dominant vibration is then analyzed. The frequency identification process is typically achieved by finding the peak of the power spectral density in the spectrum. This is because the dominant frequency component in a vibration signal will exhibit significantly higher vibration energy at its corresponding frequency point than the background noise and other frequency components. In practice, the spectrum is scanned to identify those peaks with significantly prominent amplitudes, and the frequency values ​​corresponding to these peaks are recorded. These recorded frequencies are the dominant vibration frequencies of the measuring point in that vibration direction during the current time period. Finally, the identification results of the dominant frequencies at all locations on the pipe surface and in all vibration directions are correlated with their spatial coordinates to form a space-frequency mapping map, clearly showing the location and distribution of vibrations of different frequencies on the pipe surface.

[0032] In a preferred embodiment of the present invention, the specific process of geometric parameter calibration in step S2 is as follows: A three-dimensional scanning device is used to acquire spatial coordinate data of the pipe surface after the installation is completed. The spatial coordinate data includes a set of three-dimensional coordinate points that characterize the surface of the optical fiber. Coordinate points that constitute the optical fiber path are selected from the set of three-dimensional coordinate points, and these coordinate points are divided into multiple continuous segments according to their spatial proximity. Establish the spatial distribution relationship of coordinate points within each continuous segment, and calculate the principal axis direction of the coordinate point distribution in that segment; divide the coordinate points of that segment into equally spaced slice units along the principal axis direction, calculate the geometric center position of all coordinate points in each slice unit, and connect the geometric center positions in sequence to form the center path coordinate sequence of the optical fiber; The center path coordinate sequence is processed using a curve fitting algorithm to generate a continuous optical fiber spatial trajectory function; the curvature value of the optical fiber spatial trajectory function at each point is calculated, and the extreme curvature points are identified and marked as peak feature points or trough feature points. Measure the spatial straight-line distance between adjacent wave crest feature points and record it as pitch parameter; establish a coordinate system with the pipe axis as the reference, measure the radial distance from each feature point to the pipe axis, calculate the difference in radial distance between adjacent wave crest and trough feature points, and record it as fluctuation amplitude parameter; Calculate the spatial angle between the tangent of the fiber optic trajectory at each feature point and the direction of the pipe axis, and record it as the helix angle parameter; establish a mapping relationship between the obtained pitch parameter, fluctuation amplitude parameter and helix angle parameter and the corresponding axial position coordinates of the pipe, and store them in the spatial distribution database.

[0033] In another preferred embodiment of the present invention, the specific process of acquiring dynamically changing data in step S3 is as follows: A continuous light wave generated by a broadband laser is input into an acousto-optic modulator, and a light pulse sequence with a fixed repetition frequency is formed by applying a radio frequency drive signal. The light pulse sequence is then transmitted to a sensing fiber through an optical circulator, and the polarization state of the light pulses is kept stable during transmission. Backscattered Rayleigh light is received through the return port of the optical circulator. The scattered light signals are arranged in the time sequence of the light pulses to form the original scattered signal sequence. The original scattered signal is input into the polarization beam splitter, which separates it into two orthogonal polarization components and guides them to the intensity detection path and the phase detection path, respectively. In the intensity detection path, the optical signal is converted into an electrical signal using a photodetector. After the signal amplitude is increased by the transimpedance amplifier, the voltage sequence corresponding to the light intensity is acquired by the high-speed acquisition card. In the phase detection path, the scattered light of the current pulse period and the reference light of the previous pulse period are introduced into an optical mixer to generate multiple interference signals with a fixed phase difference; a balanced detector is used to receive these interference signals and perform differential amplification to output orthogonal electrical signals characterizing the phase relationship. Orthogonal electrical signals are input into a digital signal processor, and phase data of the scattered signal is obtained through specific mathematical operations. Simultaneously, light intensity voltage sequences, phase data, and beam splitting ratio data of the polarization beam splitter are acquired and aligned with a unified time reference to form a time-synchronized dynamic data sequence.

[0034] In another preferred embodiment of the present invention, the specific process for calculating the axial vibration component of the pipeline in step S4 is as follows: The sensing fiber is pre-laid on the surface of a set of calibrated specimens with a precisely known radius of curvature. The backscattered Rayleigh light intensity value corresponding to the radius of curvature of each specimen is obtained by optical measurement device. The least squares method is used to fit and obtain a quantitative mapping relationship model between the radius of curvature and the light intensity attenuation. The collected real-time light intensity change data is input into the quantitative mapping relationship model, and the real-time curvature value at each sampling point of the sensing fiber is obtained through model inversion calculation. A spatial geometric model of the sensing fiber spiral path is established. Based on the geometric path represented by the spatial geometric model, the curvature expression at each point is calculated. The curvature expression is subjected to total differential operation to obtain the differential geometric relationship between the curvature change and the fluctuation amplitude change. Substituting the real-time curvature value into the differential geometric relationship, the sequence of fluctuation amplitude changes at each sampling point on the pipe surface is obtained through numerical calculation; a fast Fourier transform is performed on the fluctuation amplitude change sequence to obtain the spectrum analysis results containing vibration frequency and phase information. Based on the time-domain characteristics of the fluctuation amplitude change sequence and the spectral analysis results, the radial bending vibration component of the pipeline, including amplitude, frequency, phase, and direction, is obtained through vector synthesis calculation.

[0035] Sensing fibers are pre-laid on the surfaces of a set of calibration specimens with precisely known radii of curvature. The backscattered Rayleigh light intensity corresponding to the radii of curvature of each specimen is acquired using an optical measurement device. A quantitative mapping model between the radii of curvature and the light intensity attenuation is obtained using the least squares method. This step essentially utilizes the micro-bending effect of optical fibers; that is, when an optical fiber bends, it leads to an attenuation of transmitted light intensity, and the greater the curvature, the more significant the light intensity attenuation. A precise mathematical model of this physical relationship can be established through systematic calibration experiments. The collected real-time light intensity change data is then input into the quantitative mapping model. The model is used to calculate the real-time curvature values ​​at each sampling point of the sensing fiber through model inversion. This is a process of inferring the cause from the observation results using established mathematical relationships. The real-time curvature state of the fiber causing the attenuation can be directly calculated from the measured light intensity attenuation. A spatial geometric model of the spiral path of the sensing fiber is established. Based on the geometric path represented by the spatial geometric model, the curvature expression at each point is calculated. This uses the principles of differential geometry to mathematically describe the spatial curve, and accurately represents its degree of curvature through the basic differential invariants of the curve. The curvature expression is then subjected to total differential operation to obtain... The step of obtaining the differential geometric relationship between the curvature change and the fluctuation amplitude change reveals the intrinsic connection between curvature change and spatial geometric parameter change. Differential operations establish a quantitative correspondence between minute curvature changes and minute fluctuation amplitude changes. Substituting the real-time curvature value into the differential geometric relationship, numerical calculations yield a sequence of fluctuation amplitude changes at each sampling point on the pipe surface. This applies the theoretically derived differential relationship to actual measurement data, converting curvature measurements into more intuitive geometric variables through numerical calculations. A fast Fourier transform is performed on the fluctuation amplitude change sequence to obtain a spectral analysis result containing vibration frequency and phase information. This converts the time-domain vibration signal to the frequency domain for analysis, using Fourier transform to decompose complex vibrations into a superposition of different frequency components, thereby identifying the dominant vibration frequency and its phase relationship. Based on the time-domain characteristics of the fluctuation amplitude change sequence and the spectral analysis results, vector synthesis calculations are used to obtain the radial bending vibration component of the pipe, containing amplitude, frequency, phase, and direction. This integrates time-domain and frequency-domain analysis results, expanding one-dimensional amplitude information into a complete vibration description including spatial directional characteristics through vector operations.

[0036] Through rigorous mathematical modeling and physical relationship transformation, easily measurable optical intensity signals are accurately converted into pipeline mechanical vibration information with clear engineering significance. Establishing a quantitative mapping relationship between curvature and light intensity beforehand overcomes the nonlinearity problem in fiber optic sensing, ensuring the accuracy of the conversion from optical signal to mechanical deformation. Establishing a spatial geometric model of the helical path and deriving differential equations fully considers the impact of actual installation methods on measurement results, enabling the calculation process to adapt to complex spatial geometric conditions. Frequency domain analysis extracts the most valuable frequency features for fault diagnosis from complex vibration signals; these frequency features often have a direct correspondence with specific mechanical fault modes. Finally, vector synthesis yields a complete description of vibration components to provide the richest possible vibration state information, including comprehensive characteristics such as vibration magnitude, rhythm, timing, and direction. This systematic calculation process ensures that the final obtained vibration components not only have numerical accuracy but also clear physical meaning and engineering application value, providing a reliable data foundation for subsequent fault diagnosis and condition assessment. This method not only detects the existence of vibration but also deeply understands the essential characteristics and generation mechanism of vibration, thus achieving a technological leap from simple vibration monitoring to precise condition diagnosis.

[0037] In another preferred embodiment of the present invention, the specific process of establishing the spatial geometric model of the sensing fiber helical path is as follows: The three-dimensional wavy path laid on the surface of the pipe is represented as a spatial curve; the parametric equation of the spatial curve is established, and the parametric equation takes the rotation angle as the independent variable and outputs the three-dimensional spatial coordinates; A spatial coordinate dataset is obtained by measuring the actual fiber optic path. The spatial coordinate dataset is then substituted into the parametric equation, and a parameter identification algorithm is used to determine the values ​​of the characteristic parameters in the equation. The determined characteristic parameters are then substituted into the parametric equation to establish a spatial geometric model of the sensing fiber optic spiral path.

[0038] Representing the three-dimensional wavy path laid on the pipe surface as a spatial curve is the foundation for abstracting the actual physical path into a mathematical description, because any continuous path can be precisely represented mathematically by a parametric curve. The parametric equations of these spatial curves are established, with rotation angles as independent variables and outputting three-dimensional spatial coordinates. The principle behind this design is that a helical path is essentially a curve that periodically winds around the pipe axis, and using rotation angles as independent variables best reflects this periodic characteristic. For example, a typical helical parametric equation would include key geometric parameters such as pipe radius, pitch, and undulation amplitude. Different values ​​of these parameters can describe various helical shapes. By measuring the actual layout... The process involves acquiring a spatial coordinate dataset of the fiber optic path. This is achieved by using techniques such as 3D laser scanning or photogrammetry to obtain precise 3D coordinates of a large number of discrete points on the surface of the duct. These coordinate data reflect the actual spatial form of the fiber optic deployment. The spatial coordinate dataset is then substituted into the parametric equation, and a parameter identification algorithm is used to determine the values ​​of the characteristic parameters in the equation. The essence of this step is to find a set of characteristic parameter values ​​through optimization methods, so that the overall difference between the theoretical curve calculated by the parametric equation and the measured spatial coordinate dataset is minimized, allowing the mathematical model to approximate physical reality to the greatest extent possible. The determined characteristic parameters are then substituted into the parametric equation to establish a spatial geometric model of the sensing fiber optic spiral path.

[0039] In another preferred embodiment of the present invention, the specific process for calculating the axial vibration component of the pipeline in step S4 is as follows: The sensing fiber is pre-laid on the surface of a set of standard specimens with precisely known axial strain. The interference phase drift corresponding to each strain value is obtained through an optical measurement device. The least squares method is used to fit and obtain a quantitative mapping relationship model between axial strain and interference phase drift. The collected real-time interference phase drift data is input into the quantitative mapping relationship model, and the axial strain value at each sampling point of the sensing fiber is obtained through model inversion calculation. A spatial geometric model of the sensing fiber helical path is established, the functional relationship between the total helical length and the pitch parameter is calculated and total differential operation is performed to obtain the differential geometric relationship between axial strain and pitch change. Substituting the real-time axial strain value into the differential geometric relationship, the sequence of pitch change at each sampling point on the pipe surface is obtained through numerical calculation. A fast Fourier transform is performed on the pitch change sequence to obtain a spectrum analysis result containing vibration frequency and phase information. Based on the time-domain characteristics of the pitch change sequence and the spectrum analysis result, the axial vibration component of the pipeline, including amplitude, frequency, phase and direction, is calculated through kinematic relationships.

[0040] The sensing fiber is pre-laid on the surface of a set of standard specimens with precisely known axial strain. The interference phase shift corresponding to each strain value is acquired using an optical measuring device. A quantitative mapping model between axial strain and interference phase shift is obtained using the least squares method. This step is based on the principle of fiber optic interferometry. When the fiber is subjected to axial strain, its physical length and refractive index change simultaneously. Both factors cause a change in the phase of light propagation in the fiber, and this change is proportional to the strain magnitude. A precise mathematical expression for this proportional relationship can be established through systematic calibration experiments. The acquired real-time interference phase shift data is input into the quantitative mapping model. The axial strain value at each sampling point of the sensing fiber is obtained through model inversion calculation. This utilizes the established phase-strain conversion relationship to derive the strain value, which is difficult to measure directly, from the easily measurable phase change. A spatial geometric model of the sensing fiber's helical path is established. The functional relationship between the total helical length and the pitch parameter is calculated and total differential is performed to obtain the differential geometric relationship between axial strain and pitch change. The mathematical principle of this step is based on the helical... The total length of the spiral is determined by the pitch, pipe radius, and number of spiral turns. When the pipe experiences axial vibration, the pitch parameter changes accordingly. A precise mathematical relationship between the rate of change of spiral length and the rate of change of pitch can be established through total differential calculation. Substituting the real-time axial strain value into the differential geometric relationship, a sequence of pitch changes at each sampling point on the pipe surface is obtained through numerical calculation. This converts strain measurements into more intuitive geometric parameter changes, as pitch changes directly reflect the axial expansion and contraction of the pipe. A fast Fourier transform is performed on the pitch change sequence to obtain a spectral analysis result containing vibration frequency and phase information. This decomposes the complex time-domain vibration signal into a superposition of different frequency components through frequency domain analysis, thereby identifying the main vibration frequency characteristics. Based on the time-domain characteristics of the pitch change sequence and the spectral analysis result, the axial vibration components of the pipe, including amplitude, frequency, phase, and direction, are calculated through kinematic relationships. This converts the changes in geometric parameters into a complete kinematic description, and the pitch change rate is linked to the axial vibration velocity through kinematic relationships, thus obtaining a complete characteristic description of the vibration.

[0041] Through multi-level physical relationship transformation, optical measurement signals are accurately converted into axial vibration information with clear engineering significance. Establishing a quantitative mapping relationship between strain and phase beforehand fully utilizes the high sensitivity of interferometric measurement technology to ensure the detection of minute strain changes. Establishing a geometric model of the helical path and deriving the differential relationship between strain and pitch addresses the measurement complexity caused by the helical fiber layout in practical applications, converting strain in the fiber direction into geometric changes along the pipe axis. Frequency domain analysis extracts crucial frequency characteristics for fault diagnosis from complex vibration signals; these frequency characteristics often have a direct correspondence with specific mechanical faults. Finally, obtaining a complete vibration component description through kinematic relationships provides comprehensive vibration information including amplitude, frequency, phase, and direction, meeting the requirements of engineering diagnosis for complete vibration characteristics.

[0042] In another preferred embodiment of the present invention, the specific process for calculating the torsional vibration component of the pipeline in step S4 is as follows: The sensing fiber is pre-laid on the surface of a set of calibration specimens with a precise known torsion angle. The polarization state rotation angle data corresponding to each torsion angle is obtained through an optical measurement device. The least squares method is used to fit and obtain a quantitative mapping relationship model between the torsion angle and the polarization state rotation angle. The collected real-time polarization state rotation angle data is input into the quantitative mapping relationship model, and the real-time torsion angle value at each sampling point of the sensing fiber is obtained through model inversion calculation. Establish a spatial geometric model of the sensing fiber helical path, calculate the differential geometric relationship between the change in helical angle and the actual torsion angle of the pipe, and calibrate the parameters. Substituting the real-time torsion angle value into the differential geometric relationship, the sequence of helix angle changes at each sampling point on the pipe surface is obtained through numerical calculation. A fast Fourier transform is performed on the helix angle change sequence to extract the frequency components and corresponding phase information of the vibration signal; combined with the time-domain amplitude characteristics and spectrum analysis results of the helix angle change sequence, the torsional vibration components of the pipeline, including amplitude, frequency, phase and direction, are calculated through coordinate transformation.

[0043] In another preferred embodiment of the present invention, the specific process of reconstructing the three-dimensional full-field vibration distribution of the pipe surface in step S5 is as follows: The radial bending vibration component, axial vibration component, and torsional vibration component of the pipeline are spatiotemporally aligned according to the acquisition timestamp and the spatial coordinates of the pipeline. The three vibration components after alignment are vector synthesized according to the coordinate system of the pipeline surface to obtain the three-dimensional vibration vector of each spatial coordinate point. Spatial interpolation is performed on the three-dimensional vibration vector of all spatial coordinate points on the pipeline surface to generate a continuous three-dimensional vibration vector field. The three-dimensional vibration vector field is mapped to the geometric model of the pipeline surface to form a three-dimensional full-field vibration distribution that includes spatial position and vibration characteristics.

[0044] In another preferred embodiment of the present invention, the specific process of obtaining the dominant vibration frequency at different spatial locations of the nuclear power unit pipeline in step S6 is as follows: Frequency domain transformation is performed on the vibration time history data of each spatial coordinate point in the three-dimensional full-field vibration distribution to obtain the frequency domain vibration spectrum of each point; the peak frequencies of each frequency domain vibration spectrum with amplitudes exceeding a preset threshold are selected, and the selected frequencies are associated with the corresponding pipe spatial coordinates; the spatial distribution consistency of the associated frequencies is verified, frequency components that do not recur in adjacent spatial positions are removed, and the dominant vibration frequencies and corresponding vibration energy parameters of each spatial position on the pipe surface are output.

[0045] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A broadband vibration measurement method for nuclear power units based on distributed optical fiber sensing, characterized in that, Includes the following steps: S1, Distributed sensing optical fibers are laid out along the surface of the nuclear power unit pipeline in a spiral path to construct a three-dimensional sensing structure that changes in tandem with the deformation of the pipeline surface. S2, calibrate the geometric parameters of the three-dimensional sensing structure and establish a spatial distribution database of the three geometric parameters of the spiral path: pitch, undulation amplitude and spiral angle. S3, inject broadband probe light signal into the fiber optic sensing structure, and simultaneously collect dynamic change data of intensity, phase and polarization state of backscattered Rayleigh light signal; S4. Based on the dynamic change data of the intensity and the fluctuation amplitude parameters in the spatial distribution database, calculate the radial bending vibration component of the pipeline; based on the dynamic change data of the phase and the pitch parameters in the spatial distribution database, calculate the axial vibration component of the pipeline; based on the dynamic change data of the polarization state and the helix angle parameters in the spatial distribution database, calculate the torsional vibration component of the pipeline. S5, the calculated radial bending vibration components, axial vibration components and torsional vibration components are spatiotemporally aligned and data fused to reconstruct the three-dimensional full-field vibration distribution on the pipe surface; S6. Frequency domain features are extracted from the three-dimensional full-field vibration distribution to obtain the dominant vibration frequencies at different spatial locations of the nuclear power unit pipeline.

2. The broadband vibration measurement method for nuclear power units based on distributed optical fiber sensing according to claim 1, characterized in that, In S2, the specific process of geometric parameter calibration is as follows: A three-dimensional scanning device is used to acquire spatial coordinate data of the pipe surface after the installation is completed. The spatial coordinate data includes a set of three-dimensional coordinate points that characterize the surface of the optical fiber. Coordinate points that constitute the optical fiber path are selected from the set of three-dimensional coordinate points, and these coordinate points are divided into multiple continuous segments according to their spatial proximity. Establish the spatial distribution relationship of coordinate points within each continuous segment, and calculate the principal axis direction of the coordinate point distribution in that segment; divide the coordinate points of that segment into equally spaced slice units along the principal axis direction, calculate the geometric center position of all coordinate points in each slice unit, and connect the geometric center positions in sequence to form the center path coordinate sequence of the optical fiber; A curve fitting algorithm is used to process the central path coordinate sequence to generate a continuous optical fiber spatial trajectory function; Calculate the curvature value of the optical fiber spatial trajectory function at each point, identify the curvature extreme points and mark them as wave crest feature points or wave trough feature points; Measure the spatial straight-line distance between adjacent wave crest feature points and record it as pitch parameter; establish a coordinate system with the pipe axis as the reference, measure the radial distance from each feature point to the pipe axis, calculate the difference in radial distance between adjacent wave crest and trough feature points, and record it as fluctuation amplitude parameter; Calculate the spatial angle between the tangent of the fiber optic trajectory at each feature point and the direction of the pipe axis, and record it as the helix angle parameter; establish a mapping relationship between the obtained pitch parameter, fluctuation amplitude parameter and helix angle parameter and the corresponding axial position coordinates of the pipe, and store them in the spatial distribution database.

3. The broadband vibration measurement method for nuclear power units based on distributed optical fiber sensing according to claim 1, characterized in that, In step S3, the specific process for acquiring dynamically changing data is as follows: A continuous light wave generated by a broadband laser is input into an acousto-optic modulator, and a light pulse sequence with a fixed repetition frequency is formed by applying a radio frequency drive signal. The light pulse sequence is then transmitted to a sensing fiber through an optical circulator, and the polarization state of the light pulses is kept stable during transmission. Backscattered Rayleigh light is received through the return port of the optical circulator. The scattered light signals are arranged in the time sequence of the light pulses to form the original scattered signal sequence. The original scattered signal is input into the polarization beam splitter, which separates it into two orthogonal polarization components and guides them to the intensity detection path and the phase detection path, respectively. In the intensity detection path, the optical signal is converted into an electrical signal using a photodetector. After the signal amplitude is increased by the transimpedance amplifier, the voltage sequence corresponding to the light intensity is acquired by the high-speed acquisition card. In the phase detection path, the scattered light of the current pulse period and the reference light of the previous pulse period are introduced into the optical mixer to generate multiple interference signals with a fixed phase difference. These interference signals are received using a balanced detector and differentially amplified to output orthogonal electrical signals characterizing the phase relationship. Orthogonal electrical signals are input into a digital signal processor, and phase data of the scattered signal is obtained through specific mathematical operations. Simultaneously, light intensity voltage sequences, phase data, and beam splitting ratio data of the polarization beam splitter are acquired and aligned with a unified time reference to form a time-synchronized dynamic data sequence.

4. The broadband vibration measurement method for nuclear power units based on distributed optical fiber sensing according to claim 1, characterized in that, In step S4, the specific process for calculating the axial vibration component of the pipeline is as follows: The sensing fiber is pre-laid on the surface of a set of calibrated specimens with a precisely known radius of curvature. The backscattered Rayleigh light intensity value corresponding to the radius of curvature of each specimen is obtained by optical measurement device. The least squares method is used to fit and obtain a quantitative mapping relationship model between the radius of curvature and the light intensity attenuation. The collected real-time light intensity change data is input into the quantitative mapping relationship model, and the real-time curvature value at each sampling point of the sensing fiber is obtained through model inversion calculation. A spatial geometric model of the sensing fiber spiral path is established. Based on the geometric path represented by the spatial geometric model, the curvature expression at each point is calculated. The curvature expression is subjected to total differential operation to obtain the differential geometric relationship between the curvature change and the fluctuation amplitude change. Substituting the real-time curvature value into the differential geometric relationship, the sequence of fluctuation amplitude changes at each sampling point on the pipe surface is obtained through numerical calculation; a fast Fourier transform is performed on the fluctuation amplitude change sequence to obtain the spectrum analysis results containing vibration frequency and phase information. Based on the time-domain characteristics of the fluctuation amplitude change sequence and the spectral analysis results, the radial bending vibration component of the pipeline, including amplitude, frequency, phase, and direction, is obtained through vector synthesis calculation.

5. The broadband vibration measurement method for nuclear power units based on distributed optical fiber sensing according to claim 4, characterized in that, The specific process for establishing the spatial geometric model of the sensing fiber helical path is as follows: The three-dimensional wavy path laid on the surface of the pipe is represented as a spatial curve; the parametric equation of the spatial curve is established, and the parametric equation takes the rotation angle as the independent variable and outputs the three-dimensional spatial coordinates; A spatial coordinate dataset is obtained by measuring the actual fiber optic path. The spatial coordinate dataset is then substituted into the parametric equation, and a parameter identification algorithm is used to determine the values ​​of the characteristic parameters in the equation. The determined characteristic parameters are then substituted into the parametric equation to establish a spatial geometric model of the sensing fiber optic spiral path.

6. The broadband vibration measurement method for nuclear power units based on distributed optical fiber sensing according to claim 1, characterized in that, In step S4, the specific process for calculating the axial vibration component of the pipeline is as follows: The sensing fiber is pre-laid on the surface of a set of standard specimens with precisely known axial strain. The interference phase drift corresponding to each strain value is obtained through an optical measurement device. The least squares method is used to fit and obtain a quantitative mapping relationship model between axial strain and interference phase drift. The collected real-time interference phase drift data is input into the quantitative mapping relationship model, and the axial strain value at each sampling point of the sensing fiber is obtained through model inversion calculation. A spatial geometric model of the sensing fiber helical path is established, the functional relationship between the total helical length and the pitch parameter is calculated and total differential operation is performed to obtain the differential geometric relationship between axial strain and pitch change. Substituting the real-time axial strain value into the differential geometric relationship, the sequence of pitch change at each sampling point on the pipe surface is obtained through numerical calculation. A fast Fourier transform is performed on the pitch change sequence to obtain a spectrum analysis result containing vibration frequency and phase information. Based on the time-domain characteristics of the pitch change sequence and the spectrum analysis result, the axial vibration component of the pipeline, including amplitude, frequency, phase and direction, is calculated through kinematic relationships.

7. The broadband vibration measurement method for nuclear power units based on distributed optical fiber sensing according to claim 1, characterized in that, In step S4, the specific process for calculating the torsional vibration component of the pipeline is as follows: The sensing fiber is pre-laid on the surface of a set of calibration specimens with a precise known torsion angle. The polarization state rotation angle data corresponding to each torsion angle is obtained through an optical measurement device. The least squares method is used to fit and obtain a quantitative mapping relationship model between the torsion angle and the polarization state rotation angle. The collected real-time polarization state rotation angle data is input into the quantitative mapping relationship model, and the real-time torsion angle value at each sampling point of the sensing fiber is obtained through model inversion calculation. Establish a spatial geometric model of the sensing fiber helical path, calculate the differential geometric relationship between the change in helical angle and the actual torsion angle of the pipe, and calibrate the parameters. Substituting the real-time torsion angle value into the differential geometric relationship, the sequence of helix angle changes at each sampling point on the pipe surface is obtained through numerical calculation. A fast Fourier transform is performed on the helix angle change sequence to extract the frequency components and corresponding phase information of the vibration signal; combined with the time-domain amplitude characteristics and spectrum analysis results of the helix angle change sequence, the torsional vibration components of the pipeline, including amplitude, frequency, phase and direction, are calculated through coordinate transformation.

8. The broadband vibration measurement method for nuclear power units based on distributed optical fiber sensing according to claim 1, characterized in that, In step S5, the specific process of reconstructing the three-dimensional full-field vibration distribution on the pipe surface is as follows: The radial bending vibration component, axial vibration component, and torsional vibration component of the pipeline are spatiotemporally aligned according to the acquisition timestamp and the spatial coordinates of the pipeline. The three vibration components after alignment are vector synthesized according to the coordinate system of the pipeline surface to obtain the three-dimensional vibration vector of each spatial coordinate point. Spatial interpolation is performed on the three-dimensional vibration vector of all spatial coordinate points on the pipeline surface to generate a continuous three-dimensional vibration vector field. The three-dimensional vibration vector field is mapped to the geometric model of the pipeline surface to form a three-dimensional full-field vibration distribution that includes spatial position and vibration characteristics.

9. The broadband vibration measurement method for nuclear power units based on distributed optical fiber sensing according to claim 1, characterized in that, In step S6, the specific process for obtaining the dominant vibration frequencies at different spatial locations of the nuclear power unit pipeline is as follows: Frequency domain transformation is performed on the vibration time history data of each spatial coordinate point in the three-dimensional full-field vibration distribution to obtain the frequency domain vibration spectrum of each point; the peak frequencies of each frequency domain vibration spectrum with amplitudes exceeding a preset threshold are selected, and the selected frequencies are associated with the corresponding pipe spatial coordinates; the spatial distribution consistency of the associated frequencies is verified, frequency components that do not recur in adjacent spatial positions are removed, and the dominant vibration frequencies and corresponding vibration energy parameters of each spatial position on the pipe surface are output.

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