Wall plate structure health monitoring SHM sensor node network construction method

Abstract

The invention discloses a wallboard structure health monitoring SHM sensor node network construction method, and the method comprises the steps: firstly carrying out the calculation to obtain a transmission coefficient frequency spectrum of a Lamb wave, and enabling the transmission coefficient frequency spectrum to serve as a frequency selection basis when the Lamb wave carries out the structure health monitoring of a whole wallboard; reasonable threshold setting is performed on a transmission Lamb wave energy contour line, and the coverage range of a single sensor node is determined in combination with the defect detection capability and detection requirements of a sensor. A first-stage receiving sensor is taken as a starting point, the spatial layout of the monitoring sensor network in an integral wall plate is constructed based on a step-by-step recursion layout strategy, and two competition nodes which are close to each other and have approximately same coverage areas are screened and eliminated by utilizing the principle that the total length of all node links in the integral sensor network is minimum. And the purpose of optimizing the sensor network constructed in a step-by-step recursion mode is achieved. According to the method, the layout of the Lamb wave structure health monitoring sensor network in the whole panel can be realized, and the monitoring problem in actual engineering is solved.

Description

Technical Field

[0001] The present invention is a method for constructing a sensor node network for structural health monitoring (SHM) of wall panels, which belongs to the field of ultrasonic guided wave nondestructive testing and communication control technology. Aiming at the structural health monitoring problem of large integral wall panels commonly used in aerospace, the method is used to construct an ultrasonic Lamb wave monitoring sensor network to achieve large-area full-coverage monitoring of defects in the wall panels. Background Art

[0002] Metal integral panels are an important part of the aerodynamic shape of advanced aircraft in the aerospace field, and are also the main load-bearing components of aircraft wings, fuselages, fuel tanks, etc. The integral panel adopts integrated molding processing technology, and there is no mechanical connection between its structural elements such as skin and reinforcement ribs. Compared with traditional riveted composite panels, the integral panel structure can reduce weight by 10%-30% and significantly improve strength, stiffness and sealing. Aerospace aircraft have been serving in high-speed variable load conditions and extreme environments for a long time. In addition to bearing fatigue loads, the large metal integral panel structures used in their wings, fuselages and fuel tanks are also faced with high-speed impacts of external particles (such as hail, raindrops and dust, etc.), resulting in frequent defects such as skin impact damage and fatigue cracks, which seriously threaten the structural integrity and flight safety of the aircraft. Therefore, how to effectively obtain defect information in the integral panel structure in real time is a hot and difficult problem in the field of aircraft health status monitoring and life prediction.

[0003] Intelligent sensor networks are the core foundation for solving the major engineering demand of aircraft structural health monitoring. Using ultrasonic Lamb waves suitable for propagation in thin-walled plate and shell structures, Lamb wave detection technology for structural defects has been developed at home and abroad. Experiments have fully verified that Lamb waves have the advantages of long propagation distance and sensitivity to structural defects. Lamb wave technology has important application prospects in the structural health monitoring of aircraft metal integral wall panels, but there are still serious shortcomings. For example, the propagation characteristics of Lamb waves in metal integral wall panels with complex characteristic structures are unclear, making it difficult to construct and design Lamb wave sensor node networks and optimize the selection of sensor network parameters.

[0004] In view of the above-mentioned shortcomings, the present invention discloses a method for constructing a sensor node network for wall panel structural health monitoring (SHM), and realizes health monitoring of the panel structure by Lamb waves through reasonable arrangement of monitoring nodes of the sensor network.

[0005] In the present invention, the propagation characteristics of Lamb waves in the metal integral wall panel are quantitatively characterized by calculating the transmission coefficient spectrum, which serves as the basis for frequency selection when Lamb waves perform structural health monitoring on the integral wall panel. In the frequency band with higher transmission coefficient, Lamb wave contour lines are drawn based on the transmitted Lamb wave isoenergy wavefront, thereby guiding the spatial layout of sensor monitoring nodes on the contour lines. Constructing a lightweight, non-electromagnetic wave wireless communication sensor network that meets the airworthiness requirements of aircraft can effectively solve the problem of the difficulty of spatial layout of sensors in monitoring the health status of complex structures using existing ultrasonic Lamb waves. Summary of the invention

[0006] The purpose of the present invention is to solve the problem of constructing a sensor network in health monitoring of complex geometric structures using ultrasonic Lamb waves, to reveal the propagation characteristics of Lamb waves in complex geometric structures, to determine the spatial layout of Lamb wave transmission wavefronts, and to use energy density contours composed of multiple transmission wavefronts to guide the construction of the sensor network, so as to achieve the purpose of comprehensive coverage of large integral wall panels and minimum energy consumption of wireless sensor networks.

[0007] To achieve the above object, the present invention proposes a method for constructing a wireless sensor network based on ultrasonic Lamb wave monitoring of metal integral wall panels, the method mainly comprising the following steps:

[0008] 1) Simulation analysis of Lamb wave dispersion characteristics in the integral wall panel structure. Based on finite element simulation software, a variable thickness and curved wall panel structure model is established to simulate the propagation process of Lamb waves in the integral wall panel. The Lamb wave response signals at different positions in space are densely extracted, and the frequency-wave number relationship is obtained based on the two-dimensional Fourier transform to identify the modal components of the Lamb wave. The component information of the Lamb wave under different plate thickness conditions is obtained as a reference for the dispersion compensation of the Lamb wave receiving signal.

[0009] 2) Reveal the influence of different geometric characteristic structures in the wall panel structure on the propagation characteristics of Lamb waves. Keep the thickness of the whole wall panel unchanged and perform dispersion compensation based on the conclusion in step 1). Analyze the influence of geometric characteristics such as stiffeners and flaps in the wall panel structure on the propagation characteristics of Lamb waves, and focus on the influence of stiffener structures of different cross-sectional types on the propagation characteristics of Lamb waves in the plate. Compare and analyze the modal components and amplitude spectra of the incident and transmitted Lamb wave signals in a certain frequency band to reveal the influence of geometric characteristic structures on the modal conversion and energy distribution of Lamb waves.

[0010] 3) Calculate the transmission coefficient spectrum of Lamb waves in the overall panel structure to guide the selection of the optimal excitation frequency band of Lamb waves. According to the main modal components of the selected Lamb waves in the results of 2), extract the time domain waveforms of several observation points before and after the geometric features for two-dimensional Fourier transform, and calculate the ratio of the amplitude ridges (the latter to the former) in the frequency domain to obtain the Lamb wave transmission coefficient spectrum, revealing the comb filtering effect of the geometric features in the panel structure on the transmitted Lamb waves.

[0011] 4) Extract the Lamb wave energy wavefronts in different directions to construct contour lines. Select the frequency band with high Lamb wave transmission coefficient in the transmission coefficient spectrum in 3) for excitation, and monitor the health of the entire wall panel structure. Densely extract the time domain signals of Lamb waves under different propagation paths in the wall panel, and draw the wavefronts with the same Lamb wave energy. Set a reasonable threshold (such as -12dB) to construct the transmission Lamb wave energy contour line, and determine the coverage range of a single sensor node based on the sensor's defect detection capability and detection requirements.

[0012] 5) Construct a wireless sensor network based on the step-by-step recursive layout strategy of the transmission energy density contour. Set the starting point of the sensor network (aggregate node), and obtain the Lamb wave transmission energy contour corresponding to the node under the set threshold and the monitorable range of a single sensor node by 4). Combined with the angle range requirements of defect location, determine the number and position of the receiving sensor nodes on the contour, which are defined as the first-level receiving nodes. Taking the first-level receiving sensor as the starting point, repeat the above steps to determine the number and position of the second-level nodes, and recursively complete the spatial layout of the monitoring sensor network in the overall wall panel.

[0013] 6) Optimize the design of the sensor network constructed by recursive step-by-step. To reduce the redundancy of the sensor network, two nodes that are very close and have roughly the same coverage are defined as competitive nodes. The highest detection rate and the lowest correlation between two adjacent sensors are used as optimization indicators. The competitive nodes are screened and eliminated using the principle of the minimum total length of all node links in the overall sensor network. The optimized sensor network has the characteristics of comprehensive coverage and minimum redundancy.

[0014] Compared with the prior art, the present invention has the ability to perform health monitoring on metal integral wall panels with complex characteristic structures. By exploring the influence of different characteristic structures on the propagation characteristics of Lamb waves in large integral wall panels, the Lamb wave transmission coefficient spectrum is calculated to guide the selection of frequencies in health monitoring. And the design of the spatial layout of sensors in the wall panel structure can be realized by drawing contour lines. This patent has a lightweight, non-electromagnetic wave wireless communication sensor network, and after the sensor network is optimized, it not only ensures the ability to monitor defects, but also minimizes the number of sensors, which meets the stringent requirements of aircraft for airborne equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the cross-sectional shape of a typical metal integral wall panel and its reinforcement ribs.

[0016] Figure 2 It is the comb filtering effect of the structure on the Lamb wave transmission coefficient spectrum.

[0017] Figure 3It is a schematic diagram of Lamb wave transmission energy contours.

[0018] Figure 4 This is a schematic diagram of the ultrasonic Lamb wave wireless sensor network construction method.

[0019] Figure 5 It is a method for optimizing the spatial layout of sensors and building a network. DETAILED DESCRIPTION

[0020] The present invention is described in detail below with reference to the accompanying drawings and embodiments:

[0021] The present invention proposes a method for constructing a sensor node network for panel structural health monitoring (SHM) to solve the problem of sensor layout in the health monitoring of metal integral panel structures. Lamb waves have the advantages of long propagation distance and sensitivity to structural defects in thin-walled plate and shell structures. They can be used as a dual medium for structural defect information perception and communication transmission between sensor nodes. The key to realizing panel structural health monitoring is to reasonably arrange the monitoring nodes of Lamb wave sensors.

[0022] The present invention first calculates the transmission coefficient spectrum of Lamb waves as the basis for frequency selection when Lamb waves perform structural health monitoring on the integral wall panel. In the frequency band with higher transmission coefficient, the energy wavefronts of Lamb waves in different propagation directions are extracted, and the closed curves formed by their boundaries constitute the Lamb wave energy contours. Further, a reasonable threshold is set for the transmission Lamb wave energy contours, and the coverage range of a single sensor node is determined in combination with the sensor's detection capability and detection requirements for defects. Considering the angle range requirements for defect positioning, the number and position of the first-level receiving sensor nodes on the contours are determined. Starting from the first-level receiving sensor, the spatial layout of the monitoring sensor network in the integral wall panel is constructed based on the step-by-step recursive layout strategy. Finally, using the principle of the minimum total length of all node links in the overall sensor network, two competing nodes with close distances and roughly the same coverage range are screened and eliminated to reduce the redundancy of the sensor network, thereby achieving the purpose of optimizing the sensor network constructed in a step-by-step recursive manner. The invention method can realize the layout of the Lamb wave structural health monitoring sensor network in the integral wall panel and solve the monitoring problem in actual engineering.

[0023] The technical solution adopted by the present invention is a method for constructing a sensor node network for wall panel structural health monitoring (SHM), comprising the following steps:

[0024] S1. Reveal the distribution law of Lamb wave transmission coefficient spectrum in the wall structure to guide frequency selection. The specific implementation steps are: extract the time domain waveforms of several observation points before and after the geometric features for two-dimensional Fourier transform. The positive part of the wave number domain in the two-dimensional Fourier transform result of the observation point before the geometric feature structure is the incident signal, and the two-dimensional Fourier transform result of the observation point after the geometric feature structure is the transmission signal. The amplitude ratio of the transmission signal to the incident signal in the frequency domain is the Lamb wave transmission coefficient spectrum, such as Figure 2 The results reveal the comb filtering effect of geometric features in the panel structure on the transmitted Lamb wave at different frequencies, and the frequency band with high transmission coefficient is more suitable as the selection of excitation frequency in structural health monitoring.

[0025] S2. Drawing of Lamb wave transmission energy contours in metal integral wall structure. The specific implementation steps are: densely extract the time domain signals of Lamb waves under different propagation paths, quantitatively describe the propagation process of Lamb waves in the integral wall structure, draw Lamb wave transmission wavefronts with equal energy, and the closed curves formed by their boundaries are similar to the contour lines in the topographic map, which are called Lamb wave transmission energy contour lines, such as Figure 3 As shown in the figure. By setting a reasonable threshold (such as -12dB) for the Lamb wave transmission energy contour, the effective spatial range of ultrasonic Lamb wave defect monitoring and communication transmission can be quantitatively evaluated. This will provide a quantitative criterion for the coverage range of a single sensor node and guide the optimization of node spatial layout in the structural health monitoring sensor network.

[0026] S3. A recursive layout strategy for wireless sensor networks based on transmission energy density contours. The specific method is: set the starting point (aggregation node) of the sensor network, set the threshold of the Lamb wave transmission energy contour corresponding to the node, and determine the number and position of the receiving sensor nodes of the contour in combination with the angle range requirements of defect location. Taking the receiving sensor as the starting point, repeat the above steps to determine the number and position of the secondary nodes, and recursively complete the spatial layout of the sensor nodes in the overall wall panel. Figure 4 As shown in the figure. In order to reduce the redundancy of the sensor network, the principle of minimum total length of node links in the overall sensor network is used to further screen and eliminate competitive nodes. The optimized sensor network has the characteristics of comprehensive coverage and minimum redundancy.

Claims

1. A method for constructing a SHM sensor node network for siding structure health monitoring, characterized in that: The method comprises the following steps: Step 1) Simulation and analysis of Lamb wave dispersion characteristics in the overall wall panel structure; based on finite element simulation software, a variable thickness, curved wall panel structure model is established to simulate the propagation process of Lamb waves in the overall wall panel; Lamb wave response signals at different positions in space are densely extracted, and the frequency-wave number relationship is obtained based on two-dimensional Fourier transform to identify the modal components of the Lamb wave, and the component information of the Lamb wave under different plate thickness conditions is obtained as a reference for the dispersion compensation of the Lamb wave receiving signal; Step 2) reveal the influence of different geometric characteristic structures in the wall panel structure on the propagation characteristics of Lamb waves; keep the thickness of the whole wall panel unchanged, and perform dispersion compensation based on the conclusion in step 1); analyze the influence of the geometric characteristics of the stiffeners and flaps in the wall panel structure on the propagation characteristics of Lamb waves, and explore the influence of stiffener structures of different cross-section types on the propagation characteristics of Lamb waves in the plate; compare and analyze the modal components and amplitude spectra of the incident and transmitted Lamb wave signals in a certain frequency band, and reveal the influence of the geometric characteristic structure on the modal conversion and energy distribution of Lamb waves; Step 3) Calculate the transmission coefficient spectrum of Lamb waves in the overall panel structure to guide the selection of the optimal excitation frequency band of Lamb waves; According to the selected modal components of Lamb waves in the result of step 2), extract the time domain waveforms of several observation points before and after the geometric features for two-dimensional Fourier transform, and calculate the ratio of the amplitude ridge lines in the frequency domain to obtain the Lamb wave transmission coefficient spectrum, revealing the comb filtering effect of the geometric features in the panel structure on the transmitted Lamb waves; Step 4) extracting Lamb wave energy wavefronts in different directions to construct contour lines; selecting the frequency band with high Lamb wave transmission coefficient in the transmission coefficient spectrum in step 3) for excitation, and performing health monitoring on the overall wall panel structure; densely extracting the time domain signals of Lamb waves under different propagation paths in the wall panel, and drawing the wavefronts with the same Lamb wave energy; setting reasonable thresholds to construct the transmission Lamb wave energy contour lines, and determining the coverage range of a single sensor node according to the sensor's defect detection capability and detection requirements; Step 5) construct a wireless sensor network based on the step-by-step recursive layout strategy of the transmission energy density contour line; set the starting point of the sensor network, obtain the Lamb wave transmission energy contour line corresponding to the node under the set threshold and the monitorable range of a single sensor node by step 4), and determine the number and position of the receiving sensor nodes on the contour line in combination with the angle range requirements of the defect positioning, which are defined as the first-level receiving nodes; take the first-level receiving sensor as the starting point, repeat the above steps to determine the number and position of the second-level nodes, and recursively complete the spatial layout of the monitoring sensor network in the overall wall panel step by step; 6) Optimize the design of the sensor network constructed by step-by-step recursion; define two nodes with close distance and the same coverage as competitive nodes; use the highest detection rate and the lowest correlation between two adjacent sensors as optimization indicators, and use the principle of minimizing the total length of all node links in the sensor network to screen and eliminate competitive nodes.

2. A method for constructing a siding structure health monitoring SHM sensor node network according to claim 1, characterized in that: The time domain signals of Lamb waves under different propagation paths are intensively extracted to quantitatively describe the propagation process of Lamb waves in the overall wall panel structure. The Lamb wave transmission wavefronts with equal energy are drawn. The closed curves formed by their boundaries are similar to the contour lines in a topographic map, which are called Lamb wave transmission energy contour lines. By setting thresholds for the Lamb wave transmission energy contour lines, the effective spatial range of ultrasonic Lamb wave defect monitoring and communication transmission can be quantitatively evaluated.

3. A method for constructing a siding structure health monitoring SHM sensor node network according to claim 1, characterized in that: The step-by-step recursive layout strategy method of the wireless sensor network based on the transmission energy density contour is as follows: set the starting point of the sensor network, that is, the summary node, set the threshold of the Lamb wave transmission energy contour corresponding to the summary node, and determine the number and position of the receiving sensor nodes of the contour line in combination with the angular range requirements of defect positioning; take the receiving sensor as the starting point, determine the number and position of the secondary nodes, and complete the spatial layout of the sensor nodes in the overall wall panel step by step.

4. A method for constructing a siding structure health monitoring SHM sensor node network according to claim 3, characterized in that: In order to reduce the redundancy of sensor networks, the principle of minimum total length of node links in sensor networks is used to screen and eliminate competitive nodes.

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