阅读说明：本技术 一种基于超声导波的结构健康监测选频方法 (Structural health monitoring frequency selection method based on ultrasonic guided waves ) 是由 曲志刚 王秋雨 金硕 安阳 杨霄 武立群 张亚丽 王志援 于 2019-10-10 设计创作，主要内容包括：本发明提供一种基于超声导波的结构健康监测选频方法,首先绘制被测对象的频散曲线,根据频散曲线选择合适的模态,确定实验激励模态；然后采用有限元仿真软件和激光测振仪分别求解共振频率,得到几个待选频率；最后,在实验中依次采用不同频率的激励信号,根据实验结果选出激励信号的频率。本发明优点在于能够将几种结构安全健康监测中常用的选择激励信号频率的方法结合起来,更准确地找到适合结构健康监测的频率,得到更好的监测效果,这对结构安全监测有巨大的意义。(The invention provides a structural health monitoring frequency selection method based on ultrasonic guided waves, which comprises the steps of firstly drawing a frequency dispersion curve of a measured object, selecting a proper mode according to the frequency dispersion curve, and determining an experimental excitation mode; then respectively solving resonance frequencies by adopting finite element simulation software and a laser vibration meter to obtain a plurality of frequencies to be selected; and finally, sequentially adopting the excitation signals with different frequencies in the experiment, and selecting the frequency of the excitation signal according to the experiment result. The method has the advantages that the method for selecting the excitation signal frequency commonly used in the structural safety and health monitoring can be combined, the frequency suitable for the structural health monitoring can be found more accurately, a better monitoring effect is obtained, and the method has great significance for the structural safety monitoring.)

1. A structural health monitoring frequency selection method based on ultrasonic guided waves is characterized by comprising the following steps:

s1, drawing a frequency dispersion curve of the measured object, selecting a proper mode according to the frequency dispersion curve, and determining an experimental excitation mode;

s2, performing frequency domain simulation on the object to be tested by adopting finite element simulation software, and performing frequency selection according to the frequency-displacement diagram;

s3, testing the whole experimental system by using a laser vibration meter, and selecting frequency according to the obtained frequency-displacement diagram;

and S4, combining S1, S2 and S3 to apply the selected experimental excitation mode and excitation signal frequency to an experimental system, and selecting the optimal excitation frequency according to the experimental result.

2. The method of claim 1, wherein the software used in step S1 is GUIGUW.

3. The method of claim 1, wherein the software used in step S2 is COMSOL Multiphysics or ANSYS Fluent.

4. The method for frequency selection for structural health monitoring based on ultrasound guided waves according to claim 1, wherein the step S3 comprises the steps of:

s3.1, generating a frequency sweeping signal by a computer;

s3.2, amplifying the signal generated in the step S3.1 by a power amplifier, and exciting the sensor to generate vibration;

and S3.3, acquiring vibration data by using the laser vibration meter to obtain a frequency-displacement diagram of the whole experimental system.

5. The structural health monitoring frequency-selecting method based on ultrasonic guided waves of claim 1, wherein the sensor adopted by the experimental system of step S4 is an MFC sensor or a piezoelectric ceramic sensor.

Technical Field

The invention relates to a frequency selection method for structural health monitoring based on ultrasonic guided waves, and belongs to the field of structural health monitoring.

Background

Damage detection is one of the main tasks of structural health monitoring, and is used in many fields. In the field of traffic and road construction equipment, complex engineering structures and large-scale equipment are everywhere visible, for example: once a fault occurs in the running process of railway equipment, bridges, large cranes, various vehicles such as sea, land and air vehicles and the like, economic loss is caused slightly, and the life of personnel above the crisis is increased seriously; once leakage occurs, the consequences are not obvious in terms of oil and gas pipelines, power pipelines and pipeline transmission of municipal water supply systems. Therefore, it is important to monitor the health status of various structures in advance and to detect damage.

Currently, a structural health monitoring technology based on ultrasonic guided waves is the most common method. Most of the methods rely on small sensors to acquire some information (such as displacement, stress, strain, etc.) of the structure, and then acquire the characteristics of the damage through data processing and analysis at a later stage. When the ultrasonic guided waves are transmitted in a medium, the frequency is different, the transmission speed is different, and the number of excited modes is also different. When the ultrasonic guided wave is used for detecting the damage, the smaller the number of excited modes is, the less obvious the frequency dispersion characteristic is, and the better the frequency dispersion characteristic is. Therefore, the excitation frequency has a great influence on the detection effect, and it is important to select an appropriate excitation frequency.

Disclosure of Invention

The invention provides a frequency selection method for structural health monitoring based on ultrasonic guided waves, which can accurately find out the frequency suitable for structural health monitoring to obtain a better detection effect, and has great significance for structural health monitoring.

1. The technical scheme adopted by the invention is as follows: a structural health monitoring frequency selection method based on ultrasonic guided waves comprises the following steps:

s1, drawing a frequency dispersion curve of the measured object, selecting a proper mode according to the frequency dispersion curve, and determining an experimental excitation mode;

s2, performing frequency domain simulation on the object to be tested by adopting finite element simulation software, and performing frequency selection according to the frequency-displacement diagram;

s3, testing the whole experimental system by adopting a laser vibration meter, and selecting frequency according to a frequency-displacement diagram;

and S4, combining S1, S2 and S3 to apply the selected experimental excitation mode and excitation signal frequency to an experimental system, and selecting the optimal excitation frequency according to the experimental result.

2. The software adopted in step S1 is GUIGUW.

3. The software adopted in step S2 is COMSOL multiprohysics or ANSYS Fluent.

4. The step S3 includes the following steps:

s3.1, generating a frequency sweeping signal by a computer;

s3.2, amplifying the signal generated in the step S3.1 by a power amplifier, and exciting the sensor to generate vibration;

and S3.3, acquiring vibration data by using the laser vibration meter to obtain a frequency-displacement diagram of the whole experimental system.

5. The sensor adopted by the experimental system in the step S4 is an MFC sensor or a piezoelectric ceramic sensor.

Drawings

FIG. 1 is a flow chart of frequency selection for structural health monitoring.

Fig. 2 is an aircraft cable phase velocity dispersion curve.

FIG. 3 is a frequency-displacement plot obtained from COMSOL Multiphysics simulation.

Fig. 4 is an experimental diagram of a laser vibrometer test experimental system.

Fig. 5 is a graph of frequency versus displacement for a laser vibrometer.

FIG. 6 is a schematic diagram of a system for detecting defects in an insulation layer of an aircraft cable.

Fig. 7 is a graph of the excitation signal used in the experiment.

FIG. 8 is a schematic diagram of signals collected at 20.680 KHz.

FIG. 9 is a schematic diagram of signals collected at 35.200 KHz.

FIG. 10 is a schematic diagram of signals collected at 20.614 KHz.

Detailed Description

The technical solutions in the embodiments of the present invention are further described in detail below with reference to the drawings in the embodiments of the present invention. It is to be understood that the described embodiments are merely a few embodiments of the invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The invention only takes the health monitoring frequency selection of the insulating layer structure of the airplane cable as an example.

Fig. 1 is a flow chart of structural health monitoring frequency selection. Firstly, drawing a frequency dispersion curve of a measured object, selecting a proper mode according to the frequency dispersion curve, and determining an experimental excitation mode; then respectively solving resonance frequencies by adopting finite element simulation software and a laser vibration meter to obtain a plurality of frequencies to be selected; and finally, sequentially adopting the excitation signals with different frequencies in the experiment, and selecting the frequency of the excitation signal according to the experiment result.

Fig. 2 is a dispersion curve of an aircraft cable used in the experiment. From fig. 2, it can be seen that within the frequency range of 0 to 100KHz, there is only one of the longitudinal mode, the torsional mode and the bending mode, wherein the bending mode has an obvious frequency dispersion phenomenon, the torsional mode and the longitudinal mode have no frequency dispersion basically at 0 to 60KHz, and the propagation phase velocity of the longitudinal mode is obviously faster than that of the torsional mode, which provides a certain basis for selecting and exciting L-mode guided waves.

FIG. 3 is a frequency-displacement plot obtained from COMSOL Multiphysics simulation. In the COMSOL Multiphysics aircraft cable simulation, the set simulation parameters were all consistent with the cable parameters used in the experiments described below. In simulation, two-dimensional axial symmetry is adopted in space dimension, a solid mechanical interface is used, and frequency domain simulation of the solid mechanical interface in the frequency domain range of 20-60KHz is researched. The length direction of the cable is the z direction, boundary load is applied to the cross section of the z direction, L mode guided waves are excited, fixed constraint is added to the cross section of the z direction at the other end, and the change condition of displacement along with the change of frequency is observed. To ensure the accuracy of the simulation, the average cell mass of the grid division is 0.8477, and the degree of freedom of the solution is 29264. From fig. 3, we can see that there are two frequencies with larger vibration displacement, which are: 20.680KHz, 35.200 KHz.

Fig. 4 is an experimental diagram of a laser vibrometer test experimental system. Firstly, a frequency sweep signal is generated by an upper computer, then the signal is amplified by a power amplifier, a sensor is excited to generate vibration, and then vibration data is collected by a laser vibrometer (model: Polytec PSV-500) to obtain a frequency-displacement diagram of the whole experimental system, as shown in FIG. 5. As can be seen from fig. 5, in the frequency range of 0-60KHz, as the frequency increases, the displacement tends to increase first and then decrease, and there is a maximum, so that according to the frequency-displacement diagram obtained by the laser vibrometer, the frequency is selected to be 20.614 KHz.

Selecting and using L-mode ultrasonic guided waves according to a dispersion curve, and finally selecting three frequencies according to a frequency displacement graph obtained by simulation and a frequency displacement graph obtained by a laser vibration meter, wherein the three frequencies are respectively as follows: 20.680KHz, 35.200KHz and 20.614 KHz. These three frequencies were applied separately to the experiment.

The length of the aircraft cable adopted in the experiment is 200cm, the internal material is copper, the internal diameter is 2.87mm, the Young modulus is 110GPa, the Poisson ratio is 0.35, and the density is 8960Kg/m 3; the insulating layer is made of Polyvinyl chloride, the thickness is 1.18mm, the Young modulus is 2.9GPa, the Poisson ratio is 0.319, and the density is 1760Kg/m 3; two MFC8507-P1 sensors are symmetrically excited in an experiment and act on a single end of a cable to generate L-mode guided waves; a receiving sensor, model MFC2807-P2, was placed 100cm from the excitation sensor.

The schematic diagram of the experimental system is shown in fig. 6. Firstly, an upper computer generates an excitation signal, the excitation signal is amplified by a power amplifier, and an MFC (mass flow controller) is excited to vibrate to generate ultrasonic guided waves; when the ultrasonic guided wave propagates in the aircraft cable and meets defects and the tail end of the cable, impedance changes, and a reflected signal is generated. The reflected signal makes the receiving sensor MFC generate vibration, and the change of the charge quantity occurs; the charge amplifier converts the charge quantity into a voltage signal, and the voltage signal enters a computer for processing through a data acquisition card.

Fig. 7 is a signal frequently used in structural health monitoring. The center frequency of the excitation is selected according to the following method, n₀For 5, the windowing function uses a hanning window, i.e.:

U＝(1-cos(2*pi*f*t/n₀))*sin(2*pi*f*t)(t＜n₀/f)

fig. 8-10 are time displacement graphs at three frequencies, respectively. FIG. 8 shows that at 20.680KHz excitation frequency, although both defect signals and tail reflection signals can be collected, the defect reflection signals are not easily distinguished; FIG. 9 shows that at 35.200KHz, only the excitation signal is received, and neither the defect reflection signal nor the tail reflection signal is received; the signal collected by the frequency of 20.614KHz in FIG. 10 is better, and the defect reflected signal and the tail end reflected signal can be clearly distinguished, so that the center frequency of the final selected excitation signal is 20.614 KHz.

Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.