Double-layer casing modal measurement method based on Doppler laser vibration measurement system

Abstract

The invention provides a double-layer casing modal measurement method based on a Doppler laser vibration measurement system, and relates to the technical field of aero-engine structural strength test.The double-layer casing modal measurement method comprises the steps that a double-layer casing modal measurement model is established, and the Doppler laser vibration measurement system is adopted to measure the modal of the double-layer casing; scanning and measuring vibration response signals of each measuring point on the outer layer of the double-layer casing according to the modal measurement model; a vibration exciter is adopted to generate excitation on the inner layer of the double-layer casing, and an excitation response signal of each measuring point of the inner layer of the double-layer casing is obtained through a reflection galvanometer arranged outside the double-layer casing; the excitation response signals, measured by the reflection galvanometer, of the measuring points of the inner layer of the double-layer casing are obtained through the Doppler laser vibration measurement system, the vibration response signals of the measuring points of the outer layer of the double-layer casing and the excitation response signals of the measuring points of the inner layer of the double-layer casing are processed, and modal parameters of the double-layer casing are obtained. Measurement of modal parameters of the inner layer and the outer layer of the engine double-layer casing is achieved, and the problem that the inner layer of the casing cannot be directly measured is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of aircraft engine structural strength testing, and in particular to a double-layer casing modal measurement method based on a Doppler laser vibration measurement system. Background Art

[0002] With the rapid development of aviation power equipment, the demand for component assessment during testing is increasing dramatically, the assessment time is increasing, and the assessment environment is becoming more realistic and precise. Test equipment is an essential vehicle for completing test assessments. During equipment construction, it is crucial to better construct the boundary conditions required for testing and reduce errors in subsequent tests. Structural strength tests are mostly conducted in simulated environments, and environmental construction technology is one of the key technologies. Proper equipment construction can greatly enhance the testing capabilities of the project. How to better leverage the positive effects of equipment construction is also a difficult problem that needs to be overcome in current power development.

[0003] Modal testing is an important test subject for engine structural strength testing. Obtaining the vibration modal parameters of the structure supports structural strength design and analysis. As a key structural component of the engine, some casings currently have a double-layer structure. The vibration characteristics of the inner and outer layers of the casing during operation are interrelated and different. Therefore, it is crucial to obtain the modal parameters of the inner and outer layers of the double-layer casing. Relying on a Doppler laser vibration measurement system to complete the modal measurement of the double-layer casing in the strength test equipment is low-cost and highly effective. It not only meets design requirements, but also provides a new method for modal measurement of double-layer casings. Summary of the Invention

[0004] In view of this, an embodiment of the present application provides a double-layer casing modal measurement method based on a Doppler laser vibration measurement system, which completes the construction and analysis of the measurement equipment, provides data support for engine design and troubleshooting, and promotes the test equipment construction technology in the subsequent development process.

[0005] The present application provides the following technical solution: a double-layer casing modal measurement method based on a Doppler laser vibration measurement system, comprising:

[0006] A double-layer casing modal measurement model is established, and a Doppler laser vibration measurement system is used to scan and measure the vibration response signals of each measuring point on the outer layer of the double-layer casing according to the double-layer casing modal measurement model;

[0007] Using a vibration exciter to generate vibration on the inner layer of the double-layer casing, and obtaining the vibration response signal of each measuring point in the inner layer of the double-layer casing through a reflective galvanometer arranged outside the double-layer casing;

[0008] The Doppler laser vibration measurement system is used to obtain the excitation response signals of each measuring point in the inner layer of the double-layer casing measured by the reflective galvanometer, and the vibration response signals of each measuring point in the outer layer of the double-layer casing and the excitation response signals of each measuring point in the inner layer of the double-layer casing are processed to obtain the modal parameters of the double-layer casing.

[0009] According to one embodiment of the present application, the exciter is fixedly installed at the center position inside the double-layer casing, and the exciter is connected to the inner layer of the double-layer casing through a push rod.

[0010] According to one embodiment of the present application, the exciter controls the excitation frequency and amplitude of the inner layer of the casing by adjusting the frequency and amplitude, and transmits the generated excitation to the inner layer of the casing through the push rod.

[0011] According to one embodiment of the present application, the excitation point where the push rod is connected to the inner layer of the double-layer casing is not on the modal node line of the casing.

[0012] According to one embodiment of the present application, a double-layer casing modal measurement model is established, including: modeling the inner and outer measuring point structures of the double-layer casing respectively, and the number of modeled measuring points is not less than 3 times the modal order.

[0013] According to one embodiment of the present application, the method also includes: dividing the inner and outer layers of the double-layer casing into four measurement areas respectively, measuring 1 / 4 of the measuring points of the casing each time, and completing the measurement of the four measurement areas of the inner layer of the casing by rotating the reflective galvanometer.

[0014] According to one embodiment of the present application, the sampling frequency of the response signal of the Doppler laser vibration measurement system is higher than 5 times the highest modal frequency of the casing.

[0015] According to one embodiment of the present application, processing the vibration response signals of each measuring point on the outer layer of the double-layer casing and the excitation response signals of each measuring point on the inner layer of the double-layer casing includes:

[0016] The vibration response signals of each measuring point on the outer layer of the double-layer casing and the excitation response signals of each measuring point on the inner layer of the double-layer casing are normalized based on the first measurement area, and all response signals are converted into frequency response functions of the same coordinate. The frequency response functions are imported into the modal measurement model of the double-layer casing, and the modal parameters of each order of the double-layer casing are obtained by analysis.

[0017] Compared with the prior art, the beneficial effects that can be achieved by at least one of the above-mentioned technical solutions adopted in the embodiments of this specification include at least the following: a double-layer casing modal measurement method based on a Doppler laser vibration measurement system in the embodiment of the present invention realizes the measurement of the modal parameters of the inner and outer layers of the double-layer casing of the engine, breaking through the difficult problem that the inner layer of the casing cannot be directly measured, and providing great support for the structural design and optimization of engine development. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0019] Figure 1 A measurement principle diagram of a double-layer casing modal measurement method based on a Doppler laser vibration measurement system according to an embodiment of the present invention;

[0020] Figure 2 This is a flow chart of a double-layer casing modal measurement method based on a Doppler laser vibration measurement system according to an embodiment of the present invention;

[0021] Figure 3 This is a schematic cross-sectional diagram of the locations of measurement points in different regions in an embodiment of the present invention;

[0022] Figure 4 Schematic diagram of the internal rotation angle of the casing in an embodiment of the present invention;

[0023] Among them, 1-Doppler laser vibration measurement system, 2-double-layer casing, 3-exciter, 4-reflection galvanometer. DETAILED DESCRIPTION

[0024] The embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0025] The following describes the embodiments of the present application through specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the contents disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The present application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that, in the absence of conflict, the features in the following embodiments and embodiments can be combined with each other. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of this application.

[0026] like Figure 1-Figure 3 As shown, an embodiment of the present invention provides a double-layer casing modal measurement method based on a Doppler laser vibration measurement system, comprising:

[0027] A double-layer casing modal measurement model is established, and a Doppler laser vibration measurement system 1 is used to scan and measure the vibration response signals of each measuring point on the outer layer of the double-layer casing 2 according to the double-layer casing modal measurement model;

[0028] The inner layer of the double-layer casing 2 is excited by a vibration exciter 3, and the vibration response signal of each measuring point in the inner layer of the double-layer casing 2 is obtained by a reflective galvanometer 4 arranged outside the double-layer casing;

[0029] The Doppler laser vibration measurement system 1 obtains the excitation response signals of each measuring point in the inner layer of the double-layer casing measured by the reflective galvanometer 4, and processes the vibration response signals of each measuring point in the outer layer of the double-layer casing and the excitation response signals of each measuring point in the inner layer of the double-layer casing to obtain the modal parameters of the double-layer casing 2.

[0030] In some embodiments of the present invention, the vibration exciter is fixedly installed at a central position inside the double-layer casing, and the vibration exciter is connected to the inner layer of the double-layer casing through a push rod.

[0031] During specific implementation, the method of the embodiment of the present invention includes building a platform, structural modeling, measuring the inner and outer layers of the casing, and modal analysis. The building platform is composed of a Doppler laser vibration measurement system 1, an exciter 3, and a reflective galvanometer 4. One end of the push rod is connected to the exciter 3 and fixed, and the other end is connected to the inner side of the inner casing. Specifically, the double-layer casing 2 is placed on an elastic flat pad or a foam board, and the exciter 3 is fixedly installed inside the casing. The exciter 3 excites the casing through the push rod. A modal measurement model of the double-layer casing is established. The Doppler laser vibration measurement system 1 scans and measures the vibration response signals of each external measuring point according to the modal measurement model of the double-layer casing, and then measures the vibration response signals of each internal point through the reflective galvanometer 4. Modal analysis is performed based on the established model to obtain the modal parameters of the double-layer casing. The exciter 3 is installed and fixed inside the casing. The exciter 3 is connected to the inside of the casing through the push rod. The exciter 3 excites the casing by adjusting the frequency and amplitude.

[0032] During specific implementation, cylindrical coordinates are established, and a double-layer casing modal measurement model is established in a grid manner. A test plan is set up in the Doppler laser vibration measurement system. The inner and outer layers of the double-layer casing are divided into four measurement areas, and each area is measured separately for the inner and outer layers. Each time, 1 / 4 of the casing is measured. The measurement of the four measurement areas of the inner layer of the casing is completed by rotating the reflective galvanometer. The external vibration signal measurement of 1 / 4 of the casing is completed point by point by scanning. Among them, the casing measurement response points must correspond one-to-one to the points of structural modeling and be evenly arranged to reduce the probability of missing modes and also contribute to the dynamic beauty of the modal vibration shape. The number of casing measurement points cannot be less than the requirement. The Doppler laser vibration measurement system is aligned with the reflective galvanometer. The measurement points of the inner part of the casing can be measured through the reflection of the galvanometer. When a vertical row of side surfaces is completed, the reflective galvanometer is rotated a certain angle until the measurement of the internal measurement points of 1 / 4 of the casing is completed. Rotate the casing 90° and continue to measure the vibration signals of each external and internal point in another area point by point according to the above method. Follow this step to complete the measurement of all points on the casing in four times.

[0033] Specifically, the outer layer of the upper casing is measured using a Doppler laser vibrometry system, which scans vertically and horizontally. The Doppler laser vibrometry system scans vertically to acquire vibration signals from the inner measurement points, while circumferential movement is achieved through the rotation of a reflective galvanometer. The galvanometer rotates intermittently, with the pause time between each rotation equal to the time it takes to measure a vertical row of points. To ensure data accuracy, the signal from each point is averaged at least three times.

[0034] like Figure 4 As shown, the Doppler laser vibration measurement system is aligned with the reflective galvanometer. Via reflection from the galvanometer, the measurement points inside the casing can be measured. Once a vertical row of side surfaces is completed, the reflective galvanometer rotates a certain angle until the measurement of the measurement points within 1 / 4 of the casing is completed. The time it takes to complete a vertical row of measurement points is T, and the interval between the rotations of the reflective galvanometer is T. For N circumferential measurement points within the 1 / 4 of the casing, and the angle between the two points is θ, then N = 90 / θ. Each rotation angle of the reflective galvanometer is θ / 2, and the corresponding starting angle is consistent. For example, if the angle of the first row of measurement points on the casing is δ, then the corresponding angle of the reflective galvanometer is δ / 2. For example, if the first row of measurement points is measured starting from a casing angle of -45°, the starting angle of the reflective galvanometer is -22.5°.

[0035] Rotate the casing 90° and continue to measure the vibration signals of each external and internal point in another area point by point according to the above method. Follow this step to complete the measurement of all points on the casing in four times.

[0036] In some embodiments of the present invention, the vibration response signals of each measuring point on the outer layer of the double-layer casing and the excitation response signals of each measuring point on the inner layer of the double-layer casing are processed, including: normalizing the vibration response signals of each measuring point on the outer layer of the double-layer casing and the excitation response signals of each measuring point on the inner layer of the double-layer casing according to the same cylindrical coordinates based on the first measurement area, converting all response signals into frequency response functions of the same coordinates, importing the frequency response functions into the modal measurement model of the double-layer casing, and analyzing to obtain various modal parameters of the double-layer casing, including the modal frequency, vibration shape and damping parameters of the overall structure of the double-layer casing.

[0037] During implementation, all measured points were normalized to the same cylindrical coordinate system. Using the first region as the reference, all other points were converted to frequency response functions (FRFs) of the same coordinate system. These were then imported into the established model to analyze and obtain the modal parameters of the double-layer casing. The FRFs of the measured points in the second, third, and fourth regions remained unchanged in the Z and R directions, with only the angular coordinates converted based on the region. The angular coordinates held the following relationship: angle α2 = α1 + 90° for the measured points in the second region; angle α3 = α1 + 180° for the measured points in the third region; and angle α4 = α1 + 270° for the measured points in the fourth region. For example, if the measured angular coordinate of a point in the second region is 15°, it will be converted to 105°. Similarly, if the measured coordinate of the fourth region is -15°, it will be converted to 255°.

[0038] In specific implementations, the excitation point where the ejector pin connects to the inner layer of the double-layered casing is not on the casing's modal node line. The inner and outer measurement point structures of the double-layered casing are separately modeled, with the number of modeled measurement points being no less than three times the modal order. The Doppler laser vibration measurement system's sampling frequency for the response signal is higher than five times the casing's highest modal frequency.

[0039] This embodiment of the present invention utilizes a double-layer casing modal measurement method based on a Doppler laser vibration measurement system to accurately measure the modal parameters of the inner and outer layers of a double-layer aircraft engine casing. This overcomes the traditional method of measuring only the outer casing modal parameters. This method provides a new measurement method for similar problems in engine development.

[0040] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A double-layer casing modal measurement method based on a Doppler laser vibration measurement system, characterized in that: include: A double-layer casing modal measurement model is established, and a Doppler laser vibration measurement system is used to scan and measure the vibration response signals of each measuring point on the outer layer of the double-layer casing according to the double-layer casing modal measurement model; Using a vibration exciter to generate vibration on the inner layer of the double-layer casing, and obtaining the vibration response signal of each measuring point in the inner layer of the double-layer casing through a reflective galvanometer arranged outside the double-layer casing; The Doppler laser vibration measurement system is used to obtain the excitation response signals of each measuring point in the inner layer of the double-layer casing measured by the reflective galvanometer, and the vibration response signals of each measuring point in the outer layer of the double-layer casing and the excitation response signals of each measuring point in the inner layer of the double-layer casing are processed to obtain the modal parameters of the double-layer casing.

2. The double-layer casing modal measurement method based on the Doppler laser vibration measurement system according to claim 1 is characterized in that: The exciter is fixedly installed at the center position inside the double-layer casing, and the exciter is connected to the inner layer of the double-layer casing through a push rod.

3. The double-layer casing modal measurement method based on the Doppler laser vibration measurement system according to claim 2 is characterized in that: The exciter controls the excitation frequency and amplitude of the inner layer of the casing by adjusting the frequency and amplitude, and transmits the generated excitation to the inner layer of the casing through the ejector rod.

4. The double-layer casing modal measurement method based on the Doppler laser vibration measurement system according to claim 2 is characterized in that: The excitation point where the push rod is connected to the inner layer of the double-layer casing is not on the modal node line of the casing.

5. The double-layer casing modal measurement method based on the Doppler laser vibration measurement system according to claim 1 is characterized in that: Establishing a double-layer casing modal measurement model includes: modeling the inner and outer measuring point structures of the double-layer casing respectively, and the number of modeled measuring points is not less than 3 times the modal order.

6. The double-layer casing modal measurement method based on the Doppler laser vibration measurement system according to claim 1 is characterized in that: The method further includes: dividing the inner layer and the outer layer of the double-layer casing into four measurement areas respectively, measuring 1 / 4 of the measurement points of the casing each time, and completing the measurement work of the four measurement areas of the inner layer of the casing by rotating the reflective galvanometer.

7. The double-layer casing modal measurement method based on the Doppler laser vibration measurement system according to claim 1 is characterized in that: The sampling frequency of the response signal of the Doppler laser vibration measurement system is higher than 5 times the highest modal frequency of the casing.

8. The double-layer casing modal measurement method based on the Doppler laser vibration measurement system according to claim 6, characterized in that: Processing the vibration response signals of each measuring point on the outer layer of the double-layer casing and the excitation response signals of each measuring point on the inner layer of the double-layer casing includes: The vibration response signals of each measuring point on the outer layer of the double-layer casing and the excitation response signals of each measuring point on the inner layer of the double-layer casing are normalized based on the first measurement area, and all response signals are converted into frequency response functions of the same coordinate. The frequency response functions are imported into the modal measurement model of the double-layer casing, and the modal parameters of each order of the double-layer casing are obtained by analysis.

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