Continuous scanning laser doppler vibrometry method for thin-walled enclosure outer surface

Abstract

The present application provides a continuous scanning laser Doppler vibration test method for the outer surface of a thin-walled casing. Firstly, the continuous scanning vibration test is performed on the outer surface of the thin-walled casing, and the vibration time-domain signals of the outer surface of the thin-walled casing are collected. Then, the vibration displacement amplitude of the outer surface of the thin-walled casing is obtained by processing the tested time-domain signals through a band-pass filter and a Hilbert transform. Next, the laser continuous scanning path point coordinate model of the variable cross-section outer surface of the thin-walled casing is established, and the laser continuous scanning path point coordinates of the outer surface of the thin-walled casing at the missing hole are deleted by comparing with the coordinate model of the UG of the thin-walled casing. The vibration displacement amplitude based on the laser continuous scanning path point coordinates is obtained. The continuous scanning modal shape of the planar expansion of the outer surface of the thin-walled casing is obtained. Finally, the three-dimensional continuous scanning modal shape of the outer surface of the thin-walled casing is obtained through a coordinate conversion formula. Compared with the traditional test method for the outer surface of a thin-walled cylinder, the test efficiency is greatly improved, and the range of the test structure is expanded.

Description

Technical Field

[0001] This invention belongs to the field of dynamic continuous scanning non-contact modal testing technology for cylindrical structures such as thin-walled casings, and specifically relates to a continuous scanning laser Doppler vibration testing method for the outer surface of thin-walled casings. Background Technology

[0002] As the heart of an aircraft, the aero-engine provides the power for flight. It is a highly complex and precise aerodynamic and thermodynamic rotating machine, influencing the reliability, safety, and various performance characteristics of the aircraft during flight. In structural design, lightweight, thin-walled cylindrical structures with excellent structural mechanical properties are widely used in various casings of modern aero-engines, effectively improving engine performance. As a load-bearing component of the aero-engine, the cylindrical casing is subjected to vibration loads and random loads such as airflow under various engine operating conditions during aircraft operation. Therefore, its dynamic characteristics are particularly critical to improving the overall engine performance. One modern method for analyzing the dynamic characteristics of casing structures is modal testing and analysis. Modal testing uses modal tests to obtain the structure's dynamic characteristics. Traditional contact sensor modal vibration testing often uses accelerometers or eddy current sensors to collect vibration signals. The mass of these sensors affects the structural rigidity, leading to significant testing errors. Furthermore, due to limitations in the number of sensors and space, the spatial resolution of the measurement points is low, failing to fully reflect the overall vibration and deformation of the casing.

[0003] In this context, scan-by-scan laser Doppler vibration measurement (SLDV) technology has developed rapidly. It eliminates the influence of added mass and enables automated multi-point testing, significantly reducing operational difficulty and improving efficiency. However, for SLDV testing, as the number of measurement points required on the structural surface increases, the modal testing time also increases. Furthermore, SLDV technology inherently cannot solve the problem of spatial information dispersion. Therefore, continuous scanning laser Doppler vibration testing technology has emerged. Based on the characteristics of continuous scanning laser Doppler vibration testing technology, a CSLDV testing method for the inner surface of thin-walled cylindrical structures has been researched abroad. A stepper motor is installed along the axis inside the cylinder, and by controlling the axial stepping of the motor, a laser is continuously and uniformly scanned along the circumferential direction on the inner surface of the structure, thus achieving continuous scanning vibration testing of the entire inner surface of the cylinder. Domestically, a continuous scanning laser Doppler vibration testing method for thin-walled cylindrical structures with smooth surfaces and no pores has been researched.

[0004] Foreign continuous scanning laser Doppler vibration testing techniques for the inner surface of casings are complex, inefficient, and have limited engineering application value. While domestic continuous scanning laser Doppler vibration testing techniques for the outer surface of simple thin-walled cylinders are efficient, they are only applicable to simple cylindrical structures without missing holes. For actual casings with numerous missing holes and variable cross-sections, these techniques cannot handle the vibration modes at these missing holes, nor can they effectively and accurately reflect the true vibration displacement amplitude of the thin-walled casing's outer surface due to the variable cross-section of the casing and the resulting large errors in the coordinate model of the laser continuous scanning path points. This work proposes a continuous scanning laser Doppler testing method for the outer surface of thin-walled casings to overcome the inefficiencies of continuous scanning testing for inner surfaces and the simplistic structure of continuous scanning testing for the outer surface of thin-walled cylinders. This work investigates the processing method for continuous scanning vibration test signals on the outer surface of thin-walled casings, solving the problems of large errors in the coordinate model of the continuous scanning path points caused by the variable cross-section of the thin-walled casing and the handling of vibration modes at missing holes. Furthermore, the continuous scanning laser Doppler vibration test method for thin-walled casings is applicable to most axisymmetric thin-walled casing structures. Summary of the Invention

[0005] To address the challenge of applying traditional continuous scanning laser Doppler vibration testing technology to the outer surface of thin-walled casings, this invention provides a method for continuous scanning laser Doppler vibration testing of the outer surface of thin-walled casings. First, a continuous scanning laser Doppler vibration testing system is used to perform continuous scanning vibration testing on the outer surface of the thin-walled casing and acquire the vibration time-domain signal. Then, the time-domain signal is processed using a bandpass filter and Hilbert transform to obtain the vibration displacement amplitude of the outer surface of the thin-walled casing. Next, based on the working principle of the laser head, a coordinate model of the laser continuous scanning path points on the variable cross-section outer surface of the thin-walled casing is established. By comparing this model with the coordinate model of the UG (Uniformly Gear) thin-walled casing, the coordinates of the laser continuous scanning path points at the missing holes on the outer surface of the thin-walled casing are deleted, along with the vibration displacement amplitude based on the laser continuous scanning path point coordinates. This yields the continuous scanning mode shape of the planar unfolded outer surface of the thin-walled casing. Finally, the three-dimensional continuous scanning mode shape of the outer surface of the thin-walled casing is obtained through coordinate transformation formulas.

[0006] Technical solution:

[0007] A continuous scanning laser Doppler vibration testing method for the outer surface of a thin-walled casing includes the following steps:

[0008] Step (1): Use a laser continuous scanning vibration test system to perform laser continuous scanning on the outer surface of the thin-walled casing, obtain the laser continuous scanning path points, and acquire and obtain the time domain signal of the outer surface of the thin-walled casing based on the laser continuous scanning path points;

[0009] Step (2): Denoise reduction and Hilbert transform are performed on the time-domain signal to obtain the vibration displacement amplitude of the outer surface of the thin-walled casing based on the laser continuous scanning path points;

[0010] Step (3): Complete the mapping relationship conversion between the laser preset path coordinate points and the actual path coordinate points scanned on the variable cross-section surface of the thin-walled casing, and realize the establishment of the laser continuous scanning path coordinate point model on the outer surface of the thin-walled casing;

[0011] Step (4): By referring to the UG model of the thin-walled casing, delete the laser continuous scanning path points at the missing holes on the outer surface of the thin-walled casing, and construct a coordinate model of the laser continuous scanning path points considering the missing holes on the outer surface of the thin-walled casing.

[0012] Step (5): Consider the coordinate model of the laser continuous scanning path points with missing holes on the outer surface of the thin-walled casing, delete the vibration displacement amplitude at the missing holes on the outer surface of the thin-walled casing, and construct the planar unfolded mode shape of the thin-walled casing by combining the laser continuous scanning path with missing holes on the outer surface of the thin-walled casing.

[0013] Step (6): Using the coordinate transformation formula, the transformation from the planar unfolded mode shape of the thin-walled casing to the three-dimensional mode shape is completed, realizing the continuous scanning laser Doppler vibration test of the outer surface of the thin-walled casing.

[0014] Preferably, the implementation process of step (1) is as follows:

[0015] Step (11): Set up a laser continuous scanning vibration testing system, place the thin-walled casing on the laser continuous scanning vibration testing system, start the continuous scanning laser Doppler vibration test on the outer surface of the thin-walled casing, and collect the laser test signal on the outer surface of the thin-walled casing:

[0016] v(x,t)=V(x)cos(w b t+θ)

[0017] v(x,t) represents the vibration velocity at coordinate (x,0,0) at time t, V(x) is the maximum amplitude at coordinate (x,0,0), and w b Let θ be the frequency of the sinusoidal excitation force, and θ be the phase angle of the vibration at coordinate (x,0,0).

[0018] Step (12): Convert the laser test signal into a time-domain signal of the thin-walled casing outer surface based on the continuous laser scanning path points:

[0019] v(x,t)=V{g(t)}cos(w b t)cosθ-V{g(t)}sin(w b t)sinθ

[0020] V{g(t)}cos(wb t) represents the real vibration displacement amplitude of the outer surface of the thin-walled casing, -V{g(t)}sin(w) b t) represents the imaginary vibration displacement amplitude of the outer surface of the thin-walled casing; g(t) represents the laser continuous scanning path point function of the outer surface of the thin-walled casing.

[0021] Preferably, the implementation process of step (2) is as follows:

[0022] Step (21): Convert the time-domain signal into a frequency-domain signal using Fast Fourier Transform (FFT):

[0023] v(w) = FFT(v(t))

[0024] Step (22): Pass the frequency domain signal v(w) through bandpass filter B s (w), filtering out invalid frequencies, yields the denoised frequency domain signal V(w), where the bandpass filter B s (w) is:

[0025]

[0026] Then the frequency domain signal V(w) is:

[0027] V(w)=v(w)·B s (w)

[0028] Step (23): Perform an inverse fast Fourier transform (IFFT) on the frequency domain signal V(w) to obtain the denoised time domain signal V(t):

[0029] V(t)=IFFT(V(w))=Φ{g(t)}cosw b t+Ψ{g(t)}sinw b t

[0030] In the formula: Φ{g(t)}=V{g(t)}cosθ, Ψ{g(t)}=-V{g(t)}sinθ;

[0031] Step (24): Perform a Hilbert transform on the time-domain signal V(t), which is expressed as follows:

[0032]

[0033] In the formula, V(τ) is the time-domain signal. The time-domain signal after Hilbert transform;

[0034] (25): Construct a system of equations from the functional relationships in steps (23) and (24), solve the system of equations, and obtain the vibration displacement amplitude of the outer surface of the thin-walled casing based on the laser continuous scanning path points:

[0035]

[0036] Preferably, the implementation process of step (3) is as follows:

[0037] Step (31): Based on the working principle of the laser head in the laser continuous scanning vibration testing system, the laser tester includes two motors and an electron microscope. The scanning area of ​​the laser head is a plane area perpendicular to the laser head, which is expressed as follows:

[0038] α1=Sθ1

[0039] α2=Sθ2

[0040] In the formula, α1 and α2 are the voltages received by the two motors, θ1 and θ2 are the rotation degrees of the electron microscope, and S is the rotation coefficient of the electron microscope.

[0041] Step (32): Based on the working principle of the laser head and the characteristics of the variable cross-section surface of the thin-walled casing, construct the mapping function between the preset laser path coordinates and the actual path points of the variable cross-section of the thin-walled casing. By solving the mapping function, obtain the coordinate model of the actual continuous laser scanning path points on the outer surface of the thin-walled casing. The characteristics of the variable cross-section surface of the thin-walled casing are obtained through the UG model of the thin-walled casing.

[0042] Preferably, in step (4): the coordinate model of the laser continuous scanning path points on the outer surface of the thin-walled casing obtained in step (32) is compared with the UG model of the thin-walled casing in the same coordinate system, and the laser continuous scanning path points at the missing holes on the outer surface of the thin-walled casing are deleted to obtain the coordinate model of the laser continuous scanning path points considering the missing holes on the outer surface of the thin-walled casing.

[0043] Preferably, the implementation process of step (5) is as follows:

[0044] (51): By comparing the coordinate model of the laser continuous scanning path point considering the missing hole on the outer surface of the thin-walled casing, the vibration displacement amplitude at the coordinate of the missing hole on the outer surface of the thin-walled casing based on the laser continuous scanning path point is deleted, and the vibration displacement amplitude based on the laser continuous scanning path point of the missing hole on the outer surface of the thin-walled casing is obtained.

[0045] (52): The vibration displacement amplitude based on the laser continuous scanning path point with the missing hole on the outer surface of the thin-walled casing is combined with the corresponding laser continuous scanning path coordinate point to obtain the working deformation of the thin-walled casing plane unfolding.

[0046] Preferably, in step (6): the transformation from the planar unfolded mode shape of the thin-walled casing to the three-dimensional mode shape is completed using the coordinate transformation formula:

[0047]

[0048] and V represents the x and y mode vectors of the three-dimensional mode shape of the thin-walled casing after conversion. R,i,j Let I represent the axial mode vector of the outer surface of the vertical thin-walled casing, and let I represent the casing plane being divided into a total of I parts on average, i = 1, 2, ..., I.

[0049] Beneficial effects:

[0050] This invention relates to a continuous scanning laser Doppler vibration testing method based on the outer surface of a thin-walled casing. It successfully completed continuous scanning vibration testing of a variable cross-section thin-walled casing structure with numerous surface defects, obtaining abundant dynamic data and accurately demonstrating the vibration characteristics of the thin-walled casing structure. Compared with existing continuous scanning laser Doppler vibration testing methods for the outer surface of thin-walled cylinders, this invention offers the following advantages:

[0051] (1) High efficiency and wide applicability;

[0052] The continuous scanning laser Doppler vibration testing method for the outer surface of thin-walled casings can quickly and efficiently complete the continuous scanning vibration test of the outer surface of thin-walled casings, obtain the first five mode shapes of the thin-walled casing, and can be applied to axisymmetric thin-walled casing structures with different characteristics. Compared with the traditional thin-walled cylindrical outer surface testing method, it greatly improves the testing efficiency and expands the range of test structures.

[0053] (2) It has broad engineering application value;

[0054] The continuous scanning laser Doppler vibration testing method for the outer surface of thin-walled casing proposed in this invention can test different axisymmetric thin-walled casing structures, providing rich and accurate vibration data for various axisymmetric thin-walled casing structures. It can be widely used in the fields of dynamic modeling and fault diagnosis of axisymmetric thin-walled casings, and has broad engineering application value.

[0055] In summary, this invention provides a foundation for the study of the dynamic vibration characteristics of various axisymmetric thin-walled casing structures in engineering. Attached Figure Description

[0056] Figure 1 This is a flowchart of the present invention;

[0057] Figure 2 This is a diagram of the continuous scanning laser Doppler vibration testing system of the present invention.

[0058] Figure 3 This is a diagram of the experimental apparatus for an example of the present invention;

[0059] Figure 4 This is a schematic diagram illustrating the principle of continuous scanning of the outer surface of the structure in this invention example.

[0060] Figure 5 This is a time-domain diagram of a certain order vibration signal of the structure in this invention example;

[0061] Figure 6 This is a frequency domain diagram of a certain order vibration signal of the structure in this invention example;

[0062] Figure 7 This is a time-domain diagram of a certain order vibration signal of the structure in this invention after noise reduction;

[0063] Figure 8 This is a continuous scanning vibration displacement amplitude diagram of the outer surface of the structure in this invention example;

[0064] Figure 9 This is a schematic diagram illustrating the working principle of the laser head of the laser testing instrument in this invention.

[0065] Figure 10 This is a diagram showing the mapping relationship between the outer surface of the variable cross-section structure of the present invention and the laser scanning path;

[0066] Figure 11 This is a coordinate model diagram of the actual laser continuous scanning path points on the outer surface of the structure in this invention example;

[0067] Figure 12 This is a comparison diagram of the coordinate model of the continuous scanning path points on the outer surface of the structure in this invention example and the UG coordinate model of the structure;

[0068] Figure 13 This is a three-dimensional coordinate model diagram of the continuous scanning path points of the missing holes on the outer surface of the structure in this invention example;

[0069] Figure 14 This is a planar unfolded coordinate model of the continuous scanning path points of the missing holes on the outer surface of the structure in this invention example.

[0070] Figure 15 This is a planar unfolded mode shape diagram of the outer surface of the structure in this invention example;

[0071] Figure 16 This is a three-dimensional modal shape diagram of the outer surface of the structure in this invention example; Detailed Implementation

[0072] The invention will be further illustrated below with reference to examples.

[0073] This invention discloses a method for continuous scanning laser Doppler vibration testing of the outer surface of a thin-walled casing. The method is characterized by employing a continuous scanning laser Doppler vibration testing system to perform continuous scanning vibration testing on the outer surface of the thin-walled casing and acquiring the vibration time-domain signal of the outer surface. Then, the time-domain signal is processed using a bandpass filter and Hilbert transform to obtain the vibration displacement amplitude of the outer surface. Based on the working principle of the laser head, a coordinate model of the laser continuous scanning path points on the variable cross-section outer surface of the thin-walled casing is established. By comparing this model with the coordinate model of the thin-walled casing (UG), the coordinates of the laser continuous scanning path points at the missing holes on the outer surface of the thin-walled casing are deleted, along with the vibration displacement amplitude based on the laser continuous scanning path point coordinates. This yields the continuous scanning mode shape of the outer surface of the thin-walled casing as unfolded in plane. Finally, the three-dimensional continuous scanning mode shape of the outer surface of the thin-walled casing is obtained through coordinate transformation formulas.

[0074] The present invention will be further described below with reference to embodiments and accompanying drawings. Specific implementation steps are as follows:

[0075] The present invention will now be analyzed using the continuous scanning laser Doppler modal vibration test method on the outer surface of the turbojet combustion chamber casing.

[0076] The specific steps of step (1) are as follows:

[0077] (11): Build a laser continuous scanning vibration testing system (e.g. Figure 2 The thin-walled casing is placed on a rotating platform on the test system (e.g., Figure 3 The laser vibrometer and rotating platform are controlled to perform continuous scanning vibration testing on the outer surface of the thin-walled casing in the form of a square wave (e.g., ...). Figure 4 Simultaneously, laser test signals are acquired from the surface of the thin-walled casing.

[0078] v(x,t)=V(x)cos(w b t+θ)

[0079] v(x,t) represents the vibration velocity at coordinate (x,0,0) at time t, w b Let V(x) be the frequency of the sinusoidal excitation force, V(x) be the maximum amplitude at that point, and θ be the phase angle of the vibration at that point.

[0080] (12): Based on the principle of continuous scanning laser output signal on the surface of thin-walled casing, the continuous scanning path point of the laser is combined with the output signal to obtain the time-domain signal defined on the continuous scanning path point of the laser on the surface of thin-walled casing that varies with time (e.g., ...). Figure 5 ):

[0081] v(x,t)=V{g(t)}cos(w b t)cosθ-V{g(t)}sin(w bt)sinθ

[0082] V{g(t)}cos(w b t) and -V{g(t)}sin(w b t) represent the real and imaginary vibration displacement amplitudes of the corresponding thin-walled casing outer surface, respectively, and g(t) represents the laser continuous scanning path point function of the thin-walled casing surface.

[0083] The specific steps of step (2) are as follows:

[0084] (21): The continuous scanning time-domain signal of the outer surface of the thin-walled casing is converted into a frequency-domain signal (e.g., using Fast Fourier Transform (FFT)). Figure 6 ):

[0085] v(w) = FFT(v(t))

[0086] (22): The continuous scanning frequency domain signal v(w) of the outer surface of the thin-walled casing is passed through a bandpass filter B. s (w), filtering out invalid frequencies, yields the noise-reduced frequency domain signal V(w):

[0087]

[0088] V(w)=v(w)·B s (w)

[0089] (23): Perform a fast inverse Fourier transform (IFFT) on the denoised frequency domain signal to obtain the denoised time domain signal (e.g., Figure 7 ):

[0090] V(t)=IFFT(V(w))=Φ{g(t)}cosw b t+Ψ{g(t)}sinw b t

[0091] In the formula, Φ{g(t)}=V{g(t)}cosθ, Ψ{g(t)}=-V{g(t)}sinθ, and V(t) is the continuous scanning time-domain signal of the outer surface of the thin-walled casing after noise reduction.

[0092] (24): The Hilbert transform of the continuous scanning time-domain signal V(t) on the outer surface of the thin-walled casing is expressed as follows:

[0093]

[0094] In the formula, V(τ) is the time-domain signal function. This is the time-domain signal after Hilbert transform.

[0095] (25) Construct a system of equations from the functional relationships in steps (23) and (24), solve the system of equations, and obtain the vibration displacement amplitude that can represent the working deformation of the outer surface of the thin-walled casing:

[0096]

[0097] In the formula, Φ{g(t)} represents the vibration displacement amplitude based on the continuous scanning path points on the outer surface of the thin-walled casing (e.g., ...). Figure 8 ).

[0098] The specific steps of step (3) are as follows:

[0099] (31): According to the working principle of the laser head in the laser testing instrument, its scanning area is a plane area perpendicular to the laser head (e.g., Figure 9 ), and its form of expression is:

[0100] α1=Sθ1

[0101] α2=Sθ2

[0102] In the formula, α1 and α2 are the voltages received by the two motors, θ1 and θ2 are the rotation degrees of the electron microscope controlled by the motors, and S is the rotation coefficient of the electron microscope itself.

[0103] (32): Based on the working principle of the laser head and the characteristics of the variable cross-section surface of the thin-walled casing, a mapping function is constructed between the preset scanning path point of the laser and the actual path point scanned to the variable cross-section of the thin-walled casing (e.g., Figure 10 By solving the mapping function, the coordinate model of the actual laser continuous scanning path points of the thin-walled casing with variable cross-section is obtained (e.g., Figure 11 ).

[0104] Based on the working principle of the laser head, the test coordinates of the laser are inconsistent with the actual coordinates of the casing surface. The surface vibration mode information cannot correspond to the actual coordinate points. As a result, the laser scanning path test model of the casing cannot be accurately established and cannot correspond to the vibration mode of the scanning points on the casing surface, causing an overall vibration mode deviation.

[0105] The deflection angle of the scanning lens in the laser head is controlled by the input voltage, and the range of the test coordinates is controlled by the test distance between the laser and the structure. During laser vibration testing, a program written in LabVIEW outputs voltage to the Y-axis motor to control the deflection angle in the Y direction, ensuring it precisely sweeps across the range from the upper to the lower boundary of the housing. Since the actual outer surface of the housing is curved, a mapping relationship is formed between the laser's set scanning range (ab) in the Y direction and the range (ac) that is swept across the housing surface.

[0106] After the laser scans the entire outer surface of the casing, the exported coordinate data is within the range (ab). This data cannot reflect the actual height of points on the casing surface or the corresponding radius information, resulting in an inaccurate test model of the actual casing. To obtain a test model of the actual casing's scanning path, the exported coordinates within the range (ab) need to be mapped to the range (ac) to obtain information about the scanning points on the casing surface, thereby establishing an accurate test model. By placing the actual casing and the laser head in the same coordinate system, the fitting equation f for the casing's arc is first obtained using the UG model coordinates of the casing. x Given the laser deflection angle σ y Given a test distance (Aa), then based on point A of the laser head, construct a system of linear equations y within the range of (ab). x ,f x With y x The intersection point n corresponds to the point within the range (ab) that is mapped onto (ac). The test model constructed using the points within the range (ac) can accurately reflect the complete test information of the outer surface of the casing from the laser scan.

[0107] The specific steps of step (4) are as follows:

[0108] (41): The coordinate model of the laser continuous scanning path points of the thin-walled casing with variable cross-section obtained in step (32) (e.g.) Figure 11 ) and the UG coordinate model of the thin-walled casing (e.g. Figure 12 By comparing the data in the same coordinate system and deleting the laser continuous scanning path points at the missing holes on the outer surface of the thin-walled casing, a three-dimensional coordinate model of the laser continuous scanning path points at the missing holes on the outer surface of the thin-walled casing is obtained (e.g., ...). Figure 13 ), and obtain the planar unfolded coordinate model of the laser continuous scanning path points of the missing holes on the outer surface of the thin-walled casing through coordinate transformation (e.g. Figure 14 ).

[0109] The specific steps of step (5) are as follows:

[0110] (51): By comparing the coordinate model of the laser continuous scanning path point of the missing hole on the outer surface of the thin-walled casing with the laser continuous scanning path point, the vibration displacement amplitude at the coordinate of the missing hole on the outer surface of the thin-walled casing based on the laser continuous scanning path point is deleted, and the vibration displacement amplitude based on the laser continuous scanning path point of the missing hole on the outer surface of the thin-walled casing is obtained.

[0111] (52): By combining the vibration displacement amplitude of the laser continuous scanning path point based on the missing hole on the outer surface of the thin-walled casing with its corresponding laser continuous scanning path coordinate point, the working deformation of the thin-walled casing planar unfolding is obtained (e.g. Figure 15 ).

[0112] The specific steps of step (6) are as follows:

[0113] (61) The transformation from planar unfolding deformation to three-dimensional working deformation of the thin-walled casing is completed using coordinate transformation formulas (e.g., Figure 16 ):

[0114]

[0115] and V represents the x and y mode vectors of the three-dimensional working deformation of the thin-walled casing after conversion. R,i,j This represents the axial mode vector of the vertical thin-walled casing surface.

[0116] The above description is merely a specific embodiment of the present invention, and further details the purpose, technical solution, and beneficial effects of the present invention. Finally, it should be noted that the above description is only a preferred embodiment of the present invention and does not impose any limitations on the present invention. For those skilled in the art, any non-innovative modifications, variations, and alterations made to the technical solution of the present invention based on the above content without departing from the scope of the present invention should also be considered within the protection scope of the present invention.

Claims

1. A method for continuous scanning laser Doppler vibration testing of the outer surface of a thin-walled casing, characterized in that, Includes the following steps: Step (1): Use a laser continuous scanning vibration test system to perform laser continuous scanning on the outer surface of the thin-walled casing, obtain the laser continuous scanning path points, and acquire and obtain the time domain signal of the outer surface of the thin-walled casing based on the laser continuous scanning path points; Step (2): Denoise the time-domain signal and perform Hilbert transform to obtain the vibration displacement amplitude of the outer surface of the thin-walled casing based on the laser continuous scanning path points; Step (3): Complete the mapping relationship conversion between the laser preset path coordinate points and the actual path coordinate points scanned on the variable cross-section surface of the thin-walled casing, and realize the establishment of the laser continuous scanning path coordinate point model on the outer surface of the thin-walled casing; Step (4): By referring to the UG model of the thin-walled casing, delete the laser continuous scanning path points at the missing holes on the outer surface of the thin-walled casing, and construct a coordinate model of the laser continuous scanning path points considering the missing holes on the outer surface of the thin-walled casing. Step (5): Consider the coordinate model of the laser continuous scanning path points with missing holes on the outer surface of the thin-walled casing, delete the vibration displacement amplitude at the missing holes on the outer surface of the thin-walled casing, and construct the planar unfolded mode shape of the thin-walled casing by combining the laser continuous scanning path with missing holes on the outer surface of the thin-walled casing. Step (6): Using the coordinate transformation formula, the transformation from the planar unfolded mode shape of the thin-walled casing to the three-dimensional mode shape is completed, realizing the continuous scanning laser Doppler vibration test of the outer surface of the thin-walled casing.

2. The continuous scanning laser Doppler vibration testing method for the outer surface of a thin-walled casing as described in claim 1, characterized in that, The implementation process of step (1) is as follows: Step (11): Set up a laser continuous scanning vibration testing system, place the thin-walled casing on the laser continuous scanning vibration testing system, start the continuous scanning laser Doppler vibration test on the outer surface of the thin-walled casing, and collect the laser test signal on the outer surface of the thin-walled casing: ； Representative at Time coordinates Vibration velocity at that location, coordinates The maximum amplitude at that point, The frequency of the sinusoidal excitation force is... coordinates The phase angle of the vibration at that point; Step (12): Convert the laser test signal into a time-domain signal of the thin-walled casing outer surface based on the continuous laser scanning path points: ； This represents the amplitude of the real vibration displacement on the outer surface of the thin-walled casing. This represents the amplitude of the imaginary vibration displacement on the outer surface of the thin-walled casing. This represents the laser continuous scanning path point function on the outer surface of the thin-walled casing.

3. The continuous scanning laser Doppler vibration testing method for the outer surface of a thin-walled casing as described in claim 2, characterized in that, The implementation process of step (2) is as follows: Step (21): Convert the time-domain signal into a frequency-domain signal using Fast Fourier Transform (FFT): ； Step (22): Convert the frequency domain signal Through bandpass filter After filtering out invalid frequencies, the denoised frequency domain signal is obtained. Among them, bandpass filter for: ； Then there is a frequency domain signal for: ； Step (23): For the frequency domain signal Perform an inverse fast Fourier transform (IFFT) to obtain the denoised time-domain signal. : ； In the formula: , ; Step (24): For the time domain signal The Hilbert transform is represented as follows: ； In the formula For time-domain signals, The signal is in the time domain after Hilbert transform; (25): Construct a system of equations from the functional relationships in steps (23) and (24), solve the system of equations, and obtain the vibration displacement amplitude of the outer surface of the thin-walled casing based on the laser continuous scanning path points: 。 4. The continuous scanning laser Doppler vibration testing method for the outer surface of a thin-walled casing as described in claim 1, characterized in that, The implementation process of step (3) is as follows: Step (31): Based on the working principle of the laser head in the laser continuous scanning vibration testing system, the laser tester includes two motors and an electron microscope. The scanning area of ​​the laser head is a plane area perpendicular to the laser head, which is expressed as follows: ； In the formula and It is the voltage received by the two motors. and It is the rotation of the electron microscope. It is the rotation factor of the electron microscope; Step (32): Based on the working principle of the laser head and the characteristics of the variable cross-section surface of the thin-walled casing, construct the mapping function between the preset laser path coordinates and the actual path points of the variable cross-section of the thin-walled casing. By solving the mapping function, obtain the coordinate model of the actual continuous laser scanning path points on the outer surface of the thin-walled casing. The characteristics of the variable cross-section surface of the thin-walled casing are obtained through the UG model of the thin-walled casing.

5. The continuous scanning laser Doppler vibration testing method for the outer surface of a thin-walled casing as described in claim 4, characterized in that, In step (4): the coordinate model of the laser continuous scanning path points on the outer surface of the thin-walled casing obtained in step (32) is compared with the UG model of the thin-walled casing in the same coordinate system. The laser continuous scanning path points at the missing holes on the outer surface of the thin-walled casing are deleted to obtain the coordinate model of the laser continuous scanning path points considering the missing holes on the outer surface of the thin-walled casing.

6. The continuous scanning laser Doppler vibration testing method for the outer surface of a thin-walled casing as described in claim 5, characterized in that, The implementation process of step (5) is as follows: (51): By comparing the coordinate model of the laser continuous scanning path point considering the missing hole on the outer surface of the thin-walled casing, the vibration displacement amplitude at the coordinate of the missing hole on the outer surface of the thin-walled casing based on the laser continuous scanning path point is deleted, and the vibration displacement amplitude based on the laser continuous scanning path point of the missing hole on the outer surface of the thin-walled casing is obtained. (52): The vibration displacement amplitude of the laser continuous scanning path point based on the missing hole on the outer surface of the thin-walled casing is combined with the corresponding laser continuous scanning path coordinate point to obtain the working deformation of the thin-walled casing plane unfolding.

7. The continuous scanning laser Doppler vibration testing method for the outer surface of a thin-walled casing as described in claim 6, characterized in that, In step (6): the transformation from planar unfolded mode shape of the thin-walled casing to three-dimensional mode shape is completed using the coordinate transformation formula: ； and These represent the x and y mode vectors of the three-dimensional modal vibration of the thin-walled casing after conversion. Let I represent the axial mode vector of the outer surface of the vertical thin-walled casing, and let I represent the casing plane being divided into a total of I equal parts, i=1,2,...,I.

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