A method for obtaining modal parameters

Abstract

The application discloses a modal parameter obtaining method, comprising the following steps: determining an initial resonance frequency and an initial time for a same resonance point according to a response diagram of an obtained vibration test signal, wherein the response diagram is a relationship diagram between time and frequency of the vibration test signal; determining a data segment corresponding to a preset time period according to the initial time and the preset time period, wherein the preset time period contains the initial time; obtaining a curve for representing time-varying characteristics of vibration based on the data segment, wherein the curve for representing time-varying characteristics of vibration is composed of energy parameters and time parameters corresponding to each small data segment; reading a rotating speed signal in an arbitrary time period, and obtaining modal parameters according to the curve for representing time-varying characteristics of vibration. The application can obtain higher identification precision when identifying modal parameters of a small-damping-ratio blade.

Description

Technical Field

[0001] This invention relates to the field of engine technology, and in particular to a method and apparatus for obtaining modal parameters. Background Technology

[0002] Modal frequency and modal damping are two important modal parameters of engine blades, and accurate acquisition of these parameters is crucial for blade vibration design. The experimental modal parameters of blades under operating conditions are mainly obtained through dynamic stress testing. Typical blades have relatively low damping (damping ratio usually below 0.5%). When engine speed changes, the blade exhibits a large resonance peak response within a short period, which decays rapidly with increasing speed, making it difficult to accurately obtain a smooth frequency response curve and resulting in significant errors in modal parameter identification.

[0003] In engineering, the test modal parameters of rotating blades are generally identified using the frequency domain method. The key to frequency domain identification is the quality of the frequency response function. To obtain high accuracy in modal parameter identification, the frequency response function should have high frequency resolution and high amplitude accuracy. Frequency domain identification mainly uses Fourier transform to obtain the vibration response at specific frequency components at different rotational speeds, revealing the variation of the response with frequency, and further identifying the blade's modal parameters based on this. Transforming from the frequency domain to the time domain requires selecting test data over a period of time for analysis. Since time resolution and frequency resolution are inversely proportional, a longer time period is needed to obtain higher frequency resolution. However, blades resonate and decay within a very short timeframe. When analyzing data over a longer period, the vibration amplitude will be averaged, resulting in a lower amplitude value that cannot accurately reflect the variation of amplitude with frequency. Furthermore, for truncated non-integer period signals, leakage occurs during Fourier transform. Although windowing can reduce leakage to some extent, it is unavoidable. Therefore, errors will occur during the transformation from the time domain to the frequency domain.

[0004] Common methods for calculating modal damping ratios include the logarithmic decay method and the half-power bandwidth method. The logarithmic decay method is a time-domain analysis method that can be used to identify modal damping ratios under free vibration conditions, but it requires only the first-order mode to vibrate and cannot be used to identify modal damping in the resonant state of rotating blades. The half-power bandwidth method calculates modal damping by analyzing the amplitude variation with frequency, and can be used for both frequency and time domain identification. However, due to the difficulty in simultaneously meeting high frequency and time resolution requirements, its accuracy is generally low when used for frequency domain modal parameter identification in the resonant state of small-damped blades. Since dynamic stress test data is obtained by sampling discrete points, the time-response curve obtained from the test differs from the ideal state, making it difficult to accurately read the vibration amplitude and frequency information directly from the time-domain graph. Furthermore, actual blade vibration may have multiple frequency components, such as… Figure 1As shown. Therefore, the half-power bandwidth method is also difficult to use for conventional time-domain modal damping identification.

[0005] In summary, existing technologies mainly suffer from the following problems: 1. Conventional frequency domain analysis methods struggle to simultaneously achieve high time and time-frequency resolution, resulting in low-quality frequency response curves and low accuracy in modal parameter identification. This is particularly true for blades with low modal damping, where modal parameters under resonant conditions during engine acceleration and deceleration are difficult to accurately identify; 2. Conventional frequency domain analysis methods are prone to leakage when transforming signals from the time domain to the frequency domain, affecting analysis accuracy; 3. Directly reading amplitude and frequency signals from the time domain plot introduces significant errors. Summary of the Invention

[0006] The purpose of this invention is to propose a method for obtaining test modal parameters, which can achieve high identification accuracy when identifying modal parameters of blades with small damping ratios.

[0007] To achieve the above objectives, the present invention provides a method for obtaining modal parameters, comprising:

[0008] Based on the response diagram of the obtained vibration test signal, the initial resonance frequency and initial time for the same resonance point are determined. The response diagram is a graph showing the relationship between time and frequency of the vibration test signal.

[0009] Based on the initial time and the preset time period, a data segment corresponding to the preset time period is determined, wherein the preset time period includes the initial time.

[0010] Based on the data segment, a curve representing the time-varying characteristics of vibration is obtained, which is composed of energy parameters and time parameters corresponding to each small data segment.

[0011] Read the rotational speed signal over any time period and obtain the modal parameters based on the curve representing the time-varying characteristics of the vibration.

[0012] Optionally, the above methods also include:

[0013] Obtain vibration test signals;

[0014] The vibration test signal is processed by short-time Fourier transform to obtain the response diagram of the vibration test signal.

[0015] Optionally, the vibration response values ​​at the beginning and end of the preset time period are both lower than the vibration response value at the initial time.

[0016] Optionally, based on the data segment, obtaining the curve representing the time-varying characteristics of the vibration includes:

[0017] The data in the data segment is subjected to signal filtering processing to obtain filtered data;

[0018] The filtered data is segmented to obtain a curve representing the time-varying characteristics of the vibration.

[0019] Optionally, the step of reading the rotational speed signal at any time interval and obtaining the modal parameters based on the curve representing the time-varying characteristics of the vibration includes:

[0020] Read the rotation speed signal at any time interval and obtain the curve showing the relationship between the rotation speed signal and time;

[0021] Modal parameters are obtained based on the curve representing the time-varying characteristics of vibration and the curve showing the relationship between the rotational speed signal and time.

[0022] Optionally, obtaining the modal parameters based on the curve representing the time-varying characteristics of the vibration and the curve showing the relationship between the rotational speed signal and time includes:

[0023] Based on the relationship curve between the rotation speed signal and time, the excitation order corresponding to resonance is obtained.

[0024] Based on the curve representing the time-varying characteristics of vibration and the curve showing the relationship between the rotational speed signal and time, the acceleration / deceleration rate of the rotational speed is obtained;

[0025] Modal parameters are obtained based on the rotational speed acceleration / deceleration rate, the excitation order corresponding to the resonance, the curve representing the time-varying characteristics of the vibration, and the curve showing the relationship between the rotational speed signal and time.

[0026] The present invention also provides an apparatus for obtaining modal parameters, comprising:

[0027] The initial resonance frequency and initial time determination unit is used to determine the initial resonance frequency and initial time for the same resonance point based on the response diagram of the obtained vibration test signal, wherein the response diagram is a graph showing the relationship between time and frequency of the vibration test signal.

[0028] A time period determination unit is used to determine a data segment corresponding to the preset time period based on the initial time and the preset time period, wherein the preset time period includes the initial time.

[0029] A curve acquisition unit representing the time-varying characteristics of vibration is used to obtain a curve representing the time-varying characteristics of vibration based on the data segment. The curve representing the time-varying characteristics of vibration is composed of energy parameters and time parameters corresponding to each small data segment.

[0030] The modal parameter acquisition unit is used to read the rotational speed signal at any time and obtain the modal parameters according to the curve representing the time-varying characteristics of the vibration.

[0031] Optionally, the apparatus further includes: a response map determination unit;

[0032] The response map determination unit is used to obtain the vibration test signal; and to perform short-time Fourier transform processing on the vibration test signal to obtain the response map of the vibration test signal.

[0033] Optionally, the vibration response values ​​at the beginning and end of the preset time period are both lower than the vibration response value at the initial time.

[0034] Optionally, based on the data segment, obtaining the curve representing the time-varying characteristics of the vibration includes:

[0035] The data in the data segment is subjected to signal filtering processing to obtain filtered data;

[0036] The filtered data is segmented to obtain a curve representing the time-varying characteristics of the vibration.

[0037] Optionally, the step of reading the rotational speed signal at any time interval and obtaining the modal parameters based on the curve representing the time-varying characteristics of the vibration includes:

[0038] Read the rotation speed signal at any time interval and obtain the curve showing the relationship between the rotation speed signal and time;

[0039] Modal parameters are obtained based on the curve representing the time-varying characteristics of vibration and the curve showing the relationship between the rotational speed signal and time.

[0040] Optionally, obtaining the modal parameters based on the curve representing the time-varying characteristics of the vibration and the curve showing the relationship between the rotational speed signal and time includes:

[0041] Based on the relationship curve between the rotation speed signal and time, the excitation order corresponding to resonance is obtained.

[0042] Based on the curve representing the time-varying characteristics of vibration and the curve showing the relationship between the rotational speed signal and time, the acceleration / deceleration rate of the rotational speed is obtained;

[0043] Modal parameters are obtained based on the rotational speed acceleration / deceleration rate, the excitation order corresponding to the resonance, the curve representing the time-varying characteristics of the vibration, and the curve showing the relationship between the rotational speed signal and time.

[0044] The technical effects and advantages of this invention are as follows:

[0045] This invention provides a method for obtaining modal parameters, comprising: determining the initial resonant frequency and initial time for the same resonant point based on the response diagram of an obtained vibration test signal, wherein the response diagram is a graph showing the relationship between time and frequency of the vibration test signal; determining a data segment corresponding to the preset time period based on the initial time and the preset time period, wherein the preset time period includes the initial time; obtaining a curve representing the time-varying characteristics of vibration based on the data segment, wherein the curve representing the time-varying characteristics of vibration is composed of energy parameters and time parameters corresponding to each small data segment; reading the rotational speed signal within any time period, and obtaining the modal parameters based on the curve representing the time-varying characteristics of vibration. This invention can achieve high recognition accuracy when identifying modal parameters of blades with small damping ratios.

[0046] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention can be realized and obtained by means of the structures pointed out in the description and the drawings. Attached Figure Description

[0047] Figure 1 A schematic diagram of the time-response curves obtained under ideal and measured conditions;

[0048] Figure 2 A flowchart of the method for obtaining modal parameters;

[0049] Figure 3 This is a schematic diagram of the RT curve;

[0050] Figure 4 To select RT curves for different time length segments dT;

[0051] Figure 5 This is a flowchart of the device for obtaining modal parameters. Detailed Implementation

[0052] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0053] To address the shortcomings of existing technologies, this invention discloses a method for obtaining modal parameters, comprising: determining the initial resonant frequency and initial time for the same resonant point based on the response graph of an obtained vibration test signal, wherein the response graph is a graph showing the relationship between time and frequency of the vibration test signal; determining a data segment corresponding to the preset time period based on the initial time and the preset time period, wherein the preset time period includes the initial time; obtaining a curve representing the time-varying characteristics of vibration based on the data segment, wherein the curve representing the time-varying characteristics of vibration is composed of energy parameters and time parameters corresponding to each small data segment; reading the rotational speed signal within any time period, and obtaining the modal parameters based on the curve representing the time-varying characteristics of vibration. This invention can achieve high recognition accuracy when identifying modal parameters of blades with small damping ratios.

[0054] To facilitate a better understanding of this invention, the method for obtaining modal parameters will be described in detail below, such as... Figure 2 As shown:

[0055] (1) Resonance identification stage

[0056] A short-time Fourier transform is performed on the vibration test signal to obtain a time-frequency-response contour plot. The resonance points in the contour plot are analyzed to preliminarily determine the initial resonance frequency f. st The initial time T corresponding to the resonance point st The resonant frequency may have a large error and is only used as an input parameter in step (2), not as the actual modal frequency parameter of this method.

[0057] (2) Data segment selection stage

[0058] Select a data segment of a certain duration (preset time period) from the original test data, with the start time of the data being T. st -0.5ΔT, the data ends at time T. st +0.5ΔT, where ΔT is the time length of the data segment. The vibration response magnitudes analyzed in step (1) at the start and end times of the data segment must be significantly lower than T. st It is recommended that this value not exceed 10% of the vibration response magnitude at time T0.

[0059] (3) Signal filtering stage

[0060] Since a signal may contain multiple frequency components, this application employs a bandpass filter to filter the selected data segment. The center frequency of the bandpass filter's passband is f. st The filtered signal should appear as a sine wave in the time domain.

[0061] (4) Signal time-varying feature extraction stage

[0062] For the filtered sampled data in step (3), starting from the first sampled data, divide it into m segments, each segment having a data length of n and a corresponding time length of dT = n / fs. Discard the data after the m·nth sampled data. m is the largest integer satisfying the following formula:

[0063]

[0064] Among them, f s The sampling frequency.

[0065] Introducing the energy parameter R i Calculate for each small segment of data, R i The definition is as follows:

[0066]

[0067] in: x i,j The corresponding time is T i,j .

[0068] Calculate the time parameter T for each segment. i T i The definition is as follows:

[0069]

[0070] R i and T i By combining them sequentially, we obtain the RT function, where:

[0071] R = [R1, R2, ..., R] m-1 ,R m ]

[0072] T = [T1,T2,…,T] m-1 ,T m ]

[0073] The RT curves above can be used to represent the time-varying characteristics of vibration, and to express the amplitude-time variation characteristics of vibration.

[0074] (5) Speed ​​information acquisition stage

[0075] Read the engine speed signal N within time period T to obtain the NT curve. Let T be... st The rotational speed at time N st (Unit: rpm) The excitation order K corresponding to blade resonance can be calculated, where K is an integer that approximately satisfies the following formula:

[0076]

[0077] (6) Modal parameter calculation stage

[0078] Based on the RT curve obtained in step (4), find the maximum value of R, R0, corresponding to the time T0, and find the curve where R is... The two corresponding times T a and T b ,like Figure 3 As shown. Calculate T based on the rotational speed signal obtained in step (5). a To T b The acceleration / deceleration rate λ (in rpm / s) over the time range can also be used as the engine speed control signal input during vibration testing. The formula for calculating λ is as follows:

[0079]

[0080] Where, N a and N b T respectively a and T b The rotational speed corresponding to a given moment.

[0081] The modal frequency f0 and modal damping η of the blade can be obtained from the following equations:

[0082]

[0083]

[0084] or

[0085] To better demonstrate the feasibility of this invention, the following experiments will be conducted for verification:

[0086] The results of modal parameter identification using simulated signals were verified, and the relevant parameters of the simulated signals are shown in Table 1. Different time lengths (dT) were selected for analysis, and the results are shown in Table 2. The obtained RT curves are shown below. Figure 4 As shown in the figure. Analysis results show that when the data segment duration is 0.01s, the identified modal frequency and damping ratio are 600Hz and 0.2%, respectively, consistent with the theoretical values. Because this method avoids the time-domain to frequency-domain conversion, it has high accuracy.

[0087] Table 1 Simulation signal parameters

[0088] Theoretical resonant frequency 600Hz Theoretical damping ratio 0.20％ Excitation order K 20 Rate of change of rotational speed λ 240rpm / s sampling frequency fs 6000Hz

[0089] Table 2 Modal parameter identification results

[0090] Time length dT(s) <![CDATA[Identify the modal frequency f0 (Hz)]]> Identify the modal damping ratio η (%) 0.01 600.0 0.20 0.04 599.8 0.21 0.08 600.0 0.21 0.10 599.6 0.23

[0091] In summary, this invention has the following advantages: 1. Frequency domain analysis is only used as an auxiliary means to find the resonance time period. The calculation of modal parameters is performed entirely in the time domain. The analysis results do not incorporate parameters from the frequency domain analysis, avoiding energy leakage during the time-to-frequency domain conversion and avoiding the problem of simultaneously satisfying time resolution and frequency resolution, thus achieving high analysis accuracy. 2. Through signal filtering and signal energy (R-value) analysis, the problem of accurately obtaining the amplitude-time curve of discrete sampled data in the time domain is solved, resulting in a smoother RT change curve. By introducing rotational speed signals and excitation order, the amplitude-frequency response characteristics of the signal are obtained. 3. It can achieve rapid identification of modal frequencies and damping, with high efficiency.

[0092] The present invention also provides a modal parameter acquisition device, please refer to [reference needed]. Figure 5 The device includes: an initial resonance frequency and initial time determination unit, used to determine the initial resonance frequency and initial time for the same resonance point based on the response graph of the obtained vibration test signal, wherein the response graph is a graph showing the relationship between time and frequency of the vibration test signal; a time period determination unit, used to determine a data segment corresponding to the preset time period based on the initial time and the preset time period, wherein the preset time period includes the initial time; a curve obtaining time-varying characteristics of vibration, used to obtain a curve representing the time-varying characteristics of vibration based on the data segment, wherein the curve representing the time-varying characteristics of vibration is composed of energy parameters and time parameters corresponding to each small data segment; and a modal parameter acquisition unit, used to read the rotational speed signal at any time and obtain modal parameters based on the curve representing the time-varying characteristics of vibration.

[0093] Since this device corresponds to the method described above, it will not be explained further here. Please refer to the explanation section of the method above for relevant information.

[0094] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for obtaining modal parameters, characterized in that, include: Based on the response diagram of the obtained vibration test signal, the initial resonance frequency and initial time for the same resonance point are determined. The response diagram is a graph showing the relationship between time and frequency of the vibration test signal. Based on the initial time and the preset time period, a data segment corresponding to the preset time period is determined, wherein the preset time period includes the initial time. Based on the data segment, a curve representing the time-varying characteristics of vibration is obtained, which is composed of energy parameters and time parameters corresponding to each small data segment. Read the rotational speed signal over any time period and obtain the modal parameters based on the curve representing the time-varying characteristics of the vibration.

2. The method according to claim 1, characterized in that, Also includes: Obtain vibration test signals; The vibration test signal is processed by short-time Fourier transform to obtain the response diagram of the vibration test signal.

3. The method according to claim 1 or 2, characterized in that, The vibration response values ​​at the beginning and end of the preset time period are both lower than the vibration response value at the initial time.

4. The method according to claim 1, characterized in that, Based on the aforementioned data segment, a curve representing the time-varying characteristics of vibration is obtained, including: The data in the data segment is subjected to signal filtering processing to obtain filtered data; The filtered data is segmented to obtain a curve representing the time-varying characteristics of the vibration.

5. The method according to claim 1, characterized in that, The process of reading the rotational speed signal at any given time and obtaining the modal parameters based on the curve representing the time-varying characteristics of the vibration includes: Read the rotation speed signal at any time interval and obtain the curve showing the relationship between the rotation speed signal and time; Modal parameters are obtained based on the curve representing the time-varying characteristics of vibration and the curve showing the relationship between the rotational speed signal and time.

6. The method according to claim 5, characterized in that, The process of obtaining modal parameters based on the curve representing the time-varying characteristics of vibration and the curve showing the relationship between the rotational speed signal and time includes: Based on the relationship curve between the rotation speed signal and time, the excitation order corresponding to resonance is obtained. Based on the curve representing the time-varying characteristics of vibration and the curve showing the relationship between the rotational speed signal and time, the acceleration / deceleration rate of the rotational speed is obtained; Modal parameters are obtained based on the rotational speed acceleration / deceleration rate, the excitation order corresponding to the resonance, the curve representing the time-varying characteristics of the vibration, and the curve showing the relationship between the rotational speed signal and time.

7. A device for obtaining modal parameters, characterized in that, include: The initial resonance frequency and initial time determination unit is used to determine the initial resonance frequency and initial time for the same resonance point based on the response diagram of the obtained vibration test signal, wherein the response diagram is a graph showing the relationship between time and frequency of the vibration test signal. A time period determination unit is used to determine a data segment corresponding to the preset time period based on the initial time and the preset time period, wherein the preset time period includes the initial time. A curve acquisition unit representing the time-varying characteristics of vibration is used to obtain a curve representing the time-varying characteristics of vibration based on the data segment. The curve representing the time-varying characteristics of vibration is composed of energy parameters and time parameters corresponding to each small data segment. The modal parameter acquisition unit is used to read the rotational speed signal at any time and obtain the modal parameters according to the curve representing the time-varying characteristics of the vibration.

8. The apparatus according to claim 7, characterized in that, The device further includes: a response map determination unit; The response map determination unit is used to obtain the vibration test signal; and to perform short-time Fourier transform processing on the vibration test signal to obtain the response map of the vibration test signal.

9. The apparatus according to claim 7, characterized in that, The vibration response values ​​at the beginning and end of the preset time period are both lower than the vibration response value at the initial time.

10. The apparatus according to claim 7, characterized in that, Based on the aforementioned data segment, a curve representing the time-varying characteristics of vibration is obtained, including: The data in the data segment is subjected to signal filtering processing to obtain filtered data; The filtered data is segmented to obtain a curve representing the time-varying characteristics of the vibration.

11. The apparatus according to claim 7, characterized in that, The process of reading the rotational speed signal at any given time and obtaining the modal parameters based on the curve representing the time-varying characteristics of the vibration includes: Read the rotation speed signal at any time interval and obtain the curve showing the relationship between the rotation speed signal and time; Modal parameters are obtained based on the curve representing the time-varying characteristics of vibration and the curve showing the relationship between the rotational speed signal and time.

12. The apparatus according to claim 11, characterized in that, The process of obtaining modal parameters based on the curve representing the time-varying characteristics of vibration and the curve showing the relationship between the rotational speed signal and time includes: Based on the relationship curve between the rotation speed signal and time, the excitation order corresponding to resonance is obtained. Based on the curve representing the time-varying characteristics of vibration and the curve showing the relationship between the rotational speed signal and time, the acceleration / deceleration rate of the rotational speed is obtained; Modal parameters are obtained based on the rotational speed acceleration / deceleration rate, the excitation order corresponding to the resonance, the curve representing the time-varying characteristics of the vibration, and the curve showing the relationship between the rotational speed signal and time.

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