Method and device for acquiring structural response frequency time history based on rotating speed

Abstract

The invention provides a method and a device for acquiring a structural response frequency time history based on a rotating speed, which dynamically correct a concerned frequency value and a change interval thereof by tracking the change characteristic of the rotating speed of a rotor system in the whole flight process, ensure that frequency components related to the rotating speed of a rotor are completely extracted, and improve the accuracy of the structural response frequency time history. A foundation is laid for accurate analysis of frequency response characteristics during ground operation and air flight of the helicopter, and the method is also suitable for structure frequency response analysis of which the response frequency comes from a transmission system, an engine, a speed reducer and the like.

Description

Technical Field

[0001] The present application belongs to the field of helicopter vibration technology, and in particular, relates to a method and device for acquiring a structural response frequency time history based on rotation speed. Background Art

[0002] During the test flight of a helicopter, the structural response characteristics are often measured, such as the load on the structure or the vibration of key parts. By analyzing the measurement results, designers can judge the regularity, repeatability or consistency of the structural response process, and can also analyze whether there are abnormal responses of the structure (such as resonance, structural failure, etc.).

[0003] Helicopters provide lift and achieve maneuverable flight through the rotor system. Every time the rotor system rotates one circle, the aerodynamic force acts once, and the structure will respond accordingly to the action of the aerodynamic force. Therefore, the response frequency of the helicopter structure is generally dominated by the rotor. At the same time, rotating components such as transmission and engine will also affect structures such as the fuselage. The structural response frequency is generally the speed frequency or multiple frequency of the rotating components. The helicopter structure is in different positions, and the response frequency may be one or a superposition of multiple frequencies. The response frequency directly reflects the working characteristics of the components or systems, and can predict possible structural abnormalities in advance.

[0004] The periodic response frequency analysis usually adopts the fast Fourier transform (FFT). The FFT analysis result lacks time information and can only analyze a limited amount of data starting from a certain time point. It is impossible to obtain the frequency response change of the helicopter structure during the whole flight process. Therefore, the short-time Fourier transform (STFT) was proposed. The STFT calculation result includes the change history of the response frequency of all components of the structure over time.

[0005] When analyzing structural responses, it is often necessary to extract components related to blade speed from complex frequency response histories. The common approach to extracting frequencies of interest is to specify a frequency point and a frequency fluctuation range. However, the rotor speed of a helicopter is not constant during ground operation and air flight. During large maneuvering or unpowered flight, the rotor's fluctuation range is large. In special designs or situations, the rotor also has a variable speed state. Therefore, the commonly used method of setting a fixed frequency point and a frequency fluctuation range is difficult to capture all changes in the response frequency. Summary of the invention

[0006] The present invention proposes a method and device for acquiring the time history of structural response frequency based on rotational speed. Based on the helicopter rotor rotational speed and structural response measurement data (such as load or vibration), by extracting the fluctuation characteristics of the rotor during flight and combining with fast Fourier transform, the time history of the response frequency of interest is dynamically extracted from the response measurement data, eliminating the loss of the extraction of the response frequency of interest caused by the change of the rotor rotational speed, so as to improve the accuracy of the structural response characteristic analysis.

[0007] The first aspect of the present invention provides a method for obtaining a structural response frequency time history based on a rotation speed, comprising:

[0008] Step 1, obtaining structural response data, as well as the recording time T, sampling rate RATE, line number LI, and overlap rate D of the structural response data;

[0009] Step 2: According to the recording time T, sampling rate RATE, line number LI, and overlap rate D, obtain the data number VALUE and the required number N of structural response frequency analysis;

[0010] Step 3: read N VALUE data from the structural response data to obtain the initial data fx'(i,j), perform windowing function processing on the initial data fx'(i,j), and obtain the data fx(i,j) after the windowing function is added;

[0011] The starting data point of each reading is the VALUE*(1-D / 100)*i data point in the structure response data, i=0,1,2,…,N-1, j=0,1,2,…,VALUE-1;

[0012] Step 4: Perform fast Fourier transform on the windowed data fx(i,j) to obtain each frequency point k and its corresponding amplitude Am(k), and obtain a frequency amplitude array Am(k); k=0,1,2,…,VALUE / 2;

[0013] Step 5. In the frequency amplitude array Am(k), all frequency points are divided into N segments according to the frequency point to be analyzed fq / frequency range to be analyzed [fq0, fq1], the maximum amplitude value in each frequency segment is determined, and the maximum value is multiplied by the amplitude correction coefficient Xwin of the window function to obtain the change history of the frequency point to be analyzed / the central frequency point of the frequency range to be analyzed over time.

[0014] Optionally, the starting point of the frequency point of the i-th segment is INT(x0+pc[i]*x0) and the end point is INT(x1+pc[i]*x1)-1;

[0015] Among them, INT(x) means rounding x;

[0016] x0=freq-fq*(sgm[i]-xs)*VALUE / RATE;

[0017] x1=freq1+fq1*(sgm[i]-xs)*VALUE / RATE;

[0018] freq=INT((fq-fq1*xs)*VALUE / RATE);

[0019] freq1=INT((fq1+fq1*xs)*VALUE / RATE);

[0020] xs is the fluctuation coefficient of the frequency response value;

[0021] When the input frequency range to be analyzed is [fq0,fq1], fq=(fq0+fq1) / 2;

[0022] When the input is the frequency point fq to be analyzed, fq1=fq;

[0023] pc[i] is the deviation between the average value of the rotating component speed in the data point read for the i-th time and the rated speed mNr;

[0024] sgm[i] is the fluctuation rate of the rotation speed of the rotating component in the data point read for the i-th time.

[0025] Optionally, when the input is the frequency range to be analyzed [fq0,fq1], xs=0;

[0026] When the input is the frequency point to be analyzed fq,

[0027] xs=0.005+(2.699-log10(fq)) / 2.699*0.095(fq<500);

[0028] xs=0.001+(3.477-log10(fq)) / 0.7782*0.004(500= <fq<3000);

[0029] xs=0.001(fq>=3000).

[0030] Optionally, pc[i] = ((max0+min0) / 2-mNr) / mNr;

[0031] sgm[i]=(max0-min0) / (max0+min0);

[0032] Where max0 = MAX(Nr i (kk)); min0 = MIN (Nr i (kk));

[0033] Nr i (kk) represents the rotating component speed data corresponding to the kkth sampling point in the i-th segment; the starting point of kk in the i-th segment is RATE1*i*dy, and the end point is RATE1*dy*(i+1), kk is a positive integer; RATE1 is the sampling rate of the rotating component speed; dy=LI*(1-D / 100).

[0034] Optionally, the number of data VALUE for structural response frequency analysis is determined using the following formula:

[0035] VALUE=POW(2,INT(0.5+log10(RATE*LI) / log10(2)));

[0036] Among them, INT(x) means rounding x, and POW(x,y) means calculating x to the power of y.

[0037] Optionally, the number of times N required for structural response frequency analysis is T*RATE / (VALUE*(1-D / 100)).

[0038] Optionally, the rotating parts are aircraft rotors, transmissions, and engines.

[0039] The second aspect of the present invention further provides a device for acquiring a structural response frequency time history based on a rotation speed, for executing the method as described in any one of the first aspects.

[0040] The present invention proposes a method and device for obtaining the time history of structural response frequency based on rotation speed. By tracking the changing characteristics of the rotation speed of the rotor system during the entire flight process, the frequency value of interest and its changing range are dynamically corrected to ensure that the frequency components related to the rotor speed are completely extracted, laying a foundation for the accurate analysis of the frequency response characteristics of the helicopter during ground operation and air flight. This method is also suitable for the structural frequency response analysis of the response frequency derived from the transmission system, engine, reducer, etc. Based on the helicopter rotor speed and structural response measurement data (such as load or vibration), the present invention extracts the fluctuation characteristics of the rotor during flight, combines fast Fourier transform, and dynamically extracts the change history of the response frequency of interest over time from the response measurement data, avoiding the frequency response amplitude extraction error caused by the change of the rotor speed, and accurately captures the structural response frequency characteristic information of the entire flight domain. The present invention can automatically realize the time history extraction of different response frequencies for each flight take-off and landing through computer language, and has been applied in models such as Z10, ZX8, AC313, etc., improving the efficiency and accuracy of structural response characteristic analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is the calculation principle of the structural response frequency changing with time based on the helicopter rotor speed. DETAILED DESCRIPTION

[0042] The specific contents of the technical solution provided by the present invention are introduced below in conjunction with the accompanying drawings.

[0043] The present invention provides a method and device for acquiring a time history of a structural response frequency based on a rotation speed, the acquisition method comprising:

[0044] Step 1, obtaining structural response data, as well as the recording time T, sampling rate RATE, line number LI, and overlap rate D of the structural response data;

[0045] Step 2: According to the recording time T, sampling rate RATE, line number LI, and overlap rate D, obtain the data number VALUE and the required number N of structural response frequency analysis;

[0046] Step 3: read N VALUE data from the structural response data to obtain the initial data fx'(i,j), perform windowing function processing on the initial data fx'(i,j), and obtain the data fx(i,j) after the windowing function is added;

[0047] The starting data point of each reading is the VALUE*(1-D / 100)*i data point in the structure response data, i=0,1,2,…,N-1, j=0,1,2,…,VALUE-1;

[0048] Step 4: Perform fast Fourier transform on the windowed data fx(i,j) to obtain each frequency point k and its corresponding amplitude Am(k), and obtain a frequency amplitude array Am(k); k=0,1,2,…,VALUE / 2;

[0049] Step 5. In the frequency amplitude array Am(k), all frequency points are divided into N segments according to the frequency point to be analyzed fq / frequency range to be analyzed [fq0, fq1], the maximum amplitude value in each frequency segment is determined, and the maximum value is multiplied by the amplitude correction coefficient Xwin of the window function to obtain the change history of the frequency point to be analyzed / the central frequency point of the frequency range to be analyzed over time.

[0050] Optionally, the starting point of the frequency point of the i-th segment is INT(x0+pc[i]*x0) and the end point is INT(x1+pc[i]*x1)-1;

[0051] Among them, INT(x) means rounding x;

[0052] x0=freq-fq*(sgm[i]-xs)*VALUE / RATE;

[0053] x1=freq1+fq1*(sgm[i]-xs)*VALUE / RATE;

[0054] freq=INT((fq-fq1*xs)*VALUE / RATE);

[0055] freq1=INT((fq1+fq1*xs)*VALUE / RATE);

[0056] xs is the fluctuation coefficient of the frequency response value;

[0057] When the input frequency range to be analyzed is [fq0,fq1], fq=(fq0+fq1) / 2;

[0058] When the input is the frequency point fq to be analyzed, fq1=fq;

[0059] pc[i] is the deviation between the average value of the rotating component speed in the data point read for the i-th time and the rated speed mNr;

[0060] sgm[i] is the fluctuation rate of the rotation speed of the rotating component in the data point read for the i-th time.

[0061] Optionally, when the input is the frequency range to be analyzed [fq0, fq1], xs = 0;

[0062] When the input is the frequency point to be analyzed fq,

[0063] xs=0.005+(2.699-log10(fq)) / 2.699*0.095(fq<500);

[0064] xs=0.001+(3.477-log10(fq)) / 0.7782*0.004(500= <fq<3000);

[0065] xs=0.001(fq>=3000).

[0066] Optionally, pc[i] = ((max0+min0) / 2-mNr) / mNr;

[0067] sgm[i]=(max0-min0) / (max0+min0);

[0068] Where max0 = MAX(Nr i (kk)); min0 = MIN (Nr i (kk));

[0069] Nr i(kk) represents the rotational speed data of the rotating component corresponding to the kk-th sampling point in the i-th segment; the starting value of kk in the i-th segment is RATE1 * i * dy, the ending value is RATE1 * dy * (i + 1), and kk is a positive integer; RATE1 is the sampling rate of the rotational speed of the rotating component; dy = LI * (1 - D / 100).

[0070] Optionally, the number of data VALUE for structural response frequency analysis is determined by the following formula:

[0071] VALUE = POW(2, INT(0.5 + log10(RATE * LI) / log10(2)));

[0072] where INT(x) represents taking the integer part of x, and POW(x, y) represents calculating the y-th power of x.

[0073] Optionally, the number of times N required for structural response frequency analysis is N = T * RATE / (VALUE * (1 - D / 100)).

[0074] Optionally, the rotating component is an aircraft rotor, transmission, or engine.

[0075] Exemplarily, as Figure 1 shown, the present invention provides a method for obtaining a structural response frequency time history based on rotational speed, and the method includes the following:

[0076] 1) Open a structural response curve data file for a flight landing. The structural response data can be a flight load time history or a flight vibration time history, and is generally obtained through strain or vibration sensors and acquisition systems in flight tests;

[0077] 2) Obtain the recording time T of the structural response data file and the sampling rate RATE of the data;

[0078] 3) Input the response frequency value fq or the response frequency range fq0, fq1 (fq0 < fq1) to be processed. When the input is a response frequency range, the response frequency value fq = (fq0 + fq1) / 2;

[0079] The response frequency of a helicopter is generally the rotational speed frequency or multiple frequency of the rotor, transmission, engine, etc., and can reflect the working characteristics of components or systems;

[0080] When the input is a frequency response value, calculate the fluctuation coefficient xs of the frequency response value according to formula (1). When the input is a frequency response range, xs = 0;

[0081] xs = 0.005 + (2.699 - log10(fq)) / 2.699 * 0.095 (if fq < 500)

[0082] xs=0.001+(3.477-log10(fq)) / 0.7782*0.004(if 500= <fq<3000)

[0083] xs=0.001(if fq>=3000) (1)

[0084] 4) Select the line number LI, overlap rate D and FFT window function of the response data processing, and calculate the number of data VALUE of the response frequency analysis according to formula (2);

[0085] VALUE=POW(2,INT(0.5+log10(RATE*LI) / log10(2))) (2)

[0086] Where: INT(x) is the integer of x

[0087] POW(x,y) calculates x raised to the power of y

[0088] log10(x) calculates the base 10 logarithm of x

[0089] Note: Prevent the situation where the sampling rate of the structural response measurement is not a power of 2.

[0090] 5) Calculate the number of times N required to complete a landing structure response frequency FFT analysis according to formula (3);

[0091] N=T*RATE / (VALUE*(1-D / 100)) (3)

[0092] 6) Read the rotor speed data Nr(ii) of the same flight takeoff and landing, ii = 0, 1, 2, ..., T*RATE1, RATE1 is the sampling rate of the rotor speed;

[0093] 7) According to the response frequency, the number of times N and the overlap rate D need to be calculated, and the maximum value max0 and the minimum value min0 of the rotor speed in each data segment (length is VALUE / RATE*RATE1) are found according to formula (4), and then the fluctuation rate sgm[i] of the rotor speed in the data segment and the deviation pc[i] of its average value from the rated speed mNr are calculated;

[0094] max0=MAX(Nr(kk))

[0095] min0=MIN(Nr(kk))

[0096] pc[i]=((max0+min0) / 2-mNr) / mNr

[0097] sgm[i]=(max0-min0) / (max0+min0) (4)

[0098] Where: kk is a variable that starts from RATE1*i*dy and grows to RATE1*dy*(i+1) with a step size of 1

[0099] dy=LI*(1-D / 100)

[0100] i=0,1,2,…,N-1

[0101] mNr is the rated speed of the rotor

[0102] MAX(Nr(kk)), MIN(Nr(kk)) find the maximum and minimum values ​​from the data sequence

[0103] 8) For the i-th time, read VALUE data from the VALUE*(1-D / 100)*i data point in the structural response data file, record all data as data fx'(i,j), and use the selected window function according to formula (5) to perform windowing processing on the data fx'(i,j);

[0104] fx(i,j)=fx'(i,j)*WIN(j) (5)

[0105] Where: WIN(j) window function

[0106] i=0,1,2,…,N-1

[0107] j=0,1,2,…,VALUE-1

[0108] 9) Perform fast Fourier transform (FFT transform) on the windowed data fx(i,j) to obtain each frequency point k and its corresponding amplitude Am(k), k=0,1,2,…,VALUE / 2;

[0109] 10) Calculate the fluctuation range of the frequency point where the amplitude after the FFT change is located corresponding to the response frequency value fq according to formula (6);

[0110] freq=INT((fq-fq1*xs)*VALUE / RATE)

[0111] freq1=INT((fq1+fq1*xs)*VALUE / RATE) (6)

[0112] Where: INT(x) is the integer of x

[0113] 11) If sgm[i]>xs, correct the frequency fluctuation range according to formula (7);

[0114] x0=freq-fq*(sgm[i]-xs)*VALUE / RATE

[0115] x1=freq1+fq1*(sgm[i]-xs)*VALUE / RATE (7)

[0116] Where: i = 0, 1, 2, ..., N-1

[0117] 12) In the frequency amplitude array Am(k), find the maximum value Vmax according to formula (8), multiply the maximum value by the amplitude correction coefficient Xwin of the window function, and save the result in Fre(i)

[0118] Vmax=MAX(Am(k))*Xwin

[0119] Fre(i)=Vmax (8)

[0120] Where: i = 0, 1, 2, ..., N-1

[0121] k=INT(x0+pc[i]*x0),…,INT(x1+pc[i]*x1)-1, step size is 1

[0122] INT(x) rounds x to its integer

[0123] 13) Fre(i), (i=0,1,2,…,N-1) is the change history of the structural response frequency fq over time.

[0124] Enter different structural response frequency values ​​or fluctuation ranges, and repeat steps 3) to 12 to obtain the time history of different response frequencies.

Claims

1. A method for obtaining a structural response frequency time history based on rotation speed, characterized in that: include: Step 1, obtaining structural response data, as well as the recording time T, sampling rate RATE, line number LI, and overlap rate D of the structural response data; Step 2: According to the recording time T, sampling rate RATE, line number LI, and overlap rate D, obtain the data number VALUE and the required number N of structural response frequency analysis; Step 3: read N VALUE data from the structural response data to obtain the initial data fx'(i,j), perform windowing function processing on the initial data fx'(i,j), and obtain the data fx(i,j) after the windowing function is added; The starting data point of each reading is the VALUE*(1-D / 100)*i data point in the structure response data, i=0,1,2,…,N-1, j=0,1,2,…,VALUE-1; Step 4: Perform fast Fourier transform on the windowed data fx(i,j) to obtain each frequency point k and its corresponding amplitude Am(k), and obtain a frequency amplitude array Am(k); k=0,1,2,…,VALUE / 2; Step 5. In the frequency amplitude array Am(k), all frequency points are divided into N segments according to the frequency point to be analyzed fq / frequency range to be analyzed [fq0, fq1], the maximum amplitude value in each frequency segment is determined, and the maximum value is multiplied by the amplitude correction coefficient Xwin of the window function to obtain the change history of the frequency point to be analyzed / the central frequency point of the frequency range to be analyzed over time.

2. The method for acquiring the structural response frequency time history based on the rotation speed according to claim 1 is characterized in that: The starting point of the frequency point of the i-th segment is INT(x0+pc[i]*x0), and the end point is INT(x1+pc[i]*x1)-1; Among them, INT(x) means rounding x; x0=freq-fq*(sgm[i]-xs)*VALUE / RATE; x1=freq1+fq1*(sgm[i]-xs)*VALUE / RATE; freq=INT((fq-fq1*xs)*VALUE / RATE); freq1=INT((fq1+fq1*xs)*VALUE / RATE); xs is the fluctuation coefficient of the frequency response value; When the input frequency range to be analyzed is [fq0,fq1], fq=(fq0+fq1) / 2; When the input is the frequency point fq to be analyzed, fq1=fq; pc[i] is the deviation between the average value of the rotating component speed in the data point read for the i-th time and the rated speed mNr; sgm[i] is the fluctuation rate of the rotation speed of the rotating component in the data point read for the i-th time.

3. The method for acquiring the structural response frequency time history based on the rotation speed according to claim 2 is characterized in that: When the input frequency range to be analyzed is [fq0,fq1], xs=0; When the input is the frequency point to be analyzed fq, xs=0.005+(2.699-log10(fq)) / 2.699*0.095(fq<500); xs=0.001+(3.477-log10(fq)) / 0.7782*0.004(500= <fq<3000); xs=0.001(fq>=3000).

4. The method for acquiring the structural response frequency time history based on the rotation speed according to claim 2 is characterized in that: pc[i]=((max0+min0) / 2-mNr) / mNr; sgm[i]=(max0-min0) / (max0+min0); Where max0 = MAX(Nr i (kk)); min0 = MIN (Nr i (kk)); Nr i (kk) represents the rotating component speed data corresponding to the kkth sampling point in the i-th segment; the starting point of kk in the i-th segment is RATE1*i*dy, and the end point is RATE1*dy*(i+1), kk is a positive integer; RATE1 is the sampling rate of the rotating component speed; dy=LI*(1-D / 100).

5. The method for acquiring the structural response frequency time history based on the rotation speed according to claim 1, characterized in that: The number of data VALUE for structural response frequency analysis is determined by the following formula: VALUE=POW(2,INT(0.5+log10(RATE*LI) / log10(2))); Among them, INT(x) means rounding x, and POW(x,y) means calculating x to the power of y.

6. The method for obtaining the time history of structural response frequency based on rotation speed according to claim 1, characterized in that: The number of times N required for structural response frequency analysis is T*RATE / (VALUE*(1-D / 100)).

7. The method for acquiring the structural response frequency time history based on the rotation speed according to claim 1 is characterized in that: The rotating parts are the aircraft rotor, transmission, and engine.

8. A device for acquiring a structural response frequency time history based on rotation speed, characterized in that: Used to perform the method according to any one of claims 1 to 7.

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