A method for processing dynamic derivative data based on discrete Fourier transform

Abstract

The present invention discloses a method for processing dynamic derivative data based on discrete Fourier transform, belonging to the technical field of special test data processing for aeronautical aerodynamic wind tunnels. It solves the problem of low result accuracy caused by non-multiple frequency phenomena in the traditional dynamic derivative data processing method in the prior art; the present invention collects the pitching moment signal and angle element signal of the aircraft model during vibration through a balance; calculates the resolution frequency according to the set sampling rate and number of samples; obtains the discrete Fourier transform formula at the main vibration frequency based on the correlation function calculation formula and the resolution frequency; calculates the phase difference between the collected pitching moment signal and angle element signal according to the first phase difference and the second phase difference; calculates the final dynamic derivative value according to the dynamic derivative calculation formula in the pitching direction and the phase difference. The present invention effectively improves the accuracy of the processing result of the dynamic derivative of the aircraft model and can be applied to the processing of the dynamic derivative test data of the aircraft model.

Description

Technical Field

[0001] The present invention relates to a method for processing dynamic derivative data, and in particular to a method for processing dynamic derivative data based on discrete Fourier transform, belonging to the technical field of data processing for special tests of aerodynamic wind tunnels of aircraft. Background Technique

[0002] The dynamic derivative test in a high-speed wind tunnel is a special wind tunnel test for obtaining the unsteady aerodynamic force of an aircraft. The currently common test process is to apply a vibration system to force the aircraft model to perform simple harmonic vibration in the wind tunnel test flow field, measure the aerodynamic coefficient and angular vibration displacement of the aircraft model during the movement through a balance, and then obtain the final dynamic derivative test value of the aircraft model through data processing.

[0003] When the aircraft model makes forced vibration in the wind tunnel, the torque signal reflected by the balance includes not only the basic vibration torque signal (fundamental pitch torque signal), high-order harmonic signals, static torque signal, and random noise signals, etc.;

[0004] The formula for the torque signal collected during forced vibration is expressed as:

[0005] ;

[0006] Among them, is the collected signal, is the static torque signal, is the fundamental pitch torque signal, that is, the signal generated by the main vibration frequency, is the high-order harmonic signal, is the random noise signal;

[0007] In the processing of dynamic derivative test data, the fundamental pitch torque signal is a useful signal. Multiply both sides of the formula for the torque signal collected during forced vibration by the sine function and the cosine function respectively, and then perform integration to obtain the integrated signal formula;

[0008] The integrated signal formula is expressed as:

[0009] ;

[0010] ;

[0011] From the properties of trigonometric functions, it is deduced that , , among which, is the amplitude of the fundamental pitch torque signal, is the phase difference between the angle element signal and the torque fundamental wave signal. According to the calculation formula of the dynamic derivative in the pitch direction, it can be known that To obtain the necessary values of the model dynamic derivatives, in order to obtain values, common data processing methods include the signal cross-correlation method and the ellipse area method. The signal cross-correlation method is to multiply the collected angular element signal by the collected vibration torque signal, which can remove the influence of the static torque signal, high-order harmonic signals, and random noise signals. The data acquisition device can filter out some useless signals by setting the low-pass filter frequency, and then extract the necessary values through digital operations and the amplitude of the angular element signal, and finally obtain the dynamic derivative value of the aircraft model; the ellipse area method means that the collected dynamic torque and angle curve is a hysteresis loop, which can be regarded as an ellipse, and the size of the dynamic derivative is estimated according to the size of the ellipse area. However, the ellipse area method is only used for verification and cannot be applied in engineering.

[0012] Therefore, the most mainstream method for solving dynamic derivative data at present is the signal cross-correlation method. However, the application premise is that the model vibration is sinusoidally stable, and during the model vibration process, the collected signals do not contain non-multiple-frequency components of the fundamental frequency. However, often during the test process, due to the aerodynamic unsteadiness of the aircraft model itself, strut vibration, movement mechanism clearance, etc., it is impossible to ensure that the collected signals are completely high-order harmonic signals, and non-multiple-frequency signal phenomena often exist, that is, in the signal formula after integration is not an integer. In this case, the non-multiple-frequency phenomenon cannot be eliminated by the orthogonality of trigonometric functions. For this situation, the formula derived from the properties of trigonometric functions will not hold, and the above two methods will no longer be applicable. At the same time, during the data processing process, often the necessary values are extracted together, the individual phase angles are not calculated, and the torque amplitude of each cycle is not analyzed. When the torque waveform does not meet the test requirements, it will seriously affect the result accuracy.

[0013] In summary, when there are non-multiple-frequency phenomena in the signals collected by the vibration model, the conventional test processing methods have obvious deficiencies, and a dynamic derivative data processing method based on discrete Fourier transform that can accurately obtain the model dynamic derivatives is needed. Summary of the Invention

[0014] A brief overview of the present invention is given below in order to provide a basic understanding of certain aspects of the present invention. It should be understood that this overview is not an exhaustive overview of the present invention. It is not intended to identify the key or important parts of the present invention, nor is it intended to limit the scope of the present invention. Its purpose is only to present certain concepts in a simplified form as a prelude to the more detailed description to follow.

[0015] In view of this, in order to solve the problem of low result accuracy caused by non-multiple-frequency phenomena in the traditional dynamic derivative data processing methods in the prior art, the present invention provides a dynamic derivative data processing method based on discrete Fourier transform.

[0016] The technical solution is as follows: A method for processing dynamic derivative data based on discrete Fourier transform, comprising the following steps:

[0017] S1. Conduct a dynamic derivative test, and collect the pitching moment signal and the angle element signal of the aircraft model during vibration through a balance.

[0018] S2. Calculate the resolution frequency according to the set sampling rate and the number of samples.

[0019] S3. Based on the correlation function calculation formula and the resolution frequency, obtain the discrete Fourier transform formula at the main vibration frequency.

[0020] S4. According to the discrete Fourier transform formula, calculate the amplitude and the first phase difference of the pitching moment signal at the main vibration frequency and the amplitude and the second phase difference of the angle element signal at the main vibration frequency.

[0021] S5. Calculate the phase difference between the collected pitching moment signal and the angle element signal according to the first phase difference and the second phase difference.

[0022] S6. Calculate the final dynamic derivative value according to the dynamic derivative calculation formula in the pitching direction and the phase difference.

[0023] Further, in the S1, the pitching moment signal is expressed as , where is the amplitude of the fundamental wave pitching moment signal, is the static moment signal, is the sum of the noise signals of all harmonic vibration signals, is the main vibration frequency, is the first phase difference, is the time;

[0024] The angle signal is expressed as , where is the amplitude of the angle element signal, is the interference signal, is the second phase difference.

[0025] Further, in the S2, the resolution frequency is expressed as:

[0026] ;

[0027] Where is the sampling rate, is the number of samples.

[0028] Further, in the S3, the correlation function calculation formula is expressed as:

[0029] ;

[0030] Among them, is the sampled value, is the serial number, is the k th relevant function value under the serial number;

[0031] The discrete Fourier transform formula is expressed as:

[0032] ;

[0033] Among them, .

[0034] Furthermore, in the above S5, the phase difference between the pitching moment signal and the angle element signal is expressed as:

[0035] .

[0036] Furthermore, in the above S6, for the pitching vibration process in the high-speed dynamic derivative wind tunnel test, the amplitude and the phase difference of the fundamental wave pitching moment signal obtained in steps S4 and S5 are substituted into the calculation formula of the dynamic derivative in the pitching direction to obtain the final dynamic derivative value;

[0037] The calculation formula of the dynamic derivative in the pitching direction is expressed as:

[0038] ;

[0039] Among them, is the angular velocity of the vibration of the aircraft model, , is the dynamic derivative value in the pitching direction caused by the change of the angular velocity, is the dynamic derivative value in the pitching direction caused by the change of the angle of attack, The sum of and

[0040] The beneficial effects of the present invention are as follows: The present invention proposes a dynamic derivative processing method based on the discrete Fourier transform. By setting the minimum frequency, the vibration waveforms contained in the collected signals are all integer multiples of the minimum frequency. Based on the discrete Fourier transform solution method, the phase difference between the pitching moment signal and the angle element signal is obtained, and finally the dynamic derivative value of the model is obtained. The present invention can solve the problems of unstable sinusoidality of the vibration of the aircraft model and inaccurate conventional test data processing methods in the case of non-multiple frequencies in the collected signals. It can accurately obtain the moment, angular displacement and their phase angles of the aircraft model at the vibration frequency, and accurately obtain the dynamic derivatives of the aircraft model. The present invention can process the collected signals with poor sinusoidality containing multiple frequencies such as multiple frequencies and non-multiple frequencies. The present invention only needs to process the original signal, the signal processing process is simple, and the obtained results are accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The drawings described herein are used to provide a further understanding of the present invention, and constitute a part of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention, and do not constitute an improper limitation of the present invention. In the drawings:

[0042] Figure 1 It is a schematic flow chart of a dynamic derivative data processing method based on the discrete Fourier transform;

[0043] Figure 2 It is a schematic diagram of an embodiment of a dynamic derivative data processing method based on the discrete Fourier transform. Among them, (a) is a schematic diagram of an embodiment using the original signal value without signal extraction, (b) is a schematic diagram of an embodiment using a 1 Hz resolution frequency for signal extraction, and (c) is a schematic diagram of an embodiment using a 0.5 Hz resolution frequency for signal extraction. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0044] In order to make the technical solutions and advantages in the embodiments of the present invention clearer, the following further details the exemplary embodiments of the present invention with reference to the drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than an exhaustive list of all embodiments. It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0045] Refer to Figure 1 and Figure 2 This embodiment is described in detail. A dynamic derivative data processing method based on the discrete Fourier transform specifically includes the following steps:

[0046] S1. Conduct a dynamic derivative test, and collect the pitching moment signal and the angle element signal of the aircraft model during vibration through a balance;

[0047] S2. Calculate the resolution frequency according to the set sampling rate and the number of samples;

[0048] S3. Based on the relevant function calculation formula and the resolution frequency, obtain the discrete Fourier transform formula at the main vibration frequency;

[0049] S4. According to the discrete Fourier transform formula, calculate the amplitude and the first phase difference of the pitching moment signal at the main vibration frequency and the amplitude and the second phase difference of the angle element signal at the main vibration frequency;

[0050] Specifically: Substitute all the above-obtained values into the discrete Fourier transform formula to obtain the real and imaginary parts of the relevant function value at the k th serial number, thereby obtaining the amplitude of the fundamental wave pitching moment signal , the first phase difference , the amplitude of the angle element signal , and the second phase difference ; ;

[0051] S5. According to the first phase difference and the second phase difference, calculate the phase difference between the collected pitching moment signal and the angle element signal;

[0052] S6. According to the calculation formula of the dynamic derivative in the pitching direction, obtain the final dynamic derivative value.

[0053] Further, in the above S1, the pitching moment signal is expressed as , where is the amplitude of the fundamental wave pitching moment signal, is the static moment signal, is the sum of the noise signals of all harmonic vibration signals, is the main vibration frequency, is the first phase difference, is the time;

[0054] The angle signal is expressed as , where is the amplitude of the angle element signal, which depends on the dynamic derivative vibration mechanism, is the interference signal, is the second phase difference;

[0055] Further, in the above S2, the resolution frequency is expressed as:

[0056] ;

[0057] where is the sampling rate, is the number of samples.

[0058] Specifically, to make the resolution frequency As small as possible, and increase the sampling time as much as possible during the data acquisition process.

[0059] Further, in S3, the correlation function calculation formula is expressed as:

[0060] ;

[0061] Among them, is the sampling value, is the serial number, is the k th correlation function value under the serial number;

[0062] The discrete Fourier transform formula is expressed as:

[0063] ;

[0064] Among them, .

[0065] Further, in S5, the phase difference is expressed as:

[0066] .

[0067] Further, in S6, for the pitching vibration process in the high-speed dynamic derivative wind tunnel test, substitute the amplitude and the phase difference of the fundamental wave pitching moment signal obtained in steps S4 and S5 into the calculation formula of the dynamic derivative in the pitching direction to obtain the final dynamic derivative value;

[0068] The calculation formula of the dynamic derivative in the pitching direction is expressed as:

[0069] ;

[0070] Among them, is the angular velocity of the vibration of the aircraft model, , is the dynamic derivative value in the pitching direction caused by the change in angular velocity, is the dynamic derivative value in the pitching direction caused by the change in angle of attack, The sum of and

[0071] is the final dynamic derivative value in the pitching direction in the forced vibration dynamic derivative test;

[0072] Specifically, by collecting the yaw moment signal and angle signal, and the roll moment signal and angle signal of the aircraft model during the vibration process through the balance, the calculation formula of the dynamic derivative in the yaw direction and the calculation formula of the dynamic derivative in the roll direction can be obtained;

[0073] ;

[0074] Among them, is the dynamic derivative value in the yaw direction caused by the change in angular velocity, is the dynamic derivative value in the yaw direction caused by the change in sideslip angle, is the angle of attack, is the amplitude of the yaw moment signal, is the amplitude of the yaw vibration angle;

[0075] The calculation formula for the dynamic derivative in the roll direction is expressed as:

[0076] ;

[0077] Among them, is the dynamic derivative value in the roll direction caused by the change in angular velocity, is the dynamic derivative value in the roll direction caused by the change in sideslip angle, is the amplitude of the roll moment signal, is the amplitude of the roll vibration angle;

[0078] The principle of the present invention lies in: for the dynamic derivative test, assuming that the collected signals are identified with a particularly small resolution, the information of all signals at the resolution frequency and its integer multiple frequencies can be obtained, that is, the main vibration frequency of the aircraft model of concern is taken using the discrete Fourier formula , applying the discrete Fourier formula, it can be considered that the pitch moment signal and the angle element signal are compared with the standard signal , the first phase difference between the pitch moment signal and the standard signal and the amplitude of the pitch moment signal can be obtained, the second phase difference between the angle signal and the standard signal and the amplitude of the angle element signal, and at this time, the phase difference between the pitch moment signal and the angle element signal is obtained, so that the value of the model dynamic derivative can be obtained according to formula 5.

[0079] Usually in the dynamic derivative test, is solved together, but the present invention does not solve simultaneously, but solves the amplitude and the phase difference separately. When the resolution frequency is as small as possible during the calculation process, the non-multiple frequency influence can be eliminated;

[0080] Referring to Figure 2 , different frequency resolutions have an impact on signal extraction. For a signal, , as shown in Figure (a), it includes vibration signals of 6 hz, 8.5 hz, and 11 hz. As shown in Figure (b), when the resolution frequency is 1 hz, the waveform of the 8.5 hz signal cannot be resolved at this time, and there is also an error in the amplitude of the resolved 11 hz signal, which is significantly less than 3.5. However, according to the implementation of the present invention, when the resolution frequency is 0.5 hz, all signals can be resolved without error.

[0081] Although the present invention has been described based on a limited number of embodiments, those skilled in the art in this technical field will understand, based on the above description, that other embodiments can be envisioned within the scope of the present invention thus described. In addition, it should be noted that the language used in this specification is mainly selected for readability and teaching purposes, rather than for the purpose of explaining or limiting the subject matter of the present invention. Therefore, many modifications and changes will be obvious to those of ordinary skill in the art in this technical field without departing from the scope and spirit of the appended claims. For the scope of the present invention, the disclosure made for the present invention is illustrative rather than restrictive, and the scope of the present invention is defined by the appended claims.

Claims

1. A method for processing dynamic derivative data based on discrete Fourier transform, characterized in that: The following steps are involved: S1. Perform a dynamic derivative test to collect the pitch moment signal and angle element signal of the aircraft model during vibration through a balance; S2. Calculate the resolution frequency according to the set sampling rate and number of samples; S3. Based on the correlation function calculation formula and the resolution frequency, the discrete Fourier transform formula at the main vibration frequency is obtained; S4. According to the discrete Fourier transform formula, the amplitude and the first phase difference of the pitch moment signal at the main vibration frequency and the amplitude and the second phase difference of the angle element signal at the main vibration frequency are calculated; S5. Calculate the phase difference between the pitch moment signal and the angle element signal collected according to the first phase difference and the second phase difference; S6. Calculate the final dynamic derivative value according to the dynamic derivative calculation formula in the pitch direction and the phase difference.

2. The method for processing dynamic derivative data based on discrete Fourier transform according to claim 1, characterized in that: In S1, the pitch moment signal is expressed as ,in, is the amplitude of the fundamental pitch moment signal, is the static torque signal, is the sum of the noise signals of all simple harmonic oscillation signals, is the main vibration frequency, is the first phase difference, For time; The angle signal is expressed as ,in, is the amplitude of the angle element signal, is the interference signal, is the second phase difference.

3. The method for processing dynamic derivative data based on discrete Fourier transform according to claim 2, characterized in that: In S2, the resolution frequency It is expressed as: ； in, is the sampling rate, is the number of samples.

4. The method for processing dynamic derivative data based on discrete Fourier transform according to claim 3, characterized in that: In S3, the calculation formula of the correlation function is expressed as: ； in, is the sampling value, is the serial number, For the k The relevant function value under the sequence number; The discrete Fourier transform formula is expressed as: ； in, .

5. The method for processing dynamic derivative data based on discrete Fourier transform according to claim 4, characterized in that: In S5, the phase difference between the pitch moment signal and the angle element signal It is expressed as: 。 6. The method for processing dynamic derivative data based on discrete Fourier transform according to claim 5, characterized in that: In S6, for the pitch vibration process in the high-speed dynamic derivative wind tunnel test, the amplitude of the fundamental pitch moment signal obtained in step S4 and step S5 is and phase difference Substitute the dynamic derivative calculation formula in the pitch direction to obtain the final dynamic derivative value; The calculation formula of the dynamic derivative in the pitch direction is expressed as: ； in, is the angular velocity of the aircraft model vibration, , is the dynamic derivative value in the pitch direction caused by the change of angular velocity, is the dynamic derivative value in the pitch direction caused by the change of the angle of attack, and The sum is the final dynamic derivative value in the pitch direction in the forced vibration dynamic derivative test.

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