Elastic vibration suppression method based on notch frequency self-adaptive slippage

Abstract

The invention discloses an elastic vibration suppression method based on notch frequency self-adaptive slippage. The method comprises the following steps: acquiring a theoretical value omega L (t) of an elastic vibration frequency of an aircraft according to a ground modal test; selecting a frequency feature points in the active section according to the change trend of the omega L (t); designing a notch filter transfer function and setting a notch filter expectation index; the values of the filtering frequency and the damping ratio at each frequency characteristic point are omega i and xii, and i = 1, 2,..., a; omegai is made to be equal to the theoretical elastic vibration frequency of the corresponding feature point, the range of xii is set to be 0.1-1.0, Omegai and xii are substituted into a transfer function of the notch filter, whether amplitude-frequency characteristics meet the expected index of the notch filter or not is verified, if yes, the next feature point is designed, and if not, xii is adjusted till the expected index is met; and combining the filtering parameters of all the feature points, and designing the filtering parameters of the notch filter by using a dynamic difference value to obtain an adaptive notch filter.

Description

Technical Field

[0001] The present invention belongs to the field of aircraft control, and in particular relates to an elastic vibration suppression method based on adaptive slip of notch frequency. Background Art

[0002] With the continuous advancement of modern science and technology, aircraft performance, such as range, maneuverability, and payload capacity, is becoming increasingly advanced, and the application of new materials and technologies in engineering is becoming increasingly widespread. The overall design of aircraft is moving towards lightweight design and a larger aspect ratio, resulting in a decreasing elastic vibration frequency and increasing coupling with rigid motion. Furthermore, during flight, the continuous consumption of propellant causes the aircraft's mass to fluctuate continuously, causing wide variations in the elastic vibration frequency and increasing uncertainty in the frequency.

[0003] To address the aeroservoelasticity issues of aircraft, fixed-parameter notch filters are widely used in engineering to suppress elastic vibrations. Although these filters have a certain notch width, they are not ideal due to the wide range of elastic vibration frequencies. When the notch filter's center frequency is close to the aircraft's elastic vibration frequency, the filter can effectively suppress the adverse effects of the aircraft's elastic vibrations and ensure aircraft stability. However, as the difference between the notch filter's center frequency and the elastic frequency increases, the notch filter's effectiveness gradually weakens. When the frequency difference exceeds the notch filter's width, the notch filter has little effect on suppressing elastic vibrations and may even cause system instability. Summary of the Invention

[0004] In view of this, the present invention provides an elastic vibration suppression method based on adaptive sliding of notch frequency, which can meet the elastic vibration suppression requirements during the entire flight time period.

[0005] The technical solutions for implementing the present invention are as follows:

[0006] A method for suppressing elastic vibration based on adaptive slip of notch frequency comprises the following steps:

[0007] Step 1: Based on the ground modal test, obtain the theoretical value ω of the aircraft's elastic vibration frequency changing with flight time t L (t); according to ω L (t) The changing trend, select a frequency feature points in the active segment;

[0008] Step 2: Design the notch filter transfer function and set the expected index of the notch filter; the filter frequency and the damping ratio of the filter at each frequency characteristic point are taken as ω i and ξ i , I=1,2,…,a;

[0009] Step 3: Let ω i Equal to the theoretical elastic vibration frequency of its corresponding characteristic point, set the damping ratio ξ i The range is 0.1~1.0, and ω i and ξ i Substitute into the notch filter transfer function and check whether the amplitude-frequency characteristic meets the expected index of the notch filter. If it does, design the next characteristic point. If not, adjust ξ i , until the expected indicators are met;

[0010] Step 4: Combine the notch parameters at all feature points and use dynamic interpolation to design the filtering parameters of the notch filter to obtain an adaptive notch filter that suppresses the elastic vibration frequency of the aircraft.

[0011] Furthermore, in step 1, the frequency characteristic points are selected as: the starting point of the active segment, the ending point of the active segment and ω L The turning point of the frequency feature points; let the number of frequency feature points be a, and the flight time corresponding to each feature point is: t1, t2, ..., t a , where t1 = 0; t a =t pass ;t pass is the end time of the engine active section, then the corresponding frequencies at each characteristic point are: ω L (t1),ω L (t2),…,ω L (t a ).

[0012] Furthermore, the notch filter transfer function G f (s) is:

[0013]

[0014] Where s is the complex variable in Laplace transform, ω is the filtering frequency of the second-order notch filter, and ξ is the damping ratio of the second-order notch filter.

[0015] Furthermore, the notch filter expected indicators include the expected filter depth A m , the expected filter width W m and the phase delay P at the aircraft rigid motion frequency band m .

[0016] Furthermore, the amplitude-frequency characteristic meets the expected index of the notch filter, specifically: the actual filtering depth is greater than the expected depth A m , the actual filter width is greater than the expected width W n , the phase delay in the rigid motion band is less than the expected delay P m .

[0017] Furthermore, the calculation formula for the filtering parameters of the notch filter designed using dynamic interpolation is as follows:

[0018]

[0019] Where ω(t) and ξ(t) are the filter frequency and damping ratio that vary with the flight time t, respectively, and the interp1(.) function is a one-dimensional linear interpolation function.

[0020] The method of the present invention includes the following beneficial technical effects:

[0021] (1) The method of the present invention combines static engine thrust test data and ground modal test data to derive a theoretical curve of the aircraft's elastic frequency over time. Based on this theoretical curve, a method for elastic vibration suppression based on adaptive notch frequency sliding is designed to meet the elastic vibration suppression requirements throughout the entire flight period.

[0022] (2) Compared with the traditional fixed-parameter notch filter, the parameters of the notch filter designed by the method of the present invention can be adaptively changed with the flight time, and a larger effective filtering depth and filtering width can be obtained without affecting the stability of rigid motion.

[0023] (3) The present invention has been successfully applied to the development of a certain guided aircraft and has passed the verification of multiple flight tests. The technology is mature and the elastic suppression effect is obvious. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a control system block diagram of the elastic vibration adaptive suppression method of the present invention.

[0025] Figure 2 This is a design flow chart of the elastic vibration adaptive suppression method of the present invention.

[0026] Figure 3 This is the mass change curve of the aircraft according to the embodiment of the present invention.

[0027] Figure 4 The elastic vibration frequency theoretical curve and frequency characteristic points of the aircraft according to the embodiment of the present invention are shown.

[0028] Figure 5 Schematic diagram of the elastic vibration frequency change curve and effective filtering range according to an embodiment of the present invention.

[0029] Figure 6 1 is a graph showing the pitch angular velocity before and after elastic vibration suppression in an embodiment of the present invention.

[0030] Figure 7 1 is a graph showing pitch acceleration before and after elastic vibration suppression in an embodiment of the present invention. DETAILED DESCRIPTION

[0031] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0032] To address the rigid-elastic coupling and wide-range variations in elastic vibrations in aircraft, this paper provides an elastic vibration suppression method based on adaptive notch frequency sliding. This method can meet the elastic vibration suppression requirements throughout the entire flight timeframe. Furthermore, while ensuring the stability of the aircraft's rigid-body motion, it achieves a high effective filter width and filter width.

[0033] In order to achieve the above-mentioned purpose, the present invention combines the prior information of ground tests and designs a method for elastic vibration suppression based on adaptive slip of notch frequency. First, based on the ground modal test information and the engine static test thrust data, the theoretical change value of the elastic vibration frequency of the aircraft is obtained; then the notch filter structure and the expected filter depth and filter width and other indicators are proposed to meet the demand for large uncertainty of the elastic frequency. Finally, according to the theoretical change trend of the elastic vibration frequency, an adaptive change scheme of the notch filter parameters is designed to solve the problem of large-scale changes in the elastic frequency. The control system block diagram of the elastic vibration adaptive suppression method of the present invention is shown in FIG. Figure 1 shown.

[0034] The technical solution adopted by the present invention to solve the technical problem includes the following steps:

[0035] Step 1: Calculate the theoretical curve of the aircraft's elastic frequency

[0036] Step 1-1: Obtain prior information on the change of vehicle mass with flight time

[0037] In the active phase of the engine, due to the continuous consumption of fuel, the mass of the aircraft continues to decrease, and the elastic frequency of the aircraft continues to increase. Assume that the mass of the aircraft when fully loaded is M max , the mass of the aircraft when empty is M min Then, combined with the engine static test thrust data, the mass-second consumption is set to The theoretical value M(t) of the aircraft mass changing with flight time can be obtained as follows:

[0038]

[0039] Where t is the current flight time, t pass The end time of the engine active phase.

[0040] Step 1-2: Based on the ground modal test, obtain the theoretical value of the aircraft's elastic frequency changing with flight time t. Assume that the elastic frequency value at full load is ω min , the elastic frequency value when no load is ω max The change trend of the aircraft's elastic frequency is related to the change trend of its mass, and the theoretical value of the elastic vibration frequency ω can be obtained.L (t) is:

[0041]

[0042] Where, interp1() function is a one-dimensional linear interpolation function.

[0043] Step 1-3: According to ω L (t) changes, select frequency feature points in the active segment. Frequency feature points include: the starting point of the active segment, the end point of the active segment and ω L The turning point of . Let the number of frequency feature points be a, and the flight time corresponding to each feature point is: t1, t2, ..., t a (where t1 = 0; t a =t pass ). Then the corresponding frequencies at each feature point are: ω L (t1),ω L (t2),…,ω L (t a ).

[0044] Step 2: Notch filter structure design and expected performance

[0045] Step 2-1: Notch Filter Transfer Function

[0046] The transfer function G of the notch filter designed in the present invention is f (s) is:

[0047]

[0048] Where s is the complex variable in Laplace transform, ω and ξ are the parameters of the notch filter, ω is the filtering frequency of the second-order notch filter, and ξ is the damping ratio of the second-order notch filter. Assume that the values ​​of ω and ξ at each frequency characteristic point are ω i and ξ i , i=1,2,…,a.

[0049] Step 2-2: Set the desired notch filter parameters, including the desired filter depth A m , the expected filter width W m and the phase delay P at the aircraft rigid motion frequency band m .

[0050] Step 3: Design the notch filter parameters ω i and ξ i

[0051] The design flow chart of the notch filter parameters of the present invention is as follows Figure 2 shown.

[0052] Step 3-1: Select feature points and let ωi Equal to the theoretical elastic vibration frequency ω of the characteristic point L (t). Taking the first feature point as an example, let ω1=ω L (t1).

[0053] Step 3-2: Design the damping ratio ξ i , damping ratio ξ i The design range is 0.1 to 1.0.

[0054] Step 3-3: Add ω i and ξ i Substitute the notch filter transfer function G in step 2-1 into f (s), analysis of G f (s) amplitude-frequency characteristics, verify the expected indicators in step 2-2, and the actual filtering depth must be greater than the expected depth A m , the actual filter width is greater than the expected width W m , the phase delay in the rigid motion band is less than the expected delay P m .

[0055] Step 3-4: Check the index requirements. If they are met, return to step 3-1 to design the next characteristic point; if not, return to step 3-2 to adjust the damping ratio ξ i , until the index requirements are met. Increase ξ i This will increase the filter depth and width, but will also increase the phase delay of rigid motion. If all feature points have been designed, the design is complete.

[0056] Step 4: Combine the notch parameters at all feature points to design an adaptive change scheme for the notch filter.

[0057] According to the notch filter parameter ω in step 3 i and ξ i The design result is dynamically interpolated between feature points according to the flight time t. The calculation formula is as follows:

[0058]

[0059]

[0060] At this point, the design of the notch filter structure, parameters and its adaptive change scheme has been completed.

[0061] Example:

[0062] In order to verify the adaptive suppression effect of the method of the present invention on the elastic vibration of the aircraft, a six-degree-of-freedom model of an aircraft is used as the basis, and the simulation parameters are shown in Table 1.

[0063] Table 1 Priori parameter values ​​of a certain aircraft

[0064]

[0065] Combined with the engine static test thrust data, the mass change curve of the aircraft can be obtained, such as Figure 3 According to the mass change of the aircraft, the theoretical curve of the elastic vibration frequency of the aircraft can be calculated according to the formula in step 1, and 5 frequency characteristic points can be selected according to the change trend of the curve, as shown in the figure below. Figure 4 shown.

[0066] Assume the desired filter depth A m ≥20dB, expected filter width W m ≥1.8Hz, the aircraft rigid motion frequency band is 1~2Hz, and the phase delay within the frequency band is P m ≤10deg. The filter parameters and actual indicators of each feature point are shown in Table 2:

[0067] Table 2 Filter frequency parameters at each feature point

[0068]

[0069] Combined with the parameters in Table 2, the effective filtering range of the notch filter is as follows: Figure 5 In the simulation results, the pitch angular velocity curves before and after elastic vibration suppression are shown as follows: Figure 6 As shown in the figure, the pitch acceleration curves before and after elastic vibration suppression are as follows: Figure 7 The simulation results show that the method of the present invention has a good elastic vibration suppression effect when facing a large range of elastic frequency changes.

[0070] In summary, the above are only preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for suppressing elastic vibration based on adaptive slip of notch frequency, characterized in that: The following steps are involved: Step 1: Based on the ground modal test, obtain the theoretical value ω of the aircraft's elastic vibration frequency changing with flight time t L (t); according to ω L (t) The changing trend, select a frequency feature points in the active segment; Step 2: Design the notch filter transfer function and set the expected index of the notch filter; The filter frequency and the damping ratio of the filter at each frequency characteristic point are taken as ω i and ξ i , I=1,2,…,a; Step 3: Let ω i Equal to the theoretical elastic vibration frequency of its corresponding characteristic point, set the damping ratio ξ i The range is 0.1~1.0, and ω i and ξ i Substitute into the notch filter transfer function and check whether the amplitude-frequency characteristic meets the expected index of the notch filter. If it does, design the next characteristic point. If not, adjust ξ i , until the expected indicators are met; Step 4: Combine the notch parameters at all feature points and use dynamic interpolation to design the filtering parameters of the notch filter to obtain an adaptive notch filter that suppresses the elastic vibration frequency of the aircraft.

2. The elastic vibration suppression method according to claim 1, wherein: In step 1, the frequency characteristic points are selected as follows: the starting point of the active segment, the ending point of the active segment and ω L The turning point of the frequency feature points; let the number of frequency feature points be a, and the flight time corresponding to each feature point is: t1, t2, ..., t a , where t1 = 0; t a =t pass ;t pass is the end time of the engine active section, then the corresponding frequencies at each characteristic point are: ω L (t1),ω L (t2),…,ω L (t a ).

3. The elastic vibration suppression method according to claim 1, wherein: Notch filter transfer function G f (s) is: Where s is the complex variable in Laplace transform, ω is the filtering frequency of the second-order notch filter, and ξ is the damping ratio of the second-order notch filter.

4. The elastic vibration suppression method according to claim 1, wherein: The expected indicators of the notch filter include the expected filter depth A m , the expected filter width W m and the phase delay P at the aircraft rigid motion frequency band m .

5. The elastic vibration suppression method according to claim 1 or 4, characterized in that: The amplitude-frequency characteristics meet the expected indicators of the notch filter, specifically: the actual filtering depth is greater than the expected depth A m , the actual filter width is greater than the expected width W m , the phase delay in the rigid motion band is less than the expected delay P m .

6. The elastic vibration suppression method according to claim 2, wherein: The calculation formula for the filtering parameters of the notch filter designed using dynamic interpolation is as follows: Where ω(t) and ξ(t) are the filter frequency and damping ratio that vary with the flight time t, respectively, and the interp1(.) function is a one-dimensional linear interpolation function.

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