A method for determining the optimal frequency of a paddle pendulum vibration absorber

Abstract

The application discloses a method for determining optimal frequency of a paddle pendulum vibration absorber, and a frequency-adjustable pendulum vibration absorber is designed according to a theoretical formula; the pendulum vibration absorber is installed at a target position, flight test is carried out, and vibration values of the target position under each pendulum frequency are obtained; vibration of the target position is taken as an object, a relation curve between the pendulum frequency and the vibration values of the target position is drawn; and the optimal frequency of the pendulum is determined according to an inflection point of the curve. The application can avoid the problem of inaccurate design of the pendulum frequency caused by nonlinearity, structure size and distributed weight.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of helicopter vibration control, and relates to a method for determining the optimal frequency of a blade pendulum vibration absorber. BACKGROUND

[0002] The blade pendulum vibration absorber (hereinafter referred to as a pendulum) is one of the effective means for helicopter vibration control. The pendulum is installed at the root of the blade, and the vibration capacity of the blade is consumed through movement, thereby reducing the excitation force of the blade on the helicopter body structure. The frequency design of the pendulum is a key factor affecting the vibration control effect. According to the relevant theory of vibration absorption, the design of the frequency of the pendulum coincides with the frequency of the pendulum, and a better vibration control effect can be obtained. However, in actual engineering applications, the following reasons lead to the fact that the vibration control effect cannot be satisfied through theoretical design:

[0003] 1. Nonlinearity of pendulum movement, i.e. the pendulum swings around the center of rotation under the action of centrifugal force, which cannot fully meet the conditions of linear assumption;

[0004] 2. The pendulum has structural size and distributed weight, i.e. the weight distribution of the pendulum is not a concentrated mass point, but a distributed weight, including the pendulum arm and the pendulum weight, and the inertia of the relative center of mass has a significant influence on the theoretical frequency design;

[0005] Based on the above discussion, it is of great significance to determine the optimal frequency of the pendulum for better vibration control effect. SUMMARY

[0006] The purpose of the present application is to provide a method for determining the optimal frequency of a blade pendulum vibration absorber. The present application can avoid the problem of inaccurate design of the frequency of the pendulum caused by nonlinearity, structural size and distributed weight.

[0007] The technical scheme of the present application is a method for determining the optimal frequency of a blade pendulum vibration absorber, which designs a frequency-adjustable pendulum vibration absorber according to a theoretical formula; installs the pendulum vibration absorber at a target position, carries out a flight test, and obtains the vibration values of the target position at each pendulum frequency; takes the vibration control of the target position as the object, draws a relationship curve between the pendulum frequency and the vibration values of the target position; and determines the optimal frequency of the pendulum according to the inflection point of the curve.

[0008] In the foregoing method for determining the optimal frequency of a blade pendulum vibration absorber, the theoretical formula is:

[0009]

[0010] Wherein, ω is the pendulum frequency of the pendulum absorber; Ω is the blade rotation frequency; L is the pendulum installation position, indicating the distance from the rotation axis of the pendulum absorber to the center of the blade rotation; and r is the pendulum length, indicating the distance from the gravity center position of the pendulum absorber to the rotation axis thereof.

[0011] In the foregoing method for determining the optimal frequency of the pendulum absorber of the blade, the pendulum installation position L is determined according to the available space at the blade root.

[0012] In the foregoing method for determining the optimal frequency of the pendulum absorber of the blade, the pendulum frequency of the pendulum absorber is adjusted by the pendulum length r.

[0013] In the foregoing method for determining the optimal frequency of the pendulum absorber of the blade, the adjustment range of the pendulum frequency of the pendulum absorber is (N-1)Ω~(N+1)Ω, where N is the number of the blades.

[0014] In the foregoing method for determining the optimal frequency of the pendulum absorber of the blade, the drawing process of the relationship curve is as follows:

[0015] ω1, ω2...ω n are selected within the pendulum frequency range (N-1)Ω~(N+1)Ω. n ;

[0016] The relationship curve between a1, a2...a n and ω1, ω2...ω n is drawn, and three relatively low design frequency points are preliminarily obtained from the curve, so as to obtain the narrowed pendulum frequency range [ω f1 , ω f2 ];

[0017] ω 21 , ω 22 ,…ω 2n are selected within [ω f1 , ω f2 ], and a 21 , a 22 ...a 2n are measured by the flight test, where a 21 , a 22 ...a 2n are the vibrations of the target position in the constant-height and constant-speed flat flight state, and the relationship curve between [ω f1 , ω f2 ] and ω 21 , ω 22 ,…ω 2n is drawn.

[0018] In the foregoing method for determining the optimal frequency of the pendulum absorber of the blade, the interval between two adjacent frequency points of ω1, ω2...ω n is 0.2Ω.

[0019] In the foregoing method for determining the optimal frequency of the pendulum absorber, ω 21 , ω 22 , … ω 2n The interval between adjacent two frequency points is 0.1Ω.

[0020] The present application can avoid the problem of inaccurate design of the pendulum frequency caused by nonlinearity, structure size and distributed weight. By drawing the relationship curve between the theoretical frequency of the pendulum and the target vibration value, the optimal frequency of the pendulum is accurately obtained according to the inflection point of the curve, and the pendulum at the optimal frequency can achieve the optimal vibration control effect. According to the comparison, under the same weight cost, after determining the optimal frequency of the pendulum according to the present application, the vibration control effect can be improved by more than 40%.

[0021] In the present application, the frequency range is gradually reduced when drawing the relationship curve, and the accuracy of the optimal frequency of the pendulum is higher. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is the implementation flowchart of the method of the present application;

[0023] Figure 2 is a schematic diagram of the position of the pendulum absorber;

[0024] Figure 3 is an example graph of determining the optimal frequency using the method of the present application, wherein the horizontal coordinate is the design frequency of the pendulum, and the vertical coordinate is the vibration of the corresponding target position. The vibration is minimum at the inflection point, and the frequency of the pendulum at this time is the optimal frequency. The comparison result shows that the vibration at the optimal frequency is lower than that at other positions, and the vibration control effect is optimal. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0026] Example 1. To prove the applicability and effectiveness of the present application, the optimal frequency of the pendulum absorber is determined by flight test of a certain type of aircraft using the present application. The specific implementation is as follows:

[0027] [1] The vibration at the position of the helicopter pilot is determined as the target position for vibration control, and the frequency of the vibration is 21.5Hz, so the frequency of the pendulum absorber is determined as 21.5Hz (5Ω) of the rotor;

[0028] wherein the number of blades is 5;

[0029] [2] The pendulum frequency of the pendulum absorber is determined according to the following formula through the combination of the pendulum absorber installation position L and the pendulum length r:

[0030]

[0031] Wherein:

[0032] Ω is the blade rotation frequency 4.3 Hz; the pendulum installation position L is 1361 mm; and the pendulum length r is 56 mm;

[0033] [3] Determine the range of the pendulum length r

[0034] According to steps [1] [2] [3], the adjustment range of the pendulum length r is determined to be 39 mm-91 mm, so that the design frequency range of the pendulum is 4Ω-6Ω;

[0035] [4] Roughly draw the relationship curve between the target position vibration and the design frequency

[0036] With an interval of 0.2Ω, carry out flight test, measure the vibration of the target position in the constant height and constant speed flat flight state, roughly draw the relationship curve between the target position vibration and the design frequency, and preliminarily obtain three design frequency points with relatively low from the curve, and further design the frequency range [4.8Ω, 5.2];

[0037] [5] Fine draw the relationship curve between the target position vibration and the design frequency

[0038] With an interval of 0.1Ω, carry out flight test again in the frequency range [4.8Ω, 5.2Ω], measure the vibration of the target position in the constant height and constant speed flat flight state, and obtain the fine design frequency and the vibration of the target position;

[0039] [6] According to the relationship curve, the design frequency point with the lowest vibration is 4.9Ω, see Figure 3 If necessary, carry out flight test with smaller design frequency interval. Finally, the design frequency with the minimum target vibration is obtained as the optimal frequency.

[0040] Embodiment 2. A method for determining the optimal frequency of the pendulum blade absorber, see Figure 1 and Figure 2 The optimal frequency of the pendulum blade absorber is determined by flight test. The frequency-adjustable pendulum is designed according to the theoretical formula, flight test of different frequency pendulums is carried out, the vibration value of the target position is obtained, the vibration of the target position (such as the vibration of the helicopter pilot) is controlled, the relationship curve between the pendulum frequency and the vibration value of the target position is drawn, and the optimal frequency of the pendulum is determined according to the inflection point of the curve.

[0041] The specific steps are as follows:

[0042] [1] The target position of vibration control and the frequency of vibration are determined to determine the pendulum frequency of the pendulum vibration absorber, which is generally Nω of the rotor;

[0043] Wherein:

[0044] N is the number of blades;

[0045] [2] According to the available space at the root of the blade, the installation position L of the pendulum is determined;

[0046] [3] The pendulum frequency of the pendulum vibration absorber is determined according to the following formula through the combination of the installation position L of the pendulum and the length r of the pendulum:

[0047]

[0048] Wherein:

[0049] Ω is the blade rotation frequency, unit Hz;

[0050] The installation position L of the pendulum is the distance from the rotation axis of the pendulum to the center of the blade rotation, unit mm;

[0051] The length r of the pendulum is the distance from the center of gravity of the pendulum to the rotation axis of itself, unit mm;

[0052] The pendulum vibration absorber is shown in the figure Figure 2 .

[0053] [4] Determine the range of the length r of the pendulum

[0054] According to the formula in step [2], under the premise of determining the installation position L of the pendulum in step [3], the adjustment range of the length r of the pendulum is determined, so that the design frequency range of the pendulum is (N-1)ω~(N+1)ω;

[0055] [5] Develop flight test with 0.2Ω interval

[0056] Develop flight test with 0.2Ω interval, frequency ω1, ω2...ω n Flight test, measure the vibration a1, a2...a n of the target position in the constant height, constant speed and level flight state

[0057] [6] Roughly draw the relationship curve between the vibration of the target position and the design frequency

[0058] Roughly draw the relationship curve between the vibration of the target position and the design frequency, preliminarily obtain three design frequency points from the curve, and further design the frequency range [ω f1 , ω f2 ]

[0059] [7] Fine drawing of the relationship curve between the target position vibration and the design frequency

[0060] With 0.1Ω interval, the frequency range of [ω f1 ,ω f2 ] flight test is carried out again, the vibration a 21 , a 22 ...a 2n of the target position in the constant height and constant speed flat flight state is measured, and the fine relationship between the design frequency and the vibration of the target position is obtained.

[0061] [8] According to the relationship curve, the design frequency point with the lowest vibration is obtained, and if necessary, the flight test is carried out with smaller design frequency interval. Finally, the design frequency with the minimum target vibration is obtained as the optimal frequency.

[0062] The above is only a specific embodiment of the present application, which is described in detail, and the part not described in detail is the conventional technology. However, the protection scope of the present application is not limited to this, any changes or replacements that can be easily thought of by those skilled in the art within the technical range disclosed by the present application should be covered in the protection scope of the present application. The protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method of determining an optimal frequency of a paddle pendulum vibration absorber, characterized by, The frequency-adjustable pendulum vibration absorber is designed according to a theoretical formula; the pendulum vibration absorber is installed at a target position, flight test is carried out, and vibration values of the target position at different pendulum frequencies are obtained; vibration of the target position is taken as an object to be controlled, a relationship curve between the pendulum frequency and the vibration value of the target position is drawn, and the optimal frequency of the pendulum is determined according to an inflection point of the curve.

2. The method of determining the optimal frequency of a pendulum absorber according to claim 1, wherein, The theoretical formula is: wherein ω is the pendulum frequency of the pendulum vibration absorber; Ω is the blade rotation frequency; L is the pendulum installation position, representing the distance from the rotation axis of the pendulum vibration absorber to the rotation center of the blade; and r is the pendulum length, representing the distance from the gravity center position of the pendulum vibration absorber to the rotation axis thereof.

3. The method of determining the optimal frequency of a pendulum absorber according to claim 2, wherein, The pendulum installation position L is determined according to the available space at the blade root.

4. The method of determining the optimal frequency of a pendulum absorber according to claim 2, wherein, The pendulum frequency of the pendulum vibration absorber is adjusted by the pendulum length r.

5. The method of determining the optimal frequency of a pendulum absorber according to claim 2, wherein, The adjustment range of the pendulum frequency of the pendulum vibration absorber is (N-1)Ω~(N+1)Ω, wherein N is the number of the blade pieces.

6. The method of determining the optimal frequency of a pendulum absorber according to claim 5, wherein, The drawing process of the relationship curve is as follows: ω1, ω2...ωN-1 are selected in the single-pendulum frequency range (N-1)Ω~(N-1)Ω n Flight test is conducted to measure the vibration a1, a2...aN-1 of the target position in the constant height and constant speed steady state n ; Draw a1, a2...a n The relationship curve between ω1, ω2...ω n , preliminary obtain three design frequency points of relatively low from the curve, get the reduced single pendulum frequency range [ω f1 , ω f2 ]; Continue to select ω 21 , ω 22 , … ω 2n in [ω f1 , f2 ] to carry out flight test, measure the target position in the constant height, constant speed flat flying state vibration a 21 , a 22 ... a 2n , draw the relationship curve between [ω f1 , ω f2 ] and ω 21 , ω 22 , … ω 2n .

7. The method of determining the optimal frequency of a pendulum absorber according to claim 6, wherein, ω1, ω2...ω n The interval between adjacent two frequency points is 0.2Ω.

8. The method of determining the optimal frequency of a pendulum absorber according to claim 6, wherein, ω 21 , ω 22 , … ω 2n The interval between adjacent two frequency points is 0.1Ω.

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