Design method of natural frequency of pendulum in centrifugal field and vibration control method

Abstract

The application discloses a design method and a vibration control method for inherent frequency of a pendulum in a centrifugal force field, and comprises the following steps: step 1, determining a target position and a vibration frequency of a vibration control object in a helicopter according to control requirements of the helicopter; step 2, installing the pendulum at a blade root of a rotor of the helicopter, and obtaining an equivalent pendulum length of the pendulum through a test; and step 3, calculating the inherent frequency ω of the pendulum in the centrifugal force field of the rotor rotation according to the equivalent pendulum length of the pendulum. The technical scheme provided by the application solves the problem of the existing theoretical design method for the inherent frequency of the pendulum in the centrifugal force field, and the problem that the theoretical calculation method cannot obtain an accurate inherent frequency of the pendulum due to the fact that the pendulum is composed of multiple structural components and the nonlinearity of the pendulum movement.

Description

Technical Field

[0001] This invention relates to, but is not limited to, the field of helicopter vibration control technology, specifically to a method for designing the natural frequency of a pendulum in a centrifugal force field and a vibration control method. Background Technology

[0002] Helicopters experience significant vibrations during flight, which can affect the pilot's ability, efficiency, and comfort in performing missions. Based on the pilot's need for vibration reduction, a superior vibration environment is required for helicopters; therefore, additional vibration control methods are necessary. Currently, vibration control in helicopters is achieved by installing pendulum-type vibration absorbers (hereinafter referred to as: single pendulums) on the rotor blades. The natural frequency design of the single pendulum is a key factor affecting its vibration control effectiveness.

[0003] Since the added pendulum operates in the centrifugal force field of the helicopter rotor, there is currently no effective means to obtain the natural frequency of the pendulum in its operating state. Most domestic and international research on the design of the natural frequency of a pendulum in a centrifugal force field is based on theoretical studies. Because a pendulum consists of multiple structural components and its motion is nonlinear, theoretical design cannot obtain the true natural frequency of the pendulum in engineering applications. Summary of the Invention

[0004] The purpose of this invention is to address the aforementioned problems by providing a design method and vibration control method for the natural frequency of a simple pendulum in a centrifugal force field. This addresses the issue that existing theoretical design methods for the natural frequency of a simple pendulum in a centrifugal force field fail to accurately calculate the natural frequency due to the pendulum's composition of multiple structural components and the nonlinearity of its motion.

[0005] The technical solution of the present invention: The embodiments of the present invention provide a method for designing the natural frequency of a simple pendulum in a centrifugal force field, comprising:

[0006] Step 1: Determine the target position and vibration frequency of the vibration control object in the helicopter according to the control requirements of the helicopter;

[0007] Step 2: Install a pendulum at the root of the helicopter rotor blades and obtain the equivalent pendulum length L through experiments;

[0008] Step 3: Calculate the natural frequency of the pendulum in the centrifugal force field of the rotor rotation based on the equivalent pendulum length L. .

[0009] Optionally, in the design method of the natural frequency of a pendulum in a centrifugal force field as described above, the vibration control object in step 1 includes one or more of the pilot's seat, operator's seat, and crew seat in a helicopter;

[0010] The target position is the installation position corresponding to each seat, and the vibration frequency is the vibration frequency of the target position.

[0011] Optionally, in the design method for the natural frequency of a simple pendulum in a centrifugal force field as described above, step 2 includes:

[0012] Step 21: Determine the pendulum installation position based on the available space at the blade root; wherein, the vertical distance from the pendulum installation position to the center of the blade hub is R;

[0013] Step 22: Pull the pendulum of the predetermined weight to a horizontal position and place it in a free swing state to obtain the frequency f of the free swing of the pendulum;

[0014] Step 23: Calculate the equivalent pendulum length L based on the frequency f of the pendulum's free swing.

[0015] Optionally, in the design method of the natural frequency of a simple pendulum in a centrifugal force field as described above, step 22 includes:

[0016] For a pendulum in a free-swinging state, the radial acceleration of the pendulum during free swing is measured, and the frequency f of the free swing is obtained by frequency identification using Fast Fourier Transform (FFT).

[0017] Optionally, in the design method for the natural frequency of a simple pendulum in a centrifugal force field as described above, the equivalent pendulum length L calculated in step 23 is:

[0018] ;

[0019] Wherein, the equivalent pendulum length L is the distance from the actual center of gravity of the pendulum to its own axis of rotation, in mm; g is the acceleration due to gravity; and π is pi.

[0020] Optionally, in the design method for the natural frequency of a simple pendulum in a centrifugal force field as described above, step 3 includes:

[0021] Based on the vertical distance R from the pendulum's installation position to the rotor hub center and the pendulum's equivalent length L, the natural frequency of the pendulum in the centrifugal force field of the rotating rotor is calculated. for:

[0022] ;

[0023] Where Ω is the blade rotation frequency.

[0024] Optionally, in the design method of the natural frequency of a simple pendulum in a centrifugal force field as described above, step 1 further includes:

[0025] The vibration frequency of the vibration control object is taken as the target natural frequency of the pendulum; and the difference between the natural frequency of the pendulum calculated in step 3 and the target natural frequency is less than a preset frequency threshold.

[0026] Optionally, in the design method for the natural frequency of a simple pendulum in a centrifugal force field as described above, where the initial installation position of the pendulum is determined in step 21, and the vertical distance from the pendulum installation position to the center of the impeller hub is R0, then the method further includes:

[0027] Step 4: Compare the natural frequency of the pendulum calculated in Step 3. When the difference between the pendulum's natural frequency and the target natural frequency in step 1 is greater than or equal to a preset frequency threshold, the pendulum's installation position is adjusted.

[0028] This invention also provides a vibration control method for helicopters, comprising:

[0029] Step A: Using the design method of the natural frequency of a pendulum in a centrifugal force field as described in any of the above, a pendulum is installed on the vibration control object of the helicopter.

[0030] Step B involves conducting a test flight on the helicopter equipped with the pendulum to measure the vibration value of the vibration control object at the target location, in order to verify the vibration control effect of the pendulum.

[0031] The beneficial effects of this invention: This invention provides a method for designing the natural frequency of a pendulum in a centrifugal field and a vibration control method, determining the key parameters of the pendulum's natural frequency in a centrifugal field through experimentation. In implementation, to determine the natural frequency of the pendulum in a centrifugal field, firstly, the target location and vibration frequency for vibration control are defined. Based on the available space at the blade root, the pendulum installation position R is determined. A pendulum of a certain size is designed according to a predetermined weight. Under the action of ground gravity, the pendulum is pulled to a horizontal position and placed in a free-swinging state. The radial and tangential accelerations of the pendulum are measured. The frequency f of the pendulum's free swing is obtained through frequency identification methods such as Fast Fourier Transform (FFT). The equivalent pendulum length L is calculated according to theoretical formulas. Finally, the natural frequency of the pendulum in the centrifugal field of the rotating rotor is determined according to the pendulum calculation formula. Furthermore, the method provided in this invention can also be used to perform test flights on helicopters with the added pendulum, measuring the vibration value of the vibration control object at the target location to verify the vibration control effect of the pendulum. Using the technical solution provided in the embodiments of the invention, the natural frequency of a simple pendulum in the centrifugal force field of a rotating rotor is obtained through test flight. This verifies that the technical solution of the present invention provides an effective means for actively controlling vibration and has high engineering application value. Attached Figure Description

[0032] The accompanying drawings are provided to further understand the technical solutions of the present invention and constitute a part of the specification. They are used together with the embodiments of this application to explain the technical solutions of the present invention and do not constitute a limitation on the technical solutions of the present invention.

[0033] Figure 1 This is a flowchart of the design method for the natural frequency of a simple pendulum in a centrifugal force field according to the present invention;

[0034] Figure 2 A schematic diagram illustrating the relationship between the position of the simple pendulum and the equivalent pendulum length in the design method of the natural frequency of a simple pendulum in a centrifugal force field provided in an embodiment of the present invention.

[0035] Figure 3 This is a schematic diagram of the radial acceleration time-domain curve of a simple pendulum during free swing, obtained by using the design method of the natural frequency of a simple pendulum in a centrifugal force field provided in the embodiments of the present invention. Detailed Implementation

[0036] 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0037] As explained in the background section, helicopter vibration control is achieved by adding a pendulum to the rotor blades, based on the pilot's need for vibration reduction. However, most domestic and international research on the design of the natural frequency of a pendulum in a centrifugal field is based on theoretical studies. However, theoretical design cannot obtain the actual natural frequency of a pendulum in engineering applications for the following reasons:

[0038] 1. A simple pendulum has multiple structural components, including the pendulum arm and the pendulum bob. That is, the weight distribution of a simple pendulum is not a concentrated point mass, but a distributed weight. The moment of inertia of its rotation relative to the center of mass has a significant impact on the design of the theoretical natural frequency. The accurate natural frequency of a simple pendulum cannot be obtained using classical theoretical calculation formulas.

[0039] 2. Due to the nonlinearity of the simple pendulum motion, that is, the simple pendulum swings around the center of rotation under the action of the centrifugal force field, it cannot completely satisfy the conditions of the linear assumption. Therefore, the true natural frequency of the simple pendulum cannot be obtained in the centrifugal force field.

[0040] Based on the above discussion, it can be seen that in order to achieve better vibration control, proposing an engineering design method for determining the natural frequency of a pendulum in a centrifugal force field is of great significance for better vibration control.

[0041] To address the aforementioned problems and engineering design requirements, and considering the site conditions of the airport, this invention provides a method for designing the natural frequency of a simple pendulum in a centrifugal force field without affecting other helicopter flight missions.

[0042] The present invention provides the following specific embodiments, which can be combined with each other. For the same or similar concepts or processes, they may not be described again in some embodiments.

[0043] This invention, employing an engineering design and practical application of a natural frequency design method, is a novel approach. Taking the actual vibration problem encountered by a certain type of aircraft and its solution as background, this invention proposes an engineering design method for the natural frequency of a pendulum in a centrifugal force field. Firstly, through experimentation, it comprehensively considers the influence of the pendulum's distributed weight, structural dimensions, and moment of inertia (obtained through free oscillation) on the effective pendulum length, obtaining the equivalent pendulum length L, and thus calculating the natural frequency of the pendulum in the centrifugal force field of a rotating rotor. On the other hand, through engineering flight testing, the correctness and feasibility of the design method for the natural frequency of a simple pendulum in a centrifugal force field were verified, and it can be used for the engineering design of the natural frequency of a simple pendulum in a centrifugal force field.

[0044] Figure 1 A flowchart illustrating a method for designing the natural frequency of a simple pendulum in a centrifugal force field, as provided in an embodiment of the present invention. The method includes the following steps:

[0045] Step 1: Determine the target position and vibration frequency of the vibration control object in the helicopter according to the control requirements of the helicopter;

[0046] Step 2: Install a pendulum at the root of the helicopter rotor blades and obtain the equivalent pendulum length L through experiments;

[0047] Step 3: Calculate the natural frequency of the pendulum in the centrifugal force field of the rotor rotation based on the equivalent pendulum length L. .

[0048] In one implementation of this invention, the vibration control object in step 1 includes one or more of the pilot's seat, operator's seat, and crew seat in the helicopter; correspondingly, the target position is the installation position corresponding to each seat, and the vibration frequency is the vibration frequency of the target position.

[0049] In one implementation of this invention, step 2 may include:

[0050] Step 21: Determine the pendulum installation position based on the available space at the blade root; wherein, the vertical distance from the pendulum installation position to the center of the blade hub is R.

[0051] Step 22: Pull the pendulum of a predetermined weight to a horizontal position and place it in a free swing state to obtain the frequency f of the free swing of the pendulum.

[0052] The embodiment of step 22 is as follows: for a pendulum placed in a free swing state, the radial acceleration of the pendulum during free swing is measured, and the frequency f of the free swing of the pendulum is obtained by frequency identification through Fast Fourier Transform (FFT).

[0053] Step 23: Calculate the equivalent pendulum length L based on the frequency f of the pendulum's free swing.

[0054] In step 23, the specific method for calculating the equivalent pendulum length L of the simple pendulum is as follows:

[0055] ;

[0056] Wherein, the equivalent pendulum length L is the distance from the actual center of gravity of the pendulum to its own axis of rotation, in mm; g is the acceleration due to gravity; and π is pi.

[0057] In one implementation of this invention, step 2 is carried out as follows:

[0058] Based on the vertical distance R from the pendulum's installation position to the rotor hub center and the pendulum's equivalent length L, the natural frequency of the pendulum in the centrifugal force field of the rotating rotor is calculated. for:

[0059] ;

[0060] Where Ω is the blade rotation frequency.

[0061] Furthermore, in the design method of the natural frequency of the pendulum in this embodiment of the invention, step 1 above further includes: taking the vibration frequency of the vibration control object as the target natural frequency of the pendulum; correspondingly, the difference between the natural frequency of the pendulum calculated in step 3 and the target natural frequency is less than a preset frequency threshold.

[0062] Furthermore, in the method for designing the natural frequency of a pendulum according to an embodiment of the present invention, the initial installation position of the pendulum is determined in step 21, and the vertical distance from the pendulum installation position to the center of the propeller hub is R0; then the method provided by the embodiment of the present invention further includes:

[0063] Step 4: Compare the natural frequency of the pendulum calculated in Step 3. When the difference between the pendulum's natural frequency and the target natural frequency in step 1 is greater than or equal to a preset frequency threshold, the pendulum's installation position is adjusted.

[0064] Based on the design method for the natural frequency of a simple pendulum in a centrifugal force field provided in the above embodiments of the present invention, the present invention also provides a vibration control method for a helicopter, comprising:

[0065] Step A: Using the design method for the natural frequency of a pendulum in a centrifugal force field provided in any of the above embodiments, a pendulum is installed on the vibration control object of the helicopter; wherein, during the installation of the pendulum, the vertical distance R from the pendulum installation position to the center of the rotor hub is determined, and the frequency f of the pendulum's free swing, the equivalent pendulum length L, and the natural frequency of the pendulum in the centrifugal force field of the rotor rotation are calculated. ;

[0066] Step B involves conducting a test flight on the helicopter equipped with the pendulum to measure the vibration value of the vibration control object at the target location, in order to verify the vibration control effect of the pendulum.

[0067] The invention provides a method for designing the natural frequency of a pendulum in a centrifugal field and a vibration control method for a helicopter. This method determines the key parameters of the pendulum's natural frequency in a centrifugal field through experimental means. In implementation, to determine the natural frequency of the pendulum in a centrifugal field, the target location and vibration frequency for vibration control are first defined. Based on the available space at the blade root, the pendulum installation position R is determined. A pendulum of a certain size is designed according to a predetermined weight. Under the action of ground gravity, the pendulum is pulled to a horizontal position and placed in a free-swinging state. The radial and tangential accelerations of the pendulum are measured. The frequency f of the free swing of the pendulum is obtained through frequency identification methods such as Fast Fourier Transform (FFT). The equivalent pendulum length L is calculated according to theoretical formulas. Finally, the natural frequency of the pendulum in the centrifugal field of the rotating rotor is determined according to the pendulum calculation formula. Furthermore, the method provided in this invention can also be used to perform test flights on the helicopter with the pendulum installed, measuring the vibration value of the vibration control object at the target location to verify the vibration control effect of the pendulum. Using the technical solution provided in the embodiments of the invention, the natural frequency of a simple pendulum in the centrifugal force field of a rotating rotor is obtained through test flight. This verifies that the technical solution of the present invention provides an effective means for actively controlling vibration and has high engineering application value.

[0068] Example:

[0069] This embodiment provides a method for designing the natural frequency of a simple pendulum in a centrifugal force field. The specific steps of this embodiment are as follows:

[0070] Step 1: Determine the target position and vibration frequency of the vibration control object in the helicopter according to the control requirements of the helicopter;

[0071] In this step, the vibration control objects include one or more of the pilot's seat, operator's seat, and crew seats in the helicopter; correspondingly, the target position is the installation position of each seat, and the vibration frequency is the vibration frequency of the target position.

[0072] Step 2: Determine the pendulum installation position based on the available space at the blade root. Specifically, the vertical distance from the pendulum installation position to the center of the blade hub is R.

[0073] Step 3: Pull the pendulum of the predetermined weight to a horizontal position and place it in a free swinging state. Measure the radial acceleration of the pendulum during free swinging.

[0074] Step 4: Based on the measured radial acceleration of the pendulum during free oscillation, determine the frequency f of the free oscillation of the pendulum;

[0075] In this step, the frequency f of the pendulum's free swing is obtained by frequency identification methods such as Fast Fourier Transform (FFT).

[0076] Step 5: Calculate the equivalent pendulum length L based on the frequency f of the pendulum's free swing.

[0077] In this step, according to the formula Calculate the equivalent length L of the simple pendulum.

[0078] Wherein, the equivalent pendulum length L is the distance from the actual center of gravity of the pendulum to its own axis of rotation, in mm; g is the acceleration due to gravity; and π is pi.

[0079] Step 6: Using the pendulum's installation position R and equivalent length L, obtain the natural frequency of the pendulum in the centrifugal force field of the rotating rotor. ;

[0080] In this step, the natural frequency of the simple pendulum is determined according to the following formula. :

[0081] ;

[0082] Where Ω is the blade rotation frequency.

[0083] Example 2

[0084] To demonstrate the applicability and effectiveness of the design method for the natural frequency of a simple pendulum in a centrifugal field provided in this embodiment of the invention, the method provided in Embodiment 2 was used to determine the natural frequency of a simple pendulum in a centrifugal field on a certain type of aircraft through flight testing. The specific implementation is as follows:

[0085] Step 1: Determine the target location for vibration control based on the vibration at the helicopter pilot's location. The vibration frequency is 5Ω (which is 5 times the rotor blade rotation frequency). Therefore, the natural frequency of the pendulum can be determined to be around 5Ω.

[0086] The number of blades is 5.

[0087] Step 2: Based on the available space at the blade root, determine the pendulum installation position. The vertical distance R from the pendulum installation position to the center of the blade hub is 1361mm. Figure 2 The diagram shown illustrates the relationship between the pendulum position and the equivalent pendulum length in the design method for the natural frequency of a pendulum in a centrifugal force field provided by an embodiment of the present invention.

[0088] Step 3: Pull the pendulum of the predetermined weight to a horizontal position and place it in a free swinging state. Measure the time-domain curve of the radial acceleration of the pendulum during free swing, as shown below. Figure 3 The figure shown is a schematic diagram of the radial acceleration time domain curve of a simple pendulum during free swing, obtained by using the design method of the natural frequency of a simple pendulum in a centrifugal force field provided in the embodiment of the present invention.

[0089] Step 4: Determine the frequency f of the pendulum's free oscillation;

[0090] The frequency f of the pendulum's free swing was determined to be 2.00 Hz using frequency identification methods such as Fast Fourier Transform (FFT).

[0091] Step 5: Determine the equivalent pendulum length L of the simple pendulum as 62.38 mm;

[0092] According to the formula Determine the equivalent length L of the simple pendulum;

[0093] Wherein, the equivalent length L of the simple pendulum is the distance from the center of gravity of the simple pendulum to its own axis of rotation, in mm;

[0094] Step 6: Using the pendulum's installation position R and equivalent length L, obtain the natural frequency of the pendulum in the centrifugal force field of the rotating rotor. It is 4.78Ω.

[0095] Specifically, the natural frequency of a simple pendulum is determined according to the following formula. :

[0096] ;

[0097] Where Ω is the blade rotation frequency; the pendulum installation position R is 1361mm.

[0098] While the embodiments disclosed in this invention are as described above, they are merely illustrative of the embodiments to facilitate understanding of the invention and are not intended to limit the invention. Any person skilled in the art to which this invention pertains may make any modifications and variations in the form and details of the implementation without departing from the spirit and scope disclosed herein; however, the scope of patent protection for this invention shall still be determined by the scope defined in the appended claims.

Claims

1. A method for designing the natural frequency of a simple pendulum in a centrifugal force field, characterized in that, include: Step 1: Determine the target position and vibration frequency of the vibration control object in the helicopter according to the control requirements of the helicopter; Step 2: Install a pendulum at the root of the helicopter rotor blades and obtain the equivalent pendulum length L through experiments; Step 3: Calculate the natural frequency of the pendulum in the centrifugal force field of the rotor rotation based on the equivalent pendulum length L. ; Step 2 includes: Step 21: Determine the pendulum installation position based on the available space at the blade root; wherein, the vertical distance from the pendulum installation position to the center of the blade hub is R; Step 22: Pull the pendulum of the predetermined weight to a horizontal position and place it in a free swing state to obtain the frequency f of the free swing of the pendulum; Step 23: Calculate the equivalent pendulum length L based on the frequency f of the pendulum's free oscillation. Step 22 includes: For a simple pendulum in a free swing state, the radial acceleration of the pendulum during free swing is measured, and the frequency f of the free swing of the pendulum is obtained by frequency identification method of fast Fourier transform (FFT). In step 23, the equivalent pendulum length L of the simple pendulum is calculated as follows: ； Where, the equivalent pendulum length L is the distance from the actual center of gravity of the pendulum to its own axis of rotation, in mm; g is the acceleration due to gravity; and π is pi. Step 3 includes: Based on the vertical distance R from the pendulum's installation position to the rotor hub center and the pendulum's equivalent length L, the natural frequency of the pendulum in the centrifugal force field of the rotating rotor is calculated. for: ； Where Ω is the blade rotation frequency.

2. The method for designing the natural frequency of a simple pendulum in a centrifugal force field according to claim 1, characterized in that, The vibration control objects in step 1 include one or more of the pilot's seat, operator's seat, and crew seats in the helicopter. The target position is the installation position corresponding to each seat, and the vibration frequency is the vibration frequency of the target position.

3. The method for designing the natural frequency of a simple pendulum in a centrifugal force field according to any one of claims 1 to 2, characterized in that, Step 1 further includes: The vibration frequency of the vibration control object is taken as the target natural frequency of the pendulum; and the difference between the natural frequency of the pendulum calculated in step 3 and the target natural frequency is less than a preset frequency threshold.

4. The method for designing the natural frequency of a simple pendulum in a centrifugal force field according to claim 3, characterized in that, The method further includes: The initial installation position of the pendulum is determined in step 21, and the vertical distance from the pendulum installation position to the center of the propeller hub is R0; Step 4: Compare the natural frequency of the pendulum calculated in Step 3. When the difference between the pendulum's natural frequency and the target natural frequency in step 1 is greater than or equal to a preset frequency threshold, the pendulum's installation position is adjusted.

5. A vibration control method for a helicopter, characterized in that, include: Step A: Using the design method of the natural frequency of a pendulum in a centrifugal force field as described in any one of claims 1 to 4, a pendulum is installed on the vibration control object of the helicopter; Step B involves conducting a test flight on the helicopter equipped with the pendulum to measure the vibration value of the vibration control object at the target location, in order to verify the vibration control effect of the pendulum.

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