Method and device for acquiring modal parameters of airframe through simulation analysis

Abstract

The invention belongs to the field of structural strength design of helicopters, and relates to a method and a device for acquiring modal parameters of an airframe through simulation analysis. The method comprises the following steps: optimizing a full-aircraft dynamic model based on the requirements of ground resonance and tail rotor and tail beam coupling stability calculation; aiming at the requirement of tail rotor and tail beam coupling stability calculation, increasing the structural damping of a machine body in an existing full-machine dynamic model; for a typical state, performing complex modal calculation based on the kinetic model of the airframe on the undercarriage to obtain the modal frequency, the modal damping ratio, the modal mass, the modal shape and the modal vector of the airframe on the undercarriage; obtaining a modal shape of one key point from the modal shapes, and obtaining a modal vector of the key point from the modal vectors according to the modal shape of the key point; according to the modal vectors of the key points, the modal mass is converted into the modal mass normalized according to the key points, and therefore the corresponding modal rigidity and modal damping are calculated.

Description

Technical Field

[0001] The invention belongs to the field of helicopter structural strength design and relates to a method and a device for obtaining body modal parameters through simulation analysis. Background Art

[0002] To ensure helicopter safety, stability simulation and analysis are crucial. A key factor in successful stability simulation is the rapid and accurate input of the airframe modal parameters. Understanding the stability of helicopters and developing stability control plans during the initial stages of model development, before stability testing, is crucial for ensuring flight safety. On the one hand, stability testing typically requires significant time and effort, impacting model development progress. On the other hand, resolving stability issues or achieving the goal of predicting unstable areas often requires optimizing the rotor system, airframe structure, and landing gear system. This makes it difficult to modify the design or implement stability control measures during the test flight phase.

[0003] The traditional method is to obtain the airframe modal parameters through the main rotor hub center dynamic characteristics test or the tail rotor hub center dynamic characteristics test. The main rotor hub center dynamic characteristics test or the tail rotor hub center dynamic characteristics test can only be carried out under the condition that a scientific research prototype has been available in the trial production stage. The acquisition of the airframe modal parameters is relatively lagging. At this time, it is found that the ground resonance or the rotor tail beam coupling characteristics cannot meet the requirements, resulting in design iterations. At the same time, it takes more time and development costs, and even brings about disruptive improvements, which brings great risks to model development. Summary of the Invention

[0004] Purpose of the invention: To propose a method for quickly obtaining the modal parameters of an aircraft body through simulation analysis. Compared with the traditional method of obtaining modal parameters, the method is simpler, more direct and easier to operate, and can accurately predict the ground resonance and tail rotor tail boom coupling stability in the early stage of model design.

[0005] Technical solution:

[0006] In a first aspect, a method for obtaining body modal parameters through simulation analysis is provided, comprising:

[0007] Optimize the full-aircraft dynamics model based on the needs of ground resonance and tail-rotor-tail-boom coupled stability calculations: To meet the needs of ground resonance calculations, the stiffness and damping parameters of the landing gear are added to the existing full-aircraft dynamics model based on the performance parameters of the landing gear. To meet the needs of tail-rotor-tail-boom coupled stability calculations, the structural damping of the airframe is added to the existing full-aircraft dynamics model.

[0008] For a typical state, complex modal calculation is performed based on the dynamic model of the airframe on the landing gear to obtain the modal frequency, modal damping ratio, modal mass, modal vibration shape and modal vector of the airframe on the landing gear.

[0009] The modal vibration shape of a key point is obtained from the modal vibration shape, and the modal vector of the key point is obtained from the modal vector according to the modal vibration shape of the key point; the key points are selected as the center of the main rotor hub and the center of the tail rotor hub. If it is used as the input of the ground resonance, the center of the main rotor hub is used as the key point; if it is used as the input of the tail rotor and tail boom coupling stability calculation, the center of the tail rotor hub is used as the key point;

[0010] According to the modal vectors of the key points, the modal mass is converted into the modal mass normalized by the key points, so as to calculate the corresponding modal stiffness and modal damping.

[0011] Furthermore, the modal mass calculation method includes:

[0012] According to the modal frequency and damping ratio of the airframe on the landing gear, the modal mass and modal vibration shape are obtained.

[0013] Furthermore, the method further comprises:

[0014] All modal parameters of the same key point under different typical states are obtained to carry out stability calculations; the modal parameters of the key point include: modal mass, modal damping, modal stiffness, modal frequency, damping ratio normalized by the key point, and modal vibration shape of the key point.

[0015] Furthermore, the r-th modal mass M normalized by the key point is r The calculation formula is:

[0016] ;

[0017] in, is the modal mass before conversion; is the r-th order modal vector of key point i.

[0018] Furthermore, the r-th order modal stiffness K normalized by the key point is r The calculation formula is:

[0019] ;

[0020] in, is the rth order modal frequency.

[0021] Furthermore, the r-th modal damping C normalized by the key point is r The calculation formula is:

[0022] ;

[0023] in, is the r-th order modal damping ratio.

[0024] In a second aspect, a device for obtaining body modal parameters through simulation analysis is provided, comprising:

[0025] The optimization module is used to optimize the full-aircraft dynamics model based on the needs of ground resonance and tail-rotor-tail-boom coupling stability calculations. To meet the needs of ground resonance calculations, the stiffness and damping parameters of the landing gear are added to the existing full-aircraft dynamics model based on the performance parameters of the landing gear. To meet the needs of tail-rotor-tail-boom coupling stability calculations, the structural damping of the airframe is added to the existing full-aircraft dynamics model.

[0026] A processing module is used to perform complex modal calculation based on a dynamic model of the aircraft body on the landing gear for a typical state to obtain the modal frequency, modal damping ratio, modal mass, modal vibration shape and modal vector of the aircraft body on the landing gear;

[0027] An acquisition module is used to obtain the modal vibration shape of a key point from the modal vibration shape, and obtain the modal vector of the key point from the modal vector according to the modal vibration shape of the key point; the key points are selected as the center of the main rotor hub and the center of the tail rotor hub. If it is used as the input of the ground resonance, the center of the main rotor hub is used as the key point; if it is used as the input of the tail rotor and tail boom coupling stability calculation, the center of the tail rotor hub is used as the key point;

[0028] The conversion module is used to convert the modal mass into the modal mass normalized by key points according to each order modal vector, so as to calculate the corresponding modal stiffness and modal damping.

[0029] Furthermore, the processing module is specifically used to:

[0030] According to the modal frequency and damping ratio of the airframe on the landing gear, the modal mass and modal vibration shape are obtained.

[0031] Beneficial effects:

[0032] The present invention proposes a method for rapidly obtaining airframe modal parameters through simulation analysis, which meets the need for rapid and accurate stability assessment in the early stages of model development, and provides accurate and reliable airframe modal parameters for helicopter stability and strength design, which is of great significance for ensuring helicopter flight safety.

[0033] The present invention can obtain the airframe modal parameters more quickly, ensure the needs of helicopter stability simulation, provide an accurate and reliable simulation analysis method for stability strength design, and can carry out stability simulation strength design more accurately, with high universality and engineering application value.

[0034] The present invention proposes to directly obtain modal parameters through the dynamic model of the fuselage on the landing gear for stability calculation. The modal parameters include modal mass, modal damping, modal stiffness, modal frequency, damping ratio and vibration mode at key positions, forming a method for rapid evaluation of helicopter stability. It is achieved in the early stage of model design that the fuselage modal parameters are obtained as input for ground resonance and tail rotor tail boom coupling to achieve precise design of ground resonance and tail rotor tail boom coupling, and achieve the purpose of accurately predicting the stability of ground resonance and tail rotor tail boom coupling. It has high engineering value in new aircraft stability analysis, vibration problem troubleshooting and vibration control plan work. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a flow chart of a method for obtaining body modal parameters through simulation analysis;

[0036] Figure 2 It is a schematic diagram of a dynamic model of a typical weight state and a typical lift state according to the present invention. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the implementation of this application clearer, the technical solutions in the implementation of this application will be described in more detail below in conjunction with the drawings in the implementation of this application. In the drawings, the same or similar numbers throughout represent the same or similar elements or elements with the same or similar functions. The described implementation is a part of the implementation of this application, not all of the implementations. The implementation described below with reference to the drawings is exemplary and is intended to be used to explain this application, and should not be understood as a limitation on this application. Based on the implementation in this application, all other implementations obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application. The implementation of this application is described in detail below in conjunction with the drawings.

[0038] In the description of the present invention, it should be understood that the terms "center", "axial", "vertical", "up", "down", "upper end", "bottom end", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the scope of protection of the present invention.

[0039] This invention uses a dynamic model of the aircraft on the landing gear to quickly obtain modal parameters: modal mass, modal damping, modal stiffness, modal frequency, damping ratio, and vibration mode at key locations. The modal parameters of the aircraft are then selected for stability calculation. The basic formula designed in this patent is as follows:

[0040] The equation of motion is simplified into the following form:

[0041] ;

[0042] Where [M], [K], and [C] are the mass matrix, stiffness matrix, and damping matrix;

[0043] After solving, the natural frequency of the system is obtained ;

[0044] The matrix composed of modal vectors of each order is called the modal matrix ;

[0045] The modal matrix consists of the contribution of each mode to the response ;

[0046] The response of the system is written in modal coordinates as follows:

[0047] ;

[0048] ;

[0049] ;

[0050] Among them, K r and M r represent the r-th order modal stiffness and modal mass respectively;

[0051] After solving, the relationship between modal frequency, modal stiffness and modal damping can be expressed as:

[0052] ;

[0053] From the relationship between damping ratio, damping and frequency:

[0054] .

[0055] like Figure 1 The specific steps are as follows:

[0056] [1] Based on the requirements of ground resonance and tail rotor and tail boom coupling stability calculation, the full aircraft dynamics model is optimized. In order to meet the requirements of ground resonance calculation, the stiffness and damping parameters of the landing gear are added to the existing full aircraft dynamics model according to the performance parameters of the landing gear. In order to meet the requirements of tail rotor and tail boom coupling stability calculation, the structural damping of the aircraft body is added to the existing full aircraft dynamics model.

[0057] [2] Based on step [1], the dynamic model of the aircraft body on the landing gear is established and the complex modal calculation is performed according to mass normalization.

[0058] 2.1 Select the dynamic model of the aircraft on the landing gear in typical weight and lift states for complex modal calculation;

[0059] 2.2 Obtain the modal frequency and damping ratio of the fuselage on the landing gear.

[0060] [3] Based on the calculation results of step [2], the modal mass and vibration shape are obtained.

[0061] According to the purpose of the modal parameters, the key points are generally selected as the center of the main rotor hub and the center of the tail rotor hub. If it is used as the input of the ground resonance, the key point is selected as the center of the main rotor hub. If it is used as the input of the tail rotor and tail boom coupled stability calculation, the key point is selected as the center of the tail rotor hub.

[0062] [4] The modal mass normalized according to the vibration mode of a certain key point is obtained through the modal mass; the rth order modal mass normalized according to the key point is obtained. The calculation formula is:

[0063] ;

[0064] in, is the r-th order modal mass before conversion; is the r-th order modal vector of key point i.

[0065] [5] Through the modal mass M r Get the modal stiffness K r ;K r The calculation formula is:

[0066] ;

[0067] in, is the rth order modal frequency.

[0068] [6] Modal damping is obtained by damping ratio, modal mass and modal frequency; modal damping C r The calculation formula is:

[0069] ;

[0070] in, is the r-th order modal damping ratio.

[0071] [7] According to steps [1] to [6], all modal parameters of typical weight state and typical lift state are obtained and stability calculation is carried out.

[0072] Application examples:

[0073] To demonstrate the applicability and effectiveness of the present invention, the present invention was applied to a certain type of machine in the early stages of design by obtaining modal parameters through simulation analysis and performing stability calculations. The specific implementation is as follows:

[0074] S1: Based on the dynamic model of the aircraft on the landing gear in the typical weight state and typical lift state, the complex modal calculation is performed according to mass normalization to obtain the modal frequency and damping ratio of the aircraft on the landing gear. The dynamic model of the typical lift in the typical weight state is shown in Figure 2 , the calculation results of modal frequency and damping ratio, mass normalized modal mass and modal vibration shape are shown in Table 1;

[0075] Table 1 Modal parameters obtained by simulation calculation

[0076] Modal Name Modal mass (kg) Modal frequency (Hz) Damping ratio Vibration Shape X Vibration mode Y Mode Z Navigation level 1 1 0 0 0.0085 0.0000 0.0000 Lateral first order 1 0.5289 0.0848 0.0001 0.0140 0.0001 Heading Level 2 1 0.5605 0.0841 0.0055 0.0002 0.0047 Lateral second order 1 3.2227 0.0989 0.0001 0.0106 0.0000

[0077] S2: According to the calculation results of step 1, obtain the modal mass and mode shape. The mode shape calculation results are shown in Table 1;

[0078] S3: Modal mass normalized by mass The modal mass M is obtained by normalizing the mass according to the hub center modal vibration mode. r , the calculation results are shown in Table 2;

[0079] Table 2 Modal parameters normalized according to the hub center

[0080] Modal Name Modal mass (kg) Modal stiffness (N / m) Damping (Ns / m) Vibration Shape X Vibration mode Y Mode Z Navigation level 1 13776.84 0 0 1.00000 0.00000 0.00000 Lateral first order 5128.00 56641.72 2890.86 0.00668 1.00000 0.00440 Heading Level 2 33108.18 410636.11 19606.69 1.00000 0.04459 0.85631 Lateral second order 8950.07 3669667.94 35864.54 0.00622 1.00000 0.00101

[0081] S4: By modal mass M r Get the modal stiffness K r , the calculation results are shown in Table 2;

[0082] S5: Modal damping is obtained by damping ratio, modal mass and modal frequency. The calculation results are shown in Table 2.

[0083] S6: Based on S1 to S6, the relevant modal parameters of the typical weight state and typical lift state are obtained to perform stability calculation.

[0084] Other embodiments of the present disclosure will readily occur to those skilled in the art after considering the specification and practicing the disclosure herein. This application is intended to cover any variations, uses, or adaptations of the present disclosure that follow the general principles of the present disclosure and include common knowledge or customary techniques in the art not disclosed herein. The description and examples are to be considered as exemplary only, with the true scope and spirit of the present disclosure being indicated by the following claims.

[0085] It should be understood that the present disclosure is not limited to the exact structures that have been described above and shown in the drawings, and that various modifications and changes can be made without departing from the scope thereof. The scope of the present disclosure is limited only by the appended claims.

Claims

1. A method for obtaining body modal parameters through simulation analysis, characterized in that: include: Optimize the full-aircraft dynamics model based on the needs of ground resonance and tail-rotor-tail-boom coupled stability calculations: To meet the needs of ground resonance calculations, the stiffness and damping parameters of the landing gear are added to the existing full-aircraft dynamics model based on the performance parameters of the landing gear. To meet the needs of tail-rotor-tail-boom coupled stability calculations, the structural damping of the airframe is added to the existing full-aircraft dynamics model. For a typical state, complex modal calculation is performed based on the dynamic model of the airframe on the landing gear to obtain the modal frequency, modal damping ratio, modal mass, modal vibration shape and modal vector of the airframe on the landing gear. The modal vibration shape of a key point is obtained from the modal vibration shape, and the modal vector of the key point is obtained from the modal vector according to the modal vibration shape of the key point; the key points are selected as the center of the main rotor hub and the center of the tail rotor hub. If it is used as the input of the ground resonance, the center of the main rotor hub is used as the key point; if it is used as the input of the tail rotor and tail boom coupling stability calculation, the center of the tail rotor hub is used as the key point; According to the modal vectors of the key points, the modal mass is converted into the modal mass normalized by the key points, so as to calculate the corresponding modal stiffness and modal damping.

2. The method according to claim 1, characterized in that Modal mass calculation methods include: According to the modal frequency and damping ratio of the airframe on the landing gear, the modal mass and modal vibration shape are obtained.

3. The method according to claim 1, characterized in that The method further comprises: All modal parameters of the same key point under different typical states are obtained to carry out stability calculations; the modal parameters of the key point include: modal mass, modal damping, modal stiffness, modal frequency, damping ratio normalized by the key point, and modal vibration shape of the key point.

4. The method according to claim 2, characterized in that The r-th modal mass M normalized by key points r The calculation formula is: ； in, is the modal mass before conversion; is the r-th order modal vector of key point i.

5. The method according to claim 4, characterized in that Normalized r-th modal stiffness K by key points r The calculation formula is: ； in, is the rth order modal frequency.

6. The method according to claim 5, characterized in that Normalized r-th modal damping C at key points r The calculation formula is: ； in, is the r-th order modal damping ratio.

7. A device for obtaining body modal parameters through simulation analysis, characterized in that: include: The optimization module is used to optimize the full-aircraft dynamics model based on the needs of ground resonance and tail-rotor-tail-boom coupling stability calculations. To meet the needs of ground resonance calculations, the stiffness and damping parameters of the landing gear are added to the existing full-aircraft dynamics model based on the performance parameters of the landing gear. To meet the needs of tail-rotor-tail-boom coupling stability calculations, the structural damping of the airframe is added to the existing full-aircraft dynamics model. A processing module is used to perform complex modal calculation based on a dynamic model of the aircraft body on the landing gear for a typical state to obtain the modal frequency, modal damping ratio, modal mass, modal vibration shape and modal vector of the aircraft body on the landing gear; An acquisition module is used to obtain the modal vibration shape of a key point from the modal vibration shape, and obtain the modal vector of the key point from the modal vector according to the modal vibration shape of the key point; the key points are selected as the center of the main rotor hub and the center of the tail rotor hub. If it is used as the input of the ground resonance, the center of the main rotor hub is used as the key point; if it is used as the input of the tail rotor and tail boom coupling stability calculation, the center of the tail rotor hub is used as the key point; The conversion module is used to convert the modal mass into the modal mass normalized by key points according to each order modal vector, so as to calculate the corresponding modal stiffness and modal damping.

8. The device according to claim 7, characterized in that The processing module is specifically used to: According to the modal frequency and damping ratio of the airframe on the landing gear, the modal mass and modal vibration shape are obtained.

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