Method for acquiring body modal parameters of helicopter in sliding or running process

Abstract

The invention belongs to the technical field of structural strength design of helicopters, and particularly relates to a method for acquiring sliding or running state modal parameters of a helicopter. The method comprises the following steps: drawing a change curve of an undercarriage rigidity reduction coefficient and an additional damping coefficient along with the gliding / taxiing speed and the airframe frequency and a change curve of the rigidity reduction coefficient and the airframe modal frequency under the same coordinate system to obtain an intersection point of two groups of change curves so as to obtain a variable damping coefficient of the undercarriage under different gliding / taxiing speeds; the modal parameters of the aircraft body on the undercarriage are used as input to carry out ground resonance evaluation of the sliding and running state. The requirement of rapidly and accurately evaluating the ground resonance stability of the sliding state in the initial stage of model development is met, accurate and reliable body modal parameters are provided for helicopter stability design, and the method has great significance in guaranteeing the flight safety of helicopters.

Description

Technical Field

[0001] This invention belongs to the field of helicopter structural strength design technology, specifically relating to a method for obtaining modal parameters of a helicopter in taxiing or runway conditions. Background Technology

[0002] Ground taxiing or runway running is one of the main takeoff and landing methods for helicopters, especially in high-altitude areas where overloaded takeoffs and landings are frequently required. To ensure helicopter safety, stability simulation and analysis during taxiing and runway running are crucial. Compared to stability analysis during vertical takeoff and landing, helicopters exhibit two main characteristics during ground taxiing and runway running: First, due to the decrease in lateral wheel stiffness and increase in lateral damping during taxiing and runway running, the lateral first and second-order modal frequencies of the fuselage on the landing gear decrease. Wheel lateral stiffness is related to the frequency of fuselage motion and the helicopter's taxiing speed. Generally, the fuselage mode related to ground resonance during taxiing and runway running is the lateral second-order mode; therefore, only the variation of the lateral second-order modal frequency with runway speed at different taxiing speeds is considered. The collective pitch and longitudinal periodic pitch used in taxiing and runway running differ, resulting in different lift states. Secondly, as the natural frequency of the entire aircraft's roll mode decreases, the "required" damping to eliminate ground resonance also decreases. Therefore, considering both of these factors, it is necessary to determine the relationship between the rotor's critical stable speed or rotor instability center speed and the helicopter's taxiing or runway speed, and accordingly limit the helicopter's taxiing or runway speed. Using a finite element model, the relationship curves between the lateral second-order frequency and the stiffness coefficient under typical weight and lift conditions are calculated, obtaining the stiffness coefficient relationship curves at different frequencies and taxiing / runway speeds. By using the intersection points of the two sets of curves, the wheel stiffness at different taxiing / runway speeds can be obtained. The lateral damping coefficient of the wheel corresponding to the curve intersection points is calculated. Using the wheel stiffness and damping as inputs, the modal parameters under taxiing / runway conditions can be obtained through finite element model calculations, which can be used for ground resonance calculations under taxiing / runway conditions.

[0003] Rapid and accurate input of airframe modal parameters is a key factor for successful simulation calculations of helicopter taxiing and runway stability. Understanding the stability of helicopters during taxiing and runway conditions in the early stages of model development, before conducting taxiing and runway stability tests, and formulating stability control plans are crucial for ensuring helicopter flight safety. On the one hand, stability tests generally require significant time and resources, impacting the model's development schedule; therefore, developing a method for rapidly obtaining airframe modal parameters through simulation analysis is essential. Summary of the Invention

[0004] Purpose of the invention: To provide a method for obtaining modal parameters of a helicopter during taxiing or runway conditions, so as to achieve the goal of predicting stability in the early stage of model design. This method has high engineering value in new aircraft stability analysis, vibration problem investigation and vibration control contingency planning.

[0005] To address the aforementioned technical issues, according to a first aspect of the present invention, a method for obtaining modal parameters of a helicopter during taxiing or runway conditions is proposed. The modal parameters include modal mass, modal damping, modal stiffness, modal frequency, damping ratio, and mode shape at key locations. The method comprises the following steps: Step 1: Using the equilibrium state calculation method, calculate the initial equivalent stiffness K and initial damping C at the equivalent wheel center of the helicopter landing gear system; Step 2: Based on the initial equivalent stiffness K and initial damping C calculated in Step 1, construct the dynamic model of the fuselage on the landing gear. The basic formulas are as follows: (1) In the formula, [M], [K], and [C] are the mass matrix, stiffness matrix, and damping matrix, respectively; Step 3: Calculate the stiffness reduction coefficient at different taxiing or running speeds using the relationship between the stiffness coefficient and the taxiing or running speed, and plot the curves of the stiffness reduction coefficient at different taxiing or running speeds as a function of modal frequency. Step 4: Based on the stiffness reduction coefficient obtained in Step 3, update the initial equivalent stiffness K in Step 1 to obtain the updated stiffness K1; Step 5: Calculate the additional damping coefficient for different taxiing or running speeds using the relationship between the additional damping coefficient and the taxiing or running speed, and plot the curves of the additional damping coefficient as a function of modal frequency for different taxiing or running speeds. Step 6: Based on the additional damping coefficient obtained in Step 5, update the initial damping C in Step 1 to obtain the updated damping C1; Step 7: Update the dynamic model in Step 2 using the updated stiffness K1 obtained in Step 4 and the updated damping C1 obtained in Step 6, and calculate the modal frequencies using the finite element model. Step 8: Repeat steps 4-7 to obtain the updated stiffness K1 matrix and modal frequency curves; Step 9: Plot the curves from Step 3 and Step 8 on the same coordinate system, and obtain the speed of gliding or running and the modal frequency corresponding to the stiffness reduction coefficient based on the intersection points of each curve. Step 10: Using the dynamic model from Step 2, obtain the modal mass, modal damping, modal stiffness, modal frequency, damping ratio, and mode shape at key locations through finite element analysis.

[0006] In one possible embodiment, step one specifically includes the following steps: Based on the force balance equation, the loads distributed on a single landing gear under different lift and weight conditions are calculated. Then, based on landing gear performance data, the equivalent stiffness K and equivalent damping C of the corresponding landing gear loads are obtained from a table.

[0007] in, G represents gravity, measured in N; T represents lift, measured in N; Represents the load on the main landing gear, in N; Represents the load on the tail landing gear, in N; This represents the distance of the main landing gear from the center of gravity. This represents the distance between the tail landing gear and the center of gravity.

[0008] In one possible embodiment, in step three, the relationship between the stiffness coefficient and the gliding or running speed is as shown in formula (2): (2) in, Represents the helicopter's taxiing or runway speed, measured in m / s; Represents the vibration frequency of the organism, measured in Hz; Represents the radius of the tire when it is not compressed, in m / s; It represents the reduction factor of lateral stiffness when the tire is rolling.

[0009] In one possible embodiment, step four specifically includes the following steps: The updated stiffness K1 is calculated according to the following formula (5):

[0010] in Represents the initial equivalent stiffness; K1 updated equivalent stiffness; The factor representing the reduction in lateral stiffness of a tire during rolling. In one possible embodiment, in step five, the relationship between the additional damping coefficient and the gliding or running speed is as shown in formula (3): (3) in, This represents the additional damping coefficient when the tire is rolling.

[0011] Represents the helicopter's taxiing or runway speed, measured in m / s; Represents the vibration frequency of the organism, measured in Hz; Represents the radius of the tire when it is not compressed, in m / s; In one possible embodiment, step six specifically includes the following steps:

[0012] C represents the initial equivalent damping; C1 represents the updated equivalent damping; This represents the additional damping coefficient when the tire is rolling.

[0013] In one possible embodiment, in step ten, modal mass, modal damping, modal stiffness, modal frequency, damping ratio, and mode shape at key locations are obtained through finite element calculation.

[0014] According to a second aspect of the invention, a computer-readable storage medium is provided having a computer program stored thereon, which, when executed by a processor, implements the steps of the above-described method for acquiring taxiing or runway state modal parameters of a helicopter.

[0015] According to a third aspect of the present invention, an electronic device is provided, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, it implements the steps of the above-described method for acquiring taxiing or runway state modal parameters of a helicopter.

[0016] In summary, the beneficial effects of the present invention are as follows: This invention proposes a method for obtaining airframe modal parameters during taxiing or runway operation. By plotting curves showing the variation of landing gear stiffness reduction coefficient and additional damping coefficient with taxiing / runway speed and airframe frequency, and curves showing the variation of stiffness reduction coefficient with airframe modal frequency, in the same coordinate system, the intersection of these two sets of curves is obtained. This yields the airframe modal parameters on the landing gear at different taxiing / runway speeds. These parameters are then used as input for ground resonance assessment during taxiing and runway operation. This method meets the need for rapid and accurate ground resonance stability assessment during taxiing and runway operation in the early stages of model development, providing accurate and reliable airframe modal parameters for helicopter stability design, which is of great significance for ensuring helicopter flight safety. Attached Figure Description

[0017] Figure 1 This is a flowchart of the present invention, "A method for obtaining body modal parameters in helicopter taxiing or runway state"; Figure 2 This invention relates to a schematic diagram of the stiffness reduction coefficient as a function of frequency at different gliding or running speeds; Figure 3 This invention relates to a schematic diagram of the variation of the additional damping coefficient with frequency at different gliding or running speeds. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] The features and illustrative embodiments of various aspects of the present invention will now be described in detail. Numerous specific details are set forth in the following detailed description to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention may be practiced without requiring some of these specific details. The following description of embodiments is merely intended to provide a better understanding of the invention by illustrating examples of the invention. The invention is by no means limited to any specific setups and methods set forth below, but covers any improvements, substitutions, and modifications to structures, methods, and devices without departing from the spirit of the invention. Well-known structures and techniques are not shown in the drawings and the following description to avoid unnecessarily obscuring the invention.

[0020] It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other, and the various embodiments can be referenced and cited in each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0021] like Figure 1 As shown, a method for obtaining modal parameters of a helicopter during taxiing or runway conditions, wherein the modal parameters include modal mass, modal damping, modal stiffness, modal frequency, damping ratio, and mode shape at key locations; includes the following steps: The specific implementation method is as follows: S1: Using the equilibrium state calculation method, calculate the initial equivalent stiffness K and initial damping C at the equivalent wheel center of the helicopter landing gear system; S2: Based on the initial equivalent stiffness K and initial damping C calculated in step S1, construct the dynamic model of the fuselage on the landing gear. The basic formulas are as follows: (1) In the formula, [M], [K], and [C] are the mass matrix, stiffness matrix, and damping matrix, respectively. S3: Calculate the stiffness reduction factor at different taxiing or running speeds using the relationship between the stiffness coefficient and the taxiing or running speed, and plot the curves of the stiffness reduction factor as a function of modal frequency at different taxiing or running speeds, such as... Figure 2 As shown; S4: Based on the stiffness reduction coefficient obtained in step S3, update the initial equivalent stiffness K in step one to obtain the updated stiffness K1; S5: Calculate the additional damping coefficient at different taxiing or running speeds using the relationship between the additional damping coefficient and the taxiing or running speed, and plot the curves of the additional damping coefficient as a function of modal frequency at different taxiing or running speeds, such as... Figure 3 As shown; S6: Based on the additional damping coefficient obtained in step S5, update the initial damping C in step S1 to obtain the updated damping C1; S7: Update the dynamic model in step S2 using the updated stiffness K1 obtained in step S4 and the updated damping C1 obtained in step S6, and calculate the modal frequency using the finite element model. S8: Repeat steps four through seven to obtain the updated stiffness K1 matrix and modal frequency curves, as shown in Table 3. S9: Plot the curves from step three and step eight on the same coordinate system. Based on the intersection points of each curve, obtain the gliding or running speed and the modal frequency corresponding to the stiffness reduction coefficient. For example, a gliding speed of 5 m / s corresponds to a stiffness reduction coefficient of 0.6 and a body modal frequency of 3.5 Hz. Figure 2 ; S10: Using the dynamic model in step two, obtain the modal mass, modal damping, modal stiffness, modal frequency, damping ratio, and mode shape at key locations through finite element calculation.

[0022] Complex modal calculations were performed under typical weight and lift conditions to obtain the modal parameters at the corresponding taxiing or runway speeds, namely modal mass, modal frequency, modal damping, and damping ratio. The modal parameters of the fuselage on the landing gear were used as inputs, and stability calculations were carried out using a planar model.

[0023] Table 1. Stiffness reduction coefficient matrix at different gliding or running speeds as a function of frequency (partial data shown)

[0024] Table 2. The relationship between the additional damping coefficient matrix and frequency at different gliding or running speeds (partial data shown).

[0025] Table 3. Frequency Matrix Pattern Corresponding to Stiffness Reduction Coefficient (Partial Data Displayed)

Claims

1. A method for acquiring taxiing or runway mode parameters of a helicopter, characterized in that, Includes the following steps: Step 1: Using the equilibrium state calculation method, calculate the initial equivalent stiffness K and initial damping C at the equivalent wheel center of the helicopter landing gear system; Step 2: Based on the initial equivalent stiffness K and initial damping C calculated in Step 1, construct the dynamic model of the fuselage on the landing gear. The basic formulas are as follows: (1) In the formula, [M], [K], and [C] are the mass matrix, stiffness matrix, and damping matrix, respectively; Step 3: Calculate the stiffness reduction coefficient at different taxiing or running speeds using the relationship between the stiffness coefficient and the taxiing or running speed, and plot the curves of the stiffness reduction coefficient at different taxiing or running speeds as a function of modal frequency. Step 4: Based on the stiffness reduction coefficient obtained in Step 3, update the initial equivalent stiffness K in Step 1 to obtain the updated stiffness K1; Step 5: Calculate the additional damping coefficient for different taxiing or running speeds using the relationship between the additional damping coefficient and the taxiing or running speed, and plot the curves of the additional damping coefficient as a function of modal frequency for different taxiing or running speeds. Step 6: Based on the additional damping coefficient obtained in Step 5, update the initial damping C in Step 1 to obtain the updated damping C1; Step 7: Update the dynamic model in Step 2 using the updated stiffness K1 obtained in Step 4 and the updated damping C1 obtained in Step 6, and calculate the modal frequencies using the finite element model. Step 8: Repeat steps 4-7 to obtain the updated stiffness K1 matrix and modal frequency curves; Step 9: Plot the curves from Step 3 and Step 8 on the same coordinate system, and obtain the speed of gliding or running and the modal frequency corresponding to the stiffness reduction coefficient based on the intersection points of each curve. Step 10: Using the dynamic model from Step 2, obtain the modal mass, modal damping, modal stiffness, modal frequency, damping ratio, and mode shape at key locations through finite element analysis.

2. The method for acquiring taxiing or runway mode parameters of a helicopter according to claim 1, characterized in that, Step one specifically includes the following steps: Based on the force balance equation, the loads distributed on a single landing gear under different lift and weight conditions are calculated. Then, based on landing gear performance data, the equivalent stiffness K and equivalent damping C of the corresponding landing gear loads are obtained from a table. in, G represents gravity, measured in N; T represents lift, measured in N; Represents the load on the main landing gear, in N; Represents the load on the tail landing gear, in N; This represents the distance of the main landing gear from the center of gravity. This represents the distance between the tail landing gear and the center of gravity.

3. The method for acquiring taxiing or runway mode parameters of a helicopter according to claim 1, characterized in that, In step three, the relationship between the stiffness coefficient and the gliding or running speed is shown in formula (2): (2) in, Represents the helicopter's taxiing or runway speed, measured in m / s; Represents the vibration frequency of the organism, measured in Hz; Represents the radius of the tire when it is not compressed, in m / s; It represents the reduction factor of lateral stiffness when the tire is rolling.

4. The method for acquiring taxiing or runway mode parameters of a helicopter according to claim 1, characterized in that, Step four specifically includes the following steps: The updated stiffness K1 is calculated according to the following formula (5): in Represents the initial equivalent stiffness; K1 updated equivalent stiffness; It represents the reduction factor of lateral stiffness when the tire is rolling.

5. The method for acquiring taxiing or runway mode parameters of a helicopter according to claim 1, characterized in that, In step five, the relationship between the additional damping coefficient and the gliding or running speed is shown in formula (3): (3) in, This represents the additional damping coefficient when the tire is rolling.

6. Represents the helicopter's taxiing or runway speed, measured in m / s; Represents the vibration frequency of the organism, measured in Hz; Represents the radius of the tire when it is not compressed, in m / s.

7. The method for acquiring taxiing or runway mode parameters of a helicopter according to claim 1, characterized in that, Step six specifically includes the following steps: C represents the initial equivalent damping; C1 represents the updated equivalent damping; This represents the additional damping coefficient when the tire is rolling.

8. The method for acquiring taxiing or runway mode parameters of a helicopter according to claim 1, characterized in that, In step ten, modal mass, modal damping, modal stiffness, modal frequency, damping ratio, and mode shape at key locations are obtained through finite element calculation.

9. A computer-readable storage medium, characterized in that, It stores a computer program, which, when executed by a processor, implements the steps of a method for acquiring taxiing or runway state modal parameters of a helicopter as described in any one of claims 1-7.

10. An electronic device, characterized in that, The system includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the steps of the method for acquiring taxiing or runway state modal parameters of a helicopter as described in any one of claims 1-7.

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