Coaxial helicopter vibration response prediction method and device

Abstract

The invention provides a coaxial helicopter vibration response prediction method. The method comprises the following steps: testing coaxial helicopter body vibration and rotor wing load data in a small speed range; calculating high-order dynamic loads at the centers of upper and lower rotor hubs of the helicopter at different speeds; comparing coaxial helicopter body vibration and rotor wing load data in a small speed range with a theoretically calculated high-order dynamic load at the center of a propeller hub to obtain a high-order dynamic load correction coefficient; the high-order dynamic load correction coefficient is adopted to correct the high-order dynamic load, obtained through theoretical calculation, at the center of the propeller hub; based on the corrected high-order dynamic load at the center of the propeller hub, vibration response prediction within the full-speed envelope range of the coaxial helicopter is carried out; meanwhile, the invention further provides a coaxial helicopter vibration response prediction device. According to the invention, vibration response prediction can be carried out, and the excessive vibration risk is avoided.

Description

Technical Field

[0001] The present application belongs to the technical field of helicopter dynamics, and in particular relates to a method and device for predicting the vibration response of a coaxial helicopter. Background Art

[0002] Helicopters are one of the most complex mechanical systems. The interconnection of various rotating parts with the body and system will inevitably lead to complex helicopter dynamics problems. Improper handling of these problems will inevitably lead to increased helicopter vibration and even cause major accidents. Therefore, dynamic design must be carried out throughout the helicopter design process. The goal of dynamic design is to reduce the vibration level of the helicopter. This is because the vibration level of the helicopter is one of the important indicators to measure the advancement of the helicopter. 40% of helicopter accidents are related to vibration, which is related to the success or failure of helicopter development.

[0003] For coaxial helicopters, their dynamics are complex and particular: due to the use of upper and lower rigid rotors and thrust propellers, the aerodynamic interference between them is particularly serious, and the hub vibration load is also higher than that of conventional helicopters, making the vibration load and vibration response prediction of coaxial helicopters particularly important, and the calculation method is also more complicated. Before completing the full-speed envelope test flight, it is generally necessary to predict the vibration response to avoid the risk of excessive vibration. Summary of the invention

[0004] The purpose of the present invention is: This application explores a method for predicting the vibration response of a coaxial helicopter based on the configuration characteristics of the coaxial helicopter, which can effectively guide scientific research test flights within the full speed envelope.

[0005] In a first aspect, the present application provides a method for predicting vibration response of a coaxial helicopter, the method comprising:

[0006] Test the coaxial helicopter body vibration and rotor load data within a small speed range;

[0007] Calculate the high-order dynamic loads at the center of the upper and lower rotor hubs of the helicopter at different speeds;

[0008] Compare the coaxial helicopter body vibration and rotor load data in the small speed range with the theoretically calculated high-order dynamic loads at the hub center to obtain the high-order dynamic load correction coefficient;

[0009] The high-order dynamic load correction coefficient is used to correct the high-order dynamic load at the center of the hub obtained by theoretical calculation;

[0010] Based on the corrected high-order dynamic loads at the hub center, the vibration response prediction of the coaxial helicopter within the full speed envelope is carried out.

[0011] Preferably, the rotor load data includes rotor typical profile flapping, shimmy load, inner and outer rotor shaft torque load, bending moment load and axial force.

[0012] Preferably, before testing the coaxial helicopter body vibration and rotor load data within a small speed range, the method further includes:

[0013] Based on the helicopter structure digital model and finite element modeling method, a finite element model of the coaxial helicopter's full-body dynamics is established;

[0014] Based on the established finite element model of the coaxial helicopter's full-body dynamics, the correlation analysis of the dynamic loads at the upper and lower rotor hub centers was carried out, and the force element that is more sensitive to the vibration response was obtained.

[0015] Preferably, the test of the coaxial helicopter body vibration and rotor load data within a small speed range includes:

[0016] Through test modification, the coaxial helicopter body vibration and rotor load data within a small speed range are tested on the technology verification aircraft.

[0017] Preferably, the calculation of the high-order dynamic loads at the center of the upper and lower rotor hubs of the helicopter at different speeds includes:

[0018] Based on the free wake model and uniform inflow model, the high-order dynamic loads at the center of the upper and lower rotor hubs of the helicopter at different speeds are calculated.

[0019] Preferably, before calculating the high-order dynamic loads at the center of the upper and lower rotor hubs of the helicopter at different speeds based on the free wake model and the uniform inflow model, the method further includes:

[0020] Get the free wake model and the uniform inflow model.

[0021] Preferably, the prediction of the vibration response within the full speed envelope of the coaxial helicopter based on the corrected high-order dynamic load at the hub center includes:

[0022] Applying the above loads to the full-machine dynamic finite element model of the coaxial helicopter through the high-order dynamic loads at the center of the upper and lower rotor hubs corrected by the high-speed state;

[0023] The frequency response analysis was performed using Nastran software, and the modal superposition method was used to calculate the vibration response amplitude of the driver's seat floor at the frequencies of interest.

[0024] In a second aspect, the present application further provides a coaxial helicopter vibration response prediction device, the device comprising:

[0025] Test module, used to test the vibration and rotor load data of coaxial helicopter in a small speed range;

[0026] A processing module is used to calculate the high-order dynamic loads at the center of the upper and lower rotor hubs of the helicopter at different speeds;

[0027] An analysis module is used to compare the coaxial helicopter body vibration and rotor load data within a small speed range with the theoretically calculated high-order dynamic loads at the hub center to obtain the high-order dynamic load correction coefficient;

[0028] A correction module, used to correct the high-order dynamic load at the center of the hub obtained by theoretical calculation by using the high-order dynamic load correction coefficient;

[0029] The prediction module is used to predict the vibration response of the coaxial helicopter within the full speed envelope based on the corrected high-order dynamic loads at the center of the hub.

[0030] Beneficial technical effects of this application:

[0031] The present application provides a method for predicting the vibration response of a coaxial helicopter, which performs vibration response prediction, avoids the risk of excessive vibration, and can effectively guide scientific research test flights within the full speed envelope. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a schematic diagram of a rotor shaft load test provided in an embodiment of the present application;

[0033] Figure 2 is a schematic diagram of load correction coefficients provided in an embodiment of the present application;

[0034] Figure 3 is a schematic diagram of vibration response prediction values ​​provided in an embodiment of the present application;

[0035] Figure 4 It is a coaxial helicopter vibration response prediction flow chart provided in an embodiment of the present application. DETAILED DESCRIPTION

[0036] See also Figure 1-Figure 4 The present application provides a coaxial helicopter vibration response prediction method, comprising the following steps:

[0037] Step 1: Establish a finite element model of the coaxial helicopter's full-body dynamics based on the helicopter structure digital model and finite element modeling method.

[0038] The coaxial helicopter stiffness model mainly simulates the main load-bearing components such as the fuselage structure frame, beams, floor, and skin, simplifies the structures such as the main reducer, engine, and landing gear, and does not simulate secondary structures such as pedals and maintenance covers. On the basis of the dynamic stiffness model, the weight of equipment and structure is added, the concentrated mass unit is used to simulate the weight of equipment, and the compensation mass point method is used for the mass of the structural unit and distributed cables to complete the dynamic mass modeling of the whole aircraft.

[0039] The finite element modeling of the whole aircraft dynamics follows the principles of mechanical equivalence and mass equivalence, while taking into account the calculation accuracy, calculation speed and economy. The units used in the model are:

[0040] 1) Point element: used to define the concentrated mass of the node;

[0041] 2) Rod unit: rods that only bear axial loads, engine struts, horizontal tail rudder struts, etc.;

[0042] 3) Beam unit: inner and outer flanges of frame and beam structure, ribs on webs, long stringers, cockpit frames, etc.;

[0043] 4) Shell elements: frames, beams, floors, skins, equipment installation platforms and other panels;

[0044] 5) Multi-point constraint unit: used to define rigid connection. The connection definition must be consistent with the structural load transfer relationship;

[0045] 6) Multi-point constraint unit: used to connect concentrated mass points with structures.

[0046] Step 2: Based on the established finite element model of the coaxial helicopter's full-body dynamics, the correlation analysis of the dynamic loads at the center of the upper and lower rotor hubs is performed to obtain the force elements that are more sensitive to vibration response.

[0047] Based on the full aircraft dynamics finite element model established in the first step, a unit force load [FX 上 , FY 上 , FZ 上 , MX 上 , MY 上 , MZ 上 ] and [FX 下 , FY 下 , FZ 下 , MX 下 , MY 下 , MZ 下 ], where FX 上 Indicates the horizontal force along the X direction at the center of the upper rotor hub, FY 上 Indicates the horizontal force along the Y direction at the center of the upper rotor hub, FZ 上 Indicates the force along the Z direction at the center of the upper rotor hub, MX 上 Indicates the bending moment around the X-axis at the center of the upper rotor hub, MY 上 Indicates the bending moment around the Y axis at the center of the upper rotor hub, MZ 上 Indicates the torque around the Z axis at the center of the upper rotor hub, FX 下 Indicates the horizontal force along the X direction at the center of the lower rotor hub, FY 下 It represents the horizontal force in the Y direction at the center of the lower rotor hub, FZ 下It represents the Z-direction force at the center of the lower rotor hub, MX 下 Indicates the bending moment around the X-axis at the center of the lower rotor hub, MY 下 It represents the bending moment around the Y axis at the center of the lower rotor hub, MZ 下 It represents the torque around the Z-axis at the center of the lower rotor hub.

[0048] The modal superposition method is used to perform frequency domain response analysis using Nastran software. The modal superposition method uses the undamped vibration mode (mode) of the system as the spatial basis, decouples the original driving equation through coordinate transformation, solves N independent equations to obtain the modal displacement, and then obtains the response of the system by superimposing the contribution of each order mode. The driver's seat floor is selected as the vibration response evaluation point, and the vibration response amplitude of this position at the frequency of interest is calculated. The frequency of interest is the main rotor speed frequency.

[0049] Above Rotor FX 上 Taking load as an example, ten groups of force elements are selected, and the load values ​​are 10% to 100% of the unit load, and the other force elements are all 0. They are applied to the finite element model in turn, and 10 groups of driver seat floor vibration response values ​​are calculated.

[0050] The same calculation method was adopted for the other 11 force elements, and a total of 120 sets of vibration response amplitudes were obtained. The correlation coefficient between each force element and the vibration response was calculated, and 12 correlation coefficients [P FX上 , P FY上 , P FZ上 , P MX上 , P MY上 , P MZ上 , P FX下 , P FY下 , P FZ下 , P MX下 , P MY下 , P MZ下 ], where P FX上 P represents the correlation between the horizontal force in the X direction and the vibration response at the center of the upper rotor hub, FY上 P represents the correlation between the horizontal force in the Y direction and the vibration response at the center of the upper rotor hub, FZ上 P represents the correlation between the Z-direction force and the vibration response at the center of the upper rotor hub, MX上 represents the correlation between the bending moment around the X-axis and the vibration response of the upper rotor hub center, P MY上 represents the correlation between the bending moment around the Y axis and the vibration response of the upper rotor hub center, P MZ上 P represents the correlation between the torque around the Z axis and the vibration response of the upper rotor hub center. FX下 represents the correlation between the horizontal force in the X direction and the vibration response at the center of the lower rotor hub, P FY下 represents the correlation between the horizontal force in the Y direction and the vibration response at the center of the lower rotor hub, P FZ下represents the correlation between the Z-direction force and the vibration response at the center of the lower rotor hub, P MX下 represents the correlation between the bending moment around the X-axis and the vibration response of the lower rotor hub center, P MY下 represents the correlation between the bending moment around the Y-axis and the vibration response of the lower rotor hub center, P MZ下 It represents the correlation between the torque around the Z-axis and the vibration response of the lower rotor hub center.

[0051] The correlation coefficient is Pearson's correlation coefficient, and the correlation coefficient formula of the two variables x and y is as follows: It is the product of the covariance of the variables divided by the variance of the variables. The trend range of this correlation coefficient is [-1, 1]. A value greater than 0 indicates a positive correlation, and a value less than 0 indicates a negative correlation. The closer the absolute value is to 1, the higher the degree of correlation.

[0052] Step 3: Test the coaxial helicopter rotor load data within a small speed range on the verification aircraft.

[0053] Strain gauges for measuring the axial force, bending moment and torque of the rotor shaft are arranged on the inner and outer rotor shafts. Two sets of bending moment measuring strain gauges are arranged at different sections of the inner and outer rotor shafts (at a certain distance apart), two sets of bending moment measuring strain gauges are arranged at mutually perpendicular positions on the same section, and one set of torque and axial force strain gauges are arranged on each of the inner and outer rotor shafts. All equipment must be calibrated by the measurement unit and ensured to be within the effective use range.

[0054] The rotor load data of the helicopter is measured within the range of low speed (0-40km / h), including the axial force of the inner and outer rotor shafts, the bending moment of the rotor shafts and the torque. The measured data is analyzed and processed, and each stable speed segment is selected to perform Fourier transform on the time domain load data to obtain the frequency domain response value of each load at the frequency of interest, which refers to the main rotor speed frequency.

[0055] Step 4: Based on the free wake model and uniform inflow model, calculate the high-order dynamic loads at the center of the upper and lower rotor hubs of the helicopter at different speeds.

[0056] The hub load calculation modeling is carried out based on the structural parameters of the rotor main hub and main blades. The main parameters include the mass distribution, flapping stiffness distribution, swing stiffness distribution, torsional stiffness distribution, tensile stiffness distribution, moment of inertia distribution and section center of gravity position of different blade sections, as well as the aerodynamic layout parameters of the main blades and the position parameters of the upper and lower rotor control nodes.

[0057] CAMRADⅡ was used to carry out hub load calculation. Through CAMRADⅡ software, the calculation models of coaxial twin rotors, thrust propellers and fuselage were established. The aerodynamic model of the main rotor adopted the general free wake model and elastic blade model, and the tail thrust propeller adopted the general uniform inflow model and rigid blade model.

[0058] Based on the above model, the dynamic load calculation of the main rotor hub center is carried out, and the high-order (main rotor speed frequency) dynamic load of the rotor hub center in different flight states is calculated [FX 上 , FY 上 , FZ 上 , MX 上 , MY 上 , MZ 上 ] and [FX 下 , FY 下 , FZ 下 , MX 下 , MY 下 , MZ 下 ].

[0059] Step 5: Compare the measured load data in the low-speed section with the theoretically calculated hub center load data to obtain the high-order dynamic load correction factor.

[0060] Taking the rotor shaft as an example, according to the third step, the measured load data [F, M, M1, M1', M2, M2'] in the small speed range are obtained, where F represents the axial force of the rotor shaft, M represents the torque of the rotor shaft, M1, M1', M2 and M2' represent the bending moment of the rotor shaft, the strain gauges of the bending moment M1 and M1' are in the same section and perpendicular to each other, the strain gauge of the bending moment M1 coincides with the longitudinal section of the fuselage, and the strain gauge of the bending moment M2 coincides with the transverse section of the fuselage, as shown in the figure Figure 1 The lower rotor shaft is the same as the upper rotor shaft.

[0061] According to the force translation method, the measured rotor shaft load is converted into the six force elements at the hub center. The process is as follows:

[0062] FX 实测 =(M 2’ -M 1’ ) / △L

[0063] FY 实测 =(M2-M1) / △L

[0064] FZ 实测 =F

[0065] MX 实测 =M 2’ -(M 2’ -M 1’ )×L / △L

[0066] MY 实测 =M2-(M2-M1)×L / △L

[0067] Z 实测 =M

[0068] According to the above method, the measured rotor shaft load [F, M, M1, M1', M2, M2'] is converted into the hub center six forces [FX 实测上 , FY 实测上 , FZ 实测上 , MX 实测上 , MY 实测上 , MZ 实测上 ] and [FX 实测下 , FY 实测下 , FZ 实测下 , MX 实测下 , MY 实测下 , MZ 实测下 ].

[0069] The 12 correlation coefficients [P FX上 , P FY上 , P FZ上 , P MX上 , P MY上 , P MZ上 , P FX下 , P FY下 , P FZ下 , P MX下 , P MY下 , P MZ下 ] is normalized to obtain [P FX上’ , P FY上’ , P FZ上’ , P MX上’ , P MY上’ , P MZ上’ , P FX下’ , P FY下’ , P FZ下’ , P MX下’ , P MY下’ , P MZ下’ ].

[0070] Taking the above rotor FX load as an example, it is corrected and the correction factor is μ FX , the calculation formula is as follows:

[0071] μ FX =FX 实测上 / FX 上 ×P FX上’

[0072] By analogy, we can obtain 12 load correction factors [μ FX上 , μ FY上 , μ FZ上 , μ MX上 , μ MY上 , μ MZ上 , μ FX下 , μ FY下 , μ FZ下 , μMX下 , μ MY下 , μ MZ下 ].

[0073] The measured load values ​​and calculated values ​​at each low-speed state point are corrected and calculated to obtain several groups of load correction coefficients. The arithmetic mean of each coefficient is taken as the final load correction coefficient of this type of helicopter.

[0074] Step 6: Use high-order load correction factors to correct the calculated rotor dynamic loads.

[0075] CAMRADⅡ is used to calculate the high-order dynamic loads at the center of the upper and lower rotor hubs at high speeds (100km / h to 400km / h) [FX 上 , FY 上 , FZ 上 , MX 上 , MY 上 , MZ 上 ] and [FX 下 , FY 下 , FZ 下 , MX 下 , MY 下 , MZ 下 ], only the stable forward flight state is considered.

[0076] Among them, the upper rotor hub load only considers the influence of the upper short tie rod load on the hub load, and does not consider the influence of the long tie rod on the upper rotor hub load; the lower rotor hub load considers the influence of the tie rod load on the hub load.

[0077] Multiply the high-order dynamic loads of the upper and lower rotors at high speed by the load correction coefficient obtained in step 5 to obtain the corrected high-order dynamic loads of the upper and lower rotors [FX 上’ , FY 上’ , FZ 上’ , MX 上’ , MY 上’ , MZ 上’ ] and [FX 下’ , FY 下’ , FZ 下’ , MX 下’ , MY 下’ , MZ 下’ ].

[0078] Step 7: Predict the vibration response of the coaxial helicopter within the full speed envelope based on the corrected hub center dynamic load.

[0079] Through the sixth step, the high-order dynamic loads [FX 上’ , FY 上’ , FZ上’ , MX 上’ , MY 上’ , MZ 上’ ] and [FX 下’ , FY 下’ , FZ 下’ , MX 下’ , MY 下’ , MZ 下’ ], the above loads are applied to the first step full-machine dynamics finite element model, the frequency response analysis is performed using Nastran software, and the modal superposition method is used to calculate the vibration response amplitude of the driver's seat floor at the frequency of interest.

[0080] The same method is used within the full speed envelope, and the vibration response prediction results of the coaxial helicopter within the full envelope are finally calculated.

[0081] In other embodiments of the present application, the present application provides a coaxial helicopter vibration response prediction method, comprising the following steps:

[0082] Step 1: Establish a finite element model of the coaxial helicopter's full-body dynamics based on the helicopter structure digital model and finite element modeling method.

[0083] Step 2: Based on the established finite element model of the coaxial helicopter's full-body dynamics, the correlation analysis of the dynamic loads at the center of the upper and lower rotor hubs was carried out, and the correlation coefficients of the 12 force elements [0.556, 0.648, 0.903, 0.872, 0.828, 0.675, 0.622, 0.702, 0.953, 0.861, 0.881, 0.565] were obtained.

[0084] Step 3: Through test flights, measure the coaxial helicopter rotor load data within a small speed range. In the forward flight state at 40km / h, the measured rotor loads are upper rotor shaft force 120N, upper rotor shaft bending moments 56Nm and 62Nm, and torque 92Nm; lower rotor shaft force 136N, upper rotor shaft bending moments 98Nm and 83Nm, and torque 130Nm.

[0085] Step 4: Using CAMRADⅡ to calculate, in the forward flight state of 40km / h, the high-order dynamic loads at the center of the upper and lower rotor hubs of the helicopter are [38N, 36N, 135N, 61Nm, 72Nm, 102Nm] and [47N, 64N, 142N, 105Nm, 110Nm, 148Nm].

[0086] Step 5: Compare the measured load data with the theoretically calculated hub center load data to obtain the high-order dynamic load correction factor as shown below:

[0087] [0.583,0.681,0.948,0.915,0.869,0.708,0.652,0.737,1.000,0.903,0.925,0.593].

[0088] Step 6: Use the high-order load correction coefficient to correct the calculated rotor dynamic load. In the forward flight state of 400km / h, the corrected upper and lower rotor high-order dynamic loads are [496N, 335N, 940N, 690Nm, 789Nm, 1052Nm] and [560N, 654N, 1174N, 1076Nm, 1180Nm, 1670Nm].

[0089] Step 7: Based on the corrected hub center dynamic load, the vibration response of the coaxial helicopter is predicted. In the forward flight state of 400km / h, the vibration response amplitude at the pilot seat floor is 0.78g.

Claims

1. A method for predicting the vibration response of a coaxial helicopter, characterized in that: The method comprises: Test the coaxial helicopter body vibration and rotor load data within a small speed range; Calculate the high-order dynamic loads at the center of the upper and lower rotor hubs of the helicopter at different speeds; Compare the coaxial helicopter body vibration and rotor load data in the small speed range with the theoretically calculated high-order dynamic loads at the hub center to obtain the high-order dynamic load correction coefficient; The high-order dynamic load correction coefficient is used to correct the high-order dynamic load at the center of the hub obtained by theoretical calculation; Based on the corrected high-order dynamic loads at the hub center, the vibration response prediction of the coaxial helicopter within the full speed envelope is carried out.

2. The method according to claim 1, characterized in that The rotor load data includes typical rotor profile flapping, shimmy load, inner and outer rotor shaft torque load, bending moment load and axial force.

3. The method according to claim 1, characterized in that Before testing the vibration and rotor load data of the coaxial helicopter within a small speed range, the method also includes: Based on the helicopter structure digital model and finite element modeling method, a finite element model of the coaxial helicopter's full-body dynamics is established; Based on the established finite element model of the coaxial helicopter's full-body dynamics, the correlation analysis of the dynamic loads at the upper and lower rotor hub centers was carried out, and the force element that is more sensitive to the vibration response was obtained.

4. The method according to claim 1, characterized in that: The test of the coaxial helicopter body vibration and rotor load data within a small speed range includes: Through test modification, the coaxial helicopter body vibration and rotor load data within a small speed range are tested on the technology verification aircraft.

5. The method according to claim 1, characterized in that The calculation of the high-order dynamic loads at the center of the upper and lower rotor hubs of the helicopter at different speeds includes: Based on the free wake model and uniform inflow model, the high-order dynamic loads at the center of the upper and lower rotor hubs of the helicopter at different speeds are calculated.

6. The method according to claim 5, characterized in that Before calculating the high-order dynamic loads at the center of the upper and lower rotor hubs of the helicopter at different speeds based on the free wake model and the uniform inflow model, the method further includes: Get the free wake model and the uniform inflow model.

7. The method according to claim 3, characterized in that The vibration response prediction of the coaxial helicopter within the full speed envelope based on the corrected high-order dynamic load at the hub center includes: Applying the above loads to the full-machine dynamic finite element model of the coaxial helicopter through the high-order dynamic loads at the center of the upper and lower rotor hubs corrected by the high-speed state; The frequency response analysis was performed using Nastran software, and the modal superposition method was used to calculate the vibration response amplitude of the driver's seat floor at the frequencies of interest.

8. A coaxial helicopter vibration response prediction device, characterized in that: The device comprises: Test module, used to test the vibration and rotor load data of coaxial helicopter in a small speed range; A processing module is used to calculate the high-order dynamic loads at the center of the upper and lower rotor hubs of the helicopter at different speeds; An analysis module is used to compare the coaxial helicopter body vibration and rotor load data within a small speed range with the theoretically calculated high-order dynamic loads at the hub center to obtain the high-order dynamic load correction coefficient; A correction module, used to correct the high-order dynamic load at the center of the hub obtained by theoretical calculation by using the high-order dynamic load correction coefficient; The prediction module is used to predict the vibration response of the coaxial helicopter within the full speed envelope based on the corrected high-order dynamic loads at the center of the hub.

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