A coaxial helicopter vibration response prediction method and device

Abstract

The application provides a coaxial helicopter vibration response prediction method, which comprises the following steps: testing the vibration of the body of the coaxial helicopter and the rotor load data in a small speed range; calculating the high-order dynamic load at the hub center of the upper rotor and the lower rotor of the helicopter at different speeds; comparing the vibration of the body of the coaxial helicopter and the rotor load data in the small speed range with the high-order dynamic load at the hub center calculated theoretically to obtain a high-order dynamic load correction coefficient; correcting the high-order dynamic load at the hub center obtained by theoretical calculation by using the high-order dynamic load correction coefficient; and performing vibration response prediction in the full speed envelope range of the coaxial helicopter based on the corrected high-order dynamic load at the hub center. Meanwhile, the application also provides a coaxial helicopter vibration response prediction device. The application can perform vibration response prediction and avoid excessive vibration risk.

Description

Technical Field

[0001] This application belongs to the field of helicopter dynamics technology, specifically relating to a method and apparatus for predicting the vibration response of a coaxial helicopter. Background Technology

[0002] Helicopters are among the most complex mechanical systems. The interconnections between rotating components and the airframe and other systems inevitably lead to complex helicopter dynamics problems. Improper handling of these problems can exacerbate helicopter vibrations and even cause major accidents. Therefore, dynamics design must be integrated throughout the helicopter design process. The goal of dynamics design is to reduce helicopter vibration levels, as vibration level is a crucial indicator of a helicopter's advancement. Vibration is related to 40% of helicopter accidents, impacting the success or failure of helicopter development.

[0003] For coaxial helicopters, their dynamics are complex and unique: due to the use of two rigid rotors and thrust rotors, the aerodynamic interference between them is particularly severe, and the rotor hub vibration load is also higher than that of conventional helicopters. This makes the prediction of vibration load and vibration response for coaxial helicopters especially important, and the calculation methods are also more complex. Before completing full-speed envelope test flights, vibration response prediction is generally required to avoid the risk of excessive vibration. Summary of the Invention

[0004] The purpose of this invention is to propose an exploratory method for predicting the vibration response of coaxial helicopters, which can effectively guide scientific research and flight testing across the entire speed envelope, based on the configuration characteristics of coaxial helicopters.

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

[0006] Test data on airframe vibration and rotor load of coaxial helicopters within a low speed range;

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

[0008] By comparing the data of coaxial helicopter fuselage vibration and rotor load in the low speed range with the theoretically calculated high-order dynamic load at the rotor hub center, the high-order dynamic load correction coefficient is obtained.

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

[0010] Based on the corrected high-order dynamic load at the rotor hub center, vibration response prediction is performed across the entire velocity envelope of the coaxial helicopter.

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

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

[0013] Based on helicopter structural numerical modeling and finite element modeling methods, a coaxial helicopter full-aircraft dynamic finite element model is established;

[0014] Based on the established coaxial helicopter full-aircraft dynamic finite element model, the correlation analysis of dynamic loads at the upper and lower rotor hub centers was conducted to obtain force elements that are more sensitive to vibration response.

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

[0016] Through testing and modification, data on coaxial helicopter airframe vibration and rotor load were tested on a technology demonstrator aircraft within a low speed range.

[0017] Preferably, the calculation of higher-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 the uniform inflow model, the higher-order dynamic loads at the center of the upper and lower rotor hubs of the helicopter are calculated at different speeds.

[0019] Preferably, before calculating the higher-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] Obtain the free wake model and the uniform inflow model.

[0021] Preferably, the prediction of the vibration response of the coaxial helicopter across the entire velocity envelope based on the corrected high-order dynamic load at the rotor hub center includes:

[0022] The high-order dynamic loads at the centers of the upper and lower rotor hubs, after high-speed state correction, are applied to the overall dynamic finite element model of the coaxial helicopter.

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

[0024] Secondly, this application also provides a coaxial helicopter vibration response prediction device, the device comprising:

[0025] The test module is used to test coaxial helicopter airframe vibration and rotor load data within a low speed range;

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

[0027] The analysis module is used to compare the data of coaxial helicopter fuselage vibration and rotor load in a small speed range with the theoretically calculated high-order dynamic load at the rotor hub center, and obtain the high-order dynamic load correction coefficient.

[0028] The correction module is used to correct the theoretically calculated high-order dynamic load at the center of the propeller hub using the aforementioned high-order dynamic load correction coefficient.

[0029] The prediction module is used to predict the vibration response of the coaxial helicopter across the entire velocity envelope based on the corrected high-order dynamic load at the rotor hub center.

[0030] The beneficial technical effects of this application are as follows:

[0031] This application provides a method for predicting the vibration response of coaxial helicopters, which can predict the vibration response, avoid the risk of excessive vibration, and effectively guide scientific research flight tests within the full speed envelope. Attached Figure Description

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

[0033] Figure 2 This is a schematic diagram of the load correction coefficient provided in the embodiments of this application;

[0034] Figure 3 This is a schematic diagram of the vibration response prediction values ​​provided in the embodiments of this application;

[0035] Figure 4 This is a flowchart of a coaxial helicopter vibration response prediction method provided in an embodiment of this application. Detailed Implementation

[0036] Please see Figures 1-4 This application provides a method for predicting the vibration response of a coaxial helicopter, comprising the following steps:

[0037] Step 1: Establish a coaxial helicopter full-aircraft dynamic finite element model based on helicopter structural numerical modeling and finite element modeling methods.

[0038] The coaxial helicopter stiffness model primarily simulates the main load-bearing components such as the airframe frame, beams, floor, and skin. The main gearbox, engine, and landing gear are simplified, but secondary structures such as foot pedals and maintenance access panels are not simulated. Based on the dynamic stiffness model, the weight of equipment and structures is added. Lumped mass elements are used to simulate equipment weight, and compensating mass points are applied to structural elements and distributed cables to complete the overall aircraft dynamic mass model.

[0039] The finite element modeling of the whole-machine dynamics follows the principles of mechanical and mass equivalence, while also considering computational accuracy, speed, and economy. The elements used in the model include:

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

[0041] 2) Rod unit: Rods that only bear axial loads, such as engine struts and horizontal stabilizer servo struts;

[0042] 3) Beam units: inner and outer flanges of frame and beam structures, stiffeners on the web, stringers, cabin frame, etc.

[0043] 4) Shell units: frames, beams, floors, skins, equipment mounting platforms, and other plate components;

[0044] 5) Multi-point constraint element: used to define rigid connections. The defined connection must be consistent with the load transfer relationship of the structure.

[0045] 6) Multi-point constraint element: used to concentrate mass points and connect them to the structure.

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

[0047] Based on the finite element model of the whole-engine dynamics established in the first step, a unit force load [FX] is applied at the center of the upper and lower rotor hubs. 上 FY 上 FZ 上 MX 上 MY 上 MZ 上 ] and [FX 下 FY 下 FZ 下 MX 下 MY 下 MZ 下 ], of which FX 上 FY represents the horizontal force along the X-axis at the center of the upper rotor hub. 上 FZ represents the horizontal force along the Y direction at the center of the upper rotor hub. 上 MX represents the force along the Z-axis at the center of the upper rotor hub. 上 MY represents the bending moment around the X-axis at the center of the upper rotor hub. 上 MZ represents the bending moment around the Y-axis at the center of the upper rotor hub. 上 FX represents the torque around the Z-axis at the center of the upper rotor hub. 下 FY represents the horizontal force along the X-axis at the center of the lower rotor hub. 下 FZ represents the horizontal force along the Y direction at the center of the lower rotor hub. 下MX represents the force along the Z-axis at the center of the lower rotor hub. 下 MY represents the bending moment about the X-axis at the center of the lower rotor hub. 下 MZ represents the bending moment around the Y-axis at the center of the lower rotor hub. 下 This represents the torque around the Z-axis at the center of the lower rotor hub.

[0048] The modal superposition method was employed, and frequency domain response analysis was performed using Nastran software. The modal superposition method uses the undamped mode shapes (modes) of the system as the spatial basis. Through coordinate transformation, the original dynamic equations are decoupled, and N independent equations are solved to obtain the modal displacements. The system response is then obtained by superimposing the contributions of each mode. The driver's seat floor was selected as the vibration response evaluation point, and the vibration response amplitude at this location at the frequency of interest (main rotor rotation frequency) was calculated.

[0049] The above rotor FX 上 Taking load as an example, ten sets of force elements were selected, with load values ​​ranging from 10% to 100% of the unit load, and all other force elements were set to 0. These were applied sequentially to the finite element model, and the vibration response values ​​of the driver's seat floor were calculated.

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

[0051] The Pearson correlation coefficient was chosen as the correlation coefficient. The formula for the correlation coefficient between the two variables x and y is as follows: The correlation coefficient is the product of the covariance and the variance of the variables. Its trend range is [-1, 1], where 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 stronger the correlation.

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

[0053] Strain gauges for measuring the axial force, bending moment, and torque of the rotor shafts are arranged on the inner and outer rotor shafts. Two sets of bending moment strain gauges are arranged at different cross-sections (at certain intervals) on the inner and outer rotor shafts, and two sets of bending moment strain gauges are arranged at mutually perpendicular positions on the same cross-section. One set of torque and axial force strain gauges is arranged on each of the inner and outer rotor shafts. All equipment must be calibrated by a metrology unit and guaranteed to be within its valid service life.

[0054] The rotor load data of the helicopter was measured within a low speed range (0~40km / h), specifically including the axial force of the inner and outer rotor shafts, the rotor shaft bending moment, and the torque. The measured data were analyzed and processed, and Fourier transforms were performed on the time-domain load data for each stable speed range to obtain the frequency domain response values ​​of each load at the frequency of interest, which refers to the main rotor rotational speed.

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

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

[0057] Hub load calculations were performed using CAMRAD II software. A calculation model of the coaxial twin rotor, thrust propeller, and fuselage was established using CAMRAD II software. The aerodynamic model of the main rotor adopted a general free wake model and an elastic blade model. The tail thrust propeller adopted a general uniform inflow model and a rigid blade model.

[0058] Based on the above model, the dynamic load at the main rotor hub center was calculated, and the higher-order (main rotor speed frequency) dynamic loads at the rotor hub center under different flight conditions were obtained [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 range with the theoretically calculated load data at the rotor hub center to obtain the higher-order dynamic load correction coefficient.

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

[0061] According to the force translation method, the measured rotor shaft load is converted into six force elements at the rotor 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] MZ 实测 =M

[0068] Based on the above method, the measured rotor shaft load [F,M,M1,M1',M2,M2'] is converted into the six-force element at the hub center [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] obtained in the second step 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 After normalization, we get [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, we correct it, 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] Following this pattern, a total of 12 load correction factors [μ] are obtained for both the upper and lower rotors. 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 and calculated load values ​​at each low speed point are corrected to obtain several sets of load correction coefficients. The arithmetic mean of each coefficient is taken as the final load correction coefficient for this type of helicopter.

[0074] Step 6: Correct the calculated rotor dynamic load using higher-order load correction factors.

[0075] Calculate the higher-order dynamic loads at the center of the upper and lower rotor hubs at high speeds (100 km / h to 400 km / h) using CAMRAD II [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 consider the stable forward flight state.]

[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 and its influence 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 higher-order dynamic loads of the upper and lower rotors at high speeds by the load correction coefficients obtained in step 5 to obtain the corrected higher-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 across the entire speed envelope based on the corrected rotor hub center dynamic load.

[0079] Step six yields the high-order dynamic loads at the centers of the upper and lower rotor hubs after high-velocity state correction [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 were applied to the first step of the whole machine dynamics finite element model, and frequency response analysis was performed using Nastran software. The modal superposition method was used to calculate the vibration response amplitude of the driver's seat floor at the frequency of interest.

[0080] Using the same method across the entire velocity envelope, the predicted vibration response of the coaxial helicopter across the entire envelope was finally calculated.

[0081] In other embodiments of this application, a method for predicting the vibration response of a coaxial helicopter provided in this application includes the following steps:

[0082] Step 1: Establish a coaxial helicopter full-aircraft dynamic finite element model based on helicopter structural numerical modeling and finite element modeling methods.

[0083] Step 2: Based on the established coaxial helicopter full-aircraft dynamic finite element model, conduct a correlation analysis of the dynamic loads at the center of the upper and lower rotor hubs, and obtain the correlation coefficients of 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].

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

[0085] Step 4: Using CAMRAD II for calculation, in forward flight at 40km / h, the higher-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 higher-order dynamic load correction coefficients 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: Correct the calculated rotor dynamic load using higher-order load correction coefficients. In forward flight at 400 km / h, the corrected higher-order dynamic loads of the upper and lower rotors are [496 N, 335 N, 940 N, 690 Nm, 789 Nm, 1052 Nm] and [560 N, 654 N, 1174 N, 1076 Nm, 1180 Nm, 1670 Nm].

[0089] Step 7: Based on the corrected rotor hub center dynamic load, predict the vibration response of the coaxial helicopter. Under forward flight conditions of 400 km / 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 includes: Test data on airframe vibration and rotor load of coaxial helicopters within a low speed range; Calculate the higher-order dynamic loads at the center of the upper and lower rotor hubs of a helicopter at different speeds; By comparing the data of coaxial helicopter fuselage vibration and rotor load in the low speed range with the theoretically calculated high-order dynamic load at the rotor hub center, the high-order dynamic load correction coefficient is obtained. The higher-order dynamic load correction coefficient is used to correct the higher-order dynamic load at the center of the propeller hub obtained by theoretical calculation. Based on the corrected high-order dynamic load at the rotor hub center, the vibration response of the coaxial helicopter is predicted across the entire velocity envelope. The calculation of higher-order dynamic loads at the centers of the upper and lower rotor hubs of the helicopter at different speeds includes: Obtain the free wake model and the uniform inflow model; Based on the free wake model and the uniform inflow model, the higher-order dynamic loads at the center of the upper and lower rotor hubs of the helicopter are calculated at different speeds.

2. The method according to claim 1, characterized in that, The rotor load data includes typical rotor profile flapping, oscillation 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 coaxial helicopter fuselage vibration and rotor load data within the low speed range, the following also includes: Based on helicopter structural numerical modeling and finite element modeling methods, a coaxial helicopter full-aircraft dynamic finite element model is established; Based on the established coaxial helicopter full-aircraft dynamic finite element model, the correlation analysis of dynamic loads at the upper and lower rotor hub centers was conducted to obtain force elements that are more sensitive to vibration response.

4. The method according to claim 1, characterized in that, The test data on coaxial helicopter fuselage vibration and rotor load within a low speed range includes: Through testing and modification, data on coaxial helicopter airframe vibration and rotor load were tested on a technology demonstrator aircraft within a low speed range.

5. The method according to claim 3, characterized in that, The vibration response prediction for the coaxial helicopter across the entire velocity envelope, based on the corrected high-order dynamic load at the rotor hub center, includes: The high-order dynamic loads at the centers of the upper and lower rotor hubs, after high-speed state correction, are applied to the overall dynamic finite element model of the coaxial helicopter. Frequency response analysis was performed using Nastran software, and the vibration response amplitude of the driver's seat floor at the frequency of interest was calculated using the modal superposition method.

6. A coaxial helicopter vibration response prediction device, characterized in that, The device includes: The test module is used to test coaxial helicopter airframe vibration and rotor load data within a low speed range; The processing module is used to calculate the higher-order dynamic loads at the center of the upper and lower rotor hubs of the helicopter at different speeds; The analysis module is used to compare the data of coaxial helicopter fuselage vibration and rotor load in a small speed range with the theoretically calculated high-order dynamic load at the rotor hub center, and obtain the high-order dynamic load correction coefficient. The correction module is used to correct the theoretically calculated high-order dynamic load at the center of the propeller hub using the aforementioned high-order dynamic load correction coefficient. The prediction module is used to predict the vibration response of the coaxial helicopter across the entire velocity envelope based on the corrected high-order dynamic load at the rotor hub center. The processing module is also used to acquire a free wake model and a uniform inflow model; and to calculate the higher-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.

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