Method for testing main vibration angle of modal shape of full-size rocket structure

Abstract

The invention belongs to the field of structural strength testing, and relates to a full-size rocket structural modal shape main vibration angle testing method. The method comprises the following steps: S1, arranging a plurality of measuring points on a rocket, pasting an accelerometer on each measuring point, and connecting the measuring points with a test computer through a data collector; s2, supporting the rocket structure through a support system; s3, in a section perpendicular to the axial direction of the rocket, vibration exciters are arranged in the Y direction and the Z direction which are perpendicular to each other correspondingly; s4, the vibration exciter is connected with a power amplifier, and the power amplifier is connected with a test computer through a signal source; s5, two vibration exciters are driven to generate random excitation signals, and response data of the rocket body in the Y direction and the Z direction are collected through an accelerometer; s6, performing linear fitting according to the response data of the plurality of measuring points in the Y direction and the Z direction to obtain a slope; and S7, calculating the main vibration direction of the whole rocket according to the slope.

Description

Technical Field

[0001] This application belongs to the field of structural strength tests, and particularly relates to a method for testing the main vibration angles of the modal vibration modes of a full-scale rocket structure. Background Art

[0002] With the rapid development of the aerospace field, the demand for medium and large-sized launch vehicles is increasing day by day, and new requirements such as large thrust and high load capacity are put forward for rockets. Medium and large-sized launch vehicles usually adopt a staged design, showing characteristics such as an overall slender structure, a hollow interior with sealed storage tanks, a thin-walled cylindrical outer shell, and thrusters installed at the tails of each stage, as Figure 1 shown.

[0003] The full-scale rocket ground vibration modal test is an important verification test during the development process. It is carried out before the first flight. By means of on-ground tests on the rocket, dynamic parameters such as the resonance frequency, vibration mode, damping ratio, vibration mode slope, and overall modal main vibration direction angle of the rocket are measured, providing key data support for the design of the rocket attitude control system and the correction of the rocket numerical simulation model, and providing important technical guarantee for the successful first flight of the rocket.

[0004] Satellites, multiple engines, and complex pipeline systems are installed on medium and large-sized rockets, resulting in uneven mass distribution, which causes the overall structural mass and stiffness characteristics to be asymmetric about the axis. During vibration, the vibration directions of the natural vibration modes of each order are not the same. Therefore, during the actual test process, in addition to accurately measuring the modal frequencies, vibration modes, and damping ratios of each order of the rocket, it is also necessary to accurately measure the main vibration angles of the modal vibration modes of each order, so as to support the correction of the simulation model and the design of the attitude control system. Measuring the main vibration angle is a complex task. During the test, by applying an excitation load with a specific frequency to the rocket to make it vibrate, multiple measurement points are arranged at different cross-section positions inside and outside the rocket to collect the vibration response of the rocket body. Through the data acquisition and analysis system, the response and excitation data are analyzed to obtain the modal frequency and vibration mode data of the rocket, and then the vibration mode data is analyzed to obtain the vibration direction angles at the measurement points at different cross-section positions. Through statistical and fitting analysis methods, the overall main vibration angle of the rocket is calculated. Medium and large-sized rockets have a large diameter, a long size, and a complex structural form, bringing great difficulties and challenges to the full-scale ground vibration modal test. When arranging the measurement points, not only the coverage of the axial distribution needs to be considered, but also the local structural characteristics such as satellites and thrusters need to be considered. The number of measurement points is usually as high as several hundred, and the amount of vibration mode data is large. It is extremely difficult to select the data representing the overall vibration direction of the rocket from them and conduct analysis. Summary of the Invention

[0005] In order to solve the above problems, this application provides a method for testing the main vibration angles of the modal vibration modes of a full-scale rocket structure, which mainly includes:

[0006] Step S1: Arrange multiple measurement points on the rocket, paste accelerometers at each measurement point, and connect them to the test computer through a data collector;

[0007] Step S2: Support the rocket structure through a support system;

[0008] Step S3: In a cross-section perpendicular to the rocket's axial direction, arrange one shaker along each of two perpendicular Y-directions and Z-directions respectively;

[0009] Step S4: Connect the shakers to a power amplifier, and connect the power amplifier to the test computer through a signal source;

[0010] Step S5: Drive the two shakers to generate random excitation signals, and collect the response data of the rocket body in the Y-direction and Z-direction through the accelerometers;

[0011] Step S6: Perform linear fitting based on the response data in the Y-direction and Z-direction of multiple measurement points to obtain the slope;

[0012] Step S7: Calculate the main vibration direction of the entire rocket according to the slope.

[0013] Preferably, in Step S1, multiple measurement points are arranged on the rocket surface, satellite, support, thruster, and pipeline structure, and one accelerometer is arranged along the Y-direction and Z-direction respectively at each measurement point.

[0014] Preferably, in Step S2, the support system is connected to the rocket root by a fixed support method to make the rocket in a flexible suspension state.

[0015] Preferably, in Step S3, the shakers are installed by fixed installation or flexible suspension, the output end of the shaker is connected to the rocket body through a connecting rod and a suction cup, and the suction cup is connected to a vacuum generator through a rubber hose.

[0016] Preferably, Step S5 further includes performing multiple averaging processes on the response data in the Y-direction and Z-direction of each collected measurement point.

[0017] Preferably, further include eliminating the abnormal points among all measurement points before Step S6.

[0018] Preferably, in Step S7, the main vibration direction α is calculated through the following formula:

[0019] α = (180 / π) arctank;

[0020] where k is the slope.

[0021] This application improves the test efficiency and at the same time improves the test accuracy. Description of the Drawings

[0022] Figure 1 It is a schematic diagram of the structure of medium and large-sized rockets.

[0023] Figure 2 It is a flowchart of a preferred embodiment of the full-scale rocket structure modal vibration mode and principal vibration angle test method of the present application.

[0024] Figure 3 It is a schematic diagram of the layout direction of accelerometers.

[0025] Figure 4 It is a schematic diagram of the layout scheme of exciters.

[0026] Figure 5 It is a schematic diagram of the principal vibration angle of the rocket

[0027] Among them, 1 - satellite fairing; 2 - satellite; 3 - bracket; 4 - pipeline; 5 - second-stage thruster; 6 - interstage section; 7 - storage tank; 8 - tail rudder; 9 - first-stage thruster. Specific implementation manners

[0028] To make the purpose, technical solutions and advantages of the implementation of the present application clearer, the technical solutions in the implementation manners of the present application will be described in more detail below with reference to the accompanying drawings in the implementation manners of the present application. In the accompanying drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The described implementation manners are some but not all of the implementation manners of the present application. The implementation manners described below by referring to the accompanying drawings are exemplary and are intended to explain the present application and should not be construed as limiting the present application. All other implementation manners obtained by those of ordinary skill in the art based on the implementation manners in the present application without creative efforts belong to the scope of protection of the present application. The implementation manners of the present application will be described in detail below with reference to the accompanying drawings.

[0029] The present application provides a full-scale rocket structure modal vibration mode and principal vibration angle test method, as Figure 2 shown, mainly including:

[0030] Step S1: Arrange a plurality of measuring points on the rocket, paste accelerometers at each measuring point, and connect them to a test computer through a data collector;

[0031] Step S2: Support the rocket structure through a support system;

[0032] Step S3: In a cross-section perpendicular to the axial direction of the rocket, arrange an exciter along each of two perpendicular Y-directions and Z-directions;

[0033] Step S4: Connect the exciter to a power amplifier, and connect the power amplifier to the test computer through a signal source;

[0034] Step S5: Drive two exciters to generate random excitation signals, and collect the response data of the rocket body in the Y and Z directions through accelerometers.

[0035] Step S6: Perform linear fitting based on the response data in the Y and Z directions of multiple measuring points to obtain the slope.

[0036] Step S7: Calculate the main vibration direction of the entire rocket according to the slope.

[0037] Step S1 is used to select measuring points and arrange sensors, accelerometers, and data acquisition systems.

[0038] In some alternative embodiments, in step S1, a plurality of measuring points are arranged on the rocket surface, satellite, support, thruster, and pipeline structure, and an accelerometer is arranged in each measuring point along the Y and Z directions respectively.

[0039] First, refer to Figure 5 Define a three-dimensional coordinate system, where the X-axis points from the top of the rocket to the tail direction, and the Y-axis and Z-axis are perpendicular to each other in a plane perpendicular to the X-axis. For example, after arbitrarily specifying and dividing four quadrants clockwise in this plane, the Y-axis points from the first quadrant to the third quadrant, and the Z-axis points from the fourth quadrant to the second quadrant.

[0040] In step S1, first, according to the test requirements, as Figure 1 shown, 92 measuring points are arranged at positions such as the cylinder, connection section, satellite 2, bracket 3, tank 7, pipeline 4, and engine. Among them, 59 measuring points are arranged on the outer wall of the rocket cylinder. Three sensors, namely in the X, Y, and Z directions, are arranged on the odd-numbered measuring points, and two accelerometers, namely in the Y and Z directions, are arranged on the even-numbered measuring points. As Figure 3 shown, there are a total of 148 accelerometers; 33 measuring points are arranged at positions such as the internal connection section of the rocket body (such as the inter-stage section 6), satellite 2 (including the satellite fairing 1), bracket 3, tank 7, pipeline 4, thruster (such as the first-stage thruster 9, second-stage thruster 5), etc. Three sensors, namely in the X, Y, and Z directions, are arranged on each measuring point, with a total of 99 sensors. A total of 247 accelerometers are arranged on the entire rocket.

[0041] According to the designed measuring point scheme, paste 247 accelerometers at the positions of each component of the thin-walled cylinder structure, then connect the accelerometer connection wires to the data collector, and connect the data collector to the test computer through the test cable.

[0042] Step S2 is used to support the rocket structure.

[0043] In some alternative embodiments, in step S2, the support system is connected to the rocket root in a fixed support manner to make the rocket in a flexible suspension state.

[0044] Steps S3 and S4 are used for installing the vibration excitation system.

[0045] In some alternative embodiments, in step S3, the vibrator is installed by means of fixed installation or flexible suspension. The output end of the vibrator is connected to the rocket body through a connecting rod and a suction cup, and the suction cup is connected to a vacuum generator through a rubber hose.

[0046] In this embodiment, first, according to the test requirements, a certain number of vibrators are prepared and installed by means of fixed installation or flexible suspension. Then, a suitable sectional position is selected along the axial direction of the rocket cylinder, and two vibrators are arranged circumferentially. The installation angles of the two vibrators differ by 90 degrees. The vibrators are connected to the rocket body through connecting rods and suction cups. The vibration excitation directions of the vibrators are perpendicular to each other. The control cables on the vibrators are connected to the corresponding power amplifiers, the power amplifiers are connected to the signal source, and finally the signal source is connected to the test computer.

[0047] As Figure 4 shown, two vibrators are installed at the bottom of the rocket and connected to the rocket load-bearing frame part. The connecting rod of vibrator No. 1 points to the Y direction, and the connecting rod of vibrator No. 2 points to the Z direction.

[0048] After step S4, it further includes e) connecting the force vector controller, power amplifier, vibrator, accelerometer, data collector and test computer through cables to form a test system and conduct overall debugging.

[0049] After the test system is connected, turn on power amplifier No. 1 and power amplifier No. 2, and send out two pure random vibration excitation signals with an amplitude of 1V through the signal generator to drive the two vibrators to vibrate simultaneously. Collect the vibration response of the rocket body through the accelerometer, check the working conditions of each system according to the measured vibration response, and troubleshoot problems until the entire system works normally. After debugging is completed, turn off power amplifier No. 1 and power amplifier No. 2.

[0050] Step S5 is used for conducting a formal test. Turn on each power amplifier in sequence, adjust the vibration excitation phase of the vibrator to make the rocket body vibrate, and obtain the main modal parameters of each order of the rocket body by adjusting the vibration excitation frequency and the magnitude of the vibration excitation force.

[0051] In this embodiment, power amplifier No. 1 and power amplifier No. 2 are turned on, and two pure random excitation signals with an amplitude of 1V are sent out through a signal generator to drive two exciters to perform excitation at the same time, and the vibration response of the arrow body is collected through an accelerometer. In some optional implementations, step S5 further includes multiple averaging processing of the response data in the Y direction and the Z direction of each measuring point collected, for example, averaging the tested frequency response function 20 times to reduce the error, and performing modal identification and separation based on the frequency response function obtained from the test to obtain the frequency, vibration shape and damping coefficient of each order of main modes of the arrow body.

[0052] Step S6 and step S7 are used to process the measured data to obtain the main vibration angle.

[0053] In step S6, the vibration mode measurement data of each channel is read. Since there are many local modes inside the rocket body, 59 measurement points on the outer tube wall of the rocket are selected in this example to analyze the main vibration angle of the overall vibration mode. The corresponding relationship between the measurement direction of each measurement point and the response channel is determined, as shown in formula (1) and formula (2), where i represents the measurement point number and c represents the measurement channel. The vibration direction α of each measurement point is calculated according to the vector synthesis law. i , see formula (3), the calculation results show that the vibration direction of most measuring points is between 55° and 75°. In some optional implementations, the relationship between the vibration directions at each measuring point is analyzed by a linear regression method, and the singular points 48, 49, 50, 51, 52, 54, 55, 56, and 57 are eliminated. In this example, linear regression analysis is performed on the Y-direction and Z-direction response data of the 50 measuring points after eliminating the singular points. The calculation results in k = 0.4538, and thus the overall main vibration direction is α = (180 / π) arctan k. The main vibration angle of the first-order overall lateral bending vibration mode of the rocket in this example is calculated to be 65.59° from the Y axis to the Z axis, and a schematic diagram of the main vibration angle is drawn, as shown in the figure. Figure 5 As shown in Figure 2, α is the main vibration angle of the first-order overall transverse bending mode. According to this method, the main vibration angles of other overall modes of the rocket can be measured in turn.

[0054]

[0055] Finally, the test data was sorted out to confirm that there were no omissions in the test results. Then the connections between the excitation system, test system, and support system and the rocket were removed in turn, and the equipment of each subsystem was dismantled and sorted out. This test obtained all the modal parameters of the rocket to be tested, and obtained the main vibration angles of each order of main modes. The test efficiency and result accuracy were high, and good results were achieved.

[0056] In this application, accelerometers are installed at multiple positions of the structure. By designing the positional and directional relationships between the accelerometers, the overall vibration response of the structure is collected. Then, the response data at important positions of the structure are selected for processing, and the principal vibration angles of the modal vibration modes of the full-scale rocket structure are calculated. Through this method, a standardized process can be established to carry out batch calculation and processing. By reasonably selecting the acceleration measurement points and removing abnormal response points, the calculation efficiency and accuracy of the principal vibration angles can be effectively improved.

[0057] In this application, aiming at the problem that the vibration directions of the natural vibration modes of each order of the rocket structure are not completely the same and the traditional test methods cannot meet the test requirements for the principal vibration angles of the modal vibration modes, considering comprehensively the difficult problems such as the structural characteristics, the spatial combination relationship of the acceleration measurement points, the excitation force application method, the response point selection principle and the processing method, etc., a test method for the principal vibration angles of the modal vibration modes of the full-scale rocket structure is proposed, which can meet the test requirements for the principal vibration angles of the modal vibration modes of the full-scale rocket structure. By arranging multiple accelerometers and exciters on the structures of each component of the rocket and installing the accelerometers according to the designed quantity, position and spatial combination method, through a specific combination method, the combined excitation of the structure by multiple exciters is realized, effectively improving the accuracy and effectiveness of the measurement of the vibration response of the rocket structure.

[0058] As mentioned above, it is only the specific implementation manner of this application, but the protection scope of this application is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed in this application should be covered within the protection scope of this application. Therefore, the protection scope of this application should be subject to the protection scope of the claimed rights.

Claims

1. A method for testing the main vibration angle of a full-scale rocket structure modal shape, characterized in that: include: Step S1, multiple measuring points are arranged on the rocket, each measuring point is attached with an accelerometer, and connected to a test computer through a data acquisition device; Step S2, supporting the rocket structure through a support system; Step S3, in a cross section perpendicular to the axial direction of the rocket, an exciter is arranged along two perpendicular Y directions and Z directions respectively; Step S4, connecting the exciter to the power amplifier, and connecting the power amplifier to the test computer via the signal source; Step S5, driving two exciters to generate random excitation signals, and collecting response data of the rocket body in the Y direction and the Z direction through the accelerometer; Step S6, performing linear fitting according to the response data of the Y direction and the Z direction of the multiple measuring points to obtain the slope; Step S7, calculating the main vibration direction of the entire rocket according to the slope.

2. The method for testing the main vibration angle of the full-scale rocket structure modal vibration type according to claim 1, characterized in that: In step S1, a plurality of measuring points are arranged on the rocket surface, satellite, support, thruster, and pipeline structure, and an accelerometer is arranged at each measuring point along the Y and Z directions respectively.

3. The method for testing the main vibration angle of the full-scale rocket structure modal vibration type as claimed in claim 1, characterized in that: In step S2, the support system is connected to the root of the rocket by a fixed support method so that the rocket is in a flexible suspension state.

4. The method for testing the main vibration angle of the full-scale rocket structure modal vibration type as claimed in claim 1, characterized in that: In step S3, the exciter is installed by fixed installation or flexible suspension, and the output end of the exciter is connected to the rocket body through a connecting rod and a suction cup, and the suction cup is connected to the vacuum generator through a rubber hose.

5. The method for testing the main vibration angle of the full-scale rocket structure modal vibration type according to claim 1, characterized in that: Step S5 further includes performing multiple averaging processes on the response data collected in the Y direction and the Z direction of each measuring point.

6. The method for testing the main vibration angle of the full-scale rocket structure modal vibration type according to claim 1, characterized in that: Before step S6, the process further includes eliminating the singular points among all the measuring points.

7. The method for testing the main vibration angle of the full-scale rocket structure modal vibration type as claimed in claim 1, characterized in that: In step S7, the main vibration direction α is calculated by the following formula: α=(180 / π)arctank; Where k is the slope.

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