Full-size rocket structure modal shape main vibration angle testing method

Abstract

The application belongs to the field of structural strength test, and relates to a full-size rocket structure modal vibration mode main vibration angle test method.The method comprises the following steps: S1, arranging multiple measuring points on the rocket, pasting an accelerometer on each measuring point, and connecting the accelerometer with a test computer through a data collector; S2, supporting the rocket structure through a support system; S3, arranging one exciter along two vertical Y and Z directions in a section perpendicular to the axial direction of the rocket; S4, connecting the exciter with a power amplifier, and connecting the power amplifier with the test computer through a signal source; S5, driving the two exciters to generate random excitation signals, and collecting Y and Z direction response data of the rocket body through the accelerometer; S6, linearly fitting the Y and Z direction response data of the multiple measuring points to obtain a slope; and S7, calculating the main vibration direction of the rocket as a whole according to the slope.

Description

Technical Field

[0001] This application belongs to the field of structural strength testing, and specifically relates to a method for testing the principal vibration angles of full-size rocket structures. Background Technology

[0002] With the rapid development of the aerospace field, the demand for large and medium-sized launch vehicles is increasing, placing new requirements on rockets such as high thrust and high payload. Large and medium-sized launch vehicles typically employ a staged design, characterized by a slender overall structure, a hollow interior containing sealed propellant tanks, a thin-walled cylindrical shell, and thrusters at the tail of each stage. Figure 1 As shown.

[0003] Full-scale rocket ground vibration modal testing is an important verification test in the development process. It is carried out before the maiden flight. Through on-board ground testing, the dynamic parameters of the rocket, such as resonance frequency, mode shape, damping ratio, mode shape slope, and overall modal principal vibration direction angle, are tested. This provides key data support for the design of the rocket attitude control system and the correction of the rocket numerical simulation model, and provides important technical support for the successful maiden flight of the rocket.

[0004] Large and medium-sized rockets house satellites, multiple engines, and complex piping systems, resulting in uneven mass distribution. This leads to asymmetry in the overall structural mass and stiffness characteristics about the axis, causing different vibration directions for each natural mode during vibration. Therefore, in actual testing, in addition to accurately measuring the modal frequencies, mode shapes, and damping ratios of the rocket, it is also necessary to accurately measure the principal vibration angles of each mode shape to support simulation model correction and attitude control system design. Measuring the principal vibration angle is a complex task. During testing, a specific frequency excitation load is applied to the rocket to induce vibration. Multiple measurement points are arranged at different cross-sectional locations inside and outside the rocket to collect the vibration response. The response and excitation data are analyzed using a data acquisition and analysis system to obtain the rocket's modal frequencies and mode shape data. Further analysis of the mode shape data yields the vibration direction angles at the measurement points at different cross-sectional locations. Statistical and fitting analysis methods are then used to calculate the overall principal vibration angle of the rocket. Large and medium-sized rockets have large diameters, long dimensions, and complex structures, which brings great difficulty and challenges to full-scale ground vibration modal testing. When arranging measurement points, it is necessary to consider not only the coverage of the axial distribution, but also the local structural characteristics of satellites, thrusters, etc. The number of measurement points is usually as high as several hundred, and the amount of vibration mode data is large. Selecting data that represents the overall vibration direction of the rocket and analyzing it is extremely difficult. Summary of the Invention

[0005] To address the aforementioned issues, this application provides a method for testing the principal vibration angles of full-scale rocket structures' modal vibration modes, mainly including:

[0006] Step S1: Set up multiple measuring points on the rocket, attach an accelerometer to each measuring point, and connect it to the test computer through a data acquisition device;

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

[0008] Step S3: In a cross-section perpendicular to the rocket's axial direction, arrange an exciter along two perpendicular Y-directions and Z-directions respectively.

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

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

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

[0012] Step S7: Calculate the overall main vibration direction of the rocket based on the slope.

[0013] Preferably, in step S1, multiple 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.

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

[0015] Preferably, in step S3, the vibrator is installed by fixed installation or flexible suspension, and 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 the vacuum generator through a rubber hose.

[0016] Preferably, step S5 further includes averaging the response data in the Y and Z directions of each collected measurement point multiple times.

[0017] Preferably, step S6 further includes removing outliers from all measurement points.

[0018] Preferably, in step S7, the principal vibration direction α is calculated using the following formula:

[0019] α = (180 / π)arctank;

[0020] Where k is the slope.

[0021] This application improves testing efficiency and accuracy. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of a large or medium-sized rocket.

[0023] Figure 2 This is a flowchart of a preferred embodiment of the method for testing the principal vibration angles of full-size rocket structures according to this application.

[0024] Figure 3 This is a schematic diagram showing the arrangement of the accelerometers.

[0025] Figure 4 This is a schematic diagram of the vibrator arrangement.

[0026] Figure 5 This is a schematic diagram of the rocket's principal vibration angle.

[0027] Among them, 1-satellite fairing; 2-satellite; 3-support frame; 4-pipeline; 5-second stage thruster; 6-interstage section; 7-propellant tank; 8-tail rudder; 9-first stage thruster. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be described in more detail below with reference to the accompanying drawings. In the drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The described embodiments are only some, not all, of the embodiments of this application. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application. The embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0029] This application provides a method for testing the principal vibration angles of full-scale rocket structures' modal vibration modes, such as... Figure 2 As shown, it mainly includes:

[0030] Step S1: Set up multiple measuring points on the rocket, attach an accelerometer to each measuring point, and connect it to the test computer through a data acquisition device;

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

[0032] Step S3: In a cross-section perpendicular to the rocket's axial direction, arrange an exciter along two perpendicular Y-directions and Z-directions respectively.

[0033] Step S4: Connect the exciter to the 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 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 of multiple measurement points in the Y and Z directions to obtain the slope;

[0036] Step S7: Calculate the overall main vibration direction of the rocket based on the slope.

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

[0038] In some alternative implementations, in step S1, multiple 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.

[0039] First refer to Figure 5 Define a three-dimensional coordinate system, where the X-axis points from the tip of the arrow to the tail of the arrow, and the Y-axis and Z-axis are perpendicular to each other in a plane perpendicular to the X-axis. The coordinates can be arbitrarily specified. For example, after dividing the plane into four quadrants clockwise, the Y-axis points from quadrant I to quadrant III, and the Z-axis points from quadrant IV to quadrant II.

[0040] In step S1, firstly, according to the test requirements, such as... Figure 1 As shown, 92 measuring points are arranged at locations including the rocket body, connecting section, satellite 2, support 3, storage tank 7, pipeline 4, and engine. 59 measuring points are arranged on the outer wall of the rocket body. Odd-numbered measuring points have three sensors (X, Y, and Z directions) and even-numbered measuring points have two accelerometers (Y and Z directions). Figure 3 As shown, there are a total of 148 accelerometers; 33 measuring points are arranged in the internal connecting sections of the rocket body (e.g., interstage section 6), satellite 2 (including satellite fairing 1), support 3, tank 7, pipeline 4, thrusters (e.g., first stage thruster 9, second stage thruster 5), etc., with 3 sensors arranged at each measuring point, respectively in the X, Y and Z directions, for a total of 99 sensors, and a total of 247 accelerometers arranged on the entire rocket.

[0041] According to the designed measurement point scheme, 247 accelerometers were attached to the positions of each component of the thin-walled cylindrical structure. The accelerometer connection wires were then connected to the data acquisition unit, and the data acquisition unit was connected to the test computer through the test cable.

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

[0043] In some alternative implementations, in step S2, the support system is connected to the rocket root by a fixed support to enable the rocket to be in a flexible suspension state.

[0044] Steps S3 and S4 are used to install the vibration system.

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

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

[0047] like Figure 4 As shown, two vibrators are installed at the bottom of the rocket and connected to the rocket's load-bearing frame. 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] Step S4 is followed by e) connecting the force vector controller, power amplifier, exciter, accelerometer, data acquisition unit and test computer via cables to form a test system and perform overall debugging.

[0049] After connecting the test system, turn on power amplifiers 1 and 2, and send two 1V pure random excitation signals through the signal generator to drive the two exciters to vibrate simultaneously. Collect the vibration response of the rocket body through the accelerometer, check the operation of each system based on the measured vibration response, and troubleshoot until the entire system is working properly. After debugging, turn off power amplifiers 1 and 2.

[0050] Step S5 is used to conduct the formal test. Each power amplifier is turned on in sequence, and the excitation phase of the exciter is adjusted to make the rocket body vibrate. By adjusting the excitation frequency and the magnitude of the excitation force, the main modal parameters of each order of the rocket body are obtained.

[0051] In this embodiment, power amplifiers 1 and 2 are turned on, and two pure random excitation signals with an amplitude of 1V are emitted through the signal generator to drive two exciters to vibrate simultaneously. The vibration response of the rocket body is collected by the accelerometer. In some optional embodiments, step S5 further includes averaging the Y and Z direction response data of each measurement point multiple times. For example, the frequency response function of the test is averaged 20 times to reduce the error. Modal identification and separation are performed based on the frequency response function obtained from the test to obtain the frequency, mode shape and damping coefficient of each main mode of the rocket body.

[0052] Steps S6 and S7 are used to process the measured data to obtain the principal vibration angle.

[0053] In step S6, the mode shape measurement data of each channel are read. Due to the large number of local modes inside the rocket body, 59 measuring points on the outer wall of the rocket are selected in this example for the principal vibration angle analysis of the overall mode shape. The correspondence between the measurement direction of each measuring point and the response channel is determined, as shown in formulas (1) and (2), where i represents the measuring point number and c represents the measurement channel. The vibration direction α of each measuring point is calculated according to the vector synthesis rule. i As shown in formula (3), the calculation results show that the vibration direction of most measuring points is between 55° and 75°. In some optional embodiments, the relationship between the vibration directions at each measuring point is analyzed by linear regression, and outliers 48, 49, 50, 51, 52, 54, 55, 56, and 57 are removed. In this example, linear regression analysis is performed on the Y-direction and Z-direction response data of the 50 measuring points after removing outliers. The calculated value of k = 0.4538 gives the overall principal vibration direction α = (180 / π)arctan k. The principal vibration angle of the first-order overall transverse bending vibration mode of the rocket in this example is calculated to be 65.59° off the Z-axis from the Y-axis. A schematic diagram of the principal vibration angle is then drawn, as shown below. Figure 5 As shown, α is the principal vibration angle of the first-order overall transverse bending mode. Following this method, the principal vibration angles of other overall modes of the rocket can be measured sequentially.

[0054]

[0055] Finally, the test data were compiled to confirm that no results were missed. Then, the connections between the excitation system, testing system, and support system and the rocket were disconnected in sequence, and the equipment of each subsystem was dismantled and organized. This experiment obtained all the test modal parameters of the rocket and the principal vibration angles of each major mode. The experiment achieved high efficiency and accuracy, yielding excellent results.

[0056] This application installs accelerometers at multiple locations on 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 of important locations on the structure are selected for processing, and the principal vibration angles of the full-size rocket structure mode are calculated. This method can establish a standardized process for batch calculation processing. By reasonably selecting acceleration measurement points and eliminating abnormal response points, the efficiency and accuracy of principal vibration angle calculation can be effectively improved.

[0057] This application addresses the issue that traditional testing methods cannot meet the requirements for measuring the principal vibration angles of modal modes in rocket structures because the vibration directions of different natural modes are not entirely the same. Taking into account structural characteristics, the spatial combination of acceleration measurement points, the method of applying excitation force, the principles for selecting response points, and processing methods, this application proposes a method for measuring the principal vibration angles of modal modes in full-scale rocket structures. This method can meet the requirements for measuring the principal vibration angles of modal modes in full-scale rocket structures. By arranging multiple accelerometers and exciters on various rocket components, and installing the accelerometers according to a designed number, location, and spatial combination, a specific combination method is used to achieve joint excitation of the structure by multiple exciters, effectively improving the accuracy and effectiveness of rocket structure vibration response measurement.

[0058] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for testing the principal vibration angles of full-size rocket structures' modal vibration modes, characterized in that, include: Step S1: Set up multiple measuring points on the rocket, attach an accelerometer to each measuring point, and connect it to the test computer through a data acquisition device; Step S2: Support the rocket structure using a support system; Step S3: In a cross-section perpendicular to the rocket's axial direction, arrange an exciter along two perpendicular Y-directions and Z-directions respectively. Step S4: Connect the exciter to the power amplifier, and connect the power amplifier to the test computer through a signal source; Step S5: Simultaneously drive two exciters to generate random excitation signals, and collect response data of the rocket body in the Y and Z directions through accelerometers; Step S6: Perform linear fitting based on the response data of multiple measurement points in the Y and Z directions to obtain the slope; Step S7: Calculate the overall main vibration direction of the rocket based on the slope.

2. The method for testing the principal vibration angles of full-size rocket structures as described in claim 1, characterized in that, In step S1, multiple 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.

3. The method for testing the principal vibration angles of full-size rocket structures as described in claim 1, characterized in that, In step S2, the support system is connected to the rocket root by a fixed support to make the rocket in a flexible suspension state.

4. The method for testing the principal vibration angles of full-size rocket structures as described in claim 1, characterized in that, In step S3, the vibrator is installed by 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. The suction cup is connected to the vacuum generator through a rubber hose.

5. The method for testing the principal vibration angles of full-size rocket structures as described in claim 1, characterized in that, Step S5 further includes averaging the response data in the Y and Z directions of each collected measurement point multiple times.

6. The method for testing the principal vibration angles of full-size rocket structures as described in claim 1, characterized in that, Step S6 is preceded by removing outliers from all measurement points.

7. The method for testing the principal vibration angles of full-size rocket structures as described in claim 1, characterized in that, In step S7, the principal vibration direction α is calculated using the following formula: ； Where k is the slope.

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