CN110006522B - Nonlinear modal optical measurement system and method for space reentry gas-filled structure - Google Patents
Nonlinear modal optical measurement system and method for space reentry gas-filled structure Download PDFInfo
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- CN110006522B CN110006522B CN201910180982.XA CN201910180982A CN110006522B CN 110006522 B CN110006522 B CN 110006522B CN 201910180982 A CN201910180982 A CN 201910180982A CN 110006522 B CN110006522 B CN 110006522B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M7/00—Vibration-testing of structures; Shock-testing of structures
- G01M7/08—Shock-testing
Abstract
The invention relates to a nonlinear modal optical measurement system and a method for a space reentry gas filled structure; the imaging module images the process that the space reenters the inflatable structure and is knocked to generate vibration, and the imaging result is transmitted to the data processing module; the calibration module calibrates the inner orientation element, the outer orientation element and the aberration coefficient of the imaging module and transmits the inner orientation element, the outer orientation element and the aberration coefficient to the data processing module; the data processing module receives the imaging result transmitted by the imaging module, and receives the inner orientation element, the outer orientation element and the aberration coefficient transmitted by the calibration module; and calculating the out-of-plane motion displacement and speed of the space reentry inflatable structure in the modal vibration process according to the imaging result, the inner orientation element and the outer orientation element, and obtaining the nonlinear modal parameters of the space reentry inflatable structure through Fourier transform. The invention adopts an optical measurement method to accurately measure the out-of-plane displacement, the speed and the nonlinear mode of the space reentry inflatable structure.
Description
Technical Field
The invention belongs to the field of vibration mechanics, and relates to a nonlinear modal optical measurement system and method for a space reentry inflatable structure.
Background
The space reentry inflation structure is a novel spacecraft integrating the functions of thermal protection, pneumatic deceleration, landing buffering, water floating and the like. The structure can also be applied to rapid descending and returning of space stations and scientific test satellite test articles and cargos and can provide help for safe landing of the deep space probe.
Since the dynamic characteristics of the space reentry inflatable structure are closely related to the inflation pressure, it is necessary to explore the relationship between the modal characteristics of the space reentry inflatable structure and the inflation pressure. At present, the domestic research result on the aspect of flexible structure nonlinear modal measurement is almost not available. In the conventional measurement of structural modal characteristics, an acceleration sensor is generally used for non-contact measurement. The measuring method has high measuring cost and complex device, and is easy to interfere with the structural characteristics of the structure to be measured.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the system and the method overcome the defects of the prior art, provide the nonlinear optical measurement system and the method for the space reentry inflatable structure, and solve the defect that the prior art adopts a contact type measurement scheme. The speckles are distributed on the space reentry inflatable structure, a calibrated high-speed imager is used for carrying out image acquisition on the modal vibration process of the space reentry inflatable structure, camera parameters obtained through calibration are combined, image data are processed to obtain out-of-plane displacement and speed of the positions of the speckles on the space reentry inflatable structure at each moment, and nonlinear modal parameters of the space reentry inflatable structure are obtained through Fourier transformation.
The invention is realized by the following technical scheme: a spatial reentry plenum nonlinear modal optical measurement system, comprising: the system comprises a calibration module, an imaging module, a calibration plate, a data processing module and a synchronous triggering module;
an imaging module: imaging the modal vibration process of the space re-entering the inflatable structure to obtain a modal vibration process imaging result of the space to be detected re-entering the inflatable structure, and transmitting the modal vibration process imaging result of the space to be detected re-entering the inflatable structure to the data processing module; imaging the calibration plate to obtain a calibration imaging result, and transmitting the calibration imaging result to a calibration module;
a calibration module: receiving a calibration imaging result, calibrating an inner orientation element, an outer orientation element and an aberration coefficient of a high-speed imager in an imaging module, and transmitting the calibrated inner orientation element, outer orientation element and aberration coefficient to a data processing module;
a data processing module: receiving a modal vibration process imaging result of the space to be measured reentering the inflatable structure transmitted by the imaging module, and receiving the calibrated inner orientation element, outer orientation element and aberration coefficient transmitted by the calibration module, and calculating out-of-plane movement displacement and speed of the space reentering the inflatable structure in a modal vibration process; and then Fourier transform is carried out on the out-of-plane movement displacement and speed to obtain nonlinear modal parameters of the space reentry inflatable structure.
The imaging module comprises two or more high-speed imagers for imaging the space reentry inflatable structure modal vibration process; the arrangement positions of the two adjacent high-speed imagers meet the requirement that when the two high-speed imagers image a vibration process that a space to be measured enters the inflatable structure again, the included angle of the optical axes of any two high-speed imagers ranges from 15 degrees to 60 degrees.
The calibration plate occupies more than 80% of an image surface when the high-speed imager images, and the image is clear.
The system also comprises a synchronous triggering module; and the synchronous triggering module is used for enabling the high-speed imager to synchronously image the modal vibration process of the reentry of the space to be measured into the inflatable structure.
The L ED light source is placed around a test piece of a space reentry inflatable structure, so that light is uniform during imaging, and the phenomenon that the aperture is increased and the depth of field is reduced due to too dark light is avoided.
The nonlinear modal parameters of the space to be measured and the gas filled structure comprise a knocking mode, a first-order mode, a second-order mode and a third-order mode.
A method for carrying out nonlinear modal measurement on a space reentry gas filled structure by using the nonlinear modal optical measurement system of the space reentry gas filled structure comprises the following steps:
1) the calibration imaging module calibrates the inner orientation element, the outer orientation element and the aberration coefficient of the obtained calibration imaging result;
2) imaging the modal vibration process of the space to be measured entering the inflatable structure again by using an imaging module to obtain the modal vibration process imaging data of the space to be measured entering the inflatable structure again;
3) and resolving nonlinear modal parameters of the space reentry inflatable structure according to the internal orientation element, the external orientation element and the aberration coefficient determined in the step 1) and the imaging data determined in the step 2).
The method for calibrating the inner orientation element, the outer orientation element and the aberration coefficient of the calibrated imaging result obtained by the calibration imaging module in the step 1) comprises the following steps:
placing a calibration plate with known parameters in a field of view of a high-speed imager, and controlling the calibration plate to slightly shake; and (3) utilizing a high-speed imager to form 30-50 images on a calibration plate with known parameters, and calibrating the inner orientation element, the outer orientation element and the aberration coefficient of the imaging module.
The method for calculating the nonlinear modal parameters of the space reentry inflation structure in the step 3) specifically comprises the following steps:
31) arranging speckles on a space detector to be detected;
32) determining out-of-plane displacement and speed values of the space reentering the inflatable structure in the modal vibration process of the position of the speckle according to the inner orientation element, the outer orientation element and the imaging data of the imaging module;
33) fourier transform is carried out on the out-of-plane displacement and speed values in the modal vibration process of the position of the speckle on the space reentry inflatable structure determined in the step 32) to obtain knocking frequency, first-order frequency, second-order frequency and third-order frequency, and further nonlinear modal parameters of the space reentry inflatable structure are obtained.
The speckle density is 50%, and the speckle size is 5-10 pixels.
Compared with the prior art, the invention has the beneficial effects that:
1) the invention firstly adopts an optical measurement method to measure the nonlinear mode of the space reentry inflatable structure, researches the relation between the vibration mode characteristic and the inflation pressure of the space reentry inflatable structure, the measurement precision is 0.04 mm, and in the domestic public display data, the optical measurement method is firstly used to realize the nonlinear mode parameter measurement of the space reentry inflatable structure, which is in the leading domestic and international advanced status
2) The invention adopts an optical measurement method to measure the nonlinear modal parameters of the space reentry inflatable structure, adopts a non-contact measurement method, overcomes the influence of factors such as the shape, the size, the external environment and the like of a target to be measured on the measurement, and can measure the out-of-plane displacement and the speed of the position of speckles of the space reentry inflatable structure with high precision.
3) The invention adopts an optical measurement method to measure the nonlinear modal parameters of the space reentry inflatable structure, and overcomes the defects of high cost, complex equipment and influence on the structural characteristics of the target to be measured in a contact type measurement mode.
4) The invention adopts the physical synchronous trigger receiving device in the synchronous trigger module to collect the image, has low equipment cost and simple operation, and has no synchronous error.
5) The nonlinear modal parameters of the space reentry inflatable structure are obtained by Fourier transform of the out-of-plane displacement and the speed of the position of the speckle on the inflatable structure, and the modal value can be directly obtained simply and effectively through the out-of-plane displacement and the speed.
Drawings
FIG. 1 is a block diagram of a measurement system according to the present invention.
Detailed Description
The invention provides a system and a method for optically measuring nonlinear modal parameters of a space reentry gas-filled structure, which are particularly suitable for measuring the modal parameters of the gas-filled structure. The invention adopts an optical measurement method to accurately measure the out-of-plane vibration displacement and the speed of the position of the speckle position after the space reentry inflatable structure modal vibration, and obtains the modal parameters of the space reentry inflatable structure by a Fourier transform method. The high-speed imager is controlled by adopting a physical synchronous triggering mode, and the synchronous acquisition of vibration image data can be realized. Knocking the space reentry inflatable structure by using a hammering method, simultaneously carrying out image acquisition on the inflatable structure by using a binocular high-speed imager with calibrated parameters, and obtaining the in-plane vibration displacement and speed of the position of speckles on the inflatable structure through data processing, wherein the displacement measurement precision is 0.04 mm. The method belongs to the field of measurement of nonlinear modal parameters of a space reentry gas-filled structure by using an optical measurement method for the first time.
The invention is described in further detail below with reference to the following figures and specific examples:
as shown in fig. 1, a nonlinear modal space-optical measuring system of a space reentry gas filled structure according to the present invention includes: the system comprises a calibration module, an imaging module, a data processing module and a synchronous triggering module;
the target speckle density is about 50%, the speckle size is 5-10 pixels, and the target speckle is fixed in the space and then enters the outside of the inflatable structure;
a calibration module: receiving a picture of a calibration plate acquired by a high-speed camera, calibrating an inner orientation element, an outer orientation element and an aberration coefficient of the high-speed imager by combining parameters of the calibration plate, and transmitting the inner orientation element, the outer orientation element and the aberration coefficient to a data processing module;
an imaging module: imaging the space to be measured in the mode vibration process of the inflatable structure, and transmitting the imaging result to a data processing module; the imaging device comprises more than two high-speed imagers used for imaging the modal vibration process of the space reentry inflatable structure, the image acquisition frequency of the high-speed imagers is more than 400 frames/s, the arrangement positions of the more than two high-speed imagers meet the requirement that when any two adjacent high-speed imagers image the vibration process of the space reentry inflatable structure to be measured, the included angle value range of the optical axes of any two adjacent high-speed imagers is 15-60 degrees (15-30 degrees is optimal), and the common view field of the two high-speed imagers is the largest as possible;
and the synchronous triggering module is used for enabling the high-speed imager to synchronously image the modal vibration process of the space to be measured reentering the inflatable structure.
A data processing module: and receiving the inner orientation element, the outer orientation element and the aberration coefficient transmitted by the calibration module and the imaging result transmitted by the imaging module. Firstly, calculating the in-plane vibration displacement and the vibration speed of the speckles by using a digital image correlation method according to the imaging result, the inner azimuth element, the outer azimuth element and the aberration coefficient, and then carrying out Fourier transform on the in-plane vibration displacement and the vibration speed of the speckles to obtain nonlinear modal parameters of the space reentry inflatable structure.
The invention relates to a method for optically measuring nonlinear modal parameters of a space reentry gas-filled structure by using the nonlinear modal parameter optical measuring system of the space reentry gas-filled structure, which comprises the following steps:
1) acquiring images of a calibration plate by using a high-speed camera in an imaging module to obtain a plurality of calibration images, and transmitting the calibration images and parameters of the calibration plate to a calibration module; and the calibration module receives the calibration image transmitted by the imaging module and the size parameters of the calibration plate to calibrate the inner orientation element, the outer orientation element and the aberration coefficient of the high-speed imager in the imaging module.
2) Arranging speckles at the position to be detected, where the space to be detected enters the inflatable structure again;
3) imaging the modal vibration process of the space to be measured entering the inflatable structure again by using an imaging module to obtain imaging data of the modal vibration process of the space to be measured entering the inflatable structure again;
4) calculating the in-plane vibration displacement and speed of the position of the speckle on the space reentering the inflatable structure by using a data processing module according to the internal orientation element, the external orientation element, the aberration coefficient and the imaging data of the imaging module obtained by calibration of the calibration module;
5) and 4) carrying out Fourier transform according to the in-plane vibration displacement and speed of the position of the speckle on the inflatable structure determined in the step 4) to obtain nonlinear modal parameters of the space reentry inflatable structure.
Examples
The imaging module comprises 2 sets of tripods and tripod heads, 1 computer, 2 high-speed imagers, and 2L ED light sources, the synchronous triggering module comprises 1 set of synchronous triggering receiving device, the data processing module comprises 1 computer and a set of optical measurement data processing software, wherein:
the tripod and the tripod head are used for fixing the position of the high-speed imager;
a computer: and debugging parameters such as exposure time, aperture size, automatic gain and the like of the high-speed imager, and displaying and storing the image acquired by the high-speed imager.
A high-speed imager: the device is arranged on a tripod and a tripod head, is connected with a computer of a data processing module, and shoots and records the modal vibration process of the space reentry inflatable structure.
L ED light source placed in the space and then around the test piece of the inflatable structure to make the light uniform during imaging;
a synchronous triggering module: during testing, 2 high-speed imagers in the imaging module are synchronously triggered to acquire images.
Before measurement, target speckles need to be arranged at the positions to be measured of the space reentry inflatable structure.
Target speckle arrangement: target speckles are arranged outside the inflatable structure in space in a printing mode, the density of the speckles is about 50%, and the size of the speckles is 5-10 pixels.
The high-speed imager faces a target to be tested, namely a space reentry inflatable structure test piece, is distributed on two sides of the target to be tested, the position and the posture of the high-speed imager are adjusted, after the test is started, the position of the high-speed imager is unchanged, the intersection angle of the imagers ranges from 15 degrees to 60 degrees (15 degrees to 30 degrees are optimal), and the common view field of the two high-speed imagers is maximized as much as possible. When the high-speed imager focuses, the target is required to be imaged clearly, the definition of the calibration plate during calibration is also considered, and the uniformity of light during imaging is ensured.
The two high-speed imagers are American Phantom MIRO C120 high-speed digital cameras, the resolution is 1280 x 1024 pixels, the camera lens is an NIKON fixed focus 10mm focal length lens, 1 computer, a set of physical synchronous trigger receiving device, two sets of tripods and a tripod head.
The measuring steps are as follows:
1) and arranging speckles on the space reentry inflatable structure, wherein the size of the speckles is 7 mm and the density of the speckles is 50% according to the camera parameters and the actual imaging range.
2) The space reentry inflation structure is placed on the three pneumatic tires, so that the space reentry inflation structure is freely suspended in the air, is in a free state in the horizontal direction and faces the high-speed imager.
3) The two high-speed imagers are erected and distributed on two sides of the inflatable structure in the space to be measured all the time, the intersection angle of the imagers ranges from 15 degrees to 60 degrees (30 degrees is optimal), when the cameras focus, speckles of the inflatable structure are clear, and the definition of the calibration plate is considered. In all the tests, the frame frequency of the high-speed imager is selected to be 400 frames per second.
4) And (3) carrying out image acquisition on the calibration plate by using the high-speed imager, and calibrating the inner orientation element, the outer orientation element and the aberration coefficient of the 2 high-speed imagers by combining the parameters of the calibration plate.
5) The pneumatic structure is knocked once every 3s by a force hammer, the 2 high-speed imagers are controlled by a physical synchronous trigger receiving device to acquire images, and the images are acquired from before knocking.
6) The internal pressure of the space re-entering the inflatable structure is respectively 3KPa, 6KPa,8KPa,10KPa,12KPa and 15KPa, and the tests are respectively carried out.
7) After the test is finished, in the data processing module, data calculation is carried out according to the inner orientation element, the outer orientation element and the aberration coefficient obtained by calibration of the high-speed imager in combination with test data in the vibration process, and the out-of-plane vibration displacement and the out-of-plane vibration speed of the space where the speckles enter the inflatable structure are obtained.
9) In a data processing module, Fourier transformation is carried out on the out-of-plane vibration displacement and speed of the position of the speckles of the space reentry inflatable structure obtained in the step 7), and nonlinear modal parameters of the space reentry inflatable structure are obtained.
The above description is only for the best mode of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.
Those skilled in the art will appreciate that the invention may be practiced without these specific details.
Claims (4)
1. A system for nonlinear modal optical measurement of a space reentry plenum, comprising: the system comprises a calibration module, an imaging module, a calibration plate, a data processing module and a synchronous triggering module;
an imaging module: imaging the modal vibration process of the space re-entering the inflatable structure to obtain a modal vibration process imaging result of the space to be detected re-entering the inflatable structure, and transmitting the modal vibration process imaging result of the space to be detected re-entering the inflatable structure to the data processing module; imaging the calibration plate to obtain a calibration imaging result, and transmitting the calibration imaging result to a calibration module;
a calibration module: receiving a calibration imaging result, calibrating an inner orientation element, an outer orientation element and an aberration coefficient of a high-speed imager in an imaging module, and transmitting the calibrated inner orientation element, outer orientation element and aberration coefficient to a data processing module;
a data processing module: receiving a modal vibration process imaging result of the space to be measured reentering the inflatable structure transmitted by the imaging module, and receiving the calibrated inner orientation element, outer orientation element and aberration coefficient transmitted by the calibration module, and calculating out-of-plane movement displacement and speed of the space reentering the inflatable structure in a modal vibration process; fourier transformation is carried out on the out-of-plane movement displacement and speed to obtain nonlinear modal parameters of the space reentry inflatable structure;
the imaging module comprises two or more high-speed imagers for imaging the space reentry inflatable structure modal vibration process; the arrangement positions of any two adjacent high-speed imagers meet the requirement that when the two high-speed imagers image a space to be detected in a vibration process of entering the inflatable structure again, the included angle of the optical axes of any two adjacent high-speed imagers ranges from 15 degrees to 60 degrees;
the calibration plate occupies more than 80% of an image surface when the high-speed imager images, and the image is clear;
the L ED light source is placed around a test piece of a space reentry inflatable structure, so that light is uniform during imaging, and the phenomenon that the aperture is increased and the depth of field is reduced due to too dark light is avoided.
2. The system according to claim 1, further comprising a synchronization triggering module; and the synchronous triggering module is used for enabling the high-speed imager to synchronously image the modal vibration process of the reentry of the space to be measured into the inflatable structure.
3. The system according to claim 1, wherein the nonlinear modal parameters of the space reentry gas filled structure to be measured include a tapping mode, a first-order mode, a second-order mode, and a third-order mode.
4. A method for performing nonlinear modal measurements of a space reentry plenum using the nonlinear modal optical measurement system of a space reentry plenum of claim 3, comprising the steps of:
1) calibrating an inner orientation element, an outer orientation element and an aberration coefficient of a high-speed imager in the imaging module;
2) imaging the modal vibration process of the space to be measured entering the inflatable structure again by using an imaging module to obtain the modal vibration process imaging data of the space to be measured entering the inflatable structure again;
3) resolving nonlinear modal parameters of the space reentry inflatable structure according to the internal orientation element, the external orientation element and the aberration coefficient determined in the step 1) and the imaging data determined in the step 2);
the method for calibrating the inner orientation element, the outer orientation element and the aberration coefficient of the high-speed imager in the imaging module in the step 1) comprises the following steps:
placing a calibration plate with known parameters in a field of view of a high-speed imager, and controlling the calibration plate to slightly shake; utilizing a high-speed imager to form 30-50 images on a calibration plate with known parameters, and calibrating the inner orientation element, the outer orientation element and the aberration coefficient of the imaging module;
the method for calculating the nonlinear modal parameters of the space reentry inflation structure in the step 3) specifically comprises the following steps:
31) arranging speckles on a space detector to be detected;
32) determining out-of-plane displacement and speed values of the space reentering the inflatable structure in the modal vibration process of the position of the speckle according to the inner orientation element, the outer orientation element and the imaging data of the imaging module;
33) fourier transform is carried out on the out-of-plane displacement and speed values in the modal vibration process of the position of the speckle on the space reentry inflatable structure determined in the step 32) to obtain knocking frequency, first-order frequency, second-order frequency and third-order frequency, and further nonlinear modal parameters of the space reentry inflatable structure are obtained;
the speckle density is 50%, and the speckle size is 5-10 pixels.
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