Method for testing double-wave impact response of shock absorber based on digital image correlation method

Abstract

The invention discloses a shock absorber double-wave impact response test method based on a digital image correlation method, and the method comprises the steps: arranging two high-speed cameras, and carrying out the shooting of the front part and the side part of a test bench; pasting mark points on the surfaces of the test bed and the load, and measuring and recording the relative positions of the mark points; arranging an acceleration sensor, connecting a camera with the sensor through a time synchronization trigger, and completing synchronization of displacement and acceleration response measurement equipment; setting a shooting frame rate, an exposure rate and a triggering moment of camera control software, and stopping high-speed shooting and acceleration acquisition after one impact test is completed; the camera video is processed, the displacement of the test bed and the load in the impact process is solved through the technology based on the digital image correlation method, and the average value of the displacement difference value of the test bed and the load is the impact displacement response of the shock absorber. According to the invention, the response of the shock absorber in the double-wave impact test can be measured.

Description

Technical Field

[0001] The invention belongs to the field of ship equipment anti-shock test evaluation, and in particular relates to a method for double-wave shock response test of a shock absorber based on digital image correlation (DIC). Background Art

[0002] As the "heart" of the ship, the ship's power system and its equipment provide the power and electricity required by the entire ship, ensuring the ship's navigation and daily life needs, and occupy a very important position in ship equipment. During navigation, the ship's power equipment may be seriously damaged by impact loads, resulting in the collapse of the entire ship's power equipment or even the power system. In order to improve the impact resistance of ship power equipment, light or medium impact machines or floating impact platforms are used to carry out impact tests on power equipment.

[0003] In order to test and assess the impact resistance of ship equipment, countries around the world have conducted in-depth research on ship equipment assessment methods and formed corresponding standards and specifications. These standards stipulate corresponding impact test methods such as lightweight impact, medium-weight impact, explosion impact, double-wave impact, etc. A large number of actual ship explosion test results show that the impact input environment generated by the underwater explosion energy transmitted to the equipment foundation is expressed as a displacement / velocity / acceleration impact spectrum in the frequency domain, which can be equivalent to positive and negative impact pulse waves in the time domain. In the past, the impact machine was mainly based on impact energy simulation, and could only simulate simple waveforms such as half-sine. The new dual-wave impact test bench for marine equipment generates positive wave pulses by the impact machine hammer hitting the elastic waveform generator just below the center of the test machine platform. The platform moves upward under the impact force and interacts with the buffer (negative wave generator) installed on the platform to generate negative wave shock pulses. The energy required for the positive and negative waves required by the test conditions is generated by adjusting the different impact air pressures of the impact test machine hammer.

[0004] In the test, it is necessary to measure the response of the object under the impact load in a timely and effective manner. The commonly used displacement measurement methods can be divided into contact measurement and non-contact measurement. Contact measurement usually includes resistance strain gauges and extensometers. These contact methods have the advantages of high accuracy, high sensitivity and strong environmental adaptability, but generally can only perform point measurement, and cannot obtain full-field deformation detection of the measured object, and the operation and wiring are complicated. Summary of the invention

[0005] In order to measure the displacement response of the shock absorber under the double-wave impact test and solve the above technical problems, the present invention provides a method for testing the double-wave impact response of the shock absorber based on the digital image correlation method. The shock absorber is installed in the double-wave impact test bench fixture. At the same time, the digital image correlation method (DIC) is used as a non-contact measurement method to realize the full-field deformation detection of the object by optical means, which is an efficient computer vision method for deformation measurement. Based on this method, the present invention measures the response of the shock absorber in the double-wave impact test.

[0006] In order to achieve the above object, the present invention adopts the following technical scheme:

[0007] A method for testing the double-wave impact response of a shock absorber based on a digital image correlation method, comprising:

[0008] Two high-speed cameras are deployed to shoot the front and sides of the test bench;

[0009] Paste marking points on the test bench and the load surface, and measure and record the relative positions of the marking points;

[0010] Arrange acceleration sensors, connect high-speed cameras and sensors through time synchronization triggers, and complete the synchronization of displacement and acceleration response measurement equipment;

[0011] Set the shooting frame rate, exposure rate and trigger time of the camera control software, and stop high-speed video and acceleration acquisition after one impact test is completed;

[0012] For video processing, digital image correlation technology is used to solve the displacement of the test bench and the load during the impact process. The average value of the displacement difference between the two is the impact displacement response of the shock absorber.

[0013] Furthermore, the high-speed camera uses binocular vision to shoot continuously at a speed of more than 1000 frames per second to achieve real-time image acquisition of the impact surface and load surface of the shock absorber, and records and stores the movement of the impact surface and load surface at each moment during the experiment in the form of images.

[0014] Furthermore, the digital image correlation method is a three-dimensional digital image correlation method, which performs full-field response measurement of the entire test bench in a non-contact and non-destructive manner.

[0015] Furthermore, the high-speed camera simultaneously shoots the front and side of the test bench to generate intersecting fields of view, and compares and identifies the marking points of the captured images through the macroscopic displacement measurement method of the digital image correlation method.

[0016] Furthermore, the shock absorber is installed in a double-wave impact test bench fixture, and the shock absorber is fixed to the impact table and the load by bolts.

[0017] Furthermore, the acceleration sensor is a special sensor for impact test. After measuring the load and test bench acceleration, a deep neural network model combined with a wavelet transform method is used to filter the acceleration response noise to achieve the actual acceleration response output of the object under impact.

[0018] Furthermore, the working process of the time synchronization trigger is based on the Global Navigation Satellite System (GNSS) time as the standard time source to tame the constant temperature crystal oscillator, and output a pulse signal at a certain frequency to the high-speed camera and acceleration sensor to achieve synchronous real-time measurement of relative displacement and acceleration response.

[0019] Beneficial effects:

[0020] The present invention can perform high-frequency real-time image acquisition for the dual-wave impact test of the shock absorber, and perform full-field response measurement of the entire test bench in a non-contact and non-destructive manner, with strong anti-interference performance. By pasting the marking points on the test bench and the load, the number of mismatched points of the DIC recognition technology can be guaranteed to be extremely low, and finally, the noise influence in the response can be effectively filtered out by combining the deep neural network with the wavelet analysis, so as to realize the accurate measurement of the dual-wave impact response of the shock absorber. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The figure is a flow chart of the method for testing the double-wave impact response of a shock absorber based on the digital image correlation method of the present invention.

[0022] Figure 2 The diagram of the installation of the shock absorber and the fixture of the method for testing the double-wave impact response of the shock absorber based on the digital image correlation method of the present invention is shown.

[0023] Figure 3 The present invention is a schematic diagram of marking points for the method of testing the dual-wave impact response of a shock absorber based on the digital image correlation method.

[0024] Figure 4 The diagram is a plan view of the camera arrangement of the method for testing the double-wave shock response of a shock absorber based on the digital image correlation method of the present invention. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0026] like Figure 1 As shown, the method for testing the double-wave shock response of a shock absorber based on the digital image correlation method of the present invention comprises the following steps:

[0027] S101. Two high-speed cameras are deployed to shoot the front and sides of the test bench;

[0028] S102, sticking marking points on the test bench and the load surface, and measuring and recording the relative positions of the marking points;

[0029] S103, deploying acceleration sensors, connecting the camera and the sensors through a time synchronization trigger, and completing the synchronization of the displacement and acceleration response measurement equipment;

[0030] S104, setting the shooting frame rate, exposure rate and triggering time of the camera control software, and stopping the high-speed camera and acceleration acquisition after the impact test is completed;

[0031] S105. The video is processed and the DIC technology is used to solve the displacement of the test bench and the load during the impact process. The average value of the displacement difference between the two is the impact displacement response of the shock absorber.

[0032] Preferably, in S101:

[0033] Furthermore, in the shock response measurement method, binocular vision DIC technology is used to measure the displacement response of the shock absorber in the double-wave shock test. The commonly used contact measurement method is sensitive to shock waves in the shock test, resulting in large errors in the measured values. The non-contact measurement completes the position, shape and motion measurement of the object without contacting the measured object, which can not only eliminate the influence of the shock afterwave on it, but also can detect the overall test and improve the measurement accuracy.

[0034] Furthermore, if Figure 2 As shown, the high-speed cameras in the shock response measurement method are arranged in front of and on the side of the test bench to record the entire test. The shock absorber load is For large-sized components weighing up to 1 ton, the load is prone to tilting by no more than 1° during the test. The displacement is recorded and measured at two angles of the test bench, and the average is taken as the final displacement response value to eliminate the displacement measurement error caused by overturning.

[0035] Furthermore, the high-speed camera in the shock response measurement method is arranged at a distance of at least 1.5 m from the test bench. The double-wave shock test has a fast impact speed and high energy, and the shock afterwave will propagate outward in a decreasing manner, affecting the stability of the camera. At the same time, the high-speed camera is arranged on solid ground, which effectively reduces the impact of the shock afterwave on the camera and reduces measurement errors.

[0036] Furthermore, in the method for measuring shock response, the field of view plane of the high-speed camera is parallel to the plane being measured, and sufficient space is reserved in the upper half of the field of view. In the double-wave shock test, the displacement of the shock absorber is small, while the displacement of the shock platform is large. The field of view of the camera needs to meet the overall vertical displacement stroke to ensure that each component is captured and recorded by the camera during the entire test process.

[0037] Preferably, in S102:

[0038] Furthermore, if Figure 3 As shown, the shock absorber in the shock response measurement method is connected to the test bench and the load by bolts, the relative displacement of the top of the shock absorber is the same as the load, and the bottom displacement is the same as the test bench. The test bench and the load are both large-sized components. The two and other components are combined into a double-wave impact test bench fixture. The shock absorber is located in the middle position inside the fixture. It is difficult to directly measure the displacement response of the shock absorber during the impact process. The marking points are respectively pasted on the load and the test bench. The impact displacement response of the shock absorber is indirectly obtained by measuring the relative displacement difference between the load and the test bench, which effectively reduces the difficulty and time of the test measurement operation.

[0039] Preferably, in S103:

[0040] Furthermore, if Figure 4 As shown in the figure, the high-speed camera and acceleration sensor in the shock response measurement method have different measurement principles, and it is difficult to start measurement at the same time. Through the time synchronization trigger, based on the GNSS principle, pulse signals are output to the two measurement devices at a certain frequency, thereby realizing synchronous real-time measurement. The synchronization accuracy is better than 200ns to complete the correspondence between displacement and acceleration at the same time. The mathematical formula can be expressed as:

[0041] (1)

[0042] Where Q is the state of the flip-flop, is the time received from GNSS, is the sum of signal transmission delay and local clock deviation, is the state of the input data of the trigger, and t represents the time.

[0043] Preferably, in S104:

[0044] Furthermore, the high-speed camera system in the method for measuring impact response is mainly composed of a high-speed camera, a lens, a bracket and a pan / tilt. Due to the limitations of high-speed camera shooting speed, low exposure and other conditions, the requirements for external light sources are extremely high. When shooting high-frame rate videos, an external supplementary light source is required to make up for the problem of insufficient light entering the high-speed camera COMS. The system used in the present invention adopts two sets of 300w-led flicker-free gold shell light sources. When the working distance is 2m, the brightness can reach 9450LUX with the reflector. The main function is to provide supplementary light for indoor delivery targets. Because it is necessary to stay away from the test area during the impact test, and considering the size of the on-site space and the impact of the aftermath of the impact on the stability of the camera, the focal length evaluation calculation formula is used:

[0045] (2)

[0046] Among them, f is the focal length of the lens, D is the working distance, w is the target width of the camera, and W is the field of view width. After evaluation, the system used in the present invention selects a 16-50mm lens for medium-distance shooting, and the field of view of the subject is 2 2m, the shooting distance will reach 3-5m, ensuring that the test personnel operate outside the safe distance, avoiding the impact of the aftershock on the camera. Preferably, the system used in the present invention uses a Phantom high-speed camera and a matching lens, with a frame rate of ≥1000 frames / s and a storage time of >1min.

[0047] Preferably, in S105:

[0048] Furthermore, the time domain response of the acceleration sensor in the shock response measurement method in the shock test has a lot of noise. First, wavelet decomposition is used to decompose it into a series of wavelet coefficients with different resolutions, and soft threshold processing is used to suppress the noise. The mathematical formula can be expressed as:

[0049] (3)

[0050] in, is the wavelet coefficient, j is the scale, k is the position at scale j, is the wavelet coefficient after threshold processing, is the threshold, sign is the sign function, and max is the maximum value function.

[0051] The time domain response after wavelet decomposition and soft threshold denoising is input into the deep neural network for learning. By training at each scale, a more accurate noise intensity is obtained, so that the deep neural network model can be directly used to remove noise. The mathematical formula can be expressed as:

[0052] (4)

[0053] in, is the noise linear combination of the jth layer, is the soft threshold matrix, is the output of the previous layer, is the bias vector, σ is the noise intensity, To measure the signal, is the denoised signal, For noise, is the noise intensity matrix. is the output of the jth layer.

[0054] Example:

[0055] The test piece of the embodiment of the present invention adopts a certain type of ship gas turbine isolation system shock absorber, the test bench adapter plate in the fixture is made of 45 steel, and the counterweight is made of ordinary carbon steel. The embodiment of the present invention is designed according to the double wave impact test of a certain ship isolation system shock absorber, and the shock absorber is fixed on the test bench by a double wave impact test fixture.

[0056] like Figure 2 As shown, in an embodiment of the present invention, the shock absorber is connected to the load and the test bench by bolts, and the fixture is fixed to the test impact bench by bolts. The hammer impact and the buffer provide double half-sine shock waves for the fixture and the shock absorber. The impact test bench and the fixture move vertically under high-energy impact, and the vertical stroke of the test bench is much larger than the relative displacement of the shock absorber.

[0057] like Figure 3 As shown, in the embodiment of the present invention, three marking points are pasted on the lower positions of the test bench and the load, forming three pairs of six measurement objects in total. The test bench and the load are connected and fixed to the shock absorber by bolts. The connection position does not produce any relative displacement during the entire impact process. The displacement of the test bench is the same as the bottom of the shock absorber, and the displacement of the load is the same as the top of the shock absorber. The relative displacement difference between the two is the shock displacement response value of the shock absorber.

[0058] like Figure 4 As shown, in an embodiment of the present invention, a high-speed camera is arranged in front of and on the side of the test bench, and high-frequency images are recorded in two directions. The relative displacement of the shock absorber is obtained by comparing and tracking the marked points using the DIC technology. The average of the measured values ​​in the two directions can effectively reduce the displacement response error. At the same time, considering that the deviation of the displacement caused by the possible tilt of the load can be eliminated by the average.

[0059] After the shock absorber is installed in the fixture, two high-speed cameras are deployed, and the cameras shoot the front and side of the test bench at a certain distance; the camera field of view plane is kept relatively parallel to the measured plane, and sufficient space is reserved in the upper half of the field of view; the acceleration sensor is deployed, and the high-speed camera and the sensor are connected through a time synchronization trigger to complete the correspondence between the displacement and acceleration measurement response; the camera cable is connected and the control software is started, and the shooting frame rate, exposure rate and trigger time are set; the lighting system is aimed at the shooting area, and the camera image is observed to fine-tune the lens posture, focal length, aperture size and lighting position to make the image bright and clear; after an impact test is completed, the high-speed camera and acceleration sensor acquisition are stopped, and the cropped video clips are stored; the camera video is processed, and the DIC technology is used to solve the displacement response of the test bench and the load during the impact process; the relative displacement values ​​of each pair of marked points are sorted out, and the average value is calculated as the shock absorber impact displacement response value.

[0060] The embodiment of the present invention is directed to a double-wave impact test of a single shock absorber design. When a double-wave impact test is performed on different test pieces or a different number of test pieces, the present invention can also be used to measure the displacement response value of the test piece.

[0061] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection, an electrical connection, or communication with each other; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0062] Obviously, the embodiments described above are only some embodiments of the present invention, rather than all embodiments. The preferred embodiments of the present invention are given in the accompanying drawings, but they do not limit the scope of protection of the present invention. The present invention can be implemented in many different forms. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive. Although the present invention has been described in detail with reference to the aforementioned embodiments, for those skilled in the art, it is still possible to modify the technical solutions recorded in the aforementioned specific implementation methods, or to replace some of the technical features therein with equivalents. Any equivalent structure made using the contents of the specification and drawings of the present invention, directly or indirectly used in other related technical fields, is also within the scope of protection of the patent of the present invention.

Claims

1. A method for testing the double-wave impact response of a shock absorber based on digital image correlation method, characterized in that: include: Two high-speed cameras are deployed to shoot the front and sides of the test bench; Paste marking points on the test bench and the load surface, and measure and record the relative positions of the marking points; Arrange acceleration sensors, connect high-speed cameras and sensors through time synchronization triggers, and complete the synchronization of displacement and acceleration response measurement equipment; Set the shooting frame rate, exposure rate and trigger time of the camera control software, and stop high-speed video and acceleration acquisition after one impact test is completed; For video processing, digital image correlation technology is used to solve the displacement of the test bench and the load during the impact process. The average value of the displacement difference between the two is the impact displacement response of the shock absorber.

2. The method for testing the double-wave impact response of a shock absorber based on digital image correlation method according to claim 1, characterized in that: The high-speed camera uses binocular vision to shoot continuously at a speed of more than 1000 frames per second to achieve real-time image acquisition of the impact surface and load surface of the shock absorber, and records and stores the movement of the impact surface and load surface at each moment during the experiment in the form of images.

3. The method for testing the double-wave shock response of a shock absorber based on digital image correlation method according to claim 1, characterized in that: The digital image correlation method technology is a three-dimensional digital image correlation method, which performs full-field response measurement of the entire test bench in a non-contact and non-destructive manner.

4. The method for testing the double-wave impact response of a shock absorber based on digital image correlation method according to claim 1, characterized in that: The high-speed camera simultaneously shoots the front and side surfaces of the test bench to generate intersecting fields of view, and compares and identifies the marking points of the collected images through a macroscopic displacement measurement method of a digital image correlation method.

5. The method for testing the double-wave shock response of a shock absorber based on digital image correlation method according to claim 1, characterized in that: The vibration absorber is installed in a double-wave impact test bench fixture, and the vibration absorber is connected and fixed to the impact table surface and the load through bolts.

6. The method for testing the double-wave impact response of a shock absorber based on digital image correlation method according to claim 1, characterized in that: The acceleration sensor is a special sensor for impact test. After measuring the load and test bench acceleration, a deep neural network model combined with a wavelet transform method is used to filter the acceleration response noise to achieve the actual acceleration response output of the object under impact.

7. The method for testing the double-wave shock response of a shock absorber based on digital image correlation method according to claim 1, characterized in that: The working process of the time synchronization trigger is based on GNSS time as the standard time source to tame the constant temperature crystal oscillator, and output pulse signals at a certain frequency to the high-speed camera and acceleration sensor to achieve synchronous real-time measurement of relative displacement and acceleration response.

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