A method for shock response testing of a shock absorber based on digital image correlation method

Abstract

The application discloses a shock absorber double-wave impact response test method based on a digital image correlation method, which comprises the following steps: two high-speed cameras are arranged to shoot the front and side of a test table; mark points are pasted on the test table and a load surface, and the relative positions of the mark points are measured and recorded; an acceleration sensor is arranged, the camera and the sensor are connected through a time synchronization trigger, and the synchronization of displacement and acceleration response measurement equipment is completed; the shooting frame rate, exposure rate and trigger moment of the camera control software are set, and the high-speed camera and acceleration acquisition are stopped after one impact test is completed; the camera video is processed, the displacement of the test table and the load in the impact process is solved based on the digital image correlation method technology, and the average value of the displacement difference of the test table and the load is the impact displacement response of the shock absorber. The application can measure the response of the shock absorber in the double-wave impact test.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of ship equipment shock resistance test evaluation, and particularly relates to a shock absorber double-wave shock response test method based on a digital image correlation method (DIC). BACKGROUND

[0002] The ship power system and its equipment, as the heart of the ship, provide the power and electricity required by the whole ship, and guarantee the ship navigation and daily life needs, and thus occupy a very important position in the ship equipment. In navigation, the ship power equipment may be seriously damaged due to impact load, and the whole ship power equipment or even the power system may collapse. In order to improve the anti-shock performance of the ship power equipment, a light or medium shock machine or a floating shock platform is used to carry out shock test on the power equipment,

[0003] In view of the anti-shock capacity test of the ship equipment, the world has carried out in-depth research on the test method of the ship equipment, and formed corresponding standards and specifications. These standards specify corresponding shock test methods such as light shock, medium shock, explosion shock and double-wave shock. A large number of explosion test results of real ships show that the shock input environment generated by underwater explosion energy transmission to the equipment foundation is characterized by displacement / speed / acceleration shock spectrum in the frequency domain, which can be equivalent to positive and negative shock pulse in the time domain. The previous shock machine mainly simulates the impact energy, and can only simulate simple waveforms such as half-sine. The new double-wave shock test bench for ship equipment generates a positive wave pulse by impacting the center of the elastic wave generator below the test bench body with the hammer head of the shock machine. The positive wave impact pulse is generated by the interaction between the buffer (negative wave generator) installed on the test bench body and the test bench body under the action of the impact force. The required energy of the positive and negative waves required by the test conditions is generated by adjusting the different impact air pressures of the hammer head of the shock test machine.

[0004] In the test, the response of the object under the impact load needs to be measured in time and effectively. The commonly used displacement measurement methods can be divided into contact measurement and non-contact measurement. The contact measurement usually includes resistance strain gauges and extensometers, etc. These contact methods have the advantages of high precision, high sensitivity and strong environmental adaptability, but generally can only perform point measurement, and cannot obtain the full-field deformation detection of the measured object, and the operation wiring is complex. SUMMARY

[0005] To measure the displacement response of a vibration damper under a dual-wave impact test and solve the aforementioned technical problems, this invention provides a method for testing the dual-wave impact response of a vibration damper based on digital image correlation (DIC). The vibration damper is mounted in a dual-wave impact test fixture. DIC, as a non-contact measurement method, uses optical means to achieve full-field deformation detection of the object, belonging to a highly efficient computer vision method for deformation measurement. This invention measures the response of the vibration damper under a dual-wave impact test based on this method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for testing the dual-wave impact response of a vibration damper based on digital image correlation includes:

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

[0009] Marking points were affixed to the test bench and the load surface, and the relative positions of the marking points were measured and recorded.

[0010] An accelerometer is deployed, and a high-speed camera and the sensor are connected via a time synchronization trigger to synchronize the 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 recording and acceleration acquisition after one impact test is completed;

[0012] For video processing, the digital image correlation method 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 is a binocular vision camera that continuously captures images at a speed of over 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 motion of the impact surface and load surface at each moment during the experiment in the form of images.

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

[0015] Furthermore, the high-speed camera simultaneously captures images of the front and sides of the test platform, generating intersecting fields of view. The macroscopic displacement measurement method based on digital image correlation is used to compare and identify the marker points in the acquired images.

[0016] Furthermore, the vibration damper is installed in the fixture of the dual-wave impact test bench, and the vibration damper is fixed to the impact table and the load by bolts.

[0017] Further, the acceleration sensor is a special sensor for impact test, after measuring the load and test bench acceleration, the acceleration response is filtered by using a deep neural network model combined with wavelet transform method, and the actual acceleration response output of the measured object under impact is realized.

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

[0019] Beneficial effects:

[0020] The present application can perform high-frequency real-time image acquisition for the double-wave impact test of the shock absorber, and can measure the full-field response of the test bench non-contact and losslessly, and has strong anti-interference. Through the mark points pasted on the test bench and the load, the number of mismatched points of the DIC identification technology can be ensured to be extremely low, and finally the noise influence in the response is effectively filtered by combining the deep neural network with wavelet analysis, so that the precise measurement of the double-wave impact response of the shock absorber is realized. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 It is a flowchart of the method for testing the double-wave impact response of the shock absorber based on the digital image correlation method of the present application.

[0022] Figure 2 It is a schematic diagram of the installation of the shock absorber and the clamp for the method for testing the double-wave impact response of the shock absorber based on the digital image correlation method of the present application.

[0023] Figure 3 It is a schematic diagram of the pasting of the mark points for the method for testing the double-wave impact response of the shock absorber based on the digital image correlation method of the present application.

[0024] Figure 4 It is a schematic diagram of the camera arrangement plane for the method for testing the double-wave impact response of the shock absorber based on the digital image correlation method of the present application. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application is further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application, and are not used to limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0026] As Figure 1 shown, the method for shock absorber double-wave impact response test based on digital image correlation method of the application comprises the following steps:

[0027] S101, two high-speed cameras are arranged to take pictures of the front and side of the test bench;

[0028] S102, mark points are pasted on the test bench and the load surface, and the relative positions of the mark points are measured and recorded;

[0029] S103, acceleration sensors are arranged, the cameras and the sensors are connected through time-synchronous triggers, and the synchronization of the displacement and acceleration response measurement devices is completed;

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

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

[0032] Preferably, in the S101,

[0033] Further, in the method for measuring impact response, the displacement response of the shock absorber in the double-wave impact test is measured based on the binocular vision DIC technology, the commonly used contact type measurement method is sensitive to the impact wave in the impact test, resulting in a large error in the measurement value, the non-contact measurement can complete the position, shape and motion measurement of the object without contacting the object, can eliminate the influence of the impact residual wave, and can detect the whole test to improve the measurement accuracy.

[0034] Further, as Figure 2 shown, the high-speed cameras in the method for measuring impact response are arranged in front of and on the side of the test bench to record the video of the whole test, and the load of the shock absorber is a large-size component with a weight of 1t, and the load is prone to tilt by not more than 1° in the test. The displacement is measured by taking pictures of two angles of the test bench, and the average value is taken as the final displacement response value, so that the displacement measurement error caused by the tilting phenomenon is eliminated.

[0035] Further, the high-speed cameras in the method for measuring impact response are arranged at a distance of at least 1.5m away from the test bench, the impact speed of the double-wave impact test is fast and the energy is large, the impact residual wave will decrease and spread outward to affect the stability of the camera, and the high-speed cameras are arranged on a solid ground to effectively reduce the influence of the impact residual wave on the camera and reduce the measurement error.

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

[0037] Preferably, in the S102,

[0038] Further, as Figure 3 shown, the shock absorber in the measuring impact response method is connected to the test bench and the load through bolts. The relative displacement of the top of the shock absorber is the same as that of the load, and the displacement of the bottom is the same as that of the test bench. The test bench and the load are both large-size components. They and other components are combined into a double-wave impact test bench clamp. The shock absorber is located in the middle of the clamp. It is difficult to directly measure the displacement response of the shock absorber during the impact process. Marking points are pasted on the load and the test bench, respectively. The relative displacement difference between the load and the test bench is indirectly obtained to obtain the impact displacement response of the shock absorber, effectively reducing the difficulty and time of the test measurement operation.

[0039] Preferably, in the S103,

[0040] Further, as Figure 4 shown, the high-speed camera and the acceleration sensor in the measuring impact response method have different measurement principles, and it is difficult to start measuring at the same time. Through a time synchronization trigger, based on the GNSS principle, a pulse signal is output to the two measurement devices at a certain frequency, and then the synchronous real-time measurement is realized. The synchronization accuracy is better than 200ns to complete the correspondence of displacement and acceleration at the same time. The mathematical formula can be expressed as:

[0041] (1)

[0042] Wherein, Q is the state of the trigger, 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 time.

[0043] Preferably, in the S104,

[0044] Further, the high-speed camera system in the method for measuring impact response mainly consists of a high-speed camera, a lens, a support and a holder. Due to the limitation of low exposure of the high-speed camera, the requirement for external light source is extremely high, and an external light source is needed to make up for the insufficient light amount of the COMS of the high-speed camera when high-frame-rate video is shot. The system used in the application adopts two sets of 300w-led non-flickering goldbe light sources, and the brightness can reach 9450LUX when the working distance is 2m, and the main function is to provide light for indoor target placement. Since the impact test needs to be away from the test area, and considering the influence of the space size of the scene and the impact residual wave on the stability of the camera, according to the focal length evaluation formula:

[0045] (2)

[0046] Wherein, f is the focal length of the lens, D is the working distance, w is the target surface width of the camera, and W is the field of view width. The system used in the application selects a 16-50mm lens for medium distance shooting after evaluation, and the main field of view is 2 2m, and the shooting distance will reach 3-5m, which ensures that the test personnel operate outside the safe distance and avoids the influence of the impact residual wave on the camera. Preferably, the system used in the application adopts a Phantom high-speed camera and a matching lens, the frame rate is greater than or equal to 1000 frames / s, and the storage time is greater than 1min.

[0047] Preferably, in the S105, the method comprises:

[0048] Further, the time domain response of the acceleration sensor in the method for measuring impact response has a large amount of noise in the impact test. Firstly, the wavelet decomposition is used to decompose the noise into a series of wavelet coefficients with different resolutions, and the soft threshold processing is used to suppress the noise, and the mathematical formula can be expressed as:

[0049] (3)

[0050] Wherein, is the wavelet coefficient, j is the scale, k is the position under the 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 a deep neural network for learning, the noise intensity is obtained through training under each scale, and the deep neural network model is directly used to remove the noise, and the mathematical formula can be expressed as:

[0052] (4)

[0053] Wherein, is a noise linear combination of the jth layer, is a soft threshold matrix, is a previous layer output, is a bias vector, and sigma is a noise intensity, is a measurement signal, is a denoised signal, is noise, is a noise intensity matrix. is an output of the jth layer.

[0054] Embodiment:

[0055] The test piece of the embodiment of the application adopts a certain type of marine gas turbine isolation system damper, the test bench adapter plate in the clamp is made of 45 steel, and the counterweight is made of ordinary carbon steel. The embodiment of the application is designed according to the double-wave impact test of a certain ship isolation system damper, and the damper is fixed on the test bench through the double-wave impact test clamp.

[0056] As shown in the embodiment of the application, the damper is connected with the load and the test bench through bolts, the clamp is fixed on the test impact bench through bolt connection, the hammer head and the bumper provide the clamp and the damper with a double half-sine shock wave, the impact test bench and the clamp vertically move under a large energy impact, and the vertical stroke of the test bench is much larger than the relative displacement of the damper. Figure 2 As shown in the embodiment of the application, three mark points are pasted on the lower positions of the test bench and the load respectively, forming three pairs of six measurement objects, the test bench and the load are connected and fixed with the damper through bolts, no relative displacement is generated at the connection position during the entire impact process, the displacement of the test bench is the same as the bottom of the damper, the displacement of the load is the same as the top of the damper, and the difference between the relative displacements of the two is the impact displacement response value of the damper.

[0057] Figure 3 As shown in the embodiment of the application, one high-speed camera is arranged in front of the test bench and on the side, high-frequency image recording is performed on the two directions, the DIC technology is used to compare and track the mark points, so that the relative displacement of the damper is obtained, the average of the measurement values in the two directions can effectively reduce the displacement response error, and the inclination of the load that may cause displacement deviation can be eliminated through the average.

[0058] As shown in the embodiment of the application, one high-speed camera is arranged in front of the test bench and on the side, high-frequency image recording is performed on the two directions, the DIC technology is used to compare and track the mark points, so that the relative displacement of the damper is obtained, the average of the measurement values in the two directions can effectively reduce the displacement response error, and the inclination of the load that may cause displacement deviation can be eliminated through the average. Figure 4

[0059] ​​After the damper is installed into the fixture, two high-speed cameras are arranged to shoot a certain distance in front and side of the test bench; the camera field plane is kept relative parallel to the measured plane, and enough space is reserved in the upper half of the field; the acceleration sensor is arranged, the high-speed camera and the sensor are connected through a time synchronization trigger, and the displacement and acceleration measurement responses are matched; the camera cable is connected and the control software is started, the shooting frame rate, exposure rate and trigger time are set; the lighting system is aligned to the shooting area, the camera picture is observed, and the lens posture, focal length, aperture size and lighting lamp position are fine-tuned to make the picture bright and clear; after one impact test is completed, the high-speed camera and the acceleration sensor are stopped, and the video clip is stored; the camera video is processed, the DIC technology is used to solve the displacement response of the test bench and the load in the impact process; the relative displacement values of each pair of mark points are sorted out, and the average value is the impact displacement response value of the damper.

[0060] The embodiment of the present application is aimed at the double-wave impact test of a single damper design, and the displacement response value of the test piece can also be measured by using the present application when double-wave impact tests are performed on different test pieces or different numbers of test pieces.

[0061] In the present application, unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connecting", "fixing" and the like should be understood in a broad sense, for example, can be fixed connection, can be detachable connection, or can be integrated; can be mechanical connection, or can be electrical connection or communication with each other; can be directly connected, or can be indirectly connected through an intermediate medium; can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise explicitly limited. For those skilled in the art, the specific meanings of the above terms in the present application can be understood according to the specific circumstances.

[0062] Obviously, the above-described embodiments are only a part of the embodiments of the present application, and are not all the embodiments. The preferred embodiments of the present application are given in the drawings, but do not limit the protection scope of the present application. The present application can be realized in many different forms, and contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments, or equivalently replace some technical features. Any equivalent structure made by using the contents of the present application specification and drawings, directly or indirectly applied to other related technical fields, is also within the protection scope of the present application.

Claims

1. A method of shock response test of a damper based on digital image correlation method, characterized in that, The shock absorber is mounted in a double-wave impact test bench clamp, the double-wave impact test bench clamp comprises a test bench and a load, both of which are large-size components, and the shock absorber is located at a middle position inside the clamp; the shock absorber is fixed by bolt connection with an impact platform of the test bench and the load; Two high-speed cameras are arranged to shoot the front and side of the test bench; A plurality of mark points are pasted on the surface of the test bench and the load, and the relative positions of the plurality of mark points are measured and recorded; An acceleration sensor is arranged, the high-speed camera and the sensor are connected through a time synchronization trigger, and the synchronization of displacement and acceleration response measurement devices is completed; The shooting frame rate, exposure rate and trigger time of the camera control software are set, the high-speed camera and acceleration collection are stopped after one impact test is completed; The camera video is processed, the digital image correlation method is used to solve the displacement of the test bench and the load in the impact process, and the average value of the displacement difference of the two is the impact displacement response of the shock absorber; The digital image correlation method is a three-dimensional digital image correlation method, which is non-contact and lossless for full-field response measurement of the test bench. The high-speed camera is a binocular vision shooting, which continuously shoots at a speed of more than 1000 frames per second to realize real-time image collection of the impact surface of the shock absorber and the load surface, and record and store the motion of the impact surface and the load surface at each time in the form of images.

2. The method for shock response test of a shock absorber based on digital image correlation method according to claim 1, characterized in that: The high-speed camera shoots the front and side of the test bench at the same time, produces an intersecting field of view, and compares and identifies the mark points of the collected images through the macro displacement measurement method of the digital image correlation method.

3. The method for shock response testing of a shock absorber based on digital image correlation method of claim 1, wherein: The acceleration sensor is a special sensor for impact test, after measuring the acceleration of the load and the test bench, a deep neural network model is used in combination with a wavelet transform method to filter the acceleration response, and the actual acceleration response of the measured object under impact is output.

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

5. The method for shock response testing of a shock absorber based on digital image correlation method of claim 1, wherein: ​

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