Underwater explosion shock wave overpressure optical measurement method and system based on OpenCV

Abstract

In order to solve the technical problems that the existing electric measurement method cannot accurately measure the underwater explosion shock wave overpressure and cannot obtain the flow field parameters of underwater explosion, the application provides an underwater explosion shock wave overpressure optical measurement method and system based on OpenCV. The method obtains the shock wave front image at different times, identifies the contour of each frame of shock wave front based on the OpenCV image recognition algorithm, then respectively calculates the contour radius of the shock wave front and the shock wave propagation speed, and combines the Rankine-Hugoniot formula to calculate and obtain the overpressure peak value of the underwater explosion shock wave. The measurement system comprises a light source, an image acquisition device, a mounting holder and a protection device, the light source is used for light supplementing of the image acquisition system, the image acquisition device is used for acquiring the propagation image of the underwater explosion shock wave, the mounting holder is used for fixing and supporting the image acquisition device, and the protection device is located at the periphery of the image acquisition device and the mounting holder, so that the image acquisition device is protected from damage.

Description

Technical Field

[0001] This invention relates to a method for measuring overpressure of explosion shock waves, and more particularly to an underwater explosion shock wave overpressure optical measurement method and system based on OpenCV. Background Technology

[0002] Underwater blasting technology is commonly used in civil engineering projects such as dam construction and canal excavation. Shock waves are the most important research subject in underwater blasting studies. Because the attenuation of the impact from an underwater explosion is exponential, the destructive power of the shock wave is mainly concentrated in the near field. However, the peak pressure of underwater explosion shock waves is high, often reaching GPa levels in the near field. Simultaneously, there are complex phenomena such as short pressure rise times, rapid expansion of the pressure wave front, and the expansion and destruction of detonation products. Therefore, measuring the overpressure of near-field shock waves has always been a challenge in underwater explosion parameter measurement.

[0003] Currently, the common measurement method is electrical measurement, which uses pressure sensors. However, commonly used sensors in electrical measurement, such as manganin, PVDF pressure sensors, tourmaline sensors, and piezoelectric ceramic sensors, have limitations in their application in underwater explosion near-field overpressure measurement due to their small measurement range, difficulty in installation and protection, and high noise in pressure signal recording. These limitations prevent accurate measurement of underwater explosion shock wave overpressure. Furthermore, in addition to the peak value of the shock wave overpressure, underwater explosion flow field parameters (such as the shape of the shock wave front and bubbles, the shock wave development process, and the propagation velocity in different directions) are also crucial for underwater explosion research, but existing electrical measurement methods cannot effectively obtain these parameters. Summary of the Invention

[0004] To address the technical problems of existing electrical measurement methods being unable to accurately measure the overpressure of underwater explosion shock waves and obtain underwater explosion flow field parameters, this invention provides an optical measurement method and system for underwater explosion shock wave overpressure based on OpenCV.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] An optical measurement method for underwater explosion shock waves based on OpenCV, characterized by the following steps:

[0007] 1) Acquire images of underwater explosion shock waves using an image acquisition device, wherein the shock wave images include multiple consecutive shock wave front images during the propagation of the shock wave;

[0008] 2】The contours of the shock wave fronts in each frame of the shock wave front image are identified based on the OpenCV image recognition algorithm;

[0009] 3. Using the NumPy matrix operation library, the contour of each identified shock wave front is calculated to obtain the expansion radius R of each shock wave frame. Then, the first fitting formula for the change of the shock wave expansion radius R with time t is obtained. Where t represents the time of the shock wave propagation process;

[0010] 4. Using the first fitting formula Differentiation yields the second fitting formula for the shock wave velocity D as a function of time t. ;

[0011] 5. The pressure P of the shock wave is calculated based on the second fitting formula and the Rankine-Hugoniot formula, thereby obtaining the overpressure of the underwater explosion shock wave in each frame; the expression for the pressure P of the shock wave is:

[0012] ;

[0013] Where P0 is the hydrostatic pressure at the measuring point, u is the velocity of the water particles, and ρ0 is the density of the water in the undisturbed area.

[0014] Furthermore, in step 1], the shock wave image also includes multiple consecutive pulsating bubble images during the propagation of the shock wave.

[0015] Further, in step 2], the Canny high-level operator in the OpenCV image recognition algorithm is used to identify the contour of the shock wave front in each frame of the shock wave front image, and at the same time, the boundary of the pulsating bubble in each frame of the pulsating bubble image is identified. Based on the boundary of the pulsating bubble, the shape information of the shock wave front and the pulsating bubble can be obtained, and then the underwater explosion flow field parameters can be obtained.

[0016] Further, step 3 specifically involves using the matrix operation library NumPy to calculate the contour of each identified shock wave front, obtaining the expansion radius R corresponding to each frame of the shock wave, and using MATLAB to plot the duration curve of the shock wave expansion radius R versus time t. Nonlinear fitting is then performed on this curve to obtain the first fitting formula for the change of the shock wave expansion radius R with time t. .

[0017] Furthermore, in step 5, the velocity u of the water particles is expressed as follows:

[0018] ;

[0019] By substituting the velocity u of the water particles into the expression for the pressure P of the shock wave, and combining it with the second fitting formula, the overpressure of the underwater explosion shock wave can be accurately obtained.

[0020] In addition, the present invention also provides an underwater explosion shock wave overpressure optical measurement system based on OpenCV, which is characterized by including an image acquisition device, a gimbal and a protection device set on one side of the underwater explosion shock wave source;

[0021] The image acquisition device is used to acquire images of the propagation of underwater explosion shock waves;

[0022] The mounting platform is located at the bottom of the image acquisition device and is used to fix and support the image acquisition device;

[0023] The protective device is located around the image acquisition device and the mounting platform, and is used to protect the image acquisition device from damage by shock waves.

[0024] Furthermore, it also includes a light source, which is used to provide supplemental lighting for the image acquisition system; the light source and the image acquisition device are located on both sides of the underwater explosion shock wave source, and the light source, the underwater explosion shock wave source and the image acquisition device are located on the same straight line.

[0025] Furthermore, the image acquisition device is a high-speed camera with a full-frame resolution greater than 1280*800, a full-frame shooting rate greater than 1,000,000 frames / second, and a black-and-white SR-CMOS sensitivity greater than 38,000.

[0026] Furthermore, the protective device is a box-shaped structure, and its material is tempered glass with high impact resistance, so as to achieve the function of protecting the experimental device.

[0027] Furthermore, the light source is selected as a variable-focus laser fill light.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] 1. The measurement method of the present invention obtains shock wave front images at different times, identifies the contour of the shock wave front in each frame based on the OpenCV image recognition algorithm, and then calculates the contour radius and shock wave propagation velocity of the shock wave front respectively. The overpressure peak value of the underwater explosion shock wave is calculated by combining the Rankine-Hugoniot formula, thereby realizing the accurate measurement of the overpressure of the underwater explosion shock wave.

[0030] 2. The measurement method of the present invention can also identify the boundary of pulsating bubbles, obtain the shape information of the shock wave front and pulsating bubbles, and thus effectively obtain the underwater explosion flow field parameters, providing data support for the study of underwater explosion shock waves.

[0031] 3. In the measurement method of the present invention, the OpenCV image recognition algorithm can accurately identify the boundaries of the explosive ball, the shock wave boundary and the bubble boundary in the states of the explosive ball before detonation, the initial stage of explosion and the later stage of explosion. It has the advantages of high accuracy and short time, and can meet the working requirements. Attached Figure Description

[0032] Figure 1 This is a flowchart of an embodiment of the underwater explosion shock wave overpressure optical measurement method based on OpenCV of the present invention.

[0033] Figure 2 This is a schematic diagram illustrating the identification process of the shock wave front and the boundary of the pulsating bubble in an embodiment of the underwater explosion shock wave overpressure optical measurement method based on OpenCV of the present invention.

[0034] Figure 3 This is a time-varying curve of the shock wave expansion radius R versus time t in an embodiment of the underwater explosion shock wave overpressure optical measurement method based on OpenCV of the present invention.

[0035] Figure 4 This is a graph showing the change of shock wave velocity with proportional distance in an embodiment of the underwater explosion shock wave overpressure optical measurement method based on OpenCV of the present invention.

[0036] Figure 5 This is a graph showing the variation of particle velocity in the explosion flow field with proportional distance in an embodiment of the underwater explosion shock wave overpressure optical measurement method based on OpenCV of the present invention.

[0037] Figure 6 This is a graph showing the change of shock wave pressure with proportional distance in an embodiment of the underwater explosion shock wave overpressure optical measurement method based on OpenCV of the present invention.

[0038] Figure 7 This is a comparison diagram of the underwater explosion shock wave overpressure obtained by the optical method provided by this invention with the results of empirical formulas and numerical solutions. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It is worth mentioning that the specific examples described herein are merely illustrative and not intended to limit the scope of the invention.

[0040] Reference Figures 1 to 7 This invention provides an underwater explosion shock wave overpressure optical measurement method based on OpenCV, which includes the following steps:

[0041] 1】The underwater explosion shock wave image is acquired by an image acquisition device. The shock wave image includes multiple consecutive shock wave front images and multiple consecutive pulsating bubble images during the propagation of the shock wave.

[0042] To achieve a comprehensive representation of underwater explosion shock waves and bubble phenomena, this embodiment employs an OpenCV-based underwater explosion shock wave overpressure optical measurement system for image acquisition. This system includes a light source, an image acquisition device, a mounting platform, and protective devices. The light source provides supplementary illumination for the image acquisition system, typically using a variable-focus laser light to obtain clear and complete images of the shock wave front and pulsating bubbles. The image acquisition device acquires images of the underwater explosion shock wave propagation. The light source and image acquisition device are located on opposite sides of the underwater explosion shock wave source, and are aligned on a straight line to improve the image clarity. Furthermore, the specific installation position can be adjusted according to actual testing requirements. The image acquisition device is a high-speed camera with a full-frame resolution greater than 1280*800, a full-frame shooting rate greater than 1,000,000 frames / second, and a monochrome SR-CMOS sensitivity greater than 38,000. Since underwater explosions typically occur in the microsecond and millisecond range, the technical specifications of high-speed cameras can ensure accurate capture of the detonation process of the explosive pellets, the generation of the explosion shock wave, the propagation of the shock wave, and the pulsation of the bubbles.

[0043] The gimbal is located at the bottom of the image acquisition device to fix and support it, enabling the acquisition of images from the same time base and the same spatial base. A protective device is located around the image acquisition device and the gimbal to protect the image acquisition device from damage caused by an blast shockwave. In this embodiment, the protective device is a box-shaped structure made of highly impact-resistant transparent tempered glass. Alternatively, another protective device can be installed around this testing system as needed to shield personnel and the surrounding environment from damage during the experiment.

[0044] The image acquisition device in this embodiment is a high-speed camera with a full-frame resolution greater than 1280*800, a full-frame shooting rate greater than 1,000,000 frames / second, and a black-and-white SR-CMOS sensitivity greater than 38,000.

[0045] 2】Based on the Canny high-level operator in the OpenCV image recognition algorithm, the contour of the shock wave in each frame of each shock wave front image and the boundary of the pulsating bubble in each frame of each pulsating bubble image can be identified. Based on the boundary of the pulsating bubble, the shape information of the shock wave front and the pulsating bubble can be obtained, thereby effectively obtaining the underwater explosion flow field parameters and providing data support for the study of underwater explosion shock waves.

[0046] OpenCV is a commonly used library in computer vision, a major branch of artificial intelligence, and has powerful image processing capabilities. This embodiment uses the Canny high-level operator to develop underwater explosion shock wave and bubble boundary recognition and capture technology to achieve efficient and accurate recognition of shock wave fronts and bubble boundaries.

[0047] The logical sequence of Canny edge detection is as follows: First, Gaussian filtering is used to reduce Gaussian noise in the image to prevent short edges formed by noise from being misidentified as contours. Next, the first derivatives of the convolved image in the horizontal and vertical directions are calculated to obtain the gradient map of the image, thus obtaining the gradient and direction of the image contour. Then, the entire image is scanned, and non-maximum suppression is used to remove some non-contour points, thereby narrowing the contour and reducing its thickness. Finally, the true contour is determined by setting two values: minVal and maxVal. When the gray-level gradient of the image edge is higher than maxVal, the contour point is retained; when it is lower than minVal, the corresponding edge is discarded. When the gray-level gradient is between minVal and maxVal, points connected to the points determined as true contours are retained, and the rest are discarded.

[0048] The boundary recognition technology used in this embodiment can accurately identify the boundaries of the explosive sphere, the shock wave, and the bubble in the states of unexploded explosive sphere, the initial stage of explosion, and the later stage of explosion. It has the advantages of high accuracy and short time, and can meet the working requirements.

[0049] 3. Using the NumPy matrix operation library, the contour of each identified shock wave frame is calculated to obtain the corresponding expansion radius R. Then, using MATLAB, the evolution curve of the shock wave expansion radius R over time t is plotted. Nonlinear fitting is performed on this curve to obtain the first fitting formula for the evolution of the shock wave expansion radius R over time t. Where t represents the time of the shock wave propagation process.

[0050] 4. Using the first fitting formula Differentiation yields the second fitting formula for the shock wave velocity D as a function of time t. .

[0051] 5. The pressure P of the shock wave is calculated based on the second fitting formula and the Rankine-Hugoniot formula, thereby obtaining the overpressure of the underwater explosion shock wave in each frame; the expression for the pressure P is:

[0052] (1)

[0053] In formula (1), P0 is the hydrostatic pressure at the measuring point, u is the velocity of the water particles, and ρ0 is the density of water in the undisturbed area. The velocity u of the water particles is expressed as follows:

[0054] (2)

[0055] Substituting formula (2) into formula (1) and combining it with the second fitting formula, the overpressure of the underwater explosion shock wave can be accurately obtained.

[0056] Step 5: Specifically, when the shock wave generated by the explosion propagates within the medium, there is a discontinuity between the disturbed and undisturbed regions where the pressure P, density ρ, velocity u, and specific internal energy e of the shock wave change abruptly; this discontinuity is called a shock wave. The three conservation equations are satisfied on both sides of the shock wave, namely:

[0057] (3)

[0058] (4)

[0059] (5)

[0060] The above three equations are the mass, momentum, and energy conservation equations for a shock wave. Ignoring wavefront thickness, these equations apply to both planar and spherical wavefronts. When the velocity u0 of the undisturbed fluid is 0, the above three equations can be simplified to:

[0061] (6)

[0062] (7)

[0063] (8)

[0064] Equations (6), (7), and (8) respectively give the relationship between pressure and density inside the underwater explosion flow field. When the fluid state equation is known, the internal energy increment E-E0 of the flow field can be calculated, where E is the internal energy of the flow field after disturbance, and E0 is the initial internal energy of the undisturbed flow field. At this time, if the pressure P0 of the undisturbed fluid before the wavefront (i.e., the hydrostatic pressure P0) and the density ρ0 of the water in the undisturbed region are known, equations (6), (7), and (8) can be used to calculate the pressure immediately following the wavefront. and The relationship between the two equations is as follows: Equations (6) and (7) combined yield the shock wave velocity as a function of the pressure and density behind the shock wave front. and water particle velocity ,Right now:

[0065] (9)

[0066] (10)

[0067] The relationship between the shock wave velocity D and the water particle velocity u in water with a pressure below 45 GPa is as follows:

[0068] (11)

[0069] The velocity u of the water particle can be obtained as:

[0070] (2)

[0071] Substituting equations (2) and (11) into equation (7), we obtain the shock wave pressure as follows:

[0072] (12)

[0073] Substituting equation (12) into equation (6), we can obtain the density of water behind the wavefront as follows:

[0074]

[0075] In the above formula, For the shock wave velocity, The density of water in the undisturbed area, and Values , This refers to the near-field shock wave pressure. The hydrostatic pressure at the measuring point is denoted as .

[0076] In summary, using the above formulas, we can obtain the peak value of the shock wave overpressure, as well as information such as the flow field density and particle velocity before and after the shock wave.

[0077] To verify the method proposed in this invention, an underwater explosion experiment was conducted in a water tank, and the results were compared and verified using numerical simulation and empirical formulas. The experimental explosive pellet had an equivalent weight of 0.125 g TNT, a diameter of 5 mm, and a sampling time interval of 0.5 seconds. .

[0078] Figure 2 Based on the shock wave propagation images captured by a high-speed camera in the experiment and the shock wave and bubble boundary maps obtained by the shock wave interface recognition technology developed in this invention, the shock wave propagation radius R is obtained, and the time-lapse curve of R is established using MATLAB (e.g., Figure 3 As shown), a nonlinear fitting formula for the shock wave expansion radius R versus t is obtained by performing a nonlinear fitting on the curve. Immediately afterwards... By taking the derivative, we obtain the nonlinear relationship between the shock wave velocity D and time t. ,like Figure 4 As shown.

[0079] It is worth mentioning that, Figure 3 The x-axis represents time. , Figure 4 The x-axis represents the proportional distance. (Where R0 is the radius of the explosive ball), both have the same meaning, because this records the image of the shock wave propagating in space for each frame, and each time t corresponds to each scale distance. .

[0080] After obtaining the shock wave propagation velocity D, the relationship between particle velocity and proportional distance in the flow field after the shock wave can be obtained using the formula described above (e.g., Figure 5 As shown). By Figure 5 It can be seen that the shock wave propagation speed is relatively high at the beginning of the explosion, then rapidly decays to the speed of sound in water and then remains constant. In this embodiment, the speed of sound in water is 1562 m / s. It can be observed that the underwater explosion shock wave velocity obtained by the optical method conforms to the classical underwater explosion shock wave velocity propagation law, that is, it decays exponentially to the speed of sound in water and then remains essentially constant. Simultaneously, it was found that the flow field particle velocity in the disturbed region behind the shock wave front exhibits the same exponential decay law as the shock wave velocity, and the values ​​at each time point are all less than the shock wave velocity D.

[0081] like Figure 6 As shown, after obtaining the shock wave propagation speed D and the particle velocity... Then, the variation of the peak overpressure of the underwater explosion shock wave with proportional distance can be obtained using the aforementioned formula. Figure 6 It reflects the peak overpressure of the shock wave at each spatial point along the propagation path within the underwater explosion flow field.

[0082] like Figure 7 As shown, to verify the effectiveness and accuracy of the underwater explosion shock wave overpressure optical measurement method based on OpenCV proposed in this invention, the overpressure peak data measured by the proposed method are compared with the results of empirical formulas and numerical simulations. Figure 7 It can be seen that, overall, the measurement method of this invention exhibits an exponential decay pattern consistent with the shock wave overpressure peak curves obtained from empirical formulas and numerical simulations. Furthermore, the measurement method of this invention shows high agreement with the empirical formulas and numerical simulation data, and the trend changes are consistent. (Regarding the proportional distance...) Within the specified range, there are slight discrepancies between the measurement method, empirical formula, and numerical simulation data of this invention. This is because existing empirical formulas and numerical simulation equations for shock wave overpressure peak values ​​are not applicable to calculating the shock wave overpressure peak value generated by near-field explosive detonation. Since the measurement method of this invention is primarily based on the shock wave front image and the three conservation equations of shock waves, the measurement results show better consistency with empirical formulas and numerical simulations when measured across the entire spatial range.

[0083] In summary, the underwater explosion shock wave overpressure optical measurement method based on OpenCV proposed in this invention can effectively and accurately measure the overpressure peak value of the shock wave and completely obtain the development and evolution process of flow field parameters such as shock wave and bubbles.

Claims

1. A method for underwater explosion shock wave overpressure optical measurement based on OpenCV, characterized in that, Includes the following steps:

1. Underwater explosion shock wave images are acquired using an image acquisition device. The shock wave images include multiple consecutive shock wave front images and multiple consecutive pulsating bubble images during the propagation of the shock wave. The image acquisition device is a high-speed camera with a full-frame resolution greater than 1280*800, a full-frame shooting rate greater than 1,000,000 frames / second, and a black and white SR-CMOS sensitivity greater than 38,000. 2】Based on the Canny advanced operator in the OpenCV image recognition algorithm, the contour of each shock wave front in each frame of the shock wave front image and the boundary of each pulsating bubble in each frame of the pulsating bubble image can be identified. Based on the boundary of the pulsating bubble, the shape information of the shock wave front and the pulsating bubble can be obtained, and then the underwater explosion flow field parameters can be obtained.

3. Using the NumPy matrix operation library, the contour of each identified shock wave front is calculated to obtain the expansion radius R of each shock wave frame. Then, the first fitting formula for the change of the shock wave expansion radius R with time t is obtained. Where t represents the time of the shock wave propagation process; 4. Using the first fitting formula Differentiation yields the second fitting formula for the shock wave velocity D as a function of time t. ; 5. The pressure P of the shock wave is calculated based on the second fitting formula and the Rankine-Hugoniot formula, thereby obtaining the overpressure of the underwater explosion shock wave in each frame; the expression for the pressure P of the shock wave is: ； Where P0 is the hydrostatic pressure at the measuring point, ρ0 is the density of water in the undisturbed region, and u is the velocity of the water particles, expressed as follows: .

2. The underwater explosion shock wave overpressure optical measurement method based on OpenCV according to claim 1, characterized in that: Step 3: Specifically, the contour of each identified shock wave front is calculated using the NumPy matrix operation library to obtain the expansion radius R corresponding to each frame of the shock wave. Then, the expansion radius R of the shock wave is plotted as a function of time t using MATLAB. This curve is then subjected to nonlinear fitting to obtain the first fitting formula for the change of the shock wave expansion radius R with time t. .

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