Method for evaluating measurement accuracy of shock wave overpressure based on high-speed camera system

Abstract

The present application belongs to the technical field of shock wave overpressure test and data analysis, and particularly relates to a shock wave overpressure measurement precision evaluation method based on a high-speed camera system. The method comprises the following steps: S1: constructing a shock wave wave velocity measurement error model based on optical parameters of the high-speed camera system; S2: calculating a zero-order overpressure measurement error value based on the shock wave wave velocity measurement error model; S3: calculating a physical space wave velocity and an undisturbed air sound velocity based on explosion image sequences collected by the high-speed camera system; and S4: calculating a velocity correction factor based on the physical space wave velocity and the undisturbed air sound velocity to obtain overpressure measurement precision. The present application can accurately calculate the shock wave overpressure measurement precision of the optical measurement method, effectively solve the difficult problem of the wave velocity dependence on the overpressure measurement error uncertainty, and provide an effective basis for subsequent optical measurement method optimization and shock wave field three-dimensional measurement.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of shock wave overpressure test and data analysis, and particularly relates to a shock wave overpressure measurement precision evaluation method based on a high-speed camera system. BACKGROUND

[0002] Shock wave overpressure measurement is of great significance in various explosion-related power tests and damage evaluation analysis. The traditional electric measurement method uses a pressure sensor to record the shock wave overpressure signal, which needs to lay a large number of sensors, and the sensors are easily affected by the environment, and there are problems of long preparation time, high test cost, low data acquisition reliability and the like. The optical measurement method is based on a high-speed camera system and an image processing method, and has the characteristics of non-contact measurement, easy layout and digital processing, and is more and more applied in explosion tests. Among them, the overpressure measurement error is the core of quantitatively analyzing the measurement precision of the shock wave of the optical measurement method. The optical measurement method directly records the time sequence images of the explosion process, and in principle, the high-speed camera system measures the shock wave overpressure and does not depend on the pressure sensor, and there are two difficulties in evaluating the measurement precision thereof: one is that there is no theoretical model, and it is difficult to quantitatively calculate the measurement error and various related factors; and the other is that the measurement precision is related to the wave speed, the wave speed is a measurable unknown quantity in the optical measurement method, needs to be given a reference value, and the wave speed gradually decays in the explosion process, resulting in large measurement uncertainty. SUMMARY

[0003] Therefore, the application creates a shock wave overpressure measurement precision evaluation method based on a high-speed camera system to solve the problems that the prior art lacks a theoretical model, the measurement precision is related to the wave speed, the wave speed is a measurable unknown quantity in the optical measurement method, needs to be given a reference value, and the wave speed gradually decays in the explosion process, resulting in large measurement uncertainty, and the application can accurately calculate the shock wave overpressure measurement precision of the optical measurement method, effectively solves the difficult problem that the wave speed dependence causes large uncertainty of the overpressure measurement error, and provides an effective basis for subsequent optimization of the optical measurement method and three-dimensional measurement of the shock wave field.

[0004] To achieve the above-mentioned purpose, the technical scheme of the application creates is as follows:

[0005] A shock wave overpressure measurement precision evaluation method based on a high-speed camera system, specifically comprising the following steps:

[0006] S1: constructing a shock wave wave speed measurement error model based on optical parameters of the high-speed camera system;

[0007] S2: calculating a zero-order overpressure measurement error value based on the shock wave wave speed measurement error model;

[0008] S3: calculating a physical space wave speed and an undisturbed air speed based on explosion image sequences collected by the high-speed camera system;

[0009] S4: calculating a velocity correction factor based on the physical space wave velocity and the undisturbed air sound velocity, if the ratio of the physical space wave velocity and the undisturbed air sound velocity is less than a threshold value, taking the zero-order overpressure measurement error value as the overpressure measurement error, otherwise correcting the zero-order overpressure measurement error value by using the velocity correction factor, and taking the corrected overpressure measurement error value as the overpressure measurement precision.

[0010] Further, in step S1, the shock wave velocity measurement error model is:

[0011] ;

[0012] wherein, is the horizontal resolution of the high-speed camera system, is the theoretical value of the shock wave velocity, is the pixel number setting value of the wave front extraction error, is the wave front profile extraction error, is the focal length of the lens, is the interval frame number setting value, is the pixel size of the high-speed camera system, is the horizontal distance between the high-speed camera system and the explosion center, is the frame frequency of the high-speed camera system, is the field curvature error of the high-speed camera system, is the key frame extraction error.

[0013] Further, step S2 specifically includes:

[0014] S21: calculating the wave velocity measurement error based on the shock wave velocity measurement error model:

[0015] ;

[0016] wherein, is the true value of the shock wave velocity, is the wave velocity measurement error;

[0017] S22: calculating the zero-order overpressure measurement error value based on the wave velocity measurement error:

[0018] ;

[0019] wherein, is the shock wave overpressure, is the shock wave overpressure measurement error.

[0020] Further, in step S3, the calculation formula used for calculating the physical space wave velocity is:

[0021] ;

[0022] ;

[0023] wherein, is a scale, is a frame interval number a corresponding wave front profile moving pixel number, is a horizontal direction resolution of the high-speed camera system, is a pixel size of the high-speed camera system, is a focal length of the lens;

[0024] The calculation formula used for calculating the undisturbed air sound speed is:

[0025] ;

[0026] wherein, is an undisturbed air pressure, is an undisturbed air density, is an undisturbed air isentropic index.

[0027] Further, in step S4, the velocity correction factor is calculated based on the physical space wave speed and the undisturbed air sound speed The calculation formula used is:

[0028] .

[0029] Further, in step S4, the threshold value is 0.1.

[0030] Further, in step S4, the calculation formula of the overpressure measurement accuracy is: .

[0031] Further, the frame frequency of the high-speed camera system is greater than or equal to 2000.

[0032] Compared with the prior art, the present application can achieve the following beneficial effects:

[0033] The shock wave overpressure measurement accuracy evaluation method based on the high-speed camera system according to the present application, based on the physical law of shock wave propagation, reasonably constructs a shock wave speed measurement error model, and gives the wave speed combined with the wave front extraction algorithm, effectively analyzes the influence of various influencing factors of the optical measurement method on the wave speed measurement error, accurately calculates the overpressure measurement accuracy, and effectively solves the difficult problem of large overpressure measurement error uncertainty caused by wave speed change, and the calculation is simple and easy to apply. BRIEF DESCRIPTION OF DRAWINGS

[0034] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application and are incorporated in and constitute a part of this application. The embodiments of the application illustrated in the drawings are provided to enable a person skilled in the art to make or use the application and to explain the principles of the application. In the drawings:

[0035] Figure 1 Flowchart of the shock wave overpressure measurement precision evaluation method based on a high-speed camera system according to an embodiment of the application;

[0036] Figure 2 Schematic diagram of a shock wave wavefront and air state near the wavefront generated by an explosion according to an embodiment of the application;

[0037] FIG. 3(a) is a first explosion diagram according to an embodiment of the application;

[0038] FIG. 3(b) is a schematic diagram of extracting a shock wave wavefront in the first explosion diagram according to an embodiment of the application;

[0039] FIG. 3(c) is a second explosion diagram according to an embodiment of the application;

[0040] FIG. 3(d) is a schematic diagram of extracting a shock wave wavefront in the second explosion diagram according to an embodiment of the application;

[0041] Figure 4 FIG. 4 is a diagram showing the influence of wavefront extraction pixel error and key frame extraction error on wave velocity measurement error according to an embodiment of the application;

[0042] Figure 5 FIG. 5 is a diagram of overpressure measurement error after wave velocity correction and high-order quantity correction according to an embodiment of the application. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical scheme and advantages of the application clearer, the application will be further described in detail below with reference to the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the application and do not constitute a limitation on the application.

[0044] It should be noted that the embodiments in the application and the features in the embodiments can be combined with each other without conflict.

[0045] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present application. In addition, the terms "first", "second" and the like are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined with "first", "second" and the like can explicitly or implicitly include one or more features. In the description of the present application, unless otherwise stated, the meaning of "a plurality of" is two or more.

[0046] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connecting" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium, or it can be connected inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood through specific circumstances.

[0047] The present application will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0048] As Figures 1-2 shown, the present application provides a shock wave overpressure measurement precision evaluation method based on a high-speed camera system, which specifically comprises the following steps: S1: constructing a shock wave velocity measurement error model based on the optical parameters of the high-speed camera system; S2: calculating a zero-order overpressure measurement error value based on the shock wave velocity measurement error model; S3: calculating a physical space wave velocity and an undisturbed air sound velocity based on the explosion image sequence collected by the high-speed camera system; S4: calculating a velocity correction factor based on the physical space wave velocity and the undisturbed air sound velocity, if the ratio of the physical space wave velocity to the undisturbed air sound velocity is less than a threshold value, then the zero-order overpressure measurement error value is taken as the overpressure measurement error, otherwise the zero-order overpressure measurement error value is corrected by using the velocity correction factor, and the corrected overpressure measurement error value is taken as the overpressure measurement precision.

[0049] It should be noted that this invention provides a non-contact method for evaluating the accuracy of shock wave overpressure measurement. This method is used to quantitatively analyze the influence of various parameters in a high-speed camera system on the overpressure measurement error, accurately calculate the wave velocity in optical measurement, and complete a high-order correction of the overpressure error. Specifically, based on the physical laws of shock wave propagation, the optical parameters and image processing parameters of the high-speed camera system are introduced into the construction of the shock wave velocity measurement error model. Each error component is derived, and the wave velocity is given by combining a wavefront extraction algorithm. A high-order correction is then performed on the overpressure error to quantitatively calculate the wave velocity measurement error and overpressure measurement error in optical measurement. This effectively solves the problem of large overpressure measurement errors due to wave velocity dependence, providing a valid basis for subsequent optimization of optical measurement methods and three-dimensional measurement of shock wave fields.

[0050] Furthermore, shock wavefront extraction algorithms are a key technology based on computer vision and image processing techniques used to identify and analyze the position of shock wavefronts generated in explosion experiments. Existing techniques typically employ edge detection algorithms (such as Canny, Sobel, or Laplacian operators) combined with thresholding and morphological processing to efficiently extract the contour and position information of the wavefront. Some advanced methods also incorporate machine learning or deep learning models (such as CNN or U-Net) to improve recognition accuracy and robustness in complex backgrounds or noisy environments. In addition, optical flow methods and spatiotemporal domain analysis are also used for tracking and reconstructing dynamic shock waves, enabling real-time monitoring of the wavefront evolution process.

[0051] First, a shock wave velocity measurement error model is established based on the physical laws of shock wave propagation. Each independent error component of the wave velocity measurement is expressed as a function of the optical system parameters and the image processing parameters. Then, the error components are synthesized using the root mean square method to obtain the wave velocity measurement error.

[0052] Next, the overpressure measurement error is solved according to the error propagation law, and it is expressed as a function of the wave velocity measurement error and the wave velocity. Then, the overpressure measurement error is expanded into the overpressure error without wave velocity (zero-order quantity, i.e., the zero-order overpressure measurement error value) and the higher-order quantity of the overpressure error that depends on the wave velocity, and the solutions are performed separately. The overpressure error (zero-order quantity, the zero-order overpressure measurement error value) is calculated from the wave velocity measurement error, and the higher-order quantity of the overpressure error is calculated from the wave velocity given by image processing.

[0053] A high-speed camera system (frame rate ≥ 2000) is used to acquire a sequence of explosion images of the explosion process or to directly import a given sequence of explosion images. The wavefront contour of each frame of the explosion image is extracted using image processing algorithms. The image wave velocity is calculated based on the number of pixels that the wavefront contour moves and the number of frame intervals. The wave velocity is then converted into physical space wave velocity using a scale bar.

[0054] After obtaining the physical space wave velocity, if the physical space wave velocity is much greater than the speed of sound of undisturbed air, then the influence of the physical space wave velocity on the overpressure error is considered negligible, and the overpressure error (zero-order quantity, i.e., zero-order overpressure measurement error value) is directly output, which is the overpressure measurement accuracy. If the difference between the physical space wave velocity and the speed of sound of undisturbed air is not large enough, then the higher-order correction amount of the overpressure measurement error or the speed correction factor is calculated based on the physical space wave velocity and added to the overpressure error (zero-order quantity, i.e., zero-order overpressure measurement error value), thereby obtaining the overpressure measurement accuracy.

[0055] The method for calculating higher-order corrections to overpressure measurement errors is as follows:

[0056] When the actual measurement point is extremely close to the explosion center, the shock wave speed will far exceed the speed of sound in air, that is... ,Will Considered to be a small amount (tending to 0), therefore, the overpressure measurement error is about... function Taking a Taylor expansion of the above equation near zero, we obtain the higher-order correction for the wave velocity to the overpressure measurement error, hence: ;

[0057] The principle behind constructing the shock wave velocity measurement error model is as follows:

[0058] The main sources of wave velocity measurement error include three aspects: wavefront profile extraction error, keyframe extraction error, and camera field curvature error.

[0059] 1) Calculate the error components for wavefront profile extraction

[0060] As shown in Figures 3(a)-3(d), assume that the shock wave front generated by the explosion at the impact point propagates freely along the hemispherical surface in space. Based on the image extraction principle of the wave front, the shock wave velocity is determined by the change in pixels of the wave front in the horizontal direction during the corresponding time interval between two frames. Therefore, the shock wave velocity can be expressed as:

[0061] (1);

[0062] In the formula, The frame rate for high-speed camera systems (such as high-speed cameras). The horizontal range of the field of view covered by the high-speed camera system. This represents the pixel variation of the wavefront in the horizontal direction. Sets the interval frame count.

[0063] When the time interval between two explosion images is sufficiently small and the change in horizontal pixels is not zero, the calculated wavefront velocity is the instantaneous velocity that can be resolved in time in the image. Therefore, the measured instantaneous velocity of the shock wave is defined as:

[0064] (2);

[0065] Assuming the theoretical value of the shock wave velocity (i.e. the physical space wave velocity) is , the explosion center (i.e. the drop center) is in the image center, and the displacement of the shock wave front in the horizontal direction is , the finite extremely short time experienced is . In this time period, the frame number between two frames is: . Assuming that the wave front extraction error of each frame of explosion image is within pixels (a total of pixels), the measurement result of the shock wave velocity will be affected by the wave front pixel extraction error:

[0066] (3);

[0067] After sorting, we get:

[0068] (4);

[0069] In the formula, is the horizontal resolution of the high-speed camera system; is the pixel number set value of the wave front extraction error (a total of pixels for two frames of explosion images); the distance from the explosion center to the edge of the field of view is not greater than the physical distance corresponding to half of the image horizontal resolution, and in the calculation, . Among them, the field of view covers the horizontal range According to the geometric relationship of the field of view angle, the focal length of the optical system , the pixel size of the high-speed camera system , and the horizontal distance between the high-speed camera system and the explosion center are calculated to obtain:

[0070] (5);

[0071] 2) Calculate the key frame extraction error component

[0072] The key frames of the shock wave velocity measurement are the initial frame of the explosion and the frame in which the wave front propagates to the leftmost (or rightmost) end of the image, so the shock wave velocity will introduce errors due to key frame extraction:

[0073] (6);

[0074] After sorting, we get:

[0075] (7);

[0076] In the formula, is the theoretical value of the shock wave velocity; is the displacement of the shock wave front in the horizontal direction; is the frame frequency of the high-speed camera system; is the true value of the selected two-frame interval frame number; is the deviation frame number of key frame extraction, which may be ahead of or lag behind the key frame, so is the positive deviation ( ) or negative deviation ( , ). Thus, the key frame error component of the shock wave speed measurement also has positive deviation or negative deviation, that is:

[0077] (8);

[0078] Therefore, the total key frame error component of the shock wave speed measurement is represented by the average value of the positive and negative deviations:

[0079] (9);

[0080] The function in the above formula monotonically increases with when is greater than or equal to 0, so the maximum value of the function in the above formula is taken at the maximum initial speed of the shock wave, i.e. the initial speed of the explosion center. The initial overpressure of the shock wave produced by TNT explosion is about 60 MPa, and thus the corresponding initial speed of the explosion center is .

[0081] 3) Calculate the camera field curvature error component

[0082] Since the field angle of the shock wave speed measurement is very small, the plane approximation is used in the previous consideration of the correspondence between the field object surface and the actual scene. The actual captured image corresponds to a surface with very small curvature. Assuming that within a very short time, the speeds calculated according to the plane (approximation) and the curved surface (reality) are respectively:

[0083] (10);

[0084] (11);

[0085] where and are the measured and true values of the speed, is the displacement of the shock wave front in the horizontal direction, is the stand-off distance, is the change angle corresponding to the position of the curved surface wave front within the time.

[0086] According to the geometric relationship, we have:

[0087] (12);

[0088] Thus, the error component introduced by the curvature of the wave front in the shock wave velocity measurement can be expressed as:

[0089] (13);

[0090] It is known that the variation angle of the wave front in the entire field of view in the shock wave velocity measurement is not greater than half of the field of view angle. In the formula, According to the geometric relationship of the field of view angle, the focal length of the lens , the pixel size of the high-speed camera system , the layout distance , the following is calculated:

[0091] (14);

[0092] 4) The comprehensive accuracy of the shock wave velocity measurement The wave front profile extraction error component , the key frame error component and the camera field of view curvature error component are synthesized according to the square root, that is:

[0093] (15);

[0094] The conversion method of the shock wave overpressure measurement error and the wave velocity measurement error, and the specific principle is:

[0095] The pressure relationship of the shock wave in the free field propagation is as follows:

[0096] (16);

[0097] In the formula, and are the wave front pressure and the undisturbed air pressure, respectively, and is the overpressure ; is the isentropic index of the undisturbed air, which is 1.4; is the density of the undisturbed air; is the wave front wave velocity; is the sound velocity of the undisturbed air, which satisfies . Further, the overpressure is expressed as a function of the wave velocity, and has:

[0098] (17);

[0099] According to the error propagation law, the overpressure measurement error can be expressed as:

[0100] (18);

[0101] in, It is the measurement error of the wavefront velocity.

[0102] Therefore, the relative error in measuring overpressure is:

[0103] (19);

[0104] At a distance from the explosion center, the shock wave velocity decreases to the speed of sound in air, which may cause the denominator of the above equation to approach 0. To avoid this situation, the above equation can be mathematically reformulated.

[0105] When the actual measurement point is extremely close to the explosion center, the shock wave speed will far exceed the speed of sound in air, that is... ,Will Considered to be a small amount (tending to 0), therefore, the overpressure measurement error is about... function Taking a Taylor expansion of the above equation near zero, we obtain the higher-order correction for the wave velocity to the overpressure measurement error, hence:

[0106] (20);

[0107] In summary, the overpressure measurement error can be quantitatively characterized by twice the wave velocity measurement error. Furthermore, by calculating the physical space wave velocity based on wavefront image processing, and by adding a higher-order correction for the overpressure measurement error, or by directly substituting the physical space wave velocity into the relative error formula for overpressure measurement, a more accurate overpressure measurement error value can be calculated, which can then be compared and verified with the pressure sensor measurement results.

[0108] The specific implementation steps of the shock wave front identification and extraction method are as follows:

[0109] The wavefront propagates in free space as a spherical wave. Considering the non-ideal sphere shape of the explosive, the wavefront is usually approximated as an ellipsoid. Given the geometric symmetry and propagation characteristics of the ellipsoidal wavefront, its major axis must coincide with the normal to the wavefront at the endpoint of the major axis. In other words, the endpoint of the major axis is the point where the wavefront propagation speed is fastest in the entire time series image (explosion image sequence), corresponding to the location of the extreme value of the refractive index gradient change. Therefore, the position of the major axis can be determined by its endpoints. Similarly, by finding the point where the wavefront propagation speed is fastest in the direction perpendicular to the major axis, the vertical axis can be determined. The intersection of the major axis and the vertical axis is the location of the explosion center.

[0110] As shown in Figures 3(b) and 3(d), the high-speed camera system and the target are at a certain viewing angle, therefore the semi-ellipsoid is tilted at a certain angle in the field of view. The geometric features that need to be extracted from the image include: the center of the ellipsoid. (Image coordinates), horizontal major axis and its inclination angle Horizontal minor axis and its inclination angle Vertical axis and its inclination angle Then, two frames with a certain sequence interval are selected from the continuous frames to determine the geometric features and wave velocity. Taking a video of a car exploding statically, the explosion point is approximately on the horizontal plane, and the wavefront contour is extracted based on the image difference method.

[0111] The image processing procedure is as follows:

[0112] 1) Regarding the first Frame explosion image and the first The exploded frame image is differentially divided in grayscale, and then the difference image is median filtered using a 5-pixel convolution kernel to obtain the semi-ellipsoidal contour of the disturbed area.

[0113] 2) Locate the left endpoint of the semi-ellipsoid in the difference diagram. and right endpoint And find the center point ,in , Solving for the horizontal major axis, we get... Find the upper endpoint of the semi-ellipsoid based on the perpendicular bisectors of the left and right endpoints. and lower endpoint (The upper and lower endpoints can be obtained by rigorously solving the equation of the rotated ellipse and the point of tangency of the line parallel to the left and right endpoints using analytic geometry), thus obtaining the horizontal minor axis. and vertical axis ;

[0114] 3) No. Frame explosion image display and The wavefront extends outwards with the same number of pixels, while The change is not obvious; this is because light from different directions refracts differently. and The plane containing the direction is perpendicular to the shooting direction, therefore the wavefront propagation speed is the same in these two directions; similarly, for the ... Frame explosion image and the first The grayscale difference image of the exploded frame image is used to determine... Direction compared to the first Pixel increment of a frame-exploded image If the upper arc coincides with the wavefront, then the pixel change rate of the wavefront in each frame of the exploded image is... This allows us to determine the wavefront profile parameters for each frame of the explosion image. and , For the first the length of the horizontal long axis of the semi-ellipsoidal frame explosion image, the first the length of the horizontal long axis of the semi-ellipsoidal frame explosion image, the image space wave velocity of the wave front in the frame explosion image, the first the length of the vertical axis of the semi-ellipsoidal frame explosion image, the first the length of the vertical axis of the semi-ellipsoidal frame explosion image, the first the first the pixel increment of the wave front position between the frame explosion images, the pixel average change rate of the wave front in each frame explosion image.

[0115] 4) Establish a conversion scale (the real distance corresponding to one pixel in the figure) according to the size and distance of a certain marker in the field of view, that is, calculate the real-time position of the wave velocity and the wave front.

[0116] Example 1

[0117] First, the wave front profile extraction error component, the key frame extraction error component, and the camera field of view curvature error component are calculated respectively from the wave velocity measurement error model, and the calculation formula is:

[0118] (21);

[0119] Next, the wave velocity measurement error is obtained by combining each error component according to the square root:

[0120] (22);

[0121] The errors of image processing are mainly introduced by the wave front profile extraction pixel error and the key frame extraction error, and the influence of the errors on the wave velocity measurement error is analyzed. For example Figure 4 The error cloud data of the wave front profile extraction pixel error and the key frame extraction error show that the wave velocity measurement error increases with the increase of the wave front profile extraction pixel error and the key frame extraction error, and in particular, the key frame extraction error is the main contribution to the total error.

[0122] Further, the overpressure measurement error (zero-order quantity, i.e. zero-order overpressure measurement error value) is calculated from 2 times the wave velocity measurement error:

[0123] (23);

[0124] Based on the explosion image sequence, the wave front profile of each frame explosion image is extracted by using the wave front profile extraction algorithm, and the number of corresponding pixels is calculated according to the number of frame intervals corresponding to the number of pixels The image wave velocity is calculated, and then the scale is calculated The physical space wave velocity is converted, and the calculation formula is:

[0125] (24);

[0126] wherein, is the scale, reflecting the length of the physical space corresponding to each pixel in the image, calculated by , wherein is the horizontal resolution of the high-speed camera system, is the pixel size of the high-speed camera system, is the focal length of the lens.

[0127] At the same time, the undisturbed air pressure , the undisturbed air density , and the isentropic index of the undisturbed air are calculated to obtain the undisturbed air sound velocity:

[0128] (25);

[0129] Then, the ratio of the undisturbed air sound velocity to the physical space wave velocity is taken as a criterion. If , the high-order error is ignored, and the overpressure measurement error (zero-order quantity), i.e., the overpressure measurement precision, is directly output. Otherwise, the velocity correction factor is calculated:

[0130] (26);

[0131] The velocity correction factor is multiplied by the overpressure measurement error (zero-order quantity, i.e., the zero-order overpressure measurement error value), and the product is the output overpressure measurement precision, i.e.:

[0132] (27);

[0133] Taking the following measurement conditions as an example: the resolution of the high-speed camera system is 1280×1024, the pixel size is 14.6μm, the focal length is 140mm, the frame frequency is 10000Hz, the layout distance is 300m, the wavefront extraction pixel error is 5 pixels, the key frame extraction error is 4 frames, and the shock wave velocity is 1000m / s (i.e. ). The wave velocity measurement error is calculated to be 15.1%, the overpressure measurement error (zero-order quantity, i.e., the zero-order overpressure measurement error value) is 30.1%, and the overpressure measurement precision is 33.6%. For a larger wave velocity, the overpressure measurement error curve calculated is shown in Figure 5It is shown that when the shock wave velocity is larger, the influence of the shock wave velocity on the overpressure precision is smaller, and the initial velocity of the TNT explosive explosion is usually as high as 6000 m / s (i.e. Taking the overpressure measurement error (zero order quantity, i.e. the zero order overpressure measurement error value) as the overpressure measurement precision can meet the zero order approximation condition. The research based on the present application shows that increasing the frame frequency of the high-speed camera system and reducing the wave front extraction pixel error and the key frame extraction error are all beneficial to improving the overpressure measurement precision.

[0134] It should be understood that the various forms of flow shown above can be used to reorder, add or delete steps. For example, the steps described in the present application can be executed in parallel, sequentially or in a different order, as long as the desired results of the technical solutions of the present application can be achieved, which is not limited herein.

[0135] The above detailed description does not constitute a limitation on the protection scope of the present application. Those skilled in the art should understand that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for evaluating the accuracy of shock wave overpressure measurement based on a high-speed camera system, characterized in that: Specifically, the steps include the following: S1: Constructing a shock wave velocity measurement error model based on the optical parameters of a high-speed camera system; S2: Calculate the zero-order overpressure measurement error value based on the shock wave velocity measurement error model; S3: Calculate the physical space wave velocity and undisturbed air sound velocity based on the explosion image sequence acquired by the high-speed camera system; S4: Calculate the velocity correction factor based on the physical space wave velocity and the undisturbed air sound velocity. If the ratio of the physical space wave velocity to the undisturbed air sound velocity is less than the threshold, the zero-order overpressure measurement error value is taken as the overpressure measurement error. Otherwise, the velocity correction factor is used to correct the zero-order overpressure measurement error value, and the corrected overpressure measurement error value is taken as the overpressure measurement accuracy.

2. The method for evaluating the accuracy of shock wave overpressure measurement based on a high-speed camera system according to claim 1, characterized in that: In step S1, the shock wave velocity measurement error model is as follows: ； in, For the horizontal resolution of a high-speed camera system, This is the theoretical value of the shock wave velocity. Set the number of pixels for wavefront extraction error. For wavefront profile extraction error, The focal length of the lens. Set a value for the interval frame number. For the pixel size of a high-speed camera system, The horizontal distance between the high-speed camera system and the explosion center. For the frame rate of a high-speed camera system, This refers to the field-of-view curvature error of a high-speed camera system. This represents the keyframe extraction error.

3. The method for evaluating the accuracy of shock wave overpressure measurement based on a high-speed camera system according to claim 2, characterized in that: Step S2 specifically includes: S21: Calculation of wave velocity measurement error based on shock wave velocity measurement error model: ； in, This represents the true value of the shock wave velocity. This is due to wave velocity measurement error; S22: Calculation of zero-order overpressure measurement error value based on wave velocity measurement error: ； in, For shock wave overpressure, This refers to the measurement error of shock wave overpressure.

4. The method for evaluating the accuracy of shock wave overpressure measurement based on a high-speed camera system according to claim 1, characterized in that: In step S3, the formula used to calculate the physical space wave velocity is as follows: ； ； in, For scale, Number of frame intervals The corresponding number of pixels that the wavefront profile moves. For the horizontal resolution of a high-speed camera system, For the pixel size of a high-speed camera system, The focal length of the lens; The formula used to calculate the speed of sound in undisturbed air is: ； in, This represents the undisturbed air pressure. The density of undisturbed air. It is the isentropic index of undisturbed air.

5. The method for evaluating the accuracy of shock wave overpressure measurement based on a high-speed camera system according to claim 4, characterized in that: In step S4, the velocity correction factor is calculated based on the physical space wave velocity and the undisturbed air sound speed. The calculation formula used is: 。 6. The method for evaluating the accuracy of shock wave overpressure measurement based on a high-speed camera system according to claim 1, characterized in that: In step S4, the threshold is 0.

1.

7. The method for evaluating the accuracy of shock wave overpressure measurement based on a high-speed camera system according to claim 5, characterized in that: In step S4, the formula for calculating the overpressure measurement accuracy is: .

8. The method for evaluating the accuracy of shock wave overpressure measurement based on a high-speed camera system according to claim 1, characterized in that: The frame rate of the high-speed camera system is greater than or equal to 2000.

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