A Line Array Camera-based Measurement Method for Dynamic Parameters of Underwater Projectiles and Supercavitation Evolution Process

doi:10.12382/bgxb.2023.0408

Abstract

Abstract:

To address the challenging underwater conditions, poor lighting, and difficulties in capturing and reconstructing the high-speed motion and supercavitation evolution of projectiles, a line array camera-based underwater projectile image acquisition system is designed. The system utilizes the principle of intersection measurement and incorporates a dual line array camera for image acquisition. An algorithm is proposed for underwater high-speed supercavitating target recognition and projectile shape reconstruction. The formulas for calculating the coordinates, attitude angles, and velocity of projectilepassing though a target are derived by using the geometric relationship of supercavitating projectile and the camera calibration data. A water entry experiment of projectiles vertically launched from a 12.7mm smoothbore gun is conducted to validate and analyze the feasibility of the system. Experimental results demonstrate that the system can effectively and rapidly acquire the underwater projectile images, accurately separate and reconstruct the projectile shapes and cavity morphology, and calculate the underwater projectile's motion velocity, attitude angles, and supercavitation parameters. The velocity calculated by the system exhibits an error of less than 1% compared to the velocity obtained from concurrently deployed high-speed cameras, indicating the high reliability and practicality of the system.

Key words: underwater projectile, high-speed camera, line array camera, projectileshape reconstruction, supercavitation, image processing

CLC Number:

TP391.4

SUN Jiawei, WAN Gang, GU Jinliang, XU Mingjie, KONG Xiaofang. A Line Array Camera-based Measurement Method for Dynamic Parameters of Underwater Projectiles and Supercavitation Evolution Process[J]. Acta Armamentarii, 2024, 45(8): 2564-2572.

Figures/Tables 23

Fig.1 Underwater projectile image acquisition system

Fig.2 Orthogonal intersection measurement target surfaceof dual line array camera

Fig.3 Original image of projectile and supercavitation

Fig.4 Original image of projectile

Fig.5 Shape reconstruction algorithm of projectiles

Fig.6 Real images of projectile and supercavitation

Fig.7 Projectile shape reconstruction diagram

Fig.8 Principle diagram of coordinate calculation formula of projectile impact

Table 1 Camera parameters

参数	取值
最高数据传输速率/(Mbit·s^-1)	1000
最高行频/kHz	80
最短曝光时间/μs	5
图像传感器	CMOS
分辨率	4096

Table 2 Lens parameters

参数	取值
焦距/mm	20
镜头结构	11组14片
最大光圈	f/1.8
视角/(°)	94
接口	尼康z卡口
尺寸/mm	84.5×108.5

Fig.9 Line array cameras and lens

Fig.10 Test layout

Fig.11 Original images of projectile and supercavitation

Fig.12 Reconstructed images of projectile and supercavitation

Fig.13 Projectile image captured by the high-speed camera

Fig.14 Reconstructed images of projectile shape

Fig. 15 Schematic diagram of the sizes of supercavitation high-speed projectile model

Fig.16 Sizes of recovered projectile

Table 3 The results of speed data processing of two line array cameras

发射次数	左侧线阵相机测速/(m·s^-1)	正面线阵相机测速/(m·s^-1)
1	277.55	283.33
2	283.33	289.36
3	295.65	302.22
4	277.55	285.43

Table 4 Speed processing results of line array camera and high-speed camera

发射次数	弹重/ g	装药量/g	线阵相机测速/ (m·s^-1)	高速相机测速/ (m·s^-1)	误差
1	106.1	7.2	277.55	275.13	0.0088
2	104.6	7.2	283.33	285.63	0.0081
3	105.3	7.2	295.65	297.71	0.0069
4	104.1	6.5	277.55	277.01	0.0019

Table 5 Attitude angle data processing results

发射次数	俯仰角/(°)	偏航角/(°)
1	34.51
2	14.65
3	2.44
4	19.65	41.10
5	36.10	39.19
6	39.19	3.18
7	1.17	34.91

Table 6 Time for supercavitation crossinga target at different speeds

发射次数	射弹速度/(m·s^-1)	空泡过靶时间/ms
1	283.33	13.42
2	309.09	11.67
3	289.36	12.12
4	277.55	13.07
5	283.33	11.16
6	295.65	12.34
7	277.55	10.64

Fig.17 Variation of supercavitation diameter of projectile at different speeds

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