UnderwaterWaste Recognition and Localization Based on Improved YOLOv5

With the continuous development of the economy and society,plastic pollution in rivers,lakes,oceans,and other bodies of water is increasingly severe,posing a serious challenge to underwater ecosystems.Effective cleaning up of underwater litter by robots relies on accurately identifying and locating the plastic waste.However,it often causes significant challenges such as noise interference,low contrast,and blurred textures in underwater optical images.A weighted fusion-based algorithm for enhancing the quality of underwater images is proposed,which combines weighted logarithmic transformations,adaptive gamma correction,improved multi-scale Retinex(MSR)algorithm,and the contrast limited adaptive histogram equalization(CLAHE)algorithm.The proposed algorithm improves brightness,contrast,and color recovery and enhances detail features resulting in better overall image quality.A network framework is proposed in this article based on the YOLOv5 model.MobileViT is used as the backbone of the network framework,detection layer is added to improve the detection capability for small targets,self-attention and mixed-attention modules are introduced to enhance the recognition capability of important features.The cross stage partial(CSP)structure is employed in the spatial pyramid pooling(SPP)section to enrich feature information,and the complete intersection over union(CIOU)loss is replaced with the focal efficient intersection over union(EIOU)loss to accelerate convergence while improving regression accuracy.Experimental results proved that the target recognition algorithm achieved a recognition accuracy of 0.913 and ensured a recognition speed of 45.56 fps/s.Subsequently,Using red,green,blue and depth(RGB-D)camera to construct a system for identifying and locating underwater plastic waste.Experiments were conducted underwater for recognition,localization,and error analysis.The experimental results demonstrate the effectiveness of the proposed method for identifying and locating underwater plastic waste,and it has good localization accuracy.

The Calibration of High-Speed Camera Imaging System for ELMs Observation on EAST Tokamak

A tangential fast visible camera has been set up in EAST tokamak for the study of edge MHD instabilities such as ELM. To determine the 3-D information from CCD images, Tsai＇s two-stage technique was utilized to calibrate the high-speed camera imaging system for ELM study. By applying tiles of the passive stabilizers in the tokamak device as the calibration pattern, transformation parameters for transforming from a 3-D world coordinate system to a 2-D image coordinate system were obtained, including the rotation matrix, the translation vector, the focal length and the lens distortion. The calibration errors were estimated and the results indicate the reliability of the method used for the camera imaging system. Through the calibration, some information about ELM filaments, such as positions and velocities were obtained from images of H-mode CCD videos.

An enhanced underwater camera apparatus for seabed observation of megabenthic epifauna in the northern Yellow Sea

Seabed photographing has been applied with various underwater camera apparatuses(UCAs)for observations of megabenthic epifauna,which reveals more details than traditional sampling tools do.In this study,we improved a UCA named a towed underwater video-camera system(TUV system)with image processing software for seabed photographing in coastal areas up to 100 m.In May 2017,the TUV system was tested at 4 stations in the Zhangzi Island marine area in the northern Yellow Sea to investigate local megabenthic epifauna,especially brittle stars.At each station,more than 500 good seabed photographs each in area of 0.1550 m2 were obtained in just 10 min.Almost all of the epifauna larger than 1 mm could be identified from the photographs,including echinoderms,bivalves,cnidarians,and crustaceans.Three dominant brittle stars(Ophiopholis mirabilis,Ophiura sarsii vadicola,and Stegophiura sladeni)were spotted,and their abundance,disc diameter,cluster size,and coverage area were calculated and analyzed from the seabed photographs.The results show that the TUV system could be applied in coastal waters of hard sandy bottoms and could be used for quantitative investigations of megabenthic epifauna.

UNDERWATER ACOUSTICS AND CAVITATING FLOW OF WATER ENTRY

The fluid mechanics of water entry is studied through investigating the underwater acoustics and the supercavitation.Underwater acoustic signals in water entry are extensively measured at about 30 different positions by using a PVDF needle hydrophone.From the measurements we obtain (1)the primary shock wave caused by the impact of the blunt body on free surface;(2)the vapor pressure inside the cavity;(3)the secondary shock wave caused by pulling away of the cavity from free surface;and so on.The supercavitation induced by the blunt body is observed by using a digital high-speed video camera as well as the single shot photography.The periodic and 3 dimensional motion of the supercavitation is revealed.The experiment is carried out at room temperature.

Shipborne Underwater Acoustic Communication System and Sea Trials with Submersible Shenhai Yongshi

The Shipborne acoustic communication system of the submersible Shenhai Yongshi works in vertical, horizontal and slant channels according to the relative positions. For ease of use, an array combined by a vertical-cone directional transducer and a horizontal-toroid one is installed on the mothership. Improved techniques are proposed to combat adverse channel conditions, such as frequency selectivity, non-stationary ship noise, and Doppler effects of the platform’s nonlinear movement. For coherent modulation, a turbo-coded single-carrier scheme is used. In the receiver, the sparse decision-directed Normalized Least-Mean-Square soft equalizer automatically adjusts the tap pattern and weights according to the multipath structure, the two receivers’ asymmetry, the signal’s frequency selectivity and the noise’s spectrum fluctuation. The use of turbo code in turbo equalization significantly suppresses the error floor and decreases the equalizer’s iteration times, which is verified by both the extrinsic information transfer charts and bit-error-rate performance. For noncoherent modulation, a concatenated error correction scheme of nonbinary convolutional code and Hadamard code is adopted to utilize full frequency diversity. Robust and lowcomplexity synchronization techniques in the time and Doppler domains are proposed. Sea trials with the submersible to a maximum depth of over 4500 m show that the shipborne communication system performs robustly during the adverse conditions. From the ten-thousand communication records in the 28 dives in 2017, the failure rate of the coherent frames and that of the noncoherent packets are both below 10%, where both synchronization errors and decoding errors are taken into account.

Electric characteristic and cavitation bubble dynamics using underwater pulsed discharge

Underwater pulsed discharge is widely applied in medicine, machining, and material modification.The induced cavitation bubble and subsequent cavitation collapse are considered the major motivations behind these applications. This paper presents an underwater pulsed discharge system.The experimental setup is established to induce and investigate the cavitation bubble assisted with a high-speed camera. Three aspects, including the characteristic of the discharge with different applied voltages and conductivities, the evolution of the cavitation bubble profile, and the energy efficiency of cavitation bubble inducing, are investigated, respectively. Especially, the mechanism of pre-discharge time delay in the low field intensity case is explained using the Joule heat effect.The results show the validity of the underwater pulsed discharger and experimental setup. The present underwater pulsed discharger is proved to be a simple, portable, and easy-to-implement device for the investigation of cavitation bubble dynamics.

Underwater Image Enhancement Based on the Dark Channel Prior and Attenuation Compensation

Aimed at the two problems of underwater imaging, fog effect and color cast, an Improved Segmentation Dark Channel Prior(ISDCP) defogging method is proposed to solve the fog effects caused by physical properties of water. Due to mass refraction of light in the process of underwater imaging, fog effects would lead to image blurring. And color cast is closely related to different degree of attenuation while light with different wavelengths is traveling in water. The proposed method here integrates the ISDCP and quantitative histogram stretching techniques into the image enhancement procedure. Firstly, the threshold value is set during the refinement process of the transmission maps to identify the original mismatching, and to conduct the differentiated defogging process further. Secondly, a method of judging the propagating distance of light is adopted to get the attenuation degree of energy during the propagation underwater. Finally, the image histogram is stretched quantitatively in Red-Green-Blue channel respectively according to the degree of attenuation in each color channel. The proposed method ISDCP can reduce the computational complexity and improve the efficiency in terms of defogging effect to meet the real-time requirements. Qualitative and quantitative comparison for several different underwater scenes reveals that the proposed method can significantly improve the visibility compared with previous methods.

Visualization of High-Speed Impact of Projectile in Granular Sheet with Destructive Collision of Particles

The impact and penetration of a projectile in a particle-laden space, which are expected to have frequently occurred during the formation of the solar system and will occur in the case of an impact probe for future planetary exploration, were experimentally simulated by using the ballistic range. A two-dimensional sheet made from small glass beads or emery powder was formed by the free-falling device through a long slit in the test chamber evacuated down to about 35 Pa. A polycarbonate projectile of a hemi-sphere-cylinder or sphere shape with the mass and diameter about 4 g and 25 mm, respectively, was launched at the velocity up to 430 m/s, and the phenomena were observed by the high-speed camera at 20,000 fps. From a series of images, the bow-shock-wave-like laterally facing U-shaped pattern over the projectile and the absence of particles in the trail behind it were clearly seen. At the impact of the particles on the projectile surface, fine grains were formed due to the destructive collision and injected outward from the projectile. The images obtained by different lighting methods including the laser light sheet were compared. The effects of the particle diameter, its material and the impact velocity were also investigated.

Visualization of High-Speed Impact of Penetrator into Icy Target

For application to exploration under the surface of icy objects in the solar system, the penetration of an impact probe into an icy target was experimentally simulated by using the ballistic range. Slender projectiles with a cylindrical body and various nose shapes were tested at the impact velocity 130 - 420 m/s. The motion of the penetrator, fragmentation of ice and crater forming were observed by the high-speed camera. It revealed that the crown-shaped ejection was made for a short time after the impact and then the outward normal jet-like stream of ice pieces continued for much longer time. The concave shape of the crater was successfully visualized by pouring the plaster into it. The two-stage structure, the pit and the spall, was clearly confirmed. The rim was not formed around the crater. Observation of the crater surface and the ice around the trace of the penetrator shows that both crushing into smaller ice pieces and recompression into ice blocks are caused by the forward motion of the penetrator. In case of a body with a flow-through duct, ice pieces entering the inlet at the nose tip were ejected from the tail, resulting in relaxation of the impact force. The correlation of the penetration distance and the crater diameter with the impact velocity was investigated.

基于线激光三维视觉的燃料组件水下在位变形测量方法

为了解决燃料组件弯曲与扭曲变形水下在位测量难题,提出了基于线激光三维视觉的燃料组件水下在位变形测量方法。通过基于单层折射的水下相机标定、基于平面约束的光平面标定算法研究解决单个测量单元的标定问题;研究基于三维标定工装的10组测量单元在位快速标定方法,解决测量系统全局坐标统一问题,并利用激光跟踪仪测量标定工装的弯扭精度,进行测量精度对比试验验证。研究表明,研制的基于线激光三维视觉的燃料组件水下在位变形测量系统扭曲测量误差限为0.15°,弯曲测量误差限为0.3 mm,且整个测量时间约在1 s,测量效率和测量误差限优于现有的测量系统。

水下天空偏振光视频采集实验装置设计与应用

水下天空偏振信息的获取是水下潜航器实现偏振光导航的重要基础,为此搭建一种水下偏振相机采集天空偏振分布的实验装置,用于采集天空光经过水面折射后的水下偏振分布。实验装置分为防水外壳和偏振光传感器两部分。防水外壳的设计主要从材质、质量和密闭性考虑,偏振光传感器的核心是通过程序实现工控机控制偏振相机拍摄0°、45°、90°、135°的偏振图像和斯托克斯的4个矢量图像。结合计算机技术,利用相关算法计算偏振角、偏振度和偏振方位角。结果表明,偏振度和偏振角在太阳子午线上呈对称分布,太阳附近的偏振度最小,并以环状向外增大。该装置采集的数据能够有效提取太阳的方位信息。

顶进节段法最终接头测控技术研究与应用

大连湾海底隧道采用顶进节段法最终接头,顶进节段无安装测量塔条件,且全程为水下施工,传统定位设备难以使用,给最终接头顶推水下定位提出了新的技术难题,为此研究以拉线位移计、摄像位移计、磁致位移传感器三者组合而成的最终接头水下定位系统,实现最终接头顶推施工全程高精度定位。

Signal waveform design to detect an underwater high-speed small target

The problem of sonar signal waveform design to detect a high-speed small target in an underwater environment is discussed. From theoretical analysis, time-frequency hop signal is regarded as the most suitable signal waveform in this application. To get precise target parameter estimation ability, the signal should have high range-Doppler resolution performance. The results of signal analysis show that hop signal with frequency serial coding as Costas array has sharp ambiguity characteristic, so it can be used in an active sonar system to detect a high speed small target. A scheme of frequency coding is also presented.

海底冷泉渗漏油气泡原位定量测定--以墨西哥湾GC600为例

海洋环境中冷泉渗漏是甲烷等有机化合物和其他温室气体进入海洋和大气的重要来源。准确定量确定冷泉渗漏的甲烷气泡通量对于评估它们对全球甲烷预算和气候变化有着重要的研究意义。采用高分辨率视频成像系统原位观察了墨西哥湾GC600冷泉渗漏区Mega Plume 2喷口,并获得了油气泡连续释放的视频片段。通过采用半自动气泡计数算法估算了Mega Plume 2喷口释放的油气泡个数及其释放速率。而通过图像处理技术确定了Mega Plume 2释放的油气泡的大小和尺寸分布。Mega Plume 2混合喷口释放的油气泡平均直径2.56mm±1.01mm,油气泡释放速率为80.25个·秒^(-1)。Mega Plume 2喷口年释放通量为177.7m^(3)·a^(-1)(19.55~106.62t·a^(-1))。然而,Mega Plume 2喷口的气泡释放速率与潮汐无关,可能与其他因素如水合物,油气藏增压及沉积层差异加载有关。只有对冷泉渗漏系统开展长期的原位在线观察,我们才能准确获取冷泉渗漏系统活动特征及其释放通量。

Flow and penetration behavior of submerged side-blown gas

To assess the widely used submerged side-blowing in pyrometallurgy,a high-speed camera-digital image processing-statistical approach was used to systematically investigate the effects of the gas flow rate,nozzle diameter,and inclination angle on the space-time distribution and penetration behavior of submerged side-blown gas in an air-water system.The results show that the gas motion gradually changes from a bubbling regime to a steady jetting regime and the formation of a complete jet structure as the flow rate increases.When the flow rate is low,a bubble area is formed by large bubbles in the area above the nozzle.When the flow rate and the nozzle diameter are significant,a bubble area is formed by tiny bubbles in the area above the nozzle.The increased inclination angle requires a more significant flow rate to form a complete jet structure.In the sampling time,the dimensionless horizontal and vertical penetration depths are Gaussian distributed.Decreasing the nozzle diameter and increasing the flow rate or inclination angle will increase the distribution range and discreteness.New correlations for a penetration depth with an error of±20%were obtained through dimensional analysis.The dimensionless horizontal penetration depth of an argon-melt system in a 120 t converter calculated by the correlation proposed by the current study is close to the result calculated by a correlation in the literature and a numerical simulation result in the literature.

利用水下平行光管测量水下相机成像分辨率

水下光学成像是重要的水下探测方式。现有水下相机成像检测方法受到水体本身以及测量方法的影响,难以准确进行成像分辨率检测。提出了基于水下平行光管的水下相机成像分辨率检测技术,通过在水中产生平行光束,直接对水下相机成像分辨率进行检测。通过仿真得出:水下平行光管在水中可见光和空气中单波长的调制传递函数(Modulation Transfer Function, MTF)基本一致。利用这一结论,提出了水下平行光管空气中装调检测的方法。针对实验室所研制的一款水下相机开展实验测试,其在水中可见光与空气中635 m光源照明条件下的分辨率相同。实验结果表明,所提出的基于水下平行光管的水下相机成像分辨率检测方法可有效消除水体对分辨率测量的影响,实现水下相机成像分辨率的准确测量。

基于事件帧与RGB帧融合的水下透明生物检测实验方案设计

为了提高水下透明生物的检测精度,在图像预处理方面,提出用事件相机转化得到的事件帧与RGB帧进行图像的像素级融合,以便加强水下透明生物的边缘特征。在检测方面,提出用改进的YOLOX算法进行水下透明生物检测,改进内容包括:添加自适应空间特征融合模块进行加权融合,充分利用不同尺度之间的特征;使用Focal loss函数,缓解数据集中类别不均衡问题;使用α-iou函数进行更准确的边界框回归,提高定位的准确率。实验结果表明,与传统的YOLOX算法相比,该文提出的算法的mAP提高了2.58%,与Faster R-CNN、SSD等算法相比也有较大提升,证明了该文改进YOLOX算法的有效性与优越性。

Experimental study on failure evolution mechanism of clastic rock considering cementation and intermediate principal stress

The study of clastic rock failure evolution under true triaxial stress is an important research topic;however,it is rarely studied systematically due to the limitation of monitoring technology.In this study,true triaxial compression tests were conducted on clastic rock specimens to investigate the effect of cementation and intermediate principal stress(s2)on the failure mechanism.The complete stressestrain curves were obtained,while the acoustic emission(AE)was monitored to indirectly evaluate the evo-lution of tensile and shear cracks,and crack evolution under true triaxial compression was imaged in real time by a high-speed camera.The results showed that the deformation and failure characteristics of clastic rock were closely related to the cementation type and intermediate principal stress.On the basis of the distribution characteristics of the ratio of rise time to amplitude(RA)and the average frequency(AF)of AE signals,tensile cracks of the contact cementation specimen propagated preferentially.Meanwhile,the enhancement of specimen cementation promoted the evolution of shear cracks,and the increase inσ_(2)promoted the evolution of tensile cracks.Moreover,the mesoscale cracking mechanism of clastic rock caused by cementation andσ_(2)under true triaxial compression was analyzed.The failure patterns of clastic rock under true triaxial compression were divided into three modes:structure-induced,structure-stress-induced and stress-induced failures.This study confirms the feasibility of high-speed camera technology in true triaxial testing,and has important implications for elucidating the disaster mechanism of deep tunnels in weak rocks.

基于红通道先验的水下障碍物双目定位方法

基于双目视觉的自主水下航行器在水下巡航过程中,由于水体对光线的衰减效应和悬浮颗粒对光线的散射作用,双目摄像机获取的图像存在对比度低、颜色失真等问题,导致水下障碍物定位的精度较低。针对以上问题,文中采用红通道先验复原算法提高水下成像质量,根据双目相机标定参数获取障碍物的双目视差图,并提出了一种基于深度视差图融合的水下障碍物定位方法。该方法通过融合深度视差图与水下复原轮廓图,对融合图像进行凸多边形检测,获取障碍物的轮廓,基于轮廓信息进行障碍物的有效深度信息提取,实现障碍物的空间定位。水下双目定位实验结果表明,文中所提方法可以使双目立体匹配的效果更理想,能够有效提高水下障碍物定位的精度。

Determination of frequencies of oscillations of cloud cavitation on a 2-D hydrofoil from high-speed camera observations

A method is presented to determine significant frequencies of oscillations of cavitation structures from high-speed camera recordings of a flow around a 2-D hydrofoil. The top view of the suction side of an NACA 2412 hydrofoil is studied in a transparent test section of a cavitation tunnel for selected cloud cavitation regimes with strong oscillations induced by the leading-edge cavity shedding. The ability of the method to accurately determine the dominant oscillation frequencies is confirmed by pressure measure- ments. The method can resolve subtle flow characteristics that are not visible to the naked eye. The method can be used for non- invasive experimental studies of oscillations in cavitating flows with adequate visual access when pressure measurements are not available or when such measurements would disturb the flow.