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Determination of the shedding frequency of cavitation cloud in a submerged cavitation jet based on high-speed photography images

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Journal of Hydrodynamics 2021年第1期33卷 127-139页

作者： Chi Peng Shou-ceng Tian Gen-sheng Li State Key Laboratory of Petroleum Resources and Prospecting China University of Petroleum(Beijing)Beijing 102249China

To accurately determine the shedding frequency of the cavitation cloud in a submerged cavitation jet,the spectral analysis and the proper orthogonal decomposition(POD)for high-speed photography images are *** spectrums of 6 different kinds of image signals(the area-averaged gray level,the line-averaged gray level,the point gray level,the cavitation length,width,and area)are calculated and *** line-averaged gray level is found to be optimal in determining the shedding frequency but an accurate frequency can only be obtained in the stable-frequency zone where the cavitation cloud *** repeated experiments,the plateau-shape distribution of the main frequency is established with a deviation of 10.8%.A revised Reynolds number Re'is defined and the shedding frequency can be correlated to Re'by a power law when the cavitation number is less than *** relationship is validated by the experimental data in *** first mode of the POD characterizes the ensemble-average of the cavitation cloud while the second mode is the major part of the cavitation cloud transient *** modes 2-5 are organized in pairs,which confirms the periodic feature of the cavitation cloud in the submerged cavitation *** the nozzle exit,the modes 2-5 are symmetrically distributed in the jet shear *** shedding frequency of the cloud cavitation can also be precisely determined by performing the spectral analysis of the weighting coefficients of the mode *** paper shows that the two parameters,namely,the line-averaged gray level and the weighting coefficients of the mode 2,can be confidently used to calculate the shedding frequency of the cavitation cloud in a submerged cavitation jet.

关键词： Cavitation jet shedding frequency high-speed photography spectral analysis proper orthogonal decomposition(POD)

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Experimental determination of restitution coefficient of garlic bulb based on high-speed photography

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International Journal of Agricultural and Biological Engineering 2021年第2期14卷 81-90页

作者： Zhaoyang Yu Zhichao Hu Baoliang Peng Fengwei Gu Ling Yang Mingjin Yang College of Engineering and Technology Southwest UniversityChongqing 400715China Nanjing Institute of Agricultural Mechanization Ministry of Agriculture and Rural AffairsNanjing 210014China

Restitution coefficient(RC)of garlic bulb is an important mechanical property that is required to establish the kinematics model of bulb collision and research the damage mechanism of bulb *** this study,kinetic equations of bulb collision were established based on Hertz's contact *** kinematics characteristics,elastoplastic deformation and contact damage during bulb collision were analyzed by using high-speed *** effects of bulb mass,moisture content,collision material,material thickness and release height on the RC were investigated by mixed orthogonal experiments and single-factor *** results showed that the movement of bulb in the compression stage was translation,and the movement in the rebound stage was translation and *** collision,the larger the rotational angular velocity of the bulb was,the smaller the measured RC would *** contact damage of bulb included internal damage of the tissue,epidermis stretch and *** significance of effects of factors on RC decreased with the following sequence:collision material,release height,material thickness,bulb mass,and moisture *** material,release height,material thickness,and bulb mass were significant *** RC between the bulb and Q235,nylon,and rubber decreased *** RC decreased with the increase of release height and bulb *** RC increased with the increase of material thickness of Q235,while it decreased with the increase of material thickness of rubber or *** determination coefficients of the regression equations between the significant factors and the RC were all greater than *** results will be helpful for damage mechanism analysis and design of garlic production equipment.

关键词： garlic bulb collision restitution coefficient high-speed photography experimental tests

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Analysis of droplet transfer of pulsed MIG welding based on electrical signal and high-speed photography

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China Welding 2009年第1期18卷 67-72页

作者：姚屏薛家祥黄文超张瑞 School of Mechanical and Automotive Engineering South China University of Technology Guangzhou 510640 Guangdong Polytechnic Normal University Guangzhou 510635

In order to study how welding parameters affect welding quality and droplet transfer, a synchronous acquisition and analysis system is established to acquire and analyze electrical signal and instantaneous images of droplet transfer simultaneously, which is based on a self-developed soft-switching inverter. On the one hand, welding current and voltage signals are acquired and analyzed by a self-developed dynamic wavelet analyzer. On the other hand, images are filtered and optimized after they are captured by high-speed camera. The results show that instantaneous waveforms and statistical data of electrical signal contribute to make an overall assessment of welding quality, and that optimized high-speed images allow a visual and clear observation of droplet transfer process. The analysis of both waveforms and images leads to a further research on droplet transfer mechanism and provides a basis for precise control of droplet transfer.

关键词： pulsed MIG welding droplet transfer high-speed photography image processing wavelet analysis

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Measurement and analysis of restitution coefficient between maize seed and soil based on high-speed photography

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International Journal of Agricultural and Biological Engineering 2017年第3期10卷 102-114页

作者： Wang Jinwu Tang Han Wang Jinfeng Jiang Dongxuan Li Xin College of Engineering Northeast Agricultural UniversityHarbin 150030China

The restitution coefficient is an important elementary physical parameter related to the research and development of agricultural *** kinematic model of maize seed in the falling and impacting processes was developed to measure the restitution coefficient between maize seed and soil.A test bench for measuring the restitution coefficient was designed and built referred to the theory of mirror *** velocities for impacting maize seed were measured and analyzed in a three-dimensional space via high-speed photography,and then restitution coefficients of in different impact conditions were *** this basis,this study took flat dent seed and round seed as *** factor tests were conducted to analyze the influences of these factors on the restitution *** impact angle,falling height,soil compaction,soil moisture,maize moisture content and different parts of seed were selected as test *** corresponding regression equations were obtained by *** results showed that,as the impact angle was bigger than 25°,the restitution coefficient increased with the increase of impact *** restitution coefficient had a linear decreasing trend with the increase of falling *** the soil compaction strength was 200-350 kPa,the restitution coefficient increased with the increase of soil *** the soil compaction strength was larger than 350 kPa,the changing trend of the restitution coefficient was relatively *** the soil moisture content was 13.5%-18%,the restitution coefficient decreased with the increase of soil *** the soil moisture content was 18%,the restitution coefficient was the *** the maize moisture content was 11%-16%,the restitution coefficient decreased with the increase of maize moisture *** rotational motion always occurred in falling process of flat dent seed and round *** probabilities of crown part and lateral part of maize seed impacting with soil were the highest

关键词： maize seed soil restitution coefficient mirror reflection high-speed photography measurement

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Research on cutting characteristics of fiber bundle with high-speed photography

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International Journal of Agricultural and Biological Engineering 2020年第3期13卷 94-99页

作者： Zhitao He Huiling Ding Sanming Du Zhen Li Jiangtao Ji Jian Li Yongzhen Zhang Wuhan Research Institute of Materials Protection China Academy of Machinery Science and TechnologyWuhan 430030China College of Agricultural Equipment Engineering Henan University of Science and TechnologyLuoyang 471023China National United Engineering Laboratory for Advanced Bearing Tribology Henan University of Science and TechnologyLuoyang 471023China

Cutting is an essential and complicated process in many *** and low-consumption cutting operations are of great significance for environmental protection and energy *** development of high performance cutting parts relies on a deep understanding of the cutting process and cutting *** this research,a new type of cutting test bench with high-speed photography was developed,and the cutting tests were conducted on the jute fiber bundle from quasi-static cutting at 10 mm/s to dynamic cutting in the speed range of 0.6-2.4 m/*** cutting process was captured by a high-speed *** shows that compression exists before quasi-static cutting,and the compression force curve with respect to the compression ratio follows an exponential *** cutting speed has a significant effect on cutting *** cutting energy consumption is not a monotonous function of cutting speed owing to the combined effect of elastic deformation and friction of *** cutting energy increases with increasing cutting speed in the range of 0.6-1.2 m/s due to the increase of the friction within fibers and the friction between the blade and *** cutting energy decreases with increasing cutting speed in the range of 1.2-1.8 m/s,and tends to be a fixed value when the cutting speed exceeds 1.8 m/s due to the stabilized elastic deformation and friction *** the perspective of energy saving,it is meaningless to increase the blade speed excessively when cutting fiber bundles.

关键词： jute fiber cutting high-speed photography energy consumption friction

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Impact Experimental Investigation of PVB Laminated Glass Based on high-speed photography: An Initial Attempt

Impact Experimental Investigation of PVB Laminated Glass Bas...

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第八届国际汽车交通安全学术会议

作者： Mengyi ZHU1 Bohan LIU1 Yueting SUN1 Jun XU1 Yibing LI1 (1State Key Laboratory of Automotive Safety & Energy Department of Automotive Engineering Tsinghua University Beijing 10084)

In this paper,a high-speed photography method combined with drop-weight test is used to study the dynamic cracking behavior of PVB （polyvinyl butyral） laminated glass subject to low-speed *** patterns,paths and velocities,derived from a series of dynamic photos,are thoroughly analyzed to explore the characteristics cracking *** addition,given the different the experimental conditions,*** crack velocities,cracking speed （including maximum speed and speed-time history curve） are examined and compared.

关键词： PVB laminated windshield high-speed photography crack.

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high-speed photographic observation of collapse of two cavitation bubbles

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Science China(Technological Sciences) 2016年第11期59卷 1707-1716页

作者： LUO Jing XU WeiLin LI Rui State Key Laboratory of Hydraulics Mountain River Engineering Sichuan University

Cavitation as a hydrodynamic phenomenon exists widely in water conservancy, shipbuilding, chemical and many other *** cavitation bubble dynamic studies mainly focused on single cavitation bubbles and their interaction with the wall. This paper studies the interaction between two cavitation bubbles under conditions with or without a wall. The results show that if the inception of two cavitation bubbles is not synchronized, the cavitation bubble of early inception collapse backwards the cavitation bubble of later inception; if the inception of two cavitation bubbles is synchronized, the two bubbles collapse towards each other; if a wall exists nearby, no matter whether the line connecting the centers of the two cavitation bubbles is vertical or parallel to the wall, the two cavitation bubbles collapse towards each other and then gradually merge, and the merged collapse body quickly moves to the wall. It is suggested that, as the number of cavitation bubbles increases, the cavitation erosion effect is not simply increased proportionally. Instead, mutual inhibitory effect may be demonstrated.

关键词： cavitation bubble high-speed photography shock wave micro-jet

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A high-speed PHOTOGRAPHIC STUDY OF ULTRASONIC CAVITATION NEAR RIGID BOUNDARY

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Journal of Hydrodynamics 2008年第5期20卷 637-644页

作者： BAI Li-xin XU Wei-lin TIAN Zhong LI Nai-wen State Key Laboratory of Hydraulics and Mountain River Engineering Sichuan University Chengdu 610065China.

This article investigated an existing steady pattern of collapse and rebound （disintegration and aggregation） of cavitation bubbles near rigid boundary in acoustic field. A deformation process of cavitation bubble was accomplished in two acoustic cycles, namely, a spherical bubble collapsed towards the boundary to its minimum volume and then rebounded and grew into a toroidal bubble （or two individual bubbles） in one acoustic cycle, and the toroidal bubble （or two individual bubbles） collapsed towards the center of ring to its minimum volume, and then rebounded into a spherical bubble in the next acoustic cycle. Inertia force plays a key role in the transition between these two states. The microjet produced during the collapse of spherical bubble and the shock wave produced during the collapse of toroidal bubble （or two individual bubbles） impacts the boundary alternately. A cavitation bubble operating in this pattena can thus be an effective corrosion mechanism of rigid boundary.

关键词： cavity ultrasonic cavitation high-speed photography visualization

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EXPERIMENTAL AND FEM STUDY OF WINDSHIELD SUBJECTED TO high speed BIRD IMPACT

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Acta Mechanica Sinica 2003年第6期19卷 543-550页

作者：杨嘉陵蔡序杰武存浩 Solid Mechanics Research Center Beijing University of Aeronautics and Astronautics Beijing 100083 China

Both experimental and finite element model (FEM) results are presented for the dynamic strength behavior of windshield subjected to bird impact. The experimental data taken from a series of high speed photographs are compared with the numerical results predicted by using FEM in which the windshield was modeled entirely with solid elements and the bird body was approximately simulated by an elastic-plastic material with failure element behavior. Effective plastic strain and element pressure were adopted as the failure criteria and once the pressure or the effective plastic strain of an element reached the critical value, the element would lose the tensile resistance capability completely. The deflection and stress distribution in the windshield were obtained. It is shown that the result from the finite element analysis agrees with those from the full-scale bird impact test.

关键词： windshield glass FEM high-speed photography bird impact

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Experimental study of the interaction between the spark-induced cavitation bubble and the air bubble

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Journal of Hydrodynamics 2013年第6期25卷 895-902页

作者：罗晶许唯临牛志攀罗书靖郑秋文 State Key Laboratory of Hydraulics and Mountain River Engineering Sichuan University China Three Gorges Corporation

Experiments are carried out by using high-speed photography to investigate the interaction between the spark-generated cavitation bubble and the air bubble in its surrounding fluid. Three problems are discussed in detail： the impact of the air bubble upon the development of the cavitation bubble, the evolution of the air bubble under the influence of the cavitation bubble, and the change of the fluid pressure during the development of a micro jet of the cavitation bubble. Based on the experimental results, under the condition of no air bubble present, the lifetime of the cavitation bubble from expansion to contraction increases with the increase of the maximum radius. On the other hand, when there is an air bubble present, different sized cavitation bubbles have similarity with one another generally in terms of the lifetime from expansion to contraction, which does not depend on the maximum radius. Also, with the presence of an air bubble, the lifetime of the smaller cavitation bubble is extended while that of the bigger ones reduced. Furthermore, it is shown in the experiment that the low pressure formed in the opposite direction to the cavitation bubble micro jet makes the air bubble in the low pressure area being stretched into a steplike shape.

关键词： cavitation bubble air bubble high-speed photography shock wave aeration in cavitation-protection

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