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EHLA 3D was developed to print nickel-based superalloy parts. The interaction of powder and laser and the behavior of the molten pool was captured by high-speed photography. The thermal cycle of the molten pool was obtained by the thermal imager, which reveals the principle of the EHLA 3D. The microstructure and mechanical properties of specimens made by LMD and EHLA 3D were compared and analyzed. The mechanism of crystal growth and precipitation formation of nickel-based superalloy is illustrated by a comparative analysis of dendrite growth and precipitation phase formation during LMD and EHLA 3D, respectively. The results show that the EHLA 3D molten pool has a higher solidification cooling rate than the LMD molten pool, which is beneficial to grain refinement, dendritic arm spacing reduction, and the coexistence of columnar and equiaxed dendrites. Moreover, the segregation of Nb and Mo can be effectively inhibited, and the formation of Laves phase can be effectively reduced. The ultimate tensile strength, yield strength, and hardness of the specimens prepared by EHLA 3D at 25 °C and 650 °C were higher than those of LMD, especially elongation was improved and the processing efficiency was increased by nearly 60%. [ABSTRACT FROM AUTHOR]

Percolation casting technology is used to produce alumina ceramic hollow spheres of different sizes that are neatly and tightly arranged according to certain rules. Then, aluminum metal melt infiltrates the gap of adjacent ceramic hollow spheres, forming a sphere-reinforced aluminum metal matrix syntactic foam (MMSF). To compare the mechanical properties between aluminum foam and MMSF, the same base material and pore size were used. Based on quasi-static testing, split Hopkinson pressure bar experiments were conducted on the MMSF and aluminum foam at different strain rates using pulse-shaping and high-speed photography techniques. The influence of alumina ceramic hollow spheres on the MMSF (including compressive strength, failure process, and energy absorption performance) was analyzed. Results indicate that the addition of alumina ceramic hollow spheres significantly enhances the compressive strength and energy absorption capacity of MMSFs. It also improves the strain rate sensitivity to some extent, rendering the composite formed by aluminum foam and ceramic hollow sphere to be strain rate-sensitive. Furthermore, the energy utilization efficiency and absorbed energy per unit volume of the MMSF were higher than those of the aluminum foam. The MMSF exhibited better strain rate sensitivity in terms of impact resistance than the aluminum foam; the higher the strain rate, the higher the absorbed impact energy. The MMSF has significant application prospects to aerospace engineering and explosion protection in the military. [ABSTRACT FROM AUTHOR]

The interaction of bubbles with phase interfaces is an important phenomenon in science and industry. In this paper, the variation in bubble behavior and the characteristics of surface liquid film formation and shedding at the oil–water interface are investigated using bubble visualization high-speed photography and numerical simulation. The results show that the bubble rise trajectories can be divided into three different sets when the bubbles rise in a system composed of two mutually incompatible liquids, and the bubble shapes are more stable in white oil compared to water. During the passage of the bubble across the oil–water interface, the water phase is entrained to form a liquid film covering the bubble. We found that the change in the bubble liquid film and the collapse process of the water column are closely related to the bubble size. The trends of Eotvos (Eo) numbers for bubbles of different diameters in the oil–water coexistence system are approximately the same, with the Eo numbers of larger bubbles being much larger than those corresponding to smaller bubbles, from the beginning to the end. After crossing the oil–water interface, the Eo number of larger-diameter bubbles keeps fluctuating over a long distance before finally stabilizing. The Eo number of small-diameter bubbles remains essentially stable after crossing the oil–water interface. [ABSTRACT FROM AUTHOR]

The waterjet propulsor is a new type of marine propulsion system, which offers the advantages of high speed, good maneuverability, and low vibration and noise. As the core component of the waterjet propulsor, the primary role of the waterjet pump is to provide sufficient thrust for the vessel. However, the waterjet pump is prone to be troubled by the hump phenomenon. As the pump operates in the hump region, it may encounter issues such as flow interference and exacerbated vibration and noise, which are closely related to cavitation phenomenon in the pump. To analyze the evolution of cavitation flow structure in the waterjet pump when operating in the hump region, this study utilized highspeed photography to obtain the cavitation flow structure at different cavitation development stages under the hump peak condition. The cavitation stages involved include the cavitation inception stage, cavitation development transition stage, first critical cavitation stage, critical cavitation stage, and breakdown cavitation stage. During different cavitation development stages under the hump peak condition, the blade tip region exhibits distinct cloud cavitation induced by the tip leakage vortex (TLV). As the NPSH decreases, the frequency of cloud cavitation shedding increases, the scale of the cavitation cloud at the leading edge of the blade decreases, and the scale of the cavitation cloud accumulated at the rear of the flow passage increases. This study on the cavitation flow of the waterjet pump is significant as it contributes to enhancing the anti-cavitation performance and reducing vibration and noise. It provides scientific guidance and engineering practice for improving the safety and stability of waterjet pumps during operation. [ABSTRACT FROM AUTHOR]

The pump hump significantly influences the vibration and operational stability of pumps. During the development of the mixed-flow waterjet pump, our team found that the pump performance curve had a hump phenomenon and the platform had vibration, so it was suspected that there was a strong secondary flow in the hump region. The calculation model is the SST k-ω turbulence model. The impeller and diffuser use structured grids. By using high-speed photography technology, we map the cavitation flow structures, thereby demonstrating the evolution of cavitation processes. The hump curve was obtained by an experimental test. By comparing the test data and numerical simulation, the consistency of the method and the hump curve is verified. A comparative analysis is performed to investigate the variations in the distribution of internal vortex structures and the evolution of rotating stalls in the impeller. In the valley condition, the main frequency of pressure pulsation in the inlet section of the impeller is 0.75 times the shaft frequency, the main frequency in the middle and outlet sections of the impeller is 1 times the shaft frequency, and the main frequency in the diffuser basin is 1.5 times the shaft frequency, the main frequency in the peak condition at the points of Span = 0.1 and Span = 0.5 of the impeller is the diffuser frequency, the main frequency at the point of Span = 0.9 is the impeller blade frequency, and the main frequency in the diffuser basin is either the shaft frequency or the diffuser blade frequency. This research reveals the characteristics of vortex flow in the pump under hump conditions. It reveals that the evolution mechanism of the hump offers a guide value for the subsequent hydrodynamic design of the hump. [ABSTRACT FROM AUTHOR]

A bubble collapsing near an interface may result in the formation of a liquid jet protruding from the distal bubble side, through the bubble, towards the interface. Ultrasound assisted jetting has been observed when subjecting, by approximation, infinite fluids to acoustic amplitudes above the inertial cavitation threshold, limiting the possibility of ultrasoundguided, bubble-assisted drug or gene delivery. However, the vascular system can be regarded as a finite fluid. The purpose of this study was to investigate the feasibility of lowamplitude jetting for fluid containing biocompatible cavitation nuclei, by placing the region of interest in a confined space to ensure a standing wave field. Droplets of QuantisonTMultrasound contrast agent were pipetted into a Perspex cylindrical compartment of 8-mm diameter and 2-mm height, which was part of an imaging system. The contrast agent was subjected to 3-cycle ultrasound pulses with a centre frequency of 1MHz whilst being observed at a frame rate of ten million frames per second. Jetting was observed to occur with microbubbles nucleated from the contrast agent in an acoustic regime whose free-field mechanical index was 0.6. Empirical curve matching showed a pulse amplification by a factor of six owing to the chosen geometry. Visible jet lengths of twice the bubble radius on the verge of collapse were measured. Owing to the confined space, the local acoustic amplitude was amplified to surpass the cavitation threshold. This finding is of interest for medical ultrasonic applications where the local environment comprises reflectors. [ABSTRACT FROM AUTHOR]

In this paper, the characteristics of a pulsating bubble collapse near the nozzle of an underwater tube were investigated both experimentally and numerically. The experiments involved generating pulsating bubbles using the electric spark discharge technology and capturing their transient behavior by high-speed photography. A boundary integral method based on potential flow theory was used to simulate the coupling between the bubble and the tube in the numerical simulation. The results show that the collapsing bubble can produce a jet directed towards the tube, which poses a safety threat to the pipeline equipment. The numerical simulation results and experimental phenomena are in good agreement. In addition, a systematic study was conducted of two dimensionless parameters, i.e., the ratio of bubble distance from the tube nozzle and the tube nozzle radius γ and the ratio of the maximum radius of the bubble and the tube nozzle radius λ. The findings indicate that when γ≤1.5, bubbles will only produce jets pointing into the tube during the collapse phase, and when γ>1.5, the tendency for bubbles to produce jets pointing into the tube increases as λ increases. Moreover, the maximum velocity of the downward jet increases with the increase of λ, and increases and then decreases with the increase of γ. Additionally, the maximum velocity of the downward jet generally increases with the increase of λ and increases and then decreases with the increase of γ. This study provides valuable insights into the dynamic behavior of bubble collapse near the nozzle of a submerged tube, which can provide safety measures for pipeline equipment.

Laser-arc hybrid welding (LAHW) technology is a versatile and widely used method that has garnered significant attention, particularly in the thick plate welding required for shipbuilding. One of the most crucial parameters in LAHW is the laser-arc distance, which has a significant impact on the interaction between the laser and arc, especially in high-power laser and high-speed welding processes. As such, investigating the effects of laser-arc distance on the welding process is of great theoretical importance for both future research and industrial applications. This study utilizes high-speed photography to capture the welding process, focusing on how the laser-arc distance affects droplet transition and the stability of weld pool flow. Additionally, numerical simulations are used to explore the mechanisms underlying welding defect formation. The results indicate that an optimal laser-arc distance can produce a well-formed weld without significant defects. When the laser-arc distance (DLA) is too small, the coupling effect between the laser and arc becomes overly strong, causing unstable droplet transition and weld pool flow, which leads to defects such as spatter and undercutting. Conversely, when the laser-arc distance is too large, the coupling effect weakens, resulting in reduced weld reinforcement and the occurrence of porosity defects. The findings of this study offer valuable insights for optimizing welding parameters and improving weld quality in industrial applications of LAHW. [ABSTRACT FROM AUTHOR]

The acoustic Lichtenberg figure (ALF) in an ultrasonic cleaner with a frequency of 28 kHz at different power levels was observed using high-speed photography. The nonlinear response of the cavitation structure was analyzed by the entropy spectrum in the ALF images, which showed the modulation influence of the primary acoustic field, exhibiting the fluctuations of the bubble distribution with time. Typical Y-branches predict the paths by which surrounding bubbles are attracted and converge into the structure, the branches are curved due to bubble-bubble interactions, and the curvature increases as the bubbles are approaching the main chain. The average travelling speed of bubbles along the branches is about 1.1 m/s, almost independent of power level of the ultrasonic cleaner. A theoretical model consisting of free bubbles and a straight bubble chain of finite length was developed to explore the evolutionary mechanism of branching. It was found that the bubble trajectories showed a bending tendency similar to the experimentally observed Y-branches, and the stationary straight bubble chain parallel to the main chain could evolve into a curved chain and eventually become a branch of the main chain. The theoretical predictions agree well with the experimental results, verifying the evolutionary mechanism of Y-branches in ALF. [ABSTRACT FROM AUTHOR]

Tip leakage flow and induced unstable cavitation can significantly damage the performance of axial waterjet pumps. This study investigated the impact of blade numbers on cavitating conditions in an axial waterjet pump by conducting tests of performance characteristics and high-speed photography experiments on three-blade and four-blade impellers. The results showed that the critical cavitation number σc of the three-blade impeller was larger, while the four-blade impeller flow pattern deteriorated more rapidly after σc. Various cavitation structures in the tip region were observed under different conditions, including clearance cavitation, shear layer cavitation, tip leakage vortex cavitation, and suction-side-perpendicular cavitating vortices (SSPCVs). Tip cavitation maps of the test impellers were drawn based on the flow rate coefficient and cavitation number variation. The three-blade impeller exhibited a wider range of severe cavitation, particularly with an increased occurrence of SSPCVs. With the cavitation number and flow rate coefficient decreased, the SSPCV generated from triangular cavitation cloud shedding presented an increased trend in scale and quantity. Conversely, in the case of the four-blade impeller, SSPCVs were often disrupted by the adjacent blade during migration and interfered with the tip cavitation in the neighboring flow passage. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) and three-dimensional (3D) numerical models are commonly employed to investigate the kinematic and hydrodynamic characteristics of fish maneuvers. In this study, we captured the posture characteristics of zebrafish during C-type maneuvers using high-speed photography and constructed a midline curvature model via the tandem principal characteristics method, which exhibited a "double peak and single valley" structure. Based on this curvature model, self-propelled simulations were conducted using the immersed boundary method with adaptive mesh refinement. The results showed that, under identical deformation conditions, the 2D simulation exhibited a 16.8% higher centroid velocity, 6.1% greater overall angular velocity, and an 11.9% larger turning angle compared to the 3D simulation. This discrepancy is primarily due to the 2D model's inability to accurately represent the fish body's mass distribution and force characteristics, resulting in artificially elevated performance. Nevertheless, 2D simulations remain applicable for studying the propulsion performance of fish with elongated cross-sections and large fin areas. Comparison between the simulated and real motion performance reveals that, under the self-propelled computational model, both 2D and 3D numerical simulations consistently capture the qualitative motion patterns. The quantitative results also reflect the actual swimming performance of the fish within an acceptable margin of error. [ABSTRACT FROM AUTHOR]

Bandsaw blades are typical band-shaped cutting tools that are characterized by their low stiffness and micro-level cutting depth, resulting in distinct wear mechanisms compared to rigid cutting tools. In this study, the wear curve and wear mechanisms of the bandsaw tooth during the bandsawing of Cr12MoV cold-working steel were investigated. The tool life was divided into two stages: a rapid wear stage (Stage I) and a homogeneous wear stage (Stage II). In Stage I, the wear was dominated by chipping, although multiple wear mechanisms were found due to their relatively low manufacturing accuracy compared to rigid cutting tools, which resulted in remarkable differences in the cutting depth of each tooth. In Stage II, abrasive and adhesive wear were the primary wear mechanisms instead of chipping, which was related to the microstructure of Cr12MoV. Furthermore, methods for increasing bandsaw performance were proposed, based on the tooth wear mechanisms. [ABSTRACT FROM AUTHOR]

C f /SiC composite is widely utilized in aerospace and defense sectors owing to their outstanding high-temperature and mechanical performance. However, this material is a typical hard-to-machining material. Building upon prior research on the novel laser-induced oxidation-assisted milling technology, this paper conducted an in-depth study of the oxidation of C f /SiC composite under laser induction. The study combined thermodynamic analysis with the detection of oxidation products to ascertain the oxidation reaction types of C f /SiC composite. The oxidation process under the induction of lasers with different energy densities was investigated by combining the oxide layer morphology, element distribution, and high-speed photography results. And the oxidation mechanism was elucidated. A second-order response surface model for the oxide layer thickness with respect to the laser energy density, scanning speed, and scanning path spacing was established, and parameter optimization was performed based on this model. Experimental validation demonstrated the reliability of the model predictions. [ABSTRACT FROM AUTHOR]

An experimental study to investigate the flow of liquid jet issued from a high aspect ratio nozzle slit into an incoming airflow by changing the orientation angle from the incoming free-stream was performed. A two-dimensional liquid sheet emerged from the narrow slit into the subsonic air crossflow. Different orientation angles between 0 and 90 degrees were studied. High-speed photography and shadowgraphy techniques were utilized to visualize the flow physics. The influence of the slit orientation angle on the flow morphology and the flow regimes of liquid sheets was investigated. Some fluid flow parameters were obtained by analyzing the images. The changes in breakup height of different orientations were measured. A model was offered for the breakup height of the liquid sheet based on the liquid-to-gas momentum ratio, gas Weber number, and a new non-dimensional parameter as a representation of the angle of slit orientation. Also, the defined sheet trajectory for each orientation angle was obtained, and the variations were examined. Empirical correlations for the defined trajectory of the sheet in terms of liquid to gas momentum ratio and gas Weber number for each orientation angle were proposed. [ABSTRACT FROM AUTHOR]

In this study, a new deep-penetration variable-polarity tungsten inert gas (DP-VPTIG) welding process, which is performed by a triple-frequency-modulated pulse, was employed in the welding fabrication of 8 mm AA7075 aluminum plates. The electric signal, arc shape, and weld pool morphology of the welding process were obtained by means of high-speed photography and an electric signal acquisition system under varying parameters of the intermediate frequency (IF) pulse current. The principle of the arc characteristics and the dynamic mechanism of the weld melting during the process are explained. In addition, the macroforming, microstructure, and microhardness of the welded joints were investigated. The results indicate that, with an intermediate frequency pulse of 750 Hz, the arc displayed a higher energy density and a more effective arc contraction, which improved weld appearance and penetration. Moreover, the impact and stirring action of the arc refined the microstructure grains of the weld center. Therefore, this new welding method is feasible for welding medium-thickness aluminum alloy plates without a groove. [ABSTRACT FROM AUTHOR]

For the prompt planting of subsequent crops, most of China's corn harvest must occur before full maturity, with a grain moisture content above 25%. Harvesting moist corn presents challenges due to significant grain damage during threshing. We conducted a high-speed photography observation test of moist corn threshing. It demonstrated that corn ears, when passing through the threshing cylinder, often break into pieces. Grains on divided corncobs can be threshed more easily and earlier than those on undivided ones, suggesting that pre-dividing corn ears reduces grain damage. An experiment using the Lianchuang 825 variety examined the effect of moisture content and the divided rate of corncobs (DRC) on grain damage. The results showed that as moisture content increased from 25% to 37%, grain damage to undivided ears increased from 3.75% to 37.71%. Dividing corn ears before threshing significantly reduced damage, with an eight-piece division reducing damage by approximately 70% across all moisture levels. Verification with the Jinyu 1233 variety confirmed that a higher DRC consistently reduced damage. This study provides a new approach to reducing damage in moist corn threshing and aids in the development of low-damage threshing devices. [ABSTRACT FROM AUTHOR]

Some high-specific-speed centrifugal pumps exhibit instability in terms of hydraulic performance and cavitation characteristics, and there's a lack of reliable numerical models to guide the optimization of cavitation instability. This paper, by conducting a study on mesh independence, analyzes the cavitation curves and cavitation counters for various mesh combinations in the numerical model, The findings indicate that the boundary layer grid not only influences the location of peak points but also the size of the peak. To achieve a stable NPSH peak position, the y+ at the blade leading edge of high-specific-speed centrifugal pumps needs to be controlled between 20–80. The turbulence model, evaporation coefficient, and condensation coefficient were simulated using the orthogonal experimental design method, analyzing the impact of these parameters on the NPSH peak. A visual high-speed photography test rig was established, and rotating cavitation and sheet cavitation is found at part-load. By comparing the cavitation and pressure counters with high-speed photography images, a numerical model was obtained that closely mirrors the experimental cavitation characteristics. [ABSTRACT FROM AUTHOR]

Green leafy vegetables are an essential component of Chinese leafy vegetables. Due to their crisp stems and tender leaves, orderly harvester generally causes significant mechanical clamping damage. The physical and mechanical properties of green leafy vegetables are one of the important basis to design the orderly harvester. At the same time, they provide important parameters for the simulation and optimization of harvester. So, this paper measured the physical characteristic parameters of roots and stems of green leafy vegetables. Then, based on the TMS-Pro texture analyzer, the elasticity modulus of the roots and stems of green leafy vegetables were measured. The static friction coefficient, dynamic friction coefficient, and restitution coefficient of green leafy vegetables root-root, stem-stem, root-steel, and stem-steel were measured separately using a combination method of inclined plane and high-speed photography. Uniaxial compression creep experiments were carried out on whole and single leaf of green leafy vegetables using the TA.XT plus C universal testing machine. The constitutive equation of the four-element Burgers model was used to fit the deformation curve of the sample with time during the constant-pressure loading stage. The fitting determination coefficients R2 were all higher than 0.996, which verified the reasonable validity of the selected model. The above experimental results provide a parameter basis and theoretical support for the design and discrete element simulation optimization of orderly harvester critical components of green leafy vegetables. [ABSTRACT FROM AUTHOR]

Background: The vulnerability of polymeric composite sandwich structures in marine applications to air explosions highlights a significant gap in our understanding of the dynamic behavior of the curved sandwich structures, which is essential for design improvements. Objective: This study aims to explore the dynamic response and failure mechanisms of curved sandwich composite panels subjected to air-blast loading, providing insights into their structural integrity under such conditions. Methods: Experiments were performed using laboratory-simulated air shocks generated by a shock tube, employing high-speed photography and digital image correlation to measure deflections on the back surface of the panels. The panels, made with PVC closed-cell foam cores of two densities (H45 and H130), were tested across three curved geometries (radii of 112 mm, 305 mm, and infinity) under various boundary conditions. Results: Findings indicate an increase in deformation with a decreased radius of curvature under simple support conditions, a trend that reverses under arrested displacement conditions. Moreover, a reduced radius significantly enhances panel strength and resistance to interfacial damage, with the primary failure mode transitioning from core shear cracking to interfacial debonding as core density increases. Conclusions: The study reveals that the radius of curvature, boundary conditions, and core density significantly affect curved sandwich panels' dynamic response and performance. Panels with smaller radii and higher core densities exhibit increased strength, though boundary conditions introduce variable effects on deformation behavior. [ABSTRACT FROM AUTHOR]

Defect effects of carbon fiber composites under dynamic impact conditions are important to mechanical behavior design in the aerospace field. Here we report the defect effect on the impact compressive behavior of 3D braided composites at high strain rates from 550/s to 1240/s. The defect effect on damage behavior was observed by high-speed photography and digital image correlation (DIC) technology. A finite element analysis (FEA) model was developed to show the defect effect on stress distribution and thermo-mechanical behavior. The defect structure reduces the compressive strength of the composite and causes more brittle and catastrophic failure compared with the perfect composite. The defect effect on the compressive behaviors is more significant at higher strain rates. FEA results show that the defect structure causes local stress concentration, high adiabatic temperature rise, and high stress in the X-shaped shear band region, thereby accelerating composite failure. [ABSTRACT FROM AUTHOR]

High speed photography technique is potentially the most effective way to measure the motion parameter of warhead fragment benefiting from its advantages of high accuracy, high resolution and high efficiency. However, it faces challenge in dense objects tracking and 3D trajectories reconstruction due to the characteristics of small size and dense distribution of fragment swarm. To address these challenges, this work presents a warhead fragments motion trajectories tracking and spatio-temporal distribution reconstruction method based on high-speed stereo photography. Firstly, background difference algorithm is utilized to extract the center and area of each fragment in the image sequence. Subsequently, a multi-object tracking (MOT) algorithm using Kalman filtering and Hungarian optimal assignment is developed to realize real-time and robust trajectories tracking of fragment swarm. To reconstruct 3D motion trajectories, a global stereo trajectories matching strategy is presented, which takes advantages of epipolar constraint and continuity constraint to correctly retrieve stereo correspondence followed by 3D trajectories refinement using polynomial fitting. Finally, the simulation and experimental results demonstrate that the proposed method can accurately track the motion trajectories and reconstruct the spatio-temporal distribution of 1.0×10³ fragments in a field of view (FOV) of 3.2 m×2.5 m, and the accuracy of the velocity estimation can achieve 98.6%. [ABSTRACT FROM AUTHOR]

The interaction between a single laser-induced cavitation bubble and an oil layer–water interface is experimentally studied through high-speed photography technology. When oscillating near an oil layer–water interface, the bubble always migrates away from the interface with a jet pointing at the same direction. Three different motions of the interface are observed: interface experiencing subtle disturbance (case 1), interface presenting a deformation resembling an inverted hill (case 2), and interface developing a jet piercing the bubble (case 3). The effect of oil layer thickness on the bubble centroid migration and the inverted hill-shaped interface deformation are investigated as well. With a decreasing dimensionless bubble-interface distance, the effect of the oil layer on the bubble oscillation becomes more significant. In case 2 and case 3, the presence of the oil layer always weakens the migration distance of the bubble centroid. [ABSTRACT FROM AUTHOR]

During the operation of a water-jet pump, cavitation generates noise and vibration, causes surface erosion of the hydraulic components, and reduces the performance of the pump. Suppressing the cavitation is beneficial for improving the stability of the energy system of the water-jet pump. In order to investigate the mechanism of cavitation suppression and optimize the cavitation performance of the water-jet pump, the unsteady cavitation flow was studied by numerical simulation and experiment in this paper. Using high-speed photography technology on a closed test platform, the cavitation flow structures in the water-jet pump were captured, and the physical process of cavitation evolution was revealed. Based on this, in order to obtain the cavitation flow characteristics closely related to the cavitation performance, the cavitation flow in the impeller tip clearance was studied by numerical simulation, the vorticity variation rate in the tip clearance was analyzed, the effects of different cavitation conditions on the vorticity in the tip clearance were revealed. Additionally, this paper analyzed the pressure pulsation characteristics of the tip clearance under different cavitation conditions, and emphatically analyzed the influence of the cavitation flow on the tip clearance pressure pulsation. [ABSTRACT FROM AUTHOR]

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Narrow gap oscillating laser welding with filler wire is a promising technique for joining high-strength steels in construction machinery. In order to investigate the influence of beam oscillation on the surface morphology and microstructure of weld joints of two types of commonly-used high-strength steels, a comparative study between oscillation welding and non-oscillation welding was conducted. High-speed photography technique was employed to reveal the microstructure and mechanical properties of the dissimilar joints. The results showed that laser beam oscillation produces two effects: one was to enlarge the heated surface of molten pool, while the other was to stir the liquid metal in molten pool periodically. Under the first effect, the fusion between sidewall and weld bead layers was promoted, while under the latter, coarse columnar grains ceased to appear, but finer grains were formed. The weld joints between Q355 and 35 steels exhibited excellent tensile impact bending performance, which was attributed to the grain refinement effect. The results also demonstrated that the oscillation welding with a contact angle less than 50° could avoid lack of fusion in multi-pass wire-filling laser welding. The influence of the oscillation welding process on the quality of welding was further discussed.

Abstract Bedload studies at the particle scale may help grasp the essence of the problem. Existing studies suffer from short filming durations, limited data volume, and a narrow range of sediment transport intensity variations. This paper employs the high‐speed photography technology and conducts experimental studies on bedload particle motion under 8 different sediment transport intensities. Using the latest image processing technology, over 6 million sediment particle coordinate points and nearly 400,000 particle motion trajectory curves were automatically obtained and used to compare the motion characteristics of bedload particles under different sediment transport intensities. The results show that under low sediment transport intensity, both the number of moving particles and particle motion velocity contribute to the bedload sediment transport rate, while under high‐intensity conditions, the transport rate mainly depends on the number of moving particles. The probability density distribution of sediment transport rate is concentrated and varies within a small range under low‐intensity conditions, exhibiting a tailing phenomenon. In contrast, under high‐intensity conditions, the range of sediment transport rate values increases, and the probability density curve tends to be symmetric, more closely approximating a normal distribution. Additionally, the paper compares the longitudinal and transverse motion velocities of particles and the coefficient of variation of the bedload sediment transport rate.

Cavitation bubbles near narrow gaps widely exist within microfluidic control devices. In the present paper, a laser-induced cavitation bubble is arranged in a narrow gap composed of two parallel plates. The inception position of the bubble is set to be at the same distance from the two plates so that the dynamic behaviors of the bubble are symmetrical. The collapse and rebound dynamics of the bubble near the boundary of a narrow gap are investigated through high-speed photography. The bubble behaviors (e.g., shape deformation, translational movement, and jet characteristics) are analyzed while considering the influence of the dimensionless distance between the bubble and the boundary and the dimensionless gap width. The principal findings include the following: (1) When the dimensionless distance is small, a violent jet towards the gap is generated during the bubble collapse stage, along with a weak counter-jet towards the boundary appearing during the rebound stage. (2) As the dimensionless distance increases, the translational distance of the bubble during the collapse stage initially decreases, then increases, and finally decreases to zero. (3) Within the parameter range considered in this paper, the dimensionless width mainly affects the expansion degree and movement direction of the bubble cloud during its rebound and subsequent stages. The above research findings can provide experimental support for bubble-driven flow control, pumping, and liquid mixing in microfluidic channels. [ABSTRACT FROM AUTHOR]

The mechanical properties of frozen fissured rock masses are crucial considerations for engineering in frozen earth. However, there has been little research on the mechanical properties of frozen fissured sandstone, including its strength, deformation, and geometric parameters. In this study, sandstone samples with three open en echelon fissures were observed using high-speed photography and acoustic emissions during uniaxial compression tests. The aim was to investigate sandstone's strength, deformability, and failure process in order to elucidate the effects of freezing on its mechanical properties. In the frozen-saturated and dried states, the uniaxial compression strength (UCS) initially decreases and then increases with an increase in fissure inclination angle. Conversely, the UCS of samples in the saturated state continuously increases. The UCS follows a decreasing trend, as follows: frozen-saturated state > dried state > saturated state. The initial crack angle decreases as the fissure inclination increases in all states, irrespective of temperature and moisture conditions. However, the initial crack stress and time show an increasing trend. The uniaxial compression strength (UCS) of frozen fissured sandstone is influenced by four mechanisms: (1) ice provides support to the rock under compression, (2) ice fills microcracks, (3) unfrozen water films act as a cementing agent under tension or shearing loads, and (4) frost damage leads to softening of the rock. [ABSTRACT FROM AUTHOR]

Municipal drainage systems can transmit harmful microorganisms such as COVID-19 virus through wastewater as well as drain airflow with suspended tiny bio-droplets. The generation of tiny droplets in drainage systems can be simplified as the phenomenon of jet impingement and splashing, which is also common in industries, but the size and velocity correlation and the kinetic energy of splashing droplets remain unclear. This paper uses high-speed photography to study splashing from a jet impinging on a horizontal plate. Since the jet can break into successive drops before impingement, successive drops impingement and continuous jet impingement are defined and their splashing modes are revealed. Successive drops impingement and continuous jet impingement, respectively, produce splashing droplets with sizes smaller than 0.25 and 0.30 times the size of the impact drops and jet, and with the velocities up to 3.0 and 1.5 times the impact velocity. Correlations between size and velocity of splashing droplets are established: the range and maximum of velocity increase as diameter decreases, and the high velocity splashing droplets have ejection angles within 10° to 20°. For successive drops impingement, the percentage of total kinetic energy of splashing droplets relative to impact kinetic energy increases with impact Weber number and can reach nearly 50%; however, it varies little with impact Weber number for continuous jet impingement, reaching only 10%. Successive drops impingement produces more splashing droplets characterized by a combination of smaller size, higher velocity and larger ejection angle, resulting in a greater risk of producing airborne microorganisms. [ABSTRACT FROM AUTHOR]

In the process of directed energy deposition-arc (DED-arc), the geometrical shape of weld bead in arc-striking (AS) and arc-extinguishing (AE) areas are usually inconsistent with that in the middle section, which directly affects the forming accuracy of component thus needs to be optimized. In this paper, high-speed photography is used to observe the molten pool behavior of nickel aluminum bronze (NAB) bead deposition, and the causes of abnormal bead shape in the AS and AE areas are analyzed. On that basis, an optimization method for AS and AE is put forward. In the AS area, the welding current and travel speed are increased. And after the arc strikes, a hovering time is used during which the torch hovers at the AS point. In the AE area, the welding current is gradually reduced while the torch keeps hovering at the AE point. Then, the optimization effect of AS parameters on the bead shape are explained through factorial experiments, and the optimization effects of AE parameters are explained through orthogonal experiments. At the same time, the optimal parameter combination of AS and AE is obtained. With the proposed method and the optimal parameters, the height and width deviation of the deposited single bead are controlled within 5%. After adopting the optimization method, the effective height ratio of the DED-arc–manufactured NAB thin wall is increased from 67.5% to 91.5% under the unidirectional deposition path, which is also increased from 88.9% to 98.3% under the bidirectional deposition path. [ABSTRACT FROM AUTHOR]

Cavitation is typically observed when high-pressure submerged water jets are used. A composite nozzle, based on an organ pipe, can increase shear stress on the incoming flow, significantly enhancing cavitation performance by stacking Helmholtz cavities in series. In the present work, the flow field of the composite nozzle was numerically simulated using Large Eddy Simulation and was paired with the response surface method for global optimizing the crucial parameters of the composite nozzle to examine their effect on cavitation behavior. Utilizing peak gas-phase volume percent as the dependent variable and the runner diameter, Helmholtz chamber diameter, and Helmholtz chamber length as independent variables, a mathematical model was constructed to determine the ideal parameters of the composite nozzle through response surface methodology. The optimized nozzle prediction had an error of only 2.04% compared to the simulation results, confirming the accuracy of the model. To learn more about the cavitation cloud properties, an experimental setup for high-pressure cavitation jets was also constructed. Impact force measurements and high-speed photography tests were among the experiments conducted. The simulated evolution period of cavitation cloud characteristics is highly consistent with the experimental period. In the impact force measurement experiment, the simulated impact force oscillates between 256 and 297 N, and the measured impact force oscillates between 260 N and 289 N, with an error between 1.5% and 2.7%. The simulation model was verified by experimental results. This study provides new insights for the development of cavitation jet nozzle design theory. [ABSTRACT FROM AUTHOR]

In urban combat, sub-millimeter inert metal powder is used to replace fragments in explosive bombs, which can effectively reduce collateral damage. In order to investigate the damage effect of high-speed metal particles on the human body, a particle ring filled with a charge was designed to create an explosion-driven particle cloud for the penetration ballistic gelatin. The particle ring was made of polytetrafluoroethylene (PTFE) and sub-millimeter tungsten powder. The dispersion properties of the particle cloud driven by the explosion were studied with high-speed photography and ballistic gelatin. Furthermore, the numerical simulation models of particle-penetrating gelatin based on the experimental results were established with the finite element method. The influences of the particle size and velocity on the penetration depth and cavity diameter was obtained. The relationship between the critical interference distance of the cavity and the distance between particles was determined. This paper provides references and theoretical support for the design of low collateral damage ammunition based on inert metal powder. [ABSTRACT FROM AUTHOR]

Microbubble-mediated therapeutic gene or drug delivery is a promising strategy for various cardiovascular diseases (CVDs), but the efficiency and precision need to be improved. Here, we propose a cavitation bubble-driven drug delivery strategy that can be applied to CVDs. A bubble-pulse-driving theory was proposed, and the formula of time-averaged thrust driven by bubble pulses was derived. The continuous motion of particles propelled by cavitation bubbles in the ultrasonic field is investigated experimentally by high-speed photography. The cavitation bubbles grow and collapse continuously, and generate periodic pulse thrust to drive the particles to move in the liquid. Particles attached to bubbles will move in various ways, such as ejection, collision, translation, rotation, attitude variation, and circular motion. The cavity attached to the particle is a relatively large cavitation bubble, which does not collapse to the particle surface, but to the axis of the bubble perpendicular to the particle surface. The cavitation bubble expands spherically and collapses asymmetrically, which makes the push on the particle generated by the bubble expansion greater than the pull on the particle generated by the bubble collapse. The time-averaged force of the cavitation bubble during its growth and collapse is the cavitation-bubble-driven force that propels the particle. Both the cavitation-bubble-driven force and the primary Bjerknes force act in the same position on the particle surface, but in different directions. In addition to the above two forces, particles are also affected by the mass force acting on the center of mass and the motion resistance acting on the surface, so the complex motion of particles can be explained.

Bandsaw blades are typical band-shaped cutting tools that are characterized by their low stiffness and micro-level cutting depth, resulting in distinct wear mechanisms compared to rigid cutting tools. In this study, the wear curve and wear mechanisms of the bandsaw tooth during the bandsawing of Cr12MoV cold-working steel were investigated. The tool life was divided into two stages: a rapid wear stage (Stage I) and a homogeneous wear stage (Stage II). In Stage I, the wear was dominated by chipping, although multiple wear mechanisms were found due to their relatively low manufacturing accuracy compared to rigid cutting tools, which resulted in remarkable differences in the cutting depth of each tooth. In Stage II, abrasive and adhesive wear were the primary wear mechanisms instead of chipping, which was related to the microstructure of Cr12MoV. Furthermore, methods for increasing bandsaw performance were proposed, based on the tooth wear mechanisms.

To investigate the movement characteristics of cylindrical particles within a slurry pump, the particle trajectories, particle distributions, particle velocity, and passing time of particles in the guide vane are tested by high speed photography. The test results indicate that the pump performance decreases and the wear of the blade pressure side deteriorates with the increase of cylindrical particle densities. The particles primarily flow into the guide vanes from the suction side and flow out from the pressure side. The velocity loss of particles in the guide vanes increases, and the time for particles passing through the guide vanes increases with particle densities. As the cylindrical particle concentrations increase, the pump performance decreases, and the wear of the blade pressure side deteriorates. Additionally, the total velocity loss of particles in the guide vane increases, and the time for particles passing through the guide vane increases with concentrations. Compared with spherical particles, the pump performance is better when the pump conveys cylindrical particles, and the cylindrical particles are more likely to wear the middle of the guide vane flow channel. The particles mainly flow into the guide vanes from the suction side and flow out from the pressure side. The velocity loss of cylindrical particles in the guide vane is smaller than that of the spherical particles. The time of cylindrical particles passing through the guide vane is shorter than that of the spherical particles. [ABSTRACT FROM AUTHOR]

This work is devoted to the study of the processes that take place in the welding gap during explosive welding (EW). In the welding gap, when plates collide, a shock-compressed gas (SCG) region is formed, which moves at supersonic speed and has a high temperature that can affect the quality of the weld joint. Therefore, this work focuses on a detailed study of the parameters of the SCG. A complex method of determining the SCG parameters included: determination of the detonation velocity using electrical contact probes, ceramic probes, and an oscilloscope; calculation of the SCG parameters; high-speed photography of the SCG region; measurement of the SCG temperature using optical pyrometry. As a result, it was found that the head front of the SCG region moved ahead of the collision point at a velocity of 3000 ± 100 m/s, while the collision point moved with a velocity of 2500 m/s. The calculation of the SCG temperature showed that the gas was heated up to 2832 K by the shock compression, while the measured temperature was in the range of 4100–4400 K. This is presumably due to the fact that small metal particles that broke off from the welded surfaces transferred their heat to the SCG region. Thus, the results of this study can be used to optimize the EW parameters and improve the weld joint quality. [ABSTRACT FROM AUTHOR]

Due to the lack of theoretical research on the amount of spatio-temporal information in high-speed photography technologies, obtaining an optimized system with the best amount of spatio-temporal information remains a challenge, resulting in insufficient effective information and observation accuracy for ultrafast events. This paper presents an ultrafast raster imaging (URI) system with a large amount of spatio-temporal information based on the all-optical raster principle in single-shot. Specifically, we derive the optimal equation of spatial resolution and the expression for the maximum amount of spatio-temporal information that can achieve excellent performance for a URI system. It serves as a general guideline for obtaining a large amount of information design in the URI system. Compared with the existing URI systems, the advanced URI system exhibits an improvement of nearly one order of magnitude in the amount of spatio-temporal information and more than twofold in spatial resolution. It shows great potential for capturing intricate and non-repetitive ultrafast events on the femtosecond time scale. [ABSTRACT FROM AUTHOR]

Cavitation is a detrimental phenomenon in hydraulic machinery, adversely impacting its performance, inducing vibration and noise, and leading to corrosion damage of overflow components. Centrifugal pump internal cavitation will lead to severe vibration and noise, and not only will the performance of hydraulic machinery be adversely affected but the impact generated by the collapse of the vacuole will also cause damage to the impeller wall structure, seriously affecting the safety of the equipment's operation. To prevent the generation and development of internal cavitation in centrifugal pumps, to prevent the hydraulic machinery from being in a state of cavitation for a long time, to avoid the failure of the unit, and to realize the predictive maintenance of centrifugal pumps, therefore, it is of great significance to research the methods for monitoring the cavitation of hydraulic machinery and the methods for suppressing the cavitation. This paper comprehensively describes the centrifugal pump cavitation mechanism and associated hazards. It also discusses the current state of centrifugal pump cavitation monitoring methods, including commonly used approaches such as the flow-head method, high-speed photography, pressure pulsation method, acoustic emission method, and vibration method. A comparative analysis of these methods is presented. Additionally, the paper explores signal characterization methods for centrifugal pump cavitation, including time-domain feature extraction, frequency-domain feature extraction, and time–frequency-domain feature extraction. The current research status is elaborated upon. Moreover, the paper presents methods to mitigate cavitation and prevent its occurrence. Finally, it summarizes the ongoing research on identifying and determining the cavitation state in centrifugal pumps and offers insights into future research directions. [ABSTRACT FROM AUTHOR]

Open-canopy pesticide application technology is not affected by the canopy structure and can substantially increase droplet penetration and deposition in the middle and lower rice canopy. However, the optimal working position of the canopy opener is difficult to determine. The purpose of this study was to examine the characteristics of rice canopy disturbances under the action of a canopy opener, verify simulation results using high-speed photography tests, and identify the spraying effect of the optimal operating parameters of a canopy opener through spray tests. The mechanical characteristic parameters of the rice heading stage were determined through experiments, and the canopy-opening process was simulated based on the finite element method of explicit dynamics. The simulation results show that when the speed of the canopy opener is 1.2 m s−1 and the height is 0.6 m, the rice canopy is the most disturbed. The spray experiment results show that under this condition, the overall coverage rate of the rice canopy is relatively high, and the coverage rates of the upper, middle, and lower layers of rice are 92.18%, 66.43%, and 52.84%, respectively. [ABSTRACT FROM AUTHOR]

The dense canopy of rice causes attenuation of droplet dispersion during pesticide application. The canopy-opening device can increase droplet deposition in the middle and lower canopy of rice by causing disturbance to the rice canopy. However, the conditions for use of the canopy-opening device are difficult to determine. Rice morphological structure parameters and material parameters were measured to study the movement mechanism of the rice stems under the action of the canopy-opening device, and the canopy-opening process was then simulated using the explicit dynamic method. The simulation scene of the rice canopy-opening process considered the combination of three different heights and three different driving velocities of the canopy-opening device. The movement mechanism of the rice stems under the operation of the canopy-opening device was investigated, and the entire movement process was separated into two stages: contact and oscillation. The simulation results and high-speed photography experimental results show a strong correlation, with a correlation coefficient of 0.733. The simulation results indicate that when the canopy-opening device is closer to the ground and the driving velocity is higher, the disturbance to the rice stem during the contact stage is stronger. However, for the oscillation stage, there exists a critical value for both the height and driving velocity of the canopy-opening device. During the oscillation stage, there is a critical value for both the height and driving velocity of the canopy-opening device. The numerical-based explicit dynamics approach was employed in this work to investigate the rice canopy motion mechanism, and this study has a definite reference value for the investigation of complicated motion mechanisms in the field crop production process. [ABSTRACT FROM AUTHOR]

Wire arc additive manufacturing (WAAM) is widely studied due to its high deposition rate. However, WAAM samples have poor forming quality compared with other additive manufacturing technologies. The quality of sample formation is directly related to the time required for subsequent mechanical processing. Hence, cycle time can further be reduced by controlling the forming quality. Additionally, better forming quality results in less material wastage. Therefore, the forming quality of samples has always been the focus of WAAM. In this paper, the droplet transfer process of the WAAM is shot with a high-speed camera. This article attempts to explain the WAAM forming process from the perspective of droplet transfer and evaluate the influence mechanism of droplet transfer on the side surface forming quality. High-speed photography is used to extract the molten pool size and droplet transfer frequency. The study also explored the variation of these factors with wire feed speed and number of layers. A two-dimensional droplet transfer model is established based on the results of high-speed photography to study the droplet transfer process. Next, the 3D sample model is built to obtain the roughness of deposition samples. Finally, the relationship between the forming quality and droplet transfer process is studied through the fitting planes. The relationship model of wire feeding speed, molten pool length/droplet transfer frequency, and roughness is obtained. The roughness of the side surface increases with higher wire feed speeds when the wire feed speed is 5.5–6.5 m/min. However, at a wire feed speed of 7.0 m/min, the roughness of the side surface suddenly decreases. The droplet transfer motion rule is then used to explain this change in forming quality. [ABSTRACT FROM AUTHOR]

With the help of an O 2 -pilot strut, the stable supersonic combustion was achieved in a scramjet combustor fueled by liquid kerosene. Objective of this work is to investigate the effect of different mass flow rate of oxygen on the cold flow and combustion characteristics to explain the role of the supplied oxygen in supersonic combustion. A series of numerical simulations and experiments were carried out under the high inflow enthalpy condition (Ma = 2.8). High-speed photography and pressure measurement were used to record the flame images and pressure of combustor. A skeleton kerosene mechanism was used for combustion simulation for more details of combustion. Simulation results indicated that by adjusting the mass flow rate of oxygen, the severe rich-kerosene zone around the ignitor could be improved. Under the low mass flow rate of oxygen condition, limited by over-high equivalence ratio the ignition delay time was too long and heat release was too small to establish the global flame. On the contrary, under the high mass flow rate of oxygen condition, limited by over-low equivalence ratio, only little kerosene could be ignited with most of the kerosene carried downstream by high-speed flow resulting in a sharp increase in flame lift distance. The boundary of mass flow rate of supplied oxygen for combustion stabilization was obtained. The results in this paper would be valuable for reveling the ignition and flame stabilization mechanism in supersonic airflow. • The flame stabilization boundary of lower and upper oxygen was obtained. • The effect of different mass flow rate of oxygen on the volume of subsonic zone was analyzed. • The influence of supplied oxygen on the least-reactive-kerosene-fraction was discussed. • The mechanism of oxygen on the flame stability and ignition delay time was investigated. [ABSTRACT FROM AUTHOR]

Experimental and numerical studies of premixed methane–air flame dynamics in an obstructed chamber are carried out. In the experiment, high-speed video photography and pressure transducer measurements are used to study the combustion dynamics. In the numerical simulation, three subgrid-scale viscosity models and three subgrid-scale combustion models are selected to evaluate their individual predictions compared to the experimental data. The high-speed photographs show that the flame propagation process can be divided into four typical stages. When the flame front passes through the obstacle, two distinct vortex structures are formed. The volute flame is the result of the flame–vortex interaction. In addition, the combustion regime experiences a transition from "wrinkled flamelets" to "corrugated flamelets" and finally arrives at a "thin reaction zone regime." [ABSTRACT FROM AUTHOR]

Experimental study is performed to investigate the dynamic response characteristics of the flame when global equivalence ratio increases suddenly during the condition transition in a cavity-based scramjet combustor. High-enthalpy supersonic flow enters the combustor on conditions that Mach number, stagnation temperature, and total pressure are 2.52, 1486 K, and 1.6 MPa, respectively. In this paper, more attention is paid to the characteristics of flame evolution after sudden increase of fuel injection pressure and combustion characteristic when the injection pressure gets stabilized again. Three flame modes after condition transition have been observed and analyzed according to the transient chemiluminescence image captured by high-speed photography. There are two kinds of stable flame modes after transition mission at a low injection pressure difference, which are mainly reflected in the distribution of flame and intensity of visible light. Whereas, once the injection pressure difference exceeds a critical value, intense periodic flame flashback phenomenon begins to appear in the combustor. It can clearly capture the back and forth motion of the flame in the combustor, along with the local blowout and reignition phenomenon. Furthermore, the dominant frequency of flame flashback decreases and contrast of combustion intensity becomes more obvious as the injection pressure difference increases. • The highlights of this article are listed in the following: • The dynamic response characteristics of flame when equivalence ratio increases suddenly during condition transition in scramjet are investigated experimentally. • Three flame modes after condition transition have been observed and analyzed. • The effect of injection pressure difference on combustion characteristics is explored. [ABSTRACT FROM AUTHOR]