Speed Camera System Research Articles

RF Overdrive Burnout Behavior and Mechanism Analysis of GaN HEMTs Based on High Speed Camera

In this work, a new method for failure analysis of electronic components, high speed camera, is used to investigate burnout failure location of GaN HEMTs under RF overdrive stress. Based on the high speed camera system and the RF test system, we can filter out most of the burn flashes, and clearly locate the weak parts of devices. To further explain the burnout mechanism, a long-term (100 h) RF overdrive stress experiment was carried out and the significant degradation was observed. The drain-source current decreases and the threshold voltage drifts forward. These phenomena show that the degradation of RF overdrive stress is based on hot electron effect (HEE), which is related to the electric field. Besides, Electroluminescence (EL) tests are used and the non-uniform but strong luminescence characteristics of the gate were found, which indicates the strong electric field is the main cause of burnout. We also explore the correlation between burnout and ambient temperature. It was found that the influence of ambient temperature on the burnout was limited. At last, a TCAD simulation is carried out to confirm the temperature and electric field distribution in the device when burnout. It can be found that the electric field inside the device exceeded the breakdown electric field of GaN, which further proves that the burnout caused by RF overdrive is mainly due to electric field rather than temperature.

Suppression effect on TLV cavitation of overhanging grooves with different tab orientations: An experimental investigation

In this paper, a high speed camera and endoscopic particle image velocimetry system are utilized to investigate the influence of tab orientations of overhanging grooves on the suppression effect of tip-leakage vortex cavitation around a truncated NACA0012 hydrofoil. Four kinds of overhanging grooves (OHGs) with different tab orientations, namely OHGs_1–4, are tested, with the original hydrofoil as a comparison. The results suggest that compared with the baseline, all the overhanging grooves tested in our experiments show the suppression effect on TLV cavitation. However, the tab orientations of overhanging grooves leave significant influence on its effect. OHGs_2 with tabs extending beyond the pressure side surface shows the best suppression effect for all the measured gap sizes, followed by OHGs_1 with tabs extending beyond both the suction and pressure side surfaces. For OHGs_3 and OHGs_4, due to the lack of tabs extending beyond the pressure side surface, the suppression effect is not so good as OHGs_1 and OHGs_2. Further analysis indicates that the reason for the better suppression effect of OHGs_2 is the interference of tabs extending beyond the pressure side surface on the fusion of tip-leakage vortex and tip-separation vortex, which decreases the tip-leakage vortex circulation and increases its radius.

Application of combined granular media with opposite wettability for demulsification of oily wastewater by microchannel filter

Oil-water separation with high efficiency and low energy consumption is a tremendous challenge in the green treatment of oily wastewater. In this paper, a novel filtration method with combined granular media for collaborative removal emulsified oil and suspended solids (SS) was proposed, followed by the exploration of demulsification feasibility and oil removal mechanism. The effect of the operation and structural parameters of the filter bed on oil separation performance was thoroughly investigated, and its feasibility for raw oily wastewater treatment was also explored. A remarkable demulsification performance was observed with the combined granular media filter, and a balance of separation efficiency and pressure drop in the emulsified oily wastewater filtration was also achieved subsequently. Effective oil droplet capture and coalescence were observed with a high speed camera system, and pore clogging could be avoided in combined media. The optimal parameters of the combined media filter (CMF) were concluded to be a combined media ratio of 1:1, a superficial velocity of 0.20 m min−1, and a bed porosity of 58.1%. The average oil and suspended solids concentrations in raw oily wastewater was decreased to 8.4 mg/L and 23.3 mg/L during the pilot-scale operation, which indicated that the novel filter composed of combined media had better performance in collaboratively removing oil and SS, even in the period of fluctuating influent parameters. It is believed that a novel and efficient oil removal method, especially including of emulsified oil removal was provided, which also shows great potential and value for the green treatment of industrial oily wastewater.

Addressing endogeneity in modeling speed enforcement, crash risk and crash severity simultaneously

Speeding is one of the major significant causes of high crash risk and the associated injury severity outcomes. To combat such significant safety concerns, a speed limit enforcement system has been adopted widely around the world. This study aims to present an econometric approach that estimates the casual effect of speed enforcement on safety while addressing the endogeneity issue by employing an instrumental variable approach within a maximum simulated likelihood framework. In our study, safety enforcement is represented as the number of speeding tickets issued from the speed camera systems, while safety profile is presented as two dimensions of interest, including total crash risk and crashes by injury severity levels. The proposed econometric model takes the form of a correlated panel random parameters model with speed enforcement endogeneity. In estimating the joint panel model, speed enforcement and crash severity components are modeled by employing Random Parameters Ordered Logit Fractional Split technique, while ‘ is modeled by employing Random Parameters Negative Binomial regression technique. In the current study context, the ‘operational duration of speed camera’ serves as the instrumental variable for controlling the endogeneity between speed enforcement and safety. Further, the analysis is augmented by a detailed policy scenario analysis. The empirical analysis is demonstrated by employing roadway segment-level crash data and speeding tickets data from Queensland, Australia, for the years 2010 through 2013. From the policy analysis, it is found that a stricter speed enforcement for serious level of speeding offenses is likely to have greater safety benefits in reducing crash severity levels. Moreover, a targeted increase in operation duration along with stricter citations for major speeding is likely to have significant safety gain. The outcome of the study will allow the decision-makers to identify a robust resource allocation and speed camera deployment plan.

Study on Townsend first ionization coefficient in a streamer filament of the pulsed electric discharge in water

Streamers in water usually consist of several weakly ionized gaseous filaments. It is important to understand the ionization and excitation processes occurring in a streamer filament. In this paper, we studied the Townsend first ionization coefficient α in a streamer filament. The emission images of streamers in water were acquired by using an ultra-high speed camera system. Based on the emission images, it was found that the luminance of a streamer filament decreased exponentially as the distance increased from the anode tip. The Townsend first ionization coefficient in the streamer filament in water was then estimated by the emission profile method. It was found that the Townsend first ionization coefficient in a streamer filament was 5.3 cm−1 on average and did not depend on the water conductivity or the applied voltage of interest in the present paper. The Townsend first ionization coefficient estimated by the emission profile method is in agreement with that deduced from the electron density profile of the streamer filament in water, indicating that the emission profile method for measuring the Townsend first ionization coefficient can be applicable to the streamers in water. We also estimated the reduced Townsend first ionization coefficient α/N in a streamer filament in water and found that the obtained value for α/N was four orders of magnitude lower than those obtained from the glow discharge in low pressure water vapor, but at least ten orders of magnitude greater than those predicted by the empirical formulas.

Study on the effects of nitro-based fuel additive on diesel engine performance and emissions

Through adding nitro-based fuel additive into diesel fuel,the influences of additive on engine performance, gaseous emission, particle number concentration and exhaust smoke were studied on a test bench. Meanwhile, the functioning mechanism and combustion characteristics were studied through constant volume combustion vessel. The system is composed of high pressure common rail fuel injection system, high pressure constant volume combustion vessel, high speed camera, data synchronization and acquisition system. The maximum diesel injection pressure is 160 MPa, and it can be heated to 1000 K under the back pressure of 3 MPa. According to the research results, adding fuel additive can decrease both exhaust smoke and exhaust temperature of engine for european steady state cycle(ESC). Moreover, The fuel additive improved the engine’s power slightly and expanded the economic fuel consumption working area. The minimum fuel consumption rate was reduced from 204.6g/kWh to 202.2g/kWh, and the highest fuel saving rate was about 2%. After adding MAZ, the mass of the recycled particles can be reduced by about 15%,and the average smoke intensity of most operating points showed a downward trend, with a maximum drop of 55%, the NOx weighted emissions of the whole cycle decreased by more than 2%. After adding nitro-based fuel additive, the ignition delay and flame lift-off length became longer in the combustion process, but the duration of combustion was shorter, which are in accordance with chemical reaction kinetics analysis.

Motion model for describing the quantity of air in droplets through changing the structure of air induction nozzle

Air induction nozzles possess good anti-drift performance, the throat and orifice sizes of the nozzles are main design parameters that affecting atomization. Therefore, Venturi tube nozzles and conventional flat fan nozzles were assembled together to investigate the flow rate, droplet size, the quantity of air in droplets affected by single design parameter of nozzles with applying high speed camera and Spraytec laser diffraction system. The results showed that: the flow rate of the air induction nozzle depended only on the throat size of Venturi tube and pressure, and it was proportional to the throat size of Venturi tube at the same pressure; The flat fan nozzle’s orifice size and Venturi tube size significantly affected volume median diameter of droplets, which generally increased after adding surfactant; A new model was established after optimizing classical equation for calculating the percentage of intake air in droplets and studying the effects of throat and orifice size of air induction nozzles on spray characteristics. By variance analysis, it was verified that the new model of quantity of air in droplets produced by all connected nozzles was correct. The calculation showed that the bubbles sizes ranged at 200-900 μm and were in proportion to the droplet size with the percentage of intake air of 10% to 90%. Contrast to the change of volume median diameter and droplet velocity, existence of intake air could influence their change degree to some extent. Keywords: throat orifice, spray characteristic, model of droplet motion, air induction nozzle DOI: 10.25165/j.ijabe.20211405.5513 Citation: Hu J, Liu C X, Wang Z C, Li Y F, Song J L, Liu Y J, et al. Motion model for describing the quantity of air in droplets through changing the structure of air induction nozzle. Int J Agric & Biol Eng, 2021; 14(5): 35–40.

Dynamic behavior of molten pool flow field for active laser welded-thick stainless steel plates

By combining numerical simulation and experimental investigation, this paper intensively investigated the influence rules of adding three active agents (SiO2, TiO2 and NaF) on the dynamic behaviors of flow field in the laser welding 304 stainless steel thick plate pool. First of all, the mathematical model of the activating laser welding stainless steel thick plate was constructed to numerically investigate the impact of active agents on the fluid flow in the pool. Secondly, based on the tungsten particle tracing principle test, the high speed camera system was adopted for real-time monitoring to investigate the mechanism of action of the active agents on the flow field in the pool. The results suggested that, the active agents partially affected the mode of fluid flow. The velocity vector from both sides of the pool to the center occurred on the pool surface, while vortex from the pool margin to the center occurred on the pool cross section. The phenomenon that the tracing tungsten particles moving from the pool margin to the center, it shows that the flow direction of the fluid changed after coating with the active agent, the fluid flew from the pool margin to the center. At the same time, the coating of active agents changed the flow velocity of fluid inside the pool, and SiO2 active agent has the most significant increase effect, the maximum velocity of fluid flow on the upper surface, the longitudinal and cross sections at the same position of the SiO2 active agent coated specimen increased by 25.8%, 8% and 33.8%, respectively, compared with that without the active agents.

ROAD SAFETY: A MAJOR PUBLIC HEALTH ISSUE

ROAD SAFETY: A MAJOR PUBLIC HEALTH ISSUE

Single-shot interferometric measurement of cavitation bubble dynamics.

We demonstrate an interferometric method to provide direct, single-shot measurements of cavitation bubble dynamics with nanoscale spatial and temporal resolution with results that closely match theoretical predictions. Implementation of this method reduces the need for expensive and complex ultra-high speed camera systems for the measurement of single cavitation events. This method can capture dynamics over large time intervals with sub-nanosecond temporal resolution and spatial precision surpassing the optical diffraction limit. We expect this method to have broad utility for examination of cavitation bubble dynamics, as well as for metrology applications such as optorheological materials characterization. This method provides an accurate approach for precise measurement of cavitation bubble dynamics suitable for metrology applications such as optorheological materials characterization.

An ePTFE Trileaflet Motion Visualization Method by a Three-way Isometric High Speed Camera System

An ePTFE Trileaflet Motion Visualization Method by a Three-way Isometric High Speed Camera System

An ePTFE Trileaflet Motion Visualization Method by a Three-way Isometric High Speed Camera System

An ePTFE Trileaflet Motion Visualization Method by a Three-way Isometric High Speed Camera System

Pool boiling heat transfer of ferrofluids on structured hydrophilic and hydrophobic surfaces: The effect of magnetic field

The combined effect of external magnetic field and surface modification on boiling heat transfer of ferrofluids was investigated in this study. Experiments were performed on suspensions of Fe3O4 nanoparticles (volume fraction of 0.025% vf%) with and without presence of magnetic field on structured (surfaces with artificial cavities) hydrophilic and hydrophobic surfaces. Surface related effects such as the hole diameter, pitch size and surface wettability on boiling heat transfer were revealed using the high speed camera system. According to the obtained results, application of magnetic field enhanced boiling heat transfer. The effect of magnetic field was more pronounced on surfaces with larger pitch sizes. Magnetic field promoted bubble nucleation on the superheated surfaces by generating an additional force via Fe3O4 nanoparticles, resulting in enhanced bubble-bubble interactions and coalescence. Furthermore, the surfaces with the larger cavity diameter performed better in terms of heat transfer. Scanning Electron Microscopy (SEM) images showed that as the cavity diameter decreased, deposited nanoparticles tended to completely fill the cavities on hydrophilic surfaces and thus deteriorate boiling heat transfer. On hydrophobic surfaces, deposition of nanoparticles led to a biphilic surface, thereby enhancing boiling heat transfer. As the cavity size increased, smaller portion of the cavities was filled with nanoparticles, and nucleation could still occur from the nucleation sites.

Developing and Testing of an Expansion Cloud Chamber for Cloud Physics Research

The expansion cloud chamber is an important equipment for the research on nucleation process and mechanism of aerosol and weather modification seeding agents. It provides experimental conditions, in which the vapor can transform to water or ice super saturated. But for a long time, expansion cloud chamber with advanced cloud particle spectrum and image measurement system is absent in China. A independently developed expansion cloud chamber is established recently to investigate cloud physical and chemical processes. It consists of cloud chamber equipment, environmental and cloud physics parameter measurement systems, data communication systems and control system.The cloud chamber system mainly includes an experimental reaction chamber and a pre-vacuum tank, and adopts the split design. They are connected through controllable valves. The inside capacity of the experimental reaction chamber and pre-vacuum tank are 1.5 m3 and 9 m3, respectively. The control target air pressure of the reaction chamber is 100 hPa, and that of the pre-vacuum tank is 30 hPa. The cloud chamber system is equipped with advanced measuring instruments, such as environmental parameter detectors, cloud particle spectrometer, the precipitation particle spectra instrument, cloud particle imager, visibility meter, aerosol particle spectrometer, high speed camera system, etc.It is the first time that the chamber system uses domestic cloud particle spectrometer and imager measurement system. Tests show that the cloud chamber system has good temperature and pressure controlling ability. The average cooling rate can reach 0.26℃·min-1 and temperature distribution in cloud chamber is uniform. In the chamber, the fog formed by expansion process lasts 4 minutes. The maximum concentration of fog droplets reaches 6.1 cm-3, the droplet spectrum range is 3-8 μm, and the average effective diameter is about 6.5 μm. At the same time, clear fog droplet images can be obtained by high speed camera. It can control the low-temperature environment from room temperature to -50℃, and achieve pressure expansion cloud simulation and microphysical parameter monitoring. The lack of indoor experimental equipment for aerosols and warm cloud seeding agents will be solved. It has important significance for verification of nuclear properties of warm cloud seeding agents and improving the technology of warm cloud precipitation enhancement.

Low frequency fluctuation study using a microwave interferometer and Hα line emission measurement systems in the Pilot-PSI device

A frequency multiplied microwave interferometer, a Hα line emission measurement system, and a high speed camera system were installed on the Pilot-PSI device for low frequency fluctuation study in the detached plasma condition. The two dimensional Hα line emission and its fluctuation were monitored with a fast visible camera with Hα filter. The coherent low frequency fluctuations of frequency of approximately 13 kHz were measured by all measurement systems. The stronger fluctuation intensities were observed in the downstream of the ionization front region in the detached plasma condition. Moreover, we show the clear difference between the strong fluctuation regions of the electron line density and Hα line emission for the first time. This means that the fluctuations of Hα line emissions was caused by not only electrons but also by hydrogen ions.

Investigation of erosion mechanism of tungsten-based cathode in Ar–N2 DC arc

Direct current arc has been used in a wide industrial field. Reducing in cathode erosion is an important issue for process cost reduction, however the erosion mechanism under molecular gas as plasma supporting gas has not been clarified yet. The purpose of this research is to elucidate the erosion mechanism of tungsten based cathodes in atmospheric pressure Ar–N2 DC arc. The metal vapor generated from the cathode surface was successfully visualized by a high speed camera system with a pair of band pass filters. Combing the visualization with the cahtode temperature measurements provides the tungsten vapor evaporation mechanism; tungsten vapor was generated not from the high temperature part of the cathode tip but from the peripheral part. The arc temperature measurement confirmed that ionization of tungsten atoms in the high-temperature region of the arc caused to this characteristic distribution of tungsten vapor. These findings advance the understanding of such electrode phenomena leading to increased use time of the electrode, and as a result the industrial use of N2 arcs is expected to expand.

Real-Time Video Surveillance Based Structural Health Monitoring of Civil Structures Using Artificial Neural Network

Modern world’s incessantly increasing outdoor traffic load has eventually led to structural health concern and continuous health monitoring of large scale civil structures such as bridges, roads, highways, etc. In this paper, we propose a computer vision based non-destructive structural health monitoring (SHM) method using high speed camera system combined with the brilliance of artificial intelligence. A number of appreciable SHM techniques had been reported that utilizes wired or wireless smart sensors, but the use of nondestructive techniques, such as, digital high speed imaging were rarely employed for detection of dynamic vibrations of civil structures. In the current research, we have developed a high speed video imaging based structural health monitoring system that utilizes blob detection based motion tracking algorithm. It provides factual information regarding localization and displacement of the target object or an existing feature in the civil structure. The modal parameters were subsequently extracted to analyze the level of severity of structural damage within the civil structures. Also, an artificial neural network is trained to infer the qualitative characteristics of structural vibrations based on vibration intensity and the network inferences can be correlated with the conditions of the structure. The efficacy of our vision system in remote measurement of dynamic displacements was demonstrated through a shaking table and a slip desk experiment. The experimental results demonstrate real-time output with satisfactory performance.

Effect of fiber reinforcement and fabrication process on the dynamic compressive behavior of PEEK composites

This paper investigates experimentally the dynamic compressive behavior of short fiber reinforced polyetheretherketone (PEEK) composites, with a specific focus on the effect of strain rate, fiber reinforcement and fabrication process. Hopkinson compressive bar system is employed to test the specimens with strain rate varies from 800–2500/s. Ultra-high speed camera system is used to record the deformation and failure process. Scanning electron microscopy (SEM) is introduced to examine the fracture surface, and to analyze the failure mechanism and its rate dependency. Three different types of PEEK composites are studied and compared to investigate the sensitivity of failure mechanism to fiber reinforcement and fabrication method (injection and extrusion). The results indicate that the ultimate stresses of PEEK and PEEK composites present different levels of sensitivity against strain rates, while the failure strain of PEEK composites decrease with the increase of strain rate. The strain rate dependency is associated with the increase of interface toughness under higher strain rate. The experimental results also identify the presence of phase transformation for matrix material during the high-rate compressive failure. The sensitivity of failure behavior against fabrication process is found to associate with the difference of fiber distributions.

Behavior of condensed droplets growth and jumping on superhydrophobic surface

Droplets on the superhydrophobic surface can fall off the surface spontaneously, which greatly promote dropwise condensation. This study considers a continuous droplet condensation process including droplet growth and droplet jumping. A droplet growth model considered NCG is developed and droplet jumping is simulated using VOF (Volume Of Fluid) model. Al–based superhydrophobic surfaces are prepared using chemical deposition and etching method. The Al-based superhydrophobic surface has a contact angle of 157°±1° and a rolling angle of 2°±1°. An observation experiment is designed to observe droplet jumping on superhydrophobic surface using a high– speed camera system. The result of droplet growth model shows a good match with experimental data in mid-term of droplet growth. Fordroplet jumping, simulation and experiment results show that droplet jumping of different diameter hasa universality in a non–dimensional form. The jumping process can be divided into 3 stages and droplet vibration is observed.

On bubble dynamics in subcooled nucleate boiling on a platinum wire

While much attention has been given to the phenomenon of boiling, the underlying physics and mechanisms are still not fully understood due to its complicated and illusive nature. In this study, an experimental investigation of subcooled pool boiling of de-ionized (DI) water, at a bulk temperature of 30 °C and atmospheric pressure, was performed on a platinum wire with a diameter of 250 μm, starting from the onset of nucleate boiling (ONB) point and rising to higher heat fluxes. A high speed camera system was utilized for visualization. Images of bubbles growth, migration, coalescence, leaping and detachment were recorded. Each of these events was investigated separately, and a comprehensive discussion undertaken. High speed camera images were analyzed by taking the most important parameters, such as surface tension, bubble-bubble interactions, nucleation site-bubble interactions, Marangoni convection and accumulation of non-condensable gases inside the bubbles. Lower applied heat fluxes led to bubble nucleation from the nucleation sites and slow growth of bubbles to a certain diameter, which were ready to migrate along the wire. Increasing the heat flux made the bubbles grow faster and favored coalescence, leaping and detaching that be observed one after another due to an increase in the temperature gradient and perturbation of the temperature field near the nucleation sites. Another important mechanism considered was the momentum of the non-condensable gases inside the bubbles, especially while the bubble tail disappeared and the bubble shrank whilst stopping near an immobile bubble or near the nucleation sites.