High-speed Video Recording Research Articles

Flame front dynamics studies at deflagration-to-detonation transition in a cylindrical tube at low-energy initiation mode

The aim of this work was to study the dynamics of deflagration-to-detonation transition (DDT) following flame acceleration in a cylindrical tube. We combined high-speed video recordings of self-luminescence and traditional local flow measurements to study the DDT process in a stoichiometric acetylene–oxygen mixture with argon dilution and nitrogen dilution. Experiments were carried out in a cylindrical tube with an inner diameter of 0.04 m and a low-energy ignition source (the ignition energy 0.8 mJ). The quantitative data on the dynamics of the shock wave and the local flame velocities, the spatial behavior of the flame during its acceleration, the flame extension, and the distance between the shock wave and the flame front were obtained. The locations of hot spots relative to the spatial configuration of the accelerating flame front and the tube walls were found as well. The local flow temperatures required for hot-spot formation were evaluated from the experimental measurements of induction zone length and the comparison of ignition delay times of similar mixtures obtained behind the reflected shock waves in shock tube tests. The following results were obtained from the experiments. At flame velocities near the isobaric sound speed of combustion products, the spatial configuration of the flame was stable, and one or several hot spots were initiated ahead of the flame near the tube wall. The distance between hot spots and the leading tip of the flame did not exceed 0.4 m. Depending on the mixture sensitivity, weak, transient, or strong ignition modes were observed. For hot-spot formation, the actual local temperature in the induction zone between the leading edge of the flame front and the shock wave should be 100–200 K higher than the post-shock temperature deduced from a one-dimensional model. The higher post-shock mixture condition in the induction zone is due to an additional local transverse adiabatic compression of unburnt mixture near the tube wall, which is generated by the inclined flame front.

Symbiotic interactions between ciliates (Ciliophora) and diatoms (Bacillariophyceae)

Introduction: Diatoms and ciliates are important components of the marine plankton community, and some species are able to develop symbiotic associations in the tropical seas. Objective: To describe the nature of the symbioses, the morphological adaptations of the members, and the possible ecological advantages of the symbiotic life versus the free-living forms. Methods: Plankton samples were collected from Mediterranean and Caribbean Seas, and the South Atlantic Ocean. Consortia were examined during laboratory incubations, including studies of the motility and the feeding currents by high-speed video recordings, and culture tests of the species as symbiotic or free-living forms. Results: The consortia of the diatoms Chaetoceros dadayi and C. tetrastichon with the tintinnid Eutintinnus spp., and C. coarctatus with the peritrich ciliate Vorticella oceanica are examples of an obligate mutualism. The cultures of the host diatoms as free-living organism were unsuccessful. The consortia between Eutintinnus lususundae and the diatoms Chaetoceros peruvianus, Hemiaulus hauckii, H. membranaceus, and Thalassionema sp. are facultative symbioses. These are examples of three or four partner consortia because Hemiaulus spp. is the host of the diazotrophic cyanobacteria Richelia intracellularis. Other example of facultative three partner consortium is the peritrich ciliate Zoothamnium pelagicum with an ectobiont bacteria, and the diatom Licmophora sp. The barrel-shaped chains of the diatom Fragilariopsis dolious encircled the lorica of Salpingella spp., while these chains were almost flat in the free-living stage. The peritrich ciliate Pseudovorticella coscinodisci lives on large pelagic diatoms such as Coscinodiscus and Palmerina. These symbioses are facultative for the diatoms, but they extended their survival under unfavorable conditions. High-speed video recordings of the consortium of Vorticella oceanica and Chaetoceros coarctatus revealed that during the stalk contraction the zooid of reached 5 400 body length s-1, being the fastest organism with respect to its size. The consortia of Chaetoceros densus and an undescribed species of Vorticella is re-discovered. Conclusions: These symbioses have allowed that the sessile peritric ciliates colonize the pelagic environment and the proliferation of diatoms with a polar origin in the tropical sea.

Secondary Atomization of a Biodiesel Micro-Emulsion Fuel Droplet Colliding with a Heated Wall

Using high-speed video recording, we establish the following regimes of hydrodynamic interaction of a biodiesel micro-emulsion fuel droplet with a heated wall: deposition (including drop spreading and receding), drop hydrodynamic breakup, and rebound. Collision regime maps are plotted using a set of dimensionless criteria: Weber number We = 470–1260, Ohnesorge number Oh = 0.146–0.192, and Reynolds number Re = 25–198. The scenarios of droplet hydrodynamic disintegration are studied for transient and film boiling. We also estimate the disintegration characteristics of a biodiesel micro-emulsion droplet (mean diameter of child droplets, their number, and evaporation surface area increase due to breakup). The study establishes the effect of water proportion on the micro-emulsion composition (8–16 vol.%), heating temperature (300–500 °C), droplet size (1.8–2.8 mm), droplet velocity (3–4 m/s), rheological properties of the examined compositions, and emulsifier concentration (10.45 vol.% and 20 vol.%) on the recorded characteristics. The results show that the initial liquid surface area can be increased 2–19 times. The paper analyzes ways to control the process. The hydrodynamic disintegration characteristics of a biodiesel micro-emulsion fuel droplet are compared using 2D and 3D recording.

Wing-fanning frequency as a releaser boosting male mating success-High-speed video analysis of courtship behavior in Campoplex capitator, a parasitoid of Lobesia botrana.

Campoplex capitator is an ichneumonid parasitoid with a narrow host range, comprising grapevine moth pests. Despite being considered one of the possible candidates for biocontrol of Lobesia botrana, knowledge about its biology is limited and mass-rearing for commercial purposes is still lacking. This research provides a quantitative analysis of the C. capitator courtship and mating behavior. C. capitator mating sequence was analyzed by high-speed video recordings. Main behavioral parameters, with special reference to male wing fanning and antennal tapping, were quantified and linked with mating success. Furthermore, we analyzed the occurrence of population-level behavioral asymmetries during C. capitator sexual interactions and their impact on male success. Results showed that male wing fanning was crucial to successfully approach the female. Males achieving higher mating success performed wing-fanning at higher frequencies over unsuccessful ones. After wing fanning, most of males palpated the female's body with their antennae, before attempting copulation. The overall mating success was >70%, with a rather long copula duration (254.76 ± 14.21 s). Male wing-fanning was lateralized on the left at population level, while antennal tapping displays were right-biased. Side-biased male displays do not differ in terms of frequency and duration of their main features. This research adds basic knowledge to the C. capitator behavioral ecology. Since rearing protocols for C. capitator are being developed, male wing fanning frequency may represent a useful benchmark for monitoring mate quality over time, tackling mating success reductions due to prolonged mass-rearing.

Influence of micropores on structural instability of the combustion wave

The article shows examples of visualization of the process of heat transfer by radiation in unstable combustion modes of porous powder materials, which are in good agreement with the results of high-speed video recording and micropyrometry. The mathematical model and the results of calculating the structure of the combustion wave in the Ni-Al system are presented. The contribution of radiative heat transfer at an adiabatic combustion temperature in the range of 810 % and the effect of its trigger shutdown with decreasing temperature were revealed.

A triboelectric and pyroelectric hybrid energy harvester for recovering energy from low-grade waste fluids

Low-grade waste energy is widely available in industrial processes, and it typically appears in the form of thermal fluids. Types of technologies are developed for harvesting the thermal energy from these fluids. However, the thermal fluid not only possesses thermal energy, but also contains a large amount of kinetic energy. In this study, a hybrid device is proposed for harvesting both the thermal and kinetic energy of the thermal fluids. A free-standing type triboelectric nanogenerator (TENG) is employed for harvesting the kinetic energy, while a pyroelectric generator (PENG) is used for harvesting the thermal energy. Output performance of discrete water droplets with temperature of 5 °C, 25 °C, 45 °C and 65 °C are compared in both the TENG and PENG devices. The effects of the device inclination angle, and droplet released height are discussed. The analyses are conducted based on high-speed video recording of the droplet dynamics on the device as well as numerical simulation. The results indicate the droplet temperature, device inclination angle and droplet released height affect the droplet dynamics significantly. Further, the variation of droplet dynamics greatly affects the output performance of both the TENG and PENG. The peak output power of the TENG decreases with the increase of droplet temperature, while the output power of the PENG increases with the temperature variation. A hybrid energy harvester was fabricated and a peak power density of 2.6 μW/cm2 was achieved. A maximum energy increment of 238% was obtained by the hybrid harvester, as compared to the pure PENG device. The harvested energy was able to light up 28 commercial LED light bulbs.

Eyelid squinting during food pecking in pigeons.

The visual control of pecking by pigeons (Columba livia) has latterly been thought to be restricted to the fixation stops interrupting their downward head movements because these stops prevent interference by motion blur. Pigeons were also assumed to close their eyes during the final head thrust of the peck. Here, we re-examined their pecking motions using high-speed video recordings and supplementary provisions that permitted a three-dimensional spatial analysis of the movement, including measurement of pupil diameter and eyelid slit width. The results confirm that pigeons do not close their eyes completely during the presumed optically ballistic phase of pecking. Instead, their eyelids are narrowed to a slit. The width of this slit is sensitive to both the ambient illumination level and the visual background against which seed targets have to be detected and grasped. There is also evidence of some interaction between pupil diameter and eyelid slit width. We surmise that besides being an eye-protecting reflex, the partial covering of the pupil with the eyelids may increase the depth of focus, enabling pigeons to obtain sharp retinal images of peck target items at very close range and during the beak-gape 'handling' of food items and occasional grit particles.

Adjusting the Punching Process of Poly Vinyl Chloride (PVC) and Polycarbonate/ Acrylonitrile Butadiene Styrene (PC/ABS) Cable Ducts Using High-Speed Video Recordings

Adjusting the Punching Process of Poly Vinyl Chloride (PVC) and Polycarbonate/ Acrylonitrile Butadiene Styrene (PC/ABS) Cable Ducts Using High-Speed Video Recordings

Acoustic Shock Emission in a Collision of a Drop with Water Surface

The collision of droplets with a water surface is being actively developed in the interests of many applied problems—transfer of matter through the ocean-atmosphere boundary, underwater acoustic noise of the marine environment, measurement of precipitation intensity, various technologies, and much more. One of the research priorities is acoustic radiation, in particular, shock sound arising at the moment a drop contacts the surface. The impact of the drop is preceded by processes that affect the shape of the drop, because of which it noticeably deviates from the spherical one. As a result, the final (contact) velocity changes–one of the most important parameters of collision. The study of the listed factors is carried out in this work by means of broadband acoustic measurements and high-speed video recording.

An Experimental Apparatus for Modeling the Processes of Electric Spark Plasma Sintering

An experimental apparatus was developed and manufactured to simulate the processes of electric spark plasma sintering. The apparatus allows direct observation and high-speed video recording of chains of powder particles in the channels of a dielectric matrix when passing short pulses of electric current. Tests performed using chains of titanium spherical particles with a diameter of up to 300 μm as an example showed the significant overheating of the contact area at the moment of transmission of a short (~1 ms) electric current pulse that is characteristic of spark plasma sintering. Thus, the developed methodology and installation provide the ability to study the mechanisms of modern technologies for the consolidation of powder materials based on pulsed electricity.

Electrochemical Emission during the Straining and Destruction of an Aluminum–Magnesium Alloy in an Aqueous Medium

The spatiotemporal structures of Portevin–Le Chatelier deformation bands at the stage of neck formation and fracture of an aluminum–magnesium alloy deformed in an aqueous medium have been studied using a complex of in situ methods, including the method of high-speed video recording of the surface and the electrochemical emission method. The latter is based on the measurement and analysis of jumps in the electrode potential of a deformed metal under conditions when discontinuous deformation is manifested. It is found that discrete electrochemical emission signals in the frequency range from 10 Hz to 10 kHz contain information on the number of deformation bands, the time of their emergence, their growth stages, their statistical temporal structure, etc. A characteristic series of signals was detected at the prefracture stage, which can be considered the electrochemical precursor of neck formation and specimen destruction. The relationship between the emergence of electrochemical emission signals and the localization of plastic deformation and the destruction of an oxide film on the surface of an aluminum alloy that is in contact with an aqueous medium is discussed.

Acoustic process monitoring in laser beam welding

Structure-borne acoustic emission (AE) measurement shows major advantages regarding quality assurance and process control in industrial applications. In this paper, laser beam welding of steel and aluminum was carried out under varying process parameters (welding speed, focal position) in order to provide data by means of structure-borne AE and simultaneously high-speed video recordings. The analysis is based on conventionally (e.g. filtering, autocorrelation, spectrograms) as well as machine learning methods (convolutional neural nets) and showed promising results with respect to the use of structure-borne AE for process monitoring using the example of spatter formation.

Fitting a biomechanical model of the folds to high-speed video data through bayesian estimation

Abstract High-speed video recording of the vocal folds during sustained phonation has become a widespread diagnostic tool, and the development of imaging techniques able to perform automated tracking and analysis of relevant glottal cues, such as folds edge position or glottal area, is an active research field. In this paper, a vocal folds vibration analysis method based on the processing of visual data through a biomechanical model of the layngeal dynamics is proposed. The procedure relies on a Bayesian non-stationary estimation of the biomechanical model parameters and state, to fit the folds edge position extracted from the high-speed video endoscopic data. This finely tuned dynamical model is then used as a state transition model in a Bayesian setting, and it allows to obtain a physiologically motivated estimation of upper and lower vocal folds edge position. Based on model prediction, an hypothesis on the lower fold position can be made even in complete fold occlusion conditions occurring during the end of the closed phase and the beginning of the open phase of the glottal cycle. To demonstrate the suitability of the procedure, the method is assessed on a set of audiovisual recordings featuring high-speed video endoscopic data from healthy subjects producing sustained voiced phonation with different laryngeal settings.

Conditions and characteristics of droplets breakup for industrial waste-derived fuel suspensions ignited in high-temperature air

This research is focused on the ignition and combustion mechanisms and characteristics of single droplets of seven different composite liquid fuels, based on wet coal processing waste (fine coal + 50 wt% of water) with 40 wt% of vegetable oils (castor, rapeseed) and used petroleum-based oils (lubricants – motor, compressor, and turbine oils; working fluid – hydraulic oil; insulating fluid – transformer oil). The combustion of waste-derived fuel suspensions is initiated by introducing single droplets into heated motionless air with a temperature of 700–1,000 °C. Threshold conditions (component composition, concentration of combustible liquid, and temperature) were detected, for which micro-explosions during the induction period resulted in the full breakup of droplets, combustion of products (vapors and fine particles) and their subsequent rapid burnout. A high-speed video recording system is used to establish consistent patterns of physical and chemical processes, as well as ignition and combustion characteristics (ignition delay times, burnout time, velocity of breakup products, and size of their burnout area) for a group of fuels under the conditions of droplet breakup. A hypothesis about how the composition of the component affects the breakup of droplets during ignition was formulated based on the results of analyzing the properties (initial boiling point and evaporation rates of oils, their surface tension and surface free energy, as well as wettability of dry coal processing waste) of separate fuel components.

Experimental observation of diffusive-thermal oscillations of burner stabilized methane-air flames

In this work we experimentally investigate the onset of the diffusive-thermal instabilities for flat burner stabilized methane-air flames at normal pressure. The structure and dynamics of combustion fronts are studied by using visual imaging, including high-speed video recording, spectroscopic and acoustic measurements. Numerical simulations with a one-dimensional model for a burner stabilized flame with detailed reaction mechanisms are also conducted. The critical conditions for the emergence of flame oscillations and the period of pulsations are determined. The experimental data obtained with different techniques are found to be in good agreement and also correlate with the numerical results. The numerically calculated data are shown to be sensitive to the choice of the reaction mechanism. Thus a direct measurement and calculation of the critical conditions and the characteristics of flame oscillations open a new perspective for the verification and validation of detailed reaction mechanisms.

Strength and fragmentation behaviour of complex-shaped catalyst pellets: A numerical and experimental study

The effects of catalyst support shapes on their final strength and fragmentation behaviour are investigated. Uniaxial compression tests by diametrical loading of solid and four-holed discs with high-speed video recordings are employed to investigate strengths and pellet crushing behaviours. The combined finite-discrete element method (FDEM) is employed to simulate the effects of geometrical features and loading orientation on the pre- and post-failure behaviour of catalysts. A comparison with experimental results is also presented and the remarkable agreement in failure evolution and mode is discussed. A methodology to derive representative fragment size distributions from defined pellet shapes and material properties is introduced, providing a further tool to understand the strength and fragmentation behaviour of catalyst supports. The results suggest that fixed-bed reactors made with solid cylindrical catalysts will be more likely to be affected by pressure drops caused by the choking effect of a significant portion of fines than if it was made with catalyst supports with four holes. Two designs of four-hole catalyst supports sintered with different porosities have also been studied, showing different fragment size distributions and fines production. Characterisation of fines production for different catalyst support designs will improve prediction of reactor clogging and pressure drops.

Dynamics of deformation band formation investigated by high-speed techniques during creep in an AlMg alloy

Dynamics of the deformation band formation during creep in an Al–Mg alloy was investigated by simultaneous high-speed video recording of deformation bands with an extremely high time resolution of 40 μs and measurement of the concomitant acoustic emission. The results are consistent with the mechanism where the trigger of a strain step on the creep curve is the nucleation and rapid widening of a primary deformation band, generating an acoustic emission signal within 1 ms. Correlations between various stages of the deformation band formation, acoustic emission, and stress response are explored in detail. Notably, the stress drop rate and the amplitude of the acoustic emission signal are found to be linearly related. The mechanism of the acoustic emission associated with the initial rapid stage of the band development is discussed.

Detailed investigation of bag-breakup process in the context of spray of droplets generation within wind-wave interaction

The main mechanism responsible for the generation of spume droplets in marine atmospheric boundary layer was investigated at the experiments carried out at the high-speed wind-wave flume of IAP RAS. Strong wind tears off water from the crest of the waves during bag breakup fragmentation of small-scale disturbances that arise at the air-water interface. Separate bag-breakup event forced to occur in a dried high-speed wind-wave flume was investigated qualitatively and quantitatively using multiperspective shadowgraph high-speed video recording.

Sprint exercise for subjects with mild-to-moderate Parkinson's disease: Feasibility and biomechanical outputs

BackgroundHigh-intensity training, a still unexplored exercise for individuals with Parkinson's disease, is positively related with increased functionality and aerobic profile in healthy individuals. The aim of this work was to evaluate the feasibility, safety, and acceptance of sprint running in individuals with mild-to-moderate Parkinson's. Additionally, we compared sprint biomechanical outputs of force, velocity and power between individuals with Parkinson's disease and healthy. MethodsPhysically trained subjects with Parkinson's, men, (n = 16, 64:9.01 years, stage between 1 and 3 in the Hoehn and Yahr, 16.8:7.1 at Unified Parkinson's disease Rating Scales, and control group (n = 21, 65:9.27 years) performed 20 m sprint sessions. We analyzed the self-reported satisfaction and acceptance using a self-administered questionnaire, and the sprint biomechanics and performance based on high-speed video recordings. FindingsAll participants completed the tests with high feasibility, acceptability and satisfaction scores. The sprint maximal force and maximal power outputs were higher in Parkinson's disease. Conversely, control group showed higher mechanical effectiveness values. Interestingly, no difference in velocity capabilities and overall 20-m sprint performance was observed between groups, possibly explained by different mechanical strategies in both groups over the sprint accelerations. Linear regression analyses showed that physical qualities are predictors of mechanical effectiveness, and mechanical variables are important determinants of sprint performance on Parkinson's disease. InterpretationSprint is a feasible exercise for people with mild-to-moderate Parkinson's disease. Even though differences in physical qualities and mechanical effectiveness exist between subjects with Parkinson's disease and healthy, there is no overall substantial impact on sprint running performance.

Rates of High-Temperature Evaporation of Promising Fire-Extinguishing Liquid Droplets

Differences in the rates of heating and evaporation of droplets with the component composition are important parameters of heat transfer processes and phase transformations. This paper presents the values of high-temperature (up to 600 °C) evaporation rates of droplets of promising fire-extinguishing compositions (water, bentonite suspension, bischofite solution, EA-5 solution, and foaming agent emulsion) at convective (in the air stream), conductive (on a heated surface), and radiation (in a muffle furnace) heating. A high-speed video recording system and tracking software algorithms are used. At identical initial sizes of droplets of fire-extinguishing suspensions, known as emulsions and solutions, the times of their complete evaporation are shown to differ 3.7 times when heating on the substrate, 1.25 times in the air flow, and 1.9 times in the muffle furnace. A general approximation expression is formulated, and the empirical constants are calculated to predict the evaporation rate of the droplets of extinguishing agents in a wide range of temperatures (up to 600 °C) and heat fluxes (up to 100 kW/m2), which are characteristic of forest fires. With the use of the experimental data obtained, it is possible to predict the completeness of evaporation of promising extinguishing liquids at different schemes of heat supply.