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Description of the impact characteristics of different types of balls has a great importance in sport science and in engineering. The primary objective of the present paper is to investigate the effect of the temperature on the impacts of different types of squash balls from a given company. The shots were performed using a self-built air-cannon. The impacts were recorded by a high-speed camera and the recorded videos were analyzed by an image-processing method based on a background subtraction technique. Summarizing the main dynamical parameters, we can conclude that increasing the initial speed will decrease the contact time, the coefficient of restitution (COR) and the rebound resilience, whereas these parameters increase at elevated temperatures. The compression tests revealed that within the low velocity range the deformation of the ball’s material and not the compression of the inner gas is the main contribution in the force needed to compress the ball. However, when the ball suffers large deformations, the internal air pressure has a huge effect on the rebound behavior. The measurements revealed that there is an optimal initial velocity distinct from the maximum one where the rebound velocity of the ball is higher than in all other cases. From the results we can state that the ball's overall stiffness grows as the temperature increases.

The batch mode electrical discharge machining (EDM) method has been developed to improve the throughput and accuracy in fabricating array structures, but the process suffers from insufficient debris removal caused by the complex electrode geometry. Tool vibration has been used to improve flushing conditions, but to date the underlying mechanism of the tool vibration on the micro EDM of array structures remains unclear. This study aimed to investigate the effect of tool vibration on the machining process by direct observation of the discharge phenomena in the discharge gap by using a high-speed camera. Micro EDM experiments using 9 and 25 array electrodes were performed, and the effect of tool vibration on the discharge uniformity and tool wear was evaluated. It was found that tool vibration improved the uniformity of the discharge distribution, increased the machining efficiency, and suppressed the tool wear. The discharges occurred in periodic intervals, and the intensity increased with the amplitude of tool vibration. The results of this study indicate that the vibration parameters determine the discharge period duration and intensity to achieve optimum stability and efficiency of the machining process.

This article contains the results of experimental tests of vibrations of a continuously variable transmission (CVT) belt transmission driven by a two-stroke internal combustion engine. The measurements were made with the use of a high-speed camera, which allowed to obtain results impossible to obtain with other measurement methods. The nonlinear integro-partial differential equation of vibrations of the moving belt is given. Based on a simplified linear equation, the observed effects on the amplitude–frequency characteristics obtained from the measurements are explained. An approximate formula is given that allows for determining the transmission belt velocities for which resonances occur.

Pulse laser grinding (PLG), as a cutting tool processing method, can not only achieve edge sharpening with high precision, but it can also produce surface modification. For example, polycrystalline cubic boron nitride (PCBN) tools processed by PLG can show increased hardness due to the reduction in defects. However, the mechanism of edge formation under PLG processing remains unclear. In this study, by observing the plasma generated during processing using a high-speed camera, the elementary process for each laser pulse of the PLG process was visualized. The plasma luminescence moved successively through four stages: multipoint luminescence, uniform luminescence, the downward movement of the luminous center, and faint luminescence. By comparing the results of three different laser pulse pitches (0.2, 2, and 20 μm), it was found that the pulse pitch had a significant influence on the PLG processing mode. When the pulse pitch was too small, the sidewall effect was likely to lead to local excess machining. The large pulse pitch resulted in processed surfaces that could not be fully covered by laser irradiation, and it was preferred to remove the decrease threshold subsequently. Thus, the moderate pulse pitch condition showed a superior processed surface compared to the others.

In this article, a feasibility study for the visualization of hidden damage using an integrated high-speed camera system was carried out. A thin, planar, and low-modulus high-density polyethylene plate with surrogate damage was chosen to represent a damaged structure for the proof of concept, and two different damage scenarios (mimicked by attaching lightweight rectangular/circular masses to the back of the plate) were investigated. The acoustic/ultrasonic guided waves were generated in the plate by a surface-mounted piezoelectric actuator under continuous sinusoidal excitation, and in-plane wavefield displacements on the surface of the plate were captured using a high-speed camera. In order to reconstruct the scattered wavefield, these in-plane wavefields which primarily include the fundamental symmetric wave mode S0 and fundamental shear horizontal wave mode SH0 (induced due to reflection/scattering of the incident S0 wave mode from the damage and plate boundaries) were then extracted using digital image correlation image analysis software. All the experimental parameters (e.g. material properties of the plate, excitation frequency, selection of lens, field-of-view, speckle size) were carefully designed, integrated, and optimized. In order to overcome the current hardware limitations (insufficient spatial/temporal resolution), sample interleaving was implemented to artificially enhance the frame rate and image stitching techniques were used to increase the total effective camera resolution. Together, these techniques provided a nearly 250-fold enhancement in the data acquisition capability of the high-speed camera. In order to fully demonstrate the efficacy of the sample interleaving technique, two frequencies were excited: 14 and 28 kHz, below and above the original Nyquist frequency, respectively. The first fundamental SH0 and S0 wave modes for both frequencies were successfully detected and identified, and the disturbances at the damage region were clearly observed in the scattered wavefield reconstructed with the SH0 mode in particular, as the SH0 mode has a shorter wavelength making it better suited for detecting smaller damage. The hidden damage was then visualized by employing a modified version of the phase-based damage imaging condition, wavenumber index, that was previously developed for visualizing hidden delamination damage in composites with a laser Doppler vibrometer scanning system.

Shot peening is a mechanical surface enhancement process that is extensively used in various industries to increase fatigue life of components. This process relies heavily on post-processing quantification such as Almen strip system. With the main objective of replacing the Almen strip system with suitable sensors, this study is performed with the intent of achieving real-time monitoring for the process and finding an alternative means to quantify it by correlating sensor signals to Almen intensity. The pressure drop across a typical shot peening nozzle using pressure sensors and its correlation to shot velocities using a high-speed camera and a ShotMeter™ obtained at different operating conditions was evaluated. The information from the pressure sensors and shot velocity was analyzed to ascertain the presence of any correlation with process inputs (pressure and mass flow rate) and process output (Almen intensity). By deploying pressure sensors at the inlet of the system and the nozzle, the study demonstrates the capability for a real-time monitoring and control of the shot peening process without using Almen strip system.

The use of image-based techniques in structural dynamics is constantly growing thanks to the decrease in the cost of high-speed cameras and the improvement in image processing algorithms. Compared to traditional sensors, such as accelerometers or velocimeters, the use of fast cameras for data acquisition allows the number of measurements points to be significantly increased. However, such an abundance of points, not always lead to an increased accuracy of damage detection algorithms. With this in mind, we compare different damage detection techniques by using displacement data and modal quantities. A small scale steel frame structure is used to validate the damage detection by using measurements acquired through a high-speed camera with different image processing techniques. The Hybrid Lagrangian Particle Tracking (HLPT) algorithm and Digital Image Correlation (DIC) are both used to extract displacement measurements from images. The results are compared with those obtained with seismic class accelerometers which are normally used in the lab for such an application. Damage localization and intensity have been determined through image-based measurements without losing the accuracy obtained with accelerometers., Funding acknowledgements: EU Research Fund for Coal and Steel 2017, Grant number 800687

Inom materialforskning och en stor del av den mekaniska och mekatroniska industrin finns ett intresse av att utnyttja blixtröntgen för att studera dynamiska händelseförlopp i inneslutna system, ej synbara med konventionella kameror. I och med att många rörelser inom de benämna områdena även sker i hyperhastighet så tillåter blixtröntgen statisk bildtagning av rörelser i flera km/s, med minimal rörelseoskärpa. Detta examensarbete har grundats i att utveckla och utvärdera koncept för en komplett systemuppställning inklusive höghastighetskamera för denna tillämpning. Syftet med arbetet har således varit att både identifiera och definiera produktens ingående produktkrav, för att spegla den funktion och syftet som önskas uppfyllas, och utifrån detta generera koncept för uppställningen på systemnivå, samt för separata komponenter. Slutligen har de utvalda koncepten utvärderats genom praktiska prestandatester för att kontrollera dess uppfyllelse av produktkraven. Datainsamlingen för arbetet skedde i form av flertalet praktiska experiment för insamling av kvantitativ data, samt återkommande uppföljningsmöten med involverade medarbetare för insamling av kvalitativ data. Undersökningen resulterade i ett koncept för en slutprodukt, benämnt funktionsprototyp som motsvarade och uppfyllde de definierade produktkraven vad gäller funktionalitet och prestanda. En diskussion fördes även för den kommande vidareutvecklingen av slutprodukten, inklusive färdigställandet av samtliga koncept och den följande designfasen. In materials research and a large part of the mechanical and mechatronic industry, there is an interest in using flash X-rays to study dynamic events in enclosed systems, not visible with conventional cameras. Since many movements within the named areas also take place at hyper-speed, flash X-rays allow to capture static images of movements in several km / s, with minimal distortion. This thesis has been based on developing and evaluating concepts for a complete system setup including a high speed camera for this application. The purpose of the work has thus been to both identify and define the product's included product requirements, to reflect the function and purpose that is desired to be fulfilled, and based on this generate concepts for the set-up at system level, as well as for separate components. Finally, the selected concepts have been evaluated through practical performance tests to check its compliance with the product requirements. The data collection for the work took place in the form of two practical experiments for the collection of quantitative data, as well as recurring follow-up meetings with involved employees for the collection of qualitative data. The study resulted in a concept for an end product, called an end concept that corresponded to, and met the defined product requirements in terms of functionality and performance. A discussion was also held for the further development of the end product, including the completion of all concepts and the subsequent design phase.

In this study, control research of chip morphology and removal is conducted theoretically and experimentally on the basis of the low-frequency vibration-assisted drilling process of titanium alloy. The chip morphology prediction model is established on the basis of the modified kinematic model, in which the shear angle variation, critical cutting thickness, and stiffness of a vibration generator system are considered. In terms of chip removal monitoring, a new monitoring method based on high speed camera is proposed in this paper. And the reliability of the new method is verified by comparing the signals obtained by the power sensor and the force sensor. An empirical prediction model for chip removal is also established on the basis of the modified kinematical model, the chip morphology prediction model, and the force balance analysis of fragmental chips. Validation experiments show that the mean error of chip radian, which can reflect the difference between the predicted chip morphology and the experimental one, is 6%. The mean error of the predicted chip removal index compared with the experimental one is 10.4%. The results obtained show that chip removal can be controlled effectively by low rotation speed, small chip radian, light chip weight, high minimum quantity lubrication cooling pressure, and high oscillation frequency. On the basis of the prediction model of chip removal, the effects of drilling parameters on chip removal behavior are analyzed, and the optimal drilling parameter combination with highest processing efficiency is given.

When an electrorheological fluid is located between two electrodes and an electrical voltage is applied to them, the particles in the fluid move and form chains along the electric field lines. This phenomenon is called the electrorheological effect. The exact behavior of the particles has not yet been studied completely. Some optical investigations of particle motion or behavior have been performed, but did not take into account the high dynamic range directly after the application of an electric field. This study is intended to help explain how the particles behave when they encounter an electric field and then try to align themselves with it. There is an investigation into how these chains develop in a microchannel within milliseconds. For this purpose, the particle behavior of the electrorheological fluid is investigated with high dynamic imaging using a microscope. A high-speed camera records videos of the first milliseconds at 3000 fps synchronously with the application of an electric field. The results provide a better understanding of the chain formation and particle behavior of the electrorheological effect in the high dynamic range and can be used for the design of electrorheological applications as well as simulations of the particle movement.

ispartof: pages:1-11 ispartof: SAE Technical Papers pages:1-11 status: Published online

The paper presents the possibilities of a high-speed camera in recording displacements of thin-walled workpiece during milling made of aluminum alloys, which allowed for an analysis in which it was compared to other methods of testing the deflection of such elements. The tests were carried out during peripheral milling with constant cutting parameters. Deflection of thin-walled workpiece due to cutting forces was measured using a high-speed camera and a laser displacement sensor. Additionally, the experimental results were compared with the theoretical results obtained with the use of the finite element method. The research proved the effectiveness of the use of high-speed camera in diagnostics of thin-walled workpieces during milling with an accuracy of up to 11% compared to measurements made with a displacement laser sensor.

Experiments were conducted to investigate the performance of choked cavitating flow in a transparent venturi reactor at different pressure ratios by high speed camera technique. Cavitation images of various flow conditions and corresponding pressure variations were analyzed to study the development performance of the cavitating flow. This work provides a thorough understanding of the evolution of cavitation regions, collapse mechanism, averaged wall pressure and pressure pulsation at different pressure ratios. The cavitation regions in venturi under choking flow condition can be divided into inception and developing region, fusion region and collapse region. Further analyses on the processed images reveal that cavitation performance can be approximately divided into two sections by a transition pressure ratio of 0.71. At smaller pressure ratios (pr 0.71), cavitation dynamics is governed by the shock wave. And the core position of collapse region moves upstream slowly with the increase of pressure ratio. The spectrum distribution of cavitation cloud in collapse region is concentrated and the peak frequency increases slowly at small pressure ratios. However, the spectrum distribution of cavitation cloud is relatively decentralized at large pressure ratios. The measured pressure data indicates that averaged pressure in diffuser goes through three stages at different slopes with the increase of pressure ratio under choking flow condition. In addition, the variations of pressure pulsation intensity (PPI) influenced by cavitation regions, collapse mechanisms, back pressure and collapse distance are exhibited in the present work.

Three-dimensional braided composite materials have been widely applied to engineering structure manufacturing. It is of a great importance to characterize the impact damage of the three-dimensional braided composite under various temperatures for optimizing the engineering structure. Here we conducted transverse impact deformation and damage of three-dimensional braided composite beams with different braiding angles at room and elevated temperatures. A split Hopkinson pressure bar with a heating device combined with high-speed camera was employed to test multiple transverse impact behaviors and to record the impact deformation developments. The results indicated that failure load, initial modulus, and energy absorption decreased with the increase of temperature, whereas the deformation increased slightly with elevated temperatures. We found that the impact brittle damages occurred earlier and the local adiabatic temperature raised higher when the temperature is lower than the glass transition temperature (Tg) of epoxy resin. While above the Tg, the impact ductile damages occurred later and the local temperature raised lower. The thermal stress distribution along the braiding yarn leads to cracks propagation in yarn direction. Part of the impact energy absorptions converted into thermal energy. In addition, the beam with larger braiding angle has high damage tolerance and crack propagation resistance.

Saturated pool boiling experiments were conducted in a scale-down three-dimensional downward facing hemispherical vessel. In this study, a high-speed digital video camera was employed to capture the bubble behavior along the overheated convex surface. The general morphology of coalescent bubble at the bottom center was analyzed based on the observed pictures and videos. The visualization results showed that the bubble behavior along the hemispherical curved surface was quite different from that on the plane and upward surfaces. It was found that the coalescent bubble was cyclical repeatedly forming a stratified vapor layer, and then randomly sliding upward along the convex surface. The downward facing boiling heat flux was directly related to the duration of the boiling cycles, which were obtained based on the visualization by high speed camera and the image processing technique. A Matlab program was developed to recognize and analyze the images, as well as to calculate the characteristic parameters of the coalescent bubble. The boiling cycle was almost constant during the nucleate boiling regime, which was independent with the heat flux level. This study also provided an in-depth physical understanding of the 3-D downward facing boiling process during ERVC that could be even useful for hydrodynamic modeling of the CHF phenomenon.

Slug flow is a prevalent and undesirable multiphase flow regime which occurs in many industrial processes, causing time varying stresses in pipes and supports and consequently causes structural fatigue damage and failure. In this study, a series of experimental tests were conducted to address the effect of the slug frequency on the stresses of structural pipes. The slug frequency was measured using non-intrusive measuring technique through utilizing Phantom 9.1 high speed camera, while the pipe wall strain was captured using bi-axial strain gauges. The effects of the superficial gas and liquid velocities on the slug frequency were investigated. Additionally, the relation between the slug frequency and the induced stresses was examined. Moreover, a Slug Frequency Stress Prediction Model (SFSPM) based on the exerted slug unit forces was developed and validated. The presented results revealed that an excellent correlation with a deviation of 0.7% between the predicted and experimental stresses was achieved.

Industrial bubble column reactors use to operate at high pressure and temperature. However, few experimental investigations have been performed under such severe conditions. In this work the effects of high pressure (0.1–6 MPa) and high temperature (293–473 K) on the bubble shape and rising velocity in silicone oil and paraffin are experimentally investigated. The experiments are carried out in a stainless steel bubble column of 50 mm I.D with three pairs of high strength quartz windows. The bubble flow is visualized and recorded through high speed camera. New correlations for bubble aspect ratio E are proposed by use of the experimental data. The correlations are divided into three parts in terms of Weber number and Morton number. For We > 12, bubble aspect ratio is independent of Weber number, and is only related to Morton number. For We

Faraday instability plays an important role to realize liquid atomization which has been widely applied in various fields. The spherical Faraday instability has different characteristics from the planar one. It is of great importance to understand the fundamental mechanisms of the surface deformation evolution and atomization of a spherical droplet induced by Faraday instability. In this paper, we first experimentally recorded the deformation and fragmentation process of a spherical droplet on a vertically vibrated plate with high speed camera. The results showed that the zonal, meridional and approximately circular standing waves in proper order exist on the surface of the spherical droplet with the increase of excitation amplitude. When Bo 3.0 , the modes of low (zonal) and high (meridional) order m of the spherical harmonic occur more easily, and as Bo is increased, the order m becomes closer to the intermediate value of spherical mode number l. The mechanism of droplet atomization is that a spike forms first on the droplet surface due to the impingement of the liquid flowing from the neighboring trough portions, and then a neck appears because of the velocity difference between the head and bottom of the spike, and the velocity difference determines whether the head liquid can form a sub-droplet ejected from the surface of the parent droplet. The Mathieu equation was derived by a linear theoretical analysis with inviscid and incompressible assumptions for the spherical Faraday instability, in which the parameters have different definitions from its planar counterpart. In the instability diagram, the iso-curves of larger linear growth rate deviate further from the ordinate axis and finally disappear. It is also validated that Lang’s equation is applicable to the spherical Faraday instability in low frequency.

International audience; Understanding the mechanism of chip formation during orthogonal cutting requires a local measurement of the displacement and strain fields in the cutting zone. These measurements can then be used in order to enhance/validate numerical simulation of metal cutting or calibrate material behavior laws for a better prediction of the thermomechanical loads inside the cutting zone. Particle tracking to identify the strain localization that is exhibited in the Adiabatic Shear Band (ASB) is a challenging task. These local measurements can be determined by images post-processing while using the Digital Image Correlation (DIC) technique or analytical models using streamline models or by micro grid analysis. Recently, the use of the DIC technique is widely increased. Texture quality has been shown to be an important factor. Various techniques of surface preparation are then discussed and classified in terms of the created pattern size. Tools for texture analysis are presented. The technique suitability for the kinematic fields measurement while using the DIC technique during machining is discussed. Various optical systems of the literature employed in the context of kinematic fields measurement during machining are discussed in this paper. The recent advances on the design of optical systems are given. Finally, the results of kinematic fields measurement during machining metallic alloys are analyzed.

Shear cutting is a prominent process in the chip-less separation of metallic sheet materials. The cut surface characteristics have been the basis for quality assessment but the shear-affected zone becomes increasingly important with regard to the functionality of the produced components, such as further processing or its final application. Multi-stage shear cutting processes may be used to specifically adjust the mechanical and geometrical properties of shear cut edges. Originally, multi-stage shear cutting was aimed at producing smooth and clean-cut surfaces with high-dimensional accuracy and improved load capacity. However, nowadays, it is also used to reduce the sensitivity to edge cracking, for example. In this paper, we present a novel approach for the experimental analysis of multi-stage shear cutting as a basis for advanced process analysis and validation. Moreover, the achieved results may serve for future database process design, modeling, and control. We developed an in-situ test design and measurement setup that preserves the real process boundary conditions of shear cutting. An enhanced high-speed optical full-field evaluation method based on optical flow methods allows local and time-resolved measurement of strain fields and strain rate fields for each shear cutting stage. A mapping of these state variables between the individual cuts enables us to analyze consistently the shear-affected zone throughout the whole multi-stage process and thus to characterize the final state of the shear-affected zone experimentally.

The transport and deposition of micro/nanoparticles in the lungs under respiration has an important impact on human health. Here, we presented a real-scale alveolar chip with movable alveolar walls based on the microfluidics to experimentally study particle transport in human lung alveoli under rhythmical respiratory. A new method of mixing particles in aqueous solution, instead of air, was proposed for visualization of particle transport in the alveoli. Our novel design can track the particle trajectories under different force conditions for multiple periods. The method proposed in this study gives us better resolution and clearer images without losing any details when mapping the particle velocities. More detailed particle trajectories under multiple forces with different directions in an alveolus are presented. The effects of flow patterns, drag force, gravity and gravity directions are evaluated. By tracing the particle trajectories in the alveoli, we find that the drag force contributes to the reversible motion of particles. However, compared to drag force, the gravity is the decisive factor for particle deposition in the alveoli.

A special mold provided with a glass window was used in order to directly evaluate the flow progression during the filling phase of the injection molding process in a thin-wall cavity and to validate the simulation of the process with particular focus on the hesitation effect. The flow of the polymer was recorded at 500 frames per second using a high-speed camera (HSC). Two unfilled thermoplastic polymers, acrylonitrile butadiene styrene (ABS), and polypropylene (PP), were used to fill two different 50 mm &times, 18 mm staircase geometry cavities, which were specifically designed to evaluate the hesitation effect with thicknesses of 1500, 1250, 1000, 750, 500 &micro, m (cavity insert no. 1) and 1500, 1200, 900, 600, 300 &micro, m (cavity insert no. 2). In addition to the video recordings, the simulations were validated using the timings and the data obtained by three pressure sensors and two thermocouples located in the cavity. For each injection cycle recorded on camera the machine data were collected to carefully implement the correct boundary conditions in the simulations. The analysis of the video recordings highlighted that flow progression and hesitation were mainly influenced not only by the thickness, but also by the velocity and the material type. The simulation results were in relatively good agreement with the experiments in terms of flow pattern and progression. Filling times were predicted with an average relative error deviation of 2.5% throughout all the section thicknesses of the cavity. Lower accuracies in terms of both filling times and injection pressure were observed at increasingly thinner sections.

International audience; Welding processes imply rapid solidification, in presence of high thermal gradient and strong fluid flows in the weld pool. This work presents, in the case of welding, an analysis of the coupling between solidification mechanisms and fluid flows at the macroscale and the microscale. An experimental setup was designed in order to observe in situ a fully penetrated weld pool generated on a Cu30Ni plate with a GTAW torch. At the macroscale, observations are carried out by three cameras: two cameras recording in visible light the top and the back side of the whole weld pool, and one infrared camera catching the thermal field on solid part at the back side. At the microscale, a high-speed camera, mounted with a microscope lens, is used to observe dendritic growth and fluid flows at the back side trailing edge of the weld pool. The observations provide a lot of data allowing analyses and discussions on the correlations between solidification mechanisms and fluid flows, with respect to welding parameters. Then, the experimental results are compared to theoretical results obtained from analytical modelling, in order to discuss the possible limitations of models and try to better understand the coupling between physical phenomena.

Experiments were conducted to investigate the cavity length pulsation characteristics in jet pumps with different area ratios during limited operation stage. Images of various cavitating flows were captured and analyzed to study the cavity length pulsation characteristics by high speed camera technology. It was found that the development tendency of time-averaged cavity length can be divided into two sections with different pulsation intensity by throat length. Further analysis indicated that the time-averaged cavity length is a function of area ratio and outlet pressure ratio independent of the inlet pressure. And the time-averaged cavity length decreases slowly and then faster with the increase of comprehensive parameters. Meanwhile, the cavity length pulsation can be decomposed into low frequency component and high frequency component. The pulsation intensity of low frequency component is relatively high during unstable limited operation stage, while it is at a low level during stable limited operation stage. Besides, smaller area ratio and inlet pressure result in larger pulsation intensity of low frequency component during unstable limited operation stage. The experimental points of high frequency component pulsation intensity collapsed around a V-shaped curve and it reached the minimum value when time-averaged cavity length is approximate to the throat length.

An experimental study on the Klystron effect of periodic injection modulated by pressure drop fluctuations on subsequent atomization is conducted. Time-resolved atomization backlit images and atomization Mie scatter images are captured by using the high speed camera. It is found that periodicity of forced atomization relies on pressure drop fluctuation amplitude and phase differences between atomization and pressure drop fluctuations relate to fluctuation frequencies. This feature of periodic atomization induced by Klystron effect corresponds to periodicities and high amplitudes of pressure fluctuations in unstable combustion chambers and chaos and low amplitudes of pressure fluctuations in stable combustions chambers. Drastically periodic varying of gross surface area of droplets with time was shown in Mie scatter images. The importance of periodic impinging jet atomization modulated by pressure drop fluctuations for acoustic liquid propellant combustion instabilities is illustrated. Keywords: Atomization, Combustion stability, Impinging jet injector, Klystron effect, Liquid rocket engine, Mie scatter

Measurements have been conducted to simultaneously consider both liquid films and droplets of the annular flow on a 3 × 3 simulating BWR fuel rod-bundle test-section with spacers. The optical system of a high-speed camera and a tele-microscope was used to record the backlight images at the gap between a corner rod and a side rod of the bundle at high time and space resolutions. The data at high time and space resolutions provided the detailed descriptions of the gas-liquid interface behaviors at the region close to the inlet as well as further downstream. The formation of the “singlet disturbance-crest” near the inlet which is suggested to be the first form of the disturbance wave was observed. An explanation on the mechanism of this formation process was proposed. Obtained images of three types of the entrainment process (bag break-up, ligament break-up, and droplet impingement) not only agreed with the previously proposed mechanisms but also included the information about wavy behavior right before and after these events and the created droplets. In addition, the side-view images of the disturbance waves at different stages of development were presented. These data can be used to evaluate other measuring techniques applied to the study of this type of waves. Moreover, a close-up observation at right up- and downstream of the spacer was conducted to describe the interactions between the two-phase flow and this structure. By using these new experimental arrangements, the interaction mechanisms among the wavy liquid film, droplets and spacer are discussed.

When the metal is melted by an arc plasma heating, convective flow is generated in the molten metal zone by various drag forces. The state of arc plasma used in this process is dependent on the current, voltage, shielding gas, and the evaporated component of the base material also affects the arc plasma. In this study, we show that oxygen content of the anode material affects the constriction of the arc plasma and changes the flow of molten metal by experiment and numerical analysis. First, after the generation of the arc plasma on ferritic stainless steels, which had different oxygen content and all other components were the same, the size of the arc plasma was compared by captured image using high speed camera. This size can be deduced from the brightness of the image, and it can be seen that the sizes of the two plasmas are slightly different from each other. Numerical simulation was carried out to confirm that these differences could affect the flow of the molten metal and final weld bead shape. As a result, the flow of the molten metal was completely different even with this slight change of plasma shape. These differences in molten metal flow was also observed in an experiment using a high speed camera. This change in flow can be explained by the interpretation that the Lorentz force is strengthened by the constriction of the arc plasma and the magnitude of the Marangoni force is increased by the increasing of thermal gradient. In conclusion, it was clearly confirmed that the oxygen content in the anode material affects the size of the fusion zone during arc plasma heating.

Advanced Heavy Water Reactor (AHWR) being developed in India is a vertical pressure tube type boiling water reactor. In case of AHWR the steam-water two-phase flow from the core is separated in horizontal steam drums purely due to gravity i.e. density difference between the steam and water. This simple principle eliminates the need for mechanical separators and associated system pressure drop. However, the separation efficiency is affected by the entrainment phenomenon, i.e. conveyance of water droplets by the separated steam out of the drum i.e. carryover. Carryover estimation for new equipment with existing empirical correlations may not be reliable and experimental investigations in relevant geometries are necessary. In the present work carryover process has been investigated in a test facility known as Air-Water Loop (AWL). The facility aims at simulation of gravity separation of two-phase flows relevant to AHWR steam drum, using air-water mixture. During the experiments, carryover at operating levels closer to exit has been measured. AWL also has a facility for optical measurements using high speed camera. Measurements on droplet size distribution have been carried out with shadowgraph technique at different operating levels. The present work also involves the analysis of carryover using 3-D Euler-Lagrangian simulations with OpenFOAM based solver.

The droplet transfer, plasma morphology and droplet morphology of laser arc hybrid welding process are collected and analyzed using high speed camera. The force magnitude and acceleration of motion droplets in the arc space are calculated by the image processing and mathematical calculations. The value and distribution of the recoil force from the metal vapor on droplets are calculated. The results show that the globular transfer mode corresponds to the welding current is approximate 180 A; the streaming transfer mode corresponds to the welding current is approximate 200 A. The laser has a compress effect on the arc, and the compression on the surface of the weld pool is stronger. The acceleration of the droplet detachment from wire is 70 m/s2 and 50 m/s2 for arc welding and laser arc hybrid welding separately. In the actual welding process, the reaction force of metal vapor on molten droplets is very small, when the distance between droplet and keyhole in the surface of the weld pool is 3 mm. The pressure difference on the surface between upper and lower of the droplet is great, which results the droplet coalescence and the transfer frequency slows down.

Purpose This paper aims to present a method to measure the rolling friction coefficient in an easy and fast way. The aim is also to measure the rolling friction coefficient between a small steel ball and a cylindrical aluminum surface. Design/methodology/approach An analytical model of the tribosystem of a freely rolling ball and a cylindrical surface is established. The rolling friction coefficient is evaluated from images recorded by a high-speed camera. The coefficient between a 1.58-mm diameter steel ball and a cylindrical aluminum surface is measured. A background subtraction algorithm is used to determine the position of the small steel ball. Findings The angular positions of the ball are predicted using the analytical model, and a good agreement is found between the experimental and theoretical results. Originality/value An optical method for evaluating the rolling friction coefficient is presented, and the value of this coefficient between a small steel ball and a cylindrical aluminum surface is evaluated.

This paper investigates the unsteady structures and the hydrodynamics of cavitating flows. Experimental results are presented for a Clark-Y hydrofoil fixed at α = 0°, 5° and 8°, for various cavitation numbers, from subcavitating flow to supercavitation. The high-speed video camera and the particle image velocimetry (PIV) are applied to observe the transient flow structures. Statistics of the cavity lengths, the velocity and vorticity distributions, as well as the turbulent intensities are presented to quantify the unsteady process. Meanwhile, the dynamic measurement system is used to record the dynamic characteristics. The experimental results show that the flow structures and the hydrodynamics of the cavitation vary considerably with various combinations of angles of attack and cavitation numbers. Under various conditions, the cavitation can be generally grouped as the inception cavitation, the sheet cavitation, the cloud cavitation and the supercavitation. The cloud cavitation exhibits noticeable unsteady characteristics. Experimental evidence indicates that the hydrodynamics are clearly affected by the cavitating flow structures, the amplitude of the load fluctuation is much higher in the cloud cavitating cases.

The study presents the die filling process of pharmaceutical powders using high-speed camera imaging. The objectives are to qualitatively visualize and to quantify the powder flow. A model die filling system with a shoe for powder storage and a moving die underneath the shoe was designed. The die filling process is captured through a high-speed camera and the images allow flow type identification and flow rate calculation. Correlations are generated to predict the fill ratios and flow rates based on particle size data, which could help in process understanding and optimization of die filling.

In this paper, we present the application of high-speed camera recordings in the mechanical analysis of machining processes. The modelling of the workpiece-machine-tool mechanical system is a very complex and challenging engineering problem having important features at multiple scales both in time and in space. The observation and experimental analysis of such phenomena are important in terms of developing and validating the corresponding mechanical models and results. This paper is dedicated to summarize our experiences regarding the optimal measurement set-up and instrumentation of mechanical investigations using a commercial Photron FASTCAM SA5 High-Speed Camera System. Furthermore, the applicability of high-speed camera recordings are also provided via the detailed case study of shear angle estimation and chatter detection.

Vibration measurements using optical full-field systems based on high-speed footage are typically heavily burdened by noise, as the displacement amplitudes of the vibrating structures are often very small (in the range of micrometers, depending on the structure). The modal information is troublesome to measure as the structure’s response is close to, or below, the noise level of the camera-based measurement system. This paper demonstrates modal parameter identification for such noisy measurements. It is shown that by using the Least-Squares Complex-Frequency method combined with the Least-Squares Frequency-Domain method, identification at high-frequencies is still possible. By additionally incorporating a more precise sensor to identify the eigenvalues, a hybrid accelerometer/high-speed camera mode shape identification is possible even below the noise floor. An accelerometer measurement is used to identify the eigenvalues, while the camera measurement is used to produce the full-field mode shapes close to 10 kHz. The identified modal parameters improve the quality of the measured modal data and serve as a reduced model of the structure’s dynamics.

An experimental study of hydrodynamic cavitation was conducted in a rectangular microchannel with a pillar. Distilled water was used as working fluid in an open fluid loop, and cavitation was obtained by applying a range of pressure differences between inlet and outlet tanks. High speed camera captured the flow patterns from inception to fully developed cavitating flow. A minimum delay of 10 min in the formation of cavitation was recorded in all experiments, which is due to the stochastic nature of phenomenon. Cavitation inception conditions were obtained in terms of the cavitation numbers, and a flow map was developed for subsequent cavitation flow. By analyzing time series of gray scale intensity of pixels inside the cavity, dominant frequencies were identified. Transient single phase numerical simulations were performed to gain a better understanding of the flow field in the microchannel, verify pressure measurements, and to relate the separation angle to the attached cavitation angle around the pillar. Emphasis was placed on characterizing the wake region downstream the pillar as it is closely related to the occurrence of the cavitation phenomena.

Interacting multi-scale physics in the Rotating Detonation Engine (RDE) lead to diverse nonlinear dynamical behavior, including combustion wave mode-locking, modulation, and bifurcations. Here, surrogate models of the RDE physics, including combustion, injection, and mixing, are sought that can reproduce mode-locked combustion waves through their interactions. These surrogate models are constructed and trained within the context of neural ordinary differential equations evolving through the latent representation of the waves: the traveling wave coordinate ξ=x−ct+a. It is shown that the multi-scale nature of the physics can be successfully separated and analyzed separately, providing valuable insight into the fundamental physical processes of the RDE.

International audience; 3D vision methods are a powerful tool for measuring full-field vibration patterns in the most varied types of surfaces. Digital Image Correlation is typically used to track noticeable features on the surface in order to measure local displacements on the tested system. In this work, a novel randomly structured light system based on laser speckle pattern projection and its calibration procedure are proposed for applying computer vision methods to the measurement of vibration in featureless or reflective objects without modifying them. A simple projector is used based on a laser beam affected by a diffuser element. A stereovision set-up with at least one high-speed camera is used to record video sequences from which the initial shape and evolution of the sample displacement are obtained. The vibration mode behavior of different steel plates are obtained using this full-field vibration measuring technique. The pros and cons of the proposed method are discussed and compared to similar stereovision set-ups.

International audience; Vibro-impact (VI) based control strategies exploit non-linear phenomena occurring during impacts between oscillating masses and vibrating structures to mitigate vibrations. They are known to be effective on a wide frequency range, in harsh environnement, and they are eco-friendly in comparison to some visco-elastic polymers used for the same application. Different assumptions emerge to explain energy dissipation such as material and contact effects, or dynamic energy transfers between the structure and the oscillating masses acting as non-linear absorbers. As classical vibratory measurement tools do not allow to accurately and easily measure what happens in the contact area and the motion of the absorber, it is difficult to validate and quantify the phenomenon. The purpose of the study is to take advantage of full field measurements of the vibro-impact phenomenon to characterise a vibro-impact absorber and to better understand the interactions occurring during impact. To reach this objective, a dedicated experimental set-up has been designed and a method involving Digital Image Correlation (DIC) and a high-speed camera is used to capture and reconstruct the motion of the oscillating mass. The characterisation allows to estimate the Coefficient Of Restitution (COR) and friction forces, and provides data that are used in two different contact modelling strategies based on the COR and on the Hertz contact theory. The quantities identified in this paper enable to better understand the physical

Hail impact damage on External Thermal Insulation Systems (ETICS) is increasingly recognised by insurance companies owing to increased storm occurrence frequency and storm intensity as well as more widespread installations of ETICS. In order to develop hail resistant ETICS for houses and to evaluate existing admission tests, high-speed-camera recordings of ice ball impacts at an angle of 45° and steel ball impacts at angles of 90° and 45° were used to characterize the impact process and to derivate the damage mode of hail impacts on facades. The major differences in the impact process of the European steel ball impact test (90°, ETAG 004) and the Swiss ice ball impact test (45°, VKF P. No. 8) are identified to be (1) a 20-40 % higher maximum indentation depth in the case of the 90° steel ball tests leading to more damage, (2) a shorter impact duration caused by the higher impact speed of the ice balls resulting in a higher strain rate and (3) the shattering of the ice ball at impact energies exceeding 6 Joule. Considerable surface parallel shear movements of the ball are observed for 45° impacts. Resulting shifts in the impact stress field cause the formation of an elongated damage pattern. The rebound of the impactor, an indicator for the elasticity of the system, is found to be 10 % higher in the 45° setups compared to the 90° setup. High strain caused by deep indentation depths is identified as the main reason for damage . First sub-surface fractures already occur shortly (tenth of milliseconds) after impact. In contrast, visible surface fractures form later during the impact processes at average indentation depths of 3-4 mm, i.e. at a time when strain localizes at the depression shoulders. Hence to avoid the observed brittle failure behaviour, the development of flexible materials with the ability to elastically accommodate impact strains is favourable to reduce hail stone impact damage. The European steel ball test is suitable to evaluate the hail resistance of materials in laboratory studies; however, ice ball tests provide more realistic conditions (impactor material, impact speed) and are therefore advisable for final admission of ETICS regarding hail resistance on-site.

Research in 60s and 70s started to deal with the shape of the chip characterization. It was possible then to do a limited study by means of measuring tool park. During such a study, different models for chip formation became familiar, such as the Time or Merchant model. The aim of article is to gain insight into some accompanying phenomena, occurring while cutting of different materials and with various tools. During an experimental design, the possible effects of different variables on each other and individually were considered. Two work-pieces (C45, POM) with two inserts (with two different edge design) were tested while changing of cutting speed and feed. During measurements cutting forces at 5000 Hz signal reception were tested or the evolution of cutting temperature at different experimental settings was evaluated. The chip characteristics are measured by a high speed camera. The camera is connected with PC for recording and controlling the experimental procedure in real-time. The frequency of High Speed Camera was similar than the frequency of the cutting force measuring system. This similarity is provided with the system set-up synchronization.

The objective of this work is to investigate yarn defects and specimen size on the impact compressive properties of 3-D angle interlock woven composites (AIWCs). The size effects on impact compressive properties were tested along in plane and out of plane directions. A new finite element model, with inherent defects in the geometrical model of yarns, was established to simulate impact compressive properties of the 3-D AIWCs. The model was further used to analyze size effects on impact compressive properties of 3-D AIWCs. We found the size effect on the 3-D AIWCs was not apparent both in experimental and numerical results; however, the random defects in yarns had a great effect on the compressive properties of 3-D AIWCs along different directions. The yarns effects will weaken the compressive stiffness and strength significantly.

The wing structure of an aircraft also served as a fuel tank containing fluid. The fuel tank and joint structure are made up of composite structures. Hydrodynamic ram (HRAM) effect occurs when the explosion or high speed object passes through the aircraft wing and high pressure is generated in the fuel tank. High pressure can cause failure in the fuel tank and on joint structure as well as other aircraft wing structures. To ensure the aircraft survivability design, we shall examine the behavior of the joint structures in HRAM effect. In this study, static tensile tests were conducted on four kinds of composite T-joints. The failure behavior of the composite T-joints was examined using strain gauges and high speed camera. The failure stresses and failure pressure of the composite T-joints were calculated by FEA. We also examined the validity of the Finite element modeling by comparing the results of FEA and static tensile tests.

When scaling the size of a body, size effects can occur. In micro range, the effects of surface tension dominate effects caused by gravitational force. This size effect is used within the laser blank rim melting process wherein the rim of a blank is locally melted by a laser beam. The melt pool forms cylindrical due to surface tension and thus locally increases the thickness of the blank, called cylindrical preform. In this paper process parameters are presented to generate cylindrical preforms with constant diameter at edges of blanks of 1.4301 (AISI 304). By observations with high speed camera and pyrometer it is found that, independent of the desired diameter of the cylindrical preform, the geometry of the melt pool needs to have a length-to-height-ratio of 3.0 ± 0.4 to generate a continuous cylindrical preform. An analytical model is set up and presented supporting this finding. For larger values of the length-to-height-ratio, the melt pool separates and forms droplets while for smaller values formation of preform was not detected.

In the tritium removal system applied in the thorium molten salt reactor, an axial gas-liquid separator was developed to separate the dilute dispersed bubbles from the reactor coolant. In order to quantify the separation efficiency for the separator and provide useful guidelines to design the separator, the separation trajectories of bubbles with different sizes in the swirl flow inside the separator are needed. To do this, an experimental study using the high speed visualizing and image processing was implemented to investigate the separation trajectories of bubbles under various bubble sizes and Reynolds numbers. A special bubble generator which is capable of generating single bubbles with controllable diameters was devised and incorporated into the separator test. By adjusting the parameters of the single bubble generator, i.e. the diameter of the needle and the rotation speed of the peristaltic pump, the trajectories of bubbles with diameters ranging from 0.2 mm to 1.1 mm, Reynolds numbers from 40,000 to 100,000 are recorded by the high speed camera and processed by a specialized image processing and analyzed. The results indicate that the bubble presents a convergent spiral path in the separating duration and eventually is entrapped by the air core. The separation length defined as the axial distance the bubble takes from the periphery of the separator to the air core will increase when decreasing the bubble diameter or increasing the Reynolds number. The experimental data obtained in this paper provides a detailed benchmark for the modeling of the bubble dynamics in the swirling flow.

Buried high explosive (HE) charges represent a high threat to military vehicles. The detonation of these charges can lead to significant momentum transfer onto vehicles and their occupants. A detailed understanding of the physical processes involved in the loading of vehicle structures is necessary for an optimization of effective countermeasures and protection systems. A quantitative description of the local momentum distribution on the vehicle underbody due to the detonation process is of special importance. In the following, a new test setup is presented that allows the experimental determination of the specific impulse distribution. It is based on a ring arrangement where the elements are nested into each other and the velocity of each ring is correlated with the local specific impulse at its position. The momentum transfer to a vehicle depends on a number of influencing factors such as: charge mass, embedding material (e.g. sand, gravel, clay), density, water content, saturation, depth of burial, ground clearance and vehicle shape. The presented technology is applied to quantify the influence of the embedding material (alluvial sand, quartz sand), the burial depth and the water content on the local specific impulse distribution. The obtained data can be used as initial condition for the numerical simulation of occupant safety assessment and as input for empirical modeling of momentum transfer on structures.

The formation of aerosols artificially is an interesting topic nowadays. This paper studied the interaction between water sheets and shock waves experimentally to seek the interaction mechanism and simulate the formation processes of water aerosol. Optical instruments like normal high speed camera and multiple-spark high speed camera were employed in the experiments and the data obtained was solved with common statistics software Statistical Product and Service Solutions (SPSS). Phase Doppler Particle Analyzer (PDPA) was also used to give a description of the water aerosol shown with diameter and velocity parameters. After the analysis of typical photos and data obtained, results showed that once past through by shock waves, the water sheet faced a surface stripping and breaking progress. The shock-wave induced in the layer of water is a compressive elastic-wave, whose magnitude is related to the ratio of acoustic impedance of the two media. Shock propagates through the thickness of the water-wall and when it reaches the next water/air interface is nearly totally reflected as a tensile wave. Such tensile wave will induce cavitation in the water-wall. Subsequent to cavitation, water keeps moving with uniform velocity and undergoes tensile strain, with small vapor bubbles forming while the water keeps moving in the direction of the blast. Finally, based on the dispersal mechanism, dimensionless parameters calculated were brought in to build the water dispersal model.

An experimental method for measuring dynamic behavior of materials at high temperatures (up to 1600 ℃) was proposed in this work. The experimental system includes a classical split Hopkinson pressure bar, a MoSi2 heating source for achieving high temperature, and two piston rods added to complement the double-synchronous assembled system. During the experiments, the specimen can be supported by asbestos and semi-Alumina ceramic tube. To estimate the thermal conduction of the tested specimen during the cold contact time (CCT), the time during which the hot specimen is in contact with the cold bars before being compressed, the CCT was measured experimentally based on an on-off circuit, and the finite element method (FEM) was also employed to calculate the thermal conduction of the tested specimen. High speed camera was employed to record images of the specimen during testing through a window in the heating furnace. For better understanding of the influence of oxidation of specimens, the system was also equipped with an argon supply system to prevent the specimen from oxidation at the high temperatures. To verify the ability of the proposed method to operate at high temperatures, experiments were conducted on an TC4 alloy at test temperatures ranging from 20 to 1400 ℃ at the strain rate of 2000 s−1, and on SiC at temperatures ranging from 20 to 1600 ℃ at the strain rate of 250 s−1.

This paper presents a novel study on performance of pulsating heat pipe using ammonia as working fluid. Firstly, a new full visualization experiment with high speed camera is conducted, to study the relationship between the flow patterns and thermo-hydrodynamics of the PHP. The tested PHP, consisting of 6 turns, is fully made of quartz glass tubes with 6 mm outer diameter and 2 mm inner diameter. The filling ratio for ammonia fluid is 70%. Wall temperature fluctuations of several key positions are recorded under a series charge of heat transfer rates, which are from 25 W to 520 W. In visualization results, the motion identities, flow pattern variations, breakup and coalescence between the vapor plugs and liquid slugs are illustrated and discussed. In addition, the actual velocity of the vapor is computed from the experimental measurement in this paper, which is never found in other literature but is very important for the mechanism study in theoretical model. Furthermore, a theoretical model including the dynamical characteristics and heat transfer is investigated coupled with the thermal driving force, friction force and capillary force variations as the flow patterns changed at different transport powers, which are derived from the full visualization experiment. The theoretical results are compared with the experimental results analytically, and the operating mechanism of PHP will be discussed in detail finally.