High-speed Photography System Research Articles

Using the multi-wire GMAW processes for controlling the formation of humping

Three-dimensional numerical models are established to investigate the convection in multi-wire GMAW processes. A high-speed photography system is used to capture the transient images of the weld pools. Based on the simulation and experimental results, the humping formation and suppression mechanisms are discussed. The results show that both the “push-pull” and outward flow patterns exist in the multi-wire GMAW weld pools, which help decrease the momentum of the backward fluid flow and widen the weld width. In high-speed GMAW process, there are three main factors that cause the formation of humping: the high momentum of the backward fluid flow, the capillary instability, and the large variation of the capillary pressure of the liquid channel in the welding direction. In twin-wire GMAW process, the first two factors are suppressed, humping is disappeared, but the variation of the capillary pressure of the liquid channel in the welding direction is still large, which causes the weld width uneven. All of those three factors are suppressed in triple-wire GMAW process, so sound weld bead can be obtained; the distance between the middle wire and trailing wire has little influence on the weld bead formation.

Experimental and numerical studies on the failure modes of steel cabin structure subjected to internal blast loading

Two series of experiments were conducted with different dimension and different masses of explosive. The failure processes of the side plate were recorded by using high-speed photography system. Damage features of the experimental results were analyzed. The results show that the damage degree increases with the increasing of TNT mass. In larger TNT mass cases, cracks produce in both the edge and the central of side plate, and some plates may eject out with relatively high launch velocity which are destructive to the adjacent cabins. During the deformation process, the edge and corner area of side plate may produce large deformation due to the intensified internal shock waves which is different from external explosion.Meanwhile, a number of numerical simulations were carried out by using the validated numerical method. Through analyzing the numerical and experimental results, three damage forms of cross-shaped damage, curve-shaped damage and sphere-shaped were observed. In cross-shaped damage form, six failure modes were concluded: plastic deformation (mode I); petalling in plates center (mode II*C); Capping in plates center (mode IIC); corner shear failure (mode IIIin); edge tearing (mode II); and shear failure over entire plate (mode III). In addition, the failure process and mechanisms of each mode were also analyzed.

Study on three-dimensional expansion characteristics of four wall combustion-gas jets in confined liquid space

To explore further the launch mechanism of the new underwater launching technology proposed in this paper, the expansion characteristics of four wall combustion-gas jets in confined liquid space must be studied firstly. The experimental device is designed, and the high-speed digital photographic system is adopted to obtain the expansion sequence processes of Taylor cavities formed by the four wall jets. Meanwhile, the influence of the injection pressure on the axial expansion property of the four wall jets is discussed. Based on the experiments, a three-dimensional unsteady mathematical model is established to simulate the turbulent flow process of the four wall jets expanding in liquid, and the temporal and spatial distribution laws of phase, pressure, temperature, and velocity and the evolution rules of vortices are illustrated in detail. Results show that, accompanied by the jets expanding downstream, the four wall combustion-gas jets get close to each other and achieve convergence eventually under induction of the interference effect between multiple jets. Meanwhile, the heads of the Taylor cavities separate from the observation chamber wall and offset to the central axis of the observation chamber with time going on. The numerical simulation results of the four wall combustion-gas jets coincide well with the experimental data.

Numerical and experimental investigation of the flow behavior of sand particles in core shooting process

The flow behavior of sand particles during the core shooting process has been studied by combination of computational fluid dynamics (CFD) simulations and experiments. In the CFD simulations, a two-fluid model (TFM), in which a kinetic-frictional constitutive correlation is incorporated, has been applied to describe the flow dynamics of core shooting process. The influences of turbulence model and boundary conditions on the modeling of core shooting process are further investigated. The simulation results indicate that there are certain sensitivities to the wall boundary condition in the sand flow behavior while no significant difference is observed between the results of the laminar and turbulence models. Using high-speed photography system and pressure measuring system, systematic experiments have been carried out to fully validate the model and good agreement is obtained between simulations and experiments. Based on the simulation and experimental results, the flow behavior of sand particles in the core box is analyzed, and the effects of nozzle dimension (D=6, 8, 10, 15mm) and shooting pressure (Pin=0.3, 0.4, 0.5MPa) on the hydrodynamic properties such as sand particle mass flux, sand volume fraction at the nozzle and distribution of sand velocity are discussed.

Expansion characteristics of multiple wall jets in cylindrical observation chamber

The objective of this study is to investigate the drag reduction effect of a new launch technology by utilizing propellant gases to drain off water in the front of the projectile inside the gunbarrel for submerged launch process of underwater gun. A static analogue visualized device was designed and the high-speed digital photographic system was adopted to investigate expansion processes of multiple wall jets in cylindrical observation chamber. The evolution laws of Taylor cavities can be obtained by dealing with the expansion sequence maps. Based on the experiments, a three-dimensional unsteady mathematical model is established to simulate the interaction process between the multiple wall jets and liquid medium, which can achieve the detailed distribution characteristics of phase, pressure, temperature and velocity in flow field. Results show that, by increasing four wall jets to eight wall jets, the decrease of the inlet turbulent kinetic energy of each jet leads to a decline in the initial axial velocity. However, the Taylor cavities achieve to converge more quickly for the case with more numbers of combustion-gas jets due to less nozzle interval distance. In addition, the convergence of Taylor cavities can enhance the drainage effect of the multiple wall jets and achieve excellent drag reduction effect for the underwater launching process, wherein the drainage effect for the case of six wall jets is the most outstanding.

Understanding of humping formation and suppression mechanisms using the numerical simulation

Three-dimensional numerical models are established to investigate the convection in normal and high speed GMAW processes. A high speed photography system is used to capture the transient images of the weld pool. Based on the simulation and experimental results, the differences of weld pool formation, convection and stability are researched. The humping formation mechanism in high speed GMAW process, and humping inhibition mechanism in the twin wire GMAW process are also discussed. The results show that in normal speed GMAW process, a clockwise circulation and a backward fluid flow pattern exist in the weld pool behind the arc. While in high speed GMAW process, three main factors are responsible for the humping formation: the high momentum of the backward fluid flow, the large variation of the capillary pressure of the liquid channel in the welding direction, and the capillary instability. The first two factors impede the backfilling of molten metal, and make the liquid channel susceptible to premature solidification, the final factor makes the weld pool unstable and susceptible to collapse. In the twin wire GMAW process, these factors are suppressed, in order to obtain sound weld bead, the trailing wire current should not be larger than the leading wire current.

Effects of nasal drug delivery device and its orientation on sprayed particle deposition in a realistic human nasal cavity

In this study, the effects of nasal drug delivery device and the spray nozzle orientation on sprayed droplets deposition in a realistic human nasal cavity were numerically studied. Prior to performing the numerical investigation, an in-house designed automated actuation system representing mean adults actuation force was developed to produce realistic spray plume. Then, the spray plume development was filmed by high speed photography system, and spray characteristics such as spray cone angle, break-up length, and average droplet velocity were obtained through off-line image analysis. Continuing studies utilizing those experimental data as boundary conditions were applied in the following numerical spray simulations using a commercially available nasal spray device, which was inserted into a realistic adult nasal passage with external facial features. Through varying the particle releasing direction, the deposition fractions of selected particle sizes on the main nasal passage for targeted drug delivery were compared. The results demonstrated that the middle spray direction showed superior spray efficiency compared with upper or lower directions, and the 10µm agents were the most suitable particle size as the majority of sprayed agents can be delivered to the targeted area, the main passage. This study elaborates a comprehensive approach to better understand nasal spray mechanism and evaluate its performance for existing nasal delivery practices. Results of this study can assist the pharmaceutical industry to improve the current design of nasal drug delivery device and ultimately benefit more patients through optimized medications delivery.

Dynamic response of expanded polystyrene concrete during low speed impact

The impact response of lightweight concrete filled with expanded polystyrene beads (EPS concrete) has been studied experimentally using a drop hammer system equipped with a high speed photography system. According to the impact force-time curves and the images of specimen surface obtained during the tests, the impact response of EPS concrete can be summarized as a four-stage procedure. The damage of EPS concrete is found to be a progressive process, which initiates from the upper part and develops downwards, leading to fluctuation of impact force. Based on the experiments, the energy dissipation capability of EPS concrete is evaluated, which demonstrates a dependence on the fracture mode of EPS concrete at the impact velocities in a range of 2–4m/s. The energy dissipation capacity of EPS concrete is found insensitive to the EPS volume fraction, when it is in a high range from 70.2 to 80.3vol%. Up to 18.6% increase in energy dissipation is observed in the concrete with 80.3vol% EPS under impact at 4m/s.

The dynamic behavior of double arc interference in high-power double wire pulsed GMAW

High-power double wire pulsed gas metal arc welding (GMAW) exhibits higher welding efficiency than traditional double wire pulsed GMAW. However, severe interference caused by the high-power double arc impairs welding stability. Based on the analysis of the double arc interference forming principle, two phase modes were examined in this study: the alternating phase mode and the synchronous phase mode. In both phase modes, the welding arc voltage and current were recorded, and double arc profiles were also achieved using the high-speed photographic system. Comparison of the experimental results showed that in high-power welding, the electric arc processes produced superior arc stiffness in synchronous phase mode compared to the alternating phase mode, and the magnetic blow was alleviated. Therefore, it can be concluded that the double arc interference in the alternating phase mode was more severe, while the double arc interference in the synchronous phase mode was significantly reduced.

Improving microalgal growth with small bubbles in a raceway pond with swing gas aerators

A novel swing gas aerator was developed to generate small bubbles for improving the mass transfer coefficient and microalgal growth rate in a raceway pond. A high-speed photography system (HSP) was used to measure the bubble diameter and generation time, and online precise dissolved oxygen probes and pH probes were used to measure the mass transfer coefficient and mixing time. Bubble generation time and diameter decreased by 21% and 9%, respectively, when rubber gas aerators were swung in the microalgae solution. When water pump power and gas aeration rate increased in a raceway pond with swing gas aerators and oscillating baffles (SGAOB), bubble generation time and diameter decreased but solution velocity and mass transfer coefficient increased. The mass transfer coefficient increased by 25% and the solution velocity increased by 11% when SGAOB was used, and the microalgal biomass yield increased by 18%.

Experiments on Jet Noise Reduction with a Liquid Column

A liquid column is designed and placed into the tail tube to effectively reduce the gas jet noise of a single rocket. The diffusion and mixing process of high-temperature high-pressure gas flow in the liquid water column in the air is studied by means of a high speed photographic system. The gas–liquid mixture jet noise has also been measured. The experimental results indicate that, when the liquid water column is put into the tail tube, the jet flow structure is changed and the jet flow parameters (velocity, temperature, etc.) are decreased due to the interaction of the gas jet with the liquid column. In addition, the jet noise is significantly reduced in the presence of the liquid column, compared with the condition without the liquid column. When the mass of the liquid column increases to 1.485 kg, the jet noise is reduced to a minimum in the shooter location. The peak sound pressure level also decreases with increasing polar angle. Most importantly, the thrust performance of the rocket engine is maintained when the liquid column is introduced.

Understanding of the weld pool convection in twin-wire GMAW process

A three-dimensional numerical model is established to study the temperature and fluid flow fields in the twin-wire gas metal arc welding (GMAW) process. The high-speed photography system is used to capture the images of the weld pool during the welding. Based on simulation and experimental results, the weld pool formation, convection, and stability in twin-wire GMAW process are investigated. Both “push-pull” and outward flow patterns exist in the twin-wire GMAW weld pool, which can contribute to decreasing the height of the bulge and increasing the width of the pool. The convection in the weld pool can proceed adequately, the arc force between the leading and trailing arcs is relatively balanced, surface tension normal force is uniform along the liquid channel, and the liquid channel is capillary stable, all of those contribute to the stability of the weld bead. The simulation results are in good agreement with those in the experiment.

Improving microalgal growth with reduced diameters of aeration bubbles and enhanced mass transfer of solution in an oscillating flow field

A novel oscillating gas aerator combined with an oscillating baffle was proposed to generate smaller aeration bubbles and enhance solution mass transfer, which can improve microalgal growth in a raceway pond. A high-speed photography system (HSP) was used to measure bubble diameter and generation time, and online precise dissolved oxygen probes and pH probes were used to measure mass-transfer coefficient and mixing time. Bubble diameter and generation time decreased with decreased aeration gas rate, decreased orifice diameter, and increased water velocity in the oscillating gas aerator. The optimized oscillating gas aerator decreased bubble diameter and generation time by 25% and 58%, respectively, compared with a horizontal tubular gas aerator. Using an oscillating gas aerator and an oscillating baffle in a raceway pond increased the solution mass-transfer coefficient by 15% and decreased mixing time by 32%; consequently, microalgal biomass yield increased by 19%.

Investigation on Dynamic Propagation Characteristics of In-Plane Cracks in PVB Laminated Glass Plates

Polyvinyl butyral (PVB) laminated glass has been widely used as an important component of mechanical and construction materials. Cracks on PVB laminated glass are rich in impact information, which contribute to its impact resistance design. In this paper, a three-dimensional (3D) numerical simulation model describing PVB laminated glass under impact loading is firstly established and validated qualitatively and quantitatively compared with the corresponding experimental results recorded by the high-speed photography system. In the meantime, the extended finite element method (XFEM) is introduced to analyze the crack propagation mechanism of laminated glass based on dynamic stress intensity factors (DSIFs) and propagations of stress waves. Parametric studies are then carried out to investigate the influence of five critical parameters, that is, plate dimension, crack length, impact energy, glass properties, and PVB properties, on crack propagation characteristics of laminated glass. Results show that the interaction between crack tip and stress waves as well as the propagations of stress waves corresponds to the fluctuations of DSIFs at crack tip. Both the structure and material variables are proven to play a very important role in glass cracking DSIFs and thus govern the crack propagation behavior. Results may provide fundamental explanation to the basic crack propagation mechanism on radial cracks in PVB laminated glass under impact loading conditions, thus to instruct its impact design improvement.

Experimental investigation into low-velocity water entry of cylinder structure

The process of low-velocity water entry is utilized on a large scale for the military and engineering purposes. However, there are rarely systematic experimental investigations into the low-velocity water entry of cylinder structure for reference. In order to obtain typical phenomena and relevant laws, we design a set of experimental facilities with adjustable parameters and better repeatability to study this process with a high-speed photography system. The influences of cylinder radius, initial velocity and entry angle on the process of lowvelocity water entry are tested. Results show that six typical phases exist in this process: structure submersion, necking, cavity formation, cavity abscission, spray at the free surface and jet formation. Three factors mentioned above are key parameters and influence the process in different degrees, and some laws obtained in this paper have a reasonable agreement with the theoretical results. Our results provide references for the relevant numerical researches and engineering applications.

Improving CO2 fixation with microalgae by bubble breakage in raceway ponds with up–down chute baffles

The aeration gas was broken into smaller bubbles with enhanced local solution velocity to improve CO2 fixation with microalgae in raceway ponds with up–down chute baffles. A high-speed photography system and online precise pH probes were used to measure bubble generation and residence times, which were affected by paddlewheel speed, aerator orifice diameter, gas flow rate, and solution depth. Bubble generation time (from gas reaching aerator orifice surface to completely escaping from the aerator) decreased because of the enhanced local solution velocity, whereas bubble residence time increased because of the vortex flow field produced by up–down chute baffles. Bubble generation time decreased by 27% and bubble residence time increased by 27% when paddlewheel speed was 10r/min with an aeration gas rate of 0.03vvm. The decreased generation time and increased residence time of aeration bubbles promoted microalgae biomass yield by 29% in optimized flow fields in raceway ponds.

Measurement and calculation of plasma drag force in arc welding based on high-speed photography technology and particle dynamics

Abstract To investigate the plasma drag force acting on the droplet in gas metal arc welding (GMAW), we used a high-speed photography system to image the metal transfer process, and proposed a method employing particle dynamics to measure the plasma drag force. Experimental results of the droplet diameter, mass, acceleration, plasma drag force and gravity acting on the droplet are presented. The results indicate that, with the increase of welding current, the droplet diameter, mass and gravity decrease, the droplet acceleration and plasma pressure increase, while the plasma drag force and the gravity acting on the droplet decrease. Moreover, we find that the plasma drag force is 10 and near 100 times the gravity acting on the droplet. The experimental values of plasma drag force and plasma pressure show good agreement with the theoretical value by fluid theory; their order of magnitudes are 10 − 4 N and 10 3 Pa, respectively, which demonstrates that it is an effective method to analyze the plasma drag force of welding arc.

Alternate Arcing Characteristics of the Triple-wire MIG Welding

As a kind of efficient welding method, triple-wire welding is taken seriously, and the arc shape and arcing characteristics are important factors in reflecting the stability of welding process and determining the weld quality and formation. Triple-wire metal inert-gas(MIG) welding system has been established in the test. In the welding process, the waveforms of welding current and arc voltage are acquired through the Mult Daq signal acquisition system while the arc behavior and metal transfer process are monitored by high-speed photography system synchronously. Then the whole welding process can be monitored in real time, the mechanism of alternate arcing in different metal transfer modes and the influence of arc voltage on alternate frequency are studied. The results of experiments show that when the welding power source can only supply less energy, the current distribution on three wires connected in parallel presents the rule of "shift", which results in alternate arcing among wires. Moreover, current distribution on three wires is decided by the location of wires in the arc space. As the increases of the arc voltage, the alternate frequency decreases. When the arc voltage is up to 34 V, the three wires start arcing simultaneously, no alternate arcing, and alternate frequency becomes 0 Hz.

Experimental investigation of non-stationary motion of single small spherical particles in an upward flow with different velocities

This experimental investigation focuses on carefully determining the drag coefficient of single spherical particles with considerable small diameters in non-stationary motion. A low-speed wind tunnel and a set of high-speed photography system are employed to confirm the displacement of each particle from its trajectory. Moreover, spherical particles of two different densities are used and the minimum diameter of these particles reaches 0.1mm. Meanwhile, the Basset force generated from the relative acceleration in the gas-particle flow is calculated approximately. The experimental results show that the maximum proportion of Basset force does not exceed 2.2%. In addition, the relationship of CD−Re for the experimental data is also determined. This research offers fundamental experimental results for industrial applications and also contributes to the research of non-stationary gas-particle flow.

Fracture toughness investigations on UHPC by spalling tests

AbstractUltra High Performance Concrete (UHPC) is defined as a new generation of concrete which shows improved performance and higher strength than traditional concrete. This allows to realize slender and much more durable structures and in this way significantly reduces the required resources. Despite its huge potential in construction, technical information about this new type of material is still limited. This contribution presents investigations on the dynamic mechanical behavior and properties of UHPC specimens by spalling experiments. Two different recipes were used to compare the properties. Due to the special specimen geometry (slender cylindrical) a flowable consistency was required to enable a sufficient degassing of the mixtures.For the test, a Split Hopkinson Pressure Bar (SHPB) has been modified and used. A high speed photograph system was focused on the fragmentation process during the test. On the basis of these experiments the dynamic E‐moduli as well as the dynamic tensile strength of the UHPC specimens were determined. By observation of the specific crack patterns on each tested specimen and corresponding times, the dynamic fracture energy is calculated.Numerical simulations also were performed and compared to the experimental result. It is concluded that the dynamic tensile strength of the UHPC increases at higher strain rates. The results of the current study provide technical information about fracture and dynamic behavior of UHPC and the obtained values could be used for future computational models. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)