High-speed Photography Method Research Articles

Dynamic response of hemispherical-shell sandwich structures subjected to underwater impulsive loading

In this study, experiments and numerical simulations are designed on aluminum sandwich structures with a hemispherical-shell core layer under underwater impact loading to investigate the dynamic response and energy absorption mechanisms. After the hemispherical-shell sandwich panels are designed and fabricated, they are loaded using an experimental apparatus incorporating fluid–structure interactions. The dynamic response of the sandwich panels is captured using the three-dimensional digital image correlation (3D-DIC) method of high-speed photography, and the energy-absorption mechanisms are analyzed via numerical simulation. This study primarily considers the effects of installation orientation, shock wave impulse and adhesive film on the sandwich panels. The results indicate that the deformation mode and impact resistance of the sandwich panels vary depending on the installation orientation. The displacement at the midpoint of the dry facesheet is linearly related to the shock wave impulse. At non-dimensional impulses exceeding 0.0085, the impact resistance of the forward installation target plate is higher. Additionally, the adhesive film significantly affects the deformation mode of the hemispherical-shell core layer. Its removal slightly increases the proportion of energy absorbed at the core. Quantitative and qualitative analyses of the structure-response-energy relationship are performed on the hemispherical-shell sandwich panels, thus providing guidance for investigations pertaining to the underwater impact resistance of future metal sandwich structures.

Experimental research on the atomization of transverse liquid jet

The transverse liquid jet is widely used in gas-steam ejection, scramjet engines, and other engineering applications. The research of transverse liquid jets can provide a basis for product design and has a wide range of engineering application value. A high-temperature and high-pressure jet experimental system was designed according to the characteristics of the cooling water jet atomization in the gas-steam ejection power system. The high-speed photography method was used to obtain the macroscopic structural characteristics of the transverse liquid jet. In this paper, experimental research of liquid jets under three conditions was carried out. The trajectory curve of the liquid jet considering momentum ratio and temperature is as follows: y/dj = 2.782q 0.422(x/dj )0.307(T/T0 )-0.785. It can provide theoretical support for improving the efficiency of gas-liquid mixing in power systems, engines, etc.

“Cutting effect” of needles on the raindrop characteristics

Plant leaves (both in the canopy and on the land surface) can substantially alter raindrop characteristics, which link to rainfall evaporation, infiltration, raindrop energy, and land surface erosion. The effect varies depending on the leaf morphology. Because of the magnitude difference between needle diameter (∼1 mm) and raindrops (up to ∼8 mm), there should be a “cutting effect” of the needle on falling raindrops. However, no study has beem performed to address how this effect alters raindrop characteristics. In this study, we investigated the effect using artificial water drops, high-speed photography, and staining method in the laboratory. Masson pine (Pinus massoniana Lamb.) needles were collected from the field including fresh green needles (FGN) withered yellow needles (WYN) partially decomposed needles (PDN). The needle properties (i.e., surface repellency, cross-section morphology, and flexural stiffness) were measured to determine the factor controlling the cutting effect. Results showed that after the cutting effect, one raindrop could be cut into up to 12 small raindrops. Their velocities owned a bimodal distribution. Compared to the diameter before the cutting effect occurred, the raindrop diameter decreased by an average of 59 %, and the raindrop velocity decreased by an average of 19 %. This caused a substantial decrease in the raindrop energy (∼85 %). The cutting effect included three sub-processes: collision, splitting, and interception. Our analysis suggested that the splitting process was the main reason for the cutting effect to reduce raindrop energy. The cutting effect was affected by the needle properties and raindrop falling heights. The cutting effect was enhanced when the needle developed from FGN and WYN to PDN. The cutting effect was positively related to the falling height of raindrops. Changes in the raindrop characteristics due to the cutting effect should enhance rainfall evaporation and infiltration and thus decrease soil erosion, which needs to be evaluated in further studies.

Measurement method and results of divergence angle of laser-controlled solid propellants used in space propulsion

The plume divergence angle is an important reference index for evaluating the thrust efficiency and propellant utilization of space propulsion systems. However, the characteristics of the dynamic variation of plume divergence angle over time cannot be measured using current methods. This paper utilizes high-speed photography and image processing methods to develop a strategy that can give a quick, non-destructive and real-time detection of the divergence angle. Effectiveness of the strategy is verified, and the characteristics of plume divergence angles of different laser-controlled solid propellants were further analyzed and fitted. The experimental results indicate that graphene could effectively reduce the divergence angle, while oxide-doped samples had larger divergence angles than alloy-doped and carbon-doped samples.

Precision Variable-rate Control System for Mini-UAV-based Pesticide Application

Mechanized and efficient pesticide application is an effective measure to prevent crop diseases, control pests, and ensure stable yield. For crops in greenhouses, due to the complex operating environment, the traditional mechanical spraying method will lead to excessive pesticide spraying and pesticide residues. Based on the ultrasonic sensor array, a small crop canopy volume calculation model is proposed, and the Pulse Width Modulation (PWM) control model of nozzle flow is established. The compensation time of opening and closing delay of the nozzle was determined to be 0.201 s by the high-speed photography method. The optimal operating speed was determined to be 0.3 m·s−1 through the benchmark test. Then, the precision variable spraying control method was integrated to develop the precision variable plant protection UAV based on an ultrasonic sensor array. The test results showed that the droplet deposition density was greater than 20 drop s·cm−2, and the droplet coverage rate of precision variable spraying was less than 30%. In the experimental area, the pesticide dosage of conventional and precision variable spraying was 0.24 L and 0.15 L, respectively, The precision variable-rate spraying saved pesticide usage by 34.5%. The system can realize precise variable spraying according to crop location and crop canopy volume changes. This study will promote the rapid development and application of precision spraying technology for small plant protection UAVs.

Visualization and analysis of the impinging spray and combustion characteristics in a lateral swirl combustion system (LSCS)

A lateral swirl combustion system (LSCS) was proposed to improve the fuel/air mixing and combustion processes, and previous results have validated its excellent combustion performance in direct injection diesel engines. To further explore the fuel/air mixture mechanism of the LSCS, the effects of convex edge height ha = 2–8 mm (corresponding to interferential angle δ = 133°-14°) on the impinging spray and flame were investigated visually in a constant volume combustion system employing high-speed shadowgraph, direct photography and two-color methods. The experimental results suggested that the combustion chamber with ha = 6 mm (δ = 48°) exhibited superior results in terms of total spray area and combustion. Regardless of whether ha increased or decreased from 6 mm, all of which impaired the synthesis result of the wall-flow-guided and interferential effects. Specifically, when the ha was 2 mm, the wall-flow-guided effect was decreased, and the excessive δ corresponding to 133° caused the neighboring wall jets to approximate a head-on collision, which inevitably resulted in the part of fuel accumulation. Modified ha to 8 mm (δ = 14°), the neighboring wall jets developed nearly in the same direction, diminishing the interferential capacity. Similar higher-temperature and higher-soot areas were observed during the burn-out process for ha = 2 and 8 mm compared to what was obtained at ha = 6 mm, except that the bright area of ha = 2 mm was located near the convex edge at the bottom, while ha = 8 mm appeared in a higher position. Therefore, the LSCS, through exerting the comprehensive effects of wall-flow-guided and interferential interactions, obtains the optimal fuel/air mixing and combustion effects.

Experimental study on continuous firing vibration response of the typical machine guns under different ground conditions

In order to study the influence of ground conditions on the continuous firing vibration response of typical machine gun, and find out under which conditions the machine gun is most stable. A high-speed photography method was used to measure the motion of multiple parts. The motion curve of each part in the shooting process are obtained, and the projectile dispersion are recorded. According to the results, the motion characteristics of each part is analyzed. The pitching and translational quasi-periodic motions of the whole gun under different ground conditions are compared by synthesizing the motion data of various parts. The working modes of gun tripod under different ground conditions are discussed, and are compared according to the corresponding projectile dispersion. The result show that, in quasi-periodic pitching motion, the upward pitching motion response of the gun under the condition of cement ground is large, the ability to restore the initial position is poor, and the corresponding vertical dispersion is the worst. Under the soil condition, the upward and downward pitching motion cycle of the gun is relatively stable, the ability to restore the initial position is strong, and the corresponding vertical dispersion is the best. In terms of quasi-periodic translational motion, the translational motion of the gun mount under the cement ground is the biggest, and the corresponding horizontal dispersion is also the biggest. Under the soil ground condition, the translational motion is the smallest, and the corresponding horizontal dispersion is also the smallest.

Study of domain wall dynamics in GdFeCo using double high-speed photography

Using the technique of double high-speed photography method, we show that an external magnetic field triggers in GdFeCo domain wall motion with velocities up to 1.2 km/s. The domain wall velocity saturates with an increase of the driving magnetic field. Contrary to earlier experiments on iron garnets, we did not succeed to detect any effect of femtosecond laser pulses on the domain wall velocity, even if the pulses were strong enough to reverse magnetization. Keywords: ferrimagnetism, domain wall dynamics, high-speed photography method, Faraday effect.

Biaxial Loading of Brazilian Disc Samples

The Brazilian test method has been widely used over the past 50 years to determine the indirect tensile strength of brittle materials, such as rocks and concrete. While the behaviour of Brazilian samples under conventional indirect tensile testing has been the subject of much research, the biaxial loading of a Brazilian sample under both horizontal and vertical compressive forces has rarely been studied. This study investigates the ultimate strength, crack propagation speed, fracture mode, and damage evolution in sandstone Brazilain samples using high-speed photography methods integrated with a newly designed hybrid biaxial-impact testing facility. The result shows that the samples fail under lower tensile stress than their Indirect Tensile Strength based on the principle of superposition.

Исследование динамики доменной границы в GdFeCo методом двукратной высоко скоростной фотографии

Using the technique of double high-speed photography method, we show that an external magnetic field triggers in GdFeCo domain wall motion with velocities up to 1.2 km / s. The domain wall velocity saturates with an increase of the driving magnetic field. Contrary to earlier experiments on iron garnets, we did not succeed to detect any effect of femtosecond laser pulses on the domain wall velocity, even if the pulses were strong enough to reverse magnetization.

Experimental and numerical study on the laminar flame characteristics for PODE3 and PODE3/iso-octane blends under elevated and sub-ambient initial pressures

• The laminar burning speeds for PODE 3 under different initial pressures are tested. • The laminar burning speeds for PODE 3 / iso -octane blends are investigated. • The accuracy of mechanism for PODE 3 and PRF/PODE n is validated. • The Markstein length and laminar flame instability are analyzed in detail. Polyoxymethylene dimethyl ether (PODE n ) is a promising alternative fuel for diesel due to its high oxygen contents (>40%) and high cetane number, thereby improving the thermal efficiency and reducing the pollutant emissions caused by the internal combustion engine. This study investigated the laminar burning speeds and Markstein length for PODE 3 and PODE 3 / iso -octane blends at wide equivalence ratios (0.7–1.6) and initial temperature of 408 K under elevated and sub-ambient initial pressures (0.5–4 bar) in a cylindrical constant-volume combustion vessel with high-speed Schlieren photography method combined with the nonlinear extrapolation model. The numerical simulation was also carried out to validate the accuracy of the mechanisms of PODE 3 and primary reference fuel (PRF)/PODE n blends and analyze the reaction sensitivities and the mole fraction profiles of key species. In addition, flame instability was discussed experimentally and theoretically. The results show that the laminar burning speed for PODE 3 decreases with the initial pressure, and the laminar burning speed for PODE 3 / iso -octane basically accords with the linear relationship to the PODE 3 volume fractions. The findings indicate that the kinetic effect has a dominant impact on the laminar burning speed for PODE 3 when compared with the thermal effect. The results also reveal that the Markstein length is negative only at an equivalence ratio between 1.5 and 1.6 under P = 2 bar, indicating that PODE 3 has more enhanced flame stability. Furthermore, the flame instability decreases with the increase of PODE 3 volume fractions, increases with the increase of initial pressure, and increases with the increase of the equivalence ratio. The differences between experimental results and theoretical results including the Markstein length, the critical radius and the critical Peclet number might be explained by the stretch rate results.

Experimental study on spray characteristics of fan nozzle for integrated afterburner in lateral airflow

The spatial distribution of fuel and high atomization quality plays a vital role in combustion performance enhancement for integrated afterburners. This study is based on integrated strut stabilizers using aviation kerosene (RP-3) as the atomizing medium. Specifically, the spray distribution characteristics of the fan nozzle were studied at ambient temperature and pressure, lateral airflow velocities within the range of 5–30 m/s, and a fuel supply pressure difference between 0.2 and 1.2 MPa. Macroscopic and microscopic spray characteristics were studied by high-speed photography method, Spraymaster, and ParticleMaster system respectively. The results show that mean droplet diameters decreased with an increasing lateral airflow velocity and a decreasing fuel supply pressure difference. The recirculation zone at the back of the struts will have an entrainment effect on the downstream of the spray, making part of the spray bend toward the recirculation zone. The results of the spray organization of a fan nozzle in this study can be used to support the design of new integrated afterburners.

Experimental investigations of underwater laser propulsion microspheres based on a tapered fiber propulsion system

An underwater propulsion microsystem is proposed in this work, which employs a nanosecond laser pulse out from the tapered fiber tip. Noteworthily, the system can generate a directional shock wave (or plasma) to propel the polystyrene (PS) microsphere. Through simulation, the shock wave propagation characteristics and the bubble dynamic are investigated. Experimentally, high-speed photography method is employed to obtain the motion image of microsphere. The results show that the propulsion efficiency is dependent on the laser energy. Meanwhile, we explain the role of the bubble dynamic process in propelling microsphere, and find that the bubble diameter increases with the laser energy. In addition, an experiment is performed to separate and remove the PS microsphere clusters in water at fixed point. Compared with conventional technology, this new method has advantages of high controllability, directional and non-contact, and can be used for directional manipulation of underwater microstructures and removal of contaminated microspheres in water environments.

Ignition, lean blowout, and flame propagation in a combustor using flameholder with a trapped vortex cavity

In this study, experiments are carried out to investigate a combustor based on the trapped vortex flame stabilization concept. The combustor involves a pilot trapped vortex cavity and a radial V-shaped flameholder. Multiple tests are conducted to measure the ignition and lean blowout performance (LBO) under a wide range, especially under sub-atmospheric pressures. High-speed photography methods are applied to capture the ignition process. The results showed that in sub-atmospheric pressure conditions, the ignition and LBO performance, flame area, and flame radial penetration length are all experiencing a significant decrease, while increasing inlet Mach number and temperature have both positive and negative impacts. Different periods of the ignition process are sorted by post-processing the images; during the ignition, the pilot flame rotates with the main vortex and propagates along the cavity; the flameholder entrains the flame into the mainstream zone. The study would establish a fundamental overview of the performance of this structure under sub-atmospheric pressure, further promoting the optimization and application of the cavity-based flame stabilization conception.

Flow field analysis for multilaser powder bed fusion and the influence of gas flow distribution on parts quality

PurposeThis study aims to investigate the influence of the gas-flow field distribution and design on the parts quality of 316L stainless steel and the vapor–spatter behavior.Design/methodology/approachBased on the hot-wire wind speed test method, the exact value of the gas velocity at different locations was accurately measured to establish the effect on the porosity and the mechanical properties of the parts. The influence of the placement of single or dual blow screens on the performance of the parts quality was also studied. Through scanning electron microscope and energy dispersive spectrometer, high-speed photography and other methods, the influence mechanism was explained.FindingsIt was found that too high or too low gas velocity both play a negative role, for 316L stainless steel, the range of 1.3–2.0 m/s is a suitable gas field velocity during the multilaser powder bed fusion process. And printing quality using dual blow screens is better than single.Practical implicationsThe optimization of gas field design and optimal gas velocity (1.3–2.0 m/s) applied during laser melting can improve the quality of ML-PBF of 316L stainless steel.Originality/valueThis study showed the influence of the gas field on the spatter–vapor in the process during ML-PBF, and the unfavorable gas field led to the formation of pores and unmelted powders.

Collapsing behavior of a spark-induced cavitation bubble near the air bubble attached to the tube nozzle

Air entrainment has been proved to be an effective method to weaken the cavitation damage. The objective of this paper is to apply high-speed photography and schlieren optical method to investigate the collapse behavior of cavitation bubble near the air bubble. The corresponding data such as bubble collapse time, collapse position and the velocity of collapse jet are analyzed. Results are presented for a cavitation bubble generated directly above an air bubble under a wide range of dimensionless standoff distances. The results show that (1) four distinctive patterns are identified by the collapse direction of the cavitation bubble and the interaction between the cavitation bubble and the air bubble. (2) The dynamic features of the cavitation bubble at collapse stage vary evidently at different patterns, including the collapse direction, high-speed jet and shock waves. (3) Compared with the cases that the cavitation bubble does not merge with an air bubble, the velocity of collapse jet and the intensity of shock waves are extremely smaller when the cavitation bubble merging with the air bubble. Investigating the influence of air bubble on the cavitation bubble has great significance to understand the mechanism of air entrainment to reduce cavitation damage.

An investigation on the perforation resistance of laminated CFRP beam and square plate

Analysis of the laminate's perforation resistance and the damage behavior is challenging due to the complex physical and geometric configurations. This work studied the mechanical behaviors both of carbon fiber reinforced plastic (CFRP) beam and square plate under transverse local load, including quasi-static indentation load and impact load. High-speed photography and non-invasive damage detective methods were used to capture specimens’ dynamic deformation, damage process, and resultant damage. Experiment results indicate that the CFRP specimens of the beam shape show higher perforation resistance as well as more damage patterns than that of the square shape. In addition, it was validated through numerical simulations by considering the strain-rate effect with rate-dependent constitutive model compiled through subroutine VUMAT.

Phase Distribution in the Tip Clearance of a Multiphase Pump at Multiple Operating Points and Its Effect on the Pressure Fluctuation Intensity

Tip clearance has a great effect on the flow and pressure fluctuation characteristics in a multiphase pump, especially at multiple operating points. The phase distribution and pressure fluctuation in tip clearance in a multiphase pump are revealed using the CFD (computational fluid dynamics) technology and high-speed photography methods. In this paper, the phase distribution, the gas-liquid two-phase velocity slip, and the pressure fluctuation intensity are comprehensively analyzed. Results show with the increase of the tip clearance, the multiphase pump pressurization performance is obviously deteriorated. In the meantime, the gas accumulation mainly occurs at the hub, the blade suction side (SS), and the tip clearance, and the maximum gas-liquid two-phase velocity difference is near the impeller streamwise of 0.4. In addition, the tip clearance improves the gas-liquid two-phase distribution in the pump, that is, the larger the tip clearance is, the more uniform the gas-liquid distribution becomes. Furthermore, the gas leads to the maximum pressure fluctuation intensity in the tip clearance which is closer to the tip leakage flow (TLF) outlet, and has a greater effect on the degree of flow separation in the tip clearance.

Some considerations for designing a pneumatic micro-droplet generator

Micro-droplet ejection is a liquid dispensing technology that has potential applications in many fields. Specifically, pneumatic ejection is actuated by a solenoid valve, which is set to ‘conduction’ state for a brief period of time Δt. High pressure gas of P 0 enters the liquid reservoir, then releases through a venting tube, creating a oscillating pressure waveform P(t), forcing the liquid out through a tiny nozzle to form a micro-droplet. For each actuation, P(t) is acquired by a high-speed pressure sensor, and the ejection state is obtained by high-speed photography and image processing methods. Some issues for the design of pneumatic micro-droplet ejector are discussed. For simulation of P(t), it is proposed within an electro-acoustic analogy picture that the acoustic resistance of the venting tube is mainly due to viscous effect and may vary with time during the whole ejection process. Based on this assumption, the calculated P(t) is more consistent with the actual measurement. Experimentally, the droplet ejection process for different length of venting tube is studied. With P 0 and Δt set, by increasing the venting tube length L, both the peak value P MAX1 and duration of the first positive pressure period increase, and more droplets are ejected from a single actuation. By setting different P 0, P MAX1 for different L is tuned to an identical and appropriate value, so that single droplet is ejected due to the first positive pressure period. However, with the increase of L, the peak value of the second positive pressure period P MAX2 increases. There is a certain probability that another droplet is ejected. It is realized that the increase of L can reduce gas consumption, but the multiple ejection is a drawback that should be considered in the design of pneumatic ejection system.

Behavior of bubble plume in shear-thinning crossflowing liquids

The behavior of bubble plume in crossflows was investigated by experimental and theoretical methods. The high-speed photography method was applied to analyze the visualization of bubble plume in tap water and carboxyl methyl cellulose (CMC) aqueous solution. The influence of crossflow velocity, superficial gas velocity and rheology of liquid phase on the inclination trajectory of bubble plume was studied. The results indicated that the trajectories of bubble plumes in tap water and CMC aqueous solutions approximated linearly, while the inclination characteristic of the bubble plume in CMC aqueous solutions were significantly different from those in tap water due to the effect of the rheological properties. The inclination angle of bubble plume in CMC aqueous solution was one-third more than that in tap water at high crossflow velocity. A correlation was developed via dimensional analysis to predict the inclination trajectories of bubble plumes in Newtonian and shear-thinning non-Newtonian fluid system. Considering the non-Newtonian rheology, the modified integral model of bubble plume was applied for theoretical calculation of centroids of bubble plume in crossflow.