Reconstruction and interpretation of photon Doppler velocimetry spectrum for ejecta particles from shock-loaded sample in vacuum

The photon Doppler velocimetry(PDV) spectrum is investigated in an attempt to reveal the particle parameters of ejecta from shock-loaded samples in a vacuum. A GPU-accelerated Monte–Carlo algorithm, which considers the multiplescattering effects of light, is applied to reconstruct the light field of the ejecta and simulate the corresponding PDV spectrum.The influence of the velocity profile, total area mass, and particle size of the ejecta on the simulated spectra is discussed qualitatively. To facilitate a quantitative discussion, a novel theoretical optical model is proposed in which the singlescattering assumption is applied. With this model, the relationships between the particle parameters of ejecta and the peak information of the PDV spectrum are derived, enabling direct extraction of the particle parameters from the PDV spectrum.The values of the ejecta parameters estimated from the experimental spectrum are in good agreement with those measured by a piezoelectric probe.

Measurement of two-phase velocities in bubble flows using laser Doppler velocimetry

The measurement of two-phase velocities in bubble flows using laser Doppler velocimetry(LDV)is studied.The key to the problem is to differentiate the LDV signals from bubbles and tracers,based on which the two-phase velocities can be characterized.In this study,two experiments are carried out.Firstly,the bubble-chain experiment is performed to investigate the optical response of bubble surface and the corresponding LDV signal.The optical response shows that the light received by the LDV detector is dominated by the reflection component,which is similar to specular reflection to some extent.There are three typical patterns of signals of large bubbles passing through the measurement volume,all of which are with high amplitude and saturated.Then,the upward-flow experiment is conducted to study the statistical characteristics of large bubbles as well as micro tracers and micro bubbles.The results show that the amplitude of signal of millimeter bubbles is about an order of magnitude larger than that of tracers or micro bubbles.Based on this significant difference of the amplitude,we propose a phase discrimination method to distinguish two-phase signals.The capability of the proposed method is tested in a complex bubble flow,and its reliability is verified by bubble tracking velocimetry(BTV)technology.

Dynamic Testing Technique Based on Multi-channel Photonic Doppler Velocimetry for Investigating the Dynamic Behavior of Materials

In the present paper,more attention is paid to develop a new optical measurement approach of split-Hopkinson pressure bar(SHPB)and wave propagation inverse analysis(WPIA)by using multi-channel photonic Doppler velocimetry(PDV).Based on the particle velocities measured by PDV,the dynamic stress-strain curve of material is obtained in SHPB tests.The strain is determined by the radial particle velocity of specimen,and the stress is determined by the free surface particle velocity of the transmit ted bar.The results obtained by the new method coincide with those obtained by the conventional strain gauge measurements.The new method is non-intrusive and insensitive to electrical noise,making it significantly more reliable than strain gauges.Using the oblique incidence of laser beam,a series of particle velocity wave propagation signals for long rod specimen are measured simultaneously.Based on the measurements of particle velocity profile,the dynamic constitutive response of polymethyl methacrylate(PMMA)is det ermined by WPIA method.The comparison bet ween the dynamic st ress-s train curve and the quasi-static one indicates that the strain-rate effect must be taken into account for PMMA.

Applicability limits of the DAX test in plastic bonded explosives

The Disc Acceleration e Xperiment(DAX)is one of the most recent experimental methods of performance characterization of new energetic materials.A cylindrical explosive charge accelerates a thin metallic disc and its velocity is measured continuously using photonic Doppler velocimetry.The detonation velocity is measured simultaneously.The DAX test can be used to obtain the Chapman-Jouguet(CJ)detonation pressure and to describe detonation products expansion using reduced amount of explosive.A series of DAX tests was performed at various charge diameters and disc thicknesses with Semtex 1 A plastic bonded explosive and sensitized nitromethane.The DAX-like evaluation was also applied to previously measured data of Semtex 1A and A-IX-1 explosives.The optimum disc thickness is determined by the disc to explosive mass ratio of 0.01-0.08.The repeatability of the Semtex 1 A detonation pressure results is about four times lower compared to the pressed and liquid explosives.

Perinatal Morbidity, Mortality, and Neurodevelopmental Outcomes of Neonates with Fetal Growth Restriction

Objective: This study aimed to assess perinatal morbidity, mortality rates, and neurodevelopmental outcomes in the management of fetal growth restriction (FGR) at a single tertiary institute. Methods: Among 2465 deliveries between 2013 and 2019, 109 cases of FGR were reviewed retrospectively for causes, indications for pregnancy termination, perinatal death, overall neonatal outcomes, and long-term prognosis. Results: Excluding FGR due to congenital anomalies (n = 17), the mortality rate was 3.3% (3/92). One neonate delivered at 23 weeks developed cerebral palsy (1.1%). Retinopathy of prematurity occurred in four neonates (4.3%). Neurodevelopmental disorders were present in six neonates (6.5%), all of whom were delivered at 32 - 38 weeks. Significantly lower gestational age at delivery, lower birth weight, and higher umbilical artery resistance indices were observed in neonates with neurodevelopmental disorders. Conclusions: Intact survival before 27 weeks of gestation at delivery with FGR is uncommon. Neurodevelopmental disorders may still develop after delivery at 32 - 38 weeks;consideration should be given to the timing of delivery usingfetal ductus venosus Doppler waveforms measurements to reduce neurodevelopmental disorders.

Hemodynamic Fetal Response to Maternal Isometric Exercise in Pregnant Patients with Diabetes

Background: Studies on physical activity during pregnancy and its impact on mother and fetus are still limited. International protocols consider only aerobic exercise and fail to provide information about other modalities such as isometric exercise. Isometric exercise promotes cardiorespiratory resistance and muscle strengthening, but it is rarely tested on pregnant women because it increases maternal blood pressure and can subsequently affect placental circulation. Objectives: To assess the fetal response by use of Doppler study in diabetes pregnant women submitted to isometric exercise. Methods: A cross-sectional experimental study was conducted on 25 diabetes pregnant women with gestational age between 26 and 36 weeks. The patients were submitted to isometric handgrip, and data were collected from the mother (blood pressure, heart rate and Doppler velocimetry for the uterine arteries) and from the fetus (heart rate, Doppler velocimetry for the umbilical artery, middle cerebral artery and ductus venosus). All variables were collected before, during and after the isometric handgrip. Results: There was a significant reduction in the pulsatilityindex (average values pre 0.77 ± 0.30, trans 0.65 ± 0.22, and post 0.75 ± 0.22, with p = 0.001), resistance index (average values pre 0.49 ± 0.12, trans 0.44 ± 0.10, and post 0.48 ± 0.90, with p =

高压短脉冲作用下HNS-Ⅳ型炸药的全发火冲击起爆判据

为了确定Hexanitrostilbene-Ⅳ(HNS-Ⅳ)炸药在高压短脉冲作用下的全发火冲击起爆判据参数,采用Exploding Foil Initiation system(EFIs,爆炸箔起爆系统)驱动三种厚度的聚酰亚胺飞片(12.5,40μm和50μm)撞击HNS-Ⅳ炸药柱,用升降法进行发火试验,获得了三种厚度飞片对应的最小全发火充电电压,Photon Doppler Velocimetry(PDV)方法获得最小全发火充电电压下飞片的撞击速度分别为3400,3100 m·s^-1和2930 m·s^-1。基于冲击波理论和动力学仿真,分别获得三种厚度飞片在该撞击速度下撞击HNS-Ⅳ型炸药的界面压力p、界面粒子速度u和持续时间τ,通过数据拟合确定HNS-Ⅳ型炸药在高压短脉冲作用下的全发火冲击起爆判据参数。研究结果表明,对于装药密度为1.56 g·cm^-3的HNS-Ⅳ装药,在撞击界面压力为10~13 GPa和持续时间为4.0~8.7 ns的范围内,全发火pnt判据为:p2.88τ≥7.21。

Experimental Investigation of Single-phase Flow in Structured Packing by LDV

To date, many models have been developed to calculate the flow field in the structured packing by the computational fluid dynamics （CFD） technique, but little experimental work has been carried out to serve the vali-dation of flow simulation. In this work, the velocity profiles of single-phase flow in structured packing are measured at the Reynolds numbers of 20.0, 55.7 and 520.1, using the laser Doppler velocimetry （LDV）. The time-averaged and instantaneous velocities of three components are obtained simultaneously. The CFD simulation is also carried out to numerically predict the velocity distribution within the structured packing. Comparison shows that the flow pattern, velocity distribution and turbulent kinetic energy （for turbulent flow） on the horizontal plane predicted by CFD simulation are in good agreement with the LDV measured data. The values of the x-and z-velocity components are quantitatively well predicted over the plane in the center of the packing, but the predicted y-component is sig-nificantly smaller than the experimental data. It can be concluded that experimental measurement is important for further improvement of CFD model.

Numerical and physical simulation of a twin-roll strip caster

The 1：1 water model of a twin-roll strip caster was set up based on the Froude number and the Reynolds number similarity criteria. A new type metal delivery system was designed for the twin-roll strip caster. The level fluctuation and the fluid flow in the pool of the water model were measured using the level detector and the 3D-LDV （laser Doppler velocimetry） technology. It is shown that a wedged delivery system can produce the desirable level fluctuation and even fluid flow distribution in the pool Numerical simulations for the water model were performed. Comparisons between the numerical and physical simulation results show good agreement near the side dams.

Intensity Tuning in Single Mode Microchip Nd：YAG Laser with External Cavity

We investigate the characteristics of intensity tuning in a single mode microchip Nd：YAG laser with an external cavity. The undulation of laser intensity in a period of A/2 change of the internal cavity length is observed. Two different optical feedback cases are performed. One is an external cavity reflector perfectly aligned and the other is an external cavity reflector tilted. However, the fluctuation frequency of laser intensity in a period of A/2 change of the internal cavity length in these two cases is found to be determined by the ratio of external cavity length to internal cavity length. Meanwhile, for the tilted external cavity, the fluctuation frequency is also related to multiple feedbacks in the tilted external cavity.

Online measurement of solids motion in fluidized bed reactor with different distributor for Fischer–Tropsch synthesis

In this paper, the distributions of particle velocity in a gas–solid fluidized bed with branched pipe distributor or circle distributor were measured by using a laser Doppler velocimetry. Our results show that, within a certain range of superficial gas velocity, when using circle distributor, the particle velocity is large and the distribution of the particle velocity is even more compared with the branched pipe distributor. On the basis of the amplitude of tangential movement statistics, the amplitude of tangential movement statistics(AVATMS) decreases with increasing the axial height under the appropriate superficial gas velocity.

JOINT INVESTIGATION OF ROTATING FLOW WITH VORTEX BREAKDOWN USING CFD, VISUALIZATION AND LDV

Vortex breakdown of the steady axisymmetic rotating flow in a confined cylindrical container with a rotating endwall was numerically and experimentally studied. High-quality precision-controlled turntable facilities were established at Shanghai Jiaotong University and Tokyo Denki University independently. Collaborative investigations of vortex breakdown were carried out using CFD, Laser Doppler Velocimetry （LDV） and streakline visualization, respectively. The characteristics of vortex breakdown were delineated in terms of comparative investigation using numerical and experimental results. SIMPLEC scheme and FMG multigrid was applied to numerical simulation. Numerical simulation was extensively compared with streakline visualization and LDV measurements, showing qualitative and quantitative agreements.

Experimental investigation of velocity fluctuations in a radial diffuser pump

The strong interaction in a radial pump due to the relative movement between the impeller and the diffuser may excite not only strong pressure fluctuations but also velocity fluctuations. In this paper, the laser Doppler velocimetry （LDV） technique is successfully applied to measure the periodic flow field in a radial diffuser pump with low-specific speed, in order to investigate the velocity fluctuations caused by the impeller-diffuser interactions both in the impeller and diffuser regions. The velocity fluctuations in the impeller region are quantitatively examined at different radial positions, and the flow structure at the radial gap between two flow components is analyzed at different relative positions. In addition, the downstream effect on the diffuser flow is quantitatively and qualitatively assessed and compared with the turbulence effect.

A Laser Imaging-LDV Coupling Measurement of Single Bubble Forming and Rising in Shear-thinning Fluid

The shape evolution of bubble formed in carboxymethylcellulose(CMC) aqueous solution was real-time observed using laser image technique. The flow fields of liquid around growing and rising bubble were measured by laser Doppler velocimetry(LDV), and the liquid mean velocity and its contour curves were obtained. The results show that bubble grows as spherical shape because of the dominant role of surface tension in the early period, and then is stretched gradually as a teardrop shape due to the common effect of buoyancy and shear-thinning of fluid. The axial mean velocity of liquid phase takes on Gaussian distribution with the symmetrical axis passing through orifice center. However, the radial mean velocity increases first and then decreases with the increase of the distance from measured point to the symmetrical axis above. Further, the axial component along symmetrical axis decreases initially and increases with the rise of height, as well as its corresponding contour map diverging gradually. The radial component, yet, decreases steadily with the rise of height, and the maximum value deviates towards the two sides until disappear, as it contour shape of butterfly's "front wing".

An Experimental Study of Air-Solid Two-Phase Flow in a 90° Bend Using LDV System

The measurements of the mean streamwise and radial velocities,the associated turbulence and the relative particle densities were made in an air-solid two-phase flow in a square sectioned (30mm×30mm)90°vertical to horizontal bend using laser Doppler velocimetry.The radius ratio of the bend was 2.0.Glass beads of 100μm in diameter were employed to form the solid phase.The measurements of air and solid phases were performed separately at the same bulk velocity 19.34m/s,corresponding to a Reynolds number of 3.87×10~4.The mass ratio of solid to air was 1.6%.The results indicate that the particle trajectories are very close to straight lines. The streamwise velocity profiles for the gas and the solids cross over near the outer wall with the solids having the higher speed.At θ=30°and 45°,particle-wall collisions happen mostly in the region from θ=30°to θ=75°,and cause a sudden change in solid velocity.The particles tend to move towards the outer wall in 90° bend.The particle concentration near the outer wall is much higher than that near the inner wall in the bend, and there are few particles in the inside of the bend.The bend leads to apparent phase separation:atθ=45°, the solids concentrate in the half of the duct near the outer wall.Afterθ=60°the second peak concentration appears,and goes gradually towards the inner wall.

Effect of Linear Electromagnetic Stirring on Behavior of Liquid Metal and Rate of Slag-Metal Interfacial Reactions

The internal flow,free surface shape,and level fluctuation of liquid metal exposed to linear electromagnetic stirring were measured and analyzed against the background of an actual metallurgical equipment with linear electromagnetic stirring system.The desulphurization process,with or without imposition of linear electromagnetic stirring,was also studied experimentally.The changes in sulfur content of hot metal with respect to time were obtained,and the volumetric mass transfer coefficients corresponding to different stirring currents were determined.The results showed that linear electromagnetic stirring can effectively promote internal flow,effectively increase the level fluctuation,and significantly improve the kinetic condition of liquid metal.The internal flow and level fluctuation of liquid metal increase in line with the increase in electromagnetic stirring intensity.The desulphurization experiments show that linear electromagnetic stirring can significantly promote the desulphurization process of hot metal,and that the technology has wide application potential in promoting various slag-metal reactions.