新型金属蜂窝板燃烧器的高效燃烧现象分析

新型金属蜂窝板燃烧器是通过采用双层或多层金属薄片制成,能有效地解决普通燃气灶具燃烧器存在的不足,使产品结构更加合理完善,性能更加稳定可靠,能效更加优越。本文以红外燃气灶具的核心部件—新型金属蜂窝板燃烧器为研究对象,利用红外摄像仪对红外燃气灶具和普通燃气灶具进行了对比研究。结果表明,红外燃气灶的火焰集中,温度分布均匀,燃烧效率比普通燃气灶高12.7%。     

On the penetration of a rotating impactor into an elastic-plastic medium

This research is devoted to the modeling of high-speed rectilinear penetration of a rigid axisymmetric body (impactor with a flat bluntness) into an elastic–plastic media with account for its rotation about the axis of symmetry. The body has an arbitrary shape of the meridian. The resistance to the motion is represented as the sum of the body drag and the contribution of friction. The dynamic system governing the body motion is derived and the qualitative and numerical analysis of the projectile movement and perforation of a slab are performed. The problem of shape optimization of impactor with a flat bluntness is studied using evolutionary algorithm.     

Qualitative and quantitative analysis of voice onset by means of a multidimensional voice analysis system (MVAS) using high-speed imaging

High-speed filming is one of the most informative methods for assessing voice physiology data. Tracing high-speed images of the glottis provides quantitative parameters such as the glottal area and the glottal width function. By way of example, a number of studies are discussed which extract quantitative data from high-speed images showing voice onsets. Furthermore, a new computer system (MVAS; multi-dimensional voice analysis system) is presented that synchronously displays a laryngoscopic high-speed film, the electroglottographical signal, and several acoustic analyses of the recorded voice sample. The automatic measurement of glottal width and glottal area from the laryngoscopic images is also provided. Looking at former studies and our analyses of voice onsets reveals a tremendous intersubject and even intrasubject variability (different prephonatory closure, different time span until full amplitude is reached, different open quotient).     

高速光脉冲的测量方法

 综述了目前国际上公认的测量高速光脉冲的几种方法，主要包括电光条纹相机（SC）、快速脉冲取样、二次谐波产生（SHG）、频率分辨光学门（FROG）以及光谱相位干涉直接电场重建（SPIDER）等。详细地阐述和分析了这些方法的原理、特点、适用范围以及它们的研究现状。     

An experimental study of impact-induced failure events in homogeneous layered materials using dynamic photoelasticity and high-speed photography

The generation and the subsequent evolution of dynamic failure events in homogeneous layered materials that occur within microseconds after impact were investigated experimentally. Tested configurations include three-layer and two-layer, bonded Homalite specimens featuring different bonding strengths. High-speed photography and dynamic photoelasticity were utilized to study the nature, sequence and interaction of failure modes. A series of complex failure modes was observed. In most cases, and at the early stages of the impact event, intra-layer failure (or bulk matrix failure) appeared in the form of cracks radiating from the impact point. These cracks were opening-dominated and their speeds were less than the crack branching speed of the Homalite. Subsequent crack branching in several forms was also observed. Mixed-mode inter-layer cracking (or interfacial debonding) was initiated when the intra-layer cracks approached the interface with a large incident angle. The dynamic interaction between inter-layer crack formation and intra-layer crack growth (or the so-called “Cook–Gordon Mechanism”) was visualized for the first time. Interfacial bonding played a significant role in impact damage spreading. Cracks arrested at weak bonds and the stress wave intensity was reduced dramatically by the use of a thin but ductile adhesive layer.     

A high-speed photographic study of the transition from deflagration to detonation wave

Experiments were conducted to investigate the DDT process of the oxyhydrogen gas in the rectangular detonation tube of 3 m long. The repeated obstacle was installed near the ignition plug and the effects of the obstacle on the DDT process were investigated. The behaviour of the combustion and detonation wave were visualized utilizing Imacon high-speed camera with the aid of Schlieren optics. As a result, DDT process was visualized, i.e. (i) multiple shock waves were induced by the expanding combustion wave, because the combustion flame played a role as a piston and compressed the unburned gases. (ii) The acceleration of the combustion wave was occurred and the distance between the shock wave and the combustion flame became shorter. (iii) Eventually, the local explosion was occurred and cause overdriven detonation wave to propagate at the velocity of about 3 kms⁻¹. An abridged version of this paper was presented at the 15th Int. Colloquium on the Dynamics of Explosions and Reactive Systems at Boulder, Colorado, from July 30 to August 4, 1995     

Formation of molten metal films during metal-on-metal slip under extreme interfacial conditions

The present paper describes results of plate-impact pressure-shear friction experiments conducted to study time-resolved growth of molten metal films during dry metal-on-metal slip under extreme interfacial conditions. By employing tribo-pairs comprising hard tool-steel against relatively low melt-point metals such as 7075-T6 aluminum alloys, interfacial friction stress ranging from 100 to and slip speeds of approximately have been generated. These relatively high levels of friction stress combined with high slip-speeds generate conditions conducive for interfacial temperatures to approach the melting point of the lower melt point metal (Al alloy) comprising the tribo-pair.A Lagrangian finite element code is developed to understand the evolution of the thermo-mechanical fields and their relationship to the observed slip response. The code accounts for dynamic effects, heat conduction, contact with friction, and full thermo-mechanical coupling. At temperatures below the melting point the material is described as an isotropic thermally softening elastic-viscoplastic solid. For material elements with temperatures in excess of the melt point a purely Newtonian fluid constitutive model is employed.The results of the hybrid experimental-computational study provides new insights into the thermoelastic-plastic interactions during high speed metal-on-metal slip under extreme interfacial conditions. During the early part of frictional slip the coefficient of kinetic friction is observed to decrease with increasing slip velocity. During the later part transition in interfacial slip occurs from dry metal-on-metal sliding to the formation of molten Al films at the tribo-pair interface. Under these conditions the interfacial resistance approaches the shear strength of the molten aluminum alloy under normal pressures of approximately 1- and shear strain rates of . The results of the study indicate that under these extreme conditions molten aluminum films maintain a shearing resistance as high as .Scanning electron microscopy of the slip surfaces reveal molten aluminum to be smeared on the tribo-pair interface. Knoop hardness measurements in 7075-T6 Al alloy at various depths from the slip interface indicate that the hardness increases approximately linearly with depth and reaches a plateau at approximately from the surface.     

Characterization of Diamond Nanoparticles by High-Speed Micro-Thermal Field-Flow Fractionation

Micro-thermal field-flow fractionation was used to characterize the particle size distribution of nanometer-sized diamond nanoparticles. Although the experimental conditions were chosen to perform high-speed separation, and, consequently, the resolution achieved experimentally was not very high, the application of the original correction method for the zone spreading allowed for obtaining of very good calculated particle size distribution or, explicitly, a true polydispersity index of the diamond nanoparticle sample. The future use of several samples of diamond nanoparticles of different average sizes and different surface chemistries should allow deeper insight into the effect of these particulate characteristics on the retention in micro-thermal field-flow fractionation.     

Variation of fiber orientation in turbulent flow inside a planar contraction with different shapes

In this study, we have investigated the influence of shape of planar contractions on the orientation distribution of stiff fibers suspended in turbulent flow. To do this, we have employed a model for the orientational diffusion coefficient based on the data obtained by high-speed imaging of suspension flow at the centerline of a contraction with flat walls. This orientational diffusion coefficient depends only on the contraction ratio and turbulence intensity. Our measurements show that the turbulence intensity decays exponentially independent of the contraction angle. This implies that the turbulence variation in the contraction is independent of the shape, consistent with the results by the rapid distortion theory and the experimental results of axisymmetric contractions. In order to determine the orientation anisotropy, we have solved a Fokker–Planck type equation governing the orientation distribution of fibers in turbulent flow. Although the turbulence variation and the orientational diffusion are independent of the contraction shape, the results show that the variation of the orientation anisotropy is dependent on shape. This can be explained by the variation of the rotational Péclet number, Pe_r, inside the contractions. This quantity is a measure of the importance of the mean rate of the strain relative to the orientational diffusion. We have shown that when Pe_r < 10 turbulence can significantly influence the evolution of the orientation anisotropy. Since in contractions with identical inlet conditions the streamwise position where Pe_r = 10 depends on the shape, the orientation anisotropy is dependent on the variation of rate of strain in a given contraction. We demonstrate the shape effect by considering contraction with flat walls as well as three contractions with different mean rate of strain variation.     

Reflection and transmission of a compression wave at a tunnel portal

Analyses are made of the interaction of the nonlinearly steepened, compression wavefront generated by a high-speed train in a tunnel with the tunnel portal ahead of the train. The ‘micro-pressure’ pulse emitted from the portal can rattle structures in nearby buildings, and the expansion wave reflected back towards the train can cause discomfort to passengers. It is concluded that the usual simplified approximation of one-dimensional propagation within the tunnel provides an adequate representation of interactions of the wave with the portal, and also with ‘windows’ in the tunnel wall near the portal. It is shown how a discrete distribution of windows can be used to produce a reflected expansion wave that varies linearly across the wavefront, and how the thickness of that wavefront can be made many times larger than the thickness of the incident compression wave profile. A detailed analysis of the wave radiated from the portal reveals that cumulative nonlinear effects of propagation over long distances make little or no contribution to the free-space radiation of the micro-pressure wave.