Micro-shock waves generated inside a fluid jet impinging on plane wall

An Nd:glass laser pulse (18 ns, 1.38 J) is focused in a tiny area of about 100-mum diam under ambient conditions to produce micro-shock waves. The laser is focused above a planar surface with a typical standoff distance of about 4 mm, The laser energy is focused inside a supersonic circular jet of carbon dioxide gas produced by a nozzle with internal diameter of 2.9 mm and external diameter of 8 mm, Nominal value of the Mach number of the jet is around 2 with the corresponding pressure ratio of 7.5 (stagnation pressure/static pressure at the exit of the nozzle), The interaction process of the micro-shock wave generated inside the supersonic jet with the plane wall is investigated using double-pulse holographic interferometry. A strong surface vortex field with subsequent generation of a side jet propagating outward along the plane wail is observed. The interaction of the micro-shock wave with the cellular structure of the supersonic jet does not seem to influence the near surface features of the flowfield. The development of the coherent structures near the nozzle exit due to the upstream propagation of pressure waves seems to be affected by the outward propagating micro-shock wave. Mach reflection is observed when the micro-shock wave interacts with the plane wall at a standoff distance of 4 mm, The Mach stem is slightly deflected, indicating strong boundary-layer and viscous effects near the wall. The interaction process is also simulated numerically using an axisymmetric transient laminar Navier-Stokes solver. Qualitative agreement between experimental and numerical results is good.

A modified thermal viscoplastic constitutive law involving the effect of temperature rise rate

At high temperature rise rate, the mechanical properties of 10 # steel were determined experimentally in a very wide range of temperature and strain rates. A new constitutive relationship was put forward, which can fit with the experimental results and describe various phenomena observed in our experiments. Meanwhile, some interesting characteristics about the temperature rise rate, strain and strain rate hardening and thermal softening are also shown in this paper. Finally, the reliability of the constitutive law and the correctness of the constitutive parameters were verified by comparing the calculation results with the experimental data.

Oil-Water Two-Phase Flow Inside T-Junction

The oil/water two-phase flow inside T-junctions was numerically simulated with a 3-D two-fluid model, and the turbulence was described using the mixture k - epsilon model. Some experiments of oil/water flow inside a single T-junction were conducted in the laboratory. The results show that the separating performance of T-junction largely depends oil the inlet volumetric fraction and flow patterns. A reasonable agreement is reached between the numerical simulation and the experiments for both the oil fraction distribution and the separation efficiency.

Fracture Mechanisms And Size Effects Of Brittle Metallic Foams: In Situ Compression Tests Inside Sem

In situ compressive tests on specially designed small samples made from brittle metallic foams were accomplished in a loading device equipped in the scanning electron microscopy (SEM). Each of the small samples comprises only several cells in the effective test zone (ETZ), with one major cell in the middle. In such a system one can not only obtain sequential collapse-process images of a single cell and its cell walls with high resolution, but also correlate the detailed failure behaviour of the cell walls with the stress-strain response, therefore reveal the mechanisms of energy absorption in the mesoscopic scale. Meanwhile, the stress-strain behaviour is quite different from that of bulk foams in dimensions of enough large, indicating a strong size effect. According to the in situ observations, four failure modes in the cell-wall level were summarized, and these modes account for the mesoscopic mechanisms of energy absorption. Paralleled compression tests on bulk samples were also carried out, and it is found that both fracturing of a single cell and developing of fracture bands are defect-directed or weakness-directed processes. The mechanical properties of the brittle aluminum foams obtained from the present tests agree well with the size effect model for ductile cellular solids proposed by Onck et al. (C) 2008 Elsevier Ltd. All rights reserved.

Standing electron plasma wave mechanism of void array formation inside glass by femtosecond laser irradiation

We investigate the mechanism of formation of periodic void arrays inside fused silica and BK7 glass irradiated by a tightly focused femtosecond (fs) laser beam. Our results show that the period of each void array is not uniform along the laser propagation direction, and the average period of the void array decreases with increasing pulse number and pulse energy. We propose a mechanism in which a standing electron plasma wave created by the interference of a fs-laser-driven electron wave and its reflected wave is responsible for the formation of the periodic void arrays.

Multi-channel 2-D pattern transfer model based on imaging optics for submarine laser uplink communication

An optical communication scheme of 2-D pattern transfer based on imaging optics for submarine laser uplink communication (SLUC) is suggested. Unlike the methods aiming at avoiding neighboring crosstalk used in traditional multi-channel optical beam transferring, we make full use of the overlapping of each spreading beam other than controlling divergence effect of each beam to avoid interference noise. The apparent parameters have been introduced to simplify theoretical analysis of optical pattern transfer problem involving underwater condition, with the help of which the complex beam propagation inside two kinds of mediums can be easily reduced to brief beam transfer only inside air medium. In this paper, optical transmission path and receiver terminal optics geometry have been described in detail. The link range equation and system uplink performance analysis have also been given. At last, results of a proof-of-concept experiment indicate good feasibility of the proposed SLUC model. © 2007 Elsevier GmbH. All rights reserved.

Effect of PbO on precipitation of laser-induced gold nanoparticles inside silicate glasses

We report on three-dimensional precipitation of Au nanoparticles in gold ions-doped silicate glasses by a femtosecond laser irradiation and further annealing. Experimental results show that PbO addition plays the double roles of inhibiting hole-trapped centers generation and promoting formation and growth of gold nanoparticles. Additionally, glass containing PbO shows an increased non-linear absorption after femtosecond laser irradiation and annealing. The observed phenomena are significant for applications such as fabrications of three-dimensional multi-colored images inside transparent materials and three-dimensional optical memory, and integrated micro-optical switches. (c) 2007 Elsevier B.V. All rights reserved.

Space-selective precipitation of Au nanoparticles inside silica gel

Au colloids were prepared by irradiation with a Nd:YAG laser. Au nanoparticles were characterized by absorption spectra, transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis. It is found that the wavelength of the laser has no effect on the size but the number of the Au nanoparticles. By irradiating a transparent silica gel doped with gold ions with the focused laser in the gel and subsequent exposing in air, a space-selective pattern of letter "P" consisting of Au nanoparticles was observed inside the silica gel.

Nano-modification inside transparent materials by femtosecond laser single beam

Periodic nanostructures along the polarization direction of light are observed inside silica glasses and tellurium dioxide single crystal after irradiation by a focused single femtosecond laser beam. Backscattering electron images of the irradiated spot inside silica glass reveal a periodic structure of stripe-like regions of similar to 20 nm width with a low oxygen concentration. In the case of the tellurium dioxide single crystal, secondary electron images within the focal spot show the formation of a periodic structure of voids with 30 nm width. Oxygen defects in a silica glass and voids in a tellurium dioxide single crystal are aligned perpendicular to the laser polarization direction. These are the smallest nanostructures below the diffraction limit of light, which are formed inside transparent materials. The phenomenon is interpreted in terms of interference between the incident light field and the electric field of electron plasma wave generated in the bulk of material.

Nonpolarizing beam splitter designed by frustrated total internal reflection inside a glass cube

A method for the design of an all-dielectric nonpolarizing prism beam splitter utilizing the principle of frustrated total internal reflection is reported. The nonpolarizing condition for a prism beam splitter is discussed, and some single layer design examples are elaborated. The concept can be applied to a wide range of wavelengths and arbitrary transmittance values, and with the help of a computer design program examples of 400-700 nm, T-p = T-p = 0.5 +/- 0.01, with incident angles of 45 degrees and 62 degrees are given. In addition, the sensitivity and application of the design are also discussed. (c) 2006 Optical Society of America.