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A Study on Swirling Flows in a Rectangular Channel(LDV Measurement, Flow Visualization and Large Eddy Simulation)

Journal of Thermal science 2001年第3期10卷 205-210页

作者： Kazuyoshi MATSUZAKI ,Yasutake HARAMOTO ,Mizue MUNEKATA Hideki OHBA dept. of mechanical engineering and materials science, Kumamoto University, Kurokami 2-39-1,Kumamoto, 860-8555, Japan Dept. of Mechanical Engineering and Materials Science Kumamoto University Kumamoto Japan

The purpose of this study is to make clear the behavior of swirling pipe flows with non-circular section. We have investigated experimentally and numerically the swirling flows in a rectangular channel with aspect ratio of 1.3, which is one of the typical pipe flow with non-circular section. In this paper, experimental apparatus with water circulation system is produced, and LDV measurement of the swirling flows is performed in order to clarify the mean velocities and turbulent quantity with higher accuracy. In addition, flow visualization for movement of vortex core region in the swirling flows is carried out using tracer method. Moreover, large eddy simulation (LES) of the flow field is made and compared with the experimental results. As results of these investigations, the behavior of the swirling flows in the rectangular channel is totally discussed.

关键词： swirling flow LDV measurement flow visualization large eddy simulation.

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Single-walled carbon nanotube production in CO laser pimped carbonmonoxide plasmas

Single-walled carbon nanotube production in CO laser pimped ...

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32nd AIAA Plasmadynamics and Lasers Conference 2001

作者： Plönjes, Elke Palm, Peter Frederickson, Kraig Adamovich, Igor V. Subramaniam, Vish V. Lempert, Walter R. William Rich, J. Babu Viswanathan, G. Fraser, Hamish L. Nonequilibrium Thermodynamics Laboratory Department of Mechanical Engineering The Ohio State University Columbus OH 43210 United States Department of Materials Science and Engineering The Ohio State University Columbus OH 43210 United States Dept. of Aerospace Engineering and Aviation United States Mechanical Engineering United States

Single-walled carbon nanotubes (SWNTs) are synthesized in a gas-phase thermally non-equilibrium plasma process. The carbon producing CO disproportionate reaction is driven very efficiently in a flow reactor, in which extreme molecular vibrational mode disequilibrium of the carbon monoxide gas is maintained by using a powerful and efficient carbon monoxide gas laser. The CO molecules absorb the laser radiation on the lowest 10 vibrational transitions and transfer energy to high vibrational states by vibration-vibration energy exchange collisions. This leads to a highly non-equilibrium energy distribution in the CO which provides enough energy for the CO disproportionation reaction to occur even at low translational temperatures. In the presence of metal catalysts, the vibrationally excited CO reacts to form CO2 and structured carbon molecules, notably SWNTs. The iron catalyst necessary for the nanotube formation is added into the flow reactor through a bubbler system in the form of iron pentacarbonyl. In addition to some thermal decomposition, the CO laser photodissociates the metal carbonyl to form iron clusters in situ. The flow reactor employed in the synthesis allows access for spectroscopic studies of the kinetic processes involved in the nanotube formation process. Presently, the vibrational distribution function of the CO and the gas translational temperature are monitored using infrared emission spectroscopy. Fe, C and C2 emission are observed with UV-Vis emission spectroscopy and the iron pentacarbonyl concentration is monitored with IR absorption spectroscopy. Transmission electron microscopy (TEM) is employed to study the nanotubes. Ropes of single-walled carbon nanotubes with a high degree of alignment have been observed in deposits for certain plasma conditions. This ordering occurs in the synthesis, without any post-production processing. Substantial quantities of nanotube containing material are produced at low pressure (50 Torr) due to the efficient c

关键词： Carbon monoxide

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Efficient shape description using NURBS 4th

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4th International Workshop on Visual Form, IWVF4 2001

作者： Brujic, Djordje Ainsworth, Iain Ristic, Mihailo Brujic, Vesna Imperial College of Science Technology and Medicine Dept. of Mechanical Engineering LondonSW7 2BX United Kingdom University of Surrey School of Mechanical and Materials Engineering SurreyGU2 7XH United Kingdom

ISBN: (纸本)3540421203

In this paper we present an efficient method for smooth surface generation from unorganised points using NURBS. This is a preferred alternative to using triangular meshes, which are expensive to store, transmit, render and are difficult to manipulate. The proposed method does not require triangulation prior to surface fitting because it generates NURBS directly. Two fundamental problems must be addressed to accomplish this task: parameterisation of measured data and overcoming ill-conditioning of the least squares surface fitting. We propose to solve the parameterisation problem by employing a suitable base surface, automatically generated from the data points, or provided as a CAD model if available. Ill-conditioning was solved by introducing additional fitting criteria in the minimisation functional, which constrain the fitted surface in the regions with insufficient number of data points. Surface fitting is performed by treating the surface as a whole without the need to either identify or re-measure the regions with insufficient data. The accuracy of fitting is dictated by the number of control points. The improvements in data compression, shape analysis and rendering are presented. The realised computational speed and the quality of the results were found to be highly encouraging. © Springer-Verlag Berlin Heidelberg 2001.

关键词： Computer aided design

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Preparation of Mesoporous Oxides for Mems Structures

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MRS Online Proceedings Library 2001年第1期657卷 731-736页

作者： Paik, Jong-Ah Kitazawa, Nobuaki Fan, Shih-Kang Kim, Chang-Jin Wu, Ming C. Dunn, Bruce Dept. of Materials Science and Engineering University of California at Los Angeles USA Dept.of Mechanical and Aerospace Engineering University of California at Los Angeles USA Dept. of Electrical Engineering University of California at Los Angeles USA

The high porosity and uniform pore size provided by mesoporous oxide films offer interesting opportunities for MEMS devices that require low density and low thermal conductivity. This paper describes recent efforts at adapting mesoporous films for MEMS fabrication. Mesoporous SiO2 and Al2O3 films were prepared using block copolymers as the structure-directing agents, leading to films which were 70% porous and < 5 nm surface roughness. A number of etchants were investigated and good etch selectivity was observed with both dry and wet systems. Micromachining methods were used to fabricate cantilevers, micro bridges and membranes.

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An electrochemical framework to explain the intergranular stress corrosion path in two Al-Cu-Mg-Ag alloys

An electrochemical framework to explain the intergranular st...

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Proceedings from materials Solutions Conference 2001

作者： Little, D.A. Connolly, B.J. Scully, J.R. Dept. of Materials Science and Eng. University of Virginia Charlottesville VA 22904-4745 United States Center of Electrochemical Sci. Eng. University of Virginia Charlottesville VA 22904-4745 United States Department of Mechanical Engineering U.S. Naval Academy Annapolis MD 21402 United States

ISBN: (纸本)0871707470

A modified version of the Cu-depletion electrochemical framework was used to explain the metallurgical factor creating intergranular stress corrosion cracking susceptibility in two aged Al-Cu-Mg-Ag alloys, C415 and C416. This framework was also used to explain the increased resistance to intergranular stress corrosion cracking with over-aging. Susceptibility in the under-aged and T8 (peak-aged) conditions is consistent with the grain boundary Cu-depletion mechanism. Improvements in resistance of the T8 + thermal exposure of 5000 h at 225°F (T8+) compared to the T8 condition can be explained by depletion of Cu from solid solution therefore reducing the viability of a copper depleted zone framework and resultant preferential dissolution path along grain boundaries.

关键词： Aluminum alloys

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Single-walled carbon nanotube formation in a high-pressure non-equilibrium carbon monoxide plasma

Single-walled carbon nanotube formation in a high-pressure n...

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Pulsed Power Plasma science

作者： E. Pl njes P. Palm G.B. Viswanathan I.V. Adamovich V.V. Subramaniam H.L. Fraser J.W. Rich Dept. of Mech. Eng. Ohio State Univ. Columbus OH USA The Ohio State University Columbus OH USA Department of Mechanical Engineering The Ohio State University Columbus OH Department of Materials Science and Engineering

Summary form only given, as follows. Single-walled carbon nanotubes (SWNTs) are synthesized in a thermally non-equilibrium flow reactor, in which extreme molecular vibrational mode dis-equilibrium of the primary feedstock, carbon monoxide (CO) gas, is maintained by using a powerful and efficient CO gas laser. The CO molecules absorb the laser radiation on the lowest 10 vibrational transitions and transfer energy to high vibrational states by vibration-vibration energy exchange collisions. This leads to a highly non-equilibrium energy distribution in the CO, which provides enough energy for the carbon-producing CO disproportionation reaction to occur. The vibrationally excited CO reacts in the presence of metal catalysts to form, primarily, carbon dioxide and structured carbon molecules, notably SWNTs, in this continuous (non-batch) process. Iron pentacarbonyl is employed as the catalyst precursor, which dissociates in the plasma and subsequently forms small iron clusters. The influence of iron pentacarbonyl concentration on the quality of the nanotube material is investigated. Ropes of single-walled carbon nanotubes with a high degree of alignment have been observed in deposits created in the CO plasma without any post-production processing. A nanotube content of better than 50% is observed in the deposited material for certain synthesis conditions. At low pressure, substantial quantities of about 20 mg/hour of nanotube containing material are produced. The non-equilibrium synthesis process has been successfully scaled to high plasma pressures up to an atmosphere. We will present results on the production rate and purity of the nanotube containing material under these conditions. IR, visible and UV spectroscopy in the flow reactor has been used to control process parameters.

关键词： Carbon nanotubes Iron Plasma materials processing Nanostructured materials Inductors Gas lasers Laser modes Laser transitions Carbon dioxide Power lasers

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Effects of Ta Addition on NiTi Shape Memory Alloys

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Journal of materials science & Technology 2000年第5期16卷 534-536页

作者： Jianlu MA, Jiangnan LIU+, Zhengpin WANG and Fei XUE (dept. of materials science & engineering, Xi’an Institute of Technology, Xi’an 710032, China) Kuang-Hsi WU and Zhongjie PU (Department of mechanical engineering, Florida International University, USA) Dept. of Materials Science and Engineering Xi'an Institute of Technology Xi'an 710032 China Department of Mechanical Engineering Florida International University United States

The effect of Ta addition on the martensitic transformation characteristics and the X-ray visibility on NiTi shape memory alloy have been studied in (Ni51Ti49)1-xTax system. It was found that the transformation temperatures of the Ni51Ti49 binary alloy increased drastically by an addition of 0～4 at. pet Ta, but only slightly when the concentration exceeded 4 at. pct; the addition of Ta greatly decreases the sensitivity of the martensitic transformations to the variation in the Ni-Ti ratio. The addition of Ta to the NiTi binary alloy can improve its X-ray visibility.

关键词： NiTi Effects of Ta Addition on NiTi Shape Memory Alloys Ta

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Natural vibrations of repetitive structures

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Journal of Mechanics 2000年第2期16卷 85-95页

作者： Wang, Dnjun Wang, C.-C. Dept. of Mechanics and Engineering Science Peking University Beijing China Dept. of Mechanical Engineering and Materials Science Rice University Houston TX United States

Natural vibration frequencies and modes of repetitive structures, including symmetric, periodic, linking structures, are considered in this work. By using the repetition of the identical parts, we reduce the eigenvalue problem of the structure to a set of eigenvalue problems of lower dimensions associated with the parts. Special forms and properties of the modes of natural vibrations are observed.

关键词： Eigenvalue problem Linking structures Modes Natural vibrations Periodic structures Repetitive structures Symmetric structures

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Energy based boundary element method for broadband high frequency sound fields

Energy based boundary element method for broadband high freq...

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6th Aeroacoustics Conference and Exhibit, 2000

作者： Franzoni, L. Bliss, D. Rouse, J. Dept. of Mechanical Engineering and Materials Science Duke University Durham NC 27708-0300 United States

An acoustic boundary element method is formulated using the time-averaged intensity and mean-square pressure. A continuous distribution of uncorrelated broadband high frequency sources is used to represent the boundaries of the enclosure. Local correlation (within a fraction of a wavelength) is accounted for by assigning a directivity pattern to the infinitesimal sources. A further refinement of the method modifies the directivity function to account for specular reflections. Using these specially designed boundary elements removes the need to discretize the boundary at high resolution for high frequency sound fields. Instead, this method requires only one element per many wavelengths. Computational savings occur due to the reduction in the number of elements and the fact that the sources are broadband. Results are shown for a two-dimensional rectangular enclosure with two absorbing walls and excellent agreement with an exact analytical solution is obtained. Different interior source types, monopole versus dipole, were used and observations are made about the resulting acoustic field. © 2000 by L. Franzoni and D. Bliss. Published by the American Institute of Aeronautics and Astronautics, Inc.

关键词： Acoustic fields

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Lattice Distortions and Domain Structure in Epitaxial Manganite Thin Films

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MRS Online Proceedings Library 2000年第1期602卷 207-218页

作者： Suzuki, Y. Wu, Yan Rüdiger, U. Yu, J. Kent, A. D. Nath, T. K. Eom, C. B. Dept. of Materials Science and Engineering Cornell University Ithaca USA Dept. of Physics New York University New York USA Dept. of Mechanical Engineering and Materials Science Duke University Durham USA

Lattice distortions, be they in the form of chemical and hydrostatic pressure in bulk or lattice mismatch between film and substrate, have significant effects on the transport as well as the magnetic properties of colossal magnetoresistance (CMR) materials. We summarize here our results on tensilely and compressively strained La0.7Sr0.3MnO3 (LSMO) thin films that indicate the important role of lattice distortions due to the lattice mismatch between the film and substrate. The strain due to lattice distortions can be used to tune the magnetic domain structure, magnetization, magnetic anisotropy and magnetotransport of LSMO thin films.

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