1,721,716 research outputs found
BIMETALLIC REACTION SYSTEMS INVOLVING GROUP 9 METALLACARBORANES - SYNTHESIS AND CHARACTERIZATION OF [CLOSO-3-CO-3-PPH(3)-7-MU-H-3,7-[CU(PPH(3))]-3,1,2-MC(2)B(9)H(10)] (M=RH, IR)
No full textSupport of this work by the Korea Science and Engineering Foundation is gratefully acknowledged
Effective Management of PASS Syndrome With Intravenous Immunoglobulin and Anti-Interleukin-1 Therapy: An Insightful Case Study
No full textCharacteristic interface conditions for multiblock high-order computation on singular structured grid
No full textA structured grid with an embedded body usually has a certain point where an abrupt change in the slope of the grid line exists. The grid metrics are discontinuous at such a point because of the discrepancy between the left- and the right-hand limits of the gradients. This leads to grid singularity. It may cause serious numerical oscillations especially when high-order finite difference schemes are applied to solving conservation-form governing equations in generalized coordinates. This problem is handled by decomposing the computational domain into blocks along the singular lines and imposing interface conditions at the block interfaces for communication between the blocks. A set of high-order finite difference schemes is used in each block: central differences on the interior nodes and one-sided differences on the near-interface nodes. The differencing stencils do not cross the block interfaces, and each block is isolated without the singularity, which results in no oscillations. For communication between the isolated blocks, the interface conditions are derived from the characteristic relations of the compressible Euler or Navier-Stokes equations. The exactness and the feasibility of the interface conditions are investigated for the high-order multiblock computation on structured grids containing singular points
Generalized characteristic boundary conditions for computational aeroacoustics
No full textAn extended conservative formalism of the characteristic boundary conditions is presented on the basis of the generalized coordinates for practical computational aeroacoustics. The formalism is derived for solving the entire conservative form of the compressible Euler or Navier-Stokes equations on the body-fitted grid mesh system by using the high-order and high-resolution numerical schemes. It includes the matrices of transformation between the conservative and the characteristic variables, which were already derived In the literature to analyze the eigenvalue-eigenvector modes in an arbitrary direction. The conservation-form governing equations with their full terms are solved at the boundaries, and no kind of extrapolation or simplification of the equations is included in this formalism. Additional correction terms are devised to preserve the conservative form of flux derivative terms in the generalized coordinates. Especially, the soft inflow conditions are presented to keep the nonreflecting features, as well as to maintain the mean value of inflow velocity at the inlet boundary. These boundary conditions are applied to the actual computation of two-dimensional viscous cylinder flows with Reynolds number of 400 on the grid meshes clustered on the cylinder surface and the downstream region. The Strouhal number due to von Karman vortex streets, root-mean-square lift coefficient, and mean drag coefficient are evaluated correctly in comparison,vith experimental data. The far-field sound pressure levels are measured directly in this computation, and the accuracy is validated by an analytic formula derived in the literature.The authors would like to acknowledge the high-performance
computer services from the Supercomputing Center of the Korea
Research and Development Information Center
PROPAGATION OF THE VELOCITY SHEAR FRONT IN SPIN-UP FROM REST IN A CUT-CONE
No full textThe behavior of the dominant azimuthal velocity field during spin-up from rest of a homogeneous fluid in a cut-cone is investigated. The fundamental mechanism of spin-lip process is recapitulated. In line with the classical flow model of Wedemeyer, the importance of the meridional circulation, driven by the Ekman layers, is stressed. The experimental apparatus, together, with the image processing technique of the visualized flow data, is described. The reliability and accuracy of this experimental method are validated by performing parallel measurements using an LDV system. The experimental results clearly indicate that the azimuthal velocity shear front propagates faster as the incline angle of the side wall decreases. In the rotating zone of the interior, the azimuthal velocities are larger in magnitude in a cut-cone than in a circular cylinder of comparable size. Plausible physical explanations are offered, and the experimental observations are supportive of these physical arguments
A STUDY ON ARC SENSOR ALGORITHM FOR WELD SEAM TRACKING IN GAS METAL ARC-WELDING OF BUTT JOINTS
No full textThe positional accuracy requirement of the welding torch with respect to the weld seam is the major impediment in arc welding robot applications. The weld seam tracking sensor is essential to improve the flexibility of arc welding robot applications. In this study, an arc sensor which utilizes the electrical signal obtained from the welding arc itself was developed for gas metal arc welding of butt joints. In order to overcome the fluctuation in the welding current signal, the current signal was fitted to a curve which is inversely proportional to the trace of the tip-to-workpiece distance by using the quadratic curve-fitting method. The availability of the curve-fitted welding current signal was investigated and the seam tracking results of the system that uses the curve-fitting method were compared with the ones of another system that controls the moving speed of the welding torch in the height direction
Adaptive nonlinear artificial dissipation model for computational aeroacoustics
No full textAn adaptive nonlinear artificial dissipation model is presented for performing aeroacoustic computations by high-order and high-resolution numerical schemes based on central finite differences. It consists of a selective background smoothing term and a well-established nonlinear shock-capturing term, which damps out spurious oscillations caused by the central differences in the presence of a shock wave and keeps the linear acoustic waves relatively unaffected. A conservative form of the selective background smoothing term is presented to calculate accurate propagation speed or location of the shock wave. The nonlinear shock-capturing term, which has been modeled by second-order derivative term, is combined with it to improve the resolution of discontinuity and enhance the numerical stability near the shock R avc. An adaptive control constant for overall amplitude of the dissipation is automatically calculated according to given grid metrics and time-dependent flow conditions. It is shown that the improved artificial dissipation model reproduces the correct profile and speed of the shock wave, suppresses numerical oscillations near the discontinuity, and avoids unnecessary damping on the smooth linear acoustic waves. The feasibility and performance of the adaptive nonlinear artificial dissipation model for the computational aeroacoustics are investigated and validated by the applications to actual problems
A STUDY ON AN ARC SENSOR FOR GAS METAL ARC-WELDING OF HORIZONTAL FILLETS
No full textThe weld joint tracking sensor is indispensable for improving the flexibility of arc welding robot applications. Recently, some sensing methods that utilize the electric arc signal, or more correctly the welding current in GMA welding, have been developed and are prevalently in use. The welding current is directly affected by the contact tip-to-workpiece distance for the given welding voltage and wire feed speed. Armed with a means of measuring the welding current, the tip-to-workpiece distance and then the weld joint geometry can be obtained by weaving the arc back and forth across the line of travel. Knowledge of the weld joint geometry relative to the welding gun permits the welding gun to trace the joint. In this study, the welding current signal was fitted to a curve, which is inversely proportional to the trace of contact tip-to-workpiece distance by using the quadratic curve-fitting method in order to extract useful information on the welding gun position from the welding current signal. Furthermore, the availability of the curve-fitted welding current signal was investigated and a joint tracking system for horizontal fillet joints was developed by using this curve-fitting method
Optimized compact finite difference schemes with maximum resolution
No full textDirect numerical simulations and computational aeroacoustics require an accurate finite difference scheme that has a high order of truncation and high-resolution characteristics in the evaluation of spatial derivatives. Compact finite difference schemes are optimized to obtain maximum resolution characteristics in space for various spatial truncation orders. An analytic method with a systematic procedure to achieve maximum resolution characteristics is devised for multidiagonal schemes, based on the idea of the minimization of dispersive (phase) errors in the wave number domain, and these are applied to the analytic optimization of multidiagonal compact schemes. Actual performances of the optimized compact schemes with a variety of truncation orders are compared by means of numerical simulations of simple wave convections, and in this way the most effective compact schemes are found for tridiagonal and pentadiagonal cases, respectively. From these comparisons, the usefulness of an optimized high-order tridiagonal compact scheme that is more efficient than a pentadiagonal scheme is discussed. For the optimized high-order spatial schemes, the feasibility of using classical high-order Runge-Kutta time advancing methods is investigated
Embodied and disembodied international spillovers of R&D in OECD manufacturing industries
No full textThis paper investigates the relationship between productivity changes and R&D in the presence of embodied and disembodied international spillovers of technology for total manufacturing industries in 14 OECD countries. The paper assumes that embodied spillovers of R&D are measured by trade and disembodied spillovers by technological distance. The Malmquist total factor productivity (TFP) change may be separated into two components: technical and efficiency changes. Our empirical results indicate that for 14 countries as a whole, both domestic R&D and disembodied spillovers of R&D have statistically significant and positive effects on TFP growth and especially on technical change. For high-R&D-intensive countries, the growth of TFP is mainly attributable to the increase in domestic R&D. For low-R&D-intensive countries, however, the international spillovers are the main factors for the TFP growth: technical innovation is attributable to disembodied international spillovers, and efficiency improvement to embodied spillovers. (C) 2003 Elsevier Ltd. All rights reserved
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