• Journal of IKEEE
• /
• v.26 no.3
• /
• pp.373-379
• /
• 2022

In this paper, since the APD(Avalanche Photo Diode) for LTV(Light to Voltage) conversion uses a high voltage in the operating range unlike other PD(Photo Diode)s, the quenching resistor must be connected in series to prevent overcurrent when using the TIA(Transimpedance Amplifier). In such a case, quenching resistance may affect the transfer function of the TIA circuit, resulting in serious stability. Therefore, in this paper, by analyzing the effect of APD quenching resistance on the voltage and current loop transfer function of TIA, we propose a loop analysis and a method for determining the quenching resistance value to improve stability. TIA circuit with quenching resistance was designed by the proposed method and the stability of operation was verified through simulation and chip fabrication.

• Journal of Power System Engineering
• /
• v.2 no.3
• /
• pp.55-59
• /
• 1998

This paper probes into the influence of tire uniformity on tire's modal parameters with the method of experimental modal analysis. Two radial tires of the same kind with different uniformity level are taken to be tested at different exciting points and real modal parameters are abstracted. The differences of their modal parameters are presented. Then tire transfer functions are constructed with experimental modal parameters and ideal modal parameters respectively. It is found that the measured transfer functions of tire of good uniformity are closer to ideal transfer function than that of tire of bad uniformity. The study shows evident interrelation of experimental modal parameters and tire uniformity, and further study should be of great value.

• The KSFM Journal of Fluid Machinery
• /
• v.10 no.3 s.42
• /
• pp.39-46
• /
• 2007

This study presents a numerical procedure to optimize the shape of staggered dimple surface to enhance turbulent heat transfer in a rectangular channel. The RBNN method is used as an optimization technique with Reynolds-averaged Navier-Stokes analysis of fluid flow and heat transfer with shear stress transport (SST) turbulence model. The dimple depth-to-dimple print diameter (d/D), channel height-to-dimple print diameter ratio (H/D), and dimple print diameter-to-pitch ratio (D/S) are chosen as design variables. The objective function is defined as a linear combination of heat transfer related term and friction loss related term with a weighting factor. Latin Hypercube Sampling (LHS) is used to determine the training points as a mean of the design of experiment. The optimum shape shows remarkable performance in comparison with a reference shape.

• Journal of Magnetics
• /
• v.16 no.2
• /
• pp.92-96
• /
• 2011

This study investigated theoretically the properties of the spin transfer torque acting on a ferromagnet in a ferromagnet-normal metal-antiferromagnet junction. Earlier work showed that the angular dependence of the spin transfer torque can be a wavy-type if the junction satisfies a special symmetry. This paper reports a simple model analysis that allows a derivation of the wavy angular dependence without taking advantage of the symmetry. This result suggests that the wavy angular dependence can appear even when the symmetry is broken. As an illustration, the angular dependence was calculated as a function of the degree of the compensation at the normal metal-antiferromagnet interface. The implications of the result for the current-induced magnetization precession are discussed.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.16 no.8
• /
• pp.714-719
• /
• 2004

The objective of the present study is to investigate the convective instability driven by buoyancy and the heat transfer characteristics of nanofluids. Using the property relations of nanofluid expressed as a function of the volume fraction of nanoparticles, the ratio of nanofluid Rayleigh number to basefluid one, f is newly defined. The results show that the density and the heat capacity of nanoparticles act as a destabilizing factor. With an increase of ${\gamma}$ which is the ratio of thermal conductivity of nanoparticles to that of basefluid, the thermal instability of nanofluid decreases but the heat transfer rate increases.

• 유체기계공업학회:학술대회논문집
• /
• 2003.12a
• /
• pp.627-630
• /
• 2003

This work presents a numerical procedure to optimize the shape of three-dimensional channel with angled ribs mounted on one of the walls to enhance turbulent heat transfer. The response surface method is used as an optimization technique with Reynolds-averaged Navier-Stokes analysis of flow and heat transfer. SST turbulence model is used as a turbulence closure. The width-to-height ratio of the rib, rib height-to-channel height ratio, pitch-to-rib height ratio and attack angle of the rib are chosen as design variables. The objective function is defined as a linear combination of heat-transfer and friction-loss related terms with weighting factor. D-optimal experimental design method is used to determine the data points. Optimum shapes of the channel have been obtained for the weighting factors in the range from 0.0 to 1.0.

• Proceedings of the Korean Society of Near Infrared Spectroscopy Conference
• /
• 2001.06a
• /
• pp.1191-1191
• /
• 2001

Generation of precise, accurate, and robust calibration models for spectroscopic methods of analysis can be time-consuming, expensive, and sometimes difficult to achieve. For these reasons, efforts have been made to find ways in which the calibration from one instrument can be moved to another with minimal performance reduction. A slight shift in nomenclature from the common term calibration transfer to the term calibration transport is used here to help resolve the subtle difference between two means of moving a calibration from one instrument to another. The former term denotes a transfer procedure that includes mathematical manipulation of the calibration data via some determined transfer function, whereas the latter term does not. Todays generation of process and laboratory FTNIR analyzers is capable of not only achieving calibration transfer, but also calibration transport often without the need of slope or bias adjustments. Several studies are used to examine the boundaries of the extent to which calibration transport is achieved in the refining industry. Data collected on multiple on-line and laboratory FTNIR analyzers located in multiple countries are considered, and the ultimate limitations discussed.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.28 no.1
• /
• pp.24-30
• /
• 2004

Analysis model for the two-phase catalytic reactor is presented. With the progress in development of micro thermofluidic devices, needs fur understanding of the phenomena in two phase reaction in cm scale has been arisen. To investigate thermal and reactive performance of down scaled two phase reactor simple analysis model that is a kind of lumped flow model is proposed. Analysis model presented is based on the experiment on mm scale model reactor. Target experiment is catalytic decomposition of 70wt％ hydrogen peroxide with existence of perovskite L $a_{0.8}$S $r_{0.2}$Co $O_3$ catalyst. It is composed of balance equations of mass and energy. Each phase is considered to be a species fur the simplicity. Axial diffusion and transversal distribution of properties are neglected. Two phase catalytic reaction is modeled as successive gasification of liquid lump around catalyst and reaction in gas phase. Heat transfer is modeled by model function ofNu number. Modeled Nu is expressed as Nu=N $u_{0}$ (1＋ $a_1$( $a_2$ $T^{-}$ $a_3$)exp( $a_4$ $T^{-1}$)exp( $a_{5}$ z). Transfer coefficients are determined by the comparison of experimental results. With the model, heat transfer characteristics are investigated. Also by the mass transfer coefficient, characteristics in mass transfer is investigated. With the result basic understanding on design and analysis of mm scale two-phase reactive device is obtained. Also it can be further applied to micro scale reactive device fabricated by micromachining.ing..

• Journal of the Korea Concrete Institute
• /
• v.22 no.1
• /
• pp.29-39
• /
• 2010

In this study, experimental test and numerical analysis were conducted to investigate the heat transfer characteristics and fiber performance of high strength concrete. The fire characteristics of the high strength concrete that couldn't be obtained through the test due to specific requirements and restrictions were forecast using numerical analysis approach. The outcome from the numerical analysis and the test were compared to verify and improve the reliability of the analysis. A numerical analysis of 80 and 100 MPa high strength concrete cases were carried out to identify the heat transfer characteristics and fire behavior using software, ABACUS (V6.8) From the results of verification experiment, a 25~55% level of beam shrinkage reduction was observed compared to the concrete without Fiber-Cocktail, indicating the improved fire resistance performance, which appeared to be attributable to the function of Fiber-Cocktail that was able to control the heat transfer characteristics and ultimately result in enhancing the fire resistance performance.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
• /
• 1999.10a
• /
• pp.371-374
• /
• 1999

This paper present the nonlinear control and the Lyapunov analysis of the nonlinear electro-hydraulic system for steering control of UCT. Electro-hydraulic system itself has the high nonlinearities arisen from the nonlinear characteristics of the pressure-fluid flow in valve and friction in cylinder. These nonlinearities are unmodeled terms in the transfer function. This paper presents the system modeling, analysis of stability based on the Lyapunov function and simulation of the nonlinear hydraulic servo system.