• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.22 no.2
• /
• pp.189-196
• /
• 2009

This paper presents the subparametric finite element model formulated by partial-linear layerwise theory for the analysis of laminate composites. The proposed model is based on refined approximations of two dimensional plane for orthotropic thick laminate plate as well as thin case. Three dimensional problem can be reduced to two dimensional case by assuming piecewise linear variation of in-plane displacement and a constant value of out-of-plane displacement across the thickness. The integrals of Legendre polynomials are chosen to define displacement fields and Gauss-Lobatto numerical integration is implemented in order to directly obtain maximum values occurred at the nodal points of each layer without other extrapolation techniques. The validity and characteristics of the proposed model have been tested by using orthotropic multilayered plate problem as compared to the values available in the published references. In this study, the convergence test has been carried out to determine the optimal layer model in terms of central deflection and stresses. Also, the distribution of displacements and stresses across the thickness has been investigated as the number of layer is increased.

• International Journal of Safety
• /
• v.1 no.1
• /
• pp.36-42
• /
• 2002

This paper is aimed at predicting the life of rubber insulating gloves under normal operating stresses from relatively rapid test performed at higher stresses. Specimens of rubber insulating gloves are subject to multiple stress conditions, i.e. combined electrical and thermal stresses. Two modes of electrical stress, step voltage stress and constant voltage stress are used in specimen aging. There are two types of test for electrical stress in this experiment: the one is Breakdown Voltage (BDV) test under step voltage stress and thermal stress and the other is lifetime test under constant voltage stress and temperature stress. The ac breakdown voltage defined as the break-down point of insulation that leakage current excesses a limit value, l0mA in this experiment, is determined. Because the very high variability of aging data requires the application of statistical model, Weibull distribution is used to represent the failure times as the straight line on Weibull probability paper. Weibull parameters are deter-mined by three statistical methods i.e. maximum likelihood method, graphical method and least squares method, which employ SAS package, Weibull probability paper and FORTRAN, respectively. Two chosen models for predicting the life under simultaneous electrical and thermal stresses are inverse power model and exponential model. And the constants of life equation for multistress aging are calculated using numerical method, such as Gauss Jordan method etc.. The completion of life equation enables to estimate the life at normal stress based on the data collected from accelerated aging test. Also the comparison of the calculated lifetimes between the inverse power model and the exponential model is carried out. And the lifetimes calculated by three statistical methods with lower voltage than test voltage are compared. The results obtained from the suggested experimental method are presented and discussed.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.5 no.4
• /
• pp.296-301
• /
• 1993

A hydrodynamic solution for the lateral spreading of a river plume which was developed by assuming a Gaussian distribution of density difference between a turbulent jet river plume and ambient salt water is verified by the field data in the Nakdong river plume. Effect of the river plume on the transport of fine-grained suspended sediment at the Nakdong Estuary is also examined. The analysis of fold data showed a reasonably good correspondence with the theoretical solution adopted in this work Therefore, the hydrodynamic solution can be used as a useful tool in dealing with the lateral spreading of a river plume. The density stratification due to the existence of a river plume seems to cause a retarded settling of the suspended sediments in the water column. and thus a farther transport of the fine sediment is expected than in the normal steady flow.

• Journal of computational fluids engineering
• /
• v.18 no.2
• /
• pp.66-71
• /
• 2013

In this paper, the supersonic flows around space launch vehicles have been numerically simulated by using a 3-D RANS flow solver. The focus of the study was made for investigating plume-induced flow separation(PIFS). For this purpose, a vertex-centered finite-volume method was utilized in conjunction with 2nd-order Roe's FDS to discretize the inviscid fluxes. The viscous fluxes were computed based on central differencing. The Spalart-Allmaras model was employed for the closure of turbulence. The Gauss-Seidel iteration was used for time integration. To validate the flow solver, calculation was made for the 0.04 scale model of the Saturn-5 launch vehicle at the supersonic flow condition without exhaust plume, and the predicted results were compared with the experimental data. Good agreements were obtained between the present results and the experiment for the surface pressure coefficient and the Mach number distribution inside the boundary layer. Additional calculations were made for the real scale of the Saturn-5 configuration with exhaust plume. The flow characteristics were analyzed, and the PIFS distances were validated by comparing with the flight data. The KSLV-1 is also simulated at the several altitude conditions. In case of the KSLV-1, PIFS was not observed at all conditions, and it is expected that PIFS is affected by the nozzle position.

• 한국지구물리탐사학회:학술대회논문집
• /
• 2003.11a
• /
• pp.390-397
• /
• 2003

A three-dimensional (3D) inversion technique has been developed for interpretation of magnetotelluric (MT) data. The inversion method is based on the linearized least-squares (Gauss-Newton) method with smoothness regularization. In addition to the underground 3D resistivity distribution, static shifts are also treated as unknown parameters in the inversion. The forward modeling is by the staggered-grid finite difference method. A Bayesian criterion ABle is applied to search the optimum trade-off among the minimization of the data misfit, model roughness and static shifts. The method has been applied to several MT datasets obtained at geothermal fields in Japan and other Asian countries. In this paper, two examples will be discussed: one is the data at the Ogiri geothermal area, southwestern Japan, and the other is at the Pohang low-enthalpy geothermal field, southeastern Korea. The inversion of the Ogiri data has been performed stably, resulting in a good fitting between the observed and computed apparent resistivities and phases. The recovered 3D resistivity structure is generally similar to the two-dimensional (2D) inversion models, although the deeper portion of the 3D model seems to be more realistic than that of the 2D model. The 3D model is also in a good agreement with the geological model of the geothermal reservoirs. 3D interpretation of the Pohang MT data is still preliminary. Although the fitting to the observed data is very good, the preliminary 3D model is not reliable enough because the station coverage is not sufficient for a 3D inversion.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2014.02a
• /
• pp.218.2-218.2
• /
• 2014

그래핀은 높은 전기 전도도와 열전도도, 기계적 강도를 가지고 있고 동시에 높은 전자이동도($200,000cm^2{\cdot}V{\cdot}^1{\cdot}s{\cdot}^1$) 특성을 갖는 물질로써 차세대 소재로 각광받고 있다. 하지만 그래핀을 소자에 응용하기 위해서는 전사공정과 lithography 공정 과정에서 발생되는 PMMA(Poly methyl methacrylate) residue를 완벽하게 제거해야 하는 문제점이 있다. 특히, lithography 공정 중 완벽하게 PMMA residue 가 제거되지 않고 잔류해 있을 경우에 소자의 life time, performance에 악영향을 준다는 보고가 있다. 이와같은 문제를 해결하기 위해 화학적 cleaning, 열처리를 통한 cleaning, 전류 인가에 의한 cleaning과 같은 방법들을 이용하여 그래핀의 PMMA residue를 제거하는 공정들이 보고되고 있지만, 화학적 cleaning 방법의 경우 chloroform 이라는 독성물질 사용으로 인해 산업적으로 응용이 어렵고, 열처리 방법은 전극 등의 금속이 $200^{\circ}C$ 이상의 높은 온도에서 장시간 노출될 경우 쉽게 손상을 입으며, 전류 인가에 의한 cleaning 방법은 국부적으로만 효과를 볼 수 있기 때문에 lithography 공정 후 PMMA residue를 효과적으로 제거하기에는 한계를 보이고 있다. 본 연구에서는 Ar을 이용하는 Ion beam 시스템을 통해 beam energy를 제어함으로써 PMMA residue를 효과적으로 제거하는 연구를 진행하였다. 최적화된 플라즈마 발생 조건을 찾기 위해 QMS(Quadrupole Mass Spectrometer)를 이용하여 입사하는 ion energy와 flux 양을 컨트롤 하였고, 250 W에서 최적화된 ion energy distribution 영역이 존재한다는 것을 확인할 수 있었다. 또한, 25 Gauss 정도의 electro-magnetic field를 이용하여 Ar의 ion energy를 10 eV 이하로 낮추어 damage를 최소화함으로써 효과적으로 그래핀을 cleaning 할 수 있었다. Cleaning과정에서 ion bombardment에 의해 발생한 damage는 $250^{\circ}C$에서 6시간 동안 annealing 공정을 거치면서 회복되는 것을 Raman spectroscopy의 D peak ($1335cm{\cdot}^1$) / G peak ($1572cm{\cdot}^1$) ratio 로 확인할 수 있었고, PMMA residue의 cleaning 여부는 G peak ($1580cm{\cdot}^1$)의 blue shift와 2D peak ($2670cm{\cdot}^1$)의 red shift를 통해 확인하였다. 그리고 AFM (Atomic Force Microscopy)을 이용하여 cleaning 공정과정에서 RMS roughness가 4.99 nm에서 2.01 nm로 감소하는 것을 관찰하였다. 마지막으로, PMMA residue의 cleaning 정도를 정량적으로 분석하기 위해 XPS (X-ray Photoelectron Spectroscopy)를 이용하여 sp2 C-C bonding이 74.96%에서 87.66%로 증가함을 확인을 할 수 있었다.

• Journal of the Korea Society of Computer and Information
• /
• v.11 no.2 s.40
• /
• pp.101-110
• /
• 2006

ADevelopment of various geographic observations, GPS, and Wireless Communication technologies make it easy to control many moving objects and to build an intelligent transport system and transport vehicle management system. However it is difficult to make a suitable system in the real world with a variety of tests to evaluate the performance fairly because real vehicle data are not enough as evaluating and testing the transport plan in the system. Therefore some moving object data generator would be used in most researches. However they can not generate vehicle trajectory according to a user scenario defined to be applied to transport plan, because the existing data generators consider only a gauss distribution, road network. In this paper we design and implement a vehicle data generator for creating vehicle trajectory data based on the user-defined scenario. The designed data generator could make the vehicle location depending on user's transport plan. Besides we store the scenario as patterns and reutilize the used scenario.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2004.03a
• /
• pp.262-270
• /
• 2004

Basic experiments were carried out using the THT-IV low-power Hall thruster to examine the influences of magnetic field shape and strength, and acceleration channel length on thruster performance and to establish guidelines for design of high-performance Hall thrusters. Thrusts were measured with varying magnetic field and channel structure. Exhaust plasma diagnostic measurement was also made to evaluate plume divergent angles and voltage utilization efficiencies. Ion current spatial profiles were measured with a Faraday cup, and ion energy distribution functions were estimated from data with a retarding potential analyzer. The thruster was stably operated with a highest performance under an optimum acceleration channel length of 20 mm and an optimum magnetic field with a maximum strength of about 150 Gauss near the channel exit and with some shape considering ion acceleration directions. Accordingly, an optimum magnetic field and channel structure is considered to exist under an operational condition, related to inner physical phenomena of plasma production, ion acceleration and exhaust plasma feature. A new Hall thruster was designed with basic research data of the THT-IV thruster. With the thruster with many considerations, long stable operations were achieved. In all experiments at 200-400 V with 1.5-3 mg/s, the thrust and the specific impulse ranged from 15 to 70 mN and from 1100 to 2300 see, respectively, in a low electric power range of 300~1300 W. The thrust efficiency reached 55 %. Hence, a large map of the thruster performance was successfully made. The thermal characteristics were also examined with data of both measured and calculated temperatures in the thruster body. Thermally safe conditions were achieved with all input powers.

• Magazine of the Korean Society of Agricultural Engineers
• /
• v.24 no.3
• /
• pp.73-83
• /
• 1982

study aims to derive a rational method for the analysis of the farm silo supported on an elastic foundation in which it is assumed that the reaction pressure of the soil at a point is proportional to the deflection at that point. In order to investigate the effects of an elastic foundation on the behaviour of the structures on it, the analysis of the farm silo resting on an elastic foundation was compared with the solution that the ground support may be assumed uniform (which was obtained from part I of this paper). To calculate the deformation of an elastic foundation, Boussinesq's solution which allows an interaction of the various parts of ground was adopted. In this case, the foundation was treated as a superparametric element additionally. In the evaluation of an element stiffness matrix, Gauss quadrature' was used. In above numerical integration, 3-point rule for the farm silo wall and the footing was introduced and 2-point rule for the evaluation of a reaction between the footing and the elastic foundation was adopted. The stresses of a farm silo on an elastic foundation were smaller than those which the distribution of contact pressure between the footing and the soil is assumed uniformly. Since the differences of stresses were remarkable in PS structures than RC structures, it is desirable that designers take into account the effect of an elastic foundation for the case of PS structures. It can be noted that while the effect of an elastic foundation was more conspicuously observed in near of the ground, the value of stresses at far from the soil was little affected by an supported soil.

• Journal of the Korean Society for Library and Information Science
• /
• v.51 no.1
• /
• pp.5-27
• /
• 2017

The goal of this study is to suggest various improvements and expanding strategies of the public library ecosystem. For this goal, researcher reviewed and analyzed the realistic landscapes and social recognitions about the public library ecosystem as local public goods, and discoursed the basic principles and structural terrain of public library ecosystem based on natural ecosystem. As a result, researcher proposed multifaceted alternatives (ensure library's identity and publicity applying Law of Karma, strengthen librarian's professionalism on the premise of overcoming the Minerva's syndrome, optimize the library service and collection management based on the Pareto principle, reduce reading room and differentiated program through resolution of Halo effect, eliminate usage bias by life cycle based on the Gauss distribution, acceptance of the digital paradigm and use-friendly spatialization that ruminates the Icarus paradox, incorporate small library into public library system through a clear understanding of the Gresham's law, and enforce communication and spread social and cultural value through the practice of the Pompeii paradox).