• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
• /
• pp.331-331
• /
• 2012

With the NAND Flash scaling down, it becomes more and more difficult to follow Moore's law to continue the scaling due to physical limitations. Recently, three-dimensional (3D) flash memories have introduced as an ideal solution for ultra-high-density data storage. In 3D flash memory, as the process reason, we need to use poly-Si TFTs instead of conventional transistors. So, after combining charge trap flash (CTF) structure and poly-Si TFTs, the emerging device SONOS-TFTs has also suffered from some reliability problem such as hot carrier degradation, charge-trapping-induced parasitic capacitance and resistance which both create interface traps. Charge pumping method is a useful tool to investigate the degradation phenomenon related to interface trap creation. However, the curves for charge pumping current in SONOS TFTs were far from ideal, which previously due to the fabrication process or some unknown traps. It needs an optimization and the important geometrical effect should be eliminated. In spite of its importance, it is still not deeply studied. In our work, base-level sweep model was applied in SONOS TFTs, and the nonideal charge pumping current was optimized by adjusting the gate pulse transition time. As a result, after the optimizing, an improved charge pumping current curve is obtained.

• 한국레이저가공학회지
• /
• 제18권3호
• /
• pp.1-5
• /
• 2015

A 3D printer based on laser powder deposition (LPD), also known as DED (direct energy deposition), has been developed for fabricating metal parts. The printer uses a ytterbium fiber laser (1070nm, 1kW) and is equipped with an Ar purge chamber, a three-dimensional translation stage and a powder feeding system composed of a powder chamber and delivery nozzles. To demonstrate the performance of the printer, a tapered cylinder of 320mm in height has been fabricated successfully using Ti-6Al-4V powders. The process parameters including the laser output power, the scan speed, and the powder feeding rate have been optimized. A 3D printed test specimen shows mechanical properties (yield strength, ultimate tensile strength, and elongation) exceeding the criteria to employed in a variety of Ti alloy applications.

• 한국자동차공학회논문집
• /
• 제16권6호
• /
• pp.26-32
• /
• 2008

This research presents a simulation for the fuel economy of parallel diesel hybrid vehicle. Diesel engines compared to gasoline engines have the advantages of higher fuel economy and lower $CO_2$ emission. One of the most ways to meet future fuel economy and emissions regulation is to combine diesel engine technology with a hybrid electric vehicle. The simulation of HEV is growing need for rapid analysis of the many configurations and component options. WAVE, a one-dimensional engine analysis tool, was used to a 2.7L diesel engine. ADVISOR, designed for rapid analysis of the performance and fuel economy of vehicle models, was used to conventional and hybrid electric vehicle by the use of output file from WAVE as the input engine data file for ADVISOR. A parallel diesel HEV is at least $19.7{\sim}36%$ higher fuel economy and improved acceleration ability compared to a conventional diesel vehicle. The energy loss of the parallel diesel HEV is $23{\sim}38%$ less than the conventional vehicle using regeneration.

• Korean Journal of Geomatics
• /
• 제1권1호
• /
• pp.95-101
• /
• 2001

In a route plan, the route selection is a complicated problem to consider the spatial distribution and influence through overall related data and objective analysis on the social, economic and technical condition. The developed system in this study was compared and estimated by deciding a practical section for its validity and efficiency. Using Geographic Information System (GIS), the various information required for route selections in database was constructed, the characteristics of subject area by executing three-dimensional terrain analysis was grasped effectively, and the control point through buffering, overlay and location operation was extracted. An optimum route was selected by calculating the sum of alternatives to the sub-criteria weight, and from this result, there is a difference between real route and proposed route according to the prioritization of decision criteria based on the importance. This research could be constructed and applied geospatial information to the reasonable route plan and an optimum route selection efficiently using GIS. Therefore, the applications are presented by applying Analytic Hierarchy Process (AHP) to the decision-making of information needed in route selection.

• 유체기계공업학회:학술대회논문집
• /
• 유체기계공업학회 2004년도 유체기계 연구개발 발표회 논문집
• /
• pp.180-186
• /
• 2004

Average Bi-directional flow tube was suggested to measure single and two phase flow rate. Its working principle is similar with Pilot tube, however, it makes it possible to eliminate the cooling system which is normally needed to prevent from flashing in the pressure impulse line of Pilot tube when it is used in the depressurization condition. 3-dimensional steady state flow analyses using FLUENT 5.4 code were performed to validate the application of the averagebi-directional flow tube in case of water and air flow In this study, sensitivity studies have been performed to optimize the design features of the average hi-directional flow tube which can be applied for the various experimental conditions. For Re numbers above 1000, the k values are nearly constant regardless of the Re numbers and flow types and calculation results and experimental data coincides quite well. The current FLUENT calculation results suggest that linearity of the k values in various design features of the average BDFT is highly promising, which means that it is quite reasonable to select the typical design of the average BDFT for the convenience of the experimental conditions.

• Smart Structures and Systems
• /
• 제2권3호
• /
• pp.253-274
• /
• 2006

The structural monitoring of multi-wire strands is of importance to prestressed concrete structures and cable-stayed or suspension bridges. This paper addresses the monitoring of strands by ultrasonic guided waves with emphasis on the signal processing and automatic defect classification. The detection of notch-like defects in the strands is based on the reflections of guided waves that are excited and detected by magnetostrictive ultrasonic transducers. The Discrete Wavelet Transform was used to extract damage-sensitive features from the detected signals and to construct a multi-dimensional Damage Index vector. The Damage Index vector was then fed to an Artificial Neural Network to provide the automatic classification of (a) the size of the notch and (b) the location of the notch from the receiving sensor. Following an optimization study of the network, it was determined that five damage-sensitive features provided the best defect classification performance with an overall success rate of 90.8%. It was thus demonstrated that the wavelet-based multidimensional analysis can provide excellent classification performance for notch-type defects in strands.

• 대한조선학회논문집
• /
• 제33권3호
• /
• pp.103-111
• /
• 1996

이미 저자들에 의해 기존의 경사처짐법을 일반화하여 일반화 경사처짐법을 정립하였으며, 일차적으로 횡강도 해석 측면에서 그 유용성을 확인하기 위해 유조선을 대상으로 frame modeling을 통한 횡강도 해석을 수행한 바 있다. 본 연구에서는 설계 측면에서의 일반화 경사처짐법의 유용성을 확인하기 위해 일반화 경사처짐법과 이산화 변수를 고려한 최적화 기법을 결합하여 최소 중량 설계 프로그램을 개발하였다. 이 프로그램을 통해 주어진 설계 조건하에서 최소 중량을 주는 유조선의 설계 치수를 결정할 수 있었으며, 실적선에 비해 상당한 양의 선각 중량이 감소가 되는 설계가 가능함을 보여 주었다.

• 대한조선학회논문집
• /
• 제40권6호
• /
• pp.12-19
• /
• 2003

Corrugated bulkheads for a bulk carrier are divided into watertight bulkheads and deep tank bulkheads. Design of the watertight bulkheads is principally determined by the permissible limit of Classification and IACS requirements. But, the verification of strength through finite element analysis is indispensable for design of the deep tank bulkheads. A stage for stress evaluation of corrugated part is required for optimum structural design of the deep tank bulkheads. Since the finite element analysis for real model requires excessive amount of calculation time, in this study one corrugated structure is replaced with beam element and is idealized as 2 dimensional frame structure connected to upper and lower stool Minimum weight design of the deep tank bulkheads is performed through generalized sloped deflection method(GSDM) as direct calculation method. The purpose of this study is the development of design system for the minimization of steel weight of deep tank bulkheads as well as watertight bulkheads. Discrete variables are used as design variables for the practical design. Evolution strategies(ES) is used as an optimization technique.

• 한국물환경학회지
• /
• 제24권1호
• /
• pp.129-134
• /
• 2008

Ultrasonic cavitational energy distributions were measured in a large-scale sonoreator. In application of 110 and 170 kHz of ultrasound, the cavitational energy was just detected near the transducer module. However 35 and 72 kHz ultrasound made good distributions from the module to the end of the sonoreactor, Especially, 72 kHz ultrasound application showed most stable and highest cavitational energy value through the whole length. In the comparison between input power and cavitational energy, linear relationships were obtained in 35 and 72 kHz and it was anticipated that these results would be used for the optimization of input power for the design of sonoreactors. And three dimensional energy distribution was depicted through the mapping of cavitaional energy. Average energy in the large-scale sonoreactor was estimated as 62.8 W, which was about 40 % of input power.

• 설비공학논문집
• /
• 제23권11호
• /
• pp.754-761
• /
• 2011

The present study numerically investigates two-dimensional flow and heat transfer in the multiple confined impinging slot jet. Numerical simulations are performed for the different Reynolds numbers(Re=100 and 200) in the range of nozzles from 1 to 9 and height ratios(H/D) from 2 to 5, where H/D is the ratio of the channel height to the slot width. The vector plots of velocity profile, stagnation and averaged Nusselt number distributions are presented in this paper. The dependency of thermal fields on the Reynolds number, nozzle number and height ratio can be clarified by observing the Nusselt number as heat transfer characteristic at the stagnation point and impingement surface. The Nusselt number at the stagnation point of the central slot shows unsteadiness at H/D=3 and Re=200. The value of Nusselt number at the stagnation point of the central slot decreases with higher Reynolds number and number of nozzle although overall area averaged Nusselt number increases. Hence careful selection of geometrical parameters and number of nozzle are necessary for optimization of the heat transfer performance of multiple slot impinging jet.