• Tribology and Lubricants
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• 제17권6호
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• pp.441-446
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• 2001

In this paper the effect of bump compliance, load, and the number of pad on the lift-off speed is studied. When the load is greater and bump compliance lower, the shaft is lifted off at higher rotating speed. And when the load is applied near the center of pad, lift-off speed is lower. When the number of pad increases, the lift-off speed is higher. The lift-off characteristics can be used to lengthen the lift time of the coating and design the rotating machinery supported by bump bearings.

• International Journal of Aeronautical and Space Sciences
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• 제2권2호
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• pp.73-81
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• 2001

This paper describes the procedure to develop a robust estimator design method for a target tracker that accounts for both structured real parameter uncertainties and unknown inputs. Two robust design approaches are combined: the Mini-p-Norm. design method to consider real parameter uncertainties and the $H_{\infty}$ design technique for unknown disturbances and unknown inputs. Constant estimator gains are computed that guarantee the robust performance of the estimator in the presence of parameter variations in the target model and unknown inputs to the target. The new estimator has two design parameters. One design parameter allows the trade off between small estimator error variance and low sensitivity to unknown parameter variations. Another design parameter allows the trade off between the robustness to real parameter variations and the robustness to unknown inputs. This robust estimator design method was applied to the longitudinal motion tracking problem of a T-38 aircraft.

• 한국디자인학회:학술대회논문집
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• 한국디자인학회 2002년도 가을학술발표대회 디자인학 연구
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• pp.118-119
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• 2002

• 한국항공우주학회지
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• 제45권10호
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• pp.872-880
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• 2017

일반적으로 추력기는 on/off 제어 방식을 이용한다. Bang-Bang Control, PWM(Pulse Width Modulator), PWPF(Pulse Width Pulse Frequency) 등이 그 방법으로 많이 이용되고 있다. PWPF를 설계할 때 파라미터($K_m$, ${\tau}$, $U_{on}$, $U_{off}$, $U_m$)를 잘못 선정하면 위상 지연, 연료 낭비, 수명 감소 등이 발생한다. 그러므로 파라미터가 시스템 성능에 미치는 영향을 분석하고 적절한 파라미터를 선정하여야 한다. 본 논문은 정적 해석을 수행하여 PWPF 파라미터 설계방안을 제시하였으며, 동적 분석 및 시뮬레이션을 수행하여 설계변수에 미치는 상호 영향을 분석하였다.

• Journal of Power Electronics
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• 제16권4호
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• pp.1256-1267
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• 2016

Distributed stray inductance exerts a significant influence on the turn-off voltages of power switching devices. Therefore, the design of low stray inductance bus bars has become an important part of the design of high-power converters. In this study, we first analyze the operational principle and switching transient of a T-type converter. Then, we obtain the commutation circuit, categorize the stray inductance of the circuit, and study the influence of the different types of stray inductance on the turn-off voltages of switching devices. According to the current distribution of the commutation circuit, as well as the conditions for realizing laminated bus bars, we laminate the bus bar of the converter by integrating the practical structure of a capacitor bank and a power module. As a result, the stray inductance of the bus bar is reduced, and the stray inductance in the commutation circuit of the converter is reduced to more than half. Finally, a 10 kVA experimental prototype of a T-type converter is built to verify the effectiveness of the designed laminated bus bar in restraining the turn-off voltage spike of the switching devices in the converter.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제49권8호
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• pp.463-467
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• 2000

In this paper, the new LIGBT structures with trap injection are proposed to improve switching characteristics of the conventional SOI LIGBT. The Simulations are performed in order to investigate the effects of the positiion, whidth and concentration of trap injection region with a reduced minority carrier lifetime using 2D device simulator MEDICI. Their electrical characteristics are analyzed and the optimum design parameters are extracted. As a result of simulation, the turn off time for the model A with the trap injection is $0.78\mus$. These results indicate the improvement of about 2 times compared with the conventional SOI LIGBT because trap injection prevents minority carriers which is stored in the n-drift region during turn off switching. The latching current is $1.5\times10^{-4}A/\mum$ and forward blocking voltage is 168V which are superior to those of conventional structure. It is shown that the trap injection is very effective to reduce the turn off time with a little increasing of on-state voltage drop if its design and process parameters are optimized.

• 한국생활과학회지
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• 제13권5호
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• pp.787-798
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• 2004

This research was designed to compare clothing fabric images between on- and off-line by fabric types and its characteristics. 125 subjects who have a fashion design major evaluated the fabric image of various 16 kinds of specimens on- and off-line. Frequency, x2-test, t-test, and Pearson correlation were used for statistical analysis by SPSS WIN 11.0. The results of this study are as follows: 1. The advantage of on-line shopping includes low price and purchasing convenience, etc. On-line shoppers mostly purchase clothing items, such as T-shirt and slacks. In most cases, texture of fabrics provides a main cause for the shoppers' discontentment with internet shopping. 2. The results of t-test for the difference of the evaluation score show that plain or pile weave and highly thick or thin fabrics-for example, Organdy, Corduroy, Nylon Taffeta, Plush, etc.-have a large difference between on-and off-line image. On the other hand, medium-thick twill weave-for example, Tweed, Flannel, etc.-or patterned weave-Chiffon, Dobby fabric, etc.-shows a small difference. 3. The results of correlation of the evaluation score indicate that wool twill fabrics like Tweed, Saxony, and Polafleece show a high correlation between two kinds of evaluation score. In texture preference, no correlation exists between on-line and off-line. 4. With an analysis on fabric image evaluation by fabric characteristics, smooth, shiny pink Satin was found the most positively-evaluated item in all evaluation fields except in pattern preference and individuality. On the other hand, thick olive green Corduroy was evaluated most negatively in the fields of elegance, luxury, and feminine. 5. When compared with real ones, thin fabrics provide a different on-line fabric image. For example, Nylon Taffeta and Organdy were evaluated positively on-line because of luster and pastel tone color. However, lusterless uneven cotton Seersucker was evaluated negatively. 6. Real fabrics preference is more negative than on-line ones. In addition, patterned or unique fabrics display a high agreement between the two kinds of images.

• 정보저장시스템학회논문집
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• 제2권2호
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• pp.130-137
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• 2006

The HDD(hard disk drive) using Load/unload(L/UL) technology includes the benefits which are increased areal density, reduced power consumption and improved shock resistance than those of contact-start-stop(CSS). It has been widely used in portable hard disk drive and will become the key technology for developing the small form factor hard disk drive. The main objects of L/UL are no slider-disk contact or no media damage. For realizing those, we must consider many design parameters in L/UL system. In this paper, we focus on lift-off force. The 'lift-off' force, defined as the minimum air bearing force, is another very important indicator of unloading performance. A large amplitude of lift-off force increases the ramp force, the unloading time, the slider oscillation and contact-possibility. To minimize 'lift-off' force we optimizes the slider and suspension using the integrated optimization frame, which automatically integrates the analysis with the optimization and effectively implements the repetitive works between them. In particular, this study is carried out the optimal design considering the process of modes tracking through the entire optimization processes. As a result, we yield the equation which can easily find a lift-off force and structural optimization for suspension.

• 대한기계학회논문집A
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• 제37권12호
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• pp.1513-1519
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• 2013

유전 알고리즘은 자연의 진화 과정에 기초한 계산 모델로서 전역 최적화 결과를 제공할 수 있다. 변화율(gradient)을 기반으로 하는 방법들과는 달리, 민감도 해석이 요구되지 않으므로 민감도 해석이 어려운 전계(electric field)에서의 나노 단위 구조물의 형상 설계에 적합하다. 본 연구는 유전 알고리즘과 ON/OFF 방법을 기반으로 위상최적화를 수행하여 가시광선 영역에서 새로운 형태의 나노개구 설계를 목표로 하였다. 연구의 목적은 나노개구 아래10nm에 위치한 측정영역에서의 전계 투과효율(transmission rate)을 최대화하며, 동시에 다른 영역에서의 전계 분포를 최소화하는 것이다. 유한요소해석 및 최적화 과정은 상용 프로그램 COMSOl과 Matlab 프로그램의 연동에 의하여 수행되었다. 최적화 모델의 결과는 초기 모델과의 전계 강도 (electric field intensity) 및 근접장의 초점치수(spot size)를 비교하여 분석하였다.

• 대한조선학회논문집
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• 제61권2호
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• pp.125-134
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• 2024

The Safe Operating Envelope (SOE) combined with Short-Take-Off and Vertical Landing (STOVL) performance is an essential consideration of a light aircraft carrier for design of hull shape with excellent seakeeping performance in terms of naval air operations as well as traditional naval ship missions such as Transit and Patrol (TAP), and Replenishment at Sea (RAS) and so on. A variety of procedures are systematically combined to determine SOE considering rather complicated missions associated with operation of aircraft onboard. The evaluation of take-off and landing safety missions onboard should consider wind effect on deck and severer seakeeping indices and standards compared with conventional naval ships. In order to support take-off and landing missions, various support activities of the crews are required. So, additional evaluation is needed for indicators such as MSI(Motion sickness Index) and MII(Motion Induced Interruptions), which are quantitative indicators of work ability that appear as a result of motion response. In this study, a standard procedure is developed including the seaworthiness performance indicators, standards, and evaluation procedures that should be considered during design of STOVL aircraft carrier. Analysis results are discussed in terns of air-wake on deck as well as seakeeping indices associated with design parameter changes in view of conceptual design of a light aircraft carrier.