• 제목/요약/키워드: discrete effect

검색결과 584건 처리시간 0.036초

이산와류법을 사용한 비평면 지면 와류전개 연구 (Study on the Wake Evolution on the Non-Planar Ground Using a Discrete Vortex Method)

  • 한철희
    • 융복합기술연구소 논문집
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    • 제6권2호
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    • pp.21-24
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    • 2016
  • Accurate simulation of wakeshapes behind a wing is important for the performance prediction of the aircraft and the wake hazard problem in the airport. In the present study, wakeshapes behind a wing inside tunnels are simulated in regard to the development of wing-in-ground effect vehicles. A discrete vortex method with a nonplanar ground modelling is used for the simulation. It was found that the wingtip vortices move toward outboard directions when the wing is in ground effect. When the wing is placed inside tunnels, the wingtip vortices move along the tunnel wall with counter clockwise direction. As the gap between the wingtip and the tunnel decreases, the wingtip vortices move further along the tunnel wall. Both vortices from bothsides of the wing will murge, which will be studied in future using a viscous computation.

A New Robust Digital Sliding Mode Control with Disturbance Observer for Uncertain Discrete Time Systems

  • Lee, Jung-Hoon
    • 전기전자학회논문지
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    • 제15권2호
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    • pp.149-156
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    • 2011
  • In this paper, a new discrete variable structure controller based on a new sliding surface and discrete version of the disturbance observer is suggested for the control of uncertain linear systems. The reaching phase is completely removed by introducing a new proposed sliding surface. The discrete version of the disturbance observer is derived for the effective compensation of the effect of uncertainties and disturbances. A corresponding control input with the disturbance compensation is selected to guarantee the quasi sliding mode on the predetermined sliding surface for guaranteeing the designed output in the sliding surface from any initial condition to the origin for all the parameter variations and disturbances. By using Lyapunov function, the closed loop stability and the existence condition of the quasi sliding mode is proved. Finally, an illustrative example is presented to show the effectiveness of the algorithm.

Ziegler-Nichols 방법을 이용한 이산형 PID제어기의 자동동조 (On the Auto-Tuning of a Discrete PID Controller Based on the Ziegler and Nichols's Method)

  • 이영일;권욱현
    • 대한전기학회논문지
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    • 제40권8호
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    • pp.774-781
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    • 1991
  • This paper proposes an auto-tuning method of a discrete -PIC controllers which is based on the Ziegler and Nichols's PID Tuning Rule. This tunign rule is derived using the Pade's first order approximation and it prevents the performance degradation caused by the time-delay effect of zero order holder when the Ziegler-Nichols tuning rule is applied to a discrete PID controller. A simple and practical auto-tuning method is proposed through combining this discrete tuning rule with the relay control. The auto-tuning scheme is implemented on a microprocessor based system and is applied to a position control system to show the effectiveness of the discrete tuning rule.

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Discrete Element Simulation of the Sintering of Composite Powders

  • Martina, C. L.;Olmos, L.;Schneiderb, L. C. R.;Bouvardc, D.
    • 한국분말야금학회:학술대회논문집
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    • 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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    • pp.262-263
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    • 2006
  • The free sintering of metallic powders blended with non sintering inclusions is investigated by the Discrete Element Method (DEM). Each particle, whatever its nature (metallic or inclusion) is modeled as a sphere that interacts with its neighbors. We investigate the retarding effect of the inclusions on the sintering kinetics. Also, we present a simple coarsening model for the metallic particles, which allows large particles to grow at the expense of the smallest.

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철로를 따라 전파되는 파동 해석을 위한 고주파수 대역 철로 모델링 (Modelling of Railway Tracks for Wave Propagation along Railway Tracks at High Frequencies)

  • 유정수
    • 한국소음진동공학회논문집
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    • 제21권3호
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    • pp.248-257
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    • 2011
  • It was reported recently that railpads can be included as a continuous elastic support of the rail and the model was justified from experiments. In general, however, railpads are installed discretely on sleepers with a regular span. The effect of the discrete railpad was not clearly examined so far in such a high frequency range. In this paper, the effect of the railpads in track modelling for high frequencies is investigated by means of the finite element analysis. To do that, the railpads are regarded as 'a continuous elastic support' and 'a discrete elastic support' in this paper. The dispersion relations and decaying features are predicted and compared between the two models up to 80 kHz.

콘크리트 슬래브 궤도의 3차원 거동해석 (3- D Analysis of Concrete Slab Track System)

  • 김정일;장승엽
    • 한국철도학회:학술대회논문집
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    • 한국철도학회 2004년도 춘계학술대회 논문집
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    • pp.955-960
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    • 2004
  • In this study, three dimensional FE analysis of concrete slab track has been performed in order to develop the realistic design of precast concrete slab track. The precast slab track system including the precast concrete slab panel and the grout layer is modeled using the three dimensional solid element with crack softening effect. The input load is computed from the one dimensional beam element model constituting the rail and several discrete springs. To investigate the effect of the longitudinal connection of slab panels, two different systems-continuous and discrete systems - are modeled. The analytical results show that the stresses of both the slab panel and the grout layer are in the range of linear elastic, and, at the interface between two adjacent panels, the primary stresses of the grout layer of the discrete system are higher than those of the continuous system. However, The overall stress levels of the grout layer are very low relative to the strength of th grout.

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웨이브렛을 이용한 잡음 제거 알고리즘 (Denoising Algorithm using Wavelet)

  • 배상범;김남호
    • 한국정보통신학회논문지
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    • 제6권8호
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    • pp.1139-1145
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    • 2002
  • 웨이브렛 변환 데이터는 신호의 상세 정보를 포함하고 있으므로 주파수 대역별로 필터링할 수 있다. 따라서, 본 논문에서는 중요한 두 가지 잡음을 웨이브렛을 사용하여 제거하였다. AWGN 환경에 대해서 hard-threshold를 적용한 UDWT(undecimated discrete wavelet transform)를 사용하였으며, 임펄스 잡음환경에 대해서는 임계치에 의한 잡음 제거와 웨이브렛에 의한 신호의 slope를 이용하여, 잡음 제거 효과를 최대로 함과 동시에 원신호의 edge를 인식하도록 하였다. 이러한 잡음 제거 효과의 판단 기준으로 SNR을 사용하였으며, 테스트 신호로서 Blocks와 DTMF(dual tone multi frequency)를 사용하였다.

DYNAMICS OF A DISCRETE RATIO-DEPENDENT PREDATOR-PREY SYSTEM INCORPORATING HARVESTING

  • BAEK, HUNKI;HA, JUNSOO;HYUN, DAGYEONG;LEE, SANGMIN;PARK, SUNGJIN;SUH, JEONGWOOK
    • East Asian mathematical journal
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    • 제31권5호
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    • pp.743-751
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    • 2015
  • In this paper, we consider a discrete ratio-dependent predator-prey system with harvesting effect. In order to investigate dynamical behaviors of this system, first we find out all fixed points of the system and then classify their stabilities by using their Jacobian matrices and local stability method. Next, we display some numerical examples to substantiate theoretical results and finally, we show numerically, by means of a bifurcation diagram, that various dynamical behaviors including cycles, periodic doubling bifurcation and chaotic bands can be existed.

AWGN 환경에서 웨이브렛을 이용한 잡음 제거 방법에 관한 연구 (A Study on Denoising Methods using Wavelet in AWGN environment)

  • 배상범;김남호
    • 한국정보통신학회논문지
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    • 제5권5호
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    • pp.853-860
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    • 2001
  • 본 논문에서는 웨이브렛을 이용한 두 가지 새로운 잡음 제거 방법으로, 공간적 상관관계를 이용한 NSSNF(new spatially selective noise filtration)과 threshold에 기초한 UDWT(undecimated discrete wavelet transform)을 제시한다. NSSNF에서는 기존의 SSNF에 새로운 파라메타를 추가하여, 융통성 있는 SNR 이득 특성을 얻도록 하였으며, UDWT에서는 hard-threshold를 적용하여, 기존의 soft-threshold를 적용한 OWT(orthogonal wavelet transform)보다 우수한 잡음 제거 효과를 얻도록 하였다. 이러한 테스트 환경으로는 AWGN을 선택하였으며, 개선 효과의 판단 기준으로 SNR을 사용하여, 기존의 잡음 제거 방법과 비교 분석하였다.

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