• 전자공학회논문지A
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• 제28A권9호
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• pp.708-714
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• 1991

In this paper, the noise contribution to the permit tivity profile reconstructed by the spectral inverse scattering scheme is investigated and a low-pass filter is proposed to reduce such the noise effects. Numerical simulations showed that the reconstructed profiles are affected by extremely large error. The suggested low-pass filter made it possible to reconstruct the permittivity profile nearly similar to the original. Furthermore, the optimal condition to the low-pass filter agreed well with the physical meaning even if several variables involved in the inverse scattering scheme were changed.

• Journal of Electrical Engineering and Technology
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• 제10권4호
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• pp.1597-1609
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• 2015

This paper introduces the fundamentals of the conventional LC low-pass filter circuit in the fractional domain. First, we study the new fundamentals of fractional-order LC low-pass filter circuit including the pure real angular frequency, the pure imaginary angular frequency and the short circuit angular frequency. Moreover, sensitivity analysis of the impedance characteristics and phase characteristics of the LC low-pass filter circuit with respect to the system variables is studied in detail, which shows the greater flexibility of the fractional-order filter circuit in designs. Furthermore, from the filtering property perspective, we systematically investigate the effects of the system variables (LC, frequency f and fractional orders) on the amplitude-frequency characteristics and phase-frequency characteristics. In addition, the detailed analyses of the cut-off frequency and filter factor are presented. Numerical experimental results are presented to verify the theoretical results introduced in this paper.

• 정보처리학회논문지A
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• 제11A권2호
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• pp.203-206
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• 2004

저자는 등각사상을 구하기 위한 기존의 여러 Theodorsen 방정식의 해법 중 가장 유효한 해법으로 알려져 있는 Wegmann의 방법을 다룬바 있다. Wegmann의 방법으로 수치실험을 한 결과 난이도가 높다고 예상되는 문제에 있어 수렴했다가 발산을 하는 불안정현상이 나타났으며 수렵하지 않는 불안정현상의 원인을 분석하여 저주파필터를 적용한 새로운 반복법을 제안하였다. 원래의 Wegmann 반복법으로는 발산하는 모튼 문제에 있어서 새로 제안한 방법에 의해서 수렴하는 수치실험 결과를 얻었는데 본 논문에서는 저주파필터를 적용한 Wegmann해법에 의해 실험적으로 수렴한 결과를 Fourier 분석기법에 의해 이론적으로 증명한다.

• 한국해안해양공학회지
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• 제19권5호
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• pp.418-428
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• 2007

Boussinesq 방정식에 의한 파랑전파의 계산과정 중 파랑의 비선형 상호작용 및 쇄파발생에 의하여 수치잡음이 흔히 발생하며 이 잡음을 적절히 제어하지 않을 경우 해가 급속히 발산하게 된다. 본 연구에서는 계산 중간과정에 주기적으로 적용하여 수치잡음을 제거하기 위한 세가지 형태의 저파수통과 필터(FFT 필터, 가우스 필터, 그리고 Shapiro 필터)의 특성에 대하여 고찰하였다. 경사면 파동장에 대한 기존의 수리실험 결과와 본 수치해석 결과를 비교하고 각 필터의 잡음 제거효과, 주 시그널의 보존성, 그리고 계산 소요시간에 대하여 검토하였다. 그 결과, Shapiro 필터의 매개변수(필터 요소수와 통과수, 그리고 필터적용주기)를 적절히 설정함으로써 계산의 정확성과 효율성을 잘 달성할 수 있는 것으로 나타났다. 적정한 매개변수 선정을 위해서는 다소의 시행착오적 계산이 요구되나 대체적으로 필터 요소수 4에 대하여 50이내의 필터 통과수와 $100{\sim}200$ 시간스텝 정도의 적용주기가 타당한 것으로 판단된다.

• 한국산업융합학회 논문집
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• 제24권4_2호
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• pp.443-451
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• 2021

It is essential to examine and analyze the power output and load responses together using real-world turbulent wind speeds. In this paper, the power controller and the drive train damper are simultaneously considered using the NREL 5MW wind turbine model, and the damage equivalent load(DEL) of the low speed shaft torque and power output responses according to the natural frequency of the second order low pass filter are simultaneously investigated. Numerical testing is carried out above rated wind speed using commercially available Bladed software. From the viewpoints of DEL reduction of the drive train shaft torque and power output responses, it is shown that the natural frequency of the low pass filter is appropriately about 6 to 10rad/s. And the reduction ratio of the DEL of the low-speed shaft torque decreases as the wind speed becomes higher, and it is confirmed that the reduction ratio is limited to about 20% at high wind speeds.

• Journal of applied mathematics & informatics
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• 제20권1_2호
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• pp.611-621
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• 2006

This paper is to discuss the numerical conformal mapping from the unit disk onto Jordan region, which can be solved by Theodorsen equation. Wegmann's method has been known as the most efficient one for the Theodorsen equation. However, we found divergence through numerical experiments by the iterative method of Wegmann. The divergence occurs especially when some degree of difficulty is high. We analyze the cause of divergence and propose an improved method by applying a low frequency pass filter to Wegmann's method. By this proposed method we can get a stable convergence for all the problems which was unstable with the Wegmann's method.

• 전기학회논문지
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• 제56권2호
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• pp.383-388
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• 2007

This paper considers a low-order dynamic output feedback controller design problem. Since the proposed control law inherently has a low-pass filter property, it can alleviate the mal-effects of the sensor noise without additional filter designs. Frequency domain analysis shows the characteristics of the proposed control law against measurement noise. The effectiveness of the proposed control law is illustrated by numerical simulations with a rotary inverted pendulum and a convey-crane. Using only one integrator the proposed control law has the advantage to the stabilization problem with sensor noise as well as it can successfully replace the measurements of derivative terms in a state feedback control law.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2009년도 추계학술대회
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• pp.821-824
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• 2009

등각사상은 함수론의 기본적인 문제의 하나로 물리학, 공학 등에 응용되고 있다. 예를 들어 선박이나 비행기의 모양을 고려할 때 나타나는 유체의 문제등에 유용하게 쓰이고 있다. 본 논문에서는 단위원 내부로부터 Jordan 영역 내부에로의 수치등각사상을 구하는 문제를 다루는데 이것은 비선형 적분방정식인 Theodorsen방정식을 푸는 것으로 귀착된다. Theodorsen방정식을 구하는 해법 중 Wegmann의 방법은 계산량에 있어서 가장 유효하다고 알려져 있다. 그러나 수치실험을 통하여 난이도가 높은 문제에 있어 수렴하지 않는 문제점을 발견하게 되었다. 본 논문에서는 수렴하지 않는 불안정의 원인을 이론적으로 분석하고 저주파필터에 의하여 개선한 방법을 제안한다. 개선한 방법에 의한 수치 실험결과를 보고한다.

• 한국정보처리학회논문지
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• 제6권10호
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• pp.2716-2721
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• 1999

The problem of determining the conformal maps from the unit disk onto a jordan region has been completed by solving the theodorsen equation that is nonlinear. For the hubners method, which has been well known for the efficient method among the many suggestions for the Theodorsen equation, it has been reproved in our early study that the convergence rate could be remarkably improved by exploring and applying a low-frequency pass filter[1]. However, in the Hubner's method with the low-frequency filter, the discrete numbers and parameters of the low-frequency filter were able to be acquired only by experience. In this paper we show algorithms that determine the discrete numbers and parameters of the low-frequency filter automatically in accordance with the given region. This results from analyzing the function, which decides the shape of the given domain under the assumption that the degree of the problem depends of the transformation of a given domain, as seen in the Fourier Transform.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1996년도 Proceedings of the Korea Automatic Control Conference, 11th (KACC); Pohang, Korea; 24-26 Oct. 1996
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• pp.385-388
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• 1996

A time delay controller with state feedback is proposed for azimuth motion control of the frictionless positioning device which is subject to the variations of inertia in the presence of measurement noise. The time delay controller, which is combined with a low-pass filter to attenuate the effect of measurement noise, ensures the asymptotic stability of the closed loop system. It is found that the low-pass filter tends to increase the robustness in the design of time delay controller as well as the gain and phase margins of the closed loop system. Numerical and experimental results support that the proposed controller guarantees a good tracking performance irrespective of the variation of inertia and the presence of measurement noise.