• Journal of the Korean Data and Information Science Society
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• 제5권2호
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• pp.87-94
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• 1994

In this paper, we consider optimum plan to determine stress change times under the three-step stress PALTs, assuming that each test units follows an exponential distribution. The tampered random variable(TRV) model for the three-step stress PALTs setup are introduced, and maximum likelihood estimators(MLEs) of the failure rate and the acceleration factors are obtained. The change times to minimize the generalized asymptotic variance(GAVR) of MLEs of the failure rate and the acceleration factors are proposed for the three-step stress PALTs.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2009년도 정보 및 제어 심포지움 논문집
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• pp.323-325
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• 2009

In this paper, we present simulation results of Dynamic Matrix Control(DMC) to a boiler steam temperature. In order to control of steam temperature, we choose the input-output variables and generate the step response model by each input variable's step test. After that, the control structure executes on-line control with optimization using step response model. Proposed controller is applied to the APESS(Doosan company's boiler model simulator) and it is observed that the simulation results show satisfactory performance of proposed control.

• 한국해양공학회지
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• 제18권2호
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• pp.46-51
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• 2004

Natural frequencies of the transverse vibration of beams with step change in cross-section are obtained by using the asymptotic closed form solution. This closed form solution is found by using WKB method under the assumption of slowly varying properties, such as mass, cross-section, tension etc., along the beam length. However, this solution is found to be still very accurate even in the case of large variation in cross-section and tension. Therefore, this result can be easily applied to many engineering problems.

• ETRI Journal
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• 제27권1호
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• pp.122-125
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• 2005

A polymer-based planar-lightwave-circuit-type variable optical attenuator (VOA) was fabricated using a hot embossing process. With an optimized one-step embossing process, forty micro-channels for the guidance of light were defined on a polymer thin film with an accuracy of ${\pm}0.5{\mu}m$. The fabricated polymeric thermo-optic VOA shows 30 dB attenuation with 110 mW electrical input power at $1.55{\mu}m$. The rise and fall times are less than 5 ms.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 추계학술대회 논문집 학회본부
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• pp.697-702
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• 1997

Control system of electric machine systems is often required to provide the good control performance even in the presence of various variable loads. In this study, time delay control technique is adopted to overcome such variable loads. Also, in this research a new approach of avoiding saturation by varying the reference model for the time delay control based systems subject to the step changes in reference inputs. These schemes are verified by applications to the position controls of the AC servo motor system and the engine throttle actuator.

• 한국음향학회지
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• 제15권6호
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• pp.33-40
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• 1996

이 논문에서는 CATV 수신기에서 QAM 복조에 널리 이용되는 stop-and-go 알고리즘을 기본으로 한 블라인드 등화기의 상호 절충(trade-off)문제를 해결하였다. Stop-and-go 알고리즘은 탭 가중치의 적응 과정에서 최소 제곱 평균(least mean square) 알고리즘을 이용하였기 때문에 등화기의 구조가 간단하기는 하지만 전형적인 최소 제곱 평균 알고리즘과 같이 수렴 속도와 정상 상태 오차 사이에 상호 절충 문제가 존재한다. 정상 상태 오차를 일정한 수준으로 유지하면서 수렴 속도를 높이기 위해 가변 스텝 크기 알고리즘을 이용하였다. 동일 수준의 정상 상태 오차를 기준으로 하였을 때, 가변 스텝 크기 알고리즘을 이용한 stop-and-go 알고리즘이 상수 스텝 크기를 이용한 알고리즘에 비해 수렴 속도가 $36%{\sim}56%$ 향상되었다.

• 한국통신학회논문지
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• 제36권3C호
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• pp.157-162
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• 2011

동시 등화는 통신 채널을 블라인드 등화 시 수렵 특성 개선에 유용하다. 그러나 동시 등화는 등화기가 정상상태에 수렴한 후에도 동시 적응을 계속함으로써 성능 개선이 제한적이다. 본 논문에서는 동시 등화의 수렴 특성과 함께 정상상태 성능을 개선하기 위해, 가변 수렴상수와 가중치기반의 탭 계수 갱신을 적용하는 새로운 동시 등화 기법을 제안한다. 제안하는 동시 vsCMA+DD 등화는 가변 수렴상수 CMA(variable step-size CMA: vsCMA)와 판정의거 (decision-directed: DD) 알고리즘의 오차 신호를 사용하여 가중치를 산출하고, 이를 이용하여 두 등화기를 각각 가중 갱신한다. 제안 방법은 vsCMA에 의해 CMA의 오차 성능을 개선하고, 가중치기반의 탭 계수 갱신에 의해 수렴 속도와 정상상대 성능을 개선하였다. 모의실험을 통해 제안 방식의 성능 개선을 검증하였다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2009년도 추계학술대회 논문집
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• pp.231-239
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• 2009

The filtered-x LMS (FX-LMS) algorithm has been applied to the active noise control (ANC) system in an acoustic duct. This algorithm is designed based on the FIR (finite impulse response) filter, but it has a slow convergence problem because of a large number of zero coefficients. In order to improve the convergence performance, the step size of the LMS algorithm was modified from fixed to variable. However, this algorithm is still not suitable for the ANC system of a short acoustic duct since the reference signal is affected by the backward acoustic wave propagated from a secondary source. Therefore, the recursive filteredu LMS algorithm (FU-LMS) based on infinite impulse response (IIR) is developed by considering the backward acoustic propagation. This algorithm, unfortunately, generally has a stability problem. The stability problem was improved by using an error smoothing filter. In this paper, the recursive LMS algorithm with variable step size and smoothing error filter is designed. This recursive LMS algorithm, called FU-VSSLMS algorithm, uses an IIR filter. With fast convergence and good stability, this algorithm is suitable for the ANC system in a short acoustic duct such as the intake system of an automotive. This algorithm is applied to the ANC system of a short acoustic duct. The disturbance signals used as primary noise source are a sinusoidal signal embedded in white noise and the chirp signal of which the instantaneous frequency is variable. Test results demonstrate that the FU-VSSLMS algorithm has superior convergence performance to the FX-LMS algorithm and FX-LMS algorithm. It is successfully applied to the ANC system in a short duct.

• 한국소음진동공학회논문집
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• 제22권2호
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• pp.146-155
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• 2012

The filtered-x LMS(FX-LMS) algorithm has been applied to the active noise control(ANC) system in an acoustic duct. This algorithm is designed based on the FIR(finite impulse response) filter, but it has a slow convergence problem because of a large number of zero coefficients. In order to improve the convergence performance, the step size of the LMS algorithm was modified from fixed to variable. However, this algorithm is still not suitable for the ANC system of a short acoustic duct since the reference signal is affected by the backward acoustic wave propagated from a secondary source. Therefore, the recursive filtered-u LMS algorithm(FU-LMS) based on infinite impulse response(IIR) is developed by considering the backward acoustic propagation. This algorithm, unfortunately, generally has a stability problem. The stability problem was improved by using an error smoothing filter. In this paper, the recursive LMS algorithm with variable step size and smoothing error filter is designed. This recursive LMS algorithm, called FU-VSSLMS algorithm, uses an IIR filter. With fast convergence and good stability, this algorithm is suitable for the ANC system in a short acoustic duct such as the intake system of an automotive. This algorithm is applied to the ANC system of a short acoustic duct. The disturbance signals used as primary noise source are a sinusoidal signal embedded in white noise and the chirp signal of which the instantaneous frequency is variable. Test results demonstrate that the FU-VSSLMS algorithm has superior convergence performance to the FX-LMS algorithm and FX-LMS algorithm. It is successfully applied to the ANC system in a short duct.

• 청정기술
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• 제18권2호
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• pp.155-161
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• 2012

본 연구의 목적은 분말 사출성형 공정에서 초임계유체를 이용하여 사출성형체로부터 결합제를 효율적으로 제거하는 것이다. 두께 1~2 mm 정도의 얇은 성형체의 경우는 기존의 초임계 추출공정을 이용하여 초기부터 온도, 압력이 높은 조건에서도 아무런 결함 없이 단시간 내에 결합제를 제거할 수 있지만, 시편이 두꺼워질수록 초기에 균열이 발생하기 때문에 일정 공정조건에서는 한계가 있다. 따라서 초기에는 낮은 공정조건에서 시작하여 단계별로 온도와 압력을 상승시키는 초임계 가변 조건 탈지공정을 연구하였다. 두께 1~4 mm의 세라믹 사출성형체 시편을 사용하여 여러 가지 초임계 조건에서 탈지실험을 수행하여 두꺼운 세라믹 사출성형체에 균열이 생기지 않으면서 가장 추출수율이 높은 가변조건 공정의 초기조건을 설정하였다. 이렇게 설정한 초기조건을 시작으로 직경 10 mm, 두께 4 mm의 두꺼운 세라믹 사출성형체 시편을 온도 333.15~343.15 K, 압력 12~27 MPa, $CO_2$ 유량 0.5~1.0 L/min 범위에서 단계별로 상승시켜 최종적으로는 5시간동안 95% 이상의 파라핀 왁스 결합제를 제거할 수 있었다.