• Journal of the Optical Society of Korea
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• 제19권4호
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• pp.357-362
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• 2015

We examine the principle of a modified Pound-Drever-Hall (PDH) technique to measure the free spectral range of a Fabry-Perot etalon (FPE). The FPE's periodic transmission of phase-modulated light allows us to adopt a sampling theorem to develop a new relationship for the PDH error signal. This leads us to find the key parameters governing the measurement accuracy: the phase modulation index ${\beta}$ and the FPE finesse. Without any additional complexity for background noise reduction, we achieve a measurement accuracy of 0.5 ppm. The improvement is mainly attributed to the wide-band phase modulation approaching ${\beta}=10$, and partly to the use of both reflected and transmitted light from the FPE and good FPE finesse.

• International Journal of Control, Automation, and Systems
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• 제4권4호
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• pp.438-447
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• 2006

Fuzzy controller's design depends mainly on the rule base and membership functions over the controller's input and output ranges. This paper presents two different approaches to deal with these design issues. A simple and efficient approach; namely, Fuzzy Subtractive Clustering is used to identify the rule base needed to realize Fuzzy PI and PD type controllers. This technique provides a mechanism to obtain the reduced rule set covering the whole input/output space as well as membership functions for each input variable. But it is found that some membership functions projected from different clusters have high degree of similarity. The number of membership functions of each input variable is then reduced using a similarity measure. In this paper, the fuzzy subtractive clustering approach is shown to reduce 49 rules to 8 rules and number of membership functions to 4 and 6 for input variables (error and change in error) maintaining almost the same level of performance. Simulation on a wide range of linear and nonlinear processes is carried out and results are compared with fuzzy PI and PD type controllers without clustering in terms of several performance measures such as peak overshoot, settling time, rise time, integral absolute error (IAE) and integral-of-time multiplied absolute error (ITAE) and in each case the proposed schemes shows an identical performance.

• Earthquakes and Structures
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• 제9권3호
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• pp.455-480
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• 2015

In the last decade, displacement-based (DB) methods have become established design procedures for reinforced concrete (RC) structures. They use strain and displacement measures as seismic performance control parameters. As for other simplified seismic design methods, it is of great interest to prove if they are usually conservative in respect to more refined, nonlinear, time history analyses, and can estimate design parameters with acceptable accuracy. In this paper, the current Direct Displacement-Based Design (DDBD) procedure is evaluated for designing simple single degree of freedom (SDOF) systems with specific reference to simply supported RC bridge piers. Using different formulations proposed in literature for the equivalent viscous damping and spectrum reduction factor, a parametric study is carried out on a comprehensive set of SDOF systems, and an average error chart of the method is derived allowing prediction of the expected error for an ample range of design cases. Following the chart, it can be observed that, for the design of actual RC bridge piers, underestimation errors of the DDBD method are very low, while the overestimation range of the simplified displacement-based procedure is strongly dependent on design ductility.

• 전기학회논문지
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• 제59권12호
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• pp.2292-2297
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• 2010

To improve the performances of Sawyer motors and to regulate yaw rotation, various feedback control methods have been developed. Almost all of these methods require information on the position, velocity or full state of the motor. Therefore, in this paper, a nonlinear observer is designed to estimate the full state of the four forcers in a Sawyer motor. The proposed method estimates the full state using only positional feedback. Generally, Sawyer motors are operated within a yaw magnitude of several degrees; outside of this range, Sawyer motors step out. Therefore, this observer design assumes that the yaw is within ${\pm}90^\b{o}$. The convergence of the estimation error is proven using the Lyapunov method. The proposed observer guarantees that the estimation error globally exponentially converges to zero for all arbitrary initial conditions. Furthermore, since the proposed observer does not require any transformation, it may result in a reduction in the commutation delay. The simulation results show the performance of the proposed observer.

• 한국연소학회지
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• 제19권1호
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• pp.39-44
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• 2014

A short reaction mechanism for premixed $CH_4/CHF_3/Air$ flames was developed with a reduction method of the combined application of simulation error minimization (SEM) which included connectivity method and principal component analysis. It consisted of 43 species and 403 elementary reactions at the condition of less than 5% of maximum error. The calculation time operated with a short mechanism was over 5 times faster than one with a detailed reaction mechanism. Good agreement was found between the flame speeds calculated by the short reaction mechanism and those by the detailed reaction mechanism for the entire range of $CHF_3/CH_4$ mole ratios and equivalence ratios. In addition excellent agreements were determined for the profiles of temperature, species concentration, and the production rates of the various species. So the short reaction mechanism was able to accurately predict the flame structure for premixed $CH_4/CHF_3/Air$ flames.

• Communications for Statistical Applications and Methods
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• 제28권4호
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• pp.351-368
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• 2021

For a probabilistic model with positively skewed data, a lognormal distribution is one of the key distributions that play a critical role. Several lognormal models can be found in various areas, such as medical science, engineering, and finance. In this paper, we propose a new estimator for a lognormal mean and depict the performance of the proposed estimator in terms of the relative mean squared error (RMSE) compared with Shen's estimator (Shen et al., 2006), which is considered the best estimator among the existing methods. The proposed estimator includes a tuning parameter. By finding the optimal value of the tuning parameter, we can improve the average performance of the proposed estimator over the typical range of σ². The bias reduction of the proposed estimator tends to exceed the increased variance, and it results in a smaller RMSE than Shen's estimator. A numerical study reveals that the proposed estimator has performance comparable with Shen's estimator when σ² is small and exhibits a meaningful decrease in the RMSE under moderate and large σ² values.

• JSTS:Journal of Semiconductor Technology and Science
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• 제9권4호
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• pp.216-224
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• 2009

The endless scaling down of the semiconductor process made the impact of the power network noise on the performance of the state-of-the-art chip a serious design problem. This paper compares the performances of two popular circuit reduction approaches used to improve the efficiency of power network noise analysis: moment matching-based model order reduction (MOR) and node elimination-based MOR. As the benchmarks, we chose PRIMA and R2Power as the matching-based MOR and the node elimination-based MOR. Experimental results indicate that the accuracy, efficiency, and memory requirement of both methods very strongly depend on the structure of the given circuit, i.e., numbers of the nodes and sources, and the number of moments to preserve for PRIMA. PRIMA has higher accuracy in general, while the error of R2Power is also in the acceptable range. On the other hand, PRIMA has the higher efficiency than R2Power, only when the numbers of nodes and sources are small enough. Otherwise, R2Power clearly outperforms PRIMA in efficiency. In the memory requirement, the memory size of PRIMA increases very quickly as the numbers of nodes, sources, and preserved moments increase.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 제13회 신호처리 합동 학술대회 논문집
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• pp.951-954
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• 2000

In this paper, we present a multi-code parallel combinatory CDMA system using bi-orthogonal modulation to reduce envelope variation and improve bit error. .rate (BER) performance. In general, the dynamic range of the amplitude of the transmit signal is very large in the case of conventional multi-code CDMA systems, resulting in severe nonlinear distortion due to high power amplifier and thus significant BER performance degradation. The proposed system exhibits reduction of peak-to-average power ratio (PAPR) of the transmit signal amplitudes and significant performance improvement. We verify the performance of the proposed system by computer simulations under AWGN channel and flat fading channel.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.290-293
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• 2008

This paper proposes a criterion to select the modes for modal truncated model of flexible rotor only supported by active magnetic bearings. The proposed approach relies on the concepts of minimum control input and output energy assuming that the system is subjected to transient disturbances. Accurate large order model for the levitated rotor is taken by finite element analysis and transformed to the modal equation. By proposed methodology, which modal states should be retained in the truncated model are investigated over the whole operational speed range by the calculation. Finally, the effectiveness is verified by checking the model error between original model and reduced model.

• 한국항행학회논문지
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• 제17권4호
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• pp.377-385
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• 2013

1950년대 후반 이후, 항공분야에서 사고율을 줄이기 위해 많은 노력을 기울여 안전 수준이 향상되었다. 전반적인 사고 비율은 지난 몇 년 동안 상당히 감소하였고, 환경 및 기계적 요인에 의한 사고는 감소하였으나, 인적오류 관련 사고는 불행히도 감소하는데 성공하지 못했다. 환경적 기계적 요소에 기인하는 사고는 줄었으나, 인적오류는 항공사고 원인 인자로 증가하고 있다. 오늘날, 모든 항공 사고의 매우 큰 비율이 직접 또는 간접적으로 인적오류의 몇 가지 형태에 비롯되고 있다. 많은 연구의 결과로, 인간의 오류 방지에 대해서 개발되고 있다. 그러나 어떤 종류의 오류 방지는 정확성, 효율성의 부족과 체계적인 접근에서 부족한 면이 고려되어야 할 것으로 보인다. 따라서 본 연구에서는 인간의 오류에 가장 효과적이고 체계적인 예방을 분석하고 인간의 오류 및 항공 안전에 대한 방법에 있어 통합에 집중 연구하였다. 본 연구에서는 인적오류 예방을 위한 여러 대안들 사이의 우선순위를 이해하고 파악함으로써 인적오류 문제를 해결하기 위한 시사점을 제시하고 한다.