• Journal of applied mathematics & informatics
• /
• 제27권5_6호
• /
• pp.1017-1031
• /
• 2009

The problem of interaction of surface water waves by small undulation at the bottom of a laterally unbounded sea is treated on the basis of linear water wave theory for both normal and oblique incidences. Perturbation analysis is employed to obtain the first order corrections to the reflection and transmission coefficients in terms of integrals involving the shape function c(x) representing the bottom undulation. Fourier transform method and residue theorem are applied to obtain these coefficients. As an example, a patch of sinusoidal ripples is considered in both the cases as the shape function. The principal conclusion is that the reflection coefficient is oscillatory in the ratio of twice the surface wave number to the wave number of the ripples. In particular, there is a Bragg resonance between the surface waves and the ripples, which is associated with high reflection of incident wave energy. The theoretical observations are validated computationally.

• Structural Engineering and Mechanics
• /
• 제44권3호
• /
• pp.405-416
• /
• 2012

In this study the investigation of large deflections subject in compliant mechanisms is presented using homotopy perturbation method (HPM). The main purpose is to propose a convenient method of solution for the large deflection problem in compliant mechanisms in order to overcome the difficulty and complexity of conventional methods, as well as for the purpose of mathematical modeling and optimization. For simplicity, a cantilever beam of linear elastic material under horizontal, vertical and bending moment end point load is considered. The results show that the applied method is very accurate and capable for cantilever beams and can be used for a large category of practical problems for the aim of optimization. Also the consequence of effective parameters on the large deflection is analyzed and presented.

• 동력기계공학회지
• /
• 제10권4호
• /
• pp.159-164
• /
• 2006

In recent, the marine engine of a large size is being realized a lower speed, longer stroke and a small number of cylinders for the energy saving. Consequently the variation of rotational torque became larger than former days because of the longer delay-time in fuel oil injection process and an increased output per cylinder. It was necessary that algorithms have enough robustness to suppress the variation of the delay-time and the parameter perturbation. This paper shows the structure of hybrid F-NFC against the delay-time and the perturbation of engine parameter as modeling uncertainties, and the design of the robust speed controller by hybrid F-NFC for the engine. And, The Parameter values of linear equation are determined by RC-GA for F-NFS. The hybrid F-NFC is combined the F-NFC and PID controller for filling up each.

• 천문학회보
• /
• 제44권1호
• /
• pp.55.5-55.5
• /
• 2019

We present our first attempt at understanding the dual impact of the large-scale density and velocity environment on the formation of very first astrophysical objects in the Universe. Following the recently developed quasi-linear perturbation theory on this effect, we introduce the publicly available initial condition generator of ours, BCCOMICS (Baryon Cold dark matter COsMological Inital Condition generator for Small scales), which provides so far the most self-consistent treatment of this physics beyond the usual linear perturbation theory. From a suite of uniform-grid simulations of N-body+hydro+BCCOMICS, we find that the formation of first astrophysical objects is strongly affected by both the density and velocity environment. Overdensity and streming-velocity (of baryon against cold dark matter) are found to give positive and negative impact on the formation of astrophysical objects, which we quantify in terms of various physical variables.

• 천문학회보
• /
• 제44권2호
• /
• pp.52.3-52.3
• /
• 2019

We present our first attempt at understanding the dual impact of the large-scale density and velocity environment on the formation of very first astrophysical objects in the Universe. Following the recently developed quasi-linear perturbation theory on this effect, we introduce the publicly available initial condition generator of ours, BCCOMICS (Baryon Cold dark matter COsMological Inital Condition generator for Small scales), which provides so far the most self-consistent treatment of this physics beyond the usual linear perturbation theory. From a suite of uniform-grid simulations of N-body+hydro+BCCOMICS, we find that the formation of first astrophysical objects is strongly affected by both the density and velocity environment. Overdensity and streming-velocity (of baryon against cold dark matter) are found to give positive and negative impact on the formation of astrophysical objects, which we quantify in terms of various physical variables.

• Communications for Statistical Applications and Methods
• /
• 제30권6호
• /
• pp.605-629
• /
• 2023

This paper proposes some diagnostics procedures for the skew-t linear regression model with censored response. The skew-t distribution is an attractive family of asymmetrical heavy-tailed densities that includes the normal, skew-normal and student's-t distributions as special cases. Inspired by the power and wide applicability of the EM-type algorithm, local and global influence analysis, based on the conditional expectation of the complete-data log-likelihood function are developed, following Zhu and Lee's approach. For the local influence analysis, four specific perturbation schemes are discussed. Two real data sets, from education and economics, which are right and left censoring, respectively, are analyzed in order to illustrate the usefulness of the proposed methodology.

• 말소리와 음성과학
• /
• 제6권3호
• /
• pp.63-72
• /
• 2014

The current study assessed the utility of acoustic analyses the most commonly used in routine clinical voice assessment including perturbation, nonlinear dynamic analysis, and Spectral/Cepstrum analysis based on signal typing of dysphonic voices and investigated their applicability of clinical acoustic analysis methods. A total of 70 dysphonic voice samples were classified with signal typing using narrowband spectrogram. Traditional parameters of %jitter, %shimmer, and signal-to-noise ratio were calculated for the signals using TF32 and correlation dimension(D2) of nonlinear dynamic parameter and spectral/cepstral measures including mean CPP, CPP_sd, CPPf0, CPPf0_sd, L/H ratio, and L/H ratio_sd were also calculated with ADSV(Analysis of Dysphonia in Speech and VoiceTM). Auditory perceptual analysis was performed by two blinded speech-language pathologists with GRBAS. The results showed that nearly periodic Type 1 signals were all functional dysphonia and Type 4 signals were comprised of neurogenic and organic voice disorders. Only Type 1 voice signals were reliable for perturbation analysis in this study. Significant signal typing-related differences were found in all acoustic and auditory-perceptual measures. SNR, CPP, L/H ratio values for Type 4 were significantly lower than those of other voice signals and significant higher %jitter, %shimmer were observed in Type 4 voice signals(p<.001). Additionally, with increase of signal type, D2 values significantly increased and more complex and nonlinear patterns were represented. Nevertheless, voice signals with highly noise component associated with breathiness were not able to obtain D2. In particular, CPP, was highly sensitive with voice quality 'G', 'R', 'B' than any other acoustic measures. Thus, Spectral and cepstral analyses may be applied for more severe dysphonic voices such as Type 4 signals and CPP can be more accurate and predictive acoustic marker in measuring voice quality and severity in dysphonia.

• Nuclear Engineering and Technology
• /
• 제21권2호
• /
• pp.99-110
• /
• 1989

원자로 지논 농도의 최적 제어는 Linear Quadratic Regulator Problem이다. 지논 농도와 아이오다인 농도는 측정할 수 없기 때문에 최적 제어를 수행하기 위해서는 측정할 수 없는 상태 변수를 예측하는 것이 필요하다. 본 연구에서 사용된 예측방법은 Luenberger Observer를 기초로 했다. 원자로 상태 방정식은 빠른 상태 방정식(중성자 속, 핵연료 및 냉각재 온도)과 느린 상태 방정식(아이오다인, 지논)의 상호작용에 의해 Stiffness 문제가 발생되는데 이러한 시스템을 "Singularly Perturbed System"이라 한다. Stiffness문제를 해결하기 위해서 원 시스템을 느린 시스템과 빠른 시스템의 두 개의 모드로 나누는 Singular Perturbation Method를 사용한다. 예측기Observer를 이용한 원 시스템의 제어기는 느린 시스템과 빠른 시스템에 대한 분리된 예측기와 제어기의 설계에 의해 결정되어진다. 특히 원자로 상태 방정식에서는 빠른 모드는 빨리 사라지게 되므로 단지 느린 시스템에 대해서만 예측기를 설계하면 된다. 컴퓨터시뮬레이션을 통한 시험 결과는 원자로의 지논 진동은 Singular Perturbation Method와 예측기를 이용해서 거의 정확하게 효과적으로 짧은 시간내에 제어할 수 있음을 알았다.수 있음을 알았다.

• 응용통계연구
• /
• 제34권1호
• /
• pp.39-56
• /
• 2021

Markowitz (1952)의 분산투자 모형 발표 이후 포트폴리오 최적화에 대한 많은 연구가 이루어졌다. 마코위츠의 평균-분산 포트폴리오 최적화 모형은 수익 분포가 정규분포를 따른다는 가정하에서 성립한다. 그러나 실생활에서는 수익 분포가 정규분포를 따르지 않는 경우가 존재한다. 또한 분산은 이상치의 영향을 많이 받는 민감한 지표이다. 이런 분산의 단점을 보완할 수 있는 하방위험인 숏폴(Shortfall)을 위험 지표로 적용함으로써 수익 분포에 대해 최적화가 가능한 평균-숏폴 포트폴리오 모형이 제안되었다. 또한 Jorion (2003)과 Park(2019)은 포트폴리오의 위험도를 최소화하는 동시에 적은 수의 자산으로 구성(sparse)되고 안정적(stable)인 포트폴리오를 얻는 퍼터베이션 방법을 제안하였다. 본 논문에서는 평균-숏폴 포트폴리오 모형에 퍼터베이션 방법과 adaptive Lasso를 적용하여 사용되는 자산의 수가 적으면서 안정적이고 쉽게 적용 가능한 포트폴리오 모형을 제안한다. 그리고 실증 데이터 분석을 통하여 모형의 타당성을 입증한다.

• 한국연소학회지
• /
• 제22권2호
• /
• pp.19-26
• /
• 2017

An experimental study investigates the flame response characteristics of jet-diffusion flame and premixed flame. The experiment was conducted while varying the amplitude. Flame lengths were quantified for OH chemiluminescence measurement and compared with the result of the flame transfer function. Flame length and flame velocity perturbation were normalized and compared with the result of the flame transfer function. The comparison results appear that velocity perturbation and flame length oscillation of premixed flame show linear behaviors on the other hand jet-diffusion flame, amplitudes are more thant 0.20, shows nonlinear behaviors of flame velocity perturbation and flame length oscillation.