• 방송공학회논문지
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• 제8권2호
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• pp.204-208
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• 2003

웨이브릿 변환 기반의 부대역(subband) 분해과정을 새로운 수학적 모델로 표현한다. 제안된 모델은 많은 계층의 분해과정에 거쳐 정규적인 다해상도 해석을 수행할 수 있다. 이러한 접근방식은 단일채널 선형 공간불변 필터링문제를 다채널로 확장할 수 있게 해주는 동시에 선형 공간불변 영상복원문제와 주파수상에서 적응적 제약적 최소제곱(Constrained Least Square:CLS) 필터에 적용될 수 있다. 제안된 필터에서 우리는 부대역의 특징에 따라 적응적으로 다른 변수를 사용할 수 있다. 본 논문에서 제안한 주파수상의 적응적 CLS 필터를 S/W로 구현하였으며, 이 실험을 통해 부대역의 특징을 정화하게 측정할 경우 제안된 주파수상 적응적 CLS 필터는 기존의 단채널 필터에서 벗어나 현저히 화질을 개선할 수 있음을 보여준다.

• 정보보호학회논문지
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• 제16권2호
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• pp.13-24
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• 2006

여러 개체가 각자의 정보를 제공하여 이를 바탕으로 정보 제공자의 프라이버시를 보존하면서 공통의 유익한 정보를 얻고자 하는 다자간 협력 계산 프로토콜에 대해서 논한다. 금융, 제조업, 통신 분야 등에서 널리 응용되는 선형계(linear system)의 일반해(general solution)와 최소제곱해(least-square solution)를 구하는 문제에서 프라이버시를 보존하는 실용적인 다자간(multi-party) 협력 계산 프로토콜을 제안한다. 본 논문에 제안된 프로토콜은 기존의 양자간(two-party) 협력 계산 방식을 확장한 새로운 것으로 효율성 측면에서 우수한 실용적인 다자간 계산 프로토콜이다.

• 한국전산구조공학회논문집
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• 제32권4호
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• pp.215-222
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• 2019

복합재료의 열전달 문제는 일반적으로 만족시켜야 하는 보존방정식과 경계조건 외에 추가적으로 만족시켜야 하는 계면경계조건의 존재로 인해 새로운 수치기법의 개발에 어려움이 있다. 계면경계조건이 미분방정식의 해에 불연속성을 유발시키기 때문에 이것을 적절하게 처리할 수 있는 특수한 함수의 도입이 필요하며, 이산화를 통한 계 방정식의 구성도 쉽지 않다. 본 논문에서는 계면경계의 불연속성을 모사하는 특수함수를 포함하면서 계면경계조건을 항상 만족시킬 수 있도록 계면경계식 자체를 매입한 미분근사식을 제안하고, 불연속 재료상수를 갖는 열전달 문제를 무요소 강형식으로 이산화한 이동최소제곱 차분법을 제시한다. 개발된 수치기법은 기존의 수치기법들과 달리 수치적분과 계면경계조건을 만족시키기 위한 별도의 구속 방정식이 필요없으며, 빠르고 정확하게 이종재료 열전달 문제의 수치해를 구해준다. 개발된 수치기법으로 다양한 복합재료 열전달 문제를 해석하고 오차의 수렴률을 조사한 결과, 높은 정확성과 계산 효율성을 갖는다는 것을 확인할 수 있었으며, 특히, 계면경계가 기하학적 특이성을 나타내는 문제에서도 우수한 성능을 발휘하는 것을 보였다.

• Communications for Statistical Applications and Methods
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• 제11권2호
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• pp.355-368
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• 2004

In order to use Kriging, one has to estimate three parameters(nugget, sill and range) of semivariogram, which shows the relationship in the given two sites. A visual fit of the semivariogram parameters to a few standard models is widely used. But, it does not give the suitable results and not provide the automated process of Kriging. The gradient based nonlinear least squares is another choices to estimate three parameters, but it has some problems such as initial value problem. In this paper, we suggest the genetic algorithm as a compatible alternative method to solve the above mentioned problem. Finally, we estimate three parameters of semivariogram of rain-fall by adapting the genetic algorithm, compute Kriging estimate and conclude its effectiveness and compatibility.

• 제어로봇시스템학회논문지
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• 제20권11호
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• pp.1118-1124
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• 2014

This paper proposes a novel controller design scheme for multimachine power systems based on the explorized policy iteration. Power systems have several uncertainties on system dynamics due to the various effects of interconnections between generators. To solve this problem, the proposed method solves the LQR (Linear Quadratic Regulation) problem of isolated subsystems without the knowledge of a system matrix and the interconnection parameters of multimachine power systems. By selecting the proper performance indices, it guarantees the stability and convergence of the LQ optimal control. To implement the proposed scheme, the least squares based online method is also investigated in terms of PE (Persistency of Excitation), interconnection parameters and exploration signals. Finally, the performance and effectiveness of the proposed algorithm are demonstrated by numerical simulations of three-machine power systems with governor controllers.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 제39회 하계학술대회
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• pp.303-304
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• 2008

For the state estimation problem, the weighted least squares (WLS) method and the fast decoupled method are widely used at present. However, these algorithms can converge to local optimal solutions. Recently, modern heuristic optimization methods such as Particle Swarm Optimization (PSO) have been introduced to overcome the disadvantage of the classical optimization problem. However, heuristic optimization methods based on populations require a lengthy computing time to find an optimal solution. In this paper, we used PSO to search for the optimal solution of state estimation in power systems. To overcome the shortcoming of heuristic optimization methods, we proposed parallel processing of the PSO algorithm based on the PC cluster system. the proposed approach was tested with the IEEE-118 bus systems. From the simulation results, we found that the parallel PSO based on the PC cluster system can be applicable for power system state estimation.

• Journal of Periodontal and Implant Science
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• 제45권1호
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• pp.2-7
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• 2015

A fundamental problem in analyzing complex multilevel-structured periodontal data is the violation of independency among the observations, which is an assumption in traditional statistical models (e.g., analysis of variance and ordinary least squares regression). In many cases, aggregation (i.e., mean or sum scores) has been employed to overcome this problem. However, the aggregation approach still exhibits certain limitations, such as a loss of power and detailed information, no cross-level relationship analysis, and the potential for creating an ecological fallacy. In order to handle multilevel-structured data appropriately, mixed effects models have been introduced and employed in dental research using periodontal data. The use of mixed effects models might account for the potential bias due to the violation of the independency assumption as well as provide accurate estimates.

• Structural Engineering and Mechanics
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• 제38권5호
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• pp.651-674
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• 2011

This paper presents a novel method for predicting the failure probability of structural or mechanical systems subjected to random loads and material properties involving multiple design points. The method involves Multicut High Dimensional Model Representation (Multicut-HDMR) technique in conjunction with moving least squares to approximate the original implicit limit state/performance function with an explicit function. Depending on the order chosen sometimes truncated Cut-HDMR expansion is unable to approximate the original implicit limit state/performance function when multiple design points exist on the limit state/performance function or when the problem domain is large. Multicut-HDMR addresses this problem by using multiple reference points to improve accuracy of the approximate limit state/performance function. Numerical examples show the accuracy and efficiency of the proposed approach in estimating the failure probability.

• Journal of Electrical Engineering and Technology
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• 제5권1호
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• pp.28-35
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• 2010

This paper presents new Adaptive Linear Combination Structure (ADALINE) for tracking/estimating voltage-current phasor and frequency of power system. To estimate the phasors and frequency from sampled data, the algorithm assumes that orthogonal coefficients and speed of angular frequency of power system are unknown parameters. With adequate sampled data, the estimation problem can be considered as a linear weighted least squares (LMS) problem. In addition to determining the phasors (orthogonal coefficients), the procedure estimates the power system frequency. The main algorithm is verified through a computer simulation and data from field. The proposed algorithm is tested with transient and dynamic behaviors during power swing, a step change of frequency upon islanding of small generators and disconnection of load. The algorithm shows a very high accuracy, robustness, fast response time and adaptive performance over a wide range of frequency, from 10 to 2000 Hz.

• 동력기계공학회지
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• 제6권1호
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• pp.96-101
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• 2002

In this paper, we address the problem of controlling an end-effector to track and grab a moving target using the visual servoing technique. A visual servo mechanism based on the image-based servoing principle, is proposed by using visual feedback to control an end-effector without calibrated robot and camera models. Firstly, we consider the control problem as a nonlinear least squares optimization and update the joint angles through the Taylor Series Expansion. And to track a moving target in real time, the Jacobian estimation scheme(Dynamic Broyden's Method) is used to estimate the combined robot and image Jacobian. Using this algorithm, we can drive the objective function value to a neighborhood of zero. To show the effectiveness of the proposed algorithm, simulation results for a six degree of freedom robot are presented.