• Proceedings of the Korean Information Science Society Conference
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• 2004.10c
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• pp.16-18
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• 2004

무선 센서 네트워크는 센서들을 무선으로 연결하여 데이터 교환을 통해 다양한 환경에서 정보를 수집할 수 있도록 하는 유용한 도구이다. 센서노드 간의 통신은 센서노드의 제한된 에너지를 효율적으로 이용하도록 만들어져야만 한다. 클러스터링에 기반한 계층적 라우팅 기법은 클러스터 내의 노드들은 클러스터헤드와만 통신을 하게하고 클러스터헤드가 한꺼번에 싱크에게 통합된 정보를 보내게 하여 에너지를 절약하는 기법이다. 본 연구에서는 이러한 클러스터링 기반의 라우팅에서 에너지 효율을 높이기 위해 싱크와 클러스터헤드 사이의 거리에 따른 최적 클러스터 크기를 계산하고, 원형의 전체 토폴로지에서 계산된 값과 일치됨을 확인해 보았다.

• Proceedings of the Korea Contents Association Conference
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• 2013.05a
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• pp.31-32
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• 2013

밀리미터 대역에서 고출력 신호를 장거리로 전송하기 위해서는 안테나 이득을 증가시켜야 한다. 이를 위해 사용되는 방법 중 하나가 금속 개구면 격자배열을 구조를 이용하여 안테나를 설계하는 것이다. 이러한 반사배열 안테나는 격자구조의 기하학적 패턴이 개구효율에 큰 영향을 미친다. 본 논문에서는 개구효율을 향상시키기 위한 최적의 기하학적 패턴을 찾기 위한 방법으로 유전알고리즘 기법을 제안한다. 유전 알고리즘 기법을 적용한 모의실험 결과는 제안한 방법이 개구효율을 향상시키는데 도움이 된다는 것을 보여주었다.

• Journal of Korean Society of Steel Construction
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• v.12 no.5 s.48
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• pp.569-579
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• 2000

An improved multi-level (IML) optimization algorithm using automatic differentiation (AD) of framed structures is proposed in this paper. For the efficiency of the proposed algorithm, multi-level optimization techniques using a decomposition method that separates both system-level and element-level optimizations, that utilizes and an artificial constraint deletion technique, are incorporated in the algorithm. And also to save the numerical efforts, an efficient reanalysis technique through approximated structural responses such as moments and frequencies with respect to intermediate variables is proposed in the paper. Sensitivity analysis of dynamic structural response is executed by AD that is a powerful technique for computing complex or implicit derivatives accurately and efficiently with minimal human effort. The efficiency and robustness of the IML algorithm, compared with a plain multi-level (PML) algorithm, is successfully demonstrated in the numerical examples.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.2
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• pp.271-275
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• 2006

In STP, network performance differs depending on topology configuration. Therefore, we need to configure right topology for the optimal efficiency of networking. This paper suggest the optimal topology configuration for efficient networking between ethernet switchs. It finds out the best topology configuration by calculation mathematical model which uses transmission time between root switch and other switchs in the same domain. And it also analysed performance difference on locations of root switch. Through the performance analysis, we could conclude that placing the root switch in the center is the most efficient.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.7
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• pp.612-618
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• 2007

The dynamic behaviors of a KT-1 family aircraft nose landing gear have been analyzed and the optimal design of an aircraft shock absorber has been conducted to improve efficiency of shock energy absorption. The nose landing gear is modeled as a 2 DOF system using ADAMS and various operational and environmental landing conditions were considered. The results of dynamic simulation for various landing conditions agree well with experiments. Also the effect of parameters of a shock strut on the dynamic behaviors and on shock energy absorption of the nose landing gear has been evaluated for optimal design to define design variables. It has been found that the parameters of a shock strut such as oil-density and orifice area have more effects on dynamic behaviors than those of operation conditions. Optimal design is performed to maximize the efficiency of shock energy absorption using Feasible Direction Method. As a result the design values of the shock strut for maximum efficiency of shock energy absorption are derived and it turns out that efficiency and dynamic behaviors of the nose landing gear were improved by the optimal design.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.16 no.3
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• pp.237-250
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• 2003

Since an orthotropic steel deck bridge has large number of design variables and shows complex structural behavior, it would be very difficult and impractical to directly use a Conventional Single Level (CSL) optimization algorithm for its optimum design. Thus, in this paper, an Improved Multi Level Design Synthesis (IMLDS) optimization algorithm is proposed to improve the computational efficiency. In the proposed IMLDS algorithm, a coordination method is introduced to divide the bridge into main girders and orthotropic steel deck with preserving the characteristics of the structural behavior. For an efficient optimization of the bridge, the IMLDS algorithm incorporates the various crucial approximation techniques such as constraints deletion, Automatic Differentiation (AD), stress reanalysis, and etc. In the case of orthotropic steel deck system, optimum design problems are characterized by mixed continuous discrete variables and discontinuous design space. Thus, a modified Genetic Algorithm (GA) is also applied to optimize discrete member design for orthotropic steel deck. From the numerical example, the efficiency and convergency of the IMLDS algorithm proposed in this paper is investigated. It may be positively stated that the IMLDS algorithm will lead to more effective and practical design compared with previous algorithms.

• Journal of Aerospace System Engineering
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• v.11 no.4
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• pp.36-43
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• 2017

Blade design optimization of QTP-UAV prop-rotor was conducted using ModelCenter(R). Performance efficiency of the blade in hover and forward flight were adopted as the multi-objective function. Required power and pitch link force applied to constraint in each flight mode and limited lower than the value of the baseline blade. Design variables of root chord length of the blade, taper ratio, twist slope, twist angle at 0.5R of the blade, anhedral angle, parabolic coefficient of a tip shape and location of airfoil were used to generate the blade planform. CAMRAD-II, the comprehensive analysis program of rotorcraft, was used for performance analysis of prop-rotor blade in design process. Performance of the optimized blade improved 1.6% of figure of merit in hover and 13.6% of propulsive efficiency in forward flight. Pitch link force also reduced approximately 30% less than that of the baseline blade.

• Proceedings of the KIEE Conference
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• 1981.07a
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• pp.156-156
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• 1981

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.11
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• pp.33-39
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• 2014

We propose an optimal number of transmit antennas which maximizes energy-efficiency (EE) in multi-user massive multiple-input multiple-output (MIMO) downlink system with the maximal ratio transmission (MRT) precoding. With full channel state information at the transmitter (CSIT), we find a closed form solution by partial differential function with proper approximations using average channel gain, independence of individual channels, and average path loss. With limited feedback, we get a solution numerically by the bisection with approximations in the same manner, and analyze an effect of feedback bits on the optimal number of transmit antennas. Simulation results show that the optimal numbers of transmit antenna getting from proposed closed form solution and exhaustive search are nearly same.

• Solar Energy
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• v.10 no.3
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• pp.35-45
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• 1990

An analytical equation to estimate the Rankine power cycle efficiency at maximum power for the given mass flow rates of heating and cooling fluids is derived. The accuracy of the result is shown by comparing the analytical values with those calculated one using detailed thermodynamic data. The results indicate that the thermal efficiency at maximum power depends primarily on the initial temperatures of the heating and cooling fluids, and it also depends on the pinch-temperature differences between the working fluid and the heating and cooling fluids. The efficiency at maximum power provides a measure of the power available in a practical Rankine heat engine.