• 한국강구조학회 논문집
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• 제12권6호
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• pp.629-638
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• 2000

알고리즘의 용이성과 전역적 최적해로의 수렴가능성 등의 이점을 가진 SA알고리즘은 구조최적화문제에 활발하게 적용되고 있으나 냉각스케줄의 설정, 모호한 종료기준, 과도한 반복해석 등의 문제점을 가지고 있다. 그러므로 본 논문에서는 기존 SA알고리즘의 단점을 보완한 MSA 알고리즘을 개발하고자한다. MSA 알고리즘은 수렴에 요구되는 반복수를 감소시키고 국부최소점이 많은 동적최적화문제의 초기설계 선택의 자율성을 확보하기 위하여 SQ 및 SA의 2단계로 구성하여 개발하였다. 또한 기존 연구에서 제안된 냉각 스케줄에 의한 수렴성 등을 비교분석하여 구조최적화에 적합한 냉각스케줄을 제안하여 그 성능을 평면가새골조 구조물의 최적내진설계에 적용하여 분석하였다.

• 한국지능시스템학회논문지
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• 제14권2호
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• pp.228-233
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• 2004

최근 들어, 다양하고 복잡한 기능을 갖는 로봇이 요구되고 있다. 그러나 이전의 알고리즘으로는 그러한 요구를 만족시킬 수 없다. 이러한 문제를 해결하기 위해, 본 논문에서는 다양한 입력과 출력을 다루는 경우에도 작은 개수의 퍼지 룰을 갖고, 효율적이고 강인하게 제어할 수 있는 2-Layer Fuzzy Controller를 소개한다. 그런데 퍼지 제어기에서의 중요한 문제점은 퍼지 룰 베이스를 어떻게 설계하는지에 달려 있다. 본 논문은 Schema Co-Evolutionary Algorithm을 이용하여 최적의 2-Layer Fuzzy Controller를 설계하는데, 이 Schema Co-Evolutionary Algorithm은 simple GA보다 더 빠르고 우수하게 최적해를 찾을 수 있다.

• 한국통신학회논문지
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• 제27권8C호
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• pp.729-740
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• 2002

본 논문에서는 광 인터넷 망의 가상망 재구성을 위하여 최적의 망 재구성 정책을 고려한 보상-비용 함수를 최대화하는 다단계 결정 문제로 정의 하였다. 그리고 트래픽 요구사항을 만족하기 위해서 노드 교환 기법에 근거한 새로운 휴리스틱 알고리즘을 제안하였다. 또한 트래픽 예측 기법을 사용하여 휴리스틱 알고리즘에 의해 발생하는 근사 문제를 해결 하고, 이를 바탕으로 트래픽 예측 다단계 재구성 정책을 제안하였다. 실험결과 다단계 재구성 정책은 물리적 자원이 제한된 환경에서 기존의 방법에 비해 뛰어난 성능을 보였다.

• 대한기계학회논문집A
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• 제27권6호
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• pp.1020-1027
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• 2003

A traditional mold design has been conducted by an experience-based trial and error, whereby the mold designer would decide the gate locations and processing conditions based on the caring characteristics and its functional requirements. The paper suggests an optimal gate location and processing conditions in the injection molding using a global search method referred to as micro genetic algorithm( ${\mu}$ GA). ${\mu}$ GA yields the optimal solution with a small size of population without respect to design variables for saving time that is needed to calculate the fitness of many individuals. Due to the reason, the paper uses a commercial analysis package of injection molding(CAPA) to analysis a state of flux. In addition to that, axiomatic approach .is applied in the beginning of design. It is a useful method to draw a well-organized and reasonable idea to handle a problem.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제14권6호
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• pp.2670-2685
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• 2020

Flying ad-hoc networks (FANETs) is a vibrant research area nowadays. This type of network ranges from various military and civilian applications. FANET is formed by micro and macro UAVs. Among many other problems, there are two main issues in FANET. Limited energy and high mobility of FANET nodes effect the flight time and routing directly. Clustering is a remedy to handle these types of problems. In this paper, an efficient clustering technique is proposed to handle routing and energy problems. Transmission range of FANET nodes is dynamically tuned accordingly as per their operational requirement. By optimizing the transmission range packet loss ratio (PLR) is minimized and link quality is improved which leads towards reduced energy consumption. To elect optimal cluster heads (CHs) based on their fitness we use k-means. Selection of optimal CHs reduce the routing overhead and improves energy consumption. Our proposed scheme outclasses the existing state-of-the-art techniques, ACO based CACONET and PSO based CLPSO, in terms of energy consumption and cluster building time.

• Smart Structures and Systems
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• 제9권1호
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• pp.35-53
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• 2012

Mechanical dampers have been proved to be one of the most effective countermeasures for vibration mitigation of stay cables in various cable-stayed bridges over the world. However, for long stay cables, as the installation height of the damper is restricted due to the aesthetic concern, using passive dampers alone may not satisfy the control requirement of the stay cables. In this connection, semi-active MR dampers have been proposed for the vibration mitigation of long stay cables. Although various studies have been carried out on the implementation of MR dampers on stay cables, the optimal damping performance of the cable-MR damper system has yet to be evaluated. Therefore, this paper aims to investigate the effectiveness of MR damper as a semi-active control device for the vibration mitigation of stay cable. The mathematical model of the MR damper will first be established through a performance test. Then, an efficient semi-active control strategy will be derived, where the damping of MR damper will be tuned according to the dynamic characteristics of stay cable, in order to achieve optimal damping of cable-damper system. Simulation study will be carried out to verify the proposed semi-active control algorithm for suppressing the cable vibrations induced by different loading patterns using optimally tuned MR damper. Finally, the effectiveness of MR damper in mitigating multi modes of cable vibration will be examined theoretically.

• Journal of Communications and Networks
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• 제10권1호
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• pp.28-37
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• 2008

In this paper, we investigate the problem of minimizing the average transmission power of users while guaranteeing the average delay constraints in time-varying uplink channels. We design a scheduler that selects a user for transmission and determines the transmission rate of the selected user based on the channel and backlog information of users. Since it requires prohibitively high computation complexity to determine an optimal scheduler for multi-user systems, we propose a low-complexity scheduling scheme that can achieve near-optimal performance. In this scheme, we reduce the complexity by decomposing the multiuser problem into multiple individual user problems. We arrange the probability of selecting each user such that it can be determined only by the information of the corresponding user and then optimize the transmission rate of each user independently. We solve the user problem by using a dynamic programming approach and analyze the upper and lower bounds of average transmission power and average delay, respectively. In addition, we investigate the effects of the user selection algorithm on the performance for different channel models. We show that a channel-adaptive user selection algorithm can improve the energy efficiency under uncorrelated channels but the gain is obtainable only for loose delay requirements in the case of correlated channels. Based on this, we propose a user selection algorithm that adapts itself to both the channel condition and the backlog level, which turns out to be energy-efficient over wide range of delay requirement regardless of the channel model.

• 한국자동차공학회논문집
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• 제13권1호
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• pp.174-183
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• 2005

A train driving requires to n the fixed distance within given time, and it is desirable to consume low energy if necessary. Reducing energy consumption depends on the train operation modes by either manual or automatic operation. In this article, an operation to reduce energy consumption by changing modes of train operation by a driver without changing the train operation requirement is investigated. The powering model, braking model and consumed energy calculation model are developed, then simulated by using a Matlab software. The accuracy of the train dynamic model established by the simulations is verified by comparing with the real experimental data. Several simulations by various operations in the real track are executed, then the desirable pattern of train driving is found.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권11호
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• pp.4087-4102
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• 2014

Two-way relaying is an effective way of improving system spectral efficiency by making use of physical layer network coding. However, energy efficiency in OFDM-based bidirectional relaying with asymmetric traffic requirement has not been investigated. In this study, we focused on subcarrier transmission mode selection, bit loading, and power allocation in a multicarrier single amplified-and-forward relay system. In this scheme, each subcarrier can operate in two transmission modes: one-way relaying and two-way relaying. The problem is formulated as a mixed integer programming problem. We adopt a structural approximation optimization method that first decouples the original problem into two suboptimal problems with fixed subcarrier subsets and then finds the optimal subcarrier assignment subsets. Although the suboptimal problems are nonconvex, the results obtained for a single-tone system are used to transform them to convex problems. To find the optimal subcarrier assignment subsets, an iterative algorithm based on subcarrier ranking and matching is developed. Simulation results show that the proposed method can improve system performance compared with conventional methods. Some interesting insights are also obtained via simulation.

• Journal of the Optical Society of Korea
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• 제18권5호
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• pp.459-465
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• 2014

Visible light communications (VLC) using the intensity modulation of light-emitting diodes (LEDs) provides a new communication medium to overcome the shortage of radio spectrum, and allows reuse of LED lighting infrastructures. Orthogonal frequency-division multiplexing (OFDM) was introduced to VLC for its merits in mitigating the fading effects resulting from delay spread, and in avoiding low-frequency ambient interference. Noise and clipping are two major factors that degrade the performance of OFDM in VLC. A larger signal easily overcomes noise, but experiences impairment by clipping. Therefore, degradation due to clipping has a trade-off relationship with that due to noise, depending on the signal amplitude of OFDM. In this paper, the optimal signal amplitude in the trade-off is obtained by simulation when the dimming and LED intensity are given. The former indicates a user's requirement for lighting, and the latter represents the channel quality. The required LED intensity-to-noise ratio, as the channel quality that guarantees dimming as well as an adequate bit-error rate (BER), is also discussed.