• 방송공학회논문지
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• 제21권3호
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• pp.341-348
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• 2016

HEVC 표준은 기존의 H.264 표준을 대체할 차세대 고효율 영상 압축 코덱이다. H.264 표준에 비해 약 50% 수준으로 비트레이트를 감소시켰지만 계산 복잡도는 약 1.4배 정도 증가하였다. 계산 복잡도를 낮추기 위해 다양한 고속화 알고리즘들이 제안되어 왔다. 인트라 코딩에는 rough mode decision(RMD) 기법이 적용되었다. 최적의 모드를 선정하기 위한 rate-distortion optimization (RDO) 과정은 복잡도가 높기 때문에 RMD를 사용하여 더 간소화된 방법으로 RDO 단계를 위한 후보 모드들을 선정한다. 그러나 큰 사이즈의 블록들의 경우 RMD 과정 역시 계산 복잡도를 줄일 필요가 있다. 본 논문에서는 RMD 과정에서 참조 픽셀을 가져오고, 예측 픽셀 생성하는 과정에서 다운 샘플링을 적용하였으며 참조 소프트웨어에 적용된 기존 RMD 방식에 비해 계산량을 70%가량 줄일 수 있었다. 이때 BDBR 증가는 0.04%로 미미한 수준이다. 제안한 다운샘플링 기법을 RMD 하드웨어에 적용하면 게이트 카운트는 약 33%, 버퍼의 크기는 약 66% 줄어든다.

• International Journal of Aeronautical and Space Sciences
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• 제18권4호
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• pp.662-674
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• 2017

This paper describes the multidisciplinary design optimization (MDO) process of a tailless unmanned combat aerial vehicle (UCAV) using global variable fidelity aerodynamic analysis. The developed tailless UAV design framework combines multiple disciplines that are based on low-fidelity and empirical analysis methods. An automated high-fidelity aerodynamic analysis is efficiently integrated into the MDO framework. Global variable fidelity modeling algorithm manages the use of the high-fidelity analysis to enhance the overall accuracy of the MDO by providing the initial sampling of the design space with iterative refinement of the approximation model in the neighborhood of the optimum solution. A design formulation was established considering a specific aerodynamic, stability and control design features of a tailless aircraft configuration with a UCAV specific mission profile. Design optimization problems with low-fidelity and variable fidelity analyses were successfully solved. The objective function improvement is 14.5% and 15.9% with low and variable fidelity optimization respectively. Results also indicate that low-fidelity analysis overestimates the value of lift-to-drag ratio by 3-5%, while the variable fidelity results are equal to the high-fidelity analysis results by algorithm definition.

• International Journal of Reliability and Applications
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• 제17권1호
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• pp.85-105
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• 2016

In this paper accelerated life testing is incorporated in quality control technique of acceptance sampling plan to induce early failures in high reliability products.Stress under accelerated condition can be applied in constant-stress, step-stress and progressive-stress or combination of such loadings. A ramp-stress results when stress is increased linearly (from zero) with time. In this paper optimum failure-censored ramp-stress accelerated life test sampling plan for log-logistic distribution has been formulated with cost considerations. The log-logistic distribution has been found appropriate for insulating materials. The optimal plans consist in finding optimum sample size, sample proportion allocated to each stress, and stress rate factor such that producer's and consumer's interests are safeguarded. Variance optimality criterion is used when expected cost per lot is not taken into consideration, and bilevel programming approach is used in cost optimization problems. The methods developed have been illustrated using some numerical examples, and sensitivity analyses carried out in the context of ramp-stress ALTSP based on variable SSP for proportion nonconforming.

• Journal of Construction Engineering and Project Management
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• 제8권1호
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• pp.1-9
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• 2018

US transportation agencies are dealing with shrinking budgets, limited work forces, and deteriorating infrastructure. In order to cope with funding uncertainty, state highway agencies are now looking into their own organizations and identifying programs, practices, and processes that have potential for cost saving. A quality assurance (QA) program is an integral part of highway construction and ensures a project's contracted level of quality. The cost of quality (conforming and nonconforming) can constitute a sizable part of total construction cost. As the quality assurance programs evolved, various practices and processes were developed over time and later adopted by state highway agencies. These practices and processes include different QA standards and specifications, varying testing methods, central testing lab vs. on site testing, performance based vs. prescribed quality assurance practices, implementation of innovative quality assurance practices, etc. Therefore, there is an opportunity to assess different QA strategies and recommend those practices that are effective and cost efficient. A national survey was conducted by the authors, which provided a detailed mapping of various QA practices and processes used as part of QA programs and identified areas where agencies can focus on for cost savings. The survey found that QA sampling and testing plans, optimization of sampling plans, optimization of QA standards and specifications, and implementation of innovative test methods and processes are the main areas the agencies should focus to lean the current QA programs.

• 한국항공운항학회지
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• 제27권2호
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• pp.1-8
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• 2019

Optimal path planning refers to find the safe route to the destination at a low cost, is a major problem with regard to autonomous navigation. Sampling Based Planning(SBP) approaches, such as Rapidly-exploring Random Tree Star($RRT^*$), are the most influential algorithm in path planning due to their relatively small calculations and scalability to high-dimensional problems. $RRT^*$-Smart introduced path optimization and biased sampling techniques into $RRT^*$ to increase convergent rate. This paper presents an improvement plan that has changed the biased sampling method to increase the initial convergent rate of the $RRT^*$-Smart, which is specified as m$RRT^*$-Smart. With comparison among $RRT^*$, $RRT^*$-Smart and m$RRT^*$-Smart in 2 & 3-D environments, m$RRT^*$-Smart showed similar or increased initial convergent rate than $RRT^*$ and $RRT^*$-Smart.

• 한국안전학회지
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• 제35권1호
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• pp.25-33
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• 2020

In most plant layout optimization researches, MILP(Mixed Integer Linear Programming) problems, in which the objective function includes the costs of pipelines connecting process equipment and cost associated with safety issues, have been employed. Based on these MILP problems, various optimization solvers have been applied to investigate the optimal solutions. To consider safety issues on the objective function of MILP problems together, the accurate information about the impact and the frequency of potential accidents in a plant should be required to evaluate the safety issues. However, it is really impossible to obtain accurate information about potential accidents and this limitation may reduce the reliability of a plant layout problem. Moreover, in real industries such as plant engineering companies, the plant layout is previously fixed and the considerations of various safety instruments and systems have been performed to guarantee the plant safety. To reflect these situations, the two step optimization problems have been designed in this study. The first MILP model aims to minimize the costs of pipelines and the land size as complying sufficient spaces for the maintenance and safety. After the plant layout is determined by the first MILP model, the optimal locations of blast walls have been investigated to maximize the mitigation impacts of blast walls. The particle swarm optimization technique, which is one of the representative sampling approaches, is employed throughout the consideration of the characteristics of MILP models in this study. The ethylene oxide plant is tested to verify the efficacy of the proposed model.

• 정보보호학회논문지
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• 제34권2호
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• pp.167-177
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• 2024

본 논문은 isogeny 기반 전자 서명 알고리즘인 SeaSign의 최적화 방안을 제안한다. SeaSign은 CSIDH의 class group action에 Fiat-Shamir with abort를 결합한 전자서명 알고리즘이다. CSIDH 기반 암호는 SIDH 기반 암호가 다항시간안에 공격됨에 따라 다시 주목받고 있지만, 이를 기반한 전자서명인 SeaSign은 비효율적인 속도로 많은 최적화가 진행되지 않았다. 본 논문에서는 SeaSign에 대한 효율적인 서명 방법을 제안한다. 제안하는 서명 방법은 간단하지만 강력하며, 알고리즘 내에서 rejection sampling의 위치 변경을 통해 이루어진다. 추가로, 본 논문에서는 제안하는 알고리즘이 최적 성능을 제공할 수 있는 파라미터를 제시한다. 제시한 결과, 기존 SeaSign의 파라미터를 사용할 경우, 본 논문에서 제안한 서명방법은 기존 SeaSign 대비 3배 빠른 성능을 보인다. 추가로 신규 제시된 파라미터와 본 논문의 서명 방법을 결합한 경우, 기존 SeaSign 대비 290배 빠른 성능과 Decru 등이 제안한 방법 대비 7.47배 빠른 성능을 제공한다.

• 대한토목학회논문집
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• 제14권5호
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• pp.1043-1053
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• 1994

본 논문에서는 태풍이나 착빙설 등 기상관련 하중을 받는 송전철탑의 실용적이고 합리적인 설계를 위하여 신뢰성에 기초한 하중저항계수설계기준(Load and Resistance Factor Design : LRFD)을 개발하였다. 이때, 설계풍하중 및 착빙하중은 송전철탑에 가해지는 풍속과 착빙설에 대한 우리나라의 가용한 통계자료를 바탕으로 MCS(Monte Carlo Simulation) 기법을 사용하여 추정하였다. 시설 송전철탑의 요소 및 체계신뢰성해석에는 AFOSM(Advanced First Order Second Moment)신뢰성방법과 IST(Importance Sampling Technique)를 사용하였다. LRFD 설계기준의 하중 및 저항계수는 합리적으로 선정된 목표 신뢰도를 기초로 AFOSM과 code 최적화기법을 사용하여 도출하였다.

• Advances in environmental research
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• 제7권2호
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• pp.87-107
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• 2018

Water quality monitoring network needs periodic evaluations based on environmental demands and financial constraints. We used a genetic algorithm to optimize the existing water quality monitoring stations on the Sefid-Rud River, which is located in the North of Iran. Our objective was to optimize the existing stations for drinking and irrigation purposes, separately. The technique includes two stages called data preparation and the optimization. On the data preparation stage, first the basin was divided into four sections and each section was consisted of some stations. Then, the score of each station was computed using the data provided by the water Research Institute of the Ministry of energy. After that, we applied a weighting method by providing questionnaires to ask the experts to define the significance of each parameter. In the next step, according to the scores, stations were prioritized cumulatively. Finally, the genetic algorithm was applied to identify the best combination. The results indicated that out of 21 existing monitoring stations, 14 stations should remain in the network for both irrigation and drinking purposes. The results also had a good compliance with the previous studies which used dynamic programming as the optimization technique.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2004년도 ICCAS
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• pp.1162-1167
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• 2004

This paper presents the design methodology of digital fuzzy controller(DFC) for the systems with time-delay. We propose the fuzzy feedback controller whose output is delayed with unit sampling period and predicted. The analysis and the design problem considering time-delay become easy because the proposed controller is syncronized with the sampling time. The stabilization problem of the digital fuzzy system with time-delay is solved by linear matrix inequality(LMI) theory. Convex optimization techniques are utilized to solve the stable feedback gains and a common Lyapunov function for designed fuzzy control system. To show the effectiveness the proposed control scheme, the network control example is presented.