• International Journal of Aeronautical and Space Sciences
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• 제17권2호
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• pp.268-283
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• 2016

Aircraft manufacturing companies have to consider multiple derivatives to satisfy various market requirements. They modify or extend an existing aircraft to meet new market demands while keeping the development time and cost to a minimum. Many researchers have studied the derivative design process, but these research efforts consider baseline and derivative designs together, while using the whole set of design variables. Therefore, an efficient process that can reduce cost and time for aircraft derivative design is needed. In this research, a more efficient design process is proposed which obtains global changes from local changes in aircraft design in order to develop aircraft derivatives efficiently. Sensitivity analysis was introduced to remove unnecessary design variables that have a low impact on the objective function. This prevented wasting computational effort and time on low priority variables for design requirements and objectives. Additionally, uncertainty from the fidelity of analysis tools was considered in design optimization to increase the probability of optimization results. The Reliability Based Design Optimization (RBDO) and Possibility Based Design Optimization (PBDO) methods were proposed to handle the uncertainty in aircraft conceptual design optimization. In this paper, Collaborative Optimization (CO) based framework with RBDO and PBDO was implemented to consider uncertainty. The proposed method was applied for civil jet aircraft derivative design that increases cruise range and the number of passengers. The proposed process provided deterministic design optimization, RBDO, and PBDO results for given requirements.

• 한국환경과학회지
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• 제8권6호
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• pp.661-667
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• 1999

Estimating dimensions of attractors are the most basic tools to analyze properties of chaotical dynamic systems. In this paper, we estimate correlation dimensions of meteorological variables, such as wind speed (v) and temperature (T) observed in Kimhae International Airport when the land-sea breeze circulation is appeared and find low non-integer values that reflect the deterministic chaos characterizing the dynamics. We compare the results with the correlation dimensions of 2-dimensional model that is calculated by finite element method. Though the correlation dimensions of the calculated wind speed ( v) are less than those of the observed wind speed ( v), we can suggest that the land-sea breeze circulation has not a unique mechanism. The land-sea breeze phenomenon is a complicated dynamics, which is constructed with various scale motions of atmosphere. In further research, we hope to find more accurate dynamics of land-sea breeze through wide observations and using of more sophisticated prediction models.

• Nuclear Engineering and Technology
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• 제36권1호
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• pp.83-103
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• 2004

The methodological framework of the Level 2 PSA appears to be currently standardized in a formalized fashion, but there have been different opinions on the way the sources of uncertainty are characterized and treated. This is primarily because the Level 2 PSA deals with complex phenomenological processes that are deterministic in nature rather than random processes, and there are no probabilistic models characterizing them clearly. As a result, the probabilistic quantification of the Level 2 PSA CET / APET is often subjected to two sources of uncertainty: (a) incomplete modeling of accident pathways or different predictions for the behavior of phenomenological events and (b) expert-to-expert variation in estimating the occurrence probability of phenomenological events. While a clear definition of the two sources of uncertainty involved in the Level 2 PSA makes it possible to treat an uncertainty in a consistent manner, careless application of these different sources of uncertainty may produce different conclusions in the decision-making process. The primary purpose of this paper is to characterize typical sources of uncertainty that would often be addressed in the Level 2 PSA and to provide a formal guidance for quantifying their impacts on the PSA Level 2 risk results. An additional purpose of this paper is to give a formal approach on how to combine random uncertainties addressed in the Level 1 PSA with subjectivistic uncertainties addressed in the Level 2 PSA.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.574-575
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• 2007

This paper proposes a method for choosing the best transmission system expansion plan using nodal/bus delivery marginal rate criterion ($BMR_k$) defined newly in this paper. The objective method minimizes a total cost which is an investment budget for constructing new transmission lines subject to the $BMR_k$ which means a nodal deterministic reliability level requirement at specified load point. The proposed method models the transmission system expansion problem as an integer programming problem. It solves for the optimal strategy using a branch and bound method that utilizes a network flow approach and the maximum flow-minimum cut set theorem. Test results on an existing 21-bus system are included in the paper. It demonstrated the suitability of the proposed method for solving the transmission system expansion planning problem in competitive electricity market environment.

• Computers and Concrete
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• 제11권5호
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• pp.411-440
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• 2013

Large fluctuations in surface strain at the level of steel are expected in reinforced concrete flexural members at a given stage of loading due to the emergent structure (emergence of new crack patterns). This has been identified in developing deterministic constitutive models for finite element applications in Ibrahimbegovic et al. (2010). The aim of this paper is to identify a suitable probability distribution for describing the large deviations at far from equilibrium points due to emergent structures, based on phenomenological, thermodynamic and statistical considerations. Motivated by the investigations reported by Prigogine (1978) and Rubi (2008), distributions with heavy tails (namely, alpha-stable distributions) are proposed for modeling the variations in strain in reinforced concrete flexural members to account for the large fluctuations. The applicability of alpha-stable distributions at or in the neighborhood of far from equilibrium points is examined based on the results obtained from carefully planned experimental investigations, on seven reinforced concrete flexural members. It is found that alpha-stable distribution performs better than normal distribution for modeling the observed surface strains in reinforced concrete flexural members at these points.

• 한국시뮬레이션학회논문지
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• 제8권3호
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• pp.49-66
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• 1999

Semiconductor wafer fabrication is known to be one of the most complex manufacturing processes due to process intricacy, random yields, product diversity, and rapid changing technologies. In this study we are concerned with the impact of lot release and dispatching policies on the performance of semiconductor wafer fabrication facilities. We consider several semiconductor wafer fabrication environments according to the machine failure types such as no failure, normal MTBF, bottleneck with low MTBF, high randomness, and high MTBF cases. Lot release rules to be considered are Deterministic, Poisson process, WR(Workload Regulation), SA(Starvation Avoidance), and Multi-SA. These rules are combined with several dispatching rules such as FIFO (First In First Out), SRPT (Shortest Remaining Processing Time), and NING/M(smallest Number In Next Queue per Machine). We applied the combined policies to each of semiconductor wafer fabrication environments. These policies are assessed in terms of throughput and flow time. Basically Weins fabrication setup was used to make the simulation models. The simulation parameters were obtained through the preliminary simulation experiments. The key results throughout the simulation experiments is that Multi-SA and SA are the most robust rules, which give mostly good performance for any wafer fabrication environments when used with any dispatching rules. The more important result is that for each of wafer fabrication environments there exist the best and worst choices of lot release and dispatching policies. For example, the Poisson release rule results in the least throughput and largest flow time without regard to failure types and dispatching rules.

• 산업경영시스템학회지
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• 제45권4호
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• pp.217-224
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• 2022

Due to the issue of the sustainability in transportation area, the number of electric vehicles has significantly increased. Most automakers have decided or planned to manufacture the electric vehicles rather than carbon fueled vehicles. However, there are still some problems to figure out for the electric vehicles such as long charging time, driving ranges, supply of charging stations. Since the speed of growing the number of electric vehicles is faster than that of the number of charging stations, there are lack of supplies of charging stations for electric vehicles and imbalances of the location of the charging stations. Thus, the location problem of charging stations is one of important issues for the electric vehicles. Studies have conducted to find the optimal locations for the charging stations. Most studies have formulated the problem with deterministic or hierarchical models. In this paper, we have investigated the fluctuations of locations and the capacity of charging stations. We proposed a mathematical model for the location problem of charging stations with the vehicle routing problem. Numerical examples provide the strategy for the location routing problems of the electric vehicles.

• Steel and Composite Structures
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• 제49권6호
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• pp.701-711
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• 2023

In order to fully reflect variation characteristics of composite concrete dam health state, the monitoring data is applied to diagnose composite concrete dam health state. Composite concrete dam lesion development to wreckage is a precursor, and its health status can be judged. The monitoring data are generally non-linear and unsteady time series, which contain chaotic information that cannot be characterized. Thus, it could generate huge influence for the construction of monitoring models and the formulation of corresponding health diagnostic indicators. This multi-scale diagnosis process is from point to whole. Chaotic characteristics are often contained in the monitoring data. If chaotic characteristics could be extracted for reflecting concrete dam health state and the corresponding diagnostic indicators will be formulated, the theory and method of diagnosing concrete dam health state can be huge improved. Therefore, the chaotic characteristics of monitoring data are considered. And, the extracting method of the chaotic components is studied from monitoring data based on fuzzy dynamic cross-correlation factor method. Finally, a method is proposed for formulating composite concrete dam health state indicators. This method can effectively distinguish chaotic systems from deterministic systems and reflect the health state of concrete dam in service.

• 한국수자원학회논문집
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• 제38권4호
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• pp.281-292
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• 2005

수자원장기종합계획에서는 물의 과부족 또는 가용한 물을 정량적으로 평가하기 위해 물수지 분석을 실시한다. 물수지 분석은 미래 예측되는 용수수요량과 공급가능량을 비교하는 단순한 과정이지만, 분석 과정에 포함되어 있는 자료와 모형의 불확실성으로 인하여 물수지 분석을 실시한 각종 보고서마다 서로 다른 결과를 보여주고 있어 국민의 신뢰를 얻지 못한 실정이다. 본 연구에서는 Monte Carlo simulation 기법 중 Latin Hypercube sampling에 기반한 확률적 모사로 물수지 분석에서의 불확실성을 표현하고 분석하였다. 대표 물수지 입력변수로 자연유량, 생공용수, 농업용수, 회귀율을 선정하여 이를 선형회귀와 entropy 이론으로 분포를 설정하였고, 불확실성 분석을 통하여 물부족량에 대한 불확실성의 범위와 위치를 규명하였다. 금강수계 3개의 소유역에 대해 불확실성 분석을 한 결과, 기존의 물수지 분석에서의 단일 물부족량이 과소 및 과대 추정될 수 있음을 보였고, 또한 민감도 분석을 통해 농업회귀율이 입력변수들 중 가장 큰 불확실성을 가지고 있으나 결과에는 거의 영향을 미치지 못하고 있음을 알 수 있었다.

• 한국농공학회지
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• 제22권4호
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• pp.108-114
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• 1980

A deterministic conceptual erosion model which simulates detachment, entrainment, transport and deposition of eroded soil particles by rainfall impact and flowing water is presented. Both upland and channel phases of sediment yield are incorporated into the erosion model. The algorithms for the soil erosion and sedimentation processes including land and crop management effects are taken from the literature and then solved using a digital computer. The erosion model is used in conjunction with the modified Kentucky Watershed Model which simulates the hydrologic characteristics from watershed data. The two models are linked together by using the appropriate computer code. Calibrations for both the watershed and erosion model parameters are made by comparing the simulated results with actual field measurements in the Four Mile Creek watershed near Traer, Iowa using 1976 and 1977 water year data. Two water years, 1970 and 1978 are used as test years for model verification. There is good agreement between the mean daily simulated and recorded streamflow and between the simulated and recorded suspended sediment load except few partial differences. The following conclusions were drawn from the results after testing the watershed and erosion model. 1. The watershed and erosion model is a deterministic lumped parameter model, and is capable of simulating the daily mean streamflow and suspended sediment load within a 20 percent error, when the correct watershed and erosion parameters are supplied. 2. It is found that soil erosion is sensitive to errors in simulation of occurrence and intensity of precipitation and of overland flow. Therefore, representative precipitation data and a watershed model which provides an accurate simulation of soil moisture and resulting overland flow are essential for the accurate simulation of soil erosion and subsequent sediment transport prediction. 3. Erroneous prediction of snowmelt in terms of time and magnitute in conjunction with The frozen ground could be the reason for the poor simulation of streamflow as well as sediment yield in the snowmelt period. More elaborate and accurate snowmelt submodels will greatly improve accuracy. 4. Poor simulation results can be attributed to deficiencies in erosion model and to errors in the observed data such as the recorded daily streamflow and the sediment concentration. 5. Crop management and tillage operations are two major factors that have a great effect on soil erosion simulation. The erosion model attempts to evaluate the impact of crop management and tillage effects on sediment production. These effects on sediment yield appear to be somewhat equivalent to the effect of overland flow. 6. Application and testing of the watershed and erosion model on watersheds in a variety of regions with different soils and meteorological characteristics may be recommended to verify its general applicability and to detact the deficiencies of the model. Futhermore, by further modification and expansion with additional data, the watershed and erosion model developed through this study can be used as a planning tool for watershed management and for solving agricultural non-point pollution problems.