• Title/Summary/Keyword: approximate model

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A Study on the Risk Assessment by Obstacles in Ship's Passage (선박 통항로 내 장해물에 따른 위험도 평가에 관한 연구)

  • Kim, Ni-Eun;Park, Young-Soo;Park, Sang-Won;Kim, So-Ra;Lee, Myoung-Ki
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.28 no.2
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    • pp.244-253
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    • 2022
  • Recently, installation projects of structures such as offshore wind farms have been increasing, and the installation of such marine obstacles could affect ships that pass nearby. Therefore, the purpose of this study was to quantitatively evaluate the risk posed to passing ships due to obstacles in their passage. Hence, parameters that affected the risk were selected, and scenarios were set based on the parameters. The scenarios were evaluated through the ES model, which is a risk assessment model, and we confirmed that the risk ratio increased as the size of the obstacle increased, the safe distance from the obstacle increased, the speed of ship decreased, and the traffic volume increased. Additionally, we found that when the traffic flow direction was designated, the risk ratio was lower than that of general traffic flow. In this study, we proposed a generalization model based on the results of the performed scenarios, applied it to the Dadaepo offshore wind farm, and demonstrated that the estimation of the approximate risk ratio was possible through the generalization model. Finally, we judged that the generalization model proposed in this study could be used as a preliminary reference for the installation of marine obstacles.

Development of a Single Allocation Hub Network Design Model with Transportation Economies of Scale (수송 규모의 경제 효과를 고려한 단일 할당 허브 네트워크 설계 모형의 개발)

  • Kim, Dong Kyu;Park, Chang Ho;Lee, Jin Su
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.26 no.6D
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    • pp.917-926
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    • 2006
  • Transportation Economies of scale are the essential properties of hub networks. One critical property of the hub network design problem is to quantify cost savings which stem from economies of scale, the costs of operating hub facilities and opportunity costs associated with delays stemming from consolidation of traffic flows. Due to the NP-complete property of the hub location problem, however, most previous researchers have focused on the development of heuristic algorithms for approximate solutions. The purpose of this paper is to develop a hub network design model considering transportation economies of scale from the consolidation of traffic flows. The model is designed to consider the uniqueness of hub networks and to determine several cost components. The heuristic algorithms for the developed model are suggested and the results of the model are compared with recently published studies using real data. Results of the analysis show that the proposed model reflects transportation economies of scale due to consolidation of flows. This study can form not only the theoretical basis of an effective and rational hub network design but contribute to the assessment of existing and planned logistics systems.

Study on the improvement of prediction model for the railway environmental noise using ISO 9613-2 (ISO 9613-2를 이용한 철도 환경소음 예측 모델 개선에 관한 연구)

  • Jang, Seungho;Koh, Hyo-In;Hong, Jiyoung
    • Journal of Environmental Impact Assessment
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    • v.26 no.1
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    • pp.11-26
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    • 2017
  • Approximate empirical equations obtained by measuring overall noise levels at different distances have been used to evaluate environmental influence of the railway noise though the accurate prediction of noise levels is important. In this paper, a noise prediction model considering the frequency characteristics of noise sources and propagation was suggested to improve the accuracy of noise prediction. The railway noise source was assorted into track, wheel, traction and aerodynamic components and they were characterized with the source strength and speed coefficient at each octave-band frequency. Correction terms for the acoustic roughness and the track/bridge condition were introduced. The sound attenuation from a source to a receiver was calculated taking account of the geometrical divergence, atmospheric absorption, ground effect, diffraction at obstacles and directivity of source by applying ISO 9613-2. For obtaining the source strength and speed coefficients, the results of rolling noise model, numerical analysis and measurements of pass-by noise were analyzed. We compared the predicted and measured noise levels in various vehicles and tracks, and verified the accuracy of the present model. It is found that the present model gives less error than the conventional one, so that it can be applied to make the accurate prediction of railway noise effect and establish its countermeasures efficiently.

An Efficient Constraint Boundary Sampling Method for Sequential RBDO Using Kriging Surrogate Model (크리깅 대체모델을 이용한 순차적 신뢰성기반 최적설계를 위한 효율적인 제한조건경계 샘플링 기법)

  • Kim, Jihoon;Jang, Junyong;Kim, Shinyu;Lee, Tae Hee;Cho, Su-gil;Kim, Hyung Woo;Hong, Sup
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.40 no.6
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    • pp.587-593
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    • 2016
  • Reliability-based design optimization (RBDO) requires a high computational cost owing to its reliability analysis. A surrogate model is introduced to reduce the computational cost in RBDO. The accuracy of the reliability depends on the accuracy of the surrogate model of constraint boundaries in the surrogated-model-based RBDO. In earlier researches, constraint boundary sampling (CBS) was proposed to approximate accurately the boundaries of constraints by locating sample points on the boundaries of constraints. However, because CBS uses sample points on all constraint boundaries, it creates superfluous sample points. In this paper, efficient constraint boundary sampling (ECBS) is proposed to enhance the efficiency of CBS. ECBS uses the statistical information of a kriging surrogate model to locate sample points on or near the RBDO solution. The efficiency of ECBS is verified by mathematical examples.

A Study on the Efficiency of Join Operation On Stream Data Using Sliding Windows (스트림 데이터에서 슬라이딩 윈도우를 사용한 조인 연산의 효율에 관한 연구)

  • Yang, Young-Hyoo
    • Journal of the Korea Society of Computer and Information
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    • v.17 no.2
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    • pp.149-157
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    • 2012
  • In this thesis, the problem of computing approximate answers to continuous sliding-window joins over data streams when the available memory may be insufficient to keep the entire join state. One approximation scenario is to provide a maximum subset of the result, with the objective of losing as few result tuples as possible. An alternative scenario is to provide a random sample of the join result, e.g., if the output of the join is being aggregated. It is shown formally that neither approximation can be addressed effectively for a sliding-window join of arbitrary input streams. Previous work has addressed only the maximum-subset problem, and has implicitly used a frequency based model of stream arrival. There exists a sampling problem for this model. More importantly, it is shown that a broad class of applications for which an age-based model of stream arrival is more appropriate, and both approximation scenarios under this new model are addressed. Finally, for the case of multiple joins being executed with an overall memory constraint, an algorithm for memory allocation across the join that optimizes a combined measure of approximation in all scenarios considered is provided.

A Study on the Prediction Models of Used Car Prices for Domestic Brands Using Machine Learning (머신러닝을 활용한 브랜드별 국내 중고차 가격 예측 모델에 관한 연구)

  • Seungjun Yim;Joungho Lee;Choonho Ryu
    • Journal of Service Research and Studies
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    • v.13 no.3
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    • pp.105-126
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    • 2023
  • The domestic used car market continues to grow along with the used car online platform service. The used car online platform service discloses vehicle specifications, accident history, inspection history, and detailed options to service consumers. Most of the preceding studies were predictions of used car prices using vehicle specifications and some options for vehicles. As a result of the study, it was confirmed that there was a nonlinear relationship between used car prices and some specification variables. Accordingly, the researchers tried to solve the nonlinear problem by executing a Machine Learning model. In common, the Regression based Machine Learning model had the advantage of knowing the actual influence and direction of variables, but there was a disadvantage of low Cost Function figures compared to the Decision Tree based Machine Learning model. This study attempted to predict used car prices of six domestic brands by utilizing both vehicle specifications and vehicle options. Through this, we tried to collect the advantages of the two types of Machine Learning models. To this end, we sequentially conducted a regression based Machine Learning model and a decision tree based Machine Learning model. As a result of the analysis, the practical influence and direction of each brand variable, and the best tree based Machine Learning model were selected. The implications of this study are as follows. It will help buyers and sellers who use used car online platform services to predict approximate used car prices. And it is hoped that it will help solve the problem caused by information inequality among users of the used car online platform service.

A Study of Stability Analysis on Unsaturated Soil Slopes Considering Rainfall (강우를 고려한 불포화 토사사면의 안정해석 연구)

  • Kim, Khi-Woong;Kim, Bum-Joo;Park, Jeong-Jun
    • Journal of the Korean Geosynthetics Society
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    • v.7 no.4
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    • pp.9-18
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    • 2008
  • Shallow slope failures in residual soil during periods of prolonged infiltration are common in Korea. This study examines an infinite slope analysis to estimate the influence of infiltration on surficial stability of slopes by the limit equilibrium method. Approximate method which is based on the Green-Ampt model have been considered to evaluate the likelihood of shallow slope failure which is induced by a particular rainfall event that accounts for the rainfall intensity and duration for various return periods. Pradel & Raad method which is devised to predict the depth of wetting front to decomposed granite soil slopes having measured soil-water characteristic curves. To compare the results with those obtained from the Pradel & Raad method, a series of numerical analysis using SEEP/W were carried out. It was found that the stability analysis of unsaturated soils calculated by using the soil-water characteristic curve of decomposed granite soils was found to be a proper analysis for shallow slope failures due to rainfall.

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Approximate Multi-Objective Optimization of a Quadcopter through Proportional-Integral-Derivative Control (PID 제어를 통한 쿼드콥터 다중목적 근사최적설계)

  • Yoon, Jaehyun;Lee, Jongsoo
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.39 no.7
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    • pp.673-679
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    • 2015
  • In this study, the nondominated sorting genetic algorithm (NSGA-II) is used to obtain the optimized proportional-integral-derivative (PID) gain value that can quickly recover the motion of a quadcopter after a disturbance. Prior to PID control, the four-rotor quadcopter interval was defined using computational fluid dynamics (CFD). Through the definition of this model, the PID control algorithm was generated. To construct a response surface model, D-optimal programming was used for the generation of experimental points. For this purpose, a gain value that satisfies both the roll and altitude PID gain values is obtained. Using the NSGA-II, the gain value of shorten time of the quadcopter motion control can be optimized.

A Study on Imposing Exact Solutions as Internal Boundary Conditions in Simulating Shallow-water Flows over a Step (계단을 지나는 천수 흐름의 모의에서 내부 경계조건으로서 정확해의 부여에 관한 연구)

  • Hwang, Seung-Yong
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.34 no.2
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    • pp.479-492
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    • 2014
  • In this study, was proposed a numerical scheme imposing exact solutions as the internal boundary conditions for the shallow-water flows over a discontinuous transverse structure such as a step. The HLLL approximate Riemann solver with the MUSCL was used for the test of the proposed scheme. Very good agreement was obtained between simulations and exact solutions for various problems of the shallow-water flows over a step. In addition, results by the numerical model showed good agreement with those of dam-break experiments over a step and stepped chute one. Developed model can simulate the shallow-water flows over discontinuous bottom such as a drop structure without additional rating curve or topography smoothing. Given the proper evaluations for the flow resistance by a step and the energy loss by the nappe flow in the future, could be simulated flooding and drying of the shallow-water flows over discontinuous topography such as a weir or the river road with retaining wall.

A Study on Breakdown Voltage of Double Gate MOSFET (DGMOSFET의 항복전압에 관한 연구)

  • Jung, Hak-Kee
    • Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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    • 2012.05a
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    • pp.693-695
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    • 2012
  • This paper have presented the breakdown voltage for double gate(DG) MOSFET. The analytical solution of Poisson's equation and Fulop's breakdown condition have been used to analyze for breakdown voltage. The double gate(DG) MOSFET as the device to be able to use until nano scale has the adventage to reduce the short channel effects. But we need the study for the breakdown voltage of DGMOSFET since the decrease of the breakdown voltage is unavoidable. To approximate with experimental values, we have used the Gaussian function as charge distribution for Poisson's equation, and the change of breakdown voltage has been observed for device geometry. Since this potential model has been verified in the previous papers, we have used this model to analyze the breakdown voltage. As a result to observe the breakdown voltage, the smaller channel length and the higher doping concentration become, the smaller the breakdown voltage becomes. Also we have observed the change od the breakdown voltage for gate oxide thickness and channel thickness.

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