• Title/Summary/Keyword: Theoretical Computation

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Validation of Numerical Model for the Wind Flow over Real Terrain (실지형을 지나는 대기유동에 대한 수치모델의 검증)

  • Kim, Hyeon-Gu;Lee, Jeong-Muk;No, Yu-Jeong
    • Journal of Korean Society for Atmospheric Environment
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    • v.14 no.3
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    • pp.219-228
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    • 1998
  • In the present investigation, a numerical model developed for the prediction of the wind flow over complex terrain is validated by comparing with the field experiments. For the solution of the Reynolds - Averaged Clavier- stokes equations which are the governing equations of the microscale atmospheric flow, the model is constructed based on the finite-volume formulation and the SIMPLEC pressure-correction algorithm for the hydrodynamic computation. The boundary- fitted coordinate system is employed for the detailed depiction of topography. The boundary conditions and the modified turbulence constants suitable for an atmospheric boundary- layer are applied together with the k- s turbulence model. The full- scale experiments of Cooper's Ridge, Kettles Hill and Askervein Hill are chosen as the validation cases . Comparisons of the mean flow field between the field measurements and the predicted results show good agreement. In the simulation of the wind flow over Askervein Hill , the numerical model predicts the three dimensional flow separation in the downslope of the hill including the blockage effect due to neighboring hills . Such a flow behavior has not been simulated by the theoretical predictions. Therefore, the present model may offer the most accurate prediction of flow behavior in the leeside of the hill among the existing theoretical and numerical predictions.

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Improving CMD Areal Density Analysis: Algorithms and Strategies

  • Wilson, R.E.
    • Journal of Astronomy and Space Sciences
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    • v.31 no.2
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    • pp.121-130
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    • 2014
  • Essential ideas, successes, and difficulties of Areal Density Analysis (ADA) for color-magnitude diagrams (CMD's) of resolved stellar populations are examined, with explanation of various algorithms and strategies for optimal performance. A CMD-generation program computes theoretical datasets with simulated observational error and a solution program inverts the problem by the method of Differential Corrections (DC) so as to compute parameter values from observed magnitudes and colors, with standard error estimates and correlation coefficients. ADA promises not only impersonal results, but also significant saving of labor, especially where a given dataset is analyzed with several evolution models. Observational errors and multiple star systems, along with various single star characteristics and phenomena, are modeled directly via the Functional Statistics Algorithm (FSA). Unlike Monte Carlo, FSA is not dependent on a random number generator. Discussions include difficulties and overall requirements, such as need for fast evolutionary computation and realization of goals within machine memory limits. Degradation of results due to influence of pixelization on derivatives, Initial Mass Function (IMF) quantization, IMF steepness, low Areal Densities ($\mathcal{A}$), and large variation in $\mathcal{A}$ are reduced or eliminated through a variety of schemes that are explained sufficiently for general application. The Levenberg-Marquardt and MMS algorithms for improvement of solution convergence are contained within the DC program. An example of convergence, which typically is very good, is shown in tabular form. A number of theoretical and practical solution issues are discussed, as are prospects for further development.

Computation of Crack Tip Mode I Stress Intensity Factor of a Specimen for Measuring Slow Crack Growth Resistance of Plastic Pipes Using Finite-Element Method (유한요소법에 의한 플라스틱 파이프의 저속균열성장 저항성 시험편 균열선단 모드 I 응력확대계수 계산)

  • Choi, Sun-Woong;Park, Yeong-Joo;Suh, Yeong-Sung
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.29 no.9 s.240
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    • pp.1225-1234
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    • 2005
  • Mode I stress intensity factor $(K_I)$ of Notched Ring Test(NRT) specimen for measuring slow crack growth resistance was found using finite-element method. The theoretical $K_I$ value of NRT was not available in any references and could not be solved analytically. At first, in order to verify the accuracy of the finite-element approach, published $K_I$ values of several cracks were calculated and compared with finite-element results. The results were in good agreement within inherent errors of theoretical $K_I$. Finally the mode I stress intensity factor of NRT was found using 2- and 3-dimensional finite-element methods and expressed as a function of the applied load. This enabled direct comparison of resistance to slow crack growth between NRT and Notched Pipe Test(NPT), which employ different loading regime.

An Approximate Shortest Path Re-Computation Method for Digital Road Map Databases in Mobile Computing Environments (모바일 컴퓨팅 환경에서의 디지털 로드맵 데이타베이스를 위한 근접 최단 경로 재계산 방법)

  • 김재훈;정성원;박성용
    • Journal of KIISE:Databases
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    • v.30 no.3
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    • pp.296-309
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    • 2003
  • One of commercial applications of mobile computing is ATIS(Advanced Traveler Information Systems) in ITS(Intelligent Transport Systems). In ATIS, a primary mobile computing task is to compute the shortest path from the current location to the destination. In this paper, we have studied the shortest path re-computation problem that arises in the DRGS(Dynamic Route Guidance System) in ATIS where the cost of topological digital road map is frequently updated as traffic condition changes dynamically. Previously suggested methods either re-compute the shortest path from scratch or re-compute the shortest path just between the two end nodes of the edge where the cost change occurs. However, these methods we trivial in that they do not intelligently utilize the previously computed shortest path information. In this paper, we propose an efficient approximate shortest path re-computation method based on the dynamic window scheme. The proposed method re-computes an approximate shortest path very quickly by utilizing the previously computed shortest path information. We first show the theoretical analysis of our methods and then present an in-depth experimental performance analysis by implementing it on grid graphs as well as a real digital road map.

High-resolution Urban Flood Modeling using Cellular Automata-based WCA2D in the Oncheon-cheon Catchment in Busan, South Korea (셀룰러 오토마타 기반 WCA2D 모형을 이용한 부산 온천천 유역 고해상도 도시 침수 해석)

  • Choi, Hyeonjin;Lee, Songhee;Woo, Hyuna;Noh, Seong Jin
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.43 no.5
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    • pp.587-599
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    • 2023
  • As climate change increasesthe frequency and risk of flooding in major cities around theworld, the importance ofsimulation technology that can quickly and accurately analyze high-resolution 2D flooding information in large-scale areasis emerging. The physically-based approaches based on the Shallow Water Equations (SWE) often requires huge computer resources hindering high-resolution flood prediction. This study investigated the theoretical background of Weighted Cellular Automata 2D (WCA2D), which simulates spatio-temporal changes offlooding using transition rules and weight-based system, and assessed feasibility to simulate pluvial flooding in the urbancatchment, theOncheon-cheon catchmentinBusan, SouthKorea.Inaddition,the computation performancewas compared by applying versions using OpenComputing Language (OpenCL) andOpenMulti-Processing (OpenMP) parallel computing techniques. Simulationresultsshowed that the maximuminundation depthmap by theWCA2Dmodel cansimilarly reproduce historical inundation maps. Also, it can precisely simulate spatio-temporal changes of flooding extent in the urban catchment with complex topographic characteristics. For computation efficiency, parallel computing schemes, theOpenCLandOpenMP, improved the computation by about 8~14 and 5~6 folds respectively, compared to the sequential computation.

Fundamental theory of curved structures from a non-tensorial point of view

  • Paavola, Juha;Salonen, Eero-Matti
    • Structural Engineering and Mechanics
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    • v.7 no.2
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    • pp.159-180
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    • 1999
  • The present paper shows a new non-tensorial approach to derive basic equations for various structural analyses. It can be used directly in numerical computation procedures. The aim of the paper is, however, to show that the approach serves as an excellent tool for analytical purposes also, working as a link between analytical and numerical techniques. The paper gives a method to derive, at first, expressions for strains in general beam and shell analyses, and secondly, the governing equilibrium equations. The approach is based on the utilization of local fixed Cartesian coordinate systems. Applying these, all the definitions required are the simple basic ones, well-known from the analyses in common global coordinates. In addition, the familiar principle of virtual work has been adopted. The method will be, apparently, most powerful in teaching the theories of curved beam and shell structures for students not familiar with tensor analysis. The final results obtained have no novelty value in themselves, but the procedure developed opens through its systematic and graphic progress a new standpoint to theoretical considerations.

Advanced Finite Element Analysis for Linear Viscoelastic Problems of a Hereditary-Type Constitutive Law (유전적분형 선형 점탄성문제의 유한요소법에 의한 효율적 해석)

  • 심우진;이성희
    • Computational Structural Engineering
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    • v.6 no.2
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    • pp.103-114
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    • 1993
  • An advanced time-domain finite element formulation is presented for the displacement and stress analysis of isotropic, linear viscoelastic problems of a hereditary-type constitutive law. The semidiscrete finite element method with linear time-stepping scheme and an elastic-viscoelastic correspondence principle are used in the theoretical development. An efficient treatment of hereditary integral is introduced to improve the numerical accuracy, to reduce the computation time, and to avoid the use of large memory storage. Two-dimensional numerical examples of plane strain and plane stress are solved under the assumption on the material property of being elastic in dilatation and like three-element Voigt model in distorsion, and compared with the analytical solutions and the past numerical results to show the versatility and efficiency of the proposed method.

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Energy-aware Management in Wireless Body Area Network System

  • Zhang, Xu;Xia, Ying;Luo, Shiyan
    • KSII Transactions on Internet and Information Systems (TIIS)
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    • v.7 no.5
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    • pp.949-966
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    • 2013
  • Recently, Wireless Body Area Network (WBAN) has promise to revolutionize human daily life. The need for multiple sensors and constant monitoring lead these systems to be energy hungry and expensive with short operating lifetimes. In this paper, we offer a review of existing work of WBAN and focus on energy-aware management in it. We emphasize that nodes computation, wireless communication, topology deployment and energy scavenging are main domains for making a long-lived WBAN. We study the popular power management technique Dynamic Voltage and Frequency Scaling (DVFS) and identify the impact of slack time in Dynamic Power Management (DPM), and finally propose an enhanced dynamic power management method to schedule scaled jobs at slack time with the goal of saving energy and keeping system reliability. Theoretical and experimental evaluations exhibit the effectiveness and efficiency of the proposed method.

COMPUTATIONAL DURABILITY PREDICTION OF BODY STRUCTURES IN PROTOTYPE VEHICLES

  • Kim, H.-S.;Yim, H.-J.;Kim, C.-B.
    • International Journal of Automotive Technology
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    • v.3 no.4
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    • pp.129-135
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    • 2002
  • Durability estimation of a prototype vehicle has traditionally relied heavily on accelerated durability tests using predefined proving grounds or rig tests using a road simulator. By use of those tests, it is very difficult to predict durability failures in actual service environments. This motivated the development of an integrated CAE (Computer Aided Engineering) methodology for the durability estimation of a prototype vehicle in actual service environments. Since expensive computational costs such as computation time and hardware resources are required for a full vehicle simulation in those environments with a very long span of event time, the conventional CAE methodologies have little feasibility. An efficient computational methodology for durability estimations is applied with theoretical developments. The effectiveness of the proposed methodology is shown by the comparison of results of the typical actual service environment such as the city mode with those of the typical accelerated durability test over the Belgian road.

A Study on Unified Vector Control of Induction Motor (유도전동기의 통일적 벡터제어에 관한 연구)

  • Kim, Y.D.;Lee, D.C.
    • Journal of Power System Engineering
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    • v.5 no.3
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    • pp.95-103
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    • 2001
  • This study is applied to common induction motor, and vector control is realized by using an indirect type of induction motor which has a simple composition. In this study extended Kalman filter is used from control theoretical viewpoint, and primary resistance and secondary resistance which change according to the temperature of motor are simultaneously estimated. This paper aims to research an indirect vector control in which the secondary resistance obtained from this estimation is consistent with secondary flux. This estimation is made by on-line estimation, but on-line estimation is difficult because extended Kalman filter takes long time in computation time. So off-line estimation was made on the assumption that the variation of temperature in motor is slow temporally.

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