• 제목/요약/키워드: variational

검색결과 1,182건 처리시간 0.031초

The Effects of Typhoon Initialization and Dropwindsonde Data Assimilation on Direct and Indirect Heavy Rainfall Simulation in WRF model

  • Lee, Ji-Woo
    • 한국지구과학회지
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    • 제36권5호
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    • pp.460-475
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    • 2015
  • A number of heavy rainfall events on the Korean Peninsula are indirectly influenced by tropical cyclones (TCs) when they are located in southeastern China. In this study, a heavy rainfall case in the middle Korean region is selected to examine the influence of typhoon simulation performance on predictability of remote rainfall over Korea as well as direct rainfall over Taiwan. Four different numerical experiments are conducted using Weather Research and Forecasting (WRF) model, toggling on and off two different improvements on typhoon in the model initial condition (IC), which are TC bogussing initialization and dropwindsonde observation data assimilation (DA). The Geophysical Fluid Dynamics Laboratory TC initialization algorithm is implemented to generate the bogused vortex instead of the initial typhoon, while the airborne observation obtained from dropwindsonde is applied by WRF Three-dimensional variational data assimilation. Results show that use of both TC initialization and DA improves predictability of TC track as well as rainfall over Korea and Taiwan. Without any of IC improvement usage, the intensity of TC is underestimated during the simulation. Using TC initialization alone improves simulation of direct rainfall but not of indirect rainfall, while using DA alone has a negative impact on the TC track forecast. This study confirms that the well-suited TC simulation over southeastern China improves remote rainfall predictability over Korea as well as TC direct rainfall over Taiwan.

VARIABLE STARS IN A FIELD OF THE OLD OPEN CLUSTER M67 PHOTOMETRIC PRECISION OF THE BOAO 1.8M TELESCOPE

  • KIM SEUNG-LEE;CHUN MOO-YOUNG;PARK BYEONG-GON;LEE SEE-WOO
    • 천문학회지
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    • 제29권1호
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    • pp.43-51
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    • 1996
  • We present test results of time-series CCD photometry to investigate the photometric precision of the BOAO (Bohyunsan Optical Astronomy Observatory) 1.8m telescope. A well-known field of the old open cluster M67, which includes two pulsating blue stragglers and two W UMa type binaries, was monitored for 3.5 hours on February 22, 1996. We have collected 148 V frames and 3 B frames. Photometric noises which consist mainly of photon noise and scintillation noise, were lowered down to about 1.9 mmag for stars of $10.\;^m5$ in M67 with exposure time of 20 seconds. From the C-M diagram for M67, a number of observational properties were derived; E(B-V) = 0.03, (V-Mv)o = 9.6, Age = 4 Gyr. We obtained light curves for four known variable stars and confirmed their variational characteristics. The pulsating blue stragglers show a low amplitude (about 0.01 mag) of light variation.

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방향성 입자를 이용한 ARAP 동적 변형 (As-Rigid-As-Possible Dynamic Deformation with Oriented Particles)

  • 최민규
    • 한국게임학회 논문지
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    • 제17권1호
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    • pp.89-98
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    • 2017
  • 본 논문에서는 물리기반 동적 변형을 실시간에 안정적으로 시뮬레이션하는 새로운 ARAP(as-rigid-as-possible) 방법을 제안한다. 1, 2, 3차원 물체의 변형을 안정적이며, 빠르고, 일관성 있게 다루기 위하여 방향성 입자로 이루어진 변형 그래프를 도입하고 그에 따른 ARAP 변형에너지를 공식화한다. 방향성 입자의 안정적인 시간 적분을 위해서는 변분 공식화에 기반을 둔 내재적 시간 적분 기법을 개발한다. 또한 국지적/전역적 최적화를 교대로 반복 적용하여 방향성 입자의 최적 위치 및 회전을 구한다. 제안된 방법은 구현이 쉽고 복잡한 변형을 실시간에 시뮬레이션할 수 있을 정도로 빠르다.

단일 E-평면구조를 이용한 협대역 도파관형 대역통과 여파기의 설계 (Design of Narrow-band Waveguide Bandpass Filters Using Single E-Plane Structures)

  • 박준석;임재봉;김철동
    • 한국전자파학회지:전자파기술
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    • 제6권2호
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    • pp.35-44
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    • 1995
  • 본 논문에서는 우수한 양산성을 감안한 협대역 도파관형 대역통과 여파기를 제작하기 위하여 미리 제작된 판 재를 도파관 튜브의 내부에 파진 스롯에 끼워넣는 단일 E 평면구조를 제안하고, 이를 변분해석볍을 사용하여 해석하였다. 그리고 통과대역 보정법에 의한 여파기 합성설계방볍을 사용하여 마이크로파대 협대역 도파관형 대역통과 여파기를 설계하는 CAD 프로그램을 개발하였다. 개발된 프로그램으로 중심주파수 3.82GHz 5단 O.002dB equi-ripple Chebyshev형 28MHz의 대역폭을 갖는 대역통과 여파기를 설계하여 튜닝구조로 제작, 여파기 특성을 미세조정과정을 거쳐 실험하였다. 그 결과 이론치와 잘 일치하는 측정결과를 얻었다.

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범밀도함수법을 이용하여 계산한 IIIB족 원소가 도핑된 ZnO의 전자상태 (Electronic State of ZnO Doped with Elements of IIIB family, Calculated by Density functional Theory)

  • 이동윤;이원재;민복기;김인성;송재성;김양수
    • 한국전기전자재료학회논문지
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    • 제18권7호
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    • pp.589-593
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    • 2005
  • The electronic states of ZnO doped with Al, Ga and In, which belong to III family elements in periodic table, were calculated using the density functional theory. In this study, the calculation was performed by two Programs; the discrete variational Xa (DV-Xa) method, which is a sort of molecular orbital full potential method; Vienna Ab-initio Simulation Package (VASP), which is a sort of pseudo potential method. The fundamental mixed orbital structure in each energy level near the Fermi level was investigated with simple model using DV-Xa. The optimized crystal structures calculated by VASP were compared to the measured structures. The density of state and the energy levels of dopant elements were shown and discussed in association with properties.

천수만의 수질환경특성과 장기변동 (Long-term Changes and Variational Characteristics of Water Quality in the Cheonsu Bay of Yellow Sea, Korea)

  • 박승윤;박경수;김형철;김평중;김전풍;박중현;김숙양
    • 한국환경과학회지
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    • 제15권5호
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    • pp.447-459
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    • 2006
  • Long-term trends and distribution patterns of water quality were investigated in the Cheonsu Bay of Korea from 1983 to 2004. Water samples were collected at 4 stations and physicochemical parameters were analyzed including water temperature, salinity, suspended solids (SS), chemical oxygen demand (COD), dissolved oxygen (DO) and nutrients. Spatial distribution patterns were not clear between stations but the seasonal variations were distinctive except COD, SS and nitrate. Twenty two year long-term trend analysis by PCA revealed the significant changes in water quality in the study area. Water quality during 1980's and early 1990's showed high SS, low nutrients and low COD which increased during the mid and late 1990's and early 2000's. Overall water duality in the Cheonsu Bay indicated the increase in nutrients and COD concentration.

An Improved Calculation Model for Analysis of [111] InGaAs/GaAs Strained Piezoelectric Superlattices

  • Kim, Byoung-Whi;Yoo, Jae-Hoon;Kim, Soo-Hyung
    • ETRI Journal
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    • 제21권4호
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    • pp.65-82
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    • 1999
  • We present a calculation model for an improved quantitative theoretical analysis of electronic and optical properties of strained-piezoelectric[111] InGaAs/GaAs superlattices (SLs). The model includes a full band-coupling between the four important energy bands: conduction, heavy, light, and spin split-off valence bands. The interactions between these and higher lying bands are treated by the k ${\cdot}$ p perturbation method. The model takes into account the differences in the band and strain parameters of constituent materials of the heterostructures by transforming it into an SL potential in the larger band-gap material region. It self-consistently solves an $8{\times}8$ effective-mass $Schr{\ddot{o}}dinger$ equation and the Hartree and exchange-correlation potential equations through the variational procedure proposed recently by the present first author and applied to calculate optical matrix elements and spontaneous emission rates. The model can be used to further elucidate the recent theoretical results and experimental observations of interesting properties of this type of quantum well and SL structures, including screening of piezoelectric field and its resultant optical nonlinearities for use in optoelectronic devices.

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A CHARACTERISTICS-MIXED FINITE ELEMENT METHOD FOR BURGERS' EQUATION

  • Chen, Huanzhen;Jiang, Ziwen
    • Journal of applied mathematics & informatics
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    • 제15권1_2호
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    • pp.29-51
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    • 2004
  • In this paper, we propose a new mixed finite element method, called the characteristics-mixed method, for approximating the solution to Burgers' equation. This method is based upon a space-time variational form of Burgers' equation. The hyperbolic part of the equation is approximated along the characteristics in time and the diffusion part is approximated by a mixed finite element method of lowest order. The scheme is locally conservative since fluid is transported along the approximate characteristics on the discrete level and the test function can be piecewise constant. Our analysis show the new method approximate the scalar unknown and the vector flux optimally and simultaneously. We also show this scheme has much smaller time-truncation errors than those of standard methods. Numerical example is presented to show that the new scheme is easily implemented, shocks and boundary layers are handled with almost no oscillations. One of the contributions of the paper is to show how the optimal error estimates in $L^2(\Omega)$ are obtained which are much more difficult than in the standard finite element methods. These results seem to be new in the literature of finite element methods.

CHIMERA 격자기법을 이용한 고속전철 주위의 전산유동해석 (Numerical Flow Simulations Around High Speed Train Using CHIMERA Grid Technique)

  • 최성욱;김인선
    • 한국전산유체공학회지
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    • 제1권1호
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    • pp.81-87
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    • 1996
  • The aerodynamic charateristics of high speed train can be improved by well-designing of its fore-body shape. In this paper, as a way of the design a fore-body shape which has optimal aerodynamic charasteristics, 9 models of fore-body shapes are proposed and the change of aerodynamic charateristics is studied through calculations of flow field around high speed train for each fore-body shape. The flow field around high speed trains are calculated using Thin-Layer Navier-Stokes equation and Chimera grid technique. The application of Chimera grid technique to these flow calculations over high speed train which has ground plane under the train makes grid generation easily. As a computaional algorithm, Pulliam and Chaussee's Diagonal algorithm, the modified form of the Beam and Warming's AF scheme which operates on block-tridiagonal matrices, is selected to reduce computaional time. Introducing hole points flag concept to this Diagonal algorithm. a algorithm for Chimera grid is generated. The variational trends of aerodynamic characteristics are studied from the results of flow calculations around high speed trains for 9 fore-body shapes.

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PSE/AS4 복합재료의 가속노화가 피로강도에 미치는 영향 (The Effects of Physical Aging of PSF/AS4 Laminate on Fatigue)

  • 김형원
    • 한국복합재료학회:학술대회논문집
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    • 한국복합재료학회 2005년도 추계학술발표대회 논문집
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    • pp.39-44
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    • 2005
  • The effects of aging of PSF/AS4 laminates on fatigue was studied using the new energy release rate analysis. The analysis by the variational mechanics has been useful in providing fracture mechanics interpretation of matrix microcracking in cross-ply laminates. This paper describes the changes of the critical energy release rate (microcracking toughness) according to the aging period under fatigue loading. The master plot by modified Paris-law gives a characterization of a material system's resistance to microcrack formation. PSF $[0/90_{s}]_{s}$ laminates were aged at four different temperature based on the glass transition temperature for 0 to 60 days. At all temperatures, the toughness decreased with aging time. The decrease of the toughness at higher temperature was faster than at lower temperature. To assess the effects of aging on fatigue, the unaged laminates were compared with the laminates which had been aged for 60 days at 170$^{\circ}C$ near 180 $^{\circ}C$ t$_g$. The slope of dD/dN versus ${\Delta}G_m$. of the aged laminates was lower than that of the unaged laminates. There was a significant shift of the aged data to formation of microcracks at the lower values of ${\Delta}G_m$.

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