• Title/Summary/Keyword: 시간전진법

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An Analysis of BVI Unsteady Rotor Aerodynamics using Unsteady Panel and Time-Marching Free Wake (비정상 패널 및 시간전진 자유후류를 이용한 BVI 비정상 로터 공력 해석)

  • Wie, Seong-Yong;Lee, Duck-Joo
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.37 no.4
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    • pp.329-335
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    • 2009
  • The unsteady panel and time-marching free wake are applied to the rotor aerodynamics and wake behaviour. Numerical results of panel and free wake are compared and validated with experimental data. Using these methods, unsteady rotor aerodynamics in BVI condition is analyzed and discussed in detail.

ANALYSIS OF TURBULENT BOUNDARY LAYER FLOWS USING A TIME MARCHING METHOD (시간 전진법을 이용한 난류 경계층 유동의 해석)

  • Gong, H.;Lee, S.
    • Journal of computational fluids engineering
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    • v.20 no.1
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    • pp.32-38
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    • 2015
  • A 3-dimensional compressible turbulent boundary layer solver has been developed. A time marching method is used to integrate the turbulent boundary layer equations. While the direct integration of the boundary layer equations is performed for unseparated flow regions, the inverse integration is performed for separated flow regions. The program is verified for flows that have analytical solutions or other numerical results. The solver will be merged with an Euler solver for viscous-inviscid interaction.

Aerodynamic Analysis of an Arbitrary Three-Dimensional Blended Wing Body Aircraft using Panel Method (패널법을 이용한 임의의 3차원 BWB 형상 항공기에 대한 공력해석)

  • Lee, Sea-Wook;Yang, Jin-Yeol;Cho, Jin-Soo
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.37 no.11
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    • pp.1066-1072
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    • 2009
  • A panel method based on potential flow theory is developed for the steady/unsteady aerodynamic analysis of arbitrary three-dimensional Blended Wing Body aircraft. The panel method uses the piecewise constant source and doublet singularities as a solution. This potential based panel method is founded on the Dirichlet boundary condition and coupled with the time-stepping method. The present method uses the time-stepping loop to simulate the unsteady motion of the aircraft. The present method can solve the three-dimensional flow over the complex bodies with less computing time and provide various aerodynamic derivatives to secure the stability of Blended Wing Body aircraft. That will do much for practical applications such as aerodynamic designs and analysis of aircraft configurations and flight simulation.

Development of Simple Dynamic Models for Ship Manoeuvring Simulation (선박 조종 시뮬레이션을 위한 단순 기동 모델 개발)

  • Kim, Dong-Jin;Yeo, Dong-Jin;Rhee, Key-Pyo
    • Journal of the Korea Society for Simulation
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    • v.19 no.3
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    • pp.17-25
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    • 2010
  • It is necessary for the ship dynamic models to realize ship dynamics and to achieve the real-time analysis in the manoeuvring simulation. Generally, simple dynamic models, such as 1st-order differential equation models of turning angle, turning rate, and forward speed, are used in the manoeuvring simulation for multiple ships. Ship dynamic modeling and parameter estimation methods based on its turning test results are proposed in this paper. Parameter estimation methods for the constant speed model and the speed-changing model are mathematically developed and verified by comparing with turning test results of a real ship.

Estimation of Large Amplitude Motions and Wave Loads of a Ship Advancing in Transient Waves by Using a Three Dimensional Time-domain Approximate Body-exact Nonlinear 2nd-order BEM (3 차원 시간영역 근사비선형 2 차경계요소법에 의한 선체의 대진폭 운동 및 파랑하중 계산)

  • Hong, Do-Chun;Hong, Sa-Young;Sung, Hong-Gun
    • Journal of the Society of Naval Architects of Korea
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    • v.47 no.3
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    • pp.291-305
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    • 2010
  • A three-dimensional time-domain calculation method is of crucial importance in prediction of the motions and wave loads of a ship advancing in a severe irregular sea. The exact solution of the free surface wave-ship interaction problem is very complicated because of the essentially nonlinear boundary conditions. In this paper, an approximate body nonlinear approach based on the three-dimensional time-domain forward-speed free-surface Green function has been presented. The Froude-Krylov force and the hydrostatic restoring force are calculated over the instantaneous wetted surface of the ship while the forces due to the radiation and scattering potentials over the mean wetted surface. The time-domain radiation and scattering potentials have been obtained from a time invariant kernel of integral equations for the potentials which are discretized according to the second-order boundary element method (Hong and Hong 2008). The diffraction impulse-response functions of the Wigley seakeeping model advancing in transient head waves at various Froude numbers have been presented. A simulation of coupled heave-pitch motion of a long rectangular barge advancing in regular head waves of large amplitude has been carried out. Comparisons between the linear and the approximate body nonlinear numerical results of motions and wave loads of the barge at a nonzero Froude number have been made.

Numerical Study of the Radiation Potential of a Ship Using the 3D Time-Domain Forward-Speed Free-Surface Green Function and a Second-Order BEM (3 차원 시간영역 전진속도 자유표면 Green 함수와 2 차 경계요소법을 사용한 선체의 방사포텐셜 수치계산)

  • Hong, Do-Chun;Hong, Sa-Young
    • Journal of the Society of Naval Architects of Korea
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    • v.45 no.3
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    • pp.258-268
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    • 2008
  • The radiation potential of a ship advancing in waves is studied using the 3D time-domain forward-speed free-surface Green function and the Green integral equation. Numerical solutions are obtained by making use of the 2nd order BEM(Boundary Element Method) which make it possible to take account of the line integral along the waterline in a rigorous manner. The 6 degree of freedom motion memory functions of a hemisphere and the Wigley seakeeping model obtained by direct integration of the time-domain 3D potentials over the wetted surface are presented for various Froude numbers.

Unsteady Aerodynamic Analysis of the Wing with Flaperon Flying over Nonplanar Ground Surface (비평면 지면 효과를 받는 플래퍼론이 있는 날개의 비정상 공력해석)

  • Joung, Yong-In;Cho, Jeong-Hyun;Cho, Jin-Soo
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.35 no.5
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    • pp.369-374
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    • 2007
  • Unsteady aerodynamic characteristics of the wing with flaperon flying over nonplanar ground surface are investigated using a boundary-element method. The time-stepping method is used to simulate the wake shape according to the motion of the wing and flaperon over the surface or in the channel. The aerodynamic coefficient according to the periodic motion of the flaperon is shown as the shape of loop. The rolling moment coefficient of the wing flying in the channel is same as that of the wing flying over the ground surface. The variation range of pitching moment is wider when the wing flies in the channel than over the ground surface. The present method can provide various aerodynamic derivatives to secure the stability of superhigh speed vehicle flying over nonplanar ground surface using the present method.

Efficient variable selection method using conditional mutual information (조건부 상호정보를 이용한 분류분석에서의 변수선택)

  • Ahn, Chi Kyung;Kim, Donguk
    • Journal of the Korean Data and Information Science Society
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    • v.25 no.5
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    • pp.1079-1094
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    • 2014
  • In this paper, we study efficient gene selection methods by using conditional mutual information. We suggest gene selection methods using conditional mutual information based on semiparametric methods utilizing multivariate normal distribution and Edgeworth approximation. We compare our suggested methods with other methods such as mutual information filter, SVM-RFE, Cai et al. (2009)'s gene selection (MIGS-original) in SVM classification. By these experiments, we show that gene selection methods using conditional mutual information based on semiparametric methods have better performance than mutual information filter. Furthermore, we show that they take far less computing time than Cai et al. (2009)'s gene selection but have similar performance.

Time-Domain Simulation of Nonlinear Free-Surface Flows around a Two-Dimensional Hydrofoil (2차원 수중익주위 비선형 자유표면유동의 시간영역 시뮬레이션)

  • Yong-J. Kim
    • Journal of the Society of Naval Architects of Korea
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    • v.31 no.2
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    • pp.45-56
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    • 1994
  • A computationally efficient numerical method based on potential flow is developed for time-domain simulation of the nonlinear free-surface flows around a 2-dimensional hydrofoil. This numerical method, namely, spectral/boundary-element method, is a mixed one of the high-order spectral method and the boundary-element method in time-domain. The high-order spectral method is used to calculate the nonlinear evolution of free-surface, and the boundary-element method is used to calculate the effects of the hydrofoil and the shed vortex. As application examples, nonlinear free-surface flows around a 2-dimensional hydrofoil which starts from the rest and translates near the free-surface with or without harmonic oscillations are calculated. Nonlinear/unsteady results of free-surface waves and hydrodynamic farces are shown and discussed. Particularly, the results of steady-state which are obtained as a special case of the present unsteady solution are compared with others' calculated and experimental results, and good agreements are observed.

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Progressive Iterative Forward and Backward (PIFAB) Search Method to Estimate Path-Travel Time on Freeways Using Toll Collection System Data (고속도로 경로통행시간 산출을 위한 전진반복 전후방탐색법(PIFAB)의 개발)

  • NamKoong, Seong
    • Journal of Korean Society of Transportation
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    • v.23 no.5 s.83
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    • pp.147-155
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    • 2005
  • The purpose of this paper is to develop a method for estimation of reliable path-travel time using data obtained from the toll collection system on freeways. The toll collection system records departure and arrival time stamps as well as the identification numbers of arrival and destination tollgates for all the individual vehicles traveling between tollgates on freeways. Two major issues reduce accuracy when estimating path-travel time between an origin and destination tollgate using transaction data collected by the toll collection system. First, travel time calculated by subtracting departure time from arrival time does not explain path-travel time from origin tollgate to destination tollgate when a variety of available paths exist between tollgates. Second, travel time may include extra time spent in service and/or rest areas. Moreover. ramp driving time is included because tollgates are installed before on-ramps and after off-ramps. This paper describes an algorithm that searches for arrival time when departure time is given between tollgates by a Progressive Iterative Forward and Backward (PIFAB) search method. The algorithm eventually produces actual path-travel times that exclude any time spent in service and/or rest areas as well as ramp driving time based on a link-based procedure.