• Title/Summary/Keyword: time marching

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A time dependent thermal and solutal convection problem in physical vapor transport of Hg2Cl2-I2 system

  • Kim, Geug Tae
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.27 no.2
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    • pp.80-88
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    • 2017
  • In this research a time dependent thermal and solutal convection was computationally investigated for the physical vapor transport of the mixture of $Hg_2Cl_2-I_2$ system with for the convective regime from thermal Rayleigh number of $2.16{\times}10^6$ up to $1.7{\times}10^7$ with marching time to a steady state problem. With time marching, the convective cells are decreased for the thermal Rayleigh number of $2.16{\times}10^6$, and increased for the thermal Rayleigh number of $1.7{\times}10^7$. The convective flow structures are found to be essentially time independent on the horizontal orientation of the enclosure with respect to the gravity vector, and on the other hand, time dependent on the vertical orientation of the enclosure with respect to the gravity vector.

A Comparative Study of PISO, SIMPLE, SIMPLE-C Algorithms in 3-dimensional Generalized Coordinate Systems (3차원 일반 좌표계에서의 PISO, SIMPLE, SIMPLE-C 알고리즘의 비교)

  • Park J. Y.;Baek J. H.
    • Journal of computational fluids engineering
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    • v.1 no.1
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    • pp.26-34
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    • 1996
  • The performance of the SIMPLE, SIMPLE-C and PISO algorithms for the treatment of the pressure-velocity coupling in fluid flow problems were examined by comparing the computational effort required to obtain the same level of the convergence. Example problems are circular duct and 90-degree bent square-duct. For circular duct case, laminar and turbulent flow were computed. For 90-degree bent square-duct case, laminar flow was simulated by the time-marching method as well as the iterative method. The convergence speed of the other two algorithms are not always superior to SIMPLE algorithm. SIMPLE algorithm is faster than SIMPLE-C algorithm in the simple laminar flow calculations. The application of the PISO algorithm in three dimensional general coordinates is not so effective as in two-dimensional ones. Since computational time of PISO algorithm is increased at each time step(or iterative step) in three dimension, the total convergence speed is not decreased. But PISO algorithm is stable for large time step by using time marching method,.

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3-D Incompressible Viscous Flow Analysis Around A Rotor-Stator with Rotor-Stator Interaction (로터-스테이터 상호작용을 고려한 3차원 유동 해석)

  • Kim K. H.;Jung Y. L.;Park W. G.;Lee S. W.
    • 한국전산유체공학회:학술대회논문집
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    • 2000.05a
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    • pp.78-83
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    • 2000
  • An iterative time marching procedure for solving incompressible internal flow has been applied to the flow around a rotor-stator. This procedure solves three-dimensional incompressible Reynolds-averaged Navier-Stokes equation on a moving, time-deforming, non-orthogonal body-fitted grid using second-order accurate schemes for the time derivatives and third/second-order accurate schemes for the spatial derivatives. To handle rotationg geometry, the multiblock technique is applied and the overall flow domain is subdivided into two blocks. In each block, a grid is generated and flowfield is solved independently of the other blocks. The boundary data for each block is provided by the neighboring blocks using bilinear interpolation technique.

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Development of Optimized Compact Finite Difference Schemes (최적화된 집적 유한 차분법을 위한 내재적 시간전진 기법의 개발)

  • Park N. S.;Kim J. W.;Lee D. J.
    • 한국전산유체공학회:학술대회논문집
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    • 1998.11a
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    • pp.7-12
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    • 1998
  • Optimized high-order compact(OHOC) schemes were proposed, which have high spatial order of truncation and resolution to simulate the aeroacoustic problems due to unsteady compressible flows. Generally, numerical schemes are categorized explicit or implicit by time-marching method. In this research, OHOC differences which were developed with explicit time-marching method is used to have implicit formulation and the implicit OHOC differences result in block hepta-diagonal matrix. This paper presents the comparisons between the explicit and implicit OHOC schemes with a second order accuracy of time in the 1-d linear wave convection problem, and between the explicit OHOC scheme of 4th-order accuracy in time and the implicit OHOC scheme of 1st-order accuracy in tine for the 1-d nonlinear wave convection problem. With these comparisons, the characteristics of implicit OHOC scheme are shown in the point of CFL number.

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Hypersonic Panel Flutter Analysis Using Coupled CFD-CSD Method

  • Tran, Thanh Toan;Kim, Dong-Huyn;Oh, Il-Kwon
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2011.10a
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    • pp.171-177
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    • 2011
  • In this paper, a square simply supported panel flutter have been considered at high supersonic flow by using coupled fluid-structure (FSI) analysis that based on time domain method. The Reynolds-Average Navier Stokes (RANS) equation with Spalart-Allmaras turbulent model were applied for unsteady flow problems of panel flutter. A fully implicit time marching schemed based on the Newmark direct integration method is used for calculating the coupled aeroelastic governing equations of it. In addition, the SOL 145 solver of MSC.NASTRAN was used to investigate flutter velocity based on PK-method of Piston theory. Our numerical results indicated that there is a good agreement result between Piston Theory in MSC.NASTRAN and coupled fluid-structure analysis.

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Preconditioned Compressible Navier- Stokes Algorithm for Low Mach Number Flows (예조건화 압축성 알고리즘에 의한 저마하수 유동장 해석기법)

  • Ko Hyun;Yoon Woong-Sup
    • 한국전산유체공학회:학술대회논문집
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    • 1998.05a
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    • pp.35-42
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    • 1998
  • Time marching algorithms applied to compressible Navier-Stokes equation have a convergence problem at low Mach number. It is mainly due to the eigenvalue stiffness and pressure singularity as Mach number approaches to zero. Among the several methods to overcome the shortcomings of time marching scheme, time derivative preconditioning method have been used successfully. In this numerical analysis, we adopted a preconditioner of K.H. Chen and developed a two-dimensional, axisymmetric Navier-Stokes program. The steady state driven cavity flow and backward facing step flow problems were computed to confirm the accuracy and the robustness of preconditioned algorithm for low Mach number flows. And the transonic and supersonic flows insice the JPL axisymmetric nozzle internal flow is exampled to investigate the effects of preconditioning at high Mach number flow regime. Test results showed excellent agreement with the experimental data.

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Helicopter BVI Noise Prediction Using Acoustic Analogy and High Resolution Airloads of Time Marching Free Wake Method (자유후류기법에 의한 고해상도 공기력과 음향상사법을 이용한 헬리콥터 로터 블레이드-와류 상호작용 소음 예측)

  • Chung, K.;Lee, D.J.;Hwang, C.
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.16 no.3 s.108
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    • pp.291-297
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    • 2006
  • The BVI(blade vortex interaction) noise Prediction has been one of the most challenging acoustic analyses in helicopter aeromechanical Phenomenon. It is well known high resolution airloads data with accurate tip vortex positions are necessary for the accurate prediction of this phenomenon. The truly unsteady time-marching free-wake method, which is able to capture the tip vortices instability in hover and axial flights, is expanded with the rotor flapping motion and trim routine to predict unsteady airloads in forward and descent flights. And Farassat formulation 1-A based on the FW-H equation is applied for the noise prediction considering the blade flapping motion. Main objective of this study is to validate the newly developed prediction code. To achieve the objective, the descent flight condition of AH-1 OLS(operational loads survey) configuration is analyzed using present code. The predicted sectional thrust distribution and sectional airloads time histories show the present scheme is able to capture well the unsteady airloads caused by a parallel BVI. Finally, the predicted noise data, observed in two different positions where are 3.44 times of rotor radius far from the hub center, are quite reasonable agreements with the experimental data compared to the other analysis results.

Analysis of Transient Scattering from Conducting Objects using Weighted Laguerre Polynomials and Electric Field Integral Equation (가중 라게르 다항식과 전장적분식을 이용한 도체의 과도 산란 해석)

  • 정백호;정용식
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.13 no.9
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    • pp.937-946
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    • 2002
  • In this paper, we present a stable solution of the transient electromagnetic scattering from the conducting objects. This method does not utilize the conventional marching-on in time (MOT) solution. Instead we solve the time domain integral equation by expressing the transient behavior of the induced current in terms of weighted Laguerre polynomials. By using this basis functions for the temporal variation, the time derivative in the integral equation can be handled analytically. Since these temporal basis functions converge to zero as time progresses, the transient response of the induced current does not have a late time oscillation. To show the validity of the proposed method, we solve a time domain electric feld integral equation and compare the results of MOT, Mie solution, and the inverse discrete Fourier transform (IDFT) of the solution obtained in the frequency domain.

Unconditionally Stable Analysis of Transient Scattering from Conductors Using Time-Domain Combined Field Integral Equations (시간영역 결합적분식을 이용한 도체 과도산란의 무조건 안정된 해석)

  • 정백호;서정훈;이원우
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.40 no.8
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    • pp.340-348
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    • 2003
  • In this paper, we propose a novel formulation to solve a time-domain combined field integral equation (CFIE) for analyzing the transient electromagnetic scattering response from closed conducting bodies. Instead of the conventional marching-on in time (MOT) technique, tile solution method in this paper is based on the moment method that involves separate spatial and temporal testing procedures. Triangular patch vector functions are used for spatial expansion and testing functions for three-dimensional arbitrarily shaped closed structures. The time-domain unknown coefficient is approximated as a basis function set that is derived from tile Laguerre functions with exponentially decaying functions. These basis functions are also used as the temporal testing. Numerical results computed by the proposed method arc stable without late-time oscillations and agree well with the frequency-domain CFIE solutions.

Numerical analysis of flow field around an automobile with variation of yaw angles (측풍의 편향각 변화에 따른 자동차 주위의 유동해석)

  • Kang D. M.;Jung Y. R.;Park W. G.;Ha S. D.
    • Journal of computational fluids engineering
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    • v.4 no.3
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    • pp.1-11
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    • 1999
  • This paper describes the flow field analysis of an automobile with crosswind effects of 15°, 30° 45° and 60° of yaw angles. The governing equations of the 3-D incompressible Navier-Stokes equations are solved by the iterative time marching scheme. The Chimera grid technique has been applied to efficiently simulate the flow around the side-view mirror. The computated surface pressure coefficients have been compared with experimental results and a good agreement has been achieved. The A- and C-pillar vortex and other flow phenomena around the ground vehicle are evidently shown. The variation of aerodynamic coefficients of drag, lift, side force and moments with respect to yaw angle is systematically studied.

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