• Title/Summary/Keyword: condition number

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Effect of Boundary Condition History on the Symmetry Breaking Bifurcation of Wall-Driven Cavity Flows

  • Cho, Ji-Ryong
    • Journal of Mechanical Science and Technology
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    • v.19 no.11
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    • pp.2077-2081
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    • 2005
  • A symmetry breaking nonlinear fluid flow in a two-dimensional wall-driven square cavity taking symmetric boundary condition after some transients has been investigated numerically. It has been shown that the symmetry breaking critical Reynolds number is dependent on the time history of the boundary condition. The cavity has at least three stable steady state solutions for Re=300-375, and two stable solutions if Re>400. Also, it has also been showed that a particular solution among several possible solutions can be obtained by a controlled boundary condition.

Effects of Characteristic Condition Number on Convergence in Calculating Low Mach Number Flows, II : Navier-Stokes Equations (저속 유동 계산의 수렴성에 미치는 특성 조건수의 영향 II : 나비어스톡스 방정식)

  • Lee, Sang-Hyeon
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.36 no.2
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    • pp.123-130
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    • 2008
  • The effects of characteristic condition number on the convergence of preconditioned Navier-Stokes equations were investigated. The two-dimensional preconditioned Navier-Stokes adopting Choi and Merkle's preconditioning and the temperature preconditioning are considered. Preconditioned Roe's FDS scheme was adopted for spatial discretization and preconditioned LU-SGS scheme was used for time integration. It is shown that the convergence characteristics of the Navier-Stokes equations are strongly affected by the characteristic condition number. Also it is shown that the optimal characteristic condition numbers for viscous flows are larger than that in inviscid flows.

A study on the effect of the condition number in the magnetic field mapping of the Air-Core solenoid

  • Huang, Li;Lee, Sangjin
    • Progress in Superconductivity and Cryogenics
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    • v.17 no.2
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    • pp.31-35
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    • 2015
  • Mapping is a useful tool in the magnetic field analysis and design. In some specific research area, such as the nuclear magnetic resonance (NMR) or the magnetic resonance imaging (MRI), it is important to map the magnetic field in the interesting space with high accuracy. In this paper, an indirect mapping method in the center volume of an air-core solenoid is presented, based on the solution of the Laplace's equation for the field. Through the mathematical analysis on the mapping calculation, we know that the condition number of the matrix, generated by the measurement points, can greatly affect the error of mapping result. Two different arrangement methods of the measurement points in field mapping are described in this paper: helical cylindrical line (HCL) method and parallel cylindrical line (PCL) method. According to the condition number, the HCL method is recommended to measure the field components using one probe. As a simple example, we mapped the magnetic fields in a MRI main magnet system. Comparing the results in the different methods, it is feasible and convenient to apply the condition number to reduce the error in the field mapping calculation. Finally, some guidelines were presented for the magnetic field mapping in the center volume of the air-core solenoid.

The Product Formula For Nielsen Root number

  • Yang, Ki-Yeol
    • Communications of the Korean Mathematical Society
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    • v.15 no.2
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    • pp.357-370
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    • 2000
  • In [6], Cheng-Ye You gave a condition equivalent to the Nielsen number product formula for fiber maps. And Jerzy Jezierski also gave a similar condition for coincidences of fiber maps. The main purpose of this paper is to find the condition for which holds the product formula for Nielsen root numbers N(f;a) = N(f;a) N(fb;a).

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PIV Measurements of Hull Wake behind a Container Ship Model with Varying Loading Condition and Reynolds number (선박 모형의 하중 (loading)조건 및 Reynolds 수의 변화에 따른 선미 반류의 PIV 속도장 측정)

  • Lee Jung-Yeop;Paik Bu-Geun;Lee Sang-Joon
    • 한국가시화정보학회:학술대회논문집
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    • 2005.12a
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    • pp.54-57
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    • 2005
  • Flow characteristics of hull wake behind a container ship model were investigated experimentally with varying loading condition and Reynolds number. Large-scale bilge vortices of nearly the same strength are formed in the near-wake region. They are symmetric and counter-rotating with respect to the wake centerline for all loading conditions tested. With going downstream for both design and ballast loading conditions, the strength of the bilge vortices decreases and the wake region expands due to diffusion and viscous dissipation. Under the design loading condition, the bilge vortices start to appear at St=0.363 transverse plane above the propeller-boss. For the ballast loading condition, however, the bilge vortices start to appear at St=0.591 below the propeller-boss. They move upward as the hull wake goes downstream and Reynolds number increases. These wake characteristics, under the ballast loading condition, may weaken the propulsion and cavitation performances of the propeller, which are usually optimized for the design loading condition.

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Heat Transfer Correlation to Predict the Evaporation of a Water Droplet in Superheated Steam during Reflood Phase of a LOCA

  • Kim, Yoo;Ban, Chang-Hwan
    • Journal of Energy Engineering
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    • v.9 no.3
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    • pp.261-268
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    • 2000
  • A heat transfer correlation to predict the vaporization of a water droplet in highly superheated steam during a loss-of-coolant accident(LOCA) of a nuclear power plant is provided. Vaporization of liquid fuel or water droplets in superheated air or steam and subsequent interface heat transfer between a liquid droplet and superheated gas is typically correlated by way of a Nusselt number as a function of Reynolds number, Prantl number, and in some cases including mass transfer number. Presently available correlations and experimental data of the evaporation of liquid droplets in air or steam are analyzed and a new Nusselt number correlation is proposed taking Schmidt number into consideration in order to account for binary diffusion of the vapor as well, Nu$\_$f/(1+B)$\^$0.7/=2+0.53Sc$\_$f/$\^$-1/5/Re$\_$M/$\^$$\sfrac{1}{2}$/Pr$\_$f/$\^$$\sfrac{1}{3}$/ for which properties are evaluated at film condition except the density of Reynolds number evaluated at ambient condition. Diverse correlations for various combinations of liquid and gas species are put into single equation. The blowing correction factor of (1+B)$\^$0.7/ is confirmed appropriate, and a criterion to distinguish so-called high- and low-temperature condition of ambient gas is set forth.

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Design of the Well-Conditioned Observer Using the Non-Normality Measure (비정규지표를 이용한 Well-Conditioned 관측기 설계)

  • Jung, Jong-Chul;Huh, Kun-Soo
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.26 no.6
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    • pp.1114-1119
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    • 2002
  • In this paper, the well-conditioned observer is designed to be insensitive to the ill-conditioning factors in transient and steady-state observer performance. A condition number based on 12-norm of the eigenvector matrix of the observer matrix has been proposed on a principal index in the observer performance. For the well-conditioned observer design, the non-normality measure and the observability condition of the observer matrix are utilized. The two constraints are specified into observer gain boundary region that guarantees a small condition number and a stable observer. The observer gain selected in this region guarantees a well-conditioned and observable property. In this study, this method is applied to the Luenberger observer and Kalman filters for small order systems. In designing Kalman filters, the ratio of the process noise covariance to the measurement noise covariance is a design parameter and its effect on the condition number is investigated.

Design of the Well-Conditioned Observer Using the Non-normality Measure (비정규지표를 이용한 Well-Conditioned 관측기 설계)

  • 정종철;허건수
    • Proceedings of the Korean Society of Machine Tool Engineers Conference
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    • 2001.10a
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    • pp.313-318
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    • 2001
  • In this paper, the well-conditioned observer is designed to be insensitive to the ill-conditioning factors in transient and steady-state observer performance. A condition number based on $L_2-norm$ of the eigenvector matrix of the observer matrix has been proposed on a principal index in the observer performance. For the well-conditioned observer design, the non-normality measure and the observability condition of the observer matrix are utilized. The two constraints are specified into observer gain boundary region that guarantees a small condition number and a stable observer. The observer gain selected in this region guarantees a well-conditioned and observable property. In this study, this method is applied to the Luenberger observer and Kalman filters. In designing Kalman filters for small order systems, the ratio of the process noise covariance to the measurement noise covariance is a design parameter and its effect on the condition number is investigated.

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Issues and Solutions of Roe Schemes for High Mach Number Flows (고마하수 유동에서 Roe 해법의 문제와 해결)

  • Won S. H.;Choi J. Y.;Jeung I. S.
    • 한국전산유체공학회:학술대회논문집
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    • 2005.04a
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    • pp.128-134
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    • 2005
  • In the CFD area, the numerical analysis of high Mach number flow over a blunt-body poses many issues. Various numerical schemes have been developed to cover the issues, but the traditional schemes are still used widely due to the complexities of new schemes and intricacy of modifying the established codes. In the present study, the well-known Roe's FDS based on TVD-MUSCL scheme is used for the solution of very high Mach number three-dimensional flows posing carbuncle and non-physical phenomena in numerical analysis. A parametric study was carried out to account for the effects of the entropy fixing, grid configurations and initial condition. The carbuncle phenomena could be easily overcome by the entropy fixing, and the non-physical solution could be eliminated by the use of the modified initial condition regardless of entropy fixing and grid configurations.

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A Study on the optimal structure of 6 D.O.F F/T Sensor using the condition number (조건수를 이용한 6자유도 F/T센서의 최적구조에 관한 연구)

  • 장완식;김재명
    • Journal of the Korean Society of Safety
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    • v.11 no.4
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    • pp.16-23
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    • 1996
  • In controlling manipulators interacting with the external environment, an important role is played by the Force/Torque(F/T) sensors. Recently, a number of structures for F/T sensors have been proposed, and some criteria for their evaluation have been introduced. This paper presents a systematic analysis of F/T sensor at the design stage. A model of the F/T sensors, based on Stewart Platform structure, is developed on the basis of static and kinematic equation. The condition number defined by the kinematic velocity and force analysis of F/T sensor is used as a performance Index. Thus, 4 optimal structure factors of 6 D.O. F. F/T sensor are determined by using the condition number.

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