• Title/Summary/Keyword: Navier-Stokes solution

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Matching inviscid and boundary layer method for incompressible and compressible flows (비압축성과 압축성 유동에 있어서 비점성 유동과 경계층 유동의 결합)

  • Sohn, Chang-Hyun;Moon, Su-Yeon;Lee, Jeong-Yun
    • Proceedings of the KSME Conference
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    • 2003.04a
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    • pp.1966-1971
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    • 2003
  • Matching inviscid and boundary layer methods are developed for hypersonic flow with thick boundray layer. The new equations match all the boundary layer properties with a variation in the inviscid solution near the edge, except for the normal velocity. Computational comparison are performed for incompressible and compressible flows over a flat plate. Results from the present method are compared with Navier-Stokes solutions. The present results are in good agreement with Navier-Stokes solutions. They show that the new technique can provide improved heating rates and skin friction predictions for preliminary design of vehicles where shear layers and entropy layer swallowing are important.

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PRECONDITIONED NAVIER-STOKES COMPUTATION FOR WEAKLY COMPRESSIBLE FLOW ANALYSIS ON UNSTRUCTURED MESH (비정렬격자와 예조건화 기법을 이용한 저압축성 점성유동해석)

  • Son, S.J.;Ahn, H.T.
    • Journal of computational fluids engineering
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    • v.18 no.3
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    • pp.79-86
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    • 2013
  • Preconditioned compressible Navier-Stokes equations are solved for almost incompressible flows. Unstructured meshes are utilized for spatial discretization of complex flow domain. Effectiveness of the current preconditioning algorithm, with respect to various Reynolds numbers and Mach numbers, is demonstrated by the solution of canonical problems for incompressible flows, e.g. driven cavity flows.

Heat Transfer Response of an Isothermal Cylinder to Fluctuating Cross Flow (맥동류에 놓인 등온 원통의 열전달 응답)

  • 권영필;이병호
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.10 no.5
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    • pp.706-712
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    • 1986
  • The unsteay heat transfer from an isothermal circular cylinder in fluctuating cross flow is simulated numerically, for the case where the amplitude of the oscillating velocity is small compared with the mean velocity. By solving the linear perturbation equations derived from the unsteady full Navier-Stokes and the energy equations, the amplitude and the phase of heat transfer response are obtained in the range of Reynolds number R$_{3}$ < 40. The effects of the velocity, the cylinder radius and the frequency on the response are expressed graphically in terms of the normalized velocity and the cylinder radius.

ANALYSIS OF FIRST-ORDER SYSTEM LEAST-SQUARES FOR THE OPTIMAL CONTROL PROBLEMS FOR THE NAVIER-STOKES EQUATIONS

  • Choi, Young-Mi;Kim, Sang-Dong;Lee, Hyung-Chun;Shin, Byeong-Chun
    • Journal of the Korean Society for Industrial and Applied Mathematics
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    • v.11 no.4
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    • pp.55-68
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    • 2007
  • First-order least-squares method of a distributed optimal control problem for the incompressible Navier-Stokes equations is considered. An optimality system for the optimal solution are reformulated to the equivalent first-order system by introducing velocity-flux variables and then the least-squares functional corresponding to the system is defined in terms of the sum of the squared $L^2$ norm of the residual equations of the system. The optimal error estimates for least-squares finite element approximations are obtained.

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Numerical simulation of the flow in pipes with numerical models

  • Gao, Hongjie;Li, Xinyu;Nezhad, Abdolreza Hooshmandi;Behshad, Amir
    • Structural Engineering and Mechanics
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    • v.81 no.4
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    • pp.523-527
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    • 2022
  • The objective of this study is to simulate the flow in pipes with various boundary conditions. Free-pressure fluid model, is used in the pipe based on Navier-Stokes equation. The models are solved by using the numerical method. A problem called "stability of pipes" is used in order to compare frequency and critical fluid velocity. When the initial conditions of problem satisfied the instability conditions, the free-pressure model could accurately predict discontinuities in the solution field. Employing nonlinear strains-displacements, stress-strain energy method the governing equations were derived using Hamilton's principal. Differential quadrature method (DQM) is used for obtaining the frequency and critical fluid velocity. The results of this paper are analyzed by hyperbolic numerical method. Results show that the level of numerical diffusion in the solution field and the range of well-posedness are two important criteria for selecting the two-fluid models. The solutions for predicting the flow variables is approximately equal to the two-pressure model 2. Therefore, the predicted pressure changes profile in the two-pressure model is more consistent with actual physics. Therefore, in numerical modeling of gas-liquid two-phase flows in the vertical pipe, the present model can be applied.

Topology Optimization of Incompressible Flow Using P1 Nonconforming Finite Elements (P1 비순응 요소를 이용한 비압축성 유동 문제의 위상최적화)

  • Jang, Gang-Won;Chang, Se-Myong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.36 no.10
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    • pp.1139-1146
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    • 2012
  • An alternative approach for topology optimization of steady incompressible Navier-Stokes flow problems is presented by using P1 nonconforming finite elements. This study is the extended research of the earlier application of P1 nonconforming elements to topology optimization of Stokes problems. The advantages of the P1 nonconforming elements for topology optimization of incompressible materials based on locking-free property and linear shape functions are investigated if they are also valid in fluid equations with the inertia term. Compared with a mixed finite element formulation, the number of degrees of freedom of P1 nonconforming elements is reduced by using the discrete divergence-free property; the continuity equation of incompressible flow can be imposed by using the penalty method into the momentum equation. The effect of penalty parameters on the solution accuracy and proper bounds will be investigated. While nodes of most quadrilateral nonconforming elements are located at the midpoints of element edges and higher order shape functions are used, the present P1 nonconforming elements have P1, {1, x, y}, shape functions and vertex-wisely defined degrees of freedom. So its implentation is as simple as in the standard bilinear conforming elements. The effectiveness of the proposed formulation is verified by showing examples with various Reynolds numbers.

Incompressible Viscous Analysis on Unstructured Meshes using Artificial Compressibility Method (가압축성 기법을 이용한 비정렬 격자상에서의 비압축성 점성해석)

  • Moon Young J.
    • 한국전산유체공학회:학술대회논문집
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    • 1995.10a
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    • pp.113-117
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    • 1995
  • Viscous analysis on incompressible flows is performed using unstructured triangular meshes. A two-dimensional and axisymmetric incompressible Navier-Stokes equations are solved in time-marching form by artificial compressibility method. The governing equations are discretized by a cell-centered based finite-volume method. and a centered scheme is used for inviscid and viscous fluxes with fourth order artificial dissipation. An explicit multi-stage Runge-Kutta method is used for the time integration with local time stepping and implicit residual smoothing. Convergence properties are examined and solution accuracies are also validated with benchmark solution and experiment.

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GLOBAL LARGE SOLUTIONS FOR THE COMPRESSIBLE MAGNETOHYDRODYNAMIC SYSTEM

  • Li, Jinlu;Yu, Yanghai;Zhu, Weipeng
    • Bulletin of the Korean Mathematical Society
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    • v.58 no.6
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    • pp.1521-1537
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    • 2021
  • In this paper we consider the global well-posedness of compressible magnetohydrodynamic system in ℝd with d ≥ 2, in the framework of the critical Besov spaces. We can show that if the initial data, the shear viscosity and the magnetic diffusion coefficient are small comparing with the volume viscosity, then the compressible magnetohydrodynamic system has a unique global solution. Our result improves the previous one by Danchin and Mucha [10] who considered the compressible Navier-Stokes equations.

Optimal Active-Control & Development of Optimization Algorithm for Reduction of Drag in Flow Problems(2) - Verification of Developed Methodologies and Optimal Active-Control of Flow for Drag Reduction (드래그 감소를 위한 유체의 최적 엑티브 제어 및 최적화 알고리즘의 개발(2) - 개발된 기법의 검증 및 드래그 감소를 위한 유체의 최적 액티브 제어)

  • Bark, Jai-Hyeong
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.20 no.5
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    • pp.671-680
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    • 2007
  • The objective of this work is to reduce drag on a bluff body within a viscous flow by applying suction or injection of fluid along the surface of the body. In addition to minimizing drag, the optimal solution tends to reduce boundary layer separation and flow recirculation. When discretized by finite elements, the optimal control problem can be posed as a large-scale nonlinearly-constrained optimization problem. The constraints correspond to the discretized form of the Navier-Stokes equations. Unfortunately, solving such large-scale problems directly is essentially intractable. We developed several Sequential Quadratic Programming methods that are tailored to the structure of the control problem. Example problems of laminar flow around an infinite cylinder in two dimensions are solved to demonstrate the methodology. We use these optimal control techniques to study the influence of number of suction/injection holes and location of holes on the resulting optimized flow. We compare the proposed SQP methods against one another, as well as against available methods from the literature, from the point of view of efficiency and robustness. The most efficient of the proposed methods is two orders of magnitude faster than existing methods.

Non-hydrostatic modeling of nonlinear waves in a circular channel (비정수압 모형을 이용한 원형 수로에서 비선형 파랑의 해석)

  • Choi, Doo-Yong
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.23 no.5
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    • pp.335-344
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    • 2011
  • A curvilinear non-hydrostatic free surface model is developed to investigate nonlinear wave interactions in a circular channel. The proposed model solves the unsteady Navier-Stokes equations in a three-dimensional domain with a pressure correction method, which is one of fractional step methods. A hybrid staggered-grid layout in the vertical direction is implemented, which renders relatively simple resulting pressure equation as well as free surface closure. Numerical accuracy with respect to wave nonlinearity is tested against the fifth-order Stokes solution in a two-dimensional numerical wave tank. Numerical applications center on the evolution of nonlinear waves including diffraction and reflection affected by the curvature of side wall in a circular channel comparing with linear waves. Except for a highly nonlinear bichrmatic wave, the model's results are in good agreement with superimposed analytical solution that neglects nonlinear effects. Through the numerical simulation of the highly nonlinear bichramatic wave, the model shows its capability to investigate the evolution of nonlinear wave groups in a circular channel.