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  • 1
    Electronic Resource
    Electronic Resource
    A vorticity method for the solution of natural convection flows in enclosures (2003)
    Bradford : Emerald
    International journal of numerical methods for heat & fluid flow 13 (2003), S. 655-671 
    Details
    ISSN: 0961-5539
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Vorticity formulations for the incompressible Navier-Stokes equations have certain advantages over primitive-variable formulations including the fact that the number of equations to be solved is reduced through the elimination of the pressure variable, identical satisfaction of the incompressibility constraint and the continuity equation, and an implicitly higher-order approximation of the velocity components. For the most part, vorticity methods have been used to solve exterior isothermal problems. In this research, a vorticity formulation is used to study the natural convection flows in differentially-heated enclosures. The numerical algorithm is divided into three steps: two kinematic steps and one kinetic step. The kinematics are governed by the generalized Helmholtz decomposition (GHD) which is solved using a boundary element method (BEM) whereas the kinetics are governed by the vorticity equation which is solved using a finite element method (FEM). In the first kinematic step, vortex sheet strengths are determined from a novel Galerkin implementation of the GHD. These vortex sheet strengths are used to determine Neumann boundary conditions for the vorticity equation. (The thermal boundary conditions are already known.) In the second kinematic step, the interior velocity field is determined using the regular (non-Galerkin) form of the GHD. This step, in a sense, linearizes the convective acceleration terms in both the vorticity and energy equations. In the third kinetic step, the coupled vorticity and energy equations are solved using a Galerkin FEM to determine the updated values of the vorticity and thermal fields. Two benchmark problems are considered to show the robustness and versatility of this formulation including natural convection in an 8×1 differentially-heated enclosure at a near critical Rayleigh number.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1108/09615530310498367
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  • 2
    Electronic Resource
    Electronic Resource
    Onset of the second wake: Dependence on the Reynolds number (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 14 (2002), S. 53 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The second wake transition occurs in the far wake of a bluff body. This transition destroys the Bénard–von Kármán vortex street originating in the near wake and produces a secondary vortex street with a lower characteristic frequency. We characterize the onset of the second wake for Reynolds numbers 50〈Re〈800 in a nearly two-dimensional soap film flow. The dimensionless distance between the cylinder and the onset of the second wake decreases with Reynolds number consistently with Re−1/2 power law. Our two-dimensional far-wake numerical simulations are in good agreement with the experiment. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1486450
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Numerical simulation of the hydrodynamic interaction between a sedimenting particle and a neutrally buoyant particle (1989)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 9 (1989), S. 263-273 
    Details
    ISSN: 0271-2091
    Keywords: Low-Reynolds-number flow ; Sedimentation ; Hydrodynamic interactions ; Two-phase flows ; Suspensions ; Boundary element method ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A new method for the simulation of the translational and rotational motions of a system containing a sedimenting particle interacting with a neutrally buoyant particle has been developed. The method is based on coupling the quasi-static Stokes equations for the fluid with the rigid body equations of motion for the particles. The Stokes equations are solved at each time step with the boundary element method. The stresses are then integrated over the surface of each particle to determine the resultant forces and moments. These forces and moments are inserted into the rigid body equations of motion to determine the translational and rotational motions of the particles. Unlike many other simulation techniques, no restrictions are placed on the shape of the particles. Superparametric boundary elements are employed to achieve accurate geometric representations of the particles. The simulation method is able to predict the local fluid velocity, resolve the forces and moments exerted on the particles, and track the particle trajectories and orientations.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/fld.1650090303
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  • 4
    Electronic Resource
    Electronic Resource
    Dynamic simulation of the hydrodynamic interaction among immersed particles in Stokes flow (1990)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 10 (1990), S. 791-809 
    Details
    ISSN: 0271-2091
    Keywords: Stokes flow ; Hydrodynamic interactions ; Suspension flows ; Two-phase ; flows ; Boundary element method ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A numerical method for the dynamic simulation of the hydrodynamic interaction among particles in Stokes flow is developed. The method couples the quasi-static Stokes equations for the fluid with the equilibrium equations for the particles. The boundary element method is used to represent the velocity at a general field point in terms of surface velocities and stresses. However, neither the stresses nor the velocities are assumed to be known on the surface of the particles. Kinematic equations relating the linear and angular velocities at the centroids of the particles to the surface velocities are combined with the discretized boundary element equations and the equilibrium equations to generate a system of linear equations. The associated coefficient matrix is correspondent to the grand resistance matrix which relates the velocities of the particles to a given geometry.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/fld.1650100706
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  • 5
    Electronic Resource
    Electronic Resource
    Numerical modelling of cavities on axisymmetric bodies at zero and non-zero angle of attack (1992)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 15 (1992), S. 251-271 
    Details
    ISSN: 0271-2091
    Keywords: Cavitation flow ; Cavity closure model ; Drag on cavitating bodies ; Boundary element method ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The flow about submerged, fully cavitating axisymmetric bodies at both zero and non-zero angle of attack is considered in this paper. A cavity closure model that relates the point of detachment, the angle that the separating streamline makes with the body and the cavity length is described. The direct boundary element method is used to solve the potential flow problem and to determine the cavity shape. A momentum integral boundary layer solver is included in the formulation so that shear stresses can be incorporated into the drag calculations. The numerical predictions based on the proposed closure model are compared with water tunnel measurements and photographs.
    Additional Material: 17 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/fld.1650150302
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  • 6
    Electronic Resource
    Electronic Resource
    Grid optimization for the boundary element method (1986)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 23 (1986), S. 2121-2136 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The quality of solution obtained using the boundary element method (BEM) is dependent on how the boundary is discretized. This is particularly true in domains of complex geometry. A rule for grid optimization for the BEM is derived on the bases of an asymptotic measure of the boundary element error that preserves the number of elements (degrees of freedom). Three example problems are provided to show the advantages of grid optimization in terms of accuracy and cost.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620231110
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  • 7
    Electronic Resource
    Electronic Resource
    A parallel boundary element formulation for determining effective properties of heterogeneous media (1994)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 37 (1994), S. 3905-3919 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper presents a parallel implementation of the boundary element method for MIMD computer architectures to determine the effective properties of two heterogeneous physical systems. The first physical system is comprised of spheres sedimenting in a viscous fluid at low Reynolds numbers. The effective property is characterized by the hindered settling function which is a measure of the average sedimentation velocity. The second physical system is a short-fibre reinforced composite. The effective property for this system is the composite modulus. The determination of effective properties of heterogeneous media requires performing statistical analyses of several realizations of physical systems based on defining characteristics of the media. The boundary element method is particularly well suited for studying such systems because of the simplification in the discretization associated with the method. However, as the number of heterogeneities to be modeled is increased so are the computational demands. Parallel computation offers the opportunity to model systems of greater complexity. We discuss a parallel boundary element formulation based on the torus-wrap mapping. In this approach, blocks of the coefficient matrix associated with the discretized boundary element equations are assigned to processors as opposed to more traditional parallel boundary element implementations where rows or columns are assigned to processors. The torus-wrap mapping can be shown to minimize communication volume between processors during the LU factorization. Therefore, the present formulation scales well with increases in the number of processors.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620372209
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  • 8
    Electronic Resource
    Electronic Resource
    A multiple-node method to resolve the difficulties in the boundary integral equation method caused by corners and discontinuous boundary conditions (1993)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 36 (1993), S. 1735-1746 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In the boundary integral equation method (BIEM), use of Lagrangian shape functions together with conforming boundary elements requires continuity of functions at the interelement boundary. When the flux or the traction is discontinuous due to the presence of corners or discontinuous boundary conditions, conforming elements can be a source of error. In this paper, we detail a multiple-node method in which this error can either be eliminated or substantially reduced. The paper is limited to the Laplace problem and the problem of elastostatics in two dimensions. However, the method can be easily extended to problems of other types and to higher dimensions.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620361008
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  • 9
    Electronic Resource
    Electronic Resource
    Surface pressure solution for boundary-element analysis of stokes flow (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Communications in Applied Numerical Methods 7 (1991), S. 367-376 
    Details
    ISSN: 0748-8025
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Analysis of creeping flow problems using the boundary-element method is now well established. The method is based on the transformation of the governing partial differential equations into a boundary integral equation for the velocity at arbitrary field points in terms of the surface velocities and tractions. Associated with the velocity boundary integral equation is a pressure boundary integral equation. The singularities contained in the kernel functions for the pressure boundary integral equation are an order higher than for the velocity boundary integral equation. Hence, for field points along the boundary of the domain, the pressure boundary integral equation is hypersingular, causing difficulties in evaluating the surface pressure. A method of regularization for the pressure boundary integral equation in which the hypersingular integral is converted into a Cauchy principal value integral is discussed. Some example applications are presented.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cnm.1630070504
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