Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 23 for “"numerical diffusion"”.
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An Improvement of Convection Fidelity in Euler Calculations
… in Euler calculations by eliminating the numerical diffusion inherent in conventional approaches. In conventional approaches which solve for the time-dependent conservation equations, the numerical diffusion is either built-in through finite truncations or added externally for reasons of …
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Modelling large scale ocean circulation : the role of mixing location and meridional pressure gradients for the Atlantic overturning dynamics
… the role of spatially inhomogeneous mixing, numerical diffusion and winds. Furthermore, the relation of the AMOC with a key quantity, the meridional pressure difference is analyzed. Due to the application of a very low diffusive tracer advection scheme, a realistic Atlantic overturning …
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Stable numerical methods for hyperbolic partial differential equations using overlapping domain decomposition
… While in wide use, the methods are prone to numerical instability unless numerical diffusion or some other form of regularization is used. This is especially true for higher-order methods. To address this, high-order, provably stable, overlapping domain decomposition methods are derived for …
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Long term morphodynamics of alternate bars in straightened rivers: a multiple perspective
… theories, laboratory experiments and recently numerical simulations, but only few studies on field cases have been performed so far. The goals of this work are: i) to quantify the morphodynamics of alternate bars in the Alpine Rhine River, with a particular emphasis on bar migration; ii) to …
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Multi-decadal morphodynamics of alternate bars in channelized rivers: a multiple perspective
… theories, laboratory experiments and since 1990s numerical simulations, but only few studies on field cases have been performed so far. The goals of this work are: i) to quantify the morphodynamics of alternate bars in the Alpine Rhine River, with a particular emphasis on bar migration; ii) to …
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Investigation of Thermocapillary Flows Around Hemispherical Bubbles
… bubble on a heated wall have been studied using numerical solutions for a wide range of Marangoni numbers (up to 10('6)). Natural convection effects and mass transfer at the bubble interface were included. Two distinct boundary conditions were examined: constant wall heat flux and constant wall …
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Computational analysis of viscoelastic fluid dynamics with applications to heat exchangers
… Pressure Linked Equations (SIMPLE). To cope with numerical diffusion and numerical stability issues the treatment of convective terms using the upwind schemes is explored. In this work, the behaviour of viscoelastic fluids is rigorously examined by analysing the convective heat transfer from the …
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Analysis of soil penetrometer using Eulerian finite element method
… to convect the soil constitutive law and prevent numerical diffusion. The current analyses use the program DiekA, developed at the University of Twente in the Netherlands. Detailed calculations have been performed to investigate the effects of elements size and load/time step size on the stability …
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Quantification of Mixing in Microchannels
… performing parametric analysis; however, due to numerical errors it is also necessary to verify and then validate the numerical models to ensure that the predictions are indeed accurate. In this study a recently developed microchannel is analyzed using CFD to determine its mixing effectiveness. …
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Analysis of gas differential diffusion through porous media using prompt gamma activation analysis
… activation analysis and later compared to a numerical diffusion model to estimate the effective diffusion coefficient. Numerical simulations using the estimated diffusivity and the experimental argon data produced results with a correlation parameter R² = 0.98. However, neglecting transport …
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Unstructured finite volume algorithms for compressible multiphase flow
… CFD code: PHYSICA. A new non-orthogonality diffusion correction relaxation parameter has been successfully introduced and tested with benchmarks from the literature. Cases involving geometries meshed with commercial packages have been successfully run with the diffusion correction methods, …
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Blade dynamics and flux measurements for model seagrass blades in waves and currents
… measured uptake was fit to a numerical diffusion model to estimate the water-side transfer velocity. The water-side transfer velocity had a non-linear dependence on velocity in that the rate of increase of the mass transfer velocity decreased with greater blade bending in flow.
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Comparison of Two Vortex-in-cell Schemes Implemented to a Three-dimensional Temporal Mixing Layer
Numerical simulations are presented for three dimensional viscous incompressible free shear flows. The numerical method is based on solving the vorticity equation using Vortex-In-Cell method. In this method, the vorticity field is discretized into a finite set of Lagrangian elements (particles) and …
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Numerical modelling of the tilt casting processes of titanium alumindes
… This thesis also presents a novel Counter Diffusion Method which was developed with suggestions from my supervisors as a corrective mechanism to counter numerical diffusion. This is a novel method to discretise the free surface equation fully implicitly in a fast, efficient way without …
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Free-Lagrange simulations of single cavitation bubble collapse.
… highly deforming fluid problems are minimal numerical diffusion and that the material interfaces are sharply resolved because the computational mesh moves with the same velocity as the local flow. In addition, the Free-Lagrange approach avoids the classical problem of mesh tangling and …
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High fidelity simulations of electrokinetic phenomena in microfluidic devices
… to solve the system of equations and thus to numerically capture essential physics of ITP and EKI in microfluidic devices. Validation of the solver is provided for one-dimensional ITP problems in which sharp gradients present in species concentration and electric fields. It is demonstrated …
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ISPH Modelling of Solitary Wave Interaction with Permeable Beaches
… to simulate porous flows, they often suffer from numerical diffusion due to large deformation of a grid. Mesh-free methods are more suitable for simulating violent free-surface flows. Smooth Particle Hydrodynamics (SPH) is a meshless and particle method, which can be applied to simulations of …
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Meshless Direct Numerical Simulation of Turbulent Incompressible Flows
… procedure is presented to perform Direct Numerical Simulations (DNS) and Large Eddy Simulations (LES) of turbulent incompressible flows in regular and irregular geometries. The proposed method is a combination of several efficient techniques found in different Computational Fluid Dynamic …
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Numerical modelling of solute transport processes using higher order accurate finite difference schemes. Numerical treatment of flooding and drying in tidal flow simulations and higher order accurate finite difference modelling of the advection diffusion equation for solute transport predictions.
… of the processes of advection and dispersion-diffusion is the most crucial factor in solute transport simulations. It is generally appreciated that the first order upwind difference scheme gives rise to excessive numerical diffusion, whereas the conventional second order central difference …
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The application of adaptive mesh modelling techniques to the study of open ocean deep convection
… difficult. As a result, theoretical and numerical investigations have become key to the development of our understanding of OODC. The scale on which OODC occurs presents a further issue, with traditional numerical representations (parameterisations) of OODC in global circulation models …
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