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Numerical modelling of jetforced circulation in reservoirs using boundaryfitted coordinate systemsBarber, Robert William January 1990 (has links)
Throughout the past decade, interest has grown in the use of boundaryfitted coordinate systems in many areas of computational fluid dynamics. The boundaryfitted technique provides an exact method of implementing finitedifference numerical schemes in curved flow geometries and offers an alternative solution procedure to the finiteelement method. The unavoidable large bandwidth of the global stiffness matrix, employed in finiteelement algorithms, means that they are computationally less efficient than corresponding finitedifference schemes. As a consequence, the boundaryfitted method offers a more efficient process for solving partial differential flow equations in awkwardly shaped regions. This thesis describes a versatile finitedifference numerical scheme for the solution of the shallow water equations on arbitrary boundaryfitted nonorthogonal curvilinear grids. The model is capable of simulating flows in irregular geometries typically encountered in river basin management. Validation tests have been conducted against the severe condition of jetforced flow in a circular reservoir with vertical side walls, where initial reflections of free surface waves pose major problems in achieving a stable solution. Furthermore, the validation exercises have been designed to test the computer model for artificial diffusion which may be a consequence of the numerical scheme adopted to stabilise the shallow water equations. The thesis also describes two subsidiary numerical studies of jetforced recirculating flow in circular cylinders. The first of these implements a BiotSavart discrete vortex method for simulating the vorticity in the shear layers of the inflow jet, whereas the second employs a stream function/vorticitytransport finitedifference procedure for solving the twodimensional NavierStokes equations on a distorted orthogonal polar mesh. Although the predictions from the stream function/vorticitytransport model are confined to low Reynolds number flows, they provide a valuable set of benchmark velocity fields which are used to confirm the validity of the boundaryfitted shallow water equation solver.

2 
The nonlinear evolution of the elliptical instability : an example of inertial wave breakdownMason, Darren M. January 1999 (has links)
No description available.

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On spectral methods for shock wave calculationsCrossley, Peter Simon January 1996 (has links)
No description available.

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Natural coordinates and high speed flows : a numerical method for reactive gasesDawes, A. S. January 1992 (has links)
No description available.

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Twodimensional vortex methods : analysis, development and applicationsDeligiannis, Christos January 2003 (has links)
No description available.

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Variational characterizations of steady twodimensional vortex motionsUnwin, Anna Theresa January 1991 (has links)
No description available.

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Some convergence enhancing schemes for systems of conservation lawsGlover, Ian Christopher January 1993 (has links)
No description available.

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Steep capillary waves on gravity wavesPopat, Nilesh R. January 1989 (has links)
The frequent presence of ripples on the free surface of water. on both thin film flows and ponds or lakes motivates this theoretical investigation into the propagation of ripples on gravity waves. These ripples are treated as "slowlyvarying" waves in a reference frame where the gravity wave flow is steady. The methods used are those of the averaged Lagrangian (Whitham 1965,1967,1974) and the averaged equations of motion (Phillips 1966) which are shown to be equivalent. The capillary wave modulation is taken to be steady in the reference frame which brings the gravity wave, or gravity driven flow, to rest. Firstly the motion over ponds or lakes is considered. Linear capillarygravity waves are examined in order to set the scene. Crapper's (1957) exact finiteamplitude waves are examined next to show the actual behaviour of the flow field. The underlying gravity driven flow is that of pure gravity waves over an' "infinite" depth liquid. These gravity waves are modelled with "numerically exact" solutions for periodic planewaves. The initial studies are inviscid and show that steep gravity waves either "absorb" or "sweepup" a range of capillary waves or, alternatively, cause them to break in the vicinity of gravity wave crests. Improvements on the theory are made by including viscous dissipation of wave energy. This leads to a number of solutions approaching "stopping velocities" or the "stopped waves solution". In addition to these effects "higherorder dispersion" is introduced for weakly nonlinear waves near linear caustics. This clarifies aspects of the dissipation results and shows that wave reflection sometimes occurs. Secondly, waves on thin film flows are considered. Linear capillarygravity waves are again examined in order to set the scene. Kinnersley's (1957) exact finiteamplitude waves are examined next to show the actual behaviour of the flow field. The underlying gravity driven flow is given by shallow water gravity waves. No modelling of these is necessary simply because they are included within Whitham's or Phillips' equations ab initio. This study is inviscid and shows the unexpected presence of critical velocities at which pairs of solution branches originate. iii

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Mathematical modelling of twophase for industrial applicationsPerera, Sattambiralalage Anura Lalindra January 1997 (has links)
No description available.

10 
A more robust wall model for use with the twoequation turbulence modelMallone, Kevin Charles January 1995 (has links)
The applicability of computational fluid dynamics (CFD) modelling schemes to turbulent wallbounded flows is a matter of concern. In the nearwall region of bounded flows, the standard high Reynolds number ke model is not valid and requires the use of empirical wall models to mimic the behaviour of this region. A theoretical study of the physics of prevalent wall modelling techniques showed that the velocity distribution took no account of the pressure gradient. To determine the effect of this shortcoming, a typical transient threedimensional flow was analysed using current CFD methods and the results compared with experimental flow measurements. Consideration of these results showed that the 'traditional' wall model was unable to replicate observed flow features in the nearwall region: further analysis of the computational results confirmed that these poor flow predictions arose from the inability of the model to consider local pressure gradient effects. Consequently, a strong case was made for a more robust wall model for use in conjunction with the standard high Reynolds number ke model. A number of boundary layer analyses were reviewed and Coles' law of the wake (1956) presented as a viable candidate for the development of a new wall modelling scheme. In theory, Coles' law (1956) provides a description of bounded flows under arbitrary pressure gradients up to the point of nearseparation and may be extended to the study of reversed flows. A generic algorithm for Coles' law was prepared and used to study the fundamental test cases of Ubend and backward facing step flows. In a comparison between documented experimentation, 'conventional' CFD modelling and Coles' law models of these flows, the Coles' law model was shown to provide a viable alternative to 'traditional' schemes. Consequently, the Coles' law model of the nearwall region, being valid for pressuredriven flows, offers an extension to the range of flows for which the standard high Reynolds number ke model may be used.

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