Exponential asymptotics and free-surface flows
When traditional linearised theory is used to study free-surface flows past a surface-piercing object or over an obstruction in a stream, the geometry of the object is usually lost, having been assumed small in one or several of its dimensions. In order to preserve the nonlinear nature of the geomet...
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ndltd-bl.uk-oai-ethos.bl.uk-5264262015-03-20T04:36:01ZExponential asymptotics and free-surface flowsTrinh, Philippe H.Chapman, Stephen Jonathan2010When traditional linearised theory is used to study free-surface flows past a surface-piercing object or over an obstruction in a stream, the geometry of the object is usually lost, having been assumed small in one or several of its dimensions. In order to preserve the nonlinear nature of the geometry, asymptotic expansions in the low-Froude or low-Bond limits can be derived, but here, the solution invariably predicts a waveless free-surface at every order. This is because the waves are in fact, exponentially small, and thus beyond-all-orders of regular asymptotics; their formation is a consequence of the divergence of the asymptotic series and the associated Stokes Phenomenon. In this thesis, we will apply exponential asymptotics to the study of two new problems involving nonlinear geometries. In the first, we examine the case of free-surface flow over a step including the effects of both gravity and surface tension. Here, we shall see that the availability of multiple singularities in the geometry, coupled with the interplay of gravitational and cohesive effects, leads to the discovery of a remarkable new set of solutions. In the second problem, we study the waves produced by bluff-bodied ships in low-Froude flows. We will derive the analytical form of the exponentially small waves for a wide range of hull geometries, including single-cornered and multi-cornered ships, and then provide comparisons with numerical computations. A particularly significant result is our confirmation of the thirty-year old conjecture by Vanden-Broeck & Tuck (1977) regarding the impossibility of waveless single-cornered ships.519Fluid mechanics (mathematics) : Ordinary differential equations : Approximations and expansions : Ocean and coastal engineering : exponential asymptotics : asymptotic approximations : free-surface flows : water waves : gravity-capillary waves : ship hydrodynamicsUniversity of Oxfordhttp://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.526426http://ora.ox.ac.uk/objects/uuid:e87b1f22-2569-4c0f-86a2-5bde76f34953Electronic Thesis or Dissertation |
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519 Fluid mechanics (mathematics) : Ordinary differential equations : Approximations and expansions : Ocean and coastal engineering : exponential asymptotics : asymptotic approximations : free-surface flows : water waves : gravity-capillary waves : ship hydrodynamics |
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519 Fluid mechanics (mathematics) : Ordinary differential equations : Approximations and expansions : Ocean and coastal engineering : exponential asymptotics : asymptotic approximations : free-surface flows : water waves : gravity-capillary waves : ship hydrodynamics Trinh, Philippe H. Exponential asymptotics and free-surface flows |
description |
When traditional linearised theory is used to study free-surface flows past a surface-piercing object or over an obstruction in a stream, the geometry of the object is usually lost, having been assumed small in one or several of its dimensions. In order to preserve the nonlinear nature of the geometry, asymptotic expansions in the low-Froude or low-Bond limits can be derived, but here, the solution invariably predicts a waveless free-surface at every order. This is because the waves are in fact, exponentially small, and thus beyond-all-orders of regular asymptotics; their formation is a consequence of the divergence of the asymptotic series and the associated Stokes Phenomenon. In this thesis, we will apply exponential asymptotics to the study of two new problems involving nonlinear geometries. In the first, we examine the case of free-surface flow over a step including the effects of both gravity and surface tension. Here, we shall see that the availability of multiple singularities in the geometry, coupled with the interplay of gravitational and cohesive effects, leads to the discovery of a remarkable new set of solutions. In the second problem, we study the waves produced by bluff-bodied ships in low-Froude flows. We will derive the analytical form of the exponentially small waves for a wide range of hull geometries, including single-cornered and multi-cornered ships, and then provide comparisons with numerical computations. A particularly significant result is our confirmation of the thirty-year old conjecture by Vanden-Broeck & Tuck (1977) regarding the impossibility of waveless single-cornered ships. |
author2 |
Chapman, Stephen Jonathan |
author_facet |
Chapman, Stephen Jonathan Trinh, Philippe H. |
author |
Trinh, Philippe H. |
author_sort |
Trinh, Philippe H. |
title |
Exponential asymptotics and free-surface flows |
title_short |
Exponential asymptotics and free-surface flows |
title_full |
Exponential asymptotics and free-surface flows |
title_fullStr |
Exponential asymptotics and free-surface flows |
title_full_unstemmed |
Exponential asymptotics and free-surface flows |
title_sort |
exponential asymptotics and free-surface flows |
publisher |
University of Oxford |
publishDate |
2010 |
url |
http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.526426 |
work_keys_str_mv |
AT trinhphilippeh exponentialasymptoticsandfreesurfaceflows |
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1716785697301463040 |