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  • 1995-1999  (3)
  • 1
    Online Resource
    Online Resource
    Gravity current flow over obstacles
    Cambridge University Press (CUP) ; 1995
    In:  Journal of Fluid Mechanics Vol. 292 ( 1995-06-10), p. 39-53
    Details
    In: Journal of Fluid Mechanics, Cambridge University Press (CUP), Vol. 292 ( 1995-06-10), p. 39-53
    Abstract: When a gravity current meets an obstacle a proportion of the flow may continue over the obstacle while the rest is reflected back as a hydraulic jump. There are many examples of this type of flow, both in the natural and man-made environment (e.g. sea breezes meeting hills, dense gas and liquid releases meeting containment walls). Two-dimensional currents and obstacles, where the reflected jump is in the opposite direction to the incoming current, are examined by laboratory experiment and theoretical analysis. The investigation concentrates on the case of no net flow, so that there is a return flow in the (finite depth) upper layer. The theoretical analysis is based on shallow-water theory. Both a rigid lid and a free surface condition for the top of the upper layer are considered. The flow may be divided into several regions: the inflow conditions, the region around the hydraulic jump, the flow at the obstacle and the flow downstream of the obstacle. Both theoretical and empirical inflow conditions are examined; the jump conditions are based on assuming that the energy dissipation is confined to the lower layer; and the flow over the obstacle is described by hydraulic control theory. The predictions for the proportion of the flow that continues over the obstacle, the speed of the reflected jump and the depth of the reflected flow are compared with the laboratory experiments, and give reasonable agreement. A shallower upper layer (which must result in a faster return velocity in the upper layer) is found to have a significant effect, both on the initial incoming gravity current and on the proportion of the flow that continues over the obstacle.
    Type of Medium: Online Resource
    ISSN: 0022-1120 , 1469-7645
    URL: Article
    DOI: 10.1017/S002211209500142X
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 1995
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    detail.hit.zdb_id: 218334-1
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    Online Resource
  • 2
    Online Resource
    Online Resource
    On meltwater under ice shelves
    American Geophysical Union (AGU) ; 1995
    In:  Journal of Geophysical Research: Oceans Vol. 100, No. C4 ( 1995-04-15), p. 6961-6965
    Details
    In: Journal of Geophysical Research: Oceans, American Geophysical Union (AGU), Vol. 100, No. C4 ( 1995-04-15), p. 6961-6965
    Abstract: The basic features of the flow of meltwater under ice shelves can be described by a set of simple relations and length scales. The flow may be divided into two regions, with different basic processes dominating in each. In the first region, melting of the underside of the ice shelf is important and the temperature and salinity of the current tend toward “equilibrium” values, such that the changes due to melting of the ice shelf are balanced by changes due to entrainment of ambient seawater. The equilibrium values change with depth owing to the effect of the change in pressure on the freezing point. As the current increases in thickness, it is no longer able to adjust sufficiently rapidly to the changing equilibrium values, arid the flow moves into the second region. The extent of the first region is governed by the location of the “ambient freezing point.” In the second region, melting is less important and the current behaves as an entraining drag‐limited gravity current in a stratified ambient fluid, leaving the shelf once the current has the same density as the ambient seawater. The heights of the two regions depend mainly on the ambient conditions and only indirectly on parameters such as slope angle, entrainment constant, drag coefficient, and turbulent transfer coefficients.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/94JC03244
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1995
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    detail.hit.zdb_id: 3094104-0
    detail.hit.zdb_id: 2130824-X
    detail.hit.zdb_id: 2016813-5
    detail.hit.zdb_id: 2016810-X
    detail.hit.zdb_id: 2403298-0
    detail.hit.zdb_id: 2016800-7
    detail.hit.zdb_id: 161666-3
    detail.hit.zdb_id: 161667-5
    detail.hit.zdb_id: 2969341-X
    detail.hit.zdb_id: 161665-1
    detail.hit.zdb_id: 3094268-8
    detail.hit.zdb_id: 710256-2
    detail.hit.zdb_id: 2016804-4
    detail.hit.zdb_id: 3094181-7
    detail.hit.zdb_id: 3094219-6
    detail.hit.zdb_id: 3094167-2
    detail.hit.zdb_id: 2220777-6
    detail.hit.zdb_id: 3094197-0
    SSG: 16,13
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  • 3
    Online Resource
    Online Resource
    Eddy formation by dense flows on slopes in a rotating fluid
    Cambridge University Press (CUP) ; 1998
    In:  Journal of Fluid Mechanics Vol. 363 ( 1998-05-25), p. 229-252
    Details
    In: Journal of Fluid Mechanics, Cambridge University Press (CUP), Vol. 363 ( 1998-05-25), p. 229-252
    Abstract: Properties of the flow generated by a continuous source of dense fluid on a slope in a rotating system are investigated with a variety of laboratory experiments. The dense fluid may initially flow down the slope but it turns (under the influence of rotation) to flow along the slope, and initial geostrophic adjustment gives it an anticyclonic velocity profile. Some of the dense fluid drains downslope in a viscous Ekman layer, which may become unstable to growing waves. Provided that the viscous draining is not too strong, cyclonic vortices form periodically in the upper layer and the dense flow breaks up into a series of domes. Three processes may contribute to the formation of these eddies. First, initial downslope flow of the dense current may stretch columns of ambient fluid by the ‘Taylor column’ process (which we term ‘capture’). Secondly, the initial geostrophic adjustment implies lower-layer collapse which may stretch the fluid column, and thirdly, viscous drainage will progressively stretch and spin up a captured water column. Overall this last process may be the most significant, but viscous drainage has contradictory effects, in that it progressively removes dense lower-layer fluid which terminates the process when the layer thickness approaches that of the Ekman layer. The eddies produced propagate along the slope owing to the combined effects of buoyancy–Coriolis balance and ‘beta-gyres’. This removes fluid from the vicinity of the source and causes the cycle to repeat. The vorticity of the upper-layer cyclones increases linearly with Γ = L α/ D (where L is the Rossby deformation radius, α the bottom slope and D the total depth), reaching approximately 2 f in the experiments presented here. The frequency at which the eddy/dome structures are produced also increases with Γ , while the speed at which the structures propagate along the slope is reduced by viscous effects. The flow of dense fluid on slopes is a very important part of the global ocean circulation system and the implications of the laboratory experiments for oceanographic flows are discussed.
    Type of Medium: Online Resource
    ISSN: 0022-1120 , 1469-7645
    URL: Article
    DOI: 10.1017/S0022112098001013
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 1998
    detail.hit.zdb_id: 1472346-3
    detail.hit.zdb_id: 218334-1
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