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This paper presents a method to statistically predict the magnitude of impact pressure (including extreme values) produced by deep water waves breaking on a circular cylinder representing a column of an ocean structure. Breaking waves defined here are not those whose tops are blown off by the wind but those whose breaking is associated with steepness. The probability density function of wave period associated with breaking waves is derived for a specified wave spectrum, and then converted to the probability density function of impact pressure. Impacts caused by two different breaking conditions are considered; one is the impact associated with waves breaking in close proximity to the column, the other is an impact caused by waves approaching the column after they have broken. As an example of the application of the present method, numerical computations are carried out for a wave spectrum obtained from measured data in the North Atlantic. 相似文献
44.
Estuary/ocean exchange and tidal mixing in a Gulf of Maine Estuary: A Lagrangian modeling study 总被引:2,自引:0,他引:2
Ata Bilgili Jeffrey A. Proehl Daniel R. Lynch Keston W. Smith M. Robinson Swift 《Estuarine, Coastal and Shelf Science》2005,65(4):607-624
A Lagrangian particle method embedded within a 2-D finite element code, is used to study the transport and ocean–estuary exchange processes in the well-mixed Great Bay Estuarine System in New Hampshire, USA. The 2-D finite element model, driven by residual, semi-diurnal and diurnal tidal constituents, includes the effects of wetting and drying of estuarine mud flats through the use of a porous medium transport module. The particle method includes tidal advection, plus a random walk model in the horizontal that simulates sub-grid scale turbulent transport processes. Our approach involves instantaneous, massive [O(500,000)] particle releases that enable the quantification of ocean–estuary and inter-bay exchanges in a Markovian framework. The effects of the release time, spring–neap cycle, riverine discharge and diffusion strength on the intra-estuary and estuary–ocean exchange are also investigated.The results show a rather dynamic interaction between the ocean and the estuary with a fraction of the exiting particles being caught up in the Gulf of Maine Coastal Current and swept away. Three somewhat different estimates of estuarine residence time are calculated to provide complementary views of estuary flushing. Maps of residence time versus release location uncover a strong spatial dependency of residence time within the estuary that has very important ramifications for local water quality. Simulations with and without the turbulent random walk show that the combined effect of advective shear and turbulent diffusion is very effective at spreading particles throughout the estuary relatively quickly, even at low (1 m2/s) diffusivity. The results presented here show that a first-order Markov Chain approach has applicability and a high potential for improving our understanding of the mixing processes in estuaries. 相似文献
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Modeling bed-load transport of coarse sediments in the Great Bay Estuary, New Hampshire 总被引:1,自引:0,他引:1
A. Bilgili M. R. Swift D. R. Lynch J. T. C. Ip 《Estuarine, Coastal and Shelf Science》2003,58(4):937-950
Current, sea level and bed-load transport are investigated in the Lower Piscataqua River section of the Great Bay Estuary, New Hampshire, USA—a well-mixed and geometrically complex system with low freshwater input, having main channel tidal currents ranging between 0.5 and 2 m s−1. Current and sea level forced by the M2M4M6 tides at the estuarine mouth are simulated by a vertically averaged, non-linear, time-stepping finite element model. The hydrodynamic model uses a fixed boundary computational domain and accounts for flooding–drying of tidal flats by making use of a groundwater component. Inertia terms are neglected in comparison with pressure gradient and bottom friction terms, which is consistent with the observed principal dynamic balance for this section of the system. The accuracy of hydrodynamic predictions in the study area is demonstrated by comparison with four tidal elevation stations and two cross-section averaged current measurements. Simulated current is then used to model bed-load transport in the vicinity of a rapidly growing shoal located in the main channel of the lower system. Consisting of coarse sand and gravel, the shoal must be dredged every five to eight years. Two approaches are taken—an Eulerian parametric method in which nodal bed-load flux vectors are averaged over the tidal cycle and a Lagrangian particle tracking approach in which a finite number of sediment particles are released and tracked. Both methods yield pathways and accumulations in agreement with the observed shoal formation and the long-term rate of sediment accumulation in the shoal area. 相似文献
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Kern E. Kenyon 《Journal of Oceanography》1997,53(1):89-92
The effects of the gravity torques acting on the angular momentum of surface gravity waves are calculated theoretically. For
short crested waves the gravity torque is caused by the force of gravity on the orbiting fluid particles acting down the slopes
of the crests and troughs and in the direction parallel to the crests and troughs. The gravity torque tries to rotate the
angular momentum vectors, and thus the waves themselves, counterclockwise in the horizontal plane, as viewed from above, in
both hemispheres. The amount of rotation per unit time is computed to be significant assuming reasonable values for the along-crest
and trough slopes for waves in a storm area. The gravity torque has a frequency which is double the frequency of the waves.
For long crested waves the gravity torque acts in the vertical plane of the orbit and tries to decelerate the particles when
they rise and accelerate them when they fall. By disrupting the horizontal cyclostrophic balance of forces on the fluid particles
(centrifugal force versus pressure force) the gravity torque accounts qualitatively for the three characteristics of breaking
waves: that they break at the surface, that they break at the crest, and that the crest breaks in the direction of wave propagation. 相似文献
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Instability analysis of three-dimensional ocean shear waves 总被引:1,自引:0,他引:1
Qiao Fangli 《海洋学报(英文版)》1996,15(1):1-8
Instabilityanalysisofthree-dimensionaloceanshearwaves¥QiaoFangli(ReceivedNovember6,1995,acceptedNovember30.1995)Abstract:Base... 相似文献
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