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1

Vertical structure of the stable boundary layer detected by RASS-SODAR and in-situ measurements in SABLES 2006 field campaign

Viana S., Yague C., Maqueda G.

Acta Geophysica

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2012

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Vol. 60, no. 5

1261-1286

EN

Data from the SABLES 2006 field campaign are used in order to analyse some of the main processes present along the nocturnal periods: surface-based inversions, low level jets, katabatic winds, wave-like motions, pressure perturbations, etc. These processes have an important influence on the vertical structure (both thermal and dynamical) of the atmospheric boundary layer, and can be better described with the synergetic combination of RASS-SODAR data and in-situ measurements (such as sonic anemometer data and high-resolution pressure series from microbarometers). It is shown how the different air masses and their evolution are easily identified when pressure and RASS-SODAR wind and temperature data are presented together. Likewise, periodic pressure fluctuations observed in the surface array of microbarometers reveal the existence of gravity wave motions whose propagation is better understood after locating the wave ducting layers with the help of RASS-SODAR average wind ant temperature profiles.

2

Multi-scale waves in sound-proof global simulations with EULAG

Prusa J.M., Gutowski W.J.

Acta Geophysica

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2011

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Vol. 59, no. 6

1135-1157

EN

EULAG is a computational model for simulating flows across a wide range of scales and physical scenarios. A standard option employs an anelastic approximation to capture nonhydrostatic effects and simultaneously filter sound waves from the solution. In this study, we examine a localized gravity wave packet generated by instabilities in Held-Suarez climates. Although still simplified versus the Earth's atmosphere, a rich set of planetary wave instabilities and ensuing radiated gravity waves can arise. Wave packets are observed that have lifetimes ≤ 2 days, are negligibly impacted by Coriolis force, and do not show the rotational effects of differential jet advection typical of inertia-gravity waves. Linear modal analysis shows that wavelength, period, and phase speed fit the dispersion equation to within a mean difference of ∼ 4 per cent, suggesting an excellent fit. However, the group velocities match poorly even though a propagation of uncertainty analysis indicates that they should be predicted as well as the phase velocities. Theoretical arguments suggest the discrepancy is due to nonlinearity - a strong southerly flow leads to a critical surface forming to the southwest of the wave packet that prevents the expected propagation.

3

A higher order nonlinear evolution equation for much broader bandwidth gravity waves in deep water

Debsarma S., Das K. P.

International Journal of Applied Mechanics and Engineering

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2007

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Vol. 12, no 2

557-563

EN

A higher order nonlinear evolution equation for gravity waves in deep water is derived from Zakharov's integral equation which is valid for a much broader bandwidth gravity waves than considered previously. The instability regions in the perturbed wave-number space for a uniform Stokes wave obtained from this equation is shown to fit nicely those obtained by McLean et al. [Phys. Rev. Lett. 46, 817-820(1981)] by exact numerical method.

4

Modelling of gravity waves in water of finite depth

Chybicki W.

Archives of Hydro-Engineering and Environmental Mechanics

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2004

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Vol. 51, nr 3

205-224

EN

An extension of shallow water theory proposed by Wilde (Wilde, Chybicki 2000), for finite water depth and based on the Lagrangian type formalism is presented. As in Bussinesq-type models the vertical dimension is being eliminated and the horizontal displacement is expanded in the even power series of vertical variable Y, but only two terms - with power null and two are taken into account. Based on continuity equation, vertical displacement is expressed in terms of horizontal displacement and its derivatives. The equations of motion are derived from a Hamilton principle applied to Lagrangian function being a difference of kinetic and potential energy. In order to solve the set of governing equations a direct method of variational calculus has been applied. The solutions preserve total energy. The numerical simulations have been verified experimentally, in terms of wave measurements in the flume, for various wave heights and ratios of wavelength to water depth, showing good conformity between measured and calculated values. The theory presented here can also be applied for the case of varying depth.

5

Hydrodynamics of offshore structures under waves and current: fundamental theory, formulation of the problem and a case study

Mendes A. C.

Vibrations in Physical Systems

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2002

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Vol. 20

34--57

EN

This lecture is devoted firstly to a statement of the physical properties of gravity waves that is followed by a review on Linear Theory of waves of small amplitude, together with the related basic equations. This material includes the calculation of water pressure and water-particle kinematics, and the establishment of mass, momentum and energy balances. On a second stage it will be given a comprehensive material concerning the methodologies applied to calculate the wave forces. In the present case we will be involved with the Morison model and the corresponding hydrodynamic coefficients, when predicting the wave forces exerted upon tubular structures. Finally, a case study will be presented, relating both theoretical and experimental results obtained with a physical model of an offshore jacket platform.