arXiv subjects

Alessandro Toffoli

Publications and source records attributed to Alessandro Toffoli.

23 records · Page 2Linked to original sources

arXiv2015

Non-Gaussian properties of second-order wave orbital velocity

A stochastic second-order wave model is applied to assess the statistical properties of wave orbital velocity in random sea states below the water surface. Directional spreading effects as well as the dependency of the water depth are investigated by means of a Monte-Carlo approach. Unlike for the surface elevation, sub-harmonics dominate the second-order contribution to orbital velocity. We show that a notable set-down occurs for the most energetic and steepest groups. This engenders a negative skewness in the temporal evolution of the orbital velocity. A substantial deviation of the upper and lower tails of the probability density function from the Gaussian distribution is noticed, velocities are faster below the wave trough and slower below the wave crest when compared with linear theory predictions. Second-order nonlinearity effects strengthen with reducing the water depth, while weaken with the broadening of the wave spectrum. The results are confirmed by laboratory data. Corresponding experiments have been conducted in a large wave basin taking into account the directionality of the wave field. As shown, laboratory data are in very good agreement with the numerical prediction.

physics.flu-dyn↗

arXiv2015

Sea ice floes dissipate the energy of steep ocean waves

Wave attenuation by ice floes is an important parameter for modelling the Arctic Oceans. At present, attenuation coefficients are extracted from linear models as a function of the incident wave period and floe thickness. Recent explorations in the Antarctic Mixed Ice Zone (MIZ) revealed a further dependence on wave amplitude, suggesting that nonlinear contributions are non-negligible. An experimental model for wave attenuation by a single ice floe in a wave flume is here presented. Observations are compared with linear predictions based on wave scattering. Results indicate that linear models perform well under the effect of gently sloping waves. For more energetic wave fields, however, transmitted wave height is normally over predicted. Deviations from linearity appear to be related to an enhancement of wave dissipation induced by unaccounted wave-ice interaction processes, including the floe over wash.

physics.flu-dyn↗

arXiv2015

An idealised experimental model of ocean surface wave transmission by an ice floe

An experimental model of transmission of ocean waves by an ice floe is presented. Thin plastic plates with different material properties and thicknesses are used to model the floe. Regular incident waves with different periods and steepnesses are used, ranging from gently-sloping to storm-like conditions. A wave gauge is used to measure the water surface elevation in the lee of the floe. The depth of wave overwash on the floe is measured by a gauge in the centre of the floe's upper surface. Results show transmitted waves are regular for gently-sloping incident waves but irregular for storm-like incident waves. The proportion of the incident wave transmitted is shown to decrease as incident wave steepness increases, and to be at its minimum for an incident wavelength equal to the floe length. Further, a trend is noted for transmission to decrease as the mean wave height in the overwash region increases.

physics.ao-ph↗

arXiv2014

An experimental model of reflection and transmission of ocean waves by an ice floe

An experimental model of reflection and transmission of ocean waves by an ice floe is presented. Evolution of mechanically-generated, regular waves is monitored in front and in the lee of a solitary, square floe, made of a synthetic material. Results confirm dependence of reflection and transmission on the period of the incident wave. Results also indicate that wave overwash on the floe affects reflection and transmission.

physics.flu-dyn↗

arXiv2011

Triggering rogue waves in opposing currents

We show that rogue waves can be triggered naturally when a stable wave train enters a region of an opposing current flow. We demonstrate that the maximum amplitude of the rogue wave depends on the ratio between the current velocity, $ U_0 $, and the wave group velocity, $ c_g $. We also reveal that an opposing current can force the development of rogue waves in random wave fields, resulting in a substantial change of the statistical properties of the surface elevation. The present results can be directly adopted in any field of physics in which the focusing Nonlinear Schrodinger equation with non constant coefficient is applicable. In particular, nonlinear optics laboratory experiments are natural candidates for verifying experimentally our results.

physics.flu-dyn↗