Miguel Onorato - Academia.edu (original) (raw)

Papers by Miguel Onorato

Physical Review Letters, Jul 7, 2020

arXiv (Cornell University), Dec 15, 2022

2020 Fourteenth International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials), 2020

Annals of Physics, 2015

The dynamics of waves in weakly nonlinear dispersive media can be described by the nonlinear Schr... more The dynamics of waves in weakly nonlinear dispersive media can be described by the nonlinear Schrödinger equation (NLSE). An important feature of the equation is that it can be derived in a number of different physical contexts; therefore, analogies between different fields, such as for example fiber optics, water waves, plasma waves and Bose-Einstein condensates, can be established. Here, we investigate the similarities between wave propagation in optical Kerr media and water waves. In particular, we discuss the modulation instability (MI) in both media. In analogy to the water wave problem, we derive for Kerr-media the Benjamin-Feir index, i.e. a nondimensional parameter related to the probability of formation of rogue waves in incoherent wave trains.

Physica D: Nonlinear Phenomena, 2016

ABSTRACT We study the nonlinear dynamics of unstable modes in the nonlinear Schroedinger equation... more ABSTRACT We study the nonlinear dynamics of unstable modes in the nonlinear Schroedinger equation (NLS). These modes have been identified with certain types of rogue waves which may occur in deep water wave trains and are here studied as a basic spectral component in the inverse scattering transform (IST) of NLS for periodic boundary conditions. Perspective for single modes and multi-mode cases is given and a simple scenario for the behavior of natural sea states is provided. Generally speaking, natural sea states provide both stable components and unstable components. The influence of current can also be included in the formulation.

Physics and Chemistry of the Earth, Part B: Hydrology, Oceans and Atmosphere, 1999

ABSTRACT It is well established that the modulational instability enhances the probability of occ... more ABSTRACT It is well established that the modulational instability enhances the probability of occurrence for extreme events if waves are long crested. Recent studies, however, have shown that the coexistence of directional wave components can substantially reduce its effects. Here, direct numerical simulations of the Euler equations are used to investigate whether the modulational instability may produce significant deviations from second-order statistical properties of surface gravity waves when short crestness (i.e., directionality) is accounted for. The case of a broad-banded directional wave field (i.e. wind sea) is investigated. Results will show that the distribution proposed by Forristall [1] provides a good estimate of the simulated crest height also at low probability levels.

The Kadomtsev–Petviashvili equation, an extension of the Korteweg–de Vries equation in two horizo... more The Kadomtsev–Petviashvili equation, an extension of the Korteweg–de Vries equation in two horizontal dimensions, is here used to study the statistical properties of random shallow water waves in constant depth for crossing sea states. Numerical simulations indicate that the interaction of two crossing wave trains generates steep and high amplitude peaks, thus enhancing the deviation of the surface elevation from the Gaussian statistics. The analysis of the skewness and the kurtosis shows that the statistical properties depend on the angle between the two wave trains.

ABSTRACT Laboratory experiments have been carried out in the directional wave tank at Marintek (N... more ABSTRACT Laboratory experiments have been carried out in the directional wave tank at Marintek (Norway) to study the nonlinear dynamics of surface gravity waves and the occurrence of extreme events, when the wave field traverses obliquely an ambient current. A condition of partial opposition has been considered. Tests on regular waves have shown that the current can trigger the formation of large amplitude waves. In random wave fields, however, this only results in a weak deviation from the statistical properties observed in absence of a current.

ABSTRACT A direct numerical simulation method is used to monitor the evolution of nonlinear rando... more ABSTRACT A direct numerical simulation method is used to monitor the evolution of nonlinear random directional wave fields. The aim is to investigate the combined effect of high order nonlinearity and directional energy distribution on the statistics of wave orbital velocity. Results show that the development of modulational wave instability and the concurrent formation of large amplitude waves lead to a substantial departure of the statistics of the horizontal velocity from the Normal (or Gaussian) probability density function when the wave field is long crested. As short crestedness increases, departure from the Normal distribution gradually diminishes and eventually vanishes for sufficiently broad directional spreading.

Journal of Computational Physics, 2014

$Research paper thumbnail of Multifractality of Air Transmittency at Small Time Scales$

Fractals, 1998

The fluctuations of air transmittency over small time scales (20–500 s), in the presence and the ... more The fluctuations of air transmittency over small time scales (20–500 s), in the presence and the absence of fog, are analyzed from different points of view: Fourier and wavelet transforms, multiscaling exponents, the multifractal spectrum and structure functions. All results indicate a multifractal structure associated with intermittency, and whose characteristics do not seem to change with the level of visibility. The origin of this multifractality, whether statistical or dynamical, cannot be established with certainty: there are however indications in favor of the presence of chaos.

ABSTRACT Recently the Benjamin-Feir instability has been considered as a possible mechanism for t... more ABSTRACT Recently the Benjamin-Feir instability has been considered as a possible mechanism for the formation of freak waves. Today the most used models for wave forecasting are based on the nonlinear energy transfer process that is ruled by the kinetic wave equa- tion which has been derived independently by K. Hasselmann and by V. Zakharov . The theory is not able to predict the Benjamin-Feir instability because it is based on the assumption that the Fourier modes are delta-correlated. Alber, followed by the works of Crawford et al. and Janssen, derived a new form of wave kinetic equation that includes at the same time a random version of the Benjamin-Feir instability and the Landau damping phenomenon. Using this theory we define the values of the Phillips' constant and the enhancement factor for which the JONSWAP spectrum is unsta- ble. By performing numerical simulations of the nonlinear Schrödinger equation we check the validity of the prediction of the related kinetic equation.

arXiv (Cornell University), Mar 11, 2022

Scientific Reports, 2016

Instabilities are common phenomena frequently observed in nature, sometimes leading to unexpected... more Instabilities are common phenomena frequently observed in nature, sometimes leading to unexpected catastrophes and disasters in seemingly normal conditions. One prominent form of instability in a distributed system is its response to a harmonic modulation. Such instability has special names in various branches of physics and is generally known as modulation instability (MI). The MI leads to a growth-decay cycle of unstable waves and is therefore related to Fermi-Pasta-Ulam (FPU) recurrence since breather solutions of the nonlinear Schrödinger equation (NLSE) are known to accurately describe growth and decay of modulationally unstable waves in conservative systems. Here, we report theoretical, numerical and experimental evidence of the effect of dissipation on FPU cycles in a super wave tank, namely their shift in a determined order. In showing that ideal NLSE breather solutions can describe such dissipative nonlinear dynamics, our results may impact the interpretation of a wide rang...