Numerical Simulation of Whitecaps and Foam Effects on Satellite Altimeter Response

The determination of wave height by active satellite remote sensing, be it Synthetic Aperture Radar (SAR) or altimeter, has been a common practice for many years and is now imbedded on many meteorological and oceanographic forecasting systems. Despite their differences, all active sensors are based on the measurement of the Normalized Radar Cross Section (NRCS) of the sea surface, i.e., of its backscattering properties, which in turn depend on the wind velocity. At small and moderate wind speeds, the main mechanism is the formation of ripples (small scale waves

A CFD approach to rubble mound breakwater design

The paper provides some developments of a numerical approach ("Numerical Calculation of Flow Within Armour Units", FWAU) to the design of rubble mound breakwaters. The hydrodynamics of wave induced flow within the interstices of concrete blocks is simulated by making use of advanced, but well tested, CFD techniques to integrate RANS equations.While computationally very heavy, FWAU is gaining ground, due to its obvious advantages over the "porous media", i.e. the possibility of accounting for the highly non stationary effects, the reduced need of ad hoc calibration of filtration parameters and also – in perspective – the evaluation of hydrodynamic forces on single blocks. FWAU however is a complex technique, and in order to turn it into a practical design tool, a number of difficulties have to be overcome.The paper presents recent results about this validation, as well as insight into fluid dynamical aspects. Keywords: Numerical simulation, Breakwaters, Run up, Reflection, Rubble moun

Overview of the FTU results

Since the 2018 IAEA FEC Conference, FTU operations have been devoted to several experiments covering a large range of topics, from the investigation of the behaviour of a liquid tin limiter to the runaway electrons mitigation and control and to the stabilization of tearing modes by electron cyclotron heating and by pellet injection. Other experiments have involved the spectroscopy of heavy metal ions, the electron density peaking in helium doped plasmas, the electron cyclotron assisted start-up and the electron temperature measurements in high temperature plasmas. The effectiveness of the laser induced breakdown spectroscopy system has been demonstrated and the new capabilities of the runaway electron imaging spectrometry system for in-flight runaways studies have been explored. Finally, a high resolution saddle coil array for MHD analysis and UV and SXR diamond detectors have been successfully tested on different plasma scenarios

Overview of the FTU results

Since the 2016 IAEA Fusion Energy Conference, FTU operations have been mainly devoted to experiments on runaway electrons and investigations into a tin liquid limiter; other experiments have involved studies of elongated plasmas and dust. The tearing mode onset in the high density regime has been studied by means of the linear resistive code MARS, and the highly collisional regimes have been investigated. New diagnostics, such as a runaway electron imaging spectroscopy system for in-flight runaway studies and a triple Cherenkov probe for the measurement of escaping electrons, have been successfully installed and tested, and new capabilities of the collective Thomson scattering and the laser induced breakdown spectroscopy diagnostics have been explored

Numerical Simulation of Whitecaps and Foam Effects on Satellite Altimeter Response

The determination of wave height by active satellite remote sensing, be it Synthetic Aperture Radar (SAR) or altimeter, has been a common practice for many years and is now imbedded on many meteorological and oceanographic forecasting systems. Despite their differences, all active sensors are based on the measurement of the Normalized Radar Cross Section (NRCS) of the sea surface, i.e., of its backscattering properties, which in turn depend on the wind velocity. At small and moderate wind speeds, the main mechanism is the formation of ripples (small scale waves); at higher speeds, whitecaps appear, and foam starts playing an essential role in determining NRCS. In the past few years much research effort has gone into clarifying these effects, thus improving the general quality of the measurements. Little work, however, has been devoted so far to consider the vertical spatial variation of backscattering properties, and in particular of the floating foam, over the sea surface. As it is shown in the present paper, the shape of the backscattered electromagnetic impulse in radar altimeters depends on the spatial distribution of foam over the water height in the sea waves and therefore the performance of these instruments in determining Significant Wave Height (Hs) and Sea Surface Level (SSL) is strongly affected by this effect. This work tackles these problems by making use of specially implemented numerical algorithms to simulate both sea surface processes and radar altimeter techniques. Results show that some causes of errors can be better understood and eventually corrected: in particular, the paper deals with the reconstruction of the electromagnetic Sea State Bias (SSB), the well known altimeter ranging error due to the presence of ocean waves on the sea surface

On the effects of wave-induced drift and dispersion in the deepwater horizon oil spill

The objective of this work is to provide an indication of the effects of waveinduced movement of oil on the sea surface in connection with the Deepwater Horizon oil spill. By making use of modeled wave fields, satellite altimeter, and buoy data, mean trajectories and wave-induced oil spreading are computed for some of the storm events which took place during the accident. The effects of mean Stokes' drift are confirmed to be an important element in most situations, causing spill movements of 30 km and more in about 5 days. The diffusion due to random wave movement is also shown to be relevant at least for smaller spills; for large accidents, its effects are less important, but it still has an influence on some aspects of the oil spreading. © 2011 by the American Geophysical Union

Wave hindcast resolution reliability for extreme analysis

Here we analyze the wave hindcast reliability for a proper description of wave climate in the Mediterranean Sea. To this aim, 6-hourly 35-years ECMWF (European Center Medium Weather Forecast) wave data at 0.7\uc2\ub0 resolution grid are compared with those provided by means of a meteocean modelling chain operative at DICCA, University of Genoa (http://www.dicca.unige.it/meteocean/) covering a 34-years temporal span at an hourly frequency on a 0.1\uc2\ub0 resolution domain. Results reveal not negligible differences in evaluating significant wave heights at peaks; in particular the tendency to underrate values in storm sea conditions performed by ECMWF dataset is here evidenced. This behavior turns directly into not-reliable long-term return level estimates for extreme wave analysis, leading to a weak description of wave climate; conversely, a wave climate robust assessment is of primary importance for maritime design

A numerical method to analyze the interaction between sea waves and rubble mound emerged breakwaters

The paper provides some results of a new procedure, developed by MEDUS, to analyze the hydrodynamic aspects of the interactions between maritime emerged breakwaters and waves, by integrating CAD and CFD software.The filtration of the fluid within the interstices of a concrete blocks breakwater is evaluated by integrating the Reynolds Averaged Navier-Stokes equations (RANS) inside the voids rather than making use of the widespread “porous media” approach. The structure is thus modelled, very much like in the real world or in the physical laboratory testing, by overlapping individual three-dimensional elements (Armour in Accropode™, Core-loc™ or Xbloc®, toe protection and filter layer in stones), and then the computational grid is fitted so as to provide enough computational nodes within the flow paths. This approach is meant to match closely the physical laboratory test procedure, and it is oriented at analyzing the hydrodynamic aspects of the phenomenon (overtopping, breaking, Run-up, reflection) as well as the stability of armour elements. Therefore, for the results' validation, the numerical Run-up and reflection effects on virtual breakwater were compared with some empirical formulas and some similar laboratory tests