On Floating Breakwaters Efficiency - a 2DV Parametric Based Analysis

In long term evolution numerical models, the interactions of a floating barrier with the wave field is then deputed to some parametrized transfer functions, which mimic wave energy transmission and dissipation in the frequency domain. This thesis provide, as final result, two transfer functions (one for incident waves, one for reflected ones) for a particular class of compact shaped floating breakwaters. These functions are based on three main parameters, which have been derived on physical model results. The first one (x) is the ratio between the incoming wave frequency and an approximation of FB heave natural frequency, based on principal FB cross section dimensions. Wave steepness has been considered to be the second variable which helps in describing the amount of dissipated energy. An FB draft to water depth ratio has been identified. Available algorithms for the decomposition into incident and reflected waves of flume records are mostly Stokes-FFT based. Therefore they suffer some limitations for relatively high wave steepness (Ch. 4). Since the latter is considered as a crucial parameter, a lot of effort has been drawn in solving some conundrums of actual methods. Two algorithms are proposed. The first one (Ch. 5), based on empirical mode decomposition, did not give satisfactory results. The second one (Ch. 6) is based on linear waves superposition, but, getting rid of linear dispersion relation, detects automatically each phase celerity. The proposed algorithm appears to be effective for relatively shallow water waves, for which the phase modulation approach is more consistent than Stokes formulations. A Stokes 2nd order algorithm has also been implemented. In Ch. 7 the experimental set up is presented. A second order analysis of transmission and reflection processes is also introduced.Results are given (and discussed) in Ch. 8. Linear transmission and reflection transfer functions are derived, based on experimental data fitting. These are finally validated with irregular wave test measurements.It is found that the transmission process mainly depends on frequency (x) and on FB relative draft. The last parameter does not enter the reflection process, which basically described by x and wave steepness. In particular, steeper waves loose more energy, and are less reflected. For transmitted waves only, a significant amount of energy transfer from primary to secondary harmonics is observed

Formula to Predict Transmission for pi-Type Floating Breakwaters

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Validation of coastal forecasts

Deliverable D2.3 del Proyecto MyWave: A pan-European concerted and integrated approach to operational wave modelling and forecasting – a complement to GMES MyOcean services. Work programme topic: SPA.2011.1.5.03 – R&D to enhance future GMES applications in the Marine and Atmosphere areas.Funded under: FP7-SPACE-2011-284455

LIMITS OF THE NEW TRANSMISSION FORMULA FOR PI-TYPE FLOATING BREAKWATERS

The aim of this work is to assess, by means of available experimental results and numerical simulations, the possible extension of the range of application of the formula proposed by Ruol et al. (J. Wat. Port, Coast. Ocean Eng., 1, 2013), giving wave transmission for chain-moored \uf050-type floating breakwaters. The formula is here applied out of the range used for its calibration and even to other types of FBs. The error between predicted and measured values is described and discussed with reference to the main geometrical variables. It appears that the formula performs fairly well for the box-type FB, but not in cases characterized by very different mooring stiffness compared to the one used for calibration. For instance in case of fixed or tethered FBs, the formula significantly overestimates the wave transmission

Experimentally Based Model to Size the Geometry of a New OWC Device, with Reference to the Mediterranean Sea Wave Environment

This note presents the Seabreath wave energy converter, basically a multi-chamber floating oscillating water column device, and the lumped model used to size its chambers, the ducts and the turbine. The model is based on extensive testing carried out in the wave flume of the University of Padova using fixed and floating models with a dummy power take off and indirect measurement of the produced power. A map with the available energy in the Mediterranean Sea is also proposed, showing possible ideal application sites. The Seabreath is finally dimensioned for a quarter scale test application in the Adriatic Sea, with a 3 kW turbine, and a capacity factor of 40%

Synergic use of altimeter and model sea level data in inner and coastal seas

We analyse high rate (20 Hz) altimeter derived sea level information, both from Synthetic Aperture Radar (SAR) altimetry missions and Low Resolution Mode missions, in an inner sea and coastal environment. They are compared versus measured and high resolution model data. After a compact description of the relevant physical processes affecting the local sea level values, we focus on three specific passes on the Adriatic Sea, East of Italy. Our main finding is that altimeters and models provide both valuable, partially overlapping, but complementary, information to be exploited in parallel with a double purpose: to progressively approach the truth and to ensure the parallel improvement of both sources. From altimeter data there is a very strong suggestion that the spatial, and implicitly temporal, variability of the fields is much higher than shown by models. The reasons are discussed

Attenuating surface gravity waves with an array of submerged resonators: an experimental study

Metamaterials and photonic/phononic crystals have been successfully developed in recent years to achieve advanced wave manipulation and control, both in electromagnetism and mechanics. However, the underlying concepts are yet to be fully applied to the field of fluid dynamics and water waves. Here, we present an example of the interaction of surface gravity waves with a mechanical metamaterial, i.e., periodic underwater oscillating resonators. In particular, we study a device composed of an array of periodic submerged harmonic oscillators whose objective is to absorb wave energy and dissipate it inside the fluid in the form of heat. The study is performed using a state-of-the-art direct numerical simulation of the Navier–Stokes equation in its two-dimensional form with free boundary and moving bodies. We use a volume of fluid interface technique for tracking the surface and an immersed boundary method for the fluid–structure interaction. We first study the interaction of a monochromatic wave with a single oscillator and then add up to four resonators coupled only fluid-mechanically. We study the efficiency of the device in terms of the total energy dissipation and find that by adding resonators, the dissipation increases in a nontrivial way. As expected, a large energy attenuation is achieved when the wave and resonators are characterized by similar frequencies. As the number of resonators is increased, the range of attenuated frequencies also increases. The concept and results presented herein are of relevance for coastal protection applications

CMEMS-Based coastal analyses: Conditioning, coupling and limits for applications

Recent advances in numerical modeling, satellite data, and coastal processes, together with the rapid evolution of CMEMS products and the increasing pressures on coastal zones, suggest the timeliness of extending such products toward the coast. The CEASELESS EU H2020 project combines Sentinel and in-situ data with high-resolution models to predict coastal hydrodynamics at a variety of scales, according to stakeholder requirements. These predictions explicitly introduce land discharges into coastal oceanography, addressing local conditioning, assimilation memory and anisotropic error metrics taking into account the limited size of coastal domains. This article presents and discusses the advances achieved by CEASELESS in exploring the performance of coastal models, considering model resolution and domain scales, and assessing error generation and propagation. The project has also evaluated how underlying model uncertainties can be treated to comply with stakeholder requirements for a variety of applications, from storm-induced risks to aquaculture, from renewable energy to water quality. This has led to the refinement of a set of demonstrative applications, supported by a software environment able to provide met-ocean data on demand. The article ends with some remarks on the scientific, technical and application limits for CMEMS-based coastal products and how these products may be used to drive the extension of CMEMS toward the coast, promoting a wider uptake of CMEMS-based predictions

Safety and efficacy of the maximum tolerated dose of givinostat in polycythemia vera: a two-part Phase Ib/II study

International audienc