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The effect of the mass of a 2D elastically-mounted circular cylinder in cross-flow on its vortex-induced vibrations and on the related vortex shedding lift forces is analyzed via a single-degree-of-freedom multi-frequency model (sdof-mf). The mechanical system in question is characterized by low mass ratio, low structural damping and Reynolds number of order 10 4 . The proposed sdof-mf model relies on the decomposition of the total hydrodynamic force in a inertia/drag force, conventionally associated with the cylinder motion in still fluid, and an additional lift force associated to pure vortex shedding. The lift force is assumed to be composed by not-Fourier-dependent harmonics; this constitutes the key point of the proposed sdof-mf model. The parameters of this model are determined via a parameter identification method based, in this case, on VIV data obtained via CFD. The simulations are carried out changing systematically the values of the mass ratio, within the range of engineering practice, and covering a wide range of flow regimes including lock-in conditions. The results from the application of the sdof-mf model highlight the large influence of the mass ratio on the response of the cylinder and on the vortex shedding lift force. The effects are clearly visible on the maximum amplitude at lock-in, on the range of incident flow velocity over which synchronization occurs, on ultra/sub harmonic behavior and phase lag of the cylinder motion, and finally on the magnitude and harmonic content of the lift force induced by pure vortex shedding. [ABSTRACT FROM AUTHOR]

A novel single-degree-of-freedom multi-frequency model ( sdof-mf ) for the prediction of the Vortex Induced Vibrations (VIV) of an elastically mounted circular cylinder in two-dimensional cross flow is presented. The proposed model treats the total hydrodynamic force as sum of conventional Morison-like inertia and drag terms related to the cylinder motion in still fluid plus additional harmonics that account for the lift force induced by vortex shedding. Amplitudes, frequencies and phase lags of these harmonics are identified using a Parameter Identification ( PI ) procedure applied to time domain data of vortex induced forces, here obtained via CFD simulations. The proposed sharp identification via PI of the independent frequencies of the vortex shedding fluid force is the peculiarity of the proposed method. The model is assessed considering a wide range of flow regimes, including lock-in conditions. From the overall results, the proposed sdof-mf model exhibits promising but consistent capabilities in the reproduction of the vortex shedding forces and cylinder motion, in terms of both amplitudes and frequencies. [ABSTRACT FROM AUTHOR]

The interaction of regular waves with a weakly submerged horizontal circular cylinder at Keulegan-Carpenter KC numbers up to 2.5 is studied by means of numerical simulations, solving the two-phase flow Navier-Stokes equations with the Finite Volume method and the Volume of Fluid interface capturing method. Experimental data from laboratory tests conducted in the past by one of the authors are used as reference data. The study is focused on the surface wave transformation, on the flow field in the near region and on the loads on the cylinder. The interest is driven on the spectral content of the transmitted waves at higher order frequencies and on the non-linear features of the wave reflected by the cylinder. The flow field in the near-body region is analyzed in terms of vortex onset, development and detachment, and correlating pressure pulses with the vorticity field at the cylinder surface. Inviscid flow simulations are carried out too, to evince the origin of higher order terms either from the free surface or from the viscous terms in the momentum equations. The steady streaming around the cylinder is analyzed, including its variability along the cylinder surface and its relationship with the vortex cores generated at the body surface. [ABSTRACT FROM AUTHOR]

The interaction of waves with a weakly submerged horizontal circular cylinder is studied numerically, solving 2-D Navier-Stokes equations with reference to former experimental sessions in a wave flume. A selection of aspects of the viscous wave-body interaction is analyzed, in particular the free surface elevation perturbed by the obstacle, the pressure at the body surface, the inertia coefficient of the Morison equation and finally the generation, persistence and merging of vorticity structures detached from the cylinder. [ABSTRACT FROM AUTHOR]

In this work we analyze by means of numerical simulations the features of breaking of two dimensional free surface waves induced by a body or a sloping bottom. The sample cases selected for the simulations characterize different aspects of wave breaking, thus they are supposed to represent rather widely a problem of large interest for ship hydrodynamics and ocean engineering applications. The simulations considered are: wave breaking induced by a fully submerged hydrofoil towed in calm water at constant speed; shallow water waves breaking on a sloping beach in spilling and plunging mode; regular intermediate depth waves breaking gently over a weakly submerged horizontal circular cylinder at a low Keulegan–Carpenter number. Each simulated case is supported by detailed comparisons with experimental data in time and frequency domain. The results presented have been obtained adopting a standard RANS approach. They show a generally good reproduction of the wave breaking characteristics even though it is rather clear that there is a case dependent potential loss of accuracy in the presence of pronounced foamy flow. [ABSTRACT FROM AUTHOR]

The present study is aimed at determining the confidence limits of design wave parameters derived from numerical modeling-for both extremes and operational conditions-over the Central and Western Mediterranean Sea. The paper presents the methodology and results of an extensive validation activity conducted on a chain of medium-resolution third-generation wave models used for hindcast purposes. The stringent requirements of state-of-the-art coastal and offshore engineering applications over this area make the adoption of medium- or high-resolution hindcast wave and wind models almost mandatory because of the complex coastal geometry, bathymetry, and orography that in turn lead to large variations of the design wave parameters even within small regions. The chains of nested meteorological and wave models used in this hindcast study belong to the ETA and WaveWatch III families, respectively. In this study the wind and wave numerical models have been run over the past 20 years, with increasing resolutions of the wave models from 0.2° up to 0.04°. The results presented herein have 0.1° resolution for both wind and wave models. The wave data obtained are compared with available measurements from 14 wave buoys in coastal zones in the Central and Western Mediterranean Sea. [ABSTRACT FROM AUTHOR]

Intense atmospheric disturbances, which impact directly on the sea surface causing a significant increase in wave height and sometimes strong storm surges, have become increasingly frequent in recent years in the Mediterranean Sea, producing extreme concern in highly populated coastal areas, such as the Gulf of Naples (Western Mediterranean Sea, Central Tyrrhenian Sea). In this work, fifty-six months of wave parameters retrieved by an HF radar network are integrated with numerical outputs to analyze the seasonality of extreme events in the study area and to investigate the performance of HF radars while increasing their distances from the coast. The model employed is the MWM (Mediterranean Wind-Wave Model), providing a wind-wave dataset based on numerical models (the hindcast approach) and implemented in the study area with a 0.03° spatial resolution. The integration and comparison with the MWM dataset, carried out using wave parameters and spectral information, allowed us to analyze the availability and accuracy of HF sampling during the investigated period. The statistical comparisons highlight agreement between the model and the HF radars during episodes of sea storms. The results confirm the potential of HF radar systems as long-term monitoring observation platforms, and allow us to give further indications on the seasonality of sea storms under different meteorological conditions and on their energy content in semi-enclosed coastal areas, such as the Gulf of Naples. [ABSTRACT FROM AUTHOR]

Cavitating phenomena, which may occur in many industrial systems, can be modelled using several approaches. In this study a homogeneous multiphase model, used in combination with three previously calibrated mass transfer models, is evaluated for the numerical prediction of cavitating flow around a marine propeller and a Kaplan turbine runner. The simulations are performed using a commercial computational fluid dynamics (CFD) solver and the turbulence effects are modelled using, alternatively, the Reynolds averaged Navier Stokes (RANS) and scale adaptive simulation (SAS) approaches. The numerical results are compared with available experimental data. In the case of the propeller the thrust coefficient and the sketches of cavitation patterns are considered. In the case of the turbine the efficiency and draft tube losses, along with the cavitation pattern sketches, are compared. From the overall results it seems that, for the considered systems, the three different mass transfer models can guarantee similar levels of accuracy for the performance prediction. For a very detailed investigation of the fluid field, slight differences in the predicted shapes of the cavitation patterns can be observed. In addition, in the case of the propeller, the SAS simulation seems to guarantee a more accurate resolution of the cavitating tip vortex flow, while for the turbine, SAS simulations can significantly improve the predictions of the draft tube turbulent flow. [ABSTRACT FROM AUTHOR]