1,720,969 research outputs found
Numerical simulations of 2-D steady and unsteady breaking waves
Full text linkIn 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 experi-
mental 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
A numerical study on the viscous effects of waves travelling past a weakly submerged cylinder
Full text linkThe 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
On the nonlinear transformation of breaking and non-breaking waves induced by a weakly submerged shelf
Full text linkThe interaction of regular quasi-monochromatic waves with a weakly submerged rectangular shelf is studied by means of CFD simulations. The fundamental incident wave frequency is kept constant for the full set of simulated cases, while the incident wave amplitude is made increase progressively, so that the interaction with the shelf is dominated by almost inviscid non-linear flow for the smallest and by breaking for the highest incident waves. A parameter identification (PI) procedure is used to adapt a reduced model to the highly resolved time-space matrix of wave elevations obtained from the numerical simulations, on the weather and lee side respectively. In particular the wave number and the frequency of the component waves in the reduced model are left uncoupled, thus computed by the PI independently. The comparison of simulated data with experiments generally shows a very good agreement. Free/locked, incident/reflected, first/higher order wave components are quantified accurately by the PI and the energy transfer to super-harmonics is clearly evidenced. Moreover the results of the PI show clearly a very large increase in the phase speed of the higher order free waves on the lee side of the shelf, with increasing deviation from the linear behavior with increasing incident wave amplitude
Numerical study of wave loads on a submerged cylinder at low KC numbers
No full textThe study of wave-induced forces on circular cylinders is traditionally one of the fundamental topics related to the design of more complex marine and offshore structures. For this reason, a relevant amount of research has been developed, particularly in the case of vertical cylinders, with the goal to contribute to the understanding of the problem of wave and current loads. In this work the case of a submerged horizontal circular cylinder in regular wavy flow with incoming wave crests parallel to the cylinder axis is analyzed by means of numerical simulations and experimental data.
In particular, when the Keulegan Carpenter number is low enough and the diffraction parameter is well above the standard diffraction threshold, then the wave-body interactions leads to higher order loads that make the standard value of the inertia coefficient of Morison equation fail completely. The results of the computations are systematically compared with those from the experimental data obtained by one of the authors. The entire set of numerical experiments are conducted at Keulegan-Carpenter number regime up to KC = 2 and varying the depth of submergence of the cylinders to highlight the influence of the free surface. The spectral analysis evidences the effects of the submergence of the cylinder axis on the surface elevation and on the higher frequency components of the pressure at the cylinder surface
On the wavy flow past a weakly submerged horizontal circular cylinder at low Keulegan–Carpenter numbers
Full text linkThe 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
A Medium-Resolution Wave Hindcast Study Over the Central and Western Mediterranean Sea
No full textThe 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-art coastal and offshore engineering applications over this area make the adoption of medium or high resolutions 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 here presented have a 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
Lagrangian dispersion in coastal applications.
No full textThe role played by the turbulent mixing in the Lagrangian dispersion of tracers
in a tidally-driven, mid-latitude, shallow-water environment is here discussed.
The Eulerian carrying flow is supplied by a turbulent oscillating boundary
layer without and with rotation. In the purely oscillating case, the dispersion
of the particulate is stronger in the near-wall region and the diffusivity along
the main flow direction is larger than the other ones. For the value of Rossby
number herein considered, rotation strongly affects particle dispersion and
increases the mixing efficiency of particles within the whole fluid column, up
to the near surface region. Diffusion along the spanwise direction is comparable
to that in the streamwise one, and consequently the time needed to completely
homogenize the physical properties associated to the particulate is reduced
NUMERICAL AND EXPERIMENTAL INVESTIGATION ON THE WAVE-WAVE INTERACTION IN BREAKING AND NON-BREAKING FOCUSING WAVES
Full text linkThe modelling of large individual waves for the computation of loads on ships and offshore structures in
extreme weather conditions is still a challenging problem. Since the early 50s the predictions of loads on
fixed offshore structures and motions of compliant or sailing structures due to surface waves are
commonly made by computations on the basis of the statistical/spectral description of the sea elevation
and of a linearized response model. Quadratic Transfer Functions or fully non-linear methods are used
only in specific cases. The linear approach is recognized to work reasonably well for the so-called
operational conditions, assuming that hydrodynamic and dynamic nonlinear effects can be neglected. On
the other hand, it is also recognized that the modelling of large amplitude motions and the modelling of
waves in the so-called survival conditions, i.e. extreme wave conditions, cannot recast a linear approach.
In these conditions the wave-wave interaction plays a fundamental role (energy transfer, down-shift, etc) in
the actual deterministic or spectral representation of the wave/flow field and thus in the related loads on
the structure.
In the present paper the nonlinear aspects related to the behavior of steep focusing breaking and non-
breaking waves are analyzed by means of numerical simulations and new experiments. The experiments
are carried out at the wave flume of the Laboratory of Maritime Engineering (LABIMA) of the Dept. of Civil
and Environmental Engineering of the University of Florence. The computations are carried out at
Hydrodynamic and MetOcean Laboratory (HyMOLab) of the Dept. of Engineering and Architecture of the
University of Trieste. The paper focuses the attention on the comparison between the results obtained with
a state-of-art viscous flow simulation and laboratory experiments, with particular emphasis on the spectral
energy exchange between component waves of a non-breaking and breaking focusing wave train. This
study is carried out as part of the research project “OpenViewSHIP Development of an integrated
computational ecosystem for the hydrodynamic design of the hull-propeller system”, co-financed by Friuli
Venezia Giulia Region in the field of industrial application of open-source CFD and High Performance
Computing
Numerical Study of Unsteady Breaking Waves Induced by a Submerged Hydrofoil at Steady Forward Speed
Full text linkIn this work we analyse the features of the unsteady breaking of two dimensional free surface waves induced by a submerged
hydrofoil at steady forward speed. The study is conducted by means of numerical simulations with OpenFOAM: interFoam and
swenseFoam solvers being used as a computational framework for the free-surface treatment with the Volume Of Fluid (VOF)
and Level Set (LS) techniques respectively. Due to the strongly unsteady behaviour of the flow, the interest is here focused on
the spectral content of the free surface elevation. The results from two interface-capturing methods, VOF and LS are discussed
and compared with experimental data from the literature. The influence of the turbulence models on the free surface shape and
spectral content is also discussed. The final goal of the entire research work is the simulation of complex two-phase flows for
robust and fast engineering applications in the ship hydrodynamics and wave loads fields, including wave breaking phenomena
OPERATIONAL EFFICIENCY AT SEA OF A NEW OCEANOGRAPHIC VESSEL AT THE DESIGN STAGE: A DETAILED STUDY OVER THE CENTRAL MEDITERRANEAN SEA USING MEDIUM RESOLUTION HINDCAST WAVE DATA
No full textThe Italian Navy is currently developing a new hydro-oceanographic vessel for the Mediterranean sea and neighbouring areas. Among other requirements, the ship is asked to withstand a given sea state during the operations, measurements or transfer. A detailed theoretical investigation has been undertaken adopting state-of-art methodologies and numerical tools able to estimate the behaviour of the ship at sea over a grid of geographic cells belonging to the central Mediterranean sea. In particular, the seakeeping performance of the ship in terms of motion, velocity and acceleration at given positions on board has been analysed with incident wave data (directional spectra) derived from a hindcast wind-wave database developed at the University of Trieste. The database covers the central Mediterranean sea with cells of 60 nm x 60 nm and the wave data consist of hourly wind-wave time series over the period 1989-2008.
The paper presents the overall methodology, with some hints of the met-ocean and seakeeping models. The results obtained by the application of the procedure to a preliminary design of the ship and hull shape still under development are presented in details
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