1,721,011 research outputs found
A Model for Spilling Breaking in RANSE Simulations
No full textA numerical model for the simulation of two-dimensional spilling breaking waves, derived from the Cointe and Tulin's theory of steady breakers, is described. With respect to the original theory, we use a new expression, based on experimental data, of the breaker height. The model has been implemented in a RANSE code, developed for the study of ship flows, through a modification in the boundary conditions. This yields an effective but simple way to reproduce the breaker influence on the underlying flow. The resulting code has been used for the simulation of the flow past a submerged hydrofoil. The numerical results are compared with the experimental data obtained by Duncan
Numerical modeling of breaking waves generated by a ship's hull
No full textA new model for the simulation of spilling breaking waves in naval flows is presented. The hydrostatic pressure is used in order to mimic the weight of the breaker on the underlying flow, as in the model of Cointe and Tulin, whereas the algorithm for detecting the breaking inception and the definition of its geometry are completely new and are suitable for the simulation of three-dimensional flows around ships' hulls. The model has been implemented in a finite-volume code developed for naval flows, and its performances have been validated against experimental data for a submerged profile, an S60 hull in drift motion, and the US Combatant DTMB 5415 model on a straight course
A model for the simulation of steady spilling breaking waves
No full textA numerical model for the simulation of two-dimensional spilling breaking waves is described. The model is derived from Cointe and Tulin's theory of steady breakers (Cointe & Tulin 1994), although some important changes have been introduced in order to obtain a stable algorithm when coupled with steady-state Reynolds averaged Navier-Stokes equations (RANSE) solvers. In particular, the shape of the breaker and its relation with the following wave height differ from the original model, and moreover, additional conditions for the tangential stress and the turbulent viscosity are proposed. The model has been implemented in a RANSE code, developed for the study of ship flows, through a modification in the free-surface boundary conditions below the breaker. This yields a simple but effective way to reproduce the breaker influence on the underlying flow. The algorithm was used for the simulation of the flow past a submerged hydrofoil. The numerical results are compared with the experimental data by Duncan (1983)
A local model for the simulation of two-dimensional spilling breaking waves
No full textA numerical model for the simulation of two dimensional spilling breaking waves is described. It is derived from a previous model which, in turn, takes its underlying ideas from the Cointe and Tulin theory of steady breakers. With respect to the former model, the present one is local, i.e., the inception, extension, and geometry of the breakers are determined through the local shape of the water surface. The model has been implemented in a RANSE code, which was developed for the simulation of ship flows, through a modification in the boundary conditions. This yields a simple and effective way to reproduce the breaker's influence on the underlying flow. The resulting code has been used to simulate the flow past a submerged hydrofoil. The numerical results are compared with those of the previous model and with the experimental data obtained by Duncan
Ship underwater noise assessment by the acoustic analogy, part III: Measurements versus numerical predictions on a full-scale ship
No full textThe acoustic analogy represents a powerful and versatile approach, able to numerically predict the noise generated by a body moving in a fluid. It is widely used to provide essential indications about the aeroacoustic behavior of aircraft and helicopters (even at a design stage) and, eventually, to pursue effective strategies aimed at desirable reduction and/or control of noise. Nevertheless, applications in the area of hydroacoustics and in the prediction of ship underwater noise are very rare. In this paper, the potential of the acoustic analogy is directly tested on a large ferry, for which a measurement campaign at sea was performed. In spite of the complexity of the tested configuration [the ship mounts two contracted and loaded tip (CLT) propellers located ahead of two rudders, and its hull is characterized by a rather elongated skeg] and the many variables not taken into account in the numerical simulation (such as the contribution from machinery noise and the probable occurrence of tip vortex cavitation), the agreement between the measured and computed noise spectra is quite satisfactory. The analysis suggests many interesting features of the ship hydroacoustic field: the dominant role played by nonlinear sources far from the body and the relevance of scattering effects from the hull surface. Furthermore, the scattered pressure seems to contribute to alter the frequency content of the resulting signatures with respect to the blade passage frequencies. Finally, an overview of future developments and applications of this numerical approach for marine/maritime problems is presented. © 2013 JASNAOE
Numerical study of confined water effects on a self-propelled submarine in steady manoeuvres
No full textThis paper deals with the analysis of the confined water effects on the manoeuvring capabilities of a submarine. The analysis is carried out by using numerical simulations based on the RANS equations. The problem under consideration is an advancing submarine with constant speed and straight path at zero and non-zero drift/pitch angles, in open water, close to bottom and close to free surface conditions. The features of the flow around the submarine are described in terms of velocity and pressure fields; the computed force and moment coefficients are presented and compared with INSEAN measurements. Copyright © 2006 by The International Society of Offshore and Polar Engineers
Analysis of the roll decay motion for a patrol boat by URANS simulations
No full textThe simulations of the flow around a vessel of the Italian Navy in free roll decay have been carried out by the numerical solution of the Reynolds Averaged Navier-Stokes equations. The focus is on the analysis of the roll motion coefficients (damping and period of oscillations) at different Froude and Reynolds numbers. To this aim, numerical simulations were carried out at three different speeds, with corresponding Froude numbers equal to 0.160, 0.227 and 0.337, and Reynolds numbers ranging from 4.073 106 to 1.300 10 7 at model scale. Computations were carried out by means of an in-house unsteady RANS solver; the scheme is based on a finite volume discretization, and it is globally second order accurate. The free surface is handled by means of a suitable single phase level set algorithm; moreover, Chimera overlapping grid capabilities have been implemented in the code, which has been also efficiently parallelized. An analysis of the roll motion, longitudinal and lateral forces and roll moment is carried out for the different speeds considered. A preliminarily grid convergence analysis is also performed. Copyright © 2009 by ASME
A Level Set Approach for Naval Applications
No full textA level set approach for the numerical simulation of high Reynolds number turbulent flows with a free surface is presented. The algorithm is based on a general pseudo-compressible Reynolds Averaged Navier-Stokes Equations (RANSE) solver, already used in conjunction with a surface-fitting approach for the numerical simulation of steady flows past ship hulls. The RANSE solver is coupled with a non-standard level set approach, the original algorithm having been modified in order to gain increased resolution in the nearby of the free surface. To this end, only the liquid phase is simulated; the level set function is used only as a tracking device to locate the actual position of the free surface. Moreover, the solution in the air region is extrapolated in a way that ensures second order accuracy also in the free surface region. Some numerical results for the flow around a submerged profile and two ship hulls are shown
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