177,284 research outputs found
On the application of the single-phase level set method to naval hydrodynamic flows
No full textThe application of the single-phase level set approach to the numerical simulations of three-dimensional free surface flows around complex geometries, at both non-breaking and breaking regimes is presented. In this approach only the liquid phase is simulated and the level set function is used as tracking device to locate the free surface position. The extrapolation of the solution in the dummy points in the gaseous phase is such that second-order accuracy is maintained also in the points adjacent to the free surface; the time evolution of the level set function and the re-initialization step have been merged so to get a function which is a distance function everywhere, and satisfies, at the same time, the kinematic condition on the free surface. The implementation of this technique into a general purpose Reynolds averaged Navier-Stokes (RANS) equations solver developed at INSEAN [Di Mascio A, Broglia R, Favini B. A Second Order Godunov-type Scheme for Naval Hydrodynamics. Kluwer Academic/Plenum Publishers; 2001, p. 253-61], is described in details; capabilities of the algorithm in dealing with non-breaking and breaking flows in the naval hydrodynamic context will be demonstrated by using a submerged hydrofoil and two different ship hulls in straight course as test cases. Comparisons with both experimental data and numerical surface fitting computations are presented; convergence properties of the algorithm, as well as validation and verification assessment will be also discussed. © 2006 Elsevier Ltd. All rights reserved
Liriope muscari (Cultivated) 4
No full textLiriope muscari, whole plant. Family Liliaceae, Subclass Liliidae. Origin: Cultivated
Modal analysis of the wake past a marine propeller
No full textModal decomposition techniques are used to analyse the wake field past a marine propeller achieved by previous numerical simulations (Muscari et al. Comput. Fluids, vol. 73, 2013, pp. 65-79). In particular, proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) are used to identify the most energetic modes and those that play a dominant role in the inception of the destabilization mechanisms. Two different operating conditions, representative of light and high loading conditions, are considered. The analysis shows a strong dependence of temporal and spatial scales of the process on the propeller loading and correlates the spatial shape of the modes and the temporal scales with the evolution and destabilization mechanisms of the wake past the propeller. At light loading condition, due to the stable evolution of the wake, both POD and DMD describe the flow field by the non-interacting evolution of the tip and hub vortex. The flow is mainly associated with the ordered convection of the tip vortex and the corresponding dominant modes, identified by both decompositions, are characterized by spatial wavelengths and frequencies related to the blade passing frequency and its multiples, whereas the dynamic of the hub vortex has a negligible contribution. At high loading condition, POD and DMD identify a marked separation of the flow field close to the propeller and in the far field, as a consequence of wake breakdown. The tonal modes are prevalent only near to the propeller, where the flow is stable; on the contrary, in the transition region a number of spatial and temporal scales appear. In particular, the phenomenon of destabilization of the wake, originated by the coupling of consecutive tip vortices, and the mechanisms of hub-tip vortex interaction and wake meandering are identified by both POD and DMD
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
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
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)
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