1,721,093 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
A numerical model for fluid-particle flows
No full textIn this paper a numerical algorithm for fluid-particle flow computation is presented. The mathematical formulation is based on the averaged continuum model, in which the effects of particles are taken into account in terms of an effective viscosity. The dispersed phase equation closure is based on sedimentation and shear-induced self-diffusion effects. The present work is the first step in the development of a general model for the simulation of the interaction between waves or currents and bottom sediment. Namely, the proposed approach allows the study of sediment transport and the evolution of the bottom shape without the need for curvilinear coordinate systems and related step-by-step regridding. In fact, pure liquid regions, suspension regions (more or less concentrated) as well as bottom sediment are studied by a unique model with a proper effective viscosity (hindrance effect and Bingham viscoplastic model). Preliminary numerical results have been obtained for 2D Bingham flow in a driven cavity by a finite difference method
An immersed boundary approach for high order weighted essentially non-oscillatory schemes
No full textA new immersed boundary approach for high order Weighted Essentially non-Oscillatory (WENO) schemes is proposed. The schemes is based on the main ideas from both the general immersed boundary algorithms and the level-set approach and can be easily applied to both finite difference and finite volume formulation. Although formally only second order accurate, numerical tests prove that the use of higher order approximation for the Eulerian fluxes can be very convenient to capture flow details and to obtain low uncertainty also with very coarse grids
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 model for fluid-particle flows
No full textIn this paper a numerical algorithm for fluid-particle flow computation is presented. The mathematical formulation is based on the averaged continuum model, in which the effects of particles are taken into account in terms of an effective viscosity. The dispersed phase equation closure is based on sedimentation and shear-induced self diffusion effects. The present model is suitable for the simulation of the interaction between waves or currents and bottom sediment. This approach allows the study of sediment transport and the evolution of the bottom shape without the need of curvilinear coordinate systems and the related step-by-step regridding. In fact, pure liquid regions, suspension regions (more or less concentrated) as well as bottom sediment are studied by a unique model with a proper effective viscosity (hindrance effect and Bingham visco-plastic model). Preliminary numerical results have been obtained for 2D Bingham flow in a driven cavity by a finite difference method
Modelli di pianificazione finanziaria, in La consulenza finanziaria. Regolamentazione, modelli di servizio e pianificazione finanziaria
No full textUn passaggio essenziale per lo sviluppo del servizio di consulenza finanziaria nel private banking è rappresentato dalla ricerca di nuove modalità di gestione della ricchezza incentrate sull’utilizzo delle tecniche proprie dell’Asset and Liability Management. L’adattamento al private banking delle tecniche di ottimizzazione di portafoglio proprie degli investitori istituzionali, consente di offrire ai clienti private soluzioni di investimento e di consulenza nell’allocazione delle risorse finanziarie che rispondono maggiormente alle esigenze degli stessi. Ciò in quanto tali tecniche sono state elaborate per poter tenere in considerazione specifici vincoli ed obiettivi connessi all’orizzonte temporale di investimento, nel processo di costruzione del portafoglio. L’ALM nel private banking deve essere funzionale, in primo luogo, alla individuazione della migliore allocazione strategica in funzione degli obiettivi degli investitori e dei rispettivi vincoli; allo stesso tempo si rende necessario attuare una gestione di vincoli ed obiettivi di breve termine, che non sono necessariamente considerati nel processo di ottimizzazione dell’Asset and Liability Management, il quale per sua predisposizione naturale si concentra su obiettivi di lungo termine. Analizzato in questa prospettiva, l’Asset and Liability Management pone le basi per sviluppare una diversa cultura di controllo del rischio, incentrata su nuovi indici e strumenti, pienamente integrata nella complessità del mondo finanziario e, al contempo, in grado di conciliare l’orientamento al lungo periodo proprio di tale modello gestionale con l’attenzione ai rendimenti dei breve termine
A two-step godunov-type scheme for the euler equations
No full textA second-order Godunov-type scheme for the Euler equations in conservation form is derived. The method is based on the ENO formulation proposed by Harten et al. The fundamental difference lies in the use of a two-step scheme to compute the time evolution. The scheme is TVD in the linear scalar case, and gives oscillation-free solutions when dealing with nonlinear hyperbolic systems. The admissible time step is twice that of classical Godunovtype schemes. This feature makes it computationally cheaper than one-step schemes, while requiring the same computer storage. © 1991 Kluwer Academic Publishers
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
Aerodynamic characterization of rolling wheels at high Reynolds numbers
No full textComplex and unstable phenomena, such as large-scale boundary layer separations, recirculation zones, and three-dimensional vortical structures, characterize the flow around rotating cylinders. These phenomena are even more interesting when the cylinder is rolling on a solid surface, like a wheel on the ground, because the knowledge of the unsteady features of the wake matters for the aerodynamic design of race cars. For this purpose, we investigated the flow past an isolated wheel in different configurations. We focus on the effect of the aspect ratio and the Reynolds number on the wake for values that reflect the actual operating conditions for a race car. We validated our Detached-Eddy simulation by comparing the results with particle image velocimetry measurements. Then, we analyzed the flow by exploiting proper orthogonal decomposition to identify the turbulence characteristics. The simulation showed excellent agreement with the available experimental data and helped highlight the physics of the wake downstream rolling wheels in different operating conditions
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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