- Rome, Italy
The investigation of the evolution of the pipe/sea-bottom configuration has a large relevance for pipeline design as the occurrence and persistence for a certain period of a free-span causes the accumulation of fatigue on the pipeline... more
The investigation of the evolution of the pipe/sea-bottom configuration has a large relevance for pipeline design as the occurrence and persistence for a certain period of a free-span causes the accumulation of fatigue on the pipeline which can lead to unacceptable damage. Of great importance is, therefore, the possibility of accurately predicting both generation and evolution of dangerous scour-induced free-spans. The onset of scouring is intimately connected with the dynamics of the bottom boundary layer and with the localized sediment transport. To this purpose various numerical tools are becoming available which allow for an accurate quantitative assessment of the local flow-sediment-pipe interaction. Among them we find all the models which permit prediction of the dynamics of two-phase flows, like the Level Set and the SPH methods. We here focus on evaluation of the performances of a hydro-morpho-dynamic model, based on the former approach, for use in pipe-soil interaction calc...
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Abstract In the present paper the study of the two-dimensional flow field past a circular cylinder for Reynolds number up to 5 · 10 5 is addressed. A Lagrangian particle method approach has been exploited and the simulations have been... more
Abstract In the present paper the study of the two-dimensional flow field past a circular cylinder for Reynolds number up to 5 · 10 5 is addressed. A Lagrangian particle method approach has been exploited and the simulations have been performed with high spatial resolutions in order to resolve all the main vortical scales. Long simulation time evolutions have been performed in order to get the vortex shedding dynamics as well as the Fourier analysis of the loads. The adopted numerical method allows to discuss both local (boundary layer and near wake dynamics) and global (far wake dynamics) aspects of the problem.The fundamental aspects related to the different identified flow states as well as the drag crisis mechanism are investigated.
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The Smoothed Particle Hydrodynamics (SPH) method, often used for the modelling of the Navier–Stokes equations by a meshless Lagrangian approach, is revisited from the point of view of Large Eddy Simulation (LES). To this aim, the LES... more
The Smoothed Particle Hydrodynamics (SPH) method, often used for the modelling of the Navier–Stokes equations by a meshless Lagrangian approach, is revisited from the point of view of Large Eddy Simulation (LES). To this aim, the LES filtering procedure is recast in a Lagrangian framework by defining a filter that moves with the positions of the fluid particles at the filtered velocity. It is shown that the SPH smoothing procedure can be reinterpreted as a sort of LES Lagrangian filtering, and that, besides the terms coming from the LES convolution, additional contributions (never accounted for in the SPH literature) appear in the equations when formulated in a filtered fashion. Appropriate closure formulas are derived for the additional terms and a preliminary numerical test is provided to show the main features of the proposed LES-SPH model.
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ABSTRACT The multi-fluid SPH formulation by Grenier et al. (2009) is extended to study practical problems where bubbly flows play an important role for production processes of the offshore industry. Since these flows are dominated by... more
ABSTRACT The multi-fluid SPH formulation by Grenier et al. (2009) is extended to study practical problems where bubbly flows play an important role for production processes of the offshore industry. Since these flows are dominated by viscous and surface tension effects, the proposed formulation includes specific models of these physical effects and validations on specific benchmark test cases are carefully performed. The numerical outputs are validated against analytical and numerical reference solutions, and accuracy and convergence of the proposed numerical model are assessed. This model is then used to simulate viscous incompressible bubbly flows of increasing complexity. These flows include the evolution of isolated bubbles, the merging of two bubbles, and the separation process in a bubbly flow. In each case, results are compared to reference solutions and the influence of the Bond number on these interfacial flow evolutions is investigated in detail.
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Abstract—The diffusive weakly-compressible SPH scheme de-scribed in Antuono et al.[1](hereinafter denoted as δ-SPH model) has been challenged in the analysis of impacts against structures generated by dam-break flows. Specifically, the 3D... more
Abstract—The diffusive weakly-compressible SPH scheme de-scribed in Antuono et al.[1](hereinafter denoted as δ-SPH model) has been challenged in the analysis of impacts against structures generated by dam-break flows. Specifically, the 3D SPHERIC benchmarks number 1 and 2 have been studied as well as a novel 2D test case characterized by complex solid boundary profiles. In all the test cases the solid boundaries have been modelled through the boundary particle technique described in Colagrossi et ...
An SPH method with numerical diffusive terms will be used to simulate 2D gravity waves generated by a wave maker and propagating into a basin. A large number of simulations will be performed for different wave steepness and height-todepth... more
An SPH method with numerical diffusive terms will be used to simulate 2D gravity waves generated by a wave maker and propagating into a basin. A large number of simulations will be performed for different wave steepness and height-todepth ratio. To validate the SPH model, the numerical results will be compared with a BEM Mixed-Eulerian-Lagrangian solver. Finally, a measure of numerical damping and shift of wave trains will be provided for different spatial resolutions.
SUMMARY. A novel technique based on ghost-fluid approach has been defined to enforce proper boundary conditions along solid profiles in Smoothed Particle Hydrodynamics schemes (SPH). The present work extends the classic ghost fluid method... more
SUMMARY. A novel technique based on ghost-fluid approach has been defined to enforce proper boundary conditions along solid profiles in Smoothed Particle Hydrodynamics schemes (SPH). The present work extends the classic ghost fluid method (see, for example,[4]) used for inviscid flows to simulate viscous laminar flows. The main idea is to couple the technique proposed by De Leffe (2011)[7] where a proper ghost fluid field is defined for each SPH differential operator, to the mirroring technique proposed by [17]. ...
Introduction. Common problems in naval hydrodynamic and coastal engineering are the studies of general internal and external flows. Classic methods of solution have to face break down when dealing with large deformations and... more
Introduction. Common problems in naval hydrodynamic and coastal engineering are the studies of general internal and external flows. Classic methods of solution have to face break down when dealing with large deformations and fragmentations of the air-water interface. Possible algorithms of solutions can be based on fixed-grid solvers of the fluid dynamic equations coupled with techniques to capture the interface evolution, like
Abstract The study of an airfoil at low Reynolds number regime was found to be a typical problem where the inception of bifurcations leads the flow evolution from a stationary or periodic behaviour to a purely chaotic one. The present... more
Abstract The study of an airfoil at low Reynolds number regime was found to be a typical problem where the inception of bifurcations leads the flow evolution from a stationary or periodic behaviour to a purely chaotic one. The present work extends the present literature where numerical investigations of the flow field past two-dimensional symmetric airfoils were performed by fixing the incidence and changing the Reynolds number (Re). Conversely, here the Reynolds number was fixed at Re = 1000 and the angle of attack (AoA) varied from 0∘ to 90∘. Different flow Modes and bifurcation phenomena are detected and, in addition, new non-linear phenomena are also identified. The latter consists of tripling period regimes and its bifurcations up to chaotic conditions. Moreover, for increasing AoA, an inverse transition from chaotic to periodic regimes is also observed. An in-depth study of these different flows is provided and new links with the time evolution of the forces acting on the airfoil, as well as with the wake structures observed, are offered. Phase portrait diagrams are evaluated through the time records of the lift force in order to highlight the eventual presence of limit cycles in the solutions. Accurate numerical simulations are performed with a Vortex Particle Method in a two-dimensional framework, using high spatial resolutions to solve in detail both the near-field and the far-field regions.
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Abstract The present paper is dedicated to the post-processing analysis of the time pressure signals when a weakly-compressible Smoothed Particle Hydrodynamics (SPH) model is used to simulate free-surface flows. Indeed, it is well known... more
Abstract The present paper is dedicated to the post-processing analysis of the time pressure signals when a weakly-compressible Smoothed Particle Hydrodynamics (SPH) model is used to simulate free-surface flows. Indeed, it is well known in literature that this particle model is characterized by the occurrence of high-frequency acoustic noise making the pressure signals unusable for engineering applications. This non-physical pressure noise is both linked to the weakly-compressible approach and to numerical inaccuracies. To reduce the latter, different enhanced SPH models have been developed in recent years. Nonetheless, even using accurate and stable SPH schemes when simulating water impacts, acoustic signals can be generated and, since the speed of sound used in the model is not the real one, these acoustic components need to be filtered in a suitable way. Indeed, for low Mach number regime the solution of the compressible Navier-Stokes equation can be decomposed in an incompressible solution plus an acoustic perturbation. In this work, a filtering technique based on Wavelet Transform is presented. In the proposed procedure the acoustic frequencies are individuated through a preliminary analysis which takes into account: the adopted speed of sound, the spatial resolutions and the fluid domain configuration. The filtering technique to remove the acoustic components is finally applied to several test-cases ranging from prototype problems to more practical applications such as a violent sloshing flow.
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Two-dimensional monophasic flow past a circular cylinder intersecting or close to a free surface at Reynolds 180 is numerically investigated using the Smoothed Particle Hydrodynamics (SPH) method. The wake behaviour for a range of... more
Two-dimensional monophasic flow past a circular cylinder intersecting or close to a free surface at Reynolds 180 is numerically investigated using the Smoothed Particle Hydrodynamics (SPH) method. The wake behaviour for a range of conditions with Froude numbers between 0.3 and 2.0, a gap ratio of 0.55 and for a half-submerged cylinder are studied. The SPH technique allows for a non-diffusive computation of the free surface evolution, even while breaking and fragmentation may occur. Vorticity shed by the cylinder, vortex generation due to free surface breaking, mixing processes, and drag and lift coefficients behaviour are discussed. It has been found that, for certain Froude numbers and for the analysed submergence ratio, a vorticity layer remains spatially localized between the cylinder and the free surface and a large recirculating wake area develops, which eventually gets detached after several shedding cycles, being advected downstream, a previously unreported form of wake instability, to the authors’ knowledge. This behaviour is blocked when the cylinder is intersecting the free surface.Copyright © 2015 by ASME
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Sloshing is an important issue for LNG tanks and in general when partially filled tanks are on-board of a vessel. This resonance phenomenon may be connected with complex motions of the filled liquid that can couple with the ship motions... more
Sloshing is an important issue for LNG tanks and in general when partially filled tanks are on-board of a vessel. This resonance phenomenon may be connected with complex motions of the filled liquid that can couple with the ship motions and can represent a danger for the tank strucure and for the stability of the ship. In this context, it is very important to identify the possible scenarios associated with the sloshing. Present analysis is a part of the research activities reported in Colagrossi et al. (2004) and Lugni et al. (2005) and uses both 2D sloshing experiments performed in a rectangular tank L = H = 1 m long and b = 0:1 m wide (see left sketch in figure 1), and the 2D SPH solver (Colagrossi and Landrini 2003 and Colagrossi 2005). In particular it is the logical continuation of the experimental investigation presented in Colagrossi et al. (2004). There, sloshing phenomena in the case of filling depth h=L = 0:35, i.e. slightly higher than the critical value h=L = 0:337 (Falt...
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A smoothed particle hydrodynamics model with numerical diffusive terms, hereinafter referred to as δ-SPH [1] is used to analyze violent water flows. The boundary conditions on solid surfaces of arbitrary shape are enforced with a new... more
A smoothed particle hydrodynamics model with numerical diffusive terms, hereinafter referred to as δ-SPH [1] is used to analyze violent water flows. The boundary conditions on solid surfaces of arbitrary shape are enforced with a new technique based on fixed ghost particles. The violent impacts studied result from dam-break water flows striking obstacles of different shapes. The numerical results are
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The study of energetic free-surface flows is challenging because of the large range of interface scales involved due to multiple fragmentations and reconnections of the air-water interface with the formation of drops and bubbles. Because... more
The study of energetic free-surface flows is challenging because of the large range of interface scales involved due to multiple fragmentations and reconnections of the air-water interface with the formation of drops and bubbles. Because of their complexity the investigation of such phenomena through numerical simulation largely increased during recent years. Actually, in the last decades different numerical models have been developed to study these flows, especially in the context of particle methods. In the latter a single-phase approximation is usually adopted to reduce the computational costs and the model complexity. While it is well known that the role of air largely affects the local flow evolution, it is still not clear whether this single-phase approximation is able to predict global flow features like the evolution of the global mechanical energy dissipation. The present work is dedicated to this topic through the study of a selected problem simulated with both single-phase and two-phase models. It is shown that, interestingly, even though flow evolutions are different, energy evolutions can be similar when including or not the presence of air. This is remarkable since, in the problem considered, with the two-phase model about half of the energy is lost in the air phase while in the one-phase model the energy is mainly dissipated by cavity collapses.
The present study refers to a very peculiar phenomenon that can appear during the sloshing flow in a partially filled tank: the flip-trough event. A 2D sloshing flow inside a tank, which is forced to oscillate horizontally, is studied... more
The present study refers to a very peculiar phenomenon that can appear during the sloshing flow in a partially filled tank: the flip-trough event. A 2D sloshing flow inside a tank, which is forced to oscillate horizontally, is studied experimentally. From the experimental point of view a novel free-surface tracking is used to characterize the details of the flip- through dynamics while impulsive wave loads are measured by using an ad hoc distributions of miniaturized pressure sensors. The extremely local character of the phenomenon investigated is used to highlight capabilities and limits of the numerical algorithms proposed: a Level Set technique to solve the Navier-Stokes equations, and a SPH method to solve the Euler equations. A suitable domain decomposition strategy is proposed to study the evolution of the air- bubble entrapped during the development of the flip- through event
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... This SPH formulation presents also similarities with one proposed by Hu & Adams4 to studymulti-fluid flows, in enhanced version1. ... Mech. Engrg. 180,97 115, (1999) [4] XY Hu and NA Adams A multi-phase SPH method for macroscopic... more
... This SPH formulation presents also similarities with one proposed by Hu & Adams4 to studymulti-fluid flows, in enhanced version1. ... Mech. Engrg. 180,97 115, (1999) [4] XY Hu and NA Adams A multi-phase SPH method for macroscopic and meso-scopic flows, J. Comput. ...
In this work two particle methods are studied in the context of viscous flows. The first one is a Vortex Particle Method, called Diffused Vortex Hydrodynamics (DVH), recently developed to simulate complex viscous flows at medium and high... more
In this work two particle methods are studied in the context of viscous flows. The first one is a Vortex Particle Method, called Diffused Vortex Hydrodynamics (DVH), recently developed to simulate complex viscous flows at medium and high Reynolds regimes. This method presents some similarities with the SPH model and its Lagrangian meshless nature, even if it is based on a different numerical approach. Advantages and drawbacks of the two methods have been previously studied in Colagrossi et al. [1] from a theoretical point of view and in Rossi et al. [2], where these particle methods have been tested on selected benchmarks. Further investigations are presented in this article highlighting analogies and differences between the two particle models.
In the present paper the study of the two-dimensional flow field past a circular cylinder for Reynolds number up to 5 · 10 5 is addressed. A Lagrangian particle method approach has been exploited and the simulations have been performed... more
In the present paper the study of the two-dimensional flow field past a circular cylinder for Reynolds number up to 5 · 10 5 is addressed. A Lagrangian particle method approach has been exploited and the simulations have been performed with high spatial resolutions in order to resolve all the main vortical scales. Long simulation time evolutions have been performed in order to get the vortex shedding dynamics as well as the Fourier analysis of the loads. The adopted numerical method allows to discuss both local (boundary layer and near wake dynamics) and global (far wake dynamics) aspects of the problem. The fundamental aspects related to the different identified flow states as well as the drag crisis mechanism are investigated.
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The Smoothed Particle Hydrodynamics (SPH) method, often used for the modelling of the NavierStokes equations by a meshless Lagrangian approach, is revisited from the point of view of Large Eddy Simulation (LES). To this aim, the LES... more
The Smoothed Particle Hydrodynamics (SPH) method, often used for the modelling of the NavierStokes equations by a meshless Lagrangian approach, is revisited from the point of view of Large Eddy Simulation (LES). To this aim, the LES ltering procedure is recast in a Lagrangian framework by dening a lter that moves with the positions of the uid particles at the ltered velocity. It is shown that the SPH smoothing procedure can be reinterpreted as a sort of LES Lagrangian ltering, and that, besides the terms coming from the LES convolution, additional contributions (never accounted for in the SPH literature) appear in the equations when formulated in a ltered fashion. Appropriate closure formulas are derived for the additional terms and a preliminary numerical test is provided to show the main features of the proposed LES-SPH model.
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This work is dedicated to the energy decomposition analysis of a viscous free-surface flow. In the presence of a free surface, the viscous dissipation for a Newtonian liquid can be decomposed into two terms: an enstrophy component and a... more
This work is dedicated to the energy decomposition analysis of a viscous free-surface flow. In the presence of a free surface, the viscous dissipation for a Newtonian liquid can be decomposed into two terms: an enstrophy component and a free-surface deformation component. The latter requires the evaluation of volume and surface integrals in the meshless framework. The analysis is based on the weakly compressible smoothed particle hydrodynamics formalism. The behavior of the energy terms is studied in standing wave problems by changing the viscosity and the wave amplitude. Finally, an analysis of a complex shallow water breaking wave case is provided. It is shown that in presence of intense breaking phenomena the two energy components are always comparable, whereas generally the free surface component is dominant on the viscous dissipation of gravity waves.