Papers by michele la rocca
Journal of Fluid Mechanics
Droplets impinging on solid surfaces, as well as the countless varieties of the resulting possibl... more Droplets impinging on solid surfaces, as well as the countless varieties of the resulting possible dynamics, are found frequently in both natural and industrial environments. Among such dynamics, the contact time with the surface, the amount of deformation and the occurrence of breaking induced by geometrical singularities of the solid surface are key aspects in a wide range of applications. We report the results of an extensive experimental activity investigating the capability of liquid droplets to jump over a gap while sliding/rolling over a hydrophobic solid plane. These drops impact on the downstream sharp edge of the gap and undergo the amount of deformation that allows them to climb the edge. We ascribe this unique behaviour to the transformation of rotational momentum into linear momentum. Such conversion can take place only if the right amount of deformation occurs upon impact. Indeed, within the explored range of Weber number $\left (0.5\lesssim {We}\lesssim 40 \right )$ ,...
In this paper the dynamics of a layered fluid system, constituted by two superimposed immiscible ... more In this paper the dynamics of a layered fluid system, constituted by two superimposed immiscible liquid layers inside a moving container, is considered. Such layered fluid system presents two moving boundaries: the separation surface and the free surface. The motion imposed to the container an oscillating rotation with given amplitude and frequency generates waves on the moving surfaces, whose dynamics is analysed by means of a suitable visualisation device. Several wave configurations are obtained by varying the angular frequency of the exciting motion and some of them compared with those obtained by numerical simulations.
The aim of this paper is the investigation of gravity currents moving on both smooth and rough be... more The aim of this paper is the investigation of gravity currents moving on both smooth and rough beds by laboratory experiments. Gravity currents were produced in a Perspex tank of rectangular cross-section by lock exchange release experiments. The tank is divided into two parts by a sliding gate: one filled with tap water and the other one filled with salt water to the same height. Nine experiments were performed varying both the bed roughness and the initial density of the gravity current. All the experiments were recorded by a camera and an image analysis technique was applied to measure the spacetime evolution of the gravity current's profile. For the experiments with a smooth bed three different phases were observed in the gravity currentās dynamics: a first slumping or constant speed phase; a second self-similar phase, in which the front speed decreased as t, where t is the time measured from release; a third viscous phase, in which the front velocity decreased as t. In the ...
International Journal of Offshore and Polar Engineering, 2013
The aim of this work is to carry out a preliminary assessment of the capacity of a two-layer Shal... more The aim of this work is to carry out a preliminary assessment of the capacity of a two-layer Shallow Water-equivalent Lattice Boltzmann Method formulation (SWLBM) to simulate the interaction of a gravity current with an emerging cylinder. The Immersed Boundary technique is employed here as it facilitates the representation of complex emerging obstacles in the SWLBM framework. The assessment is achieved by means of a comparison with numerical results obtained from a fully 3D Navier-Stokes (NS) model. The latter is first validated against both experimental and theoretical benchmark data and then used to obtain a reference numerical solution for the considered flow. The benchmark cases are 2D and an axisymmetric gravity current. Numerical results show a satisfactory agreement with the benchmark data (theoretical for the 2D and experimental for the axisymmetric gravity current). Finally, the interaction of a gravity current with a cylindrical obstacle is considered. The 3D NS model is u...
Frontiers in Earth Science, 2020
From the past few years, research has gained an ardent pace in the field of fault detection and d... more From the past few years, research has gained an ardent pace in the field of fault detection and diagnosis in induction motors. In the current scenario, software is being introduced with diagnostic features to improve stability and reliability in fault diagnostic techniques. Human involvement in decision making for fault detection is slowly being replaced by Artificial Intelligence techniques. In this paper, a brief introduction of eccentricity fault is presented along with their causes and effects on the health of induction motors. Various indices used to detect eccentricity are being introduced along with their boundary conditions and their future scope of research. At last, merits and demerits of all indices are discussed and a comparison is made between them.
Transport in Porous Media, 2020
The employment of 2D models to investigate the properties of 3D flows in porous media is ubiquito... more The employment of 2D models to investigate the properties of 3D flows in porous media is ubiquitous in the literature. The limitations of such approaches are often overlooked. Here, we assess to which extent 2D flows in porous media are suitable representations of 3D flows. To this purpose, we compare representative elementary volume (REV) scales obtained by 2D and 3D numerical simulations of flow in porous media. The stationarity of several quantities, namely porosity, permeability, mean and variance of velocity, is evaluated in terms of both classical and innovative statistics. The variance of velocity, strictly connected to the hydrodynamic dispersion, is included in the analysis in order to extend conclusions to transport phenomena. Pore scale flow is simulated by means of a Lattice Boltzmann model. The results from pore scale simulations point out that the 2D approach often leads to inconsistent results, due to the profound difference between 2D and 3D flows through porous medi...
Severe and sudden events like flash floods are considered to be one of the most hazardous environ... more Severe and sudden events like flash floods are considered to be one of the most hazardous environmental disasters. Therefore, predicting the whole process of flooding is fundamental to prevent urban damages. In this context, the simulation of flash floods is an important tool to analyse the flow processes in order to find solutions to the problem. In this work, a case study of the flash flood event of 9th March 2014 in the city of El Gouna in Egypt was carried out using the Hydroinformatics Modeling System (hms), a two-dimensional (2D) shallow water model developed at the Chair of Water Resources Management and Modeling of Hydrosystems, Technische UniversitaĢt Berlin. The flooding processes are simulated in great detail on unstructured grids. The aim of this work is to investigate the flow field around the settlement of the study area, when structures such as storage basins and dams are adopted as protection measures for the city. Different scenarios are analyzed to find out the mos...
Physical Review E, 2019
The dynamic interaction of complex fluid interfaces is highly sensitive to near-contact interacti... more The dynamic interaction of complex fluid interfaces is highly sensitive to near-contact interactions occurring at the scale of ten of nanometers. Such interactions are difficult to analyse because they couple selfconsistently to the dynamic morphology of the evolving interface, as well as to the hydrodynamics of the interstitial fluid film. In this work, we show that, above a given magnitude threshold, near-contact interactions trigger non-trivial micro-vorticity patterns, which in turn affect the effective near-contact interactions, giving rise to persistent fluctuating ripples 1
Computers & Fluids, 2018
We present a regularized version of the color gradient lattice Boltzmann (LB) scheme for the simu... more We present a regularized version of the color gradient lattice Boltzmann (LB) scheme for the simulation of droplet formation in microfluidic devices of experimental relevance. The regularized version is shown to provide computationally efficient access to Capillary number regimes relevant to droplet generation via microfluidic devices, such as flow-focusers and the more recent microfluidic step emulsifier devices.
Physics of Fluids, 2017
We present an entropic version of the lattice Boltzmann pseudo-potential approach for the simulat... more We present an entropic version of the lattice Boltzmann pseudo-potential approach for the simulation of multiphase flows. The method is shown to correctly simulate the dynamics of impinging droplets on hydrophobic surfaces and head-on and grazing collisions between droplets, at Weber and Reynolds number regimes not accessible to previous pseudo-potential methods at comparable resolution.
Ocean Modelling, 2016
This is a PDF file of an unedited manuscript that has been accepted for publication. The manuscri... more This is a PDF file of an unedited manuscript that has been accepted for publication. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content. This article is made available in accordance with the University of Delaware Faculty Policy on Open Access (4.2.15) and the publisher's policy.
Physical Review E, 2015
We present a lattice Boltzmann realization of Grad's extended hydrodynamic approach to nonequilib... more We present a lattice Boltzmann realization of Grad's extended hydrodynamic approach to nonequilibrium flows. This is achieved by using higher-order isotropic lattices coupled with a higher-order regularization procedure. The method is assessed for flow across parallel plates and three-dimensional flows in porous media, showing excellent agreement of the mass flow with analytical and numerical solutions of the Boltzmann equation across the full range of Knudsen numbers, from the hydrodynamic regime to ballistic motion.
Journal of Statistical Physics, 2015
Nonlinear Oscillations, 2003
In this work we analyse stability of a gravity wave generated on the separation surface of two im... more In this work we analyse stability of a gravity wave generated on the separation surface of two immiscible liquids inside a moving container and perturbed by a capillary wave. Such a phenomenon is experimentally observed when the amplitude and the frequency of the motion imposed to the container attain certain values. Evolution of the system is described by the variational principle. We assume that motion of the system is decomposed into two modes: the gravity mode and the capillary mode. With suitable scaling assumptions it is possible to show that the evolution of the gravity mode is determined by the forcing motion, while the capillary mode is excited by the nonlinear interactions between the capillary and gravity modes. At last, an analytical dispersion relation is obtained for the pulsation of the capillary mode. This relation is a function of several quantities, all depending on the capillary wavenumber and the characteristics of the exciting motion. ŠŠ½Š°Š»iŠ·ŃŃŃŃŃŃ ŃŃiŠ¹ŠŗiŃŃŃ Š³ŃŠ°Š²iŃŠ°ŃiŠ¹Š½ŠøŃ
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The interaction between the Nile River and the Mediterranean Sea includes water and salinity tran... more The interaction between the Nile River and the Mediterranean Sea includes water and salinity transport. To study this interaction, the last reach of Rosetta branch of the Nile River is modeled using TELEMAC3D modeling system. Hydrodynamic simulations and salinity transport simulations were first carried out for the present situation. Then the impact of climate change on such interaction was assessed by simulating three scenarios for sea level rise. The hydrodynamic simulations showed a relatively slow flow velocity throughout the domain and a free surface slope close to zero. The salinity transport simulations showed that the saltwater is intruding in the Nile for a distance ranging from 11.3 to 12 km at the surface and about 16 km near the bottom, the saltwater wedge was fluctuating in a cycle-like form. The salt concentration was found to be variable longitudinally, laterally and vertically. The sea level rise caused more saltwater intrusion. To maintain the current intrusion leng...
Physical review. E, Statistical, nonlinear, and soft matter physics, 2014
We investigate the accuracy and performance of the regularized version of the single-relaxation-t... more We investigate the accuracy and performance of the regularized version of the single-relaxation-time lattice Boltzmann equation for the case of two- and three-dimensional lid-driven cavities. The regularized version is shown to provide a significant gain in stability over the standard single-relaxation time, at a moderate computational overhead.
Physics of Fluids, 2009
The aim of this paper is the investigation of a layered sloshing fluid system using both a new Ha... more The aim of this paper is the investigation of a layered sloshing fluid system using both a new Hamiltonian mathematical model and new laboratory experiments. The mathematical model is defined for a cylindrical tank with an arbitrary shape and subjected to an arbitrary rigid motion. The model consists of a pure evolution system of partial differential first order equations in the canonical four unknowns: water elevation at the upper free surface and at the separation surface and the gap in momentum potential density computed at each fluid surface. The system of equations is obtained by avoiding the construction of the Hamiltonian and its variational derivatives. An important advantage of this formulation, with respect to the Lagrangian formulation, is that the nonevolution constraint, which imposes for each fluid the same velocity component along the normal direction of the separation surface, is fulfilled by the model itself. The model implementation needs to define the so-called Ne...
Fluid Dynamics Research, 2002
In this work a theoretical and experimental investigation is performed on the sloshing of two imm... more In this work a theoretical and experimental investigation is performed on the sloshing of two immiscible liquid layers inside of a closed square-section tank. By applying a variational approach to the potential formulation of the fluid motion, a nonlinear dynamical system is derived applying the Lagrange equations to the Lagrangian of motion defined in terms of suitable generalised coordinates. These coordinates are the time depending coefficients of the modal expansions adopted for the separation surface of the two fluids and for the velocity potentials of the fluid layers. Dissipative effects are taken into account by considering generalised dissipative forces derived by a dissipative model extensively treated in the paper. Numerical integration of the dynamical system furnish solutions which well reproduce the examined experimental configurations.
Journal of Computational Physics, 2015
In this work a Discrete Boltzmann Model for the solution of transcritical 2D shallow water flows ... more In this work a Discrete Boltzmann Model for the solution of transcritical 2D shallow water flows is presented and validated. In order to provide the model with transcritical capabilities, a particular multispeed velocity set has been employed for the discretization of the Boltzmann equation. It is shown that this particular set naturally yields a simple and closed procedure to determine higher order equilibrium distribution functions needed to simulate transcritical flow. The model is validated through several classical benchmarks and is proven to correctly and accurately simulate both 1D and 2D transitions between the two flow regimes.
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Papers by michele la rocca