UPCommons - E-prints UPC Universitat Politècnica de Catalunya
E-prints UPC cobreix dues finalitats: per una banda, és el dipòsit institucional de la UPC que recull els articles de revista, les comunicacions de congrés i els reports de recerca generats en les activitats de recerca del personal docent i investigador de la universitat; per l'altra, és una eina que permet accelerar la producció científica, allotjant versions de documents prèvies a la publicació en una revista o a les actes d’un congrés.
Articles de revista
Mostrando recursos 41 - 60 de 106
Instabilities and inertial waves generated in a librating cylinder - López, J.M.; Marqués Truyol, Francisco
A librating cylinder consists of a rotating cylinder whose rate of rotation is modulated.
When the mean rotation rate is large compared with the viscous damping rate, the flow may support inertial waves, depending on the frequency of the modulation. The modulation also produces time-dependent boundary layers on the cylinder endwalls and sidewall, and the sidewall boundary layer flow in particular is susceptible to instabilities which can introduce additional forcing on the interior flow with time scales different from the modulation period. These instabilities may also drive and/or modify the inertial waves. In this paper, we explore such flows numerically using...
The influence of wave direction on the morphological response of a double sandbar system - Thiebot, Jerome; Idier, Deborah; Garnier, Roland; Falqués Serra, Albert; Ruessink, B.G.
Nearshore sandbars are often characterized by three-dimensional bed patterns. To analyze the influence of wave direction on the morphological response of a double sandbar system, this paper uses the 2DH nonlinear surf zone model MORFO55. Depending on wave direction, different morphologies emerge as free instabilities. These morphological responses differ in terms of geometry (shape of the alongshore rhythmic patterns) and temporal evolution. Nearly shore-normal waves favor the emergence of crescentic patterns along both the inner and outer bars. These instabilities arise from “bedsurf” coupling, which is the positive feedback between the bed perturbations and the wave-breaking patterns resulting in rip-cell...
Dissipative solitons in binary fluid convection - Mercader Calvo, María Isabel; Batiste Boleda, Oriol; Alonso Maleta, María Aránzazu; Knobloch, Edgar
A horizontal layer containing a miscible mixture of two fluids can produce dissipative solitons when heated from below. The physics of the system is described, and dissipative solitons are computed using numerical continuation for three distinct sets of experimentally realizable parameter values. The stability of the solutions is investigated using direct numerical integration in time and related to the stability properties of the competing periodic state.
Observations and large-eddy simulations of entrainment in the sheared sahelian boundary layer - Canut, Guylaine; Couvreux, Fleur; Lothon, Marie; Pino González, David; Saïd, Frédérique
At the top of the planetary boundary layer, the entrainment of air, which incorporates
dry and warm air from the free troposphere into the boundary layer, is a key process
for exchanges with the free troposphere since it controls the growth of the boundary layer.
Here, we focus on the semi-arid boundary layer where the entrainment process is analyzed
using aircraft observations collected during the African Monsoon Multidisciplinary Analysis
experiment and large-eddy simulations. The role of the entrainment is specifically enhanced
in this region where very large gradients at the planetary boundary-layer top can be found
due to the presence of the moist, cold monsoon flow on...
Transitions to three-dimensional flows in a cylinder driven by oscillations of the sidewall - Panadès Guinart, Carles; Marqués Truyol, Francisco; Lopez, Juan M.
The transition from two-dimensional to three-dimensional flows in a finite circular
cylinder driven by an axially oscillating sidewall is explored in detail. The complete
symmetry group of this flow, including a spatio-temporal symmetry related to the
oscillating sidewall, is Z2xO(2). Previous studies in flows with the same symmetries,
such as symmetric bluff-body wakes and periodically forced rectangular cavities,
were unable to obtain the theoretically predicted bifurcation to modulated travelling
waves. In the simpler cylindrical geometry, where the azimuthal direction is physically
periodic, we have found these predicted modulated travelling waves as stable fully
saturated nonlinear solutions for the first time. A careful analysis of the base states and...
Long-term evolution of nourished beaches under high angle wave conditions - Van den Berg, Niels; Falqués Serra, Albert; Ribas Prats, Francesca
A nonlinear numerical model for large-scale dynamics of shoreline and nearshore bathymetry under wave action is applied to investigate the long-term evolution of a rectilinear coast dominated by high angle wave incidence, which is perturbed by a nourishment or an offshore borrow pit. Previous studies show that a coastline can be unstable due to high angle wave instability, which results from the feedback between shoreline changes and the wave field. In contrast to traditional one-line shoreline models, which always predict a diffusional behaviour, this instability can lead to the growth of shoreline perturbations. Model results suggest that due to high...
Application of the CORMIX model to assess environmental impact in the coastal area: an example of the ocean disposal system for sanitary sewers in the city of Fortaleza (Ceará, Brazil) - Maia, L. P.; Bezerra Menezes, María Ozilea; Pinheiro, L.; Redondo Apraiz, José Manuel
Cornell Mixing Zone Expert System-CORMIX software was used to simulate the behavior of effluents discharged by the underwater emissary in Fortaleza (Ceará, Brazil). This software is used to analyze and predict the discharge design in bodies of water. Application of the CORMIX model was determined to simulate the tracer discharge using local environmental parameters and underwater emissary discharge data. Data on wind, current and position in relation to the coast were used in the chosen case to obtain the discharge flow classification from the model since the hydrodynamic dispersion fields are differentiated by the predominance of different physical processes responsible...
Shoreline instability due to very oblique wave incidence: some remarks on the physics - Falqués Serra, Albert; Calvete Manrique, Daniel; Ribas Prats, Francesca
Previous research has shown that a very oblique wave incidence on a coast may render a rectilinear shoreline unstable. Here, we present some further insight into the physics of such instability. The obliqueness of wave incidence has two effects on the alongshore drift: (i) a direct effect on the relative angle between the wave fronts and the shoreline, and (ii) an indirect effect on the breakers height via the wave energy spreading as the waves refract when they approach the shore. The direct effect turns out to be, in all incidents, stabilizing, and the instability occurs only from the effects...
Experimental analysis of the flow dynamics in the suction chamber of an external gear pump - Ertürk, Nihal; Vernet, Anton; Castilla López, Roberto; Gámez Montero, Pedro Javier; Ferre, Josep Anton
Time-Resolved Particle Image Velocimetry (TRPIV) has been used to investigate the flow inside the suction chamber of an external gear pump where the movement of the fluid through the pump is maintained by the rotation of the gears. The main purpose of this paper is to study the characteristics of the complex flow pattern of this pump system in order to help in improving its total performance. The applied experimental techniques establish a method that allows visualising the flow inside the gear pump with a high rotational velocity system. Small micro air bubbles have been used as flow seeding. The...
On the multiple shooting continuation of periodic orbits by Newton-Krylov methods - Sánchez Umbría, Juan; Net Marcé, Marta
The application of the multiple shooting method to the continuation of periodic orbits in large-scale dissipative systems is analyzed. A preconditioner for the linear systems which appear in the application of Newton’s method is presented. It is based on the knowledge of invariant subspaces of the Jacobians at nearby solutions. The possibility of speeding up the process by using parallelism is studied for the thermal convection of a binary mixture of fluids in a rectangular domain, with positive results.
Super asymptotic giant branch stars. I - Evolution code comparison - Doherty, Carolyn L.; Siess, Lionel; Lattanzio, John; Gil Pons, Pilar
We present an extensive set of detailed stellar models in the mass range 7.7–10.5M over the
metallicity range Z = 10−5–0.02. These models were produced using the Monash University
version of the Mount Stromlo Stellar Structure Program (MONSTAR) and follow the evolution
from the pre-main sequence to the first thermal pulse of these super asymptotic giant branch
stars. A quantitative comparison is made to the study of Siess. Prior to this study, only
qualitative comparisons and code validations existed in this critical mass range, and the
large variations in the literature were largely unexplained. The comparison presented here
is particularly detailed due to the standardization of the...
El enigma de Osborne Reynolds - Meseguer Serrano, Álvaro; Mellibovsky Elstein, Fernando
Aunque se sigue desconociendo por qué un fl uido conducido por una tubería se vuelve turbulento, se ha dado un paso importante hacia la resolución del problema, formulado hace ya más de 125 años
Convectons in periodic and bounded domains - Mercader Calvo, María Isabel; Batiste Boleda, Oriol; Alonso, Arantxa; Knobloch, Edgar
Numerical continuation is used to compute spatially localized convection in a binary fluid with no-slip laterally insulating boundary conditions and the results are compared with the corresponding ones for periodic boundary conditions (PBC). The change in the boundary conditions produces a dramatic change in the snaking bifurcation diagram that describes the organization of localized states with PBC: the snaking branches turn continuously into a large amplitude state that resembles periodic convection with defects at the sidewalls. Odd parity convectons are more affected by the boundary conditions since the sidewalls suppress the horizontal pumping action that accompanies these states in spatially...
An efficient spectral code for incompressible flows in cylindrical geometries - Mercader Calvo, María Isabel; Batiste Boleda, Oriol; Alonso Maleta, María Aránzazu
An efficient and accurate numerical scheme is proposed to solve the incompressible Navier–Stokes equations in a bounded cylinder. The scheme is based on a projection method formulated in primitive variables to maintain the incompressibility constraint, with a second-order semi-implicit scheme for the time integration, and a pseudospectral approximation for the space variables. The Chebyshev-collocation method applied in the radial and axial directions, and the Fourier–Galerkin approximation used in the azimuthal direction lead to a sequence of two-dimensional Helmholtz and Poisson equations for every azimuthal coefficient that are solved by a diagonalization technique. Radial expansions are considered in the diameter of...
Effect of wave-bedform feedbacks on the formation of, and grain sorting over shoreface-connected sand ridges - Vis-Star, Nicolette C.; Swart, Huib E. de; Calvete Manrique, Daniel
The influence of wave–bedform feedbacks on both the initial formation of shoreface-connected sand ridges (sfcr) and on grain size sorting over these ridges on micro-tidal inner shelves is studied. Also, the effect of sediment sorting on the growth and the migration of sfcr is investigated. This is done by applying a linear stability analysis to an idealized process-based morphodynamic model, which simulates the initial growth of sfcr due to the positive coupling between waves, currents, and an erodible bed. The sediment consists of sand grains with two different sizes. New elements with respect to earlier studies on grain sorting over...
Multifractal observations of eddies, oil spills and natural slicks in the ocean surface - Platónov, Alexéi Konstantínovich; Carrillo Cortés, José Alejandro; Matulka, Anna Magdalena; Sekula, Emil; Grau Barceló, Joan; Redondo Apraiz, José Manuel; Tarquis, Ana Maria
Natural and man-made distributions of tensioactive substance concentrations in the sea surface features exhibit self-similarity at all radar reflectivity levels when illuminated by SAR. This allows the investigation of the traces produced by vortices and other features in the ocean surface. The man-made oil spills besides often presenting some linear axis of the pollutant concentration produced by moving ships also show their artificial production in the sea surface by the reduced range of scales, which widens as time measured in terms of the local eddy diffusivity distorts the shape of the oil spills. Thanks to this, multifractal analysis of the...
Experimental measurements and diffusion in harbor and coastal zones - Díez Rilova, Margarita; Bezerra Menezes, María Ozilea; Mösso Aranda, César; Castilla López, Roberto; Redondo Apraiz, José Manuel
Experimental results of turbulent flows in the sea surface near the coastline have been performed using both Lagrangian and Eulerian methods, field tests are presented using video recordings and velocity sensors. The spatial and temporal resolution is limited by the measuring instruments, which results in “filtering” out the very small scales. The experimental field-results obtained during the large-scale surf zone experiments carried out in the Ebro Delta, (Spain), under spilling/plunging breaking waves are compared with experiments performed at the Barcelona harbour. The field-measurements include several tests across the surf zone with high vertical resolution. The measured turbulent properties are compared...
Induced structures under seasonal flow conditions in the Ebro delta shelf: Laboratory and numerical models - Carrillo Cortés, José Alejandro; Redondo Apraiz, José Manuel; Fraunie, Philippe; Durand, Nathalie
The characteristic induced length scale produced by a river flow in its outlet is studied. Two experimental methods are compared: a) Physical modeling in laboratory and b) numerical mesoscale diffusion model; under low tidal and realistic seasonal flow conditions from Spring, Summer, Fall and Winter field data from the Ebro delta shelf. The physical laboratory experiences were performed on a five-meter diameter turntable, using the Froude-Rossby similarity. This paper shows complementary results from both methods investigating the vortex characteristic and the dynamics of the flow. The experimental results under rotating conditions show coherent vortex dynamics in the large-meso scale coastal...