http://hdl.handle.net/2117/1085 2013-06-19T08:52:22Z http://hdl.handle.net/2117/14928 Title: Modelling shoreline sand waves: application to the coast of Namibia Authors: Falqués Serra, Albert; Van den Berg, Niels; Ribas Prats, Francesca; Caballeria Suriñach, Miquel Abstract: The SW coast of Africa (Namibia and part of Angola) features very long sandy beaches and a wave climate dominated by energetic swells from the SSW, therefore approaching the coast with a very high obliquity. Satellite images reveal that along that coast there are many shoreline sand waves with wavelengths ranging from 2 to 8 km. A more detailed study, including a Fourier analysis of the shoreline position, confirms a high spectral density concentration at these lengths scales. Also, it becomes apparent that at least some of the sand waves are dynamically active rather than being controlled by the geological setting. A morphodynamic model is used to test the hypothesis that these sand waves could emerge as free morphodynamic instabilities of the coastline due to the obliquity in wave incidence. It is found that the wave period, Tp, is crucial to establish the tendency to stability or instability, instability increasing for decreasing period, whilst there is some discrepancy in the observed periods. Model results for Tp = 7 s clearly show the tendency for the coast to develop free sand waves at 2 km wavelength within a few years, which migrate to the north at rates of 0.6-0.7 km/yr. For Tp = 8 s, instability is weaker and rather sensitive to other factors as the underlying bathymetry. In this case, the coast seems to be nearly at neutral stability so that sand waves originated from other mechanisms can propagate downdrift with little decay. http://hdl.handle.net/2117/19559 Title: Mode competition in cylindrical flows driven by sidewall oscillations Authors: Panadès Guinart, Carles; Marqués Truyol, Francisco; Meseguer Serrano, Álvaro Abstract: The transition from a two-dimensional to three-dimensional flow in systems with spatial O(2) symmetry and spatiotemporal Z2 symmetry happens in many fluid systems, like wakes or periodically forced flows. In most of these systems, the dynamics after the first bifurcation is very complex and involves cascades of bifurcations in a very narrow parameter range. A numerical study of a flow in an enclosed cylindrical cavity driven by axial oscillations of the sidewall, which allows a detailed study of the secondary bifurcations and the corresponding mode interactions, is presented. The study focuses on a codimension-2 point that acts as the organizing center of the dynamics for moderate values of the forcing frequency. The unraveled dynamics is very rich, including slow-fast dynamics and hysteresis, and may help understand the bifurcation cascades in more complex systems. 2013-06-17T14:12:01Z http://hdl.handle.net/2117/19541 Title: Travelling convectons in binary fluid convection Authors: Mercader Calvo, María Isabel; Batiste Boleda, Oriol; Alonso Maleta, Arantxa; Knobloch, Edgar Abstract: Binary fluid mixtures with a negative separation ratio heated from below exhibit steady spatially localized states called convectons for supercritical Rayleigh numbers. With no-slip, fixed-temperature, no-mass-flux boundary conditions at the top and bottom stationary odd- and even-parity convectons fall on a pair of intertwined branches connected by branches of travelling asymmetric states. In appropriate parameter regimes the stationary convectons may be stable. When the boundary condition on the top is changed to Newton’s law of cooling the odd-parity convectons start to drift and the branch of odd-parity convectons breaks up and reconnects with the branches of asymmetric states. We explore the dependence of these changes and of the resulting drift speed on the associated Biot number using numerical continuation, and compare and contrast the results with a related study of the Swift–Hohenberg equation by Houghton & Knobloch (Phys. Rev. E, vol. 84, 2011, art. 016204). We use the results to identify stable drifting convectons and employ direct numerical simulations to study collisions between them. The collisions are highly inelastic, and result in convectons whose length exceeds the sum of the lengths of the colliding convectons. 2013-06-12T16:25:45Z http://hdl.handle.net/2117/19530 Title: Computation of azimuthal waves and their stability in thermal convection in rotating spherical shells with application to the study of a double-Hopf bifurcation Authors: Sánchez Umbría, Juan; García González, Fernando; Net Marcé, Marta Abstract: A methodology to compute azimuthal waves, appearing in thermal convection of a pure fluid contained in a rotating spherical shell, and to study their stability is presented. It is based on continuation, Newton-Krylov, and Arnoldi methods. An application to the study of a double-Hopf bifurcation of the basic state is shown for Ekman and Prandtl numbers E=10−4 and σ=0.1, respectively, radius ratios η∈[0.32,0.35], Rayleigh numbers R∈[1.8×105,6×105], and nonslip and perfectly conducting boundary conditions. The knowledge of the bifurcation diagrams, including the unstable solutions, allows one to understand the coexistence of stable thermal Rossby waves of different azimuthal wave numbers at some parameter regions, and the origin of some new intermittent solutions found, as trajectories close to heteroclinic chains. Moreover, the structure of the eigenfunctions at the secondary bifurcations explains the existence of the amplitude and shape modulated waves. 2013-06-10T12:45:23Z http://hdl.handle.net/2117/19504 Title: A parallel algorithm for the computation of invariant tori in large-scale dissipative systems Authors: Sánchez Umbría, Juan; Net Marcé, Marta Abstract: A parallelizable algorithm to compute invariant tori of high-dimensional dissipative systems, obtained upon discretization of PDEs is presented. The size of the set of equations to be solved is only a small multiple of the dimension of the original system. The sequential and parallel implementations are compared with a previous method (Sánchez et al. (2010)) [11], showing that important savings in wall-clock time can be achieved. In order to test it, a thermal convection problem of a binary mixture of fluids has been used. The new method can also be applied to problems with very low rotation numbers, for which the previous is not suitable. This is tested in two examples of two-dimensional maps. 2013-06-04T14:52:59Z http://hdl.handle.net/2117/19318 Title: Percolation experiments in complex fractal media Authors: Redondo Apraiz, José Manuel; Tarquis, Ana Maria; Cherubini, Claudia; Lopez Gonzalez-Nieto, Pilar; Vila, Teresa 2013-05-16T16:20:33Z http://hdl.handle.net/2117/19317 Title: SAR measurements of coastal features in the NW Mediterranean Authors: Redondo Apraiz, José Manuel; Martínez Benjamín, Juan José; Díez Rilova, Margarita; Lopez Gonzalez-Nieto, Pilar 2013-05-16T16:15:04Z http://hdl.handle.net/2117/19150 Title: Small-scale characteristics and turbulent statistics of the flow in an external gear pump by time-resolved PIV Authors: Ertürk, S.; Vernet, Anton; Pallarés, J.; Castilla López, Roberto; Raush Alviach, Gustavo Adolfo 2013-05-09T12:44:56Z http://hdl.handle.net/2117/18967 Title: The evolution and C, N and O yields of intermediate-mass Z = 10-5 stars in isolation and in close binary systems Authors: Gil Pons, Pilar; Doherty, Carolyn L.; Suda, T.; Campbell, Simon; Lau, H.; Mansouri Guilani, Shervin; Lattanzio, John Abstract: We have computed the evolution of Z = 10−5 stars of masses between 4 and 9 M , from their main sequence till the late TP-(S)AGB phase.We use a recent version of the Mount Stromlo Stellar Evolution code, in which molecular opacities include the effects of variable C/O abundances ratio, [1]. By computing hundreds (or thousands) of thermal pulses, we have been able either to remove the bulk of the stellar envelopes or to obtain stellar cores very close to MCh. Using [2] prescription for the mass loss rates the computed stars lose their envelopes before their cores reach MCh. This would forbid the occurrence of SN 1.5 for Z = 10−5 stars. Nevertheless the results by [3] suggest that the former prescription might overestimate the mass-loss rates. Therefore we have decreased the rates by [2]. For all the cases we present, even a decrease of one order of magnitude let the stellar cores reach MCh before the envelope is lost. Therefore the occurrence of SN1.5 at Z = 10 −5 and their potential contribution to the chemical evolution of the Universe should not be discarded. We consider the combined effects of the deep/corrosive 2 nd dredge-up and Roche Lobe Overflow (RLOF) during the E-AGB to help to constrain the contribution of massive Z = 10 −5 AGB stars to the CEMPs problem. Our results have implications for the chemical evolution of the Universe and might provide another piece for the puzzle of the CEMPs problem. 2013-04-23T14:39:01Z http://hdl.handle.net/2117/18917 Title: Frontogenesis in the meso-a and meso-ß scales in the Mediterranean basin: From cloud arch to cloud cells. Authors: Mazón Bueso, Jordi; Pino González, David 2013-04-22T12:01:45Z http://hdl.handle.net/2117/18916 Title: Nocturnal offshore precipitation near the coastline in the Mediterranean basin Authors: Mazón Bueso, Jordi; Pino González, David 2013-04-22T11:48:29Z http://hdl.handle.net/2117/18790 Title: The role of large sea-land temperature, the coastline shape and the SST in Authors: Mazón Bueso, Jordi; Pino González, David 2013-04-15T11:35:30Z http://hdl.handle.net/2117/18554 Title: Flash heat events: the case of 27th August 2010 in northeast of Iberian Authors: Mazón Bueso, Jordi; Pino González, David 2013-04-03T09:34:09Z http://hdl.handle.net/2117/18552 Title: Uncertainties in the CO2 budget associated to the diurnal variability of the boundary layer dynamics Authors: Pino González, David; Kaikkonen, Jukka-Pekka; Vilà-Guerau de Arellano, Jordi 2013-04-03T09:05:04Z http://hdl.handle.net/2117/18497 Title: Nocturnal offshore precipitation near the Mediterranean coast of the Iberian Peninsula Authors: Mazón Bueso, Jordi; Pino González, David Abstract: While nocturnal offshore precipitation, which produces rain cells and bands, has been studied in tropical areas, few studies have analyzed the occurrence of this phenomenon at higher latitudes. Using radar reflectivity, nocturnal rainfall in the western Mediterranean area has been detected near the coast of the Iberian Peninsula and North Africa. More than 50 events have been recorded since 2009. MM5 mesoscale simulations of some of the recorded events allow us to establish that the most likely causes for these precipitation events are: (1) the interaction between cold air masses conducted by drainage and kata- batic winds, and (2) a wetter and warmer synoptic wind. Two different episodes are presented: one in the north- eastern Iberian Peninsula, caused by stratiform clouds, which occurred at the mouths of three rivers; the other case, produced by convective clouds, occurred at the southern Iberian Peninsula and was caused by the drainage winds flowing down from some mountain ranges located close to the coast. 2013-03-22T13:11:41Z