866 research outputs found
Programas de respiro para cuidadores familiares
La atención a las dependencias es uno de los grandes retos que tiene planteada la
política social al comienzo del presente milenio. Uno de los problemas por resolver es la
atención y prevención de los efectos negativos que tienen los cuidados prolongados sobre
los cuidadores de familiares dependientes. En el presente trabajo se describen los objeti -
vos y los distintos formatos de los programas de apoyo a las familias con miembro s
dependientes. Se hace especial hincapié en los programas de re s p i ro por ser los mejore s
evaluados por los cuidadores informales. En concreto se analizan las situaciones de
dependencia más habituales, discapacitados y personas mayores, describiendo tanto
programas específicos como algunas de las líneas de investigación emprendidas
On the clustering of low-aspect-ratio oblate spheroids settling in ambient fluid
We have performed particle-resolved direct numerical simulations of many heavy non-spherical particles settling under gravity in the dilute regime. The particles are oblate spheroids of aspect ratio 1.5 and density ratio 1.5. Two Galileo numbers are considered, namely 111 and 152, for which a single oblate spheroid follows a steady vertical and a steady oblique path, respectively. In both cases, a strongly inhomogeneous spatial distribution of the disperse phase in the form of columnar clusters is observed, with a significantly enhanced average settling velocity as a consequence. Thus, in contrast to previous results for spheres, the qualitative difference in the single-particle regime does not result in a qualitatively different behaviour of the many-particle cases. In addition, we have carried out an analysis of pairwise interactions of particles in the well-known drafting–kissing–tumbling set-up, for oblate spheroids of aspect ratio 1.5 and for spheres. We have varied systematically the relative initial position between the particle pair and we have considered free-to-rotate particles and rotationally locked ones. We have found that the region of attraction for both particle shapes, with and without rotation, is very similar. However, significant differences occur during the drafting and tumbling phases. In particular, free-to-rotate spheres present longer drafting phases and separate quickly after the collision. Spheroids remain close to each other for longer times after the collision, and free-to-rotate ones experience two or more collision events. Therefore, we have observed a shape-induced increase in the interaction time which might explain the increased tendency to cluster of the many-particle cases
An efficient method for particle-resolved simulations of neutrally buoyant spheres
We present a simple modification of the direct-forcing immersed boundary method (IBM) proposed by Uhlmann (2005) in order to enable it to be applied to particulate flows with solid-to-fluid density ratios around unity. The main difference with respect to the original formulation lies in the particle velocity update which is performed directly after the preliminary velocity field has been computed in the absence of any IBM volume forcing term. In addition, we apply the forcing term to the entire space occupied by the immersed solid object (instead of to the vicinity of its interface only). The present approach requires the evaluation of integrals of the velocity field over the volume occupied by the solid particle, which are evaluated efficiently as sums over the respective quantities available at particle-attached force points. The resulting method can be used seamlessly for density ratios down to _∕_ > 0.5. The new formulation has been validated using three configurations: (i) lateral migration of a neutrally buoyant circular particle in two-dimensional Couette flow; (ii) the release from rest of a neutrally buoyant sphere in a free stream; (iii) the release of a particle in a free stream after an initial phase in which it is translationally fixed with an imposed angular velocity. In all three test cases the present IBM formulation yields a very good agreement with the available reference data. Thus, the proposed approach is a cost-efficient and accurate modification of the original method which allows for the simulation of fluid systems involving density-matched solid particles
Modeling and dynamics of a two-line kite
A mathematical model of a kite connected to the ground by two straight tethers of varying lengths is presented and used to study the traction force generated by kites flying in cross-wind conditions. The equations of motion are obtained by using a Lagrangian formulation, which yields a low-order system of ordinary differential equations free of constraint forces. Two parameters are chosen for the analysis. The first parameter is the wind velocity. The second parameter is one of the stability derivatives of the aerodynamic model: the roll response to the sideslip angle, known also as effective dihedral. This parameter affects significantly the lateral dynamics of the kite. It has been found that when the effective dihedral is below a certain threshold, the kite follows stable periodic trajectories, and naturally flies in cross-wind conditions while generating a high tension along both tethers. This result indicates that kite-based propulsion systems could operate without controlling tether lengths if kite design, including the dihedral and sweep angles, is done appropriately. If both tether lengths are varied out-of-phase and periodically, then kite dynamics can be very complex. The trajectories are chaotic and intermittent for values of the effective dihedral below a certain negative threshold. It is found that tether tensions can be very similar with and without tether length modulation if the parameters of the model are well-chosen. The use of the model for pure traction applications of kites is discussedThis work was supported by the Ministerio de Economía y Competitividad of Spain and the European Regional Development Fund under the project ENE2015-69937-R (MINECO/FEDER, UE). GSA work is supported by the Ministerio de Economía y Competitividad of Spain under the Grant RYC-2014-15357. MGV was partially supported by grant TRA2013-41103-P (MINECO/FEDER, UE). RS was partially supported by the projects AWESCO (H2020-ITN-642682) and REACH (H2020-FTIPilot-691173)
Three-Dimensional Effects on Plunging Airfoils at Low Reynolds Numbers
We present two-dimensional and three-dimensional (3-D) direct numerical simulations of large-amplitude plunging maneuvers at Reynolds numbers of Re=1000 and 5000, with velocity ratios of G=0.5, 1, and 2. For all cases, the evolution of the force coefficients is qualitatively similar. The lift coefficient presents a pronounced peak toward the end of the acceleration phase of the maneuver, a local minimum in the deceleration phase, and a second peak at the end of the maneuver. The amplitude of the main peak increases linearly with G, with limited effect of the Reynolds number and a negligible effect of the three-dimensionality of the flow. On the other hand, both the Reynolds number and three-dimensionality have a stronger effect on the amplitude of the maximum value of the lift coefficient at the end of the maneuver, as well as on the subsequent transient decay toward the static values. The comparison of the evolution of the flow structures near the airfoil shows that these differences in the force coefficients are due to subtle interactions between the various vortices generated during the maneuver, as well as to the development of a 3-D boundary layer on the suction side of the airfoil triggered by the instability of the trailing-edge vortices.This work was supported by the State Research Agency of Spain (AEI) under grant DPI2016-76151-C2-2-R including funding from the European Regional Development Fund (ERDF). The computations were partially performed at the supercomputer Picasso from the Red Española de Supercomputación in activity FI-2018-2-0051. We thank A. Jones and G. Perrotta for providing their experimental data.Publicad
Three-dimensional effects on the aerodynamic performance of flapping wings in tandem configuration
Direct numerical simulations have been performed to analyze how three-dimensional effects influence the performance of wings in tandem configuration undergoing a two-dimensional optimal kinematics. This optimal motion is a combination of heaving and pitching of the airfoils in a uniform free-stream at a Reynolds number and Strouhal number . Wings of two different aspect ratios, 2 and 4, undergoing the 2D motion have been considered. It has been found that the interactions between the vortical structures of the fore- and the hind-wings are qualitatively similar to the two-dimensional case for both . However, the ratio between the mean thrust of the hind-wing and the fore-wing decreases from 80% in 2D to 70% in 3D, implying that the 3D effects are detrimental for the vortical interactions between the wings in terms of thrust production. Nonetheless, the propulsive efficiency remains constant both in 2D and 3D, for both . A more realistic flapping motion has also been analyzed and compared to the heaving motion. It has been found that the aerodynamic forces decrease when the wings are in flapping motion. This detrimental behavior has been linked to a sub-optimal motion of the inboard region of the wings. This sub-optimal region of the wings entails a decrease of the mean thrust and of the propulsive efficiency compared to the heaving case, which are more pronounced for the 4 wings.This work was supported by grant DPI2016-76151-C2-2-R (AEI/FEDER, UE). The computations were partially performed at the supercomputer Tirant from the Red Española de Supercomputación in activity FI-2018-2-0025.Publicad
Flow interaction of three-dimensional self-propelled flexible plates in tandem
Tandem configurations of two self-propelled flexible flappers of finite span are explored
by means of numerical simulations. The same sinusoidal vertical motion is imposed on
the leading edge of both flappers, but with a phase shift (φ). In addition, a vertical offset,
H, is prescribed between the flappers. The configurations that emerge are characterized
in terms of their hydrodynamic performance and topology. The flappers reach a stable
configuration with a constant mean propulsive speed and a mean equilibrium horizontal
distance. Depending on H and φ, two different tandem configurations are observed,
namely compact and regular configurations. The performance of the upstream flapper
(i.e. the leader) is virtually equal to the performance of an isolated flapper, except in
the compact configuration, where the close interaction with the downstream flapper (i.e.
the follower) results in higher power requirements and propulsive speed than an isolated
flapper. Conversely, the follower’s performance is significantly affected by the wake of the
leader in both regular and compact configurations. The analysis of the flow shows that
the follower’s performance is influenced by the interaction with the vertical jet induced
by the vortex rings shed by the leader. This interaction can be beneficial or detrimental
for the follower’s performance, depending on the alignment of the jet velocity with
the follower’s vertical motion. Finally, a qualitative prediction of the performance of a
hypothetical follower is presented. The model is semi-empirical, and it uses the flow field
of an isolated flapper.This work was supported by the State Research Agency of Spain (AEI) under grant DPI2016-76151-C2-2-R including funding from the European Regional Development Fund (ERDF). The computations were partially performed at the supercomputer Caesaraugusta from the Red Española de Supercomputación in activity IM-2020-2-000
Una nueva especie ibérica de Ferulago Koch (Apiaceae)
Se describe Ferulago ternatifolia Solanas, M.B. Crespo & García Martín, sp. nov., a partir de
poblaciones encontradas en zonas litorales (Puigcampana y Vall de Gallinera) de la provincia
de Alicante y en la Sierra de Moratalla (Pico Revolcadores) de la provincia de Murcia. Se analizan
los caracteres morfológicos y estructurales que la definen y se establecen las principales
diferencias con otras especies ibéricas del género
Force and torque acting on particles in a transitionally rough open channel flow
Direct numerical simulation of open channel flow over a geometrically rough
wall has been performed at a bulk Reynolds number of approximately 2900. The
wall consisted of a layer of spheres in a square arrangement. Two cases have
been considered. In the first case the spheres are small (with diameter
equivalent to 10.7 wall units) and the limit of the hydraulically smooth flow
regime is approached. In the second case the spheres are more than three times
larger (49.3 wall units) and the flow is in the transitionally rough flow
regime. Special emphasis is given on the characterisation of the force and
torque acting on a particle due to the turbulent flow. It is found that in both
cases the mean drag, lift and spanwise torque are to a large extent produced at
the top region of the particle surface. The intensity of the particle force
fluctuations is significantly larger in the large-sphere case, while the trend
differs for the fluctuations of the individual components of the torque. A
simplified model is used to show that the torque fluctuations might be
explained by the spheres acting as a filter with respect to the size of the
flow scales which can effectively generate torque fluctuations. Fluctuations of
both force and torque are found to exhibit strongly non-Gaussian probability
density functions with particularly long tails, an effect which is more
pronounced in the small-sphere case. Some implications of the present results
for sediment erosion are briefly discussed.Comment: accepted for publication in J. Fluid Mech. (2011
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