DF - Dinàmica No Lineal de Fluids
http://hdl.handle.net/2117/1085
2016-05-04T21:47:42ZEl canvi climàtic a través dels informes de l'IPCC (1990-2014)
http://hdl.handle.net/2117/86567
El canvi climàtic a través dels informes de l'IPCC (1990-2014)
Mazón Bueso, Jordi
Des de que l’any 1990 es va publicar el primer informe del Panell Intergovernamental
del Canvi Climàtic (en anglès IPCC) quatre
més
han aparegut (els anys 1995, 2001, 2007
i 2014), els quals ens donen una visió de l’evolució en l’estat del coneixement sobre el
canvi climàtic en les diferents etapes d’aquest període 1990-2014. A partir del contingut
científic i de les conclusions més destacables recollides en aquests cinc informes, s’ha
analitzat l’evolució del coneixement sobre el canvi climàtic, les polítiques i mesures
proposades per a combatre’l. En poc més de 20 anys s’ha passat d’una exhaustiva
descripció de les bases científiques de l’efecte hivernacle i del canvi climàtic en què
es basava l’informe del 1990, amb moltes incerteses i en el què era científicament
difícil atribuir a l’ésser humà com a unic responsable d’aquest canvi de clima, al darrer
informe del 2014, el qual qualifica d’extremament probable amb un 95% de certesa de
que l’escalfaent del planeta és d’origen antròpic, el qual pot esdevenir irreversible si no
s’actua de forma urgent en la reducció de les emissions.
2016-05-04T12:40:40ZMazón Bueso, JordiDes de que l’any 1990 es va publicar el primer informe del Panell Intergovernamental
del Canvi Climàtic (en anglès IPCC) quatre
més
han aparegut (els anys 1995, 2001, 2007
i 2014), els quals ens donen una visió de l’evolució en l’estat del coneixement sobre el
canvi climàtic en les diferents etapes d’aquest període 1990-2014. A partir del contingut
científic i de les conclusions més destacables recollides en aquests cinc informes, s’ha
analitzat l’evolució del coneixement sobre el canvi climàtic, les polítiques i mesures
proposades per a combatre’l. En poc més de 20 anys s’ha passat d’una exhaustiva
descripció de les bases científiques de l’efecte hivernacle i del canvi climàtic en què
es basava l’informe del 1990, amb moltes incerteses i en el què era científicament
difícil atribuir a l’ésser humà com a unic responsable d’aquest canvi de clima, al darrer
informe del 2014, el qual qualifica d’extremament probable amb un 95% de certesa de
que l’escalfaent del planeta és d’origen antròpic, el qual pot esdevenir irreversible si no
s’actua de forma urgent en la reducció de les emissions.Conductive and convective heat transfer in fluid flows between differentially heated and rotating cylinders
http://hdl.handle.net/2117/86416
Conductive and convective heat transfer in fluid flows between differentially heated and rotating cylinders
López, José M.; Marqués Truyol, Francisco; Avila Cañellas, Marc
The flow of fluid confined between a heated rotating cylinder and a cooled stationary cylinder is a canonical experiment for the study of heat transfer in engineering. The theoretical treatment of this system is greatly simplified if the cylinders are assumed to be of infinite length or periodic in the axial direction. In these cases heat transfer in the laminar regime occurs only through conduction as in a solid. We here investigate numerically heat transfer and the onset of turbulence in such flows by using both periodic and no-slip boundary conditions in the axial direction. The influence of the geometric parameters is comprehensively studied by varying the radius ratio (0.1 <= eta <= 0.99) and the length-to-gap aspect ratio (5 <= Gamma <= 80). Similarly, a wide range of Prandtl, Rayleigh, and Reynolds numbers is explored (0.01 <= sigma <= 100, Ra <= 30,000, and Re <= 1000, respectively). We obtain a simple criterion, Ra which determines whether the infinite-cylinder assumption can be employed. The coefficient a is well approximated by a cubic fit over the whole n-range. Noteworthy the criterion is independent of the Prandtl number and appears robust with respect to Reynolds number even beyond the laminar regime. (C) 2015 Elsevier Ltd. All rights reserved.
2016-04-29T10:13:31ZLópez, José M.Marqués Truyol, FranciscoAvila Cañellas, MarcThe flow of fluid confined between a heated rotating cylinder and a cooled stationary cylinder is a canonical experiment for the study of heat transfer in engineering. The theoretical treatment of this system is greatly simplified if the cylinders are assumed to be of infinite length or periodic in the axial direction. In these cases heat transfer in the laminar regime occurs only through conduction as in a solid. We here investigate numerically heat transfer and the onset of turbulence in such flows by using both periodic and no-slip boundary conditions in the axial direction. The influence of the geometric parameters is comprehensively studied by varying the radius ratio (0.1 <= eta <= 0.99) and the length-to-gap aspect ratio (5 <= Gamma <= 80). Similarly, a wide range of Prandtl, Rayleigh, and Reynolds numbers is explored (0.01 <= sigma <= 100, Ra <= 30,000, and Re <= 1000, respectively). We obtain a simple criterion, Ra which determines whether the infinite-cylinder assumption can be employed. The coefficient a is well approximated by a cubic fit over the whole n-range. Noteworthy the criterion is independent of the Prandtl number and appears robust with respect to Reynolds number even beyond the laminar regime. (C) 2015 Elsevier Ltd. All rights reserved.Filtrado transversal adaptativo de varianza constante para la ecualización de canal
http://hdl.handle.net/2117/86209
Filtrado transversal adaptativo de varianza constante para la ecualización de canal
Vázquez Grau, Gregorio; Gasull Llampallas, Antoni; Sánchez Umbría, Juan; Oliveras Vergés, Albert
This paper describes the problem of lineal filtering of noisy data under a Maximum Likelihood objective. In this sense, the paper shows that a weighted square error cost function deals and it is necessary to weight the filtering error sequence by a factor that, basically, depends the probability density function of the error sequence and on its first derivate. As it is well known, this information used to be not available and other proposals must be made. For this purpose, going around this problem, the paper discusses the design of this weighting factor for including sorne kind of data-selection mechanism for the final filter weight-vector solution design. The underlying of the proposal is the development of a recursive algorithm in such a way that for any measure or observation, its associated
2016-04-26T14:37:29ZVázquez Grau, GregorioGasull Llampallas, AntoniSánchez Umbría, JuanOliveras Vergés, AlbertThis paper describes the problem of lineal filtering of noisy data under a Maximum Likelihood objective. In this sense, the paper shows that a weighted square error cost function deals and it is necessary to weight the filtering error sequence by a factor that, basically, depends the probability density function of the error sequence and on its first derivate. As it is well known, this information used to be not available and other proposals must be made. For this purpose, going around this problem, the paper discusses the design of this weighting factor for including sorne kind of data-selection mechanism for the final filter weight-vector solution design. The underlying of the proposal is the development of a recursive algorithm in such a way that for any measure or observation, its associatedTesting otter board hydrodynamic performances in wind tunnel facilities
http://hdl.handle.net/2117/85362
Testing otter board hydrodynamic performances in wind tunnel facilities
Mellibovsky Elstein, Fernando; Prat Farran, Joana d'Arc; Notti, Emilio; Sala, Antonello
The feasibility and potential advantages of wind tunnel testing of otter board designs are assessed. Traditional flume tank tests incur high operational costs and present some limitations in terms of flexibility and accuracy. Modern flume tanks, despite more flexible and accurate, are still expensive to operate or hire. Wind tunnel facilities are widespread, with a potential for low budget tests, and allow for an accurate control of velocity, angle of attack and sideslip as well as precise measurement of forces and moments in all three axes. A complete description of otter board hydrodynamics is paramount to optimising design and rigging and for the design of active control strategies that allow for stable trawling at a target speed and depth. We describe in detail the methodology of wind tunnel tests applied to general otter board designs, exemplify it with a commercial pelagic otter board and provide a comparison with existing flume tank results for the same design.
2016-04-07T14:06:46ZMellibovsky Elstein, FernandoPrat Farran, Joana d'ArcNotti, EmilioSala, AntonelloThe feasibility and potential advantages of wind tunnel testing of otter board designs are assessed. Traditional flume tank tests incur high operational costs and present some limitations in terms of flexibility and accuracy. Modern flume tanks, despite more flexible and accurate, are still expensive to operate or hire. Wind tunnel facilities are widespread, with a potential for low budget tests, and allow for an accurate control of velocity, angle of attack and sideslip as well as precise measurement of forces and moments in all three axes. A complete description of otter board hydrodynamics is paramount to optimising design and rigging and for the design of active control strategies that allow for stable trawling at a target speed and depth. We describe in detail the methodology of wind tunnel tests applied to general otter board designs, exemplify it with a commercial pelagic otter board and provide a comparison with existing flume tank results for the same design.Numerical simulation of the genesis of superhighway convection in a slightly inclined layer of a binary liquid mixture
http://hdl.handle.net/2117/84854
Numerical simulation of the genesis of superhighway convection in a slightly inclined layer of a binary liquid mixture
Alonso Maleta, María Aránzazu; Mercader Calvo, María Isabel; Batiste Boleda, Oriol
Convection in a fluid layer is affected by its orientation with
respect to the gravitational field. In the present work, we
investigate numerically pattern selection in a vertical cylindrical
cell heated from below for positive Soret coefficient mixtures and
analyse the effect of marginal inclinations of gravity in pattern
formation.
The dynamics of mixtures with a positive value of the Soret
coefficient without inclination has essentially been studied in
laboratory experiments, and numerical simulations reduce to periodic
domains. According to these studies, close to convective onset, the
motion is dominated by the solute gradient, and a stationary square
pattern with negligible change in heat transport is reached (Soret regime).
Far from threshold, convection selects the usual roll structure observed
in pure fluid convection, where a strong change in heat transport takes
place. In the crossover region, a cross roll regime is observed and the
competition between square and roll patterns leads to oscillations.
Interestingly, positive Soret coefficient mixtures have been used in
the recent experimental work of Croccolo et al. to investigate the effect
of inclination of the layer on the long-term stability. At small Rayleigh
numbers, the mass transfer is dominated by the induced large scale shear flow,
while at larger Rayleigh numbers, it is dominated by solutal convection.
Unexpected results are reported at the transition: drifting columnar flows moving
in opposite directions along parallel lanes in a superhighway configuration have
been observed.
We will present simulations corresponding to both non-inclined and
inclined cells. In particular, we have been able to obtain numerically
superhighway convection (SHC). The numerical analysis should shed
some light on the origin of these fast drifting columnar flows
observed in experiments.
2016-03-30T10:37:42ZAlonso Maleta, María AránzazuMercader Calvo, María IsabelBatiste Boleda, OriolConvection in a fluid layer is affected by its orientation with
respect to the gravitational field. In the present work, we
investigate numerically pattern selection in a vertical cylindrical
cell heated from below for positive Soret coefficient mixtures and
analyse the effect of marginal inclinations of gravity in pattern
formation.
The dynamics of mixtures with a positive value of the Soret
coefficient without inclination has essentially been studied in
laboratory experiments, and numerical simulations reduce to periodic
domains. According to these studies, close to convective onset, the
motion is dominated by the solute gradient, and a stationary square
pattern with negligible change in heat transport is reached (Soret regime).
Far from threshold, convection selects the usual roll structure observed
in pure fluid convection, where a strong change in heat transport takes
place. In the crossover region, a cross roll regime is observed and the
competition between square and roll patterns leads to oscillations.
Interestingly, positive Soret coefficient mixtures have been used in
the recent experimental work of Croccolo et al. to investigate the effect
of inclination of the layer on the long-term stability. At small Rayleigh
numbers, the mass transfer is dominated by the induced large scale shear flow,
while at larger Rayleigh numbers, it is dominated by solutal convection.
Unexpected results are reported at the transition: drifting columnar flows moving
in opposite directions along parallel lanes in a superhighway configuration have
been observed.
We will present simulations corresponding to both non-inclined and
inclined cells. In particular, we have been able to obtain numerically
superhighway convection (SHC). The numerical analysis should shed
some light on the origin of these fast drifting columnar flows
observed in experiments.On the determination of diffusion coefficients in two-component alloys and doped semiconductors: several implications concerning the International Space Station
http://hdl.handle.net/2117/83083
On the determination of diffusion coefficients in two-component alloys and doped semiconductors: several implications concerning the International Space Station
Sánchez Meneses, O.; Ruiz Martí, Xavier; Pujalte, Mónica; Mercader Calvo, María Isabel; Batiste Boleda, Oriol; Gavaldà, Josefina
The accurate determination of mass diffusion coefficients is a technologically relevant problem that has implications on the modelling and control of material processes such as crystal growth and casting. It is also important in the validation of different theories of atomic diffusion. The experimental determination of these coefficients, when there is a liquid phase, is difficult due to the unavoidable presence of buoyancy driven convection currents that enhance mass transport and disturb diffusion measurements. To minimize as much as possible these problems, long capillaries are used in order to confine the fluid and reduce the intensity of the convective motions. These measurements have also been done in reduced gravity environments, but the residual gravity may still be able to induce buoyancy driven convection motions. The aim of our work is to analyze the impact of low solutal Rayleigh number environments on the accuracy of the interdiffusion coefficient measurements using long capillaries. In the present study we deal with two liquid systems; photovoltaic silicon and Al-based liquid binary alloys at high temperature. We have numerically simulated two different experimental techniques used to determine the diffusion coefficients; the shear cell and the long capillary techniques. We also consider the effect of rotating the cylindrical cell along their axis as a mechanism to reduce axial convective transport even in Earth laboratories. Finally, we use typical accelerometric signals from the International Space Station (ISS) in the quasi-steady range of frequencies. The signals concentrate on typical station reboosts because the accelerometric level of the rest of potentially dangerous disturbances - dockings, undockings and Extra Vehicular Activities, EVAs - is considerably lower.
2016-02-17T18:18:32ZSánchez Meneses, O.Ruiz Martí, XavierPujalte, MónicaMercader Calvo, María IsabelBatiste Boleda, OriolGavaldà, JosefinaThe accurate determination of mass diffusion coefficients is a technologically relevant problem that has implications on the modelling and control of material processes such as crystal growth and casting. It is also important in the validation of different theories of atomic diffusion. The experimental determination of these coefficients, when there is a liquid phase, is difficult due to the unavoidable presence of buoyancy driven convection currents that enhance mass transport and disturb diffusion measurements. To minimize as much as possible these problems, long capillaries are used in order to confine the fluid and reduce the intensity of the convective motions. These measurements have also been done in reduced gravity environments, but the residual gravity may still be able to induce buoyancy driven convection motions. The aim of our work is to analyze the impact of low solutal Rayleigh number environments on the accuracy of the interdiffusion coefficient measurements using long capillaries. In the present study we deal with two liquid systems; photovoltaic silicon and Al-based liquid binary alloys at high temperature. We have numerically simulated two different experimental techniques used to determine the diffusion coefficients; the shear cell and the long capillary techniques. We also consider the effect of rotating the cylindrical cell along their axis as a mechanism to reduce axial convective transport even in Earth laboratories. Finally, we use typical accelerometric signals from the International Space Station (ISS) in the quasi-steady range of frequencies. The signals concentrate on typical station reboosts because the accelerometric level of the rest of potentially dangerous disturbances - dockings, undockings and Extra Vehicular Activities, EVAs - is considerably lower.Radial collocation methods for the onset of convection in rotating spheres
http://hdl.handle.net/2117/83082
Radial collocation methods for the onset of convection in rotating spheres
Sánchez Umbría, Juan; García González, Fernando; Net Marcé, Marta
The viability of using collocation methods in radius and spherical harmonics in the angular variables to calculate convective flows in full spherical geometry is examined. As a test problem the stability of the conductive state of a self-gravitating fluid sphere subject to rotation and internal heating is considered. A study of the behavior of different radial meshes previously used by several authors in polar coordinates, including or not the origin, is first performed. The presence of spurious modes due to the treatment of the singularity at the origin, to the spherical harmonics truncation, and to the initialization of the eigenvalue solver is shown, and ways to eliminate them are presented. Finally, to show the usefulness of the method, the neutral stability curves at very high Taylor and moderate and small Prandtl numbers are calculated and shown.
2016-02-17T17:19:45ZSánchez Umbría, JuanGarcía González, FernandoNet Marcé, MartaThe viability of using collocation methods in radius and spherical harmonics in the angular variables to calculate convective flows in full spherical geometry is examined. As a test problem the stability of the conductive state of a self-gravitating fluid sphere subject to rotation and internal heating is considered. A study of the behavior of different radial meshes previously used by several authors in polar coordinates, including or not the origin, is first performed. The presence of spurious modes due to the treatment of the singularity at the origin, to the spherical harmonics truncation, and to the initialization of the eigenvalue solver is shown, and ways to eliminate them are presented. Finally, to show the usefulness of the method, the neutral stability curves at very high Taylor and moderate and small Prandtl numbers are calculated and shown.A mechanism for streamwise localisation of nonlinear waves in shear flows
http://hdl.handle.net/2117/83078
A mechanism for streamwise localisation of nonlinear waves in shear flows
Mellibovsky Elstein, Fernando; Meseguer Serrano, Álvaro
We present the complete unfolding of streamwise localisation in a paradigm of extended shear flows, namely two-dimensional plane Poiseuille flow. Exact solutions of the Navier-Stokes equations are computed numerically and tracked in the streamwise wavenumber-Reynolds number parameter space to identify and describe the fundamental mechanism behind streamwise localisation, a ubiquitous feature of shear flow turbulence. Unlike shear flow spanwise localisation, streamwise localisation does not follow the snaking mechanism demonstrated for plane Couette flow.
2016-02-17T15:18:45ZMellibovsky Elstein, FernandoMeseguer Serrano, ÁlvaroWe present the complete unfolding of streamwise localisation in a paradigm of extended shear flows, namely two-dimensional plane Poiseuille flow. Exact solutions of the Navier-Stokes equations are computed numerically and tracked in the streamwise wavenumber-Reynolds number parameter space to identify and describe the fundamental mechanism behind streamwise localisation, a ubiquitous feature of shear flow turbulence. Unlike shear flow spanwise localisation, streamwise localisation does not follow the snaking mechanism demonstrated for plane Couette flow.Thermal convection in autogravitating spheres at low Ekman numbers
http://hdl.handle.net/2117/82106
Thermal convection in autogravitating spheres at low Ekman numbers
Net Marcé, Marta; García González, Fernando; Sánchez Umbría, Juan
2016-01-27T10:52:49ZNet Marcé, MartaGarcía González, FernandoSánchez Umbría, JuanOscillatory convection in rotating spherical shells: low Prandtl number and non-slip boundary conditions
http://hdl.handle.net/2117/82104
Oscillatory convection in rotating spherical shells: low Prandtl number and non-slip boundary conditions
García González, Fernando; Sánchez Umbría, Juan; Dormy, Emmanuel; Net Marcé, Marta
A five-degree model, which reproduces faithfully the sequence of bifurcations and the type of solutions found through numerical simulations of the three-dimensional Boussinesq thermal convection
equations in rotating spherical shells with fixed azimuthal symmetry, is derived. A low Prandtl number fluid of s=0. 1 subject to radial gravity, filling a shell of radius ratio ¿=0.35, differentially heated, and with non-slip boundary conditions, is considered. Periodic, quasi-periodic, and temporal chaotic flows are obtained for a moderately small Ekman number, E=10-4,andatsupercritical Rayleigh numbers of order
Ra~O(2Rac). The solutions are classified by means of
frequency analysis and Poincaré sections. Resonant phase locking on the quasi-periodic branches,as well as a sequence of period doubling bifurcations, are also detected.
2016-01-27T09:57:30ZGarcía González, FernandoSánchez Umbría, JuanDormy, EmmanuelNet Marcé, MartaA five-degree model, which reproduces faithfully the sequence of bifurcations and the type of solutions found through numerical simulations of the three-dimensional Boussinesq thermal convection
equations in rotating spherical shells with fixed azimuthal symmetry, is derived. A low Prandtl number fluid of s=0. 1 subject to radial gravity, filling a shell of radius ratio ¿=0.35, differentially heated, and with non-slip boundary conditions, is considered. Periodic, quasi-periodic, and temporal chaotic flows are obtained for a moderately small Ekman number, E=10-4,andatsupercritical Rayleigh numbers of order
Ra~O(2Rac). The solutions are classified by means of
frequency analysis and Poincaré sections. Resonant phase locking on the quasi-periodic branches,as well as a sequence of period doubling bifurcations, are also detected.