Articles de revista
http://hdl.handle.net/2117/1087
Tue, 25 Apr 2017 03:08:57 GMT2017-04-25T03:08:57ZOn regular rotating black holes
http://hdl.handle.net/2117/103448
On regular rotating black holes
Torres Herrera, Ramon; Fayos Vallés, Francisco
Different proposals for regular rotating black hole spacetimes have appeared recently in the literature. However, a rigorous analysis and proof of the regularity of this kind of spacetimes is still lacking. In this note we analyze rotating Kerr-like black hole spacetimes and find the necessary and sufficient conditions for the regularity of all their second order scalar invariants polynomial in the Riemann tensor. We also show that the regularity is linked to a violation of the weak energy conditions around the core of the rotating black hole.
The final publication is available at Springer via 10.1007/s10714-016-2166-7
Fri, 07 Apr 2017 11:29:58 GMThttp://hdl.handle.net/2117/1034482017-04-07T11:29:58ZTorres Herrera, RamonFayos Vallés, FranciscoDifferent proposals for regular rotating black hole spacetimes have appeared recently in the literature. However, a rigorous analysis and proof of the regularity of this kind of spacetimes is still lacking. In this note we analyze rotating Kerr-like black hole spacetimes and find the necessary and sufficient conditions for the regularity of all their second order scalar invariants polynomial in the Riemann tensor. We also show that the regularity is linked to a violation of the weak energy conditions around the core of the rotating black hole.Using archives of past floods to estimate future flood hazards
http://hdl.handle.net/2117/103084
Using archives of past floods to estimate future flood hazards
Swierczynski, Tina; Ionita, Monica; Pino González, David
Worldwide, floods cause greater economic damage and loss of human life than any other type of natural disaster. We urgently need better assessments of flood hazards to reduce the societal impact of extreme floods caused by Earth’s rapidly changing climate, among other factors.
One way of assessing flood hazards is to examine past floods using the records provided by hydrological instruments. We can extend this knowledge back through the Holocene period or beyond using historical documents and natural archives (including alluvial, marine, and lake sediments; tree rings; and cave formations). These extended records can provide valuable information about long-term flood trends.
Thu, 30 Mar 2017 09:09:23 GMThttp://hdl.handle.net/2117/1030842017-03-30T09:09:23ZSwierczynski, TinaIonita, MonicaPino González, DavidWorldwide, floods cause greater economic damage and loss of human life than any other type of natural disaster. We urgently need better assessments of flood hazards to reduce the societal impact of extreme floods caused by Earth’s rapidly changing climate, among other factors.
One way of assessing flood hazards is to examine past floods using the records provided by hydrological instruments. We can extend this knowledge back through the Holocene period or beyond using historical documents and natural archives (including alluvial, marine, and lake sediments; tree rings; and cave formations). These extended records can provide valuable information about long-term flood trends.Inertial waves in rapidly rotating flows: a dynamical systems perspective
http://hdl.handle.net/2117/102980
Inertial waves in rapidly rotating flows: a dynamical systems perspective
López Moscat, Juan Manuel; Marqués Truyol, Francisco
An overview of recent developments in a wide variety of enclosed rapidly rotating flows is presented. Highlighted is the interplay between inertial waves, which have been predicted from linear inviscid considerations, and the viscous boundary layer dynamics which result from instabilities as the nonlinearities in the systems are increased. Further, even in the absence of boundary layer instabilities, nonlinearity in the system often leads to complicated interior flows due to subcritical instabilities, Eckhaus bands and heteroclinic dynamics. The ensuing spatio-temporally complex dynamics is analysed in terms of equivariant dynamical systems, providing a general perspective for the wide range of dynamics involved.
Tue, 28 Mar 2017 14:51:51 GMThttp://hdl.handle.net/2117/1029802017-03-28T14:51:51ZLópez Moscat, Juan ManuelMarqués Truyol, FranciscoAn overview of recent developments in a wide variety of enclosed rapidly rotating flows is presented. Highlighted is the interplay between inertial waves, which have been predicted from linear inviscid considerations, and the viscous boundary layer dynamics which result from instabilities as the nonlinearities in the systems are increased. Further, even in the absence of boundary layer instabilities, nonlinearity in the system often leads to complicated interior flows due to subcritical instabilities, Eckhaus bands and heteroclinic dynamics. The ensuing spatio-temporally complex dynamics is analysed in terms of equivariant dynamical systems, providing a general perspective for the wide range of dynamics involved.Flexible rod design for educational wind balance
http://hdl.handle.net/2117/102821
Flexible rod design for educational wind balance
Raush Alviach, Gustavo Adolfo; Castilla López, Roberto; Gámez Montero, Pedro Javier; Wojciechowski, Jakub; Codina Macià, Esteban
This article provides a technical description of a flexible hinge for wind tunnel rigs. For academic purposes, the device was integrated into several rod flexures to build a home-made external wind balance system. The cylindrical elastic element incorporates several notches, and the flexure linkage is able to transmit force in the main axial direction without hindering perpendicular movement. The flexural element described here is simple and easily manufactured, and can also be used with other types of wind balance. The flexure described in this article has similar functionality to those mentioned in the reference section, but has a more compact element. The project's effectiveness was demonstrated in a series of experimental comparisons of forces and moments measured on a wing using the N.A.C.A. Clark-Y airfoil profile.
This is a copy of the author 's preprint version of an article published in the journal Experimental techniques. The final publication is available at Springer via http://dx.doi.org/10.1007/s40799-016-0017-9
Thu, 23 Mar 2017 11:45:22 GMThttp://hdl.handle.net/2117/1028212017-03-23T11:45:22ZRaush Alviach, Gustavo AdolfoCastilla López, RobertoGámez Montero, Pedro JavierWojciechowski, JakubCodina Macià, EstebanThis article provides a technical description of a flexible hinge for wind tunnel rigs. For academic purposes, the device was integrated into several rod flexures to build a home-made external wind balance system. The cylindrical elastic element incorporates several notches, and the flexure linkage is able to transmit force in the main axial direction without hindering perpendicular movement. The flexural element described here is simple and easily manufactured, and can also be used with other types of wind balance. The flexure described in this article has similar functionality to those mentioned in the reference section, but has a more compact element. The project's effectiveness was demonstrated in a series of experimental comparisons of forces and moments measured on a wing using the N.A.C.A. Clark-Y airfoil profile.Periodic orbits in tall laterally heated rectangular cavities
http://hdl.handle.net/2117/102448
Periodic orbits in tall laterally heated rectangular cavities
Net Marcé, Marta; Sánchez Umbría, Juan
This study elucidates the origin of the multiplicity of stable oscillatory flows detected by time integration in tall rectangular cavities heated from the side. By using continuation techniques for periodic orbits, it is shown that initially unstable branches, arising at Hopf bifurcations of the basic steady flow, become stable after crossing Neimark-Sacker points. There are no saddle-node or pitchfork bifurcations of periodic orbits, which could have been alternative mechanisms of stabilization. According to the symmetries of the system, the orbits are either fixed cycles, which retain at any time the center symmetry of the steady flow, or symmetric cycles involving a time shift in the global invariance of the orbit. The bifurcation points along the branches of periodic flows are determined. By using time integrations, with unstable periodic solutions as initial conditions, we determine which of the bifurcations at the limits of the intervals of stable periodic orbits are sub- or supercritical.
Tue, 14 Mar 2017 13:11:34 GMThttp://hdl.handle.net/2117/1024482017-03-14T13:11:34ZNet Marcé, MartaSánchez Umbría, JuanThis study elucidates the origin of the multiplicity of stable oscillatory flows detected by time integration in tall rectangular cavities heated from the side. By using continuation techniques for periodic orbits, it is shown that initially unstable branches, arising at Hopf bifurcations of the basic steady flow, become stable after crossing Neimark-Sacker points. There are no saddle-node or pitchfork bifurcations of periodic orbits, which could have been alternative mechanisms of stabilization. According to the symmetries of the system, the orbits are either fixed cycles, which retain at any time the center symmetry of the steady flow, or symmetric cycles involving a time shift in the global invariance of the orbit. The bifurcation points along the branches of periodic flows are determined. By using time integrations, with unstable periodic solutions as initial conditions, we determine which of the bifurcations at the limits of the intervals of stable periodic orbits are sub- or supercritical.Maxwell equations in the Debye potential formalism
http://hdl.handle.net/2117/102159
Maxwell equations in the Debye potential formalism
Fayos Vallés, Francisco; Llanta Salleras, Estanislao; Llosa, J
The authors propose a method for computing the electromagnetic test-field created by a given distribution of charges and currents using the Debye potential formalism in curved space-times. This framework has been applied explicitly to the Schwarzschild case.
Wed, 08 Mar 2017 18:24:18 GMThttp://hdl.handle.net/2117/1021592017-03-08T18:24:18ZFayos Vallés, FranciscoLlanta Salleras, EstanislaoLlosa, JThe authors propose a method for computing the electromagnetic test-field created by a given distribution of charges and currents using the Debye potential formalism in curved space-times. This framework has been applied explicitly to the Schwarzschild case.Nonlinear and detuning effects of the nutation angle in precessionally-forced rotating cylinder flow
http://hdl.handle.net/2117/101564
Nonlinear and detuning effects of the nutation angle in precessionally-forced rotating cylinder flow
Lopez Moscat, Juan Manuel; Marqués Truyol, Francisco
The flow in a rapidly rotating cylinder forced to precess through a nutation angle a
is investigated numerically, keeping all parameters constant except a, and tuned to a
triadic resonance at a = 1º. When increasing a, the flow undergoes a sequence of well-
characterized bifurcations associated with triadic resonance, involving heteroclinic and
homoclinic cycles, for a up to about 4º. For larger a, we identify two chaotic regimes.
In the first regime, with a between about 4º and 27º, the bulk flow retains remnants of
the helical structures associated with the triadic resonance, but there are strong nonlinear
interactions between the various azimuthal Fourier components of the flow. For the larger
a regime, large detuning effects lead to the triadic resonance dynamics being completely
swamped by boundary layer eruptions. The azimuthal mean flow at large angles results in a
large mean deviation from solid-body rotation and the flow is characterized by strong shear
at the boundary layers with temporally chaotic eruptions.
Fri, 24 Feb 2017 15:42:52 GMThttp://hdl.handle.net/2117/1015642017-02-24T15:42:52ZLopez Moscat, Juan ManuelMarqués Truyol, FranciscoThe flow in a rapidly rotating cylinder forced to precess through a nutation angle a
is investigated numerically, keeping all parameters constant except a, and tuned to a
triadic resonance at a = 1º. When increasing a, the flow undergoes a sequence of well-
characterized bifurcations associated with triadic resonance, involving heteroclinic and
homoclinic cycles, for a up to about 4º. For larger a, we identify two chaotic regimes.
In the first regime, with a between about 4º and 27º, the bulk flow retains remnants of
the helical structures associated with the triadic resonance, but there are strong nonlinear
interactions between the various azimuthal Fourier components of the flow. For the larger
a regime, large detuning effects lead to the triadic resonance dynamics being completely
swamped by boundary layer eruptions. The azimuthal mean flow at large angles results in a
large mean deviation from solid-body rotation and the flow is characterized by strong shear
at the boundary layers with temporally chaotic eruptions.An exactly solvable model in P.R.M.: quantization. II
http://hdl.handle.net/2117/101439
An exactly solvable model in P.R.M.: quantization. II
Iranzo Fernández, Vicente; Llosa, J; Marqués Truyol, Francisco; Molina, A
The quantization of a priori hamiltonian predictive systems is studied. It is applied to quantize the family of N-particle relativistic models presented in ref. 1. The relativistic two-particle oscillator is studied in detail and finally our results are compared with others that already appeared in the literature.; On étudié la quantification de systèmes hamiltoniens pre-prédictifs a priori. Comme application, on quantifie la famille de modèles relativistes à N particules présentes dans la référence 1. On étudié en detail l’oscillateur relativiste a deux particules. Finalement on compare les résultats obtenus avec d’autres parus précédemment.
Thu, 23 Feb 2017 09:37:44 GMThttp://hdl.handle.net/2117/1014392017-02-23T09:37:44ZIranzo Fernández, VicenteLlosa, JMarqués Truyol, FranciscoMolina, AThe quantization of a priori hamiltonian predictive systems is studied. It is applied to quantize the family of N-particle relativistic models presented in ref. 1. The relativistic two-particle oscillator is studied in detail and finally our results are compared with others that already appeared in the literature.
On étudié la quantification de systèmes hamiltoniens pre-prédictifs a priori. Comme application, on quantifie la famille de modèles relativistes à N particules présentes dans la référence 1. On étudié en detail l’oscillateur relativiste a deux particules. Finalement on compare les résultats obtenus avec d’autres parus précédemment.Are the Pyrenees a barrier for the transport of birch (Betula) pollen from Central Europe to the Iberian Peninsula?
http://hdl.handle.net/2117/101352
Are the Pyrenees a barrier for the transport of birch (Betula) pollen from Central Europe to the Iberian Peninsula?
Izquierdo Miguel, Rebeca; Alarcón Jordán, Marta; Mazón Bueso, Jordi; Pino González, David; De Linares, Concha; Aguinagalde, Xabier; Belmonte Soler, Jordina
This work provides a first assessment of the possible barrier effect of the Pyrenees on the atmospheric transport of airborne pollen from Europe to the North of the Iberian Peninsula. Aerobiological data recorded in three Spanish stations located at the eastern, central and western base of the Pyrenees in the period 2004–2014 have been used to identify the possible long range transport episodes of Betula pollen. The atmospheric transport routes and the origin regions have been established by means of trajectory analysis and a source receptor model. Betula pollen outbreaks were associated with the meteorological scenario characterized by the presence of a high-pressure system overm over Morocco and Southern Iberian Peninsula. France and Central Europe have been identified as the probable source areas of Betula pollen that arrives to Northern Spain. However, the specific source areas are mainly determined by the particular prevailing atmospheric circulation of each location. Finally, the Weather Research and Forecasting model highlighted the effect of the orography on the atmospheric transport patterns, showing paths through the western and easternmost lowlands for Vitoria-Gasteiz and Bellaterra respectively, and the direct impact of air flows over Vielha through the Garona valley.
Tue, 21 Feb 2017 17:22:07 GMThttp://hdl.handle.net/2117/1013522017-02-21T17:22:07ZIzquierdo Miguel, RebecaAlarcón Jordán, MartaMazón Bueso, JordiPino González, DavidDe Linares, ConchaAguinagalde, XabierBelmonte Soler, JordinaThis work provides a first assessment of the possible barrier effect of the Pyrenees on the atmospheric transport of airborne pollen from Europe to the North of the Iberian Peninsula. Aerobiological data recorded in three Spanish stations located at the eastern, central and western base of the Pyrenees in the period 2004–2014 have been used to identify the possible long range transport episodes of Betula pollen. The atmospheric transport routes and the origin regions have been established by means of trajectory analysis and a source receptor model. Betula pollen outbreaks were associated with the meteorological scenario characterized by the presence of a high-pressure system overm over Morocco and Southern Iberian Peninsula. France and Central Europe have been identified as the probable source areas of Betula pollen that arrives to Northern Spain. However, the specific source areas are mainly determined by the particular prevailing atmospheric circulation of each location. Finally, the Weather Research and Forecasting model highlighted the effect of the orography on the atmospheric transport patterns, showing paths through the western and easternmost lowlands for Vitoria-Gasteiz and Bellaterra respectively, and the direct impact of air flows over Vielha through the Garona valley.Precession of a rapidly rotating cylinder flow: traverse through resonance
http://hdl.handle.net/2117/100084
Precession of a rapidly rotating cylinder flow: traverse through resonance
Marqués Truyol, Francisco; López Moscat, Juan Manuel
Recent experiments using a rapidly rotating and precessing cylinder have shown that for specific values of the precession rate, aspect ratio and tilt angle, sudden catastrophic transitions to turbulence occur. Even if the precessional forcing is not too strong, there can be intermittent recurrences between a laminar state and small-scale chaotic flow. The inviscid linearized Navier Stokes equations have inertial-wave solutions called Kelvin eigenmodes. The precession forces the flow to have azimuthal wavenumber m = 1 (spin-over mode). Depending on the cylinder aspect ratio and on the ratio of the rotating and precessing frequencies, additional Kelvin modes can be in resonance with the spin-over mode. This resonant flow would grow unbounded if not for the presence of viscous and nonlinear effects. In practice, one observes a rapid transition to turbulence, and the precise nature of the transition is not entirely clear. When both the precessional forcing and viscous effects are small, weakly nonlinear models and experimental observations suggest that triadic resonance is at play. Here, we used direct numerical simulations of the full Navier Stokes equations in a narrow region of parameter space where triadic resonance has been previously predicted from a weakly nonlinear model and observed experimentally. The detailed parametric studies enabled by the numerics reveal the complex dynamics associated with weak precessional forcing, involving symmetry-breaking, hysteresis and heteroclinic cycles between states that are quasiperiodic, with two or three independent frequencies. The detailed analysis of these states leads to associations of physical mechanisms with the various time scales involved.
Wed, 25 Jan 2017 20:01:41 GMThttp://hdl.handle.net/2117/1000842017-01-25T20:01:41ZMarqués Truyol, FranciscoLópez Moscat, Juan ManuelRecent experiments using a rapidly rotating and precessing cylinder have shown that for specific values of the precession rate, aspect ratio and tilt angle, sudden catastrophic transitions to turbulence occur. Even if the precessional forcing is not too strong, there can be intermittent recurrences between a laminar state and small-scale chaotic flow. The inviscid linearized Navier Stokes equations have inertial-wave solutions called Kelvin eigenmodes. The precession forces the flow to have azimuthal wavenumber m = 1 (spin-over mode). Depending on the cylinder aspect ratio and on the ratio of the rotating and precessing frequencies, additional Kelvin modes can be in resonance with the spin-over mode. This resonant flow would grow unbounded if not for the presence of viscous and nonlinear effects. In practice, one observes a rapid transition to turbulence, and the precise nature of the transition is not entirely clear. When both the precessional forcing and viscous effects are small, weakly nonlinear models and experimental observations suggest that triadic resonance is at play. Here, we used direct numerical simulations of the full Navier Stokes equations in a narrow region of parameter space where triadic resonance has been previously predicted from a weakly nonlinear model and observed experimentally. The detailed parametric studies enabled by the numerics reveal the complex dynamics associated with weak precessional forcing, involving symmetry-breaking, hysteresis and heteroclinic cycles between states that are quasiperiodic, with two or three independent frequencies. The detailed analysis of these states leads to associations of physical mechanisms with the various time scales involved.