Articles de revista
http://hdl.handle.net/2117/1087
20180324T23:34:56Z

Numerical continuation in classical mechanics and thermodynamics
http://hdl.handle.net/2117/114957
Numerical continuation in classical mechanics and thermodynamics
Gimenez, Aleix; Chausse, Víctor; Meseguer Serrano, Álvaro
In this paper, modern numerical continuation methodologies are presented as a way of understanding and computing multiplicity of solutions in undergraduate physics problems. Mechanical and thermodynamical problems are used as a storyline to introduce the mathematical formalism required to clarify the distinction between the uniqueness and multiplicity of equilibrium solutions and the critical states of a nonlinear physical problem, as well as to illustrate how these novel numerical continuation techniques are implemented in practice. The paper provides simple numerical Matlab codes that are easily adaptable to other problems, as well as updated software and literature resources.
20180308T18:04:57Z
Gimenez, Aleix
Chausse, Víctor
Meseguer Serrano, Álvaro
In this paper, modern numerical continuation methodologies are presented as a way of understanding and computing multiplicity of solutions in undergraduate physics problems. Mechanical and thermodynamical problems are used as a storyline to introduce the mathematical formalism required to clarify the distinction between the uniqueness and multiplicity of equilibrium solutions and the critical states of a nonlinear physical problem, as well as to illustrate how these novel numerical continuation techniques are implemented in practice. The paper provides simple numerical Matlab codes that are easily adaptable to other problems, as well as updated software and literature resources.

Influence of meteorological phenomena on worldwide aircraft accidents in the period 19672010
http://hdl.handle.net/2117/113950
Influence of meteorological phenomena on worldwide aircraft accidents in the period 19672010
Mazón Bueso, Jordi; Rojas Gregorio, José Ignacio; Lozano, Miguel; Pino González, David; Prats Menéndez, Xavier; Miglietta, M.M.
Based on the information available in databases from relevant national and international organizations from 1967 to 2010, an Aviation Weather Accidents Database (AWAD) was built. According to the AWAD, the weather is the
primary cause in a growing percentage of annual aircraft accidents: from about 40% in 1967 to almost 50% in 2010. While the absolute number of fatalities and injured people due to aircraft accidents has decreased significantly, the percentage of fatalities and injured people in accidents attributed to the weather shows a slight increase in the studied period. The influence of turbulence, clear air turbulence, wind shear, low visibility, rain, icing, snow and storms on aircraft accidents was analysed, considering the different phases of flight, the meteorological seasons of the year and the spatial distribution over four zones of the Earth. These zones were defined following meteorological and climatological criteria, instead of using the typical political criteria. A major part of the accidents and accidents attributed to the weather occur in latitudes between 12º and 38º in both hemispheres. It is concluded that actions aimed at reducing the risk associated with low visibility, rain and turbulence, in this order, should have priority to achieve the most significant improvements in air transport safety.
This is the prepeer reviewed version of the following article: Mazon, J., Rojas, J. I., Lozano, M., Pino, D., Prats, X. and Miglietta, M. M. (2017), Influence of meteorological phenomena on worldwide aircraft accidents, 1967–2010. Met. Apps. doi:10.1002/met.1686, which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1002/met.1686/abstract. This article may be used for noncommercial purposes in accordance with Wiley Terms and Conditions for SelfArchiving.
20180208T16:21:45Z
Mazón Bueso, Jordi
Rojas Gregorio, José Ignacio
Lozano, Miguel
Pino González, David
Prats Menéndez, Xavier
Miglietta, M.M.
Based on the information available in databases from relevant national and international organizations from 1967 to 2010, an Aviation Weather Accidents Database (AWAD) was built. According to the AWAD, the weather is the
primary cause in a growing percentage of annual aircraft accidents: from about 40% in 1967 to almost 50% in 2010. While the absolute number of fatalities and injured people due to aircraft accidents has decreased significantly, the percentage of fatalities and injured people in accidents attributed to the weather shows a slight increase in the studied period. The influence of turbulence, clear air turbulence, wind shear, low visibility, rain, icing, snow and storms on aircraft accidents was analysed, considering the different phases of flight, the meteorological seasons of the year and the spatial distribution over four zones of the Earth. These zones were defined following meteorological and climatological criteria, instead of using the typical political criteria. A major part of the accidents and accidents attributed to the weather occur in latitudes between 12º and 38º in both hemispheres. It is concluded that actions aimed at reducing the risk associated with low visibility, rain and turbulence, in this order, should have priority to achieve the most significant improvements in air transport safety.

Effect of a positive sea surface temperature anomaly on a Mediterranean tornadic supercell
http://hdl.handle.net/2117/112941
Effect of a positive sea surface temperature anomaly on a Mediterranean tornadic supercell
Miglietta, M.M.; Mazón Bueso, Jordi; Motola, Vicenzo; Passini, Antonello
Extreme events represent a topic of paramount importance and a challenge for modelling investigations. Due to the need of highresolution models, the study of severe localized convective phenomena is even more critical, especially in relation to changes in forcing factors, such as sea surface temperatures (SSTs), in future climate scenarios. Here, we analyze the effect of changes in SSTs on the intensity of a tornadic supercell in the Mediterranean through modelling investigations. We show dramatic (nonlinear) changes for updraft helicity and vertical velocity, which measure the intensity of the supercell, even for variations of SST only of¿+¿/1¿K.
20180118T14:12:41Z
Miglietta, M.M.
Mazón Bueso, Jordi
Motola, Vicenzo
Passini, Antonello
Extreme events represent a topic of paramount importance and a challenge for modelling investigations. Due to the need of highresolution models, the study of severe localized convective phenomena is even more critical, especially in relation to changes in forcing factors, such as sea surface temperatures (SSTs), in future climate scenarios. Here, we analyze the effect of changes in SSTs on the intensity of a tornadic supercell in the Mediterranean through modelling investigations. We show dramatic (nonlinear) changes for updraft helicity and vertical velocity, which measure the intensity of the supercell, even for variations of SST only of¿+¿/1¿K.

ULISES: an open source code for extrinsic calibrations and planview generations in coastal video monitoring systems
http://hdl.handle.net/2117/112927
ULISES: an open source code for extrinsic calibrations and planview generations in coastal video monitoring systems
Simarro, Gonzalo; Ribas Prats, Francesca; Alvarez, Amaya; Guillén Aranda, Jorge; Chic, Oscar; Orfila, Alejandro
Video monitoring systems have become a powerful and lowcost tool in coastal studies. Extrinsic calibration of the cameras is compulsory to get quantitative information from the images. This paper presents an Open Source Software for extrinsic calibration and for the generation of related products such as planviews and time stacks. The methodology employed for extrinsic calibration minimizes errors comprising ground control points, the camera position, and, whenever is available, the horizon line. The dip of the horizon due to Earth curvature is corrected for. Planview generation is performed in such a way that the user can decide the smoothing degree in the transition zone between cameras. Time stack generation has been designed to save the minimum number of pixels in order to obtain the desired transect in the real world. The reader will find a versatile software meant to manage large data sets in a simple way.
20180117T21:31:56Z
Simarro, Gonzalo
Ribas Prats, Francesca
Alvarez, Amaya
Guillén Aranda, Jorge
Chic, Oscar
Orfila, Alejandro
Video monitoring systems have become a powerful and lowcost tool in coastal studies. Extrinsic calibration of the cameras is compulsory to get quantitative information from the images. This paper presents an Open Source Software for extrinsic calibration and for the generation of related products such as planviews and time stacks. The methodology employed for extrinsic calibration minimizes errors comprising ground control points, the camera position, and, whenever is available, the horizon line. The dip of the horizon due to Earth curvature is corrected for. Planview generation is performed in such a way that the user can decide the smoothing degree in the transition zone between cameras. Time stack generation has been designed to save the minimum number of pixels in order to obtain the desired transect in the real world. The reader will find a versatile software meant to manage large data sets in a simple way.

Numerical simulations of a tornadic supercell over the Mediterranean
http://hdl.handle.net/2117/112680
Numerical simulations of a tornadic supercell over the Mediterranean
Mazón Bueso, Jordi; Miglietta, M.M.; Rotunno, Richard
On 28 November 2012, a multivortex EF3 tornado occurred in southeastern Italy causing one fatality and estimated damage of 60 million euros. At approximately 1050 LT (0950 UTC), this tornado, which initially formed in association with a supercell thunderstorm over the Ionian Sea, moved inland. The environment where the tornadic supercell developed was characterized by large vertical wind shear in the lowest 1 km of the atmosphere and moderate conditional instability. Mesoscalemodel numerical simulations show that it is possible to produce a simulated supercell thunderstorm with a track, change in intensity, and evolution similar to the actual one that spawned the tornado in Taranto, southern Italy. The genesis of the simulated supercell is due to a combination of mesoscale meteorological features: warm lowlevel air advected toward the Ionian Sea, combined with midlevel cooling due to an approaching trough, increased the potential instability; the intense vertical shear favored the possibility of supercell development; and boundary layer rolls over the Ionian Sea moved in phase with the cells produced by the orography of Calabria to supply ascent, moisture, and heat to the convection. An unusual feature of the present case is the central role of the orography, which was verified in a sensitivity experiment where it was reduced by 80%.
20180111T14:09:31Z
Mazón Bueso, Jordi
Miglietta, M.M.
Rotunno, Richard
On 28 November 2012, a multivortex EF3 tornado occurred in southeastern Italy causing one fatality and estimated damage of 60 million euros. At approximately 1050 LT (0950 UTC), this tornado, which initially formed in association with a supercell thunderstorm over the Ionian Sea, moved inland. The environment where the tornadic supercell developed was characterized by large vertical wind shear in the lowest 1 km of the atmosphere and moderate conditional instability. Mesoscalemodel numerical simulations show that it is possible to produce a simulated supercell thunderstorm with a track, change in intensity, and evolution similar to the actual one that spawned the tornado in Taranto, southern Italy. The genesis of the simulated supercell is due to a combination of mesoscale meteorological features: warm lowlevel air advected toward the Ionian Sea, combined with midlevel cooling due to an approaching trough, increased the potential instability; the intense vertical shear favored the possibility of supercell development; and boundary layer rolls over the Ionian Sea moved in phase with the cells produced by the orography of Calabria to supply ascent, moisture, and heat to the convection. An unusual feature of the present case is the central role of the orography, which was verified in a sensitivity experiment where it was reduced by 80%.

An idealised study for the long term evolution of crescentic bars
http://hdl.handle.net/2117/112625
An idealised study for the long term evolution of crescentic bars
Chen, W.L.; Dodd, Nicholas; Tiessen, M.C.H.; Calvete Manrique, Daniel
© 2017 Elsevier Ltd. An idealised study that identifies the mechanisms in the long term evolution of crescentic bar systems in nature is presented. Growth to finite amplitude (i.e., equilibration, sometimes referred to as saturation) and higher harmonic interaction are hypothesised to be the leading nonlinear effects in longterm evolution of these systems. These nonlinear effects are added to a linear stability model and used to predict crescentic bar development along a beach in Duck, North Carolina (USA) over a 2month period. The equilibration prolongs the development of bed patterns, thus allowing the long term evolution. Higher harmonic interaction enables the amplitude to be transferred from longer to shorter lengthscales, which leads to the dominance of shorter lengthscales in latter poststorm stages, as observed at Duck. The comparison with observations indicates the importance of higher harmonic interaction in the development of nearshore crescentic bar systems in nature. Additionally, it is concluded that these nonlinear effects should be included in models simulating the development of different bed patterns, and that this points a way forward for longterm morphodynamical modelling in general.
20180110T17:48:48Z
Chen, W.L.
Dodd, Nicholas
Tiessen, M.C.H.
Calvete Manrique, Daniel
© 2017 Elsevier Ltd. An idealised study that identifies the mechanisms in the long term evolution of crescentic bar systems in nature is presented. Growth to finite amplitude (i.e., equilibration, sometimes referred to as saturation) and higher harmonic interaction are hypothesised to be the leading nonlinear effects in longterm evolution of these systems. These nonlinear effects are added to a linear stability model and used to predict crescentic bar development along a beach in Duck, North Carolina (USA) over a 2month period. The equilibration prolongs the development of bed patterns, thus allowing the long term evolution. Higher harmonic interaction enables the amplitude to be transferred from longer to shorter lengthscales, which leads to the dominance of shorter lengthscales in latter poststorm stages, as observed at Duck. The comparison with observations indicates the importance of higher harmonic interaction in the development of nearshore crescentic bar systems in nature. Additionally, it is concluded that these nonlinear effects should be included in models simulating the development of different bed patterns, and that this points a way forward for longterm morphodynamical modelling in general.

Extensional channel flow revisited: a dynamical systems perspective
http://hdl.handle.net/2117/111393
Extensional channel flow revisited: a dynamical systems perspective
Marqués Truyol, Francisco; Meseguer Serrano, Álvaro; Mellibovsky Elstein, Fernando; Weidman, Patrick
Extensional selfsimilar flows in a channel are explored numerically for arbitrary stretching–shrinking rates of the confining parallel walls. The present analysis embraces time integrations, and continuations of steady and periodic solutions unfolded in the parameter space. Previous studies focused on the analysis of branches of steady solutions for particular stretching–shrinking rates, although recent studies focused also on the dynamical aspects of the problems. We have adopted a dynamical systems perspective, analysing the instabilities and bifurcations the base state undergoes when increasing the Reynolds number. It has been found that the base state becomes unstable for small Reynolds numbers, and a transitional region including complex dynamics takes place at intermediate Reynolds numbers, depending on the wall acceleration values. The base flow instabilities are constitutive parts of different codimensiontwo bifurcations that control the dynamics in parameter space. For large Reynolds numbers, the restriction to selfsimilarity results in simple flows with no realistic behaviour, but the flows obtained in the transition region can be a valuable tool for the understanding of the dynamics of realistic Navier–Stokes solutions.
20171130T15:52:09Z
Marqués Truyol, Francisco
Meseguer Serrano, Álvaro
Mellibovsky Elstein, Fernando
Weidman, Patrick
Extensional selfsimilar flows in a channel are explored numerically for arbitrary stretching–shrinking rates of the confining parallel walls. The present analysis embraces time integrations, and continuations of steady and periodic solutions unfolded in the parameter space. Previous studies focused on the analysis of branches of steady solutions for particular stretching–shrinking rates, although recent studies focused also on the dynamical aspects of the problems. We have adopted a dynamical systems perspective, analysing the instabilities and bifurcations the base state undergoes when increasing the Reynolds number. It has been found that the base state becomes unstable for small Reynolds numbers, and a transitional region including complex dynamics takes place at intermediate Reynolds numbers, depending on the wall acceleration values. The base flow instabilities are constitutive parts of different codimensiontwo bifurcations that control the dynamics in parameter space. For large Reynolds numbers, the restriction to selfsimilarity results in simple flows with no realistic behaviour, but the flows obtained in the transition region can be a valuable tool for the understanding of the dynamics of realistic Navier–Stokes solutions.

Nonsingular black holes, the cosmological constant, and asymptotic safety
http://hdl.handle.net/2117/109691
Nonsingular black holes, the cosmological constant, and asymptotic safety
Torres Herrera, Ramon
Quantum gravitational effects in black hole spacetimes with a cosmological constant ¿ are considered. The effective quantum spacetimes for the black holes are constructed by taking into account the renormalization group improvement of classical solutions obtained in the framework of unimodular gravity (a theory which is identical to general relativity at a classical level). This allows us to avoid the usual divergences associated with the presence of a running ¿. The horizons and causal structure of the improved black holes are discussed, taking into account the current observational bounds for the cosmological constant. It is shown that the resulting effective quantum black hole spacetimes are always devoid of singularities.
20171103T08:37:15Z
Torres Herrera, Ramon
Quantum gravitational effects in black hole spacetimes with a cosmological constant ¿ are considered. The effective quantum spacetimes for the black holes are constructed by taking into account the renormalization group improvement of classical solutions obtained in the framework of unimodular gravity (a theory which is identical to general relativity at a classical level). This allows us to avoid the usual divergences associated with the presence of a running ¿. The horizons and causal structure of the improved black holes are discussed, taking into account the current observational bounds for the cosmological constant. It is shown that the resulting effective quantum black hole spacetimes are always devoid of singularities.

Meteodiversity: a new concept for quantifying meteorological diversity
http://hdl.handle.net/2117/109263
Meteodiversity: a new concept for quantifying meteorological diversity
Mazón Bueso, Jordi; Pino González, David
Inspired by the concept of biodiversity used by biologists and ecologists, the concept of meteodiversity is proposed as a method of characterising the variety of meteorological phenomena in a defined area within a specified period. Similarly to the term biodiversity, meteodiversity takes into account the proportion of individual meteorological phenomena belonging to the main weather that occur in a defined area. The benefits and importance of using this concept are discussed.
For quantification purposes, we propose a meteodiversity index, which, in addition to events and phenomena, should include a large number of atmospheric variables obtained from instrumental and observational records. This index itemises not only events ans phenomena, but also a large number of atmospheric variables obtained from instrumental and observational records.
We use climatic data obtained from the Met Office and European Climate Assessment and Dataset project to evaluate the meteodiversity index, first on a monthly scale for the period 1981–2014 at Llanfairpwllgwyngyll (UK), and then on an annual scale for 1962–2014 at Barcelona (Spain) and Helsinki (Finland). The weather diversity and the trends over these cities have been analyzed.
This is the peer reviewed version of the following article: Mazon, J., Pino, D. Meteodiversity: a new concept for quantifying meteorological diversity. "Weather", 10 Maig 2017, vol. 72, núm. 5, p. 143145., which has been published in final form at http://onlinelibrary.wiley.com/wol1/doi/10.1002/wea.2945/abstract. This article may be used for noncommercial purposes in accordance with Wiley Terms and Conditions for SelfArchiving.
20171026T12:18:55Z
Mazón Bueso, Jordi
Pino González, David
Inspired by the concept of biodiversity used by biologists and ecologists, the concept of meteodiversity is proposed as a method of characterising the variety of meteorological phenomena in a defined area within a specified period. Similarly to the term biodiversity, meteodiversity takes into account the proportion of individual meteorological phenomena belonging to the main weather that occur in a defined area. The benefits and importance of using this concept are discussed.
For quantification purposes, we propose a meteodiversity index, which, in addition to events and phenomena, should include a large number of atmospheric variables obtained from instrumental and observational records. This index itemises not only events ans phenomena, but also a large number of atmospheric variables obtained from instrumental and observational records.
We use climatic data obtained from the Met Office and European Climate Assessment and Dataset project to evaluate the meteodiversity index, first on a monthly scale for the period 1981–2014 at Llanfairpwllgwyngyll (UK), and then on an annual scale for 1962–2014 at Barcelona (Spain) and Helsinki (Finland). The weather diversity and the trends over these cities have been analyzed.

Selforganized kilometerscale shoreline sand wave generation: sensitivity to model and physical parameters
http://hdl.handle.net/2117/108666
Selforganized kilometerscale shoreline sand wave generation: sensitivity to model and physical parameters
Idier, Déborah; Falqués Serra, Albert; Rohmer, Jérémy; Arriaga García, Jaime Alonso
The instability mechanisms for selforganized kilometerscale shoreline sand waves have been extensively explored by modeling. However, while the assumed bathymetric perturbation associated with the sand wave controls the feedback between morphology and waves, its effect on the instability onset has not been explored. In addition, no systematic investigation of the effect of the physical parameters has been done yet. Using a linear stability model, we investigate the effect of wave conditions, crossshore profile, closure depth, and two perturbation shapes (P1: crossshore bathymetric profile shift, and P2: bed level perturbation linearly decreasing offshore). For a P1 perturbation, no instability occurs below an absolute critical angle ¿c0˜ 4050°. For a P2 perturbation, there is no absolute critical angle: sand waves can develop also for lowangle waves. In fact, the bathymetric perturbation shape plays a key role in lowangle wave instability: such instability only develops if the curvature of the depth contours offshore the breaking zone is larger than the shoreline one. This can occur for the P2 perturbation but not for P1. The analysis of bathymetric data suggests that both curvature configurations could exist in nature. For both perturbation types, large wave angle, small wave period, and large closure depth strongly favor instability. The crossshore profile has almost no effect with a P1 perturbation, whereas large surf zone slope and gently sloping shoreface strongly enhance instability under lowangle waves for a P2 perturbation. Finally, predictive statistical models are set up to identify sites prone to exhibit either a critical angle close to ¿c0 or lowangle wave instability.
20171011T16:39:52Z
Idier, Déborah
Falqués Serra, Albert
Rohmer, Jérémy
Arriaga García, Jaime Alonso
The instability mechanisms for selforganized kilometerscale shoreline sand waves have been extensively explored by modeling. However, while the assumed bathymetric perturbation associated with the sand wave controls the feedback between morphology and waves, its effect on the instability onset has not been explored. In addition, no systematic investigation of the effect of the physical parameters has been done yet. Using a linear stability model, we investigate the effect of wave conditions, crossshore profile, closure depth, and two perturbation shapes (P1: crossshore bathymetric profile shift, and P2: bed level perturbation linearly decreasing offshore). For a P1 perturbation, no instability occurs below an absolute critical angle ¿c0˜ 4050°. For a P2 perturbation, there is no absolute critical angle: sand waves can develop also for lowangle waves. In fact, the bathymetric perturbation shape plays a key role in lowangle wave instability: such instability only develops if the curvature of the depth contours offshore the breaking zone is larger than the shoreline one. This can occur for the P2 perturbation but not for P1. The analysis of bathymetric data suggests that both curvature configurations could exist in nature. For both perturbation types, large wave angle, small wave period, and large closure depth strongly favor instability. The crossshore profile has almost no effect with a P1 perturbation, whereas large surf zone slope and gently sloping shoreface strongly enhance instability under lowangle waves for a P2 perturbation. Finally, predictive statistical models are set up to identify sites prone to exhibit either a critical angle close to ¿c0 or lowangle wave instability.