DF - Dinàmica No Lineal de Fluids
http://hdl.handle.net/2117/1085
Mon, 04 Dec 2017 16:06:28 GMT2017-12-04T16:06:28ZExtensional 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 self-similar 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 codimension-two bifurcations that control the dynamics in parameter space. For large Reynolds numbers, the restriction to self-similarity 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.
Thu, 30 Nov 2017 15:52:09 GMThttp://hdl.handle.net/2117/1113932017-11-30T15:52:09ZMarqués Truyol, FranciscoMeseguer Serrano, ÁlvaroMellibovsky Elstein, FernandoWeidman, PatrickExtensional self-similar 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 codimension-two bifurcations that control the dynamics in parameter space. For large Reynolds numbers, the restriction to self-similarity 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.
Fri, 03 Nov 2017 08:37:15 GMThttp://hdl.handle.net/2117/1096912017-11-03T08:37:15ZTorres Herrera, RamonQuantum 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. 143-145., 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 non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.
Thu, 26 Oct 2017 12:18:55 GMThttp://hdl.handle.net/2117/1092632017-10-26T12:18:55ZMazón Bueso, JordiPino González, DavidInspired 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.Self-organized kilometer-scale shoreline sand wave generation: sensitivity to model and physical parameters
http://hdl.handle.net/2117/108666
Self-organized kilometer-scale 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 self-organized kilometer-scale 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, cross-shore profile, closure depth, and two perturbation shapes (P1: cross-shore bathymetric profile shift, and P2: bed level perturbation linearly decreasing offshore). For a P1 perturbation, no instability occurs below an absolute critical angle ¿c0˜ 40-50°. For a P2 perturbation, there is no absolute critical angle: sand waves can develop also for low-angle waves. In fact, the bathymetric perturbation shape plays a key role in low-angle 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 cross-shore profile has almost no effect with a P1 perturbation, whereas large surf zone slope and gently sloping shoreface strongly enhance instability under low-angle 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 low-angle wave instability.
Wed, 11 Oct 2017 16:39:52 GMThttp://hdl.handle.net/2117/1086662017-10-11T16:39:52ZIdier, DéborahFalqués Serra, AlbertRohmer, JérémyArriaga García, Jaime AlonsoThe instability mechanisms for self-organized kilometer-scale 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, cross-shore profile, closure depth, and two perturbation shapes (P1: cross-shore bathymetric profile shift, and P2: bed level perturbation linearly decreasing offshore). For a P1 perturbation, no instability occurs below an absolute critical angle ¿c0˜ 40-50°. For a P2 perturbation, there is no absolute critical angle: sand waves can develop also for low-angle waves. In fact, the bathymetric perturbation shape plays a key role in low-angle 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 cross-shore profile has almost no effect with a P1 perturbation, whereas large surf zone slope and gently sloping shoreface strongly enhance instability under low-angle 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 low-angle wave instability.Hydrological and sedimentary analysis of two recent flash floods in a Mediterranean basin with major changes in land uses and channel shape (Sió River, NE Iberian Peninsula)
http://hdl.handle.net/2117/108519
Hydrological and sedimentary analysis of two recent flash floods in a Mediterranean basin with major changes in land uses and channel shape (Sió River, NE Iberian Peninsula)
Balasch Solanes, Josep Carles; García-Rodríguez, David; Tuset Mestre, Jordi; Ruiz Bellet, Josep Lluís; Rodríguez-Ochoa, Rafael; Jacquet, Eisharc; Barriendos Valve, Mariano; Castelltort Aiguabella, Xavier; Pino González, David
Two important rain events occurred in November 2015 and November 2016 in the Sió River basin (150 km2), a
small tributary of the Segre River, within the Ebro River basin (NE Iberian Peninsula), caused two considerable
flash floods.
Mon, 09 Oct 2017 11:44:46 GMThttp://hdl.handle.net/2117/1085192017-10-09T11:44:46ZBalasch Solanes, Josep CarlesGarcía-Rodríguez, DavidTuset Mestre, JordiRuiz Bellet, Josep LluísRodríguez-Ochoa, RafaelJacquet, EisharcBarriendos Valve, MarianoCastelltort Aiguabella, XavierPino González, DavidTwo important rain events occurred in November 2015 and November 2016 in the Sió River basin (150 km2), a
small tributary of the Segre River, within the Ebro River basin (NE Iberian Peninsula), caused two considerable
flash floods.Modeling the long-term diffusion and feeding capability of a mega-nourishment
http://hdl.handle.net/2117/108377
Modeling the long-term diffusion and feeding capability of a mega-nourishment
Arriaga García, Jaime Alonso; Rutten, Jantien; Ribas Prats, Francesca; Falqués Serra, Albert; Ruessink, Gerben
A morphodynamic model based on the wave-driven alongshore sediment transport, including cross-shore transport in a simplified way and neglecting tides, is presented and applied to the Zandniotor mega-nourishment on the Dutch Delfiand coast. The model is calibrated with the bathymetric data surveyed from January 2012 to March 2013 using measured offshore wave forcing. The calibrated model reproduces accurately the surveyed evolution of the shoreline and depth contours until March 2015. According to the long-term modeling using different wave climate scenarios based on historical data, for the next 30-yr period, the Zandmotor will display diffusive behavior, asymmetric feeding to the adjacent beaches, and slow Migration to the NE. Specifically, the Zandmotor amplitude will have decayed from 960 m to about 350 m with a scatter of only about 40 m associated to climate variability. The modeled coastline diffusivity during the 3-yr period is 0.0021 m(2)/s, close to the observed value of 0.0022 m(2)/s. In contrast, the coefficient of the classical one-line diffusion equation is 0.0052 m(2)/s. Thus, the lifetime prediction, here defined as the time needed to reduce the initial amplitude by a factor 5, would be 90 yr instead of the classical diffusivity prediction of 35 yr. The resulting asymmetric feeding to adjacent beaches prodtices 100 m seaward shift at the NE section and 80 m seaward shift at the SW section. Looking at the variability associated to the different wave climates, the migration rate and the slight shape asymmetry correlate with the wave power asymmetry (W vs N waves) while the coastline diffusivity correlates with the proportion of high-angle waves, suggesting that the Dutch coast is near the high-angle wave instability threshold.
Thu, 05 Oct 2017 12:41:58 GMThttp://hdl.handle.net/2117/1083772017-10-05T12:41:58ZArriaga García, Jaime AlonsoRutten, JantienRibas Prats, FrancescaFalqués Serra, AlbertRuessink, GerbenA morphodynamic model based on the wave-driven alongshore sediment transport, including cross-shore transport in a simplified way and neglecting tides, is presented and applied to the Zandniotor mega-nourishment on the Dutch Delfiand coast. The model is calibrated with the bathymetric data surveyed from January 2012 to March 2013 using measured offshore wave forcing. The calibrated model reproduces accurately the surveyed evolution of the shoreline and depth contours until March 2015. According to the long-term modeling using different wave climate scenarios based on historical data, for the next 30-yr period, the Zandmotor will display diffusive behavior, asymmetric feeding to the adjacent beaches, and slow Migration to the NE. Specifically, the Zandmotor amplitude will have decayed from 960 m to about 350 m with a scatter of only about 40 m associated to climate variability. The modeled coastline diffusivity during the 3-yr period is 0.0021 m(2)/s, close to the observed value of 0.0022 m(2)/s. In contrast, the coefficient of the classical one-line diffusion equation is 0.0052 m(2)/s. Thus, the lifetime prediction, here defined as the time needed to reduce the initial amplitude by a factor 5, would be 90 yr instead of the classical diffusivity prediction of 35 yr. The resulting asymmetric feeding to adjacent beaches prodtices 100 m seaward shift at the NE section and 80 m seaward shift at the SW section. Looking at the variability associated to the different wave climates, the migration rate and the slight shape asymmetry correlate with the wave power asymmetry (W vs N waves) while the coastline diffusivity correlates with the proportion of high-angle waves, suggesting that the Dutch coast is near the high-angle wave instability threshold.Parametric analysis of active flow control using steady suction and steady blowing
http://hdl.handle.net/2117/107917
Parametric analysis of active flow control using steady suction and steady blowing
Prakash, Bhanu; Mellibovsky Elstein, Fernando; Bergadà Granyó, Josep Maria
Active Flow Control is implemented over NACA 2412 airfoil using Steady Suctionand Steady Blowing techniques. The pre-stall angle of attack (AOA) 12 0 is studied at a high Reynolds number (Re chord ) of 3.1*10 6 for two-dimensional, incompressible and steady flow conditions. A wide range of parametric value set is considered for Slot location (l s ), Velocity magnitude ratio (U j /U 0 ), slot width (w) and angle of perturbation (ß) using both steady suction and steady blowing independently. The numerical modeling is done using the corresponding solver in OpenFOAM, an open source CFD framework. The turbulence modeling is done using Reynolds Averaged Navier Stokes (RANS) equations, specifically k-k l -¿ model implementation in OpenFOAM. The impact of the parametric set on aerodynamic coefficients, lift (C l ) and drag( C d ), and flow separation is illustrated. Along with, the relevant boundary layer physics are explained.
Fri, 22 Sep 2017 12:38:36 GMThttp://hdl.handle.net/2117/1079172017-09-22T12:38:36ZPrakash, BhanuMellibovsky Elstein, FernandoBergadà Granyó, Josep MariaActive Flow Control is implemented over NACA 2412 airfoil using Steady Suctionand Steady Blowing techniques. The pre-stall angle of attack (AOA) 12 0 is studied at a high Reynolds number (Re chord ) of 3.1*10 6 for two-dimensional, incompressible and steady flow conditions. A wide range of parametric value set is considered for Slot location (l s ), Velocity magnitude ratio (U j /U 0 ), slot width (w) and angle of perturbation (ß) using both steady suction and steady blowing independently. The numerical modeling is done using the corresponding solver in OpenFOAM, an open source CFD framework. The turbulence modeling is done using Reynolds Averaged Navier Stokes (RANS) equations, specifically k-k l -¿ model implementation in OpenFOAM. The impact of the parametric set on aerodynamic coefficients, lift (C l ) and drag( C d ), and flow separation is illustrated. Along with, the relevant boundary layer physics are explained.NACA 2412 performance modification via using AFC
http://hdl.handle.net/2117/107734
NACA 2412 performance modification via using AFC
Summ, Thorsten; Prakash, Bhanu; Bergadà Granyó, Josep Maria; Wierschem, Andreas; Mellibovsky Elstein, Fernando
The NACA 2412 profile was numerically studied via employing 2D-DNS and implementing Active Flow Control (AFC), the Reynolds number considered was 6757, being the angle of attack of 8º. Initially, the basic flow without implementing AFC was considered, the point in which the boundary layer separates as well as the y+ value along the profile length were evaluated. A single groove location, just before the separation point, was considered, periodic forcing was employed to both modify the location of the separation point and change the separation area where vortices are present. This was undertaken resulting in a reduction of the drag coefficient while increasing the lift. Via studying a set of frequencies and amplitudes linked with the AFC periodic actuation, it was obtained the optimum set of parameters to minimize the drag while maximizing the lift.
Mon, 18 Sep 2017 12:48:14 GMThttp://hdl.handle.net/2117/1077342017-09-18T12:48:14ZSumm, ThorstenPrakash, BhanuBergadà Granyó, Josep MariaWierschem, AndreasMellibovsky Elstein, FernandoThe NACA 2412 profile was numerically studied via employing 2D-DNS and implementing Active Flow Control (AFC), the Reynolds number considered was 6757, being the angle of attack of 8º. Initially, the basic flow without implementing AFC was considered, the point in which the boundary layer separates as well as the y+ value along the profile length were evaluated. A single groove location, just before the separation point, was considered, periodic forcing was employed to both modify the location of the separation point and change the separation area where vortices are present. This was undertaken resulting in a reduction of the drag coefficient while increasing the lift. Via studying a set of frequencies and amplitudes linked with the AFC periodic actuation, it was obtained the optimum set of parameters to minimize the drag while maximizing the lift.Nonsingular black holes, the cosmological constant and asymptotic safety
http://hdl.handle.net/2117/105850
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.
Mon, 26 Jun 2017 08:31:46 GMThttp://hdl.handle.net/2117/1058502017-06-26T08:31:46ZTorres Herrera, RamonQuantum 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.Non-singular quantum improved rotating black holes and their maximal extension
http://hdl.handle.net/2117/105845
Non-singular quantum improved rotating black holes and their maximal extension
Torres Herrera, Ramon
We add a prescription to the Newman–Janis algorithm in order to use it as a means of finding new extended rotating black hole spacetimes from static spherically symmetric ones. Then, we apply the procedure to a quantum improved black hole spacetime coming from Quantum Einstein Gravity in order to get the maximally extended spacetime corresponding to a non-singular rotating black hole. We rigourously check for the existence of scalar curvature singularities in the quantum improved rotating spacetime and we show that it is devoid of them. We also analyze the horizons and causal structure of the rotating black hole and provide Penrose diagrams for the maximally extended spacetime.
The final publication is available at Springer via 10.1007/s10714-017-2236-5
Mon, 26 Jun 2017 08:04:46 GMThttp://hdl.handle.net/2117/1058452017-06-26T08:04:46ZTorres Herrera, RamonWe add a prescription to the Newman–Janis algorithm in order to use it as a means of finding new extended rotating black hole spacetimes from static spherically symmetric ones. Then, we apply the procedure to a quantum improved black hole spacetime coming from Quantum Einstein Gravity in order to get the maximally extended spacetime corresponding to a non-singular rotating black hole. We rigourously check for the existence of scalar curvature singularities in the quantum improved rotating spacetime and we show that it is devoid of them. We also analyze the horizons and causal structure of the rotating black hole and provide Penrose diagrams for the maximally extended spacetime.