Altres
http://hdl.handle.net/2117/15797
2017-11-24T18:34:05ZDetailed numerical model for the receiver of a solar power tower plant
http://hdl.handle.net/2117/111192
Detailed numerical model for the receiver of a solar power tower plant
Chiva Segura, Jorge; Lehmkuhl Barba, Oriol; Oliva Llena, Asensio
In this paper, a numerical model for the simulation of the receiver of a solar power tower plant is presented.
This global model is composed of 4 specific sub-models (heat conduction, two-phase, thermal radiation and
natural convection) which are described.
2017-11-24T18:23:26ZChiva Segura, JorgeLehmkuhl Barba, OriolOliva Llena, AsensioIn this paper, a numerical model for the simulation of the receiver of a solar power tower plant is presented.
This global model is composed of 4 specific sub-models (heat conduction, two-phase, thermal radiation and
natural convection) which are described.Direct numerical simulation of the turbulent natural convection flow in an open cavity of aspect ratio 4
http://hdl.handle.net/2117/111187
Direct numerical simulation of the turbulent natural convection flow in an open cavity of aspect ratio 4
Chiva Segura, Jorge; Lehmkuhl Barba, Oriol; Borrell Pol, Ricard; Oliva Llena, Asensio
In this paper, three-dimensional turbulent natural convection heat transfer in an open cavity with an
isothermal wall facing the overture has been studied. The aspect ratio chosen for the cavity has been 4 to complement
the studies by Trias et al. [1, 2] of closed cavities with the same aspect ratio. Direct numerical simulations
(DNS) of the cavity are presented and analyzed. Rayleigh numbers up to Ra = 1012 has been considered.
2017-11-24T18:00:33ZChiva Segura, JorgeLehmkuhl Barba, OriolBorrell Pol, RicardOliva Llena, AsensioIn this paper, three-dimensional turbulent natural convection heat transfer in an open cavity with an
isothermal wall facing the overture has been studied. The aspect ratio chosen for the cavity has been 4 to complement
the studies by Trias et al. [1, 2] of closed cavities with the same aspect ratio. Direct numerical simulations
(DNS) of the cavity are presented and analyzed. Rayleigh numbers up to Ra = 1012 has been considered.Scattering properties of a PT dipole
http://hdl.handle.net/2117/111185
Scattering properties of a PT dipole
Staliunas, Kestutis; Markos, P.; Kuzmiak, V.
Electromagnetic response of a PT dipole is studied both analytically and numerically. In the analytical approach, the dipole is represented by two point scatterers. Within the first Born approximation, the asymmetry of the scattering field with respect to the orientation of the dipole is proven. In numerical simulations, the dipole is represented by two infinitely long, parallel cylinders with opposite sign of the imaginary part of a refractive index. Numerical data confirm the validity of the Born approximation in the weak scattering limit, while significant deviations from the Born approximation were observed for stronger scatterers and in the near-field range.
2017-11-24T17:38:21ZStaliunas, KestutisMarkos, P.Kuzmiak, V.Electromagnetic response of a PT dipole is studied both analytically and numerically. In the analytical approach, the dipole is represented by two point scatterers. Within the first Born approximation, the asymmetry of the scattering field with respect to the orientation of the dipole is proven. In numerical simulations, the dipole is represented by two infinitely long, parallel cylinders with opposite sign of the imaginary part of a refractive index. Numerical data confirm the validity of the Born approximation in the weak scattering limit, while significant deviations from the Born approximation were observed for stronger scatterers and in the near-field range.Large-eddy simulation of turbulent dynamic fluid-structure interaction
http://hdl.handle.net/2117/111178
Large-eddy simulation of turbulent dynamic fluid-structure interaction
Estruch Pérez, Olga; Lehmkuhl Barba, Oriol; Borrell Pol, Ricard; Pérez Segarra, Carlos David
2017-11-24T16:29:36ZEstruch Pérez, OlgaLehmkuhl Barba, OriolBorrell Pol, RicardPérez Segarra, Carlos DavidMultiferroic and related hysteretic behavior in ferromagnetic shape memory alloys
http://hdl.handle.net/2117/111177
Multiferroic and related hysteretic behavior in ferromagnetic shape memory alloys
Gebbia, Jonathan Fernando; Castán Vidal, Teresa; Lloveras Muntané, Pol Marcel; Porta Tena, Marcel; Saxena, Avadh; Planes Vila, Antoni
We combine a Ginzburg–Landau model for a ferroelastic transition with the theory of micromagnetism to study the magnetostructural behavior leading to multicaloric effects in ferromagnetic shape memory alloys. We analyze the ferroelastic transition under different conditions of temperature, stress and magnetic field and establish the corresponding phase diagram. On the one hand, our results show that the proper combination of both fields may be used to reduce the transition hysteresis and thus improve the reversibility of the related elastocaloric effects, superelasticity and stress-mediated magnetocaloric effects. On the other hand, the stress-free magnetic field-driven and thermally driven magnetostructural evolution provides physical insight into the low-temperature field-induced domain reorientation, from which we derive strategies to modify the operational temperature ranges and thus the corresponding (magnetic) shape-memory effect.
2017-11-24T16:06:58ZGebbia, Jonathan FernandoCastán Vidal, TeresaLloveras Muntané, Pol MarcelPorta Tena, MarcelSaxena, AvadhPlanes Vila, AntoniWe combine a Ginzburg–Landau model for a ferroelastic transition with the theory of micromagnetism to study the magnetostructural behavior leading to multicaloric effects in ferromagnetic shape memory alloys. We analyze the ferroelastic transition under different conditions of temperature, stress and magnetic field and establish the corresponding phase diagram. On the one hand, our results show that the proper combination of both fields may be used to reduce the transition hysteresis and thus improve the reversibility of the related elastocaloric effects, superelasticity and stress-mediated magnetocaloric effects. On the other hand, the stress-free magnetic field-driven and thermally driven magnetostructural evolution provides physical insight into the low-temperature field-induced domain reorientation, from which we derive strategies to modify the operational temperature ranges and thus the corresponding (magnetic) shape-memory effect.Experimental characterization of the transition to coherence collapse in a semiconductor laser with optical feedback
http://hdl.handle.net/2117/111176
Experimental characterization of the transition to coherence collapse in a semiconductor laser with optical feedback
Panozzo, M.; Quintero Quiroz, Carlos Alberto; Tiana Alsina, Jordi; Torrent Serra, Maria del Carmen; Masoller Alonso, Cristina
Semiconductor lasers with time-delayed optical feedback display a wide range of dynamical regimes, which have found various practical applications. They also provide excellent testbeds for data analysis tools for characterizing complex signals. Recently, several of us have analyzed experimental intensity time-traces and quantitatively identified the onset of different dynamical regimes, as the laser current increases. Specifically, we identified the onset of low-frequency fluctuations (LFFs), where the laser intensity displays abrupt dropouts, and the onset of coherence collapse (CC), where the intensity fluctuations are highly irregular. Here we map these regimes when both, the laser current and the feedback strength vary. We show that the shape of the distribution of intensity fluctuations (characterized by the standard deviation, the skewness, and the kurtosis) allows to distinguish among noise, LFFs and CC, and to quantitatively determine (in spite of the gradual nature of the transitions) the boundaries of the three regimes. Ordinal analysis of the interdropout time intervals consistently identifies the three regimes occurring in the same parameter regions as the analysis of the intensity distribution. Simulations of the well-known time-delayed Lang-Kobayashi model are in good qualitative agreement with the observations.
2017-11-24T15:37:16ZPanozzo, M.Quintero Quiroz, Carlos AlbertoTiana Alsina, JordiTorrent Serra, Maria del CarmenMasoller Alonso, CristinaSemiconductor lasers with time-delayed optical feedback display a wide range of dynamical regimes, which have found various practical applications. They also provide excellent testbeds for data analysis tools for characterizing complex signals. Recently, several of us have analyzed experimental intensity time-traces and quantitatively identified the onset of different dynamical regimes, as the laser current increases. Specifically, we identified the onset of low-frequency fluctuations (LFFs), where the laser intensity displays abrupt dropouts, and the onset of coherence collapse (CC), where the intensity fluctuations are highly irregular. Here we map these regimes when both, the laser current and the feedback strength vary. We show that the shape of the distribution of intensity fluctuations (characterized by the standard deviation, the skewness, and the kurtosis) allows to distinguish among noise, LFFs and CC, and to quantitatively determine (in spite of the gradual nature of the transitions) the boundaries of the three regimes. Ordinal analysis of the interdropout time intervals consistently identifies the three regimes occurring in the same parameter regions as the analysis of the intensity distribution. Simulations of the well-known time-delayed Lang-Kobayashi model are in good qualitative agreement with the observations.Multi-longitudinal-mode micro-laser model
http://hdl.handle.net/2117/111174
Multi-longitudinal-mode micro-laser model
Staliunas, Kestutis
We derive a convenient model for broad aperture micro-lasers, such as microchip lasers, broad area semiconductor lasers, or VCSELs, taking into account several longitudinal mode families. We provide linear stability analysis, and show characteristic spatio-temporal dynamics in such multi-longitudinal mode laser models. Moreover, we derive the coupled mode model in the presence of intracavity refraction index modulation (intracavity photonic crystal). Graphical abstract: [Figure not available: see fulltext.].
2017-11-24T14:17:00ZStaliunas, KestutisWe derive a convenient model for broad aperture micro-lasers, such as microchip lasers, broad area semiconductor lasers, or VCSELs, taking into account several longitudinal mode families. We provide linear stability analysis, and show characteristic spatio-temporal dynamics in such multi-longitudinal mode laser models. Moreover, we derive the coupled mode model in the presence of intracavity refraction index modulation (intracavity photonic crystal). Graphical abstract: [Figure not available: see fulltext.].Un patrimoni natural i cultural a preservar. Les fonts del Montseny
http://hdl.handle.net/2117/111153
Un patrimoni natural i cultural a preservar. Les fonts del Montseny
Farrerons Vidal, Óscar; Font Valentí, Gemma
2017-11-24T10:57:34ZFarrerons Vidal, ÓscarFont Valentí, GemmaA family of gradient descent grid frequency estimators for the SOGI filter
http://hdl.handle.net/2117/111151
A family of gradient descent grid frequency estimators for the SOGI filter
Matas Alcalá, José; Martín Cañadas, María Elena; Hoz Casas, Jordi de la; Abusorrah, A.; Al-Turki, Y.A.; Al-Hindawi, M.
This paper applies the adaptive gradient descent method to the second-order generalized integrator (SOGI) filter in order to find an online estimation algorithm for the grid frequency, which leads to the proposal of three possible estimators. One of them is identical to the FLL algorithm reported in literature, which proves that it should be understood as a gradient descent estimation algorithm and not as a "frequency locked loop". The proposed gradient descent estimators are simple and suitable to be implemented into a digital processor with small computational burden. However, due to the SOGI characteristics, the estimators show to be especially sensitive to subharmonic and dc-offset voltage distortion. These problems are removed adopting a cascaded double SOGI approach, which strongly increases the rejection capability to harmonics and enhances the response to voltage sags. Simulation and experimental results are provided to validate the proposed contribution.
2017-11-24T10:14:29ZMatas Alcalá, JoséMartín Cañadas, María ElenaHoz Casas, Jordi de laAbusorrah, A.Al-Turki, Y.A.Al-Hindawi, M.This paper applies the adaptive gradient descent method to the second-order generalized integrator (SOGI) filter in order to find an online estimation algorithm for the grid frequency, which leads to the proposal of three possible estimators. One of them is identical to the FLL algorithm reported in literature, which proves that it should be understood as a gradient descent estimation algorithm and not as a "frequency locked loop". The proposed gradient descent estimators are simple and suitable to be implemented into a digital processor with small computational burden. However, due to the SOGI characteristics, the estimators show to be especially sensitive to subharmonic and dc-offset voltage distortion. These problems are removed adopting a cascaded double SOGI approach, which strongly increases the rejection capability to harmonics and enhances the response to voltage sags. Simulation and experimental results are provided to validate the proposed contribution.A multi-version algorithm for cooperative edition of hierarchically-structured documents
http://hdl.handle.net/2117/111150
A multi-version algorithm for cooperative edition of hierarchically-structured documents
Ribó, Josep Maria; Franch Gutiérrez, Javier
Several approaches do exist to solve the problem of editing a text document cooperatively in real time. We believe that those approaches could be improved in two ways: (1) preserving the intention of the participants in a better manner and (2) benefiting from a hierarchical document structure (as in XML). This article presents an algorithm for cooperative edition of documents that (1) achieves intention preservation by keeping different versions of the concurrently accessed document fragments and that (2) reduces concurrency conflicts by restricting them to hierarchically dependent fragments.
2017-11-24T09:56:10ZRibó, Josep MariaFranch Gutiérrez, JavierSeveral approaches do exist to solve the problem of editing a text document cooperatively in real time. We believe that those approaches could be improved in two ways: (1) preserving the intention of the participants in a better manner and (2) benefiting from a hierarchical document structure (as in XML). This article presents an algorithm for cooperative edition of documents that (1) achieves intention preservation by keeping different versions of the concurrently accessed document fragments and that (2) reduces concurrency conflicts by restricting them to hierarchically dependent fragments.