Forced three-wave interactions of capillary-gravity surface waves

Editors' suggestionInternational audienceThree-wave resonant interactions constitute an essential nonlinear mechanism coupling capillary surface waves. In a previous work [Haudin et al. Phys. Rev. E 93, 043110 (2016)], we characterized experimentally the generation by this mechanism of a daughter wave, whose amplitude saturates due to the viscous dissipation. Here, we show experimentally the generation of a daughter wave verifying the resonant conditions, but not the dispersion relation. By modeling the response of the free surface at the lowest nonlinear order, we explain this observation as a forced interaction. The bandwidth of the linear transfer function of the free surface is indeed increased by the significant viscous dissipation. The observation of free surface excitations not following the linear dispersion relation then becomes possible. This forced three-wave interaction mechanism could have important consequences for wave turbulence in experimental or natural systems with nonnegligible dissipation

The Alestle - Vol. 57 No. 53 - 04/12/2005

Vol. 57 No. 5

OC6 Phase II: Integration and verification of a new soil–structure interaction model for offshore wind design

This paper provides a summary of the work done within the OC6 Phase II project, which was focused on the implementation and verification of an advanced soil–structure interaction model for offshore wind system design and analysis. The soil–structure interaction model comes from the REDWIN project and uses an elastoplastic, macroelement model with kinematic hardening, which captures the stiffness and damping characteristics of offshore wind foundations more accurately than more traditional and simplified soil–structure interaction modeling approaches. Participants in the OC6 project integrated this macroelement capability to coupled aero-hydro-servo-elastic offshore wind turbine modeling tools and verified the implementation by comparing simulation results across the modeling tools for an example monopile design. The simulation results were also compared to more traditional soil–structure interaction modeling approaches like apparent fixity, coupled springs, and distributed springs models. The macroelement approach resulted in smaller overall loading in the system due to both shifts in the system frequencies and increased energy dissipation. No validation work was performed, but the macroelement approach has shown increased accuracy within the REDWIN project, resulting in decreased uncertainty in the design. For the monopile design investigated here, that implies a less conservative and thus more cost-effective offshore wind design.US Department of Energy Office of Energy Efficiency and Renewable Energy Wind Energy Technologies Office, Grant/Award Number: DE-AC36-08GO2830

From chemical gardens to chemobrionics

Chemical gardens are perhaps the best example in chemistry of a self-organizing nonequilibrium process that creates complex structures. Many different chemical systems and materials can form these self-assembling structures, which span at least 8 orders of magnitude in size, from nanometers to meters. Key to this marvel is the self-propagation under fluid advection of reaction zones forming semipermeable precipitation membranes that maintain steep concentration gradients, with osmosis and buoyancy as the driving forces for fluid flow. Chemical gardens have been studied from the alchemists onward, but now in the 21st century we are beginning to understand how they can lead us to a new domain of self-organized structures of semipermeable membranes and amorphous as well as polycrystalline solids produced at the interface of chemistry, fluid dynamics, and materials science. We propose to call this emerging field chemobrionics

OC6 project phase III : validation of the aerodynamic loading on a wind turbine rotor undergoing large motion caused by a floating support structure

This paper provides a summary of the work done within Phase III of the Offshore Code Comparison, Collaboration, Continued, with Correlation and unCertainty project (OC6), under International Energy Agency Wind Task 30. This phase focused on validating the aerodynamic loading on a wind turbine rotor undergoing large motion caused by a floating support structure. Numerical models of the Danish Technical University 10-MW reference wind turbine were validated using measurement data from a 1:75 scale test performed during the UNsteady Aerodynamics for FLOating Wind (UNAFLOW) project and a follow-on experimental campaign, both performed at the Politecnico di Milano wind tunnel. Validation of the models was performed by comparing the loads for steady (fixed platform) and unsteady wind conditions (harmonic motion of the platform). For the unsteady wind conditions, the platform was forced to oscillate in the surge and pitch directions under several frequencies and amplitudes. These oscillations result in a wind variation that impacts the rotor loads (e.g., thrust and torque). For the conditions studied in these tests, the system mainly described a quasi-steady aerodynamic behavior. Only a small hysteresis in airfoil performance undergoing angle of attack variations in attached flow was observed. During the experiments, the rotor speed and blade pitch angle were held constant. However, in real wind turbine operating conditions, the surge and pitch variations would result in rotor speed variations and/or blade pitch actuations depending on the wind turbine controller region that the system is operating. Additional simulations with these control parameters were conducted to verify the fidelity between different models. Participant results showed in general a good agreement with the experimental measurements and the need to account for dynamic inflow when there are changes in the flow conditions due to the rotor speed variations or blade pitch actuations in response to surge and pitch motion. Numerical models not accounting for dynamic inflow effects predicted rotor loads that were 9 % lower in amplitude during rotor speed variations and 18 % higher in amplitude during blade pitch actuations

Fronts et dynamiques spatio-temporelles dans l'expérience de la valve à cristaux liquides : effets de forçages spatiaux et rétroaction optique non locale

The appearance of spatial structures is a universal phenomenon. In nonlinear optics, generating transverse structures and controlling their dynamics is important not only from a fundamental point of view but also for potential applications. This work is carried out in this logic of characterizing and manipulating optical spatial structures, generated in a liquid crystal light valve experiment. The first part of the thesis is dedicated to the effects of spatial forcing on front propagation, which is done by using a spatial light modulator. A one-dimensional study, including the comparison with analytical models and numerical results, shows the existence of a pinning range inside which localized states of different size can be generated. A two-dimensional extension is also presented for different geometries of the spatial forcing. The second part deals with the effects of a nonlocal feedback on localized structures appearing in the simultaneous presence of diffraction and polarization interference. In the case of a translation effect, an advection phenomenon of structures is observed, associated with the appearance of phase singularities in their wake. Above a certain translation rate, another regime is attained, with periodicity along the direction of the drift. In the case where both translation and rotation are present, the self-organization modes of localized structures show analogies with certain modes occurring in the growing process of plants. The influence of the different parameters, in particular rotation, is characterized on the resulting patterns.L'apparition de structures spatiales est un phénomène universel. En optique non linéaire, générer des structures transverses et contrôler leur dynamique est important non seulement d'un point de vue fondamental mais aussi d'un point de vue des applications. Ce travail de thèse s'inscrit dans cette logique de caractérisation et manipulation des structures spatiales optiques, engendrées dans une expérience de valve à cristaux liquides. Une première partie est consacrée aux effets de forçages spatiaux sur la propagation de fronts, induits avec un modulateur spatial de lumière. Une étude unidimensionnelle, incluant des comparaisons avec des modèles analytiques et des résultats numériques, montre l'existence d'une région d'agrafage à l'intérieur de laquelle des états localisés de taille différente peuvent être générés. Une extension à deux dimensions est aussi présentée pour différentes géométries du forçage spatial. La seconde partie s'intéresse aux effets d'une rétroaction non locale sur les structures localisées, apparaissant en présence simultanée de diffraction et d'interférence de polarisation. Dans le cas d'un effet de translation, un phénomène d'advection des structures est observé, associé à l'apparition de singularités de phase dans leur sillage. Au-delà d'un certain taux de translation, un autre régime est atteint avec une périodicité le long de la direction de translation. Dans le cas où rotation et translation sont présentes simultanément, les modes d'auto-organisation des structures localisées présentent des analogies avec certains modes de croissance des végétaux. L'influence des différents paramètres, dont la rotation, est caractérisée sur les motifs obtenus

Fronts et dynamiques spatio-temporelles dans l'expérience de la valve à cristaux liquides (effets de forçages spatiaux et rétroaction optique vocale)

L apparition de structures spatiales est un phénomène universel. En optique non linéaire, générer des structures transverses et contrôler leur dynamique est important non seulement d un point de vue fondamental mais aussi d un point de vue des applications. Ce travail de thèse s inscrit dans cette logique de caractérisation et manipulation des structures spatiales optiques, engendrées dans une expérience de valve à cristaux liquides. Une première partie est consacrée aux effets de forçages spatiaux sur la propagation de fronts, induits avec un modulateur spatial de lumière. Une étude unidimensionnelle, incluant des comparaisons avec des modèles analytiques et des résultats numériques, montre l existence d une région d agrafage à l intérieur de laquelle des états localisés de taille différente peuvent être générés. Une extension à deux dimensions est aussi présentée pour différentes géométries du forçage spatial. La seconde partie s intéresse aux effets d une rétroaction non locale sur les structures localisées, apparaissant en présence simultanée de diffraction et d interférence de polarisation. Dans le cas d un effet de translation, un phénomène d advection des structures est observé, associé à l apparition de singularités de phase dans leur sillage. Au-delà d un certain taux de translation, un autre régime est atteint avec une périodicité le long de la direction de translation. Dans le cas où rotation et translation sont présentes simultanément, les modes d auto-organisation des structures localisées présentent des analogies avec certains modes de croissance des végétaux. L influence des différents paramètres, dont la rotation, est caractérisée sur les motifs obtenus.The appearance of spatial structures is a universal phenomenon. In nonlinear optics, generating transverse structures and controlling their dynamics is important not only from a fundamental point of view but also for potential applications. This work is carried out in this logic of characterizing and manipulating optical spatial structures, generated in a liquid crystal light valve experiment. The first part of the thesis is dedicated to the effects of spatial forcing on front propagation, which is done by using a spatial light modulator. A one-dimensional study, including the comparison with analytical models and numerical results, shows the existence of a pinning range inside which localized states of different size can be generated. A two-dimensional extension is also presented for different geometries of the spatial forcing. The second part deals with the effects of a nonlocal feedback on localized structures appearing in the simultaneous presence of diffraction and polarization interference. In the case of a translation effect, an advection phenomenon of structures is observed, associated with the appearance of phase singularities in their wake. Above a certain translation rate, another regime is attained, with periodicity along the direction of the drift. In the case where both translation and rotation are present, the self-organization modes of localized structures show analogies with certain modes occurring in the growing process of plants. The influence of the different parameters, in particular rotation, is characterized on the resulting patterns.NICE-BU Sciences (060882101) / SudocSudocFranceF

Golden spirals as phyllotactic arrangements of optical patterns

A nonlinear optical medium with nonlocal feedback is shown to have all the necessary ingredients to simulate a growthlike process that generates golden spirals and phyllotactic patterns. Elementary droplets of light are generated by the optical nonlinearity whereas the combination of rotation and translation in the feedback loop geometrically distributes them on spiraling patterns. The symmetry of the geometrical arrangements is described with the help of a simple replication algorithm. © 2013 American Physical Society.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Patterns due to an interplay between viscous and precipitation-driven fingering

Dynamics related to the interplay of viscous fingering with precipitation-driven patterns are studied experimentally in a horizontal Hele-Shaw cell with radial injection. The precipitation reaction, known to produce chemical gardens, involves a cobalt chloride metallic salt solution and a more viscous sodium silicate one. The properties of the fingering precipitation patterns are studied as a function of the flow rate of injection, of the viscosity ratio between the two solutions and of the concentration of the reactants. We show that, for the viscous silicate solution used here, viscous fingering shapes flower-like patterns at low metallic salt concentrations but is not the driving mechanism in the development of spirals and filaments at larger cobalt chloride concentrations. In some cases, enhanced convective motions induced by viscous fingering also increase the amount of precipitate by increasing the mixing between the two reactants.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Mise en relief des jardins chimiques par confinement

La nature crée des formes fascinantes comme les « jardins chimiques », structures minérales rappelant de frêles brindilles miniatures. Ces jardins, façonnés par une réaction de précipitation, interpellent depuis des siècles par leur beauté tant admirée par le public des fêtes de la science [1]. Les jardins chimiques pourraient être une clé vers de nouvelles applications en science des matériaux, en catalyse, voire dans la compréhension de l’origine de la vie sur Terre. Nous avons pu obtenir une grande variété de formes de ces jardins par des réactions chimiques en milieu confiné (fig.1). Notre étude permet de mieux comprendre la croissance de matériaux solides en condition de non-équilibre