Réduction de modèle et contrôle en couche limite décollée, au moyen de modes globaux.

Nous utilisons les modes globaux bi-dimensionnels comme base de projection pour étudier la dynamique et en tant que modèle réduit pour contrôler un prototype de couche limite décollée. Une zone de recirculation est induite dans une couche limite par la présence d'une cavité. Une étude de croissance transitoire optimale montre que la famille de modes globaux fortement non-normaux est capable de représenter la croissance convective d'une perturbation initiale localisée. De plus, un modèle réduit de l'écoulement construit en projetant les équations de Navier-Stokes sur ces modes globaux permet de décrire correctement la dynamique. Nous utilisons ce modèle linéaire dans une procédure de contrôle optimal en boucle fermée, avec une sonde et un actionneur, et montrons que l'écoulement peut être stabilisé

Analysis of current and sea level observations from Trondheimsleia

Sea level and current measurements from Trondheimsleia have been analysed and the parameters of the tidal ellipses for the major tidal components M2, S2, N SUB>2, and K1 have been calculated. Harmonic constants for sea level and tidal ellipse parameters have been compared with the corresponding data from a high resolution tidal model in order to validate the performance of the model. Short periodic oscillations with period about 40 minutes are observed at the time of peak tidal current at one station located in a channel with relatively strong tidal currents

Global stability and feedback control of boundary layer flows

In this thesis the stability of generic boundary layer flows is studied from a global viewpoint using optimization methods. Global eigenmodes of the incompressible linearized Navier-Stokes equations are computed using the Krylov subspace Arnoldi method. These modes serve as a tool both to study asymptotic stability and as a reduced basis to study transient growth. Transient growth is also studied using adjoint iterations. The knowledge obtained from the stability analysis is used to device systematic feedback control in the Linear Quadratic Gaussian framework. The dynamics is assumed to be described by the linearized Navier-Stokes equations. Actuators and sensors are designed and a Kalman filtering technique is used to reconstruct the unknown flow state from noisy measurements. This reconstructed flow state is used to determine the control feedback which is applied to the Navier-Stokes equations through properly designed actuators. Since the control and estimation gains are obtained through an optimization process, and the Navier-Stokes equations typically forms a very high-dimensional system when discretized there is an interest in reducing the complexity of the equations. A standard method to construct a reduced order model is to perform a Galerkin projection of the full equations onto the subspace spanned by a suitable set of vectors, such as global eigenmodes and balanced truncation modes.QC 2010092

Global stability and feedback control of boundary layer flows

In this thesis the stability of generic boundary layer flows is studied from a global viewpoint using optimization methods. Global eigenmodes of the incompressible linearized Navier-Stokes equations are computed using the Krylov subspace Arnoldi method. These modes serve as a tool both to study asymptotic stability and as a reduced basis to study transient growth. Transient growth is also studied using adjoint iterations. The knowledge obtained from the stability analysis is used to device systematic feedback control in the Linear Quadratic Gaussian framework. The dynamics is assumed to be described by the linearized Navier-Stokes equations. Actuators and sensors are designed and a Kalman filtering technique is used to reconstruct the unknown flow state from noisy measurements. This reconstructed flow state is used to determine the control feedback which is applied to the Navier-Stokes equations through properly designed actuators. Since the control and estimation gains are obtained through an optimization process, and the Navier-Stokes equations typically forms a very high-dimensional system when discretized there is an interest in reducing the complexity of the equations. A standard method to construct a reduced order model is to perform a Galerkin projection of the full equations onto the subspace spanned by a suitable set of vectors, such as global eigenmodes and balanced truncation modes.QC 2010092

Feedback Control of Spatially Evolving Flows

In this thesis we apply linear feedback control to spatially evolving flows in order to minimize disturbance growth. The dynamics is assumed to be described by the linearized Navier--Stokes equations. Actuators and sensor are designed and a Kalman filtering technique is used to reconstruct the unknown flow state from noisy measurements. This reconstructed flow state is used to determine the control feedback which is applied to the Navier--Stokes equations through properly designed actuators. Since the control and estimation gains are obtained through an optimization process, and the Navier--Stokes equations typically forms a very high-dimensional system when discretized there is an interest in reducing the complexity of the equations. One possible approach is to perform Fourier decomposition along (almost) homogeneous spatial directions and another is by constructing a reduced order model by Galerkin projection on a suitable set of vectors. The first strategy is used to control the evolution of a range of instabilities in the classical family of Falkner--Skan--Cooke flows whereas the second is applied to a more complex cavity type of geometry.QC 2010112

A Comprehensive Simulation Methodology for Fluid-Structure Interaction of Offshore Wind Turbines

This paper gives an overview of a comprehensive simulation methodology for fluid-structure interaction (FSI) of offshore wind turbines that is being developed at the Applied Mathematics Department of SINTEF ICT. The methodology will account for most of the scales ranging from mesoscale meteorology through microscale meteorology to the aerodynamics of wind turbine blades. The meso and micro scales are handled through a unidirectional coupling of a meso and micro scale atmospheric code while the fluid structure interaction part is dealt with an isogeometric finite element based fluid-structure simulation code IFEM. In the current work we have shown the potential of the coupled system which is actually meant to generate realistic boundary condition as a wind forecasting tool. Also we present a comparison of the IFEM computed drag, lift and moment coefficients against experimental data for flow around a 3-D oscillating airfoil.publishedVersio

Réduction de modèle et contrôle en couche limite décollée, au moyen de modes globaux.

Colloque avec actes et comité de lecture. Internationale.International audienceNous utilisons les modes globaux bi-dimensionnels comme base de projection pour étudier la dynamique et en tant que modèle réduit pour contrôler un prototype de couche limite décollée. Une zone de recirculation est induite dans une couche limite par la présence d'une cavité. Une étude de croissance transitoire optimale montre que la famille de modes globaux fortement non-normaux est capable de représenter la croissance convective d'une perturbation initiale localisée. De plus, un modèle réduit de l'écoulement construit en projetant les équations de Navier-Stokes sur ces modes globaux permet de décrire correctement la dynamique. Nous utilisons ce modèle linéaire dans une procédure de contrôle optimal en boucle fermée, avec une sonde et un actionneur, et montrons que l'écoulement peut être stabilisé