Robust feedback control of Rayleigh-Bénard convection

We investigate the application of linear-quadratic-Gaussian (LQG) feedback control, or, in modern terms, H2 control, to the stabilization of the no-motion state against the onset of Rayleigh-Bénard convection in an infinite layer of Boussinesq fluid. We use two sensing and actuating methods: The planar sensor model (Tang & Bau 1993, 1994), and the shadowgraph model (Howle 1997a). By extending the planar sensor model to the multi-sensor case, it is shown that a LQG controller is capable of stabilizing the no-motion state up to 14.5 times the critical Rayleigh number. We characterize the robustness of the controller with respect to parameter uncertainties, unmodelled dynamics. Results indicate that the LQG controller provides robust performances even at high Rayleigh numbers

Robust reduced-order controller of laminar boundary layer transitions

A framework to derive optimal and robust reduced-order controllers of fluid mechanics and plasma physics flows using linear-quadratic-Gaussian design, or, in modern terms, ℋ2 design, is presented. As a test case, two-dimensional channel flow is considered. A reduced model is derived, and a controller is designed based upon this model. Initial conditions creating transient growth of wall-shear stress are constructed. The controller is tested on a 32 wave number simulation. A wall-shear stress reduction, up to 90%, is obtained. The potential transferability of the controller to engineering applications is discussed

Advance in Boundary Layer Control: Robust Reduced-Order Transition Controller

A framework to derive optimal and robust reduced-order controllers of transitional boundary layers using linear-quadratic-Gaussian (LQG) design, or, in modern terms, H2 design, is presented. As a test case, two-dimensional Poiseuille flow is considered. A controller based on a reduced model, 8% of the order of the full size system, is designed. Initial conditions creating transient growth of wall-shear stresses are constructed. The controller is tested on a 32 wave numbers simulation. Wall-shear stresses reduction, up to 90%, is obtained. The transferability of the controller to Navier-Stokes simulations and engineering applications is discussed. Corresponding author: Telephone (310) 206-2732, Facsimile (310) 206-6673, E-mail: [email protected] The reduction of drag produced by skin friction, or, in other words, the reduction of wall-shear stresses (WSS) generated by near-wall turbulence have received wide attention. "The skin friction constitutes about 50%, 90%, and 100% of the ..

Robust feedback control of Rayleigh-Bénard convection

We investigate the application of linear-quadratic-Gaussian (LQG) feedback control, or, in modern terms, H2 control, to the stabilization of the no-motion state against the onset of Rayleigh-Bénard convection in an infinite layer of Boussinesq fluid. We use two sensing and actuating methods: The planar sensor model (Tang & Bau 1993, 1994), and the shadowgraph model (Howle 1997a). By extending the planar sensor model to the multi-sensor case, it is shown that a LQG controller is capable of stabilizing the no-motion state up to 14.5 times the critical Rayleigh number. We characterize the robustness of the controller with respect to parameter uncertainties, unmodelled dynamics. Results indicate that the LQG controller provides robust performances even at high Rayleigh numbers

State-space formulation and controller design for three-dimensional channel flows

Robust reduced-order feedback control of near wall turbulence of three dimensional Poiseuille flow in a periodic channel is investigated. Control of near-wall disturbances is achieved through wall-transpirations, and measurements of wall-shear stresses are fed back to the controller. Linear-Quadratic-Gaussian/loop-transfer-recovery synthesis and model reduction techniques are used to construct the robust feedback controllers from the linearized three dimensional Navier-Strokes equations. The quadratic cost function is composed of the total wall-shear stresses. Using Galerkin's method, the system, controller, and output are decomposed into a set of independent systems, controllers, and outputs for each pair of streamwise and spanwise wave numbers. This decomposition allows reduced-order controllers for each wave number pair to be implemented in parallel. It is assumed that the controllers and sensors will be distributed in fine enough resolution to provide the measurements and control needed. This preliminary study develops a controller for a single pair of wave numbers. The single wave number pair controller produces closed loop poles that show a more rapid decay of disturbances than the open loop system

Dysphagia Care and Management in Rehabilitation: A National Survey

Dysphagia care and management may differ between countries and healthcare settings. This study aims to describe the management and care of dysphagia in rehabilitation centres and health houses across Norway. Two national surveys were developed targeting either managers or healthcare professionals. Both surveys focused on staff and client populations; screening and assessment of dysphagia; dysphagia management and interventions; staff training and education; and self-perceived quality of dysphagia care. A total of 71 managers and clinicians from 45 out of 68 identified rehabilitation centres and health houses in Norway completed the surveys. The resulting overall response rate was 72.1%. Significant differences in dysphagia care and management were identified between rehabilitation services across Norway. Rehabilitation centres and health houses often had neither a speech therapist among their staff nor had access to external healthcare professionals. Screening was most frequently performed using non-standardised water swallows and only limited data were available on non-instrumental assessments. None of the respondents reported having access to instrumental assessments. Dysphagia interventions mainly consisted of compensatory strategies, including bolus modification, with very infrequent use of rehabilitative interventions, such as swallow manoeuvres. Although almost half of all respondents perceived the overall quality of care for clients with eating and swallowing problems as good, lack of awareness of dysphagia and its symptoms, consequences and options for treatment may have influenced quality ratings. There is a need to raise awareness of dysphagia and provide training opportunities for healthcare professionals in both screening and assessment, and dysphagia care and management