1,384 research outputs found
Data for the paper "A Sum-of-Squares approach to feedback control of laminar wake flows" by Davide Lasagna, Deqing Huang, Sergei Chernyshenko and Owen R. Tutty.
No full textThese folders/file contain data that can be used to reproduce the figures contained in the paper "A Sum-of-Squares approach to feedback control of laminar wake flows" by Davide Lasagna, Deqing Huang, Owen Tutty and Sergei Chernyshenko, published in the Journal of Fluid Mechanics.
Each folder/file is named after the figure and panel number and typically contains columns for x-y values. The precise description of the x-y data is given in each file.</span
Tikhonov regularisation in discrete vortex methods
No full textIn this study we propose the Tikhonov regularisation technique as a useful tool in discrete (blob) vortex methods (DVM). The effectiveness of Tikhonov technique is illustrated for the case of a specific blob vortex method, although the idea may be applicable to a wide class of vortex methods. The flow under consideration, modelled with blob vortices, is inviscid and two-dimensional. Flows past two geometries are considered. The first is a vertical flat plate for which the solution becomes unstable if no regularisation is used. The second is the case of a flow past a circular cylinder where it is demonstrated that the noise in the solution reduces when regularisation is applied
Data for "Expensive Control of Long-time Averages Using Sum of Squares and Its Application to A Laminar Wake Flow", Huang et al., 2016
No full textThese file contain data that can be used to reproduce the figures contained in the paper "Expensive control of long-time averages using sum of squares and its application to a laminar wake flow" by Deqing Huang, Bo Jin, Davide Lasagna, Sergei Chernyshenko and Owen Tutty available at http://arxiv.org/abs/1602.05913. Each file is named after the figure number and typically contains columns for x-y values. The precise description of the x-y data is given in each file. Files are best viewed using an UTF capable text editor/viewer.</span
Trapped vortices and a favourable pressure gradient
Get PDFIt is shown that there exist bodies such that in two-dimensional steady inviscid incompressible flow the pressure gradient is favourable over the entire surface of the body, and the lift is non-zero, if the body is immersed in a uniform stream and there are also two trapped point vortices.<br/
Fast numerical evaluation of flow fields with vortex cells
Get PDFA vortex cell (in this paper) is an aerodynamically shaped cavity in the surface of a body, for example a wing, designed specially to trap the separated vortex within it, thus preventing large-scale unsteady vortex shedding from the wing. Vortex stabilisation can be achieved either by the special geometry, as has already been done experimentally, or by a system of active control. In realistic conditions the boundary and mixing layers in the vortex cell are always turbulent. In the present study a model for calculating the flow in a vortex cell was obtained by replacing the laminar viscosity with the turbulent viscosity in the known high-Reynolds-number asymptotic theory of steady laminar flows in vortex cells. The model was implemented numerically and was shown to be faster than solving the Reynolds-aver- aged Navier–Stokes equations. An experimental facility with a vortex cell was built and experiments performed. Comparisons of the experimental results with the predictions of the model are reasonably satisfactory. The results also indicate that at least for flows in near-circular vortex cells it is sufficient to have accurate turbulence models only in thin viscous layers, while outside the viscosity should only be small enough to make the flow effectively invisci
Background flow hidden in a bound for Nusselt number
No full textThe well-known background flow method for finding bounds for time-averaged characteristics of dynamical systems, proposed by Doering and Constantin (1994, 1995) is a special case of the auxiliary functional method of Chernyshenko et al. (2014). Chernyshenko (2022) proved that bounds obtained by the direct method described by Seis (2015) can be obtained also by the auxiliary functional method and, therefore, by the background flow method when the auxiliary functional is quadratic. This brief note outlines the technique by which the background flow and more generally the auxiliary functional can be obtained when a proof of a bound for infinite time average by the direct method is known, by applying this technique to the case of the bound on the Nusselt number for infinite-Prandtl-number Rayleigh–Bénard convection obtained by Otto and Seis (2011)
Expensive control of long-time averages using sum of squares and its application to a laminar wake flow
Get PDFThe paper presents a nonlinear state-feedback control design approach for long-time average cost control, where the control effort is assumed to be expensive. The approach is based on sum-of-squares and semi-definite programming techniques. It is applicable to dynamical systems whose right-hand side is a polynomial function in the state variables and the controls. The key idea, first described but not implemented in (Chernyshenko et al., Phil. Trans. R. Soc. A, 372, 2014), is that the difficult problem of optimizing a cost function involving long-time averages is replaced by an optimization of the upper bound of the same average. As such, controller design requires the simultaneous optimization of both the control law and a tunable function, similar to a Lyapunov function. The present paper introduces a method resolving the well-known inherent non-convexity of this kind of optimization. The method is based on the formal assumption that the control is expensive, from which it follows that the optimal control is small. The resulting asymptotic optimization problems are convex. The derivation of all the polynomial coefficients in the controller is given in terms of the solvability conditions of state-dependent linear and bilinear inequalities. The proposed approach is applied to the problem of designing a full-information feedback controller that mitigates vortex shedding in the wake of a circular cylinder in the laminar regime via rotary oscillations. Control results on a reduced-order model of the actuated wake and in direct numerical simulation are reported
The Chernyshenko Conscientiousness Scales: A New Facet Measure of Conscientiousness
No full textThe current research sought to validate the Chernyshenko Conscientiousness Scales (CCS), a novel measure designed to assess six facets of conscientiousness. Data from 7,569 U.S. participants and 649 U.K. participants were analyzed to assess the internal reliability and factorial structure of the scales. Test–retest reliability, convergent and divergent validity, and criterion-related validity were also evaluated using a separate U.K. sample (n = 118; n = 80 for test–retest). The results showed that those items designed to measure industriousness, order, self-control, traditionalism, and virtue were best represented by a five-factor structure, broadly consistent with the five scales. However, the content and structure of the responsibility scale requires further investigation. Overall, the CCS has the potential to be a useful alternative to the faceted measures of conscientiousness that are currently available. However, future research is required to refine a number of problematic items and to clarify which facets can be better described as interstitial dimensions between conscientiousness and other Big Five domains
Placebo verification technique in the analysis and interpretation of turbulent velocity fields
No full textAn artificially synthesized velocity field with known properties is used as a control set of data when analysis and interpretation of turbulent velocity field isperformed. The benefits of such an approach, including a greater objectivity of the interpretation of structural features, are illustrated by considering the relationshipbetween streaks and vortices. The analysis indicates that this relationship can be less significant than it may seem
Sum-of-Squares approach to feedback control of laminar wake flows
Get PDFIn this paper a novel nonlinear feedback control design methodology for incompressible fluid flows aiming at the optimisation of long-time averages of flow quantities is presented. It applies to reduced-order finite-dimensional models of fluid flows, expressed as a set of first-order nonlinear ordinary differential equations with the right-hand side being a polynomial function in the state variables and in the controls. The key idea, first discussed in Chernyshenko et al. (Phil. Trans. R. Soc. Lond. A, vol. 372, 2014, 20130350), is that the difficulties of treating and optimising long-time averages of a cost are relaxed by using the upper/lower bounds of such averages as the objective function. In this setting, control design reduces to finding a feedback controller that optimises the bound, subject to a polynomial inequality constraint involving the cost function, the nonlinear system, the controller itself and a tunable polynomial function. A numerically tractable and efficient approach to the solution of such optimisation problems, based on sum-of-squares techniques and semidefinite programming, is proposed. To showcase the methodology, the mitigation of the fluctuation kinetic energy in the unsteady wake behind a circular cylinder in the laminar regime at , via controlled angular motions of the surface, is numerically investigated. A compact reduced-order model that resolves the long-term behaviour of the fluid flow and the effects of actuation, is first derived using proper orthogonal decomposition and Galerkin projection. In a full-information setting, feedback controllers are then designed to reduce the long-time average of the resolved kinetic energy associated with the limit cycle. These controllers are then implemented in direct numerical simulations of the actuated flow. Control performance, total energy efficiency and the physical control mechanisms identified are analysed in detail. Key elements of the methodology, implications and future work are finally discussed
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