The Experts below are selected from a list of 174 Experts worldwide ranked by ideXlab platform
Xiaowei Zhao - One of the best experts on this subject based on the ideXlab platform.
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Experimental Aerodynamic Control of a Long-Span Suspension Bridge Section Using Leading- and Trailing-Edge Control Surfaces
IEEE Transactions on Control Systems Technology, 2016Co-Authors: Kevin Gouder, Xiaowei Zhao, David J. N. Limebeer, J. Michael R. GrahamAbstract:We experimentally investigate the suppression of flutter in long-span suspension bridges. A rigid sectional model of a long-span suspension bridge is mounted in a wind tunnel on a suspension system. Control surfaces, which are used to suppress flutter, are movable flaps that are fitted to the bridge section’s leading and trailing edges. The flaps are responsive to the deck’s heave and pitch motions. In this paper, the aerodynamic force is modeled using a Thin Aerofoil Theory, although other modeling techniques can be used. The controller has a second-order passive transfer function with inputs of a combination of the deck’s pitch angle and heave position, and outputs of the flaps’ angular positions. The control system design problem is solved as an ${\mathcal{ H}}_\infty $ optimization problem.
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Modelling and Control of a Suspended-Span Bridge Section
IFAC Proceedings Volumes, 2014Co-Authors: Xiaowei Zhao, David J. N. Limebeer, J. Michael R. GrahamAbstract:Abstract We study the modelling and flutter suppression of a suspended-span bridge section using aerodynamic control means. The aerodynamic actuators are controllable leading- and trailing-edge flaps fitted to both edges of the bridge deck. The modelling is based on Thin Aerofoil Theory which describes the bridge deck - air stream interactions. The model also consider the mass and inertia effects of the flaps. Passive mechanical controllers are proposed that sense the vertical velocity of the leading- and trailing-edge flap pivots and use these signals to produce control torques and adjust the flap angles accordingly. The control system is insensitive to the wind direction in the case of identical leading- and trailing-edge mechanical controllers. The Akashi-Kaikyo bridge is used as a working example for the numerical simulation evaluation of the control system performance.
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buffet suppression in long span suspension bridges
Annual Reviews in Control, 2011Co-Authors: David J N Limebee, J M R Graham, Xiaowei ZhaoAbstract:Abstract We study the aerodynamic control of long-span suspension bridges and seek to raise the critical flutter wind speeds, while simultaneously suppressing buffeting. The control system design study is based on a simple flexible bridge section model that interacts with a constant-velocity air stream. A streamlined bridge deck is assumed and non-steady Thin Aerofoil Theory is used to describe the interactions between the bridge deck and the air stream. Classical turbulence models, first developed in the aircraft industry, are used to model the buffet forces acting on the deck. While a wide variety of control systems is possible, we focus on a compensation scheme that can be implemented using passive mechanical components such as springs, dampers and a rack and pinion mechanism. A single-loop control system is investigated that controls a trailing-edge flap by sensing movements of the bridge deck; several such mechanisms are contemplated. The first finding is that the critical wind speed for flutter can be greatly increased, with good robustness characteristics, through passive feedback control. It is also possible simultaneously to suppress flutter using the same passive mechanical controller by solving a passive mixed H 2 / H ∞ control problem. The effect of flexible controller mounting arrangements are considered briefly.
David J N Limebee - One of the best experts on this subject based on the ideXlab platform.
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aeroelastic control of long span suspension bridges with controllable winglets
Structural Control & Health Monitoring, 2016Co-Authors: K N Akis, Matteo Massaro, M S Williams, David J N LimebeeAbstract:Summary The structural-aerodynamic modelling and dynamic stabilization of a three-dimensional suspension bridge model is considered. Our emphasis is on investigating the effectiveness of leading and trailing edge flaps in suppressing aeroelastic instabilities. The East Great Belt Bridge is chosen as a design example, and its aeroelastic limits are computed using both Thin Aerofoil Theory and flutter derivatives. The problem is cast in an efficient reduced size finite element formulation with aerodynamic forces expressed in the Laplace domain by use of a high-fidelity rational function approximation. Circulatory aerodynamic forces are modelled using a feedback loop for every element, and the problem is expressed in a form suitable for implementation of modern control techniques. The structure's full multimodal response is considered, and numerical predictions show very good agreement against experimental data from the literature. In order to account for modelling errors and uncertainties while designing the controller, elements from robust control Theory are invoked. The stability and robustness of the bridge when fitted with flaps controlled by optimal and suboptimal H∞ controllers are discussed for varying lengths of control surfaces along the suspended span as the optimum configuration for aerodynamic performance is investigated. Copyright © 2016 John Wiley & Sons, Ltd.
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buffet suppression in long span suspension bridges
Annual Reviews in Control, 2011Co-Authors: David J N Limebee, J M R Graham, Xiaowei ZhaoAbstract:Abstract We study the aerodynamic control of long-span suspension bridges and seek to raise the critical flutter wind speeds, while simultaneously suppressing buffeting. The control system design study is based on a simple flexible bridge section model that interacts with a constant-velocity air stream. A streamlined bridge deck is assumed and non-steady Thin Aerofoil Theory is used to describe the interactions between the bridge deck and the air stream. Classical turbulence models, first developed in the aircraft industry, are used to model the buffet forces acting on the deck. While a wide variety of control systems is possible, we focus on a compensation scheme that can be implemented using passive mechanical components such as springs, dampers and a rack and pinion mechanism. A single-loop control system is investigated that controls a trailing-edge flap by sensing movements of the bridge deck; several such mechanisms are contemplated. The first finding is that the critical wind speed for flutter can be greatly increased, with good robustness characteristics, through passive feedback control. It is also possible simultaneously to suppress flutter using the same passive mechanical controller by solving a passive mixed H 2 / H ∞ control problem. The effect of flexible controller mounting arrangements are considered briefly.
Jack R Edwards - One of the best experts on this subject based on the ideXlab platform.
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discrete vortex method with novel shedding criterion for unsteady Aerofoil flows with intermittent leading edge vortex shedding
Journal of Fluid Mechanics, 2014Co-Authors: Kiran Ramesh, Ashok Gopalarathnam, Kenneth Granlund, Jack R EdwardsAbstract:Unsteady Aerofoil flows are often characterized by leading-edge vortex (LEV) shedding. While experiments and high-order computations have contributed to our understanding of these flows, fast low-order methods are needed for engineering tasks. Classical unsteady Aerofoil theories are limited to small amplitudes and attached leading-edge flows. Discrete-vortex methods that model vortex shedding from leading edges assume continuous shedding, valid only for sharp leading edges, or shedding governed by ad-hoc criteria such as a critical angle of attack, valid only for a restricted set of kinematics. We present a criterion for intermittent vortex shedding from rounded leading edges that is governed by a maximum allowable leading-edge suction. We show that, when using unsteady Thin Aerofoil Theory, this leading-edge suction parameter (LESP) is related to the $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}A_0$ term in the Fourier series representing the chordwise variation of bound vorticity. Furthermore, for any Aerofoil and Reynolds number, there is a critical value of the LESP, which is independent of the motion kinematics. When the instantaneous LESP value exceeds the critical value, vortex shedding occurs at the leading edge. We have augmented a discrete-time, arbitrary-motion, unsteady Thin Aerofoil Theory with discrete-vortex shedding from the leading edge governed by the instantaneous LESP. Thus, the use of a single empirical parameter, the critical-LESP value, allows us to determine the onset, growth, and termination of LEVs. We show, by comparison with experimental and computational results for several Aerofoils, motions and Reynolds numbers, that this computationally inexpensive method is successful in predicting the complex flows and forces resulting from intermittent LEV shedding, thus validating the LESP concept.
J. Michael R. Graham - One of the best experts on this subject based on the ideXlab platform.
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Experimental Aerodynamic Control of a Long-Span Suspension Bridge Section Using Leading- and Trailing-Edge Control Surfaces
IEEE Transactions on Control Systems Technology, 2016Co-Authors: Kevin Gouder, Xiaowei Zhao, David J. N. Limebeer, J. Michael R. GrahamAbstract:We experimentally investigate the suppression of flutter in long-span suspension bridges. A rigid sectional model of a long-span suspension bridge is mounted in a wind tunnel on a suspension system. Control surfaces, which are used to suppress flutter, are movable flaps that are fitted to the bridge section’s leading and trailing edges. The flaps are responsive to the deck’s heave and pitch motions. In this paper, the aerodynamic force is modeled using a Thin Aerofoil Theory, although other modeling techniques can be used. The controller has a second-order passive transfer function with inputs of a combination of the deck’s pitch angle and heave position, and outputs of the flaps’ angular positions. The control system design problem is solved as an ${\mathcal{ H}}_\infty $ optimization problem.
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Modelling and Control of a Suspended-Span Bridge Section
IFAC Proceedings Volumes, 2014Co-Authors: Xiaowei Zhao, David J. N. Limebeer, J. Michael R. GrahamAbstract:Abstract We study the modelling and flutter suppression of a suspended-span bridge section using aerodynamic control means. The aerodynamic actuators are controllable leading- and trailing-edge flaps fitted to both edges of the bridge deck. The modelling is based on Thin Aerofoil Theory which describes the bridge deck - air stream interactions. The model also consider the mass and inertia effects of the flaps. Passive mechanical controllers are proposed that sense the vertical velocity of the leading- and trailing-edge flap pivots and use these signals to produce control torques and adjust the flap angles accordingly. The control system is insensitive to the wind direction in the case of identical leading- and trailing-edge mechanical controllers. The Akashi-Kaikyo bridge is used as a working example for the numerical simulation evaluation of the control system performance.
Kiran Ramesh - One of the best experts on this subject based on the ideXlab platform.
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Unsteady lift on a high-amplitude pitching Aerofoil
Experiments in Fluids, 2020Co-Authors: Shūji Ōtomo, Kiran Ramesh, Sabrina Henne, Karen Mulleners, Ignazio Maria ViolaAbstract:The ability to accurately predict the forces on an Aerofoil in real-time when large flow variations occur is important for a wide range of applications such as, for example, for improving the manoeuvrability and control of small aerial and underwater vehicles. Closed-form analytical formulations are only available for small flow fluctuations, which limits their applicability to gentle manoeuvres. Here we investigate large-amplitude, asymmetric pitching motions of a NACA 0018 Aerofoil at a Reynolds number of $$3.2 \times 10^4$$ 3.2 × 10 4 using time-resolved force and velocity field measurements. We adapt the linear Theory of Theodorsen and unsteady Thin-Aerofoil Theory to accurately predict the lift on the Aerofoil even when the flow is massively separated and the kinematics is non-sinusoidal. The accuracy of the models is remarkably good, including when large leading-edge vortices are present, but decreases when the leading and trailing edge vortices have a strong interaction. In such scenarios, however, discrepancies between the theoretically predicted and the measured lift are shown to be due to vortex lift that is calculated using the impulse Theory. Based on these results, we propose a new limiting criterion for Theodorsen’s Theory for a pitching Aerofoil: when a coherent trailing-edge vortex is formed and it advects at a significantly slower streamwise velocity than the freestream velocity. This result is important because it extends significantly the conditions where the forces can be confidently predicted with Theodorsen’s formulation, and paves the way to the development of low-order models for high-amplitude manoeuvres characterised by massive separation. Graphic abstract
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discrete vortex method with novel shedding criterion for unsteady Aerofoil flows with intermittent leading edge vortex shedding
Journal of Fluid Mechanics, 2014Co-Authors: Kiran Ramesh, Ashok Gopalarathnam, Kenneth Granlund, Jack R EdwardsAbstract:Unsteady Aerofoil flows are often characterized by leading-edge vortex (LEV) shedding. While experiments and high-order computations have contributed to our understanding of these flows, fast low-order methods are needed for engineering tasks. Classical unsteady Aerofoil theories are limited to small amplitudes and attached leading-edge flows. Discrete-vortex methods that model vortex shedding from leading edges assume continuous shedding, valid only for sharp leading edges, or shedding governed by ad-hoc criteria such as a critical angle of attack, valid only for a restricted set of kinematics. We present a criterion for intermittent vortex shedding from rounded leading edges that is governed by a maximum allowable leading-edge suction. We show that, when using unsteady Thin Aerofoil Theory, this leading-edge suction parameter (LESP) is related to the $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}A_0$ term in the Fourier series representing the chordwise variation of bound vorticity. Furthermore, for any Aerofoil and Reynolds number, there is a critical value of the LESP, which is independent of the motion kinematics. When the instantaneous LESP value exceeds the critical value, vortex shedding occurs at the leading edge. We have augmented a discrete-time, arbitrary-motion, unsteady Thin Aerofoil Theory with discrete-vortex shedding from the leading edge governed by the instantaneous LESP. Thus, the use of a single empirical parameter, the critical-LESP value, allows us to determine the onset, growth, and termination of LEVs. We show, by comparison with experimental and computational results for several Aerofoils, motions and Reynolds numbers, that this computationally inexpensive method is successful in predicting the complex flows and forces resulting from intermittent LEV shedding, thus validating the LESP concept.