Browsing by Subject "Feedback control"
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Item Open Access Experimental results and bifurcation analysis on scaled feedback control for subsonic cavity flows(IEEE, 2006) Yuan, X.; Caraballo, E.; Debiasi, M.; Little, J.; Serrani, A.; Özbay, Hitay; Samimy, M.In this paper, we present the latest results of our ongoing research activities in the development of reduced-order models based feedback control of subsonic cavity flows. The model was developed using the Proper Orthogonal Decomposition of Particle Image Velocimetry images in conjunction with the Galerkin projection of the Navier-Stokes equations onto the resulting spatial eigenfunctions. Stochastic Estimation method was used to obtain the state estimation of the Galerkin system from real time surface pressure measurements. A linear-quadratic optimal controller was designed to reduce cavity flow resonance and tested in the experiments. Real-time implementation shows a significant reduction of the sound pressure level within the cavity, with a remarkable attenuation of the resonant tone and a redistribution of the energy into various modes with lower energy levels. A mathematical analysis of the performance of the LQ control, in agreement with the experimental results, is presented and discussed.Item Open Access Experimental study of linear closed-loop control of subsonic cavity flow(2006) Yan P.; Debiasi, M.; Yuan X.; Little J.; Özbay, Hitay; Samimy, M.A study is presented of the modeling and implementation of different concepts for linear feedback control of a single-mode resonance shallow cavity flow. When a physics-based linear model is used for cavity pressure oscillations-, an H∞ controller was designed and tested experimentally. It significantly reduced the main Rossiter mode for which it was designed, while leading to strong oscillations at other Rossiter modes. Other linear control methods such as Smith predictor controller and proportional integral derivative (PID) controller exhibited similar results. The ineffectiveness of using fixed linear models in the design of controllers for the cavity flows is discussed. A modification of the PID design produced a parallel-proportional with time-delay controller that remedied this problem by placing zeros at the frequencies corresponding to other resonance states. Interestingly, it was observed that introducing the same zero to the H∞ controller can also successfully avoid the strong oscillations at other Rossiter modes otherwise observed in the single-mode-based design. The parallel-proportional with time-delay controller was compared to a very effective open-loop method for reducing cavity resonance and exhibited superior robustness with respect to departure of the Mach number from the design conditions. An interpretation is presented for the physical mechanisms by which the open-loop forcing and the parallel-proportional with time-delay controllers reduce the cavity flow noise. The results support the idea that both controls induce in the system a rapid switching between modes competing for the available energy that can be extracted from the mean flow.Item Open Access Feedback control design for subsonic cavity flows(2009) Yuan X.; Caraballo, E.; Little J.; Debiasi, M.; Serrani, A.; Özbay, Hitay; Myatt J.H.; Samimy, M.A benchmark problem in active aerodynamic flow control, suppression of strong pressure oscillations induced by flow over a shallow cavity, is addressed in this paper. Proper orthogonal decomposition and Galerkin projection techniques are used to obtain a reduced-order model of the flow dynamics from experimental data. The model is made amenable to control design by means of a control separation technique, which makes the control input appear explicitly in the equations. A prediction model based on quadratic stochastic estimation correlates flow field data with surface pressure measurements, so that the latter can be used to reconstruct the state of the model in real time. The focus of this paper is on the controller design and implementation. A linear-quadratic optimal controller is designed on the basis of the reduced-order model to suppress the cavity flow resonance. To account for the limitation on the magnitude of the control signal imposed by the actuator, the control action is modified by a scaling factor, which plays the role of a bifurcation parameter for the closed-loop system. Experimental results, in qualitative agreement with the theoretical analysis, show that the controller achieves a significant attenuation of the resonant tone with a redistribution of the energy into other frequencies, and exhibits a certain degree of robustness when operating in off-design conditions.Item Open Access H∞-performance analysis of robust controllers designed for AQM(IEEE, 2003) Yan, P.; Özbay, HitayIt has been shown that the TCP connections through the congested routers with the Active Queue Management (AQM) can be modeled as a nonlinear feedback system. In this paper, we design H∞ robust controllers for AQM based on the linearized TCP model with time delays. For the linear system model exhibiting LPV nature, we investigate the H∞-performance with respect to the uncertainty bound of RTT (round trip time). The robust controllers and the corresponding analysis of H∞-performance are validated by simulations in different scenarios.Item Open Access Infinite dimensional and reduced order observers for Burgers equation(Taylor & Francis, 2005) Efe, M. Ö.; Özbay, Hitay; Samimy, M.Obtaining a representative model in feedback control system design problems is a key step and is generally a challenge. For spatially continuous systems, it becomes more difficult as the dynamics is infinite dimensional and the well known techniques of systems and control engineering are difficult to apply directly. In this paper, observer design is reported for one-dimensional Burgers equation, which is a non-linear partial differential equation. An infinite dimensional form of the observer is demonstrated to converge asymptotically to the target dynamics, and proper orthogonal decomposition is used to obtain the reduced order observer. When this is done, the corresponding observer is shown to be successful under certain circumstances. The paper unfolds the connections between target dynamics, observer and their finite dimensional counterparts. A set of simulation results has been presented to justify the theoretical claims of the paper.Item Open Access Modeling and feedback control for subsonic cavity flows: a collaborative approach(IEEE, 2005) Yan, P.; Debiasi, M.; Yuan, X.; Caraballo, E.; Serrani, A.; Özbay, Hitay; Myatt, J. M.; Samimy, M.Feedback control of aerodynamic flows is attracting the attention of researchers from a wide spectrum of specialties, because of its interdisciplinary nature and the challenges inherent to the problem. One of the main goals of the Collaborative Center of Control Science at The Ohio State University is to bring together researchers from different disciplines to advance the science and technology of flow control. This paper presents a comprehensive summary of the effort of the Center on modeling and feedback control of subsonic cavity-flow resonance. In particular, we give a detailed description of the experimental apparatus, including the wind tunnel testbed, the data measurement and acquisition system, and the real time control system. Reduced-order models of the flow dynamics based on physically-oriented linear models and Proper Orthogonal Decomposition are introduced and their effectiveness for control system design discussed. Finally, results obtained with experimental and model-based controller design are discussed.Item Open Access Modelling and control of a wind energy conversion system(Taylor & Francis, 1987) Saribatir, B. M.; Sezer, M. E.The dynamical model of a novel low power wind energy conversion system consisting of a wind turbine, an induction generator, a PWM a.c. inverter and a d.c. battery group is obtained. A feedback control law is developed to provide optimum power conversion and arbitrarily fast responses at steady-state. The feedback does not require measurement of the wind speed and therefore is suitable for real applications. The stability of the closed-loop system is analysed using a Liapunov-type practical stability criterion, and it is shown that the system remains stable for wind speed variations that are not both large and fast at the same time. Digital computer simulation studies on a 1 kVA test system verify the theoretical results. © 1987 Taylor & Francis Group, LLC.Item Open Access Observer based control of chaos(IEEE, 1997-08) Solak, Ercan; Morgül, Ömer; Ersoy, UmutIn this work we consider the control of forced chaotic oscillators. To obtain any desirable behavior, the system parameters are effectively modified using state feedback. The system states used in the feedback are estimated through a nonlinear observer. The application of the proposed method is illustrated for Duffing and Van der Pol oscillators.Item Open Access Observer based friction cancellation in mechanical systems(IEEE, 2014-10) Odabaş, Caner; Morgül, ÖmerAn adaptive nonlinear observer based friction compensation for a special time delayed system is presented in this paper. Considering existing delay, an available Coulomb observer is modified and closed loop system is formed by using a Smith predictor based controller as if the process is delay free. Implemented hierarchical feedback system structure provides two-degree of freedom and controls both velocity and position separately. For this purpose, controller parametrization method is used to extend Smith predictor structure to the position control loop for different types of inputs and disturbance attenuation. Simulation results demonstrate that without requiring much information about friction force, the method can significantly improve the performance of a control system in which it is applied. © 2014 Institute of Control, Robotics and Systems (ICROS).Item Open Access On the design of AQM supporting TCP flows using robust control theory(IEEE, 2004) Quet, P-F.; Özbay, HitayRecently it has been shown that the active queue management schemes implemented in the routers of communication networks supporting transmission control protocol (TCP) flows can be modeled as a feedback control system. Based on a delay differential equations model of TCPs congestion-avoidance mode different control schemes have been proposed. Here a robust controller is designed based on the known techniques for H∞ control of systems with time delays.Item Open Access Reduced-order model-based feedback controller design for subsonic cavity flows(American Institute of Aeronautics and Astronautics, 2005-01) Yuan, X.; Caraballo, E.; Yan, P.; Özbay, Hitay; Serrani, A.; DeBonis, J.; Myatt, J. H.; Samimy, M.This paper explores feedback controller design for cavity flows based on reduced-order models derived using Proper Orthogonal Decomposition (POD) along with Galerkin projection method. Our preliminary analysis shows that the equilibrium of the POD model is unstable and a static output feedback controller cannot stabilize it. We develop Linear Quadratic (LQ) optimal state feedback controllers and LQ optimal observers for the linearized models. The linear controllers and observers are applied to the nonlinear system using simulations. The controller robustness is numerically tested with respect to different POD models generated at different forcing frequencies. An estimation for the region of attraction of the linear controllers is also provided.Item Open Access A relevance feedback technique for multimodal retrieval of news videos(IEEE, 2005-11) Aksoy, Selim; Çavuş ÖzgeContent-based retrieval in news video databases has become an important task with the availability of large quantities of data in both public and proprietary archives. We describe a relevance feedback technique that captures the significance of different features at different spatial locations in an image. Spatial content is modeled by partitioning images into non-overlapping grid cells. Contributions of different features at different locations are modeled using weights defined for each feature in each grid cell. These weights are iteratively updated based on user's feedback in terms of positive and negative labeling of retrieval results. Given this labeling, the weight updating scheme uses the ratios of standard deviations of the distances between relevant and irrelevant images to the standard deviations of the distances between relevant images. The proposed technique is quantitatively and qualitatively evaluated using shots related to several sports from the news video collection of the TRECVID video retrieval evaluation where the weights could capture relative contributions of different features and spatial locations. © 2005 IEEE.Item Open Access Robust adaptive stabilization of a class of systems under structured nonlinear perturbations with application to interconnected systems(Taylor & Francis, 1996) Wei, R.; Sezer, M. Erol; Ocalı, OganThis paper presents a stabilization scheme for a dass of multi-input/multioutput systems with nonlinear additive perturbations using high-gain adaptive controllers The nominal system is assumed to satisfy some mild conditions required by standard adaptive control schemes, and the perturbations certian structural conditions. The controller is a dynamic output feedback containing a gain parameter, which is adjusted with a simple adaptation rule. The result is also applied to decentralized stabilization of a class of interconnected systems, where the interconnections are treated as perturbations to nominally decoupled subsystems.Item Open Access Robust stabilization of the wave equation against small delays(IEEE, 1994) Morgül, ÖmerIn this paper we consider a system which can be modeled by (undamped) wave equation in a bounded domain. We assume that the system is fixed at one end and is controlled by a boundary controller at the other end. We also considered two damped versions of this system, both parameterized by a nonnegative damping constant. We study two problems for these models, namely the stabilization by means of a boundary controller, and the stability robustness of the closed-loop system against small time delays in the feedback loop. We propose a class of finite dimensional dynamic boundary controllers to solve these problems. One basic feature of these controllers is that the corresponding controller transfer functions are required to be strictly positive real functions. We show that these controllers stabilize both damped and undamped models and solve the stability robustness problem for the damped models. It is also shown that while strict positive realness of the controller transfer functions is important for closed-loop stability, the strict properness is important for the stability robustness against small time delays in the feedback loop.Item Open Access Sensitivity minimization by stable controllers for a class of unstable time-delay systems(IEEE, 2006) Gümüşsoy, S.; Özbay, HitayIn this paper sensitivity minimization problem is considered for a class of unstable time delay systems. Our goal is to find a stable controller stabilizing the feedback system and giving rise to smallest H∞ norm for the sensitivity function. This problem has been solved by Ganesh and Pearson (1986) for finite dimensional plants using Nevanlinna-Pick interpolation. We extend their technique to include possibly unstable time delay systems. Moreover, we illustrate suboptimal solutions, and their robust implementation.Item Open Access Stability and control of a compass gait model walking with series-elastic ankle actuation(2017-11) Kerimoğlu, DenizPassive dynamic walking models are capable of capturing basic properties of walking behaviors and can generate stable human-like walking without any actuation on downhill surfaces. The passive compass gait model is among the simplest of such models, consisting of a planar point mass and two stick legs. A number of di erent actuation methods have been proposed both for this model and its more complex extensions to eliminate the need for a downhill sloped ground, balancing collision losses using gravitational potential energy. In this thesis, we introduce and investigate an extended compass gait model with series-elastic actuation at the ankle towards a similar goal, realizing stable walking on various terrains such as level ground, inclined surfaces and rough terrains. Our model seeks to capture the basic structure of how humans utilize toe push-o prior to leg lifto , and is intended to eventually be used for controlling the ankle joint in a lower-body robotic orthosis. We derive hybrid equations of motion for this model and obtain limit cycle walking on level and inclined grounds. We then numerically identify xed points of this system and and show numerically through Poincar e analysis that it can achieve asymptotically stable walking on level and inclined ground for certain choices of system parameters. The dependence of limit cycles and their stability on system parameters such as spring precompression and sti ness for level ground walking is identi ed by studying the bifurcation regimes of period doubling of this model, leading to chaotic walking patterns. We show that feedback control on the initial extension of the series ankle spring can be used to improve and extend system stability on level ground walking. Then, we investigate and identify the period doubling bifurcation regions of our model for spring precompression and ground slope parameter leading to various maps that we utilize for rough terrainwalking. Furthermore, we evaluate the performance of our model on rough terrains by applying ground slope feedback controllers on the spring precompression. Thereafter, we demonstrate that slope feedback along with stance leg apex velocity feedback control on the extension of the series ankle spring improves walking performance on rough terrains. The implementation of series elastic actuation on the ankle joint is realized with an experimental instantiations of active ankle foot orthosis system for the patients walking unnaturally and ine ciently with impaired ankles. Finally, we integrate the active ankle foot orthosis platform with an active knee orthosis platform where the experimentation results indicate that the integrated platform can generate e cient walking patterns.Item Open Access Stability and control of planar compass gait walking with series-elastic ankle actuation(Sage Publications Ltd., 2017) Kerimoğlu, D.; Morgül, Ö.; Saranli, U.Passive dynamic walking models are capable of capturing basic properties of walking behaviours and can generate stable human-like walking without any actuation on inclined surfaces. The passive compass gait model is among the simplest of such models, consisting of a planar point mass and two stick legs. A number of different actuation methods have been proposed both for this model and its more complex extensions to eliminate the need for a sloped ground, balancing collision losses using gravitational potential energy. In this study, we introduce and investigate an extended model with serieselastic actuation at the ankle towards a similar goal, realizing stable walking on level ground. Our model seeks to capture the basic structure of how humans utilize toe push-off prior to leg liftoff, and is intended to eventually be used for controlling the ankle joint in a lower-body robotic orthosis. We derive hybrid equations of motion for this model, and show numerically through Poincare´ analysis that it can achieve asymptotically stable walking on level ground for certain choices of system parameters. We then study the bifurcation regimes of period doubling with this model, leading up to chaotic walking patterns. Finally, we show that feedback control on the initial extension of the series ankle spring can be used to improve and extend system stability.Item Open Access Stability of delayed feedback controllers for discrete time systems(IEEE, 2003) Morgül, ÖmerWe consider the delayed feedback control (DFC) scheme for one dimensional discrete time systems. To analyze the stability, we construct a map whose fixed points correspond to the periodic orbits of the system to be controlled. Then the stability of the DFC is equivalent to the stability of the corresponding equilibrium point of the constructed map.Item Open Access A stability result for delayed feedback controllers(IEEE, 2003) Morgül, ÖmerWe consider the delayed feedback control (DFC) scheme for one dimensional discrete time systems. To analyze the stability, we construct a map whose fixed points correspond to the periodic orbits of the system to be controlled. Then the stability of the DFC is equivalent to the stability of the corresponding equilibrium point of the constructed map. We obtain a formula for the characteristic polynomial of the Jacobian of this map. Then the Schur stability of this polynomial could be used to analyze the stability of DFC. We also present some simulation results.Item Open Access Switching resilient PI controllers for active queue management of TCP flows(IEEE, 2007) Üstebay, Deniz; Özbay, HitayActive Queue Management (AQM) is used in computer networks to increase link utilization with less queueing delays. The fluid flow model or TCP based on delay differential equations supplies the mathematical background for modelling the AQM as a feedback system. Recently various PI and PID controllers arr designed for this feedback system, [7], [18]. In this paper, we consider the case for which the Round Trip Time (RTT) is time varying and we propose switching resilient PI controllers using the design method introduced in [18].