Bode Integral Constraints, Collocation, and Spillover in Active Noise and Vibration Control

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/57798/1/HongSpilloverTCST1998.pd

Real-Time Feedback Control of Flow-Induced Cavity Tones

A generalized predictive control (GPC) algorithm was formulated and applied to the cavity flow-tone problem. The control algorithm demonstrated multiple Rossiter-mode suppression at fixed Mach numbers ranging from 0.275 to 0.38. Controller performance was evaluated with a measure of output disturbance rejection and an input sensitivity transfer function. The results suggest that disturbances entering the cavity flow are collocated with the control input at the cavity leading edge. In that case, only tonal components of the cavity wall-pressure fluctuations can be suppressed and arbitrary broadband pressure reduction is not possible with the present sensor/actuator arrangement. In the control-algorithm development, the cavity dynamics were treated as linear and time invariant (LTI) for a fixed Mach number. The experimental results lend support to that treatment

Mechanical and control-oriented design of a monolithic piezoelectric microgripper using a new topological optimisation method.

International audienceThis paper presents a new method developed for the optimal design of piezoactive compliant micromechanisms. It is based on a flexible building block method, called FlexIn, which uses an evolutionary approach, to optimize a truss-like planar structure made of passive and active building blocks, made of piezoelectric material. An electromechanical approach, based on a mixed finite element formulation, is used to establish the model of the active piezoelectric blocks. From the first design step, in addition to conventional mechanical criteria, innovative control-based metrics can be considered in the optimization procedure to fit the open-loop frequency response of the synthetized mechanisms. In particular, these criteria have been drawn here to optimize modal controllability and observability of the system, which is particularly interesting when considering control of flexible structures. Then, a planar monolithic compliant micro-actuator has been synthetized using FlexIn and prototyped. Finally, simulations and experimental tests of the FlexIn optimally synthetized device demonstrate the interests of the proposed optimization method for the design of micro-actuators, microrobots, and more generally for adaptronic structures

Active vibration control of doubly-curved panels

This thesis considers active control of the vibration of doubly-curved panels. Such panels are widely used in vehicles such as cars and aircraft, whose vibration is becoming more problematic as the weight of these vehicles is reduced to control their CO2 emissions. The dynamic properties of doubly-curved panels are first considered and an analytic model which includes in-plane inertia is introduced. The results of this analytical model are compared with those from numerical modelling. Of particular note is the clustering of lower-order modes as the curvature becomes more significant. The influence of these changes in dynamics is then studied by simulating the performance of a velocity feedback controller using an inertial actuator. The feasibility of implementing such an active control system on a car roof panel is then assessed.Experiments and simulations are also conducted on a panel, mounted on one side of a rigid enclosure, which is curved by pressurising the enclosure. The active control of vibration on this panel is then implemented using compensated velocity feedback control and novel inertial actuators. It is found that the performance of the feedback control initially improves as the curvature increases, since the fundamental natural frequency of the panel becomes larger compared with the actuator resonance frequency, but then the performance is significantly degraded for higher levels of curvature, since the natural frequencies of many of the panel modes cluster together. Finally, the integration of a compensator filter in the control system ensures the robustness of the system, despite changes in curvature, which makes it a good candidate for future multi-channel implementations

Robustness and Control of a Magnetically Levitated Transportation System

Electromagnetic suspension of Magnetic Levitation Vehicles (Maglev) has been studied for many years as an alternative to wheel-on rail transportation systems. In this work, design and implementation of control systems for a Maglev laboratory experiment and a Maglev vehicle under development at Old Dominion University are described. Both plants are modeled and simulated with consideration of issues associated with system non-linearity, structural flexibility and electromagnetic force modeling. Discussion concerning different control strategies, namely centralized and decentralized approaches are compared and contrasted in this work. Different types of electromagnetic non-linearities are considered and described to establish a convenient method for modeling such a system. It is shown how a Finite Element structural model can be incorporated into the system to obtain transfer function notation. Influence of the dynamic interaction between the Maglev track and the Maglev vehicle is discussed and supported by both analytical results and theoretical examples. Finally, several control laws designed to obtain stable and robust levitation are explored in detail

Dynamics and Control of Smart Structures for Space Applications

Smart materials are one of the key emerging technologies for a variety of space systems ranging in their applications from instrumentation to structural design. The underlying principle of smart materials is that they are materials that can change their properties based on an input, typically a voltage or current. When these materials are incorporated into structures, they create smart structures. This work is concerned with the dynamics and control of three smart structures: a membrane structure with shape memory alloys for control of the membrane surface flatness, a flexible manipulator with a collocated piezoelectric sensor/actuator pair for active vibration control, and a piezoelectric nanopositioner for control of instrumentation. Shape memory alloys are used to control the surface flatness of a prototype membrane structure. As these actuators exhibit a hysteretic nonlinearity, they need their own controller to operate as required. The membrane structures surface flatness is then controlled by the shape memory alloys, and two techniques are developed: genetic algorithm and proportional-integral controllers. This would represent the removal of one of the main obstacles preventing the use of membrane structures in space for high precision applications, such as a C-band synthetic aperture radar antenna. Next, an adaptive positive position feedback law is developed for control of a structure with a collocated piezoelectric sensor/actuator pair, with unknown natural frequencies. This control law is then combined with the input shaping technique for slew maneuvers of a single-link flexible manipulator. As an alternative to the adaptive positive position feedback law, genetic algorithms are investigated as both system identification techniques and as a tool for optimal controller design in vibration suppression. These controllers are all verified through both simulation and experiments. The third area of investigation is on the nonlinear dynamics and control of piezoelectric actuators for nanopositioning applications. A state feedback integral plus double integral synchronization controller is designed to allow the piezoelectrics to form the basis of an ultra-precise 2-D Fabry-Perot interferometer as the gap spacing of the device could be controlled at the nanometer level. Next, an output feedback linear integral control law is examined explicitly for the piezoelectric actuators with its nonlinear behaviour modeled as an input nonlinearity to a linear system. Conditions for asymptotic stability are established and then the analysis is extended to the derivation of an output feedback integral synchronization controller that guarantees global asymptotic stability under input nonlinearities. Experiments are then performed to validate the analysis. In this work, the dynamics and control of these smart structures are addressed in the context of their three applications. The main objective of this work is to develop effective and reliable control strategies for smart structures that broaden their applicability to space systems

Decentralised velocity feedback control for thin homogeneous and lightweight sandwich panels

This thesis presents theoretical and experimental studies on decentralised velocity feedback control for thin homogeneous and lightweight sandwich panels. This research is motivated by the increasing interest in lightweight design for fuel efficient transportation vehicles. Lightweight sandwich panels are very appealing due to their high stiffness to weight ratio but also exhibit undesirable sound transmission properties which could cause problems with vehicle interior noise. The aim of this work is to assess the performance of decentralised velocity feedback control on lightweight sandwich panels. The first part of this thesis presents the theoretical model used to predict the structural response, sound radiation and sound transmission through active panels with decentralised velocity feedback loops. The model is then used in simulation studies on the intrinsic limitation of decentralised feedback control for thin homogeneous and sandwich active panels under distributed deterministic and stochastic excitations in the whole audio frequency range. The results suggest that decentralised velocity feedback control on lightweight sandwich panels is more efficient and can be applied over wider range of audio frequencies than for conventional thin homogeneous panels. The second part of this thesis presents experimental and simulation studies on a control system with five decentralised control units with proof-mass electrodynamic actuators, installed on conventional aluminium panel and a honeycomb sandwich panel. This study provides insight in the open and closed-loop response of the control units and gives a good understanding of the interaction between the panels and the control system. The results suggest that a practical control system that implements decentralised velocity feedback can offset some of the undesired sound transmission properties of lightweight sandwich structures by efficiently reducing structural vibration and sound power radiation in the mid audio frequency range.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Feedback control of oscillations in combustion and cavity flows

This thesis considers the control of combustion oscillations, motivated by the susceptibility of lean premixed combustion to such oscillations, and the long and expensive development and commissioning times that this is giving rise to. The controller used is both closed-loop, employing an actuator to modify some system parameter in response to a measured signal, and adaptive, meaning that it is able to maintain control over a wide range of operating conditions. The controller is applied to combustion systems with annular geometries, where instabilities can occur both longitudinally and azimuthally, and which require multiple sensors and multiple actuators for control. One of the requirements of Lyapunov-based adaptive control which is particularly troublesome for combustion systems is then addressed: that the sign of the high-frequency gain of the open-loop system is known. We address it by using an adaptive controller which employs a Nussbaum gain, and successfully apply it experimentally to combustion oscillations in a Rijke tube. Another type of fluid-acoustic resonance is then considered: the compressible flow past a shallow cavity. We start by finding a linear model of the cavity flow's dynamics, or its `transfer function', which we identify from direct numerical simulations. We compare this measured transfer function to that given by a conceptual model which is based on the Rossiter mechanism, and which models each component of the flow physics separately. We then look at using closed-loop control to eliminate these cavity oscillations. We start by designing a robust $\mathcal{H}_2$ controller based on a balanced reduced order model of the system, the model being provided by the Eigensystem Realization Algorithm (ERA). The robust controller provides closed-loop stability over a much wider Mach number range than seen in previous studies. Finally, we look at the suitability of the adaptive controller, earlier developed for combustion oscillations, for the cavity. Based on some general properties of the cavity flow, and by using collocated control, the oscillations are eliminated at all Mach numbers tested in the range $0.4 \le M \le 0.8$.This work was supported by the EPSRC and Rolls-Royce plc