Showing papers by "Andrew J. Fleming published in 2006"

Piezoelectric Transducers for Vibration Control and Damping

Abstract: Fundamentals of Piezoelectricity- Feedback Control of Structural Vibration- Piezoelectric Shunt Damping- Feedback Structure of Piezoelectric Shunt Damping Systems- Instrumentation- Multi-port Shunts- Adaptive Shunt Damping- Negative Capacitor Shunt Impedances- Optimal Shunt Synthesis- Dealing with Hysteresis- Nanopositioning

Sensorless vibration suppression and scan compensation for piezoelectric tube nanopositioners

Abstract: Piezoelectric tube scanners are employed in high-resolution positioning applications such as scanning probe microscopy and nanofabrication. Much research has proceeded with the aim of reducing hysteresis and vibration-the two foremost problems associated with piezoelectric tube scanners. In this paper, two simple techniques are proposed for simultaneously reducing hysteresis and vibration: 1) A new dc accurate charge amplifier is shown to significantly reduce hysteresis while avoiding characteristic voltage drift. 2) Piezoelectric shunt damping, a technique previously resident in the field of smart structures, has been applied to damp tube vibration. By attaching an LCR impedance to a single tube electrode, the first mechanical mode is reduced in magnitude by more than 20 dB.

Inertial vibration control using a shunted electromagnetic transducer

Abstract: Inertial drives and passive tuned-mass dampers utilize a suspended mass to reduce the vibration experienced by a host structure. Active vibration control systems typically include a voice coil type electromagnetic actuator to develop the required reaction forces. In this paper, the technique of sensorless active shunt control is applied to inertial vibration absorption. An electrical impedance is designed and connected to an electromagnetic coil with a view to minimizing structural vibration. Standard optimal control tools can be applied to design the required shunt impedance. This technique requires no additional feedback sensors. Vibration in an experimental structure is heavily attenuated by the application of an active shunt impedance.

Adaptive electromagnetic shunt damping

Abstract: This paper presents a new type of passive vibration control: adaptive electromagnetic shunt damping. We propose a single-mode resonant shunt controller that adapts to environmental conditions using two different adaptation strategies. The first technique is based on minimizing the root mean square (RMS) vibration, while the second minimizes the phase difference between two measurable signals. An experimental comparison shows that relative phase adaptation performs better than the RMS technique.

Pseudospectral Feedback Control: Foundations, Examples and Experimental Results

Abstract: Suppose optimal open-loop controls could be computed in real time. This implies optimal feedback control. These controls are, typically, nonsmooth. Nonsmooth controls raise fundamental theoretical problems on the existence and uniqueness of feedback solutions. A simple, yet powerful, approach to address these theoretical issues is the concept of a …-solution that is closely linked to the practical implementation of zero-order-hold control sampling. In other words, even traditional feedback controls involve open-loop controls through the process of sampling. In this paper, we advance the notion of

Aircraft Thermal Management Using Loop Heat Pipes: Experimental Simulation of High Acceleration Environments Using the Centrifuge Table Test Bed

Abstract: : The objective of this paper is to describe the design of an experiment that will examine the effects of elevated acceleration environments on a high-temperature, titanium-water loop heat pipe for actuator cooling An experimental test setup has been designed for mounting a loop heat pipe on an 8-ft-diameter centrifuge table, which is capable of radial accelerations of up to 12-g's A high-temperature PAO loop will interface the condenser of the loop heat pipe to simulate the rejection of the transported heat to an elevated temperature In addition to LHP experimentation, a mathematical model has been developed for aerodynamic heating of high-speed aircraft A flat plate at zero-incidence, used to model an aircraft wing, was subjected to sub- and supersonic flow to examine whether heat will be rejected or absorbed The results of this analysis will be used to determine the condenser conditions of the loop heat pipe during centrifuge testing

Mitigation of acoustic resonance using electrically shunted loudspeakers

Abstract: Low-frequency reverberant sound fields are usually suppressed by means of either adaptive feedforward control or Helmholtz resonator. In this paper, an electrical impedance is connected to the terminals of an acoustic loudspeaker, the mechanical dynamics, and hence acoustic response can be made to emulate a sealed acoustic resonator. No microphone or velocity measurement is required. In some cases, the required electrical circuit is simply the parallel connection of a capacitor and resistor. Experimental application to a closed acoustic duct results in 14 dB pressure attenuation of a single acoustic mode.

Mitigation of acoustic resonance using electrically shunted loudspeakers

Abstract: Low-frequency reverberant sound fields are usually suppressed by means of either adaptive feedforward control or Helmholtz resonator. In this paper, an electrical impedance is connected to the terminals of an acoustic loudspeaker, the mechanical dynamics, and hence acoustic response can be made to emulate a sealed acoustic resonator. No microphone or velocity measurement is required. In some cases, the required electrical circuit is simply the parallel connection of a capacitor and resistor. Experimental application to a closed acoustic duct results in 14 dB pressure attenuation of a single acoustic mode.

Centrifuge Testing of a Partially-Confined FC-72 Spray

Abstract: : The effects of elevated acceleration fields on spray cooling heat transfer are discussed in this paper. Spray cooling has proven to be one of the most efficient methods of heat removal. This technology is being transitioned into more advanced applications, such as fighter aircraft that must withstand a wide range of variable acceleration-induced body forces. Heat transfer associated with closed-loop spray cooling will be affected by acceleration body forces, the extent of which is not yet known. To test these various effects, an eight-foot-diameter centrifuge table will be outfitted with a spray cooling system to test for the effects associated with elevated gravity.