Acceleration feedback control of human-induced floor vibrations

Active vibration control (AVC) via a proof-mass actuator is considered to be a suitable technique for the mitigation of vibrations caused by human motions in floor structures. It has been observed that actuator dynamics strongly influence structure dynamics despite considering collocated actuator/sensor control. The well-known property of the interlacing of poles and zeros of a collocated control system is no longer accomplished. Therefore, velocity-based feedback control, which has been previously used by other researchers, might not be a good solution. This work presents a design process for a control scheme based on acceleration feedback control with a phase-lag compensator, which will generally be different from an integrator circuit. This first-order compensator is applied to the output (acceleration) in such a way that the relative stability and potential damping to be introduced are significantly increased accounting for the interaction between floor and actuator dynamics. Additionally, a high-pass filter designed to avoid stroke saturation is applied to the control signal. The AVC system designed according to this procedure has been assessed in simulation and successfully implemented in an in-service open-plan office floor. The actual vibration reductions achieved have been approximately 60% for walking tests and over 90% for a whole-day vibration monitoring. (C) 2009 Elsevier Ltd. All rights reserved

Programmable unitary spatial modes manipulation

Free space propagation and conventional optical systems such as lenses and mirrors all perform spatial unitary transforms. However, the subset of transforms available through these conventional systems is limited in scope. We present here a unitary programmable mode converter (UPMC) capable of performing any spatial unitary transform of the light field. It is based on a succession of reflections on programmable deformable mirrors and free space propagation. We first show theoretically that a UPMC without limitations on resources can perform perfectly any transform. We then build an experimental implementation of the UPMC and show that, even when limited to three reflections on an array of 12 pixels, the UPMC is capable of performing single mode tranforms with an efficiency greater than 80% for the first 4 modes of the TEM basis

Wavelet-based response spectrum compatible synthesis of accelerograms-Eurocode application (EC8)

An integrated approach for addressing the problem of synthesizing artificial seismic accelerograms compatible with a given displacement design/target spectrum is presented in conjunction with aseismic design applications. Initially, a stochastic dynamics solution is used to obtain a family of simulated non-stationary earthquake records whose response spectrum is on the average in good agreement with the target spectrum. The degree of the agreement depends significantly on the adoption of an appropriate parametric evolutionary power spectral form, which is related to the target spectrum in an approximate manner. The performance of two commonly used spectral forms along with a newly proposed one is assessed with respect to the elastic displacement design spectrum defined by the European code regulations (EC8). Subsequently, the computational versatility of the family of harmonic wavelets is employed to modify iteratively the simulated records to satisfy the compatibility criteria for artificial accelerograms prescribed by EC8. In the process, baseline correction steps, ordinarily taken to ensure that the obtained accelerograms are characterized by physically meaningful velocity and displacement traces, are elucidated. Obviously, the presented approach can be used not only in the case of the EC8, for which extensive numerical results/examples are included, but also for any code provisions mandated by regulatory agencies. In any case, the presented numerical results can be quite useful in any aseismic design process dominated by the EC8 specifications

Semi-active damping using a hybrid control approach

In this article, a hybrid control framework is used to design semi-active controllers for vibration reduction. It is shown that the semi-active skyhook damper, typically used for vibration reduction, can be recast in the framework of an event-driven intermittent controller. By doing this, we can then exploit the well-developed techniques associated with hybrid control theory to design the semi-active control system. Illustrative simulation examples are based on a 2 degree-of-freedom system, often used to model the dynamics of a quarter car body model. The simulation results demonstrate how hybrid control design techniques can improve the overall performance of the semi-active control system

Damage Detection in Active Suspension Bridges: An Experimental Investigation

This paper considers a Hilbert marginal spectrum-based approach to health monitoring of active suspension bridge hangers. The paper proposes to takes advantage of the presence of active cables and use them as an excitation mean of the bridge, while they are used for active damping. The Hilbert–Huang transform is used to calculate the Hilbert marginal spectrum and establish a damage index for each hanger of the suspension bridge. The paper aims to investigate the method experimentally, through a series of damage scenarios, on a laboratory suspension bridge mock-up equipped with four active cables; each active cable is made of a displacement actuator collocated with a force sensor. Different locations and levels of damage severity are implemented. For the first time, the investigation demonstrates experimentally the effectiveness of the technique, as well as its limitations, to detect and locate the damage in hangers of a suspension bridge.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Analysis, design, and optimization of structures with integral compliant mechanisms for mid-frequency response

A multi-scale paradigm is proposed that utilizes periodic, small-scale, integral compliant mechanisms within larger-scale structures for the attenuation of vibro-acoustic response. Amplification principles serve as the basis for the design of these mechanisms in achieving reduced energy transmission. The spectral finite element method is exploited for a force–velocity and energy flow analysis of the resultant truss-like structures. A genetic algorithm is employed to optimize structure size for greatest effectiveness in the frequency range of interest. This study demonstrates that a significant decrease in structural vibration is achievable and suggests promising applications including the design of acoustic isolation panels for broadband vehicle noise reduction. Copyright © 2007 John Wiley & Sons, Ltd.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/57905/1/2084_ftp.pd