Design and development of a smart panel with five decentralised control units for the reduction of vibration and sound radiation

This Technical Report discusses the design and the construction of a smart panel with five decentralised direct velocity feedback control units in order to reduce the vibration of the panel dominated by well separated low frequency resonances. Each control unit consists of an accelerometer sensor and a piezoelectric patch strain actuator. The integrated accelerometer signal is fed back to the actuator via a fixed negative control gain. In this way the actuator generates a control excitation proportional and opposite to the measured transverse velocity of the panel so that it produces active damping on the panel. First the open loop frequency response function between the sensor and the actuator of a single channel has been studied and an analogue controller has been designed and tested in order to improve the stability of this control system. Following the stability of all five control units has been assessed using the generalised Nyquist criterion. Finally the performances of the smart panel have been tested with reference to the reduction of the vibrations at the error positions and with reference to the reduction of the radiated sound. Finally in appendix to this Report, a parametric study is presented on the properties of sensor-actuator FRFs measured with different types of piezoelectric patch actuators. The results of this parametric study have been used in order to choose the actuators to be used for the construction of the smart pane

Scaling laws of electromagnetic and piezoelectric seismic vibration energy harvesters built from discrete components

This paper presents a theoretical study on the scaling laws of electromagnetic and piezoelectric seismic vibration energy harvesters, which are assembled from discrete components. The scaling laws are therefore derived for the so called meso-scale range, which is typical of devices built from distinct elements. Isotropic scaling is considered for both harvesters such that the shape of the components and of the whole transducers do not change with scaling. The scaling analyses are restricted to the case of linearly elastic seismic transducers subject to tonal ambient vibrations at their fundamental natural frequency, where the energy harvesting is particularly effective. Both resistive-reactive and resistive optimal electric harvesting loads are considered. The study is based on equivalent formulations for the response and power harvesting of the two transducers, which employ the so called electromagnetic and piezoelectric power transduction factors, \u3a0cm2 and \u3a0pe2. The scaling laws of the transduction coefficients and electrical and mechanical parameters for the two transducers are first provided. A comprehensive comparative scaling analysis is then presented for the harvested power, for the power harvesting efficiency and for the stroke of the two harvesters. Particular attention is dedicated to the scaling laws for the dissipative effects in the two harvesters, that is the Couette air losses and eddy currents losses that develop in the electromagnetic harvester and the material, air and dielectric losses that arise in the piezoelectric harvester. The scaling laws emerged from the study, are thoroughly examined and interpreted with respect to equivalent mechanical effects produced by the harvesting loads

Non-linear Isolator for Vibration and Force Transmission Control of Unbalanced Rotating Machines

Purpose: The objective of this paper is to investigate with simulations how non-linear spring and non-linear damper components of isolators can be employed to effectively reduce both the oscillations and the force transmitted to ground in the whole spinning range of unbalanced rotating machines. Methods: The principal goal of this paper is twofold. First, to present a concise and consistent formulation based on the harmonic balance approach for the vibration response of spinning machines mounted on linear/non-linear, softening/hardening, un-tensioned/pre-tensioned springs and linear/non-linear dampers. Second, to provide a comprehensive overview of the vibration and force transmission control with non-linear isolators specifically tailored to unbalanced machines. Results: The study has shown that, the best vibration isolation is provided by a pre-tensioned linear and cubic softening spring combined with a linear and negative quadratic damper. The pre-tensioned spring should be designed in such a way as it holds the weight of the machine and thus produces on the vibrating machine a symmetric elastic restoring force proportional to the linear and cubic powers of the displacement. The cubic softening stiffness should then be tuned to minimise the frequency, and thus the amplitude, of the resonant response of the fundamental mode of the machine and elastic suspension system, while preserving stability and a desired static deflection. In parallel, to reduce the force transmission to ground above the fundamental resonance frequency, the negative quadratic damping effect should be tailored to maximize the energy absorption at higher frequencies. Conclusion: The study has shown that non-linear spring and non-linear damper components can be effectively employed to control the vibration and force transmission in the whole spinning range of the machine. In particular, a pre-tensioned softening cubic non-linear spring can be used to mitigate the vibration and force transmission at low frequencies, close to the fundamental natural frequencies of the elastically suspended machine. Also, a negative quadratic non-linear damper can be used to tailor the energy dissipation of the isolator in such a way as to have high damping at low frequencies and low damping at higher frequencies, which enhances the vibration and force transmission control at low frequencies and, rather importantly, mitigates the force transmission at higher frequencies

Localized Magnetic States of Fe, Co, and Ni Impurities on Alkali Metal Films

X-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) have been used to study transition metal impurities on K and Na films. The multiplet structure of the XAS spectra indicates that Fe, Co, and Ni have localized atomic ground states with predominantly d7, d8, and d9 character, respectively. XMCD shows that the localized impurity states possess large, atomiclike, magnetic orbital moments that are progressively quenched as clusters are formed. Ni impurities on Na films are found to be nonmagnetic, with a strongly increased d10 character of the impurity state. The results show that the high magnetic moments of transition metals in alkali hosts originate from electron localization

Design of a tuned vbration absorber (TVA) for applications in transport engineering

The control of the response to tonal excitations or to broadband stochastic disturbances of a stiffened cylinder is investigated through the use of a Tuned Vibrating Absorber (TVA). In particular, the study considered both a purely passive device (Mechanical) and a semi-active one with shunt circuit (Electro-Mechanical) to evaluate the efficiencies and differences

Active control of sound transmission through an opening connecting two rooms

ISVR Technical Memorandum No. 88

Correlated Electrons Step-by-Step: Itinerant-to-Localized Transition of Fe Impurities in Free-Electron Metal Hosts

High-resolution photoemission spectroscopy and realistic ab-initio calculations have been employed to analyze the onset and progression of d-sp hybridization in Fe impurities deposited on alkali metal films. The interplay between delocalization, mediated by the free-electron environment, and Coulomb interaction among d-electrons gives rise to complex electronic configurations. The multiplet structure of a single Fe atom evolves and gradually dissolves into a quasiparticle peak near the Fermi level with increasing the host electron density. The effective multi-orbital impurity problem within the exact diagonalization scheme describes the whole range of hybridizations.Comment: 10 pages, 4 figure