Finite element modelling of beams with arbitrary active constrained layer damping treatments

This paper concerns arbitrary active constrained layer damping (ACLD) treatmentsapplied to beams. In order to suppress vibration, hybrid active-passive treatmentscomposed of piezoelectric and viscoelastic layers are mounted on the substrate beamstructure. These treatments combine the high capacity of passive viscoelastic materialsto dissipate vibrational energy at high frequencies with the active capacity ofpiezoelectric materials at low frequencies. The aim of this research is the developmentof a generic analytical formulation that can describe these hybrid couplings inan accurate and consistent way. The analytical formulation considers a partial layerwisetheory, with an arbitrary number of layers, both viscoelastic and piezoelectric,attached to both surfaces of the beam. A fully coupled electro-mechanical theory formodelling the piezoelectric layers is considered. The equations of motion, electriccharge equilibrium and boundary conditions are presented. A one-dimensional finiteelement (FE) model is developed, with the nodal degrees of freedom being the axialand transverse displacements and the rotation of the centreline of the host beam, therotations of the individual layers and the electric potentials of each piezoelectric layer.The damping behavior of the viscoelastic layers is modeled by the complex modulusapproach. Three frequency response functions were measured experimentally andevaluated numerically: acceleration per unit force, acceleration per unit voltage intothe piezoelectric actuator and induced voltage per unit force. The numerical resultsare presented and compared with experimental results to validate the FE model

Earthquake nucleation in the lower crust by local stress amplification

Deep intracontinental earthquakes are poorly understood, despite their potential to cause significant destruction. Although lower crustal strength is currently a topic of debate, dry lower continental crust may be strong under high-grade conditions. Such strength could enable earthquake slip at high differential stress within a predominantly viscous regime, but requires further documentation in nature. Here, we analyse geological observations of seismic structures in exhumed lower crustal rocks. A granulite facies shear zone network dissects an anorthosite intrusion in Lofoten, northern Norway, and separates relatively undeformed, microcracked blocks of anorthosite. In these blocks, pristine pseudotachylytes decorate fault sets that link adjacent or intersecting shear zones. These fossil seismogenic faults are rarely >15 m in length, yet record single-event displacements of tens of centimetres, a slip/length ratio that implies >1 GPa stress drops. These pseudotachylytes represent direct identification of earthquake nucleation as a transient consequence of ongoing, localised aseismic creep

Novel active noise-reducing headset using earshell vibration control

Active noise-reducing (ANR) headsets are available commercially in applications varying from aviation communication to consumer audio. Current ANR systems use passive attenuation at high frequencies and loudspeaker-based active noise control at low frequencies to achieve broadband noise reduction. This paper presents a novel ANR headset in which the external noise transmitted to the user's ear via earshell vibration is reduced by controlling the vibration of the earshell using force actuators acting against an inertial mass or the earshell headband. Model-based theoretical analysis using velocity feedback control showed that current piezoelectric actuators provide sufficient force but require lower stiffness for improved low-frequency performance. Control simulations based on experimental data from a laboratory headset showed that good performance can potentially be achieved in practice by a robust feedback controller, while a single-frequency real-time control experiment verified that noise reduction can be achieved using earshell vibration control

MEMS velocity sensor using direct velocity feedback

peer reviewe

Two-degree of freedom capacitive MEMS velocity sensor with two coupled electrically isolated mass-spring-damper systems

peer reviewe