135 research outputs found
Modal stability of inclined cables subjected to vertical support excitation
In this paper the out-of-plane dynamic stability of inclined cables subjected to in-plane vertical support excitation is
investigated. We compute stability boundaries for the out-of-plane modes using rescaling and averaging methods. Our
study focuses on the 2:1 internal resonance phenomenon between modes that occurs when the excitation frequency is twice
the first out-of-plane natural frequency of the cable. The second in-plane mode is excited directly, while the out-of-plane
modes can be excited parametrically. An analytical model is developed in order to study the stability regions in parameter
space. In this model we include nonlinear coupling effects with other modes, which have thus far been omitted from
previous models of parametric excitation of inclined cables. Our study reflects the importance of such effects. Unstable
parameter regions are defined for the selected cable configuration. The validity of the proposed stability model was tested
experimentally using a small-scale cable actuator rig. A comparison between experimental and analytical results is
presented in which very good agreement with model predictions was obtained.
r 2008 Elsevier Ltd. All rights reserved
An optimized tuned mass damper/harvester device
Much work has been conducted on vibration absorbers, such as tuned mass dampers (TMD), where significant energy is extracted from a structure. Traditionally, this energy is dissipated through the devices as heat. In this paper, the concept of recovering some of this energy electrically and reuse it for structural control or health monitoring is investigated. The energy-dissipating damper of a TMD is replaced with an electromagnetic device in order to transform mechanical vibration into electrical energy. That gives the possibility of controlled damping force whilst generating useful electrical energy. Both analytical and experimental results from an adaptive and a semi-active tuned mass damper/harvester are presented. The obtained results suggest that sufficient energy might be harvested for the device to tune itself to optimise vibration suppression
Control-based continuation of unstable periodic orbits
Copyright © 2010 American Society of Mechanical Engineers (ASME)We present an experimental procedure to track periodic orbits through a fold (saddle-node) bifurcation and demonstrate it with a parametrically excited pendulum experiment where the tracking parameter is the amplitude of the excitation. Specifically, we track the initially stable period-one rotation of the pendulum through its fold bifurcation and along the unstable branch. The fold bifurcation itself corresponds to the minimal amplitude that supports sustained rotation. Our scheme is based on a modification of time-delayed feedback in a continuation setting and we show for an idealized model that it converges with the same efficiency as classical proportional-plus-derivative control
Robust identification of backbone curves using control-based continuation
AbstractControl-based continuation is a recently developed approach for testing nonlinear dynamic systems in a controlled manner and exploring their dynamic features as system parameters are varied. In this paper, control-based continuation is adapted to follow the locus where system response and excitation are in quadrature, extracting the backbone curve of the underlying conservative system. The method is applied to a single-degree-of-freedom oscillator under base excitation, and the results are compared with the standard resonant-decay method
Layered composite entangled wire materials blocks as pre-tensioned vertebral rocking columns
This work focuses on entangled wire materials as an option for use between segments of a novel self-centring bridge pier inspired from the human spine mechanism to increase energy dissipation capability of the pier in rocking. A comprehensive set of free-decay vibration tests was conducted on small-scale columns with and without entangled wire materials. Wooden blocks are used as vertebrae with entangled wire materials as intervertebral disks. The whole system is tied together using a pre-tensioned tendon. Dynamic properties of columns (i.e. frequency and damping ratio) were then identified and compared. It is found that the use of entangled wire materials significantly increases the energy dissipation capacity of the system during rocking. This finding is very encouraging for future use of entangled wire materials composite systems in large-scale testing of the proposed rocking column, while their shear and axial stiffness needs be improved to reduce large shear and axial deformations
Experimental continuation of periodic orbits through a fold
We present a continuation method that enables one to track or continue
branches of periodic orbits directly in an experiment when a parameter is
changed. A control-based setup in combination with Newton iterations ensures
that the periodic orbit can be continued even when it is unstable. This is
demonstrated with the continuation of initially stable rotations of a
vertically forced pendulum experiment through a fold bifurcation to find the
unstable part of the branch.Comment: 4 page
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