7,783 research outputs found
Numerical Model For Vibration Damping Resulting From the First Order Phase Transformations
A numerical model is constructed for modelling macroscale damping effects
induced by the first order martensite phase transformations in a shape memory
alloy rod. The model is constructed on the basis of the modified
Landau-Ginzburg theory that couples nonlinear mechanical and thermal fields.
The free energy function for the model is constructed as a double well function
at low temperature, such that the external energy can be absorbed during the
phase transformation and converted into thermal form. The Chebyshev spectral
methods are employed together with backward differentiation for the numerical
analysis of the problem. Computational experiments performed for different
vibration energies demonstrate the importance of taking into account damping
effects induced by phase transformations.Comment: Keywords: martensite transformation, thermo-mechanical coupling,
vibration damping, Ginzburg-Landau theor
On damping created by heterogeneous yielding in the numerical analysis of nonlinear reinforced concrete frame elements
In the dynamic analysis of structural engineering systems, it is common
practice to introduce damping models to reproduce experimentally observed
features. These models, for instance Rayleigh damping, account for the damping
sources in the system altogether and often lack physical basis. We report on an
alternative path for reproducing damping coming from material nonlinear
response through the consideration of the heterogeneous character of material
mechanical properties. The parameterization of that heterogeneity is performed
through a stochastic model. It is shown that such a variability creates the
patterns in the concrete cyclic response that are classically regarded as
source of damping
Vibration control with shape-memory alloys in civil engineering structures
Dissertação apresentada à Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para obtenção do grau de Doutor em Engenharia CivilThe superelastic behavior exhibited by shape-memory alloys shows a vast potential
for technological applications in the field of seismic hazard mitigation, for civil engineering structures. Due to this property, the material is able to totally recover from large cyclic deformations, while developing a hysteretic loop. This is translated into a high inherent damping, combined with repeatable re-centering capabilities, two fundamental features of vibration control devices.
An extensive experimental program provides a valuable insight into the identification
of the main variables influencing superelastic damping in Nitinol while exploring the feasibility and optimal behavior of SMAs when used in seismic vibration control.
The knowledge yielded from the experimental program, together with an extensive
bibliographic research, allows for the development of an efficient numerical framework for the mathematical modeling of the complex thermo-mechanical behavior of
SMAs. These models couple the mechanical and kinetic transformation constitutive laws with a heat balance equation describing the convective heat problem. The seismic
behavior of a superelastic restraining bridge system is successfully simulated,
being one of the most promising applications regarding the use of SMAs in civil
engineering structures.
A small-scale physical prototype of a novel superelastic restraining device is built.
The device is able to dissipate a considerable amount of energy, while minimizing a set of adverse effects, related with cyclic loading and aging effects, that hinder the dynamic performances of vibration control devices based on passive superelastic
wires.Fundação Calouste Gulbenkian (bolsa de curta duração) and of Fundação para a Ciência e Tecnologia (FCT/MCTES grant SFRH/BD/37653/2007
A preliminary look at control augmented dynamic response of structures
The augmentation of structural characteristics, mass, damping, and stiffness through the use of control theory in lieu of structural redesign or augmentation was reported. The standard single-degree-of-freedom system was followed by a treatment of the same system using control augmentation. The system was extended to elastic structures using single and multisensor approaches and concludes with a brief discussion of potential application to large orbiting space structures
Diffusion-induced dissipation and mode coupling in nanomechanical resonators
We study a system consisting of a particle adsorbed on a carbon nanotube
resonator. The particle is allowed to diffuse along the resonator, in order to
enable study of e.g. room temperature mass sensing devices. The system is
initialized in a state where only the fundamental vibration mode is excited,
and the ring-down of the system is studied by numerically and analytically
solving the stochastic equations of motion. We find two mechanisms of
dissipation, induced by the diffusing adsorbate. First, short-time correlations
between particle and resonator motions means that the net effect of the former
on the latter does not average out, but instead causes dissipation of
vibrational energy. For vibrational amplitudes that are much larger than the
thermal energy this dissipation is linear; for small amplitudes the decay takes
the same form as that of a nonlinearly damped oscillator. Second, the particle
diffusion mediates a coupling between vibration modes, enabling energy transfer
from the fundamental mode to excited modes, which rapidly reach thermal
equilibrium.Comment: 8 pages, 7 figure
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