104 research outputs found
Dynamic problems for metamaterials: Review of existing models and ideas for further research
Metamaterials are materials especially engineered to have a peculiar physical behaviour, to be exploited for some well-specified technological application. In this context we focus on the conception of general micro-structured continua, with particular attention to piezoelectromechanical structures, having a strong coupling between macroscopic motion and some internal degrees of freedom, which may be electric or, more generally, related to some micro-motion. An interesting class of problems in this context regards the design of wave-guides aimed to control wave propagation. The description of the state of the art is followed by some hints addressed to describe some possible research developments and in particular to design optimal design techniques for bone reconstruction or systems which may block wave propagation in some frequency ranges, in both linear and non-linear fields. (C) 2014 Elsevier Ltd. All rights reserved
Dynamic Response of Tunable Phononic Crystals and New Homogenization Approaches in Magnetoactive Composites
This research investigates dynamic response of tunable periodic structures
and homogenization methods in magnetoelastic composites (MECs). The research on
tunable periodic structures is focused on the design, modeling and
understanding of wave propagation phenomena and the dynamic response of smart
phononic crystals. High amplitude wrinkle formation is employed to study a
one-dimensional phononic crystal slab consists of a thin film bonded to a thick
compliant substrate. Buckling induced surface instability generates a wrinkly
structure triggered by a compressive strain. It is demonstrated that surface
periodic pattern and the corresponding large deformation can control elastic
wave propagation in the low thickness composite slab. Simulation results show
that the periodic wrinkly structure can be used as a smart phononic crystal
which can switch band diagrams of the structure in a transformative manner. A
magnetoactive phononic crystal is proposed which its dynamic properties are
controlled by combined effects of large deformations and an applied magnetic
field. Finite deformations and magnetic induction influence phononic
characteristics of the periodic structure through geometrical pattern
transformation and material properties. A magnetoelastic energy function is
proposed to develop constitutive laws considering large deformations and
magnetic induction in the periodic structure. Analytical and finite element
methods are utilized to compute dispersion relation and band structure of the
phononic crystal for different cases of deformation and magnetic loadings. It
is demonstrated that magnetic induction not only controls the band diagram of
the structure but also has a strong effect on preferential directions of wave
propagation. Moreover, a thermally controlled phononic crystal is designed
using ligaments of bi-materials in the structure.Comment: PhD mechanical engineering, University of Nevada, Reno (2015
Heat equations beyond Fourier: from heat waves to thermal metamaterials
In the past decades, numerous heat conduction models beyond Fourier have been
developed to account for the large gradients, fast phenomena, wave propagation,
or heterogeneous material structure, such as being typical for biological
systems, superlattices, or thermal metamaterials. It became a challenge to
orient among the models, mainly due to their various thermodynamic backgrounds
and possible compatibility issues. Additionally, in light of the recent
findings on the field of non-Fourier heat conduction, it is not even
straightforward how to interpret and utilize a non-Fourier heat equation,
primarily when one aims to thermally design the material structure to construct
the new generation of thermal metamaterials. Adding that numerous modeling
strategies can be found in the literature accompanying different
interpretations even for the same heat equation makes it even more difficult to
orient ourselves and find a comprehensive picture of this field of research.
Therefore, this review aims to ease the orientation among advanced heat
equations beyond Fourier by discussing properties concerning their possible
practical applications in light of experiments. We start from the simplest
model with basic principles and notions, then proceed toward the more complex
models related to coupled phenomena such as ballistic heat conduction. We do
not enter the often complicated technical details of each thermodynamic
framework but do not aim to compare each approach. However, we still briefly
present their background to highlight their origin and the limitations acting
on the models. Additionally, the field of non-Fourier heat conduction has
become quite segmented, and that paper also aims to provide a common ground, a
comprehensive mutual understanding of the basics of each model, together with
what phenomenon they can be applied to
Mechanics of Materials
All up-to-date engineering applications of advanced multi-phase materials necessitate a concurrent design of materials (including composition, processing routes, microstructures and properties) with structural components. Simulation-based material design requires an intensive interaction of solid state physics, material physics and chemistry, mathematics and information technology. Since mechanics of materials fuses many of the above fields, there is a pressing need for well founded quantitative analytical and numerical approaches to predict microstructure-process-property relationships taking into account hierarchical stationary or evolving microstructures. Owing to this hierarchy of length and time scales, novel approaches for describing/ modelling non-equilibrium material evolution with various degrees of resolution are crucial to linking solid mechanics with realistic material behavior. For example, approaches such as atomistic to continuum transitions (scale coupling), multiresolution numerics, and handshaking algorithms that pass information to models with different degrees of freedom are highly relevant in this context. Many of the topics addressed were dealt with in depth in this workshop
Mathematical and Numerical Aspects of Dynamical System Analysis
From Preface: This is the fourteenth time when the conference “Dynamical Systems: Theory and Applications” gathers a numerous group of outstanding scientists and engineers, who deal with widely understood problems of theoretical and applied dynamics. Organization of the conference would not have been possible without a great effort of the staff of the Department of Automation, Biomechanics and Mechatronics. The patronage over the conference has been taken by the Committee of Mechanics of the Polish Academy of Sciences and Ministry of Science and Higher Education of Poland. It is a great pleasure that our invitation has been accepted by recording in the history of our conference number of people, including good colleagues and friends as well as a large group of researchers and scientists, who decided to participate in the conference for the first time. With proud and satisfaction we welcomed over 180 persons from 31 countries all over the world. They decided to share the results of their research and many years experiences in a discipline of dynamical systems by submitting many very interesting papers. This year, the DSTA Conference Proceedings were split into three volumes entitled “Dynamical Systems” with respective subtitles: Vibration, Control and Stability of Dynamical Systems; Mathematical and Numerical Aspects of Dynamical System Analysis and Engineering Dynamics and Life Sciences. Additionally, there will be also published two volumes of Springer Proceedings in Mathematics and Statistics entitled “Dynamical Systems in Theoretical Perspective” and “Dynamical Systems in Applications”
Research reports: 1990 NASA/ASEE Summer Faculty Fellowship Program
Reports on the research projects performed under the NASA/ASEE Summer Faculty Fellowship Program are presented. The program was conducted by The University of Alabama and MSFC during the period from June 4, 1990 through August 10, 1990. Some of the topics covered include: (1) Space Shuttles; (2) Space Station Freedom; (3) information systems; (4) materials and processes; (4) Space Shuttle main engine; (5) aerospace sciences; (6) mathematical models; (7) mission operations; (8) systems analysis and integration; (9) systems control; (10) structures and dynamics; (11) aerospace safety; and (12) remote sensin
The Zoo of Non-Fourier Heat Conduction Models
The Fourier heat conduction model is valid for most macroscopic problems.
However, it fails when the wave nature of the heat propagation or time lags
become dominant and the memory or/and spatial non-local effects significant --
in ultrafast heating (pulsed laser heating and melting), rapid solidification
of liquid metals, processes in glassy polymers near the glass transition
temperature, in heat transfer at nanoscale, in heat transfer in a solid state
laser medium at the high pump density or under the ultra-short pulse duration,
in granular and porous materials including polysilicon, at extremely high
values of the heat flux, in heat transfer in biological tissues.
In common materials the relaxation time ranges from to
sec, however, it could be as high as 1 sec in the degenerate cores of aged
stars and its reported values in granular and biological objects varies up to
30 sec. The paper considers numerous non-Fourier heat conduction models that
incorporate time non-locality for materials with memory (hereditary materials,
including fractional hereditary materials) or/and spatial non-locality, i.e.
materials with non-homogeneous inner structure
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