2,714 research outputs found
Vibration Energy Harvesting for Wireless Sensors
Kinetic energy harvesters are a viable means of supplying low-power autonomous electronic systems for the remote sensing of operations. In this Special Issue, through twelve diverse contributions, some of the contemporary challenges, solutions and insights around the outlined issues are captured describing a variety of energy harvesting sources, as well as the need to create numerical and experimental evidence based around them. The breadth and interdisciplinarity of the sector are clearly observed, providing the basis for the development of new sensors, methods of measurement, and importantly, for their potential applications in a wide range of technical sectors
An adaptive and energy-maximizing control of wave energy converters using extremum-seeking approach
In this paper, we systematically investigate the feasibility of different
extremum-seeking (ES) control schemes to improve the conversion efficiency of
wave energy converters (WECs). Continuous-time and model-free ES schemes based
on the sliding mode, relay, least-squares gradient, self-driving, and
perturbation-based methods are used to improve the mean extracted power of a
heaving point absorber subject to regular and irregular waves. This objective
is achieved by optimizing the resistive and reactive coefficients of the power
take-off (PTO) mechanism using the ES approach. The optimization results are
verified against analytical solutions and the extremum of reference-to-output
maps. The numerical results demonstrate that except for the self-driving ES
algorithm, the other four ES schemes reliably converge for the two-parameter
optimization problem, whereas the former is more suitable for optimizing a
single-parameter. The results also show that for an irregular sea state, the
sliding mode and perturbation-based ES schemes have better convergence to the
optimum, in comparison to other ES schemes considered here. The convergence of
PTO coefficients towards the performance-optimal values are tested for widely
different initial values, in order to avoid bias towards the extremum. We also
demonstrate the adaptive capability of ES control by considering a case in
which the ES controller adapts to the new extremum automatically amidst changes
in the simulated wave conditions
Astrophysical turbulence modeling
The role of turbulence in various astrophysical settings is reviewed. Among
the differences to laboratory and atmospheric turbulence we highlight the
ubiquitous presence of magnetic fields that are generally produced and
maintained by dynamo action. The extreme temperature and density contrasts and
stratifications are emphasized in connection with turbulence in the
interstellar medium and in stars with outer convection zones, respectively. In
many cases turbulence plays an essential role in facilitating enhanced
transport of mass, momentum, energy, and magnetic fields in terms of the
corresponding coarse-grained mean fields. Those transport properties are
usually strongly modified by anisotropies and often completely new effects
emerge in such a description that have no correspondence in terms of the
original (non coarse-grained) fields.Comment: 88 pages, 26 figures, published in Reports on Progress in Physic
Robust self-propulsion in sand using simply controlled vibrating cubes
Much of the Earth and many surfaces of extraterrestrial bodies are composed
of in-cohesive particle matter. Locomoting on granular terrain is challenging
for common robotic devices, either wheeled or legged. In this work, we discover
a robust alternative locomotion mechanism on granular media -- generating
movement via self-vibration. To demonstrate the effectiveness of this
locomotion mechanism, we develop a cube-shaped robot with an embedded vibratory
motor and conduct systematic experiments on diverse granular terrains of
various particle properties. We investigate how locomotion changes as a
function of vibration frequency/intensity on granular terrains. Compared to
hard surfaces, we find such a vibratory locomotion mechanism enables the robot
to move faster, and more stable on granular surfaces, facilitated by the
interaction between the body and surrounding granules. The simplicity in
structural design and controls of this robotic system indicates that vibratory
locomotion can be a valuable alternative way to produce robust locomotion on
granular terrains. We further demonstrate that such cube-shape robots can be
used as modular units for morphologically structured vibratory robots with
capabilities of maneuverable forward and turning motions, showing potential
practical scenarios for robotic systems
GRAINS: Proximity Sensing of Objects in Granular Materials
Proximity sensing detects an object's presence without contact. However,
research has rarely explored proximity sensing in granular materials (GM) due
to GM's lack of visual and complex properties. In this paper, we propose a
granular-material-embedded autonomous proximity sensing system (GRAINS) based
on three granular phenomena (fluidization, jamming, and failure wedge zone).
GRAINS can automatically sense buried objects beneath GM in real-time manner
(at least ~20 hertz) and perceive them 0.5 ~ 7 centimeters ahead in different
granules without the use of vision or touch. We introduce a new spiral
trajectory for the probe raking in GM, combining linear and circular motions,
inspired by a common granular fluidization technique. Based on the observation
of force-raising when granular jamming occurs in the failure wedge zone in
front of the probe during its raking, we employ Gaussian process regression to
constantly learn and predict the force patterns and detect the force anomaly
resulting from granular jamming to identify the proximity sensing of buried
objects. Finally, we apply GRAINS to a Bayesian-optimization-algorithm-guided
exploration strategy to successfully localize underground objects and outline
their distribution using proximity sensing without contact or digging. This
work offers a simple yet reliable method with potential for safe operation in
building habitation infrastructure on an alien planet without human
intervention.Comment: 35 pages, 5 figures,2 tables. Videos available at
https://sites.google.com/view/grains2/hom
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