62,942 research outputs found
Numerical approximation of poroelasticity with random coefficients using Polynomial Chaos and Hybrid High-Order methods
In this work, we consider the Biot problem with uncertain poroelastic
coefficients. The uncertainty is modelled using a finite set of parameters with
prescribed probability distribution. We present the variational formulation of
the stochastic partial differential system and establish its well-posedness. We
then discuss the approximation of the parameter-dependent problem by
non-intrusive techniques based on Polynomial Chaos decompositions. We
specifically focus on sparse spectral projection methods, which essentially
amount to performing an ensemble of deterministic model simulations to estimate
the expansion coefficients. The deterministic solver is based on a Hybrid
High-Order discretization supporting general polyhedral meshes and arbitrary
approximation orders. We numerically investigate the convergence of the
probability error of the Polynomial Chaos approximation with respect to the
level of the sparse grid. Finally, we assess the propagation of the input
uncertainty onto the solution considering an injection-extraction problem.Comment: 30 pages, 15 Figure
Spatial Wireless Channel Prediction under Location Uncertainty
Spatial wireless channel prediction is important for future wireless
networks, and in particular for proactive resource allocation at different
layers of the protocol stack. Various sources of uncertainty must be accounted
for during modeling and to provide robust predictions. We investigate two
channel prediction frameworks, classical Gaussian processes (cGP) and uncertain
Gaussian processes (uGP), and analyze the impact of location uncertainty during
learning/training and prediction/testing, for scenarios where measurements
uncertainty are dominated by large-scale fading. We observe that cGP generally
fails both in terms of learning the channel parameters and in predicting the
channel in the presence of location uncertainties.\textcolor{blue}{{} }In
contrast, uGP explicitly considers the location uncertainty. Using simulated
data, we show that uGP is able to learn and predict the wireless channel
Optimal management of bio-based energy supply chains under parametric uncertainty through a data-driven decision-support framework
This paper addresses the optimal management of a multi-objective bio-based energy supply chain network subjected to multiple sources of uncertainty. The complexity to obtain an optimal solution using traditional uncertainty management methods dramatically increases with the number of uncertain factors considered. Such a complexity produces that, if tractable, the problem is solved after a large computational effort. Therefore, in this work a data-driven decision-making framework is proposed to address this issue. Such a framework exploits machine learning techniques to efficiently approximate the optimal management decisions considering a set of uncertain parameters that continuously influence the process behavior as an input. A design of computer experiments technique is used in order to combine these parameters and produce a matrix of representative information. These data are used to optimize the deterministic multi-objective bio-based energy network problem through conventional optimization methods, leading to a detailed (but elementary) map of the optimal management decisions based on the uncertain parameters. Afterwards, the detailed data-driven relations are described/identified using an Ordinary Kriging meta-model. The result exhibits a very high accuracy of the parametric meta-models for predicting the optimal decision variables in comparison with the traditional stochastic approach. Besides, and more importantly, a dramatic reduction of the computational effort required to obtain these optimal values in response to the change of the uncertain parameters is achieved. Thus the use of the proposed data-driven decision tool promotes a time-effective optimal decision making, which represents a step forward to use data-driven strategy in large-scale/complex industrial problems.Peer ReviewedPostprint (published version
A Compressed Sampling and Dictionary Learning Framework for WDM-Based Distributed Fiber Sensing
We propose a compressed sampling and dictionary learning framework for
fiber-optic sensing using wavelength-tunable lasers. A redundant dictionary is
generated from a model for the reflected sensor signal. Imperfect prior
knowledge is considered in terms of uncertain local and global parameters. To
estimate a sparse representation and the dictionary parameters, we present an
alternating minimization algorithm that is equipped with a pre-processing
routine to handle dictionary coherence. The support of the obtained sparse
signal indicates the reflection delays, which can be used to measure
impairments along the sensing fiber. The performance is evaluated by
simulations and experimental data for a fiber sensor system with common core
architecture.Comment: Accepted for publication in Journal of the Optical Society of America
A [ \copyright\ 2017 Optical Society of America.]. One print or electronic
copy may be made for personal use only. Systematic reproduction and
distribution, duplication of any material in this paper for a fee or for
commercial purposes, or modifications of the content of this paper are
prohibite
The Complex Interstellar Na I Absorption toward h and Chi Persei
Recent high spatial and spectral resolution investigations of the diffuse
interstellar medium (ISM) have found significant evidence for small-scale
variations in the interstellar gas on scales less than or equal to 1 pc. To
better understand the nature of small-scale variations in the ISM, we have used
the KPNO WIYN Hydra multi-object spectrograph, which has a mapping advantage
over the single-axis, single-scale limitations of studies using high proper
motion stars and binary stars, to obtain moderate resolution (~12 km/s)
interstellar Na I D absorption spectra of 172 stars toward the double open
cluster h and Chi Persei. All of the sightlines toward the 150 stars with
spectra that reveal absorption from the Perseus spiral arm show different
interstellar Na I D absorption profiles in the Perseus arm gas. Additionally,
we have utilized the KPNO Coude Feed spectrograph to obtain high-resolution (~3
km/s) interstellar Na I D absorption spectra of 24 of the brighter stars toward
h and Chi Per. These spectra reveal an even greater complexity in the
interstellar Na I D absorption in the Perseus arm gas and show individual
components changing in number, velocity, and strength from sightline to
sightline. If each of these individual velocity components represents an
isolated cloud, then it would appear that the ISM of the Perseus arm gas
consists of many small clouds. Although the absorption profiles vary even on
the smallest scales probed by these high-resolution data (~30";~0.35pc), our
analysis reveals that some interstellar Na I D absorption components from
sightline to sightline are related, implying that the ISM toward h and Chi Per
is probably comprised of sheets of gas in which we detect variations due to
differences in the local physical conditions of the gas.Comment: 27 pages text; 8 figure
Dynamic Robust Transmission Expansion Planning
Recent breakthroughs in Transmission Network Expansion Planning (TNEP) have
demonstrated that the use of robust optimization, as opposed to stochastic
programming methods, renders the expansion planning problem considering
uncertainties computationally tractable for real systems. However, there is
still a yet unresolved and challenging problem as regards the resolution of the
dynamic TNEP problem (DTNEP), which considers the year-by-year representation
of uncertainties and investment decisions in an integrated way. This problem
has been considered to be a highly complex and computationally intractable
problem, and most research related to this topic focuses on very small case
studies or used heuristic methods and has lead most studies about TNEP in the
technical literature to take a wide spectrum of simplifying assumptions. In
this paper an adaptive robust transmission network expansion planning
formulation is proposed for keeping the full dynamic complexity of the problem.
The method overcomes the problem size limitations and computational
intractability associated with dynamic TNEP for realistic cases. Numerical
results from an illustrative example and the IEEE 118-bus system are presented
and discussed, demonstrating the benefits of this dynamic TNEP approach with
respect to classical methods.Comment: 10 pages, 2 figures. This article has been accepted for publication
in a future issue of this journal, but has not been fully edited. Content may
change prior to final publication. Citation information: DOI
10.1109/TPWRS.2016.2629266, IEEE Transactions on Power Systems 201
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