253 research outputs found
Inertial Motions of a Rigid Body with a cavity filled with a viscous liquid
We study inertial motions of the coupled system, S, constituted by a rigid
body containing a cavity that is completely filled with a viscous liquid. We
show that for data of arbitrary size (initial kinetic energy and total angular
momentum) every weak solution (a la Leray-Hopf) converges, as time goes to
infinity, to a uniform rotation, thus proving a famous "conjecture" of
Zhukovskii. Moreover we show that, in a wide range of initial data, this
rotation must occur along the central axis of inertia of S that has the largest
moment of inertia. Furthermore, necessary and sufficient conditions for the
rigorous nonlinear stability of permanent rotations are provided, which improve
and/or generalize results previously given by other authors under different
types of approximation of the original equations and/or suitable symmetry
assumptions on the shape of the cavity. Finally, we present a number of results
obtained by a targeted numerical simulation that, on the one hand, complement
the analytical findings, whereas, on the other hand, point out new features
that the analysis is yet not able to catch, and, as such, lay the foundation
for interesting and challenging future investigation.Comment: Some of the main results proved in this paper were previously
announced in Comptes Rendus Mecanique, Vol. 341, 760--765 (2013
A Lagrange multiplier method for a Stokes-Biot fluid-poroelastic structure interaction model
We study a finite element computational model for solving the coupled problem
arising in the interaction between a free fluid and a fluid in a poroelastic
medium. The free fluid is governed by the Stokes equations, while the flow in
the poroelastic medium is modeled using the Biot poroelasticity system.
Equilibrium and kinematic conditions are imposed on the interface. A mixed
Darcy formulation is employed, resulting in continuity of flux condition of
essential type. A Lagrange multiplier method is employed to impose weakly this
condition. A stability and error analysis is performed for the semi-discrete
continuous-in-time and the fully discrete formulations. A series of numerical
experiments is presented to confirm the theoretical convergence rates and to
study the applicability of the method to modeling physical phenomena and the
sensitivity of the model with respect to its parameters
Partitioning strategies for the interaction of a fluid with a poroelastic material based on a Nitsche's coupling approach
We develop a computational model to study the interaction of a fluid with a
poroelastic material. The coupling of Stokes and Biot equations represents a
prototype problem for these phenomena, which feature multiple facets. On one
hand it shares common traits with fluid-structure interaction. On the other
hand it resembles the Stokes-Darcy coupling. For these reasons, the numerical
simulation of the Stokes-Biot coupled system is a challenging task. The need of
large memory storage and the difficulty to characterize appropriate solvers and
related preconditioners are typical shortcomings of classical discretization
methods applied to this problem. The application of loosely coupled time
advancing schemes mitigates these issues because it allows to solve each
equation of the system independently with respect to the others. In this work
we develop and thoroughly analyze a loosely coupled scheme for Stokes-Biot
equations. The scheme is based on Nitsche's method for enforcing interface
conditions. Once the interface operators corresponding to the interface
conditions have been defined, time lagging allows us to build up a loosely
coupled scheme with good stability properties. The stability of the scheme is
guaranteed provided that appropriate stabilization operators are introduced
into the variational formulation of each subproblem. The error of the resulting
method is also analyzed, showing that splitting the equations pollutes the
optimal approximation properties of the underlying discretization schemes. In
order to restore good approximation properties, while maintaining the
computational efficiency of the loosely coupled approach, we consider the
application of the loosely coupled scheme as a preconditioner for the
monolithic approach. Both theoretical insight and numerical results confirm
that this is a promising way to develop efficient solvers for the problem at
hand
Contract agreements via logic
We relate two contract models: one based on event structures and game theory,
and the other one based on logic. In particular, we show that the notions of
agreement and winning strategies in the game-theoretic model are related to
that of provability in the logical model.Comment: In Proceedings ICE 2013, arXiv:1310.401
A computational study of cancer hyperthermia based on vascular magnetic nanoconstructs
The application of hyperthermia to cancer treatment is studied using a novel model arising from the fundamental principles of flow, mass and heat transport in biological tissues. The model is defined at the scale of the tumour microenvironment and an advanced computational scheme called the embedded multiscale method is adopted to solve the governing equations. More precisely, this approach involves modelling capillaries as one-dimensional channels carrying flow, and special mathematical operators are used to model their interaction with the surrounding tissue. The proposed computational scheme is used to analyse hyperthermic treatment of cancer based on systemically injected vascular magnetic nanoconstructs carrying super-paramagnetic iron oxide nanoparticles. An alternating magnetic field is used to excite the nanoconstructs and generate localized heat within the tissue. The proposed model is particularly adequate for this application, since it has a unique capability of incorporating microvasculature configurations based on physiological data combined with coupled capillary flow, interstitial filtration and heat transfer. A virtual tumour model is initialized and the spatio-temporal distribution of nanoconstructs in the vascular network is analysed. In particular, for a reference iron oxide concentration, temperature maps of several different hypothesized treatments are generated in the virtual tumour model. The observations of the current study might in future guide the design of more efficient treatments for cancer hyperthermia
A Deep Learning approach to Reduced Order Modelling of Parameter Dependent Partial Differential Equations
Within the framework of parameter dependent PDEs, we develop a constructive
approach based on Deep Neural Networks for the efficient approximation of the
parameter-to-solution map. The research is motivated by the limitations and
drawbacks of state-of-the-art algorithms, such as the Reduced Basis method,
when addressing problems that show a slow decay in the Kolmogorov n-width. Our
work is based on the use of deep autoencoders, which we employ for encoding and
decoding a high fidelity approximation of the solution manifold. In order to
fully exploit the approximation capabilities of neural networks, we consider a
nonlinear version of the Kolmogorov n-width over which we base the concept of a
minimal latent dimension. We show that this minimal dimension is intimately
related to the topological properties of the solution manifold, and we provide
some theoretical results with particular emphasis on second order elliptic
PDEs. Finally, we report numerical experiments where we compare the proposed
approach with classical POD-Galerkin reduced order models. In particular, we
consider parametrized advection-diffusion PDEs, and we test the methodology in
the presence of strong transport fields, singular terms and stochastic
coefficients
A Semantic-Based Framework for Summarization and Page Segmentation in Web Mining
This chapter addresses two crucial issues that arise when one applies Web-mining techniques for extracting relevant information. The first one is the acquisition of useful knowledge from textual data; the second issue stems from the fact that a web page often proposes a considerable amount of \u2018noise\u2019 with respect to the sections that are truly informative for the user's purposes. The novelty contribution of this work lies in a framework that can tackle both these tasks at the same time, supporting text summarization and page segmentation. The approach achieves this goal by exploiting semantic networks to map natural language into an abstract representation, which eventually supports the identification of the topics addressed in a text source. A heuristic algorithm uses the abstract representation to highlight the relevant segments of text in the original document. The verification of the approach effectiveness involved a publicly available benchmark, the DUC 2002 dataset, and satisfactory results confirmed the method effectiveness
An approximate randomization-based neural network with dedicated digital architecture for energy-constrained devices
Variable energy constraints affect the implementations of neural networks on battery-operated embedded systems. This
paper describes a learning algorithm for randomization-based neural networks with hard-limit activation functions. The
approach adopts a novel cost function that balances accuracy and network complexity during training. From an energyspecific perspective, the new learning strategy allows to adjust, dynamically and in real time, the number of operations
during the network’s forward phase. The proposed learning scheme leads to efficient predictors supported by digital
architectures. The resulting digital architecture can switch to approximate computing at run time, in compliance with the
available energy budget. Experiments on 10 real-world prediction testbeds confirmed the effectiveness of the learning
scheme. Additional tests on limited-resource devices supported the implementation efficiency of the overall design
approac
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