7,735 research outputs found
Magnetic Flux Leakage Method: Large-Scale Approximation
We consider the application of the magnetic flux leakage (MFL) method to the
detection of defects in ferromagnetic (steel) tubulars. The problem setup
corresponds to the cases where the distance from the casing and the point where
the magnetic field is measured is small compared to the curvature radius of the
undamaged casing and the scale of inhomogeneity of the magnetic field in the
defect-free case. Mathematically this corresponds to the planar ferromagnetic
layer in a uniform magnetic field oriented along this layer. Defects in the
layer surface result in a strong deformation of the magnetic field, which
provides opportunities for the reconstruction of the surface profile from
measurements of the magnetic field. We deal with large-scale defects whose
depth is small compared to their longitudinal sizes---these being typical of
corrosive damage. Within the framework of large-scale approximation, analytical
relations between the casing thickness profile and the measured magnetic field
can be derived.Comment: 12 pages, 3 figure
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
Polarization Rotation, Switching and E-T phase diagrams of BaTiO: A Molecular Dynamics Study
We use molecular dynamics simulations to understand the mechanisms of
polarization switching in ferroelectric BaTiO achieved with external
electric field. For tetragonal and orthorhombic ferroelectric phases, we
determine the switching paths, and show that polarization rotation through
intermediate monoclinic phases (a) facilitates switching at low fields (b) is
responsible for a sharp anisotropy in polarization switching. We develop
understanding of this through determination of detailed electric
field-temperature phase diagrams, that are fundamental to technological
applications based on electromechanical and switching response of
ferroelectrics
Retrieving highly structured models starting from black-box nonlinear state-space models using polynomial decoupling
Nonlinear state-space modelling is a very powerful black-box modelling
approach. However powerful, the resulting models tend to be complex, described
by a large number of parameters. In many cases interpretability is preferred
over complexity, making too complex models unfit or undesired. In this work,
the complexity of such models is reduced by retrieving a more structured,
parsimonious model from the data, without exploiting physical knowledge.
Essential to the method is a translation of all multivariate nonlinear
functions, typically found in nonlinear state-space models, into sets of
univariate nonlinear functions. The latter is computed from a tensor
decomposition. It is shown that typically an excess of degrees of freedom are
used in the description of the nonlinear system whereas reduced representations
can be found. The method yields highly structured state-space models where the
nonlinearity is contained in as little as a single univariate function, with
limited loss of performance. Results are illustrated on simulations and
experiments for: the forced Duffing oscillator, the forced Van der Pol
oscillator, a Bouc-Wen hysteretic system, and a Li-Ion battery model.Comment: submitted to Mechanical Systems and Signal Processin
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