45,380 research outputs found
Multi-field approach in mechanics of structural solids
We overview the basic concepts, models, and methods related to the
multi-field continuum theory of solids with complex structures. The multi-field
theory is formulated for structural solids by introducing a macrocell
consisting of several primitive cells and, accordingly, by increasing the
number of vector fields describing the response of the body to external
factors. Using this approach, we obtain several continuum models and explore
their essential properties by comparison with the original structural models.
Static and dynamical problems as well as the stability problems for structural
solids are considered. We demonstrate that the multi-field approach gives a way
to obtain families of models that generalize classical ones and are valid not
only for long-, but also for short-wavelength deformations of the structural
solid. Some examples of application of the multi-field theory and directions
for its further development are also discussed.Comment: 25 pages, 18 figure
Robust aerodynamic design of variable speed wind turbine rotors
This study focuses on the robust aerodynamic design of the bladed rotor of small horizontal axis wind turbines. The optimization process also considers the effects of manufacturing and assembly tolerances on the yearly energy production. The aerodynamic performance of the rotors so designed has reduced sensitivity to manufacturing and assembly errors. The geometric uncertainty affecting the rotor shape is represented by normal distributions of the pitch angle of the blades, and the twist angle and chord of their airfoils. The aerodynamic module is a blade element momentum theory code. Both Monte Carlo-based and the Univariate ReducedQuadrature technique, a novel deterministic uncertainty propagationmethod, are used. The performance of the two approaches is assessed both interms of accuracy and computational speed. The adopted optimization method is based on a hybrid multi-objective evolutionary strategy. The presented results highlight that the sensitivity of the yearly production to geometric uncertainties can be reduced by reducing the rotational speed and increasing the aerodynamic blade loads
Propagation of epistemic uncertainty in queueing models with unreliable server using chaos expansions
In this paper, we develop a numerical approach based on Chaos expansions to
analyze the sensitivity and the propagation of epistemic uncertainty through a
queueing systems with breakdowns. Here, the quantity of interest is the
stationary distribution of the model, which is a function of uncertain
parameters. Polynomial chaos provide an efficient alternative to more
traditional Monte Carlo simulations for modelling the propagation of
uncertainty arising from those parameters. Furthermore, Polynomial chaos
expansion affords a natural framework for computing Sobol' indices. Such
indices give reliable information on the relative importance of each uncertain
entry parameters. Numerical results show the benefit of using Polynomial Chaos
over standard Monte-Carlo simulations, when considering statistical moments and
Sobol' indices as output quantities
Efficiency of different numerical methods for solving Redfield equations
The numerical efficiency of different schemes for solving the Liouville-von
Neumann equation within multilevel Redfield theory has been studied. Among the
tested algorithms are the well-known Runge-Kutta scheme in two different
implementations as well as methods especially developed for time propagation:
the Short Iterative Arnoldi, Chebyshev and Newtonian propagators. In addition,
an implementation of a symplectic integrator has been studied. For a simple
example of a two-center electron transfer system we discuss some aspects of the
efficiency of these methods to integrate the equations of motion. Overall for
time-independent potentials the Newtonian method is recommended. For
time-dependent potentials implementations of the Runge-Kutta algorithm are very
efficient
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