Search results for "Perturbation method"

Bounding Techniques and Their Application to Simplified Plastic Analysis of Structures

1990

In the framework of the simplified analysis methods for elastoplastic analysis problems, the bounding techniques possess an important role. A class of these techniques, based on the so-called perturbation method, are here presented with reference to finite element discretized structures. A general bounding principle is presented and its applications are illustrated by means of numerical examples.

Advanced Analysis of Propagation Losses in Rectangular Waveguide Structures Using Perturbation of Boundary Conditions

2011

In this paper, propagation losses effects present in rectangular waveguide structures are rigorously considered. For this purpose, a new formulation based on the perturbation of the boundary conditions on the metallic walls of the waveguides combined with an Integral-Equation (IE) analysis technique is proposed. Following this advanced technique, the drawbacks of the classical power-loss method are overcome and a complex modal propagation constant is computed. To validate this theory, we have successfully compared our results with numerical data of lossy hollow waveguides. Next, a Computed-Aided-Design (CAD) software package based on such a novel modal analysis tool has been used to predict…

Second sound propagation in laminar and turbulent superfluid 4He via extended thermodynamics

2012

In this work, previous results on the complex propagation of second sound in laminar and turbulent superfluid 4He are reported. Furthermore the case of inhomogeneous superfluid turbulence is examined and, in particular, the wave propagation is investigated in the presence of an anisotropic vortex tangle. Two cases of physical interest are considered: wave front collinear and orthogonal to the heat flux.

MR3194685 (Review) Canuto, B. Stability results for the $N$-dimensional Schiffer conjecture via a perturbation method. Calc. Var. Partial Differentia…

2014

Wave propagation in anisotropic turbulent superfluids

2013

In this work, a hydrodynamical model of Superfluid Turbulence previously formulated is applied to study how the presence of a non-isotropic turbulent vortex tangle modifies the propagation of waves. Two cases are considered: wave front parallel and orthogonal to the heat flux. Using a perturbation method, the first-order corrections due to the presence of the vortex tangle to the speeds and to the amplitudes of the first and second sound are determined. It is seen that the presence of the quantized vortices couples first and second sound, and the attenuation of second sound is proportional to the line density L if the wave propagates orthogonal to the heat flux, while it is proportional to …

Bounds on plastic strains for elastic plastic structures in plastic shakedown conditions

2007

The problem related to the computation of bounds on plastic deformations for structures in plastic shakedown condition (alternating plasticity) is studied. In particular, reference is made to structures discretized by finite elements constituted by elastic perfectly plastic material and subjected to a special combination of fixed and cyclic loads. The load history is known during the steady-state phase, but it is unknown during the previous transient phase; so, as a consequence, it is not possible to know the complete elastic plastic structural response. The interest is therefore focused on the computation of bounds on suitable measures of the plastic strain which characterizes just the fir…

Analytical results for 2-D non-rectilinear waveguides based on a Green's function

2008

We consider the problem of wave propagation for a 2-D rectilinear optical waveguide which presents some perturbation. We construct a mathematical framework to study such a problem and prove the existence of a solution for the case of small imperfections. Our results are based on the knowledge of a Green's function for the rectilinear case.