A new method is introduced for solving equality constrained nonlinear optimization problems. This method does not use a penalty function, nor a filter, and yet can be proved to be globally convergent to first-order st...
详细信息
A new method is introduced for solving equality constrained nonlinear optimization problems. This method does not use a penalty function, nor a filter, and yet can be proved to be globally convergent to first-order stationary points. It uses different trust-regions to cope with the nonlinearities of the objective function and the constraints, and allows inexact SQP steps that do not lie exactly in the nullspace of the local Jacobian. Preliminary numerical experiments on CUTEr problems indicate that the method performs well.
This paper. deals with the influence of martensitic transformation latent heat on the superelastic behaviour modelling. Exothermic and endothermic effects are responsible for a strong evolution on the temperature fiel...
详细信息
This paper. deals with the influence of martensitic transformation latent heat on the superelastic behaviour modelling. Exothermic and endothermic effects are responsible for a strong evolution on the temperature field inside the material that modifies its mechanical response. This is responsible for a strain late effect that is taken into account by introducing a coupling equation between the production rate of martensite and the temperature change, into a micro macro modelling of the superthermoelastic behaviour with the assumption that the temperature field remains uniform but different to the test temperature imposed. numerical simulations so obtained show a good agreement with experimental results performed on Cu-based superelastic alloys. (C) 2000 Published by Elsevier Science Ltd.
We use biorthogonal filter banks to solve hyperbolic PDEs adaptively with a sparse multilevel representation of the solution. The methods described are of finite difference type, and the filter banks are used to give ...
详细信息
We use biorthogonal filter banks to solve hyperbolic PDEs adaptively with a sparse multilevel representation of the solution. The methods described are of finite difference type, and the filter banks are used to give a sparse representation of signals and to transform between grids on different scales. We derive bounds for the error and number of coefficients in the sparse representation. These bounds also apply for filter banks that are not associated with any wavelets. We develop algorithms for fast differentiation and multiplication in detail. The strength of the method is shown in various test problems.
In this paper, we obtain a canonical form for single input n-dimensional linear systems over Z and, in general, over a Bezout domain. We also give an algorithm to obtain that canonical form. (C) 2002 Elsevier Science ...
详细信息
In this paper, we obtain a canonical form for single input n-dimensional linear systems over Z and, in general, over a Bezout domain. We also give an algorithm to obtain that canonical form. (C) 2002 Elsevier Science B.V. All rights reserved.
Due to the indubitable role of vitamins in maintaining human health, a lot of attention has been paid to the methods and analytical procedures of their determination. Voltammetric methods are of particular interest as...
详细信息
Due to the indubitable role of vitamins in maintaining human health, a lot of attention has been paid to the methods and analytical procedures of their determination. Voltammetric methods are of particular interest as they do not involve complex sample preparation, however, close values of the redox potential of some vitamins may result in peak overlapping, hindering the quantitative analysis. This paper addresses the separation of overlapped reduction peak of vitamins B1 and B3 by means of Continuous Wavelet Transform (with appropriately selected mother wavelets) and differentiation of the recorded voltammograms. These numerical algorithms allowed to obtained linear, single-variable calibration functions that comply with the applied in analytical chemistry criteria regarding the correlation coefficients and the limit of detection and quantification. Their relatively simple implementation does not include any manual interpretation step;thus, these algorithms provide impartial and reproducible results. The proposed methodology has been applied in the determination of vitamins B1 and B3 in dietary supplements, providing results consistent with the declaration of the manufacturer. [GRAPHICS] .
A nonlinear viscoelastic constitutive model for solid propellant is described. It is based upon a modified form of the classical Coleman-Noll nonlinear viscoelastic constitutive model for material with "fading me...
详细信息
A nonlinear viscoelastic constitutive model for solid propellant is described. It is based upon a modified form of the classical Coleman-Noll nonlinear viscoelastic constitutive model for material with "fading memory." This constitutive model, referred to as the Burke model, was discretized in time, expressed in matrix form suitable for nonlinear incremental analysis, and incorporated into the MARC finite element code via user subroutines. An ancillary code was developed to calculate required material constants from test data. The model was subsequently applied to different test conditions and the results were compared to propellant test data in a fundamental assessment of the appropriates of this model as a constitutive model for solid propellant. This paper presents the theoretical background for the consecutive model, its discretization, and results of analyses. Additionally, the ancillary code is described. It is shown that the present implementation of the constitutive model provides a sound basis upon which to develop an accurate analysis tool for the prediction of the mechanical response of solid propellant.
We study two energy-correction algorithms for numerical simulations of Hamiltonian systems. The first algorithm, which corrects a trajectory after-the-fact, can significantly improve symplectic integrators by achievin...
详细信息
We study two energy-correction algorithms for numerical simulations of Hamiltonian systems. The first algorithm, which corrects a trajectory after-the-fact, can significantly improve symplectic integrators by achieving a higher order of energy accuracy. The second algorithm, which corrects a trajectory along-the-way, can drastically improve the conventional Runge-Kutta schemes both in energy conservation and trajectory accuracy. We present extended numerical simulation results for a nonlinear oscillator and the well-known Henon-Heiles model that exhibits chaotic dynamics.
The current methods for uncertainty analysis in dynamical systems are restricted in terms of computational cost and evaluation domain since they either use grid points or work only along trajectories. To break through...
详细信息
The current methods for uncertainty analysis in dynamical systems are restricted in terms of computational cost and evaluation domain since they either use grid points or work only along trajectories. To break through these problems we present a new method: the Rothe & maximum-entropy method which follows the steps below. A deterministic dynamical system with initial value uncertainties can be analyzed via the uncertainty propagation which is based on the Liouville equation in the form of the first-order linear partial differential equation. On this equation we conduct a semi-discretization in time via A-stable rational approximations of consistency order k and this yields the stationary spatial problem. This spatial problem now can be solved by the spatial discretization scheme: we propose the maximum-entropy approximation which provides unbiased interpolations even with fewer number of scattered points. Through these steps we finally obtain a system of linear equations for the evolution of the probability density function u t, which can be easily solved in several ways. This method can provide more efficiency in terms of computation time thanks to using fewer number of scattered points instead of grid points. Also, it enables the constant tracking of probability density functions in a specific fixed domain of interest and this is especially effective for switched systems.
A new time-dependent, finite difference scheme is developed with several specific objectives in mind. First, accurate implementation of the boundary conditions is very important due to the reflective nature of the hyp...
详细信息
A new time-dependent, finite difference scheme is developed with several specific objectives in mind. First, accurate implementation of the boundary conditions is very important due to the reflective nature of the hyperbolic equations governing noise propagation. Thus, one objective of the method is that the numerical solution should be developed around a general mapping procedure. A number of different approaches to numerical mapping may be found in the literature.
Toughness in Ceramic Matrix Composites (CMCs) is achieved if crack deflection can occur at the fiber/matrix interface, preventing crack penetration into the fiber and enabling energy-dissipating fiber pullout. To inve...
详细信息
Toughness in Ceramic Matrix Composites (CMCs) is achieved if crack deflection can occur at the fiber/matrix interface, preventing crack penetration into the fiber and enabling energy-dissipating fiber pullout. To investigate toughening in nanoscale CMCs, direct atomistic models are used to study how matrix cracks behave as a function of the degree of interfacial bonding/sliding, as controlled by the density of C interstitial atoms, at the interface between carbon nanotubes (CNTs) and a diamond matrix. Under all interface conditions studied, incident matrix cracks do not penetrate into the nanotube. Under increased loading, weaker interfaces fail in shear while stronger interfaces do not fail and, instead, the CNT fails once the stress on the CNT reaches its tensile strength. An analytic shear lag model captures all of the micromechanical details as a function of loading and material parameters. Interface deflection versus fiber penetration is found to depend on the relative bond strengths of the interface and the CNT, with CNT failure occurring well below the prediction of the toughness-based continuum He-Hutchinson model. The shear lag model, in contrast, predicts the CNT failure point and shows that the nanoscale embrittlement transition occurs at an interface shear strength scaling as tau similar to epsilon(f),CNT sigma CNT, rather than tau s similar to sigma CNT typically prevailing for micron scale composites, where epsilon f,CNT and sigma CNT are the CNT failure strain and stress, respectively. Interface bonding also lowers the effective fracture strength in SWCNTs, due to formation of defects, but does not play a role in DWCNTs having interwall coupling, which are weaker than SWCNTs but less prone to damage in the outerwall. (C) 2013 Elsevier Ltd. All rights reserved.
暂无评论