Numerical resolution of an exact heat conduction model with a delay term

In this paper we analyze, from the numerical point of view, a dynamic thermoelastic problem. Here, the so-called exact heat conduction model with a delay term is used to obtain the heat evolution. Thus, the thermomechanical problem is written as a coupled system of partial differential equations, and its variational formulation leads to a system written in terms of the velocity and the temperature fields. An existence and uniqueness result is recalled. Then, fully discrete approximations are introduced by using the classical finite element method to approximate the spatial variable and the implicit Euler scheme to discretize the time derivatives. A priori error estimates are proved, from which the linear convergence of the algorithm could be derived under suitable additional regularity conditions. Finally, a two-dimensional numerical example is solved to show the accuracy of the approximation and the decay of the discrete energy.Peer ReviewedPostprint (published version

Representation of Classical Solutions to a Linear Wave Equation with Pure Delay

For a wave equation with pure delay, we study an inhomogeneous initial-boundary value problem in a bounded 1D domain. Under smoothness assumptions, we prove unique existence of classical solutions for any given finite time horizon and give their explicit representation. Continuous dependence on the data in a weak extrapolated norm is also shown.Comment: 11 pages, 1 figur

Duhem Before Breakfast

This essay traces some of Pierre Duhem's motives for his celebrated "Quine- Duhem thesis" to a specific worry about theory underdetermination that arises within classical mechanics, concerned with the rivalry between Duhem's own thermomechanical approach and the more narrowly "mechanical" treatment pursued by Hertz and others. In the context of the treatments of "physical infinitesimals" common at the time, these two approaches seem empirically indistinguishable. After an exposition of the basic issues, this alleged "underdetermination" is then evaluated from a more modern perspective

On the stability of the μ(I)\mu(I)-rheology for granular flow

This article deals with the Hadamard instability of the so-called $\mu(I)$ model of dense rapidly-sheared granular flow, as reported recently by Barker et al. (2015,this journal, ${\bf 779}$, 794-818). The present paper presents a more comprehensive study of the linear stability of planar simple shearing and pure shearing flows, with account taken of convective Kelvin wave-vector stretching by the base flow. We provide a closed form solution for the linear stability problem and show that wave-vector stretching leads to asymptotic stabilization of the non-convective instability found by Barker et al. We also explore the stabilizing effects of higher velocity gradients achieved by an enhanced-continuum model based on a dissipative analog of the van der Waals-Cahn-Hilliard equation of equilibrium thermodynamics. This model involves a dissipative hyper-stress, as the analog of a special Korteweg stress, with surface viscosity representing the counterpart of elastic surface tension. Based on the enhanced continuum model, we also present a model of steady shear bands and their non-linear stability against parallel shearing. Finally, we propose a theoretical connection between the non-convective instability of Barker et al. and the loss of generalized ellipticity in the quasi-static field equations. Apart from the theoretical interest, the present work may suggest stratagems for the numerical simulation of continuum field equations involving the $\mu(I)$ rheology and variants thereof.Comment: 30 pages, 13 figure

Regularization Method of Restoration of Input Signals of Nonlinear Dynamic Objects that Determined by Integro-Power Volterra Series

The article offers a regularization method for solving the polynomial integral Volterra equations of the first kind while solving the problem of restoration of the input signal of a nonlinear dynamic object determined by the integro-power Volterra series. The use of integro-power Volterra series makes it possible to simplify the primary nonlinear mathematical models of nonlinear dynamic objects turning them into quasi-linear ones. Polynomial Volterra equations of the first kind are solved by introducing the additional differential regularization operator. It is offered to solve the obtained integro-differential equations using quadrature algorithms by iterative methods. This approach allows makes it possible to increase the efficiency of the process of signals restoration on the input of nonlinear dynamic objects if there is noise. The efficiency of the offered algorithm is verified for the restoration of input signal of a nonlinear dynamic object given in the form of a sequential connection of linear and nonlinear parts. At the same time, the linear part is represented by an inertial joint, while the nonlinear is represented by polynomial dependence of the second kind. There are presented the results of solving of polynomial Volterra integral equations of the first kind in the presence of different noises on the input dependencies. Based on the described method, in Matlab / Simulink, there are created simulation models and software-based methods for solving inverse problems of signal restoration on the input of nonlinear dynamic objects. The results of computational experiments demonstrated that the offered regularization method for solving the polynomial Volterra integral equations of the first kind may be effectively used to restore the input signals of nonlinear dynamical systems being described by the integro-power Volterra series

Uniqueness for a high order ill posed problem

In this work, we study a high order derivative in time problem. First, we show that there exists a sequence of elements of the spectrum which tends to infinity and therefore, it is ill posed. Then, we prove the uniqueness of solutions for this problem by adapting the logarithmic arguments to this situation. Finally, the results are applied to the backward in time problem for the generalized linear Burgers’ fluid, a couple of heat conduction problems and a viscoelastic model.Agencia Estatal de Investigación | Ref. PGC2018-096696-B-I00Agencia Estatal de Investigación | Ref. PID2019-105118GB-I0

Uniqueness for a high order ill posed problem

In this work, we study a high order derivative in time problem. First, we show that there exists a sequence of elements of the spectrum which tends to infinity and therefore, it is ill posed. Then, we prove the uniqueness of solutions for this problem by adapting the logarithmic arguments to this situation. Finally, the results are applied to the backward in time problem for the generalized linear Burgers’ fluid, a couple of heat conduction problems and a viscoelastic modelPeer ReviewedPostprint (published version

On uniqueness and instability for some thermomechanical problems involving the Moore– Gibson–Thompson equation

It is known that in the case that several constitutive tensors fail to be positive definite the system of the ther- moelasticity could become unstable and, in certain cases, ill-posed in the sense of Hadamard. In this paper, we consider the Moore–Gibson–Thompson thermoelasticity in the case that some of the constitutive tensors fail to be positive and we will prove basic results concerning uniqueness and instability of solutions. We first consider the case of the heat conduction when dissipation condition holds, but some constitutive tensors can fail to be positive. In this case, we prove the uniqueness and instability by means of the logarithmic convexity argument. Second we study the thermoelastic system only assuming that the thermal conductivity tensor and the mass density are positive and we obtain the uniqueness of solutions by means of the Lagrange identities method. By the logarithmic convexity argument we prove later the instability of solutions whenever the elasticity tensor fails to be positive, but assuming that the conductivity rate is positive and the thermal dissipation condition hold. We also sketch similar results when conductivity rate and/or the thermal conductivity fail to be positive definite, but the elasticity tensor is positive definite and the dissipation condition holds. Last sections are devoted to considering the case when a third-order equation is proposed for the displacement (which comes from the viscoelasticiy). A similar study is sketched in these cases.Peer ReviewedPostprint (author's final draft

Dynamic problems for metamaterials: Review of existing models and ideas for further research

Metamaterials are materials especially engineered to have a peculiar physical behaviour, to be exploited for some well-specified technological application. In this context we focus on the conception of general micro-structured continua, with particular attention to piezoelectromechanical structures, having a strong coupling between macroscopic motion and some internal degrees of freedom, which may be electric or, more generally, related to some micro-motion. An interesting class of problems in this context regards the design of wave-guides aimed to control wave propagation. The description of the state of the art is followed by some hints addressed to describe some possible research developments and in particular to design optimal design techniques for bone reconstruction or systems which may block wave propagation in some frequency ranges, in both linear and non-linear fields. (C) 2014 Elsevier Ltd. All rights reserved

Regularization Method of Restoration of Input Signals of Nonlinear Dynamic Objects that Determined by Integro-Power Volterra Series

The article offers a regularization method for solving the polynomial integral Volterra equations of the first kind while solving the problem of restoration of the input signal of a nonlinear dynamic object determined by the integro-power Volterra series. The use of integro-power Volterra series makes it possible to simplify the primary nonlinear mathematical models of nonlinear dynamic objects turning them into quasi-linear ones. Polynomial Volterra equations of the first kind are solved by introducing the additional differential regularization operator. It is offered to solve the obtained integrodifferential equations using quadrature algorithms by iterative methods.У статті пропонується регуляризаційний метод розв’язування поліноміальних інтегральних рівнянь Вольтерри І-го роду при розв’язуванні задачі відновлення вхідного сигналу нелінійного динамічного об’єкта, що поданий інтегро-степеневим рядом Вольтерри. Застосування інтегро-степеневих рядів Вольтерри дає змогу спростити первинні нелінійні математичні моделі нелінійних динамічних об’єктів перетворивши їх до квазілінійного вигляду. Розв’язування поліноміальних інтегральних рівнянь Вольтерри І-го роду здійснюється шляхом введення додаткового диференціального регуляризаційного оператора. Отримані інтегродиференціальні рівняння пропонується розв’язувати за допомогою квадратурних алгоритмів шляхом використання ітераційних методів