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Quadratic temporal finite element method for linear elastic structural dynamics based on mixed convolved action

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Abstract

A common approach for dynamic analysis in current practice is based on a discrete time-integration scheme. This approach can be largely attributed to the absence of a true variational framework for initial value problems. To resolve this problem, a new stationary variational principle was recently established for single-degree-of-freedom oscillating systems using mixed variables, fractional derivatives and convolutions of convolutions. In this mixed convolved action, all the governing differential equations and initial conditions are recovered from the stationarity of a single functional action. Thus, the entire description of linear elastic dynamical systems is encapsulated. For its practical application to structural dynamics, this variational formalism is systemically extended to linear elastic multidegree- of-freedom systems in this study, and a corresponding weak form is numerically implemented via a quadratic temporal finite element method. The developed numerical method is symplectic and unconditionally stable with respect to a time step for the underlying conservative system. For the forced-damped vibration, a three-story shear building is used as an example to investigate the performance of the developed numerical method, which provides accurate results with good convergence characteristics.

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A well-posed time weak form for linear structural dynamics is used to construct a Galerkin time quadrature element formulation. Radau quadrature rule and the generalized differential quadrature analog are used to turn the well-posed weak form into a set of linear equations. The stability and accuracy properties of the formulation are discussed. Numerical examples are given to show the high computational efficiency of the well-posed weak form time quadrature element formulation, as compared with a time finite element solution based on the same weak form using third-order Hermite interpolations.
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Cited By (since 1996): 42, Export Date: 10 August 2012, Source: Scopus, Art. No.: 053521, doi: 10.1063/1.2929662, Language of Original Document: English, Correspondence Address: El-Nabulsi, R. A.; Department of Nuclear and Energy Engineering, Faculty of Mechanical, Energy and Production Engineering, Cheju National University, Ara-dong 1, Jeju 690-756, South Korea; email: nabulsiahmadrami@yahoo.fr, References: Agrawal, O.P., (2002) Formulation of Euler-Lagrange Equations for Fractional Variational Problems, 272, p. 368. , J. Math. Anal. Appl.;
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The former Essay contained a general method for reducing all the most important problems of dynamics to the study of one characteristic function, one central or ra­dical relation. It was remarked at the close of that Essay, that many eliminations required by this method in its first conception, might be avoided by a general trans­formation, introducing the time explicitly into a part S of the whole characteristic function V; and it is now proposed to fix the attention chiefly on this part S, and to call it the Principal Function . The properties of this part or function S, which were noticed briefly in the former Essay, are now more fully set forth; and especially its uses in questions of perturbation, in which it dispenses with many laborious and cir­cuitous processes, and enables us to express accurately the disturbed configuration of a system by the rules of undisturbed motion, if only the initial components of veloci­ties be changed in a suitable manner. Another manner of extending rigorously to disturbed motion the rules of undisturbed, by the gradual variation of elements, in number double the number of the coordinates or other marks of position of the system, which was first invented by Lagrange, and was afterwards improved by Poisson, is considered in this Second Essay under a form perhaps a little more general; and the general method of calculation which has already been applied to other analogous questions in optics and in dynamics by the author of the present Essay, is now applied to the integration of the equations which determine these ele­ments. This general method is founded chiefly on a combination of the principles of variations with those of partial differentials, and may furnish, when it shall be ma­tured by the labours of other analysts, a separate branch of algebra, which may be called perhaps the Calculus of Principal Functions ; because, in all the chief applica­tions of algebra to physics, and in a very extensive class of purely mathematical questions, it reduces the determination of many mutually connected functions to the search and study of one principal or central relation. When applied to the integration of the equations of varying elements, it suggests, as is now shown, the consideration of a certain Function of Elements , which may be variously chosen, and may either be rigorously determined, or at least approached to, with an indefinite accuracy, by a corollary of the general method. And to illustrate all these new general processes, but especially those which are connected with problems of perturbation, they are applied in this Essay to a very simple example, suggested by the motions of projectiles, the parabolic path being treated as the undisturbed. As a more important example, the problem of determining the motions of a ternary or multiple system, with any laws of attraction or repulsion, and with one predominant mass, which was touched upon in the former Essay, is here resumed in a new way, by forming and inte­grating the differential equations of a new set of varying elements, entirely distinct in theory (though little differing in practice) from the elements conceived by Lagrange, and having this advantage, that the differentials of all the new elements for both the disturbed and disturbing masses may be expressed by the coefficients of one disturbing function.
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Traditional Lagrangian and Hamiltonian mechanics cannot be used with nonconservative forces such as friction. A method is proposed that uses a Lagrangian containing derivatives of fractional order. A direct calculation gives an Euler-Lagrange equation of motion for nonconservative forces. Conjugate momenta are defined and Hamilton's equations are derived using generalized classical mechanics with fractional and higher-order derivatives. The method is applied to the case of a classical frictional force proportional to velocity.
The Theory of Sound, Macmillan and co
  • J W S Rayleigh
J. W. S. Rayleigh, The Theory of Sound, Macmillan and co., London (1877).