In the transient analysis of engineering structures by the finite element method there are several commonly used time integration schemes such as the method of central difference, the Newmark method, the Wilson-u method, the Houbolt method and the a-method of Hilber-Hughes-Taylor. In this paper thes
TIME INTEGRATION OF NON-LINEAR DYNAMIC EQUATIONS BY MEANS OF A DIRECT VARIATIONAL METHOD
โ Scribed by M.B. ROSALES; C.P. FILIPICH
- Publisher
- Elsevier Science
- Year
- 2002
- Tongue
- English
- Weight
- 236 KB
- Volume
- 254
- Category
- Article
- ISSN
- 0022-460X
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โฆ Synopsis
Non-linear dynamic problems governed by ordinary (ODE) or partial di!erential equations (PDE) are herein approached by means of an alternative methodology. A generalized solution named WEM by the authors and previously developed for boundary value problems, is applied to linear and non-linear equations. A simple transformation after selecting an arbitrary interval of interest ยน allows using WEM in initial conditions problems and others with both initial and boundary conditions. When dealing with the time variable, the methodology may be seen as a time integration scheme. The application of WEM leads to arbitrary precision results. It is shown that it lacks neither numerical damping nor chaos which were found to be present with the application of some of the time integration schemes most commonly used in standard "nite element codes (e.g., methods of central di!erence, Newmark, Wilson-, and so on). Illustrations include the solution of two non-linear ODEs which govern the dynamics of a single-degree-of-freedom (s.d.o.f.) system of a mass and a spring with two di!erent non-linear laws (cubic and hyperbolic tangent respectively). The third example is the application of WEM to the dynamic problem of a beam with non-linear springs at its ends and subjected to a dynamic load varying both in space and time, even with discontinuities, governed by a PDE. To handle systems of non-linear equations iterative algorithms are employed. The convergence of the iteration is achieved by taking n partitions of ยน. However, the values of ยน/n are, in general, several times larger than the usual t in other time integration techniques. The maximum error (measured as a percentage of the energy) is calculated for the "rst example and it is shown that WEM yields an acceptable level of errors even when rather large time steps are used.
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