Mohammed Yousif Fattah; Mohammed J. Hamood; Shatha Hazim Dawood
Abstract
One of the limitations of the usage of the finite element method in dynamic soilstructureinteraction arises when it is used for the modelling of an infinite domain ifnothing is done ...
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One of the limitations of the usage of the finite element method in dynamic soilstructureinteraction arises when it is used for the modelling of an infinite domain ifnothing is done to prevent from artificial reflections at the mesh boundary; errors areintroduced into the results. To handle reflections, different artificial boundaries havebeen proposed. The aim of such boundaries is to make them behave as nearly aspossible as if the mesh extends to infinity. In this paper they are known as transmitting,absorbing or silent boundaries. A brief description to two different approaches ofabsorbing boundaries is made, first by using infinite elements and the second by usingviscous boundaries method. For this purpose the computer program named“MIXDYN” is modified in this study to “Mod-MIXDYN” by adding mapped infiniteelement model to the finite elements models of the program to be used for dynamicanalysis of soil-structure interaction problems. A new derivation of the mappedfunctions is made in this study for the cases when the infinite direction is extended tothe left horizontally (at negative ξ direction) and down vertically (at negative ηdirection).Two verification problems are solved to compare the results of the modifiedprogram with the results of other software, namely ANSYS and OpenSees representingother types of elements (dashpot elements) modelling boundaries as viscous boundary.It was found that the transmitting boundary absorbs most of the incidentenergy. The distinct reflections observed in the "fixed boundaries" case disappear inthe "transmitted boundaries" case. This is true for both cases of using viscousboundaries or mapped infinite elements. The viscous boundaries are more effective inabsorbing the waves resulting from dynamic loads than mapped infinite elements. Thisis clear when comparing the results of both types with those of transient infiniteelements.
