An expert system for setting time steps in dynamic finite element programs

Abstract

An expert system, ETUDES - Expert Time integration control Using Deep and Surface Knowledge System, which addresses the determination of the timestep for time integration of linear structural dynamic equations is described. This timestep may also be applicable for a moderately nonlinear simulation of the same structure. The system also determines whether an explicit or implicit method is most efficient for the particular simulation. A production rule programming system written in OPS5 is used for the implementation of this prototype expert system. Issues relating to the expert system architecture for this application, such as knowledge representation, reasoning mechanisms, and structure are discussed. The domain knowledge is comprised of the analysis of error in time integration and the behavior of structural dynamic systems. The various types of errors; frequency distortion and amplitude attenuation, and methods for measuring their effects are examined. It is shown that frequency distortion causes amplitude distortion even if the method is free of amplitude attenuation error. A mathematical model for the effect of these errors on the solution is proposed for a single degree-of-freedom system. The results are then extended to multi-degree-of-freedom systems and to approximate spectral representations of the system. Error estimation using apriori information is considered and described within the framework of a discrete spectrum model--a scenario. The prototype is evaluated by measuring its performance in various benchmark model problems.