Use of the symbolic modelling code AUTOSIM for vehicle dynamics

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Use of the symbolic modelling code AUTOSIM for vehicle dynamics

Sharp, R.S.

Large three dimensional multibody building and simulation systems have become commonplace in the automotive industry but there are small, modular alternatives to the market dominant systems, having a substantially different philosophy. AUTOSIM is a module in such an alternative arrangement, forming only a part of a fully functioning simulation system, which 'writes' simulation code for C or FORTRAN compilation or linearises system equations and 'writes' MATLAB.M code. These AUTOSIM outputs are fully documented and ready to use, as if they had been written by hand with great skill and diligence. Thus, FORTRAN code needs compiling, linking to appropriate libraries, running and post-processing (for example graphics, animation). MATLAB.M files need loading and processing through MATLAB functions (for example eigenvalues, frequency responses, optimisation). It follows, that once AUTOSIM has been used to build a model, the model becomes independent of AUTOSIM and is completely accessible, as if it were hand-written. One installation can serve many users. The paper describes what AUTOSIM is, what it is like to use and what skills are needed to use it and it demonstrates the forms in which results can be obtained. Model building in a vehicle dynamics context is illustrated by a detailed account of a three dimensional suspension kinematics analysis. Significant sections of the AUTOSIM code and of the FORTRAN program written by AUTOSIM are described.