Fundamental concepts of modeling. The science of simulation

This paper addresses the roles of simulation in science and engineering: the extended calculator, the prototyper and the intuition generation medium. Science and engineering involves thought processes which transcend the rational. Simulation has emerged as a third wing of science that is orthogonal to experimentation and theory. It has the role of the extended calculator in that simulation provides a numerical bridge between symbolic theory and hard experimental data. In this role, discovery has been assisted. But, simulation has proved to be more than a super calculator. The paper looks at the state of the art in thermalhydraulics and considers the emerging trends. A general modelling scheme is proposed and a systems view is used to suggest the criteria for 'optimum' simulation models for the working environment.