Computer simulation is a well-accepted tool for modelling the behaviour of large or complex operating systems. Less common is the use of simulation as a design aid, but Fluor's simulation group regularly applies discrete and continuous simulation models to assist with optimisation and risk management in a wide variety of mining, mineral processing and logistics applications. To demonstrate the wide applicability of simulation modelling as a design aid, this paper describes three case examples from Fluor's recent work that cover both discrete and continuous operations.