Simulation model A model expressed by a program running on a digital computer, analog computer, or hybrid computer. Use an appropriate simulation language or program.

Physical models, mathematical models and structural models can generally be transformed into simulation models. Experiments on the system itself on the effects of different control strategies or design variables on the system, or on the effects that may occur if the system is subjected to certain perturbations, are not always possible. The reasons are various. For example, experiments can be expensive; The system may be unstable, and experiments may upset the balance of the system and cause danger; The time constant of the system is large and the experiment takes a long time. The system to be designed does not yet exist. In this case, it is effective to establish the simulation model of the system. For example, the biological process of methanation is an anaerobic fermentation process that produces methane due to decomposition by bacteria. According to the knowledge of biochemistry, the simulation model of the process can be established, the steady-state value of the process can be sought by computer, and various starting methods can be studied. These studies are almost impossible to do on the system itself, because it is technically difficult to keep the process in a steady state, and the biomethanation process is slow to start, taking several weeks. However, if the (simulation) model is used on a computer, the start-up process of methanation takes only a few minutes.