Basics of Simulation

Simulation is a word that is thrown around a lot in recent years, especially with the fourth industrial revolution gaining traction. Here I hope to answer two basic questions:

At its core what are simulations and what is it used for?

The first answer is simply "it is a prediction" or "it is an imitation of something real" but this doesn't remove the mystic from the term. To explain it better I first have to explain a model, which is a mathematical equation (or set of equations) that describes a real phenomenon.

The most common of models is the ideal gas law; a simple single equation that describes the behaviour of a so-called "ideal gas". Real gasses are not ideal but in certain cases somewhere in the ballpark is enough. Alternatively, there are more complex models to consider. Development of such a model is what is called numerical modelling or empirical modelling, the prior being derived from other laws and models and the latter being derived from empirical data collected by experimentations.

In its most basic form, numerical or mathematical simulation is using a model such as ideal gas law to approximate the change in pressure of a set volume of gas undergoing temperature change. It has to be said that simulation becomes much more complex when you introduce computers accompanied by software alongside different techniques. The point remains it is not magic.

Now let's address what it is used for; again the answer comes as "predicting what will happen" but that isn't specific at all. While I am the first to admit this list will never be complete due to the extensive applications of simulation but hopefully, the four examples I discuss will give you a clear idea. I will only touch on each simulation method used for each application as I am planning to write more in-depth on them at a later date.

Prediction: I know "wow shocker" but honestly sometimes we need to know what will happen when a parameter or a set of parameters changes. We even sometimes need to know what would the pressure be of nitrogen at this temperature to select the construction material. Usually, this is a numerical simulation because the prediction is all that matters.

Design or sizing: Chemical engineers especially, use process simulation to design equipment such as distillation columns, heat exchangers and reactors. This simulation method uses the key assumption of "steady-state" which means that as time changes no disturbances occur. This allows them to find what surface area a heat exchanger needs, where energy can be recovered and how much energy can be recovered. Moreover, they can see the expected purities, energy cost and ultimate construction cost of a separation method. Empowering them to change the parameters of the design to optimize these parameters to specifications required by the client.

Control and Optimization: our drive for perfection has led to us using dynamic simulation to simulate things such as the control of equipment and abstract environments such as banks. Control of equipment is simulated to determine initial control parameters and to test the stability and effectivity of a control method. In abstract environments like the bank example, the simulation is done to optimize something like the number of tellers so that we can be sure no customer has to wait longer than a certain time to be helped. Dynamic simulation refers to a time-based simulation that is not constant. I want to note that there are different types of simulations under this category but that is for another time. Usually, models are based on statistics or experimental data and with an overview of the lifetime of the situation based on history the simulation is developed and analyzed. Note that for control, some theoretical assumptions are made to assist in the simulation development.

Prototyping: with the human race building bigger and more complex the prototyping process has become expensive and a major challenge due to scaling being inconsistent. In a simulation, one can test prototypes without building them using Computational Fluid Dynamic (CFD) simulation which may also be referred to as Thermomechanical simulation. The method has grown beyond its routes of simulating fluids to include chemical reaction, heat transfer, mechanical properties such as stress and many more. It is still referred to as CFD but I have seen thermomechanical used rarely to describe the simulation technique.