In general, how the perturbation concept (and the study) is named is based on the application. For example, in the AC/DC Module and Semiconductor Module, it is referred to as small-signal analysis, whereas in the Structural Mechanics Module it is referred to as prestressed analysis. For the Batteries & Fuel Cells Module and the Electrodeposition Module, the studies are called AC impedance. For the CFD Module, and fluid flow in general, the term perturbation is sufficient.