This is the simplest form of similarity analysis. Changing the size of the body also changes the Reynolds number, so the fluid speed or kinematic viscosity must also be changed to produce a similar flow pattern. Dimensionless parameters are a very common way of performing functional similarity analysis. If the appropriate dimensionless parameter is known, then a scaling which keeps the parameter value constant will produce a functionally similar system. Structural members under load are similar if the stress safety factor is constant.
Supersonic flows are similar if the mach number is constant.
Convective flows are similar if the Nusselt number is constant. Buckingham pi analysis is a common method of determining dimensionless parameters. The decision matrix is a quantitative approach to engineering decision making. Weights are then defined for the criteria which represent the relative importance of each criterion. Weights are usually numbers between zero and one.