Parametric Modeling

"I am modeling," I would say to my then-girlfriend-now-wife, just to impress her, every time she called. But of course it would all be shattered if I would prefix "parametric" to it.

Now I do not want to extol about the virtues of parametric modeling, we all know it, don't we? Early in my career I took upon parametric modeling very proudly, announcing to everyone who cared to listen about how easy it was to change the form, fit and function by merely playing with the key variables.I discovered the real advantage when I started performing design of experiments.

The objective of DoE is to determine the optimal value of a certain set of variables in a model would effect the desired outcome. For example, if the task on hand is to determine the optimal thickness of a beam that can withstand the maximum forces subject to it. The usual constraints would be the type of material selection, weight of the assembly and cost. A typical DoE would have more such parameters to vary, the width, height, length, supports and so on. If the beam section has 4 standard variants available with the supplier, these values would be input to the analysis program that would calculate the strength of the beam for each material and cross section. Another spreadsheet would calculate the weight and cost of the beam. The parametric modeling software would take in these values and would cycle through all the variations. (Of course some basic automation program is required to feed these values and run the program sequentially). If these values and outcomes are fed into a statistical program, we would get a transfer function, that is, a relationship between the variables fed into the tool and the desired outcome. And from this transfer function, we would get the optimal beam section and material that would yield the maximum strength at minimum cost.

The CAD software these days are all parametric by default, Unigraphics provides some non parametric features, Pro-Engineer and Solidworks by default have predefined variable names for every feature created in them and they provide a nice intuitive interface to program using them. UG also has these features but the menu is not as intuitive. Ansys has APDL and tcl-tk that is widely used to pass variables to the program. Parameters and I have been fast friends and have helped me cover change requests and perform DoEs quickly and efficiently.