Functional Modelling


What is Functional Modelling?

Functional Modelling represents the third generation of computer modelling tools in mechanical engineering design.

In Functional Modelling, the user describes a proposed design in terms of functional primitives such as 'shaft' and 'crank'. These terms carry the same shape information as the more traditional solid modelling terms 'cylinder' and 'lamina', but in addition they carry information about what the part is intended to do. The goal of Functional Modelling is to build a modeller which can analyse the design in terms of the function which each part is intended to carry out, and select suitable dimensions for the parts so that the design works as expected.

Where does it get us?

Much of the embodiment and detailed design phases of mechanical design consists of ensuring that the components in the design will not fail mechanically, either through excessive stress (plasic yield or fatigue) or through excessive deformation (including buckling). This is initially done using simple mathematical models of different areas of the design, e.g. treating a crank pin as a slender cantilever (for bending stresses and deflections), and as a shear pin for shear stresses. Only if these models suggest critical stresses are more elaborate analysis methods used, such as Finite Elements. Designs frequently fail because a particular mode of failure is overlooked by the designer, and the relevant analysis is not carried out.

A computerised Functional Modeller will carry out much of this simple analysis quite automatically, and adjust dimensions where necessary. It will therefore give enhanced confidence in the viability of a design, as well as allowing the designer to explore many more candidate concepts in depth before selecting the best one for further development.

A prototype functional modeller is currently being constructed at the Cambridge University Engineering Design Centre.

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