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DC:19. COMPUTER AIDED ENGINEERING (CAE)

•One of the fundamental features of Engineering is to make trade-offs to get optimal designs

•If we overdesign, then all designs become simple, but more expensive, and more difficult to manufacture

•If we underdesign, then our design will not fulfill our requirements

•Therefore we use knowledge and tools to achieve designs which are ‘just right’.

•There are many physical factors which can affect the quality of a design,

-Yield stress failure

-Excessive deformation

-Insufficient heat transfer

-Kinematic interference

-Too much/little air drag

-Resonance at wrong frequency

-Electromagnetic interference effects

-Non uniform cooling effects (eg. warping in plastic parts)

-etc.

DC:19.1 FINITE ELEMENT ANALYSIS (FEA)

•Why?: When we have to find an effect (stress, strain, flux, etc) which is distributed throughout a volume, and is too difficult to calculate by hand.

•How: Break a part into discrete chunks (elements), Apply driving functions, constraints, etc., then solve for physical effects.

•Elements

-different types of elements may be used in a FEM mesh

-elements that are too deformed will yield poorer results

-if a field variable will be subject to a large change over an area, then smaller elements should be used to improve the approximation.

•CAD systems will often allow a user to manually, and automatically mesh a part.

•Generative meshing algorithms will

-mesh a part roughly,

-solve the problem using the rough mesh,