Thoughts on: The Design of Design, Gordon Glegg

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ISBN 0 521 07447 9

The Design of Design is the genuine advice of someone seen who has seen (and made, analysed and corrected) his fair share of errors. Some of the advice I know and accept – for example, creative thought is best nurtured through alternating periods of extreme focus and relaxation, with inspiration usually striking whilst you relax. Some advice runs against what I have experienced and been taught – for example, I generally feel that extreme concentration of complexity in a design is the safest path, however Glegg advocates introducing a ‘complicate to simplify’ approach spreading his complexity more evenly. By taking this approach he seems at risk of unexpected interactions between seemingly unrelated items ruining several of his solutions. However he insures himself with full scale testing.

The most useful advice for me concerns his sense of ‘style’ in a design solution and finding ways of describing it – these form useful general guidelines that, once you look, crop up everywhere. These include a sense of working with, rather than fighting against, your forces and materials – do your designs have positive geometric stiffness (they get stiffer as they deform as the geometry becomes more favorable), do you use the properties of your materials such as their plasticity to provide safety mechanisms, or rely on later complex additions to make them safe? Perhaps, the most important rule for style is the number of parameters needed to define the solution and how it behaves should be as small as possible – a ruthless approach to the complexity of the solution should be made in its final turns. The same idea appears when learning about 3D modelling – ‘fairness’, usually a marine term, is taken and used as general advice.

The meaning of “fair” is much debated in the marine industry. No one can define it, but they know when they see it. Although fairing a surface is traditionally associated with hull surfaces, all visible surfaces on any object can benefit from this process. In Rhino, the first cue for fairness in a surface is the spacing of the surface display
isocurves. There are other characteristics of fair curves and surfaces. Although a curve or surface may be fair without exhibiting all of the characteristics, they tend to have these characteristics. If you keep these in mind while modeling, you will end up with a better final product.
The guidelines for creating a fair surface include:
● Use the fewest possible control points to get the curve shape.
● Use the fewest possible curves to get the surface shape

Rhino 5 User Guide

Glegg looks at solving engineering design problems in two main areas, the design of the problem and the design of the designer, which is then subdivided into the analytical, artistic and inventive components of thinking.

When designing the problem, Glegg recommends:

  1. Check for intrinsic impossibilities – are the forces so large as to crush any material that could fit in the load path, are you destroying or creating energy in order for your solution to work?
  2. Beware of myths and unchecked assumptions, the stories you hear are often wrong and outdated
  3. Define problems in figures and quantified levels, avoid any definition defined in words

The design of the designer:

Three key areas of thinking for the designer: the inventive, the artistic, the rational. A lack of any leads to a poor design, but strength in one is often enough:

The inventive:

  1. Concentration and relaxation around your work
  2. Skeptisism of tradition and folklaw
  3. Complicate to simplify – usually a small change to one small part can bring rewards
  4. Make the most of your material and processes, rather than fighting their properties – they will not give in without a fight
  5. Divide and tidy up your solution, get the the end with a solution, however ugly, that works, then refine

The artistic:

  1. Aim at continuity of energy – I extend this to include the continuity of forces through structures, are your forces changing directions? Are forces that tend to occur simultaneously taking short paths to cancel one another when they can?
  2. Avoid over-designing, take an idea to extremes and pull back into the sweet spot where your innovation is well used
  3. Choose a rational basis for what you want to achieve – know success and completion when you see it
  4. Find the appropriate medium, if you are fighting your processes and materials to find a solution, then you are likely to have made a mistake very early in the design process
  5. Avoid perpetuating arts and crafts – a inappropriate, though well optimised, process might be easy to procure, but should be carefully considered before it is chosen, there might be good economic reasons for a particular solution.

The rational:

  1. Think logically – find the right analytical tool for any given task, back up your more complicated analysis with simpler approaches
  2. Design for a predictable life – something that demands replacement regularly will be maintained and other faults are more likely to be found. Designing for a indefinite life increases the risk of sudden and catastrophic failure. Design modes of failure that are predictable, easy to fix
  3. Watch for disguised assumptions – it is easy to come up with analytical stories to convince yourself of a position, and for someone else to tell a different story to reach very different solutions. Solving for strength is easy – find any loadpath and lower bound theorem works hard to fill in the gaps. Solving for stiffness is hard – you need to find the true solution to make sure you don’t accidently break something else on the way to your strength solution…
  4. Safety is found in absorbing energy, not transferring it
  5. Overpaying is generally cheaper than failure

Well worth a read for the young engineer starting out practice. It only takes a couple of hours to read and has some nice examples to think about.

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