Multivariable optimisation in the home

Over the years, I have seen several presentations of projects that use nonlinear optimisation in design.  Some of these can be loosely classified as consumer matters.  One of the interesting ones was about the design of telephoto lenses for compact cameras.  The variables were concerned with the position of the lenses and their nature, so a typical lens involved 20 to 30 variables.  There were several objectives, such as cost, weight, sharpness of image (at several focal lengths).  I used to use this as an everyday example, though sometimes I talked about the design of jet engines as a further example of nonlinear multivariable optimisation, following another interesting presentation.  (My PhD thesis was also about nonlinear multivariable optimisation, applied to the design and operation of water supply systems.)

Latterly, although it was not a subject that I have ever heard talked about in seminars on nonlinear multivariable optimisation I used to refer to the design of the arms of a domestic dishwasher.  Where should the holes be placed?  How many?  What direction should they be?  One could discuss the engineering problems in outline, and think of objectives.  And as I loaded the dishwasher at home, I used to think that here was a successful application of operational research in the design of an everyday object. 

From time to time, though, my belief in the rationality of the design of the dishwasher has been shaken, especially when the crockery comes out with a coating of tiny tea-leaves or fragments of vegetables.  And to these experiences, this week I had the interesting experience of trying to work out why two of the jets were blocked.  The arms cannot be opened, so the way to get rid of the blockage was a heuristic (good bit of OR) called "shake the arm and add water".  Eventually several apple pips and an apple stalk emerged.  Obviously the design brief did not include provision for straining the water that goes into the arms.  Of course, a good O.R. scientist would have investigated the implementation of the solution to the nonlinear multivariable optimisation problem before allowing it to be incorporated in the design. 


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