tag:blogger.com,1999:blog-8455317162471408978.post3865657487259424497..comments2023-05-24T07:15:29.996-07:00Comments on nippleworks: TTDOEUnknownnoreply@blogger.comBlogger2125tag:blogger.com,1999:blog-8455317162471408978.post-50530344261289551242009-08-05T16:32:27.586-07:002009-08-05T16:32:27.586-07:00I think that if a non-linear response surface is o...I think that if a non-linear response surface is of concern, the number of center points can be increased. However, the factors I have described are all non-continuous (either aero or standard with no middle ground) so a function will not be a valid output as much as a Pareto plot would.-phttps://www.blogger.com/profile/03839990375976565783noreply@blogger.comtag:blogger.com,1999:blog-8455317162471408978.post-18059909815262376692009-08-05T16:00:46.288-07:002009-08-05T16:00:46.288-07:00I haven't had the DOE training, but it seems t...I haven't had the DOE training, but it seems to me that there is an implicit assumption of linearity in the relationship between variables. In other words, if f(x,y,z) has a min at x=a when y=0, then f will still have a min at x=a when y=small, where small is some minor excursion in the value of y. If this assumption of linearity fails, the utility of DOE is limited. The problem with aerodynamics is that it is inherently non-linear, as shown by the fact that drag forces increased as velocity squared. On the other hand, frontal areas do *mostly* add to C_D. Non-linearity becomes even worse when eddies at sharp edges ("turbulence") is considered.<br /><br />A trivial example of failure of linearity is that if you add a cowling to the front of the bike, messing with the placement of the rear brakes or shape of the wheel isn't going to matter much. A less trivial example is that changing the front wheel shape slightly for the better may well change the optimal brake placement.<br /><br />Analysis of aero data and trends is truly difficult. Nonetheless, I've heard that NASA Ames has shut down its wind tunnel due to confidence in calculations.Anonymousnoreply@blogger.com