"It's often the engineer's experience and judgment that plays a key role in setting the numerical value for the factor of safety."
Reminds me of the chief engineer on the Enterprise:
[the U.S.S. Enterprise is being sucked into a black hole, seconds away from doom] Scotty: I'm giving her all she's got, Captain! [the bridge ceiling begins to crack as the ship's drawn closer] James T. Kirk: All she's got isn't good enough! What else ya got? Scotty: Um... Okay, if we eject the core and detonate, the blast could be enough to push us away! I cannae promise anything, though! [the viewing window starts to rupture] James T. Kirk: DO IT, DO IT, DO IT!
Probably not a scenario he would have used a computer model for...
While a work of fiction, it still speaks to the importance of factoring in an experienced engineer's judgment that may not necessarily agree with a computer model...and that "sufficient" can also depend on the situation.
I agree. What I'm saying is that "sufficient" (as much as needed) is very subjective and based on individual perspective and opinion. My wife and I have very different views on how many diamonds are 'sufficient' for her wardrobe. One may be necessary or required to display her merital status, but we don't agree on the sufficient number.
This is an excellent post--excellent. I had a professor who always stated, " the only thing less desirous than an undersign is an over design. He was all about applying the proper safety factors to design problems and stressed that to all of his students. You were automatically "dinged" if you did not state and apply safety factors and how those affected the assembly of components.
I think we have just seen a remarkable violation of "necessary and sufficient" with programming and launch of the "Affordable Healthcare Act". A disaster due to improper planning and bogus architecture. Our country could definitely benefit from reading your post.
That is a good point. The sufficient condition is usually the bounding condition. The necessary condition is that which is called out specifically in the specification. Of course, this assumes the requirements are correct.
Great article. "Necessary" is often fairly easy to calculate knowing what is needed, but that "Sufficient" number can vary all over the place depending on perspective. I think personal experience is a variable that can have great impact on what is sufficient, so can lead to a lot of debate among peers. How safe is safe? How much is too much?
What should be the perception of a product’s real-world performance with regard to the published spec sheet? While it is easy to assume that the product will operate according to spec, what variables should be considered, and is that a designer obligation or a customer responsibility? Or both?
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