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Old 12-30-2012, 10:32 PM   #96 (permalink)
ryannoe
Not Ordinary Engineering
 
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Quote:
The bulb serves in making the transition from a body of water in rest to that same body moving sideways more gentle. There is a close relationship between the rate at which the cross section area of a body moving through water varies and the resistance it meets. As you see the variation of the cross section as a function, you need to keep the second order derivato of that function as close to zero as possible.
If this were the case, extending the bow to give a longer length to width ratio would help towards the Sears-Haack model you are referring to with the "Area Rule".

I wiki'd bulbous bow and found this. Excellent explanation of how they work (with pictures as well )

Bulbous bow - Wikipedia, the free encyclopedia

Quote:
In car terms, this means that you can compensate for anything you move into a stream by making a dent in another part close by so the total area does not change much, and the momentum of the air at some distance to the car is not disturbed.
Or you can gradually build up and recede the area just before and after the intruding bit for the same effect; like the leading and trailing spoilers at the wheels of low Cd concept cars. They work because of this principle.
I think I need to chew on it a little more. This principle is the Area Rule (referred to earlier). It's been used extensively by transonic aircraft to reduce the number of shock waves forming as the aircraft approaches mach. I'd be interested in seeing how effective it is at low speed vehicle design.

-Ryan
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