SCALING in Boat Design and why the twin towers fell down so easily

Design Changes

The contractor anchored the suspension cables of each bridge to the one above it instead of directly to the ceiling like the drawings specified. I'd say that was more than just a small design change.

 

Failure Mechanisms

On the other hand, the Tacoma Narrows bridge was built exactly as the drawings specified. The designers didn't fully understand their own design, and so didn't take into account that the lower mass of the radical design and other factors allowed aerodynamics to become a critical influence.

It has been suggested by some that the Akron and Macon airships sustained structural failures that may not have occurred if the Goodyear engineers had understood gust loads as well as their German counterparts.

 

It was so long ago, I don't remember the bridges being stacked. I do recall the detail which was published in one of the professional architectural magazines. Th cable was supposed to be continuous and terminated with a big washer and bolt on the underside of the bridge. What was built was a cable which actually ended at the top of the handrail (or ended early) and another cable slip knotted or clamped through to the bottom and YES to perhaps yet another bridge below that.

It was a real mess, but on the outside to the novice you would have no idea what was done.

Small connection, very big deal.

 

The Galloping Gertie Bridge..............good one

 

Don't shoot against model tank test....

Hydrodynamic is not an exact science...but experience and feeling help a lot in a speed forecast.

For me it is important to test large model as possible, the limit is given by the speed of the carriage.

The main problem is not to evaluate resistance in full scale but extrapolate the appendages resistance and propellers efficiency.

The appendages run at different Reynold's number than the model and the measured figures of the resistance of bosses,palms, brackets, shafts, rudders are too large. It it necessary to apply a scale effect correction.

For the propellers two possibility:
1) self propulsion tests with a stock propeller and then evaluation of the propulsive coefficients. The openwater figures for the final propeller from cavitation tunnel tests or from calculations.

Adding all figures...all approximated......one time +...one time -...at the end the results is not far from model tests evaluations.

Attached the model for the selfpropulsion tests of a 26 m long craft (model length over 2 m), speed + 45 knots.

If the model to be tested is too small.....better forget about model basin tests...

 

Careful tank testing can be close to the real thing (I know this is anecdotal, but the tank vs real images are interesting, and the ship has been operating successfully in this environment for nearly 30 years) http://www.youtube.com/watch?v=z2TXkmX--wc besides, it's cool!

 

Nice images !

 

Not to sound picky, but the basis for design was the 707, and the planes that hit WTC 1 & 2 were 767-200ER's. You're correct in the point you make, though. The 767's aren't that much heavier than the 707's.

 

I posted that video a few days ago at the Hoverclub of American website after it was posted in the Boatdesign Random Picture thread. Three or four people said they really liked it. One of them is building a tank for his next hovercraft, which will be twice as big as the 100 foot long one currently under construction in Florida.

 

just worth mentioning - Towers:

The steel was graded to easily withstand the temperatures that jetfuel fire can create.

The towers fell freefall speed. Imagine a brick suspended with strings that just and just hold the brick weight - then add this setups in a pile as high as the towers. Thenm break the strings of the top one so that it falsl on the one below - even if the strings had no strength at all the prick pile would collapse in 40 seconds or something - just because of the momentum of the mass - this is assuming no energy absorption of the structure at all. Towers fell in 11 secs or something like that.

Don't want to get out of topic - just saying.

 

George,

I'm glad others have enjoyed that video as I have. In my military days, I spent many hours riding shotgun in helicopters performing high speed low level manuevers. Flying on the deck and piloting the tug at speed in those heavy seas to get the shots must have been an interesting day at the office for a few people.

Just curious; are the folks in FL and elsewhere who are developing freight hauling hovercraft able to incorporate more energy efficient elements into their designs? I'm most familiar with military hovercraft, which tend to be big on power and speed, but not too efficient.

Cheers,

Charlie

 

The steel was graded to easily withstand the temperatures that jetfuel fire can create.

No such "steel" exists titanium maybe , but costly in a building.

What WAS MISSING was proven fire resistant covering to help the steel stand a bit longer in a fire. The usual covering ASBESTOS is a bad word to the PC , so unproven garbage was used .

FF

 

Hovercraft:
1. All composite construction, lighter weight with a little more up front cost.

2. Loading much less than LCAC, why does the military stuff 10 lbs into a 5 lb bag?

3. Hybrid diesel to electric motor drive

4. New skirts system unlike anything else, first major innovation in 30 plus years

5. Read 4th entry by "Kurt" in the thread link below.

http://www.hoverclubofamerica.org/forum/index.php?showtopic=1091



World Trade Center:
1. Insulation/fireproofing was blown off by explosion, steel loses a lot of it's strength when heated unless designed for it as in special tempered steel which building steel of the WTC was not.

 

my bad, RF, guess I need to get out the rabbit ears, start watchin PBS again...
I think my point is good, though:
I see the "art" coming in not just in aesthetics but in the creative mind needed to imagine hitherto unforseen problems.... saving the engineering side of the process from the "garbage in" syndrome.

 

You could do this through "culture" such as in Europe verses the American values of bigger is better and get straight to the point.

Example of beautiful engineering: