tom kane
03-25-2007, 12:10 AM
Scaling is a principle familiar to structural engineers and physicists.In proportion to their size, small things are stronger than big things.How do boats and ship design cope with this problem.
View Full Version : SCALING in Boat Design and why the twin towers fell down so easily
Guillermo
03-25-2007, 02:35 AM
From MARIN (http://www.marin.nl/web/show):
"Model testing of ships is usually performed at equivalent Froude numbers to obtain equal wave patterns at model scale and at full scale. However, once the Froude number is fixed, one can not also obtain equivalent Reynolds numbers. Typically, in ship design projects the Reynolds number at model scale is a factor one hundred smaller than at full scale. To account for the so-called scale effects caused by the difference in Reynolds number, extrapolation procedures are used. The primary scale effect on the flow is a decrease of the boundary-layer thickness on the hull and a corresponding decrease of the width of the wake behind the stern with increasing Reynolds number. This results in a considerable change of the velocity distribution in the propeller plane. A secondary, and therefore less pronounced, scale effect is caused by the interaction between the viscous flow and the wave pattern. Wave effects on the viscous flow around the hull may be significant for all cases with substantial wave making, as the wavy surface affects the development of the boundary layer all along the hull. On the other hand, viscous effects on the wave pattern are generally insignificant and only substantial in the stern region, as is confirmed by many validations of non-linear panel methods. Viscous effects are expected to result in a reduction of the height of the stern wave system and an upstream shift of the first wave crest behind the stern. The level of this reduction depends on the amount to which the flow itself is affected by viscosity. Since the width of the boundary layer and the wake decrease with increasing Reynolds number, so does the reduction of the stern wave system. This secondary scale effect on the wave system is not specifically accounted for in extrapolation procedures. However, with the development of solution methods for the free-surface viscous-flow problem, it has now become possible to calculate these effects."
Model test results may suffer from such scale effects related to the large difference in Reynolds number between model and ship. This difference is particularly significant for full-bodied ships, and for ships operating in shallow water. This suggests that realistic form and numerical values for the hydrodynamic efforts should be based on full-scale tests.
Cheers.
"Model testing of ships is usually performed at equivalent Froude numbers to obtain equal wave patterns at model scale and at full scale. However, once the Froude number is fixed, one can not also obtain equivalent Reynolds numbers. Typically, in ship design projects the Reynolds number at model scale is a factor one hundred smaller than at full scale. To account for the so-called scale effects caused by the difference in Reynolds number, extrapolation procedures are used. The primary scale effect on the flow is a decrease of the boundary-layer thickness on the hull and a corresponding decrease of the width of the wake behind the stern with increasing Reynolds number. This results in a considerable change of the velocity distribution in the propeller plane. A secondary, and therefore less pronounced, scale effect is caused by the interaction between the viscous flow and the wave pattern. Wave effects on the viscous flow around the hull may be significant for all cases with substantial wave making, as the wavy surface affects the development of the boundary layer all along the hull. On the other hand, viscous effects on the wave pattern are generally insignificant and only substantial in the stern region, as is confirmed by many validations of non-linear panel methods. Viscous effects are expected to result in a reduction of the height of the stern wave system and an upstream shift of the first wave crest behind the stern. The level of this reduction depends on the amount to which the flow itself is affected by viscosity. Since the width of the boundary layer and the wake decrease with increasing Reynolds number, so does the reduction of the stern wave system. This secondary scale effect on the wave system is not specifically accounted for in extrapolation procedures. However, with the development of solution methods for the free-surface viscous-flow problem, it has now become possible to calculate these effects."
Model test results may suffer from such scale effects related to the large difference in Reynolds number between model and ship. This difference is particularly significant for full-bodied ships, and for ships operating in shallow water. This suggests that realistic form and numerical values for the hydrodynamic efforts should be based on full-scale tests.
Cheers.
tom kane
03-25-2007, 03:46 AM
I did try to add an attachment I will try again
Guillermo
03-25-2007, 08:51 AM
"Despite the undeniable progress made in putting hydrodynamic hull design and performance predictions on a rational basis through the use of computational fluid dynamic (CFD) techniques, the design of hulls in commercial ships is still partly an art mainly supported by experimental evidence and with no inmediate perspective of being reduced to a fixed procedure. Present methods for design of ship hulls typically involve the following steps: 1) Definition of speed range and operational conditions, 2) Definition of preliminary hull shape using empirical methods or simple potential flow based hydrodynamic codes, 3) Manufacturing of scaled prototype, 4) Experimental testing of hydrodynamic, manouvering and seakeeping performance, 5) Empirical scale-up process, 6) Modification of prototype and repetition of steps 3-6 until the desired tolerance in ship's performance is satisfied. This is a costly and expensive process which generally does not suffice to achieve optimum cruising performance (due to the difficulties in the scaling process) giving the highest level of hydrodynamic efficiency characterized by prescribed speed and stability requirements."
http://www.cimne.upc.es/cimnel_new/archivos/project_content.asp?id=1
Something on scale effects on propellers:
http://books.nap.edu/openbook.php?record_id=10834&page=744
More info can be found through the ITTC:
http://ittc.sname.org/documents.htm
Cheers.
http://www.cimne.upc.es/cimnel_new/archivos/project_content.asp?id=1
Something on scale effects on propellers:
http://books.nap.edu/openbook.php?record_id=10834&page=744
More info can be found through the ITTC:
http://ittc.sname.org/documents.htm
Cheers.
BWD
03-25-2007, 12:52 PM
Limited, but not really OT...
Re: the towers
As I recall they did not come down until after application of around 389M kcal heat, each.
This may be an obnoxious example to introduce a topic, but it's apt as it illustrates an important problem in modern design:
The more complex, as well as the bigger, a structure is, the more things can happen to it. Doubtless the WTC engineers never said, "what if we burn a fuel tanker on the 80th floor," any more than they considered the kinetic energy of a jetliner, as has been argued before by many.
Thus other aspects of complexity need special consideration when designing a large structure, as well as those derived from size.
It is something to think about when adding another system to a boat, of any size.
Making something large or complex that will last a long time pushes the usual assumptions about probability as hard or harder than other aspects of design. This challenges computability and leaves us with the art of design, said another way in Guillermo's post above refering to the design cycle of ships.
Re: the towers
As I recall they did not come down until after application of around 389M kcal heat, each.
This may be an obnoxious example to introduce a topic, but it's apt as it illustrates an important problem in modern design:
The more complex, as well as the bigger, a structure is, the more things can happen to it. Doubtless the WTC engineers never said, "what if we burn a fuel tanker on the 80th floor," any more than they considered the kinetic energy of a jetliner, as has been argued before by many.
Thus other aspects of complexity need special consideration when designing a large structure, as well as those derived from size.
It is something to think about when adding another system to a boat, of any size.
Making something large or complex that will last a long time pushes the usual assumptions about probability as hard or harder than other aspects of design. This challenges computability and leaves us with the art of design, said another way in Guillermo's post above refering to the design cycle of ships.
Leo Lazauskas
03-25-2007, 01:21 PM
From MARIN (http://www.marin.nl/web/show):
Model test results may suffer from such scale effects related to the large difference in Reynolds number between model and ship. This difference is particularly significant for full-bodied ships, and for ships operating in shallow water. This suggests that realistic form and numerical values for the hydrodynamic efforts should be based on full-scale tests.
And if one candidate (full-size) hull is not quite right then crumple it up like a piece of paper and throw it in the bin. Then build a new one and hope it performs better. :)
The quote from Marin was excellent, by the way.
Regards,
Leo.
Model test results may suffer from such scale effects related to the large difference in Reynolds number between model and ship. This difference is particularly significant for full-bodied ships, and for ships operating in shallow water. This suggests that realistic form and numerical values for the hydrodynamic efforts should be based on full-scale tests.
And if one candidate (full-size) hull is not quite right then crumple it up like a piece of paper and throw it in the bin. Then build a new one and hope it performs better. :)
The quote from Marin was excellent, by the way.
Regards,
Leo.
Guillermo
03-25-2007, 02:38 PM
And if one candidate (full-size) hull is not quite right then crumple it up like a piece of paper and throw it in the bin. Then build a new one and hope it performs better.
You know it's not like that. :) Tank tests and the best of CFD analysys still have to be compared to the real thing, to check their accuracy relating many aspects still not well known, i.e. the loads at ships' bows when encountering very high waves. Then you learn, refine the methods and go one step upwards in the spiral. Isn't it this way?
Cheers.
You know it's not like that. :) Tank tests and the best of CFD analysys still have to be compared to the real thing, to check their accuracy relating many aspects still not well known, i.e. the loads at ships' bows when encountering very high waves. Then you learn, refine the methods and go one step upwards in the spiral. Isn't it this way?
Cheers.
SamSam
03-25-2007, 03:15 PM
" the design of hulls in commercial ships is still partly an art mainly supported by experimental evidence and with no inmediate perspective of being reduced to a fixed procedure.
That's what I was going to say, "an educated guess". Sam
That's what I was going to say, "an educated guess". Sam
Raggi_Thor
03-25-2007, 05:41 PM
Scaling is a principle familiar to structural engineers and physicists.In proportion to their size, small things are stronger than big things.How do boats and ship design cope with this problem.
In small boats you use the local stiffness as criteria for dimensions, if the deck is stiff enough to be walked on, it's also strong enough of you look at the whole boat as a beam supported in both ends and the keel and mast pushing down.
In larger boats and ships, global stiffness, the hull and deck as a beam becomes the critical issue.
Interesting side effect: Wood is the best material for small boats, steel for larger boats :-)
In small boats you use the local stiffness as criteria for dimensions, if the deck is stiff enough to be walked on, it's also strong enough of you look at the whole boat as a beam supported in both ends and the keel and mast pushing down.
In larger boats and ships, global stiffness, the hull and deck as a beam becomes the critical issue.
Interesting side effect: Wood is the best material for small boats, steel for larger boats :-)
Leo Lazauskas
03-26-2007, 12:36 AM
You know it's not like that. :) Tank tests and the best of CFD analysys still have to be compared to the real thing, to check their accuracy relating many aspects still not well known, i.e. the loads at ships' bows when encountering very high waves. Then you learn, refine the methods and go one step upwards in the spiral. Isn't it this way?
Cheers.
It certainly should be that way, Guillermo. I'm not very
confident about many CFD predictions and extrapolations,
nor do I trust many towing tank tests as being indicative
of what happens at full-scale. So yes, full-scale verification
is the ultimate test of the predictions and they should be
used to refine CFD techniques and towing tank methods. But
it's a very slow slide up (or down) the spiral!
You mentioned wave loads as one poorly understood phenomenon.
There are, of course, many others. In a real sea the effective
turbulent eddy viscosity can be quite different to that in a
towing tank. What this does to skin-friction and wave-making
is still something I'm trying to understand.
In the attached picture (similar to that produced by Fred Stern
in some of his papers), five regions of the flow at midships are
shown. Region I is the "potential" zone. Region II is the boundary
layer (BL) on the free-surface, Region III is the BL on the hull,
Region IV is the zone of interaction of the free-surface BL and
the hull BL, and Region V is the meniscus clinging to the hull.
Only Region I is considered to be reasonably well-understood
because viscosity can often be ignored. The BL on the hull is
understood for laminar flow, but this is not of much help for
anything bigger than a duck. How the extent and effects of
the five zones scale in a real sea with waves, currents and
surfactants is going to take a very long time. Add hull flex
and vibration, propulsors, and, in shallow water, complex
topography and it's almost enough to make one find a less
complicated pursuit. Almost. :)
All the best,
Leo.
Cheers.
It certainly should be that way, Guillermo. I'm not very
confident about many CFD predictions and extrapolations,
nor do I trust many towing tank tests as being indicative
of what happens at full-scale. So yes, full-scale verification
is the ultimate test of the predictions and they should be
used to refine CFD techniques and towing tank methods. But
it's a very slow slide up (or down) the spiral!
You mentioned wave loads as one poorly understood phenomenon.
There are, of course, many others. In a real sea the effective
turbulent eddy viscosity can be quite different to that in a
towing tank. What this does to skin-friction and wave-making
is still something I'm trying to understand.
In the attached picture (similar to that produced by Fred Stern
in some of his papers), five regions of the flow at midships are
shown. Region I is the "potential" zone. Region II is the boundary
layer (BL) on the free-surface, Region III is the BL on the hull,
Region IV is the zone of interaction of the free-surface BL and
the hull BL, and Region V is the meniscus clinging to the hull.
Only Region I is considered to be reasonably well-understood
because viscosity can often be ignored. The BL on the hull is
understood for laminar flow, but this is not of much help for
anything bigger than a duck. How the extent and effects of
the five zones scale in a real sea with waves, currents and
surfactants is going to take a very long time. Add hull flex
and vibration, propulsors, and, in shallow water, complex
topography and it's almost enough to make one find a less
complicated pursuit. Almost. :)
All the best,
Leo.
tom kane
03-26-2007, 05:44 AM
Many ships,airships,bridges,buildings,infact many big things have failed because of a design change often.. by accident.There is something missing in the design of big things.It is not murphys law, or What ever can happen will happen?
PI Design
03-26-2007, 06:04 AM
I'm not sure what point you are trying to make?
Big things don't always break. Little things sometimes do.
Big things don't always break. Little things sometimes do.
kach22i
03-26-2007, 07:36 AM
Many ships,airships,bridges,buildings,infact many big things have failed because of a design change often.. by accident.There is something missing in the design of big things.It is not murphys law, or What ever can happen will happen?
Good point, the cable suspended bridge that people were dancing on in a Kansas City hotel failed (ten years ago) because the contractor decided he didn't want to build it the way it was correctly drawn. The small but critical design detail change which was made by the structural engineer (a lesser in his office actually) to make it easier to build for the contractor and approved by the city could not take the rhythmatic motion set up by a 100 + people dance in step on it at the same time (who would of ever guessed?). The structural engineer lost his license but did not go to jail. Something like 30 people died in that one.
Good point, the cable suspended bridge that people were dancing on in a Kansas City hotel failed (ten years ago) because the contractor decided he didn't want to build it the way it was correctly drawn. The small but critical design detail change which was made by the structural engineer (a lesser in his office actually) to make it easier to build for the contractor and approved by the city could not take the rhythmatic motion set up by a 100 + people dance in step on it at the same time (who would of ever guessed?). The structural engineer lost his license but did not go to jail. Something like 30 people died in that one.
water addict
03-26-2007, 09:28 AM
Scaling is a principle familiar to structural engineers and physicists.In proportion to their size, small things are stronger than big things.How do boats and ship design cope with this problem.
Quantify the expected loads as best you can. Quantify the material and structural behavior as best you can. Use this knowledge to design something that will not break.
Quantify the expected loads as best you can. Quantify the material and structural behavior as best you can. Use this knowledge to design something that will not break.
RatliffFranklin
03-26-2007, 02:37 PM
Limited, but not really OT...
Re: the towers
As I recall they did not come down until after application of around 389M kcal heat, each.
This may be an obnoxious example to introduce a topic, but it's apt as it illustrates an important problem in modern design:
The more complex, as well as the bigger, a structure is, the more things can happen to it. Doubtless the WTC engineers never said, "what if we burn a fuel tanker on the 80th floor," any more than they considered the kinetic energy of a jetliner, as has been argued before by many.
Thus other aspects of complexity need special consideration when designing a large structure, as well as those derived from size.
It is something to think about when adding another system to a boat, of any size.
Making something large or complex that will last a long time pushes the usual assumptions about probability as hard or harder than other aspects of design. This challenges computability and leaves us with the art of design, said another way in Guillermo's post above refering to the design cycle of ships.
No, the WTC engineers did consider the KINETIC effects of the largest airliner flying in the late sixties, the Boeing 727, but not the thermal effects. When you compare a 727 against a 757 the gross weights are not that different, so even if it had been a 727 instead of a 757 that hit the towers, the final results may have been the same.
Re: the towers
As I recall they did not come down until after application of around 389M kcal heat, each.
This may be an obnoxious example to introduce a topic, but it's apt as it illustrates an important problem in modern design:
The more complex, as well as the bigger, a structure is, the more things can happen to it. Doubtless the WTC engineers never said, "what if we burn a fuel tanker on the 80th floor," any more than they considered the kinetic energy of a jetliner, as has been argued before by many.
Thus other aspects of complexity need special consideration when designing a large structure, as well as those derived from size.
It is something to think about when adding another system to a boat, of any size.
Making something large or complex that will last a long time pushes the usual assumptions about probability as hard or harder than other aspects of design. This challenges computability and leaves us with the art of design, said another way in Guillermo's post above refering to the design cycle of ships.
No, the WTC engineers did consider the KINETIC effects of the largest airliner flying in the late sixties, the Boeing 727, but not the thermal effects. When you compare a 727 against a 757 the gross weights are not that different, so even if it had been a 727 instead of a 757 that hit the towers, the final results may have been the same.
RatliffFranklin
03-26-2007, 02:41 PM
Good point, the cable suspended bridge that people were dancing on in a Kansas City hotel failed (ten years ago) because the contractor decided he didn't want to build it the way it was correctly drawn. The small but critical design detail change which was made by the structural engineer (a lesser in his office actually) to make it easier to build for the contractor and approved by the city could not take the rhythmatic motion set up by a 100 + people dance in step on it at the same time (who would of ever guessed?). The structural engineer lost his license but did not go to jail. Something like 30 people died in that one.
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.
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.
RatliffFranklin
03-26-2007, 02:49 PM
Many ships,airships,bridges,buildings,infact many big things have failed because of a design change often.. by accident.There is something missing in the design of big things.It is not murphys law, or What ever can happen will happen?
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.
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.
kach22i
03-26-2007, 02:58 PM
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.
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.:cool:
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.:cool:
kach22i
03-26-2007, 03:01 PM
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.
The Galloping Gertie Bridge..............good one
http://www.tacuroctr.com/images/Blog/gg003.jpg
The Galloping Gertie Bridge..............good one
http://www.tacuroctr.com/images/Blog/gg003.jpg
RANCHI OTTO
03-26-2007, 03:25 PM
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...
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...
charmc
03-26-2007, 06:09 PM
) Tank tests and the best of CFD analysys still have to be compared to the real thing, to check their accuracy relating many aspects still not well known, i.e. the loads at ships' bows when encountering very high waves.
Cheers.
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! :cool:
Cheers.
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! :cool:
RANCHI OTTO
03-26-2007, 06:15 PM
Nice images !
charmc
03-26-2007, 07:25 PM
No, the WTC engineers did consider the KINETIC effects of the largest airliner flying in the late sixties, the Boeing 727, but not the thermal effects. When you compare a 727 against a 757 the gross weights are not that different, so even if it had been a 727 instead of a 757 that hit the towers, the final results may have been the same.
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.
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.
kach22i
03-26-2007, 08:45 PM
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! :cool:
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.
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.
kerosene
03-26-2007, 11:15 PM
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.
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.
charmc
03-26-2007, 11:17 PM
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.
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
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
FAST FRED
03-27-2007, 06:24 AM
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
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
kach22i
03-27-2007, 08:40 AM
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.
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.
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.
BWD
03-27-2007, 05:19 PM
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.
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.
kach22i
03-27-2007, 05:33 PM
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:
http://www.hulubei.net/tudor/photography/photos/E/i/Eiffel-Tower-4-1000x1500.jpg
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:
http://www.hulubei.net/tudor/photography/photos/E/i/Eiffel-Tower-4-1000x1500.jpg
messabout
03-29-2007, 02:57 PM
Spectacular picture Kacchi22I. No doubt done with a tilt film plane vue camera. Focus at top nearly as good as at bottom. Your point is well taken. The "mine is bigger than yours" syndrome is rampant in America. Cars, boats, and anatomical features. We can take heart because Airbus has finally trumped our bigger is better thing.
kach22i
03-29-2007, 03:34 PM
Spectacular picture Kacchi22I. No doubt done with a tilt film plane vue camera. Focus at top nearly as good as at bottom. Your point is well taken. The "mine is bigger than yours" syndrome is rampant in America. Cars, boats, and anatomical features. We can take heart because Airbus has finally trumped our bigger is better thing.
Wait until Boeing comes out with a huge flying wing..........you will see, America is No. 1!!!!!!!!:D
Details like the leaf imprints in the towers base are wonderful.
Eiffel tower base
http://www.clt.astate.edu/wallen/digits/eiffel/default.htm
http://www.clt.astate.edu/wallen/digits/eiffel/tower02.jpg
Wait until Boeing comes out with a huge flying wing..........you will see, America is No. 1!!!!!!!!:D
Details like the leaf imprints in the towers base are wonderful.
Eiffel tower base
http://www.clt.astate.edu/wallen/digits/eiffel/default.htm
http://www.clt.astate.edu/wallen/digits/eiffel/tower02.jpg
charmc
03-29-2007, 04:42 PM
Hovercraft:
2. Loading much less than LCAC, why does the military stuff 10 lbs into a 5 lb bag?
The answer there is crew cost. The same reason the Air Force uses jumbo transports, cruise ships are pushing 250,000 tons, and bulk carriers go huge. Especially in the smaller, all volunteer force, trained man/womanpower is costly, so there is a need for largest possible carrying capacity per vehicle, within the constraints of its operating environment. Note: "largest possible carrying capacity" does not necessarily equate to "most efficient".
2. Loading much less than LCAC, why does the military stuff 10 lbs into a 5 lb bag?
The answer there is crew cost. The same reason the Air Force uses jumbo transports, cruise ships are pushing 250,000 tons, and bulk carriers go huge. Especially in the smaller, all volunteer force, trained man/womanpower is costly, so there is a need for largest possible carrying capacity per vehicle, within the constraints of its operating environment. Note: "largest possible carrying capacity" does not necessarily equate to "most efficient".
charmc
03-29-2007, 05:49 PM
Making something large or complex that will last a long time pushes the usual assumptions about probability as hard or harder than other aspects of design. This challenges computability and leaves us with the art of design....
Your point is definitely valid, BWD. Ultralarge size (2-3 times bigger than previous builds of the same type, for example) requires, actually demands, exceptionally creative thought to identify potential problem areas so engineering methodology can analyze and test for measurable effects and design solutions. Failure to imagine all the possible scenarios is what usually leads to accidents from previously unknown causes. Early in the jumbo jet era there were a series of accidents in which small planes crashed on takeoff. Eventually the cause was determined to be powerful vortices coming off the wingtips of the jumbos. They were both much more powerful and much more persistant than anyone had imagined. In the 1980's there was an incident in which a VLCC cracked its hull while being loaded at pierside; that was due to failure to watch loading patterns closely, but the mate had seen deviations in loading without problems in his previous and smaller ships; didn't think the loading plan was critical..... but it was because the new ship was larger, creating larger stresses. So close adherence to procedures was even more critical, precisely because of the larger size.
Your point is definitely valid, BWD. Ultralarge size (2-3 times bigger than previous builds of the same type, for example) requires, actually demands, exceptionally creative thought to identify potential problem areas so engineering methodology can analyze and test for measurable effects and design solutions. Failure to imagine all the possible scenarios is what usually leads to accidents from previously unknown causes. Early in the jumbo jet era there were a series of accidents in which small planes crashed on takeoff. Eventually the cause was determined to be powerful vortices coming off the wingtips of the jumbos. They were both much more powerful and much more persistant than anyone had imagined. In the 1980's there was an incident in which a VLCC cracked its hull while being loaded at pierside; that was due to failure to watch loading patterns closely, but the mate had seen deviations in loading without problems in his previous and smaller ships; didn't think the loading plan was critical..... but it was because the new ship was larger, creating larger stresses. So close adherence to procedures was even more critical, precisely because of the larger size.
charmc
03-29-2007, 05:53 PM
We can take heart because Airbus has finally trumped our bigger is better thing.
And Airbus is finding out the difficulties of designing and building the biggest thing. Meanwhile, for a change, Boeing is focusing on building a not so biggest plane, but making it more efficient to operate..... what a concept!! :P
And Airbus is finding out the difficulties of designing and building the biggest thing. Meanwhile, for a change, Boeing is focusing on building a not so biggest plane, but making it more efficient to operate..... what a concept!! :P
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