Canting keel forces

sucky bus

Super Anarchist
1,034
0
hardonya said:
YO... this is excellent work.... perhaps you can get some dosh from FARR.. or why not email your calcs to VOR sure they would love to have them!
Being a bit more serious.. having this massive bulb waving around, subject to both the vertical drops and perhaps more importantly horizontal and torsional forces.. need some form of metrics from the boats.... whilst they rams act in one plane, they aren't doing it in the others which is probably causing the failures...

Perhaps we can 'crack it' where the others can't...

:blink:
damn, a nice job really ! ! ! now I know what Ive been missin !
And I reckon there will be 'harmonics' to deal with aka. the Tahoma bridge... wonder what is the natrural frequency of a V70...... hums a bit on the Vids, perhaps the keels are shaking themselves to bits.. wonder if thats in the calcs...

 

Lost in Translation

Super Anarchist
1,243
59
Atlanta, GA
The Cariboni system looks to have an alloy frame in all three dimensions to resist twisting. The question for it would be how to mount it such that the little bit of twisting it still does is in line with the surfaces it is mounted on. Does anyone have a picture of the Farr/whomever design?

 

star-sailor

Member
151
0
Europe
The Cariboni system looks to have an alloy frame in all three dimensions to resist twisting. The question for it would be how to mount it such that the little bit of twisting it still does is in line with the surfaces it is mounted on. Does anyone have a picture of the Farr/whomever design?

i think we are a bit fast all together. what we can see on the cariboni-homepage are systems they have build in the past. we do not know if the ABN-system is also using a metal-frame. it is still possible that the "cariboni-boats" are also using a carbon-shelf-system.

or did i miss something?

 
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born2sail

Super Anarchist
And I reckon there will be 'harmonics' to deal with aka. the Tahoma bridge... wonder what is the natrural frequency of a V70...... hums a bit on the Vids, perhaps the keels are shaking themselves to bits.. wonder if thats in the calcs...
Sucky, would that be Galloping Gerdy you're referring to? If so, it's the Tacoma Narrows Bridge.

 

sucky bus

Super Anarchist
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Sucky, would that be Galloping Gerdy you're referring to? If so, it's the Tacoma Narrows Bridge.

Thanks B2S...

Some similarities here I think,

"The first Tacoma Narrows Bridge was revolutionary in its design and historic in its collapse. The failure on November 7, 1940 marked the end of a trend in bridge engineering towards a maximum of lightness, grace and flexibility. Since the turn of the century, suspension bridge construction valued structural grace and slenderness to achieve an artistic appearance. With its shallow stiffening trusses and slender towers, the bridge across the Narrows was the epitome of artistry in bridge construction.

The Tacoma Narrows Bridge was known for its tendency to sway in windstorms. The shape of the bridge was much like that of an aircraft wing and under windy conditions it would generate sufficient lift and become unstable. On November 7, 1940 a large windstorm caused severe and catastrophic failure if the bridge deck."

I will leave it to any other SA's to replace the appropriate words !!!

A MPEG.. of the 'Keel' in action.. OOPS I meant brigde...

http://www.enm.bris.ac.uk/research/nonline...oma/tacnarr.mpg

:ph34r:

 

born2sail

Super Anarchist
Many moons ago, CalTech produced a distance learning program called The Mechanical Universe. If anybody has access to the DVD's, Disc 17 has a great piece on waves and the Aolean effect involved in Galloping Gerdy's collapse. Here's the index of the disk:

Laser Disk #17 - Waves

1: Opening Sequence

2: The Physics Of Shattering A Wine Glass

3: Opening Of Tacoma Narrows Bridge

4: Tacoma Narrows Bridge Construction

5: Tacoma Narrows Bridge Resonance

6: Sunrise And Sunset

7: Resonating Musical Instruments

8: Resonance Of Piano Strings

9: Microscipic Model Of Tuning Fork And Air

10: Resonance Of Piano Strings

11: Equation Of Motion For A Mass On A String

12: Girl On A Swing

13: Oscillator Response To Periodic Motion

14: Voice Shattering A Wine Glass

15: Resonant Response Of An Oscillator

16: Voice Shattering A Wine Glass

17: Viscosity Of Glass - Euro And American

18: Rattling Windows

19: Calteck Seismic Lab

20: Engineering Models Of Buildings

21: Earthquake Damage

22: Telephone Wires As Aeolian Harps

23: Vortex Shedding From Wire

24: Telephone Wires As Aeolian Harps

25: Opening Of Tacoma Narrows Bridge

26: Destruction Of The Tacoma Narrows Bridge

27: Discovery Of The Van Karman Vortex

28: Wind Tunnel Test Of Bridge

29: Destruction Of Tacoma Narrows Bridge

30: Goodstein's Shattering Performance

PS: For anybody wanting to turn a teen onto science, physics, engineering, etc. this video series is a winner.

 
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dtoc

New member
39
2
Sucky, would that be Galloping Gerdy you're referring to? If so, it's the Tacoma Narrows Bridge.
Thanks B2S...

Some similarities here I think,

"The first Tacoma Narrows Bridge was revolutionary in its design and historic in its collapse. The failure on November 7, 1940 marked the end of a trend in bridge engineering towards a maximum of lightness, grace and flexibility. Since the turn of the century, suspension bridge construction valued structural grace and slenderness to achieve an artistic appearance. With its shallow stiffening trusses and slender towers, the bridge across the Narrows was the epitome of artistry in bridge construction.

The Tacoma Narrows Bridge was known for its tendency to sway in windstorms. The shape of the bridge was much like that of an aircraft wing and under windy conditions it would generate sufficient lift and become unstable. On November 7, 1940 a large windstorm caused severe and catastrophic failure if the bridge deck."

I will leave it to any other SA's to replace the appropriate words !!!

A MPEG.. of the 'Keel' in action.. OOPS I meant brigde...

http://www.enm.bris.ac.uk/research/nonline...oma/tacnarr.mpg

:ph34r:

Luckily to this point we have not heard of any unstable hydrodynamics for the keel fins. Being made of a single shaft of steel this is highly unlikely. It would also not be something unique to canting keels, so the issues would not be new.

As for wave propagation in the hydraulic system, I have been thinking about this.

To get a pressure wave to travel in a hydraulic system from a single initiating event, the event needs to occur faster than the wave reflections can get back and cancel the wave. The rule of thumb is 2*L/a to 10*L/a, where L is the distance to a reflection point, a point of resistance to flow, and a is the wave speed. Below 2 it is considered a rapid event and above 10 it is a slow transient. The wave speed for hydraulic fluid is approximately 1000 m/s. This gives a time of 0.000772s to 0.00386s. This is at least an order of magnitude faster than how fast the hull stops when it hits the bottom of a wave, based on my estimates. So as fast as the impact seems, it is slow for the hydraulic system.

 

sucky bus

Super Anarchist
1,034
0
Sucky, would that be Galloping Gerdy you're referring to? If so, it's the Tacoma Narrows Bridge.
Thanks B2S...

Some similarities here I think,

"The first Tacoma Narrows Bridge was revolutionary in its design and historic in its collapse. The failure on November 7, 1940 marked the end of a trend in bridge engineering towards a maximum of lightness, grace and flexibility. Since the turn of the century, suspension bridge construction valued structural grace and slenderness to achieve an artistic appearance. With its shallow stiffening trusses and slender towers, the bridge across the Narrows was the epitome of artistry in bridge construction.

The Tacoma Narrows Bridge was known for its tendency to sway in windstorms. The shape of the bridge was much like that of an aircraft wing and under windy conditions it would generate sufficient lift and become unstable. On November 7, 1940 a large windstorm caused severe and catastrophic failure if the bridge deck."

I will leave it to any other SA's to replace the appropriate words !!!

A MPEG.. of the 'Keel' in action.. OOPS I meant brigde...

http://www.enm.bris.ac.uk/research/nonline...oma/tacnarr.mpg

:ph34r:
Luckily to this point we have not heard of any unstable hydrodynamics for the keel fins. Being made of a single shaft of steel this is highly unlikely. It would also not be something unique to canting keels, so the issues would not be new.

As for wave propagation in the hydraulic system, I have been thinking about this.

To get a pressure wave to travel in a hydraulic system from a single initiating event, the event needs to occur faster than the wave reflections can get back and cancel the wave. The rule of thumb is 2*L/a to 10*L/a, where L is the distance to a reflection point, a point of resistance to flow, and a is the wave speed. Below 2 it is considered a rapid event and above 10 it is a slow transient. The wave speed for hydraulic fluid is approximately 1000 m/s. This gives a time of 0.000772s to 0.00386s. This is at least an order of magnitude faster than how fast the hull stops when it hits the bottom of a wave, based on my estimates. So as fast as the impact seems, it is slow for the hydraulic system.

A bit hard for us being somewhat distant, from the unit; however, your analysis above.. suggest that pressure waves are 'not' causing the catestrophic failures, in effect your treatment above eliminates the 'Water hammer' effect, that is common in water pipes; so leads us back too.. rather than pressure waves and 'hammers' to insufficient 'margins'.. or other vibration or torsional events that are warping the rams... or are the materials being used failing.. re: brittleness and not coping with the range of tempreture... your thoughts

:ph34r:

 

Floundered

Member
151
0
Luckily to this point we have not heard of any unstable hydrodynamics for the keel fins. Being made of a single shaft of steel this is highly unlikely. It would also not be something unique to canting keels, so the issues would not be new.

As for wave propagation in the hydraulic system, I have been thinking about this.

To get a pressure wave to travel in a hydraulic system from a single initiating event, the event needs to occur faster than the wave reflections can get back and cancel the wave. The rule of thumb is 2*L/a to 10*L/a, where L is the distance to a reflection point, a point of resistance to flow, and a is the wave speed. Below 2 it is considered a rapid event and above 10 it is a slow transient. The wave speed for hydraulic fluid is approximately 1000 m/s. This gives a time of 0.000772s to 0.00386s. This is at least an order of magnitude faster than how fast the hull stops when it hits the bottom of a wave, based on my estimates. So as fast as the impact seems, it is slow for the hydraulic system.
A bit hard for us being somewhat distant, from the unit; however, your analysis above.. suggest that pressure waves are 'not' causing the catestrophic failures, in effect your treatment above eliminates the 'Water hammer' effect, that is common in water pipes; so leads us back too.. rather than pressure waves and 'hammers' to insufficient 'margins'.. or other vibration or torsional events that are warping the rams... or are the materials being used failing.. re: brittleness and not coping with the range of tempreture... your thoughts

:ph34r:
dtoc, I can see (if I squint really hard) how the high-speed keel 'hum' is essentially filtered out and isolated from the ram system by the hydraulic fluid, but it would still propogate through the pivot mount and through the contact points of shaft on cylinder, no? When I watch the videos of ABN flying along with the loud 'hum' from the underwater appendages, I can't help but think of vibrational (non-plastic) fatigue going on somewhere. Or in English, how can that loud keel hum not be shaking something apart?

For all airmchair engineers here at SA here is a paper about canting keel loads of the Volvo's. Enjoy!

http://www.na.chalmers.se/%7Esw/YRU/VO70_Amandine.pdf
Well, well, well. The people at Chalmers did not consider acceleration forces in their FE analysis. That seems a bit naive, IMHO. Also, their DVPP predicts only 0.3g acceleration? That's not much.
I too noticed how low their Zacc was, which didn't seem to account for slamming. But reading further shows that 'slamming' is put into the 'accidental' category, i.e. they don't think it happens often. Regardless, the keels have all held together, it's the hydraulics that seem to be the biggest problem, and the above doc addresses the keel design and strength, not the hydraulics or pivot system.

The above doc referenced another interesting nugget, whose url was out of data, but I found it here:

http://tinyurl.com/9ngvc

(main page at http://www.hiswasymposium.com/symposium_papers.asp)

Fun stuff. Anyone know about "slam patch" testing on the recent batch of VOR70's? (I like the name 'slam patch', it sounds like a nicotine patch, but for beer-slamming alcoholics). :rolleyes:

 

lucas

Super Anarchist
1,550
0
In Yachting World Feb 2006 there is a small part on the hull shape around the keel construction. ABN seems to have let there yachts bounce on te ground and have a hollow space where the keel goes inside. reduced drag and probably less strange forces on the construction.

I'll try to find a scanner so The small part will be available for viewing here.

 

canstead

Anarchist
904
47
Didn't Bonduelle and Sill have issues with keel flutter? If so wouldn't that suggest that hydraulics don't get rid of vibration problems?

 
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moody frog

Super Anarchist
4,285
102
Brittany
Slightly off-thread but I suppose that most people interested in the keels problem are here, so .....

Seb Josse seems a bit more talkative than others, at least with frenchmen ;)

Here is an excerpt from a tele-conversation with a famous french blogger (PYL), which gives unpublished (I believe) info.

"Four weeks prior the start, while training in Southampton, we broke our keel canting system. We decided to change it for an heavier one, which forced us to chip around 100 kg from the bulb - for me it was as if my bowels had been taken off ! These modifications were carried in CapeTown. The other teams will have to do the same, but they will only get their new system in Rio,which means that they are not going to be that serene during the next leg ......."

 

dtoc

New member
39
2
Luckily to this point we have not heard of any unstable hydrodynamics for the keel fins. Being made of a single shaft of steel this is highly unlikely. It would also not be something unique to canting keels, so the issues would not be new.

As for wave propagation in the hydraulic system, I have been thinking about this.

To get a pressure wave to travel in a hydraulic system from a single initiating event, the event needs to occur faster than the wave reflections can get back and cancel the wave. The rule of thumb is 2*L/a to 10*L/a, where L is the distance to a reflection point, a point of resistance to flow, and a is the wave speed. Below 2 it is considered a rapid event and above 10 it is a slow transient. The wave speed for hydraulic fluid is approximately 1000 m/s. This gives a time of 0.000772s to 0.00386s. This is at least an order of magnitude faster than how fast the hull stops when it hits the bottom of a wave, based on my estimates. So as fast as the impact seems, it is slow for the hydraulic system.
A bit hard for us being somewhat distant, from the unit; however, your analysis above.. suggest that pressure waves are 'not' causing the catestrophic failures, in effect your treatment above eliminates the 'Water hammer' effect, that is common in water pipes; so leads us back too.. rather than pressure waves and 'hammers' to insufficient 'margins'.. or other vibration or torsional events that are warping the rams... or are the materials being used failing.. re: brittleness and not coping with the range of tempreture... your thoughts

:ph34r:
dtoc, I can see (if I squint really hard) how the high-speed keel 'hum' is essentially filtered out and isolated from the ram system by the hydraulic fluid, but it would still propogate through the pivot mount and through the contact points of shaft on cylinder, no? When I watch the videos of ABN flying along with the loud 'hum' from the underwater appendages, I can't help but think of vibrational (non-plastic) fatigue going on somewhere. Or in English, how can that loud keel hum not be shaking something apart?

For all airmchair engineers here at SA here is a paper about canting keel loads of the Volvo's. Enjoy!

http://www.na.chalmers.se/%7Esw/YRU/VO70_Amandine.pdf
Well, well, well. The people at Chalmers did not consider acceleration forces in their FE analysis. That seems a bit naive, IMHO. Also, their DVPP predicts only 0.3g acceleration? That's not much.
I too noticed how low their Zacc was, which didn't seem to account for slamming. But reading further shows that 'slamming' is put into the 'accidental' category, i.e. they don't think it happens often. Regardless, the keels have all held together, it's the hydraulics that seem to be the biggest problem, and the above doc addresses the keel design and strength, not the hydraulics or pivot system.

The above doc referenced another interesting nugget, whose url was out of data, but I found it here:

http://tinyurl.com/9ngvc

(main page at http://www.hiswasymposium.com/symposium_papers.asp)

Fun stuff. Anyone know about "slam patch" testing on the recent batch of VOR70's? (I like the name 'slam patch', it sounds like a nicotine patch, but for beer-slamming alcoholics). :rolleyes:
Very interesting paper, but will take some time to get through and understand what can be taken from it.

Didn't Bonduelle and Sill have issues with keel flutter? If so wouldn't that suggest that hydraulics don't get rid of vibration problems?
I had forgotten about Sill and Bonduelle. I never read a clear description of what went wrong.

My thinking last night was that keel flutter was neither enhanced nor retarted by the hydraulic system. This may be wrong.

Resonance in the hydraulics is possible if the frequency of the keel flutter matches a resonant frequency of the system. The period of the lowest frequency would be 2L/a for the cylinder. What makes this interesting is that L changes at different cant angles and a is a function of tempurature (and pressure somewhat).

Proper analysis for this takes more than a "back of an envelope" but with such analysis the appropriate hydraulic damping can be put in place to stop the resonance.

 

moody frog

Super Anarchist
4,285
102
Brittany
Didn't Bonduelle and Sill have issues with keel flutter? If so wouldn't that suggest that hydraulics don't get rid of vibration problems?
I had forgotten about Sill and Bonduelle. I never read a clear description of what went wrong.

My thinking last night was that keel flutter was neither enhanced nor retarted by the hydraulic system. This may be wrong.

Resonance in the hydraulics is possible if the frequency of the keel flutter matches a resonant frequency of the system. The period of the lowest frequency would be 2L/a for the cylinder. What makes this interesting is that L changes at different cant angles and a is a function of tempurature (and pressure somewhat).

Proper analysis for this takes more than a "back of an envelope" but with such analysis the appropriate hydraulic damping can be put in place to stop the resonance.

The Sill/Bonduelle question has never been settled.

There has been in depth work conducted by the various involved parties and outside experts.

Flutter was one of the options but others were discussed such as bulb weight and its dynamic efforts on the strut when the boat becomes airborne. They started looking at the angle to the axis the carbon fibers had been laid .............

I understood the final decision was that it was going too far for the budgets, to stop head-scratching and go back to the proven milled steel solution.

 

vibroman

Super Anarchist
It would be real easy to prove/disprove keel resonance as the issue.

We have a frequency of the "vibration" while the boat is moving...Run the audio track with the humming noise through a spectrum analyzer.

Then it would be necessary to perform impact testing on the keel and other various parts of the keel system to determine the natural frequency of the various parts of the mechanism. If a natural frequency matches the observed frequency then bingo. I find it hard to belive that fatigue failure of rams can occur in such a short period of time at the frequency of the wave cycles. Seems to me it would need to be much higher frequency to getr the number of cycles to a fatigue type number. eg keel hum or vane pass frequency from the hydraulic pumps.

VM

 

Lima November

Super Anarchist
1,330
7
Nantes, France
Well, I haven't crunched the numbers, but could cavitation be causing the humming? Or some other flow phenomenon, so not an actual vibration of the keel?

Also, I remember Bruce reporting a humming noise from his keel in the Vendee. Does any of the OP folks know if this has been solved?

 

vibroman

Super Anarchist
Well, I haven't crunched the numbers, but could cavitation be causing the humming? Or some other flow phenomenon, so not an actual vibration of the keel?
Also, I remember Bruce reporting a humming noise from his keel in the Vendee. Does any of the OP folks know if this has been solved?
Without data its tough... but without the magnification factor of a resonant condition I doubt the forces from cavitation or vortex shedding would be enough to make a large structure like that vibrate enough to be discernible. The cavitation / vortexes triggering a resonant response is more plausible.

 

dtoc

New member
39
2
It would be real easy to prove/disprove keel resonance as the issue.
We have a frequency of the "vibration" while the boat is moving...Run the audio track with the humming noise through a spectrum analyzer.

Then it would be necessary to perform impact testing on the keel and other various parts of the keel system to determine the natural frequency of the various parts of the mechanism. If a natural frequency matches the observed frequency then bingo. I find it hard to belive that fatigue failure of rams can occur in such a short period of time at the frequency of the wave cycles. Seems to me it would need to be much higher frequency to getr the number of cycles to a fatigue type number. eg keel hum or vane pass frequency from the hydraulic pumps.

VM
Vibroman, (great name for this subject)

If you've got the capabilities to get the frequencies, I would love to see the data.

One of times that I have seen pump induced resonance cause significant issues has been with a pressure relief valve on an oil lubrication system. Usually the ripples on the flow vs. time curve are not significant and damped before they created problems. Are these systems using vane, piston, gear, g-rotor or some other type of pd pump? All have noise, but some are worse.

Keel flutter seems more likely, but still unlikely with a steel fin.

It would be interesting to do the analysis, but I think we'll end up back with the two most discussed possibilities for failure: overstressing of the rams from on axis shock loads (under specified equipment), or off axis loading (torsion of structure causing misalignment).

The first can be addressed with bigger rams or by using hydraulic shock absorbing (more on that later). The second is a structures issue, not my strong suite in engineering.

 

vibroman

Super Anarchist
It would be real easy to prove/disprove keel resonance as the issue.

We have a frequency of the "vibration" while the boat is moving...Run the audio track with the humming noise through a spectrum analyzer.

Then it would be necessary to perform impact testing on the keel and other various parts of the keel system to determine the natural frequency of the various parts of the mechanism. If a natural frequency matches the observed frequency then bingo. I find it hard to belive that fatigue failure of rams can occur in such a short period of time at the frequency of the wave cycles. Seems to me it would need to be much higher frequency to getr the number of cycles to a fatigue type number. eg keel hum or vane pass frequency from the hydraulic pumps.

VM
Vibroman, (great name for this subject)

If you've got the capabilities to get the frequencies, I would love to see the data.

One of times that I have seen pump induced resonance cause significant issues has been with a pressure relief valve on an oil lubrication system. Usually the ripples on the flow vs. time curve are not significant and damped before they created problems. Are these systems using vane, piston, gear, g-rotor or some other type of pd pump? All have noise, but some are worse.

Keel flutter seems more likely, but still unlikely with a steel fin.

It would be interesting to do the analysis, but I think we'll end up back with the two most discussed possibilities for failure: overstressing of the rams from on axis shock loads (under specified equipment), or off axis loading (torsion of structure causing misalignment).

The first can be addressed with bigger rams or by using hydraulic shock absorbing (more on that later). The second is a structures issue, not my strong suite in engineering.
I've got / can get the tools is there a link to the vids/audio that have the hum anywhere ?

 
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