Canting keel forces

Rail Meat

Super Anarchist
7,192
169
Mystic, CT
Stamm's keel failed in the OSTAR for what appears to have been vibration reasons. Strut, not hydraulics. His new keel is steel.

(actually, it is Derek's keel which Derek sold to Bernard and is now milling another to replace it.)

While I think flutter could contribute, I doubt it is the major contributor. Hull flex has to play a much more significant role. Particularily on those boats that seem to have ram shelves that are integrated into the hull.

 

vibroman

Super Anarchist
Stamm's keel failed in the OSTAR for what appears to have been vibration reasons. Strut, not hydraulics. His new keel is steel.
(actually, it is Derek's keel which Derek sold to Bernard and is now milling another to replace it.)

While I think flutter could contribute, I doubt it is the major contributor. Hull flex has to play a much more significant role. Particularily on those boats that seem to have ram shelves that are integrated into the hull.

OK so having analysed audio from the ABN AMRO video the singing frequency is +/- 1011 Hz (cycles per second) or 60660 Cycles per minute. Thats a pretty high frequency and if it is resonance then the structure resonating must be very stiff. Possibly like a keel support structure or ram ?? Now If we could just get acces to the boats with an analyzer....

Anyone know how many cycles it would take to faituge Stainless or even Titanium based on the load calcs?

Are there vids from any other boats that have the keel humming? perhaps a comparison might be neat

I have the spectrum if 1.anyone is interested and 2. knows how to post images....I just look at em specially on friday !! :)

 
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dtoc

New member
39
2
OK so having analysed audio from the ABN AMRO video the singing frequency is +/- 1011 Hz (cycles per second) or 6066 Cycles per minute. Thats a pretty high frequency and if it is resonance then the structure resonating must be very stiff. Possibly like a keel support structure or ram ?? Now If we could just get acces to the boats with an analyzer....Anyone know how many cycles it would take to faituge Stainless or even Titanium based on the load calcs?

Are there vids from any other boats that have the keel humming? perhaps a comparison might be neat

I have the spectrum if 1.anyone is interested and 2. knows how to post images....I just look at em specially on friday !! :)
My initial calculation for the resonance of the hydraulic fluid in the cylinder is 1300Hz. Too close to ignor, but we are still a long way from showing that the hydraulics are involved in the vibration and that the vibrations are causing damage to the system.

Very interesting.

 

vibroman

Super Anarchist
OK so having analysed audio from the ABN AMRO video the singing frequency is +/- 1011 Hz (cycles per second) or 6066 Cycles per minute. Thats a pretty high frequency and if it is resonance then the structure resonating must be very stiff. Possibly like a keel support structure or ram ?? Now If we could just get acces to the boats with an analyzer....

Anyone know how many cycles it would take to faituge Stainless or even Titanium based on the load calcs?

Are there vids from any other boats that have the keel humming? perhaps a comparison might be neat

I have the spectrum if 1.anyone is interested and 2. knows how to post images....I just look at em specially on friday !! :)
My initial calculation for the resonance of the hydraulic fluid in the cylinder is 1300Hz. Too close to ignor, but we are still a long way from showing that the hydraulics are involved in the vibration and that the vibrations are causing damage to the system.

Very interesting.
That is pretty close

I'll have a look for more video/audio and compare

Anyone have details on the hydraulic pumps ? RPM, number of vanes/pistons?

 

sucky bus

Super Anarchist
1,034
0
OK so having analysed audio from the ABN AMRO video the singing frequency is +/- 1011 Hz (cycles per second) or 6066 Cycles per minute. Thats a pretty high frequency and if it is resonance then the structure resonating must be very stiff. Possibly like a keel support structure or ram ?? Now If we could just get acces to the boats with an analyzer....

Anyone know how many cycles it would take to faituge Stainless or even Titanium based on the load calcs?

Are there vids from any other boats that have the keel humming? perhaps a comparison might be neat

I have the spectrum if 1.anyone is interested and 2. knows how to post images....I just look at em specially on friday !! :)
My initial calculation for the resonance of the hydraulic fluid in the cylinder is 1300Hz. Too close to ignor, but we are still a long way from showing that the hydraulics are involved in the vibration and that the vibrations are causing damage to the system.

Very interesting.
I reckon 'Galloping Gerty' stikes again.. wonder if the engineers have considered or run similar analysis.... would be great to have a SA'er who is a crew to comment..... on the sounds and if they dare touch the structure when going... Although I wouldn't..

:ph34r:

 

sucky bus

Super Anarchist
1,034
0
Thought just hit me..... 'by Jesus - if they have set up a resonant system with the pressures and forces involved, these systems are literally going to be 'bombs' waiting to go off..... explains an awfull lot

:ph34r:

 

vibroman

Super Anarchist
Stamm's keel failed in the OSTAR for what appears to have been vibration reasons. Strut, not hydraulics. His new keel is steel.
(actually, it is Derek's keel which Derek sold to Bernard and is now milling another to replace it.)

While I think flutter could contribute, I doubt it is the major contributor. Hull flex has to play a much more significant role. Particularily on those boats that seem to have ram shelves that are integrated into the hull.
Agreed but I heard (saw) talk somewhere that the ram failures were fatigue failures. Surely there have not been enough cycles due to wave action etc to cause a fatigue failure? However with 1000 Cylces per second contributing they might get there.

 

vibroman

Super Anarchist
Check the ABN audio again and right at the end of the clip there is another similar but lower frequency tone. Spectrum show it at 950 Hz. Possibly other RAM?

Wish we new if they all "sing" and if they do could get audio..

 
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dtoc

New member
39
2
Thought just hit me..... 'by Jesus - if they have set up a resonant system with the pressures and forces involved, these systems are literally going to be 'bombs' waiting to go off..... explains an awfull lot
:ph34r:
Let's not get ahead of ourselves.

The analysis has probably been done by others, but I will do what I can and post it all.

 

francescobussi

New member
16
0
Hi, i read without attention the post.....

Tacoma bridge collapse was caused by a phenomenon called "flutter" in aerodynamic.

This phenomenon is caused by aerodynamic forces on structures whit a low tortional strenght....

For the Tacoma....a light wind excitated the structure that have a low tortional strenght...the wind force ,acting on bridge, produced exactly a variable force whit the same natural frequence of the bridge...this caused a resonance phenomenon (a phenom. where the movements amplitude enlarging to every cycle)..........until the forces acting on the bridge are bigger than the maximum tolerated by structure...

The flutter is typical (but well controlled by carbon use) on hight performance glider wings....this is due to their leght.......in fact you can find flutter on every airplane wings...but this are designed to avoid this fatality...

Xcuse me fo my poor english...

I think the structural damage on vor 70 keels are caused by a under extimated evaluation of forces caused by waves....and remember that every material cannot avoid imperfections...

Ciao

Francesco

 
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NoStrings

Super Anarchist
8,088
6
Richmond, CA
This is really a fascinating discussion of "remote" failure analysis. It leaves me wondering if we have more and better engineering talent here on SA than in the FYD offices. Carry on please.

 

wraith

Super Anarchist
2,195
0
Codger said:
The hypothesis to be tested is that VOR 70s were not designed to fly!
I suspect that flying isnt the problem.

Maybe the landing does need looking at, though.

 

Murphy's Law

Member
76
0
Bawlmer
No intential flames here...

I might be missing something here, and someone's already pointed this out, but your initial calcs are flawed.. You've attempted to calculate a moment based on masses. As previously stated here F=MA and moment (torque) is F x d. You've forgotten to factor in G for those loads so multiply by 9.8 m/s/s. Albeit that G drops out of the equation. Units of force are lb(f) or N (kg m/s/s)... This will give you the static load on the ram. I haven't a clue about the dynamic loading while underway. Maybe someone else can speak to that issue...

As far as the accerations experienced in on the hull itself, the calculations previously posted greatly over simplify the issue. Work and KE are not interchangeable. The buoyand forces of a pounding hull are dynamic. It is not a contstant force. As the hull is driven above or below it's equilibrium the restoring forces grow proportionally.

The important thing to remember here is that this is a dynamic system.

ML

 

wraith

Super Anarchist
2,195
0
What I find truly bizarre is that the rule disallows

"Secondary heat treatment methods which alter the properties of a steel alloy

by way of reducing resistance to corrosion in sea water and/or increasing

fatigue in variations in sea water temperature around 10C are not permitted."

I know from my own keel that post manufacture heat treatment of the welded structure is critical to relieve stresses induced in the manufacturing processes - as is post machining heat treatment of the machined parts.

The wording is unclear - but appears to disallow processes that would increase the resistance to fatique

 

dtoc

New member
39
2
No intential flames here...
I might be missing something here, and someone's already pointed this out, but your initial calcs are flawed.. You've attempted to calculate a moment based on masses. As previously stated here F=MA and moment (torque) is F x d. You've forgotten to factor in G for those loads so multiply by 9.8 m/s/s. Albeit that G drops out of the equation. Units of force are lb(f) or N (kg m/s/s)... This will give you the static load on the ram. I haven't a clue about the dynamic loading while underway. Maybe someone else can speak to that issue...

As far as the accerations experienced in on the hull itself, the calculations previously posted greatly over simplify the issue. Work and KE are not interchangeable. The buoyand forces of a pounding hull are dynamic. It is not a contstant force. As the hull is driven above or below it's equilibrium the restoring forces grow proportionally.

The important thing to remember here is that this is a dynamic system.

ML
No worries mate.

I have chosen to use kg force as my force unit, so it appears that I haven't accounted for 'g', but its in there. So everywhere you see kg, just read kgf. There are a few errors in some of the calcs I posted, mainly in how the loads are spread between the 2 rams, and I am crafting a post right now to correct and clarify.

dtoc

 

Lima November

Super Anarchist
1,330
7
Nantes, France
Stamm's keel failed in the OSTAR for what appears to have been vibration reasons. Strut, not hydraulics. His new keel is steel.
(actually, it is Derek's keel which Derek sold to Bernard and is now milling another to replace it.)

While I think flutter could contribute, I doubt it is the major contributor. Hull flex has to play a much more significant role. Particularily on those boats that seem to have ram shelves that are integrated into the hull.
Agreed but I heard (saw) talk somewhere that the ram failures were fatigue failures. Surely there have not been enough cycles due to wave action etc to cause a fatigue failure? However with 1000 Cylces per second contributing they might get there.
Well, say a boat sails 15 days with a wave every 10 seconds (seems reasonable from the AA vids). That gives 130.000 cycles, which is indeed very low for steel. But it is not impossibly low if someone screwed up... so the fatigue may be from wave impact after all.

 

moody frog

Super Anarchist
4,294
112
Brittany
Codger said:
The hypothesis to be tested is that VOR 70s were not designed to fly!
I suspect that flying isnt the problem.

Maybe the landing does need looking at, though.
My remark is slightly outside this very interesting thread, but I keep naively wondering what the bulb beeing airborne, then "landing", induces. Two very different things -hull 8+tons & bulb 5.5 tons, linked by a fin (who itself lands somehow) "landing" nearly simultaneously a few meters apart. :huh:

Also, about the 2m hypothesis, could not that be much more ?

 
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