I´m triying to test a numerical model of the parametric roll and i need experimental values of this video and the drawings of the ship and his characteristic. (mass, inertia,etc.).
@danielalonso23, unfortunately I am currently not in Finland, so I can not help with information regarding this experiment. However, best of luck with your research!
I've experienced parametric rolls in the North Atlantic during a winter storm, very sudden, unexpected. Speed change will change the roll cycle in theory but it takes far too much time on a commercial ship. An immediate hard over 90 degree course change breaks the cycle much much faster. Watch officers must monitor wave period and ship roll period, a wave period 1 half of the ships rolling period creates a situation conducive to parametric rolls.
I've experienced parametric rolls in the North Atlantic during a winter storm, very sudden, unexpected. Speed change will change the roll cycle in theory but it takes far too much time on a commercial ship. An immediate hard over 90 degree course change breaks the cycle much much faster. Watch officers must monitor wave period and ship roll period, a wave period 1 half of the ships rolling period creates a situation conducive to parametric rolls.
@Triiiop, I agree that changing the heading is much more effective than changing the speed - ships have so much momentum that I don't think anything but a crash stop would make a difference.
It's also nice to know that at least on some ships the crew pays attention to this phenomenon. I've made some trips on cargo ships and I've never noticed anyone doing anything like that. But then again, I've never experienced parametric roll either...
Ship should have on one side of the bow a spoiler that it can move out hydraulically to change the angle of the bow. This would stop the movement. Or assymetric bow.
@ev13wt, the easiest way to stop parametric roll is to change the ship's speed or heading so that the resonance stops. I'm not sure how the spoiler you suggested would affect to the natural frequency of the roll motion - if I recall correctly, bilge keels (and perhaps fin stabilizers) have some effect to this phenomenon, but I'm not a specialist of hydromagics...
Mr Tupsumatu:
I´m triying to test a numerical model of the parametric roll and i need experimental values of this video and the drawings of the ship and his characteristic. (mass, inertia,etc.).
can you help?
Thanks.
danielalonso23 4 months ago
@danielalonso23, unfortunately I am currently not in Finland, so I can not help with information regarding this experiment. However, best of luck with your research!
tupsumato 4 months ago
@tupsumato Ok.Thanks for respond.
danielalonso23 4 months ago
Comment removed
danielalonso23 11 months ago
I think this phenomenom only can happen if :
1) the body is no simetrical.(a box)
2) the lenght of the wave is less than the lenght of the body.
danielalonso23 11 months ago
@danielalonso23, the hull is symmetric along the centerline, which is parallel to the direction of the waves.
tupsumato 11 months ago
Comment removed
danielalonso23 11 months ago
Comment removed
danielalonso23 11 months ago
Comment removed
danielalonso23 11 months ago
@danielalonso23, that's true. I might've misunderstood your first message.
tupsumato 11 months ago
Comment removed
danielalonso23 11 months ago
This has been flagged as spam show
I've experienced parametric rolls in the North Atlantic during a winter storm, very sudden, unexpected. Speed change will change the roll cycle in theory but it takes far too much time on a commercial ship. An immediate hard over 90 degree course change breaks the cycle much much faster. Watch officers must monitor wave period and ship roll period, a wave period 1 half of the ships rolling period creates a situation conducive to parametric rolls.
Triiiop 1 year ago
I've experienced parametric rolls in the North Atlantic during a winter storm, very sudden, unexpected. Speed change will change the roll cycle in theory but it takes far too much time on a commercial ship. An immediate hard over 90 degree course change breaks the cycle much much faster. Watch officers must monitor wave period and ship roll period, a wave period 1 half of the ships rolling period creates a situation conducive to parametric rolls.
Triiiop 1 year ago
@Triiiop, I agree that changing the heading is much more effective than changing the speed - ships have so much momentum that I don't think anything but a crash stop would make a difference.
It's also nice to know that at least on some ships the crew pays attention to this phenomenon. I've made some trips on cargo ships and I've never noticed anyone doing anything like that. But then again, I've never experienced parametric roll either...
tupsumato 1 year ago
Ship should have on one side of the bow a spoiler that it can move out hydraulically to change the angle of the bow. This would stop the movement. Or assymetric bow.
Try it.
:)
Send me money.
ev13wt 1 year ago
@ev13wt, the easiest way to stop parametric roll is to change the ship's speed or heading so that the resonance stops. I'm not sure how the spoiler you suggested would affect to the natural frequency of the roll motion - if I recall correctly, bilge keels (and perhaps fin stabilizers) have some effect to this phenomenon, but I'm not a specialist of hydromagics...
tupsumato 1 year ago
Ship should have on one side of the bow a spoiler that it can move out hydrologically to change the angle of the bow.
ev13wt 1 year ago
Thanks for uploading this! I was trying to explain a p. r. to someone, and this video was the perfect example :)
savmorda 1 year ago