Seakeeping Fast Ships - ULisboa · 6 – SOME NOTES ON THE SEAKEEPING OF FAST SHIPS • High speed...
Transcript of Seakeeping Fast Ships - ULisboa · 6 – SOME NOTES ON THE SEAKEEPING OF FAST SHIPS • High speed...
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6 – SOME NOTES ON THE SEAKEEPING OF FAST SHIPS
• High speed craft: (HSC code, IMO, 1995)
• Alternatively Fn > 0.4 • Frequent and and severe slamming
occurrences• Large vertical accelerations• Nonlinear responses in waves• Dynamic instabilities
• Computational methods
• Incorporate seakeeping into desing
( )smV /7.3 1667.0max ∇≥
NUNO FONSECA - IST
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Classificação de navio rápido pelo critério do HSC code
Velocidade mínima para classificação de navio rápido
0
5
10
15
20
25
30
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40
1 10 100 1000 10000 100000
Deslocamento (m3)
Vel
ocid
ade
(nós
)
( ))/7.3 1667.0 smV ∇=
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Velocidade mínima para classificação de navio rápido
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10
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0 50 100 150 200 250
comprimento (m)
Vel
ocid
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(nós
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Fn = 0.4
Classificação hidrodinâmica de navio rápido
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Navios de deslocamento
Fn < 0.4, peso do navio suportado por forças hidrostáticas
Classificação hidrodinâmica dos navios
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Classificação hidrodinâmica dos navios
Navios de semi-deslocamento
0.4 < Fn < 1.1, peso do navio suportado por forças hidrostáticas e de sustentação
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Classificação hidrodinâmica dos navios
Embarcações planantes
Fn > 1.1, peso do navio suportado essencialmente por forças de sustentação
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Classificação das embarcações rápidas
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Características dos navios rápidos / embarcações rápidas
� Velocidades elevadas
� Potências específicas elevadas (consumos específicos elevados)
� Economicamente viáveis para o transporte de carga valiosa em curtas e médiasdistâncias (actualmente!)
� Tendem a ser construídos em materiais leves (aços de alta resistência, alumínio, fibra de vidro e materiais compósitos)
� Tipo de sistema motor: normalmente são motores diesel rápidos, mas também em alguns casos turbinas a gás
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Potência específica em função da velocidade paradiversos tipos de veiculos
(1 HP = 0.746 kW)
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6.1 – MONOHULLS
Specific characteristics that distinguish the the seakeeping of high speed monohulls from conventional monohulls are:• Lower resistance to the advance in still water and in waves• Frequency and severity of slamming occurrences• Larger accelerations• Important nonlinear effects• Possibility of dynamic instabilities
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Important nonlinear effects
Model test results for a fast monohull in head regular waves. U = 27knots, Lw/Lpp = 1.22, Hw/T = 0.40 (from research project WAVELOADS)
Vertical Bending Moment at station 15
-2.0E+04
0.0E+00
2.0E+04
4.0E+04
6.0E+04
time
VB
M (K
Nm
)
Steady VBM
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Dynamic instabilities
Figure from Cohen and Blount (1986)
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6.2 – CATAMARANS
• Lower resistance to the advance in still water and in waves
• Possibility of dynamic instabilities
• Critical global loads on the cross deck structure
• Possibility of very severe wetdeck impacts
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Possibility of severe wetdeck impacts
Critical global loads on the cross deck structure
(Figure from Nordenstromet al., 1971)
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6.3 – SMALL WATERPLANE AREA TWIN-HULLS (SWATH)
• Lower resistance to the advance in still water and in waves
• Long natural periods of pitch and heave resulting in low level of accelerations
• Possibility of dynamic instabilities / active control stabilizers
• Critical global loads on the cross deck structure
• Possibility of very severe wetdeck impacts
• Viscous damping associated with vertical motions
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Viscous damping associated with vertical motions
( )( )rrDD
v vvCaUxBF += αρ 022
21
Empirical model for estimation vertical viscous forces:
Heave and pitch motion of a SWATH in head regular waves at 20 knots (Lee and Curphey, 1977)Vertical
motion
Lower hull
Viscous force
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6.4 – SURFACE EFFECT SHIPS (SES)
• Partly supported by a pressurized cushion of air enclosed between two hulls and flexible seals at bow and stern
• Lower resistance to the advance and better seakeeping characteristics
• Cobblestone effect: resonance pressure variations in the air cushion that occur for small wave periods
• Air leakage from the cushion at higher seastates
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(D) Navio de Efeito de Superfície (SES)
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6.5 – FOILCATAMARAN
• Catamaran with foils either fully submerged or partly submerged • At high speeds the hulls come out of the water• Much lower resistance to the advance in calm water and small seastates• Fully submerged foils have moving flaps coupled to a ride control system• Lower vertical motions and accelerations in waves
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6.6 – PENTAMARAN
• Very slender hull with four sponsons
• Lower resistance to the advance both in still water and in waves
• Better seakeeping behavior than conventional containerships
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9.3 Mercado Actual dos Navios Rápidos e Tendências Futuras
Navios de passageiros em serviço em 1999 (Nigel Gee and Associates LTD)
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Dimensão e velocidade dos navios de passageiros em serviço em 1999 (Nigel Gee and Associates LTD)
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Nota: a tabela inclui navios que transportam 50 ou mais passageiros e com velocidade de serviço mínima de 25 nós
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Tendências futuras e possíveis soluções (Nigel Gee and Associates LTD)
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Cargeiro transatlântico de alta velocidade (Pentamaran)
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Porta-contentores (Pentamaran)
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• Testado em 1967• Capacidade de 544 ton• Vel de 280 nós• 13 turbinas de 98 kN
WIG (Wing Ground Effect)
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• Cargeiro de alta capacidade• 150 m de envergadura• Capacidade de 1400 ton
WIG (Wing Ground Effect)
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Catamaran super esbelto