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Hydrodynamics of High Speed Craft
Dr. D.A. Hudson, Professor A.F. Molland
School of Engineering Sciences, Ship Science, University of Southampton.
London Branch RINA
17th March, 2006
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MotivationMotivation
To improve ship design, safety and operation through a better understanding of ship hydrodynamics:
Resistance and propulsion Wave wash Ship motions Human factors – very high speed
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Resistance componentsResistance components
• Resistance components– Total Hull Resistance = Viscous + Wave
• Monohulls
• Catamarans
and are hull interaction coefficients
WFT CCkC 1
WFT CCkC 1
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ModelsModels
Model hull forms
• Vary hull form• Vary separation of hulls• Also test as monohull
(a) (b)
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Wave resistanceWave resistance
• Wave resistance measurement • Wave probes in tank: drive model past
ghV crit
Shallow water
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Wave resistanceWave resistanceC
T
Fn0.2 1.0
DEEP10m5m ghV crit
Shallow water
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Viscous resistanceViscous resistance
• Viscous resistance measurement– Total viscous and viscous interaction
from viscous wake traverse in tank– Viscous interaction from wind tunnel tests
and CFD analysis
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Viscous resistanceViscous resistance
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VISCOUS RESISTANCE
Viscous resistanceViscous resistance
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Wind tunnel tests: generic shapes
AERODYNAMIC RESISTANCE
Aerodynamic resistanceAerodynamic resistance
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C D = 0 .88
C D = 0 .67
C D = 0 .50
C D = 0 .56
C D = 0 .55
C D = 0 .64
C D = 0 .50
N o. 0
N o. 1
N o. 2
N o. 3
N o. 3a
N o. 4
N o. 5
S uperstructure shape D rag C oeffic ien t
The aerodynam ic drag coeffic ien t C D is based on the to ta ltransverse fron ta l a rea o f superstructu re and hu lls
Aerodynamic resistanceAerodynamic resistance
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Wave washWave wash
• Generated by ship• Propagated to shore (with decay)• Impact on safety (e.g. beaches, small craft)• Impact on environment (coastal erosion,
plants, animals, etc.)
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Wave washWave wash
• Need to estimate ship waves:– Influence of hull form/type– Speed– Shallow water effects
• Estimate size of waves at shore• Possible limits on wave heights (or energy)• Passage plans, shallow water, critical speeds
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35 0
Divergent wavesTransverse waves
Directi
on of propagatio
n
of dive
rgent wave
s
cos -1 (1/Fn h)
Sub-critical Fn h < 1.0
Supercritical Fn h > 1.0
gh
VFnh
Wave washWave wash
Sub-critical
Supercritical
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WASHWave washWave wash
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Wave washWave wash
Comparison of wave profiles
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0.0
1.0
2.0
3.0
4.0
5.0
10 12 14 16 18 20 22 24Ship Speed (knots)
Pro
puls
ive
Pow
er /
Dis
plac
emen
t
SHALLOW
DEEP
DISTANCE
WA
VE
HE
IGH
T
SHIP SHORE
POSSIBLE LIMITSON WAVE SIZE(Height, Period,Energy)
H y-n
n=0.5 transverse
n=0.33 diverging
n=0.2, 0.4 shallow
0
0.5
1
1.5
2
10 12 14 16 18 20 22 24Ship Speed (knots)
Wav
e He
ight
/ W
ave
heig
ht a
t 18.
4 kn
ots
Wave washWave wash
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Critical speed - water depth relationship
Wave washWave wash
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Wave washWave wash
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Ship motionsShip motions
• Pitch, heave, roll, accelerations– (yaw, sway, surge)
• Safety – strength, cargo, crew, passengers• Comfort – motion sickness
Different limits: strength, comfort, operability
Statistics – e.g. RMS values, probabilities of exceedance
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Ship motion analysis - overviewShip motion analysis - overview
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Ship motions - modelsShip motions - models
Model hull forms
• Vary hull form – L=1.6m, L=4.5m• Vary separation of hulls – S/L=0.2, 0.4• Vary heading to waves • Fn=0.2, 0.53, 0.65, 0.80• Also test as monohull
(a) (b)
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Ship motionsShip motions
Measurement of motions – model scale
NPL 5b, S/L=0.2, Fn=0.65: head seas (180 deg)
NPL 5b, S/L=0.4, Fn=0.65: oblique seas (150 deg)
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Ship motionsShip motions
Measurement of motions – model scale
Southampton water: NPL 5b, S/L=0.2, Fn=0.65
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Ship motionsShip motions
Heave measurements
5S, S/L=0.2, oblique seas 5S, S/L=0.4, oblique seas
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Ship motions – theoretical analysisShip motions – theoretical analysis
• Development of numerical methods• Detailed validation of numerical methods• What are the choices?
– 2D strip theory– 3D Green’s function (or panel methods)– 3D time domain– 3D Rankine panel– Linear or (partly) non-linear– ‘CFD’
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Ship motions – numerical methodsShip motions – numerical methods
• At Southampton:– 2D strip theory - linear– 3D Green’s function
• Zero speed• Forward speed
– 3D time domain• Linear (under development)• Partly non-linear
– 3D Rankine panel• Linear (under development)• non-linear (under development)
– ‘CFD’ – under development
5S, S/L=0.2, 700 panels
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Ship motions – head wavesShip motions – head waves
5S, S/L=0.4, head seas 5S, S/L=0.2, head seas
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Ship motions – oblique wavesShip motions – oblique waves
5S, S/L=0.4, head seas 5S, S/L=0.2, head seas
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Ship motionsShip motions
Fn=0.0 Fn=0.2
Fn=0.5
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Ship motions Ship motions
• Detailed investigations into:– Numerics of Green’s function – 2
alternative formulations– ‘Irregular’ frequencies – removal– Transom stern effects
Prediction
Towing tank
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Ship motions - summaryShip motions - summary
• For multi-hull craft must account for hull-hull interaction
• Forward speed Green’s function is promising– Correct trends with wave heading
• …but…– Numerically complex– Pitch still over-predicted
• Fn>0.70 need alternative approaches – planing craft
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Human FactorsHuman Factors
• Modern small, very high-speed vessels:– Fatigue, injury, long-term pain
• Quantify effects on operator (UCC)– Heart rate, blood chemistry, muscle
fatigue, oxygen uptake
• Link to naval architecture attributes– Boat design, sea-state, operating manner
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Human Factors – model testingHuman Factors – model testing
WAL/GKN tank – up to 12 m/s– Calm water and regular/irregular waves
Conventional RIB form at 45kts
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Human Factors – Full scale testingHuman Factors – Full scale testing
• Robust measurement system– 11 channels accelerations– Wave buoy data– GPS track– Heart-rate of crew
Conventional RIB form at 30kts
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Human FactorsHuman Factors
• Assisting ‘Team Kali’– Gas turbine propelled wave-piercing RIB– Attempt Round Britain <30ft record
Kali at 52kts
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SummarySummary
• Resistance – understanding of components• Wave wash – operating guidelines• Ship motions
– Experimental and numerical techniques
• Human factors– Experimental techniques– Collaboration with sports science– Design techniques and operator guidelines
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Thanks – and questions?Thanks – and questions?
Prof. W.G. Price
Prof. P. Temarel
Prof. R.A. Shenoi
Dr. S.X. Du
Dr. E. Ballard
Dr. T. Ahmed
Dr. P. Bailey
Dr. S. Georgoudis
Dr. D. Taunton
Mr. O. Diken
Ms. R. Spink Mr. M. Yuceulug
Mr. T. D’Arcy Mr. P. Kingsland
Mr. I. House LR – UTC
Ms. C. Damecour RNLI - ATP
Team ‘Kali’
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