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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’