The effect of ship shape and anemometer location on wind speed measurements obtained from ships
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The effect of ship shape and anemometer location on wind speed measurements obtained from ships B I Moat 1 , M J Yelland 1 , A F Molland 2 and R W Pascal 1 Southampton Oceanography Centre, UK School of Engineering Sciences, Ship Science, University of Southampton, UK

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The effect of ship shape and anemometer location on wind speed measurements obtained from ships l.jpg

The effect of ship shape and anemometer location on wind speed measurements obtained from ships

B I Moat1, M J Yelland1, A F Molland2 and R W Pascal1

Southampton Oceanography Centre, UK

School of Engineering Sciences, Ship Science,

University of Southampton, UK

4th International Conference on Marine CFD, University of Southampton, 30-31 March 2005.

NOTE: as of 1st May 2005 Southampton Oceanography Centre

becomes National Oceanography Centre, Southampton


Slide2 l.jpg


Outline l.jpg
OUTLINE presence of the ship

  • Background

  • Description of the CFD code

  • CFD code validation

  • Results

    • research ships (individual ships)

    • tankers/bulk carriers/general cargo ships (generic modelling approach)

    • Container ships

  • Conclusions


Background l.jpg
Background presence of the ship

  • Research ships limited coverage, but measurements of high quality.

  • Merchant ships routinely report meteorological parameters at sea surface (wind speed and direction)

  • Data used in satellite validation, ocean atmosphere modelling forcing and climate research


Background impact of flow distortion on climate studies l.jpg
Background: impact of flow distortion on climate studies presence of the ship

  • 10 % error in mean wind speed

    • 27 % bias in the momentum exchange

    • 10 % bias in the heat exchange


Cfd code description l.jpg
CFD code description presence of the ship

  • Commercial RANS solver VECTIS

  • Mesh generation

    • Non-uniform Cartesian mesh

    • (generate 500,000 cells/hour)

  • 3-dimensional and isothermal

  • MEAN FLOW ONLY (STEADY STATE)

  • RNG turbulence model

  • Simulations based on up to 600,000 cells

  • All results normalised by the wind speed profile at the measurement site


Validation l.jpg
VALIDATION presence of the ship

  • Comparison to 2 previous wind tunnel studies

    • Martinuzzi and Tropea (1993)

    • Minson et al. (1995)

  • Comparison to in situ wind speed measurements made from a ship

    • Moat et al. (2005)


Validation channel flow over a surface mounted cube l.jpg
Validation: channel flow over a surface mounted cube presence of the ship

tunnel roof

accelerated

flow

  • Good comparison with RNG

H = cube

height

Re=105

decelerated flow

z/H

cube top

normalised wind speed


Validation boundary layer flow over a surface mounted cube l.jpg
Validation: boundary layer flow over a surface mounted cube presence of the ship

  • Good comparison with RNG

decelerated flow

H = cube

height

Re=4x104

z/H

accelerated

flow

normalised wind speed


Slide10 l.jpg

Validation: In situ wind speed measurements from RRS presence of the shipCharles Darwin

Measurements were

made using 6

anemometers.

Instruments were located on a 6 m mast.

Only beam-on wind speed data used.

Wind speed profile measured above a ‘block like’ ship.


Validation comparison with in situ wind speed measurements l.jpg
Validation: comparison with in situ wind speed measurements presence of the ship

  • Agreement to within 4%

decelerated flow

H = bridge to

sea level height

Re=1.3x107

z/H

accelerated flow

normalised wind speed


Accuracy of cfd simulations l.jpg
Accuracy of CFD simulations presence of the ship

  • Comparisons of simulations show variations of:

    • Mesh density (1 %)

    • Turbulence model (2 %)

    • Scaling the geometry (3 %)

    • Wind speed profile (4 %)

  • VECTIS agrees to 4 % or better with in situ wind speed data


Results research ships l.jpg
RESULTS: research ships presence of the ship

  • Project running since 1994

  • Over 11 ships have been studied

    • American, British, Canadian, French and German

  • Present results from well exposed anemometers in the bow of 2 UK ships

    • RRS Discovery

    • RRS Charles Darwin


Results rrs discovery l.jpg
Results: RRS Discovery presence of the ship

typical

anemometer

location

  • Wind speed measurements are biased by about 5 %

length overall = 90 m


Results rrs charles darwin l.jpg
Results: RRS Charles Darwin presence of the ship

typical

anemometer

location

  • Wind speed measurements are biased by about 10%

length overall = 70 m


Results research ships16 l.jpg
Results: research ships presence of the ship

RRS Discovery

bow

Wind speed bias (%)

port starboard

RRS Charles Darwin

Streamlined superstructure needed

Locate anemometers as high as possible above the platform, not in front

Relative wind direction


Research ship design rrs james cook l.jpg
Research ship design: presence of the shipRRS James Cook

Anemometer location

  • CFD will be used to determine the best sensor locations

First steel cut 26th January 2005


Results tankers bulk carriers and general cargo ships l.jpg
RESULTS: tankers, bulk carriers and general cargo ships presence of the ship

Typical

anemometer

location

www.shipphotos.co.uk

Large number of ships. Cannot be studied individually.

The ships are large complex shapes


Slide19 l.jpg

Results: A generic ship model presence of the ship

  • Ship dimensions from RINA publication Significant ships (1990-93)

  • Tankers/bulk carriers/general cargo ships can be represented by a simple shape.

bow stern


Slide20 l.jpg

Results: A generic ship model presence of the ship

bridge

anemometers

  • Perform CFD simulations over the simple geometry

  • Bridge anemometers

  • Flows directly over the bow

bow stern


Wind tunnel flow visulisation l.jpg
Wind tunnel: flow visulisation presence of the ship

mean flow direction

Standing vortex

in front of the

deck house


Wind tunnel flow visulisation22 l.jpg
Wind tunnel: flow visulisation presence of the ship

mean flow direction

  • Decelerated region increases with distance from the leading edge

Vortices produced

above the bridge top

Standing vortex

in front of the

deck house


Wind tunnel flow visulisation23 l.jpg
Wind tunnel: flow visulisation presence of the ship

mean flow direction

Less disturbance

with increase in

height

  • Complex flow pattern

Vortices produced

above the bridge top

Standing vortex

in front of the

deck house


Slide24 l.jpg

CFD: Airflow above the bridge presence of the ship

accelerated flow

3D simulation of the airflow over the tanker.

(RNG turbulence closure)

decelerated flow

with recirculation.

Tanker

Flow direction

Qualitatively, the numerical model reproduces the general flow pattern quite well.


Slide25 l.jpg

CFD: Airflow above the bridge presence of the ship

accelerated flow.

3D simulation of the airflow over the tanker.

(RNG turbulence closure)

decelerated flow

with recirculation.

Tanker

Flow direction

Qualitatively, the numerical model reproduces the general flow pattern quite well.


Normalised wind speed profile l.jpg
Normalised wind speed profile presence of the ship

  • Wind speed accelerated by about 10 %

  • Decelerated by up to 100 %

deceleration and

recirculation

z/H

H

bow stern

Normalised wind speed


Normalised wind speed profile27 l.jpg
Normalised wind speed profile presence of the ship

deceleration and

recirculation

z/H

H

bow stern

Normalised wind speed

Region of high

velocity gradients


Results typical merchant ships l.jpg
RESULTS: typical merchant ships presence of the ship

  • Anemometers will be less distorted in the bow

  • Locate anemometers as high above the deck as possible and above the leading edge

Anemometer position

Bridge

height, z (m)

Depth of the

recirculation region

Bow

Distance from leading edge, x (m)


Container ships l.jpg
Container ships presence of the ship

Anemometer

locations

  • More complex shape than a typical tanker

  • Irregular container loading ???

www.shipphotos.co.uk


Container ships general flow pattern l.jpg
Container ships: General flow pattern presence of the ship

1.0

accelerated

1.0

accelerated

container ship

decelerated

1.0

bow bridge

accelerated

1.0

1.0

accelerated

decelerated

decelerated

(Moat et al. 2005)


Container ships general flow pattern31 l.jpg
Container ships: General flow pattern presence of the ship

1.0

accelerated

1.0

accelerated

  • Bow influences the bridge flow

  • Complex flow and the subject of future work

container ship

decelerated

1.0

bow bridge

accelerated

1.0

1.0

typical tanker

accelerated

decelerated

decelerated

(Moat et al. 2005)


Application of results merchant ships l.jpg
APPLICATION OF RESULTS: MERCHANT SHIPS presence of the ship

  • To predict the wind speed bias

    • Ship type

    • Ship length

    • Anemometer position

  • Parameters are now available (WMO-47)


Conclusions research ships l.jpg
CONCLUSIONS: Research ships presence of the ship

  • CFD is a valid research tool to examine the mean airflow over ships

  • anemometers biased by about 10% or less (highly dependent on position)

  • Streamlined superstructure needed for accurate wind speed measurements


Conclusions tankers bulk carriers general cargo l.jpg
CONCLUSIONS: Tankers/bulk carriers/general cargo presence of the ship

  • anemometers biased high by 10% and low by 100%

  • Position anemometers as high as possible above the deck

  • If possible: locate anemometers in the bows of the ship


Future work l.jpg
FUTURE WORK presence of the ship

  • How does the turbulence structure change with ship shape ?

time = 3 sec


Future work36 l.jpg
FUTURE WORK presence of the ship

  • Good representation of atmospheric turbulence in the wake region of a ship

LES code GERRIS

Iso-surface of

wind speed

at 90% of the

inflow velocity

time = 3 sec


Slide37 l.jpg

Acknowledgements presence of the ship

Partial funding from Meteorological Service

of Canada and the Woods Hole

Oceanographic Institution, USA.

Contact

[email protected]

www.soc.soton.ac.uk/JRD/MET/cfd_shipflow.php


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