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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

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
Wind speed measurements can be severely biased by the presence of the ship
  • CFD can be used to predict/correct wind speed measurements
outline
OUTLINE
  • 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
Background
  • 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
Background: impact of flow distortion on climate studies
  • 10 % error in mean wind speed
    • 27 % bias in the momentum exchange
    • 10 % bias in the heat exchange
cfd code description
CFD code description
  • 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
VALIDATION
  • 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
Validation: channel flow over a surface mounted cube

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
Validation: boundary layer flow over a surface mounted cube
  • Good comparison with RNG

decelerated flow

H = cube

height

Re=4x104

z/H

accelerated

flow

normalised wind speed

slide10

Validation: In situ wind speed measurements from RRS Charles 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
Validation: comparison with in situ wind speed measurements
  • 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
Accuracy of CFD simulations
  • 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
RESULTS: research ships
  • 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
Results: RRS Discovery

typical

anemometer

location

  • Wind speed measurements are biased by about 5 %

length overall = 90 m

results rrs charles darwin
Results: RRS Charles Darwin

typical

anemometer

location

  • Wind speed measurements are biased by about 10%

length overall = 70 m

results research ships16
Results: research ships

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
Research ship design: RRS 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
RESULTS: tankers, bulk carriers and general cargo ships

Typical

anemometer

location

www.shipphotos.co.uk

Large number of ships. Cannot be studied individually.

The ships are large complex shapes

slide19

Results: A generic ship model

  • 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

Results: A generic ship model

bridge

anemometers

  • Perform CFD simulations over the simple geometry
  • Bridge anemometers
  • Flows directly over the bow

bow stern

wind tunnel flow visulisation
Wind tunnel: flow visulisation

mean flow direction

Standing vortex

in front of the

deck house

wind tunnel flow visulisation22
Wind tunnel: flow visulisation

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
Wind tunnel: flow visulisation

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

CFD: Airflow above the bridge

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

CFD: Airflow above the bridge

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
Normalised wind speed profile
  • 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
Normalised wind speed profile

deceleration and

recirculation

z/H

H

bow stern

Normalised wind speed

Region of high

velocity gradients

results typical merchant ships
RESULTS: typical merchant ships
  • 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
Container ships

Anemometer

locations

  • More complex shape than a typical tanker
  • Irregular container loading ???

www.shipphotos.co.uk

container ships general flow pattern
Container ships: General flow pattern

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
Container ships: General flow pattern

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
APPLICATION OF RESULTS: MERCHANT SHIPS
  • To predict the wind speed bias
    • Ship type
    • Ship length
    • Anemometer position
  • Parameters are now available (WMO-47)
conclusions research ships
CONCLUSIONS: Research ships
  • 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
CONCLUSIONS: Tankers/bulk carriers/general cargo
  • 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
FUTURE WORK
  • How does the turbulence structure change with ship shape ?

time = 3 sec

future work36
FUTURE WORK
  • 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

Acknowledgements

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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