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www.babcockinternational.com Marine Land Aviation Nuclear
6 Degrees-of Freedom Towed Buoy Dynamic Assessment Kristian Geleff – UDT, Glasgow, 2018
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UDT 2018
Marine Land Aviation Nuclear
Introduction
UDT, 2018 2
6 Degrees-of Freedom Towed Buoy Dynamic Assessment
• Introduction of the system
• Purpose of developing this capability
• Challenges
• Simulation
• Key Performance Indicators
• Conclusion
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UDT 2018
Marine Land Aviation Nuclear
Introduction
UDT, 2018 3
Comms at Speed and Depth
Environment (waves, wind etc)
Long Towing Cable
Speed, depth, manoeuvres
Operating window
Water properties
Towing Platform
Wave Affected Zone
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Marine Land Aviation Nuclear
Purpose
UDT, 2018 4
Provide confidence across a number of areas:
• Assess simulation performance against test data
• Validation activities
• Assess performance impact of design changes
• Developmental tool - improve design & performance
• Assess performance across wide range of operating scenarios
• Time and availability of platforms make this very challenging to achieve with testing
• Define operating envelope – interpolate between measured points of data
• De-risking tool – increase likelihood of full scale trials being successful
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UDT 2018
Marine Land Aviation Nuclear
Challenges
UDT, 2018 5
Scale
• Underway towed systems are very large
‒ Towed body to towing platform spans hundreds of meters
• No test facilities large enough to accommodate full scale testing
• Requires towing platform
‒ Often actual platform due to lack of suitable research platforms
• High risk going from the drawing board to full scale tests
Hydrodynamic scaling
• Different for turbulent transition (Reynolds Number Re) and wave making resistance (Froude Number Fr)
• Not possible to scale for both simultaneously
• Scale based on Fr and add leading edge trips to artificially trigger turbulent transition at lower Reynolds Numbers.
Tank Testing
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Marine Land Aviation Nuclear
Challenges
UDT, 2018 6
Operating Environment
• Wind and waves by nature are chaotic and turbulent
• Repeatable experiments cannot be achieved
• Sea states are characterised in statistical terms i.e. significant wave height, period..
• Statistical methods of analysing performance becomes necessary
0 500 1000 1500 2000 2500
Time (s)
Ele
vatio
n (m
)
Wave Elevation
-4 -3 -2 -1 0 1 2 3 4
Pro
babi
lity
Den
sity
Standard Deviation
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Marine Land Aviation Nuclear
Challenges
UDT, 2018 7
The highly coupled nature of a towed buoy system makes testing of sub-systems and components of limited value.
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UDT 2018
Marine Land Aviation Nuclear
Challenges
• Simulation in the wave affected zone:
• Full 6 degree of freedom buoy dynamics
required for complex shape
• Hydrodynamic coefficients required for all
impingement angles
• Hydrodynamic scaling challenges
0 1 2 3 4 5 6 7 8-1.5
-1
-0.5
0
0.5
1
1.5Fluid Velocity: 0° sea heading
Flu
id V
eloc
ity (
m/s
)
Vf luid x
Vf luid y
Vf luid z
0 1 2 3 4 5 6 7 8-1.5
-1
-0.5
0
0.5
1
1.5Fluid direction (xz plane)
Flu
id V
eloc
ity (
m/s
)
Time (s)
8
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Marine Land Aviation Nuclear
Simulation
UDT, 2018 9
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Marine Land Aviation Nuclear
Key Performance Indicators
UDT, 2018 10
Monitor KPIs: Availability
• Antenna depth
• Antenna orientation
Results:
• Availability (%)
• Min, max, mean, standard deviation
0 500 1000 1500 2000 2500
Time (s)
Dep
th (m
)
Towed Buoy Depth
Towed Buoy Depth
Mean
Upper Depth Bound
Lower Depth Bound
Minimum Depth
Maximum Depth
Op
era
ting W
ind
ow
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UDT 2018
Marine Land Aviation Nuclear
Key Performance Indicators
UDT, 2018 11
Assessment of KPI across
operating scenarios
• Identify operating scenarios
where performance
improvements required
• Quantify performance of
design changes
• Performance prediction for
end user
Note: Random data used to demonstrate
visualisation
Depth
(m) z z z z z z z z z z z z z z z
y
y
y
y
y
y
y
y
y
y
y
y
y
y
y
y
y
y
x
x
x
Sea State b Sea State b Sea State b
Speed
(kts)
Heading Heading Heading
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Marine Land Aviation Nuclear
Conclusion
UDT, 2018 12
Challenges facing development of submarine towed buoy systems have been discussed
• Full scale testing is expensive and logistically difficult
• Scaling effects and highly coupled natured limits value of small scale/sub element testing
• Operating environment is chaotic and not easily replicated in a controlled test
• Statistical validation
Simulation is an enormously valuable tool
• Design and development
• Cost and risk reduction
• Predicting operating envelope
• Reducing development timescales
• Maximising chance of success for full scale testing
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UDT 2018
Marine Land Aviation Nuclear UDT, 2018 13
