Arctic Floater Design
Arctic Floater Design John Murray SNAME Luncheon Houston, Texas 12 January 2010
1
© FloaTEC 2009
Presentation Outline Challenges Ice types Structure types Floater options Spar (model test example ) Summary
2
Arctic Conditions The Arctic presents a particularly difficult environment for platform design and offshore operations. Waves similar to the GoM Ice and extreme cold Isolation Transportation Platform evacuation 3
Cold Atmosphere Freezing Spray
4
New Environment for Floaters - Marine Icing
Designs must include mitigation measures against atmospheric and sea spray icing The industry needs tools to design as well as operational planning 5
Sheet Ice/Pack Ice - Sea Ice
Sea ice is formed from frozen seawater (first-year ice) As ice ages, brine drains out and the ice becomes stronger (multi-year ice)
Wave action breaks the ice into pans called floes that form pack ice Pack ice is driven mainly by wind and currents, it dampens waves in heavy concentrations 6
Ice Ridges
15
Dimensions: Length – 1000’s m Width – 100’s m Height – 10’s m
7
Ridge elevation (m)
Sail
Consolidated Layer
0
- 15 Keel Keel
- 30 0
50
100 Ridge width (m)
150
200
Ice Bergs – Glacial Ice Ice bergs are calved (originate) from glaciers Are composed of frozen freshwater of average 5,000 years
Berg Sizes: Large: 10-E06 tonnes/ Current driven Medium: 10-E03 tonnes/ Waves & current driven Bergy bits: 10-E02 tonnes/ Wave driven 8
Comparison of Ice Loads by Type Range of Ice Loads
Global Force (tons)
20,000 16,000 12,000 8,000 4,000 0 Level Ice
Ice Ridges
Ice Type
9
Icebergs
Present Level of Experience Mainly gained in the 1970s in the US and Canadian Arctic Some limited recent experience in moderate ice conditions Mainly related to shallow waters New projects planned for both coastal and deep waters
10
10
FPSO Design
SeaRose
Terra Nova
11
Floater Design Methods Limitations of Existing Tools
12
Test Facility IOT Canada
13
Model Tests In Ice
Ship Shape in Pack Ice 14
FPSO Response in Pack Ice
640
Mean Mooring Force
- 200 - 250 - 300 - 350
480
0.0
320 160 0 1.00 0.90 0.80 co nc en tra 0.70 tio 0.60 n
15
Mooring Force(s tons)
Mooring Force(s tons)
- 150
1.50 0.00
1.00 0.50 (kts ) y t i c Velo
2.00
120
240 Surge (sec)
360
Disconnectable FPSO Design
16
Arctic Spar Design
Connected Mode 17
Disconnected Mode
Mooring Disconnect Design
Figure 3. Mooring Disconnect System
18
Truncated Model
19
Total Mass & Inertia
20
Models Tested
21
Model Mooring System
22
Mooring System Stiffness
23
Model Tests In Ice
Spar in Level Ice and Ridges 24
1:50 Scale Setup
25
Results of Fixed Tests
26
Ice Load Estimates
27
Estimates of Dynamic Amplification Factors (DAF)
28
Design Considerations Ice Cover
Open Water
8,000
8,000
6,000
6,000
on
d
lin
e
e
te
te ns
ns i
lo a
w ab
le
lin
e lin le
m ea n n w w av in d e dr ift fo m rc ea e n cu rr m en ax t dy m na ax m ic lin al lo e w t en ab si le on lin e te ns io n
te ns
ns i te e w ab
m ea
on
d lo a lin al lo
te ns
ic e m ax
on e le w ab
al lo
m ax
lin
lin
e
dy
te
na
ns i
m ic
t rr en cu
m ax
n
m ea
dr ift f
w n w
av e
m ea n m ea
io n
0 io n
0 or ce
2,000
in d
2,000
io n
4,000
al lo
4,000
ic e
Load
10,000
Load
10,000
Ice Cover
m ax
Open Water
Balance Design • Optimize between open water and ice cover conditions • Avoid creating a hydrodynamic problem to solve an ice problem or vice versa
29
General Remarks
Replacing reserves of oil and gas from Arctic sources will present new challenges to the industry Innovation is the key to success - new ideas will have to be brought to fruition Regulatory guidelines have to be reviewed and standards developed
30
Model Test Design Tools
31
1
© FloaTEC 2009
Presentation Outline Challenges Ice types Structure types Floater options Spar (model test example ) Summary
2
Arctic Conditions The Arctic presents a particularly difficult environment for platform design and offshore operations. Waves similar to the GoM Ice and extreme cold Isolation Transportation Platform evacuation 3
Cold Atmosphere Freezing Spray
4
New Environment for Floaters - Marine Icing
Designs must include mitigation measures against atmospheric and sea spray icing The industry needs tools to design as well as operational planning 5
Sheet Ice/Pack Ice - Sea Ice
Sea ice is formed from frozen seawater (first-year ice) As ice ages, brine drains out and the ice becomes stronger (multi-year ice)
Wave action breaks the ice into pans called floes that form pack ice Pack ice is driven mainly by wind and currents, it dampens waves in heavy concentrations 6
Ice Ridges
15
Dimensions: Length – 1000’s m Width – 100’s m Height – 10’s m
7
Ridge elevation (m)
Sail
Consolidated Layer
0
- 15 Keel Keel
- 30 0
50
100 Ridge width (m)
150
200
Ice Bergs – Glacial Ice Ice bergs are calved (originate) from glaciers Are composed of frozen freshwater of average 5,000 years
Berg Sizes: Large: 10-E06 tonnes/ Current driven Medium: 10-E03 tonnes/ Waves & current driven Bergy bits: 10-E02 tonnes/ Wave driven 8
Comparison of Ice Loads by Type Range of Ice Loads
Global Force (tons)
20,000 16,000 12,000 8,000 4,000 0 Level Ice
Ice Ridges
Ice Type
9
Icebergs
Present Level of Experience Mainly gained in the 1970s in the US and Canadian Arctic Some limited recent experience in moderate ice conditions Mainly related to shallow waters New projects planned for both coastal and deep waters
10
10
FPSO Design
SeaRose
Terra Nova
11
Floater Design Methods Limitations of Existing Tools
12
Test Facility IOT Canada
13
Model Tests In Ice
Ship Shape in Pack Ice 14
FPSO Response in Pack Ice
640
Mean Mooring Force
- 200 - 250 - 300 - 350
480
0.0
320 160 0 1.00 0.90 0.80 co nc en tra 0.70 tio 0.60 n
15
Mooring Force(s tons)
Mooring Force(s tons)
- 150
1.50 0.00
1.00 0.50 (kts ) y t i c Velo
2.00
120
240 Surge (sec)
360
Disconnectable FPSO Design
16
Arctic Spar Design
Connected Mode 17
Disconnected Mode
Mooring Disconnect Design
Figure 3. Mooring Disconnect System
18
Truncated Model
19
Total Mass & Inertia
20
Models Tested
21
Model Mooring System
22
Mooring System Stiffness
23
Model Tests In Ice
Spar in Level Ice and Ridges 24
1:50 Scale Setup
25
Results of Fixed Tests
26
Ice Load Estimates
27
Estimates of Dynamic Amplification Factors (DAF)
28
Design Considerations Ice Cover
Open Water
8,000
8,000
6,000
6,000
on
d
lin
e
e
te
te ns
ns i
lo a
w ab
le
lin
e lin le
m ea n n w w av in d e dr ift fo m rc ea e n cu rr m en ax t dy m na ax m ic lin al lo e w t en ab si le on lin e te ns io n
te ns
ns i te e w ab
m ea
on
d lo a lin al lo
te ns
ic e m ax
on e le w ab
al lo
m ax
lin
lin
e
dy
te
na
ns i
m ic
t rr en cu
m ax
n
m ea
dr ift f
w n w
av e
m ea n m ea
io n
0 io n
0 or ce
2,000
in d
2,000
io n
4,000
al lo
4,000
ic e
Load
10,000
Load
10,000
Ice Cover
m ax
Open Water
Balance Design • Optimize between open water and ice cover conditions • Avoid creating a hydrodynamic problem to solve an ice problem or vice versa
29
General Remarks
Replacing reserves of oil and gas from Arctic sources will present new challenges to the industry Innovation is the key to success - new ideas will have to be brought to fruition Regulatory guidelines have to be reviewed and standards developed
30
Model Test Design Tools
31
