Best Practice Scour Predictions vs. Scour Survey Data of a … · 2019-04-08 · The mudmat does...
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Best Practice Scour Predictions vs. Scour Survey Data of a Subsea Structure Scott Draper, Weidong Yao, Liang Cheng, Phil Watson Meysam Banimahd Antonio Borges Rodriguez 15 th March, 2019 AOG Conference 2019
Transcript of Best Practice Scour Predictions vs. Scour Survey Data of a … · 2019-04-08 · The mudmat does...
Best Practice Scour Predictions vs. Scour
Survey Data of a Subsea StructureScott Draper, Weidong Yao, Liang Cheng, Phil Watson
Meysam Banimahd
Antonio Borges Rodriguez
15th March, 2019AOG Conference 2019
Whitehouse et al. 2011
Yao et al. 2018
≡D
h
D
hAA
≡
≡D
hAA
Section A-A
1. Increase the parameter space spanned by experiments
2. Use structure-specific best-practice method
How do we improve on this …
1. Increase the parameter space spanned by experiments
2. Use structure-specific best-practice method
How do we improve on this …
h1/D1, D2/D1, h2/D2
Yao et al. (2018,
2019 a,b)
1. Increase the parameter space spanned by experiments
2. Use structure-specific ‘best-practice’ method
FOCUS OF TODAYS TALK!
How do we improve on this …
Field observations and data
Laboratory experiments
Laboratory-based estimates of scour
Comparison to field observations
Best Practice Scour Predictions vs. Scour Survey
Data of a Subsea Structure
Two ‘identical’ structures
ROV survey data
Scour surveys
• 4.5 months
• 17.5 months
ROV survey data
Scour surveys
• 4.5 months
• 17.5 months
ROV survey data
Scour surveys
• 4.5 months
• 17.5 months
Site specific sediment properties
Core sample located <100 m from structures
𝜂 = 𝐴 𝜏 − 𝜏𝑐𝑟𝐵
Site specific metocean conditions
0 50 100 150 200 250 300 350 4000
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Days after 15th December 2015
Vel
oci
ty [
m/s
]
Days
Days
Threshold
𝛽 = 36°
Field observations and data
Laboratory experiments
Laboratory-based estimates of scour
Comparison to field observations
Experiments
1. Experiments to assess shear stress amplification factor
2. Experiments to simulate shallow’ scour
Amplification factors
No mudmat
Full structure
Mudmat only
Amplification factors
No mudmat
Full structure
Mudmat only
Shallow scour experiments
t
S
𝝉/𝝉𝒄𝒓 [-]t [s]
S/D
[-]
Field observations and data
Laboratory experiments
Laboratory-based estimates of scour
Comparison to field observations
Laboratory-based estimates of scour
(i) Account for time varying currents
𝑆 𝑡 = න0
𝑡 𝑑𝑆
𝑑𝑡𝑑𝑡 = න
0
𝑡
𝜉[𝜏 𝑡, 𝜏𝑐𝑟 ]𝑑𝑡
(ii) Scale results to field conditions
qmaxqmax
ss
Flow
direction
𝜉 =𝜕𝑆
𝜕𝑡∝
𝜕𝑞
𝜕𝑠,
𝜉 ∝𝜕𝑞
𝜕𝑠∝
𝑞𝑚𝑎𝑥
𝐷,
𝜉𝐹
𝜉𝐿=
𝑞𝑚𝑎𝑥,𝐹
𝑞𝑚𝑎𝑥,𝐿
𝐷𝐿
𝐷𝐹,
𝜉𝐹
𝜉𝐿=
𝐴𝐹 𝛼𝜏𝜏−𝜏𝑐𝑟,𝐹𝐵𝐹
𝐴𝐿 𝛼𝜏𝜏−𝜏𝑐𝑟,𝐿𝐵𝐿
𝐷𝐿
𝐷𝐹
Field observations and data
Laboratory experiments
Laboratory-based estimates of scour
Comparison to field observations
Scour calculations
Using site
specific soil data
Lab sediment
only
Soulsby (1997)
17.5 month survey
Field data is invaluable for better understanding scour and reducing
uncertainty in predictive methods
Reasonable agreement is obtained using laboratory-based scour estimates if
site specific soil and metocean conditions are considered together with
specific geometry of structure
3D printing and appropriate scaling arguments can make bespoke laboratory-
based estimates practical in design
The mudmat does provide inherent scour protection – reduced amplification
factor and reduced scour rate (more systematic study on this aspect is under
peer review)
Conclusions
Best Practice Scour Predictions vs. Scour
Survey Data of a Subsea StructureScott Draper, Weidong Yao, Liang Cheng, Phil Watson
Meysam Banimahd
Antonio Borges Rodriguez
15th March, 2019AOG Conference 2019
