Part A | 3
72 Part A Fundamentals
3.8 Conclusions
The metocean environment controls many aspects of
facility design and operation so errors in quantifying
metocean conditions can cascade though the design and
operational decisions. Errors can result in damage and
lost lives. Conversely, if the variables are overestimated,
costs will be overestimated perhaps to the point that the
project becomes uneconomic and is never built.
Metocean criteria are typically broken into two categories: operating and extreme. The former involves
quantification of metocean conditions in which the facility or vessel should be capable of achieving the routine functions of its primary purpose. In contrast, extreme conditions occur rarely and are often generated by
episodic events (e.g., storms). Both categories may start
with the same databases but the analysis techniques and
final design specifications will differ substantially.
There are a host of sophisticated methods and tools
that can be used to quantify the most important metocean variables that impact offshore facilities. We have
suggested methods drawn largely from the offshore oil
and gas industry but they are also generally applicable
to other engineering applications involving the design
and operation of vessels, coastal structures, offshore
wind farms, navigational aids, coastal geomorphology,
and pollution studies.
When developing a metocean design basis for a major project, the metocean engineer should first identify
the variables of primary importance. This is because
the sea and atmosphere are filled with complicated
processes, many of which are site specific and poorly
understood. If aggressive filtering is not undertaken
then too much time can be spent quantifying variables
that make little difference to the design or operation of
the facility. The first and best way to eliminate variables
from investigation is to understand the basic responses
of the particular facility. In other words to answer the
question: which metocean variables impact this facility
most and which have little or no impact?
Finally, it should be noted that the methods, tools,
and databases cited in this chapter reflect a snapshot in
time; they are continually being updated and improved.
The reader should always consider these citations as
a starting point and check the web and journals for updates before proceeding with the analysis.
References
3.1
ANSI/API: Recommended Practice 2MET. Derivation
of Metocean Design and Operating Conditions (API,
Washington 2014)
3.2
U.S. Army Corps of Engineers: Coastal Engineering Manual, Report Num. EM1110-2-1100 http://chl.
erdc.usace.army.mil/cem
3.3
L.F. Richardson: Atmospheric diffusion shown on a
distance-neighbor graph, Proc. R. Soc. London Ser.
A 110, 709–737 (1926)
3.4
NORSOK Standards: N-003: Actions and Action Effects. Rev. 2 (Standards Norway, Lysaker 2007)
3.5
P.J. Vickery: Analysis of hurricane winds, Proc. Offshore Tech. Conf. (2014)
3.6
Engineering Sciences Data Unit: Strong winds in the
atmospheric boundary layer, Part 1: Mean hourly
wind speed, No. 82026 (ESDU, London 1982)
3.7
Engineering Sciences Data Unit: Strong winds in the
atmospheric boundary layer, Part 2: Discrete gust
speeds, No. 83045 (ESDU, London 1983)
3.8
W.G. Large, S. Pond: Open ocean momentum
flux measurements in moderate to strong winds,
J. Phys. Oceangr. 11, 324–336 (1981)
3.9
P.J. Vickery, D. Wadhera, M.D. Powell, Y. Chen:
A hurricane boundary layer and wind field model
for use in engineering applications, J. Appl. Meteor.
Climate 48, 381–405 (2009)
3.10
M.D. Powell, P.J. Vickery, T.A. Reinhold: Reduced
drag coefficient for high wind speeds in tropical
cyclones, Nature 422, 279–283 (2003)
3.11
M.A. Donelan, B.K. Haus, N. Reul, W.J. Plant, M. Stiassnie, H.C. Graber, O.B. Brown, E.S. Saltzman: On
the limiting aerodynamic roughness of the ocean
in very strong winds, Geophys. Res. Lett. 31, L18306
(2004)
3.12
M. Powell: New findings on hurricane intensity,
wind field extent and surface drag coefficient behavior, 10th Int. Workshop Wave Hindcast. Forecast.
Coast. Hazard Symp. (2007) pp. 11–16
3.13
S. Frolov: Ocean response to hurricanes in presence
of the Loop Current, Offshore Technol. Conf. (2010)
3.14
J.W. Miles: On the generation of surface waves by
shear flows, J. Fluid Mech. 6, 568–582 (1957)
3.15
D.M. Glover, W.J. Jenkins, S.C. Doney: Modeling
Methods for Marine Science (Cambridge Univ. Press,
Cambridge 2011)
3.16
Y. Goda: Random Seas and the Design of Marine
Structures (Univ. of Tokyo Press, Tokyo 1985)
3.17
M.K. Ochi, E.N. Hubble: Six parameter wave spectra,
Proc. 15th Coast. Eng. Conf. (1976) pp. 301–328
3.18
K. Torsethaugen, S. Haver: Simplified double
peaked spectral model for ocean waves, 14th Int.
Offshore Polar Eng. Conf. (2004)
3.19
G.Z. Forristall: On the statistical distribution of
wave heights in a storm, J. Geophys. Res. 83, 2353–
2358 (1978)
3.20
G.Z. Forristall: Wave crest distributions: Observations and second-order theory, J. Phys. Oceanogr.
30, 1931–1943 (2000)
72 Part A Fundamentals
3.8 Conclusions
The metocean environment controls many aspects of
facility design and operation so errors in quantifying
metocean conditions can cascade though the design and
operational decisions. Errors can result in damage and
lost lives. Conversely, if the variables are overestimated,
costs will be overestimated perhaps to the point that the
project becomes uneconomic and is never built.
Metocean criteria are typically broken into two categories: operating and extreme. The former involves
quantification of metocean conditions in which the facility or vessel should be capable of achieving the routine functions of its primary purpose. In contrast, extreme conditions occur rarely and are often generated by
episodic events (e.g., storms). Both categories may start
with the same databases but the analysis techniques and
final design specifications will differ substantially.
There are a host of sophisticated methods and tools
that can be used to quantify the most important metocean variables that impact offshore facilities. We have
suggested methods drawn largely from the offshore oil
and gas industry but they are also generally applicable
to other engineering applications involving the design
and operation of vessels, coastal structures, offshore
wind farms, navigational aids, coastal geomorphology,
and pollution studies.
When developing a metocean design basis for a major project, the metocean engineer should first identify
the variables of primary importance. This is because
the sea and atmosphere are filled with complicated
processes, many of which are site specific and poorly
understood. If aggressive filtering is not undertaken
then too much time can be spent quantifying variables
that make little difference to the design or operation of
the facility. The first and best way to eliminate variables
from investigation is to understand the basic responses
of the particular facility. In other words to answer the
question: which metocean variables impact this facility
most and which have little or no impact?
Finally, it should be noted that the methods, tools,
and databases cited in this chapter reflect a snapshot in
time; they are continually being updated and improved.
The reader should always consider these citations as
a starting point and check the web and journals for updates before proceeding with the analysis.
References
3.1
ANSI/API: Recommended Practice 2MET. Derivation
of Metocean Design and Operating Conditions (API,
Washington 2014)
3.2
U.S. Army Corps of Engineers: Coastal Engineering Manual, Report Num. EM1110-2-1100 http://chl.
erdc.usace.army.mil/cem
3.3
L.F. Richardson: Atmospheric diffusion shown on a
distance-neighbor graph, Proc. R. Soc. London Ser.
A 110, 709–737 (1926)
3.4
NORSOK Standards: N-003: Actions and Action Effects. Rev. 2 (Standards Norway, Lysaker 2007)
3.5
P.J. Vickery: Analysis of hurricane winds, Proc. Offshore Tech. Conf. (2014)
3.6
Engineering Sciences Data Unit: Strong winds in the
atmospheric boundary layer, Part 1: Mean hourly
wind speed, No. 82026 (ESDU, London 1982)
3.7
Engineering Sciences Data Unit: Strong winds in the
atmospheric boundary layer, Part 2: Discrete gust
speeds, No. 83045 (ESDU, London 1983)
3.8
W.G. Large, S. Pond: Open ocean momentum
flux measurements in moderate to strong winds,
J. Phys. Oceangr. 11, 324–336 (1981)
3.9
P.J. Vickery, D. Wadhera, M.D. Powell, Y. Chen:
A hurricane boundary layer and wind field model
for use in engineering applications, J. Appl. Meteor.
Climate 48, 381–405 (2009)
3.10
M.D. Powell, P.J. Vickery, T.A. Reinhold: Reduced
drag coefficient for high wind speeds in tropical
cyclones, Nature 422, 279–283 (2003)
3.11
M.A. Donelan, B.K. Haus, N. Reul, W.J. Plant, M. Stiassnie, H.C. Graber, O.B. Brown, E.S. Saltzman: On
the limiting aerodynamic roughness of the ocean
in very strong winds, Geophys. Res. Lett. 31, L18306
(2004)
3.12
M. Powell: New findings on hurricane intensity,
wind field extent and surface drag coefficient behavior, 10th Int. Workshop Wave Hindcast. Forecast.
Coast. Hazard Symp. (2007) pp. 11–16
3.13
S. Frolov: Ocean response to hurricanes in presence
of the Loop Current, Offshore Technol. Conf. (2010)
3.14
J.W. Miles: On the generation of surface waves by
shear flows, J. Fluid Mech. 6, 568–582 (1957)
3.15
D.M. Glover, W.J. Jenkins, S.C. Doney: Modeling
Methods for Marine Science (Cambridge Univ. Press,
Cambridge 2011)
3.16
Y. Goda: Random Seas and the Design of Marine
Structures (Univ. of Tokyo Press, Tokyo 1985)
3.17
M.K. Ochi, E.N. Hubble: Six parameter wave spectra,
Proc. 15th Coast. Eng. Conf. (1976) pp. 301–328
3.18
K. Torsethaugen, S. Haver: Simplified double
peaked spectral model for ocean waves, 14th Int.
Offshore Polar Eng. Conf. (2004)
3.19
G.Z. Forristall: On the statistical distribution of
wave heights in a storm, J. Geophys. Res. 83, 2353–
2358 (1978)
3.20
G.Z. Forristall: Wave crest distributions: Observations and second-order theory, J. Phys. Oceanogr.
30, 1931–1943 (2000)