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Metocean Criteria
DR. SHU ‐HAO CHANG, P.E. AT 台灣離岸風機研討會
MCT ENGINEERING, INC.HOUSTON, TEXAS, USA
Presentation Overview METOCEAN DATA AND APPLICATIONS
EXISTING STANDARDS & GUIDELINES
INTRODUCTION TO API RP 2MET
RESPONSE-BASED DESIGN
SUMMARY
2
• Meteorological Wind (velocity, direction, profile) Atmospheric pressure Temperature Others: precipitation, humidity, fog and etc.
• Oceanographic Waves (height, period, direction, energy) Currents (velocity, direction, profile) Others: marine growth, salinity, oxygen content and etc.
Metocean Data
3
• Site selection and field development feasibility• Engineering design (construction, transportation, installation and etc.)
• Operation and maintenance• Environmental impact assessment• Model validation
Metocean Data Applications
4
• Oil and gas standards ISO 19901-1 (2005):
General requirements for the determination and use of Metocean conditions for the design, construction and operation of offshore structures of all types.
API RP 2MET (2014):Home for all API RP metocean criteria, aligned with ISO 19901-1.
OTHERS:NORSOK N-002, DNV-RP-C205, DNV-OS-H101 and etc.
Existing Standards & Guidelines
5
• RP 2MET Purpose General requirements for developing metocean criteria
‒ Determining conditions‒ Translating conditions into design parameters
Clarify terms/definitions General guidance on regional phenomena Common metocean reference for all other RPs
‒ Indicative criteria, use may be allowed without metocean study for some 2A / 2SIM / 2SK applications
Introduction to API RP 2MET
6
• Evolution of RP 2MET
Introduction to API RP 2MET
7
RP 2A-WSD Section 2.3(21st Edition, 2000)
ISO 19901-1 (2005)Bulletin 2INT-MET
(May 2007)
ISO 19901-1 / RP 2MET(Nov 2014)
RP 2MET(2011-12)
• Changes from 2A, 2INT-MET to 2MET General metocean study guidelines Wave / current interaction from 2A, estimating
extreme waves and crests Interim guidance on hurricane conditions in the
GOM Wave spectra / spreading More Gulf study indicatives:
‒ Winter storms‒ Loop current / eddy‒ TRWs
Introduction to API RP 2MET
8
• Comparison of API RP 2MET (ISO 19901-1) with RP 2A Sections / 2INT-MET
Introduction to API RP 2MET
RP 2MET Section (ISO 19901-1) RP 2A Section / 2INT-MET1. Scope2. Normative references3. Terms and definitions4. Symbols and abbreviated terms5. Determining the relevant metocean parameters 1.3.1 General Metocean Considerations6. Water depth, tides and storm surges 1.3.4 Tides7. Wind 1.3.2 Winds8. Waves 1.3.3 Waves; local wave crest from 2INT-MET9. Currents 1.3.5 Currents10. Other environmental factors 1.3.6 IceAnnex A: Additional information and guidanceA.1 ScopeA.2 Normative ReferencesA.3 Terms and DefinitionsA.4 Symbols and AbbreviationsA.5 Determining the Relevant Metocean ParametersA.6 Water Depth, Tides and Storm SurgesA.7 Wind 2.3.2 WindA.8 Waves 2.3.1 Waves; local wave crest from 2INT-META.9 Currents 2.3.3 CurrentsA.10 Other Environmental FactorsAnnex B: Discussion of wave frequency spectraB.1 The Pierson-Moskowitz spectrumB.2 The JONSWAP spectrumB.3 Comparison of P-M and JONSWAP spectraB.4 Ochi-Hubble spectraAnnex C: Regional informationC.1 GeneralC.2 Northwest EuropeC.3 West Coast of AfricaC.4 US Gulf of Mexico 2.3.4c, 2.3.4d, 17.6.2a GOM Conditions; hurricane site-specific guidance
and indicative conditions from 2INT-METC.5 US Coast of California 2.3.4e, 2.3.4f, 17.6.2b Other US WatersC.6 Other US Waters 2.3.4e, 2.3.4fC.7 East coast of CanadaBibliography
9
• Core Document – Key SectionsIntroduction to API RP 2MET
RP 2MET Section (ISO 19901-1)1. Scope2. Normative references3. Terms and definitions4. Symbols and abbreviated terms5. Determining the relevant metocean parameters6. Water depth, tides and storm surges7. Wind8. Waves9. Currents10. Other environmental factors
Extreme (10-2 / year) & abnormal (10-3~10-4 / year)Long-term distributionsNormal environmental conditions
Water depth: reference datum of water depth (e.g. MSL);Wind: mean and the standard deviation of speed (order of an hour), mean direction,
wind profile (10m above MSL as a reference);Waves: height, crest elevation , period and direction
wave energy spectra / surface elevation (t) for structural dynamic responsesea state (assumed to be 3 hours but depends);
Currents: total velocity, profile, blockage;Others: marine growth (may increase mass, dimension and Cd)
tsunamis, seiches, sea ice, snow and etc. 10
• Core Document – Key SectionsIntroduction to API RP 2MET
RP 2MET Section (ISO 19901-1)Annex A: Additional information and guidanceA.1 ScopeA.2 Normative ReferencesA.3 Terms and DefinitionsA.4 Symbols and AbbreviationsA.5 Determining the Relevant Metocean ParametersA.6 Water Depth, Tides and Storm SurgesA.7 WindA.8 WavesA.9 CurrentsA.10 Other Environmental FactorsAnnex B: Discussion of wave frequency spectraB.1 The Pierson-Moskowitz spectrumB.2 The JONSWAP spectrumB.3 Comparison of P-M and JONSWAP spectraB.4 Ochi-Hubble spectra
Annex A: more guidance on core topics
Appendix B: wave spectra formulas
11
• Core Document – Key SectionsIntroduction to API RP 2MET
RP 2MET Section (ISO 19901-1)Annex C: Regional informationC.1 GeneralC.2 Northwest EuropeC.3 West Coast of AfricaC.4 US Gulf of MexicoC.5 US Coast of CaliforniaC.6 Other US WatersC.7 East coast of Canada
Appendix C: regional information for various parts of the world, of different detail / quality
Houston
12
C.4: US Gulf of Mexico
• Extreme metocean parameters ( US GOM) Hurricanes; Winter storms; Loop current and loop current eddies (LCE); Combined loop current and storm events; Topographic Rossby waves (TRWs); Air and sea temperatures.
Introduction to API RP 2MET
13
• Hurricane Guidance Guidance:
‒ Use 50-100 year data set, including through 2008
‒ Site pooling or averaging to account for track shift
‒ Use synthetic/deductive for long return periods
Indicative:‒ Three areas for “annual” conditions
‒ Central most severe
Introduction to API RP 2MET
14Figure C.13 - Full Population Hurricane Areas of the Gulf
• “Sudden” Hurricane GuidanceGuidance:
‒ Develop using “watch circle” approach, time of arrival of storm conditions appropriate to operation considered
Indicative:‒ One set for GOM, representative of those storms bringing tropical storm-
force winds to sites north of 28 o N 24 hours after storm formation
Introduction to API RP 2MET
15
• Seasonal Hurricane GuidanceGuidance:
‒ Can evaluate hazard as pre- and
post-peak periods
‒ Should not base on single months
‒ Consider other hazards (winter storm)
outside of hurricane peak
Indicative:‒ Two sets provided, West/Central and East, deepwater areas
‒ Early (May-July) and Late (October-November) season periods
Introduction to API RP 2MET
16
• Winter Storm GuidanceGuidance:
‒ Important for operations, especially October-March
‒ Use measurements (NDBC buoys), hindcasts as appropriate
‒ Include 1980’s
‒ Highest observed ~ 9 m Hs
Indicative:‒ One set of conditions for deepwater
Introduction to API RP 2MET
17
Infrared satellite images of the “Storm of the Century” (March 13, 1993) .Image credit: CIMMS Satellite Blog
• Loop Current GuidanceGuidance:
‒ Govern mooring design for some facilities, and riser/tendon design
‒ Use historical record through 2008, caution with pre-1985 years
‒ Site pooling and averaging
‒ Consider joint Loop-hurricane occurrence
Indicative:‒ Maximum surface current case
‒ Provided for 10- and 100-year
Introduction to API RP 2MET
18
Figure C.29 — 10-year loop current/eddy surface speeds (m/s)
Figure C.30 — 100-year loop current/eddy surface speeds (m/s)
• Topographic Rossby Wave Guidance Guidance:
‒ TRW condition important for risers and drilling operations along Sigsbee Escarpment
‒ Ability to model evolving, recommend 1-2 years of measurements at site
‒ May be correlated to Loop proximity
Indicative:‒ 10- and 100-year conditions provided
Introduction to API RP 2MET
19https://ars.els-cdn.com/content/image/1-s2.0-S0967064510001712-gr1.jpg
• Operational Operational Hs-Tp
‒ Data from NDBC 42001
‒ Set does not represent extreme events
Wind roses for June, December‒ From 42001
Sea, air temperature ranges‒ From industry, NDBC measurements
Introduction to API RP 2MET
20Figure 31 — June/December wind roses — Northwest Gulf of Mexicohttp://www.ndbc.noaa.gov/images/stations/scoop.jpg
• US Gulf Annex Summary Site-specific criteria is always preferred – annex values do not
override a proper site-specific study
Select Gulf annex values may be used with 2A and 2SIM for depths less than 120 m, as mapped from L- and A- to appropriate return periods
May be used with 2SK for low consequence operations
Introduction to API RP 2MET
21
• Metocean conditions for structural designResponse-Based Analysis
StructuralModel
WindWaveCurrentDirectionality
Operational: 1-yearExtreme: 100-year (10-2)Abnormal: 1000- ~ 10000-year(10-3 ~ 10-4)
WindWaveCurrentDirectionality
WindWaveCurrentDirectionality!
Fixed jacket
Floating system
Extreme: 100-year (10-2)Abnormal: 1000- ~ 10000-year(10-3 ~ 10-4)
Extreme: 100-year (10-2)Abnormal: 1000- ~ 10000-year(10-3 ~ 10-4)
22
• Metocean conditions for structural design Independent extremes (guideline)− API: extreme independent with associated conditions (API)
Response based conditions− Based on extreme response
− Long-term environmental dataset (30 years)
− Jacket model
Response-Based Analysis
Table C.28 — Factors for combining independent extremes into load cases in shallow water(10 m ≤ depth ≤ 50 m) 23
• Response of offshore structuresResponse-Based Analysis
https://wonderopolis.org/wp-content/uploads/2014/07/dreamstime_xl_22656707-custom.jpg
Metocean Environment
https://i.pinimg.com/originals/f4/cf/32/f4cf32dc2b9c6b9df8aa89cf4910283e.jpg
Offshore Structures
Response Based Metocean Design
ConditionsResponses
Extreme Value Analysis on Responses
Operatingbehavior Design Cases for
N-year responseN-year values for responses
Jobs for metocean specialists
24
• General procedure of RBA Response-Based Analysis
(1)• Develop a long-term metocean database
(2)• Use peak-over-threshold method to identify independent storm
(3)• Select sea states from identified storm that may cause critical response
(4)• Generate short-term responses for selected sea states
(5)• Choose the most critical response and associated sea state from each
storm event (multiple sea states)
(6)• Rank the selected peak responses of all storms and calculate their
probabilities
(7)• Fit peak response and probability and calculate the design response for
the N-year return period
(8)• Estimate the design environmental conditions likely to produce the
responses of a chosen N-year return period
(9)• Estimate the safety (load) factors required to ensure target reliability
25
• General procedure of RBA (cont.)Response-Based Analysis
(1) • Develop a long-term metocean database
(2)• Use peak-over-threshold method to identify independent storm
(3)• Select sea states from identified storm that may cause critical response
(4)• Generate short-term responses for selected sea states
(5)• Choose the most critical response and associated sea state from each
storm event (multiple sea states)
(6)• Rank the selected peak responses of all storms and calculate their
probabilities
(7)• Fit peak response and probability and calculate the design response for
the N-year return period
(8)• Estimate the design environmental conditions likely to produce the
responses of a chosen N-year return period
(9)• Estimate the safety (load) factors required to ensure target reliability
26
• requires a long-term database of:Waves− wave height, period and direction or− directional wave spectrum or− wind-sea and swell
Winds− Speed and direction− Wind spectrum− Wind profile
Currents− current speed and direction− current profile
Response-Based Analysis
27
• General procedure of RBA (cont.)•
Response-Based Analysis
(1)• Develop a long-term metocean database
(2)• Use peak-over-threshold (POT) method to identify
independent storm
(3)• Select sea states from identified storm that may cause critical response
(4)• Generate short-term responses for selected sea states
(5)• Choose the most critical response and associated sea state from each
storm event (multiple sea states)
(6)• Rank the selected peak responses of all storms and calculate their
probabilities
(7)• Fit peak response and probability and calculate the design response for
the N-year return period
(8)• Estimate the design environmental conditions likely to produce the
responses of a chosen N-year return period
(9)• Estimate the safety (load) factors required to ensure target reliability
28
• Peak-over-threshold (POT) filteringResponse-Based Analysis
Picture source from Shell Exploration and Production 29
• General procedure of RBA (cont.)•
Response-Based Analysis
(1)• Develop a long-term metocean database
(2)• Use peak-over-threshold (POT) method to identify independent storm
(3)• Select sea states from identified storm that may cause
critical responses
(4)• Generate short-term responses for selected sea states
(5)• Choose the most critical response and associated sea state from each
storm event (multiple sea states)
(6)• Rank the selected peak responses of all storms and calculate their
probabilities
(7)• Fit peak response and probability and calculate the design response for
the N-year return period
(8)• Estimate the design environmental conditions likely to produce the
responses of a chosen N-year return period
(9)• Estimate the safety (load) factors required to ensure target reliability
30
• Selected sea states from a stormResponse-Based Analysis
31
• General procedure of RBA (cont.)•
Response-Based Analysis
(1)• Develop a long-term metocean database
(2)• Use peak-over-threshold (POT) method to identify independent storm
(3)• Select sea states from identified storm that may cause critical
responses
(4) • Generate short-term responses for selected sea states
(5)• Choose the most critical response and associated sea state from each
storm event (multiple sea states)
(6)• Rank the selected peak responses of all storms and calculate their
probabilities
(7)• Fit peak response and probability and calculate the design response for
the N-year return period
(8)• Estimate the design environmental conditions likely to produce the
responses of a chosen N-year return period
(9)• Estimate the safety (load) factors required to ensure target reliability
32
• Short-term responseResponse-Based Analysis
33
• Long-term extreme response analysis methodResponse-Based Analysis
(Tromans and Vanderschuren, 1995)
34
• Effect of short-term variabilityResponse-Based Analysis
(Forristal, Larrabee and Mercier, 1991)35
• General procedure of RBA (cont.)•
Response-Based Analysis
(1)• Develop a long-term metocean database
(2)• Use peak-over-threshold (POT) method to identify independent storm
(3)• Select sea states from identified storm that may cause critical
responses
(4)• Generate short-term responses for selected sea states
(5)• Choose the most critical response and associated sea
state from each storm event (multiple sea states)
(6)• Rank the selected peak responses of all storms and calculate their
probabilities
(7)• Fit peak response and probability and calculate the design response for
the N-year return period
(8)• Estimate the design environmental conditions likely to produce the
responses of a chosen N-year return period
(9)• Estimate the safety (load) factors required to ensure target reliability
36
• Critical responses of fixed platform Displacement Shear force Bending moment
Response-Based Analysis
37
• General procedure of RBA (cont.)•
Response-Based Analysis
(1)• Develop a long-term metocean database
(2)• Use peak-over-threshold (POT) method to identify independent storm
(3)• Select sea states from identified storm that may cause critical
responses
(4)• Generate short-term responses for selected sea states
(5)• Choose the most critical response and associated sea state from each
storm event (multiple sea states)
(6)• Rank the selected peak responses of all storms and
calculate their probabilities
(7)• Fit peak response and probability and calculate the design response for
the N-year return period
(8)• Estimate the design environmental conditions likely to produce the
responses of a chosen N-year return period
(9)• Estimate the safety (load) factors required to ensure target reliability
38
• Calculate the probabilities of selected sea statesResponse-Based Analysis
39
• General procedure of RBA (cont.)•
Response-Based Analysis
(1)• Develop a long-term metocean database
(2)• Use peak-over-threshold (POT) method to identify independent storm
(3)• Select sea states from identified storm that may cause critical
responses
(4)• Generate short-term responses for selected sea states
(5)• Choose the most critical response and associated sea state from each
storm event (multiple sea states)
(6)• Rank the selected peak responses of all storms and calculate their
probabilities
(7)• Fit peak response and probability and calculate the
design response for the N-year return period
(8)• Estimate the design environmental conditions likely to produce the
responses of a chosen N-year return period
(9)• Estimate the safety (load) factors required to ensure target reliability
40
• Fit peak response and probabilityResponse-Based Analysis
41
• General procedure of RBA (cont.)•
Response-Based Analysis
(1)• Develop a long-term metocean database
(2)• Use peak-over-threshold (POT) method to identify independent storm
(3)• Select sea states from identified storm that may cause critical
responses
(4)• Generate short-term responses for selected sea states
(5)• Choose the most critical response and associated sea state from each
storm event (multiple sea states)
(6)• Rank the selected peak responses of all storms and calculate their
probabilities
(7)• Fit peak response and probability and calculate the design response for
the N-year return period
(8)• Estimate the design environmental conditions likely to
produce the responses of a chosen N-year return period
(9)• Estimate the safety (load) factors required to ensure target reliability
42
• N-year return periodResponse-Based Analysis
Hmps_100
Q(Hmps|n-years)
Q(Hmps|100-years)
43
• General procedure of RBA (cont.)•
Response-Based Analysis
(1)• Develop a long-term metocean database
(2)• Use peak-over-threshold (POT) method to identify independent storm
(3)• Select sea states from identified storm that may cause critical
responses
(4)• Generate short-term responses for selected sea states
(5)• Choose the most critical response and associated sea state from each
storm event (multiple sea states)
(6)• Rank the selected peak responses of all storms and calculate their
probabilities
(7)• Fit peak response and probability and calculate the design response for
the N-year return period
(8)• Estimate the design environmental conditions likely to produce the
responses of a chosen N-year return period
(9)• Estimate the safety (load) factors required to ensure
target reliability 44
• Response of offshore structuresResponse-Based Analysis
https://wonderopolis.org/wp-content/uploads/2014/07/dreamstime_xl_22656707-custom.jpg
Metocean Environment
https://i.pinimg.com/originals/f4/cf/32/f4cf32dc2b9c6b9df8aa89cf4910283e.jpg
Offshore Structures
Response Based Metocean Design
ConditionsResponses
Extreme Value Analysis on Responses
Operatingbehavior Design Cases for
N-year responseN-year values for responsesJobs for
offshore structural engineer 45
• Design Cases for N-year responseJacket In-place Structural Analysis
100-year Extreme Storm wave, wind and current 5-year Operating Storm wave, wind and current
46
Thank you!
Questions?
Photo source from http://dudgeonoffshorewind.co.uknewsnewsimagesnews02-06-16-jacket-sail-away.jpg
47