Implications Of Hurricane Ivan On Deepwater Gulf Of Mexico Metocean Design Criteria

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractHurricane Ivan (September 2004) generated the highest waves ever measured or hindcast in the Gulf of Mexico. The implications of Ivan on deepwater Gulf of Mexico metocean design criteria are examined from three aspects: (1) whether there is an obvious deficiency in the ODGP wind and wave hindcast model, (2) whether Ivan generated "freak" conditions that break the NTS/API gust factor relationships and wind spectra characterizations or the Forristall wave height and crest height distributions, and (3) whether Ivan is, from a statistical standpoint, truly an "unexpected" event. To address the first two issues, wind and wave measurements collected on two industry platforms near Ivan's track are examined. Excellent comparisons are found between the industry measurements and the ODGP hindcast model, which further corroborate the findings of [2]. Analysis of the industry wind measurements suggests NTS/API gust factors are valid for Ivan, while the NTS/API spectra are found to agree reasonably well with the measured spectra except perhaps for a tendency of API to overestimate low-frequency energy. Measured wave heights and wave crests are found to fit the Forristall distributions quite well, providing no support for "freak" waves during Ivan. To address the last issue, the Gulf of Mexico hindcast record is examined. The maximum wave heights generated by Ivan correspond to roughly a 2,500-year local return period, assuming the extremal distribution before Ivan was correct. Adding Ivan to the existing hindcast database is found to raise 100-year H s values close to the storm track by 1.0 m or more. Through consideration of hurricane encounters in a finer spatial sense (160 km zones) rather than simply considering the entire Gulf as a single encounter zone, a strong argument can be made that the conditions generated by Ivan could reasonably be expected at a local level within the context of 105 years of hurricane experience throughout the Gulf. However, while Ivan may be described as a rare but not unexpected event at the local level, prudence dictates that winds and waves generated by Ivan be included in the hindcast database used for future Gulf of Mexico designs, as opposed to treating them as local outliers to existing extremal distributions and neglecting them.

Wave Crest Heights and Deck Damage in Hurricanes Ivan, Katrina, and Rita

“…These measurements were described by Cooper et al [9]. If the spectral variance is confined to one angular band, or to two bands that are 180º apart, IVR = 1.0.…”

The Spatial Analysis of an Extreme Wave in a Model Basin

“…A secondorder fit is not realistic above the cut-off frequency since third-and higher order effects are bound to occur. The exact formulation for the cut-off frequency (or cut-off wave number k max ) is taken from [13] and equals: (6) in which σ is the standard deviation of the wave record and N the number of independent amplitudes, estimated from the zero up-crossing period and the duration of the signal.…”

“…In the offshore and shipping industry, the last few years there has been a lot of attention to extreme wave events [1][2][3]. Hurricanes Ivan, Katrina and Rita in the Gulf of Mexico confirmed the importance of these extreme waves for all types of offshore structures [4][5][6][7][8]. At the 'Marco Polo' TLP [8] a maximum wave height of more than 28 m was recorded during hurricane Rita.…”

Full Scale Monitoring Marco Polo Tension Leg Platform

“…During the measurement campaign the Marco Polo TLP already encountered three major Hurricanes; Ivan (in Sep 2004 passed within 120 nm), Katrina (in Aug 2005 passed within 45 nm) and Rita (in Sep 2005 passed within 60 nm), see Figure 2. Measurements on other platforms during hurricane Ivan have been described by Perego (2005), Cox (2005) and Cooper (2005). In this paper the instrumentation of the Marco Polo Proceedings of the 26th International Conference on Offshore Mechanics and Arctic Engineering OMAE2007 June 10-15, 2007, San Diego, California, USA OMAE2007-29635 platform will be described and characteristic results of the ongoing monitoring campaign will be presented.…”