The hurricane metocean conditions presently contained in the 21st edition of API RP2A are in the process of being revised, to account for both the effects of recent major hurricanes as well as changes in understanding regarding the occurrence of severe hurricanes that has taken place since the RP2A conditions were last updated in 1993. This paper contains information on the process used to develop new hurricane metocean conditions, including the hurricane hindcast information used as the basis for the conditions and the statistical methodology used to analyze the data. A summary of the present draft version of the new conditions is also included. The new conditions, when accepted by API, will eventually be published as part of a separate stand-alone API recommended practice on metocean conditions which can then in turn be referenced by other API recommended practices covering offshore structures and operations, such as those addressing shallow-water fixed platforms, jackups, deepwater platforms, and floating MODUs. New draft hurricane metocean conditions are provided for four regions spanning the northern Gulf of Mexico from southern Florida to southern Texas, for all water depths 7.5 m and deeper. The new conditions between 86.5o and 90o W are significantly higher than the conditions currently contained in RP2A, due to the recent severe storms, most notably Opal (1995), Ivan (2004), and Katrina (2005); however, the new conditions in the other three regions are similar to those currently in RP2A. The new conditions are based on the hurricane record from 1950 to the 2005. Unlike common practice in previous hurricane metocean studies, storms before 1950 were excluded from the statistical analysis because the quantity and quality of data available for those storms is considered too uncertain. The division into four regions recognizes the geographical variability of hurricane conditions across the Gulf of Mexico and is an improvement over the uniform conditions described in RP2A. However, a site-specific metocean study is the only way to more thoroughly account for regional variability in developing design and operational metocean criteria for major development projects. Introduction The arrival of major hurricanes Ivan, Katrina, and Rita, three of the most severe storms on record in the Gulf of Mexico, within two hurricane seasons (2004 and 2005), caused massive interruptions in the production of oil and gas in the Gulf of Mexico due to damage to facilities. Given the impact of these storms, and changes that have occurred in the understanding of hurricane conditions in the Gulf of Mexico since 1993 (the year the conditions in API RP2A were last updated), it was decided by the API Hurricane Evaluation and Assessment Team (HEAT) that the hurricane metocean conditions presently contained in the 21st edition of API RP2A (1) should be re-evaluated and, if necessary, revised. An API Task Group, composed of the authors of this paper, was formed to develop new hurricane conditions. It was also decided that the new hurricane conditions would not be included in API RP2A but would be included in a stand-alone API recommended practice document on metocean conditions, which could then in turn be referenced by other API recommended practices.
The paper decribes the revised guideline design wave force calculation procedure approved for the 20th edition of the API-RP2A WSD and the first edition of the API-RP2A LRFD and contrasts it with the procedures in previous editions of RP2A. It also briefly dicusses the new metocean criteria for the Gulf of Mexico. The revised procedure was developed by the API Task Group on Wave Force Commentary. It embodies research results obtained over the last 25 years. It is a significant revision of the guideline wave force calculation procedures that have been part of the RP2A since the 1976 edition. INTRODUTION The paper decribes the revised guideline design wave force calculation procedure approved for the 20th edition of the API-RP2A WSD1 and the first edition of the API-LRFD2 and contrasts it with the procedure in the 19th edition of RP2A3. it also briefly discuesses the new metocean criteria for the Gulf of Mexico. The intent of the paper is to make personnel involved in structure design and assessment aware of the significant changes in the new editions of RP2A and the bases for these changes. The main reference for this paper is the 20th edition of the RP2A, which has a detailed commentary, with an extensive set of reference, that discusses the basis for each element of the revised wave force procedure. The same information is also contained in the first edition of RP2A LRFD. The revised procedure was developed by the API Task Group on Wave Force Commentary. It embodies research results obtained over the last 25 years. It is a significant revision of the guideline wave force calculation procedures that have been part of RP2A since the 1976 edition. BACKGROUND The task group was formed at the request of API to write a commentary on the existing RP2A procedure. The first task group meeting was held in December 1987 to discuss objectives and scope, and procedures to archieve them. After reviewing the RP2A procedures the task group concluded that a commentary consistent with the existing guideline disign calculation procedures could not be written. A considerable body of new knowlegde on wave forces had been developed since the first guidelines appeared in the 1976 edition of RP2A. Therefore the task group decided to expand the scope by developing new guidelines and a supporting commentary. Before defining the new guidelines, the task group performed a series of wave force comparison studies to (a) ascertain the accurancy of the computer codes in performing wave force calculations for given environmental conditions, force coeffients, and structure geometry; (b) evaluate differences in Gulf of Mexico (GOM) design wave forces that were being used at that time; (c) and evaluate differences in "best" estimates of GOM 100-yr wave forces. Results of these studies showed significant differences in GOM design force levels (up to a factor of two) but better agreement in the "best" estimates of the 100-yr wave forces. And very importantly, the "best" 100-yr wave forces were considerably higher than the values obtained using RP2A. The study, its conclusions, and recommendations were presented to the API Subcommittee on Fixed Systems Criteria In October 1989. Before accepting the higher forces the task group recommended the following (a) set up an API task group to review uncertainties and biases in structural capacity; (b) have the wave force task group complete its work and expand the scope to develop 100-yr hurricane wave, wind, and current criteria for the GOM incorporating the latest hindcasts; and (c) have industry try the wave force recipe to see if it is consistent with experience in the Gulf of Mexico. The Subcommittee supported the recom
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