ABSTRACT

A joint industry program, "Ocean Response to a Hurricane", was conducted by Horizon Marine, Inc. in cooperation with ten oil companies and NOAA. The objective was to observe hurricane-driven gravity waves and ocean currents at the surface, mixed layer, and thermo cline. The development of the air-deployed expendable current profiler (AXCP) made possible, for the first time, a systematic observation and analysis of these velocities during two major hurricanes.

INTRODUCTION

Design engineers and operations managers in the offshore exploration industry have a need for a comprehensive evaluation of the forces induced by ocean currents and surface gravity waves on offshore structures. While currents have always been an important consideration in the planning of operations such as ocean floor pipe laying, on-site loading, and the installation of offshore facilities, engineering standards in the past were primarily concerned with wave-generated stresses. Since more extreme environments and greater ocean depths are now being exploited in search of new resources, the focus of structure design criteria has shifted. In depths over 800 feet, it has been found that it is not waves which constitute the greatest stress components, but currents.

While permanent and transient current features have been surveyed extensively in the past, there is a distinct void in our knowledge of ocean response to extreme weather conditions, i.e., hurricanes and severe extra-tropical storms. Wind induced currents generated in these storms have been directly observed only on a sporadic basis by oceanographic buoys or platform-mounted current meters that were fortuitously located in the path of a passing hurricane. This data deficiency which has impeded the calculation of appropriate engineering standards in the past can now be largely eliminated with recent advancements in measurement and interpretive techniques. The development of the expendable current profiler and its adaptation for air deployment (AXCP) provides the capability to observe ocean velocities and temperature profiles during hurricanes. These data can be evaluated and analyzed using numerical methods and compared to values predicted by ocean response models.

The joint industry program, "Ocean Response to a Hurricane", was conceived and conducted by Horizon Marine, Inc. A consortium of ten oil companies sponsored the project, and NOAA's Hurricane Research Division (HRD) and Office of Aircraft Operations (DAD) provided engineering and operational expertise. The program was a first-ever attempt to systematically survey ocean velocities and temperature perturbations under severe meteorological conditions. Thirty-one AXCP's were deployed in a pre-determined pattern into each of two hurricanes: Norbert in the eastern Pacific and Josephine in the western Atlantic.

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