ABSTRACT

The rapidly expanding need for better Oceanographic and environmental design criteria for offshore installations and environment prediction has prompted a new interest in buoy technology. Many buoy installations have been made in the ocean with little knowledge concerning their dynamic performance under environmental extremes such as result from the passage of a hurricane. This paper presents a digital computer analysis of the nonlinear buoy movement under such wave and current action.

Dynamic buoy response is considered in three widely separated areas of the United States. The areas considered include the northern Gulf of Alaska [offshore from Alaska], the Texas coast, and the Atlantic coast offshore from New Jersey. Each of these areas is considered to be a likely petroleum production province. Further, each area is subject to different environmental means and extremes.

The computer program used for design purposes in this paper-gives buoy response curves for a given set of buoy and ocean parameters. Typical parameters which may be varied are buoy size, weight, drag coefficient, inertial coefficient, virtual mass coefficient, ocean depth, buoy depth, wave height and period, current profiles, and buoy initial displacement and motion conditions. Previous information about the area in question [such as typical ocean depth, wave characteristics, and current magnitude and direction] is used in establishing initial design conditions. Buoy mounted instrumentation can be used to correlate the environmental parameters with the actual buoy response.

INTRODUCTION

The oil and gas industry is currently spending about $2.5 billion a year on the development of offshore petroleum reserves. During the last year alone, $1.9 billion were invested in new leases offshore from Louisiana, Texas and California. It is estimated that oil industry investment will exceed $25 billion within the next decade. Spurring this investment are predictions that petroleum reserves of 86 billion bbl of oil and 100 trillion cu ft of gas will be found on the continental shelf area of the world. In addition to oil and gas developments, certain petroleum-oriented companies have begun to invest in subsidiaries who are evaluating all types of undersea resources including food and drugs.

The President's National Council on Marine Resources and Engineering Development has recently stated, "How fully and wisely the United States uses the sea in the decades ahead will affect profoundly its security, its economy, its ability to meet increasing demands for food and materials, its position in the world community, and the quality of the environment in which its people live." This commission report urges greatly accelerated development of environmental data such as may best be obtained by offshore buoy systems.

The military importance of better oceanographic data which may be obtained by ocean buoy systems can hardly be overemphasized. Knowledge of winds; waves; tides; currents; temperature; pressure; salinity and other oceanographic parameters which can be measured by buoy systems are of critical importance in anti-submarine warfare and in ocean weather predictions. Technology already exists for interrogating buoy systems from passing vessels or satellites. This capability has greatly increased buoy-system potential for telemetering environmental factors data to key use centers.

Since taut-line buoy systems are subject to movement which is difficult to predict by linear-wave theory; many open ocean data gathering projects have resorted to tripod buoy mooring systems.

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