OTEC Cold Water Pipe Program Status

Abstract

ABSTRACT In this paper, the results and current work efforts of the Ocean Thermal Energy Conversion (OTEC) Cold Water Pipe (CNP) program will be presented. The program, sponsored by the Department of Energy and developed and technically managed by the National Oceanic and Atmospheric Administration, is one of the largest civil ocean engineering activities underway at the present time. The uniqueness of the OTEC GNP is derived from its physical magnitude, namely, pipes that are being designed with a diameter of 9 meters" and a length of 1000 meters. Details of the three phases of the program: the analytical procedures used to predict pipe responses, the model test projects and the large scale at-sea tests, will be discussed. The procedures used in planning the program will be highlighted. Problems and their solutions will be specified. Projects currently underway or just completed will be synopsized. INTRODUCTION The cold water pipes (GNP) required in Ocean Thermal Energy Conversion (OTEC) Plants present a formidable challenge to ocean engineers and marine constructors. The GNP size alone is impressive: 1000 meters in length, 9 meters to 30 meters in diameter depending on the OTEC plant size. The magnitude of the pipe forces and the pipe structural responses, plus pipe development and deployment procedures, pose additional problems for the designer. The uniqueness of the GNP as a marine structure, however, lies not so much in its unprecedented mass as in its need to be a flexible structure which interacts dynamically with the hostile ocean environment. This factor amplifies the concern for structural fatigue to the point where only abnormally low stress levels can be tolerated and factors of safety based on stresses alone become meaningless. There is only one GNP in an OTEC plant, which must be designed to survive all environmental conditions for the duration of the plant, namely, 30 years, and not be damaged nor cause damage to the other parts of the OTEC plant. A federal program has been formulated over the past four years, directed toward the solution of the major GNP problems. The end products of the program will be designs, data and procedures that can be utilized in the final design and development of several viable alternative GNP concepts. In this paper the current status of the CWP program will be presented. The program formulation will be discussed and the major elements of the program will be explained. PROGRAM OUTLINE The original concept of an OTEC GNP was that it was a simple vertical tube appendage attached rigidly to an OTEC platform. By making the pipe large in diameter, the cold water flow could be limited to 2 meters/sec to reduce pipe head losses to a minimum. To ensure pipe survivability, pipe concepts were made rigid from such materials as concrete and steel.