&nbsp; An Ocean Thermal Energy Conversion(OTEC) is one of the ocean renewable energy which is converted from a temperature difference between surface seawater and deep seawater. In the 1980s, power production on a floating plant has been succeeded by the small scale experiment in Hawaii. &nbsp;The OTEC is considered to have a large advantage of scale, therefore the cost reduction by increasing the scale has begun studying from the 2010s. Adiputra et.al.(2020) proposed a 100MW-net floating plant that converted from a pre-owned ship for an offshore of Indonesia. Such a structure has 800m length and 12m diameter Cold Water Pipe(CWP). The CWP is a bottleneck on increasing the scale of an OTEC plant.&nbsp; The structure of the CWP has some design conditions that are a combination of operating conditions and environmental conditions. In this study, a parked condition and extreme environment are chosen so that we discuss the establishment against Ultimate Limit State(ULS) as a preliminary design. In this condition, the power production is assumed to stop and internal fluid in the pipe or ship is also stationary. The CWP is always exposed to waves, current, and ship motions. In particular, the interaction between the ship-shaped floating body and lateral vibration of a large diameter pipe is considered predominant. To design the CWP, comprehension of a character of the coupled system is reasonable in the preliminary process.&nbsp; In this paper, we formularize the equation of motion of the coupled system in such a way as to facilitate the preliminary design.&nbsp; In the first section of this paper, we derive the equation of motion of the coupled system. The reaction between the ship and pipe is considered as an unknown quantity, thereby both of the equations of motion of the ship and pipe are derived. The pipe is discretized by Galerkin’s method and hydrodynamic forces are linearized. The linear simultaneous equations are setting up by eliminating the reaction. In the second section, the analysis model of the ship, mooring system, CWP, and environmental conditions are shown and compare the presented formula and a numerical simulation. The Response Amplitude Operator(RAO) of the analysis model is calculated by solving the equation of motion and statistics responses in 3 hours can be compared with a numerical simulation by OrcaFlex. As the result of the comparison, the theoretical model is generally consistent with the numerical simulation. In the third section, a parametric study of the CWP is performed by assumed materials and dimensions.

Simplified Formulation of Coupled System Between Moored Ship and Elastic Pipe for Otec Plantship

Paper Proceedings: https://asmedigitalcollection.asme.org/OMAE/OMAE2021/volume/85116

OMAE 2021

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