Current Developments in the Validation of Numerical Methods for Predicting the Responses of an Ocean Thermal Energy Conversion (OTEC) System Cold Water Pipe

Abstract

Ocean Thermal Energy Conversion (OTEC) was a subject of intense research in the late 1970s and early 1980s in response to a historical jump in oil prices from the 1973 oil embargo. The principal author for this paper first met Prof. Paulling as a participant in a National Research Council (NRC) Panel to review OTEC Technology around 1982. Prof. Pauling had authored a frequency domain program to analyze the coupled response of a platform and OTEC pipe. The author was involved in model tests to validate the program. The United States (U.S.) Department of Energy (DoE) and National Oceanic and Atmospheric Administration (NOAA) had sponsored this work, along with the development of other numerical methods. Shortly after the NRC completed its review, oil prices fell and interest in renewable energy, including OTEC, evaporated. Fast forward to the 2000s, the price of oil skyrocketed again, and OTEC research saw a rebirth. Lockheed Martin and others have been working on new OTEC designs over the course of the last several years. As was the case thirty-five years ago, the cold water pipe remains a key technical challenge. A commercial scale OTEC plant requires a pipe diameter of about 10-meter (m) and a length of 1,000m to pump about half the average discharge of the Colorado River from the deep ocean to the surface and through heat exchangers. Because of the large effective mass of the CWP and entrained water, the dynamic response of the OTEC CWP and the platform can only be considered as a coupled system. This conclusion is not new, but is worth repeating and doubly important to consider when the supporting platform is a semi-submersible as opposed to a large water plane ship shaped vessel. A new generation of software is available to analyze the cold water pipe-platform responses, including the important effect of the fluid flow inside the pipe and the local effects at the connection of the pipe to the platform. The DoE and Lockheed Martin recently sponsored a 1:50 scale wave basin model test of a commercial OTEC platform with an elastically scaled model of a 10m pipe. The purpose of the test was to validate the use of current software for the large CWP diameters in the designs of a pilot or commercial systems in the near future. This paper will briefly review past work on the OTEC cold-water pipe and present the current state of the art in numerical modeling and the results of the model tests recently completed. It will include recommendations for further experimental and numerical work to be prepared for the future design of OTEC systems.

Experimental investigation on the dynamic responses of a free-hanging water intake riser under vessel motion

“…The difference is that the local response of the WIR will be affected by the riser responses at nearby locations (spanwise correlation), this is seen in the discrepancy on N mainly at station No. 16. The similarity is that considering the WIR has a local KC number ranging from 1.9 to 25.5(based on Fig.…”

“…Luis [15] conducted a large scale field test on WIR connected to a barge, he reported the modal frequency dependent pipe added mass coefficients were in the range from 0.26 to 0.78. Recently, Halkyard [16] conducted a WIR model test in an ocean basin, which mainly focused on the riser global dynamic responses under vessel motion. However, other WIR responses, such as internal flow effect and vortex induced vibrations were not addressed.…”

Vibrational Responses of an Ultra-Large Cold-Water Pipe for Ocean Thermal Energy Conversion: A Numerical Approach

“…Cao et al [13] conducted model tests to explore the global responses of a CWP generated by low bending modes and their curvatures, which the analytical model after calibration effectively anticipated. Halkyard et al [14] reviewed prior work on an OTEC CWP and discussed the present state of numerical modeling and Research has focused on applicable mechanical issues in the cold-water pipe (CWP) system ever since ocean thermal energy conversion (OTEC) was first proposed. McGuinness and Scotti [9] reported a substantial CWP development program sponsored by the United States Department of Energy (DoE), encompassing design, analysis, and at-sea testing.…”

“…Cao et al [13] conducted model tests to explore the global responses of a CWP generated by low bending modes and their curvatures, which the analytical model after calibration effectively anticipated. Halkyard et al [14] reviewed prior work on an OTEC CWP and discussed the present state of numerical modeling and the results of recent model testing. He et al [15] examined the contribution of bottom tension and top tension to the vibration problem of a CWP using robust adaptive boundary controllers.…”

Comportamento dinâmico de um riser captador de água do mar

“…O uso de risers captadores de água foi inicialmente proposto pela planta Ocean Thermal Energy Conversion (OTEC) no final dos anos 70. Os desenvolvimentos passados da OTEC e o seu estado da arte atual podem ser encontrados na revisão feita por Halkyard et al (2014). Ao longo dos anos, vários estudos foram realizados através de experimentos e simulações numéricas com o intuito de avançar no projeto conceitual do captador.…”