Wave-induced coupled dynamics of an OTEC spar platform with cold water pipe: An experimental investigation

Ocean Thermal Energy Conversion (OTEC) is a promising renewable energy technology capable of providing continuous baseload power while simultaneously supporting freshwater production and other deep-seawater applications. As a carbon-neutral energy source, OTEC aligns with global Sustainable Development Goals related to clean energy and climate action. However, the commercial deployment of large-scale floating OTEC plant requires a thorough understanding of the coupled hydrodynamic behaviour of the floating platform and the cold water pipe (CWP), a critical component unique to OTEC plants. Although previous studies have largely focused on individual subsystems and numerical modelling, experimental data for validating floater-CWP interactions remain limited. In this study, experimental investigations were conducted on a spar-supported floating OTEC platform with and without an attached CWP. A 1:175 scale model was developed while maintaining similar hydrostatic characteristics, including draft and centre of gravity, for both configurations. Decay, regular-wave, and random-wave tests were performed to evaluate the influence of the CWP on platform dynamics. The results indicate that the CWP significantly alters the system's natural response characteristics, including a shift in the pitch natural frequency. Compared with the standalone spar, the spar-CWP configuration exhibited approximately 70% reductions in surge and pitch responses, While the heave response varied with wave conditions, reductions of up to 40% and increases of up to 30% were observed, with an average variation of approximately ±14%. Detailed analyses under regular and random waves further highlighted the role of the CWP in modifying platform motion characteristics. The experimental results provide valuable insights into floater-CWP interactions and offer reference data for the future development and validation of numerical models for floating OTEC platforms.