Physical model tests of Backward Bent Duct Buoy: A review

Backward Bent Duct Buoy (BBDB) is a special type of oscillating water column wave energy converter. Since its proposal in 1986, BBDB's potential for improving efficiency and practicality has attracted increasing research efforts. Studies have explored the BBDB from different perspectives and proposed diverse design modifications. However, so far, few reviews have focused on physical model tests of BBDB and its variants. The lack of structured summaries and statistical analysis could leave research themes unorganized and conclusions fragmented. Therefore, this review systematically summarizes and categorizes the major monitored indicators (dependent variables) and investigated characteristics (independent variables) in previous studies involving BBDB physical model tests. Key patterns and design insights are identified through statistical examination of data from 102 publications, including an optimal wavelength-to-device-length ratio around 2.2, an average efficiency reduction of 32 % under irregular waves, an optimal nozzle ratio clustering near 1.0 % and energy capture behavior that differs from traditional OWCs as wave tank breadth varies. Furthermore, available information on BBDB sea trial instances is compiled to bridge model-scale results with full-scale performance. This work provides the research community with a consolidated foundation for future research and design optimization, highlighting both a comprehensive compilation of previous studies and underexplored areas requiring future investigation, such as the decoupled and coupled effects of motions, performance discrepancy between turbines and orifices, assessments of variable sensitivity and array interactions.