An isomorphic Froude scaling approach to bulbous-bottomed buoys in wave energy converters for smart floating cities

Testing full-scale point absorber buoys with enhanced power absorption is challenging and crucial to improving their viability for applications in smart floating cities and marine infrastructure. Bulbous-bottomed (BB) buoys are efficient in hydrodynamics and power absorption for point absorber wave energy converters (PA-WEC). Their experimental validation demands adaptable scaling algorithms to facilitate model-scale tests. This study utilizes a state-of-the-art theoretical algorithm by combining Froude scaling with an isomorphic buoy design approach, facilitating model-scale tests to investigate whether the BB buoys would equally be efficient compared to the reference hemispherical-bottomed (CHS) buoy when deployed and tested experimentally under identical conditions. Additively manufactured scaled buoy models were tested in a laboratory-scale wave flume in both regular waves (inside and outside resonance) and irregular waves, followed by a similarity analysis for performance prediction on the prototype scale. A feasibility study was also established to justify the BB buoy application in real-time PA-WECs. The BB buoys outperformed the CHS buoys within and without resonance in regular and irregular waves, justifying that they can replace them for good. Under the same deployment and test settings, the model-scale BB buoy exhibited a 20$-$27 % greater heave motion than the reference without resonance. A full-scale BB buoy could absorb significantly greater wave power than the reference. The case study showed that a CHS-to-BB transition resulted in a 35 % rise in the capture width ratio of a WEC. The WEC, combined with a 5G-IoT and LSTM network, could facilitate self-powered and self-sensing marine applications in a smart floating city.