SEAKEEPING PERFORMANCE AND HYDRODYNAMIC RESPONSE OF AN OCEAN BUOY: A MODEL-SCALE INVESTIGATION

Abstract

Seakeeping performance and hydrodynamic response play a critical role in the design and operation of ocean buoys used in offshore applications. Ocean buoys are widely used for offshore monitoring, wave energy harvesting, and marine navigation, where maintaining stable hydrodynamic behaviour is essential. Their seakeeping performance—defined by stability, motion response, and resistance to environmental loads—determines the effectiveness and durability of these systems. This study addresses the need for experimentally validated data to improve buoy design under realistic sea conditions. A 1:5 scale model of a floating ocean buoy was experimentally analysed under irregular wave conditions. The moment of inertia was calculated using the bifilar pendulum method, which provided accurate values for both the buoy and associated setup components. Wave calibration was carried out via Power Spectral Density (PSD) analysis using the Welch method, producing a significant wave height of 120 mm and closely matching the JONSWAP spectrum, thus ensuring realistic hydrodynamic conditions. To evaluate motion behaviour, Response Amplitude Operators (RAOs) were measured using optitrack motion sensors and cross-spectral density analysis. The results revealed strong frequency-dependent resonance in heave RAO (140.84 and 18.28), indicating amplified vertical motion at certain wave frequencies. In contrast, pitch RAO values were significantly lower (9.002 × 10⁻⁵ and 4.6907 × 10⁻⁵), confirming minimal angular instability. These findings suggest that while the buoy exhibits notable heave response under resonant frequencies, it maintains excellent pitch stability—an advantageous trait for offshore deployment. The study demonstrates the importance of mass distribution, spectral calibration, and frequency response analysis in buoy design.