Experimental investigation on mooring tensions of a single semi-submersible offshore floating photovoltaic platform

Offshore floating photovoltaic systems are increasingly regarded as a promising solution to alleviate land-use constraints and exploit abundant solar resources in marine environments. This study conducts time-domain measurements to investigates the mooring tension responses of a semi-submersible offshore floating photovoltaic platform based on 1:25 physical model tests under both regular and irregular wave conditions. A series of experiments covering multiple combinations of wave heights and periods was conducted to systematically measure and analyze the tension characteristics of mooring lines. Results show that, under regular waves, the peak and mean tensions of windward mooring lines are significantly higher than those of the leeward side, with maximum values occurring under short-period and high-wave conditions, and when the wave height was 2 m and the wave period was 4 s the peak windward tension reached 2.8 t, over 2 t higher than the leeward side. At a constant wave height, tension decreases with increasing period, and for the regular-wave cases at 2 m the windward mean tension dropped from about 1.16 t at 4 s to 0.14 t at 7 s (≈ 88% reduction), indicating a strong sensitivity to wave period. The vibration amplitude of windward mooring lines also exceeds that of the leeward side, especially in short-period cases. Under irregular waves, the overall variation trend is consistent with that of regular waves, but with wider fluctuation ranges due to wave group effects. The findings reveal a coupled influence of wave height and period, where short-period and large waves are more likely to induce extreme tensions. This work provides quantitative insights into mooring system design and safety assessment, supporting the long-term operation and wave-resistance optimization of offshore floating photovoltaic platforms.