Experimental investigation on hydrodynamic response of pump-free transport system in regular waves

• Safe fiber rope tension levels (dynamic amplification factor < 1.2) across all operational phases. • Reduced pitch and roll accelerations of the STW under loaded conditions. • Tension inversely correlated with wave period and increased with wave height. The growing demand for critical metals has intensified global interest in deep-sea mining, but conventional pump-based systems face environmental and operational challenges. This study proposes a novel Pump-free transport system (PFTS) utilizing a winch-controlled mechanism with a suspended storage and transport warehouse (STW) and ultra-high-molecular-weight polyethylene (UHMWPE) fiber ropes. Through scaled physical model tests (1:25) under regular wave conditions, the hydrodynamic responses were systematically investigated. Results demonstrate that fiber rope tension maintains safe levels with dynamic amplification factors below 1.2 (peak tension: 85.498–98.490 N), while loaded conditions reduce pitch and roll accelerations by 25.0 % and 15.4 % respectively compared to unloaded states. Spectral analysis reveals distinct response characteristics: unloaded STW exhibits near wave-following behavior at 0.78–0.82 Hz, while loading induces a 20 % frequency shift to 0.66–0.70 Hz due to increased inertia, with no signs of resonance. Tension correlates inversely with wave period and increases with wave height, confirming the system's operational robustness. These findings validate the PFTS as a technically feasible and environmentally sustainable solution for deep-sea mineral transport.