Theoretical and experimental study on the performance of the hydraulic power unit employed on full ocean depth manned submersible

Abstract

With the growing demand for deep-sea exploration and resource development, full ocean depth manned submersibles play a crucial role in these efforts. Within the submersibles, hydraulic power unit (HPU) experiences performance changes due to the high pressure in the deep-sea environments. This study systematically investigates the performance evolution of HPUs in such conditions, focusing on pressure-induced variations in hydraulic oil properties (viscosity, density, and bulk modulus) and their effects on the components. A theoretical model was developed using Amesim to simulate the dynamics of HPU, considering depth-dependent fluid characteristics. Experimental validation was conducted in a high-pressure chamber with an ambient pressure of 115 MPa under no-load and 19 MPa load conditions. It is found that, from the surface to full ocean depth, the power consumption of the HPU increased by 0.792 kW (under no-load conditions) and by 0.825 kW (under loaded conditions). This increase is attributable to the amplified viscous losses resulting from the increased viscosity. Conversely, the enhanced fluid damping effect under high pressure stabilizes the flow output. The theoretical model demonstrated good agreement with the experimental data, confirming its predictive capability for HPU behavior in deep-sea environments. These results provide critical insights into the design of deep-sea HPUs.