The Impact of Shell Geometry on Noise Reduction in Deep-Sea Hydraulic Power Units

In deep-sea environments, Hydraulic Power Units (HPU) are often sealed in cases and placed outside the submersible pressure hull to reduce their size. A pressure compensator balances the pressure in the cases with the external pressure. However, this arrangement decreases stealth performance as the pump's vibration and noise are more easily detected by sonar due to the lack of sound shielding from the hull. This study investigates the influence of geometric characteristic parameters on the noise reduction capabilities of HPU shells in deep-sea environments. Three typical HPU shell shapes (hemispherical, cylindrical, and cubic) and three dimensionless geometric parameters (shell radius-to-sound source radius ratio, shell thickness-to-sound source radius ratio, and aspect ratio) were analyzed to examine sound transmission characteristics over a frequency range of 100–10000 Hz. Results indicate that sea depth has minimal impact on HPU sound transmission loss. Reducing shell size and increasing shell thickness and aspect ratio can improve HPU noise reduction capabilities. In the low-frequency range, hemispherical shells exhibit higher sound transmission loss than cylindrical and cubic shells, and the sound transmission loss of the hemispherical shell is 4 dB higher than that of the cylindrical shell and 12 dB higher than that of the cubic shell at 1000 Hz at the basic settings; however, compact arrangement of hydraulic components within hemispherical shells presents a challenge. These findings provide valuable guidance for HPU shell design in deep-sea equipment to enhance environmental protection and stealth capabilities.