Pipeline Pressure Loss in Deep-Sea Hydraulic Systems Considering Pressure-Dependent Viscosity Change of Hydraulic Oil

Abstract

The high ambient pressure in deep-sea conditions greatly increases the viscosity of hydraulic oil and then the pipeline pressure loss in deep-sea hydraulic systems. Large pipeline pressure loss can lead to a further change of viscosity on the basis of the viscosity increase caused by the ambient pressure when the hydraulic oil flows through the pipeline. Therefore, the classic Poiseuille’s law can no longer accurately calculate the pipeline pressure loss in deep-sea conditions since it treats the viscosity as a constant. In this paper, based on laminar flow theory and the viscosity-pressure characteristics of hydraulic oil, a novel equation for pipeline pressure loss is proposed, in which the viscosity change when flowing through the pipeline is taken into account. A CFD (Computational Fluid Dynamics) model of a pipeline in the deep-sea hydraulic system has been established, and CFD simulations have been conducted to verify the correctness of the proposed equation for pipeline pressure loss. Theoretical analysis shows that the proposed novel equation for pipeline pressure loss is equivalent to the classic Poiseuille’s law when the pipeline pressure loss or the viscosity change is low. The research results in this paper can provide theoretical support for work efficiency optimization, load capacity improvement, and precise control of deep-sea operation equipment or deep-sea hydraulic systems.