Nonlinear dynamic characteristics of suction-vortex-induced pressure fluctuations based on chaos theory for a water jet pump unit

Abstract

To improve the effective use of ocean energy by water jet propulsion pump, it is necessary to study the underwater suction vortex (USV), which affects the propulsion and stealth performance of water jet propulsion pump. This paper analyses the time-frequency and nonlinear dynamic characteristics of the pressure fluctuation induced by USV through high-speed photography and high-frequency pressure fluctuation tests. The nonlinear characteristics of pressure fluctuations under the conditions with and without USV are compared and analyzed based on the chaotic time series analysis theory. The results show that the chaotic characteristics of the pressure fluctuation signal are unaffected by the occurrence of USV. However, the singular attractor structure of the pressure fluctuation signals induced by USV is highly complex, and the largest Lyapunov exponent increases. Therefore, the pressure fluctuation signals induced by USV have stronger chaotic characteristics. Note that the saturation correlation dimension of the pressure fluctuation signal in the period without USV is larger than that with USV, mainly because the influence factor of the pressure fluctuation signal in the USV period is relatively single, which is primarily induced by USV. The nonlinear characteristics analysis of the pressure fluctuation signal can effectively identify the presence of USV.