Water-exit dynamics and system identification for a hybrid aerial underwater vehicle

Abstract

Affected by the sudden change of medium, the water-exit process of the hybrid aerial underwater vehicles (HAUVs) brings tremendous challenges to the stable control of these special vehicles, such as complex fluid dynamics and modeling difficulties. In present work, two major challenges are addressed: qualitatively and quantitatively describing the flow mechanisms and accurately modeling the dynamical characteristics for HAUVs during the water-exit process. To achieve this goal, a propeller – and rotor-driven HAUV is numerically studied in detail. Firstly, the time-varying water-exit process is divided into four representative stages, each with different multiphase features, and the evolution of water surface and flow field surrounding HAUV is presented. The influence of rotational speeds of the propeller and the rotor on the dynamical trans-medium process is further explored. Secondly, the dynamic water surface effect (DWSE), exerting on moving rotors and resulting in lift increase, is discussed at length. Compared with the static water surface effect (SWSE), the DWSE leads to a more complex lift variation, and the reasons for the lift deviation between the SWSE and DWSE are speculated. Besides, the influence of the rotor lift under the DWSE on the water-exit motion is explored. Finally, based on Gaussian process, a non-parametric system identification method is proposed to identify the non-parametric dynamical model during the HAUV’s water-exit process. Compared with the existing parametric modeling methods, the predictive accuracy is improved by more than two times, indicating the reliability and efficiency of the non-parametric modeling method. Our work contributes to the elucidation and accurate modeling of water-exit dynamics and lays a good foundation for the stable control of HAUVs in the future, which are of great significance for the design and improvement of the HAUVs.

Topics & Concepts