The most commonly used under water acoustic equipment on the maritime research vessel, sonar, is usually enclosed by a fairing to reduce the influence of the bubble sweep-down, resulting in additional appendage resistance. It is important to study the appendage resistance and bubble sweep-down phenomenon of a double-screw research vessel. The study focuses on exploring above two aspects based on a RANS solver together with the discrete element method. The pressure and velocity distributions show that the bubble sweep-down is more likely to occur at high speed. The state of the side thruster and draft would affect the bubble motion.
Exploration of marine resources is key to increasing our understanding of the ocean and protection of the maritime ecological environment. Research vessels equipped with special tools and technology are essential for the effective management and use of ocean sources that are vital to economy and our lives. Aiming at providing stable platform to the survey of ocean information and exploration operation, the ocean research vessel often installs a variety of appendages to improve its stability and maneuverability, such as the multi-beam sonar, shaft bracket, rudder, and side thruster. The influence of different appendages on the resistance performance of the research vessel cannot be ignored. Moreover, the multi-beam sonar, as the "eye" of the research vessel, is of great concern at the early design stage, because its functional realization plays a critical role in the accuracy of the research vessel's detection results (Wang, 2020). In practical engineering, the factors that possibly impose limitations on the measurement accuracy of sonar include the mechanical vibration noise, hydrodynamic noise, appendage cavitation, propeller bubble noise, bubble sweep-down, etc. Among them, the underwater bubbles are the most serious consequences, which may aggravate the unsteady dynamic behavior of the fluid flow around the sonar. A fairing is often used to enclose the sonar to smooth the surrounding fluid flow with fewer bubbles, and thus improve the detection performance of the sonar. It is therefore of great significance to study the resistance performance of appendage on research vessels and the bubble sweep-down phenomenon around research vessels.
