Numerical study on the distance between the propeller with pre-swirl duct and rudder considering fatigue characteristics

Abstract

Recently, there has been increasing awareness about greenhouse gases, resulting in considerable efforts to increase the fuel efficiency of ships and reduce the amount of gases they emit. Thus, pre-swirl ducts (PSDs) have been widely adopted in ships due to their high fuel efficiency. However, attaching PSDs induces a change in the fatigue characteristics of ship structures, as evidenced by the reported crack in the rudder of a ship with an attached PSD. Nevertheless, the arrangement of a ship’s rudder, which is a crucial factor in a rudder’s fatigue characteristics, continues to rely on the empirical rule without any consideration of fatigue characteristics. This study investigated a propeller–rudder interaction distance ensuring fatigue stability with the PSD attachment and developed a procedure for designing it considering fatigue characteristics. In the developed procedure, the fatigue characteristics of rudders due to the propeller wake were obtained through frequency domain finite element method (FEM) analysis utilizing computational fluid dynamics (CFD) analysis results of a rudder’s surface pressure fluctuations. In addition, the potential for fatigue failures in ship rudders was evaluated by employing damage factors. A comparative analysis of rudder fatigue characteristics considering the presence of PSDs revealed that attaching them increased the stresses in the rudder. Furthermore, the analysis results demonstrated that PSD attachment can result in the fatigue failure of rudders. Finally, the propeller–rudder interaction distance of ships with an attached PSD was newly proposed using the developed procedure. The proposed propeller–rudder interaction distance is expected to enable the design of appropriate rudder arrangements for ships with attached PSDs while ensuring fatigue stability.