Prediction Of Hydrodynamic Interference Between SWATH And Fin Stabilizers

Because of its small waterplane area, SWATH has excellent hydrodynamic performance in terms of seakeeping, natural frequency and wave loads. Its added resistance is less than the typical monohull vessels at high speed. However the small waterplane area causes some disadvantages. Munk torque acting on the submerged body leads to serious trim at the high speed, which cause the loss of longitudinal stability and threaten the safety of navigation.Currently,the main measure to solve this problem is to install stabilizers fin between submerged hulls. In this paper, the flow characteristics around the fin and SWATH are studied by using the RANSE solver. After that, the complex flow interference between the fin and SWATH is simulated and analyzed.On the surface of fin stabilizers, it tends to occur transition at the boundary layer. In order to study the impact of the transition on the lift and the near field flow, numerical investigation is conducted for the flow around a 2D NACA hydrofoil. The results show that the transition significantly affects the surface flow around the fin and triggers the vortex shedding at large attack angle. It is indispensable to capture the transition since it has great impact on the lift of the fins.The hydrodynamic features of SWATH are quite distinctive because of its specific structure. In order to have a comprehensive understanding on its hydrodynamic feature, the simulation for flow around the SWATH is conducted . The simulation reveals that there is strongly non-linear interaction between the hulls themselves and meanwhile the resistance and motion is affected by the pressure distribution and the wave interference. In general, the resistance of SWATH is larger twice more than the resistance of the monohull since the thicker boundary layer and adverse wave interference cause the increase of resistance. On the other hand, favorable interference can be observed at several speed, corresponding to situations where the wave systems tend to cancel some waves and decrease the resistance.Meanwhile, the trim is directly related to the magnitude and the position of wave trough and hump.There is a complex hydrodynamic interaction between fins and hulls. The hulls have the effects on the fin lift and the fins also change the SWATH’s navigation performance. The calculation of the SWATH with the fin stabilizers is carried out and hydrodynamic interference between the SWATH and fins is analyzed. The result show that the resistance,trim as well as heave curves are in good agreement with the experimental results. Although stabilizers increase the resistance of the SWATH, they will reduce the value of trim and heave.Further investigations on near field around fins show that hulls have an influence on the incidence angle of fins, resulting in the oscillation of trim curve. Similarly, the fin stabilizers also have an impact on near field flow around the hull. For instance, the distance between the stern fin and propeller is quite small, causing the wake coefficient increased. Meanwhile the vortex produced by fin increases the vorticity of wake. In addition to the interaction between fins and hulls, fins which near the bow will influence the flow around the stern fins. For instance, the larger pitch angle of bowfins tends to increase the actual incidence angle of stern fins.To summarize, this paper makes a deep analysis on the flow around fins and SWATH;clarifies the complex mechanism of hydrodynamic interference between fins and hulls. A complete method to predict the resistance and motion of SWATH with fin stabilizers is presented.