Longituidnal motion simulation and stability analysis of SWATH
Abstract: SWATH is a kind of new high performance ship with the excel seaworthiness.The stability of the longitudinal motion of SWATH is the important part of SWATH stability. This paper analyzes stability of longitudinal motion of SWATH according to Routh – Hurwitz stability criterion. A simplified method to determine stability of longitudinal motion and to calculate the critical speed for engineering purpose is introduced.
The simulation of longitudinal motion of SWATH is mainly about the simulation of the longitudinal motion performance of SWATH in regular and irregular wave. According to the simulation results, the longitudinal motion performance of SWATH and the distinction between the situation with stabilizing fins and that without stabilizing fins were analysed
The restoring moment of the longitudinal motion of SWATH is small because of the small waterline area. With the speed increasing, MUNK moment acted on the lower hulls increases quickly. The MUNK moment is the main factor that results in the unstability of SWATH. In order to ensure the stability of SWATH, the stabilizing fins can be adopted. And this all can improve the seaworthiness of SWATH.
In addition, the parameters such as position, aspect ratio, area etc. affect stability of longitudinal motion. For example, the forward fin can promote unstability, but it can accelerate the convergence of the longitudinal motion oscillation SWATH. And it is usually used in combination with the tail fin. The area of forward fin is also smaller than the tail fin. Increasing the tail area can also improve the stability of SWATH, but it cann’t exceed the structure limit of SWATH.
Keywords: small waterplane area twin-hulls; Munk moment ; longitudinal motion ; Stability criteria