The influence of vertical towed array on seakeeping performance of a SWATH vessel was investigated in frequency domain by the boundary element method based on the three dimensional translating-pulsating source Green Function (3DTP). Three factors that differ from conventional monohull ships, but may have great influence on SWATH were included in the motion equations, namely the hydrodynamic interaction between the twin hulls, the viscous damping and the effect of the stabilizing fins. Comparisons of motion transfer functions with the experimental results were made to validate the present method. Then the influence of the vertical towed array was added to the motion equations by modifying the added mass, damping coefficients and wave excitation forces. The results indicate that the motion responses of the SWATH vessel decrease with the presence of the vertical towed array, especially at the resonant zone. The reason for this phenomenon lies in the increases of both the heave-heave damping coefficient and pitchpitch damping coefficient.
The ocean towed system serves as an efficient detection device in the oceanographic research and prospection at the present time (Shin, 2012). The towed system generally consists of the surface towing vessel, guide cable, zero buoyancy cable and towed body, where various sensors and detection devices are equipped to carry out different kinds of missions, such as sound detection and geophysical exploration (Choi, 2011). The surface towing vessel generate surge, sway, heave, roll, pitch and yaw motions with the influences of wind, wave and current, while the underwater cable and devices also generate swing and drift motions as a result of current and swell. Since the towing vessel and the towed body are linked together by the cable, critical coupling effect occurs between their motions. With the increasing volume and displacement of the towed body, more and more attention has been paid to the hydrodynamic interaction between the towing vessel on the water and the towed body underwater.
The early research about cable dynamics dated back to Ablow (1983). He established a dynamic model using the finite difference approximation to solve the three dimensional differential equations which describe the motions between the towing vessel and the towed cable. Liao (1997) conducted numerical simulations to study the influence of heave motion of the towing vessel on the dynamic response of the towed body and it was found that the heave motion of the surface towing vessel has significant influence on the first-class towed body. A lot of researchers investigated the steady motion of the towed array with the towing ship sailing at a constant speed or turning circles based on the Ablow's method (Yuan, 2013; Wang, 2015; Zhang, 2013).