Time-Domain Seakeeping Simulations for a High Speed Catamaran with an Active Ride Control System

This paper describes time-domain seakeeping simulations for a high speed wave piercing catamaran with an active ride control system, and the validation of the simulations using data from full-scale sea trials. The simulations are performed using the Large Amplitude Motion Program (LAMP), a time-domain potential flow panel code that solves the 3-D wave-body hydrodynamics and rigid-body dynamics problems. The lift forces produced by ride control devices such as trim tabs, interceptors, and foils are modeled as external forces in the time-domain simulation. The paper describes several modifications to the modeling of active ride control systems in LAMP, including the development of new models for the lift forces on trim tabs and interceptors. Validation studies have been performed with LAMP for catamarans without ride control systems (Zhang et al. 2003), but there has been very little validation of the program for vessels with active ride control systems, in part because the availability of suitable seakeeping data for high speed vessels with active ride control systems is very limited. Seakeeping model tests are usually performed without active ride control systems because the small size of model-scale fins, trim tabs, and/or interceptors would result in significant scaling effects, thereby limiting their value. When using data from full-scale trials for validation, the uncertainties relating to the direction and variability of the wave field can be considerable. The details of the ride control algorithm and gain settings used during the trials were unknown, but the time history of the trim tab and Tfoil deflection angles were recorded. The general PID control algorithm in LAMP was used with the controller gains adjusted to match the RMS foil and tab deflection angles measured during the trials. The results from the time-domain simulations are also compared with previously published simulations from frequency domain seakeeping simulations of the same catamaran and active ride control system performed using the VERES seakeeping code (Hughes 2010). The LAMP time-domain simulations are able to model some non-linear aspects of the ride control system that cannot be modeled in a linear frequency domain simulation, such as the nonlinear lift curve for interceptors and the reduction in lift on foils from stall and cavitation inception.