Numerical Research on a T-Foil Control Method for Trimarans Based on Phase Lag

Abstract

The lift force of a T-foil, which varies with ship motion, can counteract the wave exciting force during wave encounters. The phase difference between the periodic lift force and the wave exciting force significantly impacts the T-foil’s effectiveness. This study investigates the phase difference between lift force and motion to optimize the control equation for the T-foil’s angle, thereby reducing negative feedback. The T-foil’s hydrodynamic performance is first calculated using computational fluid dynamics. Time-domain calculations of the phase lag between lift force and motion under open-loop control in still water are then used to determine the dimensionless phase lag of the T-foil’s angle at various frequencies, facilitating further optimization of the control method. Finally, calculations of trimaran heave and pitch in regular waves are conducted. The results demonstrate that, under phase lag control, the T-foil’s lift force phase precedes ship motion by approximately 0.2 s, reducing hysteresis in the anti-vertical motion effect. Comparisons of vertical hull motions between different control methods reveal a 20% reduction in vertical motion with phase lag control compared to pitch control. This study concludes that phase lag is a crucial factor in T-foil control optimization.