Seakeeping control of HYSUCATs

[摘要] This thesis investigates practical methods of modelling and control of the verticalmotions of a hydrofoil assisted catamaran, the HYSUCAT. The aim of thecontrol application is to reduce the motions, and consequently the motionsickness of the passengers.First, a potential flowcommercial program, POWERSEA,was used to modelthe system. This uses 2-D strip methods to model the planing hull-form ofthe vessel, and the Peter du Cane hydrofoil theory for modelling of the foils.These simulations are compared to experimental towing tank results, with fairagreement at lower speeds, but limited applicability at high speeds. Thus forthe control design the agreement was insufficient.As an alternative, a simple coupled 2 degree-of-freedom spring - mass -damper model is proposed, for which the equations of motion are derived.This has 9 unknown parameters; three of these aremeasured directly, two aremodelled, and the remaining four were identified using an experimental parameterestimation technique. Representative parameter values were calculatedfrommultiple experiments for application in the control design.The design of a control system was based on the above model. First, anoutput-weighted Linear Quadratic Regulator (LQR) was designed to obtainthe full state feedback gains. A non-linear 'bang-bang' control design wasthen implemented to try and speed up the response of the system. Thesecontrol strategies, as well as no control, were applied in the towing tank inregular waves, with good results at low and medium frequencies. At the designpoint, 32% and 65% reductions in rms motions were achieved for pitchand heave, respectively. At high frequencies, though, not much improvementwas achieved due to the bandwidth limitation of the control system. The LQRresults were better overall (reduced motions) across the frequency range thanthe bang-bang controller, as well as having a lower added resistance in waves.The control design of the output-weighted LQR was then revised to bebased on alternative outputs, as a possible improvement. However, a furthertwo controller designs did not yield any noticeable improvement and werenot developed further.

[发布机构] Stellenbosch University