An Experimental Investigation of Ride Control Algorithms for High-Speed Catamarans Part 2: Mitigation of Wave Impact Loads

Abstract

High-speed craft frequently experience large wave impact loads due to their large motions and accelerations. One solution to reduce the severity of motion and impact loadings is the installation of ride control systems. Part 1 of this study investigates the influence of control algorithms on the motions of a 112 m high-speed catamaran using a 2.5 m model fitted with a ride control system. The present study extends this to investigate the influence of control algorithms on the loads and internal forces acting on a hydro-elastic segmented catamaran model. As in Part 1, the model active control system consisted of a centre bow T-Foil and two stern tabs. Six motion control feedback algorithms were used to activate the model scale ride control system and surfaces in a closed loop system: local motion, heave and pitch control, each in a linear and nonlinear application. The loads were further determined with a passive ride control system and without control surfaces fitted for direct comparison. The model was segmented into seven parts, connected by flexible links that replicate the first two natural frequencies and mode shapes of the 112 m INCAT vessel, enabling isolation and measurement of a centrebow force and bending moments at two cross-sections along the demi-hulls. The model was tested in regular head seas at different wave heights and frequencies. From these tests it was found that the pitch control mode was most effective and in 60 mm model scale waves it significantly reduced the peak slam force by 90% and the average slam induced bending moment by 75% when compared to a bare hull without ride controls fitted. This clearly demonstrates the effectiveness of a ride control system in reducing wave impact loads acting on high-speed catamaran vessels. Nomenclature a Distance between centre of elastic link and centreline of the demi-hull pin joint mount (m) b Distance between centre of starboard and port elastic links of centre bow transverse beams (m) c Distance between centreline of forward and aft centre bow transverse beams (m) C Lα Control surface lift coefficient derivative (dC L /dα) (dimensionless) ! Differential strain measured on elastic link α ST Stern tabs angular deflection (radian, positive producing upward lift) α STd Control system demand stern tabs angular deflection (radian, positive producing upward lift) α TF T-Foil angular deflection (radian, positive producing upward lift) α TFd Control system demand T-Foil angular deflection (radian, positive producing upward lift)

An experimental investigation on slamming kinematics, impulse and energy transfer for high-speed catamarans equipped with Ride Control Systems

“…Linear gains ensured that control deflections only just reached maximum possible amplitudes whereas nonlinear gains always employed maximum up or down control forces subject to the constraint of the control surface slew rates (approximately 300°/s) between these conditions. Whilst the intent of the model RCS feedback settings was to produce motion damping, significant phase shifts in the small model scale feedback system resulted in control actions which effectively included additional motion stiffness effects [7,8]. As will be seen this was a beneficial aspect of the model RCS system.…”

“…A comprehensive literature review of RCS has been previously presented by the authors [7,8]. Although some studies on ship motions and motion control systems have been undertaken by numerical computations, experimental investigations and full-scale sea trials , there is still limited knowledge on the mechanisms of the whole motion control system and to date there has been little published work on their optimum mode of operation.…”

“…The other study by the authors [8] investigated the influence of the ride control system on the structural loads, including vertical bending moments and wave induced slam loads on the central bow. From this investigation it was found that the pitch control mode was indeed the most effective and in 60 mm model scale waves (full scale 2.69 m) it significantly reduced the peak slam force by up to 90% and the average slam induced bending moment by up to 75%, when compared to a bare hull with no ride controls fitted [8]. This clearly demonstrated the effectiveness of a ride control system in reducing wave impact loads on high-speed catamarans that could be a significant consideration for the future design of this type of vessel.…”

Wet-deck slamming loads and pressures acting on wave piercing catamarans

“…Examples of relevant studies for motion and wet-deck slamming in catamarans can be found in [27][28][29][30][31][32][33][34][35][36].…”

Slam loads and pressures acting on high-speed wave-piercing catamarans in regular waves

“…Several model experiments in irregular [17,18,30] and regular waves [1,14,16], including systematic tests on CB designs [5,6,31] and ride control performance [32,33] have been conducted over the past decade to identify slamming loads and motions of WPCs in various operational conditions. However, very few have measured pressure, especially in combination with slam loads.…”