Trans RINA, Vol 157, Part A3, Intl J Maritime Eng, Jul-Sep 2015
particular, it is not clear what is the best control algorithm for linking detected ship motions to control surface activity.
Figure 1: Location of the T-Foil and the trim tabs on the 112m INCAT Tasmania catamaran vessel [1].
Although an active ride control system is installed in the 112m INCAT Tasmania wave-piercer catamaran, the 2.5m hydroelastic segmented model used for model tests [10] does not currently include an active ride control system. Trim tabs are installed in the model but they are statically mounted and no T-foil is currently fitted. Therefore a model scale T-foil has been developed to fit to the model. Figure 2 shows a photo of the electrically activated model T-foil. The overall aim of the model scale ride control system is the evaluation of the effect of ride controls on motions and loads at model scale under more controlled conditions than is possible at full scale. Model scale motions and loads data, in conjunction with numerical computations and full scale sea trials data will ultimately assist in the optimisation of motion control system algorithms, leading to improved ship motions, passenger comfort and reduced structural loads. Full- scale data of foil and tab loads is difficult to measure and so is not available as it has not been measured directly.
In order to optimise the ride control system and design an appropriate algorithm to control ship motion, it is necessary to effectively activate the control surfaces according to vessel response. Some studies of the lifting performance of model
scale trim tabs have been
undertaken at the University of Tasmania [6, 9]. The present work investigates the lift and drag characteristics as well as frequency response of the model T-Foil by both static and dynamic tests. As the T-Foil is to be used in the ride control system and its angle of attack is to be changed based on the measured unsteady heave and pitch motion and designated algorithms, it
is important to
conduct dynamic tests on the T-Foil to investigate its performance prior to installation for testing on the 2.5 m hydroelastic catamaran model [11].
Owing to the small scale of the model T-foil it necessarily operates at low Reynolds Number and this creates uncertainty in predicting its lift performance. Predictions of lift performance are also complicated by the relatively low aspect ratio of the planform (AR = 3.6) which tapers strongly towards the foil tips. At a model test speed of approximately 2.7 m/s simulating a full- scale speed of 35 knots the T-Foil Reynolds Number is 105,305 which is sufficiently large that the lift performance is not expected to be diminished by laminar
A-176
separation [12]. In the present investigation the combined effect of both aspects of low Reynolds Number and low aspect ratio on T-foil performance for a realistic design is to be confirmed in terms of similar research on two dimensional low Reynolds number foils [13-16] and low aspect ratio lifting wing theory. It was expected from previous investigations that this model scale T-Foil will perform acceptably as a control surface on the bow of a 2.5 m hydro-elastic segmented catamaran model, but the precise detail of the lifting performance needs to be known. Whilst the primary application considered here is to the INCAT Tasmania wave piercing configuration, similar ride control systems can of course be applied also to other types of vessels
such as Trimarans and
SWATHs. Foil immersion is in general sufficiently deep that Froude number is not significantly relevant to the performance of a submerged T-foil.
Figure 2: Electrically activated model T-foil. 2. APPARATUS AND INSTRUMENTATION
All the experimental tests were carried out in a closed circuit circulating water tunnel in the University of Tasmania Hydraulics Laboratory (Figure 3). The water
©2015: The Royals Institution of Naval Architects
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