Slam excitation scales for a large wave piercing catamaran and the effect on structural response

A unique slamming process is observed on high speed wave piercing catamarans (WPCs) such as those manufactured by INCAT Tasmania (shown in Fig. 1). For conventional catamarans, wet-deck slamming constitutes a significant design load and is managed through proper design of the tunnel height for the proposed operating conditions. While methods have been developed for prediction of wet-deck slam occurrence and slam magnitude in conventional catamarans (for example Ge et al., 2005) the significant differences in geometry limit application to wave piercing catamarans. Although slamming of wave piercing catamarans may be categorised as a wet-deck slam, the INCAT Tasmania wave piercing catamarans include a forward centre bow to prevent deck diving which significantly alters the water entry and slamming characteristics

Effect of Slam Force Duration on the Vibratory Response of a Lightweight High-Speed Wave-Piercing Catamaran

When the surface of a ship meets the water surface at an acute angle with a high relative velocity, significant short-duration forces can act on the hull plating. Such an event is referred to as a slam. Slam loads imparted on ships are generally considered to be of an impulsive nature. As such, slam loads induce vibration in the global hull structure that has implications for both hull girder bending strength and fatigue life of a vessel. A modal method is often used for structural analysis whereby higher order modes are neglected to reduce computational effort. The effect of the slam load temporal distribution on the whipping response and vertical bending moment are investigated here by using a continuous beam model with application to a 112 m INCAT wave-piercing catamaran and correlation to full-scale and model-scale experimental data. Experimental studies have indicated that the vertical bending moment is dominated by the fundamental longitudinal bending mode of the structure. However, it is shown here that although the fundamental mode is dominant in the global structural response, the higher order modes play a significant role in the early stages of the response and may not be readily identifiable if measurements are not taken sufficiently close to the slam location. A relationship between the slam duration and the relative modal response magnitudes is found, which is useful in determining the appropriate truncation of a modal solution

An Experimental Investigation of Ride Control Algorithms for High-Speed Catamarans Part 1: Reduction of Ship Motions

Ride control systems are essential for comfort and operability of high-speed ships, but it remains an open question what is the optimum ride control method. To investigate the motions of a 112-m high-speed catamaran fitted with a ride control system, a 2.5-m model was tested in a towing tank. The model active control system comprised two transom stern tabs and a central T-Foil beneath the bow. Six ideal motion control feedback algorithms were used to activate the model scale ride control system and surfaces in a closed-loop control system: heave control, local motion control, and pitch control, each in a linear and nonlinear version. The responses were compared with the responses with inactive control surfaces and with no control surfaces fitted. The model was tested in head seas at different wave heights and frequencies and the heave and pitch response amplitude operators (RAOs), response phase operators, and acceleration response were measured. It was found that the passive ride control system reduced the peak heave and pitch motions only slightly. The heave and pitch motions were more strongly reduced by their respective control feedback. This was most evident with nonlinear pitch control, which reduced the maximum pitch RAO by around 50% and the vertical acceleration near the bow by about 40% in 60-mm waves (2.69 m at full scale). These reductions were influenced favorably by phase shifts in the model scale system, which effectively contributed both stiffness and damping in the control action

The influence of the centre bow and wet-deck geometry on motions of wave piercing catamarans

The effects of tunnel height and centre bow length on the motions of a 112-m wave-piercer catamaran with an above-water centre bow were investigated through model tests. Five alternative centre bow configurations were considered, and multiple series of model tests were conducted in regular head sea waves. The results showed that both heave and pitch increased over a wide range of wave encounter frequency as the wet-deck height of the catamaran model increased. However, increasing the length of the centre bow showed an increase in the pitch but a decrease in the heave for a limited range of wave encounter frequency near the heave and pitch resonance frequencies of the catamaran model. The positions of minimum vertical displacement were found to be aft of the longitudinal centre of gravity, between 20% and 38% of the overall length from the transom. Increase in the wet-deck height and consequently the archway clearance between the main hulls and centre bow also resulted in an increase in the vertical displacement relative to the undisturbed water surface in the centre bow area. The results also indicated the vulnerability to wet-deck slamming for the different bow and wet-deck designs

Centre bow and wet-deck design for motion and load reductions in wave piercing catamarans at medium speed

For wave piercing catamarans, the centre bow length and tunnel clearance are important design factors for slamming, passenger comfort and deck diving. This experimental study determined the influence of centre bow (CB) and wet-deck geometry on their motions and loads at reduced speed using five configurations. A 2.5 m hydroelastic segmented catamaran model was tested in regular head seas in wave heights equivalent to 2.7 m, 4.0 m and 5.4 m at full scale. Higher wet-decks had higher vertical accelerations but reduced slamming loads. The greatest peak vertical CB loads ranged between 18–105% of the total hull weight. Regression models were obtained for the vertical loads and bending moments. A reduction of speed from 38 knots to 20 knots reduces the maximum slam loads by approximately 30% in regular waves. Considering both low and high speeds, the Short CB was found to be a consistent design for slamming reduction

The effect of centre bow and wet-deck geometry on wet-deck slamming loads and vertical bending moments of wave-piercing catamarans

An experimental study was performed to determine the influence of centre bow length and tunnel height on the magnitude of the wave slamming loads and bending moments acting on a 112 m Incat wave-piercer catamaran vessel. A 2.5 m hydroelastic segmented catamaran model was tested in regular head sea waves at a high model speed in multiple test series, whilst five centre bow (CB) and wet-deck configurations were considered, designated here as the parent, low, high, long and short CBs. The model global motions, centre bow slam loads, accelerations, and slam induced vertical bending moments of the catamaran model in waves were measured. It was found that the slamming force, the centre bow entry force and slam induced bending moment all increase as the centre bow length increases. Increasing the wet-deck height increased the motions but reduced the maximum slam load in moderate waves. It was seen that the short CB was the best design for the alleviation of slam loads. The high CB was the second best choice for operation in moderate waves but it was the worst configuration in terms of heave and pitch motions among various CB configurations tested

Using Remote Monitoring And Machine Learning To Classify Slam Events Of Wave Piercing Catamarans

An onboard monitoring system can measure features such as stress cycles counts and provide warnings due to slamming. Considering current technology trends there is the opportunity of incorporating machine learning methods into monitoring systems. A hull monitoring system has been developed and installed on a 111 m wave piercing catamaran (Hull 091) to remotely monitor the ship kinematics and hull structural responses. Parallel to that, an existing dataset of a similar vessel (Hull 061) was analysed using unsupervised and supervised learning models; these were found to be beneficial for the classification of bow entry events according to key kinematic parameters. A comparison of different algorithms including linear support vector machines, naïve Bayes and decision tree for the bow entry classification were conducted. In addition, using empirical probability distributions, the likelihood of wet-deck slamming was estimated given a vertical bow acceleration threshold of 1 in head seas, clustering the feature space with the approximate probabilities of 0.001, 0.030 and 0.25