Query: wave-piercing catamarans

title: Wet deck slamming loads and pressures acting on wave piercing catamarans
abstract: The wet deck height and centre bow configuration in wave piercing catamarans are critical design factors which influence slamming occurrence and severity.  In this paper, the wet deck slamming loads and pressures acting on a 112 m catamaran with a centre bow were investigated in regular waves in two wave heights.  A 2.5 m hydroelastic model with three alternate configurations of wet deck vertical clearance was tested at a speed of 2.89 m/s (38 knots full scale equivalent)  The results showed that at the instant of slamming the centre bow immersion depth relative to the undisturbed incident wave elevation was less than two thirds of the maximum immersion depth during the wet deck slam event. The location of maximum slamming pressure was found to be in the range between 77% and 80% of the overall length from the transom. The relationship between the relative velocity at impact and slamming force indicated that slamming loads in the order of the vessel weight can occur for the parent design when the relative velocity at slam is about a quarter of the forward speed.  Overall, increasing the wet deck height was more beneficial for reduction of slamming loads and pressures in smaller waves than in large waves.

title: Design ride control system using two stern flaps based 3 DOF motion modeling for wave piercing catamarans with beam seas
abstract: A ride control system (RCS) based linear quadratic regulator (LQR) and genetic algorithm (GA) design is presented, to reduce the heave, roll and pitch motion (three degrees of freedom motion (3 DOF motion) of the wave piercing catamarans (WPC) in beam waves. A detailed 3 DOF ride control model which consists of the coupling and decoupling relationships between longitudinal and transverse motion is proposed for the WPC vessel. And the complex hydrodynamic coefficients and disturbances induced by beam waves are analyzed. Moreover, two stern flaps are designed for the system in the way of alternate flapping. In the controller design, the LQR method based on GA method is adopted to reduce the 3 DOF motion of the ship. Depending on the robust search mechanism and global optimum of GA, weighting parameters can be obtained to calculate the desired gain. Finally, the motion reduction and motion sickness incidence (MSI) results demonstrate the feasibility and effectiveness of the proposed controller, and the comfort of passengers and crews can also be improved.

title: Slam loads and pressures acting on high speed wave piercing catamarans in regular waves
abstract: Slamming loads and pressures on high speed catamarans with a centre bow (CB) differ from those on conventional catamarans with flat deck structures. The latter are well covered by class rules, which provide empirical formulae to calculate the design slamming pressure. An experimental study was therefore performed to quantify slamming pressures in the archways between bow and main hulls and the CB slamming force on a 112m wave piercing catamaran. The CB length was systematically varied on a 2.5m hydroelastic segmented catamaran model, which was tested in regular head sea waves at a speed of 2.89 m/s, full scale equivalent of 38 knots. Slamming pressures were measured by 18 pressure transducers fitted into the CB, while data obtained from CB accelerometers and load cells enabled identification of the slamming force. The results indicate that slamming loads increase significantly with increasing CB length while the maximum peak slamming pressures varies to a lesser extent. It was also found that wave encounter frequency has a strong effect on the location of maximum pressure along the CB, considerably more so than any influence of CB configuration. The distribution of the peak pressures within the CB archway shows that the inboard peak pressures are larger than those at the top of the arch and the outboard locations.

title: Centre bow and wet deck design for motion and load reductions in wave piercing catamarans at medium speed
abstract: 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.

title: CLASSIFYING BOW ENTRY EVENTS OF WAVE PIERCING CATAMARANS IN RANDOM WAVES USING UNSUPERVISED AND SUPERVISED TECHNIQUES
abstract: 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 geometrically 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 the kinematic parameters. A comparison of different algorithms including linear support vector machines, naive 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 vertical bow acceleration thresholds.

title: The influence of the centre bow and wet deck geometry on motions of wave piercing catamarans
abstract: 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.

title: Design a software real time operation platform for wave piercing catamarans motion control using linear quadratic regulator based genetic algorithm
abstract: This work presents optimal linear quadratic regulator (LQR) based on genetic algorithm (GA) to solve the two degrees of freedom (2 DoF) motion control problem in head seas for wave piercing catamarans (WPC) The proposed LQR based GA control strategy is to select optimal weighting matrices (Q and R) The seakeeping performance of WPC based on proposed algorithm is challenged because of multi input multi output (MIMO) system of uncertain coefficient problems. Besides the kinematical constraint problems of WPC, the external conditions must be considered, like the sea disturbance and the actuators (a T foil and two flaps) control. Moreover, this paper describes the MATLAB and LabVIEW software plats to simulate the reduction effects of WPC. Finally, the real time (RT) NI CompactRIO embedded controller is selected to test the effectiveness of the actuators based on proposed techniques. In conclusion, simulation and experimental results prove the correctness of the proposed algorithm. The percentage of heave and pitch reductions are more than 18% in different high speeds and bad sea conditions. And the results also verify the feasibility of NI CompactRIO embedded controller.

title: Fluid structure interaction simulation of slam induced bending in large high speed wave piercing catamarans
abstract: A ship in waves may experience a water impact event known as a slam. In this paper, slam induced bending of wave piercing catamarans in head seas is predicted by way of fluid structure interaction simulations. The flow field during slamming of a wave piercing catamaran is highly non linear and cannot be accurately captured using potential flow methods as a result of the interactions between the flow fields produced by water entry of the separate demihulls and centre bow. Thus, the Reynolds Averaged Navier Stokes (RANS) equations are solved for rigid body motion of a vessel at model scale. Verification and validation is conducted using model scale data from a Hydroelastic Segmented Model (HSM) One way and two way interactions are computed considering vibration of the hull girder. In the case of one way interactions, the computed fluid loads affect the structure, but the structural response does not affect the fluid domain solution whereas for the two way interactions the structural response affects the fluid solution. A new method for capturing the non linear time variation in added mass is developed and deemed necessary when computing one way interactions, primarily as a result of the large changes in forward wetted area present for a wave piercing catamaran. It is shown that two way interaction simulation is not needed for predicting the slam induced hull girder loads. One way interaction simulation can therefore be used allowing reduced computational effort.

title: Slam loads and kinematics of wave piercing catamarans during bow entry events in head seas
abstract: Centre bow (CB) design for wave piercing catamarans (WPCs) is a critical compromise between minimization of slamming and protection against deck diving. To inform the design process, this article investigates the slam loads and kinematics during bow entry events in regular head seas for a 112 mWPC with systematic variations to its CB and wet deck geometry. Model tests using a 2.5 m hydroelastic segmented catamaran considered five different CB configurations, designated as the parent, high, low, long, and short CB. The results indicated that changes in the CB length had little effect on the general kinematic trends obtained for the pitch, heave, and bow vertical displacement at the instant of slamming, but increasing the wet deck height resulted in an increase in heave (but not pitch) at slamming. Two new design ratios are proposed. The CB immersion depth to arch height ratio showed slamming occurring in the range of 0.3 0.6 depending on the wave encounter frequency and the CB configuration. The CB buoyancy in the encountered waves was estimated by considering both immersion depth and area along the CB in waves through relative motion analyses. It was found that the buoyancy to slam force ratio increased with increasing wet deck height but not with increasing CB length. This suggests that an optimal CB configuration could be achieved by first modifying the arched cross structure to reduce the arch filling effect on slamming severity and then maximizing the CB buoyancy to slam force ratio by increasing either the wet deck height or the CB length.

title: The effect of centre bow and wet deck geometry on wet deck slamming loads and vertical bending moments of wave piercing catamarans
abstract: 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.