Wave-piercing Catamaran Research Articles

Reducing wave impacts on high-speed catamarans through deployment of ride control: Analysis of full-scale measurements

Full-scale trials on a 98 m wave piercer catamaran were conducted in the North Sea and North Atlantic region. In order to examine, amongst other things, the effectiveness of the ride control system, the ship was deliberately operated in sea conditions likely to induce a large number of wave impact events. Primary ship motion and structural response parameters, such as angles, rates and accelerations, and strains at various locations were recorded. Slam and minor wave impact events were identified in the data records and analysed to determine the influence of wave headings, vessel speeds, sea states and ride control system activation on their occurrence rates and severity. The Empirical Mode Decomposition technique was used to remove both noise and the rigid body response from the acceleration signals. This was based on prior work by the authors and found to provide more reliable slam identification than traditional methods. A prediction of extreme slam occurrences was modelled using logistic regression. A key outcome of the study was the finding that the activation of ride control significantly reduces the probability of extreme slams occurring.

Comparing linear damage hypothesis to linear elastic fracture mechanics in the estimation of fatigue life in a high speed light craft

Linear elastic fracture mechanics methods provide a more comprehensive representation of crack propagation compared to traditional methods such as the linear damage hypothesis (or SN curve approach). These techniques have been widely adopted in the aerospace industry, however, their usage in the design of marine structures remains limited. The presented research uses full-scale trial data measured onboard a 111 m wave-piercing catamaran to compare the results obtained from linear elastic fracture mechanics and SN curve-based methods. The results reveal significant differences in estimated fatigue life between SN curve-based methods and fracture mechanics methods. These differences are likely due to limitations in the fracture mechanics model during the crack initiation phase. Changes in fracture mechanics parameters also had a significant effect on fatigue life, suggesting that if accuracy is important then material specific parameters are required. Despite the limitations shown, linear elastic fracture mechanics methods have a higher level of tailor-ability when compared to SN curve based methods and could offer benefits in situations such as the tracking of known flaws or in the assessment of changes to vessel configuration, or usage profiles.

A novel CFD approach for the prediction of ride control system response on wave-piercing catamaran in calm water

Ride Control Systems (RCS) on high-speed vessels help improve passenger comfort and mitigate dynamic structural loads. Incat Tasmania Wave-Piercing Catamarans (WPC) use RCS consisting of a central T-foil, and a stern tab on each deli-hull. Previous towing tank studies on a 2.5 m model of a 112 m WPC have demonstrated significant reductions in motions with the use of a T-foil and stern tabs. To extend this work, this study examines the use of Computational Fluid Dynamics (CFD) to predict the ship's response with RCS implemented. The model-scale WPC was simulated in calm water conditions, traveling at 2.89 m/s (Fr∼0.6), with step responses applied at the T-foil and stern tabs, to determine the trim and sinkage. The T-foil was implemented in CFD using two methods: 1) Overset mesh; 2) Forcing function. By replacing the geometric mesh with a lift force coefficient and forcing function, the setup difficulty and computational cost were reduced. Only about 7% difference was observed between CFD and experiments, but no significant difference was found between the methods of overset mesh and forcing function. This has proven the ability of CFD to predict vessel responses to RCS step changes in calm water, and the simplified forcing function method is recommended.

Slamming impact induced hydrodynamic response in wave-piercing catamaran beam elements with controller

When subjected to a slamming load, wave-piercing catamarans may be vulnerable to damage and deck diving. Aluminum beams are one of the key components of catamaran vessels and improving their stiffness and dynamic smart management is crucial to reducing the impact of waves at sea. The numerical analysis and mathematical modeling of the wave-piercing catamaran beam elements are fresh topics that largely depend on smart control issues. Based on a 2D Wanger type impact force model, this work presents a numerical benchmark study for the hydrodynamic analysis and smart control of wave-piercing catamaran beam elements. The Rankine panel approach also takes into account the impact of the wave-piercing catamaran's forward speed. The wave-piercing catamaran's smart control system consists of a proportional-differential (PD) controller with two piezoelectric layers acting as an actuator and a sensor on the top and bottom surfaces of the beams, respectively. Carbon nanotubes (CNTs) are employed as reinforcement to increase the stiffness of porous beams while assuming their agglomeration effects based on the Mori-Tanaka model. Refined zigzag shear deformation beam theory (RZSDBT) is used to mathematically represent the smart structure, and the related motion equations are generated using the energy technique. The differential quadrature method (DQM) and the Newmark method are used to solve the framework in order to capture the dynamic deflection and flexural moment and describe the Gibbs phenomenon. The effects of the controller, externally applied voltage, CNTs as reinforcement, forward speed, modification of shape and pressure distribution, porosity, deadrise angle, and external loads caused by demi-hulls and the cross-deck are all investigated using numerical studies. These studies look at how these factors affect dynamic deflection, flexural moment and Gibbs phenomenon. Regarding the primary goal of this work, the findings showed that the harmful effects can be greatly controlled with a PD controller. In other words, we can state unequivocally that the controller's assistance reduces the pressure distribution's discontinuity or spike while enhancing the beam's dry area. Additionally, the dynamic deflection and flexural moment are decreased by 49% and 37%, respectively, by employing the controller. The use of CNTs as beam reinforcement, which can reduce dynamic deflection and flexural moment by around 50% and 33%, respectively, is another goal of this work.

Estimation of torsional and global loads for a wave-piercing high-speed catamaran at full-scale in irregular bow quartering seas using CFD simulation

Catamarans experience more types of global load than monohulls, these include pitch connecting moment, transverse bending moment, and split force. High-speed catamarans are widely used for passenger transportation but as the speed and size increase the severity of loads rises due to slam induced effects. In this study, full-scale CFD simulations are undertaken to investigate the loads acting on a 98m Incat wave-piercer catamaran (Hull 061) HSV2 Swift. Simulations are performed for conditions of a selected sea trial run in bow quartering seas at 20 knots forward speed undertaken by the Naval Surface Warfare Center, Carderock Division (NSWCCD), enabling comparisons and validation. In order to estimate internal global loads at different sections of the vessel, rigid body dynamics is applied based on the hydrodynamic and inertia forces. Those internal loads include longitudinal bending moment (LBM), pitch connecting moment (PCM), torsional moment (TorM), transverse bending moment (TBM), split force and prying moment. The estimated and measured global loads are also compared with design loads limits provided by DNV GL rules, and peak values of pitch and roll accelerations corresponding to each slam load are determined at the same wave height and wave period as the sea trial. The application of CFD to simulate sea trials runs in oblique seas is shown to provide a reliable estimation of slam induced loads for application in early design stages.

Analysis of slamming loads on a catamaran section with a centre-bow appended by spray rail

ABSTRACT Wave-piercing catamarans have center-bow to diminish slamming pressure and acceleration in sea waves. Bow section modification of marine craft towards low slamming loads is an on-going research topic. This study suggests insertion of a flat-bar, called spray rail, to center-bow to reduce both slamming pressure and acceleration. A section which is called J1-section from previous research is adopted for further modification. Modification is made via appending the spray rail to its center-bow, and the new section is called J1-section with spray rail. Evaluation of the slamming pressure and acceleration of both sections are experimentally accomplished using the water entry test facilities of Amirkabir Laboratory of Hydrodynamics. J1-section with spray rail in comparison with J1-section has shown peak acceleration and pressure drop of about 60% and 70%, respectively. This study suggests that the insertion of appendages to the catamaran sections is a superior solution for the slamming impact load reduction.

Influence of an active T-foil on motions and passenger comfort of a wave-piercing catamaran based on sea trials in oblique seas

In this paper the influence of a Ride-Control System (RCS) on the Response Amplitude Operator (RAO) of a full-scale high-speed catamaran was investigated using sea trials data. A T-foil and stern tabs were installed on a Wave-Piercing Catamaran (Incat Tasmania Hull 061) to improve ship motions and passenger comfort. More than 40 total effective hours of sea trials were conducted by the US Navy in 2004, encountering sea states 4–5 in the Atlantic Ocean near the United Kingdom. The reduction in Motion Sickness Incidence (MSI) was estimated in order to examine the effectiveness of the RCS in improving passenger comfort. By comparing the case of active RCS (T-foil plus stern tabs) with the case of active stern tabs only, it was found that the T-foil plays a vital role in the passenger comfort enhancement. Based on ISO recommended MSI calculation of a 2-h seaway, the percentage reduction in MSI was estimated, and hence the effectiveness of the T-foil deployment, along with the influence of speeds, headings, location on board and encountered wave height were analysed. A notable improvement in passenger comfort was observed in the real world bow quartering sea by deploying the RCS. An MSI reduction of 21% in high speeds (30–35 knots, [Formula: see text] 0.6) was observed, which was almost twice the MSI reduction (11%) in low speeds (15–20 knots, [Formula: see text] 0.3). However, in terms of MSI percentage reduction, the ability of T-foil in vessel motion control in oblique seas was found to be limited compared to the results in head seas.

Fatigue Estimation on a High-Speed Wave Piercing Catamaran During Normal Operations

The estimation of fatigue life in the design process is particularly important for weight-optimised ships such as high-speed aluminium craft, but to date no research has been published on the fatigue accumulation on large wave-piercing catamarans, focusing on long-term operations. This paper assesses the applicability of classification society rules for high-speed catamarans with respect to fatigue design. This was achieved by comparing the long-term distributions of stress, measured on a 111m long wave-piercing catamaran ferry whilst operating in the Canary Islands and during the delivery voyage, with load spectra estimated using a method accepted by the classification society, DNV. The paper also proposes an improved distribution fitment method for fatigue analysis. A detailed method to convert measured stress histories in the time domain into an appropriate stress-spectrum and fitment of Weibull parameters is presented. Results show that the simplified method accepted by the classification society is highly conservative regarding fatigue estimation compared to fatigue results based on measured data. The proposed combined Weibull fitment method substantially improves the accuracy of simplified fatigue analysis methods.

THE INFLUENCE OF CENTRE BOW LENGTH ON SLAMMING LOADS AND MOTIONS OF LARGE WAVE-PIERCING CATAMARANS

The effect of various centre bow lengths on the motions and wave-induced slamming loads on wave-piercing catamarans is investigated. A 2.5 m hydroelastic segmented model was tested with three different centre bow lengths and towed in regular waves in a towing tank. Measurements were made of the model motions, slam loads and vertical bending moments in the model demi-hulls. The model experiments were carried out for a test condition equivalent to a wave height of 2.68 m and a speed of 20 knots at full scale. Bow accelerations and vertical bending moments due to slamming showed significant changes with the change in centre bow, the longest centre bow having the highest wave-induced loads and accelerations. The increased volume of displaced water which is constrained beneath the bow archways is identified as the reason for this increase in the slamming load. In contrast it was found that the length of centre bow has a relatively small effect on the heave and pitch motions in slamming conditions.

HIGH-SPEED WAVE-PIERCING CATAMARAN GLOBAL LOADS DETERMINED BY FEA AND SEA TRIALS

Wave-piercing catamaran hull forms are widely used for high-speed ferry applications due to the hull slenderness, suitable for achieving high speeds. The global loads acting on these craft are of great interest as there is limited knowledge on determining the magnitude of the loads, in particular when operating in random sea conditions. Longitudinal and transverse bending moments as well as pitch connecting moments and hull torsion loads act on the hull simultaneously. This paper investigates the estimation of these global loads from full-scale catamaran sea trials strain gauge data using finite element methods. Det Norske Veritas (DNV) load cases are applied to a finite element model in order to determine the conversion between local strain values observed during sea trials and prevailing global loads. Comparisons are thus made of global loads determined from strain data collected from sea trials with DNV global load cases. The results show that this method is relatively reliable for the prediction of hull global loads in the absence of slamming. Comparisons have been made for different heading angles. The quasi-static design loads are important during the ship design stage, as they are good proxies in wavelengths comparable to the hull length for rationally determined loads obtained from a first-principles dynamic analysis. The broad aims here are to demonstrate the use of strain sensor data obtained during sea trials for determination of global sea loads, to reconcile the loads thus determined with DNV load cases and thereby to improve the accuracy of the predicted loads used in design to increase the structural efficiency of vessel design.

PERFORMANCE PREDICTION OF A 112M WAVE-PIERCING CATAMARAN

The prediction of power required to propel a high-speed catamaran involves the hydrodynamic interactions between the hull surface and the surrounding fluid that may be difficult to compute numerically. In this study model-scale experiments are used as a basis for comparison to full-scale sea trials data measured on a 112m Incat wave-piercing catamaran to predict the full-scale powering requirements from model-scale testing. By completing water jet shaft power measurements on an Incat vessel during sea trials, comparison of these results was made to model-scale test results to provide good correlation. The work demonstrates that the International Towing Tank Conference (ITTC) extrapolation techniques used provide a good basis for extrapolating the data from model-scale to full-scale to predict the power requirements for the full-scale catamaran vessel operating at high Froude Number with water jet propulsion. This provides a useful tool for future designers and researchers for determining the power requirements of a catamaran vessel through model tests.

LOADING RESPONSE OF STERN TAB MOTION CONTROLS IN SHALLOW WATER

The ride control systems of high-speed vessels frequently use active stern tabs for both motion control and maintenance of correct trim at various speeds and sea conditions. This paper investigates the effect of water depth on the lift force provided by stern mounted trim tabs, of the type fitted to INCAT high speed wave-piercer catamaran vehicle ferries and similar vessels. This investigation was carried out at model scale with the use of a test apparatus in a flume tank in the University of Tasmania hydraulics laboratory. The lift force magnitude and location were measured over a range of tab angles and flow depths. This was used to calculate the lift coefficient of the tab and asses the performance of the tab over the range of flow depths. It was found that the lift force increased and the force location progressed further forward of the hinge as flow depth decreased. The lift curve slope of the stern tab increased by a factor of over 3 relative to the deep water value when the water depth below the hull was approximately equal to the tab chord. The deep water lift curve slope appears to be approached only when the water depth exceeded 4 or more tab chord lengths. The centre of pressure of the lift force was more than two chord lengths ahead of the tab hinge, showing that most of the lift produced by the tab was under the hull rather than on the surface of the tab itself.

LOW REYNOLDS NUMBER PERFORMANCE OF A MODEL SCALE T-FOIL

Submerged T-foils are an essential forward component of the ride control systems of high speed ferries. A model scale T-Foil for a 2.5m towing tank model of a 112m INCAT Tasmania high-speed wave-piercer catamaran has been tested for both static and dynamic lift performance. The tests were carried out using a closed-circuit water tunnel to investigate the lift and drag characteristics as well as frequency response of the T-Foil. The model T-Foil operates at a Reynolds number of approximately 105, has an aspect ratio of 3.6 and a planform which is strongly tapered from the inboard to outboard end. All of these factors, as well as strut and pivot interference, influence the steady lift curve slope ( of the model T-foil which was found to be 61% of the value for an ideal aerofoil with elliptic loading. The T-foil dynamic performance was limited primarily by the stepper motor drive system and connection linkage. At the frequency of maximum motion of the 2.5 m catamaran model (about 1.5Hz) the model T-foil has approximately 5% reduction of amplitude and 15 degrees of phase shift relative to the low frequency response. Only very small limitations arose due to the unsteady lift as predicted by the analysis of Theodorsen. It was concluded that the model scale T-foil performed adequately for application to simulation of a ride control system at model scale.

PRESSURE DISTRIBUTION DUE TO STERN TAB DEFLECTION AT MODEL SCALE

Trim tabs form an important part of motion control systems on high-speed watercraft. By altering the pitch angle, significant improvements in propulsion efficiency can be achieved by reducing overall resistance. For a ship in heavy seas, trim tabs can also be used to reduce structural loads by changing the vessel orientation in response to encountered waves. In this study, trials have been conducted in the University of Tasmania hydraulics laboratory using a closed- circuit water tunnel to measure model scale trim tab forces. The model scale system replicates the stern tabs on the full- scale INCAT Tasmania 112 m high-speed wave-piercer catamaran. The model was designed for total lift force measurement and pressure tappings allowed for pressures to be measured at fixed locations on the underside of the hull and tab. This investigation examines the pressures at various flow velocities and tab deflection angles for the case of horizontal vessel trim. A simplified two-dimensional CFD model of the hull and tab has also been analysed using ANSYS CFX software. The results of model tests and CFD indicate that the maximum pressure occurs in the vicinity of the tab hinge and that the pressure distribution is long-tailed in the direction forward of the hinge. This accounts for the location of the resultant lift force, which is found to act forward of the tab hinge.

DETERMINATION OF WAVE SLAMMING LOADS ON HIGH-SPEED CATAMARANS BY HYDROELASTIC SEGMENTED MODEL EXPERIMENTS

A 2.5m hydroelastic segmented catamaran model has been developed based on the 112m INCAT wave-piercer catamaran to simulate the vibration response during the measurement of dynamic slam loads in head seas. Towing tank tests were performed in regular seas to measure the dynamic slam loads acting on the centre bow and vertical bending moments acting in the demihulls of the catamaran model as a function of wave frequency and wave height to establish the operational loads acting on the full-scale 112m INCAT catamaran vessel. Peak slam forces measured on the bow of the model are found to approach the weight of the model, this being similar to the findings of full-scale vessel trials. A review of the motions of the hydroelastic segmented catamaran model found that the heave and pitch motions give a good indication of slamming severity in terms of the dimensionless heave and pitch accelerations. The dynamic wave slam forces are closely related to the relative motion between the bow and the incident wave profile.

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.

Slam load estimation for high-speed catamarans in irregular head seas by full-scale computational fluid dynamics

Global loads acting on high-speed wave-piercing catamarans are investigated using computational fluid dynamics (CFD). Catamaran vessels are subjected to load cases that are not present on mono-hull vessels, such as transverse bending moment, pitch connecting moment and splitting force. As the speed and size of a catamaran increases the severity of loads rises with slam induced effects. Full-scale CFD simulation is undertaken to investigate the pressure distributions and resultant global loads acting on the 98 m INCAT wave-piercer catamaran HSV2 Swift, validated against sea trial tests. Rigid body dynamics are then applied to estimate the internal loads at different sections of the vessel based on the relative hydrodynamic and inertial force distributions. The estimated global loads are then checked according to DNV GL rules by comparing “design load limits”. Global loads are estimated for the 98 m INCAT HSV2 Swift catamaran in headseas at a forward speed of 20 knots. Splitting forces are found to have a longitudinal distribution along the catamaran hull, which causes prying moments. Peak values for LBM are examined relative to corresponding instantaneous wave height prior to the slam event. In addition, it is found that pitch acceleration has a linear correlation with LBM slam loads.

Dynamic analysis in beam element of wave-piercing Catamarans undergoing slamming load based on mathematical modelling

Dynamic analysis of wave-piercing Catamarans undergoing slamming has tracked widespread attention in the design of marine structures. Hence, our investigation on the dynamic response relies heavily on the beam element of wave-piercing Catamarans subjected to slamming load. In the present paper, a numerical method and a mathematical modelling are developed to analyze the dynamic response of beam elements in wave-piercing Catamarans due to impacting moving fluid load. With assuming the initial phase of slamming force, an elastic linear hyperbolic shear deformation beam theory (HSDBT) with uniform thickness is utilized for modelling. For presenting a more realistic model, the porosity and structural damping of the Aluminum beam are considered. In addition, for improving the stiffness of the mentioned structure against the slamming load, graphene platelet (GPLs) are used for reinforcement of the beam. To capture the dynamic deflection of the porous GPL-reinforced beam, differential quadrature method (DQM) along with Newmark method is utilized. The aim of this work is to illustrate the influences of deadrise angle, vertical speed of impact, GPLs volume percent and distribution, geometrical parameters, porosity, structural damping and boundary conditions on the dynamic deflection of the structure. The results indicated that reinforcing the facesheets by CNTs reduces the dynamic deflection up to 59%.

Operation of Ride Control Systems to Minimise Slamming of Wave-Piercing Catamarans

Wave slam produces dynamic loads on the centre bow of wave piercing catamarans that are related to the relative vertical motion of the bow to the encountered wave surface. Rapid slam forces arise when the arch sections between centre bow and main hulls fill with rising water. In this paper time domain solutions for high speed ship motion in waves, including the action of active motion controls, are used to compute the slam forces. Slamming occurs at specific immersions of the bow whilst the peak slam force is characterised by the maximum relative vertical velocity of the bow during bow entry. Vertical motions of bow and encountered wave are in antiphase at encounter frequencies where slamming is most severe. The range of encounter frequencies where slamming occurs increases with wave height. Wave slam loads reduce ship motions, the heave motion being most reduced. Deployment of a fixed, inactive T-foil can reduce slamming loads by up to 65 %. With active controls peak slamming loads on the bow can be reduced by up to 73% and 79% in 4 m and 3 m seas, local control feedback being marginally the most effective mode of control for reduction of slamming.

Hydrodynamic and Structural Investigations of Catamaran Design

The type of hull in the catamaran is developed by following the design criteria. A catamaran has advantages over a monohull in terms of broad layout, excellent stability, and obstacles on small vessels. The catamaran design follows the semi SWATH type design by having two hulls with a small hull front corner and modeling on INCAT wave-piercing catamaran to determine the structural response to the ship, and the wave slamming process. In the simulation analysis using fluid-structure interaction with RANS and also the strength of the catamaran structure using the FE method and large base scale. In modeling also to show the hydroelastic response to the ship structure that makes the dynamic interaction between waves and ship structure more practical. Then, the design optimization of the catamaran is directed to the addition of keel fins and the application of titanium materials.