Wave Resistance Study of Wave piercing Catamarans

Present paper researches the theoretical method for calculating the wave resistance of wave piercing catamarans.As an example the wave resistance of a wave piercing csatamaran is calculated.The comparison among the theoretical calculation results,the model test results and the diagram evaluation results shows the efficiency of present theoretical method.At last the dependence wave resistance of wave piercing catamarans on some parameters is investigated based on the theoretical method.

Numerical Analysis of the RAP Characteristics of a Catamaran Vessel for Niger Delta Pliability

A proper characterization of catamarans performance in relation to demi-hull separation ratio (Sc/L) is imperative for optimal design and applications. Resistance, propulsion and good sea-keeping characteristics for various demi-hull separation ratios at different operating conditions are prime considerations. This work evaluates the Resistance and Propulsion (RAP) characteristics of a 72 m long catamaran for various values of Sc/L (0.3, 0.4 and 0.5). Both physical models and numerical methods are implemented for the analysis. The analysis shows that the frictional resistance (RF) of catamaran is parabolic and slightly higher than those of monohulls. However, catamarans have superior sea-keeping performance. The RF of catamaran dominates the total resistance (RT) at low speeds;however, at high Froude number (Fn > 0.25), wave-making resistance (Rw) becomes dominant, especially during humps. Consequently, the RT-curve and the effective power PE-curve oscillate in rhythm with the Rw-curve as the velocity increases. Again, the effect of residuary resistance interference due to demi-hulls separation ratio is marginal, except during humps. Also, four speed-regimes are identified such as: 1) Low-speed (Fn st hump (0.23 nd hump, high-speed (Fn > 0.60). The catamaran PE for Fn > 0.6 is very high and uneconomical. Therefore, for optimal performance, catamarans should have service speed limits not exceeding Fn = 0.6.

Discussion of Grid Generation for Catamaran Resistance Calculation

In order to get some useful parameters for grid generation of catamaran, the CFD software FLUENT is used to investigate the main effects of grid generation on flow field calculation. The influences of some elements are investigated with a series of calculations in the present paper, and some alteratives are proposed. The proposed alteratives based on the analysis of the effects are used for a catamaran resistance calculation, comparisons of the calculated results with experimental data show good agreement. It shows that the research result of this paver is useful for the numerical calculation of catamaran.

Overlapping Grid Technique for Numerical Simulation of a Fast-Cruising Catamaran Fitted with Active T-Foils

In marine engineering,appendages such as fin stabilizers and/or T-foils are made to rotate and to reduce the motion of ships.Research on the hydrodynamics of ships fitted with active appendages has significantly improved the design and control of such ships.However,most studies focus on fixed rather than rotating appendages,thereby ignoring the hydrodynamic unsteadiness of active appendages.To enhance the reliability and precision of the numerical simulations,we propose the use of overlapping grids for simulating advanced catamarans fitted with a pair of rotating T-foils under each bow.The fundamental purpose of the overlapping grid technique is to realize information exchange via regional overlap sharing in each subdomain of the computing domain,instead of using the method of boundary sharing,thus greatly alleviating the difficulty of generating the subdomain grid;moreover,the technique guarantees the quality of the subdomain grid.Within the main computational domain,a subdomain was allocated to accommodate the T-foil.Overlapping meshes near the interface between the two domains enable information flow during the simulation;the overlapping grids are updated at every iteration step because the subdomain rotates.The instantaneous trim and sinkage responses of the catamaran to the T-foil rotation were reproduced.From the moment the active T-foil stopped moving,there was no change in the ship’s sailing attitude,indicating that the response was in real time.By comparing with EFD data,the numerical results showed reasonable agreement,indicating the feasibility and effectiveness of the technique in simulating the hydrodynamics of ships fitted with active appendages.

Solar Energy for a Traditional Coastal Fishing Platform

In order to introduce clean environment and sustainable energy to traditional coastal fishing community, the objective of this study is to encourage the Indonesian traditional coastal fishing community to use green and renewable energy in their fishing activities. Introducing solar power as the main source of energy for fish-attracting lights and boat propulsion can reduce the use of fossil fuels, and sustain clean and healthy environment. As the world’s largest archipelago, Indonesia accounts for a high percentage of traditional fishing communities spread out along its islands. This fishing communities use various traditional fishing boats, and platforms. The fishing platforms are usually made of bamboo and placed on top of supporting structures on the seabed. Diesel electric generators are used to obtain electricity needed for lighting to attract the fish at night, and as the source of power for lifting the fishing net. The structure and fuel used are neither environmentally friendly nor clean;thus, an innovation is introduced. Traditional fishing practices using a fishing platform were studied, including the common size of the platform and the power needed for the fishing light. Based on the gathered information, this study proposes a catamaran vessel with a special top structure designed for fish lifting outfitting, and equipped with photovoltaic solar cells as the energy source for the fishing lights and vessel propulsion. Through this innovative break through, the vessel can be moved to the shore and will not be a threat to ship navigation and the environment. Furthemore, powered by clean and sustainable energy, the vessel can be directed to the best fishing ground.

Analysis of structural dynamic characteristics of a high speed light special catamaran

In this paper,structural dynamic characteristics of a high-speed light special catamaran-wave piercing catamaran are analyzed using the FEA software MSC-NASTRAN. The dynamic reduction method is introduced to eliminate the local vibration modes in order to obtain the whole ship＇s mode shapes. In the post-processor, a lot of accessorial methods are adopted to eliminate the local vibrations, so that the whole ship＇s mode shapes can be identified. The modal analysis indicates that the dynamic reduction method fits for mode shapes identifying. In the end,the test results of a catamaran named Frederick G. Greed are used for reference to validate the obtained results. The comparison process shows that the results are credible. A special mode shape, which is quite different with that of conventional monohull ship, is also pointed out. The obtained results provide a valuable reference for the coming computation of catamaran＇s vihration characteristics.

Study on the Form Factor Estimation Method of High-Speed Catamaran with Asymmetrical Hulls

The method used to estimate the form factor of low-speed vessel will cause a large error when estimating the form factor of high-speed catamaran because of the interference effects. A method based on computational fluid dynamics( CFD) method is proposed to estimate the form factor of high-speed catamaran with asymmetrical hulls. This paper focused on a 2000-toners catamaran with asymmetrical hulls to compare the difference between normal method and CFD method. The resistance of this catamaran is calculated by the CFD method,and it was compared to the model test data to verify the validity of this method. The form factors calculated by CFD method are very different from the results calculated by Prohaska method in high speed area.Thus,the method used to estimate the form factor of low-speed vessel is not applicative for high-speed catamaran. It is more accurate and efficient when using the CFD method to estimate the form factor of high-speed catamaran with asymmetrical hulls.

Motion Responses Analysis for Tidal Current Energy Platform: QuadSpar and Catamaran Types

ωOne approach to support floating tidal current turbines is by using a moored catamaran, a barge type platform.Considering its low draft, one might expect that it performs best at typical straits with sea states of small wavelets to small waves. The problem is that the high rotational motion responses of the catamaran due to wave loads tend to reduce the turbine performance. This paper looks for a possibility to deteriorate these rotational responses by introducing a platform with four buoyant legs referred to as a quad-spar considering its good stability performance.The platforms are moored by four catenary cables as their mooring system. The motion response modeling was undertaken by Computational Fluid Dynamic(CFD) simulation based on three-dimensional potential flow theory.Considering sea states of straits with typical tidal current energy potentials, the environmental load was set on random wave with the significant wave height, Hs, of about 0.09 to 1.5 m and the wave period, T, of about 1.5 to 6 s corresponding to the wave frequency,, of about 1.1 to 4.2 rad/s. This study found that lower motion responses can be satisfied by the quad-spar, in which its yaw, roll and pitch responses are on average about 5%, 44%, and 38%,respectively, compared to those of the catamaran. This result indicates that the quad-spar is more effective in reducing rotational motion responses needed to keep a high performance of the tidal current energy system.

Dynamic characteristics of a WPC-comparison of transfer matrix method and FE method

To find the difference in dynamic characteristics between conventional monohull ship and wave penetrating catamaran (WPC), a WPC was taken as an object; its dynamic characteristics were computed by transfer matrix method and finite element method respectively. According to the comparison of the nature frequency results and mode shape results, the fact that FEM method is more suitable to dynamic characteristics analysis of a WPC was pointed out, special features on dynamic characteristics of WPC were given, and some beneficial suggestions are proposed to optimize the strength of a WPC in design period.

Numerical and Experimental Investigation of the Aero-Hydrodynamic Effect on the Behavior of a High-Speed Catamaran in Calm Water

In this paper,the effect of water and air fluids on the behavior of a planing catamaran in calm water was studied separately in calm water by using experimental and numerical methods.Experiments were conducted in a towing tank over the Froude number range of 0.49–2.9 with two degrees of freedom.The model vessel displacement of 5.3 kg was implemented in experimental tests.Craft behavior was evaluated at the displacements of 5.3,4.6,and 4 kg by using the numerical method.The numerical simulation results for the hull’s resistance force were validated with similar experimental data.The fluid volume model was applied to simulate two-phase flow.The SST k-ωturbulence model was used to investigate the effect of turbulence on the catamaran.The results showed that in the planing mode,the contribution of air to pressure resistance increased by 55%,40%,and 60%at the mentioned displacements,whereas the contribution of air to friction resistance was less than 15%on average.The contribution of the air to the total lift force at the abovementioned displacements exceeded 70%,60%,and 50%in the planing mode but was less than 10%in the displacement mode.At the displacements of 5.3 and 4 kg,the area under the effect of maximum pressure moved around the center of gravity and caused porpoising longitudinal instability at the Froude numbers of 2.9 and 2.4,respectively.However,at the displacement of 4.6 kg,this effect did not occur,and the vessel maintained its stability.

Fuzzy robust attitude controller design for hydrofoil catamaran

A robust attitude controller for hydrofoil catamaran throughout its operating envelope is proposed, based on Tagaki-Sugeno (T-S) fuzzy model. Firstly, T-S fuzzy model and robust attitude control strategy for hydrofoil catamaran is presented by use of linear matrix inequality (LMI) techniques. Secondly, a nonlinear mathematical model of hydrofoil catamaran is established, acting as the platform for further researches. The specialty in interpolation of T-S fuzzy model guarantees that feedback gain can be obtained smoothly, while boat's speed is shifting over the operating envelope. The external disturbances are also attenuated to achieve H ∞ control performance, meanwhile. Finally, based on such a boat, HC200B-A1, simulation researches demonstrate the design procedures and the effectiveness of fuzzy robust attitude controller.

Experimental Study on Hysucat Vessels

The paper contains the results of an experimental study on a planing catamaran. The aim of this study is resistance reduction with application of foils. Experiments are performed in different conditions and the results are compared with each other. The foils are used in different configurations and it is concluded that unsuitable design may result in larger resistance. But, it is also shown that, for a good design, the resistance may be reduced considerably.

The Failure of Fast Ferry Catamaran Operations in New Zealand and Hawaii

Fast ferry catamarans have been in use for several decades. They possess the advantage of overcoming one of the major deficiencies of water transportation: low speed. Although their operation has spread throughout different parts of the world, an overall analysis of the implementation and failures of this technology remains underdeveloped in the transport literature. This paper presents and compares two unsuccessful experiences of the use of fast ferry catamarans in New Zealand and Hawaii. Although both attempts possess major differences in terms of their contexts, particularly regarding competition, regulatory and environmental issues, some of the common lessons learned from both experiences can significantly contribute to a better understanding of this water transport technology and the challenges involved in its operation.

WAVE MAKING COMPUTATION IN TIME DOMAIN FOR MULTI-HULL SHIPS

A method Green function satisfying of three-dimensional time domain linear conditions at free surface and body surface boundary was employed to analyze the wave resistance and wave profile of a displacement multi-hull ship. The wave profile induced by a moving time domain point source was compared with those by a Havelock source, and satisfactory results were obtained. The panel method based on the time domain source distribution on the ship mean wetted hull surface was used to perform the wave making com- putations tbr mono-hull ships, catamaran and trimaran. Reasonable results were also obtained. Using the numerical method the wave profile simulations of multi-hull ships for a given Froude number were conducted.

COMPARISON OF RESISTANCE FOR SEVERAL DISPLACEMENT HIGH PERFORMANCE VEHICLES

According to the linear wave resistance theory, a comparison among the ship resistance for the high speed round bilge ships, the deep “Vee” vessels, the wave-piercing catamarans, and the high speed trimarans was given by using the high-speed round-bilge ship as a benchmark. And the optimal speed range of each ship form was also suggested by using the analysis of the research results.

Observations and computations of narrow Kelvin ship wakes

Computations of far-field ship waves,based on linear potential flow theory and the Hogner approximation,are reported for monohull ships and catamarans.Specifically,far-field ship waves are computed for six monohull ships at four Froude numbers F≡V/√gL=0.58,0.68,0.86,1.58 and for six catamarans with nondimensional hull spacing s≡S/L=0.25 at two Froude numbers F s≡V/√gS=1 and 2.5.Here,g is the gravitational acceleration,V and L denote the ship speed and length,and S is the separation distance between the twin hulls of a catamaran.The computations show that,although the amplitudes of the waves created by a ship are strongly influenced by the shape of the ship hull,as well known,the ray angles where the largest waves are found are only weakly influenced by the hull shape and indeed are mostly a kinematic feature of the flow around a ship hull.An important practical consequence of this flow feature is that the apparent wake angle of general monohull ships or catamarans(with arbitrarily-shaped hulls)can be estimated,without computations,by means of simple analytical relations;these relations,obtained elsewhere via parametric computations,are given here.Moreover,the influence of the two parameters F s and s that largely determine the ray angles of the dominant waves created by a catamaran is illustrated via computations for three catamarans with hull spacings s=0.2,0.35,0.5 at four Froude numbers F s=1,1.5,2,2.5.These computations confirm that the largest waves created by wide and/or fast catamarans are found at ray angles that only depend on F s(i.e.that do not depend on the hull spacing s)in agreement with an elementary analysis of lateral interference between the dominant waves created by the bows(or sterns)of the twin hulls of a catamaran.The dominant-waves ray angles predicted by the theory of wave-interference effects for monohull ships and catamarans are also compared with the observations of narrow Kelvin ship wakes reported by Rabaud and Moisy,and found to be consistent with these observations.