Twenty-First Symposium on Naval Hydrodynamics (1997) / Chapter Skim
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Hydrodynamic Optimization of Fast-Displacement Catamarans
Hydrodynamic Optimization of Fast-Displacement Catamarans
Pages 697-714
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From page 697... ...
Alternative mathematical models and computer algorithms for the wave resistance of arbitrarily shaped hull forms have been developed and applied herein, namely simplified approaches based on Michell's original source distribution concept, but accounting for the interaction of the demihulls and for any asymmetries of the slender/thin demihull forms through a doublet centerplane distribution, and alternatively a Neumann-Kelvin 3D panel source approach that is generally applicable to arbitrary hull forms. The developed theoretical-numerical methods have been applied systematically to the hull form development of a variety of Fast Displacement Catamarans and they are in general validated through model tests.
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From page 698... ...
The present paper is focusing on the calm water perfo~ance of Fast Displacement Catamarans and their hull form optimization with respect to least horsepower requirement, assuming the desired vessel's speed and displacements known and considering various geometric parameters set by design or by other operational constraints. The employed optimization procedure consists of two basic stages, namely, in the first phase a global procedure leading to the main dimensions and integral form and weight characteristics of the ship, whereas in the second phase a local form optimization is performed leading to the exact geometric characteristics and the final hull form of the vessel under consideration.
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From page 699... ...
2. DESIGN METHODOLOGY Due to the innovative character of the design of Fast Displacement Catamarans, including SWATEIs and Hybrids, it is essential to set-up a specific computer-aided design procedure, allowing the convenient and reliable repeat of the necessary steps following the design spiral.
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From page 700... ...
This method, that proves to be very efficient and fast, was applied successfully in the past to the design of several SWATEIs and thin, but symmetric, Catamarans and the theoretical predictions have been validated, in most cases, successfully by model experiments. Whereas the above procedure is limited to symmetric catamaran hull forms only, a fair portion of existing and under development displacement Catamarans have non-symmetric demihull forms for manifold practical reasons, including the hydrodynamic performance in calm water and in waves.
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From page 701... ...
, the only tool practically available to the designer is the variation of the waterplane area and, to a certain limited degrees, the variation of the ship's underwater hull form determining the "added" mass and moment values. The slenderness and thinness of the demihulls of Fast Displacement Catamarans and the generally small waterplane area will contribute, in general terms, to a shift of the natural periods in heave, pitch and roll to relatively high values, therefore outside the range of resonance with short period waves, typical to many coastal areas9.
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From page 702... ...
However, Fast Displacement Catamaran hull forms and Hybrids, deviating from the original SWATH concept as to the smallness of the waterplane area and the underwater hull form, will naturally exhibit worse seakeeping behaviour, at the benefit of increased vertical plane stability. The main design tools for the tuning of the natural periods, to be positioned outside the range of the possible wave encounter periods, are: with excellent seakeeP~rc · For the roll natural period: limitation of the transverse metacentric height GMT through the smallest possible'° separation distance of the dern~hulls and the positioning of heavy loads as high as possible.
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From page 703... ...
In the following figures we present theoretical and experimental results for the horsepower requirement of four optimized Fast Displacement Catamaran hull forms, namely for two designed SWATH ships and two displacement catamarans with hybrid hull form features. In Figs 8 and 9 the theoretical predictions for the effective horsepower requirement of the 1.030 tons displacement SWATH Passenger car ferry design "Aegean Queen" and the 610 tons displacement SWATH Multipurpose Research Vessel SMURV are compared with data from model experiments, performed at the Ship Hydrodynamics Laboratory of NTUA.
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From page 704... ...
Alternative mathematical models and computer algorithms for the wave resistance of arbitrarily shaped hull forms have been developed and applied herein, namely simplified thin ship theory approaches based on Michell's original source distribution concept but accounting for asymmetries of the slender/thin demihull forms through a doublet distribution and alternatively a 3D panel source method, that is based on the 3D Green function approach and is generally applicable to arbitrary hull forms. The developed theoretical-numerical methods have been applied to the hull form development of a variety of Fast Displacement Catamarans.
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From page 705... ...
_ ~ , 12. Koskinas, C., "On the Solution of the Neumann-Kelvin Problem by a 3D Panel Source Method and Applications to Catamaran Hull Form Optimization", Dr.-Eng.
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From page 706... ...
denotes the open domain bounded by the calm fluid surface X3 = 0 and the demibull cent erplanes ROB (0~' i = 1, 2, to which degenerate the wetted surfaces Bit) i = 1,2, at the limit e= 0.
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From page 707... ...
. Furthermore, let the separation distance 2s, between the axes of the two demihulls, be large enough so that local interference effects can be neglected.
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From page 708... ...
Appendix B : The Wave Resistance of Arbitrarily Shaped Catamarans In this appendix we describe a method for evaluating the wave resistance of a steadily moving catamaran with arbitrarily shaped demihulls. In this case, the perturbation potential MOPS can be represented as ~(P)
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From page 709... ...
.7i 1.6 ' 1 5 o 1.4 E 1.3 <~ 1.2 `1.1 E 1.0 0.9 1 0.8 0.7 0.6 0.5 0.4 n ~ MODEL 1 (Wigicy) S/L-0.4 - ~.2 0.3 O.4 0.S 0.6 0.7 0~0.9 1.0 1.1 FROUDE NUV8~ Fig.7 InteractioI1 wave resistance coefficient of sy~etric and asymmetric WIGLEY twin-hulls 709
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From page 710... ...
f~i ° 11 1 ~ o~= = o 0 aa _ o o c r, _ o - \ ~ \ - ~ \ ~ ~ c 0 q, c ~\ ~\ |
From page 711... ...
Fig. 13 Comparison between theoretical predictions and model expenments for the Effective Horse Power of GOUTCAT - 6000 _!
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From page 712... ...
Doctors, the authors would like to clarify that the depicted wave resistance coefficients are defined in the common way, namely with reference to the wetted surface area. Because of the slenderness of the studies hulls, the differences in the wetted area between Type B twin-hull and Type A or C, which all have the same displacement, are very small, therefore the results change very little.
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From page 713... ...
in fact all demihull forms (inward and outward flattened WIGLEY hulls and symmetric ones) tend to deliver similar results (see Fig.
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From page 714... ...
0.1 0.2 0.3 0.4 1 1 1 1 ___~_ S/L Fig. 15 Influence of separation distance on the total resistance coefficients of symmetric WIGLEY demihulls (L/B=10, B/T=1.6, exp.
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