Investigations into the drag of ellipsoids in proximity have been carried out experimentally using a low-speed wind tunnel and numerically using a commercial computational fluid dynamics (CFD) code (CFXTM). The purpose of the investigations was to improve the understanding of the viscous resistance and viscous interaction effects between twin bodies in proximity, such as the hulls of a catamaran, and consequently to improve the techniques for estimating the resistance and powering of commercial catamarans. The wind tunnel tests were carried out on a single ellipsoid with a length-diameter ratio ( L/D) of 6.0 and a pair of similar ellipsoids in proximity at separation-length ratios ( S/L) of 0.27, 0.37, 0.47 and 0.57 at Reynolds number values up to 3.2 ×106. The ellipsoids thus represented a reflex (or reflected) model of a catamaran hull. In the numerical work, investigations were carried out on ellipsoids with the same geometry as those tested in the wind tunnel and ellipsoids with a larger length-diameter ratio. Results of the wind tunnel tests and numerical investigations are presented and compared. It is found from the investigations that viscous form effects and viscous interactions are present for such bodies and that CFD techniques can make very useful contributions to the investigations of these effects.

Resistance or drag is one of the most important factors in ship design, in particular in connection with the development of more efficient and environmentally friendly vessels. The shape of the hull under water will affect the fluid flow characteristics around the ship, hence causing the resistance to increase or decrease. If the resistance increases, the size of main engine and subsequently, the fuel consumption increases accordingly and this is not often anticipated by ship designers and operators. The use of a catamaran for passenger carriers is well known and its application for fishing vessels has received serious attention in the last few years, due to its advantages to produce wider deck area and smaller size of engine at the same displacement as the monohulls. The conversion of monohull fishing vessels in Cilacap the waters into a catamaran hull is an interesting topic in association with the development of better fishing vessels in this region. The resistance investigation of the conversion vessel was carried out by Computational Fluid Dynamics (CFD) approach and this is combined with classical slender body theory. In terms of mathematical calculation, the results between CFD and the combination of empirical formulas and slender body theory shows such a good agreement and the difference between the two is less than 5%. In terms of naval architecture, the results showed that the modification of a monohull vessel into a catamaran can increase the payload capacity up to two times. Conversely, this causes the resistance to increase about almost four times and this is certainly unpopular for the fishermen.

This article will look into to the environmental and economic issues in the maritime sector that arise due to biofouling. For the shipping industry, biofouling is known to increase hull roughness that would lead to an increase in friction resistance and fuel consumption. Here we present a short review regarding ship-hull roughness due to biofouling and its associated increase in skin friction drag, and analysis of fuel consumption from an operating ship with two different anti-fouling coating. The data shows that a higher quality antifouling would result in a low biofouling attachment on the hull surface, resulting in a lower fuel consumption.

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Abstract. Vertical-axis hydrokinetic turbines with fixed pitch blades typically suffer from poor starting torque, low efficiency and shaking due to large fluctuations in both radial and tangential force with azimuth angle. Maximizing the turbine power output can be achieved only if the mechanism of generation of the hydrodynamic force on the blades is clearly identified and tools to design high-performance rotors are developed. This paper describes an initial experimental investigation to understand more of the performance on vertical-axis turbine related to the effect of fixed-pitch and passive variable-pitch application using airfoil NACA 0018. Comparative analysis according to aspects of rotation and tip speed ratios was discussed. Information regarding the changes of foil position in passive variable-pitch during rotation at a limited range of flow velocity variations test was obtained and analyzed.

The paper presents the results of experimental and numerical investigations into the calm water resistance characteristics of slender catamarans and the interference effects of hull separation. The model hull forms comprise modern symmetrical catamaran hulls with lateral separation. A series of tests were conducted in a towing tank with lateral separation of the hulls of Sc/L = 0.2 -0.4 and speeds corresponding to Froude number up to 0.65. Tests were carried out in a low speed wind tunnel to determine viscous interference effects between the hulls. Numerical computational fluid dynamics modelling was also used to estimate interference effects on the resistance components. It was found that the experimental and numerical investigations were in excellent agreement and provide satisfactory estimates of the resistance components. Results in the paper offer some practical data and further insight into wave and viscous interference effects.

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