International Shipbuilding Progress - Volume 62, issue 3-4

Authors: Guha, Amitava | Falzarano, Jeffrey

Article Type: Research Article

Abstract: The growing number of large ships demands predicting their optimum performance with respect to travel time, fuel efficiency and the safety of cargo and personnel in specified shipping routes. This can be achieved using efficient and easy to use numerical tools capable of predicting hydrodynamic loads on floating vessels with steady forward speed and solving their motion response in various wave conditions. A three-dimensional potential theory based code using the Green function method is developed with consideration of forward speed effects. The generalized coordinate system is used to allow motion response calculations with respect to any desired body coordinate system …and a common quadrilateral meshing format. The formulation and calculation of added mass and damping coefficients at zero and infinite frequency in forward speed case has been also provided. A number of structures including simple geometries and full ship hull forms have been analyzed and validated against published theoretical, numerical and experimental results. The comparison results are found to be in excellent agreement. The theoretical formulation, numerical implementation and result comparisons are presented here. Show more

Keywords: Forward speed, potential theory, 3D panel method, Green function

DOI: 10.3233/ISP-150118

Citation: International Shipbuilding Progress, vol. 62, no. 3-4, pp. 113-138, 2015

Authors: Islam, M. | Akinturk, A. | Veitch, B.

Article Type: Research Article

Abstract: This paper presents various aspects of propulsive performance of a dynamic azimuthing puller podded propulsor in open water condition derived from an experimental research. A model podded propulsor was instrumented to measure thrust, torque and rotational speed of the propeller, three orthogonal forces and moments, azimuthing angle and azimuthing rate of the unit. Experiments were carried out in which the azimuthing angle was varied dynamically at multiple azimuthing rates and propeller rotational speeds for different advance speeds. The model podded propulsor was capable of azimuthing or yawing continuously in the range of −180° to +180°, 0° (straight-ahead) being the design operating …condition and positive azimuthing means a counter-clockwise rotation. The performance coefficients of the propeller and the pod unit showed a strong dependence on the propeller loading and azimuthing angle. The open water characteristics were mostly irregular for the astern thrust conditions in the azimuthing angle beyond the normal inflow condition and the fluctuation of the magnitude of the performance coefficients showed a considerable range. The azimuthing rate showed little or no effect on the performance coefficients in the range of azimuthing angles examined. Both at high and moderate propeller loading conditions, an increase in the shaft speed resulted in slight change in the performance coefficients and the change was more obvious as the azimuthing angle was increased. The increase in the performance coefficients due to the increase of propeller shaft speed was not noticeably affected by the change of azimuthing rate. Show more

Keywords: Podded propulsor, dynamic azimuthing, azimuthing rate, propulsive performance, unit forces and moments

DOI: 10.3233/ISP-150119

Citation: International Shipbuilding Progress, vol. 62, no. 3-4, pp. 139-160, 2015

Authors: Kara, Fuat

Article Type: Research Article

Abstract: The numerical predictions of the seakeeping characteristics of catamarans with and without forward speed are presented using a direct time domain approximation. Boundary-Integral Equation Method (BIEM) with three-dimensional transient free surface Green function and Neumman–Kelvin linearization is used for the solution of the hydrodynamic interactions in the gap between catamaran hulls and solved as impulsive velocity potential. The numerical results have shown that the response of the fluid between multi-hulls can affect seakeeping performance and influence the hydrodynamic forces and the motion amplitude operators of the floating multi-bodies. It is also shown numerically if the critical reduced frequency is smaller …than the ratio of vessel length to hull separation, the wave interactions between hulls are very significant due to trapped waves in the gap of twin-hull. A hemi-spheroid catamaran, Wigley catamaran, and DUT high speed catamaran hull forms are used for the numerical analyses and the comparisons of the present ITU-WAVE numerical results for added-mass, damping coefficients, exciting force, and response amplitude operators show satisfactory agreement with existing numerical and experimental results. Show more

Keywords: Seakeeping, multi-hull vessels, catamaran, time domain, transient free-surface wave Green function, boundary integral equation method, Neumman–Kelvin linearization

DOI: 10.3233/ISP-160120

Citation: International Shipbuilding Progress, vol. 62, no. 3-4, pp. 161-187, 2015

Article Type: Other

Citation: International Shipbuilding Progress, vol. 62, no. 3-4, pp. 189-189, 2015