14:00
Ship hydromechanics resistance II
Chair: Marcelo Neves
14:00
30 mins
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THE SEAKEEPING EVALUATION FOR THE VLCC WITH NEW TYPE SECTION
Jinfang Wei, Shan Wang, Jingpu Chen
Abstract: For the purpose of environment protection and energy saving, reducing the ballast water technique was introduced to ship design, which caused the ship has new type section, such as “V” type. It is necessary to research the hydrodynamics performance of the new type section ship before putting into use. In this paper, the research of the motion in wave has been carried out by strip method between the VLCC with new type section and the VLCC with normal section, thus a new type of VLCC section shape was optimized.The result of the checking calculations by three-dimensional time domain method based on rankine source and seakeeping model test showed that the calculation outcome and model test results was similar, so strip method can be used as a reliable and quickly assessment means to select the optimal case. The work in the paper supplied technology foundation for the practicability of the VLCC with new type section.
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14:30
30 mins
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AN INVESTIGATION ON ITTC 78 SCALING METHOD FOR UNCONVENTIONAL PROPELLERS
Surya Kiran Peravali, Rickard Bensow, Walter Gyllenram, Abolfazl Shiri
Abstract: The effort to find solutions to the environmental and energy saving problems regarding the operation of ships is always a matter of concern. Several new unconventional propeller designs have been introduced in the recent years. These unconventional propellers are designed with non-planar lifting surfaces and a design approach to improve the energy efficiency by reducing the tip vortex loss and having a better lift/drag ratio. Suspicions have been raised that the standard methods for evaluation of model tests such as the ITTC 78 method does not take the full effect of unconventional propellers in to account [1]. In the present investigation, the performance of two propellers (one conventional and one unconventional) are analyzed using CFD (RANS) in model and full scale in different operating conditions (open-water and behind a hull). The validation studies are performed in model scale and compared with the experimental data. Further the computations are extended to full scale to study the scaling effects on the propulsive efficiency and different propulsive coefficients. The outcome is compared with the predictions from ITTC 78 method applied on different geometries and conditions.
The RANS assessment showed additional scaling effect for the present unconventional propeller compared to the conventional propeller. At the design condition the RANS study estimates the unconventional propeller has lower effective wake and hull efficiency compared with the conventional propeller. However, the propeller efficiency and total efficiency is higher for the unconventional propeller. The CFD estimations in full scale contradict the estimations from the ITTC 78 method. In this paper, the differences between the CFD and ITTC 78 method are presented and the areas of further research are identified.
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