Design approach for reducing the wave added resistance by hull form optimisation

Abstract

The primary objective of this project is to investigate if the designed hull form when realistic wave conditions are taken into account should be more slender than the current blunt bows. The added resistance is also highly dependent upon environmental forces like wave conditions the vessel experiences. Also, ship operators are mostly interested in fuel savings with minimum modifications in hull form; thus, a study has been made on one operation regime considering the wave data for all the design variations. MOERI KVLCC2 has been considered for this study http://www.simman2008.dk/KVLCC/KVLCC2/tanker2.html, as it is available in public domain and widely used for CFD calculations in industry. Hull forms have been transformed using FFD transformation in NAPA looped with optimisation and CFD tools in NAPA. Systematic algorithm was used to do optimisation. Six designs have been investigated changing the water lines and entrance angles resulted from blunt to sharp. In this thesis, KVLCC2_0 is the original design of MOERI tanker with no flare. KVLCC2_-1.5, KVLCC2_-1 and KVLCC2_-0.5 are blunt designs than the other design variations used. KVLCC2_0.5, KVLCC2_1 and KVLCC2_2 are more slender ships by moving the volume from the shoulder to the bulb area. KVLCC2_-1.5 is more blunt ship and has some restrictions in calculating the full-scale resistance after CFD study, so this design variation is neglected in the reports. However, to show the design variations, it has been shown at some places. KVLCC2_0 has been elongated by 8m and can be seen in KVLCC2_2 design. One route has been chosen to represent the actual operational areas of a similar vessel. The route selected is from Arabian Gulf (AG) to Japan. Resistance of calm water has been calculated and verified with experimental data. The wave resistance was calculated numerically using NAPA. KVLCC2_-1 has the greatest calm water resistance compared to rest of the designs. Designs KVLCC2_0, KVLCC2_0.5 and KVLCC2_1 have very similar calm water resistance but slightly lower than KVLCC2_-0.5 and KVLCC2_2. The added resistance was calculated by NAPA seakeeping subsystem. Sharper bow designs have lower resistance in the regime considered as expected. Fuel consumption calculations were done by including operational profile of the voyage, viscous resistance, added resistance, and propulsion characteristics in NAPA. The results show that KVLCC2_0.5 and KVLCC2_1 have good fuel efficiency of 11.8 and 12.6%, respectively. From the results, it is obvious that a sharper bow will have better advantage over a blunter bow when actual operational conditions are considered.