Vijayakumar Rajagopalan

This paper discusses the effect of modifying the hangar shape on the dynamic interaction of ship airwake and rotor downwash of the helicopter using computational fluid dynamics (CFD). A traditional 1:100 scaled simplified frigate ship (SFS-2) is modified to obtain trapezoidal and rectangular configurations of the hangar. The coupled interaction of ship airwake formed behind the ship subjected to free stream velocity of 6 m/s with the downwash generated by helicopter rotor hovering at 5000 rpm is simulated using STARCCM + CFD solver. The Reynolds-averaged Navier–Stokes equation is solved with conventional k-ω two-equation turbulence model to simulate the flow. The helicopter rotor thrust coefficient on hovering plane and landing plane is calculated for all the three SFS-2 configurations. The resultant velocity flow field of the ship airwake and rotor downwash is surveyed to compare the turbulence intensities at four equidistant lateral planes along the flight deck for a zero wind-over-deck (WOD) angle. The modified hangar configurations are shown to improve the coupled flow aft of the hangar.

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.

Autonomous underwater gliders are a class of AUVs that execute motions using change in buoyancy in conjunction with wings. Lack of conventional propeller restricts the speed of the vehicle. Speed of vehicle depends on operation of the buoyancy engine. Gliders follow a saw-tooth profile path and spiral path for undertaking motions in 2D and 3D planes. Traditionally, “legacy gliders” have been using roll and pitch correction mechanisms for conducting the 3D motion. This paper attempts to characterize the mass definitions of one laboratory-based AUG being developed at IIT Madras and predicts the path the glider will execute with participation of roll and pitch correction mechanisms that are being developed. The laboratory-scale gliding fish (small-scale glider) consists of a rudder and a roll control mechanism. The roll control mechanisms consist of movable mass, rotating and traversing about the principal axis of the glider. The effect of rudder and roll control mechanism on the path traversed by glider in 3D steady state is studied individually and in combination by solving the equations of motion using FSOLVE algorithm of MATLAB.

The increase in fuel costs and looming restrictions on carbon dioxide emissions are driving the shipowner into reducing the ship’s resistance and required installed power. It was earlier reported that, merchant vessels operating at lower speeds, the frictional drag accounts of almost 70–80% of the total drag; thus, there is a strong demand for the reduction in the fluid frictional drag, especially in the marine transportation business. The use of air as a lubricant, by injecting below the plate or the body, which is famously known as microbubble drag reduction (MBDR) in order to reduce that frictional drag is an active research topic. Latest developments in this field suggests that there is a potential reduction of 80% in frictional drag in case of flat plates and about 30% reduction in case of ships, which encourages researchers to investigate further. In this study, 3D numerical investigations into frictional drag reduction by microbubbles were carried out in Star CCM+ on a channel for different flow velocities, different void fractions and different cross sections of flow at the injection point. This study is the first of its kind in which variation of coefficient of friction both in longitudinal and transverse directions was studied along with actual localized variation of void fraction at these points. The numerical framework consists of the Reynolds-averaged Navier–Stokes (RANS) equations and the standard k−ε turbulence model with standard wall function treatment, which is validated in both conditions of with and without microbubbles with the existing experimental data. The design exploration study was carried out for various flow speeds, injector flow rates, cross sections of the channel/heights of channels and of course void fractions. Coefficient of friction and void fraction values are measured at 12 longitudinal positions, and at each longitudinal position, 11 in number transverse and 10 in number depthwise positions were studied. In all, for one simulation, data at more than 1000 positions were collected. More than 60 simulations were carried out to understand the effect. From the study, it is concluded that since it is a channel flow and as the flow is restricted in confined region, effect of air injection is limited to smaller area in transverse direction as bubbles were not escaping in transverse direction.

As oil and gas exploration moves toward deeper, harsher waters, and marginal fields, the issues concerning the associated floating production storage and offloading ships (FPSOs) get more complex. Traditionally, at the early stage of the design of FPSOs, subsystem design is individually taken up and subsystem interactions are accounted for through an uncoupled approach, as against a more rigorous fully coupled approach. In fully coupled approach, the system components and mutual interactions are coupled concurrently. Issues related to mooring system of FPSOs are some of the key aspects needing close attention. Approaches for determining the peak behavior belonging to turret-moored FPSOs to random wind, seawater flow, and wave forces for a specified life are still evolving. In the case of weathervaning FPSOs, special consideration is essential for the representation of realistic non-collinear environments. Also, choice of location of turret inside hull is an important design decision, as turret position influences motions. Similarly, another aspect requiring attention is the development of resonant sloshing due to excitation owing to external waves. Also combined piston modes happen within the turret and in the volume between turret and moon pool walls, which is an important hydrodynamic phenomenon. The flow parting via chain table openings heavily damps the piston mode. The paper reviews the literature on some of these hydrodynamic aspects concerning motion response of turret-moored FPSOs.

Hydrodynamic drag of ocean-going vessels imposes severe penalty with regard to exhaust emissions and fuel consumption. Stern flaps have been extensively used as a cost-effective energy saving device, largely by the US Navy. Experimental analysis to identify an optimum stern flap fitted at the transom stern end of a generic high-speed displacement vessel operating at Froude number regime of 0.17–0.48 is described. In this study, twelve different stern flap configurations were studied. Identification of optimum stern flap was based on systematic analysis of extensive model test resistance data of various stern flap configurations over twelve different Froude numbers.