This study is a parametric investigation of the application of a compact type of pre-swirl duct for a slender aft-body 158k crude oil carrier. The International Maritime Organization (IMO) has created the Energy Efficiency Design Index (EEDI), which is an index related to carbon dioxide emissions, to enforce regulations on newly built ships; many solutions have been proposed, including an increase in propulsion efficiency. In the present study, a new type of energy-saving device (pre-swirl duct), the so-called ring stator, is proposed for 158k crude oil carriers, the hull form of which has been developed as a slender after-body full form to reduce the resistance by delaying separation. A conventional pre-swirl duct is no longer effective at the slender aft-body hull forms because of the small radial flow to the propeller. A parametric study was conducted through Computational Fluid Dynamics (CFD) analysis using the commercial program Star-CCM+, and an improvement of approximately 3% in the propulsion efficiency was achieved in the present study. The efficiency gain was validated through a comparison with the experimental results. The developed ring stator may become applicable to container ships through further parametric studies in the near future.

Owing to environmental regulations, ships are equipped with a pre-swirl stator (PSS), which is one of the most effective energy-saving devices (ESDs) that is widely applied to various kinds of ships. It improves energy efficiency by recovering the rotational kinetic energy of the propeller with the aid of a PSS placed in front of the propeller. In this study, an asymmetric PSS system is applied to the 2500 TEU eco-friendly liquefied natural gas (LNG) fuel feeder container ship, aimed at optimizing the position of stator blades, using a potential-based program. Additionally, a parametric study was conducted for evaluating the optimum pitch angle and blade spacing. STAR-CCM+ was used for validating the efficiency of the final design. The Samsung towing tank and large cavitation tunnel were also utilized to verify the improvement in the performance of the proposed PSS. Although the efficiency gain is not largely affected by blade position optimization, the cavitation and pressure fluctuation issues are addressed by improving the in-flow to the propeller. Therefore, blade spacing optimization of the stator is important for container ships whose cavitation performance is very significant, especially the relatively high-speed commercial vessels.

An improved wavy twisted rudder (WTR) is proposed based on a previous study. The misalignment of the wavy and propeller centers and the computational work of the previous study are supplemented to determine the effectiveness of the developed wavy twisted rudder. The aligned wavy twisted rudder (AWTR) was also applied to a KRISO container ship (KCS). The resistance, self-propulsion performance, and rudder forces due to the angular variation in the WTR and AWTR were compared using computational fluid dynamics (CFD). The numerical results were compared with the experimental results. The self-propulsion performance of the AWTR was superior to that of the WTR, with an efficiency gain of approximately 0.3% in both the model test and numerical analyses. The effectiveness of the AWTR was demonstrated using CFD; the CFD improved for the WTR in comparison with a conventional twisted rudder, especially at large rudder angles. The stall point of the AWTR was approximately 5° greater than that of the WTR in both directions. The results confirm the superiority of the AWTR in terms of its delayed stall and high lift-to-drag ratio, which was investigated by visualizing the streamline around the rudder. The actual maneuverability, such as the turning circle, realized with AWTR shall be compared with that realized with a WTR and conventional TR in the near future.

The maneuverability performance of a KCS with energy-saving devices was investigated. A bulb-type wavy rudder and an asymmetric pre-swirl stator were used as energy-saving devices because their use resulted in considerable efficiency gain. A validated simulation method based on the maneuvering modeling group model was used for the simulation in this study. Turning circle, 10/10 zigzag, and 20/20 zigzag tests were simulated to compare various cases with and without a stator as well as conventional full-spade and bulb-type wavy rudders. Remarkable maneuverability performance was achieved, particularly with a bulb-type wavy rudder, and starboard–port unbalancing due to the one-directional propeller action was almost eliminated using these devices. The findings of this study will be useful in the development of more reliable autonomous maritime surface ships.

Fluctuating pressure generated during ship operation is closely related to propeller vibration, noise, and structural safety, and its frequency spectrum is a key design indicator in the propeller design stage. However, water tunnel experiments to measure fluctuating pressure generated by high-speed propellers require high-pressure facilities and involve complex procedures, high costs, and long lead times when experimental conditions are modified or new propellers are tested. To overcome these limitations, this study proposes a deep learning-based network, referred to as MSPFS-Net (Model-Test Ship Pressure Frequency Spectra Network), to estimate the frequency spectrum of fluctuating pressure from model test data. The proposed method uses propeller CAD data, principal design parameters, wake data, and water tunnel test conditions as inputs, and is trained in a supervised learning framework using frequency-domain data obtained by transforming experimentally measured fluctuating pressure signals. The trained network can predict the fluctuating pressure frequency spectrum without direct sensor measurements, even under conditions not present in the training dataset. The results of this study demonstrate the potential to reduce dependence on water tunnel experiments and to efficiently evaluate fluctuating pressure characteristics in the early design stage, indicating that the proposed approach can serve as a practical design support tool in terms of both cost and time efficiency.