International Journal of Naval Architecture and Ocean Engineering最新文献

Freak wave occurs unexpectedly in the ocean with an extreme wave crest and focused wave energy, resulting in many marine accidents. The interaction between a container ship and freak waves in beam sea is studied in this paper to better understand the influence of freak waves on ships. A three-dimensional in-house solver is developed and validated for the freak wave generation and the wave-ship interaction. Characteristics of the interaction process, motion responses of the ship and the green water loadings induced by the freak waves are obtained and analyzed. Comparisons are carried out to reveal the influences of the freak wave crest and sequence on the roll, heave and impact pressures. Relations between motion responses of the ship and the green water event are discussed. Influences of ship speeds on the wave-ship interaction are addressed.

When constructing a low-noise submarine, it is crucial to consider the non-cavitating noise from the propeller. Non-cavitating noise reduction is crucial for submarine stealth and survivability. Recently, several studies have been conducted on the use of flexible propellers as a means of reducing non-cavitating noise. However, there are no studies on the use of flexible propellers with adaptive characteristics to reduce noise in wake fields. Thus, this study investigated the noise reduction effect of adaptive characteristics on non-cavitating noise for the flexible propeller in the wake field. Numerical investigations on the main propeller variables were conducted based on the proposed procedure using fluid-structure interaction and acoustic analysis models. The results were compared with those of rigid propellers to determine the possible reasons for noise reduction. Finally, the acoustic analysis results of the flexible propeller were compared with those of the rigid propeller to reveal the effectiveness of the adaptive characteristics.

Pipe routing during the design process of a ship depends on the design experience or knowledge of experts. In this study, an expert system that can systematize expert knowledge was constructed to enhance the design of a ship's pipe routing, which relies on experts. In addition, a method for pipe routing using a pathfinding algorithm was proposed. An arrangement template model (a type of data structure for pipe routing) and an arrangement evaluation model (a type of expert system) were proposed to systematically concretize and computerize expert knowledge. To review several alternatives for pipe routing in a short time and derive an optimal alternative, an optimization technique was combined with an expert system, and the optimization problem was mathematically formulated. That is, the design alternatives for pipe routing were evaluated using the arrangement evaluation model, and the results were used as one of the objective functions of the optimization problem for optimal pipe routing. To verify the proposed method, examples were selected, pipe routing was performed on the examples, and the results were compared with those of the manual design. As a result, an improved pipe routing could be obtained using the proposed method.

Struts are attached to a submarine to maintain its submerged depth when conducting the model tests. While previous studies have mentioned that the attachment of the struts has a negligible effect on the performance of a submarine, it is difficult to find studies that clearly explain the effects of the struts. The present study examines the effect of struts with a circular cross-section on the resistance and propulsion performances of a submarine under both straight-ahead (β = 0°) and static-drift (β = 6° and 12°) conditions. For this analysis, the open-source computational fluid dynamics (CFD) toolkit OpenFOAM was utilized. A generic submarine Joubert BB2 was selected as a test model, which was modified by the Maritime Research Institute Netherlands (MARIN). Analyses of resistance were conducted in straight-ahead and static-drift conditions, and the flow characteristics such as pressure, velocity, vorticity, and turbulent kinetic energy were compared to identify differences caused by the struts on the BB2 submarine. The results showed that as the drift angle increased, the struts had a smaller effect on the submarine along the hull to the propeller plane. From the results, it was predicted that the effect of the struts should be considered during the design process for the submarine.

High-density polyethylene (HDPE) is considered an eco-friendly material for boat construction worldwide. However, managing thermal distortion in HDPE welding is challenging, impacting productivity. Traditional steel shipbuilding has established methods to predict welding-induced thermal distortion, but HDPE lacks comprehensive studies and standards. This research explores applying the elastic Finite Element (FE) approach, commonly used in steel structures, to HDPE welding. The elastic FE approach simplifies complex welding simulations, enabling its use in large structures like ship hulls. Our research assesses whether HDPE welded specimens exhibit similar distortion patterns to conventional welded structures and whether consistent parameters yield similar thermal distortion. Alignment between our FE analysis, based on specimen data, and experimental results validates the feasibility of using the elastic FE approach to predict HDPE thermal distortion. This study suggests it as a practical method to enhance HDPE boat manufacturing productivity.

Heat shields are an essential safety facility on offshore structures to protect the workers and the equipment on deck from the violent radiant heat flux and the high temperatures of the flare tower. In this study, a series of Computational Fluid Dynamics (CFD) simulations were performed to investigate the thermal characteristics of radiant heat shields on offshore structures in order to obtain a precise prediction of those reduction performances on heat flux and temperature. CFD methodologies for the radiant heat transfer simulation were suggested for grid, iteration, and time step with physical modelling methods of heat transfer considering the convection effect and the heat flux sensor, including the scaling method for the simulation of a perforated heat shield. The reduction ratios of the heat flux and temperature were obtained for the case without the heat shield and for a flat and perforated heat shield under the heat source of 25 kW/m² for various distances from the heat shield, and the results were compared with the experimental results. Analytical estimation methods were included in the study of the radiant heat flux and temperature, and an empirical formula was provided for the performance of the heat shields based on the CFD results.

Since ammonia and liquid hydrogen are the optional future shipping cargo and fuels, the applicability was crucial using the current technologies and expectations. Existing studies for the economic feasibility of the energies had limitations: empirical evaluation with assumptions and insufficiency related to causality. A distorted estimation can result in failure of decision-making or policy in terms of future energy. The present study aimed to evaluate the transportation costs of future energy including ammonia and liquid hydrogen in comparison to LNG for overcoming the limitations. An integrated mathematical model was applied to the investigation for economic feasibility. The transportation costs of the chosen energies were evaluated for the given transportation plan considering key factors: ship speed, BOR, and transportation plan. The transportation costs at the design speed for LNG and liquid hydrogen were approximately 55% and 80% of that for ammonia without considering the social cost due to CO₂ emission. Although ammonia was the most expensive energy for transportation, ammonia could be an effective alternative due to insensitivity to the transportation plan. If the social cost was taken into account, liquid hydrogen already gained competitiveness in comparison to LNG. The advantage of liquid hydrogen was maximized for higher speed where more BOG was injected into main engines.

To mitigate environmental issues and implement energy management strategies, hydrogen is emerging as the most promising and sustainable energy source to help achieve decarbonization targets and meet world energy demands. However, hydrogen poses significant storage and transportation challenges due to its low volumetric and gravimetric density. Hence, ammonia is a potential candidate for a hydrogen storage medium because it contains 17.65% hydrogen by weight, and its volumetric hydrogen density is 45% higher than that of liquid hydrogen. In the maritime sector, these available fuels of ammonia and hydrogen are utilized via internal combustion engines, fuel cells, and gas turbines, which are employed on board ships. This study investigates the possibility of using ammonia and hydrogen as fuels for Solid Oxide Fuel Cells (SOFCs). A combined SOFC-Gas Turbine (GT) system was proposed to generate power for marine propulsion plants. This system was designed and modeled with support from Aspen HYSYS V.12.1. Thermodynamics performances of the proposed system were analyzed using the first and second laws of thermodynamics. The energy efficiencies of direct ammonia and hydrogen SOFCs were 60.96 and 64.46%, respectively. The energy efficiencies of the combined systems increased by 12.37 and 13.97% when using ammonia and hydrogen as fuels, respectively, compared with that of single SOFC systems. The exergy destruction of the primary components with each fuel was examined. Furthermore, a parametric study was performed to select the most suitable fuel utilization factor for the system. This analysis proved that ammonia has the potential as a hydrogen carrier and that waste heat recovery is an effective method to improve the thermodynamic performance of an SOFC system.

The experimental dataset is presented for flow kinematics and pressure distribution of green water phenomenon on a rectangular structure. The green water experiments were performed in a 2-D wave flume with a fixed structure varying its flare angle under regular wave conditions. The structure and wave conditions were determined by scaling down with a ratio of 1:125 from the BW Pioneer Floating Production Storage and Offloading (FPSO) operated in the Gulf of Mexico. The experimental dataset includes the wave elevation, water velocities measured using Particle Image Velocimetry (PIV), bubbly flow velocities measured using Bubble Image Velocimetry (BIV), and pressure distributions obtained on the surface of the structure using the pressure sensors. The presented dataset can improve understanding of the physical kinematics of green water loading, which has a violent multi-phase flow and high-nonlinear characteristics. The dataset also can be used as benchmark data for numerical models to estimate the green water loading on ships and offshore structures.

Floating Production Storage and Offloading Unit (FPSO) is designed to produce, store and transport hydrocarbon products. FPSO's hawsers may be exposed to both extreme and fatigue loads during operations. Hence prediction of their fatigue life is important for operational safety. During some unloading operations, consistent hawser tensions could develop as a result of internal friction in nylon ropes, casing wear and accumulated fatigue damage. Methodology, suggested in this study, may be effectively employed at the vessel design phase, when optimizing vessel parameters, reducing potential FPSO hawser tension fatigue damage. This study aims to contribute to development of novel fatigue assessment approaches, in order to use limited available datasets more effectively. Stresses occurring within FPSO hawsers have been modelled, using actual in situ environmental conditions. Simulated continuous stress time series were used as input for the rainflow counting analysis; the cumulative fatigue damage was then evaluated. Note on experimental validation has been provided.