International Journal of Naval Architecture and Ocean Engineering最新文献

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.

A conceptual design of a liquid hydrogen FPSO was developed in this research, and its hull dimensions were optimized under the environment at the Donghae gas field in South Korea. During the conceptual design stage, a process of production, storage, and offloading of liquid hydrogen was studied, and the topside and hull layouts for the liquid hydrogen FPSO were proposed. The capacities of each module were determined based on the operation scenario. The corresponding required areas and weight of each module were estimated from the literature review and the data from the ongoing project (KRISO, 2022). The optimized hull dimensions were presented by a Multi-Objective Evolutionary Algorithm (MOEA) with two objectives, minimization of the hull steel weight and the motion level considering the constraints related to geometry, stability, and hydrodynamic performances. The obtained Pareto set shows three classified solution types depending on the active constraints, which is able to propose a wide range of design alternatives for the liquid hydrogen FPSO with unique constraints compared to general ships.

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.

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.

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.

This paper aims to investigate the applicability and reliability of an experimental method measuring the underwater acoustic radiation efficiencies of floating plate structures in a reverberant water tank. For the purpose, an experimental method for estimating the acoustic power of a source in a reverberant sound field has been introduced and applied to measure the acoustic radiation efficiencies of two floating box-type plate structures excited by a logarithmic sine sweeping force in a water tank. The validity of the adopted experimental method has been examined by the comparison with numerical results obtained by a fully coupled vibroacoustic analysis with an infinite radiation boundary condition for the structures. From the results, it is confirmed that the experimental method for measuring the underwater acoustic radiation efficiency of floating plate structures in a reverberant water tank is reliably applicable for high-frequency ranges above the Schroeder frequency of the water tank.

In this study, the wave attenuation by the inclined porous plates has been evaluated through a numerical approach. As a numerical method, we used the dual boundary element method (DBEM) that solves two distinct boundary integral equations (singular and hyper-singular) derived at the coincident source points on each side of the degenerate plate boundary. A quadratic velocity model with the porosity-dependent drag coefficient is adopted to account for energy dissipation through the porous plate. The developed DBEM tool is validated through the comparison with self-conducted experiments at a two-dimensional wave tank. Then it is used to assess the reflection coefficients and wave forces with various design parameters such as porosities, inclined angles, plate arrangements, and wave characteristics. The dual inclined porous plates arranged in either a serial or parallel configuration did not enhance the wave-absorbing efficiency significantly, compared to a single inclined porous plate with optimal values of porosity (P = 0.1) and inclined angle (θ = 10°).

Most of the existing studies developed and improved local path planning algorithms independently of global planning, i.e., ignoring the global optimal constrains. To meet the requirements of practical applications, this paper presented an energy-efficient hierarchical collision avoidance algorithm for unmanned surface vehicle operating in clustered dynamic environments. For the global level, genetic algorithm was modified by strategies of greedy-inspired population initialization, penalty-based multi-objective fitness function, and joint crossover. For the local level, velocity obstacle was combined with dynamic window approach to provide the kinematic constraints of the vehicle to its admissible velocities and simplified collision avoidance rules to guide the evasive maneuvers. Simulations showed that the proposed global algorithm was superior to three other algorithms in terms of path length, path smoothness, and convergence speed regardless of the environment size. The performance of the local algorithm was also verified for various encounter scenarios and speed ratios. In addition, the combination of the global and local planning can effectively solve the path optimization and dynamic obstacle avoidance in a designed offshore environment of fish cage culture.

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.

Large-size catamarans' structural behavior is sensitive and critical during the slamming phenomenon. “Ventilation pipes” within the center bow structure are proposed to discharge these cumulative pressure and related loads. The validation case is comprising two different simulation schemes, static and dynamic wedge. First, the appropriate method is chosen based on the accuracy and needed computational running time criteria. The numerical solution approach solves the RANS equation using the Open Field Operation and Manipulation (OpenFOAM) library called “InterFoam and OverInterDyMFoam for static and dynamic mesh respectively. Totally three different impact conditions with four different impact velocities (12 case studies) were considered for the case with added ventilation pipes (amended hull) and the standard model (parent-hull). Apart from the limitation of the proposed plan which is discussed, the results indicate that the recorded pressure and total force decreases by about (15%–50%), and (5%–25%) respectively.