International Journal of Naval Architecture and Ocean Engineering最新文献

Corrosion reduces the thickness of a structure, making it less safe and reducing its lifespan. In particular, ships are vulnerable to corrosion because they are always submerged in seawater. This corrosion is identified through regular inspections of the ship structure, and gradually increases in scope if no action is taken at an early stage. In this study, we developed a model to detect the corrosion areas and predict the depth of corrosion in the detected areas. The corrosion area detection model used a machine learning model based on Mask R-CNN. The 35,753 images were used to map corrosion images and measured corrosion depths. Four different color maps and regression algorithm were used to predict corrosion depths and their performance was compared. The new attempt to predict the corrosion depth from images in this study will contribute to improving existing corrosion control methods by providing information for corrosion prevention and maintenance.

With the recent intensification of climate change due to global warming, the importance of renewable energy has been highlighted, emphasizing the need for renewable energy development. In the case of renewable energy power generation, it is installed and operated on a large scale to meet energy demand, economic efficiency, and optimize local resources. Therefore, the number of cases of installation on water and sea with high space utilization is gradually increasing. When operating large-scale power systems, conservative design and review are necessary because damage to the structures can cause cascading failures, leading to major accidents. In particular, for photovoltaic systems, the method of expansion by connecting individual unit structures is commonly used. Therefore, it is necessary to analyze the characteristics of the unit structures and the connection methods. In this study, a fluid-structure coupled analysis was performed on the unit structures of a multi-linked floating offshore structures, which can be large-scale expansion, developed by the Korea Research Institute of Ships and Ocean Engineering. The characteristics were analyzed based on the connection method. The analysis results showed that when the connection method was a hinged condition, the pitch motion increased compared to the fixed condition, but since the peak occurred at a high frequency with a 4-s period, it is advantageous to avoid resonance. In particular, it was confirmed that the maximum stress was reduced by approximately three times, which is beneficial for structural integrity. Additionally, it was found that as the stress distribution moved from the center to the edges, it is also advantageous in terms of maintenance. In addition, the numerical method of the multi-linked floating offshore structures and the characteristics of hinged condition were verified through model tests.

Propellers produce fluctuating thrust and torque as they rotate in a non-uniform wake field. They contribute most of the vibration and noise generated by the propeller and can lead to mechanical damage to shafts and bearings. Recently, the demand for electric propulsion ships has increased. As the torque and speed fluctuations are generated in marine propellers, harmonic components in the current and voltage of the propulsion motor occur and lead to increased losses, device degradation, and torque pulsations. In this study, a harmonic injection method is proposed to reduce the impact of motor and mechanical vibration caused by the fluctuating load torque of the propeller. A harmonic component is applied to the current of the motor to generate a motor torque with a different phase of the same magnitude as the variation of the load torque of the motor. In this study, a computational fluid dynamics simulation was performed to obtain the torque of the target vessel, medium range tanker, and a MATLAB Simulink was used to model the motor simulation. It was found that the harmonic injection method can reduce the mechanical torque fluctuation of the motor by 87%.

With the steady growth of international trade, sea transport has become indispensable, leading to an increase in maritime accidents. The sinking of the Russian Black Sea Fleet flagship, the guided missile cruiser “Moskva,” underscores the critical need for enhanced maritime safety. However, the dynamics of ship stability, particularly under transverse wind and wave conditions, remain unclear. We aimed to explore ship navigation safety by using the Moskva incident as a case study. Specifically, our objective was to investigate the influence of wind and waves on ship stability, calculate the capsizing probability of the vessel, and devise a fast and safe return path to port. We conducted a comprehensive review of existing literature on ship stability and path-planning algorithms. Leveraging this knowledge, we established the dynamics equation under transverse wind and wave conditions and integrated risk and vulnerability indicators to obtain a quantitative sea-area risk zoning map. Additionally, we employed the A* algorithm to plan a path under International Maritime Organization rules restrictions. Our findings reveal insights into ship stability dynamics and the importance of considering environmental factors in navigation safety. We calculated the capsizing probability of Moskva and devised a fast and safe return path to port, highlighting the practical application of our methodology. This study contributes to the understanding of ship navigation safety by addressing the knowledge gap in ship stability dynamics. Our findings underscore the significance of considering environmental factors in navigation safety planning. However, limitations exist in terms of data availability and model accuracy. Future research should explore additional factors impacting ship stability and refine path-planning algorithms for enhanced safety.

The shape of the slit that injects the jet from the surface of the propeller was optimized through numerical computations. The high-pressure drop on the propeller surface caused by jet injection could be improved by modifying the hydrofoil geometry of the propeller. As the cover length increased and the slit was located at the center of the propeller, the volume of jets leading to the trailing edge increased, and the propulsion performance was improved. As the height of the slit increased, the thrust increased due to the Coanda effect, and the torque decreased because of the thrust of the jet. The jet injection pattern differed according to the area of the slit and tunnel, which caused a difference in the propeller performance. The jet pattern changed according to the area of the slit and tunnel, leading to a change in propeller performance. It was effective in improving the efficiency by injecting from as wide an area as possible, and the efficiency was improved by approximately 2 % considering the pump efficiency through optimization of the slit shape.

The service history of a naval destroyer, HMCS IROQUOIS, was analyzed to develop an operational profile for structural fatigue assessment. The data from 1972 through 2012 provides insights for developing data sample requirements and wave data collection approaches applicable to other aging vessels. The results show that capturing daily wave data at the recorded position sufficiently describes the encountered seaways. Artificially reducing the data set to represent incomplete hull monitoring or operational data indicates that 5–9 years of wave data were required to limit the damage rate coefficient of variation to within 15%. However, operational changes, such as those observed after this destroyer’s midlife refit, may increase data requirements. Similar requirements for convergence were observed in duration-at-sea data derived from annual days at sea or distance sailed. The findings, consistent across the class and another class of ships, show that results for this ship are not anomalous.

Ships are constructed using the shipbuilding method, which involves several blocks. Every block produced in each unit process features a different production speed depending on the block shape, number of members used, and process complexity. Consequently, the blocks produced in one process is stored in the stockyard for the next process operation. As the number of blocks stacked in the stockyard increases, the movement of the blocks and that of their transporters increase, thus resulting in an increase in operating costs. Hence, we propose a method for monitoring the block storage status based on drone images and shipyard Geographic Information System (GIS) information to support the efficient use of block stockyards. Shipyard GIS information is mapped onto the image acquired from the drone, and the area of the stacked block is detected in the image. The block storage area and storage load factor of the stockyard are calculated using the saved block areas and shipyard GIS information. By evaluating shipyard stockyards, we confirmed the possibility of monitoring the status of shipyard block storage based on drone images and GIS information.

The deterioration in the technical conditions of the main engine, hull, and propeller over time in service is natural and causes adverse effects on ship operating performance, so determining and overcoming this phenomenon is necessary. However, effectively solving this problem is not simple because it is affected by many complex and random factors such as engine deterioration, increased roughness of hull and propeller surfaces, changes in sea state and ship load, etc. In this study, our new approach based on the black-box method and detailed propeller diagrams provides an effective way to assess and improve ship performance both under specific operating conditions and after a period of service. This method was verified and validated with the test data of the Glory Star oil tanker and applied to the Duong River dry cargo ship in Vietnam to determine its performance degradation and provide solutions to overcome this problem. The results showed that after 5 years out of dry dock, the study ship's performance or propulsion efficiency was reduced by about 8.6%, resulting in an increase in fuel consumption of about 6.5% and a decrease in ship speed of about 14.7%. By applying technical solutions such as tuning the engine operating mode and choosing a practical propeller design point, the performance of this ship was greatly improved and brought about high economic and technical efficiency. Especially, the cutting of the propeller edges not only solved the torque-rich phenomena occurring on the study ship's main engine after 5 service years, but also saved 5.1% and 4.9% in hourly fuel consumption, and increased 3.9% and 4.9% in ship speed, calculated for ballast and full load sea trials, respectively.