This study examines the optimal cross-sectional design of a submerged breakwater to enhance its efficiency in reducing the mean water level behind the structure. The objective is to achieve effective wave control and reduce the mean water level behind the structure to mitigate the damage caused by high waves at the coast. The numerical wave tank is employed to verify the validity and feasibility of the submerged structure by comparing its wave control characteristics and the hydraulic properties of the mean water level behind the structure with the results of existing hydraulic model experiments. The hydraulic characteristics are calculated from the computed free surface data using the wave reflection and transmission splitting method. The mean water level behind the structure is compared by nondimensionalizing the averaged free surface with the incident wave height. The important results of the examined optimal cross-sectional shape are as follows: An optimal cross-section is identified when it is larger than or equal to 1.8 of the incident wave height. Herein, the examined breakwater achieves a reduction of approximately 72% in the mean water level behind the structure and wave attenuation of at least 10%. Therefore, the submerged breakwater cross-sectional shape examined in this study can appropriately regulate the increase in the mean water level behind the structure while providing wave control.

The 2011 Fukushima Daiichi nuclear disaster, caused by tsunami inundation, highlighted the severe risks facing coastal nuclear power plants (NPPs) owing to marine hazards. Motivated by this event, this study quantitatively evaluates storm surge hazards at four NPP sites (Kori, Saeul, Weolseong, and Hanul) along Korea’s eastern coast, where storm surges pose greater risks than tsunamis. Approximately 3,000 synthetic typhoons were generated using the tropical cyclone risk model (TCRM), and 37 scenarios were simulated with the advanced circulation (ADCIRC) model; validation was performed using Typhoon Maemi (0314). The key meteorological parameters (central pressure, maximum wind speed, and the radius of maximum wind) as well as the closest approach distance were evaluated against maximum storm surge height (MSSH) and time-integrated storm surge height (TISSH). The MSSH increased with lower central pressure, higher wind speed, and smaller radius of maximum wind, and decreased with greater closest approach distance. The Kori and Saeul NPPs were more sensitive to the MSSH, whereas the Hanul NPP showed a small MSSH because typhoons did not directly approach, but prolonged water level rise caused a large TISSH. These findings indicate that storm surge hazards are governed by typhoon intensity and track proximity, and indices, such as TISSH, are essential for assessing sustained inundation and overtopping.

The Nakdong River Estuary, characterized by ecological diversity and economic importance, faces challenges from salinity intrusion owing to estuary bank operations. This study aimed to develop a rapid and accurate prediction system for salinity concentrations to support effective water resource management. Time series data from 2021 were analyzed to identify correlations between salinity and environmental factors. Granger causality analysis determined that discharge, seawater inflow, tidal level, and rainfall significantly influence salinity, with optimal temporal lags for each variable. A random forest model, combined with a sliding window approach, was used to forecast salinity for short-term (1–6 h) and medium-term (12–24 h) horizons. The model incorporating lagged variables achieved high accuracy in short-term predictions (coefficient of determination > 0.9), effectively capturing the physical travel time of water. Medium-term predictions also showed improved performance compared with baseline models, though prediction uncertainty increased with longer horizons due to environmental variability. Incorporating lagged variables based on physical and statistical analysis enhances the accuracy of salinity forecasts in the Nakdong River Estuary. These findings support the development of data-driven management strategies for estuarine environments.

Simultaneous LNG bunkering operations involve the concurrent execution of on/off loading and LNG bunkering. While this approach is economically advantageous due to reduced bunkering time, it also increases operational hazards. Consequently, the need for standardized safety regulations for bunkering simultaneous operations has become increasingly urgent. In this study, the safety of such operations under ocean wave conditions is investigated through numerical analysis for both the receiving and bunkering ships. The analysis considers both ship-to-ship (STS) and ship-to-wall (STW) configurations, examining how motion responses are affected by environmental conditions. The results confirm that both vessels are significantly influenced by wave reflections from the quay wall. Additionally, the bunkering ship is further affected by the presence of the receiving ship. When irregular waves act on the side-by-side moored vessels at the quay wall, the motion of the relatively smaller bunkering ship exhibits greater sensitivity to wave. Notably, the heave and roll responses of the bunkering ship become pronounced at certain significant wave heights. These findings highlight the necessity of developing detailed standards for LNG bunkering simultaneous operations, which should be addressed in future research.

Recently, digital transformation has become crucial for the safe operation and extended lifespan of ships and offshore structures. Structural health management is gaining importance and driving interest in digital twin technology for monitoring structural integrity. Digital twins enable proactive maintenance through the real-time monitoring and prediction of structural responses. This study developed a reduced-order model (ROM) for a container ship and validated it against a full-scale model. To address irregular wave loading challenges, we applied a snapshot-based Krylov subspace method. Unlike conventional methods that use unit force vectors in axial directions, this approach considers time-varying pressure distributions from irregular waves. Numerical simulations showed that with 20 reduced orders, the structural response had a relative root mean squared error of 0.02% compared with the full-scale model, whereas computation time decreased by over 99%. The ROM maintained performance under varying heading angles and ship speeds, with 20–30 reduced orders balancing accuracy and efficiency. Thus, Krylov subspace-based model-order reduction is a valuable tool for predicting the structural responses of ships and offshore structures under real-time irregular waves. It is expected to be widely used in digital twins for structural health assessment, including damage detection and fatigue strength evaluation.

Buoyancy engines used in underwater gliders require durability due to repeated operation over months. Using a hyperbaric chamber for durability testing is not only expensive but also challenging to operate, as the chamber require continuous monitoring for several days. In our laboratory, we develop a hydrostatic test device that allows us to test a buoyancy engine in open air to verify its durability. The hydrostatic test device allows us to observe problems associated with the buoyancy engine, which is repeatedly exposed to high-pressure environments in the laboratory, and to verify its durability via repeated operation under varying environmental pressures, which mimics the actual situation. The hydrostatic test achieves more than 1,000 cycles, which is equivalent to three months of operation of an underwater glider. As the power source used in this case is a battery, the amount of power consumed is measured to ensure that it is within the capacity of the battery used. The result shows that it is within the acceptable range.

Storm surges induced by typhoons pose a significant threat to coastal regions, particularly in areas with complex shorelines and shallow waters. In this study, we investigated the impact of typhoon tracks on storm surges along the Korean Peninsula through numerical simulations based on synthetic typhoon scenarios derived from historical data. Specifically, the Advanced Circulation (ADCIRC) model was employed to simulate storm surges using scenarios based on six historical typhoons that followed common tracks into the West, South, and East seas of the Korean Peninsula. The results indicate that storm surge heights and volumes are significantly influenced not only by typhoon intensity but also by coastal morphology and landfall location. The west and south coasts, characterized by intricate bay structures, experienced amplified storm surge heights owing to water accumulation effects, whereas the east coast exhibited relatively low surge levels. The temporal evolution of storm surges further revealed that prolonged surge durations contribute to increased inundation risk. Additionally, storm surge heights varied notably when historical typhoons were simulated along different tracks, highlighting the importance of track uncertainty in storm surge forecasting. These findings emphasize the need for region-specific coastal disaster mitigation strategies, considering the combined effects of typhoon intensity, track, and coastal morphology.

Greenland's abundant renewable energy resources position it as a potential producer of green hydrogen, a promising energy carrier for global decarbonization efforts. This research aims to evaluate the economic feasibility of hydrogen transportation in Greenland, focusing on compressed gas via pipelines and liquefied hydrogen via maritime routes. The study employs a comprehensive methodology that includes economic analysis of production, liquefaction, and transportation costs. This approach integrates a wide range of methods available in the literature and considers various components of the hydrogen supply chain, going beyond the typical focus on transportation strategies alone. Results indicate that pipelines are more cost-effective for shorter distances (<1,500 km) and higher demand, whereas shipping is better suited for longer distances and larger volumes. A case study of transporting hydrogen from Paamuit to Nuuk revealed that for a production capacity of 40 t/d, the cost of pipeline transport was 1.3 USD/kg, whereas for shipping it was 2.7 USD/kg. These findings contribute significantly to the development of a hydrogen economy and highlight Greenland's potential as a competitive player in the global green hydrogen market. The research provides valuable insights for decision-makers in planning efficient and economical hydrogen transportation strategies.

This study systematically analyzes the impact of sediment disasters, such as those due to debris flows, on key facilities near the Gori nuclear power plant, aiming to identify limitations in the current safety management system. Using 62 years of rainfall data from the Busan weather station, probable rainfall values for return periods of 30, 50, 100, and 200 years were analyzed. These values were applied to various debris flow scenarios to evaluate the flow characteristics and impact forces on structures. The analysis reveals that the impact forces of debris flows increase sharply for return periods of 100 years or more, indicating that existing safety protocols may not adequately account for the topographical characteristics. This study highlights the necessity of a comprehensive safety assessment framework that integrates site-specific risks such as slope and sediment dynamics. By utilizing actual rainfall data, this study provides a safety evaluation that reflects the unique geographical hazards faced by nuclear facilities. The findings offer essential data to guide future policy decisions regarding site selection, design, and operational management of nuclear facilities, ultimately improving the disaster preparedness for high-risk locations in a way that differs from existing studies.