Woo-Dong Lee

Decompression sickness (DCS) has been a persistent safety concern in diving operations since its recognition among 19th-century caisson workers. This review consolidates the theoretical foundations and historical development of decompression theory, from Dalton’s and Henry’s laws to representative algorithms used in contemporary diving practice. Dissolved-gas models, including Haldane’s tissue-compartment theory, Workman’s M-value framework, Bühlmann ZH-L algorithms, and Thalmann exponential–linear models, along with the gradient factor approach, are reviewed together with bubble-based approaches, including the thermodynamic model, varying permeability model, and reduced gradient bubble model. Their core assumptions, mathematical formulations, and operational implications are examined in a unified framework. A comparison of a 40-m air dive with a 30-min total bottom time showed that total decompression time differed by up to 3.6-fold among algorithms, reflecting differences in model assumptions, conservatism settings, and implementation-specific characteristics rather than any inherent superiority of a particular algorithm. The review further discusses implications for dive planning under dynamic marine conditions and integrated diver and remotely operated vehicle operations. This narrative review provides a consolidated reference for informed algorithm selection and safer dive planning across recreational, technical, commercial, military, and marine salvage and rescue diving contexts.

Point-estimate accuracy for local pier scour has improved; however, bridge-foundation design also requires prediction intervals that achieve nominal coverage. Conformal prediction provides finite-sample marginal coverage under exchangeability, but this guarantee may fail when evaluation conditions extend beyond the training range. This study analyzed 1,152 field records from the U.S. Geological Survey pier-scour database, partitioned at the 70% quantile of flow intensity to create a controlled covariate shift. Split conformal, which produces fixed-width intervals, and conformalized quantile regression (CQR), which produces input-dependent intervals, were compared using an extreme gradient boosting model configured for quantile regression over five random seeds. Both methods achieved coverage close to the target levels in the in-distribution region. In the shifted region, at the 90% target, the coverage of split conformal fell to 0.783 (11.7 percentage points below the target), whereas CQR maintained 0.898. The mean CQR interval width increased from 1.116 to 1.432 because of a larger base quantile spread rather than the calibration term. The higher shifted-region coverage of CQR remained consistent across split ratios of 0.6–0.9. Because neither method retains a theoretical guarantee under distribution shift, CQR's higher coverage is empirical and reflects wider intervals rather than improved physical extrapolation.

Although tsunami-driven drifting debris poses a critical secondary hazard to coastal infrastructure, quantifying the resulting impact forces is challenging because of the limited post-event observations and a lack of full-scale experimental data. This paper presents a coupled numerical framework integrating a numerical wave tank (NWT) with LS-DYNA to estimate the debris-induced impact forces under tsunami-like inundation conditions. The NWT was used to simulate wave generation, propagation, overtopping, and the resulting nearshore hydrodynamics. In contrast, the arbitrary Lagrangian–Eulerian (ALE) formulation in LS-DYNA was used to resolve debris transport and collision dynamics. Validation against existing hydraulic experiments showed that the proposed framework captures the overall sequence of debris drift and collision reasonably well. Nevertheless, some discrepancies remain in the drift initiation and collision velocity because of the simplified representations of friction and contact. The results further suggest that local contact conditions during collision and the momentum characteristics of the inundation flow strongly influence the maximum impact force. The proposed framework provides conservative estimates of debris-induced impact forces because the numerical model tends to produce surface-to-surface collisions owing to suppressed rotational motion. Overall, the coupled NWT–LS-DYNA framework provides a rational and conservative basis for assessing debris-collision hazards and supporting the structural design of tsunami-prone coastal infrastructure.

Complex interactions between seawater and freshwater govern intrusion and stabilization in coastal aquifers. Previous studies have primarily relied on interface-based analyses, limiting full-field spatial quantification of seawater distribution. This paper proposes a computer vision–based method for quantifying seawater behavior in laboratory sand tank experiments. Experimental videos were acquired under controlled hydraulic and lighting conditions, and an image analysis framework was established in Python using OpenCV, including preprocessing, red–green–blue (RGB) and hue–saturation–value (HSV) color-space analysis, threshold determination, binary segmentation, region extraction, area calculation, and temporal filtering. Rhodamine-B dye enabled robust segmentation, and the H channel provided the most reliable separation with reduced sensitivity to illumination variations. The extracted seawater area time series showed an initial rapid increase, a temporary decrease associated with interface readjustment, a gradual reintrusion stage, and eventual stabilization. A fourth-order Butterworth low-pass filter with a cutoff frequency of 0.001 Hz was applied to suppress the high-frequency noise and clarify the convergence toward seawater–freshwater pressure equilibrium. Stabilization was defined as the stage at which the one-hour-averaged relative area-change rate fell below 1%. These findings suggest that the proposed framework enables the non-intrusive, reproducible quantification of seawater behavior and provides a practical alternative to conventional interface-based methods.

Tsunami-like waves pose a serious threat to coastal infrastructure, necessitating effective mitigation measures to reduce inundation and associated damage. This study uses a numerical wave tank (NWT) to investigate the hydrodynamic mitigation mechanisms of a submerged horizontal plate (SHP) under tsunami-like wave conditions. Long-period solitary waves are used to represent tsunami-like forcing. The NWT is validated against hydraulic experiments for wave profiles and hydrodynamic coefficients, including reflection, transmission, and dissipation. Using the NWT, the spatiotemporal evolution of wave, flow, and vortex fields, together with momentum flux, is analyzed for various SHP geometries, placements, and incident wave conditions. The results demonstrate that SHP performance is not governed by a single nondimensional parameter but by the combined effects of breaking regime and the distribution of flow above and below the plate. Although stronger breaking increases energy dissipation, momentum flux attenuation does not increase monotonically under plunging breaker conditions because dissipation efficiency saturates. In contrast, a stable and efficient reduction of transmitted momentum flux is achieved within the collapsing breaker regime. These findings highlight the importance of optimizing SHP geometry and placement to induce efficient breaking prior to saturation, providing practical guidance for tsunami-like wave mitigation design.

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.

Maritime disasters pose substantial social and economic challenges and often require complex, resource-intensive search and rescue operations to minimize loss of life and damage to infrastructure. This study proposes a sustainable and quantitative framework for planning and managing underwater search and rescue operations in strong tidal current environments, with reference to the Sewol ferry disaster. Hydrodynamic current predictions over a 31-day period were analyzed to determine tidal-induced diving cycles and to estimate the depth-specific diveable time (DAT) under safe operating limits of 1 knot for a self-contained underwater breathing apparatus (SCUBA) and 1.5 knots for surface-supplied diving systems (SSDSs). Two representative dive profiles were developed: a no-decompression SCUBA plan for 26 m hull diving and a staged-decompression SSDS plan for 48 m seabed diving, considering oxygen toxicity and nitrogen narcosis limits. Workable time (WAT) analysis indicated SCUBA as optimal for hull tasks (WAT/DAT = 0.83), whereas the SSDS provided extended efficiency for deep-water operations. A redeployment model based on surface interval constraints reduced diver staffing requirements by approximately 28%. The proposed framework enhances the sustainability and resilience of marine disaster response by optimizing diver safety, operational efficiency, and resource management, contributing to sustainable marine safety systems and long-term emergency preparedness.