Subsea pipelines are vulnerable to anchor-induced structural damage during ship mooring operations, particularly from raising and dragging interactions. This study quantified the effects of the pipeline burial depth on the structural damage response under these two loading scenarios in a soft clay seabed. Three-dimensional finite element analyses were conducted using Abaqus/Explicit with the Coupled Eulerian-Lagrangian method, simulating a 6-ton stockless anchor on a soft clay seabed modeled using the Mohr–Coulomb constitutive model. Half-buried (1/2D, Case 1) and unburied (Case 2) conditions were compared using the equivalent plastic strain (PEEQ), von Mises stress, contact characteristics, and energy dissipation as primary damage indicators. In the raising scenario, both pipelines remained within the elastic regime (PEEQ = 0), but the unburied pipeline showed 44% higher von Mises stress, 58.7% greater lateral displacement, and 32% larger resulting displacement compared to the half-buried case. For the dragging scenario, the unburied pipeline showed 4.9 and 2.97 times higher PEEQ and peak contact pressure, respectively, while the half-buried pipeline exhibited 6.7 times more contact nodes and 61% higher plastic dissipation energy. These findings show that pipeline burial provides consistent protection under anchor dragging and raising conditions, underscoring the need for scenario-specific burial design standards.
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.
A reliable assessment of large-amplitude roll phenomena such as parametric roll requires an accurate characterization of roll damping. In this study, free roll decay model tests were conducted on the Duisburg test case container ship at large initial heel angles exceeding 30°, and linear and nonlinear roll damping coefficients were determined from the free decay results using the Froude energy method. The roll time series was reproduced with the fourth-order Runge–Kutta method using the estimated damping coefficients and compared with the experimental results. In addition, the speed dependence of the damping characteristics was examined using an equivalent linear damping coefficient. In the large-amplitude free roll decay tests, linear damping alone was insufficient to reproduce the measured response, whereas including a quadratic nonlinear damping term substantially reduced the prediction error. In addition, the damping coefficients identified from the small-amplitude region of the large-amplitude free roll decay tests underestimated the damping in the large-amplitude regime. The equivalent linear damping coefficients further showed that damping increased with the forward speed. These results suggest that an accurate prediction of large-amplitude roll responses requires nonlinear damping coefficients obtained from large-amplitude free roll decay tests.
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.
Predicting submarine motion during emergency rising requires accurate estimation of the moments of inertia during ballast tank blowing, yet prior studies approximate tanks as simple cubes or cylinders that may not reflect real mass distributions. This study develops a voxelization framework that computes moments of inertia directly from computer-aided design geometry without simplification. Three tanks of identical volume and mass (cube, cylinder, and U-shaped) were analyzed under stepwise blowing (100–40% mass) and pitch rotation (0–30 degrees), and the resulting inertia was coupled with the hull inertia. At full mass, the U-shaped tank showed 113.3% and 50.0% higher roll-axis inertia (Ixx) than the cube and cylinder, respectively. Ixx decreased by 55–57% as mass fell to 40%, with a further 9–11% reduction under a 30-degree pitch rotation for the cylinder and U-shaped tanks but none for the cube. When coupled with the hull inertia, the geometry-induced difference in total inertia remained within 3.3% for the roll axis and below 0.1% for the pitch and yaw axes, for which the position inertia term dominates. Tank geometry therefore strongly affects tank self-inertia but influences overall submarine inertia only in roll motion, governed by Ixx. The proposed approach offers an efficient tool for evaluating simplified ballast tank models.
