Search Results (4,997)

In the context of economic globalization, waterborne transportation plays an important role in international trade and logistics. However, waterborne traffic accidents pose a severe threat to life, property safety, and the environment. To gain a deeper understanding of the causal mechanisms behind waterborne traffic accidents, we conducted a data-driven analysis of the causal chain of waterborne traffic accidents. By constructing a hybrid framework integrating an improved HFACS (Human Factors Analysis and Classification System) with a Bayesian network model, we conducted a multi-dimensional analysis of accident causes. The constructed model was quantitatively analyzed by applying genie software to the accident samples collected from the China MSA. The results indicate that there are 12, 3, 6, 2, 4, and 7 causal chains leading to collisions, contact, fires/explosions, windstorm accidents, sinking, and other types of accidents, respectively. These research results can serve as a reference for the enhancement of the safety of waterborne transportation. Full article

Predicting the roll damping coefficient of a ship is a crucial factor in determining the dynamic stability of the vessel. However, a nonlinear analysis that considers the viscosity of the fluid is required to accurately estimate the roll damping coefficient. This study numerically analyzed the hydrodynamic coefficients related to the roll motion of ships, focusing on the eddy-making damping coefficient. A series of forced vibration tests were conducted on a two-dimensional triangular cylinder floating on the water surface. The overset method and the volume-of-fluid method were applied, and the governing equations were solved using the open-source software OpenFOAM v2106. Uncertainties in the grid size and time intervals were identified through the International Towing Tank Conference (ITTC) procedure, and the obtained hydrodynamic coefficients were compared with available experimental data and potential flow results. Additionally, eddy-making damping was extracted from the shed vortex for various excitation frequencies and amplitudes. The study found that the uncertainty in the roll damping coefficient was less than 8%, with eddy-making damping being the dominant factor influencing the results. Numerical results showed a good agreement with experimental data, with an average deviation of 4.4%, highlighting the importance of considering nonlinear effects at higher excitation amplitudes. Comparison with experimental data and empirical formulas revealed that the nonlinearity due to the excitation amplitude must be considered in empirical formulations. Full article

Mapping anthropic activities in aquatic environments is crucial to support their sustainable management. Aquatic traffic is one of the human-related activities gaining relevance nowadays, and remote sensing can support the description of the distribution of vessels, particularly small boats or other vessels not tracked with other tools. Following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, we performed a systematic review of the literature to describe current trends, key methodologies, and gaps, with special regard to the challenges of monitoring small boats that are not equipped with Global Positioning System (GPS) transponders. A total of 133 studies published between 1992 and 2024 were included. The research effort is mainly dedicated to developing new methods or upgrading existing ones, with only a few studies focusing on applications in a contest of environmental studies and, among these, only a few focusing on small boats. To promote the use of remote sensing by environmental scientists, coastal, and fishery managers, explicative case studies are delineated, showing how boat identification through satellites can support environmental studies. Moreover, a guideline section for using remote sensing to integrate monitoring of small boats is given to promote newcomers to this field. Full article

This study investigates the strength development of cement-stabilized marine clay, which is influenced by a complex interplay of microstructural factors. To optimize its performance for coastal and offshore engineering, we explored the relationship between microstructure and unconfined compressive strength (UCS). Using Scanning Electron Microscopy (SEM) and the Pore/Crack Analysis System (PCAS), we analyzed samples with varying cement contents (10%, 15%, and 20%) and curing times (3, 7, 14, and 28 days). Key microstructural parameters, including porosity, particle shape, size, and arrangement, were quantified and correlated with UCS results. A novel comprehensive micro-parameter was introduced to encapsulate the combined effects of these factors, revealing an exponential relationship with strength development. The findings provide a quantitative framework for predicting the performance of cement-stabilized marine clay, contributing to more efficient solutions in geotechnical engineering. Full article

An ocean target electric field signal is an effective approach for analyzing the ocean environment and is widely used for detecting ocean targets, extracting their features, and tracking them. Low-frequency analysis and recording (LOFAR) is a commonly used time–frequency analysis tool that provides the time–frequency spectrum of a signal; however, its reliance on the Fourier transform (FT) results in a low frequency resolution and signal-to-noise ratio (SNR), which limits its target detection capabilities. To address this problem, we propose a method called low-frequency analysis and recording based on basis pursuit (LOFAR-BP) for analyzing and detecting ocean target electric field signals. LOFAR-BP uses basis pursuit (BP) with the L1 norm for frequency analysis, whereas LOFAR utilizes the FT. We demonstrate that the FT is the L2 norm mathematically. LOFAR-BP generates the time–frequency spectrum in the same way that LOFAR does. By extracting characteristic values from the time–frequency spectrum, targets can be detected using an appropriate threshold. Both simulation and ocean experiments showed that LOFAR-BP effectively enhances target signals and suppresses noise. Compared with LOFAR, LOFAR-BP improved the frequency resolution by 60% in both experiments and increased the SNR by 54.82 dB in the simulation experiment and by 39.59 dB in the ocean experiment. When applied to target detection, LOFAR-BP can detect targets 6 s earlier than LOFAR can. Full article

The automatic identification system (AIS) is an essential tool for modern ships, enabling the broadcast of identification and location information. However, the current AIS standard lacks security features, meaning that messages exchanged via AISs are transmitted in plaintext, which leads to security issues such as privacy leakage. Most existing solutions rely on public key cryptography. This paper proposes a physical-layer key generation protocol based on the current AIS standard (ITU-R M.1371-5). In the case of unicast AIS communication, the protocol utilizes channel randomness to generate symmetric keys for securing communications. Compared to public key cryptography, the proposed protocol offers advantages such as low overhead, elimination of third parties, and ease of implementation. Finally, this paper discusses the security of the protocol against various threats as well as evaluates its performance and overhead. Under common speed and signal-to-noise ratio (SNR) conditions, The protocol generates Advanced Encryption Standard (AES) keys of different lengths in under 4000 ms, and these keys successfully pass the National Institute of Standards and Technology (NIST) randomness test. Full article

This study evaluates the serviceability of floating structures designed for marine cities by incorporating wave-dissipating modules. Small-scale model tests in a 2D wave flume were conducted to compare the serviceability of structures with and without these modules under different wave conditions (1-year and 100-year return period waves). The results showed that wave-dissipating modules significantly reduced vertical acceleration, with reductions of approximately 44~45% levels for 1-year return period waves and 54~57% levels for 100-year return period waves. When a topside building was included, the reductions were similarly pronounced, reaching 64% and 63~64% levels for 1-year and 100-year return period waves, respectively. The modules also mitigated inclination (angle), with reduction rates ranging from 55~77% levels, depending on wave conditions and the presence of a topside building. These findings suggest that incorporating wave-dissipating modules around the periphery of floating structures can enhance their serviceability by creating more comfortable and stable environments for human activities, while also improving the stability of the structures themselves. Future research should focus on scaling up the model tests and conducting field experiments to validate these findings under real conditions, as well as optimizing module designs for different wave conditions and structural configurations. Full article

To enable early identification of failure risks in ship systems and equipment, a dynamic cloud center of gravity model is developed for real-time system-level health assessment. First, the Functional Analysis System Technique (FAST) was applied to decompose the operational functions and dependencies of the intelligent machinery room system, enabling the structured establishment of a hierarchical evaluation index system. The comprehensive weight is derived through synergistic application of the fuzzy set (FS) theory and entropy weight. This process integrated expert-defined functional boundaries with measurable parameters critical to system performance. Then, an improved cloud center of gravity method based on the Gaussian cloud model and sliding time window method is used for the system’s adaptive health value calculation. The dynamic health model can achieve continuous online assessment and track the further evolution of the system. Finally, the proposed model is applied to the Fuel Oil Supply System (FOSS). The integration of system performance output and disassembly inspection results demonstrates that the method proposed in the article more accurately reflects the true health status changes in the system when mapping health values. Full article

This study investigates the spatiotemporal density aggregation and pattern distribution of vessel traffic amidst bustling maritime logistics scenarios. Firstly, a relatively new spatiotemporal segmentation and reconstruction method is proposed for ship AIS trajectories to address trajectory disruptions caused by berthing, anchorage, and other factors. Subsequently, a trajectory filtering algorithm utilizing time window panning is introduced to mitigate position jumps and deviation errors in trajectory points, ensuring that the dynamic trajectory adheres to the spatiotemporal correlations of ship motion. Secondly, to establish a geographical spatial mapping of dynamic trajectories, spatial gridding is applied to maritime traffic areas. By associating the geographical space of traffic activities with the temporal attributes of dynamic trajectories, a dynamic trajectory temporal density model is constructed. Finally, a case study is conducted to evaluate the effectiveness and applicability of the proposed method in identifying spatiotemporal patterns of maritime traffic and spatiotemporal density aggregation states. The results show that the proposed method can identify dynamic trajectory traffic patterns after the application of compression algorithms, providing a novel approach to studying the spatiotemporal aggregation of maritime traffic in the era of big data. Full article

This study presents a foam sandwich structure reinforced with carbon fiber columns (FSS-CFC), which exhibits strong mechanical and sound insulation properties. The FSS-CFC consists of two face-sheets and a polyvinyl chloride (PVC) core containing multiple CFC cylinders arranged in a periodic array. The sound transmission loss (STL) measured in acoustic tube experiments closely aligns with the finite element simulation results, validating the reliability of the present research. Through characteristic analyses, the study reveals the sound insulation mechanism of FSS-CFC, identifying three distinct sound insulation dips caused by the standing wave resonance of the core, column-driven same-direction bending vibrations, and column-constrained opposite-direction bending vibrations in the sheets. It is also demonstrated that the sound insulation performance of FSS-CFC is insensitive to hydrostatic pressure changes. Finally, the FSS-CFC is optimized by the genetic algorithm in MATLAB and COMSOL. The optimized FSS-CFC displays good improvements in both mechanical and acoustic performance compared to the initial structure. The average STL in the frequency of 500 Hz to 25,000 Hz has increased by 3 dB, representing an improvement of approximately 25%. The sound insulation mechanism in FSS-CFC could provide valuable insights for the development of a pressure-resistant acoustic structure for use on deep-water vehicles. Full article

Prediction of the spatial configuration of the umbilical cable during deep-sea mining in-situ tests is of great significance because dynamic change may cause the umbilical cable to touch the ground or overturn the mining vehicle. In the present paper, a real-time prediction method for the dynamic spatial configuration of the umbilical cable during the deep-sea mining process is proposed. At first, the environmental information, position and motion of the vessel–umbilical cable–mining system were collected by sensors arranged at different locations. Then, the data were converted and transformed to the local vessel coordinate system. After that, the commercial software OrcaFlex was employed to conduct real-time simulation, in which the spatial configuration of the umbilical cable was predicted by the lumped mass method. Furthermore, the proposed real-time simulation method was employed in a sea trial test of deep-sea mining in an area with a water depth of 1100 m. Comparing the prediction results with the trajectory of the USBL beacon obtained from the monitoring data, the maximum distance of some specific points was close to 5 m, and most of them were less than 3 m. Meanwhile, it could also give the dynamic responses of the deep-sea mining system. For example, the maximum top tension of the umbilical cable was less than 15 kN, which could be used to evaluate the health condition of the system. During the sea trial test, the proposed method played an important role in ensuring the safety of the umbilical cable during wide-range movement of the mining vehicle. With characteristics of good real-time performance, accurate prediction, high reliability and stability, the proposed method could enhance the confidence of engineers for on-site operation as a powerful digital tool for visualization of the subsea working state. Full article

Horizontal-axis turbines have been well-studied; however, there is a serious lack of information on the behaviour of vertical-axis turbines under unsteady operating conditions. Among unsteady flows, waves can cause significant mechanical fatigue and modify the flow downstream of the tidal turbines. Consequently, this paper aims to characterize the effects of waves on the hydrodynamic performance and wake development of a 1/20 scale model of a ducted twin vertical axis 1 MW-rated demonstrator. Power measurements were taken from the turbine and the velocity measurements downstream of the machine using a three-component Laser Doppler Velocimeter. The results show that, in the presence of waves, the mean wake characteristics present greater average height and width compared to the current-only condition. Moreover, the wake recovery happens faster downstream due to the sheared wake region homogenization, induced by the presence of higher intensity vortices. Through the Turbulence Kinetic Energy estimation, we also observe some increased fluctuations around the turbine and close to the free surface due to the presence of waves. Full article

The escalating global demand for containerized cargo has intensified pressure on container terminals, which serve as vital nodes in maritime logistics. This study aims to enhance operational efficiency in non-automated container terminals by examining two meta-heuristic approaches—Ant Colony Optimization (ACO) and a hybrid Greedy Randomized Adaptive Search Procedure (GRASP)—Genetic Algorithm (GA)—for quay crane scheduling. Their performance is benchmarked across various problem scales, with process completion time serving as the primary metric. Based on these findings, the most effective approach is integrated into a newly developed Decision Support System (DSS) to streamline practical implementation. Statistical analyses confirm the robustness of both methods, underscoring how meta-heuristics combined with a DSS can optimize quay crane utilization, bolster maritime logistics, and ultimately boost terminal productivity. Full article

Gassy soil is prevalent in coastal regions, and the presence of gas bubbles can significantly alter the mechanical properties of soil, potentially leading to various marine engineering geological hazards. In this study, a series of triaxial tests were conducted on fine-grained gassy soils under different consolidation pressures (p_c’), stress paths, and initial pore water pressures (u_w0). These tests were also used to verify the applicability of a newly proposed constitutive model. According to the test results, the response to excess pore pressure and the stress–strain relationship of fine-grained gassy soils strongly depend on the initial pore water pressure (u_w0), with the degree of variation being influenced by the consolidation pressure (p_c’) and stress path. As u_w0 decreases, the undrained shear strength (c_u) of fine-grained gassy soils gradually increases, and this is lower under the reduced triaxial compression (RTC) path compared to the conventional triaxial compression (CTC) path, which can be attributed to the destruction of the pore structure due to an increase in gas volume. The newly proposed model accurately predicts the pore pressure and stress–strain relationship of fine-grained gassy soils at low consolidation pressures (p_c’), but it falls short in predicting the mechanical behavior during shear progression under high p_c’ or the RTC path. Although the model effectively predicts the excess pore pressure and deviator stress at the shear failure point (axial strain = 15%), further improvement is still required. Full article