Search Results (303)

To address the neglect of real-time mass transfer effects by traditional analysis methods during the side-by-side offloading process of Floating Production Storage and Offloading (FPSO) and shuttle tankers, a numerical model incorporating the variable mass effect is established to enable the simulation of dynamic offloading processes. Using this model, the dynamic response characteristics under different offloading rates and sea conditions are systematically investigated and validated against towing tank tests. Based on the previously optimized benchmark configuration, which includes 16 side-by-side mooring lines, six floating fenders, and an anchor line angle of 60° for the FPSO, the evolution laws of mooring line tension and fender pressure under different offloading rates were systematically investigated under normal and extreme sea conditions. The results show that an increase in offloading rate significantly amplifies the system’s fender load; when the offloading rate reaches approximately 1.4 t/s, the system transitions from the quasi-static response region to a significant nonlinear coupling region, demonstrating obvious sea condition–rate coupling characteristics. Under the combined action of high offloading rates and severe sea conditions, fender pressure rapidly approaches the design limit, becoming the primary safety bottleneck for the system. Model test results indicate that the numerical model can well predict mechanical responses under low and medium offloading rate conditions. The research results can provide a reference for offloading rate control, safety assessment, and operational window determination during FPSO side-by-side dynamic offloading operations. Full article

Targeting the “Fishtailing Effect” associated with shallow-water, pile-founded column single point mooring (SPM) systems, this study investigates the vessel’s motion characteristics under multiple operational scenarios using a numerical calculation method validated by model tests. A refined classification of combined wind, wave, and current conditions was conducted. The study examines the vessel’s sway and mooring line tension response under both collinear and non-collinear combinations of these environmental forces. Furthermore, methods for suppressing vessel motion were explored. The results indicate that vessel motion leading to the “Fishtailing Effect” is more prone to occur under collinear wind, wave, and current conditions. Wave and wind energy can, to some extent, mitigate the vessel motion. When the current speed exceeds a certain critical threshold, the extreme values of the mooring forces on the swaying vessel undergo an abrupt change. Applying a stern tug force and reducing the mooring line length are both effective in decreasing the vessel motion range and the tension in the mooring lines. The findings shed light on the fishtailing-effect characteristics of tankers moored at pile-founded column SPM systems, providing a valuable reference for the safety and stability design of such mooring systems. Full article

To ensure the safe operation of floating LNG offloading hoses in bow-loading systems, this study investigates the key factors affecting the dynamic response of an LNG offloading hose string. A fully coupled dynamic model of the hose string, the LNG carrier (LNGC), and the FLNG is established based on the lumped-mass method. The sensitivities of hose loads and deformation indicators to the hose-string length, vessel stand-off distance, tanker-heading offset, internal flow velocity, ocean current speed, and wave height are quantified. Based on these results, a low-load operating configuration is identified and a preliminary operational envelope is proposed. The results show that, under the considered operational sea state, a hose-string length of 170.6 m and an FLNG–LNGC distance of 80 m yield the minimum effective tension. The recommended limiting environmental conditions for safe operations are a surface current speed of 1.1 m/s and a maximum wave height of 7.0 m. The present study provides a practical basis for preliminary configuration design, response assessment, and operational-limit determination of floating LNG export hoses in bow-loading applications. The main contributions of this study are threefold. First, a coupled time-domain framework combining AQWA-based vessel motions and OrcaFlex hose dynamics is established. Second, the effects of key configuration and environmental parameters are systematically quantified. Third, a preliminary operating envelope and a recommended configuration are proposed based on effective tension, bending moment, and curvature. These contributions distinguish the present study from previous work focusing mainly on local hose mechanics or qualitative system description. Full article

Marine Protected Areas (MPAs) are essential for preserving marine biodiversity; yet they face challenges from various human pressures, including vessel activities. This study examines the extent, spatial distribution, and temporal variability of vessel activity within the Southwest Marine Protected Area (MT101), a Natura 2000 site off the Maltese Islands, with the aim of identifying where and to what degree different vessel categories overlap with protected marine habitats. Using Automatic Identification System (AIS) data spanning 2017–2022, a cumulative, normalised vessel density approach was applied to five vessel types: passenger, fishing, cargo, tanker, and tug and towing vessel, and spatially integrated with the distribution of four Annex I habitat types, including sandbanks, Posidonia oceanica meadows, reefs, and sea caves. The analysis reveals distinct spatial and temporal hotspots of vessel presence, with passenger and fishing vessels showing consistently high overlap with ecologically sensitive habitats, particularly within bay areas and along sections of the MPA boundary, while cargo, tanker, and tug activities are more concentrated offshore. While direct ecological impacts were not quantified and vessel density serves as a proxy for potential pressure, the results highlight areas where vessel-related pressures are likely to be most pronounced and where management intervention is most urgently required. By linking long-term vessel activity patterns with habitat distribution, this study delivers a spatially explicit and transferable framework for assessing cumulative maritime pressures, providing an evidence base to support targeted, habitat-specific management measures, improved enforcement, and marine spatial planning within MPAs. Full article

Ship design is a particularly complex and time-consuming process, comprising a series of phases from concept to detail design. Ideally, the designer needs to deliver a design that complies with the operational and regulatory requirements, while at the same time being optimized with respect to one or more specified objectives. The aim of the present study is to describe an innovative design framework for the parametric modelling of large oil tankers, enabling the elaboration and assessment of numerous design alternatives in search of the optimum design. The hull form, internal layout, and 3D structural arrangement of each design alternative are generated automatically in NAPA^® software. Suitable tools have been developed, assessing the ship’s hydrodynamic performance, structural integrity, compliance with regulatory requirements, and economic viability, facilitating the evaluation of large numbers of variants in a practically acceptable computing time. The developed parametric model has been linked with suitable optimization algorithms, enabling the systematic optimization of the design of large oil tankers, subject to user-specified operational requirements and constraints. Typical application results from the optimization of Suezmax oil tankers are presented and discussed. Full article

Carbon capture and storage technologies are widely adopted, primarily in conventional power plants. Maritime transport must align with the 2050 targets and sharply reduce its environmental footprint. Onboard Carbon Capture and Storage (OCCS) appear to be an immediately feasible solution until alternative fuels are adopted and fully implemented. This study presents a regulatory compliance assessment and a techno-economic analysis of the implementation of OCCS. An LNG tanker was selected as a case study due to the inherent compatibility between LNG storage systems and CO₂ storage on board. The examined regulation includes the calculation of the corresponding penalties arising from the enforcement of the EU ETS, FuelEU Maritime, and the IMO NZF framework. The cost of installing the OCCS is also considered when evaluating the proposal’s sustainability. The results demonstrate that OCCS shows real promise in the fight against maritime transport emissions, but at present, it is not economically viable. Its viability depends mainly on clear regulatory guidelines and effective incentives that encourage its adoption, while offsetting investment and operating costs. Finally, the current study also seeks to resolve an ambiguity in the existing legislation that renders the OCCS a viable option. Full article

This paper proposes a physics-informed hybrid digital CO₂ emission-control technology for maritime transport, designed for adaptive ship speed optimization along a predefined geographical route between two ports, discretized into quasi-stationary segments and evaluated under forecasted metocean conditions, subject to economic and regulatory constraints associated with maritime decarbonization. The framework integrates two exact optimization methods, Backtracking (BT) and Dynamic Programming (DP), with a reinforcement learning approach based on Proximal Policy Optimization (PPO), operating on a unified physical, economic, and regulatory modeling core. By reducing propulsion fuel demand, the system acts as an upstream CO₂ emission-control mechanism for ship propulsion. This operational stabilization of the engine load creates favourable boundary conditions for advanced combustion processes and reduces the volumetric flow of exhaust gas, thereby lowering the technical burden on potential post-combustion carbon capture systems. Segment-wise speed profiles are optimized subject to propulsion limits, Estimated Time of Arrival (ETA) feasibility, and regulatory constraints, including the Carbon Intensity Indicator (CII), the European Union Emissions Trading System (EU ETS) and FuelEU Maritime. The physics-based propulsion and energy model is validated using full-scale operational data from four real voyages of an oil/chemical tanker. A detailed case study on the Milazzo–Motril route demonstrates that adaptive speed optimization consistently outperforms conventional cruise operation. Exact optimization methods achieve voyage time reductions of approximately 10% and fuel and CO₂ emission reductions of about 9–10%. The reinforcement learning approach provides the best overall performance, reducing voyage time by approximately 15% and achieving fuel savings and CO₂ emission reductions of about 13%. At the route level, the Carbon Intensity Indicator is reduced by approximately 10% for the exact methods and by about 13% for PPO. Backtracking and Dynamic Programming converge to nearly identical globally optimal solutions within the discretized decision space, while PPO identifies solutions located on the most favourable region of the cost–time Pareto front. By benchmarking reinforcement learning against exact discrete solvers within a shared physics-informed structure, the proposed digital platform provides transparent validation of learning-based optimization and offers a scalable decision-support technology for pre-fixture evaluation of fixed-route voyages. The system enables quantitative assessment of CO₂ emissions, ETA feasibility, and regulatory exposure (CII, EU ETS, FuelEU Maritime penalties) prior to transport contracting, thereby supporting economically and environmentally informed operational decisions. Full article

In this study, the contamination of two drinking water catchments in Australia by per- and polyfluoroalkyl substances (PFAS) was investigated. PFASs in water and sediment were found at hazardous concentrations in waterways affected by transport accidents 24 and 33 years earlier. The exact cause(s) of the PFAS pollution remains unclear due to large data gaps. Both locations experienced burning fuel tankers suppressed using PFAS foam. PFAS contamination of a Blue Mountains water supply triggered the closure of two drinking water reservoirs 3–5 km downstream of the accident site. PFAS contamination of Central Coast’s Ourimbah Creek was concentrated in two floodplain wetlands adjacent to the accident site. The Ourimbah PFAS-affected wetlands are within 500 m of a drinking water groundwater bore field and 1.2 km from a raw water offtake used as part of Central Coast’s drinking water supply. The Blue Mountains contamination has impaired the Blue Mountains World Heritage Area, with perfluorooctane sulfonate (PFOS) exceeding aquatic ecosystem protection guidelines by 100 times. The mean PFOSs in stream water near the area of the Blue Mountains road accident were 2.16 µg L⁻¹ and 213.3 µg kg⁻¹ in stream sediment. This research demonstrates how spillages of small quantities of PFASs can cause major harm due to their extreme persistence, and their levels have exceedance of environmental and health guidelines for decades, with major adverse implications for drinking water supplies and conservation areas. Full article

Fire represents a relatively infrequent but potentially severe hazard for bridges, with collapse rates comparable to or exceeding those caused by seismic events. Despite this, fire risk is often neglected in bridge design and assessment, particularly for existing infrastructures in urban contexts. Beyond collapse, fire can induce significant post-event consequences, including material degradation, serviceability loss, traffic disruption, and economic and social impacts. Existing studies highlight the influence of bridge material, fire scenario, and traffic characteristics—especially the presence of fuel tankers—on damage severity. In this context, this paper proposes a rapid fire-risk assessment methodology applicable to large bridge stocks. The approach adapts and modifies existing methods from the literature, integrating them into the multi-risk framework defined by the Italian Guidelines for existing bridges, where fire is not explicitly addressed. The methodology is specifically adapted to urban and suburban bridges and European roadways, validated through its application to a stock of 30 bridges along the Palermo ring road. The results enable the classification of bridges by fire risk, supporting infrastructure Authorities in prioritizing detailed assessments and intervention strategies on the most vulnerable bridges. Multi-risk assessment considering the fire–seismic risk is also addressed, by adopting a simplified seismic risk approach consistent with the Italian Guidelines for existing bridges and comparing it with internationally accepted methods, particularly the North American HAZUS system. Results show that accounting for the actual condition and deterioration of bridges leads to higher seismic risk classes, more consistent with the fire risk assessment procedure proposed. In contrast, expedited methods such as HAZUS, which neglect maintenance conditions, may underestimate seismic risk. Full article

Autonomous aerial refueling is a key technology for enhancing the endurance of unmanned aerial vehicles; however, the wingtip vortices generated by the tanker create a strong three-dimensional wake-vortex flow field, whose downwash and lateral airflow can impose significant rolling moments on the follower Unmanned Aerial Vehicle (UAV), posing a serious threat to flight safety. To address this issue, this study proposes an integrated framework that combines wake-vortex risk-field modeling with optimal path planning. The classical Hallock–Burnham (HB) model is first employed to predict vortex descent and lateral transport, while a two-phase model is used to characterize the temporal decay of vortex circulation. The predicted vortex parameters are then coupled with the UAV’s aerodynamic characteristics, and the rolling-moment coefficient (RMC) is introduced as a risk metric to compute its spatiotemporal distribution in three dimensions, thereby transforming the invisible wake-vortex disturbance into a visualizable and quantifiable dynamic three-dimensional risk map. On this basis, a wake-vortex-aware path-planning algorithm based on particle swarm optimization (PSO) is developed, incorporating adaptive weighting and elitist mutation strategies. A multi-objective cost function considering path length, safety, and smoothness is further constructed to search for an optimal safe path under wake-vortex influence. Simulation results indicate that, compared with the classical A* and Rapidly-Exploring Random Tree (RRT) algorithms, the proposed method reduces cumulative risk exposure by approximately 90% and 75%, respectively, while limiting the increase in path length to about 8% (significantly lower than the increases of 40% for A* and 44% for RRT). In addition, the maximum turning angle is constrained within 10°, and the computation time remains around 0.052 s, satisfying real-time requirements. These results demonstrate that the proposed method can generate safe, efficient, and dynamically feasible paths for UAV aerial refueling and provide a valuable reference for wake-vortex avoidance in similar aerospace missions. Full article

A key limitation of conventional early-stage oil tanker structural design is that the accidental limit state performance is rarely included as an explicit design objective, even though major topology and arrangement decisions are taken before detailed nonlinear analyses become feasible. This paper proposes a crashworthiness-driven structural design methodology for the concept design phase (CDP), in which crashworthiness is introduced as an explicit safety-related performance measure through surrogate modeling and used within a multi-objective optimization framework. Crashworthiness is represented by the internal energy absorption of a double-hull side structure under collision, which is obtained from a limited set of high-fidelity nonlinear simulations and approximated by response surface surrogate models to enable computationally efficient design-space exploration. The optimization framework considers structural weight and crashworthiness while enforcing rule-based adequacy constraints consistent with current classification practice, and it can be extended to additional safety-related measures. Application to an Aframax tanker case study demonstrates that Pareto-optimal solutions can be generated that improve the collision energy dissipation capability without disproportionate increases in structural weight at a stage where topology changes are still practical. The results confirm that crashworthiness-oriented criteria can be embedded within CDP design workflows in a manner compatible with established industrial practice. Full article

Bird survival is influenced by both natural and anthropogenic factors, including weather conditions and oil spills. In this study, we examined the impact of a major oil spill (Prestige oil tanker) and climatic conditions (precipitation and wind) on survival and recapture probability in the Kentish plover (Anarhynchus alexandrinus) population in Galicia (NW Spain). To this end, we applied the Cormack–Jolly–Seber (CJS) live recapture model to a sample of 372 adult birds captured between 1994 and 2023. The best-fit model indicated that survival was best explained by the interaction between precipitation and the Prestige oil spill, indicating a decrease in survival post-spill, especially in the periods Post1 (years 2003–2007) and Post2 (2008–2015). Precipitation showed a negative influence on adult survival, but wind had no significant influence. Recapture probability was influenced by the interaction between time, sex, and Prestige, with males showing higher values, probably due to behavioural and detectability differences. Environmental monitoring and preparedness for pollution events are therefore essential to improve the long-term viability of the species. Full article

To investigate the leakage characteristics of damaged double-hull oil tanks in still water, this study conducted both model tests and numerical simulations on the leakage process of a damaged double-hull oil tank model. Based on a 75,000 DWT oil tanker, a scaled model was designed according to similarity criteria. The effects of different damaged locations (side-shell and bottom) and various breach sizes on the tank’s leakage behavior were examined. The evolution of multiphase flow inside the tank and the surrounding flow field was captured, and the leakage pressure under fixed model conditions was measured. The model test results indicate that larger breach sizes lead to a more rapid stabilization of the pressure load during leakage and the liquid exchange process. For side shell breaches, after an initial phase of pressure-difference-driven leakage, a density-driven flow develops at the stable liquid interface. Bottom breaches cause flooding that results in an oil sealing phenomenon at the bottom, leading to a pronounced oil–water stratification. Corresponding numerical simulations of the model tests were performed, and the results were compared and validated against the model test data. Full article

To enhance the potential application of ships in energy conservation and emission reduction, a parallel hybrid power system simulation model was developed using Matlab/Simulink based on the operational scenario of a 3300 m³ inland LPG tanker. A rule-based control strategy was employed to simulate and analyze the impact of different power modes on the energy efficiency and emissions of the ship’s power system. An optimization method for an energy management strategy based on the ship’s operating cycle was proposed. The results show that using an LNG engine as the main engine in the hybrid system significantly reduces fuel consumption and pollutant emissions throughout the ship’s operating cycle. When the hybridization ratio is 0.2, the system achieves relatively optimal overall energy consumption and emission levels. Building on this, an Equivalent Consumption Minimization Strategy (ECMS) was introduced, and multi-objective optimization was carried out using an improved particle swarm optimization algorithm. Additionally, reinforcement learning was applied to optimize the energy management strategy, resulting in further reductions in fuel consumption over the operating cycle. Full article

Improving the efficiency of energy consumption, conversion, and transmission on merchant ships has become a critical challenge due to rising fuel costs, increasingly stringent environmental regulations, and the introduction of operational efficiency requirements such as the IMO CII. Existing energy-efficiency metrics are predominantly based on absolute or design-oriented indicators and do not adequately capture the latent reserves of energy savings embedded in ship energy systems. This study addresses this gap by proposing a methodological framework for quantifying energy efficiency through the concept of relative energy-saving potential. The proposed approach integrates ship energy balance analysis with a hierarchical assessment of relative theoretical, technical, and economically feasible energy-saving potentials. The framework is demonstrated using an illustrative numerical example for a representative medium-size product tanker. The presented calculations are intended to demonstrate the applicability of the methodology rather than to provide vessel-specific operational recommendations. The results indicate that a significant share of energy losses can be identified and reduced by technical and economic feasibility considerations. The study concludes that relative energy-saving potentials offer an effective and scalable foundation for ship energy management, supporting SEEMP implementation, CII compliance strategies, and integration into digital twin and AI-based energy management systems. Full article