Search Results (95)

The determination of principal dimensions in the early ship design stage requires iterative calculations based on the basis ship particulars and ship owner’s requirements, demanding considerable time and engineering effort. In modern shipbuilding practice, errors introduced at the early design stage carry a high risk of necessitating a complete redesign, particularly under the mandatory EEDI Phase 3 requirements. To address these challenges, this study presents an automated optimization system for the determination of principal dimensions, adopting $L_{BP}$ (Length Between Perpendiculars), B (Breadth), D (Depth), and $C_B$ (Block Coefficient) as design variables. The NSGA-II (Non-Dominated Sorting Genetic Algorithm) is employed to minimize total resistance ($R_T$), specific fuel oil consumption (SFOC), and lightweight (LWT) as objective functions, with EEDI Phase 3 compliance and minimum freeboard requirements imposed as design constraints. The developed program was applied to a 114K Aframax Tanker with VLSFO/LNG dual-fuel capability, yielding a reduction in total resistance of approximately 65 kN relative to the basis ship with improved propulsive efficiency and economic feasibility. The proposed methodology is expected to enhance the efficiency of the early ship design process and provide a systematic framework for meeting stringent environmental regulations. Full article

Overtopping wave energy converters share a similar geometry with traditional slope-ramp breakwaters, allowing integrated development that simultaneously ensures the basic protection function of the structure and realizes wave energy absorption. This study proposes a dual-level overtopping wave energy converter (DULOW) integrated with a pier-type slope-ramp breakwater, specifically designed for oceanic environmental conditions characterized by smaller wave heights and larger tidal ranges. An experimental laboratory investigation was conducted in a wave tank to evaluate the overtopping performance of the DULOW model under regular and irregular wave conditions. The experimental results show that the overtopping discharge increases with the number of plane collectors, and that the discharge collected by the plane collectors is significantly larger than that of the quadrant cone collector. At the higher still water level, the presence of the lower collector reduces the overtopping discharge captured by the high-level collectors. Under irregular wave conditions, the averaged overtopping discharges are lower than those observed under regular wave conditions. Furthermore, a semi-empirical formula is proposed to describe the variation trend of overtopping discharge with effective crest freeboard for the tested DULOW configuration. Full article

Hydraulic regime transitions and localized backwater responses can develop in gently sloped tunnels when shafts and short expansion–contraction transitions act as localized hydraulic controls. This study investigates a tunnel–shaft system using a combined theoretical, numerical, and experimental framework. A momentum-based spreadsheet model was first used to identify the discharge range at which backwater development and unsteady behavior begin. The analysis was then extended with EPA–SWMM to represent system-scale unsteady behavior and with a finite element model to resolve local hydraulic gradients near the transition. Numerical results were compared with observations from a Froude-scaled physical model. All approaches consistently showed that backwater develops primarily upstream of the shaft and that the most critical hydraulic zone is concentrated at the geometric discontinuity. A regulated entrance geometry was then evaluated as a mitigation measure. For the case analyzed, entrance regulation reduced inlet depth from 6.12 m to 3.50 m and relative filling from y/D = 0.87 to y/D = 0.503, shifting operation toward a lower-depth operating state with greater freeboard and reduced susceptibility to pressurization. The results demonstrate that shaft transitions should be explicitly considered in tunnel design and that entrance regulation can materially improve hydraulic performance. Full article

Riverine bridges are critical infrastructure that are increasingly exposed to severe hydrological hazards. This study proposes and validates a synergistic methodology for the assessment of riverine bridge resilience, integrating the conceptual 4R framework (robustness, rapidity, resourcefulness, and redundancy) with field inspections, hydrological and hydraulic modeling, including scour evaluation, within a multicriteria analysis scheme. The methodology comprises: (i) a systematic review of literature and regulations to construct a 30-parameter matrix across five dimensions (technical, economic, social, organizational, and environmental); (ii) data acquisition through field inspections, detailed topography, and technical studies; and (iii) one-dimensional hydraulic modeling in HEC-RAS under extreme scenarios (return periods of 100 to 750 years and a critical 500 m³/s scenario representing a potential overflow of the Aguada Blanca reservoir). The Bridge Resilience Index (BRI) is computed through a weighted additive model and a sensitivity analysis. Application to the San Martín Bridge (Arequipa, Peru), a structure with more than 60 years of service and recurrent preventive closures during flood events, revealed critical conditions: minimum freeboard of 0.26 m, absence of hydraulic protections, and limited institutional capacity. The resulting BRI value (1.898) indicates a low resilience level. The proposed framework provides a useful tool for risk-informed decision-making, the prioritization of interventions, and the strengthening of resilience in critical infrastructure. Full article

This paper builds a one-dimensional transient numerical model of mixed fuel of woody and non-woody biomass to simulate the multistage conversion process of biomass in a moving grate-fired bed, including drying, pyrolysis, gasification, and char combustion. Based on time and space discretization, the model comprehensively considers the conservation of mass, momentum, and energy. It also introduces reaction kinetics and freeboard radiation coupling effects to more accurately describe the bed temperature distribution and reaction process. The analysis focuses on the effects of different non-woody biomass mixing ratios and moisture content. This provides references for optimization of the design of future furnaces and operating parameters and mixed fuel composition. The simulation results show that, for pure woody biomass, the surface temperature reaches approximately 200 °C in the first zone, followed by char reactions with peak temperatures up to 592 °C. The whole conversion process takes about 62% of the grate length. Increasing the pepper mixing ratio leads to lower bed temperatures due to the higher moisture content. The maximum bed temperature in the first zone decreases from 592 °C for pure wood to 551 °C at 30 wt.% pepper, with delayed pyrolysis and a thinner char reaction zone. When the pepper mixing ratio is below 20 wt.%, the combustion process maintains a stable temperature gradient and a continuous reaction front, compared to the mixing ratio of 30% pepper case. This confirms the feasibility of non-woody biomass application to combustion technology. Although a higher pepper mixing ratio leads to a slight temperature decrease, the reaction remains stable along the grate, indicating reliable combustion performance. Full article

Ports are vital components of global and regional supply chains, supporting trade, transport connectivity, and socio-economic development. However, their functionality is increasingly threatened by climatic hazards such as sea-level rise and heat stress, both of which are projected to intensify under future climate change. This study presents a comprehensive framework for assessing the criticality of ports within a national network, demonstrated through its application to the Greek port system, which encompasses a multitude of ports of all types from large international hubs to small island ones. The framework combines openly accessible geospatial and socio-economic data with projections of exposure to sea-level rise and extreme heat within a structured multi-criteria decision-making (MCDM) approach, enabling the identification of critical ports and the prioritization of adaptation needs. Results show that large mainland ports dominate in socio-economic importance and network centrality, while smaller island ports are vital locally due to limited redundancy and high exposure to climatic hazards. By 2100, nearly all ports are projected to experience freeboard reductions below operational thresholds and increased heat-related stress. These results highlight the need for targeted adaptation measures, including engineering interventions for mainland ports and redundancy-enhancing actions for island ports. The proposed framework provides a replicable, data-driven tool to guide evidence-based prioritization of adaptation investments and strengthen climate-resilient maritime transport and coastal management, thereby contributing to the achievement of Sustainable Development Goals (SDGs) 1.5, 9 and 13. Full article

This study investigates the hydraulic transient behavior and optimization of air-vent configurations in the combined tailrace–diversion system of a hydropower station. The inlet flow boundary conditions were derived from the method of characteristics (MOC), and flow variations were incorporated into the CFD model using a user-defined function (UDF). The CFD results were validated by comparing them to MOC-based simulations of surge oscillations in the downstream chamber. Six different air-vent configurations, varying in number and diameter, were tested under high-water-level load-acceptance and load-rejection conditions. The results demonstrate that increasing the vent diameter, particularly to 3 m, significantly improves pressure regulation and air exchange efficiency, enhancing system stability. In contrast, simply increasing the number of vents did not lead to noticeable improvements. Sensitivity analysis of vent height revealed that raising the vent height from 12 m to 15 m provides sufficient freeboard to prevent overflow, without overdesign. These findings provide practical guidance for optimizing air-vent configurations in hydropower tailrace systems, improving hydraulic stability, and ensuring safe operation. Full article

This study conducts a numerical investigation of the geometry of the oscillating water column (OWC) wave energy converter under realistic irregular wave conditions found off the coast of Rio Grande, southern Brazil. Two OWC models were compared: the conventional design and the L-shaped configuration (L-OWC). The OWC structure consists of a hydropneumatic chamber and an air duct, where a turbine is coupled to an electric generator. Additionally, in the L-shaped chamber configuration, a water intake duct is considered. The constructal design method was employed for the geometric evaluation of the devices. For the L-OWC, the influence of the height-to-length ratio of the water intake duct on the obtained hydropneumatic power available was analyzed. In parallel, for the conventional OWC, the free-board submergence was investigated. Subsequently, the optimal geometry for each OWC model was selected to study the height-to-length ratio of the hydropneumatic chamber. Numerical simulations were performed using ANSYS Fluent software. Thus, the performance of the converters was improved by approximately 35.76 times for the L-OWC and 3.78 times for the conventional OWC. However, it is noteworthy that the optimal configuration of the conventional OWC achieved a performance 2.62 times higher than the optimal L-OWC geometry. Full article

The increasing share of renewable energy sources in power grids demands greater load flexibility from thermal power plants. Circulating Fluidized Bed (CFB) combustion systems, while offering fuel flexibility and high thermal inertia, face challenges in maintaining hydrodynamic and thermal stability during load transitions. This study investigates partial flue gas recirculation (FGR) as a strategy to enhance short-term load flexibility in a 1 MW_th CFB pilot plant fired exclusively with solid recovered fuel. Two experimental test series were conducted. Under conventional operation, where fuel and fluidization air are reduced proportionally, load reductions to 86% and 80% led to operating regime shift. Particle entrainment from the riser to the freeboard and loop seal decreased, circulation weakened, and the temperature difference between bed and freeboard zone increased by 71 K. Grace diagram analysis confirmed that the system approached the boundary of the circulating regime. In contrast, the partial FGR strategy maintained total fluidization rates by replacing part of the combustion air with recirculated flue gas. This stabilized pressure conditions, sustained particle circulation, and limited the increase in the temperature difference to just 7 K. Heat extraction in the freeboard remained constant or improved, despite slightly lower flue gas temperatures. While partial FGR introduces a minor efficiency loss due to the reheating of recirculated gases, it significantly enhances combustion stability and enables low-load operation without compromising fluidization quality. These findings demonstrate the potential of partial FGR as a control strategy for flexible, waste-fueled CFB systems and supports its application in future low-carbon energy systems. Full article

This study presents a finite element-based numerical simulation of a shipwreck scenario at the 4th-century BC underwater archaeological site near the island of Žirje, integrating engineering analysis with archaeological interpretation. The site is notable for the wide scattering of amphorae across the seafloor. A scaled model, based on the well-documented Kyrenia shipwreck, found off the coast of Cyprus, was developed to approximate the estimated parameters of the Žirje vessel, incorporating reduced dimensions, an adjusted freeboard, and a total deadweight of approximately six tons. The finite element model of the ship, its cargo, and the seabed was developed using LS-DYNA R11.1. software. Instead of fluid modelling, the study employed explicit dynamic analysis with a rigid seabed, gravitational loading, and automatic contact to reduce computational cost. A series of parametric simulations explored the effects of roll, yaw, and varying gravitational forces on the sinking behaviour and cargo dispersion. Results indicate that only certain non-uniform sinking conditions, combined with seabed currents, accurately replicate the archaeological distribution of the amphorae. This approach underscores the value of integrating finite element analysis (FEA) with archaeological data to generate digitally supported hypotheses, demonstrating how numerical reconstruction can enhance the interpretation of complex underwater archaeological sites. Full article

Coastal high tide flooding doubled in the U.S. between 2000 and 2022 and sea level rise (SLR) due to climate change will dramatically increase exposure and vulnerability to flooding in the future. However, standards for elevating buildings in flood hazard areas, such as base flood elevations set by the Federal Emergency Management Agency, are based on historical flood data and do not account for future SLR. To increase flood resilience in flood hazard areas, federal, state, regional, and municipal planning initiatives are developing guidance to increase elevation requirements for occupied spaces in buildings. However, methods to establish a flood elevation that specifically accounts for rising sea levels (or sea level rise-adjusted design flood elevation (SLR-DFE)) are not standardized. Many municipalities or designers lack clear guidance on developing or incorporating SLR-DFEs. This study compares guidance documents, policies, and methods for establishing an SLR-DFE. The authors found that the initiatives vary in author, water level measurement starting point, SLR scenario and timeframe, SLR adjustment, freeboard, design flood elevation, application (geography and building type), and whether it is required or recommended. The tables and graph compare the different initiatives, providing a useful summary for policymakers and practitioners to develop SLR-DFE standards. Full article

Breakwater dams are critical infrastructures that protect the safety of ports. However, these coastal structures are facing the compounding threats of sea level rise, storm surge, and dam subsidence. Heterogeneous deformations in these infrastructures arise from differential construction sequencing, sediment consolidation, and filling materials, yet traditional in situ monitoring remains spatially limited or even unavailable to trace back and continuously monitor deformation evolutions. In contrast, Interferometric Synthetic Aperture Radar (InSAR) offers valuable insights in providing the spatially and temporally covered dam deformation. In this study, we used two Sentinel-1 tracks from 2016 to 2025, and the persistent and distributed scatterers InSAR methods to map the long-term deformation of Xuwei Port, Lianyungang, China. We utilized six sites of leveling measurements to validate the InSAR-derived vertical deformation and indicate Root Mean Square Errors (RMSEs) ranging from −0.9–1.2 cm. We find, for the rock-sand filled section, the deformations show consolidating subsidence ranging from −63.8 cm to −40.6 cm. In contrast, the concrete tubular structure remains stable, with cumulative deformation ranging from −10.6 cm to −5.2 cm. The enclosing reclaimed land undergoes a period of accelerated settlement with subsidence rates of −64.9–−39.3 cm/yr, which are higher than original subsidence rates of −10.1–−9.7 cm/yr. Additionally, we integrated the consolidation model and tide gauge to quantify that the freeboard will decrease to 0.08–0.31 m in the following 100 years with the continuous sea level rise and dam subsidence. This study benefits our understandings of coastal dam and reclaimed land. It highlights InSAR as a valuable tool to evaluate the critical risk between sea level rise and coastal infrastructure subsidence. Full article

To enhance the hydrodynamic stability of offshore floating photovoltaic (OFPV) platforms under complex sea conditions, this study proposes a novel arc-plate dual-pontoon floating breakwater. A combined methodology of experimental investigation and numerical simulation was integrated to systematically study its hydrodynamic responses and attenuation performance. A two-dimensional numerical wave flume was established in FLOW-3D, and the results were validated against experimental data. The results reveal that the wave energy reduction is primarily achieved through the wave reflection in front of the pontoons and turbulence-induced dissipation guided by the arc plate. The effects of key structural parameters (pontoon draft depth, arc plate span, and the relative freeboard height) were studied to optimize its performance. The results show that both the increasing draft depth and arc plate span can significantly improve the attenuation under long-period waves. Additionally, higher relative freeboard heights help to reduce both the transmission coefficient and horizontal wave force, with the optimal value identified as 0.7. The findings suggest theoretical insights and possible indications for the design of the floating breakwater system in offshore renewable energy applications. Full article

This work deals with the catalytic steam reforming of raw syngas to increase the efficiency of coupling gasification with downstream processes (such as fuel cells and catalytic chemical syntheses) by producing high-temperature, ready-to-use syngas without cooling it for cleaning and conditioning. Such a combination is considered a key point for the future exploitation of syngas produced by steam gasification of biogenic solid fuel. The design and construction of an integrated gasification and gas conditioning system were proposed approximately 20 years ago; however, they still require further in-depth study for practical applications. A 3D model of the freeboard of a pilot-scale, fluidized bed gasification plant equipped with catalytic ceramic candles was used to investigate the optimal operating conditions for in situ syngas upgrading. The global kinetic parameters for methane and tar reforming reactions were determined experimentally. A fluidized bed gasification reactor (~5 kWth) equipped with a 45 cm long segment of a fully commercial filter candle in its freeboard was used for a series of tests at different temperatures. Using a computational fluid dynamics (CFD) description, the relevant parameters for apparent kinetic equations were obtained in the frame of a first-order reaction model to describe the steam reforming of key tar species. As a further step, a CFD model of the freeboard of a 100 kWth gasification plant, equipped with six catalytic ceramic candles, was developed in ANSYS FLUENT^®. The composition of the syngas input into the gasifier freeboard was obtained from experimental results based on the pilot-scale plant. Simulations showed tar catalytic conversions of 80% for toluene and 41% for naphthalene, still insufficient compared to the threshold limits required for operating solid oxide fuel cells (SOFCs). An overly low freeboard temperature level was identified as the bottleneck for enhancing gas catalytic conversions, so further simulations were performed by injecting an auxiliary stream of O₂/steam (50/50 wt.%) through a series of nozzles at different heights. The best simulation results were obtained when the O₂/steam stream was fed entirely at the bottom of the freeboard, achieving temperatures high enough to achieve a tar content below the safe operating conditions for SOFCs, with minimal loss of hydrogen content or LHV in the fuel gas. Full article

The conventional practice in the design of storm drainage systems is based on statistically stationary load and resistance conditions that remain invariant over time. However, uncertainties in the variables affect the design accuracy and the satisfactory performance of these hydrosystems during their operation and service. To overcome this limitation, a design methodology for a storm drainage channel was proposed using a probabilistic framework that incorporates uncertainty analysis of random variables and estimates the system’s probability of failure in terms of design depth and maximum allowable velocity. This methodology employs the Monte Carlo simulation technique and offers an alternative design and analysis approach to strengthen the conventional sizing method for drainage channels in urban watersheds. Based on uncertainty criteria associated with hydraulic design, operation, and prospective changes in the watershed and the channel, appropriate dimensions were estimated regarding design depth and freeboard. The results of this study demonstrate that the annual probability of failure of a channel, when considering uncertainty, is significantly higher than the yearly exceedance probability associated with the hydrological design return period event. Therefore, the proposed methodology is appropriate for estimating the system’s capacity and potential failure risk. This methodology may also be applied to sizing other stormwater drainage structures. Full article