Search Results (1,005)

Predicting wave slamming pressures on bulbous bows is essential for ship structural safety. This study employs an overset-grid RANS-VOF framework to investigate viscous scale effects on bulbous bow slamming loads. Multi-scale simulations were conducted across four geometric scale ratios of 1:50, 1:20, 1:15, and 1:10 (α = 50, 20, 15, 10) under critical pitch-heave resonant head waves (λ/L_WL = 1.2). While global motion responses follow Froude similitude, local dynamic slamming pressures show notable scale disparities. Smaller physical models develop a relatively thicker viscous boundary layer that acts as a hydrodynamic cushion, reducing peak pressures while broadening pulse durations. Consequently, direct Froude scaling from small-scale models tends to underestimate full-scale impact loads. To account for these viscous scale effects, an engineering extrapolation approach based on multi-scale regression is proposed, which demonstrates a reasonable linear correlation across the investigated range (R² = 0.88–0.99) in the primary impact region. This study provides physical insights into the scaling behavior of bulbous bow slamming and offers a practical reference for full-scale load estimation. Full article

Trans-medium vehicles, including supercavitating torpedoes, submarine-launched projectiles, and high-speed hydroballistic bodies, demonstrate increasingly diverse applications in crossing the air–water interface. For such vehicles, the truncated-cone (flat-headed) configuration represents a geometry of significant engineering relevance, as it is widely adopted in the nose sections of supercavitating projectiles and certain underwater ballistic penetrators where the flat head promotes rapid vaporization and cavity generation during high-speed water entry. The air-to-water transition process typically generates extreme hydrodynamic impact loads due to complex multiphase flow and fluid–structure coupling interactions, with water compressibility playing a significant role under hydroballistic conditions. This study focuses on the water-entry regime at velocities ranging from 300 to 1100 m/s, corresponding to hydroballistic speeds relevant to supercavitating vehicles (e.g., the Shkval torpedo operates at approximately 370 m/s) and the initial impact phase of high-speed trans-medium projectiles. Parametric studies are conducted with varying entry velocities (Mach 0.20~0.73 in water), impact angles, and structural dimensions to systematically investigate their effects on the peak slamming overload, using a dynamic mesh technique coupled with a VOF multiphase model with compressibility effects for both air and water phases. The results demonstrate that compressibility effects induce a pronounced air cushion effect during water impact, wherein compression waves generated during high-speed entry dominate the load formation process. Velocity is identified as the most sensitive factor affecting peak overload, followed by structural size parameters. The findings provide valuable guidance for the protective design of high-speed water-entry structures operating in the hydroballistic regime. Full article

Tension-leg platform (TLP) horizontal-axis wind turbines (TLP-HAWTs) have become increasingly important in deep-water offshore wind energy development. However, their performance is strongly affected by coupled platform motions induced by wind and wave loads, making fully coupled simulations a critical prerequisite for accurate performance assessment. Conventional fully coupled approaches often struggle to balance computational efficiency and numerical fidelity. In this study, a simplified sequential coupled modeling framework is proposed based on the commercial solvers OrcaFlex and STAR-CCM+. In this framework, OrcaFlex is employed to simulate the hydrodynamic response of the floating platform, and the resulting platform motions are subsequently imposed as prescribed inputs in high-fidelity CFD-based aerodynamic simulations. Based on the proposed framework, a series of case studies of a 15 MW TLP-HAWT are conducted to investigate the effects of wind-induced and wave-induced platform motions on aerodynamic performance. The results indicate that wind-induced platform motions have a negligible impact on local inflow conditions and vortex intensity, and their influence on mean blade loads and wake topology can be safely ignored under rated conditions. In contrast, wave-induced motions significantly enhance unsteady aerodynamic loads, intensify vortex shedding, alter torque distribution along the blades, and increase wake turbulence intensity as well as velocity deficit. These findings suggest that wave-induced platform dynamics dominate the unsteady aerodynamic response and wake evolution of TLP-HAWTs under rated conditions, while wind-induced motions play a secondary role. The results provide valuable insights for reduced-order modeling, control strategy development, and the design optimization of efficient floating offshore wind turbines. Full article

Despite the growing use of FLNG in offshore gas development, LNG hose safety during tandem offloading remains a critical challenge. Existing studies often analyze mooring dynamics and hose mechanics separately, lacking a unified framework that integrates multiple failure modes. This fragmented approach leads to unclear safety boundaries and inadequate risk control. Therefore, this study proposes a multi-parameter safe operating zone threshold method based on coupled dynamic analysis. First, a three-dimensional time-domain dynamic analysis model is developed using OrcaFlex, which integrates the floating bodies, hoses, and mooring system into a unified coupling framework based on hydrodynamic theory, simulating the dynamic response of the offloading system under combined wind, wave, and current actions. Second, tension, bending moment, and curvature are selected as safety evaluation parameters. These three parameters correspond to the core criteria of typical failure modes, namely axial overload failure, ultimate bending failure, and local joint failure, respectively. By comparing them with their allowable values, the safety status of the hose under various operating conditions is determined. Finally, a coupled safety threshold analysis method incorporating both “sea state return period” and “operational vessel distance” is proposed. The results indicate that, at a fixed vessel distance, the dynamic response of the hose increases significantly with worsening sea states. Tension satisfies the safety factor requirements under most sea conditions. However, the bending moment first exceeds the limit starting from the 5-year return period, making it the primary failure control indicator. Curvature exceeds the limit notably under the 50-year return period and beyond, becoming the main risk source under extreme sea states. The safe operational vessel distances under different sea states are also calculated, systematically revealing the response patterns and failure sequences of tension, curvature, and bending moment of the LNG hose under combined wind, wave, and current actions. Furthermore, by integrating safety margin calculations, an operational classification standard comprising a safe zone, a warning zone, and a danger zone is proposed, along with the upper limits of safe vessel distance and operational windows for each sea state. The threshold determination method established in this paper can provide effective engineering support for FLNG offloading operation planning, hose selection, and operational risk management. Full article

As critical components of offshore wind farms, suspend export cables have attracted increasing attention owing to their complex dynamic responses under combined wave–current loading and cable–soil interaction, leading to structural failure and fatigue damage. A numerical framework is developed in the present study to investigate the dynamic responses of a power cable extending from an offshore wind turbine foundation located in the South China Sea. The model of the cable is described by using the absolute nodal coordinate formulation, considering the hydrodynamic load and cable–seabed interaction via the Morison equation and Randolph–Quiggin model, respectively. After model validation, the response characteristics of the cable under different metocean conditions are analyzed. The effects of waves, currents, and related environmental factors on structural strength, fatigue damage, and wear damage are further evaluated. The dynamic response of the cable exhibits pronounced non-uniformity along the arc length. The wave return period mainly affects the response amplitude, whereas the incident angle has a more significant influence on the dynamic response. Damage assessment further shows that instantaneous strength failure is not critical, as the maximum stresses remain below the allowable stress. Instead, fatigue damage and contact wear are concentrated near the transition region and touchdown point, where oblique wave–current action intensifies cyclic bending and wear growth. The results are expected to provide theoretical support and useful reference for the design, installation, operation and maintenance of cables in offshore wind farms. Full article

Surge waves generated by rapid landslide entry into canyon reservoirs can threaten near-dam hydraulic structures. This study examines a representative post-failure hydrodynamic scenario for the localized unstable Zone B of the No. 1 deformation body slope near Yangqu Hydropower Station. A three-dimensional numerical model was constructed from DEM terrain data and validated using a 1:200 physical model under reservoir water levels of 2710 m and 2715 m. The simulation represents the landslide mass as a prescribed moving rigid body and focuses on wave generation, propagation, and dam-front response after landslide initiation. For the Zone B case at 2715 m with a volume of 1.0 × 10⁶ m³ and an entry velocity of 15 m/s, the first wave reached the opposite bank at about 10 s, the prescribed landslide front reached the riverbed region at about 20 s, and distinct secondary and reflected waves developed at about 50 s. The first-wave height at the downstream monitoring point was about 3.15 m, and the maximum wave height was approximately 3.58 m. Comparison with the 1:200 physical model shows that the numerical results reproduce the first-wave arrival time, main peak height, and main secondary-wave phase reasonably well for the prescribed Zone B scenario. The simulated dam-front response is spatially non-uniform, indicating that the results are most suitable for preliminary screening of hydrodynamic risk under specified local landslide scenarios. Full article

Rapidly deployable floating bridges face coupled challenges in compact deployment, structural load-bearing, and controllable module maneuvering, which cannot be fully evaluated through a single-stage structural or hydrodynamic assessment. To close this gap, this study proposes a rigid–flexible hybrid floating bridge composed of rigid deck plates, inflatable buoyancy bladders, scissor linkages, and integrated waterjet propulsors. A multi-stage assessment was conducted through inflation and calm-water maneuvering tests, gas–solid coupled finite-element analysis, and hydrodynamic and mooring simulations. The inflation experiment revealed three stages in the inflation process of the rigid–flexible specimen, including filling, transition, and pressurization stages. A remotely controlled scale model completed longitudinal, lateral, rotational, and compound motions, demonstrating the feasibility of module-level maneuvering under manual remote control. The finite-element results showed that increasing the initial internal pressure improved the load-bearing capacity and reduced local plastic deformation of the upper deck, while further improvement became limited above 70 kPa. Under the specified wave–current conditions, the ten-module assembly exhibited maximum mooring tension, horizontal displacement, and rotation of 34.7 kN, 0.276 m, and 5.525°, respectively. These results demonstrate the potential of the proposed configuration for bearing capacity, rapid deployment, and resistance to the investigated current and wave conditions while providing a multi-stage framework for further engineering design. Full article

This paper presents a mathematical model to investigate how waves and currents interact with a flexible perforated floating membrane in finite water depth within the framework of linear wave theory. The perforated flexible membrane is modeled based on Darcy’s law and the one-dimensional string equation. The complex dispersion relation in the presence of current velocity is derived from the Green’s function technique using a fundamental source potential solution. The dispersion curve is analyzed by comparing the phase and group velocities for different water depths. Further, a physical model associated with the effect of current on a moored finite floating perforated flexible membrane integrated with a vertical wall is formulated. Then, the theoretical solution of a physical boundary value problem near a vertical rigid wall is obtained using the matching technique and the roots of the dispersion relation derived from the Green’s function technique. Numerical simulations are provided to verify the convergence of the series solution and the accuracy of the obtained analytical findings are evaluated against previously published analytical and experimental datasets. Further, several numerical results on the membrane deflection, hydrodynamic coefficients, and horizontal force on the wall for various structural parameters, mooring stiffness, and current velocities are analyzed. It is observed that the present analysis with this perforated membrane breakwater will be helpful to coastal and marine engineers to understand the influence of current velocity. Full article

Coastal flood exposure indicators are increasingly needed to support climate adaptation and sustainable coastal planning in small island regions, yet regional-scale assessments that translate hydrodynamic simulations into spatially explicit exposure indicators remain limited across the Caribbean. This study develops a spatially explicit coastal flood exposure framework by integrating LISFLOOD-FP simulations with settlement dynamics, land-cover change, and population distribution data. Coastal inundation was simulated under baseline (1985–2014) and SSP5-8.5 (2015–2050) 100-year extreme sea-level conditions and overlaid with land-cover, settlement, and WorldPop data to assess land-cover, settlement, and population exposure across Caribbean island systems. The results show that SSP5-8.5 generally increases coastal inundation extent relative to the baseline, although the broad regional pattern remains similar. Large islands with extensive low-lying coastal plains show greater absolute inundation, whereas several smaller islands exhibit higher proportional exposure because of limited land area and concentrated coastal settlements. Wetlands constitute the largest share of exposed terrestrial land cover, while built-up land shows increasing exposure. These findings suggest that future coastal flood exposure in the Caribbean is shaped by both increasing hazard intensity and persistent human concentration in flood-prone coastal zones. Because the modelling framework does not explicitly represent wave setup/runup, compound flooding, or coastal defences, the results are interpreted as regional-scale screening indicators rather than locally calibrated flood-risk estimates. Full article

Amphibious assault vehicles serve as core equipment for coastal defense and amphibious operations worldwide, with irreplaceable strategic value. Featuring outstanding comprehensive performance, modern amphibious assault vehicles can maintain stable navigation under Sea States 3–4 and adapt to complex nearshore hydrological environments, emerging as the primary platform for mechanized landing operations of the Marine Corps. Cluster navigation is an inevitable tactical form in the operational application of amphibious assault vehicles. When multiple vehicles sail in formation, the wave-making and water pressure effects induced by individual vehicles generate prominent wave interference drag within the formation, which significantly impacts the overall navigation efficiency and stability. Based on the nearshore combat background of amphibious landing, this paper investigates different formation layouts of amphibious assault vehicle clusters to determine the optimal configuration for group navigation. First, a numerical simulation and a physical experiment are combined; a certain type of amphibious assault vehicle is taken as the prototype for 3D geometric modeling via SOLIDWORKS. Then, adopting the CFD numerical simulation method, with navigation speed and optimal inter-vehicle spacing fixed, variables including formation layout and number of vehicles are controlled to simulate the flow field characteristics and total resistance of different cluster formations in calm water. Meanwhile, 3D printing technology is applied to manufacture scaled-down models for towing tank tests. The experimental results are in good agreement with numerical simulations, revealing the fundamental hydrodynamic laws of formation navigation. Under optimal inter-vehicle spacing, the longitudinal tandem formation achieves the best drag-reduction effect, while the double-column staggered formation (diamond/V formation) can effectively suppress wave interference drag and improve the overall hydrodynamic performance and tactical coordination. The research provides a solid theoretical basis and data support for optimizing formation sailing strategies, enhancing cluster navigation stability and safety, and improving maritime maneuver efficiency. It is also of universal reference value for the tactical deployment of amphibious combat equipment globally. Full article

Developing autonomous navigation systems for small fishing vessels is required to improve path-tracking robustness and mitigate severe wave-induced roll motions. This study proposes a Deep Q-Network (DQN)-based operational path planning methodology that explicitly incorporates roll motion reduction into the reward function, combining a maneuvering model with hydrodynamic analyses. Simulation results under varying wave directions and heights demonstrate that the vessel actively adjusts its heading to minimize the roll response. Based on statistical evaluations across five independent runs, the proposed model effectively reduced the average and maximum roll responses by an average of 3% and 2%, respectively, under the evaluated wave headings at a wave height of 1.0 m, while maintaining operational path tracking, despite a slight increase in the total operational path length. Future research will focus on integrating complex environmental conditions with wind and current, and performing the model test for the validation of the established DQN model. Full article

Laboratory experiments and numerical modeling are essential tools for understanding the performance of engineered tsunami mitigation measures, enabling controlled investigation of complex hydrodynamic processes that are difficult to capture in real events. This review critically evaluates current research on key structural countermeasures, seawalls, breakwaters, and water-filled canals, focusing on findings from physical modeling and computational simulations. Evidence from numerical and laboratory studies demonstrates that properly designed mitigation structures can reduce tsunami wave energy, delay inland inundation, and decrease forces on downstream infrastructure. The effectiveness of these measures is strongly influenced by structural geometry, placement, and maintenance, as well as by accurate representation of flow dynamics in experiments and simulations. Despite significant advances, important gaps remain, including the validation of numerical models against high-fidelity experiments, the assessment of extreme events, and the evaluation of hybrid or integrated strategies combining multiple mitigation measures. This review identifies these gaps and highlights research priorities aimed at improving predictive capabilities, optimizing structural designs, and supporting the development of reliable, scalable, and context-specific tsunami mitigation solutions. Full article

To optimize the hydrodynamic conditions of the converter vanadium extraction process, a three-dimensional multiphase flow model of the top-blowing system in a 200 t vanadium extraction converter was established based on computational fluid dynamics (CFD). Conventional 3-hole and “3+1”-hole (with a central nozzle) oxygen lance schemes were designed to investigate the effects of nozzle design Mach numbers and inter-nozzle flow distributions on jet characteristics, impact cavity morphology, and internal molten bath flow fields, aiming to select the optimal oxygen lance nozzle structure. The results indicate that for oxygen lances without a central nozzle, lowering the design Mach number mitigates shock wave energy dissipation and enlarges the gas–liquid reaction surface area; however, due to the lack of longitudinal penetrating force from a central jet, a large stagnation dead zone is prone to forming at the bottom. For oxygen lances with a central nozzle, the inter-nozzle flow distribution governs the impact cavity morphology and the evolution of the flow field. Excessive central flow causes the impact cavity to exhibit a “deep and narrow” profile and exacerbates surface kinetic energy dissipation, whereas insufficient central flow results in a “shallow and wide” cavity that makes it difficult to drive deep circulation. Based on a multi-objective evaluation, the “3+1” configuration adopting a 1:1 balanced flow ratio between the central nozzle and a single peripheral nozzle (Case 2#) effectively balances the allocation of jet momentum between radial expansion and longitudinal penetration, achieving synergistic optimization of the gas–liquid reaction interface expansion and deep-bath stirring, thus serving as the optimal scheme. The findings of this study provide an important theoretical reference for the engineering design and industrial trials of oxygen lance nozzles in large-tonnage vanadium extraction converters. Full article

This study employs a multi-region coupled method to investigate the motion responses and aerodynamic load variations of the IEA 15 MW semi-submersible floating wind turbine (FOWT) under extreme focused wave conditions. The methodology employs the self-developed MRFoam solver within OpenFOAM to integrate aerodynamic and hydrodynamic analyses. The computational framework combines an incompressible viscous flow model with kOmegaSST turbulence closure and an actuator line representation of turbine blades. Extreme wave conditions are generated using NewWave theory, with systematic variations in wave height and wind speed to evaluate coupled effects. Results demonstrate that platform heave responds predominantly to wave excitation, showing minimal wind sensitivity. Turbine thrust maintains consistent mean values across wave conditions but exhibits wind-speed-dependent fluctuations. Mooring dynamics correlate strongly with surge motions, showing amplified tension variations from wave-induced platform displacements, though mean tensions remain stable under uniform wind regardless of wave magnitude. Full article

This study investigates the hydrodynamic behavior of the OC4-DeepCwind floating offshore wind turbine, with a specific focus on the influence of wave reflection and hydrodynamic interaction effects between the platform components. The OC4-DeepCwind semi-submersible platform, supporting the NREL 5 MW reference wind turbine, is analyzed using the commercial software ANSYS AQWA 2024 R1 and the in-house codes HAMVAB and SEMISUB. While ANSYS AQWA and HAMVAB account for multiple wave scattering effects within the multi-column configuration, SEMISUB neglects hydrodynamic interactions, enabling a systematic assessment of their influence on the predicted response. Interaction effects are most pronounced in the surge degree of freedom, where neglecting wave reflection distorts the exciting wave force above 0.65 rad/s, and in the surge, heave, and pitch added mass and radiation damping coefficients, with substantial deviations above approximately 0.6 rad/s. The influence of column separation distance on these diffraction loads is also examined. Stochastic-wave simulations of the moored wind turbine under realistic JONSWAP sea states show normalized errors across all examined sea states of 16.6% (heave), 14.6% (surge), and 9.9% (pitch) in platform motions when interactions are neglected, whereas tower-base loads and mooring line tensions are less sensitive, with errors of 11.5% (vertical shear force), 9.4% (horizontal shear force), 9.2% (bending moment), 8.7% (downstream mooring tension), and 5.6% (upstream mooring tension). These results indicate that hydrodynamic interaction effects are critical for predicting platform motions and hydrodynamic coefficients but have a comparatively limited effect on design-governing structural and mooring loads, offering quantitative guidance on when simplified interaction-free models remain adequate for semi-submersible FOWT design. Full article