Search Results (713)

Because of the large dynamic range of scales between 3D turbulence and global circulation, the effects of small-scale turbulence, and indeed turbulence at many scales, often need to be parameterized in some way for input into large global-scale computer models. Ideally, it would be good to have a computer program large enough and powerful enough to solve all motions at all scales simultaneously, but this objective is still far from being possible. Yet if implemented poorly, parameterization can lead to errors that can propagate through the model. While turbulence is often considered a “wastebasket” for larger-scale motions, here we look in the other direction and examine how these smaller-scale motions work back to affect the larger-scale flows. The nature of background drag and diffusive forces is reviewed in the context of their impact on larger-scale motions, and the ways that these forces are implemented in models are discussed. The lack of use of measured (as distinct from hypothetical) small-scale turbulence data is noted. It is also noted that vertical diffusion is conceptually more important for atmospheric coupling than horizontal diffusion, and so-called two-dimensional (2D) “turbulence,” sometimes discussed in regard to atmospheric mixing, is less capable of vertical mixing because associated organized vertical motions are generally weak. Very strong evidence from the Global Atmospheric Sampling Program (GASP) for a dominant gravity-wave spectral region at horizontal scales of 200–1000 km, as low in altitude as the tropopause, is presented. Errors in the interpretation of earlier well-cited analyses of these data (often incorrectly cited as evidence for 2D turbulence) are presented. These errors have a profound impact on previous beliefs about the relative roles of gravity waves and nominally 2D turbulence. Non-Kolmogorov diffusive processes that contribute to drag, diffusion and mixing but have rarely been practically employed are considered, including the impact of intermittency, wave saturation, “whitecaps” and Stokes diffusion. When these processes are included, typical realistic diffusion coefficients seem to be 2–3 × higher than those predicted by the COSPAR International Reference Atmosphere. Finally, a comparison between diffusivities using the Whole Atmosphere Community Climate Model (WACCM6) at the National Center for Atmospheric Research in the USA and the Japanese Atmospheric GCM for Upper Atmosphere Research (JAGUAR), which use very different strategies, is undertaken. Full article

Floating offshore wind turbines (FOWTs) experience six-degree-of-freedom motions and related forces acting on their mooring systems. Under combined wind, wave, and current loading, platform motions and mooring line tensions are dynamically coupled. To support ballast control decisions without repeatedly running high-fidelity coupled simulations, this paper developed a specialized computational framework combining FAST-AQWA time-domain simulation, short-term mooring tension prediction, and ballast control optimization. Five predictive models were trained and evaluated using the same sliding window dataset. After training, the predicted mooring tension data were used for ballast control calculations. In this study, the bidirectional long short-term memory (BiLSTM) model showed the highest prediction accuracy for mooring tension and the Model Prediction Control (MPC) produced a smoother control action and significantly reduced the amplitude of low-frequency roll and pitch. The proposed framework provides a practical approach for combining short-term response prediction with ballast control and demonstrates that explicit mooring tension constraints must be incorporated into the design considerations of subsequent control systems. Full article

The quality factor is a key metric for evaluating the performance of micro-electro-mechanical and nano-electro-mechanical system resonators. Although reducing device dimensions enhances resonator sensitivity, it also intensifies energy dissipation, thereby degrading the quality factor. Among the dominant dissipation mechanisms in micro-/nano-resonators, support loss is strongly influenced by surface effects at small scales, particularly the surface elastic modulus and initial surface stress. In this study, support loss in a double-clamped micro-/nano-beam resonator with surface effects incorporated is investigated. A dynamic model incorporating the surface elastic modulus and initial surface stress is developed based on Euler–Bernoulli beam theory and Gurtin–Murdoch surface elasticity theory. A quality-factor calculation method is then established by combining elastic wave radiation in the supports with an energy-based formulation. The theoretical predictions are validated using a three-dimensional finite element model comprising the resonator with a surface layer, supports, and a perfectly matched layer. Further, the effects of the surface elastic modulus, initial surface stress, characteristic size, and dimensionless geometric parameters on support loss are examined. The results show that the surface elastic modulus and initial surface stress increase support loss and reduce the quality factor, with the initial surface stress exhibiting the stronger influence. The influence of these parameters becomes more pronounced as the characteristic size decreases, and variations in the length-to-thickness and width-to-thickness ratios further modify their contribution to support loss. Mechanistically, surface effects alter the effective bending stiffness and axial force, thereby changing the dynamic loads transmitted to the supports and resulting elastic-wave radiation. These findings provide theoretical insights for the design of high-quality-factor micro-/nano-devices. Full article

The Gulf of Aden (GA) is a strategically dynamic water basin linking the Red Sea basin with the Arabian Sea via the Bab el Mandeb Strait. In spite of its importance for oil transportation globally and regional hydrodynamics, tidal propagation remains relatively understudied. Thus, in this study, a depth-averaged 2D barotropic hydrodynamic model based on the Delft3D modelling system with a uniform resolution of 5 km was set up, calibrated, and validated to model the tidal propagation within the GA. The open boundaries were forced with eight primary astronomical tidal constituents, four semidiurnal (M₂, S₂, N₂, K₂) and four diurnal (K₁, O₁, P₁, Q₁) components. The model performance was assessed using hourly water level observations as well as current measurements. Sensitivity analyses were carried out on key parameters, with the Chézy bottom roughness coefficient of 35 m^1/2 s⁻¹ providing the optimal performance. Statistical parameters revealed a strong match between the modelled and the observations. Mean Absolute Error (MAE) was observed to vary from 0.07 to 0.08 m (about 2.7–5.1% of the local mean tidal range), with large inconsistencies found at ME and MW stations, while the Root Mean Square Error (RMSE) varied from 0.08 to 0.10 m (about 3.1–6.4% of the local mean tidal range). The Index of Agreement (IOA) was found significant across all stations (0.91 to 0.95). Among all constituents, the semidiurnal M₂ and diurnal K₁ tidal waves exhibit the largest amplitudes. The amplitudes of S₂ and N₂ attain approximately 43% and 30% of M₂, while O₁ represents about 38% of K₁. The co-tidal charts show that semidiurnal and diurnal tides propagate as coastally influenced long waves with a double-maximum structure along coastal boundaries, reaching maximum surface elevation amplitudes near Bab el Mandeb Strait and the eastern boundary (~0.48 m to 0.60 m for M₂, and up to 0.48 m for K₁). Rossby radius of deformation and quarter-wave resonance indicate that the semidiurnal band lies close to the fundamental resonant period of the GA, generating a co-oscillation-like response with small phase gradients, while the diurnal band more closely resembles a freely propagating Kelvin wave. Form Factor values within the GA range between 0.7 and 0.9, indicating a predominantly mixed, mainly semidiurnal tidal regime throughout the Gulf. Full article

The Peregrine breather (PB), a classical localized solution of the nonlinear Schrödinger equation (NLSE), is widely used to describe the evolution of deep-water rogue waves. However, the influence of variable bathymetry on PB focusing remains insufficiently understood. A two-dimensional RANS–VOF numerical wave tank is therefore established using computational fluid dynamics (CFD) to investigate deterministic PB propagation over variable bathymetry. The model is validated through mesh- and time-step-sensitivity analyses and comparison with the analytical PB solution. Relative water depth, bathymetric interaction length, and bathymetric position are systematically examined. The results reveal for the first time a bathymetry-induced delayed-focusing phenomenon: the PB undergoes local defocusing over elevated topography and refocuses farther downstream after re-entering deeper water. The delay increases as water depth decreases. For k₀h_shelf > 1.363, increasing the interaction length mainly enhances the focusing delay, while self-focusing recovers in deeper water. In contrast, for k₀h_shelf < 1.363, an interaction length of approximately two carrier wavelengths disrupts the coherent PB structure and splits it into two wave packets. The onset position of bathymetric forcing has only a minor effect on the final delay. These results clarify how variable bathymetry modulates PB focusing and structural stability and provide a theoretical reference for nearshore extreme-wave risk assessment. Full article

The wave of digital transformation has driven profound changes in construction mode. As the core driving force for the sustainable development of digital construction, organizational capabilities have gradually attracted widespread attention from both the academic community and practitioners. This study comprehensively analyzes the structural dimensions and influencing factors of construction project organizations’ capabilities in digital construction mode. Further, employing an analytical approach based on dynamic Bayesian networks, the organizational capability model is constructed to explore the key dimensions, influencing factors, and influence paths of organizational capabilities from a dynamic perspective. The results show that innovation capabilities serve as the pivotal drivers for advancing organizational capabilities, with a probability reaching 88.40%. In the short term, simultaneously enhancing innovation capabilities and leadership capabilities has the best effect on improving organizational capabilities, with a probability of up to 94.89%. However, from a long-term perspective, the probability distribution of various combined strategies is similar to that of the single-dimensional strategies. Consistency in core values stands as the key influencing factor, while the two influence chains symbolizing “technical hard power” and “organizational soft power” constitute the core paths for enhancing organizational capabilities. The research findings contribute to clarifying the priority order and core factors of organizational capability development in the digital construction mode, thereby providing a quantitative decision-making basis for optimizing resource allocation in construction project organizations. Full article

Weakly nonlinear free-surface flows past disturbances are traditionally modeled using the forced Korteweg–de Vries (fKdV) equation with a prescribed instantaneous pressure field. However, physical wake responses possess finite relaxation times and advection scales that diagnostic algebraic closures fail to capture. This paper introduces a novel coupled system in which the surface pressure is a dynamical field governed by an advection–reaction–diffusion equation driven by band-limited curvature. Using linear spectral theory and numerical validation, we derive a phase-speed criterion demonstrating that energy transfer is determined by the comparison between the pressure drift speed and the surface phase speed. A sharp stability theorem proves that, to leading order in the coupling strength and for a non-negative even response transfer function whose drift speed exceeds the Froude detuning, the system is spectrally stable if and only if the response is band-limited below a critical wavenumber $k_c$. Furthermore, an exact energy identity establishes that passivity and linear stability are equivalent. Finally, we demonstrate resonance steering: while coupling typically increases the wave resistance for monotone spectra, tuning the response to a spectral zero of a multi-lobe footprint reduces the drag significantly relative to its classical value. This result identifies an explicit performance–strongness trade-off, providing a mathematically strong structure for wave drag minimization through dynamic pressure control. Full article

In this paper, the nonlinear Nurshuak–Tolkunay–Myrkakulov (NTM-III) equation is analyzed using the methods of dynamical systems theory and exact solution techniques. The NTM-III model is reduced to a second-order nonlinear ordinary differential equation by using appropriate reductions, then written as a planar Hamiltonian dynamical system. Analytical study of the equilibrium points, bifurcation structures, and stability properties is conducted using Jacobian matrices and eigenvalue theory. Different parameter combinations are shown in various phase portraits, with the saddle and center equilibrium states present and their stability indicated. An external periodic perturbation is added to the system to study complex nonlinear dynamics. Using phase portraits, time-series analysis, return maps, Lyapunov exponents, sensitivity analysis, and multistability diagnostics, the resulting forced dynamical model is investigated. Chaotic behavior, strong dependence on initial conditions, and multiple coexisting attractors for the same set of parameters are illustrated through numerical simulation. In addition, a set of exact analytical solutions, including trigonometric, hyperbolic, and exponential wave structures, is obtained using the Multivariate Generalized Exponential Rational Integral Function (MGERIF) method. The solutions obtained display interesting nonlinear wave interactions, multi-peakon formations, and localized propagation patterns. The findings show the complex relationship among bifurcation, chaos, multistability, and nonlinear wave propagation in the NTM-III equation and provide new insight into the equation’s mathematical and physical properties. Full article

To investigate the influence of oblique SV-wave incidence on the dynamic response and seismic resilience of subway stations, the viscoelastic artificial boundary combined with the equivalent nodal force method was used to implement the oblique SV-wave input, and a 3D soil-structure interaction finite element model was developed. The results indicate that when subjected to oblique SV-wave incidence at small angles, the subway station structure is dominated by shear deformation. Then, the rocking response gradually rises as the angle increases. At the near-critical-angle incidence, both the rocking angle and inter-story drift ratio increase sharply, resulting in exacerbated structural damage and a degradation of lateral stiffness. Time-history analyses were conducted using 11 ground-motion records, and seismic resilience was assessed through Monte Carlo simulation. Compared with vertical incidence, the results show that oblique incidence at the near-critical angle significantly degrades the structure’s seismic resilience. Its resilience rating drops significantly. Repair costs and repair time are much higher than the values at vertical incidence. The structure’s functional recoverability was substantially reduced. The rating for the casualty index decreased sharply, exposing serious safety hazards. These results indicate that resilience assessments derived from vertical incidence cause the seismic resilience of subway stations to be overestimated. Full article

Searching by numerical simulation for structures with optimal damping properties among viscoelastic hollow cylindrical bodies with a filler is usually associated with a large amount of computation. Formulating the mechanical problem as one of natural vibrations and natural wave propagation makes it possible to evaluate the dissipative properties of such a structure independently of external force and kinematic actions, and thereby to reduce the computational cost substantially. The solution of the natural vibration problem for a piecewise homogeneous viscoelastic hollow cylindrical body with a filler yields complex natural frequencies, the real part of which represents the vibration frequency and the imaginary part the damping factor (attenuation rate). The mechanical behavior of the viscoelastic material is described by the linear Boltzmann–Volterra hereditary theory with a three-parameter Koltunov–Rzhanitsyn relaxation kernel, within which the material characteristics are represented by complex dynamic moduli—the shear modulus and the bulk modulus—that, as a rule, depend on frequency. In the natural vibration problem these moduli become functions of the real part of the sought complex natural frequency alone, which makes the standard eigenvalue procedures of commercial finite-element codes inapplicable. The paper presents an algorithm that removes this difficulty. The dispersion relation of the piecewise homogeneous cylinder is obtained analytically in the form of a complex determinant of order 12 for a two-layer and 18 for a three-layer configuration, the elements of which are Bessel and Neumann functions of complex argument; the global stiffness and mass matrices needed for the general configuration can be assembled automatically in a general-purpose finite-element code such as ABAQUS; the resulting complex characteristic equation is solved by Muller’s method—every iteration of which evaluates the determinant by Gaussian elimination with partial pivoting, so that no expansion of the determinant is required. The efficiency of the algorithm is demonstrated for a two-layer viscoelastic hollow cylindrical body with a filler, the outer load-carrying layer being made of Kh12 steel and the inner layer (the filler) of 30 L steel. The real and imaginary parts of the complex natural frequencies, of the phase velocities and of the attenuation are obtained as functions of the dimensionless wave number, of Poisson’s ratio, of the ratio of the layer radii and of the ratio of the instantaneous elastic moduli of the layers. 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 presents a multivariate spatio-temporal clustering framework to characterise joint wind–wave regimes across European seas using the fifth-generation atmospheric reanalysis produced by the European Centre for Medium-Range Weather Forecasts (ERA5; 1979–2014). Seasonal and annual statistics of significant wave height, mean wave period, wind speed, and wave/wind direction were computed at 0.5° resolution. Principal component analysis was used to reduce dimensionality, retaining 30 components that captured 99% of the variance. K-means clustering was then used to identify nine coherent dynamical regimes with persistent spatio-temporal signatures. These regimes were grouped into open-ocean, transitional, and enclosed/semi-enclosed categories based on internal variability, directional spread, and geographic exposure. Open-Atlantic regimes are found to be energy-rich, exhibiting clear December–February maxima in significant wave height ($H_s$), mean wave period ($T_{02}$), and 10 m wind speed ($W_{s10}$); enclosed and semi-enclosed basins show lower amplitudes and reduced variability, while transitional shelves and the southern Mediterranean display intermediate conditions, characterised by moderate $T_{02}$ levels and seasonal rotation of wave and wind directions, reflecting a mixed influence of locally generated seas and remotely forced swell. Dispersion analysis highlights a clear Atlantic–Mediterranean partition, with transitional shelves forming a dynamical bridge between open-ocean and enclosed basins. Teleconnection analysis shows that the North Atlantic Oscillation and Arctic Oscillation dominate Atlantic regimes, while the Scandinavia, East Atlantic, and Polar/Eurasia patterns modulate variability and directional persistence in transitional and enclosed seas. The classification defines a climatological framework of European wind–wave conditions and establishes a practical basis for renewable energy assessment, engineering design, and long-term change analysis, with methods transferable to other basins. Full article

Jacket foundations, with their excellent adaptability and economic efficiency, have been increasingly widely applied in medium-deep water areas. However, the scouring and erosion effects in the marine environment, coupled with complex wind-wave loads, have severely restricted the long-term safe service of jacket foundations. In this study, a structure-pile-soil coupled dynamic response model considering the effects of scour depth and changes in wind and wave directions for the jacket-type offshore wind turbine is developed by integrating the wind and wave load generation capability of OpenFAST and the nonlinear pile-soil interaction analysis function of OpenSees. By quantitatively analyzing key response parameters such as tower top displacement, nacelle acceleration, and internal forces of the foundation tower and pile shaft, this study reveals the significant influence of soil stiffness degradation induced by scour on structural dynamic characteristics, and verifies the effective suppression mechanism of the feathering shutdown strategy on structural responses under extreme loads. The research results indicate that scour has a negligible impact on the fundamental frequency of the jacket-type offshore wind turbine structure, while it significantly reduces the high-order frequencies and leads to a substantial increase in pile shaft internal forces; the effect of wind-wave angle intensifies the spatially coupled vibration response of the structure. The study provides important theoretical and technical support for the anti-scour design, multi-directional load assessment, and formulation of safety control strategies for jacket foundations in complex deep-sea environments. Full article

Submesoscale processes in marginal seas are central to the ocean’s energy cascade, mixed-layer dynamics, and biogeochemical exchanges and are typically driven by complex mechanisms influenced by local background currents as well as external forcings such as winds, tides, and topography. Among these drivers, however, the role of surface gravity waves has received comparatively little attention. In this study, we investigate the influence of surface waves on nearshore submesoscale processes in the northern South China Sea using high-resolution nested simulations with the Coastal and Regional Ocean COmmunity model (CROCO). The model implements the Eulerian wave-averaged current equations based on the vortex-force formalism, accounting for wave-induced effects. Our results reveal that onshore Stokes drift induces an onshore transport of water masses, thereby raising the nearshore sea level and intensifying nearshore currents. The strengthened currents, in turn, enhance convergence- and strain-induced frontogenesis, leading to the intensification of nearshore submesoscale fronts. These findings elucidate a specific mechanistic link between wave-induced sea-level changes and submesoscale dynamics, contributing to a better understanding of the role of surface waves in shaping coastal circulation. Full article