Search Results (64)

Harmonic summation and amplification by winds blowing contrary to currents are known contributions to rogue waves in the region of the Agulhas current, but the causes of the observed wave steepness, asymmetric form, and non-breaking are poorly understood. The potential effect of bathymetric and meteorological features has not been addressed. Vortex theory was applied to develop a theory of wave formation, based on conceptual reasoning. Rogue wave formation is attributed to the following: (1) wind lee vortices causing steepening of a wave’s leeward face, and suppressing wave breaking; (2) boundary layer vortices from the meteorological cold front transferring energy to the wind lee vortices thereby sharpening the wave; (3) Agulhas current boundary layer vortices interacting with water lee vortices to accelerate a jet of water between them, thereby steepening the wave and enhancing the preceding trough; (4) bathymetric topology, especially a canyon on the continental slope, generating a vortex in the Agulhas current. This vortex is detached from the canyon by prising of the coastal downwelling current (induced by the meteorological cold front) and combines with the water lee vortex to heighten the wave, and (5) jetting, which arises when the canyon vortex and the Agulhas current boundary layer vortices pass each other, thereby accentuating wave height, steepness, and asymmetry. Full article

Vorticity budgets in traditional height or pressure coordinates are commonly examined to help explain how tropical cyclones evolve over time. One disadvantage of using these coordinates is that the vorticity flux due to diabatic heating cannot be easily assessed. Isentropic coordinates naturally lend themselves to determine the effect of diabatic heating—the vorticity budget simplifies, and a clear-cut distinction can be made between adiabatic (advective) and diabatic vorticity fluxes. Above the boundary layer, advective vorticity fluxes alone would lead to a quick spin-down of the mature tropical cyclone. Do diabatic processes prevent this from happening? If so, how? This paper investigates the vorticity budget of Hurricane Irma (2017) in its mature quasi-steady phase. We analyse a simulation of Irma with an operational high-resolution weather forecasting model. During Irma’s remarkably long period (37 h) of steady peak intensity, the radially outward advective isentropic vorticity flux in the eyewall above the boundary layer is balanced by a radially inward diabatic isentropic vorticity flux. Frictional effects and asymmetrical flow properties are of little importance to the maintenance of cyclone intensity in its mature phase, provided enough latent heat is released in the eyewall to maintain an inward vorticity flux that balances the advective flux. Full article

The main objective of this study was to investigate boiling heat transfer during refrigerant flow in a mini-channel heat sink. The test section consisted of multiple parallel mini-channels, each with a depth of 1 mm. The working fluid was heated by a thin layer of Haynes-230 alloy with a thickness of 0.1 mm. The outer surface temperature of the heater was measured using infrared thermography, while other thermal and flow-based parameters were recorded via a dedicated data acquisition system. The mini-channel heat sink was tested in seven different spatial orientations, with inclination angles relative to the horizontal plane of 45°, 60°, 75°, 90°, 105°, 120°, and 135°. The analysis focused on the early stage of the experiment, corresponding to the forced convection, boiling incipience, and subcooled boiling region. A time-dependent, two-dimensional model of heat transfer during flow boiling of a refrigerant in asymmetrically heated mini-channels was developed. The temperatures of both the heating foil and the working fluid (Fluorinert FC-770) were described using appropriate forms of the Fourier–Kirchhoff equation, subject to relevant boundary conditions. Two sets of time-dependent Trefftz functions were employed to solve the governing equations: one set corresponding to the two-dimensional Fourier equation and another, newly derived, for the energy equation in the fluid. The results include thermographic images of the heated surface, temperature distributions, fluid temperatures, local heat-transfer coefficients, and boiling curves. A comparison of the heat-transfer coefficients obtained using the Trefftz-based approach and those calculated using Fourier’s law demonstrated satisfactory agreement. Full article

This paper considers impulsive systems with singularities. The main novelty of this study is that the impulses (impulsive functions) and the initial value are singular. The asymptotic convergence of the solution to a singularly perturbed initial problem with an infinitely large initial value, as $\epsilon \to 0,$ to the solution to a corresponding modified degenerate initial problem is proved. It is established that the solution to the initial problem at point $t=0$ has an initial jump phenomenon, and the value of this initial jump is determined. The theoretical results are supported by illustrative examples with simulations. Singularly perturbed problems are characterized by the presence of a small parameter multiplying the highest derivatives in the differential equations. This leads to rapid changes in the solution near the boundary or at certain points inside the domain. In our problem, symmetry is violated due to the emergence of a boundary layer at the initial point and at the moments of discontinuity. As a result, the problem as a whole is asymmetric. Such asymmetry in the behavior of the solution is a main feature of singularly perturbed problems, setting them apart from regularly perturbed problems in which the solutions usually exhibit smoother changes. Full article

Detecting manipulated document images is essential for verifying the authenticity of official records and preventing document forgery. However, forgery artifacts are often subtle and localized in fine-grained regions, such as text boundaries or character outlines, where visual symmetry and structural regularity are typically expected. These manipulations can disrupt the inherent symmetry of document layouts, making the detection of such inconsistencies crucial for forgery identification. Conventional CNN-based models face limitations in capturing such edge-level asymmetric features, as edge-related information tends to weaken through repeated convolution and pooling operations. To address this issue, this study proposes an edge-focused method composed of two components: the Edge Attention (EA) layer and the Edge Concatenation (EC) layer. The EA layer dynamically identifies channels that are highly responsive to edge features in the input feature map and applies learnable weights to emphasize them, enhancing the representation of boundary-related information, thereby emphasizing structurally significant boundaries. Subsequently, the EC layer extracts edge maps from the input image using the Sobel filter and concatenates them with the original feature maps along the channel dimension, allowing the model to explicitly incorporate edge information. To evaluate the effectiveness and compatibility of the proposed method, it was initially applied to a simple CNN architecture to isolate its impact. Subsequently, it was integrated into various widely used models, including DenseNet121, ResNet50, Vision Transformer (ViT), and a CAE-SVM-based document forgery detection model. Experiments were conducted on the DocTamper, Receipt, and MIDV-2020 datasets to assess classification accuracy and F1-score using both original and forged text images. Across all model architectures and datasets, the proposed EA–EC method consistently improved model performance, particularly by increasing sensitivity to asymmetric manipulations around text boundaries. These results demonstrate that the proposed edge-focused approach is not only effective but also highly adaptable, serving as a lightweight and modular extension that can be easily incorporated into existing deep learning-based document forgery detection frameworks. By reinforcing attention to structural inconsistencies often missed by standard convolutional networks, the proposed method provides a practical solution for enhancing the robustness and generalizability of forgery detection systems. Full article

Accurately simulating near-surface wind speeds is indispensable for wind energy development, particularly under extreme weather conditions. This study utilizes the Weather Research and Forecasting (WRF) model with a 6 km resolution to evaluate 80 m wind speed simulations over Europe, using the ECMWF (European Centre for Medium-Range Weather Forecasts) reanalysis version 5 (ERA5) as initial and lateral boundary conditions. Two cases were analyzed: a normal case with relatively weak winds, and an extreme case with intense cyclonic activity over 7 days, focusing on offshore wind farm regions and validated against Forschungsplattformen in Nord- und Ostsee (FINO) observational data. Sensitivity experiments were conducted by modifying key physical parameterizations associated with wind simulation to assess their impact on accuracy. Results reveal that while the model realistically captured temporal wind speed variations, errors were significantly amplified in extreme cases, with overestimation in weak wind regimes and underestimation in strong winds (approximately 1–3 m/s). The Asymmetrical Convective Model 2 (ACM2) planetary boundary layer (PBL) scheme demonstrated superior performance in extreme cases, while there were no significant differences among experiments under normal cases. These findings emphasize the critical role of physical parameterizations and the need for improved modeling approaches under extreme wind conditions. This research contributes to developing reliable wind speed simulations, supporting the operational stability of wind energy systems. Full article

This study presents an improved deep-learning model, termed Enhanced Time Series Mixer (E-TSMixer), for the prediction of particulate matter. By analyzing the temporal evolution of PM_2.5 concentrations from multivariate monitoring data, the model demonstrates significant prediction capabilities while maintaining consistency with observed pollutant transport characteristics in the urban boundary layer. In E-TSMixer, a fully connected output layer is proposed to enhance the predictive capability for complex spatiotemporal dependencies. The relevant data on air quality and traffic flow are fused to achieve high-precision predictions of PM_2.5 concentrations through a multivariate time-series forecasting model. An asymmetric penalty mechanism is added to dynamically optimize the loss function. Experimental results indicate that the proposed E-TSMixer model achieves higher accuracy for the prediction of PM_2.5, which significantly outperforms the traditional models. Additionally, an intelligent dual regulation of fixed and dynamic threshold model is introduced and combined with E-TSMixer for the decision-making model of the real-time adjustments of the frequency, routes, and timing of water truck operation in practice. Full article

Ejectors, as widely utilized devices in the field of industrial energy conservation, exhibit a performance that is significantly affected by their structural parameters. However, the study of the influence of nozzle geometry parameters on asymmetric ejector performance is still limited. In this paper, the effect of the nozzle upper divergent angle on the operating characteristics of an asymmetric rectangular section ejector was comprehensively investigated. The results indicated that the entrainment ratio gradually decreased with an increase in the nozzle upper divergent angle, and the maximum decrease could be 20%. At the same time, the relationship between the upper and lower divergent angles was closely linked to the trend of change in the secondary fluid mass flow rate. The analysis of flow characteristics found that the deflection of the central jet was caused by the pressure difference between the walls of the upper and lower divergent sections of the nozzle. Additionally, quantitative analysis of the development of the mixing layer showed that the mass flow rate of the secondary fluid inlet was related to the development of the mixing boundary. Shock wave analysis demonstrated that the deterioration in ejector performance was due to the reduction in the shock wave strength caused by Mach reflection and the increase in the Mach stem height. Full article

The salient object detection (SOD) of forward-looking sonar images plays a crucial role in underwater detection and rescue tasks. However, the existing SOD algorithms find it difficult to effectively extract salient features and spatial structure information from images with scarce semantic information, uneven intensity distribution, and high noise. Convolutional neural networks (CNNs) have strong local feature extraction capabilities, but they are easily constrained by the receptive field and lack the ability to model long-range dependencies. Transformers, with their powerful self-attention mechanism, are capable of modeling the global features of a target, but they tend to lose a significant amount of local detail. Mamba effectively models long-range dependencies in long sequence inputs through a selection mechanism, offering a novel approach to capturing long-range correlations between pixels. However, since the saliency of image pixels does not exhibit sequential dependencies, this somewhat limits Mamba’s ability to fully capture global contextual information during the forward pass. Inspired by multimodal feature fusion learning, we propose a hybrid CNN–Transformer–Mamba architecture, termed FLSSNet. FLSSNet is built upon a CNN and Transformer backbone network, integrating four core submodules to address various technical challenges: (1) The asymmetric dual encoder–decoder (ADED) is capable of simultaneously extracting features from different modalities and systematically modeling both local contextual information and global spatial structure. (2) The Transformer feature converter (TFC) module optimizes the multimodal feature fusion process through feature transformation and channel compression. (3) The long-range correlation attention (LRCA) module enhances CNN’s ability to model long-range dependencies through the collaborative use of convolutional kernels, selective sequential scanning, and attention mechanisms, while effectively suppressing noise interference. (4) The recursive contour refinement (RCR) model refines edge contour information through a layer-by-layer recursive mechanism, achieving greater precision in boundary details. The experimental results show that FLSSNet exhibits outstanding competitiveness among 25 state-of-the-art SOD methods, achieving MAE and ${\mathit{E}}_{\mathit{\xi }}$ values of 0.04 and 0.973, respectively. Full article

This text investigates the bending/buckling behavior of multi-layer asymmetric/symmetric annular and circular graphene plates through the application of the nonlocal strain gradient model. Additionally, the static analysis of multi-sector nanoplates is addressed. By considering the van der Waals interactions among the layers, the higher-order shear deformation theory (HSDT), and the nonlocal strain gradient theory, the equilibrium equations are formulated in terms of generalized displacements and rotations. The mathematical nonlinear equations are solved utilizing either the semi-analytical polynomial method (SAPM) and the differential quadrature method (DQM). Also, the available references are used to validate the results. Investigations are conducted to examine the effect of small-scale factors, the van der Waals interaction value among the layers, boundary conditions, and geometric factors. Full article

The influences of surface layer (SL) physics schemes on the simulated intensity and structure of Typhoon Rai (2021) are investigated using the WRF model. Numerical experiments using different SL physics schemes—revised MM5 scheme (MM5), Eta similarity scheme (CTL), and Mellor–Yamada–Nakanishi–Niino scheme (MYNN)—are conducted. The results show that the intensity forecast of Typhoon Rai is largely influenced by SL physics schemes, while its track forecast is not significantly affected. All three experiments can successfully capture the movement of Rai, while CTL provides better intensity simulation compared to the other two experiments. The higher ratio of enthalpy exchange coefficient to drag coefficient (C_K/C_D) in CTL than MM5 and MYNN leads to significantly increased surface enthalpy fluxes, which are crucial for the typhoon intensification of the former. To explore the influence of SL physics on the structural evolution of the typhoon, the azimuthal-mean angular momentum (AM) budget is utilized. The results indicate that asymmetric eddy terms may also largely contribute to the AM tendencies, which are relatively more comparable in the weaker TC for MM5, compared to the stronger TC with the dominant symmetric mean terms for CTL. Furthermore, the extended Sawyer–Eliassen (SE) equation is solved to quantify the transverse circulations of the typhoon induced by different forcing sources for CTL and MM5. The SE solution indicates that the transverse circulation above and within the boundary layer is predominantly induced by diabatic heating and turbulent friction, respectively, for both CTL and MM5, while all other physical forcing terms are relatively insignificant for the induced transverse circulation for CTL, except for the large contribution from the eddy forcing in the upper-tropospheric outflow for MM5. With the stronger connective heating in the eyewall and boundary-layer radial inflow, the linear SE analysis agrees much better with the nonlinear simulation for CTL than MM5. Full article

To clarify the influence of the serpentine nozzle configurations on the flow characteristics and aerodynamic performance of aircraft, the flow features and aerodynamic performances of the double-ducted serpentine nozzles with different aspect ratios (AR), length–diameter ratios (LDR) and shielding ratios (SR) are numerically investigated. The results show that the asymmetric nozzle flow occurs due to the curved profile of serpentine nozzles, and a local accelerating effect exists at the S-bend, causing the increase in wall shear stress. The unilateral unsymmetrical expansion of the tail jet in the upward direction interacts with the separated external flow of the afterbody, forming an obvious cross-shock wave and shear layer structure. The surface pressure of the afterbody increases along the external flow direction, and decreases sharply in the separation point of the boundary layer. With the increase in AR and LDR, the local accelerating effect of the nozzle flow weakens, while with the increase in SR, the accelerating effect increases. The total pressure recovery coefficient, flow coefficient and axial thrust coefficient all decrease with the increase in AR, LDR, and SR. The thrust vector angle decreases with the increase in AR but is less affected by LDR and SR. Full article

Although recent research suggests that the morphology and crustal structure of slow–ultraslow-spreading ridges are mainly controlled by melt supply, there is a lack of quantitative understanding of the effect of systematic changes in melt supply on the seafloor spreading state of mid-ocean ridges. In this study, we used bathymetry, free-air gravity anomaly, and sediment thickness data to calculate the residual bathymetry, mantle Bouguer gravity and crustal thickness of the Reykjanes Ridge. According to the gradient of changes in crustal thickness and residual bathymetry along the axis, the influence of melt supply on the spreading state of the Reykjanes Ridge can be divided into three zones: ultra-strong effect zone (0–160 km), strong effect zone (160–610 km), and weak effect zone (610–930 km). In the ultra-strong effect zone, excess melt supply and a higher melting degree result in a strong upwelling and large melt eruption. The change in relative position between the Reykjanes Ridge and the Iceland hotspot results in the spreading state of the Reykjanes Ridge transforming from asymmetric spreading to symmetric spreading. In the strong effect zone, the decrease in melt supply and melting degree weakens the mantle upwelling and enhances the viscosity of the dehydrated mantle layer. Sufficient viscosity of the dehydrated mantle layer forces asymmetric asthenosphere rise along the sloping boundary of the lithosphere, resulting in symmetric spreading. In the weak effect zone, the pattern of magma upwelling becomes a focused magma supply pattern similar to that of the slow–ultraslow-spreading of the mid-ocean ridge, and tectonics dominate the spreading process. The asymmetry of this weak effect zone may be due to the concentration of tectonic and magmatic activity on one flank of the ridge. Full article

This study used the revised Sawyer–Eliassen (SE) equation, taking the relaxed thermal wind balance into account, to chart the development of Supertyphoon Yutu (2018) based on symmetric vortex dynamics. The mean vortex and associated forcing sources for solving the SE equation were taken from three-dimensional numerical simulations using the ocean-coupled HWRF. The SE solutions indicate that the induced transverse circulation is sensitive to the static stability of the mean vortex, which can be significantly underestimated when the static instability is greatly increased. The impacts on the SE solution, caused by the agradient imbalance and nonhydrostatics, were not significantly large in the troposphere. Moreover, the impact of numerical residue in the tangential wind tendency equation mainly occurred in the upper troposphere, below a height of 18 km, and near the lower eyewall. Furthermore, the structural misplaced change in the forcing source may have caused a more disorganized induced transverse circulation, whereas the collocated intensity change only resulted in a proportional enhancement during the same phase. During the rapid intensification of Yutu, the tangential-wind velocity tendency, caused by the revised SE solution, was close to the actual nonlinear tendency; however, the lowest boundary layer exhibited stronger turbulent friction. The mid- to upper-tropospheric vortex intensification inside of the eyewall and outside of the eyewall can mainly be attributed to the mean and asymmetric horizontal advection and vertical advection, respectively; conversely, most of the spindown that occurred in the eyewall was caused by the mean and asymmetric horizontal advection. At lower levels, the vortex intensification near the inner eyewall was mainly induced by the effects of asymmetric vertical advection. Full article

The low-gas permeability area of a fully mechanized up-dip working face was quantitatively studied using a physical similarity simulation test and theoretical analysis under varying dip angles of rock strata. Based on the theory of fractal geometry, this study obtained the fractal dimensions of the low-gas permeability area, the boundary area of the low-gas permeability region, and various layer areas of the low-gas permeability area by increasing the dip angle of rock strata. The findings reveal that the goaf’s high penetration area moved from a symmetrical shape to an asymmetrical one as the dip angle of rock strata increased. The high penetration area on the open-off cut side is notably larger than that on the working face side, due to the effects of advancement at the working face. In the goaf, the lateral length of the cavity decreases as the rock strata’s dip angle increases, while the longitudinal width expands and then contracts until it vanishes because of sliding. In the goaf, the lateral length of the cavity decreases as the rock strata’s dip angle increases, while the longitudinal width expands and then contracts until it vanishes because of sliding. In the goaf, the lateral length of the cavity decreases as the rock strata’s dip angle increases, while the longitudinal width expands and then contracts until it vanishes because of sliding. Moreover, the low-gas permeability area has a larger fractal dimension. The fractal dimension of the area with low gas permeability steadily decreased as periodic weighting emerged, ultimately reaching values of 1.24, 1.27, and 1.34. Moreover, the area’s fractal dimension was greater on the open-off cut side in comparison to the working face side. As the distance from the rock strata floor decreased, the fractal dimension of the area with low gas permeability increased. According to the gradient evolution law, the low-gas permeability area may be divided from bottom to top into three areas: strongly disturbed, moderately disturbed, and lowly disturbed. Based on the theory of mining fissure elliptic paraboloid zones and experimental findings, a mathematical model has been developed to analyze the fractal characteristics of low-gas permeability areas that are influenced by the rock strata’s dip angle. Finally, this study established a dependable theoretical foundation for precisely examining the development of cracks in the area of low gas permeability and identifying the storage and transportation region of pressure relief gas, which is affected by various dip angles of rock strata. It also offered assistance in constructing a precise gas extraction mechanism for pressure relief. Full article