Thick Boundary Research Articles

CTCD-Net: A Cross-Layer Transmission Network for Tiny Road Crack Detection

Crack detection is essential for the safety maintenance of road infrastructure. However, there are two major limitations to detecting road cracks accurately: (1) tiny cracks usually possess less distinctive features and are more susceptible to noises, so they are apt to be ignored; (2) most existing methods extract cracks with coarse and thicker boundaries, which needs further improvement. To address the above limitations, we propose CTCD-Net: a Cross-layer Transmission network for tiny road Crack Detection. Firstly, we propose a cross-layer information transmission module based on an attention mechanism to compensate for the disadvantage of unobvious features of tiny cracks. With this module, the feature information from upper layers is transmitted to the next one, layer by layer, to achieve information enhancement and emphasize the feature representation of tiny crack regions. Secondly, we design a boundary refinement block to further improve the accuracy of crack boundary locations, which refines boundaries by learning the residuals between the label images and the interim coarse maps. Extensive experiments conducted on three crack datasets demonstrate the superiority and effectiveness of the proposed CTCD-Net. In particular, our method largely improves the accuracy and completeness of tiny crack detection.

Diffuse-Interface Blended Method for Imposing Physical Boundaries in Two-Fluid Flows.

Multiphase flows are commonly found in chemical engineering processes such as distillation columns, bubble columns, fluidized beds and heat exchangers. The physical boundaries of domains in numerical simulations of multiphase flows are generally defined by a conformal unstructured mesh which, depending on the complexity of the physical system, results in time-consuming mesh generation which frequently requires user-intervention. Furthermore, the resulting conformal unstructured mesh could potentially contain a large number of skewed elements, which is undesirable for numerical stability and accuracy. The diffuse-interface approach allows for the use of a simple structured meshes to be used while still capturing the desired physical (e.g., solid-fluid) boundaries. In this work, a novel diffuse-interface method for the imposition of physical boundaries is developed for the incompressible two-fluid multiphase flow model. This model is appropriate for dispersed multiphase flows which are pervasive in chemical engineering processes, in that this flow regime results in high levels of mass and energy transfer between phases. A diffuse interface is used to define the physical boundaries and boundary conditions are imposed by blending the conservation equations from the two-fluid model with that of the nondeformable solid. The results from the diffuse-interface method are compared with results from a conformal unstructured mesh for different interface functions and widths. For small interface widths, the accuracy of the flow profile is unaffected by the choice of interface function and the phase fraction distribution and flow behavior are within 3% compared to those from a conformal mesh. As the interface width increases, the diffuse-interface solution deviates from the conformal mesh solution in both the localized gas fraction and the overall gas hold-up, resulting in a difference up to 30%. In the case of flow past a cylinder, where the solid interacts with the flow, the presence of the diffuse interface extends the thickness of the solid boundary and results in a deviation from the conformal mesh solution as time increases.

Chemical reactive second-grade nanofluid flow past an exponential curved stretching surface: Numerically

The exponentially stretching curved surface is considered for second-grade fluid flow. The slip effects are applied at the assumed surface. The Brownian motion, chemical reaction, and thermophoresis effects are studied to determine the influence of the second-grade fluid. The boundary layer approximation is applied to the governing equation which is reduced in terms of partial differential equations. These partial differential equations become the dimensionless form after using the appropriate transformations. Further, the numerical approach is imposed on the dimensionless system to calculate the problem-related results. Graphs and tables are used to show how involving physical parameters have an effect. The velocity profile and skin friction have been increased due to increasing values of curvature parameters. The velocity function declined due to an increment in the second-grade fluid parameter. It means that the thickness of the boundary layer shown as decline when the second-grade fluid parameter rises while the second-grade fluid parameter has an inverse relation with viscosity. The Prandtl number increased which increased the temperature function. Physically, the thickness of the thermal boundary is controlled by the Prandtl number, and temperature increases by increasing the value of the Prandtl number.

Feasibility analysis of fixed plates in chord-dominated dynamic ground effect wind tunnel experiment

The dynamic ground effect (DGE) refers to the take-off and landing process where the distance between airplane and ground constantly changes with time. In the wind tunnel experiment of DGE, fixed plates are often adopted to substitute the moving-belt ground, which will affect experimental reliability. In this paper, the landing process of an airfoil is simulated to study the feasibility of fixed plates in the chord-dominated DGE experiment. The height is divided into two regions based on the aerodynamics and flow patterns. In Region I (large height), DGE is dominated by the static ground effect (SGE), using a fixed plate can effectively balance the camber effect, blocking effect and boundary layer effect to reproduce result of the moving-ground condition. In Region II (small height), DGE is dominated by the compression work effect, where the downwash is highly compressed to diverge into a forward stream and a backward stream. When using fixed plates, the downwash exhibits two kinds of escaping behavior: the leading-edge-preferred escaping behavior for most fixed plates due to thick boundary layer and the trailing-edge-preferred escaping behavior for the very short plate due to the suddenly weakened camber effect. No plate can balance the two kinds of flow to accurately reproduce pressure distribution on airfoil lower surface and flow physics of moving-ground condition. Thus, the use of a fixed plate is infeasible.

Sub-two-micron ultrathin proton exchange membrane with reinforced mechanical strength

Proton exchange membranes (PEM) serve as indispensable components in fuel cells, flow batteries, and other electrochemical applications. Over the past six decades, PEMs of diverse compositions and structures have been developed for various industrial scenarios. Among all parameters, the thickness is pivotal in affecting the performance, cost, and stability of PEM. Yet for either pure or composite PEM, there is a lower boundary of thickness if the PEM is still targeted to practical utilization. As there is a trade-off between thickness and mechanical stability for a freestanding membrane. We selected ultra-high molecular weight polyethylene (UHMWPE) for its outstanding processability and high modulus intrinsically to breakthrough this trade-off. By biaxially stretching UHMWPE into ∼300 nm thin porous membranes and impregnating Nafion interiorly, with careful interfacial engineering, a type of ∼1.6-μm thin composite PEM was prepared. As the thinnest freestanding PEM with practical use ever reported, surficial, cross-sectional, and interfacial structures were rigorously characterized to explain its performance. In the end, this thin PEM demonstrated a membrane power density of up to 663.69 mW cm−2 for H2–O2 fuel cell set-up. This work provides new insight into the structure-performance correlation of PEM with a near-sub-micron thickness. And it may also inspire future research to further address the performance-stability paradox of PEM with thin/ultrathin thickness range.

Room-Temperature Synthesis of Zeolite Membranes toward Optimized Microstructure and Enhanced Butane Isomer Separation Performance.

Room temperature (RT) synthesis of high-performance zeolite membranes, which is profound from techno-economic and eco-friendly perspectives, remains a grand challenge. In this work, we pioneered the RT preparation of well-intergrown pure-silica MFI zeolite (Si-MFI) membranes, which was realized through adopting highly reactive NH4F-mediated gel as nutrient during epitaxial growth. Benefiting from the introduction of fluoride anions as mineralizing agent as well as precisely tuned nucleation and growth kinetics at RT, both their grain boundary structure and thickness could be deliberately controlled, resulting in the formation of Si-MFI membranes showing unprecedented n-/i-butane separation factor (96.7) and n-butane permeance (5.16 × 10-7 mol m-2 s-1 Pa-1) in the case of a feed molar ratio of 10/90, which well transcended the state-of-the-art membranes reported in the literature. This RT synthetic protocol was also proven effective for preparing highly b-oriented Si-MFI film, thus showing great promise for the preparation of diverse zeolite membranes with optimized microstructure and superior performance.

Comparison of flow characteristics behind squareback bluff-bodies with and without wheels

The wake dynamics of two referenced variations of the squareback Windsor model with and without wheels is numerically studied by performing improved delayed detached eddy simulation. Numerical assessments are validated against publicly available experimental data. The focus of this study is on the wake states influenced by the wheels and the thick oncoming floor boundary layer. Results show that the addition of the wheels significantly changes the aerodynamic forces, the underbody flow, and the wake topology. The wake bi-stability is also enhanced with wheels in place due to the increased curvature of lateral shear layers in the near wake. However, the bi-stable behavior is largely suppressed when immersed in a thick boundary layer. These alterations depend on the degree of interaction between the wake recirculation and the bottom flow, and such degree is strongly affected by the underbody flow momentum. The evolution of low-order flow organizations and complementary spectral analysis highlight the differences in the coherent dynamics of the wake. The finding of this present work suggests that the wake bi-stability behind the squareback body can exist not only for a simplified geometry but also for a more realistic car with wheels in real-world upstream conditions.

Macromagnetic Approach to the Modeling in Time Domain of Magnetic Losses of Ring Cores of Soft Ferrites in Power Electronics

This article presents a new modeling approach capable of predicting Eddy current losses in soft ferrite cores as a function of the winding current. The proposed model is formulated in the time domain, which defines the magnetic core as a repeated regular structure of magnetic material grains and grain boundary in space. In this way, the homogenization process of the material is avoided, which is intended as the definition of a set of physical parameters of a continuous material equivalent to the real structure of the material. The distribution of the current density in the core and the core losses are computed utilizing the physical and geometric parameters of the grain of the magnetic material and of the grain boundary. To address the uncertainty in the definition of the physical and geometrical parameters of the magnetic grain and the grain boundary, a dedicated optimization procedure has been formulated, which takes into account the inaccuracy in the parameter measurement and the fact that the grain contour is an irregular surface and the boundary thickness is neither constant nor uniform. The performance assessment of the model is carried out over a broad frequency range using several experiments with a power amplifier and a dc–dc converter.

Geometrically Nonlinear Aeroelastic Flutter Characteristic of Laminated Composite Shell Panels Under Supersonic Flow

The nonlinear aeroelastic flutter characteristics of laminated composite curved (flat and cylindrical) panels are reported in this paper by obtaining the finite element (FE) solutions under the supersonic flow. The panel model has been derived from the third-order shear deformation theory framework including full geometrical nonlinearity via Green–Lagrange strain. In contrast, the flutter due to aerodynamic loading is included via the first-order piston theory. The current predicted solution accuracy and their validations have been demonstrated by relating the free vibration frequency, coalescence frequency, and critical aerodynamic pressure with the available numerical data. The initial free vibration eigenvalue responses are compared with in-house experimental values. Finally, a few numerical examples are presented by varying parameters like the effect of fiber orientation, flow angle, end boundary conditions, aspect ratio, modular ratio, thickness ratio, and amplitude ratio on the supersonic flutter boundaries of shell panels. The critical aerodyanamic pressure for simply supported cross-ply flat panels increases by 42.85% when the amplitude ratio increases from 0 to 0.75.

Analysis of the Effect of the Leading-Edge Vortex Structure on Unsteady Secondary Flow at the Endwall of a High-Lift Low-Pressure Turbine

The horseshoe vortex system at the leading edge of a low-pressure turbine (LPT) has unsteady flow characteristics, and the flow field in the downstream cascade channel also has unsteady characteristics. In this study, CFD simulations are performed with the help of commercial software CFX, and experimental checks are performed using a fan-shaped cascade test bench to investigate the flow characteristics of the endwall of the PACKB blade type of a high-lift LPT under the same incoming Reynolds number and two incoming boundary layer thickness conditions. The obtained results show that there are different flow alteration characteristics and alteration frequencies of the horseshoe vortex system, among which the vortex system with a thicker boundary layer is larger in size and less spaced from each other, which is more likely to induce the fusion of vortex systems. The centrifugal instability causes the instability of the horseshoe vortex system, and the instability frequency is inversely proportional to the thickness of the boundary layer. With two inlet boundary layers, the instability frequencies of the vortex system are 125 Hz and 175 Hz, respectively, and the ratio of the frequency to the thickness of the boundary layer is reciprocal to each other. The stimulation effect of the unstable horseshoe vortex system on the downstream secondary flow intensity is greater than that of the steady state. The thin boundary layer case generates a greater unsteady loss in the cascade channel than the thick boundary layer case due to the poor stability of the vortex system.

Mental Boundaries Relationship with Self-Esteem and Social Support: New Findings for Mental Boundaries Research

The current study examines Mental Boundaries and the relationship between self-esteem and social support. Thick and thin boundaries are a crucial part of Mental Boundary research. Currently, there is limited research on Mental Boundaries and their connection to counseling and other constructs. The current research study examines correlations between Mental Boundaries, self-esteem, social support, and understanding if Mental Boundaries and social support can predict self-esteem levels. By examining self-esteem and social support, the current study provides how Mental Boundaries can be adapted for counselors when working with clients. The current study found significant negative correlations between Mental Boundaries, self-esteem, and social support. However, linear regression found that Mental Boundaries and social support independently predicted self-esteem. Finally, the current discusses future research and the current study's limitations.

Computational fluid dynamics for naval hydrodynamics

This article describes key issues which have to be addressed to apply Computational Fluid Dynamics to Naval Hydrodynamics. The specific aspects of Naval Hydrodynamics are discussed and illustrated by recent simulations and comparisons with available experiments. Free-surface flows with or without waves and even violent phenomena such as ventilation or cavitation can be modelled with mixture-fluid surface capturing. Turbulence modelling of thick boundary layers and vortical flows requires anisotropic RANS models or hybrid RANS/LES in case of strongly separated flows. Moreover, fluid–structure interaction in the form of rigid or flexible body motion and multi-body systems is crucial to represent ship manoeuvring and propulsion. Finally, the paper underlines the central role played by anisotropic adaptive grid refinement in the accurate simulation of marine flows.

Numerical Simulation of the Blast Resistance of SPUA Retrofitted CMU Masonry Walls

Through numerical simulation, the blast-resistant performance of spray polyurea elastomer (SPUA) retrofitted concrete masonry unit (CMU) masonry infill walls under far-range blast loading was studied. From an engineering perspective, the effects of boundary conditions and thickness of a SPUA layer on enhancing the blast resistance of masonry infill walls are discussed, and the blast resistance of SPUA-retrofitted and grouted CMU masonry infill walls are compared. It is concluded that the boundary constraint conditions and the anchorage length of SPUA layer have limited improvement on the blast-resistant performance of the wall; the thickness of SPUA layer can significantly improve the blast-resistant performance of the wall as the blast loading increases. In addition, SPUA retrofitting shows relatively better performance to reinforce masonry infill walls.

Surface wave phase velocity variations underneath the Indian Ocean geoid low

The Indian plate has undergone a long tectonic journey since its separation from the Gondwanaland. Its protracted rift-drift motion has rendered several enigmatic features in the Indian Ocean. One such feature is the large geoid deficit (−106 m), observed in the south of Sri Lanka that is known as the Indian Ocean geoid low (IOGL). A broad consensus about plausible explanations behind the IOGL anomaly still remains elusive. For the first time, 17 Ocean Bottom Seismometers (OBSs) were deployed in the IOGL region to characterize the subsurface structural variations. Here, we examine the inter-station Rayleigh wave phase velocity variations within the period range of 15–197 s. We construct 1-D velocity-depth sections down to c.a.380 km or less along with N-S and E-W profiles, using ≥5.2 magnitudes (Mw) earthquake data that occurred at a depth ≤ 100 km at regional/teleseismic distances. Our result demarcates the regional Moho depths varying from c.a.11.6 ± 0.8 km to c.a.19.8 ± 1.2 km along the OBS array from south to north respectively. A thickened oceanic crust (c.a.9–10 km) is attributed to magmatic underplating in the lower crust near the aseismic Comorin ridge. The lithospheric thickness ranges between c.a.47.6 ± 2.9 km and c.a. 75.1 ± 3.6 km along a south-north profile. We observe a c.a. 20–23 km thick lithosphere-asthenosphere boundary (LAB). The depth interval between c.a.87 km and c.a. 280 km is characterized by a distinct low-velocity zone (LVZ). A thick LVZ appears to be associated with a thin lithosphere, which implies a hot thermal regime in the upper mantle. We envisage a possible connection of this hot thermal regime with the African LLSVP (large low shear velocity province) and/or a vertically deep mantle upwelling directly beneath the IOGL region. Our findings have significant implications for deciphering the possible causes behind the source of mantle upwelling, the large geoid anomaly and extensive lithospheric deformation across this region.

Prediction of natural frequencies of functionally graded circular and annular plate via differential quadrature method (DQM)

In this paper, numerical approach for free vibration response of functionally graded material (FGM) circular and annular plate is examined using differential quadrature method (DQM), and first-order shear deformation theory. The effective material properties through the thickness of the plate are obtained via power-law distribution. The governing partial differential equations (GDEs) are obtained using Hamilton’s principle. The five GDEs are discretized via DQM. Several comparison studies were carried out by those published in the literature. The free vibration analysis is investigated to reveal the effects of outer radius to thickness ratio, grading index, radii ratio and boundary conditions.

Post-buckling Partial Similitude Scaled Model for Stiffened Cylinders under Axial Compression by Energy Method

Considering the geometric nonlinearity and geometric imperfection of stiffened cylinders, the generalized similitude conditions and scaling laws for axial compression post-buckling are established by applying the similitude transformation to the total energy of the structure. The post-buckling similarity of stiffened cylinders is numerically analyzed, and scale laws, through innovative application of the stiffness formulas and deformation scale factor. Based on three type geometrical imperfections, the effects of radius to effective thickness ratios, stiffened cross-sections, boundary conditions and imperfection coefficients are investigated by post-buckling partial similarity simulation of stiffened cylinders under axial compression. The results show that the partial similarity can be well realized by changing other parameters or selecting a model with a similar Poisson’s ratio for the prototypical material on the premise of invariant stiffness scale factors. Partial similarity simulation of axial compression post-buckling of stiffened cylinders is not affected by radius to effective thickness ratios (23.76–268.95), classical simply supported and fixed support boundary conditions, rectangular or T-type stiffened cross-sections and three type of geometric imperfections.

The Spatial Extent of Magnetopause Magnetic Reconnection From In Situ THEMIS Measurements

AbstractMagnetic reconnection at the magnetopause has long been studied with multi‐spacecraft observations. In this work, data from the five satellite THEMIS mission during the years of 2008–2010 are used to generate statistics regarding the spatial extent of magnetopause reconnection. The presence of a reconnecting magnetopause is determined with the Walén relation as two satellites cross the magnetopause simultaneously. In some cases both satellites measure reconnection whereas in others one satellite measures reconnection and the other does not. This study finds that two spacecraft are more likely to observe a contiguous reconnection region the closer they are spatially, and that reconnection is not always extended around the entire magnetopause. Plasma β gradient drifts are investigated as a cause of local reconnection suppression. Spacecraft position along the magnetopause flanks is also investigated as a possible spatial limitation to reconnection due to changes in shear flow or boundary thickness.

Vibration analysis of thick-section sandwich structures in thermal environments

An ultra-light sandwich structure with a thin ceramic-based composite face sheet bonded to a thick thermal insulator is developed as an integrated thermal protection system (ITPS) structure to protect the substructure of a hypersonic flight vehicle. For vibration fatigue assessment and failure prediction, the global dynamic response of the three-dimensional ITPS structure when subjected to a combination of thermal and harmonic excitation is desired. In this study, a novel unified model for vibration analysis of a thick-section sandwich structure is proposed based on the variational asymptotic method. The original 3D sandwich structure problem is reduced to one-dimensional through-the-thickness analysis and two-dimensional (2D) reference plane analysis. The stiffness matrices, including an equivalent transverse shear matrix, are obtained; hence, a shear correction factor is not required. The mechanical response of the 2D reduced-order plate under general boundary conditions in thermal environments is investigated. The static thermal deformation and forced vibration of the sandwich structure with the temperature gradient in the thickness direction are determined using a set of algebraic orthogonal polynomials through the Gram–Schmidt procedure. The thermal deflection is first introduced into the kinematic relationship to modify the total strain energy for the sandwich plate with temperature-independent material properties. To demonstrate the validity and applicability of the model, some numerical results relating to displacements and fundamental frequencies of simply supported sandwich plates are presented and compared to those obtained by other models. The effects of temperature gradients in the thickness direction, boundary conditions, core thickness, and temperature-dependent material properties on the dynamic characteristics and forced vibration of the sandwich structure are discussed by a detailed parametric study. The global dynamic strain response is first obtained using the plate model, which is desirable to determine the 3D local stress and strain field and predict vibration fatigue failure for the ITPS structure.

Fluid–shell structure interactions with finite thickness using immersed method

This study presents a computational framework for simulating shell structures interacting with fluids using the immersed approach. The approach captures the complex movement and motion of a thin structure represented with shell elements that have a finite thickness. Utilizing the concept of the immersed approach, the fluid domain is described using a fixed set of Eulerian grids and the shell structure uses finite element shell Lagrangian descriptions, thus allowing non-intrusive coupling of independent fluid and shell finite element solvers. Different from the traditional immersed boundary method where the boundary cannot replicate the thickness of the thin boundary or shell structures, our approach projects the shell structure along the directions normal to the shell surface based on a given thickness to create a volumetric structure. Such projection allows robust, accurate and realistic interfacial loading and immersed geometry when interacting with the surrounding fluid. The dynamic solution of the mid-surface obtained from the shell solver is extended and extrapolated into the thickness direction, which is then used to calculate the forces acting on the Eulerian grid nodes to manage the effects of the overlapping solid. The volume representation also helps in calculating consistent nodal forces and moments acting on the shell surface. In particular, the moments yielded across the thickness capture the additional bending that would otherwise be missed for an infinitely thin boundary. Allowing the volumetric representation of the thin shell thickness, deformation modes such as bending and shearing can be more accurately calculated. Intricate transformations between local shell element coordinate and global coordinate were also considered to enable the coupling process. The presented fluid–shell coupling algorithm is carefully verified and validated using three numerical test cases. The accuracy and the robustness of the results also demonstrate the versatility of the developed coupling technique for thin shells and structures with finite thickness.

Mean wake and aerodynamic forces for surface-mounted finite-height square prisms of very small aspect ratio

The mean flow field, aerodynamic forces, bending moment and Strouhal number (St) were investigated for isolated surface-mounted finite-height square prisms of very small aspect ratio (AR). The Reynolds number was Re =7.5×104 for the velocity measurements and 9×104 for the force, bending moment and St measurements. Prisms with AR = 0.5, 0.7 and 1 were considered, under two different boundary layer thicknesses of δ/D=0.7–0.8 (thin) and δ/D=1.3 (thick). For both boundary layers, the mean drag force coefficient showed a sharper increase with AR compared with taller prisms, and the mean normal force coefficient increased smoothly, with a lower magnitude than pressure-based normal force coefficients. An approximately constant point of action of the drag force was found for AR < 1. While the thick boundary layer caused the spectral peaks to weaken and St to decrease, some periodicity was still found for all AR. These features were connected to the changes in the mean wake of the prisms with AR and δ/D. A smaller AR and larger δ/D had similar effects, causing the wake to shorten, the probability and type of reattachment of the flow on the free end to change, and the mean wake structure to transition from a streamwise wake vorticity pattern to an inner vorticity pattern. The prism with AR = 1 showed a dipole wake structure similar to that of taller prisms, while the unique wake topology of prisms with AR < 1 was found to be responsible for the different force and St trends identified in this range of AR.