Interface Conditions Research Articles

Spurious Accelerations in Finite Element Analysis of Geotechnical Problems: Cause and Remedy

Present study investigates the response of the two distinct geotechnical problems under earthquake loading. These two problems are: 1) nailed soil slope and 2) 1-D site response analysis. The aim of the study is to understand the cause of spurious accelerations and suggest a remedy. Two distinct interface conditions were considered in modelling the nailed soil slope. In first, the soil nail interface was considered to be perfectly bonded. In second case, the sliding at the interface was allowed. The analysis resulted into the physically acceptable deformations. However, the dumbbell shaped spurious acceleration pattern was observed in perfect bonding case. Further, the maximum acceleration was found to span from 4 g to 13 g. Such extremely high accelerations are unphysical and hence, unacceptable. In case of 1-D site response analysis, misleading acceleration spike of magnitude twice that of true acceleration was noted. The introduction of the numerical damping successfully removed the spurious accelerations and resulted in physically acceptable response for both problems.

Systematic derivation of [formula omitted] equations, its discretization using GTIN method and development of a switchable SP3 to [formula omitted] neutron transport solver

The Generalized Simplified Spherical Harmonics (GSPN) method has drawn recent interest owing to the fact that theoretically, it is equivalent to the PN and does not rely on any assumption other than piecewise homogeneity. Its level wise approach to PN offers an agreeable balance between the accuracy and computational efficiency making it a valuable mathematical tool for analyzing neutron transport problems pertaining to nuclear engineering and reactor physics. The lowest level approximation for N = 3, expressed as GSP3(0), offers reducing the complexity while still capturing the essential physics. In the current work, GSP3(0) equations are derived along with the interface and boundary conditions for linear anisotropic scattering. These equations are then discretized using the generalized transverse integration nodal method for a two-dimensional system of piecewise homogeneous rectangular regions. The discretization is done with an option kept for reducing the GSP3(0) formalism to the conventional SP3. Subsequently, a computer code has been developed to solve these discretized equations in the multigroup structure for vacuum, reflective or albedo boundaries. At present, this switchable SP3/GSP3(0) code has the capability of estimating k-eigenvalue and position dependent scalar neutron flux within a given two-dimensional rectangular geometry. The code has been verified by solving SP3, GSP3(0) and other benchmark problems from available literature. The results obtained from our code demonstrate that GSP3(0) is superior to the conventional SP3 and comparable to the recently proposed SDPN (N = 1,2,3) [M. Nazari, A. Zolfaghari, M. Abbasi, Prog. Nucl. Energy, 2023; 166, 104,933] in terms of accuracy as well as computation time.

Unraveling conditions for W-shaped interface and undercooled melts in Cz-Si growth: A smart approach

In Cz-Si growth, concave and W-shaped solid–liquid interfaces and undercooled melts are primary contributors to the degradation of crystal quality, particularly structure loss, defect generation, non-uniform dopant distribution, and crystal twisting, making their avoidance crucial. We employed a classification tree machine learning approach to investigate the importance of 15 process and furnace design parameters and their critical ranges for the formation of various types of W-shaped interfaces and undercooled melts at different scales, both in dimensional and dimensionless forms, and across a wide range of process conditions. Moreover, symbolic regression was used to predict minimal melt temperature based on the aforementioned inputs. Training data were obtained by CFD modeling. The classification tree for combined output identified the Grashof, Reynolds for crystal, and Stefan numbers, along with the percentage of silicon solidified, as the most decisive inputs. Symbolic regression for the temperature of undercooled melt highlighted crucible diameter, pulling rate, and the power of the bottom heater as key parameters.

Space charge effects in mixed ionic-electronic conducting electrodes for solid-state batteries.

Mixed ionic-electronic conductors are widely used as electroactive materials in energy applications. The contact of a mixed conductor with another phase plays a crucial role in charge storage and transport in energy devices. However, the interfacial chemistry at the heterojunctions comprising mixed conductors and its interplay with the bulk chemistry remains imperative yet inadequately understood. This study addresses the fundamentals of space charge effects by exploring the equilibrium situations for contacts consisting of mixed conductors. From the perspective of defect chemistry, and by unifying the bulk and interfacial conditions with the electrochemical potential, our treatment allows for predicting the built-in potential at heterojunctions, profiling the space charge distributions, and evaluating the resulting interfacial charge storage and transport. The treatment can be related to experimental characterization, including coulometric titration, conductivity, and capacitance measurements at electrochemical interfaces in all-solid-state batteries. Besides, our treatment also highlights the significance of size and doping effects in nanocrystalline electrodes. This work provides a comprehensive framework for understanding and engineering the heterojunctions in electrochemical devices.

Simulating film boiling with sharp interface and direct calculation of mass transfer to investigate the hydrodynamic and thermal transport phenomena near the interface

The current study presents a computational fluid dynamics (CFD) model for film boiling using two fluids, including liquid nitrogen. Ansys Fluent was customized using user-defined functions (UDFs) to accurately model thermal and fluid dynamic interactions. The UDFs accommodate mass transfer at the liquid-vapor interface, maintaining a sharp interface by accounting for the saturation temperature. Direct heat and mass transfer calculations are implemented rather than relying on empirical correlations. Mesh analysis was performed with grid sizes of 615, 410, 307, and 123 μm, with the 307 μm grid selected for its agreement with average Nusselt number values and accurate bubble shape and height. Verification using the Stefan problem showed a maximum error of 0.45 % for interface displacement and 0.1 % for temperature distribution. Validation against the Berenson correlation demonstrated good agreement in Nusselt number values. Qualitative validation of the developed method is performed using the shapes of the growing bubble. The results obtained show that the sharp interface is preserved throughout the simulation, with temperature contours showing significant variations during bubble growth and departure. Local heat transfer coefficient analysis identified peak values of 2170 W/m²-K at locations of minimal film thickness. Velocity vector analysis revealed velocities of 2 m/s in the vapor phase, influencing bubble shape during growth and departure. The study highlights the impact of thermal film thickness on heat transfer, with the highest Nusselt number of 5.69 observed at a film thickness of 0.5 mm. The results demonstrate the application of VOF sharp interface tracking and direct calculation of interfacial conditions utilizing customized Ansys Fluent in the modeling of film boiling as a way to understand the fundamental aspects of the fluid and thermal behavior.

Capillary-Assisted Assembly of Polymer Gel-Supported Lipid Bilayers.

The polymer-supported lipid bilayer represents an attractive supramolecular assembly in numerous biophysical and bioanalytical applications. The assembly of polymer-supported membranes with a polymer layer thickness of just a few nanometers is now well-established, but bilayer properties in such a membrane architecture are still influenced by the nearby solid substrate. Polymer-supported lipid bilayer systems with a several micrometers thick polymer layer will overcome this shortcoming. However, formation of a fluid lipid bilayer on a fully hydrated, micrometer thick polymer film using traditional methods (e.g., vesicle fusion and lipid monolayer deposition techniques) remains a challenging task due to the rather unfavorable interfacial conditions for bilayer formation in such a system. Here, we report for the first time on the facile capillary-assisted formation of a lipid bilayer on the surface of a fully hydrated, several micrometers thick polyacrylamide (PAA) gel, in which forced molecular crowding of lipids at the air-water interface of the capillary results in monolayer instability and collapse, thereby forming a lipid bilayer on the top of the polymer gel inside the capillary. Stable bilayer attachment on the surface of the polymer gel can be achieved via physisorption or specific chemical linkages (tethering) on both cross-linked and non-cross-linked PAA films. Unlike the traditional solid-supported lipid bilayer (SLB), the lipid lateral diffusion in the polymer gel-supported lipid bilayer is not anymore perturbed by a solid substrate. Instead, more like a plasma membrane, it is mainly influenced by the properties of the underlying polymer and the nature/distribution of polymer-bilayer attachments. Polymer gel-supported lipid bilayers built using the capillary-assisted assembly approach show attractive self-healing properties, resulting in superior long-term stability relative to the SLB. We hypothesize that the described capillary-assisted assembly method can be applied to a wide range of polymeric materials and lipid compositions, opening exciting opportunities as an advanced model membrane system.

Comparing New Smartphone-Connected Handheld Ultrasound Device vs. Traditional Ultrasound in Vitreo-Retinal Disease Diagnosis.

(1) Background: Ocular emergencies account for 1.5-3% of emergency department (ED) visits and require urgent diagnosis to prevent serious complications. Ultrasonography is a crucial, non-invasive diagnostic tool for these conditions but traditionally lacks portability and integration with modern electronic smart devices. The purpose of this study was to assess the accuracy and performance of a new handheld ultrasound device in comparison to a conventional cart-based sonographic machine in patients attending to the ED for vitreo-retinal diseases. (2) Methods: three specialists in ophthalmology, with at least 4-year experience in vitreo-retinal diseases and eye ultrasound, evaluated images of 50 eyes with both portable and traditional ultrasound probes. Each specialist made the diagnosis based on the images captured with both probes and then rated their overall image quality and confidence of diagnosis with a five-point Likert scale. The concordance of diagnosis between the two probes was evaluated. (3) Results: The sample comprised 42 patients. Twenty (40%) healthy eyes and thirty eyes with the following vitreo-retinal interface conditions were examined: 12 retinal detachment (24%), 8 vitreous hemorrhage (16%), and 10 posterior vitreous detachment (20%). The overall accuracy of the two devices appeared to be comparable (70.7% vs. 69.3%). The Butterfly iQ+ probe showed similar sensitivity in retinal detachment diagnosis (91.7% vs. 94.4% of the Accutome B-scan Pro), while it showed poor performance in diagnosing posterior vitreous detachment (sensitivity = 27.2%); (4) Conclusions: The Butterfly iQ+ device demonstrated high sensitivity in the diagnosis of retinal detachment. Significant adjustments are still needed to improve the resolution of the vitreous body.

Application of Slip Interface Conditions in the Elastic Parabolic Equation

The parabolic equation method is the most effective approach for solving wave propagation problems in environments with strong vertical variations and gradual horizontal variations. This approach efficiently provides accurate solutions for problems involving sloping fluid-fluid interfaces, sloping solid-solid interfaces, and sloping solid boundaries. There remains a need for improvement for the case of sloping fluid-solid interfaces. The most promising approach to date is the combination of a single-scattering approximation and the treatment of part of the fluid layer as a solid layer with low shear speed. This is a singular perturbation, which results in rapid oscillations near the interface between the low-speed layer and the true solid layer. It is demonstrated here that the rapid oscillations may be eliminated by using slip conditions at the interface between the low-speed layer and the true solid layer. Stability problems were encountered when attempting to directly implement the slip conditions, but this problem was resolved by using an equivalent condition involving the normal derivative of the tangential displacement. This progress does not fully resolve the case of the sloping fluid-solid interface. There remains a need to find a vertical interface condition that is compatible with the slip conditions and that provides accurate results for problems involving sloping fluid-solid interfaces.

Two-phase magnetohydrodynamic blood flow through curved porous artery

Blood arteries are important part of our cardiovascular system. A comprehensive study of shape and anatomy of blood arteries allows to elucidate the dynamics of blood flow in these arteries. Typically, the arteries are a curved-tube like structure, with arterial walls exhibiting a composition of various porous layers. The current study embarks on a theoretical exploration of a two-fluid model of blood flow and heat transfer through the curved artery under an influence of a magnetic field. The artery walls are composed of Brinkman and Darcy layers. The blood flows through a curved artery exerts centrifugal forces on the arterial walls that leads to change the blood flow patterns. The significant effects of curvature along with the intensity of an applied magnetic field on the blood flow patterns, heat transfer, and resistance impedance in curved artery have been investigated in the present work. The mathematical model of the proposed work is tackled by the homotopy analysis method using physically relevant boundary and interface conditions. The significant outcome of the present work is that the heat transfer rate increases with the increase in the curvature parameter, and it reduces on raising the couple stress parameter and Hartmann number. The novelty of this work lies in the consideration blood flow and heat transfer in inner endothelial layers of curved porous artery. The result presented in this work is vital to assess the condition of atherosclerosis, aneurysms, vasculties, blood clot, etc.; beyond this, the present model can be extended for medical diagnostics, treatment planning, medical device design, drug delivery optimization, and biomedical engineering research. This study can ultimately contribute for improved patient care and outcomes in cardiovascular medicine.

Reflection and Transmission of Plane Waves at the Interface of Fluid and Porous Media with Seismoelectric Effect

Abstract The relationship between energy flux reflection and transmission coefficient of seismoelectric plane waves in plane layered media and incident angle and frequency is studied. Pride equations is adopted to describe the coupling phenomenon between elastic waves and electromagnetic fields in subsurface fluid-saturated porous media. The Helmholtz decomposition is used to derive the energy flux expression for seismoelectric plane waves propagating in fluid-saturated porous media. It shows that the impermeable interface conditions have a great influence on the reflection and transmission coefficient of seismoelectirc waves. The transmission coefficient of slow longitudinal waves under impermeable interface is much smaller than that of permeable interface conditions Reflection coefficient of longitudinal wave, transmission coefficients of the fast longitudinal waves and transverse waves are all larger under impermeable interface conditions than that of permeable cases. And the reflection coefficient of electromagnetic wave under impermeable interface conditions is almost one order of magnitude smaller than that permeable case.

Spectral properties for discontinuous Dirac system with eigenparameter‐dependent boundary condition

In this paper, Dirac system with interface conditions and spectral parameter dependent boundary conditions is investigated. By introducing a new Hilbert space, the original problem is transformed into an operator problem. Then the continuity and differentiability of the eigenvalues with respect to the parameters in the problem are showed. In particular, the differential expressions of eigenvalues for each parameter are given. These results would provide theoretical support for the calculation of eigenvalues of the corresponding problems.

A mixed-dimensional formulation for the simulation of slender structures immersed in an incompressible flow

We consider the simulation of slender structures immersed in a three-dimensional (3D) flow. By exploiting the special geometric configuration of the slender structures, this particular problem can be modeled by mixed-dimensional coupled equations. Taking advantage of the slenderness of the structure and thus considering 3D/1D coupled problems raise several challenges and difficulties. From a mathematical point of view, these include defining well-posed trace operators of co-dimension two. On the computational standpoint, the non-standard mathematical formulation makes it difficult to ensure the accuracy of the solutions obtained with the mixed-dimensional discrete formulation as compared to a fully resolved one. Here we proposed to circumvent theses issues by imposing the fluid–structure coupling conditions on the 2D fluid–structure interface but in a reduced way still taking advantage of the 1D dynamic of the slender structure. We consider the Navier–Stokes equations for the fluid and a Timoshenko beam model for the structure. We complement these models with a mixed-dimensional version of the fluid–structure interface conditions, based on the projection of kinematic coupling conditions on a finite-dimensional Fourier space on each beam cross section. Furthermore, we develop a discrete fictitious domain formulation within the framework of the finite element method, establish the energy stability of the scheme, provide extensive numerical evidence of the accuracy of the discrete formulation, notably with respect to a fully resolved (ALE based) model and a standard reduced modeling approach.

Diffuse interface modeling of non‐isothermal Stokes‐Darcy flow with immersed transmissibility conditions

AbstractThe coupling between free and porous medium flows has received significant attention since it plays an important role in a wide range of problems from fluid‐soil interactions to biofluid dynamics. However, modeling this coupled process remains a difficult task as it often involves a domain decomposition algorithm in conjunction with a special treatment at the interface. The problem can become more challenging under non‐isothermal conditions because it requires the iterative procedure at every time step to simultaneously meet the transient mass continuity, force equilibrium, and energy balance for the entire system. This article presents a diffuse interface framework for modeling non‐isothermal Stokes‐Darcy flow and the corresponding finite element formulation that bypasses the need for explicitly splitting the domain into two, which enables the unified treatment for distinct regions with different hydrothermal flow regimes. To achieve this goal, we employ the Allen‐Cahn type phase field model to generate the diffuse geometry, where the solution field can be seen as a regularized approximation of the Heaviside indicator function, allowing us to transfer the interface conditions into a set of immersed boundary conditions. Our formulation suggests that the isothermal operator splitting strategy can be adopted without compromising accuracy if the heat and mass transfer processes are decoupled by assuming that the density and viscosity of the phase constituents are independent to the temperature. Numerical examples are also introduced to verify the implementation and to demonstrate the model capacity.

Impact of material-dependent radiation – longitudinal optical phonon interaction on thermal electric-dipole radiation from surface metal − semiconductor grating structures

Infrared thermal radiation emission in the 8.5 – 28 THz frequency region is obtained using surface metal–semiconductor grating structures on undoped (u-) GaAs, u-GaP, u-ZnO, u-GaN, and n-type SiC in a temperature range of 430 – 630 K. These emissions resonate with longitudinal optical (LO) phonon or LO-like lattice vibration energies determined by the zero points of the real parts of the dielectric functions in the surface structures. The emissions of materials with Reststrahlen bandwidths of a few tens of cm−1 show the emissions resonating with their LO phonon modes, while materials with bandwidth of more than 170 cm−1 show peak energies significantly lower than the LO phonon: LO-like phonon resonance. The emission intensity is found to be dominated by the balance of radiative and nonradiative LO or LO-like phonon annihilation rates. The radiative rate is dominated by the LO-phonon–radiation interaction Hamiltonian and the Bose-Einstein factor. High emission intensity is obtained for the structure on u-ZnO with intense LO-like phonon–radiation interaction. The dependence of the emission intensity on temperature and emission window width for various materials shows the effect of material-dependent metal/semiconductor interface conditions on the emission efficiency.

Microscopic instabilities in single crystal matrix composites

A finite strain micromechanical analysis is presented for the prediction of the loss of microscopic stability of a class of metal matrix composites that are subjected to axial compressive loading and undergoing large deformations. The metallic constituent behavior is modeled by the single crystal anisotropic plasticity theory in which, due to the resolved shear stresses, plastic deformations occur along certain pre-defined slip planes. Thus, this incremental plasticity theory is capable of providing the effect of the applied axial loading on the induced shear stresses which dominate the microbuckling. The composites are assumed to possess slight imperfections at the interfaces, and in order to satisfy the interfacial conditions, a perturbation expansion is employed which yields zero and first order micromechanical analysis problems. The zero order problem corresponds to the micromechanical modeling of the composite with no imperfections, whereas the solution of the first order problem is utilized to obtain the critical stresses and deformations at which bifurcation buckling occurs. Both problems are solved by employing the finite strain high-fidelity generalized method of cells (HFGMC) micromechanics. Applications are given for various types of single crystal matrix composites including layered, particulate, continuous and short fiber composites. Finally, a comparison between the compressive strengths of a standard metal matrix boron/aluminum and SiC/single crystal composites is presented and discussed.

Airway epithelial cell response to RSV is mostly impaired in goblet and multiciliated cells in asthma

BackgroundIn patients with asthma, respiratory syncytial virus (RSV) infections can cause disease exacerbation by infecting the epithelial layer of the airways, inducing subsequent immune response. The type I interferon antiviral...

Torsional dynamic response of a large-diameter pipe pile in transversely isotropic unsaturated soils considering construction disturbance

Large-diameter pipe piles are widely applied in various civil engineering fields due to their outstanding load-bearing capability. The unsaturated characteristics, anisotropy, and heterogeneity of the soil jointly affect the dynamic response of the pipe pile. However, most previous studies were limited to single-phase or two-phase soil. This paper develops an analytical model for the torsional vibration of a pipe pile in transversely isotropic unsaturated soils considering construction disturbance. Based on transversely isotropic unsaturated soil theory, a pipe pile-soil interaction model has been developed, while the effect of construction disturbance is simulated by the radial heterogeneity of the soil. The general solution for the unsaturated soil is obtained using the separation of variables method with the boundary conditions. Then, the solution for the whole pipe pile-soil system is derived by considering the pile-soil interface conditions. The accuracy of the proposed solution is verified through comparisons with previous research results. The results show that unsaturated characteristics, construction disturbance, and transverse isotropy of the soil have significant effects on the impedance of large-diameter pipe piles. Specifically, with a low degree of saturation, there will be significant prediction errors when using previous works based on single-phase or two-phase soil theory to predict the dynamic response of large-diameter pipe piles.

Flexible composite films with ultrahigh through-plane thermal conductivity yet low graphene content

Graphene-based polymeric composites have become one of the promising thermal interface materials (TIMs) for the high integration electronic devices due to the excellent intrinsic thermal conductivity of graphene. However, the challenges still remain, such as ordered alignment of graphene in elastic polymer and regulation of phonon scattering at graphene/graphene interface. In this study, a vertically oriented graphene framework within a flexible silicone rubber matrix was fabricated by non-solvent induced phase separation (NIPs) coupled with an in in-situ welding technique. The as-prepared film exhibits an outstanding through-plane thermal conductivity of 29.5W/mK at low graphene loading of 7.5 wt%, which indicates an exceptionally high thermal conductivity enhancement per 1 wt% graphene content (specific TCE) over 1950 %/wt%. Furthermore, the composite films demonstrate excellent conformability inherited from the silicone rubber matrix and achieves low contact resistance of 40–70 Kmm2W−1 under various pressure and interfacial conditions. This study contributes to a deeper insight into the development of the high-performance graphene-based polymeric TIMs.

Non-standard interface conditions in flexure of mixture unified gradient Nanobeams

Structural schemes of applicative interests in Engineering Science frequently encounter the intricate phenomenon of discontinuity. The present study intends to address the discontinuity in the flexure of elastic nanobeam by adopting an abstract variational scheme. The mixture unified gradient theory of elasticity is invoked to realize the size-effects at the ultra-small scale. The consistent form of the interface conditions, stemming from the established stationary variational principle, is meticulously set forth. The boundary-value problem of equilibrium is properly closed and the analytical solution of the transverse displacement field of the elastic nanobeam is addressed. As an alternative approach, the eigenfunction expansion method is also utilized to scrutinize the efficacy of the presented variational formulation in tackling the flexure of elastic nanobeams with discontinuity. The flexural characteristic of mixture unified gradient beams with diverse kinematic constraints is numerically illustrated and thoroughly discussed. The anticipated nanoscopic features of the characteristic length-scale parameters are confirmed. The demonstrated numerical results can advantageously serve as a benchmark for the analysis and design of pioneering ultra-sensitive nano-sensors. The established variationally consistent size-dependent framework paves the way ahead in nanomechanics and inspires further research contributing to fracture mechanics of ultra-small scale elastic beams.

A piecewise extreme learning machine for interface problems

Deep learning methods have been developed to solve interface problems, benefiting from meshless features and the ability to approximate complex interfaces. However, existing deep neural network (DNN) methods for usual partial differential equations encounter accuracy limitations where after reaching a certain error level, further increases in network width, depth, and iteration steps do not enhance accuracy. This limitation becomes more notable in interface problems where the solution and its gradients may exhibit significant jumps across the interface. To improve accuracy, we propose a piecewise extreme learning machine (PELM) for addressing interface problems. An ELM is a type of shallow neural network where weight/bias coefficients in activation functions are randomly sampled and then fixed instead of being updated during the training process. Considering the solution jumps across the interface, we use a PELM scheme — setting one ELM function for each side of the interface. The two ELM functions are coupled using the interface conditions. Our numerical experiments demonstrate that the proposed PELM for the interface problem significantly improves the accuracy compared to conventional DNN solvers. The advantage of new method is shown for addressing interface problems that feature complex interface curves.