Interface Method Research Articles

The electromagnetic scattering from multiple arbitrarily shaped cavities with inhomogeneous anisotropic media

We study the electromagnetic scattering problem from multiple arbitrarily shaped cavities filled with inhomogeneous anisotropic media. A local-refined Petrov-Galerkin finite element interface (PGFEI) method is developed for solving the scattering problem. By introducing the transparent boundary condition, the unbounded scattering problem can be reduced into bounded domain problem with coupled boundary conditions on the apertures of multiple cavities. The multiple cavity scattering in transverse magnetic (TM) and transverse electric (TE) polarizations are both investigated based on uniform non-body-fitted meshes. We adopt the level-set functions to capture the irregular cavity wall and the interfaces of inhomogeneous media. The special basis is constructed to satisfy the jump conditions across the interfaces of different materials further. The local-refined algorithm is proposed to enhance the accuracy of the solutions around the discontinuous interfaces. The generation of the grid points facilitates a special numbering scheme which enables a stepwise Schur complement decomposition of the discrete linear system derived by the PGFEI method. It could be an alternative method for solving the scattering problems which have similar structures. The proposed method can handle matrix coefficients caused by the permittivity and permeability tensor of anisotropic media. Numerical experiments illustrate the validity and efficiency of the method for solving the scattering from multiple arbitrarily shaped cavities with inhomogeneous anisotropic media in TM and TE polarization.

Monodisperse covalent organic nanosheets by in-situ oxidation method for efficient ion/molecule separation

Two-dimensional (2D) covalent organic nanosheets (CONs) are layered crystalline porous polymers comprising periodically extended graphene-like structures, and have great application potential in membrane separation field due to the advantages of abundant optional monomers, tunable pore size and structure, facilely-tailored functionality and pre-designed properties. However, unlike graphene oxide (GO) membranes, it is hard to directly prepare 2D CON membranes by vacuum filtration because of the difficulties in preparation of ultra-thin, large-sized and well-dispersed 2D CONs. Herein, an improved buffering interlayer interface method was proposed to realize a facile one-step synthesis of GO-like CON oxides by using H2O2 as an in-situ oxidant in the buffer layer. The stereoscopic fulcrum-oxygen sites introduced into the structure of CONs lead to weaken interactions between CON layers and increased hydrophilicity, which contributes to subsequent preparation of monodisperse nanosheets. The membranes fabricated with the as-prepared monodisperse nanosheets can realize high-efficiency transport of metal ions with a precise charge-discriminated group separation ability and efficient ion rejection. The strategy of in-situ oxidation to prepare monodisperse CONs proposed in this study provides a valuable approach for the preparation of novel functionalized CONs and the achievement of fast membrane separation performance.

A novel homogenization method for periodic piezoelectric composites via diffused material interface

In this article, we propose a novel homogenization method for piezoelectric composites with periodic microstructures. In the proposed homogenization method, one can find the analytical expressions for the material properties of the composites in the representative volume element (RVE) via diffused material interface method. The availability of analytical expressions for the material properties in the entire domain of the RVE enables one to determine the effective homogenized material properties with the standard finite element method. As the proposed homogenization method regularizes the discontinuity in material properties across the interfaces, there is no need to explicitly track the material interfaces while implementing the finite element method for determining the effective material properties. Hence, one can implement the proposed homogenized method for any piezoelectric composites with complicated material interfaces and determine the effective material properties. In this study, we have considered the piezoelectric composites to be comprised of periodic microstructures where the RVE constitutes a matrix with an inclusion of a specific shape. We have carried out a study on the effect of the shape of inclusion viz. square-shaped, I-shaped, T-shaped, and plus-shaped, and the size of inclusion on the effective piezoelectric material properties. We have also studied the influence of shape and size of inclusion on the electro-mechanical response of a homogenized piezoelectric continuum. To implement the proposed homogenization method, we have used Gridap, an open-source finite element toolbox in Julia that provides very compact codes freely available to all the researchers and makes a third-party verification of the proposed method straightforward.

Detection method of coal-rock interface and low-resistivity anomalous body based on azimuth electromagnetic wave

Detection method of coal-rock interface and low-resistivity anomalous body based on azimuth electromagnetic wave

Coupling Design and Validation Analysis of an Integrated Framework of Uncertainty Quantification

The uncertainty quantification is an indispensable part for the validation of the nuclear safety best-estimate codes. However, the uncertainty quantification usually requires the combination of statistical analysis software and nuclear reactor professional codes, and it consumes huge computing resources. In this paper, a design method of coupling interface between DAKOTA Version 6.16 statistical software and nuclear reactor professional simulation codes is proposed, and the integrated computing workflow including interface pre-processing, code batching operations, and interface post-processing can be realized. On this basis, an integrated framework of uncertainty quantification is developed, which is characterized by visualization, convenience, and efficient computing. Meanwhile, a typical example of small-break LOCA analysis of the LOBI test facility was used to validate the reliability of the developed integrated framework of uncertainty quantification. This research work can provide valuable guidance for developing an autonomous uncertainty analysis platform in China.

Review on fluid-structure interaction problem modeling and recent developments

The fluid-structure interaction (FSI) problem plays significant roles in engineering simulations and design. This problem considers the interaction between the fluid domain and structural domain with one-way or two-way data transfer. There are several algorithms to solve the problem, mainly numerical duo to the complexity and nonlinearly. The numerical schemes focus on the modeling method of the coupling interface. However, there are several algorithms that merge the interface in the equations and deal with the domains as a unified set of equations. Future development could include artificial intelligence modeling and the inclusion of more physical domains into the systems.

Dual-functional gold nanorods micro pattern guiding cell alignment and cellular microenvironment monitoring

Surface topography has become a powerful tool to control cell behaviors, however, it’s still difficult to monitor cellular microenvironment changes during topography-induced cell responses. Here, a dual-functional platform integrating cell alignment with extracellular pH (pHe) measurement is proposed. The platform is fabricated by assembling gold nanorods (AuNRs) into micro pattern via wettability difference interface method, which provides topographical cues and surface-enhanced Raman scattering (SERS) effect for cell alignment and biochemical detection respectively. Results demonstrate that contact guidance and cell morphology changes are achieved by the AuNRs micro pattern, and pHe are also obtained by the changes of SERS spectra during cell alignment, where the pHe near cytoplasm is lower than nucleus, revealing the heterogeneity of extracellular microenvironment. Moreover, a correlation between lower extracellular pH and higher cell migration ability is revealed, and AuNRs micro pattern can differentiate cells with different migration ability, which may be an inheritable character during cell division. Furthermore, mesenchymal stem cells response dramatically to AuNRs micro pattern, showing different morphology and increased pHe level, offering the potential of impacting stem cell differentiation. This approach provides a new idea for the research of cell regulation and response mechanism.

Effect of process parameters on interlaminar properties of thermoplastic composite: Molecular dynamics simulation and experimental verification

Interlaminar properties are one of the most important indicators of thermoplastic composite quality. In this paper, the unidirectional carbon fibre reinforced polyether ether ketone (CF/PEEK) thermoplastic composite was taking as the research object, an all-atom model constructing method of the interlaminar interface was proposed, the influence mechanism of process parameters including forming pressure and temperature on interlaminar properties were studied by molecular dynamics (MD) simulation and experimental verification. The simulation results showed that a reasonable forming pressure could promote the non-bonded interaction between polymer molecules, and an appropriate raising of forming temperature could promote the thermal motion of polymer molecules, which was conducive to the interlaminar diffusion and penetration of polymer, thereby improving the interlaminar bonding strength, the interlaminar properties were more sensitive to the changes of forming temperature than pressure. The experimental results were in good agreement with the MD simulation result in terms of the significance and the trend of process parameters influence on the interlaminar properties. Illustrating that it is effective to explore the forming mechanism of thermoplastic composite and guide the forming process by MD simulation.

Melting Curve of Cobalt using Molecular Dynamics Simulation

Molecular dynamics simulation is used to estimate the melting point of cobalt using the embedded atomic model (EAM) potential by heat until melting, void, hysteresis and interface methods. For instance, the estimated melting temperature are 2102 K, 1944.15 K, 1731 K and 1725±25 K using these methods, respectively. Then, the melting points at different pressures are calculated. A graph depicting the variation of melting point with pressure is drawn and compared with the available simulation and experimental results. The melting point at a low-pressure range is similar to the previous diamond anvil cell experiments. Besides, using the Simon equation, we calculated the melting slope at 0 GPa pressure of 36 K/GPa for one phase and 40 K/GPa for two-phase methods.

Spurious currents suppression by accurate difference schemes in multiphase lattice Boltzmann method

Spurious currents are often observed near curved interfaces in multiphase simulations based on diffuse interface methods. These unphysical phenomena negatively affect both computational accuracy and stability. In this paper, the origin and suppression of spurious currents are investigated using the multiphase lattice Boltzmann method driven by a chemical potential. Both the difference error and insufficient isotropy of the discrete gradient operator give rise to directional deviations in the nonideal force, leading to spurious currents. Nevertheless, a high-order finite difference scheme produces far more accurate results than a high-order isotropic difference scheme. We compare several finite difference schemes that have different levels of accuracy and resolution. When a large proportional coefficient is used, the transition region is narrow and steep, and the resolution of the finite difference scheme provides a better indication of the computational accuracy than the formal accuracy. Conversely, for a small proportional coefficient, the transition region is wide and gentle, and the formal accuracy of the finite difference gives a better indication of the computational accuracy than the resolution. Numerical simulations show that the spurious currents calculated in the three-dimensional situation are highly consistent with those in two-dimensional simulations; in particular, the two-phase coexistence densities calculated by the high-order accuracy finite difference scheme are in excellent agreement with the theoretical predictions of the Maxwell equal-area construction down to a reduced temperature of 0.2.

Brain Computer Interface-Based Signal Processing Techniques for Feature Extraction and Classification of Motor Imagery Using EEG: A Literature Review

A communication path for people having severe neural disorders is provided by Brain Computer Interaction. The Brain–Computer Interface in an electroencephalogram is an important and challenging one for managing non-stationary EEG signals. EEG signals are more vulnerable to noise and artifacts. The Motor Imagery-based Brain–Computer Interface is used as a communication channel for people with neural disorders who have no muscular activity. For a well-established and accurate BCI system, two important steps have been used in MI-BCI, such as feature extraction and feature classification. Spectral methods and spatial methods are used for the feature extraction methods. The classifiers translate the features into the device commands. Linear Discriminant Analysis is the most widely used classification algorithm. So far, Support Vector Machine has been used as a classification method. In recent studies, Deep Neural Networks and Convolutional Neural Networks have been used. In this study, the feature extraction approaches as well as the signal classification methods for the motor imagery brain computer interface are thoroughly reviewed and presented.

An ADER discontinuous Galerkin method on moving meshes for Liouville's equation of geometrical optics

Liouville's equation describes light propagation through an optical system. It governs the evolution of an energy distribution on phase space. This energy distribution is discontinuous across optical interfaces. Curved optical interfaces manifest themselves as moving boundaries on phase space. In this paper, an ADER discontinuous Galerkin (DG) method on a moving mesh is applied to solve Liouville's equation. In the ADER approach a temporal Taylor series is computed by replacing temporal derivatives with spatial derivatives using the Cauchy-Kovalewski procedure. The result is a fully discrete explicit scheme of arbitrary high order of accuracy. A moving mesh is not sufficient to be able to solve Liouville's equation numerically for the optical systems considered in this article. To that end, we combine the scheme with a new method we refer to as sub-cell interface method. When dealing with optical interfaces in phase space, non-local boundary conditions arise. These are incorporated in the DG method in an energy-preserving manner. Numerical experiments validate energy-preservation up to machine precision and show the high order of accuracy. Furthermore, the DG method is compared to quasi-Monte Carlo ray tracing for two examples showing that the DG method yields better accuracy in the same amount of computational time.

Open nanocavity-assisted Ag@PDMS as a soft SERS substrate with ultra-sensitivity and high uniformity.

To achieve high sensitivity and uniformity simultaneously in a surface-enhanced Raman scattering (SERS) substrate, this paper presents the preparation of a flexible and transparent three-dimensional (3D) ordered hemispherical array polydimethylsiloxane (PDMS) film. This is achieved by self-assembling a single-layer polystyrene (PS) microsphere array on a silicon substrate. The liquid-liquid interface method is then used to transfer Ag nanoparticles onto the PDMS film, which includes open nanocavity arrays created by etching the PS microsphere array. An open nanocavity assistant soft SERS sample, "Ag@PDMS," is then prepared. For electromagnetic simulation of our sample, we utilized Comsol software. It has been experimentally confirmed that the Ag@PDMS substrate with silver particles of 50 nm in size is capable of achieving the largest localized electromagnetic hot spots in space. The optimal sample, Ag@PDMS, exhibits ultra-high sensitivity towards Rhodamine 6 G (R6G) probe molecules, with a limit of detection (LOD) of 10-15 mol/L, and an enhancement factor (EF) of ∼1012. Additionally, the substrate exhibits a highly uniform signal intensity for probe molecules, with a relative standard deviation (RSD) of approximately 6.86%. Moreover, it is capable of detecting multiple molecules and can perform real detection on non-flat surfaces.

Monitoring method of phase transition interface for natural gas hydrate based on thermoacoustic effect

In the drilling and exploitation for natural gas hydrate, the decomposition of combustible ices creates the interface between their solid state and liquid state, which would play an important role in the dynamic monitoring while exploitation. In this paper, a monitoring method based on the thermoacoustic effect is proposed to detect the position of the interface. The mechanism of the thermoacoustic coupling is introduced into the natural gas hydrate, that is, the physical model of thermoacoustic effect is established and detailed when the hydrate is excited by a strong electrical pulse. Two kinds of acoustic sources, the thermoelastic source and the phase transition acoustic source, are proposed to explain the obviously enhanced acoustic signals. By modeling and simulating, it is verified that the acoustic signals can be generated by the phase transition around the interface in hydrate. At the same time, many influencing factors on the thermoacoustic signals are researched based on simulations, such as the size of hydrate, the latent heat absorption coefficient and the amplitude of the transient electrical pulse. Finally, the experimental system both for hydrate generation and for thermoacoustic monitoring is built. We prepared carbon dioxide hydrate in a high-pressure reactor at an initial pressure of 5 MPa and temperature of −5 °C. Then take the hydrate into the environment of room temperature and standard pressure, apply the transient electrical pulse to the hydrate and use the ultrasonic probe to detect the acoustic signals. The results show that acoustic signals emitted from the position of the solid-liquid interface can be employed to monitor the hydrate decomposition experimentally and actually.

A sharp interface Lagrangian-Eulerian method for flexible-body fluid-structure interaction

This paper introduces a sharp-interface approach to simulating fluid-structure interaction (FSI) involving flexible bodies described by general nonlinear material models and across a broad range of mass density ratios. This new flexible-body immersed Lagrangian-Eulerian (ILE) scheme extends our prior work on integrating partitioned and immersed approaches to rigid-body FSI. Our numerical approach incorporates the geometrical and domain solution flexibility of the immersed boundary (IB) method with an accuracy comparable to body-fitted approaches that sharply resolve flows and stresses up to the fluid-structure interface. Unlike many IB methods, our ILE formulation uses distinct momentum equations for the fluid and solid subregions with a Dirichlet-Neumann coupling strategy that connects fluid and solid subproblems through simple interface conditions. As in earlier work, we use approximate Lagrange multiplier forces to treat the kinematic interface conditions along the fluid-structure interface. This penalty approach simplifies the linear solvers needed by our formulation by introducing two representations of the fluid-structure interface, one that moves with the fluid and another that moves with the structure, that are connected by stiff springs. This approach also enables the use of multi-rate time stepping, which allows us to use different time step sizes for the fluid and structure subproblems. Our fluid solver relies on an immersed interface method (IIM) for discrete surfaces to impose stress jump conditions along complex interfaces while enabling the use of fast structured-grid solvers for the incompressible Navier-Stokes equations. The dynamics of the volumetric structural mesh are determined using a standard finite element approach to large-deformation nonlinear elasticity via a nearly incompressible solid mechanics formulation. This formulation also readily accommodates compressible structures with a constant total volume, and it can handle fully compressible solid structures for cases in which at least part of the solid boundary does not contact the incompressible fluid. Selected grid convergence studies demonstrate second-order convergence in volume conservation and in the pointwise discrepancies between corresponding positions of the two interface representations as well as between first and second-order convergence in the structural displacements. The time stepping scheme is also demonstrated to yield second-order convergence. To assess and validate the robustness and accuracy of the new algorithm, comparisons are made with computational and experimental FSI benchmarks. Test cases include both smooth and sharp geometries in various flow conditions. We also demonstrate the capabilities of this methodology by applying it to model the transport and capture of a geometrically realistic, deformable blood clot in an inferior vena cava filter.

Gesture Interface and Transfer Method for AMR by Using Recognition of Pointing Direction and Object Recognition

This paper describes a gesture interface for a factory transfer robot. Our proposed interface used gesture recognition to recognize the pointing direction, instead of estimating the point as in conventional pointing gesture estimation. When the autonomous mobile robot (AMR) recognized the pointing direction, it performed position control based on the object recognition. The AMR traveled along our unique path to ensure that its camera detected the object to be referenced for position control. The experimental results confirmed that the position and angular errors of the AMR controlled with our interface were 0.058 m and 4.7° averaged over five subjects and two conditions, which were sufficiently accurate for transportation. A questionnaire showed that our interface was user-friendly compared with manual operation with a commercially available controller.

Bearing life prediction based on critical interface method under multiaxial random loading

The bearing was a key component of the mining machine tire unloader machine and was subjected to random multiaxial stress during operation. Therefore, the life prediction of bearing was of safety guidance. In this paper, a bearing life prediction method based on the critical plane method under multiaxial random loading was proposed. Firstly, a virtual prototype model was built based on the actual working conditions of the tire unloader machine to obtain the time load history of the bearing. Transient dynamic analysis of the bearing was carried out to obtain the triaxial stress-strain time histories at the hazardous locations of the bearing. A new coordinate system was established using the hazard node as the coordinate origin, and the location of the critical plane was searched for based on the critical plane multiaxial fatigue theory, combined with the maximum shear strain amplitude on the critical plane for multi-axial rain flow cycle counting to obtain the damage amount in each direction. At the same time, the life calculated from the maximum damage amount was used as the final life, resulting in a cycle count of the bearing of 268,303 cycles and a duration of 1490.58h. The results of this study could be used as a guide to predict the service life of the bearing in large machinery subjected to multiaxial random stress conditions.

On ghost fluid method-based sharp interface level set method on a co-located grid and its comparison with balanced force-based diffuse interface method

This paper, on Computational multi-Fluid Dynamics (CmFD) development, presents an extension of the Ghost Fluid Method (GFM)-based Sharp Interface Level Set Method (SI-LSM) (originally proposed on a staggered grid) for a co-located grid system. Further, this paper presents a comparative study for the GFM-based SI-LSM and a balanced force method (BFM)-based Diffuse Interface Level Set Method (DI-LSM). The BFM-based DI-LSM avoids a pressure-interfacial force decoupling, during the implementation of the MIM, by a proper-discretization of the surface tension term; not needed for the single-phase flow. Whereas, the GFM-based SI-LSM implicitly couples two immiscible, incompressible fluids via interface jump condition, which makes the Momentum Interpolation Method (MIM) for the two-fluid flow same as that for a single-fluid flow. A unified, for both SI-LSM and DI-LSM, mathematical and numerical formulations are presented. Order of accuracy is demonstrated in-between first-order and second-order; similar to that reported earlier for the various CmFD methods. Finally, validation and relative-performance study are presented for four test cases: static droplet, dam break, drop coalescence, and Rayleigh-Taylor instability. For the static droplet, the relative-performance of the present SI-LSM as compared to the DI-LSM is found similar to that in the literature for SI-VOF (Volume of Fluid) method as compared to DI-VOF method. For the various test cases, superior performance is demonstrated for the SI-LSM as compared to DI-LSM. This paper presents a broader perspective to the MIM for a single-versus-two fluid-flow and diffuse-versus-sharp approaches; and a novel GFM-based SI-LSM on a co-located grid.

Numerical investigation of shock-induced bubble collapse dynamics and fluid–solid interactions during shock-wave lithotripsy

In this paper we investigate the bubble collapse dynamics under shock-induced loading near soft and rigid bio-materials, during shock wave lithotripsy. A novel numerical framework was developed, that employs a Diffuse Interface Method (DIM) accounting for the interaction across fluid–solid-gas interfaces. For the resolution of the extended variety of length scales, due to the dynamic and fine interfacial structures, an Adaptive Mesh Refinement (AMR) framework for unstructured grids was incorporated. This multi-material multi-scale approach aims to reduce the numerical diffusion and preserve sharp interfaces. The presented numerical framework is validated for cases of bubble dynamics, under high and low ambient pressure ratios, shock-induced collapses, and wave transmission problems across a fluid–solid interface, against theoretical and numerical results. Three different configurations of shock-induced collapse applications near a kidney stone and soft tissue have been simulated for different stand-off distances and bubble attachment configurations. The obtained results reveal the detailed collapse dynamics, jet formation, solid deformation, rebound, primary and secondary shock wave emissions, and secondary collapse that govern the near-solid collapse and penetration mechanisms. Significant correlations of the problem configuration to the overall collapse mechanisms were found, stemming from the contact angle/attachment of the bubble and from the properties of solid material. In general, bubbles with their center closer to the kidney stone surface produce more violent collapses. For the soft tissue, the bubble movement prior to the collapse is of great importance as new structures can emerge which can trap the liquid jet into induced crevices. Finally, the tissue penetration is examined for these cases and a novel tension-driven tissue injury mechanism is elucidated, emanating from the complex interaction of the bubble/tissue interaction during the secondary collapse phase of an entrapped bubble in an induced crevice with the liquid jet.

A compact sixth-order implicit immersed interface method to solve 2D Poisson equations with discontinuities

This paper proposes a compact sixth-order accurate numerical method to solve Poisson equations with discontinuities across an interface. This scheme is based on two techniques for the second-order derivative approximation: a high-order implicit finite difference (HIFD) formula to increase the precision and an immersed interface method (IIM) to deal with the discontinuities. The HIFD formulation arises from Taylor series expansion, and the new formulas are simple modifications to the standard finite difference schemes. On the other hand, the IIM allows one to solve the differential equation using a fixed Cartesian grid by adding some correction terms only at grid points near the immersed interface. The two-dimensional equation is then solved by a nine-point compact sixth-order scheme named HIFD-IIM. Fourth- and second-order methods result in particular cases of the proposed method. Furthermore, the sixth-order method requires similar computational resources to a fourth-order formulation because the resulting matrices in both discretizations are the same. However, higher-order methods require the knowledge of more jump conditions at the interface. From the theoretical derivation of the proposed method, we expect fully six-order accuracy in the maximum norm. This order has been confirmed from our numerical experiments using nontrivial analytical solutions.