Location Of Interface Research Articles

Interface retaining coarsening of multiphase flows

Multiphase flows are characterized by sharp moving interfaces, separating different fluids or phases. In many cases, the dynamics of the interface determines the behavior of the flow. In a coarse, or reduced order model, it may, therefore, be important to retain a sharp interface for the resolved scales. Here, a process to coarsen or filter fully resolved numerical solutions for incompressible multiphase flows while retaining a sharp interface is examined. The different phases are identified by an index function that takes different values in each phase and is coarsened by solving a constant coefficient diffusion equation, while tracking the interface contour. Small flow scales of one phase, left behind when the interface is moved, are embedded in the other phase by solving another diffusion equation with a modified diffusion coefficient that is zero at the interface location to prevent diffusion across the interface, plus a pressure-like equation to enforce incompressibility of the coarse velocity field. Examples of different levels of coarsening are shown. A simulation of a coarse model, where small scales are treated as a homogeneous mixture, results in a solution that is similar to the filtered fully resolved field for the early time Rayleigh–Taylor instability.

A grid based ADI method for the problem of two phase solidification

This paper proposes a transformation based, unconditionally stable, Alternating Direction Implicit (ADI) scheme for solving two-phase Stefan problems of solidification in arbitrary bounded domains. The governing equations of each phase are transformed, from a complex physical domain to a fixed rectangular domain, using body-fitted coordinates. ADI method is used to solve the transformed equations of each phase separately. The unconditional stability of the proposed ADI scheme is discussed numerically using von-Neumann method. Several numerical experiments are carried out for the case of stable solidification to verify the applicability of the proposed method. An excellent agreement has been found between the numerically generated values and the exact/existing solutions. Further, the developed scheme has also been tested on the problems of unstable solidification with mild surface tension and kinetic mobility. Once again the interface location with time has been computed very accurately.

Numerical Simulation of the Streamwise Transport of a Delta Wing Leading-Edge Vortex

Longitudinal vortices are a common flow phenomenon in the flow around aircraft. They emerge wherever sharp edges are encountered and affect the stability of the boundary layers with which they interact. Hence, for an optimal aircraft design, it is necessary to accurately predict not only the formation of these vortices, but also their downstream evolution. This paper presents a numerical simulation approach for the formation and downstream transport of longitudinal vortices. The approach consists in a hybrid Reynolds-averaged Navier–Stokes/large eddy simulation (RANS/LES) method with synthetic turbulence forcing for which different RANS/LES interface locations are investigated. To provide a quantitative analysis, an isolated sharp-edged delta wing configuration is adopted that allows to get rid of unwanted uncertainties. The presented RANS/LES approach is validated against particle image velocimetry data and compared with a wall-modeled LES and to a differential Reynolds stress model simulation. The results show that the RANS simulation is able to accurately predict the formation of the bulk vortical structure. However, its downstream transport can be accurately predicted only by a scale-resolving simulation. The hybrid RANS/LES approach allows to achieve this while saving computational resources by modeling the roll-up of the vortex. Nevertheless, its predictive accuracy highly depends on the appropriate placement of the RANS/LES interface.

Revealing the degree and impact of inhomogeneous electrolyte distributions on silver based gas diffusion electrodes

Silver based oxygen depolarized cathodes (ODC) are a promising technology to reduce the specific electrical energy demand of chlor-alkali electrolysis by around 30 %. Here we present the first modeling approach of an ODC for evaluating the influence of inhomogeneities on electrochemical performance and electrode dynamics. The focus is laid on the electrolyte distribution in the electrode because it is crucial for the gas-electrolyte interface and thus electrode performance and dynamics. To model the inhomogeneities, several one-dimensional three-phase models with different flooding degree of the electrode are coupled in parallel. The model is validated against polarization curves and electrochemical impedance spectra for ODC with silver content of 92, 97, 98 and 99 wt-% Ag. The electrochemical impedance spectroscopy measurements show flattened semicircles in the Nyquist plot with one apparent fast time constant, which ranges from 0.0015s to 0.03s depending on the respective ODC composition. The fast time constants result from electrochemical reaction and double layer; no time constant for a mass transport was identified. According to the simulations, the distorted form of the semi-circles is caused by local distribution of the liquid electrolyte within the ODC. It is revealed that there are strong gradients in local performance inside the electrode. Domains with a low intrusion of liquid electrolyte seem to be electrochemically highly active whereas flooded domains are almost inactive. The comparison of ODC with varying silver/polytetrafluoroethylene ratio suggests that the size and location of the gas-liquid interface, rather than the wetted catalyst surface area, is the key to achieving high ODC performance. We reveal that the electrochemical impedance spectroscopy is sensitive to the electrolyte distribution, while polarization curves do not contain sufficient information about the location and distribution of the electrolyte.

The Fat-glandular Interface and Breast Tumor Locations: Appearances on Ultrasound Tomography Are Supported by Quantitative Peritumoral Analyses.

To analyze the preferred tissue locations of common breast masses in relation to anatomic quadrants and the fat-glandular interface (FGI) using ultrasound tomography (UST). Ultrasound tomography scanning was performed in 206 consecutive women with 298 mammographically and/or sonographically visible, benign and malignant breast masses following written informed consent to participate in an 8-site multicenter, Institutional Review Board-approved cohort study. Mass locations were categorized by their anatomic breast quadrant and the FGI, which was defined by UST as the high-contrast circumferential junction of fat and fibroglandular tissue on coronal sound speed imaging. Quantitative UST mass comparisons were done for each tumor and peritumoral region using mean sound speed and percentage of fibroglandular tissue. Chi-squared and analysis of variance tests were used to assess differences. Cancers were noted at the FGI in 95% (74/78) compared to 51% (98/194) of fibroadenomas and cysts combined (P < 0.001). No intra-quadrant differences between cancer and benign masses were noted for tumor location by anatomic quadrants (P = 0.66). Quantitative peritumoral sound speed properties showed that cancers were surrounded by lower mean sound speeds (1477 m/s) and percent fibroglandular tissue (47%), compared to fibroadenomas (1496 m/s; 65.3%) and cysts (1518 m/s; 84%) (P < 0.001; P < 0.001, respectively). Breast cancers form adjacent to fat and UST localized the vast majority to the FGI, while cysts were most often completely surrounded by dense tissue. These observations were supported by quantitative peritumoral analyses of sound speed values for fat and fibroglandular tissue.

Solving three-dimensional interface problems with immersed finite elements: A-priori error analysis

Immersed finite element methods are designed to solve interface problems on interface-unfitted meshes. However, most of the study, especially analysis, is mainly limited to the two-dimension case. In this paper, we provide an a priori analysis for the trilinear immersed finite element method to solve three-dimensional elliptic interface problems on Cartesian grids consisting of cuboids. We establish the trace and inverse inequalities for trilinear IFE functions for interface elements with arbitrary interface-cutting configuration. Optimal a priori error estimates are rigorously proved in both energy and L2 norms, with the constant in the error bound independent of the interface location and its dependence on coefficient contrast explicitly specified. Numerical examples are provided not only to verify our theoretical results but also to demonstrate the applicability of this IFE method in tackling some real-world 3D interface models.

Syngas production by methane-rich combustion in a divergent burner of porous media

The superadiabatic combustion in porous media contributes to the efficient conversion of methane to syngas. In this paper, a divergent packed bed burner of two-layer was proposed to obtain the characteristics of methane partial oxidation. The divergent angle, interface location and pellet diameter were used to study the temperature and species distributions. Results indicate that the upper limit of velocity gradually decreased as the equivalence ratio increased and the limit of the divergent burner is obviously higher than that of the cylindrical one. The increasing of the divergent angle within a certain range enhances the methane conversion and the 15° shows the best among the selected five angles. The mole fractions of H2 and CO gradually decrease when the interface locations move from the cylindrical region to the divergent one. As the equivalence ratio increased from 1.3 to 3.5, the yields of H2 and CO and the energy conversion efficiency of syngas increase first and then decrease, and the maximum efficiency of 45.9% appears at the equivalence ratio of 2.0. The divergent region weakens the influence of inlet velocities and contributes to the stability of reforming reactions.

Evaluation of Design Provisions for Horizontal Shear Strength in Composite Precast Concrete Beams with Different Interface Conditions

In a precast concrete (PC) composite beam, the horizontal interface between the PC beam and the cast-in-place (CIP) slab is located either on the compression side or on the tensile side of the cross-section. If the CIP slab is on the compression side, it becomes C-type interface, and if it is on the tensile side, it becomes T-type interface. Tensile cracks in the CIP slab may cause the horizontal shear strength of composite beams to decrease because of the reduced anchorage performance of shear reinforcements as well as the sliding on the interface. Such a tendency can be found from previous test results of specimens having T-type interface. In this study, the results of the push-off test and the beam flexure test were collected and analyzed to evaluate effects on the horizontal shear strength depending on the interface conditions, such as the interface location, surface roughness, concrete compressive strength, and clamping stress by shear connectors. The horizontal shear strength equations of ACI, PCI, AASHTO LRFD, and MC 2010 were evaluated with a database composed of 84 push-off tests and 95 beam tests from previous studies. According to the evaluation, evaluation results show that the design codes predict the horizontal shear strength conservatively for conditions other than the interface location. The horizontal shear strength deviated largely depending on the interface locations. The design codes conservatively estimate the horizontal shear strength for C-type interface, but the horizontal shear strength of T-type interface is overestimated. Based on current studies, it is recommended to use a friction coefficient of 0.7 as MC 2010 when calculating the horizontal shear strength of a composite beam with roughened T-type interface.

A new linearly unstable mode in the core-annular flow of two immiscible fluids

Abstract

Deformation mechanism and mechanical behavior of tunnel within contact zone: a case study

During the construction of a tunnel passing through a contact zone stratum, the supporting structure is at risk of large deformation, cracking, and collapse, which affects the safety of tunnel construction. Based on the Jiayuan Tunnel project, this study used field monitoring data and numerical simulation to conduct a case study on the support mechanism and deformation of the supporting structure of a tunnel passing through the contact zone stratum. The results obtained for four monitoring sections reveal that the supporting structure under the contact zone stratum receives more surrounding rock pressure compared with the general stratum. In this case, the stress and deformation of the supporting structure are larger. Moreover, the deformation and mechanical behavior were uneven at different parts of the supporting structure. Using the numerical software FLAC3D, the deformation mechanism and mechanical behavior of the supporting structure were analyzed and are related to the surrounding rock parameters and interface location. Combined with the feature of the supporting structure in the contact zone stratum, the supporting structure should be strengthened to avoid stress concentration, while the steel arch foot should receive more attention when the interface coincides with the step surface.

On the internal transition layer to some inhomogeneous semilinear problems: Interface location

We are concerned with the location of the internal transition layer for some classes of solutions to an inhomogeneous one-dimensional elliptic problem with Neumann boundary conditions. We generalize and extend some known results with a variational method based on the Young's inequality and the co-area formula. As an application, we establish the location of the internal transition layer to the problem posed on some symmetric Riemannian manifolds.

A nonlinear geometric model for pre-stressed steel–concrete composite beams

Steel–concrete composite beams are commonly employed in civil constructions such as multi-storey building floors and long-span bridges. In case of significant span to depth ratios, excessive deflections and noticeable crack widths at the concrete slab may occur at the serviceability stage. In this context, internal or external pre-stressed tendons can be used as a remediation. In the latter case, significant effects of geometric non-linearity may arise due to the strain incompatibility between the external tendon and the composite member, resulting in a variable tendon eccentricity during deformation. In this paper, second-order effects are evaluated in eight pre-stressed steel–concrete composite beams for which experimental results are available. Hence, a three-dimensional finite element model using a Lagrangian description is proposed. The external tendons are represented by one-dimensional catenary elements, whereas the reinforced concrete slab and steel profile are modeled by shells finite elements. Slipping at the slab-beam interface and tendon-deviator locations are also included in the analysis. For the studied externally pre-stressed beams, the introduction of nonlinear geometric behavior yields lower collapses loads in relation to its linear counterpart, varying this difference between 6.4 and 9.1%.

Nonlinear rotordynamics of a MDOF rotor–stator contact system subjected to frictional and gravitational effects

Rotating machines are intrinsically susceptible to expensive and high-risk faults such as rotor–stator rub. During a rub event normal and tangential forces are generated by the contact and friction that cause wear at the contacting interfaces. In the present work, such forces are computed by assuming linear elastic contact and Coulomb friction at multiple interface locations. A finite element shaft-line model of a horizontally mounted rotor is used to demonstrate the approach and the model is reduced for computational efficiency. The modal assurance criterion is used to identify the linear modes that contribute to a given solution. It is observed that bouncing solutions exist with rotor–stator contact in complex machines that can be viewed as internal resonances involving a small number of modes. The responses can become complex because different modes can combine to give the internal resonance (and hence a larger range of frequency ratios) and because of asymmetries, such as gravity. One design goal is to avoid any contact in the system and the analysis in this paper identifies the conditions for internal resonance that should be avoided in a real machine. The complicated dynamics shown here reveal some of the distinct features of contacting solutions and could also be used in condition monitoring to characterise faults.

Water seepage detection using resistivity method around a pumped storage power station in China

To detect water seepage and ensure the safety of Pumped Storage Power Station (PSPS) facilities, we apply the electrical resistivity method to evaluate the leakage when the water level is on the rise. We check whether there is a leakage channel near the cavern group of the underground powerhouse. We conduct the field survey and integrate the results with regional geological data to determine the distribution of faults and large cracks. Granite intrusions generate a variation of high and low resistance phases, representing granite porphyry and tuff, respectively. The interface between the two lithologies is the location of the fault zone. In general, the apparent resistivity of two does not change much, indicating that the rock masses are relatively stable. The internal fractures of the rock masses are not developed, and there is no visible water content. However, from the location of the lithological contact interface, the rock mass is broken. Therefore, we recommend that before constructing the lower reservoir, anti-seepage treatment should be carried out.

Fire Plume in a Sharply Stratified Ambient Fluid

The present work analyses theoretically and numerically fire plumes evolving in a two-layer stratified environment. The ambient fluid consists of a lower cold (heavy) layer and an upper warm (light) layer with a sharp interface. The fire plume is controlled by the fire heat release rate Q. Depending on the density interface location, the temperatures of the layers and on the fire source conditions, the fire plume can rise indefinitely or can be captured by the density stratification. To determine a criterion between these two situations, a theoretical model is proposed. With this model, it is found that the trapping/escaping criterion of the fire plume is determined in terms of a stratification parameter \(\varLambda > 0.88\). This stratification parameter \(\varLambda\) is a function of the fire heat release, the density interface location and the ambient stratification. The model also allows the plume height to be determined analytically. The comparison with the numerical data shows an excellent agreement. Finally, for practical purposes, we propose a simplified correlation to estimate the height of the trapped plume as a function of the interface height, the temperatures of the layers and the fire heat release rate.

Numerical study on melting of phase change material in an enclosure subject to Neumann boundary condition in the presence of Rayleigh-Bénard convection

This research study investigated the melting process of a phase change material (PCM), heated from the bottom, under Neumann boundary conditions, in the presence of Rayleigh-Bénard convection. The problem was numerically simulated for a range of domain sizes (1×1−8×8cm2) and heat fluxes (0.5−2W/cm2) using the enthalpy porosity technique, which is mostly applicable in cooling heat exchangers of electronic devices. Scaling analysis and the numerical results were employed to find the relationship between the Nusselt number and the solid-liquid interface location with other dimensionless parameters and develop correlations to predict the Nusselt number and the solid-liquid interface location for this type of melting problem. The results of this research could be used to better understand the heat transfer regimes formed during melting in an enclosure heated from the bottom and predict the Nusselt number and the solid-liquid interface location. It was found that the temperature and Nusselt number fluctuations are initiated in the coarsening subregime when the Rayleigh number was not larger than 106 and thus may not occur for small-sized domains. It can be concluded the coarsening and turbulent subregimes may not occur in small enclosures, while the melting process mostly occurs during turbulent subregiem in large enclosures. The numerical results revealed the fastest advance of heat transfer rate and consequently, solid-liquid interface occur during the formation of Bénard cells when the Rayleigh number was on the order of 104. The Nusselt number and solid-liquid interface location correlations developed in this study were later validated using two new cases of numerical data. The results revealed that these correlations could accurately predict the Nusselt number and solid-liquid interface location.

Automated interface detection in liquid-liquid systems using self-calibrating ultrasonic sensor

Detection of liquid-liquid interface is critical in solvent extraction equipment/contactors typically used in petroleum and hydrometallurgical industries. An instrumentation system, comprising of a self-calibrating ultrasonic sensor and a novel signal processing algorithm is reported. It can be used to estimate location of liquid-liquid interface along with speed of sound in both the liquids without any manual/user intervention. The algorithm involves use of discrete wavelet transform and matched filter. The system has been tested at laboratory scale under wide range of industrially relevant conditions. The system works for any pair of liquid without apriori knowledge of their acoustic characteristics, is insensitive to changes in temperature and/or compositions. It also works for dirty interfaces contaminated with particulate matter or emulsion. The above mentioned features truly impart the sensor system “deploy-and-forget” capabilities. The range, accuracy and resolution of the system, with respect to interface location, are 40–200 mm, 0.45% FS (Full-scale) and less than 1 mm, respectively.

Plastic forming processes of transverse non-homogeneous composite metallic sheets

Abstract In this work an analysis of the radial stress and velocity fields is performed according to the J 2 flow theory for a rigid/perfectly plastic material. The flow field is used to simulate the forming processes of sheets. The significant achievement of this paper is the generalization of the work by Nadai &amp; Hill for homogenous material in the sense of its yield stress, to a material with general transverse non-homogeneity. In Addition, a special un-coupled form of the system of equations is obtained where the task of solving it reduces to the solution of a single non-linear algebraic differential equation for the shear stress. A semi-analytical solution is attained solving numerically this equation and the rest of the stresses term together with the velocity field is calculated analytically. As a case study a tri-layered symmetrical sheet is chosen for two configurations: soft inner core and hard coating, hard inner core and soft coating. The main practical outcome of this work is the derivation of the validity limit for radial solution by mapping the “state space” that encompasses all possible configurations of the forming process. This configuration mapping defines the “safe” range of configurations parameters in which flawless processes can be achieved. Several aspects are researched: the ratio of material's properties of two adjacent layers, the location of layers interface and friction coefficient with the walls of the dies.

Estimation Technique for a Contact Point Between two Materials in a Stationary Heat Transfer Problem

An inverse problem for a stationary heat transfer process is studied for a totally isolated bar on its lateral surface, of negligible diameter, made up of two consecutive sections of different, isotropic and homogeneous materials. At the left boundary, a Dirichlet type condition is imposed that represents a constant temperature source while a Robin type condition that models the heat dissipation by convection is considered at the right one. Many articles in the literature focus on thermal and stress analysis at the interface but no one is dedicated to the estimation of the contact point location between the two materials. In this work, it is assumed that the interface position is unknown. A technique to determine it from a unique noisy flow measurement at the right boundary is introduced. Necessary and sufficient conditions are derived in order to obtain the estimation of the interface point from a heat flux measured at the right boundary. Numerical solutions are obtained together with an expression for the estimation error. Moreover, an elasticity analysis is included to study the influence of data errors. The results show that our approach is useful for determining the location of the materials interface.

Withdrawal: Automated interface detection in liquid‐liquid systems using self‐calibrating ultrasonic sensor, Debmalya Mukherjee, Nirvik Sen, K. K. Singh, Shilpi Saha, K.T. Shenoy, and P. P. Marathe

Abstract Detection of liquid-liquid interface is critical in solvent extraction equipment/contactors typically used in petroleum and hydrometallurgical industries. An instrumentation system, comprising of a self-calibrating ultrasonic sensor and a novel signal processing algorithm is reported. It can be used to estimate location of liquid-liquid interface along with speed of sound in both the liquids without any manual/user intervention. The algorithm involves use of discrete wavelet transform and matched filter. The system has been tested at laboratory scale under wide range of industrially relevant conditions. The system works for any pair of liquid without apriori knowledge of their acoustic characteristics, is insensitive to changes in temperature and/or compositions. It also works for dirty interfaces contaminated with particulate matter or emulsion. The above mentioned features truly impart the sensor system “deploy-and-forget” capabilities. The range, accuracy and resolution of the system, with respect to interface location, are 40–200 mm, 0.45% FS (Full-scale) and less than 1 mm, respectively.