Interface Displacement Research Articles

Effect of Pre-applied Annulus Back Pressure Cementing on Radial Stress of Interfaces in Double Layer Casing System

Pre-applied annular back pressure cementing successfully increases the sealing ability of cement sheath and reduce the annulus pressure buildup problems. In order to accurately understand the mechanical mechanism of its function, the process of cementing operation is considered. In addition, elastic mechanics and the continuous condition of interfacial displacement is used to establish a model for calculating the the radial stress on casing-cement interfaces and the mechanism of pre-applied annular back pressure cementing method improving the sealing ability of cement sheath double casing well is studied. The accuracy of the theoretical model established in this paper is verified by experimental results. The results show that the higher applied annular back pressure during cementing work can significantly increase the radial compressive stress on the interfaces and the sealing ability of cement sheath will be improved. The radial stress on interfaces increase linearly with the increase of applied annular pressure. The sealing ability of inner casing-cement sheath interface is greater improved by pre-applied annulus back pressure cementing than the cement-outer casing interface. The higher elastic modulus of cement sheath cause larger radial stress on interface. The results show that the pre-applied annular back pressure cementing can significantly increase the stress on the interfaces and the established model in this paper provides quantitative calculation method for the radial stress of the interface. The research in this paper is useful for the design and operation of annular pressure cementing technology in oil and gas wells.

The proper orthogonal decomposition: A powerful tool for studying drop oscillations.

Liquid metal drops are released onto different wettable solid substrates. Their post-impact oscillations are recorded at 1000 images/s as soon as the triple line is at rest. The proper orthogonal decomposition (POD) is used to get and identify the frequencies involved. The POD is a technique widely used in the fluid dynamics community to study turbulent flows, but it is not used to determine droplet-free oscillation frequencies. The vertical and horizontal vibration frequencies of the sessile drop center of mass are successfully extracted from the images by POD. The first POD mode captures the vertical displacement frequency, and the second or third POD mode captures the horizontal displacement frequency of the drop center of mass. The spatial structure of the modes is the characteristic of the vertical and horizontal movement. Therefore, the POD can be used instead of the interface displacement tracking to determine the free oscillation frequencies of liquid metal drops and, more generally, of any vibrating sessile drops. As it is a standardized method, it can be used with confidence for routine measurements, especially for sensors.

Perturbative solution of a propagating interface in the phase field model

When a stable ordered phase and a metastable disordered phase are separated by a flat interface, the metastable state changes to the stable state through the propagation of the interface. For cases in which latent heat is generated, the interface displacement during some time interval is proportional to the square root of the time interval when the extent of supercooling is less than a certain value. We demonstrate this behavior by deriving a perturbative solution for a propagating interface in the phase field model. We calculate the leading-order contribution explicitly, and find that the interface temperature deviates from the equilibrium transition temperature in proportion to the interface velocity.

A Hybrid Microstructure Piezoresistive Sensor with Machine Learning Approach for Gesture Recognition

Developments in flexible electronics have adopted various approaches which have enhanced the applicability of human–machine interface fields. Recently, microstructural integration and hybrid functional materials were designed for realizing human somatosensory. Nonetheless, designing tactile sensors with smart structures using facile and low-cost fabrication processes remains challenging. Furthermore, using the sensors for recognizing stimuli and feedback applications remains poorly validated. In this study, a highly flexible piezoresistive tactile sensor was developed by homogeneously dispersing carbon black (CB) in a microstructure porous sugar/PDMS-based sponge. Owning to its high flexibility and softness, the sensor can be mounted on human or robotic systems for different clinical applications. We validated the applicability of the proposed sensor by applying it to recognizing grasp and release forces in an open setting and to classifying hand motions that surgeons apply on the master interface of a robotic system during intravascular catheterization. For this purpose, we implemented the long short-term memory (LSTM)-dense classification model and five traditional machine learning methods, namely, support vector machine, multilayer perceptron, decision tree, and k-nearest neighbor. The models were used to classify the different hand gestures obtained in an open-setting experiment. Amongst all, the LSTM-dense method yielded the highest overall recognition accuracy (87.38%). Nevertheless, the performance of the other models was in a similar range, showing that our sensor structure can be applied in intelligence sensing or tactile feedback systems. Secondly, the sensor prototype was applied to analyze the motions made while manipulating an interventional robot. We analyzed the displacement and velocity of the master interface during typical axial (push/pull) and radial operations with the robot. The results obtained show that the sensor is capable of recording unique patterns during different operations. Thus, a combination of the flexible wearable sensors and machine learning could yield a future generation of flexible materials and artificial intelligence of things (AIoT) devices.

Monitoring of steel corrosion and cracking in cement paste exposed to combined sulfate–chloride attack with X-ray microtomography

The degradation process of reinforced cement paste exposed to cyclic wetting and drying with a designated salt solution was monitored through X-ray microtomography (μCT). Three exposure conditions (a 3 wt% NaCl solution, a 5 wt% Na2SO4 solution, or a mixed solution of 3 wt% NaCl and 5 wt% Na2SO4) were studied to investigate the potential synergistic effects between chloride and sulfate ions on the deterioration of reinforced cement-based materials. The time-dependent evolution of steel corrosion and cracking of cement paste cover were tracked and visualized, while the volumes of steel loss, corrosion products and cracks were quantified by image analysis. The results indicated that the presence of sulfate ions significantly delayed the initiation of chloride-induced corrosion, but did not seem to greatly affect the corrosion rate once the corrosion occurred. The existence of chloride ions, in turn, also mitigated the damage of cement paste cause by sulfate attack as evidenced by the reduced volumes of cracks. The conventional volume expansion coefficient of corrosion products can be measured by μCT, but this coefficient may not be applicable for modelling the corrosion-induced cracking process when sulfate ions were present. The use of μCT provides a new angle to directly measure the interfacial displacement in reinforced cement paste, which can be used as a valuable input for modelling non-uniform chloride-induced corrosion in the presence of sulfate ions.

Parametric responses of carbon-epoxy composite with delamination using cohesive gap element

This paper focuses on the various parametric responses of the delaminated carbon-epoxy composite beam using a gap element. The analysis is based on the cohesive zone modelling approach, and it is implemented using the finite element software ANSYS APDL. In the study, a zero-thickness cohesive gap element that varies the cohesive stresses with the interfacial opening displacement along the localized fracture process zone is used. The available published results of the double cantilever beam test are used to validate the results obtained from the current analysis. The effects of fracture length, number of layers, angle of plies and thickness on delamination of a composite cantilever beam with edge pull is considered in this paper. The results show that the separation between the composite plies is proportional to the stiffness of the cohesive element, and an increase in the number of layers depicts a transition from anisotropy to orthotropy. Under mode I delamination, composite plies with 450 fibre angles exhibits increased torsional stiffness and global resistance. Also, a comparison between thin and thick laminates demonstrate that a laminate of 5 mm thick dissipates about 85% more energy than a composite laminate of 50 mm thick.

Analysis of Vertical Load Transfer Mechanism of Assembled Lattice Diaphragm Wall in Collapsible Loess Area

Based on analysis of the formation mechanism and characteristics of the negative friction in collapsible loess areas, this study investigates the load transfer law of a wall-soil system under a vertical load, establishes the vertical bearing model of a lattice diaphragm wall, and analyzes the vertical bearing capacity of an assembled latticed diaphragm wall (ALDW) in a loess area. The factors influencing the vertical bearing characteristics of the ALDW in a loess area are analyzed. The vertical bearing mechanism of the lattice diaphragm wall in the loess area is investigated. The failure modes of the ALDW in the loess area are mainly shear failure of the soil around the wall and failure of the wall-soil interface. In the generation and development of negative friction, there is always a point where the relative displacement of the wall-soil interface is zero at a certain depth below the ground; at this point, the wall and soil are relative to each other. The collapsibility of loess, settlement of the wall and surrounding soil, and rate and method of immersion are the factors affecting the lattice diaphragm wall. The conclusions of this study provide a reference for the design and construction of ALDWs in loess areas.

Free-surface effects induced by internal solitons forced by shearing currents

Free-surface effects induced by internal solitary waves (ISWs) propagating through a background shear current are theoretically investigated in a shallow water framework. Following the Hamiltonian approach, we implement a mathematical formulation valid for a free surface, two-layer stratified system in the presence of mobile layers. Associated to the undisturbed condition characterized by the background fluid at rest, solitons with both positive and negative polarities are considered. To reproduce the typical oceanic conditions, we focus on theoretical predictions for a density ratio set to 0.99. Although under Boussinesq conditions a rigid-lid at the top of the theoretical domain is considered a good approximation, our analysis shows that main ISWs features may change when the fluid system, forced by shear currents, is modeled with a free surface. Signs assumed by three dimensionless quantities, i.e., the deformation parameter, the background velocity, and the undisturbed amplitude, allowed us to uniquely predict how the undisturbed solitons modify their interfacial profiles and change their celerity, in response to the background forcing. Our results show that waves celerity predicted by the rigid-lid model can be lower than the one resulting from the Hamiltonian formulation, although this never occurs in the absence of mobile layers. Theoretical predictions reveal that shearing current can induce deviations from the standard ISWs free-surface profile. We discuss the role of nonhydrostatic pressures in inducing free-surface short disturbances, in the form of undulated or multihumped profiles. The typical phase-opposition between interfacial and surface displacements can be lost as the free-surface displacements assume multihumped configurations.

Giant ferroelectric modulation of barrier height and width in multiferroic tunnel junctions

The high tunneling electroresistance (TER) effect, generally caused by ferroelectric (FE)-modulated barrier height or width, is essential for the applications of multiferroic tunnel junctions in data storage. It is traditionally obtained by distinct electrical screening lengths of electrodes. Interface engineering can enhance the TER effect further. In this work, taking $\mathrm{Co}\text{\ensuremath{-}}{({\mathrm{TiO}}_{2}\text{\ensuremath{-}}\mathrm{BaO})}_{N}\text{\ensuremath{-}}\mathrm{Co}$ tunnel junctions as examples, we demonstrate a distinct principle than the screening lengths for designing extraordinary TER effect. We reveal that when the interfacial FE displacement is much larger than that of the FE bulk, it will bend the barrier band near the interface violently, and the interfacial polarization direction pointing to or away from the interface determines whether the energy band rises or falls. The large interfacial Ba-O displacement and its corresponding polarization direction in $\mathrm{Co}\text{\ensuremath{-}}{\mathrm{BaTiO}}_{3}\text{\ensuremath{-}}\mathrm{Co}$ tunnel junctions can be significantly modulated by the direction of FE polarization, resulting in a metallic-insulating transition of the entire thin ${\mathrm{BaTiO}}_{3}$ barrier. For thick ${\mathrm{BaTiO}}_{3}$ barrier ($N=25$, $\ensuremath{\sim}10$ nm), the effective tunnel barrier width shifts between about 2 nm and 6.5 nm as the polarization of ${\mathrm{BaTiO}}_{3}$ switches direction, which can dramatically modulate the tunneling efficiency. This effect shed light on a novel route for enhancing TER through the interface engineering.

A novel smoothed particle hydrodynamics and finite element coupling scheme for fluid–structure interaction: The sliding boundary particle approach

A novel numerical formulation for solving fluid–structure interaction (FSI) problems is proposed where the fluid field is spatially discretized using smoothed particle hydrodynamics (SPH) and the structural field using the finite element method (FEM). As compared to fully mesh- or grid-based FSI frameworks, due to the Lagrangian nature of SPH this framework can be easily extended to account for more complex fluids consisting of multiple phases and dynamic phase transitions. Moreover, this approach facilitates the handling of large deformations of the fluid domain respectively the fluid–structure interface without additional methodological and computational efforts. In particular, to achieve an accurate representation of interaction forces between fluid particles and structural elements also for strongly curved interface geometries, the novel sliding boundary particle approach is proposed to ensure full support of SPH particles close to the interface. The coupling of the fluid and the structural field is based on a Dirichlet–Neumann partitioned approach, where the fluid field is the Dirichlet partition with prescribed interface displacements and the structural field is the Neumann partition subject to interface forces. To overcome instabilities inherent to weakly coupled schemes an iterative fixed-point coupling scheme is employed. Several numerical examples in form of well-known benchmark tests are considered to validate the accuracy, stability, and robustness of the proposed formulation. Finally, the filling process of a highly flexible thin-walled balloon-like container is studied, representing a model problem close to potential application scenarios of the proposed scheme in the field of biomechanics.

Design and Calibration of a Hall Effect System for Measurement of Six-Degree-of-Freedom Motion within a Stacked Column.

This paper presents the design, development and evaluation of a unique non-contact instrumentation system that can accurately measure the interface displacement between two rigid components in six degrees of freedom. The system was developed to allow measurement of the relative displacements between interfaces within a stacked column of brick-like components, with an accuracy of 0.05 mm and 0.1 degrees. The columns comprised up to 14 components, with each component being a scale model of a graphite brick within an Advanced Gas-cooled Reactor core. A set of 585 of these columns makes up the Multi Layer Array, which was designed to investigate the response of the reactor core to seismic inputs, with excitation levels up to 1 g from 0 to 100 Hz. The nature of the application required a compact and robust design capable of accurately recording fully coupled motion in all six degrees of freedom during dynamic testing. The novel design implemented 12 Hall effect sensors with a calibration procedure based on system identification techniques. The measurement uncertainty was ±0.050 mm for displacement and ±0.052 degrees for rotation, and the system can tolerate loss of data from two sensors with the uncertainly increasing to only 0.061 mm in translation and 0.088 degrees in rotation. The system has been deployed in a research programme that has enabled EDF to present seismic safety cases to the Office for Nuclear Regulation, resulting in life extension approvals for several reactors. The measurement system developed could be readily applied to other situations where the imposed level of stress at the interface causes negligible material strain, and accurate non-contact six-degree-of-freedom interface measurement is required.

On-chip micro pressure sensor for microfluidic pressure monitoring

In this work, a novel on-chip micro pressure sensor was developed for microfluidic pressure monitoring. Polydimethylsiloxane (PDMS) microfluidic chip contained a working fluid channel with a sealed detection channel beneath it. Any change in pressure in the working fluid channel would change the volume of the detection channel. A mixture of two immiscible fluids was sealed in the detection channel. The pressure of the working fluid can be monitored by measuring the interface displacement of the two fluids in the detection channel. A PDMS film between the working channel and detection channel can avoid cross-contamination between fluids. We acquired a calibration curve of the pressure sensor for measurement and optimized the performance of the sensor through parametric studies. Moreover, two pressure sensors were integrated into a microchip to characterize the pressure drop in the microchannel. The developed pressure sensor is inexpensive and easy to be integrated into microfluidic devices to monitor the flow conditions for cell culture, fluid mixing, and droplet manipulation.

The interfacial load-transfer enhancement mechanism of amino-functionalised carbon nanotube reinforced epoxy matrix composites: A molecular dynamics study

This work provides a comprehensive and comparative study on the interfacial load transfer properties of amino-functionalised carbon nanotube (CNT)/epoxy composites via molecular dynamics simulations. Three models were constructed: (i) a pristine CNT embedded in epoxy resin, (ii) an amino-functionalised CNT embedded in epoxy resin without crosslinking interactions between amino groups and the epoxy resin matrix, and (iii) an amino-functionalised CNT embedded in epoxy resin with crosslinking interactions. The pull-out process was simulated using a steering molecular dynamics simulation to examine the sidewall load transfer effect of the CNTs. The travelling of amino groups along the CNTs was simulated by changing the topology of the functionalised CNT using a polymer consistent force field during the pull-out process. The mean interfacial shear stress, pull-out energy, stress, and atomic displacement were analysed. The results show that the interfacial shear strength as well as the compatibility and cooperativity between the CNTs and the matrix can be efficiently enhanced by introducing amino functional groups. In particular, a dramatic enhancement can be obtained by considering the crosslinking interactions. In addition, the interfacial load transfer between the end of the CNTs and the matrix was studied. The axial normal stress at the end of the CNTs was calculated by placing one diglycidyl ether bisphenol A molecule near the end of the CNT. The results show that there was a large interaction between the end of the CNTs and matrix, which cannot be neglected. Thus, the assumption of zero traction between the fibre end and matrix in the classical shear lag model should be modified at the nanoscale.

Pore-scale effects during the transition from capillary- to viscosity-dominated flow dynamics within microfluidic porous-like domains

We perform a numerical and experimental study of immiscible two-phase flows within predominantly 2D transparent PDMS microfluidic domains with disordered pillar-like obstacles, that effectively serve as artificial porous structures. Using a high sensitivity pressure sensor at the flow inlet, we capture experimentally the pressure dynamics under fixed flow rate conditions as the fluid–fluid interface advances within the porous domain, while also monitoring the corresponding phase distribution patterns using optical microscopy. Our experimental study covers 4 orders of magnitude with respect to the injection flow rate and highlights the characteristics of immiscible displacement processes during the transition from the capillarity-controlled interface displacement regime at lower flow rates, where the pores are invaded sequentially in the form of Haines jumps, to the viscosity-dominated regime, where multiple pores are invaded simultaneously. In the capillary regime, we recover a clear correlation between the recorded inlet pressure and the pore-throat diameter invaded by the interface that follows the Young–Laplace equation, while during the transition to the viscous regime such a correlation is no longer evident due to multiple pore-throats being invaded simultaneously (but also due to significant viscous pressure drop along the inlet and outlet channels, that effectively mask capillary effects). The performed experimental study serves for the validation of a robust Level-Set model capable of explicitly tracking interfacial dynamics at sub-pore scale resolutions under identical flow conditions. The numerical model is validated against both well-established theoretical flow models, that account for the effects of viscous and capillary forces on interfacial dynamics, and the experimental results obtained using the developed microfluidic setup over a wide range of capillary numbers. Our results show that the proposed numerical model recovers very well the experimentally observed flow dynamics in terms of phase distribution patterns and inlet pressures, but also the effects of viscous flow on the apparent (i.e. dynamic) contact angles in the vicinity of the pore walls. For the first time in the literature, this work clearly shows that the proposed numerical approach has an undoubtable strong potential to simulate multiphase flow in porous domains over a wide range of Capillary numbers.

A Biomechanical, Cadaveric Evaluation of Single- Versus Double-Row Repair Techniques on Stability of Bony Bankart Lesions

Background: Previous studies comparing stability between single- and double-row arthroscopic bony Bankart repair techniques focused only on the measurements of tensile forces on the bony fragment without re-creating a more physiologic testing environment. Purpose: To compare dynamic stability and displacement between single- and double-row arthroscopic repair techniques for acute bony Bankart lesions in a concavity-compression cadaveric model simulating physiologic conditions. Study Design: Controlled laboratory study. Methods: Testing was performed on 13 matched pairs of cadaveric glenoids with simulated bony Bankart fractures with a defect width of 25% of the inferior glenoid diameter. Half of the fractures were repaired with a double-row technique, and the contralateral glenoids were repaired with a single-row technique. To determine dynamic biomechanical stability and ultimate step-off of the repairs, a 150-N load and 2000 cycles of internal-external rotation at 1 Hz were applied to specimens to simulate early rehabilitation. Toggle was quantified throughout cycling with a coordinate measuring machine. Three-dimensional spatial measurements were calculated. After cyclic loading, the fracture displacement was measured. Results: The bony Bankart fragment–glenoid initial step-off was found to be significantly greater (P < .001) for the single-row technique (mean, 896 µm; SD, 282 µm) compared with the double-row technique (mean, 436 µm; SD, 313 µm). The motion toggle was found to be significantly greater (P = .017) for the single-row technique (mean, 994 µm; SD, 711 µm) compared with the double-row technique (mean, 408 µm; SD, 384 µm). The ultimate interface displacement was found to be significantly greater (P = .029) for the single-row technique (mean, 1265 µm; SD, 606 µm) compared with the double-row technique (mean, 795 µm; SD, 398 µm). Conclusion: Using a concavity-compression glenohumeral cadaveric model, we found that the double-row arthroscopic fixation technique for bony Bankart repair resulted in superior stability and decreased displacement during simulated rehabilitation when compared with the single-row repair technique. Clinical Relevance: The findings from this study may help guide surgical decision-making by demonstrating superior biomechanical properties (improved initial step-off, motion toggle, and interface displacement) of the double-row bony Bankart repair technique when compared with single-row fixation. The double-row repair construct demonstrated increased stability of the bony Bankart fragment, which may improve bony Bankart healing.

Experimental study of liquid-liquid interface oscillating in radial hele-shaw cell

The dynamics of the interface between two immiscible liquids with a high viscosity contrast is studied experimentally under steady displacement of interface and periodic variation of the flow rate of the pumped liquid in radial Hele-Shaw cell. Classic Saffman–Taylor instability, which develops when the viscous fluid is monotonously displaced by the inviscid one, is well known. In the present work, the excitation of Saffman–Taylor instability by means of oscillations of the liquid-liquid interface is demonstrated. The interphase boundary performs axisymmetric radial oscillations at small amplitude of oscillations and in the absence of an average pumping. With the growth of the amplitude of radial oscillations the interface instability is excited, which manifests itself in the development of an azimuthally periodic finger structure during a part of the period. “Finger-like” instability is determined by the relative amplitude of the oscillations of the interphase boundary and under the conditions of the performed experiments depends neither on the oscillation frequency nor on the radial size of the interface.

Effects of the soil water content and relative roughness on the shear strength of silt and steel plate interface

Using a self-developed large-scale direct shear apparatus, 72 series of tests on the interface of a silt-steel structure and 18 series of direct shear tests of silt were performed. The effects of the water content of soil, interface roughness and normal stress on the shear mechanical behavior of silt-steel structure interface were studied. The test results confirm that the water content obviously affects the hardening–softening behavior of the silt-structure interface. The curve of the shear stress with shear displacement of the silt-steel interface was similar to the trend of the direct shear test results of the silt. The shear strength of the rough interface (Rmax > 0 mm) was significantly greater than the results of the direct shear test of silt, and the shear strength of the smooth interface (Rmax = 0 mm) was less than the shear strength of the direct shear of silt. In the process of the interface shear test, the deformation of the soil body gradually increased with the decrease in soil water content and increase in interface roughness. The contribution of matric suction of unsaturated silt to the interface peak shear stress was more prominent and hardly affected the residual shear stress. The interface shear strength for unsaturated soil was modeled. The comparison between model results and experimental results shows that the calculation model can accurately predict the shear strength of the unsaturated silt-steel interface under different interface roughness conditions.

Nonlocal layerwise formulation for bending of multilayered/functionally graded nanobeams featuring weak bonding

The size-dependent bending of perfectly/imperfectly bonded multilayered/stepwise functionally graded nanobeams, e.g. multiwalled carbon nanotubes with weak van der Waals forces, with any arbitrary numbers of layers, exhibiting different material, geometrical, and length-scale properties, is studied through a layerwise formulation of the stress-driven nonlocal theory of elasticity and the Bernoulli-Euler beam theory. The formulation is also valid for the continuously graded nanobeams, where the through-the-thickness material gradation with any arbitrary distribution is approximated in a stepwise manner through many layers. The size-dependency of each layer is accounted for through nonlocal constitutive relationships, which define the strains at each point as the output of integral convolutions in terms of the stresses in all the points of the layer and a kernel. Linear elastic uncoupled interfacial laws are implemented to model the mechanical response of the interfaces. The size-dependent system of equilibrium equations governing the deformations of the layers are derived and subjected to the variationally consistent edge boundary conditions and the constitutive boundary conditions associated with the stress-driven integral convolution. The formulation is applied to multilayered and sandwich nanobeams and the effects of the interfacial imperfections on the displacement fields and the interfacial displacement jumps are studied. It is found that the interfacial imperfections have greater impact on the field variables of multilayered nanobeams than that of the multilayered beams with the large-scale dimensions.

Comparison of thermal and chemical enhanced recovery of DNAPL in saturated porous media: 2D tank pumping experiments and two-phase flow modelling

Pumping experiments were performed in a 2D tank in order to estimate the recovery yield of pure heavy chlorinated organic compounds (DNAPL; dense non-aqueous phase liquids) by varying different parameters: permeability of the saturated zone, pumping flow rates, addition of surfactant and heating. Surfactant was added to decrease capillary forces involved in the entrapment of DNAPL in porous media while temperature was increased to reduce DNAPL viscosity (and hence increase its mobility). Chemical enhancement was performed with the addition of Sodium Dodecyl Benzene Sulfonate (SDBS) (at its Critical Micelle Concentration, to avoid DNAPL dissolution) and thermal enhancement was performed at 50 °C (to avoid DNAPL volatilization). The experiments were monitored with photography allowing, on the basis of image interpretation, to convert optical densities (OD) into water saturations (Sw). Image interpretations were compared with modelling results. The two-phase flow modelling was performed with the pressure-pressure formulation using capillary pressure and relative permeability functions based on the van Genuchten–Mualem equations. Measured volumes of DNAPL recovered as well as the displacement of the DNAPL-water interface (radius and height of the cone of depression) are consistent with the modelling results. Furthermore, chemical enhancement results in a significant increase in the recovery rates of DNAPL. The observed improvement in the recovery of DNAPL with chemical enhancement is due to the fact that: (i) the residual saturation inside the cone of depression is lower and (ii) the cone of depression radius and height increase. Thermal enhancement had no beneficial effect on DNAPL recovery rate or yield. This study shows that it is possible to accurately determine water and DNAPL saturations by image interpretation during pumping tests in a 2D tank in the laboratory. For field-scale applications, the two-phase flow model allows to determine remediation yields as well as the volumes of the cone of depression according to the different operating conditions.

A fully coupled ALE interface tracking method for a pressure-based finite volume solver

Simulation of two-phase gas-liquid flows is a challenging problem in terms of predicting the interface position and appropriately coupling the phases. Stability restrictions induced by surface tension of the liquid phase may increase the level of difficulty of the simulation. The Arbitrary Lagrangian-Eulerian (ALE) method along with an interface tracking technique is an approach for a precise prediction of the interface position. The restrictions in the simulation due to surface tension necessitate an implicitly coupled solution algorithm. In this research, the interface kinematic condition equation is discretized in a new coupled form, including an interface displacement variable as well as the interface velocity components. Furthermore, an implicitly discretized formulation of interface curvature is implemented in the interface normal force balance to facilitate the complete coupling of the interface displacement movement to the hydrodynamic behaviour of the flow. Finally, the governing equations of both phases as well as complete set of interface equations are solved simultaneously in a system of linearized algebraic equations. A partially coupled interface tracking (PCIT) method and a fully coupled interface tracking method (FCIT) are developed and evaluated in predictions of a backward-facing step flow, of liquid falling films with and without interaction with a gas phase flow, of an oscillating drop, and of a rising bubble. The results show that in the viscocapillary regime, the FCIT method keeps its stability in a wide range of CFL numbers, whereas the PCIT method is stable only for CFL ≤1. When the surface tension is ignored in a backward-facing step flow, the PCIT method also remains stable for higher CFL number due to the coupled formulation of interface displacement and slope. The present results are in excellent agreement with previous numerical and experimental work results reported in the literature.