Movement Of Front Research Articles

Soaking in CO2 huff-n-puff: A single-nanopore scale study

CO2 Huff-n-Puff is a promising method for enhancing the oil recovery from unconventional reservoirs and sequestering CO2. Optimizing the operation of Huff-n-Puff requires a fundamental understanding of the thermodynamic and transport phenomena of CO2 and oil in nanopores. Here, we investigate the soaking step of CO2 Huff-n-Puff in a single, 4 nm-wide calcite pore using molecular dynamics simulations. We show that the CO2 molecules entering the pore can become adsorbed on pore walls and diffuse along with walls or are transported into the pore's interior as free CO2 molecules. Decane molecules are displaced from the pore walls and out of the bulk zone in the pore. Before reaching the pore's end, the movement of the density fronts of adsorbed and free CO2 molecules inside the pore obeys a t1/2 scaling law with effective diffusion coefficients ∼50% smaller than that of bulk CO2. Except at the very beginning period of soaking, the accumulation of adsorbed and free CO2 molecules occurs at a similar rate and follows the diffusive scaling law. These pore-scale results highlight the importance of surface adsorption in the storage and transport of CO2 during the soaking process in unconventional oil reservoirs.

Lower extremity energy absorption strategies at different phases during single and double-leg landings with knee valgus in pubertal female athletes

Dynamic knee valgus (DKV) malalignment affects the biomechanical characteristic during sports activities. This cross-sectional study was conducted to evaluate mechanical energy absorption (MEA) strategies at initial contact (IC) and total landing (TL) phases during single-leg landing (SLL), and double-leg landing (DLL). Twenty-eight female athletes with DKV (age 10–14) were invited. MEA analysis of lower extremity joints was done in sagittal and frontal motion planes employing 8 Vicon motion capture cameras and 2 Kistler force plates. Statistical analysis was done using IBM Statistics (version24) by Bivariate Pearson Correlation Coefficient test. Knee extensors MEA during SLL (IC: P = 0.008, R = 0.522/TL: P < 0.001, R = 0.642) and DLL (IC: P < 0.001, R = 0.611/TL: P = 0.011, R = 0.525), and knee abductors during SLL (IC: P = 0.021, R = 0.474) were positively correlated with increased DKV angle. Ankle plantar flexors during SLL (TL: P = 0.017, R = − 0.477) and DLL (TL: P = 0.028, R = − 0.404), and hip extensors during SLL (TL: P = 0.006, R = − 0.5120) were negatively correlated with increased DKV angle. Compensated MEA in knee extensors was correlated with less ankle plantar flexion MEA during SLL (IC: P = 0.027, R = − 0.514/TL: P = 0.007, R = − 0.637) and DLL (IC: P = 0.033, R = − 00.412/TL: P = 0.025, R = − 0.485). These outcomes indicated a knee-reliant MEA strategy in female athletes with DKV during puberty, putting them at higher risks of ACL injuries during landing.

Closed‐form analysis of undetected range errors due to ionospheric impacts for GBAS category I operations

Ionospheric anomalies may cause large differential range errors in Ground-Based Augmentation System (GBAS) users. To mitigate those integrity threats, worst-case ionosphere-induced position errors for potentially usable satellite geometries must be bounded by the GBAS ground facility. This mitigation method requires us to compute the worst-case range error for each satellite affected by a hypothetical ionospheric front. This paper presents a simulation-based method for deriving a closed-form expression of undetected ionosphere-induced range errors. Two types of ionospheric impact scenarios are defined in terms of the motion of an ionospheric front. Explicit expressions for outputs of the code-carrier smoothing filter and the code-carrier divergence monitor are derived to reduce the computational load of ionospheric impact simulations. An exhaustive search algorithm is applied to generate the worst undetected range error among all possible ionospheric impact conditions. Finally, a closed-form expression that bounds the maximum ionospheric range errors is determined as a linear function of the magnitude of gradient and the relative speed of the ionospheric front.

New insights into the dissociation of mixed CH4/CO2 hydrates for CH4 production and CO2 storage

Recent but limited studies have shown that multistep slow depressurization based on mixed CH4/CO2 hydrate dissociation can enhance CH4 recovery and increases CO2 storage after CO2 injection into CH4 hydrate [1,2]. For the first time, the resistivity variation and gas recovery and storage variation was investigated to study the change in hydrate saturation and production/storage yield. Lab-scale CH4 and CO2 rich mixed hydrates were synthesized to mimic the production and injection well scenario. The mixed hydrates were synthesized in sandstone with moderate to high water saturation using two different CH4/CO2 gas mixtures. Furthermore, mixed CH4/CO2 hydrates were dissociated three to six steps based on cyclic depressurization. Pressure, resistivity and gas chromatography data were collected. The presence of two thermodynamic stability zones provided an opportunity for additional CH4 recovery and CO2 storage during mixed hydrate dissociation. Gas and water migration between the injection and production well caused CO2 hydrate reformation, improvement in CO2 sweep area and movement of the CO2 hydrate front toward the production well. Multiple peaks in CH4 recovery and CO2 storage suggest major dissociation and reformation. Peak values were independent of mixed hydrate type. Peaks values of CH4 rich hydrates occurred at high pressure than peak values of CO2 rich hydrates. The slight change in resistance during depressurization below pure CH4 hydrate stability pressure confirms the loss of CH4 hydrate mass recovered by the formation of CO2 hydrate mass. This study discusses the correlation between the change in resistivity and type of guest molecule and its concentration and initial water saturation. The results of this study will be useful to explore the application of slow depressurization for the dissociation of CH4/CO2 mixed hydrates to improve CH4 recovery and CO2 storage.

Cellulase as an “active” excipient in prolonged-release HPMC matrices: A novel strategy towards zero-order release kinetics

Hydrophilic matrices are of utmost interest for oral prolonged release of drugs. However, they show decreasing release rate over time, mainly due to lengthening of the diffusional pathway across the gel formed upon glass-rubber transition of the polymer. Therefore, achievement of zero-order release kinetics, which could reflect in constant drug plasma levels, is still an open issue. With the aim of improving the release performance of hydroxypropyl methylcellulose (HPMC) systems, the use of cellulolytic enzymes was proposed to aid erosion of the swollen matrix, thereby counteracting the release rate decrease particularly toward the end of the process. The effectiveness of this strategy was evaluated by studying the mass loss and drug tracer release from tableted matrices consisting of high-viscosity HPMC (Methocel® K4M), Acetaminophen and increasing amounts (0.5–10% on HPMC) of a cellulolytic product (Sternzym® C13030). A faster erosion and progressive shift to linearity of the overall release profiles were observed as a function of the enzyme concentration. Release was markedly linear from matrices containing 5 and 10% Sternzym® C13030. In partially coated matrices with these cellulase concentrations, such results were in agreement with data of erosion and swelling front movement, which exhibited early and long-lasting synchronization.

Experimental Analysis of NiTi Alloy during Strain-Controlled Low-Cycle Fatigue.

The interaction between the stress-induced martensitic transformation and resistivity behavior of superelastic NiTi shape memory alloy (SMA) was studied. Strain-controlled low-cycle fatigue up to 6% was monitored by in situ electrical resistivity measurements. The experimental results show that a great motion of martensite fronts results in a significant accumulation of defects, as evidenced by transmission electron microscopy (TEM), before and after the tensile cycles. This gives rise to an overall increase of the resistivity values up to the maximum deformation. Therefore, the research suggests that shape memory alloy wire has great potential as a stress sensor inside bulk materials.

On the Propagation of Reaction Fronts in a Sandy Aquifer Over 20+ Years: Lessons From a Test Site in Northwestern Germany

AbstractDespite reduction measures, nitrate and aluminum concentrations remain high in aquifers in northwestern Europe. To evaluate the effectiveness of groundwater protection policies, the long‐term fate of these contaminants in groundwater needs to be understood. The groundwater catchment of the Haren water works, NW Germany, was characterized hydrogeochemically in the late 1990s, which provides an opportunity to study the solute fronts over a two‐decade period and conduct a post‐audit of the predicted front movement. Results indicate that, despite a significant reduction of the atmospheric acid loads, the acidification of soil and groundwater at the forest site persists. Removal of sorbed aluminum is required to induce a noticeable improvement, which will take at least several decades. The unexpected appearance of nitrate at the site, caused by a land use change in 1998, highlights the need for long‐term monitoring. Core data at the agricultural site show that the denitrification front has moved very little between 1998 and 2017, in accordance with previous forecasts. Denitrification by‐products, mainly sulfate and nitrogen, have migrated from the upper into the lower aquifer. A reactive transport model demonstrated how the link between the regional groundwater flow, pyrite oxidation, and the temporal variability of the nitrate concentration in recharge water, as reconstructed from age tracers, result in the observed vertical distribution of sulfate and nitrogen. This study demonstrates how long‐term monitoring, aided by model‐based data interpretation, can be used to successfully study and predict the fate of contaminants in groundwater.

Liquid crystal thermography based study on melting dynamics and the effect of mushy zone constant in numerical modeling of melting of a phase change material

Melt front tracking is vital in a solid–liquid phase change process to understand the melting process and quantify the system’s liquid faction, sensible and latent energies. This study presents a method to track the solid–liquid interface during the melting of a phase change material using liquid crystal thermography. The melt front movement is captured simultaneously through temperature influenced color variation in Thermochromic Liquid Crystal (TLC) sheet and direct visualization. Experiments have been performed for the cases of (i) heating from the bottom and (ii) heating from the top. Further, three-dimensional numerical simulations have been performed to validate the mushy zone temperatures and understand the effect of the mushy zone constant in the mushy zone temperature and liquid fraction. The results show that the TLC easily captures the dynamic motion of the solid–liquid interface during melting. From numerical simulations, it is found that the mushy zone constant affects the numerical prediction of melting in the bottom heating case with the low and high mushy zone constants, respectively, over predicting and under predicting the mushy zone temperatures during melting. Additionally, in this case, it is seen that the Rayleigh–Benard convection creates a wavy interface and accelerates the melting rate of the PCM. In the case of heating from the top, the numerical prediction of melting is independent of the mushy zone constant. Besides, a flat interface is observed in this case due to the absence of convection in the PCM during melting. Additionally, in the case of heating from the top, the combination of the PCM’s low thermal conductivity and heat diffusion through conduction leads to the self insulation effect of the PCM during melting. The convection-driven melting of PCM maintains the heater temperature lower by up to 35%, reduces the melting thermal resistance up to 78%, and increases the average volumetric melting to 92% over the case of melting without convection in the PCM.

Directional movement of consumer fronts associated with creek heads in salt marshes.

Consumers often deplete local resources and aggregate along edges of remaining resources, forming "consumer fronts." We examined the factors that promote Sesarma reticulatum crab aggregations at saltmarsh creek heads to explain the directional but slow movement of these fronts. We also created artificial creek heads to test the hypothesis that hydrological conditions at creek heads create superior habitat for crabs. Soil temperatures were ˜11-12% cooler, hydrogen sulfide concentrations lower (0.0 vs. ˜0.58mg/L), and dissolved oxygen concentrations twofold higher at the creek head versus the marsh platform. In the artificial creek-head experiment, altering hydrological conditions led to lower dissolved sulfide levels, higher dissolved oxygen levels, and increased densities of crab burrows and Sesarma crabs. Moreover, the elevation of the soil surface declined rapidly at artificial creek heads versus controls, suggesting that crabs were increasing erosion. Our results suggest that abiotic conditions for crabs are better at the leading edge of the creek head than the trailing edge, explaining the directional movement of the front. Moreover, the speed at which the front propagates appears to be limited by the rate at which the creekhead erodes, rather than by crab mobility. The directional and slow movement of Sesarma fronts compared to consumer fronts of other invertebrates appears to result from the inextricable link between Sesarma and marsh geomorphology, whereas other consumer fronts are associated mostly with food resources.

Methodology for the nonlinear coupled multi‐physics simulation of mineral dissolution

AbstractThis article presents a numerical methodology for the simulation of mineral dissolution which couples brine flow, dissolved mineral transport, and cavity evolution. The proposed model considers both (1) the varying density brine flow within the cavity governed by the compressible Navier‐Stokes equations and (2) the evolution of the cavity boundary using a sharp interface model with a physically‐derived dissolution rate equation. The proposed nonlinear multi‐physics model can capture complex flow patterns such as the generation of a vortex in the cavity. The impact of those complex flow patterns on the cavity development can be studied because of the coupling of brine flow and dissolution front movement. The model employs a new strategy to explicitly track the dissolution front, which results in low computational cost for long‐term dissolution simulations. The proposed model is verified through a convergence analysis, showing both spatial and temporal convergence. Numerical simulations of mineral dissolution in horizontal cavities are conducted to investigate the flow velocity, mass fraction of dissolved mineral, cavity shape evolution, and dissolution rate over time. Additionally, a discussion on the effect of Peclet number on mineral dissolution in the cavity is undertaken.

Prediction of solute concentration gradients during growth of discontinuous precipitates in a Fe-13.5 at.% Zn alloy

The influence of Zn-concentration gradient on the occurrence of discontinuous precipitation has been analyzed in a Fe-13.5 at.% Zn alloy using the simulation method and Cahn′s diffusion model. The results have shown that the reaction front (RF) movement takes place by go- and -stop fashion accompanied by appropriate changes of Cahn′s parameter reaching maximum values, Cmax at the end of go- period. Then, the value of C decreases enabling relaxation of the RF and beginning of the next go- event. In this way, the simulation is the only one source of data showing how the solute concentration across the α phase lamella changes during the stop- period of the growth of discontinuous precipitates.The smaller thickness of the α phase lamellae and larger Cmax, the longer whole go- and –stop cycle, but not exceeding few seconds. The distance of RF movement is characterized by certain optimum value which is close to v = 45 nm/s regardless of the value of α phase lamella thickness.

A comprehensive investigation of the influence of clay minerals on oxidized and pyrolyzed cokes in in situ combustion for heavy oil reservoirs

Coke is the most important intermediate product during an in situ combustion for maintaining the combustion front stability. Coke is classified as oxidized and pyrolyzed based on the reaction mechanism. The clay minerals exhibit a catalytic effect on the formation and reaction of coke. In this study, a comprehensive experiment was performed to investigate the influence of four clay minerals on oxidized and pyrolyzed cokes. Results showed that these clay minerals exhibited a catalytic effect on the generation and reaction of coke at different levels. In the oxidation process montmorillonite and kaolinite exhibited an excellent catalytic effect on the generation of oxidized coke. In the pyrolysis process, montmorillonite, kaolinite, and illite could promote the breakage of C–S, C–N, and C–O bonds and reduce the number of heteroatoms. In the reaction process, the catalytic effect of montmorillonite induced the aggravation of the polymerization of hydrocarbon derivative with a large molecular weight, resulting in a low activity of the oxidized coke. Moreover, the montmorillonite can induce coke reaction in a low-temperature range, whereas the others exert only suppression effects on coke decomposition. The pyrolyzed coke achieves lower activation energy than the oxidized coke, proving that the pyrolyzed coke can be easily ignited under the reservoir condition. All clay minerals investigated herein can promote the reaction of pyrolyzed coke to different degrees. The montmorillonite achieves the lowest activation energy at 35 °C–100 °C and 350 °C–600°C stages, which benefits the movement of the combustion front.

Asymmetrical superelastic behavior of thermomechanically processed semi-equiatomic NiTi alloy in tensile and compressive modes of deformation

In the present work two different cold working and annealing schemes were utilized, and the asymmetric superelastic response of thermomechanically processed materials were then assessed through cyclic tensile and compressive modes of deformation. The values of transformation stress, transformation strain, and pseudoelastic strain were measured for each treated and solutionized specimens and the asymmetric response was compared. In the solution annealed state, the difference of these parameters at different deformation modes was negligible due to the weak texture of the material, while for thermomechanically treated ones, development of specific deformation and recrystallization texture components was identified to be one of the underlying reasons of intensified asymmetry. The evolved substructure during the thermomechanical processing also played a substantial role in determining the asymmetric response. The presence of fine grains and dense dislocation substructure could hinder the movement of the transformation front, thus limiting the range of transformation. In tensile mode, the transformation stress was lower, but higher transformation strain was achieved, which was discussed relying on the slip activity in specified oriented grains. The lower transformation strain in compression mode led to lower pseudoelastic strain due to the narrow transformation range which finally degraded superelastic response of the material.

Numerical study of the mechanisms of enhanced oil recovery using nanosuspensions

The results of the numerical study of oil recovery enhancement using nanosuspension are presented. The research was carried out using the volume of fluid method (VOF) for a 2D microporous core model. Experimentally measured values of interfacial tension (IFT) and the contact angle (CA) were used for numerical modeling. An aqueous suspension with silicon oxide nanoparticles (5 nm) is used. It was shown that when 1 wt% of nanoparticles are added to the displacing liquid, its density increases by about 1%, the viscosity increases by 10%, the IFT decreases by 10%, and the contact angle increases from 70 to 145 $$^\circ $$ . The results of numerical study showed that the injection of nanoparticles has a significant effect on the displacement front movement in the microporous model. It has been shown that the nanosuspension can increase the oil recovery factor (ORF) almost twice as compared to water. To clarify the mechanisms of increasing the oil recovery during the reservoir flooding with nanofluid, a systematic study of factors affecting the displacement process efficiency was carried out. Viscosity, interfacial tension and the wetting angle of the displacing fluid were considered as such factors. As a result of systematic research, it has been shown that the main factor affecting the increase in the oil recovery flooding of nanosuspensions is a variation of wettability.

The Intra-Tidal Characteristics of Tidal Front and Their Spring–Neap Tidal and Seasonal Variations in Bungo Channel, Japan

The intra-tidal variations of a tidal front in Bungo Channel, Japan and their dependence on the spring–neap tidal cycle and month were analyzed utilizing high-resolution (~2 km) hourly sea surface temperature (SST) data obtained from a Himawari-8 geostationary satellite from April 2016 to August 2020. A gradient-based front detection method was utilized to define the position and intensity of the front. Similar to previous ship-based studies, SST data were utilized to identify tidal fronts between a well-mixed strait and its surrounding stratified area. The hourly SST data confirmed the theoretical intra-tidal movement of the tidal front, which is mainly controlled by tidal current advection. Notably, the intensity of the front increases during the ebb current phase, which carries the front toward the stratified area, but decreases during the flood current phase that drives the front in the opposite direction. Due to a strong dependence on tidal currents, the intra-tidal variations appear in a fortnight cycle, and the fortnightly variations of the front are dependent on the month in which the background stratification and residual current changes occur. Additionally, tidal current convergence and divergence are posited to cause tidal front intensification and weakening.

Modeling a Large Coastal Upwelling Event in Lake Superior

AbstractAn extraordinary strong wind‐driven upwelling event occurred in Lake Superior in summer of 2010 when the lake was strongly stratified. In this paper, a detailed three‐dimensional (3‐D) investigation of the current and thermal structures during the upwelling event was conducted using in situ observations, remote sensing products, and the results of a long‐term numerical simulation. A 3‐D finite‐volume coupled ice–ocean model tailored for the Laurentian Great Lakes was employed for this purpose. The model was validated with temperature observations at National Oceanic and Atmospheric Administration buoys and mooring data from 2010. The upwelling event observed in satellite imagery and at a mooring station was reproduced by the model, showing a cooling of as much as 10°C in August 2010 along the northwestern coast. The relationship between the alongshore wind and the offshore thermocline displacement (upwelling front) derived in theoretical work (Csanady, 1977, https://doi.org/10.1029/JC082i003p00397) was used to calculate upwelling front movement offshore and found to be in in close agreement with model prediction. A significant correlation between alongshore wind stress and lake temperature change in the upwelling zone was found with a correlation coefficient of −0.87. A simple linear heat balance model explained most of variability in temperature.

Insights into the kinetic processes of solute migration by unidirectional freezing in porous media with micromodel visualization at the pore-scale

Field investigations have proved that frozen soil does not act as a completely impermeable barrier for contaminants in cold regions. However, the subsurface behaviors of solutes in freezing and frozen porous media are still unclear. To unveil their nature, the pore-scale behavior of potassium permanganate in saturated porous media subjected to the unidirectional freezing was investigated using micromodel visualizations. An optical microscope was applied to obtain the pore-scale kinetics of solute redistribution in a two-dimensional micromodel using a calibration curve between the color intensity and concentration. We found that (1) the solute migration was not only limited to the ice-water interface but also occurred in the freezing area; (2) the redistribution of solutes had a significant hysteresis effect relative to the freezing front movement during the freezing of the porous media. By combining these results with the theory of sea ice, we suggested that the formation and re-motion of solute-rich inclusions in the mushy layer appear to be vital processes responsible for these phenomena. It was believed that the major mechanism for the re-motion of liquid inclusions was brine diffusion and expulsion in this experiment. The results of this study provide a better understanding of the physics of contaminant migration and their complex kinetics at the pore scale, which has important implications for the assessment and remediation of contaminated soils in seasonal frozen soils and permafrost.

Characteristics of inverted saturated zone under unclogged streams

Unclogged streams are widespread in nature and can generate dynamic inverted saturated zones (ISZ) underneath the streams above the regional water tables. This study is devoted to investigating the evolutional process of such an ISZ and its frontal movement. It defines a uniform saturation zone by moving the boundary of saturation flow from the inverted water table (IWT) to the end of the capillary saturation zone. Consequently, the conventional concept of specific yield, infiltration rate and governing equation at the ISZ frontal surface (IFS) must be revisited. Two new ISZ models are developed and quantified with great details with infiltration rate being constant and variable. The equations of hydraulic head profile development and the IFS are obtained. This study indicates that classical free surface equations, locating at IWT, is not self-consistent. The water balance requirement is not satisfied at IFS in the Green and Ampt (1911) model or the Polubarinova-Kochina (1962) model, causing physically unrealistic spatial variables. The increase of the IFS with time exhibits three different modes depending on the infiltration rate and the saturated hydraulic conductivity. The maximum depth of an IFS (corresponding to a depth with infiltration rate being stable) is linearly correlated with stream stage and air-entry head. The streambed infiltration flux decreases with time and appears to exhibit three modes similar to the IFS evolution. The findings of this study reconstruct the theoretical basis of the dynamic evolution process of stream-aquifer system and can help for better understanding of physical connotation of free surface equations and basic characteristics of ISZ evolution.

Propagation of one-dimensional planar and nonplanar shock waves in nonideal radiating gas

The present study seeks to investigate a quasilinear hyperbolic system of partial differential equations which describes the unsteady one-dimensional motion of a shock wave of arbitrary strength propagating through a nonideal radiating gas. We have derived an infinite hierarchy of the transport equation which is based on the kinematics of one-dimensional motion of shock front. By using the truncation approximation method, an infinite hierarchy of transport equations, which governs the shock strength and the induced discontinuities behind it, is derived to study the kinematics of the shock front. The first three transport equations (i.e., first, second, and third-orders) are used to study the growth and decay behavior of shocks in van der Waals radiating gas. The decay laws for weak shock waves in nonradiating gas are entirely recovered in the second-order truncation approximation. The results obtained by the first three approximations for shock waves of arbitrary strength are compared with the results predicted by the characteristic rule. Also, the effect of nonideal parameters and radiation on the evolutionary behavior of shock waves are discussed and depicted pictorially.

Изменение торка фронтальных зубов с оценкой толщины костной ткани на конусно-лучевом компьютерном томографе

Changing the vestibulo-oral inclination (torque) of the frontal teeth is an important component of orthodontic treatment. Cone-beam computed tomography is recommended as an accurate diagnostic tool allowing the orthodontist to estimate the safety of frontal tooth movement and inclination. This tool is helpful in measuring bone thickness at different levels of the tooth root and estimating incisal inclination and position. The aim of our study was to analyze bone thickness in patients with pathologically and normally inclined teeth using CT images and to create a universal table that will provide useful information about the thickness of the bone around different segment of the root required for a safe change in tooth inclination. Using the proposed table, the orthodontist can assess the feasibility of the planned tooth movement in the setting of changed tooth inclination, with due account of critical bone deficit regions. This will ensure the safety of tooth movement, stable retention and a positive treatment outcome.