Shear Effects Research Articles

A guidance of solid element application in predicting the ultimate strength of flat plates in compression

With the increasing demand in ocean engineering field for the ultimate limit state (ULS) analysis of thick plates, the solid (3D) element has been more frequently used in the ULS analysis. Compared to 2D element, 3D element can better consider the transverse shearing effect during the analysis which usually occurs on thick plates, due to its reliable reflection of geometrical characteristics and kinematic equations of the structures. Besides, 3D element can also facilitate the introduction of influencing factors into the ULS analysis, such as the erosions, cracks and residual stress. This may improve the simulation precision of ULS analysis of thick plate models. Until now, there is a lack of 3D element modelling technique in the ULS analysis of flat/stiffened plates. The present study aims to provide helpful information on 3D elements in the ULS analysis of flat plates under axial compression load. A total of 350 plate scenarios were adopted in the parametric study to consider the effects of 3D element shape (αyz). It is found that the element shape significantly influences the ULS analysis of flat plates, where planar-like 3D element is not recommended. An empirical formula for determining the optimal 3D element shape of the finite element (FE) model is proposed based on the parametric results. A guidance for implementing the 3D elements is then documented, which may help engineers further understand the ultimate strength characteristic of very thick flat plates.

Theory of Stimulated Brillouin Scattering in Fibers for Highly Multimode Excitations

Stimulated Brillouin scattering (SBS) is often an unwanted loss mechanism in both active and passive fibers. Highly multimode excitation of fibers has been proposed as a novel route toward efficient SBS suppression. Here, we develop a detailed, quantitative theory which confirms this proposal and elucidates the physical mechanisms involved. Starting from the vector optical and scalar acoustic equations, we derive appropriate nonlinear coupled mode equations for the signal and Stokes modal amplitudes and an analytical formula for the SBS (Stokes) gain with applicable approximations, such as the neglect of shear effects. This allows us to calculate the exponential growth rate of the Stokes power as a function of the distribution of power in a highly multimode signal. The peak value of the gain spectrum across the excited modes determines the SBS threshold—the maximum SBS-limited power that can be sent through the fiber. The theory shows that the peak SBS gain is greatly reduced by highly multimode excitation due to gain broadening and relatively weaker intermodal SBS gain. The inclusion of exact vector optical modes in the calculation is crucial in order to capture the incomplete intermodal coupling due to mismatch of polarization patterns of higher-order modes. We demonstrate that equal excitation of the 160 modes of a commercially available, highly multimode circular step index fiber raises the SBS threshold by a factor of 6.5 and find comparable suppression of SBS in similar fibers with a D-shaped cross section. Published by the American Physical Society 2024

Adsorption Behavior of Different Components of a Polymer/Surfactant Composite Control System along an Injection-Production Channel in Sand Conglomerate Reservoirs.

Sandy conglomerate reservoirs have become an important replacement area for unconventional energy to increase reserves and production. The polymer/surfactant composite control flooding system can effectively alleviate the water flooding front breakthrough caused by the interlayer or plane heterogeneity of the sand conglomerate reservoir and is an effective production method to reduce the water cutoff of the well and increase the oil recovery. In the process of controlling the oil displacement process of the system, the chromatographic separation effect was found due to the different viscosities of each component and the adsorption difference between the components and the rock, which weakened the development effect of the reservoir. It is necessary to study the adsorption law of each component of the complex controlled displacement system along the injection-production channel in the sand conglomerate reservoir. In this study, the microstructure and mineral composition of sandy conglomerates were determined by scanning electron microscopy and X-ray diffraction tests. The main particle size distribution was counted through a rock particle sieving experiment. A new characterization method called the large-size core physical model was used. The composite control system of sulfonate and betaine was used as the surfactant component, and the adsorption degree of each component in the displacement process was analyzed. The experimental results showed that the mass fraction of the sandy conglomerate increased with the decrease in particle size. The particles with a size of less than 0.08 mm account for a relatively high proportion, with a mass fraction of 60%. The content of brittle minerals, such as quartz and feldspar, in the glutenite was relatively high, and micrometer-sized pores and fractures were developed. The main factors affecting the viscosity of the composite system were the concentration and molecular weight of the polymer. The increase of injection volume of the flooding system is conducive to the maintenance of ultralow interfacial tension migration to the deep core. In the displacement process, when the polymer molecular chain was cut to a certain extent, the effect of throat shear was also slowed due to the short molecular chain. However, the shortened polymer molecules were more easily adsorbed on the surface of rock particles and the adsorption rate increased. The adsorption capacity of each component gradually decreased with the increase of the injection volume and injection concentration. The relative content of the composite control system and crude oil affects the type of emulsion, which undergoes a corresponding transformation during the driving process from a water-in-oil emulsion to an oil-in-water one. The research results of this paper enrich the mechanism of enhancing oil recovery of sand conglomerate reservoirs by polymer-surfactant composite regulation technology.

Influence of feed entrance angle on transverse tearing burr formation in the milling of superalloy honeycomb with ice filling constraint

In the end milling of superalloy honeycomb cores, the contact form between the cutting tool and honeycomb wall and the force state of the honeycomb wall are variable, there will be difficulties in chip removal. The irregular extension of transverse tearing burrs can deteriorate the machining quality of honeycomb core surfaces, thereby adversely affecting the assembly and service performance of sandwich structures. Based on kinematic analysis, modeling of the removal and deflection process of honeycomb walls was conducted. The feed entrance angle in the case of machining thin walls with high feed speeds was characterized, and the force state of the honeycomb wall and the degree of shear or compression it bears were analyzed. Analytical models of damage scale and single-tooth cutting state were established under different feed entrance angles. The impact of feed entrance angle on the minimum burr length and the minimum constraint failure width was analyzed. The milling experiments of GH4099 superalloy honeycomb wall with ice filling constraint were designed and conducted to clarify the influence of different feed entrance angles on cutting force and transverse tearing burr length. The morphology of burrs and the wear form of the cutting tool were analyzed, and the formation mechanism of transverse tearing burr on the honeycomb sidewalls was revealed. The research results indicate that the feed force Fx is 2.1 to 4.7 times greater than the main force Fy or the back force Fz. When the feed entrance angle is <90°, transverse tearing burrs either do not occur, or occur crimped burrs that are gradually removed. Particularly within the range of 0° to 30°, the machining quality is better. The cutting force has a significant shearing effect on the honeycomb wall, making it susceptible to plastic deformation and reaching the fracture strain. The cutting edge can effectively remove material from the honeycomb wall, resulting in normal wear on the minor flank face and tip of the cutting tool. When the feed entrance angle is greater than 90°, it is easy to form large banded burrs, and the burr length is relatively similar to about 1500 μm. The cutting force has a significant extrusion effect on the honeycomb wall, resulting in minimal deflection deformation of the honeycomb wall, and making it difficult to fracture. The cutting tool fails to perform effective cutting, leading to increased friction between the cutting tool and honeycomb wall, which continuously induces irregular extension of the burrs. The research findings are of great significance for achieving damage control in metal honeycomb core machining and guiding process and clamping optimization.

Bio-inspired helicoidal hemp/basalt/polyurethane rubber bio-composites: Experimental, numerical and analytical ballistic impact study with residual velocity prediction using artificial neural network

Recent body armour trends emphasize mobility, flexibility, and cost reduction while maintaining ballistic effectiveness through the use of natural fiber composite. This study evaluates the ballistic impact performance of soft and hard armor using experimental, analytical, numerical, and machine learning methods. We developed a soft armor bio-composite using monolithic, hybrid, and helicoidal structured Hemp (H)/Basalt (B)/Polyurethane (PU) rubber and tested its V50 ballistic limit according to Millitary-Standred-662 F. For hard armour, a multi-layer armor system (MAS) consisting of Al2O3/SiC ceramic, intermediate soft armour bio-composites, and an Aluminum (Al)-5052 plate backing was tested with armour-piercing bullets as per National Institute of Justice (NIJ)-0101.06 standards (Level IV). Soft armor performance was evaluated using macro-homogeneous finite element (FE), the Ipson-Retch analytical, and an Artificial Neural Network (ANN) regression model. Results showed minimal discrepancies from experimental data, with differences of 13.33 %, 12.08 %, and 8.08 % in V50 ballistic limit. The mechanical and thermal behaviors of bio-composites were assessed using un-notched Charpy, FTIR, and TGA methods. Helicoidal laminates improved Charpy toughness by 9.44 %, 19.30 %, and 40.28 % compared to hybrid and monolithic ([H]15 and [H]10) laminates, and exhibited lower weight reduction at high degradation temperature of 395.76 ℃. Helicoidal laminates increased V50 ballistic performance by 155.80 %, 76.22 %, and 16.61 % compared to [H]10, [H]15, and hybrid laminates, respectively. Due to spiral load distribution reduces stress concentration and enhanced the damage resistance of the laminate. Stand-alone soft armor demonstrates crater formation and radial cracks (petaling) due to fiber wedging and the shearing effect of a bullet. In conclusion, MAS revels a maximum back face deformation (BFD) of 18.06 mm. Al2O3/Helicoidal/Al-plate MAS reduced weight and cost by 69.21 %, and 233.72 % compared to Kevlar™-based MAS, promoting sustainable, lightweight, economical designs. Due to its higher fracture toughness and lower density, SiC ceramic in MAS provides lower trauma and further reduced weight compared to Al2O3 ceramic.

Investigation into the shear effect of torsion extrusion process

Torsion extrusion (TE) is a severe plastic deformation (SPD) technique with the potential to be used for the preparation of large bulk materials with enhanced mechanical properties. Shear deformation is the key factor for SPD to enhance the materials properties. However, it is not clear by far that what shear strains are dominant in torsion extrusion process and how they distribute in the extruded materials. These issues are crucial to the working parameters design of the torsion extrusion process for maximizing the shear effect. To this end, a plasticine billet with two colors was applied as experimental material, and the material flow pattern was revealed by measuring the twisted bicolor interfaces. The torsion extrusion was implemented using a die with a wavy cross-sectional bearing segment (W-TE), which is able to prevent the circumferential sliding of the materials against the die. Flow velocities were re-built according to the bicolor interfaces at each section in a cylindrical system. Strain rates and shear strains induced by torsion deformation along the radius of the material were formulated based on the velocity field and Eulerian variable derivatives, from which the dominant shear strain can be recognized. A shear effect index (SEI) was proposed to evaluate the contribution of the shear strains induced by torsion, and the distribution of SEI was analyzed. Furthermore, the W-TE experiments on the as-cast TiB2/2026 Al composite were carried out to demonstrate the positive correlation between the shear effect and the microstructural improvement, and finite element simulation for such experiments showed the consistency of the simulated deformation patterns with the plasticine measured ones. The evaluation method and the experimental results deepened the understanding to the shear effect of torsion extrusion process.

Properties of polyphenylene sulfide/multiwalled carbon nanotubes composites: a comparison between compression molding and microinjection molding

Abstract This work comparatively studied the electrical, morphological, and thermal properties of polyphenylene sulfide/multiwalled carbon nanotubes (PPS/CNT) composites which were prepared by compression molding (CM) and microinjection molding (μIM), respectively. The subsequent samples were termed as CM composites and microparts, respectively. Results revealed that the electrical conductivity of PPS/CNT microparts was lower than that of CM PPS/CNT composites, which was ascribed to the difference in shearing influence that affected microstructural evolution in resultant moldings. In addition, SEM observations revealed that the distribution of CNTs became better in the PPS/CNT microparts, which was related to the prevailing higher shearing effect in μIM. The tensile strength of PPS/CNT microparts dropped for filler concentrations ≤2 wt% and it started to increase after that reached 10 wt%; in comparison with the PPS/CNT microparts, the tensile strength of CM PPS/CNT samples exhibited an opposite trend when the filler concentration was ≤3 wt%. After that, the tensile strength of CM samples showed a monotonic increase with increasing CNT concentrations. Both the uniform distribution of CNT and increase of crystallinity were crucial to improving the tensile strength of PPS/CNT moldings. This work showed that PPS/CNT moldings with good electrical conductivity and mechanical performance can be molded at relatively high filler concentrations, which is critical for applications in demanding engineering sectors.

Shear strengthening and damage control effects of CFRP and self-prestressing iron-based SMA for concrete columns

Although prestressed shape memory alloy (SMA) has shown a great performance in flexural retrofitting of slender RC columns, its shear strengthening effect for squat RC columns has been barely studied. This study explores the shear strengthening and damage control effects of iron-based SMA (Fe SMA) for squat RC columns. The heat-activated prestressing of Fe SMA was evaluated first at material level, then applied to component level structural testing of RC columns. The four circular RC columns with different retrofitting schemes were tested under quasi-static lateral cyclic loading. The specimens strengthened with carbon fiber-reinforced polymer (CFRP) sheet and Fe SMA strip exhibited satisfactory global responses without showing significant shear failure. From the visual inspection and non-destructive damage assessment, the prestressed Fe SMA was found to be superior in delaying damage accumulation in concrete compared to CFRP.

Nonlinear three-dimensional modeling for encapsulated microbubble dynamics subject to ultrasound

Encapsulated microbubbles (EMBs) stabilized by thin coatings have been used as contrast agents for ultrasound sonography as well as having been demonstrated as a promising new technology for targeted drug delivery. The dynamics of EMBs is three-dimensional (3D) because EMBs within micro-vessels inevitably interact with boundaries, but the theoretical and numerical studies are limited to spherical, weakly non-spherical, and/or axisymmetric EMBs. Here, we have developed physical, mathematical, and numerical models for nonlinear 3D EMB dynamics. The liquid flow is evaluated using the boundary integral method. The EMB coating is modeled as a thin viscoelastic shell including stretching, bending, and shear effects and simulated using the finite element method. These models are coupled through the kinematic and dynamic boundary conditions at the interface. The model is in good agreement with the Hoff equation for spherical EMBs and the asymptotic theory for weakly non-spherical deformation of EMBs. Using this model, a numerical study for EMB dynamics near a rigid boundary subject to an ultrasonic wave is performed. The migration, non-spherical oscillation, resonant oscillation, and jetting of EMBs are displayed and analyzed systematically. If the ultrasound wave is strong, a high-speed liquid jet forms at the final stage of the collapse, orientated between the directions of the wave and toward the wall. The EMB jet is weaker and slower and has less momentum, as the non-spherical deformation of the coating and the jetting are suppressed by the viscoelastic property of the coating. If the ultrasound is not strong, the EMB remains spherical for many cycles of oscillation but the EMB undergoes resonant oscillation and becomes significantly non-spherical after several oscillation cycles, when the wave frequency is equal to its natural frequency. The numerical capability has the potential to be developed for the optimization of sonography or drug delivery.

Unveiling the underlying physics of two-phase boiling heat transfer enhancement through shearing of coalescing bubbles

The upcoming energy scarcity problem has driven research toward developing energy-efficient two-phase heat exchangers essential for various cooling applications. This research is rooted in the principles of pool boiling, essential for effective heat transfer in various heat exchangers. A well-known reported problem in heat exchangers is the dry-out phenomena of heated surfaces due to bubble coalescence. To tackle this undesirable problem, an innovative technique has been introduced in this study, which involves the shearing of bubbles through liquid jet impingement over the heated surface. The study has been carried out in a two-dimensional domain numerically, in the wall superheat range of 9–16 K. To study the underlying physics involved in this pool boiling phenomenon, the bubble dynamics parameters such as departure frequency, bubble diameter, cold spot (bubble base) temperature, and vapor volume fraction have been analyzed. The results show that with the jet shearing effect, a maximum enhancement of 25% in heat transfer rate is observed at higher wall superheat. The investigation also highlights that the liquid jet enhances vapor volume fraction, indicating enhanced steam generation, particularly an enhancement of 27% observed at elevated wall superheat. An early onset necking effect is also observed with the shearing effect, which leads to the formation of smaller bubbles with higher departure frequencies. This study is a benchmark to the fundamental physics of enhancing two-phase heat transfer through bubble shearing, offering promising insights for energy conservation in two-phase heat exchanger design, particularly within the context of pool boiling.

Ice nucleation in supercooled water under shear

Classical nucleation theory (CNT) provides a good framework for understanding the nucleation phenomenon in metastable conditions. However, there is still no satisfactory understanding of the shear effect. Here, we propose an ice nucleation model considering the rebounded deformation energy to analyze the ice nucleation rate. It is concluded that: (1) The effect is more pronounced by changing the contact angle to regulate the free energy when both the supercooled degree and the shear rate are small. (2) The variation trend of the nucleation ratio Jhet,sh/Jhet,no increases at first but it may decrease when the contact angle is small, or keeps increasing when the contact angle is large. (3) The probability of the shear nucleation is about several ten orders of magnitude to that of static nucleation. (4) The key factor in the acceleration of the supercooled liquid nucleation is the released deformation energy after encountering the obstruction.

Causality Bounds on Dissipative General-Relativistic Magnetohydrodynamics.

We derive necessary and sufficient conditions under which a large class of relativistic generalizations of Braginskii's magnetohydrodynamics with shear, bulk, and heat diffusion effects is causal and strongly hyperbolic in the fully nonlinear regime in curved spacetime. We find that causality severely constrains the size of nonideal effects and the onset of kinetic instabilities. Our results are crucial for assessing the regime of validity of fluid dynamical simulations of plasmas near supermassive black holes.

Synergistic interplay of photobioreactor mixing and static mixer configuration on Rhodoseupdomonas palustris’s growth and biohydrogen production

Inducing light/dark (L/D) cycles through mixing or recirculating the media in a photobioreactor improves light utilization for biohydrogen production during photoferentation. However, the mutual shading effect is a key challenge for photofermentation using purple non-sulphur bacteria (PNSB). In this study, mixing was explored as a mitigating methodology through the investigation of three different static mixer configurations: concentric, spiral, and half-moon, across four laminar flowrates: 1.2 L/min, 0.71 L/min, 0.31 L/min and 0.15 L/min. At 0.15 L/min, the half-moon and spiral static mixers significantly improved specific and cumulative hydrogen production by 11.2-fold and 114 %, respectively. Also, recirculating the fluid via a peristaltic pump resulted in a significant shearing effect, impacting cell viability. Inducing L/D cycles via a static mixer was thus beneficial for hydrogen production over an increased flow rate. Additionally, biomass productivity increased by up to 70 %, reaching a cell dry weight of 7.0 g/L with the spiral static mixer configuration at 0.15 L/min flow rate. Interestingly, this study found that the static mixers only significantly increased specific hydrogen production and light conversion efficiency at the lowest flow rate of 0.15 L/min, beyond which they showed no significant improvement in biohydrogen production. This indicates that high L/D cycling frequencies are unnecessary to alleviate the mutual shading effect for R. palustris, which is advantageous for upscaling. These findings emphasise the potential of static mixers as an alternative to increase light conversion efficiency and industrial hydrogen production.

Enhanced evaporation and heat transfer of sessile droplets via coupling electric field and temperature field

Controllable evaporation of sessile droplets is essential in diverse applications, ranging from thermal management to chemical reactions and combustion. Despite considerable advances, further enhancement of droplet evaporation is still challenging. Here, an experimental system that couples uniform/non-uniform electric fields with temperature fields to enhance hydrophilic droplet evaporation is introduced. The electric field can generate Coulomb force by changing the redistribution of charges at the droplet interface, which enables highly flexible and precise control of the sessile droplet. By leveraging the uniform electric field, the droplet is stretched upwards, which increases the heat transfer thermal resistance and the vapor concentration near the droplet interface, leading to the deterioration of droplet evaporation. Whereas the application of a non-uniform electric field will flatten the droplets due to the shear effect of the corona wind on the droplet interface, and the reduction of the heat transfer thermal resistance of the droplets, as well as the vapor concentration near the interface, which promotes the droplet evaporation. The coupling of uniform electric and temperature fields could reverse the inhibition effect of droplet evaporation caused by a purely uniform electric field, and the maximum enhancement ratio reaches 5.11 times. The coupling of a non-uniform electric field and temperature field can enhance droplet evaporation up to 29.34 times. The corresponding numerical simulation study reveals the flow and temperature distribution inside the droplet. This research provides critical insights into the precise manipulation of droplet evaporation by applying an electric field.

Fuel transport mechanisms and power generation enhancement in air-breathing microfluidic fuel cells with discrete-hole anode

Current challenges in air-breathing microfluidic fuel cells (AMFCs) technology include insufficient fuel transfer and unsatisfactory power density. To address these issues, this study develops a three-dimensional computational model to optimize the performance of AMFC with a discrete-hole anode. This model reveals that the "petal-shaped" non-uniform fuel distribution is due to the shearing and dilution effects of the electrolyte. Additionally, discrete-hole structures such as size have a slight influence on fuel transport and current production, with performance deviations under 1.6%. Significant improvements are achieved by reducing the electrolyte flow rate and electrode length. Transitioning from a single cell with a long anode to a series/parallel stack of cells with short electrodes significantly boosts net power output and fuel utilization. Under optimal conditions, a maximum power density of 349.9 mW cm−3 and an output of 19.2 mW are obtained. This research provides valuable insights into fuel transport mechanisms and power enhancement strategies in the AMFCs, guiding the future design and optimization of microfluidic reactors for energy conversion.

Experimental and theoretical study on the shear behaviors of an innovative precast UHPC composite beams reinforced with inverted T-shaped steel

The innovative precast composite beam consisted of reinforced UHPC beam and inner inverted T-steel shape (forming ITSRU composite beam) is proposed for the marine structures serviced in harsh environment and subjected to complicated loading conditions. The novel composite beam possesses the advantages of lightweight, high strength and ductility, enhanced durability. To study the shear behaviors of ITSRU beams, a shear test program consisted of seven composite beams were conducted to study the effects of shear span-to-depth ratio, steel fiber volume fraction, stirrup ratio and inverted T-steel web thickness. UHPC used in this paper possess compressive strength more than 125 MPa, ultimate tensile strength more than 8.9 MPa and ultimate tensile strain more than 2256με. The inverted T-steel and steel rebar used in this paper have grades of Q355 and HRB400, respectively. A segmented loading control method was used in the shear test, in which a forced-controlled with a rate of 20 kN/min was used before the beam yield and the displacement control was implemented at a rate of 0.5 mm/min after reaching the yield load. The test results revealed that the ITSRU beams exhibited admirable deformation capacity and considerable residual shear capacity even for the composite beam with shear span-to-depth ratio of 1.0. The increasing of stirrup ratio, steel fiber volume fraction and inverted T-steel web thickness could improve the shear resistance and the ductility as well as suppress the appearance of the diagonal shear critical cracks. Based on the test results, an analytical shear model considering the contributions of UHPC in shear compression region, stirrups, steel fibers and inverted steel web was developed to predicted the shear resistance of ITSRU beams. The interaction mechanism of the different components in the ITSRU beams was considered in the analytical shear model. The accuracy of the developed calculation method was verified by the test results.

Application and Optimization of Rheological Mathematical Models in Preparation and Injection Process of Polymer Flooding

The impact of shear on the properties of polymer solutions is not fully accounted for in the simulation of conventional rheological models. To optimize the application of these mathematical models, the shear rheological characteristics of polyacrylamide at various concentrations were investigated under different shear rates and shear modes. The results indicate that pseudoplastic fluid polymers exhibit two distinct rheological characteristics within their "shear thinning" rate range. The critical shear rate at this threshold signifies the point at which shear stress begins to disrupt the structure of the polymer solution, resulting in a rheological curve that transitions from high to low shear rates without reverting back to a low-to-high state. The concentration of the solution has minimal effect on the critical shear rate of the polymer, which is primarily determined by the inherent properties of the polymer itself. The application of rheological models during preparation and injection processes can elucidate the effects of shear on polymers by analyzing changes in apparent viscosity. Furthermore, the rheological model following supercritical shear rates requires modifications to the consistency coefficient (K) and flow index (n) based on shear rheological data obtained from high to low shear rates.

Experimental study on in-situ emulsification of heavy oil in porous media

Under the strategic goal of “dual-carbon”, reducing oil viscosity by in-situ emulsification using chemical method has become a new direction for high-efficiency and low-carbon development of heavy oil reservoirs. This technology can transform the originally immovable heavy oil into movable dispersed oil droplets through in-situ emulsification, and thus enhances heavy oil recovery. However, there is still a lack of sufficient understanding about the characteristics and influencing laws of in-situ emulsification of heavy oil in porous media. So, this paper carried out experimental studies on in-situ emulsification and influencing factors for heavy oil in porous media. The results show that, due to the transport and adsorption loss of viscosity reducer in porous media, the emulsification area expands gradually from the inlet to the outlet. At the same sampling position, with the increase of injection volume, the dispersed oil droplet size decreases, the distribution density increases, and the color of produced liquid changes from light yellow to dark brown. Under the same injection volume, the closer to the outlet, the smaller the particle size of the dispersed oil droplets and the higher the distribution density, which is resulted from the shearing effect of the porous media. With the increase of injection rate, the hydrodynamic shear effect is enhanced, so the in-situ emulsification of heavy oil starts earlier and the emulsification oil ratio curves have a higher slope and distribute more densely. With the increase of agent concentration, the adsorbed number of viscosity reducer molecules on the oil–water interface is increased, making it easier to emulsify the remaining oil. With the increase of pre-conversion oil recovery, the remaining oil in the porous media is more dispersed and the oil–water contact surface increases, so the emulsification is easier and the percentage of dispersed oil droplets in the produced oil phase increases. The research results based on sampling analysis deepen our understanding on in-situ emulsification of heavy oil in porous media, which provides valuable reference for designing suitable viscosity reducer agent and effectively enhancing heavy oil recovery in the future.

Shaking table test for near-valley underground station: Influence of diaphragm walls

Diaphragm walls are commonly employed as a permanent support for the building of metro stations near urban valley, and in conjunction with the interior sidewalls of the station structure to withstand the pressure from surrounding soils. Despite their prevalent use, the effect of underground diaphragm walls on the seismic response of stations is not yet fully understood. In this paper, a series of 1-g shaking table tests is designed to investigate the seismic response of a near-valley station with underground diaphragm walls within the elastic range. Modeling the stratum-structure-diaphragm walls system is accomplished by employing granular concrete reinforced with galvanized steel wires and synthetic model soils, and a station without diaphragm walls is included, serving as a benchmark for comparative analysis to understand the influence of diaphragm walls on the seismic behavior of the station. The experiment was designed for three depth-to-width ratios (DWRs), i.e. 1/3, 1/4, and 1/8, of arc-shaped valley topography, as well as the seismic excitations for the test include actual seismic records with the amplitude of 0.2 g, 0.4 g, and 0.8 g, respectively. Results show that the underground diaphragm walls enhance the lateral stiffness of the near-valley station compared to structures without diaphragm walls, and thus significantly reducing the racking deformation of structure during earthquakes. The presence of diaphragm wall would decrease the amplification of dynamic earth pressure caused by valley effect at the structural sidewalls, and significantly reduce the lateral vibration and shear effect of the station near a valley with a larger DWR. Notably, bending moment response at the connection between the diaphragm walls and structural sidewalls are dramatically amplified under strong seismic loading, and such adverse effects gradually increase with the DWR of the valley.

Microstructural characteristics with process-microstructure-property relations during high-frequency ultrasonic vibration-assisted cutting of metallic material

Microstructural characteristics of chips and machined surfaces are influenced by the multiphysics fields distribution. This study investigates the multiphysics-induced microstructural deformation behaviors of CuZn37 metallic alloy during high-frequency ultrasonic vibration-assisted cutting (HFUVAC) and conventional cutting (CC). One the one hand, the multiphysics field distribution was established to clarify the chip formation of cutting characteristics and transient deformation process. The multiphysics field distribution of HFUVAC exhibited periodic changes due to tool intermittent movement, resulting in reduced cutting temperature and force. This intermittent movement also enhanced the sharpening shear effect due to instantaneous impact stress, transitioning from fragmented quasi-shear strain to continual multiple-shear strain during chip formation. One the other hand, the microstructural changes were examined to explain material removal mechanisms. The microstructure of CC demonstrated grain refinement and dislocation slip induced by friction and significant shear deformation. The microstructure of HFUVAC revealed the formations of dynamic recrystallization, twinning structures, and stacking faults, which were associated with enhanced plastic activity and limited slipping due to high-frequency impacts. The work reveals the response of the workpiece microstructure under the composite effects of high-frequency impacts and cutting process, which provides theoretical basis for the microstructure modification design through cutting technology.