Shearing Action Research Articles

Sliding and merging of strongly sheared droplets

A mathematical and numerical framework is proposed to compute the displacement and merging dynamics of sliding droplets under the action of a constant shear exerted by a gas flow. An augmented formulation is implemented to model surface tension including the full curvature of the free surface. A set of shallow-water evolution equations is obtained for the film thickness, the averaged velocity, an additional quantity (with dimension of a velocity) taking into account the capillary effects and a tensor called enstrophy. The enstrophy accounts for the deviation of the velocity profile from a constant velocity distribution. The formulation is consistent with the long-wave expansion of the basic equations with a conservative part and source terms including the effect of viscosity, in the form of a viscous friction and the effect of the shear stress. The model is hyperbolic with generalised diffusion terms due to capillarity. Finally, our model is completed with a disjoining pressure formulation that is able to account for the hysteresis of the static contact angle. In this formulation, the advancing or receding nature of the contact line is assessed by the accumulation or reduction of mass of the droplet at the contact line. Simulations of sliding water droplets are performed with periodic boundary conditions in a domain of limited size. Hysteresis of the static contact angle causes a slowdown of the drops and a delay in the sequence of coalescence of the drops.

Experimental investigation on the seismic behavior of composite steel plate shear wall restrained by ECC panels

The composite structures using engineered cementitious composites (ECC) and steel are promising to achieve good seismic performance due to their excellent deformability and energy dissipation. This paper proposed a novel composite steel plate shear wall restrained by ECC panels. The shear wall system consists of boundary frame, steel plate and precast ECC panels. The steel plate is sandwiched between two precast ECC panels by bolts. Then, the sandwich panel is bolted to the boundary frame by angle steels. Experimental investigation was conducted on the proposed composite shear walls to evaluate their seismic performance. Five one-story one-span specimens with ECC panels considering the effects of panel-frame connection types, reinforcement ratio in ECC panels and aspect ratio were tested, as well as a control specimen with concrete panels. Test results revealed that compared with ordinary buckling-restrained steel plate shear wall, the proposed composite shear walls displayed sufficient ductility, high initial stiffness and satisfactory energy dissipated capacity. Severe cracking and spalling of concrete panels were detected, while the ECC panels still maintained integrity and had high residual strength in the later stage of loading. ECC panels made a considerable contribution to shear resistance in addition to effectively restraining the buckling of the steel plate. In comparison with the specimen using partial four-side connection, the shear capacity, initial lateral stiffness and accumulated dissipated energy of the specimen using four-side connection were notably enhanced by 103%, 22.8% and 108%, respectively. Moreover, using two-side connection weakened the shear capacity and initial lateral stiffness of the specimen by 29.4% and 29.8%, because it could not exhibit complete shear and tension field actions as the specimen using four-side connection.

Experimental Study of Condensate Vaporization into Bubbles under Different Operating Parameters

Produced water (PW) is a natural by-product of the oil and gas production process, where crude oil is dispersed in the form of micron-sized emulsified droplets in the produced water due to mixing between crude oil and water caused by equipment, piping and valve shear action. Flotation is the main method for treating emulsified oil droplets in oilfield produced water. The conventional flotation technology suffers from a series of problems such as large reflux ratio and poor flotation effect, thus limiting its further application. In this paper, bubbles are prepared by vaporization of low boiling point condensate through theoretical analysis and experimental study. In this paper, the law of bubble generation from condensate solution at different temperatures after decompression and release is investigated. The results demonstrate that the median particle size of gas bubbles generated from condensate is related to the condensate content, mixing pressure, release pressure, and temperature. The median particle size can reach 9.65 μm when mixed at 2.0% condensate content, 0.2 MPa mixing pressure, and 35°C, and released at atmospheric pressure, which is much smaller than the size of gas bubbles generated by dissolved air flotation. The condensate bubbles as alkane congeners are more likely to adhere to the oil droplets in the extracted water, which is conducive to improving the air flotation oil removal efficiency of oily wastewater.

An innovative model to estimate the tension field inclination considering crack growth for steel plate shear wall

The Steel Plate Shear Walls (SPSWs) are known as a capable system to use in steel structures due to their significant advantages. Despite extensive studies concerning this system, few researchers have scrutinized thecrack effect on SPSW behavior. However, the crack dramatically affected the experimental results. In the currentpaper, the effect of central and edge cracks, therefore, has been studied in jointed plates at mid-height of SPSW.Results indicated that the central crack is more destructive than the edge crack. The central crack having a long initial length also makes a sudden wall fracture in the elastic zone and consequently cannot be used in high seismic regions. Due to the dependence of the wall on the diagonal tension field and its angle, an equationis proposed taking into account shear, axial, and moment actions in columns, axial and moment actions in beams, as well as shear and axial actions in the plate which conform to finite element results. Because of thecomplication of the stress intensity factor for mode I and mode II calculations, this confidence is derived and offered.

Effect of dynamic vulcanization time on the performance of thermoplastic vulcanizates based on hydrogenated acrylonitrile butadiene rubber/thermoplastic polyester elastomer

AbstractThermoplastic vulcanizates (TPVs) are obtained by dynamic vulcanization (DV). Time is a crucial processing parameter. This work aims to develop heat‐ and oil‐resistant TPVs with hydrogenated acrylonitrile butadiene rubber (HNBR) and thermoplastic polyester elastomer (TPEE). It focuses on the effect of DV time on the morphology and properties of the resulting TPVs. The investigation demonstrates that as the DV time increases from 2 to 6 min, the rubber network progressively reinforces and the HNBR domain size decreases under more adequate shearing action, resulting in a more homogeneous morphology. This leads to a significant improvement in tensile properties, elasticity, rheological properties, thermal stability, and oil resistance of the TPV. A further extension in DV time (over 8 min) results in a slight deterioration in elasticity and thermal stability of the TPV because of excessive degradation of the TPEE. Accordingly, an appropriate DV time for HNBR/TPEE‐TPV preparation is between 6 and 8 min under the specified DV conditions.

Design method of HSS welded H-section beams subjected to bending-shear combination

High-strength steel (HSS) welded H-section beams are increasingly used in steel structures considering their advantage of high strength, but the stability is a concern especially near the supports, where the beams are prone to buckling under the combined actions of bending and shear. In this paper, finite element method was used to analyze the mechanical performance of HSS welded H-section beams under shear and bending-shear loads. A parametrical analysis for the H-section beams under pure shear loads was conducted, and a new shear buckling coefficient calculation method considering the interaction between plates was proposed. This coefficient was then applied to calculate the shear strength, and a design method for shear buckling strength based on the direct strength method (DSM) was proposed. Finally, a new bending-shear interaction curve was developed to predict the ultimate resistance of HSS welded H-section beams under bending-shear combination, and the reliability analysis results demonstrate the feasibility and safety of the design method proposed in this paper for HSS welded H-section beams.

Flexural–shear deformation theory (FSDT) for modeling of mechanical responses of RC beams strengthened in shear with ETS-FRP bars

The flexural–shear deformation theory (FSDT) approach for simulating the shear behavior of reinforced concrete (RC) beams strengthened in shear with embedded-through section fiber-reinforced polymer (ETS-FRP) bars is developed in this study. The key feature of the FSDT approach is to mix both flexural and shear deformation parameters constituted in the beam into an algorithm, which is able to simplify the analysis and shorten the computation time. Most of the formulations adopted in the model are built on the basis of mechanics by applying a few common theories involved in stress and strain fields. Particularly, to couple the participation of the ETS-FRP strengthening system into the developed FSDT, the newly developed bonding-based mechanism between the ETS-FRP bar and concrete is used. The calculation outcome produces the vertical strain (εv), which is the main parameter used to determine the resistance of shear reinforcement. The shear contribution of concrete is derived via the concrete principal tensile strain (ε1). Then, the minimized discrepancy between shear forces induced by flexural (VT) and shear actions (Vtotal) is the condition for termination of the calculation. Through the broad corroboration of the developed model to the experimental data with respect to structural responses, excellent agreement and high accuracy are found. To offer prospects for the design practice of ETS-strengthened beams, a parametric study on the effects of important design variables is implemented against the results assessed by a guideline released by the American Concrete Institute (ACI). Consequently, the proposed FSDT approach provides more insight into the responses of ETS-strengthened beams than the ACI guideline, which is helpful for practitioners.

Road Piezoelectric Power Output Model and Experimental Study under Bidirectional Vehicle Load Excitation

Recently, piezoelectric transducers have gained significant attention for energy recovery applications in road engineering. However, in laboratory tests, vehicle loads are often simplified using vertical vibration loads, thus ignoring the role of vehicle tangential loads. In this study, a power output model of a piezoelectric transducer under vertical and tangential loads was proposed through theoretical analysis. A bidirectional cyclic dynamic load test was conducted on the piezoelectric-concrete specimens in combination with a large dynamic and static straight shear instrument, and the power output law of the piezoelectric transducer under vertical and horizontal shear was investigated. The results revealed that the vertical vibration load was the main factor affecting the output performance of the piezoelectric transducer; however, with the addition of the tangential load, the electric energy output of piezoelectric pavement increased with an increase in the horizontal shear rate and displacement. When vibrating vertically (200 kPa and 4 Hz), the electric energy output of piezoelectric pavement was 4.979 μW. However, under the action of vertical vibration and horizontal shear with the working conditions of 200 kPa and 4 Hz, and 0.1 mm and 1 Hz, the electric energy output of piezoelectric pavement was 21.04 μW, which was 3.2 times that of the vertical vibration load alone. Therefore, by considering the influence of vehicle tangential loads, the power output of piezoelectric transducers can be calculated more accurately, which provides a reference for actual installed capacities in real engineering applications.

INVESTIGATION OF 3D SURFACE TOPOGRAPHY FEATURES ON THE POLYCRYSTALLINE DIAMOND TURNING OF ALUMINA

The product’s surface quality and service performance depend on the surface integrity features formed by the machining process. Surface integrity consists of many features including surface topography and others. In this work, 3D (areal) surface topography features, particularly height variations, were investigated on the polycrystalline diamond (PCD) turning of alumina. Variations of the areal unevenness and height distribution parameters, namely arithmetic mean deviation (Sa), maximum peak height (Sz), skewness (Ssk) and kurtosis (Sku), with respect to turning parameters such as spindle speed (1000, 2000 n 3000 rpm), feed rate (0.05, 0.075 & 0.1 mm/rev) and depth of cut (1, 3 & 5 [Formula: see text]m) were studied. The Taguchi technique was carried out in this study based on the L9 standard orthogonal array for optimizing the turning parameters for the generation of better topography features. The error analysis was done with the experimental results and the error variations were noticed to be less than 10%. Based on the experimental results, the best surface figure combination of Sa 0.67 [Formula: see text]m, Sz 3.18 [Formula: see text]m, Ssk 0.0039 and Sku 3.06 was found at the employment of spindle speed of 1500 rpm, feed rate of 0.1 mm/rev, and depth of cut of 1 [Formula: see text]m. The distribution of peaks and valleys formed over the PCD-turned alumina surfaces may influence the different functional properties such as fatigue, friction, wear, etc. Besides, the results were examined through means of responses and analysis of variance (ANOVA). The test results also reported that the depth of cut outperforms other hard turning parameters over the surface topography features of the turned alumina ceramics. At a lower depth of cut, the cutting tool is involved in the shearing action which causes the stable material removal of alumina ceramics through an appreciable chip formation.

Damage detection of concrete segment in steel-concrete hybrid wind turbine tower

The steel–concrete hybrid tower (SCHT) has been applied as an alternative supporting structure for wind turbines due to its advantages of higher hub height and loading bearing capacity. To improve the construction efficiency of such a tower on site, the lower concrete section was divided into several prefabricated segments and the connection between different segments was achieved by grouting joints, which may become the weakest part of the tower under the combined action of compression, bending, shear and torsion, leading to progressive collapse or other undesirable failures of the SCHT. However, up to now, there were limited studies focused on the monitoring system detecting the damage of the concrete segment and most of them required inspection at downtime. To fill up the research gap, this paper developed a real-time monitoring system for detecting the possible failure of the concrete segment effectively and accurately. To start with, the formulation of the damage index based on the dynamic acceleration responses is firstly presented based on the mechanical characteristics of the wind turbine towers. Then, an experimental investigation and parametric analysis based on numerical simulation are arranged to validate the reliability of the proposed method. The analysis results indicate the proposed method can provide a reference for the damage monitoring of the SCHT.

Experimental Investigation of the Effects of Aperture Ratio, Chamber Pressure and Soil Conditioning on the Clogging Behavior of EPB Shields

Earth pressure balance (EPB) shield excavation in cohesive strata frequently encounters cutterhead clogging, consuming time and economic costs. Engineering practice shows that cutterhead aperture ratio, soil chamber pressure and soil conditioning have important influences on the clogging behavior of EPB shields. In order to study these factors, a series of laboratory tests were conducted using a setup that can closely simulate the shield tunnelling process. The indicators analyzed were excavation speed, torque, specific energy and soil distribution on the cutterhead. The results indicate that cutterhead aperture and cutter arrangement are important factors in clogging potential. Clogging creates a significant reduction in excavation speed. Torque is not a sensitive parameter reflecting clogging because of the effect of the consolidated soil on the cutters. The presence of soil chamber pressure makes it difficult to remove the clogging through the shearing action of the excavation surface. The injection of a sufficient amount of foam can reduce the risk of shield clogging, but it may lead to an increase of soil adhesion on the cutterhead. The amount of soil that adheres to the cutterhead cannot be used as a classification criterion for clogging potential. Based on experimental phenomena and established studies, a mechanical model called ‘beam-bridge’ was proposed to study the behavior of the soil through the cutterhead opening and damage form of clogging. The results will help to the excavation control of EPB shields.

Shear performance test and nominal bearing capacity on the transfer beams of steel reinforced concrete in subway station structure

To investigate the shear behaviors of steel reinforced concrete (SRC) transfer beams in subway station structure, the shear performance tests of 13 specimens on the transfer beams were investigated under the concentrated loads. The design parameter variables of transfer beams in the experiments main included the shear span ratio, profile steel ratio and section form of profile steel. The failure modes, load–displacement curves and strain characteristics of transfer beams were also analyzed in detail. The results show that the vertical cracks appeared in the transfer beams firstly, then the main oblique cracks appeared on both sides of the middle span of transfer beams, and finally the concrete at the support and the loading point of transfer beams fell off due to the shear action, which was a typical shear failure. Compared with reinforced concrete (RC) transfer beams, the shear bearing capacity and ductile deformation ability of SRC transfer beams have been significantly improved, and the shear bearing capacity of SRC transfer beams is 112.05% higher than that of RC transfer beams at the same shear span ratio. Reducing the shear span ratio can enhance the shear bearing capacity of transfer beams, but it is not good for their ductility. With the profile steel ratio from 5.41 % to 5.89 %, the shear bearing capacity of channel steel reinforced concrete transfer beams and I-shaped steel reinforced concrete transfer beams increases by 11.81 % and 12.14 % respectively. However, the section form of profile steel has less influence on the shear behavior of transfer beam. According to the mechanical properties and failure mechanism of SRC transfer beams, the calculation formulas on the shear bearing capacity of SRC transfer beams was proposed based on the truss-arch model. The calculation accuracy on the modified formulas of SRC transfer beams were evaluated by the comparison between the calculated values and test values.

Bending restoring force model of angle-steel reinforced concrete columns under combined torsion

To explore the restoring force model of an angle steel truss reinforced concrete column (ASRC) under the combined action of compression, bending, shear, and torsion, nine ASRC columns under a combined torsion environment were tested and analyzed. This study observed and summarized the failure mode characteristics of different component columns, distinguished different failure modes, and analyzed the hysteresis curve and energy dissipation capacity of component columns. Then, a trilinear skeleton curve model suitable for ASRC columns is adopted, and the calculation method of skeleton curves in different stages under the combined action of compression, bending, shear, and torsion is given. Finally, the ASRC hysteresis rule is simplified, and fitting produces the formulae for positive and negative hysteresis curve unloading stiffness. The restoring force model of the ASRC column under coupled torsion is established, and the test results validate the restoring force model. The results show that the established restoring force model can predict the hysteretic behavior of ASRC under combined torsion. This research can be used as a theoretical foundation as well as an experimental reference for the technical use of ASRC.

Characterization of Lubrication Layer of Fresh Concrete Acquired Using the Modified Pipe Flow Apparatus

A thin layer of micromortar called a lubrication layer (LL) forms around the inner periphery of the pipe during the pumping of fresh concrete. This LL aids in the movement of concrete under pressure. The composition of the LL is of prime importance in understanding the flow behavior of concrete under the action of shear and the prediction of pressure for pumping applications. In the present study, an attempt was made to determine the LL composition of the concrete mixtures using fly ash, ground granulated blast-furnace slag, and limestone calcined clay as supplementary cementitious materials with a water to binder (w/b) ratio ranging from 0.3 to 0.5 supplemented with a superplasticizer. In this regard, the LL was extracted by modifying the existing pipe flow apparatus. The collected LL was characterized for its composition, which includes w/b, binder to sand ratio (b/s), and particle-size distribution. The results indicated that the nominal maximum particle size of LL was around 600 μm. The average binder to sand ratio of LL obtained was 3.0. The w/b of LL was found to be higher than that of the bulk concrete. The characterization of LL carried out in the current work generated a database regarding the potential composition of LL, which would aid in the rheological studies for fundamental understanding and the pressure prediction of concrete.

Characteristic Analysis of Relationship Between Precipitation and Turbulence in the Troposphere and Lower Stratosphere Over Tropical Western Pacific

AbstractThis study aims to analyze the distribution characteristics of turbulence in the western Pacific tropical region and determine the correlation between turbulence and precipitation. The obtained results show that due to the combined action of large wind shear and thermal convection, the near‐surface layer is conducive to the generation of large‐scale turbulence, and the maximum Thorpe scale can reach more than 600 m. A strong mixing zone of turbulence is generated in 10–16 km, with the monthly average occurrence rate of turbulence being about 40% and the maximum value reaching 50%. There is less turbulence in lower stratosphere due to the rapidly increased atmosphere static stability. All Thorpe scales in stratosphere are less than 100 m. The response of turbulence to precipitation in the upper troposphere is strongly affected by clouds. At the altitude in the clouds, the enhancement of precipitation has a negative relationship with turbulence. The average value of and turbulence layer thickness on rainy days are both smaller than those when the precipitation weakened. At the altitude above the clouds, the enhancement of precipitation has a slight promotion effect on the turbulence, especially for the emergence of large‐scale turbulence. When the precipitation intensifies, the amount of turbulence with greater than 150 m accounts for 6.7% of the total, while the proportion is only 2.6% on less rainy days.

Development of hybrid rubber damper-restrainer (HRDR) system for structures under sever dynamic excitation

Nowadays, high damping rubber materials are extensively implementing in various types of structure to mitigate harmful effect of imposed vibration and dynamic force to the structure. Although, the rubbers exhibit noticeable damping in the shear action, however, de-bounding, shear rupture and delamination of rubber layers under cyclic loads, undermine the load-bearing capacity of the rubber dampers and increase their maintenance costs. Hence, the action of the rubbers is considerably high under applied compression to generate resistant force to restrain the deformation.For this reason, in this research, a new hybrid rubber damper-restrainer (HRDR) system is proposed. The system comprises a high-damping rubber component designed to dissipate applied vibrations, along with a pair of hyper-elastic rubbers intended to restrain displacement. Therefore, the developed HRDR device is capable of dissipating vibrations while restraining large movements to prevent any damage and debounding of the rubber layers and also, protect the structure from excessive displacements.To examine the performance of the proposed device, the numerical model of a HRDR was developed using the finite element simulation and subsequently, nonlinear dynamic analyses were conducted for the 6 storey prototype steel structure furnished with HRDR device. The findings revealed that the structure equipped with the HRDR device exhibited outstanding response against applied earthquake excitation which is proving high efficiency of HRDR device to diminish vibration effect on structure and prevent any excessive deformations. The HRDR device is applicable to any types of framed structures through installing via chevron brace system in steel structures or short wall in reinforced concrete structures. Furthermore, the developed HRDR device can be implemented in bridge structures, between the deck and pier of bridge to effectively dissipate vibrations and restrain the movement of the bridge span under traffic loads.

РАСЧЕТ ЖЕЛЕЗОБЕТОННЫХ ЭЛЕМЕНТОВ ПО ПРОЧНОСТИ НАКЛОННЫХ СЕЧЕНИЙ ПРИ ДВУХОСЕВОМ ДЕЙСТВИИ ПОПЕРЕЧНЫХ СИЛ

In the current standards for the design of reinforced concrete structures no methods for calculating inclined sections with a biaxial action of shear forces are presented. At the same time, a significant part of reinforced concrete structures is subjected to the action of shear forces in two planes. The relevance of the article is determined by the lack of standard methods for calculating of reinforced concrete elements inclined sections for the biaxial action of shear, which forces designers to use simplifications in calculations. The article reviews the Russian and foreign literature on the theory of design of reinforced concrete elements for the action of transverse forces and analyzes the design methods proposed in the current Russian and foreign design standards, as well as in the standards of past years. In the analysis of methods for calculating reinforced concrete elements for the action of transverse forces, consideration is given in various methods for calculating the factors that affect the strength of inclined sections on the action of transverse forces in normal and biaxial bending in two planes, such as the shear span, the angle of inclination of the force plane, the amount of longitudinal tensile reinforcement, the influence of longitudinal forces, size-effect.
 The main directions for further research of the issue are identified and recommendations are given that summarize domestic and foreign experience.

Numerical study on the mixing enhancement induced by the interaction between the hydrogen/air coaxial jets and oblique shock wave at Mach 3 supersonic crossflow

The comprehensive performance of the scramjet is greatly influenced by the supersonic fuel mixing process. In the research, the mixing properties of the combination between the hydrogen/air coaxial jets and oblique shock at Mach 3 supersonic crossflow are investigated. The focus of the investigation is to reveal the mixing enhancement mechanism of coaxial jets and the impact of oblique shock on the mixing process. The numerical simulation is based on three-dimensional compressible RANS equations combined with the SST k-ω turbulence model. The hydrogen spatial distribution, flow features, vortex structure, penetration depth, stagnation pressure loss and mixing efficiency with different working conditions are evaluated and studied. Our computational results demonstrate that the coaxial jets enhance mixing through the intense shear action between the annular fuel jet with the inner and outer air layers, and the oblique shock contributes to the mixing process by strengthening the interaction between jet and airflow, improving fuel distribution and inducing streamwise vorticity. In addition, the hydrogen distribution and mixing properties are affected by the action position of the incident shock. According to the achieved results, the coaxial jets combined with the oblique shock impinging downstream of the jet have the highest mixing efficiency, which is improved by 63.27% compared to the reference case.

Compensation for Merchant’s Circle Diagram to predict cutting force in orthogonal micro turning

Cutting force for conventional orthogonal machining can be predicted by Merchant’s Circle Diagram (MCD) considering the shearing action of chip formation. However, the effect of plowing action is significant for micro turning, which has not been considered in MCD. Therefore, a large error has been observed in the prediction of cutting force in micro turning by MCD theory. In this study, a compensated model has been developed for orthogonal micro turning based on MCD. The theory has taken shearing and plowing actions into consideration. The compensated model involved material flow stress, cutting parameters, and tool geometry, including cutting edge radius. This model has predicted tangential cutting force with an average prediction error of 3.75% for micro turning of Ti6Al4V, whereas the average prediction error was 14.9% for axial cutting force.

Effect of shear ratio on rheological properties of suspension in two-step flocculation process for fine iron tailings

In the two-step flocculation process, shear has a significant impact on the rheological properties of the flocculating slurry. In this study, the orthogonal experiments of two-step flocculation process for fine iron tailings were designed. Based on the change of shear ratio, different shear rates and shear time were designed, the yield stress, plastic viscosity and maximum packing fraction of the flocculated suspension in each group were measured and calculated with a rheometer. The result of range and variance analysis shows the shear rate in the primary broken phase was the biggest factor affecting the yield stress and plastic viscosity of the flocculated slurry in two-step flocculation process. When the shear rate increased from 100 s-1 to 400 s-1, the yield stress and the plastic viscosity of the flocculated slurry increased by 7.14% and 21.30%, respectively. When the shear rate changed from 400 s-1 to 800 s-1, they decreased by 23.27% and 33.17%, respectively. Since the shear ratio in a two-step flocculation process is also related to both shear action and floc structure parameter, the shear ratio was introduced into the first-order reversible kinetic rate equation. Through establishing the relationship between the shear ratio and the floc structural parameter of flocculating suspension, a theoretical model of the shear-dependent maximum packing fraction was established. The measured values and theoretical calculated values of the maximum packing fraction in two-step flocculation experiments were in good agreement and the error was within 5%. Last but not least, the internal mechanism of the theoretical model was discussed from the microscopic point of view.