Shear Stripping Research Articles

Experimental and mechanism study on wax deposit dissolution characteristics by light crude oil

During the sequential transportation of waxy crude oil and light oil, the previous formed wax deposits on the pipe wall will dissolve by light oil, which brings risks to the flow safety of the pipeline. This paper adopted a Couette wax deposit dissolution experimental device to systematically study the effects of dissolution duration, oil temperature, rotation speed and wax deposit properties on the dissolution characteristics of wax deposits. It is found that the dissolution of wax deposits is a process that starts quickly and then slows down. Moreover, the wax content of wax deposit also decreased during the dissolution process. The wax deposit dissolution process is mainly divided into five stages such as diffusion of wax molecules from wax deposit to the light oil and from bottom layer deposit to the wax deposit-oil interface, dissolution of wax crystal particles, weakening of wax deposit structural strength, and shear stripping of wax deposits. Finally, an empirical model of wax deposit dissolution was established and the undetermined parameters were fitted based on experimental data. The prediction results have good prediction accuracy with the experimental values.

Scale-Resolving Simulation of Shock-Induced Aerobreakup of Water Droplet

Two different scale-resolving simulation (SRS) approaches to turbulence modeling and simulation are used to predict the breakup of a spherical water droplet in air, due to the impact of a traveling plane shock wave. The compressible flow governing equations are solved by means of a finite volume-based numerical method, with the volume-of-fluid technique being employed to track the air–water interface on the dynamically adaptive mesh. The three-dimensional analysis is performed in the shear stripping regime, examining the drift, deformation, and breakup of the droplet for a benchmark flow configuration. The comparison of the present SRS results against reference experimental and numerical data, in terms of both droplet morphology and breakup dynamics, provides evidence that the adopted computational methods have significant practical potential, being able to locally reproduce unsteady small-scale flow structures. These computational models offer viable alternatives to higher-fidelity, more costly methods for engineering simulations of complex two-phase turbulent compressible flows.

WS2 nanosheets-based electrochemical biosensor for highly sensitive detection of tumor marker miRNA-4484

In this paper, a few-layer WS2 nanosheets-based electrochemical biosensor was fabricated for the highly sensitive detection of breast cancer tumor marker miRNA-4484. Firstly, few-layer WS2 nanosheets were prepared by shear stripping and characterized by SEM, TEM, AFM and UV spectrophotometer. After modification of few-layer WS2 nanosheets on the electrode surface, the miRNA probe was fixed on the few-layer WS2 nanosheets by polycytosine (PolyC). Then short-chain miRNA containing PolyC was used as the blocking agent to close the excess active sites on the surface of WS2 nanosheets to complete the fabrication of the sensor biosensing interface. Finally, the current changes caused by the specific binding of miRNA-4484 to the probe were analyzed by differential pulse voltammetry (DPV). The results showed that the sensor had a good linear relationship for the detection of miRNA-4484 in the concentration range of 1 aM–100 fM, and the detection limit was as low as 1.61 aM. In addition, the electrochemical sensor had excellent selectivity, stability and reproducibility. The artificial sample tests indicated that the developed biosensors have the potential for clinical application in the future.

Experimental study on wax deposition of highly paraffinic oil in intermittent gas-oil flow in pipelines

Oil-gas two phase wax deposition is a fairly common and open-ended question in flow assurance of multiphase transportation pipelines. This paper investigated the two main aspects of oil-gas two phase wax deposition layer: apparent thickness and crystal structure characteristics. A typical highly paraffinic oil in Bohai Sea, China, was used as the experimental material to investigate the wax deposition thickness in oil-gas two phase under the influence of different oil temperatures, superficial gas/liquid phase velocities and gas-oil ratios by using multiphase flow loop experimental device. Just as in the classical theory of wax molecular diffusion, it showed that wax deposition thickness of oil-gas two phase increased with increasing oil temperature. Analysis of the impact of different superficial phase velocities found that the actual liquid flow heat transfer and shear stripping was the gas phase dominant mechanisms determining wax deposit thickness. In addition, the crystal structure of the wax deposition layer was characterized with the help of small-angle X-ray scattering (SAXS) for different circumferential positions, flow rates and gas-oil ratios. The bottom deposition layer had a complex crystal structure and high hardness, which were subject to change over flow rate variations. Furthermore, the SAXS results provided evidence that the indirect effect of the actual liquid velocity modified by the gas phase was the main mechanism. Our study of the effect of gas phase on the wax deposition of oil-gas two phase will help shed light onto the mechanism by which this important process occurs. Our findings address a very urgent need in the field of wax deposition of highly paraffinic oil to understand the flow security of oil-gas two phase that occurs easily in multiphase field pipelines.

Study on the Interface Instability of a Shock Wave–Sub-Millimeter Liquid Droplet Interface and a Numerical Investigation of Its Breakup

This study investigated the influence of instability on the interaction between sub-millimeter liquid droplets and shock waves. Experiments were conducted using 0.42 mm diameter droplets with varying shock wave Mach numbers. The investigation quantified the effects of Weber numbers and initial diameters on the development of Rayleigh–Taylor and Kelvin–Helmholtz instabilities at the shock wave–sub-millimeter liquid droplet interface. Three-dimensional numerical simulations were performed to investigate the deformation and breakup behaviors of sub-millimeter liquid droplets under the impact of a shock wave with a Mach number of 2.12. The post-shock gas flow environment in this condition was in a supersonic state. The simulations utilized the volume-of-fluid method to model the gas–liquid interface, employed unsteady Reynolds-averaged Navier–Stokes methods to simulate turbulence, and incorporated grid gradient adaptive technology to enhance computational efficiency. The results revealed that by increasing the Weber number or decreasing the initial diameter, both the growth rate and the wavenumber extremum of the Rayleigh–Taylor and Kelvin–Helmholtz instability waves increased. The variation in the K–H instability’s growth rate extremum increasing Weber number surpassed that of the R–T’s instability. This indicated that both the R–T and K–H waves on sub-millimeter liquid droplets tended to exhibit increased growth rates and reduced scales. Moreover, as the Weber number increased, the K–H instability became dominant in the aerodynamic fragmentation. The numerical simulations showed good qualitative agreement with the experimental data, affirming the viability of numerical methods for addressing such challenges. The evolution of the sub-millimeter liquid droplets was marked by two primary stages, flattening and shear stripping, signifying that the K–H instability-driven SIE mechanism governed the aerodynamic breakup in the supersonic post-shock airflow.

An experimental study on structural performance of reinforced concrete beams strengthened for combined flexure and shear by using NSM-GFRP strips

Near surface mounted fiber reinforced polymer (NSM-FRP) technique is the latest & most effective techniques used in strengthening the existing structural components, which requires strengthening against increased service loads, faulty design, environmental effects, etc. In the past, many researches on NSM technique have been carried out by using different cross-sectional shapes & dimensions of FRP materials to strengthen for shear & flexure. In the present experimental study, the behaviour of R.C. beams strengthened for combined flexure & shear studied. The beams of 150x150x700 mm size with M30 grade of concrete & Fe500 steel were considered. The control beams (unstrengthened) & strengthened beams using GFRP (Glass fibre reinforced polymer) strips were subjected to three point loading to study the behaviour of beams in combined shear & flexure. The main objectives were to assess the behaviour of strengthened beams with control beams & to study the influence of the orientation of shear strips. The beams were studied for the failure characteristics, yield & ultimate load carrying capacity, stress-strain behaviour, deflection, & crack patterns. From the test results, it’s been observed that, the load carrying capacity of the strengthened beams were increased, the improved in deflection, when compared to the control beams. The ultimate load carrying capacity of beams with shear strip orientation of 45°, 60° & 90° were increased by 50.3%, 39.3% & 25% respectively, compared to the control beams. This NSM strengthening technique can be advantageous & suitably adopted to enhance the load carrying capacity of the beams.

Seismotectonics of Southern Calabria Terrane (South Italy)

Seismic data of earthquakes recorded during the last 40 years in southern Calabria have been compared with geological data in order to obtain a seismotectonic picture of the area. We sought for any possible correlation between the main regional tectonic structures, the distribution of earthquake hypocentres and the focal mechanism of earthquakes with magnitude (Ml)≥3. Studies of historical and recent seismicity and analysis of geological structures allowed to define the main shear strips on a regional scale. More than 2600 earthquakes with 1.5 ≤ Ml ≤ 4.5 have been considered. The focal mechanisms of earthquakes with Ml≥3 have been compared with the kinematics of known faults and used to give insight on the current active stress field. From the analysis carried out it was possible to expand the cognitive framework regarding the activity of the main tectonic structures present in the area. This study also served to identify areas of high seismicity which do not correspond to any evidence of tectonic structures on the surface, and areas where recognized tectonic structures have not shown any seismicity during the last decades. These cases could be the subject of future investigation in order to correctly assess the seismic hazard in Calabria. This task is important in the context of seismic hazard evaluation and mitigation.

Insights into the differential fragmentation processes in rock avalanche emplacement from field investigation and experimental study

Fragmentation is a universal phenomenon associated with rock avalanches, resulting in an abundance of complex sedimentological structures. If studied in detail, these structures can provide insights into rock avalanche emplacement processes. Here, six typical avalanche cases are carefully analyzed in conjunction with an analogue experiment. Findings reveal the carapace facies is characterized by clast-supported structures composed of large blocks with sedimentological structures that include retained stratigraphic sequences, imbricate structures, and jigsaw structures. The body facies presents a high degree of fragmentation, with block-rich zones, fine matrix-rich zones, jigsaw structures, and inner shear zones. The basal facies displays the highest degree of fragmentation, however, it is mainly composed of millimeter grains with thin shear strips. Consistent with the field investigations, differential fragmentation is also observed in the analogue tests, with the vertical dimension of the carapace facies mainly fragmented along the lines of pre-existing structures; the body facies fragmented with an abundance of new fractures; and the basal facies fragmented into fine grains. Meanwhile, layer sequences preserved in longitudinal and vertical profiles are also observed in the analogue tests, indicating a low disturbance in the propagation. We, therefore, propose that a process characterized by a sparse state, dominated by collisions, minor disturbance, and pervasive dynamic fragmentation likely occurs in the carapace facies, with fragmentation mainly controlled by the breakage of pre-existing, fully-persistent structures. The body facies is mainly controlled by the fracturing of the weak, less-persistent structures, and the basal facies displays the highest degree of fragmentation with an abundance of new fractures. In the entire propagation, the avalanche mass displays low-disturbance laminar flow.

A spray of puree: Wave-augmented transonic airblast non-Newtonian atomization

Characterization of viscous, non-Newtonian atomization by means of internal waves is presented for a twin-fluid injector. Atomization of such fluids is challenging, especially at low gas–liquid mass ratios. This paper details mechanisms that enhance their disintegration in a “wave-augmented atomization” process. The working fluid, banana puree, is shear-thinning and described by the Herschel–Bulkley model. Unlike a conventional airblast injector, an annular flow of banana puree is injected into a core steam flow, encouraging regular puree waves to form inside the nozzle. A pulsing flow develops with three distinct stages: stretch, bulge, and burst, leading to an annular puree sheet stretching down from the nozzle exit. Rayleigh–Taylor instabilities and viscosity gradients destabilize the surface. During wave collapse, the puree sheet bulges radially outward and ruptures violently in a radial burst. Near-nozzle dynamics propagate axially as periodic Sauter mean diameter fluctuations in a wave pattern. Numerical simulations reveal three atomization mechanisms that are a direct result of wave formation: (1) wave impact momentum, (2) pressure buildup, and (3) droplet breakaway. The first two are the forces that exploit puree sheet irregularities to drive rupture. The third occurs as rising waves penetrate the central steam flow; steam shear strips droplets off, and more droplets break away as the wave collapses and partially disintegrates. Waves collapse into the puree sheet with a radial momentum flux of 1.7 × 105 kg/m s2, and wave-induced pressure buildup creates a large pressure gradient across the puree sheet prior to bursting.

Parameters affecting the behaviour of RC beams strengthened in shear and flexure with various FRP systems

An experimental investigation was carried out on rectangular RC beams strengthened with FRP in different strengthening forms in shear and flexure. The parameters examined in this study are as follows: The shear span to effective depth ratio (a/d), the number of FRP layers in shear, strengthening form (completely wrapping, U-wrapping, and side-bonding), FRP types (Glass or Carbon), and FRP strips width to spacing ratios (wf/sf). The experimental results showed that strengthening with FRP enhanced the load-carrying capacity, deflection capacity, initial stiffness, and ductility capacity with respect to the reference beams. Increasing the number of FRP layers in shear did not provide a proportional increase in the contribution of FRP to shear strength. The FRP types, FRP strips width to spacing ratios (wf/sf), the number of FRP layers in shear, a/d, and strengthening form affect the cracking patterns and loads of tested beams compared to reference beams. In addition, strengthening with FRP could change the failure modes of RC beams from brittle shear failure to more ductile flexural failure. It was also found that the equations used to calculate FRP contribution to shear strength (ACI 440.2R (2017), Fib-TG 9.3 (2001), Khalifa (2002), Triantafillou (1998), Bukhari (2010)) overestimated the FRP contribution and gave unconservative results, especially for U-wrapped and side bonded beams compared to the experimental results.

Build of Machine Learning Proxy Model for Prediction of Wax Deposition Rate in Two Phase Flow Water-Oil

Wax deposit is one of the major fl ow assurance experienced in the process of oil production and transportation from sub- surface to surface. Large amounts of data are required to perform modeling using existing thermodynamic models such as carbon number data from HGTC. In this paper, a machine learning algorithm using unifi ed model approach from Huang (2008). Two types of input are implemented in order to simulate infl uence of feature selection used in training and testing machine learning which are input A consists of water volume fraction (fw), shear stress (τw), effective viscosity (μe), wax concentration gradient (dC/dT), and temperature gradient (dT/dR) and input B consists of water volume fraction (fw), shear stress (τw), effective viscosity (μe), wax concentration gradient (dC/dT), temperature gradient (dT/dR), shear stripping variable (SV) dan diffusion variable (DV). The random forest with Ntree = 500 known to be the best machine learning method compared to others. Based on accuracy parameter it achieves error parameter R-squared (R2) for training, testing and total data for input A and B are 0.999, 0.992, 0.9975 and 0.999, 0.993, 0.9977, respectively.

An electrochemical biosensor based on few-layer MoS2 nanosheets for highly sensitive detection of tumor marker ctDNA.

An electrochemical biosensor based on few-layer molybdenum disulfide (MoS2) nanosheets was fabricated for the highly sensitive detection of tumor marker circulating tumor DNA (ctDNA) in this paper. The MoS2 nanosheets with few layers were prepared by the shear stripping. Compared with the mechanical stripping method and the lithium ion intercalation method, this method is simpler to operate, and the prepared MoS2 nanosheets had good electrochemical activity. The biosensing platform was fabricated based on the discriminative affinity of MoS2 nanosheets towards single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA). Methylene blue (MB) was used as the signal molecule. The results showed that the detection of ctDNA by this sensor showed an excellent linear relationship in the concentration range of 1.0 × 10-7 M to 1.0 × 10-16 M, and the detection limit was 2.5 × 10-18 M. In addition, this sensor exhibited outstanding stability and specificity. This strategy provides an alternative approach for ctDNA detection and an effective sensing strategy for future in vitro cancer diagnosis by label-free detection.

Secondary Atomization of Liquid Metal Droplets at Moderate Weber Numbers

Atomization of liquid metal is an essential process in a variety of production methods such as spray forming or laser sintering. A critical part of all atomization processes is the breakup of single droplets, also termed secondary atomization. While it has been widely analyzed for conventional liquids, studies focusing on the influence of the specific properties of liquid metals remain rare. To identify differences, this work investigates single liquid metal Galinstan droplets exposed to a shock-induced crossflow by recording the breakup with a high-speed camera. The experimental test series covers a Weber number range of 11-104, and results show that the breakup morphology of Galinstan droplets follows the known sequence of bag, bag-and-stamen, multimode, and shear stripping breakup. We identify transition Weber numbers of ~15, ~35, and ~80, respectively, but also show that transition between modes is a continuous process with gradual changes. Compared to conventional liquids, the initial deformation of Galinstan droplets is very similar with respect to the shape, the initial deformation time, and the maximum cross-stream diameter. In contrast, later stages of the breakup process show clear differences. We observe that the onset of breakup appears significantly earlier in non-dimensional time, that Galinstan bags inflate much less, and that the bag breakup does not exhibit the same phenomenology as that of a water droplet. Further differences in the droplet shape and fragmentation suggest that the elastic oxide layer forming on Galinstan plays an essential role.

Slip system activity in gradient enhanced crystal plasticity: Grain boundary modelling and bi-crystal response

In gradient enhanced crystal plasticity formulations, additional conditions are required on grain boundaries which impact slip system activity in their neighborhood. In the case when gradient effects are caught through a dislocation density tensor, these conditions are prescribed on the flow of this tensor through the boundary or on the dual microforce. Gurtin (2008) proposed to derive the grain boundary behavior from a free energy potential function of a surface dislocation density tensor, the evolution of which equals the balance of flows on both sides. In this case, the response of a bi-crystal is driven by energy minimizing considerations extending the approach developed by Petryk and co-workers to gradient plasticity and grain boundary (GB) behavior: slip activity is then an optimum between deformation accommodation and limitation of accumulated bulk and GB defects energies and depends on their respective moduli. This is illustrated for the one dimensional problem of a bi-layered strip in simple shear and different cases are analyzed in terms of slip system orientations and strain hardening. Still, in the case of low angle GBs, the internal structure is assumed to be constituted of dislocation arrays accommodating the lattice misorientation between the two grains; an intrinsic dislocation density tensor can be associated to this structure and incorporated in the GB modeling.

Optimization of kenaf fibre reinforced polymer laminate for shear strengthening of RC beams using embedded connector

Kenaf fibre reinforced polymer (KFRP) laminate has gained its potentiality in shear strengthening of reinforced concrete beams recently, thus, method to obtain the minimal required dimension of KFRP shear strip is the utmost demand. The main aim of this research was to optimize the dimension of KFRP laminate for shear strengthening of RC beam. In experimental programme, high strength KFRP laminate and seven full scale RC beams were fabricated. The beams were shear strengthened using 7.5 mm thick and 20 mm, 30 mm and 35 mm widths of KFRP laminate, the dimensions of those shear strips were based on design strains of 0.007, 0.0045 and 0.004 respectively. Beams were also shear strengthened using CFRP laminates with similar widths of KFRP laminates for comparison. All beams were numerically analysed. Parametric study on design strain based on theoretical model was also conducted. Results showed that shear strengthened beam with 0.007 strain of KFRP laminate failed due to fracture of laminate. However, beams with laminate strains of 0.0045 and 0.004 did not show fracture or debonding of KFRP laminates, both beams had shown ductile flexural mode of failures with higher failure loads. In contrast, all CFRP laminate strengthened beams failed because of cover separation of laminates followed by shear. The failure loads of KFRP laminates strengthened beams were found to be higher as compared to those of CFRP laminates. The KFRP laminates were effectively enhanced shear capacity of strengthened beams without showing any premature failure even with the design strain of 0.0045, while, CFRP laminate showed premature cover separation failure with design strain of 0.002. Theoretical model showed that higher strength of concrete and length of laminate increased debonding or design strain of laminate. The numerical model predicted flexural and shear behaviour of shear strengthened beams. The flexural behaviour of strengthened beams based on numerical analysis were closely comparable with those of experimental findings. However, the model had limitation to predict local debonding failure of shear strip due to cracks and the effects of debonding on shear behaviour of strengthened beams.

Strain compatibility model to optimise CFRP laminate for shear strengthening of RC beam

ABSTRACT Optimisation of CFRP shear strip in presence of connectors/anchors is the current interest to reduce retrofitting cost of structures. The main aim of this research was to propose design guideline considering strain compatibility nature between shear reinforcement and externally bonded CFRP laminate to optimise the dimension of CFRP laminate for shear strengthening of RC beam in presence of embedded connectors. The guideline had been experimentally verified through the structural investigations on five reinforced concrete beams. Results showed that the proposed guideline with connectors reduced the dimension of CFRP laminate significantly. The optimal strengthened beams had shown the highest flexural capacities, maximum ductility and cost effective structural performances. Shear reinforcement and externally bonded CFRP laminate had shown identical nature of strains until shear crack and micro debonding of laminate. The optimal strengthened beams with connector did not fail by shear or debonding of laminates prior to theoretical design shear capacities of beams. The design shear capacities of optimal strengthened beams (182 kN) were very close to those of flexural failure loads (181 kN and 184 kN). Overall experimental results satisfactorily verified the proposed design guideline.

Experimental investigation of shock-induced tandem droplet breakup

For deeper insights into the dynamics of dense sprays, the present experimental work investigates the shock-induced breakup of two identically sized water droplets in tandem formation. The breakup process is visualized in a shadowgraph system and captured by an ultra-high-speed camera. The experimental Weber number ranges from 13 to 180, and the separation distance between the droplets is varied between 1.2 and 10.5 times of the droplet diameter. While the tandem formation exerts marginal influence on the lead droplet, the breakup intensity of the trailing droplet is consistently attenuated as the separation distance falls below critical levels. The time of initial deformation is postponed, the maximum cross-stream diameter is reduced, and the mean drag coefficient is lowered. These effects are more profound at lower Weber numbers and closer separation distances. The attenuation of the breakup intensity is also reflected by the formation of smaller bags in bag and bag-and-stamen morphologies and by the narrower cross-stream dispersion of fragments in multibag and shear stripping morphologies. When positioned in close proximity to the lead droplet, the trailing droplet fails to follow the conventional breakup morphologies. Instead, it either punctures or coalesces with the lead droplet.

EVALUATING THE MECHANISMS OF WAX DEPOSITION IN CRUDE OIL PIPELINES

Flow assurance standstill as a massive issue as it involves ensuring fluid flows in well, flowline and trunk line. One of the major decisive for flow assurance crude oil is its constitution and solid deposits successful management. Wax deposition challenges and its control can be determined with the right prediction from wax deposition modelling. Certain factors like pipeline inclination that influences the rate of wax deposition need to be taken into consideration. For inclined wells, the model is tuned to account for low concentration slurries under inclined angles. Regarding this, a complete wax deposition model is developed to predict the rate of wax deposition by investigating all the possible wax deposition mechanisms which contribute actively for better wax deposition management in the oil fields. A thorough analysis has been carried out to show the significance of each deposition mechanisms and parameters in wax deposition model like rate of wax deposition, deposit thickness, the temperature in the pipeline, pressure drop in the pipeline. Based on the results achieved, it can be deduced that the shear stripping and rate enhancement effect due to oil trap has the highest contribution towards the wax deposition in the pipeline but the gravity settling velocity cannot be neglected without valid assumptions.Keywords: flow assurance, wax deposition, wax deposition mechanisms, wax deposition modelling, shear stripping, gravity settling velocity

Effect of Mach number on droplet aerobreakup in shear stripping regime

The present experimental study investigates the shear stripping breakup of single droplets in subsonic and supersonic gaseous flows. In contrast to most research that places emphasis on the Weber number (We), we focus on the individual effects exerted by flow Mach (M∞) and Reynolds numbers (Re). Millimeter-sized droplets made of either ethylene glycol or water are exposed to shock-induced flows. Shadowgraph and schlieren images of the breakup process are recorded by an ultra-high-speed camera. The experimental We is constrained at 1100, while M∞ is varied from 0.3 to 1.19 and Re from 2600 to 24,000. A systematic analysis of the experiment series reveals that the breakup pattern alters with M∞ although a constant We is maintained. The classical stripping behavior with fine mist shed from the peripheral sheet changes to rupture of multiple bags along the periphery at M∞ = 0.63, and further to stretching of ligament structures from the leeward surface at M∞ = 1.19. The corresponding breakup initiation is delayed and the resultant fragments are sized less uniformly and distributed over a narrower spread. In terms of the early-stage deformation, droplets experience less intense flattening and slower sheet growth at higher M∞. The change of Re introduces additional variations, but only to a minor extent.Graphical abstract

Two Dimensional Deformation of a Multilayered Thermoelastic Half-Space Due to Surface Loads and Heat Source

This article deals with a 2-D problem of quasi-static deformation of a multilayered thermoelastic medium due to surface loads and heat source. The propagator matrix is obtained for the multilayered formalism of thermoelastic layers. Analytical solutions, in terms of the displacements, stresses, heat flux and temperature function, are obtained for normal strip and line loads, shear strip and line loads and strip and line heat sources. Numerical computation of the obtained analytical expressions is also done. The effects of layering have been studied. For the verification of the results, results of earlier studies have been obtained as particular cases of the present study.