Global Friction Research Articles

Pressure Source Model of the Production Process of Natural Gas from Unconventional Reservoirs

This work is focused on developing a computational model to predict the production rate and pressure evolution of natural gas from unconventional reservoirs, particularly shale gas deposits. The model is based on the principle of conservation of mechanical energy and was developed from the transient solution of Bernoulli’s equation. This solution was obtained by computing the pressure evolution in the well resulting from the combined action of extracting the free gas and of gasification from kerogen. The transient behavior of gas production by hydraulic fracturing was calculated by numerically integrating Bernoulli’s equation. The curves representing gas flow evolution were considered as a series of stepwise steady states under a constant gas flow rate, similar to the pressure–time curves. These time steps were connected by instantaneous drops in pressure or gas flow rates. On the other hand, the delayed release of the adsorbed and dissolved gas in the kerogen was accurately calculated by introducing a semi-empirical gas pressure source term into the gas well pressure equation. The effect of this source is to gradually increase the gas pressure in the reservoir, emulating the gas release mechanisms from the organic matter. Model validation was based on production data from the unconventional reservoirs Eagle Ford, U.S.A., and Burgos basin, México. The initial measured gas production rate was used to determine a global friction factor of the gas flowing out from soil cracks and ducts. Additionally, measured production rate data were used to determine the coefficients of the source term function. Pearson correlation coefficients of 0.97 and 0.96 were obtained for Eagle Ford and Burgos basins data, respectively. In contrast, the corresponding coefficients calculated from the traditional Arps’ model were 0.89 and 0.5, respectively. The present pressure source model (PSM) represents a new approach to characterize the process of gas production from unconventional reservoirs, proving to be accurate in forecasting both the gas flow rate and pressure evolution during gas production. The postulated pressure source term was shown to mimic the desorption and diffusion kinetics, which release free gas from the kerogen.

Transient skin friction behavior associated with hemisphere-based vortex ring collisions

Global and local transient skin friction variations resulting from a large-eddy simulation study on ReΓ0=3000 vortex rings colliding with surface-mounted hemispheres of hemisphere-to-vortex-ring diameter-ratios of 0.5≤D/d≤2 are investigated here. Skin friction distribution changes due to the approaching primary vortex ring, formation of secondary/tertiary vortex rings, subsequent mutual interactions between various vortex ring structures, and azimuthal instabilities are clarified with a view to better establish their relationships when the relative hemisphere size varies. Results show that the primary vortex ring produces the highest skin friction levels when it is close to or collides with the hemisphere/flat wall. Additionally, entrainment of wavy secondary/tertiary vortex rings leads to them entangling around the primary vortex ring and resulting in segmented skin friction regions at later stages of the collision process, regardless of the diameter-ratio. Unlike smaller hemispheres, the largest D/d=2 hemisphere here restricts all skin friction changes along its surface with the flat wall unaffected. It is also revealed here that while the diameter-ratio governs the global skin friction distributions, how secondary/tertiary vortex rings interact with the primary vortex ring and how azimuthal instabilities manifest and evolve for all the various vortex rings confer strong influences on the breaking-up and dissipation of regions with high skin friction levels.

Effects of Proline on Internal Friction in Simulated Folding Dynamics of Several Alanine-Based α-Helical Peptides.

We have studied in silico the effect of proline, a model cosolvent, on local and global friction coefficients in (un)folding of several typical alanine-based α-helical peptides. Local friction is related to dwell times of a single, ensemble-averaged hydrogen bond (HB) within each peptide. Global friction is related to energy dissipated in a series of configurational changes of each peptide experienced by increasing the number of HBs during folding. Both of these approaches are important in relation to future atomic force microscopic-based measurements of internal friction via force-clamp single-molecule force spectroscopy. Molecular dynamics (MD) simulations for six peptides, namely, ALA5, ALA8, ALA15, ALA21, (AAQAA)3, and H2N-GN(AAQAA)2G-COONH2, have been conducted at 2 and 5 M proline solutions in water. Using previously obtained MD data for these peptides in pure water as well as upgraded theoretical models, we obtained variations of local and global internal friction coefficients as a function of solution viscosity. The results showed the substantial role of proline in stabilizing the folded state and slowing the overall folding dynamics. Consequently, larger friction coefficients were obtained at larger viscosities. The local and global internal friction, i.e., respective, friction coefficients approximated to zero viscosity, was also obtained. The evolution of friction coefficients with viscosity was weakly dependent on the number of concurrent folding pathways but was rather dominated by a stabilizing effect of proline on the folded states. Obtained values of local and global internal friction showed qualitatively similar results and a clear dependency on the structure of the studied peptide.

Friction measurement of aircraft wing based on optimized FlowNet2.0

Few studies have applied the deep optical flows model to global friction measurements of aircraft wing. This study used an optimized FlowNet2.0 model to measure friction of wing based on fluorescent oil film, which achieved the first integration of deep learning and friction measurement. Two input images of the traditional FlowNet2.0 model were extended to multiple images so that more flow features and details could be with them. It is the specific part of optimization that will also further improve the measurement accuracy of FlowNet2.0. Simulation experimental results show that the optimized FlowNet2.0 model reduces the Mean Absolute Percentage Error (MAPE) error by 8.51% and increases Root Mean Square Error (RMSE) by only 0.0138 when compared to the hybrid optical flow method, which indicate that the optimized FlowNet2.0 model has great potential for friction measurement. Measurements in continuous transonic wind tunnel tests demonstrate that FlowNet2.0 can calculate clearer and more accurate flow velocity than hybrid optical flow, and the solved friction magnitude distribution is consistent with the actual flow, which will be of great practical application in wind tunnel engineering.

Machine learning for the prediction of the local skin friction factors and Nusselt numbers in turbulent flows past rough surfaces

Turbulent flows past rough surfaces can create substantial energy losses in engineering equipment. During the last decades, developing accurate correlations to predict the thermal and hydrodynamic behavior of rough surfaces has proven to be a difficult challenge. In this work, we investigate the applicability of convolutional neural networks to perform a direct image-to-image translation between the height map of a rough surface and its detailed local skin friction factors and Nusselt numbers. Additionally, we propose the usage of separable convolutional modules to reduce the total number of trainable parameters, and PReLU activation functions to increase the expressivity of the neural networks created. Our final predictions are improved by a new filtering methodology, which is able to combine the results of multiple neural networks while discarding non-physical oscillations likely caused by over-fitting. The main study is based on a new DNS database formed by 80 flow cases at a friction Reynolds number of Reτ=180 obtained by applying random shifts to the Fourier spectrum of the grit-blasted surface originally scanned by Busse et al. (2015). The results show that machine learning can accurately predict the skin friction values and Nusselt numbers for a rough surface. A detailed comparison with existing correlations in the literature revealed that the maximum errors generated by deep learning were only 8.1% for the global skin friction factors Cf¯ and 2.9% for the Nusselt numbers Nu¯, whereas the best classical correlations identified reached errors of 24.9% and 13.5% for Cf¯ and Nu¯ respectively. The deep learning results also proved stable with respect to rough surfaces with abrupt changes in their roughness elements, and only presented a minor sensitivity with respect to variations in the dataset size.

Influence of applied pressure on the tribological behaviors of a wet multi-disc clutch during the running-in process

PurposeThis paper aims to explore the influence of applied pressure on the tribological properties of the friction component in a wet multi-disc clutch during the running-in process.Design/methodology/approachThe running-in evolutionary was explored in terms of global friction performance. The variation of friction torque and mean COF of the initial 300 engagement cycles was obtained by full-scale tests. Finally, an optical microscope was used to detect the wear characteristics of friction surfaces.FindingsThe applied pressure showed a significant influence on the tribological behaviors of wet clutches during the running-in process. The mean COF decreased and then increases with the increase of the applied pressure. A higher applied pressure contributed to more asperity summits being sheared, thus resulting in a smoother surface. Considering a suitable wore performance, properly applied pressure is necessary.Originality/valueThe results provide theoretical guidance for selecting the optimal applied pressure in the running-in of wet clutches.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-08-2022-0256/

Boxes-Based Representation and Data Sharing of Road Surface Friction for CAVs

Vehicles can easily lose control unexpectedly when encountering unforeseen hazardous road friction conditions. With automation and connectivity increasingly available to assist drivers, vehicle performance can significantly benefit from a road friction preview map, particularly to identify where and how friction ahead of a vehicle may be suddenly decreasing. Although many techniques enable the vehicle to measure the local friction as driving upon a surface, these encounters limit the ability of a vehicle to slow down before a low-friction surface is already encountered. Using the connectivity of connected and autonomous vehicles (CAVs), a global road friction map can be created by aggregating information from vehicles. A challenge in the creation of these global friction maps is the very large quantity of data involved, and that the measurements populating the map are generated by vehicle trajectories that do not uniformly cover the grid. This paper presents a road friction map generation strategy that aggregates the measured road-tire friction coefficients along the individual trajectories of CAVs into a road surface grid. In addition, through clustering the friction grids further, an insight of this work is that the friction map can be represented compactly by rectangular boxes defined by a pair of corner coordinates in space, a friction value, and a confidence interval within the box. To demonstrate the method, a simulation is presented that integrates traffic simulations, vehicle dynamics and on-vehicle friction estimators, and a highway road surface, where friction is changing in space, particularly over a bridge segment. The experimental results indicate that the road friction distribution can be measured effectively by collecting and aggregating the friction data from CAVs.

Study of Strain-rate Effect in Two-dimensional Biaxial Test on Granular Material using Discrete Element Method

Numerical study to investigate the effect of various strain rates on global friction angle in the sand has been performed. Granular material behavior is influenced by several factors, among others: pack configuration, grain macro and micro roughness, confinement pressure, loading rate, etc. Sand is a granular material composed of discrete particles that the most refined microscopic techniques are needed to study its mechanical properties. In Indonesia, research related to the Discrete Element Method is still very limited. The two-dimensional discrete element method is capable to calculate the motion and interparticle contacts of large number of small particles, and each particle is modeled as a rigid circular element. The study started with the validation of the DEM model using YADE. Particles with a local friction angle of 35° are arranged in a closed rectangular box (frictionless wall). The number of particles used in this model validation simulation is 1000 sphere-type particles with monodisperse particle gradations. The simulation was done by a drained biaxial test with confinement stress of 100 kPa, thereafter varying strain rate are applied. Based on the deviatoric stress–axial strain curve from YADE, the result can be depicted on the Mohr circle to obtain the value of the global friction angle. It is found that the different value of strain rate affects its global friction angle. Increasing the value of the strain rate can increase the material global friction angle, which increases the strain rate from 1% to 5%, 10%, 25%, and 50% will increase its global friction angle by 5%, 5%, 14%, and 18%, respectively.

Mechanical Behavior of Variable Nozzle Guide Vane Systems Based on Full-Scale Testing

Abstract A full-scale test bench for the analysis of frictional and modal behavior of nozzle guide vanes (NGV) is an advanced tool enabling high design accuracy for these components equipped with an increasing number of turbo-expanders. This subassembly is a key feature enabling operational flexibility for the expander. During the NGVs design, great attention must be paid to the natural frequencies of its kinematic chain, which are influenced by internal clearances and by friction. In this paper, the results of a testing campaign performed on an NGV assembly employing realistic blade geometry are presented together with details concerning the test bench commissioning and setup procedure. The testing campaign involves three different combinations of blade orientation and preload corresponding to typical design conditions of the expander. In addition, two bushing clearance values corresponding to different worn-out conditions were investigated. The measurements of the global friction coefficient based on actuator force detection are summarized. After that, the reconstruction of mode shapes based on experimental modal analysis is explained. The results highlight the importance of loading conditions on the actual value of friction force and their influence on blade natural frequencies. The testing campaign was used to properly validate finite element models to be used for further investigations.

Effect of Swept Shockwave Boundary-Layer Interaction Strength on Surface Skin Friction

This investigation examines the flowfield topology beneath the single fin-generated shockwave boundary-layer interaction as a function of shock interaction strength and incoming boundary-layer thickness. A systematic application of oil film interferometry produced an experimental reconstruction of global skin friction maps for various Mach number and fin angle combinations. To determine the effect of boundary-layer thickness, data from the current study were compared against existing experimental data sets with thinner incoming boundary layers. Results for identically matching flow/geometric conditions show a good agreement between trends seen across the conical region of the interaction and exhibit skin friction coefficient peaks in the same position. Cases corresponding to a relatively thicker boundary layer showed higher skin friction coefficient values along the interaction periphery and upstream regions. An angular scaling was applied to align the inviscid shocks of data sets that matched interaction strength, and the results show similar behavior. The peak skin friction coefficient shows a monotonic increase with increasing shock strength. Conversely, the upstream normalized peak skin friction coefficient depends on boundary-layer thickness and shock strength. These findings indicate that boundary-layer effects are limited to the interaction periphery, whereas viscous effects driven by shockwave–boundary-layer interactions dominate the interior region.

NF XP P94-424 standard shear test for estimating the mechanical properties of rock joints sampled from Yaounde gneisses (Cameroon)

This study is a contribution to the knowledge of rocks mechanical properties in Yaounde, with a scope on failure parameters. In most instances, this goal is achieved by carrying out XP P94-424 standard shear tests. Thus, the tests were carried out on two joint samples, using the experimental device of the Fondasol laboratory (France). However, the pairs of shear – normal stress values were plotted or computed to determine other relevant parameters. The results are expressed as graphs and value reports. (1) The global friction angle ranges around 36° for unsmoothed joints, and decreases up to 34° for smoothed joints. The friction angle ranges around 49° - 46° for unsmoothed joints, and decreases up to 3.90° for smoothed joints. The dilatancy i depend on the roughness and the type of joint surfaces; e. g. it ranged around 7° for the roughest surface while it ranged around 4° on the other. (2) At the peak the cohesion ranges around 81 kPa however, the wetness might affect this parameter up to its nullifying. At residual the cohesion ranges around 91 – 135 kPa.

Experimental study on drag reduction control of porous media wall turbulence

In order to study the control law and effect of the related mechanism of porous media on the turbulent drag reduction of a plate wall, experimental research of a plate laid with porous media was carried out in a low-turbulence, re-flow wind tunnel. First, the hot wire was used to acquire the time-averaged statistics and fluctuation data inside the boundary layer on the plate surface by single point measurement. Then, the fluorescenct oil flow was applied to obtain the global skin friction distribution downstream of the porous media. Finally, through Time-resolved Particle Image Velocimetry technique, the normal velocity flow field on the surface and the structural information of the near-wall strip were captured in quantitative terms, and the Dynamic Mode Decomposition (DMD) was adopted to analyze the strip’s structural features with the mode reduction. The results showed that the drag reduction effect of porous media had a trend of first increasing and then decreasing in the flow direction, with the maximum drag reduction rate on the surface of porous media. Meanwhile, the porous media changed the internal structure of the turbulent boundary layer, reduced the velocity gradient of the viscous bottom layer, and decreased the momentum exchange between the inner and outer layers, which suppressed the development of large-scale strip structure and promoted the lift of the spanwise vortices. The results of DMD analysis further explained that the porous media could effectively weaken the strip energy fluctuation and accelerate its spatio–temporal evolution process. Moreover, the second and higher order modes could reach a stable state in shorter time.

Design and multi-objective optimization of a new annular constructal bifurcation Stirling regenerator using response surface methodology

The irreversible losses such as the flow loss and axial heat conduction loss in traditional porous regenerators have limited the specific power and thermal efficiency of Stirling engines to a great degree. Thereby, the objective of this paper is to design and optimize a novel annular constructal bifurcation regenerator for diminishing the flow and axial heat conduction losses in the regenerator based on constructal concept and response surface methodology. First, the bifurcation type structure units with an inclined angle to the flow direction and the layered approach were applied to construct the regenerator matrix. Thereafter, the numerical simulations were employed to investigate the gas flow and heat transfer characteristics of the constructal bifurcation regenerator. Based on the numerical data, the quadratic polynomial regression models between the geometric parameters and the regenerator performance were established using response surface methodology, and the specific effects of the geometric dimensions were analyzed via 2-D and 3-D response surface plots. Subsequently, a multi-objective optimization was conducted to minimize the flow resistance and maximize the heat transfer rate by genetic algorithm. A most eclectic solution with the global friction factor f = 3.478 and the number of heat transfer units NTU = 1.135 was selected from the optimal Pareto front. Finally, the overall performance of the constructal bifurcation regenerator was compared with that of the porous regenerator and the parallel geometry regenerator. The results indicate that a low flow resistance, low axial heat conduction, and high thermal performance are obtained by the constructal bifurcation regenerator. Therefore, it is reasonable to conclude that the annular constructal bifurcation regenerator achieves a high comprehensive performance, with the potential to improve the performance of Stirling engines. The findings of this paper may provide some new ideas and guidelines for the design and optimization of the regenerator structures.

Experimental study on flat plate skin friction control by porous media based on global fluorescent oil film measurement technology

Skin friction is a primary source of total aircraft drag. It is important, therefore, in science and engineering, to achieve drag reduction control in a boundary layer. In this paper, under the experimental conditions of Reθ = 5909 (x/c = 0.55) and with a zero-pressure gradient, the drag reduction control of a plate boundary layer in porous media is studied. The global skin friction of the plate is measured using fluorescent oil film test technology. The results show that, in contrast with the downstream frictional resistance coefficient of a flat plate that possesses a smooth surface, the coefficient for porous media reduced significantly. Also, the lower the pores per inch (PPI) of the porous media, the greater the drag reduction effect. Among the three porous media with different PPI, porous media with ten PPI has the best drag reduction effect. With increasing distance from the porous media, the drag reduction effect decreases gradually. Porous media significantly increase the slope of the logarithmic region of the velocity profile of the downstream turbulent boundary layer, the dimensionless wall velocity u+ moves upward, and the velocity pulsation in the logarithmic region increases so as to reduce skin friction.

Effect of the Streamwise Orientation of a Pair of Vortex Generator on the Flow and Heat Transfer Characteristics in a Plain Channel

Abstract For a rectangular channel flow, a variant of delta winglet vortex generator (VG) in common flow up (CFU) orientation is presented to enhance the thermal performance factor by decreasing the friction losses. The new vortex generator is a simple reversal of a standard CFU orientation such that the leading edge and suction side of the conventional CFU orientation of the winglet become the trailing edge and pressure side for the reverse common flow up (RCFU) orientation of the winglet, respectively. Numerical simulations were carried out for a three-dimensional, steady, laminar, and incompressible rectangular channel flow with and without the two VG configurations. Performance analysis was done for global Nusselt number and friction factor for different inter-winglet spacings of the VG pair at a Reynolds number of 1478. An increase of 2.3% in the thermal enhancement factor was achieved in RCFU compared to CFU orientation at an inter-winglet spacing equal to 0.02 times the channel height. At the highest inter-winglet spacing equal to 0.6 times the channel height, the CFU orientation exhibited a gain of 3.2% in the enhancement factor over the RCFU orientation. Heat transfer downstream of the vortex generator was shown to be impacted in the reverse configuration (RCFU) due to stronger vortex formation compared to a standard CFU configuration at the least inter-winglet spacing.

Effect of ATF temperature on the friction-wear characteristic of a wet multi-disc clutch during the running-in process

PurposeThis paper aims to explore the effect of automatic transmission fluid (ATF) temperature on the dynamic friction-wear properties of the friction component in a wet multi-disc clutch during the running-in process.Design/methodology/approachThe running-in evolution was explored in terms of global friction performance and instantaneous friction characteristics. The variation of friction torque of the initial 300 engagement cycles was obtained by wet-clutch tests. Finally, an optical microscope was used to detect the wear mechanism of friction surfaces.FindingsThe ATF temperature showed a significant effect on the friction-wear performance in the clutch running-in process. The mean coefficient of friction decreased with the increase of the ATF temperature and decreased rapidly in the approximately initial 60 clutch engagements. The higher the ATF temperature was, the thinner the ATF film was, and more asperity summits were cut, thus leading to a smoother surface. Considering the slightly instantaneous friction fluctuation and the wear performance, a proper ATF temperature is necessary.Originality/valueThe results provide theoretical guidance for selecting the optimal ATF temperature during the running-in process.

3D CFD study of hydrodynamics and mass transfer phenomena for spiral wound membrane submerged-type feed spacer with different node geometries and sizes

Modification of the spacer geometry is a promising approach to increase the efficiency of reverse osmosis (RO) spiral wound membrane modules. Column nodes and spherical nodes are considered in this three-dimensional computational fluid dynamic (CFD) study to evaluate the hydrodynamic and mass transfer performance of submerged spacers with different node geometries and sizes. Small-scale CFD analysis results reveal that the column node has better mass transfer performance than the spherical node geometry because column nodes divert more flow to the filaments, leading to higher local velocity at the region between the filament and wall. Furthermore, when the dimensionless node diameter ratio of the column nodes increases from 0.3 to 1.2, Sherwood number and wall shear increase by 25% and 8% respectively at the expense of higher global friction factor (44%). A sea water RO full-scale analysis revealed that column node spacers yield higher average flux than spherical nodes and conventional spacers at high feed inlet velocity (> 0.1 m/s), because the mixing effects by the spacer that improve mass transfer are more prominent.

The ‘miniature silo’ test: A simple experimental setup to estimate the effective friction coefficient between the granular solid and a horizontally-corrugated cylindrical metal silo wall

Corrugated walls are widely employed in the construction of metal silos. Despite the long history of testing to establish bulk material parameters for silo design, there does not appear to be an established test procedure to directly determine the effective friction coefficient for a corrugated wall other than an adaptation of a classical direct shear test. EN 1991-4: 2006 prescribes a simple weighted average formula for this coefficient based on the internal friction angle of the granular solid and a ‘flat’ wall friction coefficient. This paper describes a set of miniature-scale silo tests performed at the University of Bologna intended to establish a simple but useful procedure to directly estimate an average global friction coefficient between the granular solid and a corrugated silo wall. These ‘miniature silo’ tests are simple enough to be performed in any civil engineering laboratory with standard equipment. • Particle-wall friction coefficient is fundamental for structural design of silos. • No tests are available to measure the effective friction for a corrugated wall. • A novel straightforward experimental test is proposed to fill this gap. • The miniature-silo test can be built using basic tools easy to be found in any lab. • The obtained results are in accordance with EN-1991-4 average formula predictions.

Stable channel flow with spanwise heterogeneous surface temperature

Recent studies have demonstrated that large secondary motions are excited by surface roughness with dominant spanwise length scales of the order of the flow's outer length scale. Inspired by this, we explore the effect of spanwise heterogeneous surface temperature in weakly to strongly stratified closed channel flow (at$Ri_\tau =120$, 960;$Re_\tau = 180$, 550) with direct numerical simulations. The configuration consists of equally sized strips of high and low temperature at the lower and upper boundaries, while an overall stable stratification is induced by imposing an average temperature difference between the top and bottom. We consider the influence of the width of the strips (${\rm \pi} /8 \leq \lambda /h \leq 4{\rm \pi} $), Reynolds number, stability and upper boundary condition on the mean flow structure, skin friction and heat transfer. Results indicate that secondary flows are excited, with alternating high- and low-momentum pathways and vortices, similar to the patterns induced by spanwise heterogeneous surface roughness. We find that the impact of the surface heterogeneity on the outer layer depends strongly on the spanwise heterogeneity length scale of the surface temperature. Comparison to stable channel flow with uniform temperature reveals that the heterogeneous surface temperature increases the global friction coefficient and reduces the global Nusselt number in most cases. However, for the high-Reynolds cases with$\lambda /h \geq {\rm \pi} /2$, we find a reduction of the friction coefficient. At stronger stability, the vertical extent of the vortices is reduced and the impact of the heterogeneous temperature on momentum and heat transfer is smaller.

A transaction cost perspective on blockchain governance in global value chains

AbstractThis study advances theoretical insights into blockchain adoption in the context of global value chains from a transaction cost theory perspective. The research has adopted an exploratory qualitative approach using the Netnography method to scrutinize the case of TradeLens—a thriving blockchain‐enabled ecosystem that Maersk and IBM jointly developed. This study applies textual and audiovisual data from company websites and social media. Our findings indicate blockchain technology's salient and strategic relevance in streamlining business processes, improving efficiency, enhancing visibility, transparency, and traceability for value creation in the global value chains. This investigation supports the notion that blockchain, as a disruptor, will transform global trade with the digital tools to share real‐time information and collaborate security to reduce search and information cost, policing and enforcement cost in global economic transactions and administrative friction in trade. In contrast, the bargaining cost will increase if the information for the transaction is hard to verify where human actor intervention will be required, implying relatively higher designing costs in codifying the agreements in smart contracts.