Friction Variation Research Articles

Speed excursion simulation of PIG using improved friction models

This study proposes two novel friction models of pipeline inspection gauges (PIGs) to simulate and predict speed excursions in long pipeline system pigging operations. Speed excursion of PIG indicates its sudden acceleration mainly caused by gas compressibility and frictional variation in low-pressure and low-flowrate gas pipelines. The first friction model adopts a dynamic friction table coupled with an exponential friction model to simulate the speed excursion caused by variations in friction. The second friction model utilizes a linear equation for friction variation caused by changes in wall thickness and pipe bends, then weight parameters are applied to determine the influence of each factor. These two friction models are tuning models based on field data to simulate speed excursions caused by frictional variation, which can be strategically selected according to the purpose of the simulation. In the numerical model, the transient gas flow equations are solved by the method of characteristics (MOC), and then the Runge–Kuta method is used to solve the dynamic equation of the PIGs. Simulation results applying the proposed friction models are compared to the field pigging data for three different routes operated by the Korea Gas Corporation (KOGAS), and the obtained simulation results are in good agreement with the field pigging data. The first model, tuned friction model, was able to simulate the average pigging velocity and speed excursions of the total distance ratio with high accuracy. The second proposed model, weighted friction model, was slightly less accurate than the first friction model, however it was able to predict the average pigging velocity and speed excursions under different operating conditions. These results mean that the speed excursion can be simulated and predicted with high accuracy using the proposed friction models through the tuning process. Therefore, these two novel friction models would provide insights for the operators to simulate and predict the unstable movement of the PIGs in their pipeline networks.

Heat and mass transfer in non-coaxial rotation of radiative MHD Casson carbon nanofluid flow past a porous medium

The heat and mass transfer of a radiative Casson nanofluid with single-wall and multi-wall carbon nanotubes in a non-coaxial rotating frame is analyzed in this article. The effects of thermal radiation, magnetic field and porosity are considered. Casson human blood is used to suspend both types of carbon nanotubes. The governed dimensional momentum, energy and concentration equations associated with initial and moving boundary conditions are converted into dimensionless expression by applying appropriate dimensionless variables. The exact solutions are determined by solving the dimensionless governing partial differential equations using the Laplace transform method. The obtained solutions are verified by comparing the present results with the published results. The validity of the solutions is assured since a precise agreement between the results is accomplished. The variation of the skin friction, Nusselt number, and Sherwood number for various values of the embedded parameters are presented in tables. The impacts of embedded parameters on the velocity, temperature and concentration profiles are illustrated in graphs. The distribution of the velocity and temperature is enhanced by the nanoparticles volume fraction but a reverse effect is observed for concentration profile. The radiation parameter has amplified the velocity and temperature of the Casson nanofluid. The emergence of porosity effect has aided to the smoothness of fluid flow but the presence of magnetic field reports the opposite effect on the velocity.

Assisting and opposing flow of a MHD hybrid nanofluid flow past a permeable moving surface with heat source/sink and thermal radiation

The aim of the current investigation is to study the assisting and opposing flow effects on hybrid nanofluid ( SiO 2 - MoS 2 /water) flow past a moving surface under the impact of heat source/sink, thermal radiation and velocity slip. Also, the moving surface is exposed to convective heating and surface is assumed to be permeable in an attempt to achieve the suction/injection of hybrid nanofluid boundary layer through the surface. As a novelty, we have presented a comparative analysis of all the results for assisting and opposing flow cases. Similarity transformations are utilized to transcribe the momentum and thermal equations in non-dimensional form. The “bvp4c” solver is used to solve the hybrid nanofluid flow problem numerically. Effects of the assisting and opposing flow with nanoparticles volume fraction, heat source/sink, Biot number, thermal radiation parameter, velocity slip parameter and suction/injection parameter on the temperature and velocity profiles are studied. The variations in skin friction and heat transfer coefficient are discussed through tables outlined and three-dimensional figures. Results reveals that hybrid nanofluid velocity is higher in case of assisting flow in comparison to opposing flow. The role of increasing values of Biot number and thermal radiation parameter is to surge the temperature of the hybrid nanofluid ( SiO 2 - MoS 2 /water) flow as well as rate of heat transfer at the surface. The nanoparticles volume fraction (of MoS 2 and SiO 2 ) also enhances the temperature at the wall. It is revealed that slip parameter has contrary effects on both heat transfer and skin friction coefficient for assisting and opposing flow.

Robust fuzzy sliding mode controller for a skid-steered vehicle subjected to friction variations.

Skid-steered vehicles (SSV) are gaining huge importance in the market due to their applications like construction, agricultural work, material handling etc. The accuracy of performing such tasks require a robust control algorithm. The design of such controller is very challenging task due to external disturbances caused by wheel-ground interaction and aerodynamic effects. This paper proposes robust fractional and integral order fuzzy sliding mode controllers (FSMC, FFSMC) for a skid-steered vehicles with varying coefficient of friction and a displaced center of gravity (CG). FFSMC controller reduces the outcome of forces generated as a result of ground tire interaction during skidding and friction variations. The proposed controllers are implemented for a four-wheel SSV under high-speed turning motion. A simulation environment is constructed by implementing the SSV dynamics with wheel-road model and the performance of the proposed algorithms is tested. The simulation test is conducted for a Pioneer-3AT (P-3AT) robot SSV vehicle with displaced CG and variable coefficient of tires friction. Simulation results demonstrate the efficiency of the proposed FFSMC algorithm in term of reduced state errors and minimum chattering. The proposed controller compensates the effect of different responses of the wheels generated as a result of variable CG. The chattering phenomenon generated by conventional SMCs is also minimized by fuzzy tuning approach.

Simplified analytical method for static and stability analysis of circular tapered friction piles

This paper presents a new, simplified analytical method to study the static and stability response of circular tapered friction piles in homogeneous or non-homogeneous Pasternak soil. The governing differential equation (GDE) of the proposed element is derived in a classical manner and solved using the Differential Transformation Method (DTM). This complex analysis is reduced to solve a system of two linear algebraic equations, which solution is readily available and easy to code. The proposed formulation is of practical interest for both onshore and offshore structures, and it can be used to conduct: (a) lateral load–deformation, (b) elastic stability, and (c) second-order analysis of prismatic and tapered friction piles. Tapered friction piles with various distributions of end-bearing resistance and skin friction can be investigated. The proposed formulation includes the effect of (i) any end-boundary condition at the ends of the element (i.e., translational and rotational constraints), (ii) a uniform or linear variation of skin friction, and (iii) a uniform or linear variation of the modulus of subgrade reaction. Five examples are presented to validate the accuracy of the proposed approach.

Revealing Pt-seed-induced structural effects to tribological/electrical/thermoelectric modulations in two-dimensional PtSe2 using scanning probe microscopy

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) provide an opportunity to investigate diverse scientific phenomena at an atomic level and have effective technological potential. In recent times, unlike conventional TMDCs, platinum diselenide (PtSe2) has garnered considerable attention owing to its i) fascinating electrical and optical features coupled with mechanical strain and ii) scalable synthesis method. However, its local electrical/tribological/mechanical properties are yet to be examined in detail. In this study, we prepared two different types of PtSe2 layers by controlling the thickness of the Pt-seed film: i) one with horizontal alignments, which are made from ultrathin Pt films and ii) one with vertical and horizontal alignments, which are made from a relatively thick Pt film. Then, the local tribological, mechanical, and electrical properties of PtSe2 were evaluated mainly with scanning probe microscopy (SPM). The local friction study unveiled the marked friction variation depending on the layer directions. An additional study on the local mechanical property indicated that the apparent modulus difference between the two growth directions can lead to dissimilar friction behaviors. Furthermore, local current probing using SPM showed that PtSe2 with both layer directions provides ohmic features to both directions, although the magnitude of conductance along the horizontal direction is ~100 times smaller than that along the vertical one. On the contrary, PtSe2 with only in-plane alignments is configured with multiple horizontal PtSe2 layers, densely stitching themselves together one after another with a very narrow trench region at their boundary. Surprisingly, a local current–voltage spectroscopy analysis showed a small current gap on the bridged trench region, in contrast to the ohmic behavior of the grain interior. This indicates that the local metal-to-semiconductor transition is available, owing to thin PtSe2 layers in the trench regions. The following study at macroscale showed how the overall electrical and thermoelectric properties of PtSe2 can be influenced by local structures triggered by the variation in Pt-seed thickness. The results not only provide a new insight on better understanding the intrinsic features of 2D PtSe2, but also offer important characterization guidance on tailoring their functionalities.

Rheology of two-dimensional granular chute flows at high inertial numbers

Contrary to the popular inertial number-based rheology of dense granular flows, recent studies suggest a non-monotonic variation of the effective friction coefficient μ(I) with the inertial number I in plane shear flows. While the popular rheology assuming monotonic variation of μ(I) with I suggests existence of an upper limit of inclination angle for steady chute flows, the non-monotonic variation suggests the possibility of two different flow states for chute flows at a given inclination angle. In this work, we perform DEM simulations of chute flow of frictional inelastic disks and show that steady, fully developed flows are possible at inclinations much higher than those predicted from the monotonic μ−I rheology. We observe steady flows up to inertial number I≈2 and find non-monotonic variation of the effective friction at high inertial numbers for chute flow of disks. The flows at high inertial numbers exhibit a constant density bulk region supported on top of a very dilute energetic basal layer of particles. We show that, in addition to a modified effective friction law that accounts for the non-monotonic variation of μ(I) and the dilatancy law relating the solids fraction ϕ with I, the rheological description also needs to account for the stress anisotropy by means of a normal stress difference law. By accounting for the presence of the normal stress difference, we also establish that only a single flow state is possible at any given inclination angle despite the non-monotonic variation of the effective friction coefficient.

Modeling the Greenland englacial stratigraphy

Abstract. Radar reflections from the interior of the Greenland ice sheet contain a comprehensive archive of past accumulation rates, ice dynamics, and basal melting. Combining these data with dynamic ice sheet models may greatly aid model calibration, improve past and future sea level estimates, and enable insights into past ice sheet dynamics that neither models nor data could achieve alone. Unfortunately, simulating the continental-scale ice sheet stratigraphy represents a major challenge for current ice sheet models. In this study, we present the first three-dimensional ice sheet model that explicitly simulates the Greenland englacial stratigraphy. Individual layers of accumulation are represented on a grid whose vertical axis is time so that they do not exchange mass with each other as the flow of ice deforms them. This isochronal advection scheme does not influence the ice dynamics and only requires modest input data from a host thermomechanical ice sheet model, making it easy to transfer to a range of models. Using an ensemble of simulations, we show that direct comparison with the dated radiostratigraphy data yields notably more accurate results than calibrating simulations based on total ice thickness. We show that the isochronal scheme produces a more reliable simulation of the englacial age profile than traditional age tracers. The interpretation of ice dynamics at different times is possible but limited by uncertainties in the upper and lower boundary conditions, namely temporal variations in surface mass balance and basal friction.

The Snow-Friction of Freestyle Skis and Snowboards Predicted From Snow Physical Quantities

Previous research has shown that friction between ski and snow can vary substantially due to changes in snow conditions. The variation of friction affects the speed a freestyle skier or snowboarder (athlete) reaches during the in-run of a jump. Athletes risk severe injuries if their take-off speed is not within the right margin to land in the “sweet spot” zone. To reduce the risk of injury, snow park designers and competition managers need to calculate the speed athletes reach during the in-run. However, despite multiple attempts over the last decades, to date no model can predict ski-snow friction from snow physical quantities. Hence, simulations of in-run speeds suffer from insufficient validity. For the first time, this work combines kinematic athlete data and comprehensive snow surface measurements to infer the coefficient of friction of freestyle skis and snowboards across a wide range of snow conditions. Athletes’ point mass kinematics were recorded at more than 200 straight gliding runs with differential global navigation satellite systems. The subjects’ air drag and lift were deployed from wind tunnel measurements. Along with the kinematic data and data from wind measurements, a mechanical model of the athlete was established to solve the equation of motion for the coefficient of friction between ski/snowboard and snow. The friction coefficients for ski (snowboard) ranged from 0.023 ± 0.006 (0.026 ± 0.008) to 0.139 ± 0.018 (0.143 ± 0.017) and could be explained well (Radj2 = 0.77) from the measured snow parameters using a multivariate statistical model. Our results provide a new quantitative tool for practitioners to predict the friction of skis and snowboard on snow of various conditions, which aims to increase athletes’ safety in slopestyle and big air.

Non-linear convective flow of the thin film nanofluid over an inclined stretching surface

To enhance the surface properties of solids the mechanism of thin films is frequently used. Penetration, degradation, stiffness, illumination, diffusion, absorption, and electric performance are all characteristics of a bulk substance medium that a thin film can improve. In nanotechnology, thin film processing can be extremely useful. Therefore, the time-dependent nonlinearly convective stream of thin film nanoliquid over an inclined stretchable sheet with magnetic effect is investigated in current work. The features of mass and heat transport processes are explained using important factors like thermophoresis and Brownian movement. Nonlinear partial differential equations are obtained to model the time-dependent liquid film flow over an inclined surface, which are then turned into couple ordinary differential equations utilizing appropriate alterations. The results of the computation of the model problem are collected using an analytical approach Homotopy Analysis Method and presented the final finding numerically and graphically. During the flow assessment, the impact of individual flow factors such as magnetic, Brownian, and thermophoresis parameters on regular profiles (temperature, velocity, and concentration) are analyzed and found to be quite remarkable. Furthermore, the consequence of M and Nt factors on the velocity, concentration and thermal distribution leads to diminishing conduct. On the other hand, the thermal profile of the liquid film rises in response to the thermophoresis factor. The % wise variation in the skin friction, Nusselt number and Sherwood number versus physical parameters has been obtained and discussed.

OHAM analysis of Newtonian heating in mixed convective flow of CNTs over a stretched cylinder

This work reports mathematical modeling and analysis of mixed convection flow of nanofluids with stagnation point by a stretching cylinder. Carbon nanotubes are dispersed as nanomaterial in the baseliquid of water. Heat transfer characteristics are explored through Newtonian heating. Transformation method is employed in order to obtain ODEs. Furthermore series solutions are developed. Variations in flow, temperature, skin friction and local Nusselt number under influential variables have been plotted. It is elaborated that fluid velocity intensifies with rise in curvature parameter, conjugate parameter, mixed convection parameter, nanoparticle volume fraction and velocity ratio parameter. Similarly decay in temperature of the fluid is analyzed for higher velocity ratio parameter while it enhances with increment in nanoparticle volume fraction, mixed convection parameter, conjugate parameter and curvature parameter. Skin friction can be minimized via higher estimations of mixed convection parameter, velocity ratio parameter and nanoparticle volume fraction. Heat transfer rate or cooling process (Nusselt number) is regulated through higher conjugate and curvature parameters. During comparative analysis of SWCNTs with MWCNTs, better performance is shown by SWCNTs. Skin friction coefficient in limiting sense is also compared with previously published articles.

Thermal Radiation and Magnetohydrodynamics Effect on Unsteady Squeezing Non-Newtonian Nanofluids with Heat and Mass Transfer

The research article primarily deals with non-Newtonian squeezing nanofluid flow between parallel plates by taking into account different phenomena in the modeled problem. The thermal radiation and magneto hydrodynamics impact in fluid flow model is mainly focused in this analysis. The proposed nanofluid model also encompasses thermophoresis and the Brownian movement effects. The basic equations of nanofluids model such as velocity, heat and concentration equations are transformed into ordinary differential equations with the help of appropriate similarity transformations. As a tool, the semi numerical scheme is used for solving the proposed problem with the greatest possible accuracy for the purpose of illustration and analysis. The basic physical parameters involved in velocity, heat and concentration profiles in the nanofluids flow are discussed in detail. The variation of skin friction, Nusselt number and Sherwood number along with their impacts on the velocity, heat and concentration are determined. It is also focused to show the influence of different physical parameters graphically as well as in tabulated form. Excellent agreement between the results of semi analytical method and already published work is obtained, indicating the validity of the semi analytical approach. The study presented herein fills the gap in the literature, and will have a broad impact in industrial and biomedical fields.

A Novel Signal Processing Method for Friction and Sliding Wear

Abstract This current study proposed a new computationally efficient and comparatively accurate algorithm for calculating both static and dynamic coefficients of friction from high-frequency data. Its scope embraced an application in a real-time friction-based system, such as active braking safety systems in automobile industries. The signal sources were from a heavy-duty reciprocating dry sliding wear test platform, focused on experimental data related to friction induced by stick-slip phenomena. The test specimen was a polytetrafluoroethylene (PTFE)-coated basalt/vinyl ester composite material, tested at a large scale. The algorithm was primarily aimed to provide scalability for processing significantly large tribological data in a real-time. Besides a computational efficiency, the proposed method adopted to evaluate both static and dynamic coefficients of friction using the statistical approach exhibited a greater accuracy and reliability when compared with the extant models. The result showed that the proposed method reduced the computation time of processing and reduced the variation of the absolute values of both static and dynamic frictions. However, the variation of dynamic friction was later increased at a particular threshold, based on the test duration.

Short comments on chaotic behavior of a double pendulum with two subharmonic frequencies and in the main resonance zone

AbstractThe parametric pendulum and others different pendular mechanisms were extensively analyzed in current literature because of the chaotic motions. Recently, practical reasons, like energy harvesting, motivated the study of some pendular systems. The resonance and the chaos may occur in multiple and submultiple frequencies based on the natural frequency of the pendulum. In the present paper, a double pendulum is analyzed with two subharmonic frequencies and in the main resonance zone. The results found demonstrate high similarities of the double pendulum with the parametric pendulum when compared the bifurcation diagrams based on varying the amplitude. The conditions in the numerical simulation include a variation in the viscous friction in the joints and different amplitudes and frequency of excitation. The differential equations used dimensionless parameters representing time, frequency, amplitude, friction, position and velocities. Concerning the results, all tests performed have pointed that the same type of motion takes place in the two pendulums after the transient time have already elapsed.

A Sticky Situation or Rough Going? Influencing Haptic Perception of Wood Coatings Through Frictional and Topographical Design

Improving the tactile aesthetics of products that can be described as touch intensive is an increasing priority within many sectors, including the furniture industry. Understanding which physical characteristics contribute to the haptic experience of a surface, and how, is therefore highly topical. It has earlier been shown that both friction and topography affect tactile perception. Thus, two series of stimuli have been produced using standard coating techniques, with systematic variation in (physical) friction and roughness properties. This was achieved through appropriate selection of matting agents and resins. The stimuli sets were then evaluated perceptually to determine the extent to which discrimination between pairs of surfaces followed the systematic materials variation. In addition to investigating the role of the physical properties in discrimination of the surfaces, their influence on perceived pleasantness and naturalness was also studied. The results indicate that changes in tactile perception can be understood in terms of friction and roughness, and that varying the matting agents (topography) and resins (material properties) in the coatings provide the controlling factors for furniture applications. Perceived pleasantness is associated with low friction and smoother topography, whilst perceived naturalness is found to be described by an interaction between tactile friction and the average maximum peak height of the surface features.Graphic

Influence of radiative heat flux in nonlinear convection of quartic order in Casson fluid past a vertical permeable plate with variable suction and Hall current

The current study centralizes on unsteady free convection slip flow of Casson fluid past a vertical permeable plate with Hall current, radiative heat flux, and variable suction. The nonlinear convection is subjected to quartic order. Perturbation method is used to convert the non-linear coupled partial differential equation of the momentum and energy to a system of ordinary differential equations. The dimensionless governing equations are solved analytically for velocity and temperature profiles. The graphs are plotted for sundry parameters for variations in the distinct flow fields w.r.t distance from the plate. Variation in the skin friction for the axial and transverse cases are presented in the form of graphs for various parameters. It is observed that with the increase in the order of non-linear convection and value of radiation parameter, the velocity field increases in Casson fluid. The increase in heat absorption parameter and Prandtl number decreases the temperature profile and increase in radiative heat flux parameter increases the temperature profile.

Effect of two parallel intruders on total work during granular penetrations.

The intrusion of single passive intruders into granular particles has been studied in detail. However, the intrusion force produced by multiple intruders separated at a distance from one another, and hence the effect of their presence in close proximity to one another, is less explored. Here, we used numerical simulations and laboratory experiments to study the force response of two parallel rods intruding vertically into granular media while varying the gap spacing between them. We also explored the effect of variations in friction, intruder size, and particle size on the force response. The total work (W) of the two rods over the depth of intrusion was measured, and the instantaneous velocities of particles over the duration of intrusion were calculated by simulations. We found that the total work done by the intruders changes with distance between them. We observed a peak in W at a gap spacing of ∼3 particle diameters, which was up to 25% greater than W at large separation (>11 particle diameters), beyond which the total work plateaued. This peak was likely due to reduced particle flow between intruders as we found a larger number of strong forces-identified as force chains-in the particle domain at gaps surrounding the peak force. Although higher friction caused greater force generation during intrusion, the gap spacing between the intruders at which the peak total work was generated remained unchanged. Larger intruder sizes resulted in greater total work with the peak in W occurring at slightly larger intruder separations. Taken together, our results show that peak total work done by two parallel intruders remained within a narrow range, remaining robust to most other tested parameters.

Impact of Hall Current and Nonlinear Thermal Radiation on Jeffrey Nanofluid Flow in Rotating Frame

This research article deals with the nonlinear thermally radiated influences on non-Newtonian nanofluid considering Jeffrey fluid in a rotating system. The governing equations of the nanofluid have been transformed to a set of differential nonlinear equations, using suitable similarity variables. The Homotopy Analysis Method (HAM) and Runge–Kutta Method of order 4 (RK Method of order 4) are used for the solution of the modeled problem. The variation of the skin friction, Nusselt number, Sherwood number, and their impacts on the velocity distribution, temperature distribution, and concentration distribution have been examined. The influence of the Hall effect, rotation, Brownian motion, porosity, and thermophoresis analysis are also investigated. Moreover, for comprehension of the physical presentation of the embedded parameters, Deborah numberβ, viscosity parameterR, rotation parameterKr, Brownian motion parameterNb, porosity parameterγ, magnetic parameterM, Prandtl numberPr, thermophoretic parameterNt, and Schmidt numberSchave been plotted and deliberated graphically. For large values of Brownian parameter, the kinetic energy increases, which in turn increases the temperature distribution, while the thermal boundary layer thickness decreases by increasing the radiation parameter, and the Hall parameter increases the motion of the fluid in horizontal direction. Also, the mass flux has been observed as a decreasing function at the lower stretching plate.

Experimental and modelling study of interaction between friction and galling under contact load change conditions

The galling process remains one of the least understood phenomena in metal forming. The transfer of material from a work-piece onto the tool surface can cause an evolutionary increase in friction coefficient (COF) and thus the use of a constant COF in finite element (FE) simulations leads to progressively inaccurate results. For an aluminium work-piece, material transfer, which has history and pressure dependency, is determined by a dynamic balance between the generation and ejection of wear particles acting as a ‘third body’ abrasive element at the contact interface. To address this dynamic interactive phenomenon, pin-on-disc tests between AA6082 and G3500 were performed under step load change conditions. The COF evolutions, morphologies of the transfer layer and its cross-section were studied. It has been found that contact load change will disequilibrate and rebuild the dynamic balance and high load will increase the generation and ejection rate of third body and vice versa. Moreover, based on the experimental results, an interactive model was developed and presented to simulate the dynamic formation process of the aluminium third body layer under load change conditions, enabling multi-cycle simulations to model the galling distribution and friction variation.

On the prediction of power loss in helical gearbox via simulation approach

Abstract Frictional loss, load variation, viscosity and speed are major causes of power loss in helical gears under normal operating conditions. The study presents the major theoretical findings to predict the possible power loss in a helical gear box. First, an analytical technique was employed to model the frictional loss and coefficient of friction resulting from the heat generated for a pair of helical gear in mesh. Then, a finite element method and Comsol Multiphysics was applied to model the helical gear structure as well as the surface displacements under static and moving conditions of the pinion. It was observed that the highest amplitude in surface displacement was 14 × 10 − 6 (m) against when the pinion was stationary which is 20 × 10 − 6 (m). This can cause a significance wear depth and tooth surface pressure which eventually will lead to increase in fatigue. More so, As the frictional loss increase, there is an increase in the corresponding power loss factor with the highest being 180 for a frictional loss of 270. This shows that friction between a pair of meshing helical gear teeth influences power loss in a gearbox under normal operating condition. Thus, the results are an indication that good predictions during gear design would lead to a better gear transmission efficiency.