Friction Balance Research Articles

A two component friction balance based on ultrathin fiber Bragg grating pairs

We have designed a two component friction balance based on an ultrathin fiber Bragg grating pairs to monitor external friction resistance, and statically calibrated it with weights. Friction resistance can cause the support beam of the fiber optic friction balance to tilt, while also driving the strain of the fiber optic grating. Therefore, the change in the center wavelength of the grating can be used to measure external frictional resistance. The experimental results show that the static calibration output of the friction balance is stable, reproducible. The wavelength change of the grating is proportional to the size of the load, and the two exhibit a good linear relationship. The range of the fiber optic friction balance is ±0.03 N. The sensitivity of the balance sensor in the X component is about 62.28 nm/N, and the sensitivity in the Y component is about 25.36 nm/N. In addition, we also conducted tests on the built-in temperature compensation of the fiber Bragg grating pairs.

Modeling of a screw extruder 3D printer using pellets or crushed polymer waste as the raw material

In this article, the process of moving polymer material in the screw extruder of a 3D printer, which uses granules or crushed polymer waste as raw materials, is chosen as the object of mathematical modeling. It is noted that the modeling of screw extruders is a highly relevant task, as it is an essential tool for optimizing production processes in the polymer industry and other industries where they are used. It allows you to study and optimize the material cylinder's processes thoroughly. It is noted that the modeling of screw extruders for 3D printers, which use granules or shredded plastic waste, is a critical factor in supporting innovation, increasing production efficiency, improving product quality, and developing new technological solutions in various industries. It was noted that during the movement of the material along the channel of the extruder screw, several of its states continuously changed from a solid at the entrance of the channel to a viscous liquid at the exit. In the feed zone, the polymer is solid and moves along the material cylinder due to friction. A physical model was used in the simulation, in which compacted polymer particles do not move relative to each other during movement through the channel. This is because the internal friction forces in the polymer greatly outweigh the friction of the polymer on the steel, and the particles move as a single elastic compressible medium due to the balance of dry friction between the cylinder wall and the screw. The geometrical parameters of the extruder in the feed zone are shown. A diagram of the expanded extruder channel for calculating productivity is given. A diagram of the movement of material in it was drawn up to determine the productivity of the extruder feed zone. A mathematical model of productivity was obtained depending on the diameter of the screw, the frequency of rotation, the depth of the screw channel, and the angle of elevation of the screw line of the screw cutting. The pressure in the extruder channel was calculated. A scheme for calculating the forces acting on the material in the feeding zone is given. A formula was obtained for determining the pressure in the material loading zone from the hopper, which connects the characteristics of the polymer material and the geometric parameters of the loading hopper. Keywords: 3D printer, screw extruder, modeling; polymer material; loading area; bunker; productivity; pressure.

A study on shear transfer behavior between fractured layers of a concrete composite structure

Aiming at problems of interlayer continuous destruction and shear transfer weakening of concrete composite structures caused by fracturing of the former, three-dimensional measurements and digital reconstruction of a composite structure cracked interlayer interface appearance were carried out, through shear modeling tests and reverse engineering. Additionally, the shear transfer behavior and its origins were analyzed and explored quantitatively and discretely. The results showed that a digital reconstruction based on reverse engineering can precisely implement an analysis of the interlayer interface appearance and force features. Shear capacity between structural layers was a result of coordination and balance of bulge fracture and surface friction on the interface. The differences of shear behavior between different layers were mainly due to the shape and quantity of bulges on the interface. The interlayer shear transfer ability of a longitudinal and transverse (bidirectional) roughness design was better than that of a longitudinal or transverse (unidirectional) roughness design, but the latter was more stable. Mattock and Barton's interlayer shear transfer formula was partly modified since in theory the normal force vs. shear force correlation curve of shear behavior does not start from zero.

Analysis of the Energy Balance of Friction on the Rolling Contact

Analysis of the Energy Balance of Friction on the Rolling Contact

Effect of minimum friction coefficient on vibration stability in cold rolling mill

Mill chatter is a major restriction in the high-speed rolling of high-strength and thin strips. To maintain mill stability, the friction coefficient must be kept within a certain range. Unfortunately, there is no model to calculate the lower limit of the friction. In this paper, a new model is developed to capture the minimum friction coefficient. This model is proposed based on mixed lubrication theory and monotonicity analysis in the friction curve. The verification results showed that the established model could accurately predict the minimum friction and the friction balance in tandem rolling mills. The model was utilized to design the optimal rolling conditions to expand the stability range of the friction and improve mill vibration stability.

Evaluation and Balance of Cognitive Friction: Evaluation of Product Target Image Form Combining Entropy and Game Theory

With the great progress of product development technology, product forms have been greatly enriched by cognitive differences; users and designers have formed a “cognitive friction” phenomenon in the product evaluation process, which results in designers being unable to grasp user emotions accurately and risks of product development failure. This paper aims to balance the cognitive differences between cognitive subjects (users and designers) and evaluates the product image form. First, image entropy is used to evaluate and extract the weight of the product target image. Second, fuzzy Theil entropy is used to evaluate the cognitive friction between cognitive subjects, and its existence and size are visually presented. Then, a cognitive friction balance model is built by combining game theory, the comprehensive evaluation weight between cognitive subjects is obtained, and the product image form is ranked and optimized. Finally, all the research steps are described in the form of a household hair dryer. The results show that fuzzy Theil entropy and game theory have significant advantages in the evaluation and balance of cognitive friction in product design. Thus, the cognitive friction evaluation and balance model constructed from the fuzzy Theil entropy and game theory do not only enable different cognitive subjects to achieve cognitive symmetry, but also screen out product forms that meet the cognitive needs of users. This finding provides the theoretical basis and practical significance for the establishment of a closed-loop model in cognitive friction balance and the reduction of cognitive differences between cognitive subjects in the entire process of product design. It also introduces new ways of thinking and methods for cognitive science research.

On mechanisms of impurity leakage and retention in the tokamak divertor

Impurity seeding into a tokamak divertor for radiative cooling is considered as a tool for achieving detached/semi-detached regimes required to meet the condition of acceptable heat loads on divertor plates. Experiments aimed at searching for an operational window with a significant reduction of poloidal heat fluxes due to the impurity radiation and without decrease of confinement are performed on many tokamaks. A critical issue in these experiments is how large a fraction of impurities is retained in the divertor region and how much is extracted upstream to the scrape-off layer. In the present paper a physical mechanism of impurity transport from a divertor towards upstream and back to the divertor is analyzed. It is demonstrated that the widespread concept that the impurity leaks if the parallel thermal force exceeds the friction due to main ions and is retained otherwise—is not correct. In this paper, we contend that the impurity leaks if it crosses the stagnation point of the impurity ion poloidal velocity profile before being ionized, and is retained if it ionizes closer to the target than the location of that stagnation point. Thus the leakage efficiency depends on the relative spatial positions of the impurity atom ionization source and the stagnation point of the impurity ion poloidal velocity profile. The impurity ion poloidal velocity is to large extent the sum of the poloidal projection of its parallel velocity and the E × B drift velocity, where the former is derived from the parallel impurity force balance equation. It is demonstrated that the solution of this equation may be approximated by the balance of friction and thermal forces in all regimes, while other terms are smaller. This allows for expressing the impurity parallel velocity through the main ion one and makes the distribution of the parallel (poloidal) fluxes of the main ions, including Pfirsch–Schlüter fluxes and E × B drift fluxes, to be an important element of the impurity transport. It is shown that the impurity distribution in the edge plasma is rather sensitive to the value of the impurity ion ionization rate. This analysis is supported by simulation results obtained for the ASDEX Upgrade tokamak with various seeding rates of N and Ne with the SOLPS-ITER code. The importance of the inclusion of self-consistent drift flows is demonstrated by comparison to results of corresponding simulations with the drifts turned off.

Fuzzy method is used to solve the friction balance problem

Fuzzy method is used to solve the friction balance problem

On the relationship between radial structure heterogeneities and efficiency of chromatographic columns

The general dispersion theory of Aris is applied to predict the virtual asymptotic dispersion behavior of packed columns. The derived model is also used to estimate the actual pre-asymptotic dispersion behavior of modern 2.1 mm × 50 mm columns packed with sub-2 μm fully porous particles (FPPs) during the transient dispersion regime. The model accounts for the actual radial distribution of the flow velocity across the column diameter. From the wall to the center of the column, focused-ion-beam scanning electron microscopy (FIB-SEM) experiments were recently performed to reveal the existence of a thin (0.15dp wide, dp is the average particle diameter) hydrodynamic boundary layer (THBL), a thin (3dp wide) and loose orderly packed layer (TLOPL), a 60dp wide and dense randomly packed layer (WDRPL), and a large (≃460dp) randomly packed bulk central region [1].The theoretical calculations of the actual pre-asymptotic reduced van Deemter curves (2.1 mm × 50 mm column, sub-2 μm BEH-C18 FPPs, n-hexanophenone analyte, acetonitrile/water eluent, 80/20, v/v, flow rate from 0.05 to 0.35 mL/min) confirm that the impact of the sole THBL on column dispersion can be neglected. In contrast, the contribution of the TLOPL to the reduced plate height (RPH) is about 0.2 h unit at optimum reduced velocity. Most remarkably, the negative impact of the TLOPL on column performance may be fully compensated by the presence of the adjacent WDRPL if the depth of the velocity well were to be 5% of the bulk velocity. In actual 2.1 mm × 50 mm columns packed with sub-2 μm FPPs, this velocity depth is as large as 25% of the bulk velocity causing a significant RPH deviation of 0.7 h unit from the RPH of the bulk packing free from wall effects. Maximum column performance is expected for a reduction of WDRPL density. This suggests optimizing the packing process by finding the proper balance between the stress gradient across the WDRPL (responsible for the deep velocity well) and the friction forces between the packed particles (responsible for the rearrangement of the particles during bed consolidation). Past and recently reported RPH data support the theoretical insights: the stress gradient/particle friction balance in the WDRPL is better realized when packing superficially porous particles (SPPs) rather than FPPs in 2.1–4.6 mm i.d. columns (the RPH deviation is reduced to 0.4 h unit) or sub-2 μm particles in 100 cm × 75 μm i.d. capillaries combining high slurry concentrations and sonication (the RPH deviation is reduced to only 0.15 h unit).

Wind‐induced variability of estuarine circulation in a tidally energetic inlet with curvature

AbstractIn numerous studies, the functioning of estuarine circulation has been investigated, under idealized conditions, by means of numerical models. This has led to a deep understanding of the theory of estuarine residual flows. However, the question as to how estuarine circulation is established in real estuaries, in response to their topographical and forcing characteristics, remains. The present study uses a highly accurate three‐dimensional numerical model simulation to calculate estuarine circulation in a curved, tidally energetic channel of the Wadden Sea in the southeastern North Sea. The specific momentum balance of this curved inlet shows an approximate pressure‐gradient—frictional balance in the longitudinal direction and a pressure gradient—centrifugal balance in the lateral direction. A local Wedderburn number is introduced to quantify the varying contributions of wind stress and gravitational forcing on estuarine circulation. A total exchange flow (TEF) analysis is combined with an analysis of the intensity of the vertical overturning circulation to understand the dynamics of estuarine exchange in this inlet. The results show how established forcing mechanisms of residual circulation, such as horizontal buoyancy gradients and wind stress, act in a combined way. In general, the strength of estuarine circulation is always positively correlated with wind stress, with frequent reversals of residual flow for wind stress directed toward higher buoyancy. Only during calm weather conditions are longitudinal and lateral estuarine circulation highly correlated with the respective buoyancy gradients.

The Annual Cycle of the Japan Sea Throughflow

AbstractThe mechanism responsible for the annual cycle of the flow through the straits of the Japan Sea is investigated using a two-layer model. Observations show maximum throughflow from summer to fall and minimum in winter, occurring synchronously at the three major straits: Tsushima, Tsugaru, and Soya Straits. This study finds the subpolar winds located to the north of Japan as the leading forcing agent, which first affects the Soya Strait rather than the Tsushima or Tsugaru Straits. The subpolar winds generate baroclinic Kelvin waves along the coastlines of the subpolar gyre, affect the sea surface height at the Soya Strait, and modify the flow through the strait. This causes barotropic adjustment to occur inside the Japan Sea and thus affect the flow at the Tsugaru and Tsushima Straits almost synchronously. The barotropic adjustment mechanism explains well why the observations show a similar annual cycle at the three straits. The annual cycle at the Tsugaru Strait is further shown to be weaker than that in the other two straits based on frictional balance around islands, that is, frictional stresses exerted around an island integrate to zero. In the Tsugaru Strait, the flows induced by the frictional integrals around the northern (Hokkaido) and southern (Honshu) islands are in opposite directions and tend to cancel out. Frictional balance also suggests that the annual cycle at the Tsugaru Strait is likely in phase with that at the Soya Strait because the length scale of the northern island is much shorter than that of the southern island.

Experimental study on performance of multidirectional geogrid and its application in engineering of high slope

By analyzing the grille mechanical property, tensile strength and creep tests, and the field tests, we investigated the characteristics and the reinforcement principle of multidirectional geogrid, and obtained the effect factors of grid characteristics, load and time curve and the shear stress of grille and sand interface. The reinforcement effect of geogrid in combination of typical project cases was illustrated and the following conclusions were presented. Firstly, multidirectional geogrid has ability to resist structural deformation, node distortion or soil slippage under stress, and can effectively disperse load. Secondly, with the increase of tensile rate, grille intensity increases and the creep value also increases with the increase of load. Thirdly, the frictional resistance balance between horizontal thrust of damaged zone and reinforced soil in stable region can avoid slope failure due to excessive lateral deformation. Fourthly, the multidirectional geogrid is able to withstand the vertical, horizontal and diagonal forces by combing them well with three-dimensional orientation, realizing the purpose of preventing soil erosion and slope reinforcement, which has a wide range of application and development in engineering field.

Using Depth-Normalized Coordinates to Examine Mass Transport Residual Circulation in Estuaries with Large Tidal Amplitude Relative to the Mean Depth

Abstract Residual (subtidal) circulation profiles in estuaries with a large tidal amplitude-to-depth ratio often are quite complex and do not resemble the traditional estuarine gravitational circulation profile. This paper describes how a depth-normalized σ-coordinate system allows for a more physical interpretation of residual circulation profiles than does a fixed vertical coordinate system in an estuary with a tidal amplitude comparable to the mean depth. Depth-normalized coordinates permit the approximation of Lagrangian residuals, performance of empirical orthogonal function (EOF) analysis, estimation of terms in the along-stream momentum equations throughout depth, and computation of a tidally averaged momentum balance. The residual mass transport velocity has an enhanced two-layer exchange flow relative to an Eulerian mean because of the Stokes wave transport velocity directed upstream at all depths. While the observed σ-coordinate profiles resemble gravitational circulation, and pressure and friction are the dominant terms in the tidally varying and tidally averaged momentum equations, the two-layer shear velocity from an EOF analysis does not correlate with the along-stream density gradient. To directly compare to theoretical profiles, an extension of a pressure–friction balance in σ coordinates is solved. While the barotropic riverine residual matches theory, the mean longitudinal density gradient and mean vertical mixing cannot explain the magnitude of the observed two-layer shear residual. In addition, residual shear circulation in this system is strongly driven by asymmetries during the tidal cycle, particularly straining and advection of the salinity field, creating intratidal variation in stratification, vertical mixing, and shear.

Subinertial and tidal currents on the Abrolhos Bank shelf

Analysis of simultaneous current measurements in the middle (point PA1) and outer (point PA2) Abrolhos Bank shelf showed different characteristics and forcing mechanisms between the two shelf regions. The mean currents at both positions point generally southwestward but are weak due to the high time variability; at PA1, the mean along-shelf currents are almost one order of magnitude larger than the mean cross-shelf currents, while at PA2, both mean current components exhibit the same order of magnitude. At both points, the tidal currents are more important in the cross-shelf direction than they are in the along-shelf direction. The subinertial currents are mainly barotropic and along-shelf at PA1, while at PA2, the baroclinic first mode dominates the subinertial variability, especially in the cross-shelf direction, though the currents are also more energetic in the along-shelf direction. Correlations are significant between the along-shelf subinertial currents and synoptic winds at PA1, showing a local response (almost in phase) to the wind stress. At PA2, the correlations between winds and currents are generally not significant, showing that the subinertial current variability near the shelf break is forced by other mechanisms; the mesoscale variability of the Brazil Current is most likely important at this position. A simple frictional balance model allows a dynamical interpretation of the significant correlations between winds and currents at PA1.

Infrared Based Wall Shear Stress Measurement Techniques

The paper presented here introduces two novel, infrared based wall shear stress measurement techniques. The first provides wall shear stress visualizations with a high spatial and temporal resolution as well as spatial quantitative information. The other technique enables sensor-based measurements of the wall shear stress magnitude and direction. Both techniques are based on the close link between momentum and heat transport in the boundary layer and correlate the surface temperature distribution of a heated surface (first technique) or a heated spot (second technique), which is measured using infrared thermography, with the wall shear stress. For the spatial qualification and quantification, the temporal surface temperature evolution of a heated structure subjected to a flow is linked to the wall shear stress distribution. The second, sensor-based technique heats a small spot on an otherwise unheated surface. The temperature distribution, or thermal tuft, around this heated spot is closely related to the local wall shear stress magnitude and direction. Results are presented for both techniques and compared to reference measurements and visualizations, respectively. Reference measurements of the wall shear stress were obtained using a skin friction balance; oilflow visualizations were used as a reference visualization technique.

Effect of micro-surface defect on tribological property of UHMWPE

The article studied the friction and wear properties of UHMWPE when the surface was probed with micro-defect. The results indicated that the friction coefficient decreased when the micro-defect holes were gradually distributed on the friction surface uniformly. That was mainly because the uniform micro-defect holes formed regular texture, increasing the balance of friction and wear. The wear loss of UHMWPE decreased gradually with the increase of the amount of micro-defect holes, and there was a good linear relationship between them. When the friction surface was filled with uniformly distributed micro-defect holes, not only the wear loss decreased, but also wear debris with ideal size distribution was obtained. So, the theoretical and experimental basis was provided for the idea of the surface texturization of artificial arthrosis.

Rough wall skin friction measurements using a high resolution surface balance

This paper describes the design of a floating element friction balance which is based upon a commercially available micro force balance. The balance has a perfectly linear calibration function and was successfully applied to rough wall flows in a channel and a diffusor. Extrapolation of the turbulent shear stress measured by two component LDA to the wall matched very well the shear stress measured using the friction balance. Also, the wall shear stress obtained from the balance in the fully developed channel flow agreed with the stress that could be derived from the pressure gradient to within 3%.

The Shear-Thinning Elastohydrodynamic Film Thickness of a Two-Component Mixture

Lubricant base oils are often blends of different molecular weight cuts to arrive at a specified ambient pressure viscosity and, to improve the temperature-viscosity behavior or to simply increase the viscosity, viscosity-modifying polymer additives are often added to the base oil. This paper investigates the effect of mixture rheology on elastohydrodynamic lubrication (EHL) film thickness using EHL contact measurements and a full numerical analysis for three synthetic lubricants including two single-component lubricants PAO650 and PAO100 and a mixture of these. The pressure and shear dependences of the viscosity of these lubricants were measured with high-pressure viscometers; viscosities were not adjusted to fit experiment. The point contact film thicknesses for these lubricants in pure rolling were measured using a thin-film colorimetric interferometry apparatus. Numerical simulations based on the measured rheology show very good agreement with the measurements of film thickness while the Newtonian prediction is up to twice the measurement. These results validate the use of realistic shear-thinning and pressure-viscosity models, which originate from viscosity measurements. It is conceivable that simulation may provide a means to “engineer” lubricants with the optimum balance of film thickness and friction through intelligent mixing of components.

End‐labeled free‐solution electrophoresis of DNA

DNA is a free-draining polymer. This subtle but "unfortunate" property of highly charged polyelectrolytes makes it impossible to separate nucleic acids by free-flow electrophoresis. This is why one must typically use a sieving matrix, such as a gel or an entangled polymer solution, in order to obtain some electrophoretic size separation. An alternative approach consists of breaking the charge to friction balance of free-draining DNA molecules. This can be achieved by labeling the DNA with a large, uncharged molecule (essentially a hydrodynamic parachute, which we also call a drag-tag) prior to electrophoresis; the resulting methodology is called end-labeled free-solution electrophoresis (ELFSE). In this article, we review the development of ELFSE over the last decade. In particular, we examine the theoretical concepts used to predict the ultimate performance of ELFSE for single-stranded (ssDNA) sequencing, the experimental results showing that ELFSE can indeed overcome the free-draining issue raised above, and the technological advances that are needed to speed the development of competitive ELFSE-based sequencing and separation technologies. Finally, we also review the reverse process, called free-solution conjugate electrophoresis (FSCE), wherein uncharged polymers of different sizes can be analyzed using a short DNA molecule as an electrophoretic engine.

Heat transfer and flow of He II in narrow channels

Heat transfer and fluid flow of He II in a long, narrow channel connected to a bath that supplies a constant supply of heat have been investigated by numerical simulations by using the simplified model of Kitamura et al. [Cryogenics 37 (1) (1997) 1]. Such channels are used to cool compact, stable, low-temperature magnets. The fluid flow is driven by natural convection and the mutual friction between the normal fluid and the superfluid. In this model, the thermomechanical effect and the Goter–Mellink mutual friction balance each other. A consequence of this balance is that the velocity and temperature distributions of He II can be characterized by a dimensionless, dependent parameter equal to the ratio of the fluid speeds of internal convection to the total fluid flow. After a sudden application of heat flux, the internal convection dominates over the total fluid flow until the establishment of steady-state temperature gradients. This predicts that the time required to set up the steady-state total fluid flow is proportional to the total heat capacity in the channel.