Estimation Of Friction Coefficient Research Articles

311 自己組織化単分子膜間の相対すべり摩擦特性の分子動力学解析(GS-1.4 分子動力学)

Designing the configuration patterns of molecules in self-assembled mono-layers (SAM) is one of the promising processes that decrease friction between interfacial surfaces of the elements in MEMS. A typical SAM, in which heptane molecules on Au substrate, is modeled and is studied by using the molecular dynamics method. We discuss the direction dependence of the friction coefficient as well as the model size dependence of it. Significant anisotropy and size dependence are not observed and the estimated friction coefficient for the all models is 0.18.

GPS-based real-time identification of tire-road friction coefficient

Vehicle control systems such as collision avoidance, adaptive cruise control, and automated lane-keeping systems as well as ABS and stability control systems can benefit significantly from being made road-adaptive. The estimation of tire-road friction coefficient at the wheels allows the control algorithm in such systems to adapt to external driving conditions. This paper develops a new tire-road friction coefficient estimation algorithm based on measurements related to the lateral dynamics of the vehicle. A lateral tire force model parameterized as a function of slip angle, friction coefficient, normal force and cornering stiffness is used. A real-time parameter identification algorithm that utilizes measurements from a differential global positioning system (DGPS) system and a gyroscope is used to identify the tire-road friction coefficient and cornering stiffness parameters of the tire. The advantage of the developed algorithm is that it does not require large longitudinal slip in order to provide reliable friction estimates. Simulation studies indicate that a parameter convergence rate of 1 s can be obtained. Experiments conducted on both dry and slippery road indicate that the algorithm can work very effectively in identifying a slippery road.

Power law fluid flow over a bundle of cylinders at intermediate Reynolds numbers

Extensive theoretical estimates of pressure, friction and total drag coefficients for the cross flow of power law fluids normal to an array of long circular cylinders are reported in this paper. The equations of continuity and of momentum have been solved numerically for the unknown velocities and pressure which, in turn, have been processed further to infer the values of drag coefficients. The inter-cylinder interactions have been approximated by the two commonly employed “concentric cylinders” cell models. The results reported herein embrace the following ranges of physical and kinematic conditions: power law flow behaviour index: 0.5, 0.6, 0.8 and 1; Reynolds number, 1–500 and the voidage of 0.4 and 0.5, albeit limited results are also presented for voidage values of 0.6 and 0.9. The accuracy of the numerical solution procedure has been established by carrying out extensive comparisons with the previously available analytical and/or numerical results for the flow of Newtonian and power law fluids. Similarly, the applicability of this simple approach of the cell model has been demonstrated by presenting detailed comparisons between the present predictions and the limited experimental results available in the literature for the flow of shear-thinning polymer solutions over banks of cylinders.

Taking Tire Slip Ratio into Account and Estimating Friction Coefficients in Rear-End Collisions on Winter Roads

Road surface conditions in winter are very transient. A small change in the friction coefficient can have a large effect on vehicular movements. A friction coefficient measured at the scene directly after an accident may be different from the one at the time when the accident occurred. A traffic accident reconstruction method that can estimate friction coefficients based indirectly on in situ data is presented. First, it is pointed out that the friction coefficient is largely dependent on the tire slip ratio, in particular that of studless tires whose tread rubber is very soft and adhesive. It is emphasized that it makes sense to use a tire model that considers the slip ratio to estimate the friction coefficients more precisely. Rear-end collision accident data were collected. The types of vehicles involved in accidents were identified, and their friction coefficients at the time of skidding were estimated by the new reconstruction model. The friction coefficients estimated by this model were compared with those estimated by a conventional rigid-body model. In addition, by inversely calculating the friction coefficient required to avoid accidents, how an increment in the friction coefficient could greatly improve traffic safety is considered. Finally, it is shown that a threshold defined as the intersection of the cumulative curves of both friction coefficients provides useful information for winter maintenance.

Wall friction coefficient estimation through modelling of powder die pressing experiment

Forming of PM components through powder pressing is a process, which is influenced by the friction between the powder and the tool walls. For good performance of the pressing process it is of great interest to understand and estimate the effects of powder–wall friction. However, quantification of the friction coefficient between the powder and the tool is a delicate task. Local contact conditions, such as contact stress, must be measured or otherwise estimated in order to evaluate the coefficient of friction. Here, the friction coefficient is estimated by combining an experiment with modelling of the experiment. Two methods for assessment of friction are presented, an optimisation approach using finite element analyses and an analytical approach. Experimental data are taken from the single action cold pressing of a cylinder shaped component.

Étude en soufflerie thermique du refroidissement de parois poreuses par effusion de gaz

A heated air tunnel and specially its test section features, designed for studies of wall protection from high temperature gases, are described. A coolant, moving through the porous wall, flush fitted in the horizontal test section floor, achieves its thermal protection. Preliminary velocity measurements, carried out at ambient temperature and without injection, within the test section, pointed out the following aerodynamic characteristics: stationarity and turbulence intensity in the potential flow, boundary layer features over the porous wall according to the entrance test section boundary conditions, wall friction coefficient estimation. Velocity and temperature profiles, in non-isothermal conditions, over the porous wall with or without cooling air injection, are reported. They point out the injection rate influence, variable from 0 to 2 %.

Adaptive Yaw Rate Feedback 4WS with Tire/Road Friction Coefficient Estimator

SUMMARY This paper proposes an adaptive yaw rate feedback control system for a four-wheel-steering (4WS) vehicle which involves a tire/road friction coefficient estimator. The adaptive 4WS system has been developed so that the vehicle possesses desirable lateral characteristics even on slippery roads and in critical driving situations. The friction coefficient is estimated on real time from the yaw rate response of the controlled vehicle with the least squares. The control system adopts a two degree of freedom structure which consists of a feedforward compensator and a feedback control subsystem. The feedforward compensator is determined with the estimated friction coefficient to minimize the steady-state and transient vehicle slip angle in spite of changes in tire/road conditions. The feedback subsystem adopts the Internal Model Control (IMC) structure in order to compensate for nonlinearities and to realize robustness against modelling and estimation errors.

Optimal estimation of Eddy viscosity and friction coefficients for a Quasi‐three‐dimensional numerical tidal model

Abstract It is shown that the parameters in a quasi‐three‐dimensional numerical tidal model can be estimated accurately by assimilation of data from current meters and tide gauges. The tidal model considered is a semi‐linearized one in which advective nonlinearities are neglected but nonlinear bottom friction is included. The parameters estimated are the eddy viscosity, bottom friction coefficient, water depth and wind drag coefficient, the first three of which are allowed to be position‐dependent. The adjoint method is used to construct the gradient of a cost function defined as a certain norm of the difference between computed and observed current and surface elevations. On the basis of a number of tests, it is shown that very effective estimation of the nodal values of the parameters can be achieved using the current data either alone or in combination with elevation data. When random errors are introduced into the data, the estimated parameters are quite sensitive to the magnitude of the errors, and in particular the eddy viscosity is unstably sensitive. The sensitivity of the viscosity can be stabilized by incorporating an appropriate penalty term in the cost function or alternatively by reducing the number of estimated viscosity values via a finite element approximation. Once stabilized, the sensitivity of the estimates to data errors is significantly reduced by assimilating a longer data record.

Estimating friction coefficients of mixed globular/chain molecules, such as protein/DNA complexes

Existing methods for predicting translational friction properties of complex molecules start by explicitly building up their three-dimensional shape with spherical subunits. This treatment has been used especially for two types of systems: rigid assemblies and flexible chain molecules. However, many protein/DNA complexes such as chromatin consist of a small number of globular, relatively rigid, bound protein interspersed by long stretches of flexible DNA chain. I present a higher level of treatment of such macromolecules that avoids explicit subunit modeling as much as possible. An existing analytical formulation of the hydrodynamics equations is shown to be accurate when used with the present treatment. Thus the approach is fast and can be applied to hydrodynamic studies of highly degenerate multiple equilibria, such as those encountered in problems of the regulation of chromatin structure. I demonstrate the approach by predicting the effect of a hypothetical unwinding process in dinucleosomes and by simulating the distribution of sedimentation coefficients for cooperative and random models for a chromatin saturation process.

Period Times and Helix Alignment during the Cyclic Migration of DNA in Electrophoresis Gels Studied with Fluorescence Microscopy

Fluorescence microscopy of YOYO-stained DNA molecules has been used to study the periodicity of the cyclic migration during constant field electrophoresis in agarose gels. The distribution of period times is asymmetric and wide, with a ratio of standard deviation to mean value of 0.50 for fields between 3 and 24 V/cm. The average period time decreases with the electric field strength, E, as E -1.2 , and increases with increasing molecular weight (38-740 kbp) and increasing gel concentration (0.5-2%). The period times for T2 DNA (164 kbp) are in good agreement with the time to the orientation undershoot, as measured in a separate linear dichroism study of YOYO-stained DNA undergoing ordinary zone electrophoresis (Carlsson et al., manuscript in preparation). This shows that linear dichroism can be used to quantify the period time of the cyclic motion and to investigate effects of changes in DNA or gel properties. The cyclic conformational changes in the global DNA conformation during migration have been characterized in terms of the apparent length L μ and end-to-end distance h μ of the molecular paths in the gel. The formation of U conformations dominates the cycle time, since it is slow compared to U slipping and retraction. The maximum and cycle-averaged orientation factors for the apparent molecular path are evaluated from the images to be 0.70 and 0.67 ± 0.03, respectively, for T2 DNA at 8 V/cm in 1% agarose. From these values the degree of helix orientation below the level of microscope resolution could be estimated by comparison with the total orientation factor for the DNA helix as measured with linear dichroism. The maximum and cycle-averaged orientation factor for the helix with respect to the global path were 0.27 and 0.22 ± 0.01, respectively. These orientation factor values demonstrate (1) a very high degree of field alignment of the global path and (2) a degree of stretching of the helix along that path which is considerable, and stronger than expected for a wormlike chain spanning a cavity with the average pore size. If the imaged path corresponds to the reptation tube, the estimated friction coefficient for motion along the tube is found to be close to the value in the buffer.

Exploring the Maxwell-Stefan description of ion exchange

An ion exchange, water and several ions diffuse simultaneously, with different velocities. They are driven by activity, electrical and pressure gradients. We describe these complicated processes with the Maxwell-Stefan equation. This equation for multi-component diffusion requires one diffusivity or friction coefficient for each pair of components in the mixture. In this article, we explore the behaviour of these coefficients in the liquid and solid phases of ion exchange. Friction coefficients between ions and liquid are similar to those between uncharged species. They increase with the size of the ions, and depend only weakly on composition. Friction coefficients between positive and negative ions are much larger, especially between ions with multiple charges. They decrease with increasing concentrations. Ions of like charge usually have negative friction coefficients; their behaviour mirrors that of ions with unlike charges. The many coefficients in the solid can only be obtained by combining data on ion exchange and electrodialysis membranes. In the matrix, we can estimate friction coefficients with water from free solution values and a ‘tortuosity’ correction. Friction between counter-ions and the charged matrix is important. It is much larger than the (free solution with tortuosity) prediction. This is especially so for ions with multiple charges. This type of friction also seems to depend on the polymer morphology. At the high concentrations in the matrix, friction coefficients between different counter-ions with a like charge are usually positive. The friction can be appreciable. Our knowledge of friction coefficients within the solid is still incomplete; we end with a few remarks on this.

In-situ organization of nanoparticles by scanning force microscopy under terrestrial and microgravity conditions

Scanning force microscopy (SFM) is proposed as a tool to organize logical and other operative nanostructures constructed from prefabricated, 10-nm-sized particles randomly deposited onto suitable substrate materials by a “bottom-up” technology. The “nanoconductors” are prepared from metals or semiconductors by evaporating into a thermalizing background gas: the vapour is cooled down to a supersaturated state until particle nucleation sets in. The choice of gas pressure and vaporization rate serves to controlling both the size and total number of particles in a wide range. Fitting to the present purpose, by this technique, individual nanoconductors can be produced in a very small number and — using several independent heaters — also from different substances. The application of a metal-covered tip-cantilever system in an SFM instrument does not only allow to study the surface morphology of conducting and insulating particles, but also to analyse their electronic and optical properties. Upon selection, it is intended to displace specified particles to predetermined positions on the substrate surface and to build up functional schemes. By modifying the force detection system, the SFM may be used to measure forces acting on these particles. Under terrestrial and microgravity (μg) conditions, comparative studies are suggested to examine (a) the influence of gravity on nucleation behaviour and particle growth, (b) basic physical phenomena, and (c) the possibility of organizing logical and cybernetic systems: (a) There is general agreement that even tiny influences may have significant effects on non-equilibrium processes such as nucleation. For modem nanotechnology, where the respective habitus and structure of single particles are of considerable importance, comparative fabrication under μg-conditions is strongly recommended. (b) The characterization of forces acting between the SFM tip and a nanoparticle, between nanoparticles among one another, as well as between nanoparticles and substrate materials on a nanometer- or even atomic-scale is essential for the elucidation of interaction phenomena and estimation of friction coefficients. In addition, structural, electronic, and optical properties of individual particles will be inspected as a function of size and material. (c) The fashioning of systems consisting of two or more nanoparticles and the investigation of the resulting electrical properties as a function of size, material, and separation of adjacent particles. μg-conditions also open up access to the third dimension. Many degrees of freedom provided by μg-conditions, the specific physical properties of nanoparticles, and the “bottom-up” technology permit the formation of electrical devices or sensors on a nanometer-scale exhibiting well known characteristics. Moreover, the range of potential applications can be much more extended by the opportunity of constructing various ingenious particle arrangements operating as logical or cybernetic systems.

Techniques for the Determination of the Static and Dynamic Internal Friction Coefficients of Ceramic Powder

Abstract This paper discusses different techniques for the experimental estimation of the static and dynamic internal friction coefficients of fragmented ceramics. These were applied to the powders of two ballistic ceramics, SiC and Al2O3. The relationship between the fragment sire and the internal friction coefficients of the powders was determined. The results obtained with the different techniques are compared.

Slow non‐newtonian flow through packed beds: Effect of zero shear viscosity

AbstractThe slow non‐Newtonian (inelastic) flow through packed beds of mono‐size spherical particles has been simulated by solving the equations of motion numerically. The inter‐particle interactions have been modelled by using a simple cell model. Theoretical estimates of pressure, friction and total drag coefficients as function of the pertinent physical (l≥n≥ 0.2; 0.3 ≤ e ≤ 0.5) and kinematic parameters (0.01 ≤ '≤ 100) for a fixed value of Reynolds number {Re = 0.001) have been obtained. The theoretical predictions reported herein have been validated using the suitable experimental results available in the literature, and the importance of including the zero shear viscosity in analyses for the creeping flow problems is convincingly demonstrated.

Development of a takeoff performance monitoring system

The development and testing of a real-time takeoff performance monitoring system is discussed. The algorithm is madeup of two segments: a pretakeoff segment and a real-time segment. One-time inputs of ambient conditions and airplane configuration information are used in the pretakeoff segment to generate schedule performance data for that takeoff. The real-time segment uses the scheduled performance data generated in the pretakeoff segment, runway length data, and measured parameters to monitor the performance of the airplane throughout the takeoff roll. Airplane and engine performance deficiencies are detected and annunciated. An important feature of this algorithm is the one-time estimation of the runway rolling friction coefficient. The algorithm was tested using a six degree of freedom airplane model in a computer simulation. Results from a series of sensitivity analysis are also included.

Magnetohydrodynamic free convection flow about a semi-infinite plate at whose surface the heat flux is uniform

The magnetohydrodynamic free convection flow of an electrically conducting fluid past a vertical, semi-infinite plate in a strong cross field has been examined when a uniform heat flux is present at the plate. Formulation in terms of a characteristic length has enabled a full numerical solution to be obtained providing details of skin friction and heat transfer at all stations along the plate for a range of Prandtl numbers appropriate to liquid metal coolants. Series solutions are also presented which give good estimates of the skin friction and heat transfer coefficients.

Wave energy losses in intermediate depths

Recent work on wave power devices has encouraged interest in the processes whereby waves lose energy and change direction in shoaling water, and especially in detailed calculations of their effects. 1,2 Here one of the most comprehensive sets of measurements available is examined, for four sites in depths of 15 to 100 m off South Uist in the Hebrides. The mean directional spectrum is recalculated for each site, and a proper allowance found for refraction which raises the estimates of net energy flux in intermediate depths by up to 10%. Indeed, the pattern of losses between 100 m and 23 m depths fits well with that expected from bottom friction. The estimated friction coefficient is quite high, as might be expected in view of the very rough sea bottom in the area. 3

Plastic deformation and sliding friction of metals

Most theories of sliding friction have emphasized surface roughness or adhesion. In some cases plastic deformation has been invoked to account for energy dissipation. After a brief review of published explanations of friction, a new model is described for the source of friction during the steady state sliding of metals. It focuses on the plastic work done in the near-surface region, described in terms of work hardening, recovery and the microstructure existing during steady state sliding. The model is discussed with respect to several alternate ways in which plastic deformation has been incorporated in recent theories of friction. Reasonable results are found when the new model is used to estimate friction coefficients for metals. Also, the model appears to be consistent with a number of published observations on the relation of friction to load, sliding distance, surface temperature and microstructure, and with a model for sliding wear which has been presented earlier.

Nearshore currents off Long Island

Currents were observed for a 25-day period in September 1975 at 11 km south of Long Island, where the water is 32 m deep, at three levels by using electromagnetic current meters. Tidal currents were found to be moderately strong, of the order of 20 cm s−1. Nontidal flow is caused by wind stress, horizontal density contrasts due to fresh water influx, and a longshore surface level gradient sloping down south-westward. The time-averaged flow has simple characteristics, adequately described by classical Ekman models in frictional equilibrium. By suitable changes in the averaging period, quantitative estimates of a bottom friction coefficient and a longshore pressure gradient are deduced from the data. The bottom friction coefficient agrees with what one would estimate from boundary layer theory for roughness elements of about 70-cm height. The longshore pressure gradient deduced from the behavior of currents agrees with the evidence of geodetic leveling.

Low friction coefficient estimation for model material experiments

A previously suggested method of estimating low friction coefficients from the bulk deformation of long rectangular laminae during plastic compression, was used for wax specimens with various lubricants to enable the choice of the best lubricant for experiments with model materials. This method was also used for aluminium specimens with liquid and solid lubricants. Existing theory was extended to cover both the Amonton friction model and that of constant friction stress. Friction coefficients for certain waxes lubricated with vaseline were found to be as low as 0.01. With molybdenum disulphide grease on aluminium, the friction coefficient was found to decrease as compression proceeded. Friction coefficients with lead foil were found to agree with their independently known values. Lubrication breakdown at the periphery of specimens was observed in some tests, causing overestimation of the friction coefficient.