Equivalent Friction Coefficient Research Articles

Analysis of the influence of drydock main pumps drive on electric network

The influence of unadjustable-speed AC drive and adjustable-speed DC drive of the drydock main pumps on the network of the Okean shipyard (Ukraine) is investigated in MatLab SimPowerSystems. To accurately simulate deep-bar induction motors, the own method of determining the parameters of the T-shaped equivalent circuit and viscous friction coefficient of a virtual motor according to catalog data is used. This method is based on formulas that correspond to the T-shaped and refined L-shaped equivalent circuit. It is proposed to introduce the corrected values of the initial starting and critical torque ratio into the calculation. The rated power factor is determined indirectly and compared with the catalog value. The dependences of rotor resistance are approximated by elementary functions, which provide almost constant values of these parameters at subcritical slip values. As a result of the simulation, it became clear that even with the alternate starting of unregulated electric pump units, there is a significant voltage drop in the network. The mathematical model of DC drives was built with a common dual-circuit automatic speed control system. A resonance filter is included at the input of each synchronized 6-pulse generator, thereby eliminating possible errors in operation. The simulation results prove that during the operation of DC drives, there are switching voltage variations in the network, substantially non-sinusoidal current consumption and reactive power consumption. Given the stray capacitance of the cable line, high-frequency voltage fluctuations occur, which are dangerous for electric equipment. Through the use of the harmonic filtering and reactive power control device, these negative phenomena can be eliminated, thus, the DC drive will surpass unadjustable-speed induction motor drive in many respects. To minimize reactive power consumption, an automatic control system with an integrated variable gain reactor power controller can be used

Numerical Study of Mobilized Friction along Embedded Catenary Mooring Chains

Understanding the soil resistance along an embedded anchor chain is imperative for efficient and economic design of an overall mooring system as it determines the magnitude and direction of the load at the padeye of the anchor. The tensioning process of an embedded chain for catenary moorings was modeled using a coupled Eulerian–Lagrangian (CEL) finite-element approach simulating the large deformations of the chain as it cuts through the soil to form an inverse catenary. The analyses reveal that the configuration of the embedded chain and the relationship between tension and chain angle at the padeye show excellent agreement with previously published analytical predictions. However, the ratio of the tension at the padeye to that at the mudline obtained from CEL is significantly higher than the theoretical values, mainly due to partial mobilization of the frictional soil resistance along the length of the chain. The CEL results indicate that the partial mobilization is a result of the combined-loading effect during failure of the soil around the embedded chain as it cuts through the seabed, in contrast with the conventional assumption that the ultimate frictional and normal soil resistances are mobilized simultaneously. A new design approach is proposed for calculating the local equivalent coefficient of friction based on the yield locus for a deeply embedded chain and the normality rule.

Anisotropic Vibration Tactile Model and Human Factor Analysis for a Piezoelectric Tactile Feedback Device.

Tactile feedback technology has important development prospects in interactive technology. In order to enrich the tactile sense of haptic devices under simple control, a piezoelectric haptic feedback device is proposed. The piezoelectric tactile feedback device can realize tactile changes in different excitation voltage amplitudes, different excitation frequencies, and different directions through the ciliary body structure. The principle of the anisotropic vibration of the ciliary body structure was analyzed here, and a tactile model was established. The equivalent friction coefficient under full-coverage and local-coverage of the skin of the touch beam was deduced and solved. The effect of system parameters on the friction coefficient was analyzed. The results showed that in the full-coverage, the tactile effect is mainly affected by the proportion of the same directional ciliary bodies and the excitation frequency. The larger the proportion of the same direction ciliary body is, the smaller the coefficient of friction is. The larger the excitation frequency is, the greater the coefficient of friction is. In the local-coverage, the tactile effect is mainly affected by the touch position and voltage amplitude. When changing the touch pressure, it has a certain effect on the change of touch, but it is relatively weak. The experiment on the sliding friction of a cantilever touch beam and the experiment of human factor were conducted. The experimental results of the sliding friction experiment are basically consistent with the theoretical calculations. In the human factor experiment, the effects of haptic regulation are mainly affected by voltage or structure of the ciliary bodies.

Study on Low-Speed Steering Resistance Torque of Vehicles Considering Friction between Tire and Pavement

Electric power steering (EPS) systems under existing vehicle power systems cannot provide enough power for heavy-duty commercial vehicles under pivot or low-speed steering conditions. To solve this problem, the paper proposes an EPS system that is based on the hybrid power system constituted by the vehicle power system and the supercapacitor in parallel. In order to provide a theoretical basis for the intervention and withdrawal mechanisms of a super-capacitor in the new EPS, the law of steering resistance torque at a low or extremely low vehicle speed should be explored. Firstly, the finite element model of tire/pavement was established to conduct the simulation and calculation of the low-speed steering friction force between the tire and pavement, and to obtain the fitting expression of the equivalent steering friction coefficient with the running speed of the tire. Secondly, the expression of the steering friction torque was deduced based on the calculus theory and mathematical model of the low-speed steering resistance torque, including the steering friction torque and aligning torques, established to conduct the simulation of the equivalent resistance torque applied on a steering column under low-speed condition. Subsequently, the real vehicle experiments were carried out and comparisons of the experimental results and simulation results was performed. The consistency indicated that the model of low-speed steering resistance torque had a high accuracy. Finally, the law of low-speed steering resistance torque with a vehicle speed and steering wheel angle were analyzed according to the 3D surface plot drawn from the simulation results.

多楔带张紧力对当量摩擦系数的影响规律

多楔带张紧力对当量摩擦系数的影响规律

Effect of different surface asperities and surface hardness induced by shot-peening on the fretting wear behavior of Ti-6Al-4V

An experimental investigation on the fretting wear of Ti–6Al–4V was conducted using a self-designed test machine. The wear morphologies and the cracking phenomena of as-received and shot-peened specimens were comparatively analyzed by the combining the applications of a laser scanning confocal microscope and a scanning electron microscope. The results showed that shot-peening exhibited an increase in the wear volume during the early fretting wear period, while it reduced the material loss in the long-term fretting wear process. The dominant wear mechanism was transformed from adhesion/peeling to delamination in both the as-received/shot-peened specimens. The wear rates under the peeling and delamination mechanism was explained by the equivalent friction coefficient of the contacting point and the thickness of cracked surface layer. The optimal strengthening effect was obtained under a moderate shot-peening intensity of 0.3 mmA, which produced a proper curvature radius of asperity and a good combination between hardness and toughness of the surface material.

Developing empirical relationships to predict loess slide travel distances: a case study on the Loess Plateau in China

To improve landslide hazard mapping quality, a functional relationship with travel distance prediction is essential. To obtain a more accurate empirical relationship for predicting loess slide travel distances, we developed a loess slide database for the central Loess Plateau using a combination of remote sensing image interpretations, existing datasets, and an intensive field survey. The loess slide travel distance was concentrated within less than 200 m, according to a cumulative frequency analysis. Our results reveal that the loess slide volume, slope height, and slope inclination of the sliding area control the travel distance, and this relation is well-described by a power law function. Furthermore, statistical analysis suggested that the equivalent coefficient of friction decreases with an increase in loess slide volume but increases with an increase in slope inclination. We compared the prediction performances of four empirical relationships proposed in this study using the mean absolute percentage error and Theil inequality coefficient methods. We discovered that the empirical relationship with three independent variables can more accurately predict the loess slide travel distance than the relationships with one or two independent variables.

The mechanism of earthquake

The physical mechanism of earthquake remains a challenging issue to be clarified. Seismologists used to attribute shallow earthquake to the elastic rebound of crustal rocks. The seismic energy calculated following the elastic rebound theory and with the data of experimental results upon rocks, however, shows a large discrepancy with measurement — a fact that has been dubbed as “the heat flow paradox”. For the intermediate-focus and deep-focus earthquakes, both occurring in the region of the mantle, there is not reasonable explanation either. This paper will discuss the physical mechanism of earthquake from a new perspective, starting from the fact that both the crust and the mantle are discrete collective system of matters with slow dynamics, as well as from the basic principles of physics, especially some new concepts of condensed matter physics emerged in the recent years. (1) Stress distribution in earth’s crust: Without taking the tectonic force into account, according to the rheological principle of “everything flows”, the normal stress and transverse stress must be balanced due to the effect of gravitational pressure over a long period of time, thus no differential stress in the original crustal rocks is to be expected. The tectonic force is successively transferred and accumulated via stick-slip motions of rock blocks to squeeze the fault gouge and then exerted upon other rock blocks. The superposition of such additional lateral tectonic force and the original stress gives rise to the real-time stress in crustal rocks. The mechanical characteristics of fault gouge are different from rocks as it consists of granular matters. The elastic moduli of the fault gouges are much less than those of rocks, and they become larger with increasing pressure. This peculiarity of the fault gouge leads to a tectonic force increasing with depth in a nonlinear fashion. The distribution and variation of the tectonic stress in the crust are specified. (2) The strength of crust rocks: The gravitational pressure can initiate the elasticity–plasticity transition in crust rocks. By calculating the depth dependence of elasticity–plasticity transition and according to the actual situation analysis, the behaviors of crust rocks can be categorized in three typical zones: elastic, partially plastic and fully plastic. As the proportion of plastic portion reaches about 10% in the partially plastic zone, plastic interconnection may occur and the variation of shear strength in rocks is mainly characterized by plastic behavior. The equivalent coefficient of friction for the plastic slip is smaller by an order of magnitude, or even less than that for brittle fracture, thus the shear strength of rocks by plastic sliding is much less than that by brittle breaking. Moreover, with increasing depth a number of other factors can further reduce the shear yield strength of rocks. On the other hand, since earthquake is a large-scale damage, the rock breaking must occur along the weakest path. Therefore, the actual fracture strength of rocks in a shallow earthquake is assuredly lower than the average shear strength of rocks as generally observed. The typical distributions of the average strength and actual fracture strength in crustal rocks varying with depth are schematically illustrated. (3) The conditions for earthquake occurrence and mechanisms of earthquake: An earthquake will lead to volume expansion, and volume expansion must break through the obstacle. The condition for an earthquake to occur is as follows: the tectonic force exceeds the sum of the fracture strength of rock, the friction force of fault boundary and the resistance from obstacles. Therefore, the shallow earthquake is characterized by plastic sliding of rocks that break through the obstacles. Accordingly, four possible patterns for shallow earthquakes are put forward. Deep-focus earthquakes are believed to result from a wide-range rock flow that breaks the jam. Both shallow earthquakes and deep-focus earthquakes are the energy release caused by the slip or flow of rocks following a jamming–unjamming transition. (4) The energetics and impending precursors of earthquake: The energy of earthquake is the kinetic energy released from the jamming–unjamming transition. Calculation shows that the kinetic energy of seismic rock sliding is comparable with the total work demanded for rocks’ shear failure and overcoming of frictional resistance. There will be no heat flow paradox. Meanwhile, some valuable seismic precursors are likely to be identified by observing the accumulation of additional tectonic forces, local geological changes, as well as the effect of rock state changes, etc.

Mathematical model of vibration sensor for dynamic viscosity

The article is devoted to the solution of the problem of increasing the accuracy of control and measurement of the dynamic viscosity of a liquid by the vibrational method. The critical task for today is to provide remote monitoring of the viscosity of solutions in real industrial technological processes.Most of the existing viscometers are instruments predominantly of the laboratory class and for a number of reasons cannot fulfill the assigned task. The most accurate measuring instruments for dynamic viscosity are vibrational amplitude and frequency dynamic viscosity sensors that contact the liquid with the surface of sensitive element (resonator) in the form of an oscillating rod or plate.Most theoretical studies of such resonators are based on an analytical description, which is limited to the case of an infinite plate performing harmonic oscillations in an infinite viscous medium. Such an approach does not provide an opportunity to describe correctly the behavior of the sensor in real conditions of its operation. Therefore, the article is devoted to the development of a mathematical model of the dynamic viscosity sensor of a liquid with a sensitive element in the form of a tubular single tuning fork, the prongs of which are filled with a controlled liquid. The mathematical model is based on the equilibrium equation according to the d’Alembert’s principle.The article presents the main relationships for determining the equivalent mass of the prong of the tuning fork, equivalent rigidity of the prong of the tuning fork and the equivalent coefficient of linear friction in the prong of the tuning fork. The obtained relationships are completely confirmed by the theory of oscillations and the theory of deformation of solids in the linear region, and can be used in the development of a vibration control method for viscosity by the damping ratio of the tuning fork or by Q-control.

Prediction of landslide runout based on influencing factor analysis

Landslide runout predictions are essential for producing hazard maps and siting mitigation structures. Data from 55 catastrophic historical landslides in the mountainous area of China are used to determine how topography, material, triggering factors, volume, and initial posture of the slide mass influence runout. Plots and regressions between slide mobility, expressed in terms of the equivalent coefficient of friction (ratio of the fall height to the runout distance), and the slide volume show the necessity to exclude data from zones where motion is blocked by steep orthogonal slopes (“T-type topography”) in defining meaningful empirical relationships. Landslide material exerts strong control on runout, with colluvium showing the strongest dependence on slide volume. Rainfall-induced rockslides have higher mobility than gravity-induced rockslides, but rockslides triggered by great earthquakes may have lower mobility than gravity-induced rockslides. The extra sum of squares analysis results demonstrate that slide volume is the dominant predictor for estimating runout, with posture also influencing the runout distance of non-seismic rockslides. These results provide the basis for our new, multiple-factor predictive method for runout distance. The predicted runout distance in the test case was about 115% of the actual distance. This method may enhance the accuracy of runout distance estimates for landslides in the mountainous area of China.

Calculation of equivalent friction coefficient for castor seed by single screw press

Based on the traction angle and transportation rate equation, castor beans were pressed by application of single screw under different cake diameter and different screw speed. The results showed that the greater the cake diameter and screw rotation speed, the greater the actual transmission rate was. The equivalent friction coefficient was defined and calculated as 0.4136, and the friction coefficients between press material and screw, bar cage were less than the equivalent friction coefficient value.

Distribution and characteristics of landslide in Loess Plateau: A case study in Shaanxi province

Every year about one third of the geohazards in China occur in the Loess Plateau causing human loss, damaging gas and oil pipelines, destroying highways, railways and degrading farmland. Field investigation and monitoring, in-situ tests and laboratory experiments were performed to improve our understanding of the factors effecting the distribution, characteristics and causes of loess landslides. First, we find that 79% of the landslides are shallower than10m, 85% have a volume of less than 100,000m3. Second, landslides on the Loess Plateau occur primarily on concave slope profiles that have slope angles of 20–35° and that face south-east. Third, the equivalent coefficient of friction of loess landslides is very low resulting in long run-out with a low angle sliding surface. Loess landslides generally transform into mud-flows resulting in an increase in volume in transit and forming a geohazard chain. Antecedent rainfall plays an important role in triggering loess landslides. Finally, clusters of landslides in the Loess Plateau occur because the loess easily disintegrates under high pressure due to its loose and highly porous structure. There is a sharp decrease in cohesive strength with increase in deformation and water content and thus landslides tend to undergo static liquefaction during sliding.

A New Structure of Geotextile Called Soil Nets for Reinforcement

This paper proposes a new reinforcement structure called soil nets firstly, which is capable of strengthening foundations, slopes, and other structures with better effect than that of soilbags. This proposed geotextile structure typically contains several layers of soil net, which are placed in a unique way. One layer of soil net can be described as a collection of spherical soilbags that are connected together in two directions, one in which they are connected by ropes and another in which they are connected by the PP woven bags that contain the soil. A mechanical property analysis of the soil nets shows that the yield stress of the soil within the soil nets is improved, the tensile capacity of the soil nets is greater than that of the soil with which it is filled, and the equivalent coefficient of interlayer friction between the connected soil nets is larger than that for soilbags. Applications of this new reinforcement structure in the reinforcement of a foundation and a slope are considered, and the corresponding reinforcement effects are calculated. The calculation results demonstrate that the soil nets concept yields efficient reinforcement structures with many advantages.

粉体シミュレーションによる粒子偏析現象の解析

A method for analyzing quantitatively the effects of particle shape and size distribution on the size segregation of particles using DEM simulation, which employ spherical particles with an equivalent friction coefficient to efficiently incorporate the effect of particle shape was proposed. In order to quantitatively evaluate the particle size segregation occurring during gravity filling of a container, two metrics were used: a segregation index and the percolation index.

Optimization Design of Friction Drum of Farm Winch

The friction traction and radial composite stress of each ring of traditional friction roll have a huge difference. In order to solve the problem the paper has a conclusion through mechanical analysis and experimental verification, that the radial integrated stress of each ring is the same when the friction traction is same. Each groove of multi-groove friction roll is designed with different section according to the results of mechanical analysis, and then the different groove has different equivalent friction coefficient. As a friction reel with 2-slot, which equivalent friction coefficient of one groove is 0.6, another one is 0.2. Such 2-slot friction reel can provide the traction force as well as the traditional 4-slot friction do, so that the volume can be reduced by one half. The difference of each groove of 2-slot friction reel is less than 5%, which is less than 1% of the difference of traditional friction reel. So this friction reel with various section grooves is a good way of winch lightweight design for its force balance and light weight.

Formulation of off-axial interfacial debonding and sliding problem by constrained conditional finite element method

In ceramics matrix composites (CMCs), fiber-matrix interfacial debonding and sliding are the main toughening mechanisms. An interfacial debonding and sliding problem was formulated in this study, using the constrained conditional finite-element method (CC-FEM). In this formulation, the equivalence of nodal displacements at the interface and the equilibrium of contact forces are assumed as constrained conditions in which Coulomb’s law of friction is taken into account. As a distinguished advantage, numerical solutions are obtainable by a single calculation without an iterative algorism. We earlier treated a case in which fibers were oriented along the loading direction. In actual CMCs, however, fibers are not necessarily oriented along the loading direction. The fiber diameter also fluctuates along the axis. In this study, therefore, the off-axial interfacial debonding and sliding problem based on CC-FEM was formulated. Its validity was discussed by comparison with ANSYS. In both cases of on-axis and off-axis, the resultant fiber and matrix stress distributions agreed well with those of ANSYS. Comparison between on-axis and off-axis cases showed that the matrix stress in the latter recovered more steeply because of the higher equivalent friction coefficient.

A dissipative particle dynamics algorithm for fluid-solid conjugate heat transfer

Dissipative particle dynamics with energy conservation (eDPD) is developed to simulate fluid-solid conjugate heat transfer in a microchannel. A temperature reset region placed ahead of a parallel-plate microchannel and a periodic boundary condition with a body force applied in the streamwise direction are used to generate the hydrodynamically developed, thermally developing flow. To insure the temperature and heat flux continuities at the fluid-solid interface, heat transfer in the fluid zone and solid zone is solved entirely, and an equivalent mesoscopic heat friction coefficient is proposed in the eDPD simulation. The results by eDPD method with the new numerical schemes agree well with those by the finite volume method (FVM) for the predictions of heat transfer in a thick-wall microchannel.

Impact of the equivalent center of mass separating from the sliding surface on the isolation performance of friction pendulum bearings

A new equivalent center of mass model of FPBs (friction pendulum bearings) is introduced, and based on this model, coefficient j of the equivalent center of mass separating from the sliding surface is defined. It is thought in theory that j has a significant impact on the isolation parameter of FPBs, since the equivalent post-yielding stiffness and friction coefficients are not simply determined by sliding radius and sliding friction pairs. The results of numerical simulation analysis using ABAQUS conducted on two groups of FPBs support this viewpoint. For FPBs with the same sliding radius and sliding friction pairs, the FPB modules of structural analysis software such as ETABS could only distinguish the equivalent transformation using j one by one. The seismic response data obtained in a base isolation calculation example of FPBs are very different, which reveals that j’s impact on the isolation effectiveness of FPBs cannot be ignored. The introduction of j will help improve the classical structural theory of FPBs and the weak points of structural analysis software based on this theory, which is important in achieving more accurate analyses in structural design.

Transient response of a ship to an abrupt flooding accounting for the momentum flux

Numerical non-linear time domain simulation method for damaged ship motions is presented. Floodwater motion modelling is based on the lumped mass method with a moving free surface. The ship and floodwater motions are fully coupled. The variation of the floodwater mass is accounted for. A model to account for the flooding ingress transporting the momentum is presented. The experiments of abrupt flooding have shown that the ship may experience the first large roll towards the undamaged side, especially when a large undivided compartment is flooded. The presented time domain model is validated against the experimental data on the roll damping of the flooded ship and transient flooding. Two different initial stability conditions and two different compartment layouts are studied. Viscous dissipation of the floodwater motions is modelled with an equivalent friction coefficient. The impact of the viscous damping is studied. Transient flooding tests show that the inflow momentum has to be accounted for when the undivided compartment is flooded. The simulation model is capable of capturing the impact of the inflooding jet and the first roll on the opposite side of the damage is reproduced.

Lubrication characteristics of a textured porous sliding bearing

This study investigates the lubrication characteristics of a textured bearing sliding on a porous layer. To properly implement the porous layer effect in the bearing, the Brinkman-extended-Darcy model is employed, which results in a modified Reynolds equation. This equation is then evaluated to examine the effects of the porous layer’s material and geometric properties on the lubrication characteristics through the use of (semi-)analytic and numerical approaches. The cavitation effect is reflected in the numerical treatment of the model equation, and an adaptive finite difference scheme is employed to efficiently model the bearing system with finite dimples that may be far smaller than the overall bearing dimensions. Along with the variation trends of the bearing performance with respect to the material and geometric properties of the porous layer, the pattern effects of textured surfaces on the bearing performance indices (load capacity and equivalent friction coefficient) are also thoroughly investigated. Here, the pattern comprised a set of regularly spaced identical dimples either in semi-spherical or semi-ellipsoidal shape, and the effects of size and orientation of the dimples are comprehensively explored to separately identify their influence on the bearing performance indices.