Negative Friction Research Articles

Computer simulation and model test study on influence of water immersion degree on wind power generation pile stress

The force of foundation piles in collapsible soil is a complex and important issue. Different degrees of collapsibility will have different effects on the force of foundation piles. In order to analyze and discuss the distribution and change law of the axial force and negative friction resistance of the foundation pile in moe detail, this paper summarized the existing research results on the influence of immersion collapsibility on the development of the axial force and negative friction of the foundation pile, and through model test research, the strain of the loaded foundation pile and the unloaded foundation pile under the same site conditions were measured as the site was wet.The test shows that the degree of collapsibility is positively correlated with the force of foundation piles in collapsible loess site. The presence or absence of a load on the top of the pile has a greater impact on the development process of the pile's force during the immersion of the site; but it has little effect on the distribution of the pile side friction when the site is fully immersed and saturated.

Origin of friction hysteresis on monolayer graphene

Load-dependent friction hysteresis is an intriguing phenomenon that occurs in many materials, where the friction measured during unloading is larger than that measured during loading for a given normal load. However, the mechanism underlying this behavior is still not well understood. In this work, temperature-controlled friction force microscopy was utilized to explore the origin of friction hysteresis on exfoliated monolayer graphene. The experimental observations show that environmental adsorbates from ambient air play an important role in the load dependence of friction. Specifically, the existence of environmental adsorbates between the tip and graphene surface gives rise to an enhanced tip-graphene adhesion force, which leads to a positive friction hysteresis where the friction force is larger during unloading than during loading. In contrast to positive friction hysteresis, a negative friction hysteresis where the friction force is smaller during unloading than during loading is observed through the removal of the environmental adsorbates upon in situ annealing. It is proposed that the measured friction hysteresis originates from the hysteresis in the contact area caused by environmental adsorbates between the tip and graphene. These findings provide a revised understanding of the friction hysteresis in monolayer graphene in terms of environmental adsorbates.

Neoliberal Economic, Social, and Spatial Restructuring: Valparaíso and Its Agricultural Hinterland

The analysis of the neoliberal restructuring of Chilean port cities and their hinterland suggests there was a functional coupling of neoliberalisation, precarisation, reterritorialisation, extraction, and logistics. To address this process properly, we expanded the boundaries of our analytical scale to include not only the port city, but also its hinterland, and be able to examine the flow of commodities and labour. The analysis demonstrated that the effects of neoliberal restructuring of Valparaíso and its hinterland has had interconnected ambivalent effects. Although social and economic restructuring of agricultural hinterland and port terminals in Chile increased land and port productivity and economic competitiveness, this pattern of capitalist modernisation benefitted neither the increasing masses of temporary precarious workers in the countryside nor port cities such as Valparaíso, marked by territorial inequality, socioecological damage, urban poverty, and a growing sense of closure of the littoral and reduced access to the ocean. These negative externalities and frictions have triggered local political controversies, commercial and economic disputes, labour strikes, and urban and socio-territorial conflicts.

Analysis of Vertical Load Transfer Mechanism of Assembled Lattice Diaphragm Wall in Collapsible Loess Area

Based on analysis of the formation mechanism and characteristics of the negative friction in collapsible loess areas, this study investigates the load transfer law of a wall-soil system under a vertical load, establishes the vertical bearing model of a lattice diaphragm wall, and analyzes the vertical bearing capacity of an assembled latticed diaphragm wall (ALDW) in a loess area. The factors influencing the vertical bearing characteristics of the ALDW in a loess area are analyzed. The vertical bearing mechanism of the lattice diaphragm wall in the loess area is investigated. The failure modes of the ALDW in the loess area are mainly shear failure of the soil around the wall and failure of the wall-soil interface. In the generation and development of negative friction, there is always a point where the relative displacement of the wall-soil interface is zero at a certain depth below the ground; at this point, the wall and soil are relative to each other. The collapsibility of loess, settlement of the wall and surrounding soil, and rate and method of immersion are the factors affecting the lattice diaphragm wall. The conclusions of this study provide a reference for the design and construction of ALDWs in loess areas.

Experimental Study of Thermal Response of Vertically Loaded Energy Pipe Pile

Energy piles are a relatively new technology that have dual function as heat transferring and load bearing. Due to the influence of temperature cycles, additional thermal stress and relative displacement of the pile will be generated; this is different from the load transferring mechanism of the conventional pile. In order to study the thermodynamic characteristics of the energy pipe pile under dual working conditions and temperature cycles, field tests were carried out on the PHC (prestressed high-strength concrete) energy pipe pile without constraining on the top of the piles. Displacement gauges were arranged on the top of the pile, and concrete strain gauges (temperature, strain) were embedded in the pile. The variation laws of temperature, thermal strain, thermal stress, side friction resistance, and displacement of the pile top during the temperature cycling were analyzed. The test results show that the heat exchange system reached a stable state after being heated for 5 days in summer. The average temperature of the pile increased by 15.17 °C, to 34.68 °C; it was low at both ends and high in the middle part. After 5 days in the winter environment, the average temperature of the pile decreased by 10.09 °C, to 9.54 °C, which was high at both ends and low in the middle. The thermal stress was generated inside the pile, and the maximum compressive stress was 3.446 MPa and the maximum tensile stress was 2.69 MPa. The neutral point of the side friction resistance appeared 8 m below the pile top, about 2/3 of the pile length. The maximum negative side friction resistance under the summer condition was 42.06 KPa, the maximum positive side friction resistance under the winter condition was 29.93 KPa, and the lateral resistance of the pile degraded in winter. Under the influence of thermal load, the final pile top displacements in the summer and winter were −0.7 mm (0.175%D) and 0.77 mm (0.193%D), respectively.

Stability of a dust cloud in the radio frequency low-pressure gas discharge

We analyze stability of a three-dimensional cloud of the dust particles in the low-pressure radio frequency discharge under microgravity conditions. The parameters of such complex plasma are assumed to conform to the recently developed ionization equation of state that includes the effects of the ion–atom collisions on the particle charge and of the ion–particle collisions on the ion mean free path. Propagation of the particle number density perturbation in a cloud is treated using the fluid approach. The equation for dust cloud dynamics allows for the electric and ion drag forces that are not compensated in a nonstationary state and yields the wave equation for the dust acoustic waves with either a positive or negative effective friction coefficient. The resulting dispersion relation defines a condition of the instability onset, which is written for the maximum ambipolar field and dust number density gradient. Analysis of the available experimental data reveals a satisfactory correspondence with the theory. In particular, it is demonstrated that the maximum dust density gradient in the cloud increases with the increase in the particle diameter and in the pressure of plasma-forming gas.

Determination of additional load on the bridge foundation pile under karst deformation

It is necessary to assess the additional loads transferred to the piles during the growth of a karst cavity in karst soils for designing bridge support pile foundations in karst areas. Additional loads arise due to the displacement of the soil mass above the cavity and the emergence of “negative friction” forces on the pile lateral surface. The paper proposes a method for determining the additional load on the pile depending on the distance from the pile bottom to the karst soil roof and the predicted diameter of the cavity in karst soils. A method for numerical variation calculations based on the analysis of the change of shear stresses on the pile lateral surface at different stages of loading with the growth of a cavity and the stable arch over the cavity is proposed. The correct design model and criteria for stability evaluation of the arch over the cavity are selected. A series of numerical calculations are made. An analytical solution to determine the additional load on the pile depending on the distance from the pile bottom to the karst soil roof and the predicted diameter of the cavity in karst soils is obtained.

Model test on bearing capacity characteristics of energy piles in saturated clay

Based on model tests, the load transfer mechanism of energy piles in saturated clay was studied, and the variation rules of pile and soil temperature, pile tip displacement, pile tip resistance, pile stress and lateral friction resistance were analyzed. The results show that the pile temperature decreases from top to bottom while the soil temperature decreases from the pile center to the radial direction. Under zero load, the pile expands by heat, and the pile top has a large upward displacement. Thermal consolidation of soil, settlement of soil surface and negative lateral friction occur under the alternating action of cooling and heating loads. Under working load, after applying cooling and heating load, the pile will produce unrecoverable accumulative settlement.

Study on negative friction of pile foundation in single homogeneous soil layer in collapsible loess area of Northwest China

Study on negative friction of pile foundation in single homogeneous soil layer in collapsible loess area of Northwest China

Frictional characteristics of graphene layers with embedded nanopores

Graphite possessing extraordinary frictional properties has been widely used as solid lubricants. Interesting frictional characteristics have been observed for pristine graphene layers, for defective graphene, the frictional signal shows richer behaviors such as those found in topological defective graphene and graphene step edges. Recently discovered nanoporous graphene represents a new category of defect in graphene and its impact on graphene frictional properties has not yet been explored. In this work, we perform molecular dynamics simulations on the frictional responses of nanoporous graphene layers when slid using a silicon tip. We show that the buried nanopore raises maximum friction signal amplitude while preserving the stick-slip character, the size of the nanopore plays a key role in determining the maximum frictional force. Negative friction is observed when the silicon tip scanned towards the center of the nanopore, this phenomenon originates from the asymmetrical variation of the in-plane strain and the out-of-plane deformation when indented by the silicon tip. Moreover, the layer dependent frictional character is examined for the buried graphene nanopores, showing that increasing graphene layers weakens the effect of nanopore on the frictional signal.

Pulse Discharge Technology for Strengthening of Foundations

The problem of increasing the bearing capacity of a foundation is always an urgent one in today’s geotechnical construction. With significant loads transferred to foundations, the use of traditional technologies is not always justified. There is often an urgent need to use non-standard methods of strengthening the foundations. In many cases, the geotechnical situation is aggravated by the presence of weak underlying layers with unstable physical and mechanical characteristics in the engineering-geological sections. When reinforcing such foundations with the help of traditional piles, the latter can receive negative friction, which significantly reduces their bearing capacity on the ground, sometimes reaching zero values. This can lead to additional precipitation of objects being erected and objects already erected in the zone of geotechnical influence. The use of Electric Discharge Technology (EDT) piles in most cases successfully solves many complex geotechnical problems.

Erratum: Simulation of a compact object with outflows moving through a gaseous background

A compact object moving relative to surrounding gas accretes material and perturbs the density of gas in its vicinity. In the classical picture of Bondi-Hoyle-Lyttleton accretion, the perturbation takes the form of an overdense wake behind the object, which exerts a dynamical friction drag. We use hydrodynamic simulations to investigate how the accretion rate and strength of dynamical friction are modified by the presence of outflow from the compact object. We show that the destruction of the wake by an outflow reduces dynamical friction, and reverses its sign when the outflow is strong enough, in good quantitative agreement with analytic calculations. For a strong isotropic outflow, the outcome on scales that we have simulated is a negative dynamical friction, i.e., net acceleration. For jet-like outflows driven by reprocessed accretion, both the rate of accretion and the magnitude of dynamical friction drop for more powerful jets. The accretion rate is strongly intermittent when the jet points to the same direction as the motion of the compact object. The dynamical effects of outflows may be important for the evolution of compact objects during the common envelope phase of binary systems, and for accreting compact objects and massive stars encountering AGN discs.

Study on the Pressure Drop Variation and Prediction Model of Heavy Oil Gas-Liquid Two-Phase Flow

To explore the pressure drop variation with the viscosity of heavy oil gas-liquid two-phase flow, experiments with different viscosity gas-liquid two-phase flows are carried out. The experimental results show that the total pressure drop increases with increasing liquid viscosity when the superficial gas and liquid flow rates are the same. The liquid superficial velocity is 0.52 m/s, and the superficial gas velocity is 12 m/s in the vertical and inclined pipes, as there is a negative friction pressure drop when the superficial gas and liquid velocities are small. Additionally, the increased range of the total pressure drop decreases with increasing liquid viscosity. Considering the heavy oil gas-liquid two-phase flow, a prediction model of the pressure drop in high-viscosity liquid-gas two-phase flow is established. The new model is verified by experimental data and compared with existing models. The new model has the smallest error, basically within 15%. Based on the prediction of the wellbore pressure distribution of four wells in the BeiA oilfield, the new model prediction results are closer to the measured results, and the error is the smallest. The new model can be used to predict pressure drops in high-viscosity gas-liquid two-phase flow.

Development and Analysis of Negative Stiffness Friction Damping Device

A new type of negative stiffness friction damping device (NSFDD) was developed in this study, which can solve the problem of poor energy dissipation of the existing passive negative stiffness damping device. The friction force is generated by squeezing the friction plate with the preloaded nitrogen spring vertically. When the NSFDD is working, the friction plate causes the nitrogen spring to rotate and negative stiffness force and friction force are generated. The results of the performance test show that the NSFDD can achieve negative stiffness in the hysteretic model. Comparing with the existing negative stiffness device, the NSFDD has larger stroke, more stable negative stiffness and better energy dissipation capacity. The finite element software has been used to simulate the low cycle reciprocation of a structure, and the results show that the NSFDD reduces the stiffness of the structure while increasing the damping of the structure. The results of the simulation and analysis of the shock absorption plan of the NSFDD show that the NSFDD reduces the stiffness of the floor, thereby effectively control on the shear force, displacement and acceleration response of the structure.

Predicting the Healthy Operation of Heavy Oil Well Casings in Permafrost Regions

This study explores the distribution of stress and deformation on casings in heavy oil recovery wells and the distribution of stress in the thaw bulb in permafrost areas. Considering the expansion of the thaw bulb, the simulation analysis method is used to explore the internal mechanisms of vertical settlement displacement development and stress redistribution within thawed soil and casing. Calculation results show the following: (a) The maximum settlement of the thawed soil and the casing was positively correlated with the expansion of the thaw bulb. Although the settlement of the thawed soil was greater than that of the casing, the initial increase in maximum settlement difference between the thawed soil and the casing eventually tended to be constant due to stabilization of the thaw bulb’s expansion. (b) The size of the thaw bulb directly affects the redistribution of internal stress in thawed soil, leading to different distribution rules for the vertical displacement of thawed soil and casing with depth. (c) Beyond a certain formation depth, the vertical stress of thawed soil gradually transits from a tensile stress state to a compressive stress state. The depth of a soil layer whose horizontal stress value is initially greater than its vertical stress value will gradually deepen with an increase in thaw bulb radius. (d) There is no significant negative friction on the lateral wall of casing in yield state, but significant negative friction exists on the lateral wall of casing in elastic state. The vertical stress of casing in elastic state increased gradually with the increase of casing depth, due to the existence of continuous negative friction and dead weight.

Experimental Study on Bearing Characteristics and Soil Deformation of Necking Pile with Cap Using Transparent Soils Technology

This paper will employ the transparent soil experiment technology to explore the influences of shallow necking on the vertical bearing capacity of single pile with cap. Model experiment is carried out on one intact pile and nine shallow necking piles. The load-settlement curves of all piles are obtained, which are used to study bearing characteristics of piles. The displacement fields of soil around piles are employed to investigate the reasons for the loss of vertical bearing capacity of piles with shallow necking. The vertical bearing capacity is greatly reduced which is caused by shallow necking. When the axial dimension of necking is the same, the larger the radial size is, the greater the loss of vertical bearing capacity is. When the radial dimension of necking is the same, the greater the axial size is, the greater the loss of vertical bearing capacity is. The soil near the pile shaft and under the pile cap produces a large area of vertical downward deformation, which causes the relative displacement between the pile shaft and the soil to greatly reduce. Therefore, it is easy that the necking piles with caps develop negative friction, which causes the vertical bearing capacity of piles to reduce. When the radial dimension of the shallow necking is 80% of pile diameter, the pile is easy to be damaged.

Multistage-based evaluation of tunnelling effects on the skin friction of adjacent building piles in layered media

Pile skin friction performance has been recognized as a significant role in the stability of structures adjacent to underground tunnel constructions. Many previous studies paid attention to the ultimate bearing capacity of the pile when undergoing tunnel excavations, but the skin friction response to multistage tunnelling process is still far from clear. This paper conducted multistage-based modelling about the effect of tunnelling process on the pile-soil interaction in layered soil media, which aims at examining the skin friction performance of the single pile and pile group subject to both vertical building loads and adjacent shield tunnelling. Based on the multistage modelling of the tunnel excavation process, the distribution features and mobilization patterns of the skin friction on single piles were obtained as tunnel excavation continuously proceeded towards the single pile and away from it. In addition, the skin friction behaviours of the double piles and pile group adjacent to shield tunnelling in multi-stages were compared with that of the single pile under the same conditions. The research results show that adjacent tunnelling could cause stress release and additional settlement of the surrounding soils and thus change the distribution features of skin friction of building piles. For double piles, the isolation and dragging effects from the interaction between the front pile and the rear pile are presented and examined. The skin friction distribution on double piles during tunnelling process is primarily dependent on the distance of the pile from the tunnel centreline. For pile groups, the negative skin frictions are easy to appear on the side piles and the centre pile subjected to both vertical loading and adjacent tunnelling.

ПРИМЕНЕНИЕ МЕТАЛЛОПОЛИМЕРНЫХ КОМПОЗИЦИЙ ДЛЯ РЕМОНТНОГО ПРОИЗВОДСТВА И ВОССТАНОВЛЕНИЯ ДЕТАЛЕЙ МАШИН

At repair enterprises, various metal-polymer materials are used to restore the interfaces. Metal-polymer materials can be filled with the following components: steel, bronze, aluminum, titanium. The main advantages of metal polymers are their resistance to negative environmental influences, mechanical friction and high temperatures. (Research purpose) The research purpose is in analyzing the possibilities of metal-polymer materials for effective use in the restoration of machine parts and to give suggestions for improving their physical and mechanical properties during the restoration work. (Materials and methods) Authors studied metal-polymer materials of well-known companies: "Belzona" (USA), "Durmetal" (Switzerland), "Diamant" (Germany), "Loctite" (USA), Chester Molecular (Poland). The article presents the data on their use in the restoration of various parts. The metal polymer materials of foreign companies are characterized by stable quality and high physical and technical characteristics; domestic materials are still inferior to imported ones due to the low quality of the incoming components. (Results and discussion) The main property of coatings is the adhesive strength, which largely determines the resource of the restored part. The main factors that affect the adhesive strength are described in the article. It is possible to significantly increase the adhesive strength of the coatings due to the preliminary electric spark treatment of the worn part. The article presents data on the effectiveness of electric spark coatings as an independent technological process in the restoration of the part. The use of a combined technology of electric spark processing with subsequent application of metal-polymer materials provides undeniable advantages in the restoration of parts. (Conclusions) To improve the physical and mechanical properties of coatings, it is advisable to combine the technology of electric spark processing with the use of metal-polymer coatings. This will expand the possibilities of using part recovery technologies.

Improvement of methods for pile foundations design on settlement

Introduction. The paper describes a new approach for pile foundations design. The system of mechanical impacts is described in a new way for the pile foundation design based on the foundation settlement taking into account the distribution of elastic deformation of the pile material in a soil base.
 
 Materials and methods. In contrast to the existing approaches to determining the pile settlement due to elastic deformations of the pile material, all impacts in the form of load from the pile cap, friction forces on the pile lateral surface and the actual reaction at the pile tip are taken into account differentially according to the principle of forces independence. The new design equation is proposed to describe the distribution of friction forces on the lateral surface of the pile. The friction forces in a homogeneous soil of the base are represented as a parabolic distribution function, and not as a linearly increasing one, as established in the standards.
 
 Results. As a result, the equation is obtained for a pile settlement design due to the elastic strain of pile material. An example of calculating the pile settlement according to the proposed method and comparing the results with existing methods is given. Negative friction forces from the reaction of the soil under the lower end of the pile increase the value of the elastic deformation of the pile shaft.
 
 Conclusions. The refined equation for calculating the elastic component of the pile settlement makes it possible to obtain a lower value of the settlement in comparison with the standard approach by taking into account the influence of friction forces of the soil along the pile lateral surface. The proposed method for pile foundations design based on the settlement can serve as a justification for the reserve of the load-bearing capacity of the pile foundation according to the settlement criterion which will allows obtaining a certain economic effect.

Performance assessment of a novel mechanism design of spark- ignition internal combustion engine

ABSTRACT In this study, the performance of an internal combustion engine with a novel and recently patented mechanism design is studied. The novel mechanism uses a rack and pinion assembly connected to a crank rocker four-bar mechanism instead of the connecting rod. This new design eliminates all the negative friction loss effects of the side-thrust load and the piston slap problems encountered in existing conventional internal combustion engines. The novelty of the patented engine design is in the elimination of the connecting rod and wrist pin used in conventional slider-crank mechanisms. The new mechanism design improves the performance of the engine and removes significant sources of noise accompanied by conventional slider-crank mechanisms. A mathematical model including kinematics and thermodynamics analysis is presented. A simulation code using MATLAB® is developed to obtain the performance curves of the engine with a new design including a pressure-volume diagram, work, and piston velocity. It was found that the new novel engine design produces about 27% higher work per cycle than the conventional engine with identical dimensions, which means that the thermal efficiency is raised by 27%. Furthermore, the new design provides a unique motion profile that decreases the ignition delay time and therefore allows more time for the entire air-fuel mixture to be burned.