Particle Friction Coefficient Research Articles

Crystallization in load-controlled shearing flows of monosized spheres.

Identical, inelastic spheres crystallize when sheared between two parallel, bumpy planes under a constant load larger than a minimum value. We investigate the effect of the inter-particle friction coefficient of the sheared particles on the flow dynamics and the crystallization process with discrete element simulations. If the imposed load is about the minimum value to observe crystallization in frictionless spheres, adding small friction to the granular assembly results in a shear band adjacent to one of the planes and one crystallized region, where a plug flow is observed. The ordered particles are arranged in both face-centered cubic and hexagonal-closed packed phases. The particles in the shear band are in between the crystalline state and the fluid state, but the latter is never reached, which results in a large shear resistance. As the particle friction increases, the shear band disappears, and the ordering in the core region is destroyed. A significant portion of the particles are in a fluid state with a zero shear rate, leading to a substantial and unexpected reduction in the shear resistance with respect to the frictionless case. If the imposed load is increased well above the minimum from the onset of crystallization, we observe the formation of one shear band in the core, where the particles are again between the crystalline state and the fluid state, surrounded by two crystallized regions near the boundaries, in which most of the particles are in the face-centered cubic phase and translate as a rigid body with the boundaries themselves. In this case, the macroscopic shear resistance is independent of the particle friction.

Lattice Boltzmann Modeling of Additive Manufacturing of Functionally Graded Materials.

Functionally graded materials (FGMs) show continuous variations in properties and offer unique multifunctional capabilities. This study presents a simulation of the powder bed fusion (PBF) process for FGM fabrication using a combination of Unity-based deposition and lattice Boltzmann method (LBM)-based process models. The study introduces a diffusion model that allows for the simulation of material mixtures, in particular AISI 316L austenitic steel and 18Ni maraging 300 martensitic steel. The Unity-based model simulates particle deposition with controlled distribution, incorporating variations in particle size, friction coefficient, and chamber wall rotation angles. The LBM model that simulated free-surface fluid flow, heat flow, melting, and solidification during the PBF process was extended with diffusion models for mixture fraction and concentration-dependent properties. Comparison of the results obtained in simulation with the experimental data shows that they are consistent. Future research may be connected with further verification and validation of the model, by modeling different materials. The presented model can be used for the simulation, study, modeling, and optimization of the production of functionally graded materials in PBF processes.

Preparation of Soybean Fiber/Sodium Alginate Microgel and Its Application in Low-Fat Yogurt.

This study investigates the oral processing characteristics and application of soybean fiber and sodium alginate microgel in enhancing the texture and sensory attributes of low-fat yogurt. By combining soybean fiber with sodium alginate, a stable composite microgel system was developed with a uniform particle-size distribution. Oral lubrication performance was assessed by evaluating particle size, texture, friction coefficient and rheological properties, providing insights into how microgels improve food lubricity. The results showed that adding soybean fiber/sodium alginate microgel to low-fat yogurt significantly enhanced lubrication, texture and sensory quality compared to standard low-fat yogurt. The yogurt sample containing 2 wt% microgel achieved optimal sensory results, improving hardness and adhesiveness. This study suggests that soybean fiber/sodium alginate microgel offer a promising strategy for enhancing the sensory quality in low-fat dairy products, supporting healthier food innovations.

Influence of wake field inhomogeneity on the vibrational spectra of two dust particles in a plasma with an ion flow

A charged colloidal (dust) particle immersed in a plasma with an ion flow creates a disturbed region behind it, known as a wake. The paper considers a system of two charged and strongly coupled microparticles aligned along the ion flow in a weakly ionized plasma (e.g., in the plasma sheath of a ground-based RF discharge) and confined vertically by an external electric field. Using the OpenDust code, a fully self-consistent numerical simulation of the dynamics of dust particles and the ionic component is carried out. It is demonstrated that the inhomogeneity of the wake field from the upstream particle can significantly change the spectrum of vertical (longitudinal) vibrations of both particles in the system and has a negligible effect on their horizontal (transverse) vibrations. In particular, a relationship exists between horizontal and vertical particle oscillations, manifested as an additional mode of vertical vibrations of particles corresponding to the doubled frequency of their relative horizontal vibrations. In accordance with the model of nonreciprocally coupled stochastically driven oscillators, analytical expressions are derived for the vibrational spectra of particles taking into account the spatial variations in particle charges caused by inhomogeneities in the surrounding plasma. The proposed theory improves the experimental method of spectral response to stochastic processes, enabling the measurement of effective forces, particle friction coefficients, and temperatures of their heat sources, as well as the horizontal charge gradient of the lower particle oscillating in the wake field of the upper one.

Kinematic mechanics study of silicon wafers and glass particles oscillatory separation based on friction coefficient differences

Kinematic mechanics study of silicon wafers and glass particles oscillatory separation based on friction coefficient differences

DEM study on the force chain evolution of biaxial compression of pebble bed

DEM study on the force chain evolution of biaxial compression of pebble bed

Numerical Study on the Anti-Sloshing Effect of Horizontal Baffles in a Cargo Hold Loaded with Liquefied Cargo

Sloshing of liquefied bulk granular cargoes weakens the stability of cargo carriers when at sea. Using the horizontal rectangle baffle is a promising way to restrain its sloshing motion. But the location height and optimal baffle area rate to achieve a better anti-sloshing effect should be studied first. The discrete element method was adopted to establish the simulation model, and the direct shear test was used for verification. Through the static tilt tests, the definite relationship between the effects of moisture content on cargo motion and particle friction coefficients was acquired. Then, liquefied cargo motion in a cargo hold without baffles and with one and two pairs of horizontal baffles was simulated. Based on variations in the cargo gravity center offset and the sloshing-induced force on the cargo hold, the anti-sloshing effect of different settings of the baffles was compared. Results show that the baffles have the ability to restrain cargo sloshing, and this is important for sea transportation safety. The anti-sloshing effect is better when the baffle plane is right on the cargo top surface compared to the other location heights. Further, there is an optimal length–width combination, e.g., a single baffle plane with a length of 0.26 L and a width of 0.46 B, at which a better anti-sloshing effect could be achieved with the smallest baffle area rate. This study could be useful for the practical application of horizontal baffles for bulk granular cargo carriers.

The interactive force between fat, oil, and grease (FOG) deposits and the effect of food waste disposers on kitchen drainage systems

Food waste disposers (FWDs) streamline kitchen waste management and facilitate waste classification, whether they would increase the potential of blockage in kitchen drainage system is still unknown. This study conducted a theoretical analysis of the interactive forces between fat, oil, and grease (FOG) deposits and their aggregation on pipe walls. The study involved grading food waste particles processed by FWDs using sieving and weighing techniques to determine the mean weight diameter (MWD) of various aggregations. A full-scale experimental system, implemented in a 60-m high test tower, simulated blockages in horizontal pipes of high-rise buildings. The effect of pipeline materials and particle sizes on blockage were examined by measuring the adhesion of deposits on horizontal pipes. Energy dispersive spectrometer (EDS) analysis suggested that liquid bridge force is a primary factor in aggregate formation. Hand-cut particles formed aggregates with the highest MWD value. Particle size analysis revealed that sizes ranging from 2.36 to 4.75mm, 1.18-2.36mm, and 0.60-1.18mm constituted over 80% of particles ground by FWDs, with an average size of 2.16mm. Results of full-scale experiment indicate particle diameters, friction coefficients and lipophilic coefficient significantly affected the propensity of these aggregates to adhere to pipes. Notably, particles processed by FWDs tended to cause blockages more frequently than hand-cut particles. These findings elucidate the deposition mechanism of FOG deposits and offer strategies to reduce blockages in kitchen drainage systems, such as reducing current grinding particle size by 18% to 1.77mm or selecting pipes like cast iron and high-density polyethylene.

Numerical investigation of the instability of dry granular bed induced by water leakage

AbstractUnderground pipe defects or cracks under transport infrastructure can cause water leakage to upper soil layers (e.g. subgrade and capping), inducing local cavities or even failure of overlying road/railway formation. Although numerous studies on the instability of granular beds induced by injected water have been conducted, most of them focused on the behaviour of saturated granular beds, while research on dry granular beds is still limited. This paper aims to address this gap using a numerical model coupling volume of fluid method with discrete element method. We observed that dry granular beds go through three distinct regimes as water jet velocity increases including stationary, stable deformation with heave and fluidisation. However, the flow velocities required to deform and fluidise dry granular beds are significantly higher than those required for saturated beds. Increasing granular bed thickness can alter its failure mechanism from full depth to localised erosion, leading to cavity formation around pipe cracks prior to the bed fluidisation. The gravitational and frictional components of granular mass are identified as two main resisting forces of dry granular beds against water jet force, evidenced by the increase of critical jet velocities as particle density and friction coefficient increase. Nevertheless, the moblised zone of granular mass is practically independent of both the buried depth of dry granular beds.

Microrheology of active suspensions.

We study the microrheology of active suspensions through direct hydrodynamic simulations using model pusher-like microswimmers. We demonstrate that the friction coefficient of a probe particle is notably reduced by hydrodynamic interactions (HIs) among a moving probe and the swimmers. When a swimmer approaches a probe from the rear (front) side, the repulsive HIs between them are weakened (intensified), which results in a slight front-rear asymmetry in swimmer orientation distribution around the probe, creating a significant additional net driving force acting on the probe from the rear side. The present drag-reduction mechanism qualitatively differs from that of the viscosity-reduction observed in sheared bulk systems and depends on probing details. This study provides insights into our fundamental knowledge of hydrodynamic effects in active suspensions and serves as a practical example illuminating distinctions between micro- and macrorheology measurements.

Innovative design and experimental validation of dynamic balance in rotary compressors based on particle damping energy dissipation technology

Dynamic imbalance is one of the primary issues in rotary compressor applications, which can generate significant vibration. A dynamic balance design is required to minimize the moment and additional inertia force, which can be eliminated by adding a counterweight. This paper utilized a solid plate that has cavities filled with particle damper as a novel design to satisfy the dynamic balance. Vibrational energy is dissipated in collisions between particles through momentum exchange and is converted into energy for consumption that consists of inelastic collision energy and frictional energy. The discrete element method (DEM) and multi-body dynamics (MBD) were applied for two-way coupling for a dynamic balance simulation. The impact of particle size, friction coefficient, and restitution coefficient on energy dissipation in rotary compressors was evaluated, and the particle radius of 1 mm produced the most satisfactory. The experiment measured the vibrational acceleration in the tangential and radial directions at a particular duration and frequency to reflect the particle damper’s dynamic balance and energy dissipation effect. Both simulation and experimental results confirmed that the novel design features are more acceptable than the original to satisfy the dynamic balance of a rotary compressor.

Comment on "Brownian motion with time-dependent friction and single-particle dynamics in liquids".

Recently, Lad, Patel, and Pratap [Phys. Rev. E 105, 064107 (2022)10.1103/PhysRevE.105.064107] revisited a microscopic theory of molecular motion in liquids, proposed by Glass and Rice [Phys. Rev. 176, 239 (1968)10.1103/PhysRev.176.239]. They argued that the friction coefficient for a Brownian particle in a liquid should exponentially depend on time and derived an equation of motion for the particle's velocity autocorrelation function (VAF). The equation was solved numerically and fitted to the results of molecular dynamics simulations on different liquids. We show that this solution, obtained under the condition of zero derivative of the VAF at time t=0, is physically incorrect at long times. This is evidenced by our exact analytical solution for the VAF, not found by Lad etal., and numerically, by using the same method as in the commented work.

Influence of the interparticle friction coefficient on the mechanical behaviour of breakable granular materials with realistic shape

Influence of the interparticle friction coefficient on the mechanical behaviour of breakable granular materials with realistic shape

Numerical Simulation of Ground Subsidence Factors Resulting from Unpressurized Pipeline Rupture Below the Water Table

The rupture of an unpressurized pipeline below the water table can lead to the leakage of groundwater along with soil particles into the pipeline. This not only causes blockages in the pipeline but, more critically, can result in ground subsidence. Understanding the factors influencing this phenomenon is a subject of great interest. To delve into this matter, this study employs the DEM-CFD methodology to synergistically encompass particle dynamics and interactions within the flow domain. It introduces an innovative framework for simulating water and soil erosion subsequent to the rupture of subaqueous unpressurized pipelines. This pioneering approach introduces a novel modeling and simulation paradigm catering to the analysis of intricate phenomena of this nature. Upon validating the flow field, our investigation specifically focused on three key factors: particle friction coefficient, groundwater level, and particle size distribution. We conducted a thorough examination of the process and mechanism of water and soil loss at the pipeline leakage point and the subsequent development of stratum subsidence. Our results indicate that particles with a friction coefficient of 0.6 had a reduced maximum displacement by 8.9%, compared to particles with a friction coefficient of 0.3. Similarly, a groundwater depth of 2 m resulted in a 29.6% decrease in maximum displacement compared to a 4 m depth, with a corresponding 160.9% increase in maximum force chain strength. Discontinuous particle gradation, in contrast to continuous gradation, yielded a notable 40.3% reduction in maximum displacement and a substantial 495.1% increase in maximum force chain strength. This underscores the noteworthy influence of particle friction coefficient, groundwater table elevation, and soil particle diameter on the stability of the overlying soil strata in the vicinity of a compromised unpressurized conduit.

Generalized Langevin equation for solute dynamics in fluids with time-dependent friction

Generalized Langevin equation for solute dynamics in fluids with time-dependent friction

DEM calibration for simulating bulk cohesive materials

The Discrete Element Method (DEM) has the prospect of accurately modelling the bulk flows of cohesive materials if the cohesive input parameters are reliably calibrated. Accordingly, bulk calibration of the linear cohesive contact model’s parameters was investigated. To this end, three grades of dry (non-cohesive) sand were calibrated using conventional approaches. Additionally, the effects of particle upscaling on the parameters were concurrently examined. Subsequently, water-induced cohesivity was introduced to the samples. It was found that the induced cohesivity did not alter the particle stiffness or the particle–particle friction coefficient. Furthermore, it was found that the calibrated particle stiffness increased with particle scale and that the friction coefficient was scale invariant. In addition, measuring the angle of repose with a vertical displacement mechanism provided a means of quantifying the angle of repose’s increase with cohesivity if the angle did not approach the vertical. The latter was combined with the draw-down and rotating drum test to calibrate the two sand grades with less prominent cohesion. Finally, a granular centrifuge was utilised to quantify the smallest sand grade’s distinct cohesive behaviour. Consequently, the cohesive contact parameter’s rupture force increased cubically with particle scale, whilst the rupture distance was insensitive to scale.

Study of cone penetration test in granular soil considering realistic particle shapes by discrete element method in 3D

This paper aims to investigate the impact of the particle shape of granular soil particles on the results of cone penetration test (CPT). The discrete element method (DEM) was used to model the CPT in soil particle samples in 3D. The influence of particle shape is studied by parameters of overall regularity (OR), which is obtained from different mixing ratios of the real shape particles and spherical particles. The real particle shapes are obtained from a 3D laser scanner for the simulations. The particle refinement method is applied to enhance computation efficiency. The cone resistance and sleeve resistance curves are smoothed by fitting equations. The factors of OR of soil, particle friction coefficient, particle roundness and initial porosity were demonstrated to have considerable influences on the cone tip resistance and sleeve resistance. The displacement field and the rotational field were plotted to study the microscopic behaviour of granular soils during the penetration process.

Predicting residual friction angle of lunar regolith based on Chang’e-5 lunar samples

With the rapid development of human lunar exploration projects, the lunar base establishment and resource utilization are on the way, and hence it is urgent and significant to reasonably predict engineering properties of the lunar regolith, which remains to be unclear due to limited lunar samples currently accessible for geotechnical tests. In this contribution, we aim to address this outstanding challenge from the perspective of granular material mechanics. To this end, the 3D multi-aspect geometrical characteristics and mechanical properties of Chang'e-5 lunar samples are for the first time evaluated with a series of non-destructive microscopic tests. Based on the measured particle surface roughness and Young's modulus, the interparticle friction coefficients of lunar regolith particles are well predicted through an experimental fitting approach using previously published data on terrestrial geomaterials or engineering materials. Then the residual friction angle of the lunar regolith under low confining pressure is predicted as 53° to 56° according to the particle overall regularity and interparticle friction coefficients of Chang'e-5 lunar samples. The presented results provide a novel cross-scale method to predict engineering properties of the lunar regolith from particle scale information to serve for the future lunar surface engineering construction.

3D DEM Simulations and Experiments on Spherical Impactor Penetrating into the Elongated Particles.

In this study, a brass or glass spherical impactor vertically penetrating into a granular bed composed of mono-sized spherical or elongated particles was simulated with three-dimensional (3D) discrete element method (DEM). Good agreement of the particle masses in the cup before and after penetration can be found in the simulations and experiments. The effects of particle length (Lp), friction coefficient, and particle configuration on the penetration depth of the impactor, ejecta mass, and solid volume fraction describing the response of the granular bed are discussed. The penetration depth is negatively correlated with Lp as the corresponding solid volume fraction of the granular bed decreases. A smaller friction coefficient leads to a larger penetration depth of the impactor and more ejection of particles. When the impactor is penetrating the Lp = 10 mm elongated particles, the penetration depth is negatively correlated to the order parameter and solid volume fraction.

Insight on bulk shear strength parameters of clay using discrete element approach incorporating physics-based interparticle force model

Insight on bulk shear strength parameters of clay using discrete element approach incorporating physics-based interparticle force model