Granular Matter最新文献

Granular dampers are systems used to attenuate undesired vibrations produced by mechanical devices. They consist of cavities filled by granular particles. In this work, we consider a granular damper filled with a binary mixture of frictionless spherical particles of the same material but different size using numerical discrete element method simulations. We show that the damping efficiency is largely influenced by the composition of the binary mixture.

The non-coaxiality of monotonous loading for granular materials has been studied in laboratory tests and simulations using the discrete element method (DEM). However, the non-coaxiality and its relation to the fabric evolution under the stress path of circular rotational shear in the deviatoric plane remain largely unanswered. To address this issue, we report a series of true triaxial DEM simulations on initial isotropic samples to investigate the effects of stress-induced anisotropy on non-coaxiality and its fabric evolution. The mechanical behavior was captured by continuously changing the Lode angle (theta _sigma) under a wide range of confining pressure (sigma _c), while the deviatoric stress q remains constant. In addition, the role of inter-particle friction on the non-coaxial response has been explored to elaborate on the effects of the changing of micro-structure on the macro-mechanical performance. Simulation results indicate that the non-coaxiality is the function of the stress ratio (eta), confining pressure (sigma _c), and inter-particle friction, which could be related to the orientation variation of contact fabric. The deviation of (theta _{text {d}varvec{varepsilon }}) from the loading direction (theta _{text {d}varvec{sigma }}) gradually increase as the rise of stress ratio (eta), while it shows an obvious decrease trend with the increase of confining pressure (sigma _c) and inter-particle friction coefficient (mu). As for fabric evolution, it verifies the correlation between the non-coaxial response and fabric evolution in rotational shear. The directional evolution of incremental fabric (theta _{text {d}varvec{F}}) are sensitive to stress ratio (eta), while it is insensitive to confining pressure (sigma _c) and inter-particle friction coefficient (mu) than the non-coaxial response.

Graphical Abstract

A particle damper (PD) is an enclosure partially filled with small particles that can help to dampen the vibration of a structure. Despite its simplicity, the reliable prediction of the behavior of such a device in arbitrary operative conditions appears to be very difficult due to the complex non-linear interactions between the particles and the system. An experimental methodology is defined with the aim of minimizing the bias due to the PD non-linear response. The effect of the mutual orientation of motion, gravity, and enclosure and of different disturbance inputs on the performance of a PD is investigated in order to make available a set of reference experimental results for correlation purposes with prediction tools. An open-access database, gathering all the test results, is made available.

Graphical abstract

Vibratory feeders are vastly used in a variety of applications such as minerals, petrochemical and food industries in order to transport the small parts such as granular materials. In this research, a flow of black pepper seeds in a vibratory feeder is modelled using discrete element method. The effects of tank vibration frequency, amplitude, and slope and the angle in which the motor orients on mass flow rate and motor required power are studied. The aim of this study is to reach an optimal design of vibratory feeder to obtain higher efficiency. The results of simulations are analyzed using analysis of variance. It is found that the most effective parameters on the mass flow rate and the required power are the motor orientation and the tank frequency, respectively. The best outcome corresponding to the maximum mass flow rate and the minimum required power is found to occur at the frequency of 15 Hz, amplitude of 15 mm, the tank slope of 5° and the motor angle of 45°.

Graphical abstract

Variations of the mass flow rate of pepper seeds and required power of motor with the four parameters

Two-dimensional discrete element method (DEM) is used to study the undrained cyclic behavior and cyclic resistance of dense granular materials under cyclic triaxial loading without stress reversals, and to clarify the effect of initial static shear on liquefaction resistance and the underlying micro-mechanism. A series of undrained stress-controlled cyclic triaxial tests were simulated with different combinations of cyclic stress ratio CSR and initial static shear stress ratio α, where the cyclic behavior of “residual deformation accumulation” was identified. Two types of residual excess pore pressure generation patterns were distinguished by the degree of stress reversal D (D = CSR/ α). The growth rate of residual axial strain is both CSR- and α -dependent. The evolution of internal structure of the granular materials was quantified using a contact-normal-based fabric tensor and mechanical coordination number MCN. The larger α (i.e., smaller consolidation stress ratios in triaxial tests) leads to higher degree of stress-induced fabric anisotropy. The cyclic resistance of dense granular materials increases with initial fabric anisotropy. During cyclic loading, the dense granular materials with higher initial fabric anisotropy exhibited slower reduction in mechanical coordination number between soil particles. The present study shed lights on the underlying mechanism that why the presence of initial static shear is beneficial to the cyclic resistance for dense granular materials under cyclic triaxial test condition.

Gas permeation and consequent powder consolidation during gas pressurization process easily cause deterioration of powder flowability. The effects of pressurization rate and powder properties on gas permeation and powder consolidation were investigated to reveal the change mechanism of powder flow properties in a sealed silo. The permeation time and gas velocity within the powder were examined to acquire the gas permeation characteristics at different pressurization rates. The distribution and evolution laws of powder stress were explored during the gas pressurization process. The powder stress during gas pressurization was more than 100 times that without aeration. A formula was derived for calculating the powder stresses and the results were compared with experimental data to confirm the consolidation mechanism. Based on the evolution of consolidation stress, the variation of the powder flow properties at different pressurization rates was revealed. The tensile strength of the powder and its change law in the gas pressurization process were examined with an adhesion force model.

Gravel cushions are widely laid on the top of structures or rock sheds to absorb the impact energy of rockfalls in mountainous districts. Based on the discrete element method, a numerical model of a rockfall impacting a 2D mixed-size gravel cushion layer at an initial angular velocity was established in this study. The penetration depth of the rockfall, impact force of the cushion surface, and energy dissipation ratio were investigated. Increasing the initial angular velocity and decreasing the particle size of the cushion were found to evidently reduce the maximum penetration depth of the rockfall and increase the impact force of the cushion surface, respectively. The energy dissipation ratio after collision was affected by the particle size of the cushion and the ratio of the angular kinetic energy. Omitting the initial angular velocity led to an underestimation of the energy dissipation ratio, by up to 40.8%. With decreasing particle size of the cushion, the energy dissipation ratio first increased but then decreased. The study results provide a theoretical basis for the design of gravel cushions intended for rockfall protection.

This work presents an experimental study of the response of a liquid bridge formed between a sphere and a plane solid surface subjected to a vertical sinusoidal vibration. The amplitude and frequency of the oscillations can be varied. The successive movement of the particle along with the bridge deformation is registered to follow the dynamics of the system. The motivation is to figure out how capillary and viscosity forces can be modeled with the help of the experimental data obtained and to settle down a simplified theoretical approach capable of being implemented in the description of many phenomena involving wet granular grains. The results indicate that the viscosity effects can be neglected as soon as the amplitude of the movement is not too small, still obtaining a reasonable description of the dynamical behavior of the sphere/liquid-bridge system.

Graphical abstract