Numerical Simulation of Granular Column Collapse with Fractal Particle Size Distribution Using Discrete Element Method

This study conducts numerical simulations of the granular column collapse with Fractal Particle Size Distributions (FPSDs) via the Discrete Element Method (DEM) and investigated kinetic behaviours of dry granular flows. The aim of this paper is to explore the effects of the fractal dimension of FPSD on the kinetics of dry granular flows. When the fractal dimension of the flows consisting of granular materials increases, the horizontal particle translational velocities become greater and the mobility improves, whereas the particle rotational velocities decrease. Meanwhile, the change in the potential energy increases, and the particle kinetic energy in the rotational form reduces; thus, the particle kinetic energy in the translational form increases. The reducing particle rotational movement may be related to the reducing particle shearing behaviours because only the contact shearing can affect particle rotational motion. In conclusion, a larger fractal dimension of FPSD of a dry granular flow leads to a longer spreading distance and a smaller rotational velocity.

Fracture, aggregation and segregation in dry, granular flows

Particle fracture, the formation of small particles as the result of the breakage of large ones, and aggregation, the formation of large particles as the result of the combination of small ones, have important implications in industry (e.g. food processing, pharmaceutical production) and geophysics (e.g., snow avalanches and rock debris flows). Also, the presence of particles of different size that result from fracture and aggregation can induce segregation, resulting in the migration of large and small particles to different regions of the flow. Here, we formulate simple models for fracture and agglomeration and analyze the evolution of measures of the relative concentration of two sizes of spheres due the combined effects of fracture, aggregation, and segregation in dense, dry, granular flows. Particle breakage and combination is influenced by the frequency of collisions, by the local number density of the spheres, and by the particle kinetic energy. Segregation is predicted using a kinetic theory proposed by Larcher & Jenkins [2].

Fully Correlated Stochastic Inter-Particle Collision Model for Euler–Lagrange Gas–Solid Flows

In Lagrangian stochastic collision models, a fictitious particle is generated to act as a collision partner, with a velocity correlated to the velocity of the real colliding particle. However, most often, the fluid velocity seen by this fictitious particles is not accounted for in the generation of the fictitious particle velocity, leading to a de-correlation between the fictitious particle velocity and the local fluid velocity, which, after collision, leads to an unrealistic de-correlation of the real particle velocity and the fluid velocity as seen by the particle. This de-correlation, in turn, causes a spurious decrease of the particle kinetic energy, even though the collisions are assumed perfectly elastic. In this paper, we propose a new model in which the generated fictitious particle velocity is correctly correlated to both the real particle velocity and the local fluid velocity at the particle, hence preventing the spurious loss of the total particle kinetic energy. The model is suitable for small inertial particles. Two algorithms for integrating the collision frequency are also compared to each other. The models are validated using large eddy simulation (LES) of mono-dispersed particle-laden stationary homogeneous isotropic turbulence. Simulations are conducted with spherical particles with different turbulent Stokes number, $$St_t = [0.75 - 5.8]$$ S t t = [ 0.75 - 5.8 ] , and volume fractions, $$\alpha _p = [0.014 - 0.044]$$ α p = [ 0.014 - 0.044 ] , and are compared to the results of the LES using a deterministic discrete particle simulation model.

Studying particle acceleration from driven magnetic reconnection at the termination shock of a relativistic striped wind using particle-in-cell simulations

A rotating pulsar creates a surrounding pulsar wind nebula (PWN) by steadily releasing an energetic wind into the interior of the expanding shockwave of supernova remnant or interstellar medium. At the termination shock of a PWN, the Poynting-flux- dominated relativistic striped wind is compressed. Magnetic reconnection is driven by the compression and converts magnetic energy into particle kinetic energy and accelerating particles to high energies. We carrying out particle-in-cell (PIC) simulations to study the shock structure as well as the energy conversion and particle acceleration mechanism. By analyzing particle trajectories, we find that many particles are accelerated by Fermi-type mechanism. The maximum energy for electrons and positrons can reach hundreds of TeV.

Energy cutoff effect in CORSIKA on the detected particles of ππ0 decay channel

CORSIKA (COsmic Ray SImulations for Kascade) has various features in the creation of the extensive air showers with several characteristics where the users can configure the input card to achieve the desired result. ECUT is a parameter defined as the low energy cutoff of the particle kinetic energy for hadrons, muons, electrons, and photons. We investigate the effect of the different ECUT values on the detected particles in 107 – 5 × 108 GeV primary particle energy range where π–π0 decay channel chosen with 5 km shower development length. The selected ECUT values in this study are 0.05 and 0.1 GeV for both hadrons and muons and 0.05 GeV for electrons and photons. The effect of the reducing by half on the energy cutoff value is studied for the detector array located on an inclined plane, which is planned for upward τ detection.

INSTRUMEN TES ISLAM KIMIA (ITIK) UNTUK MENDETEKSI PEMAHAMAN LEVEL MIKROSKOPIS MATERI AIR

The study aims to develop instrument to measurethe level of understanding of students and microscopic level material phase changes of water. The method used is R&D (Research and Development) Borg and Gall, which have procedure were are following step (1) Need assessment/ Plan (2) Design product/ Organization (3) Created product/ implementation. Implementation with one shot design study with samples used a number of 71 students of 10th grade MA Wahid Hasyim and senior high school MBS Yogyakarta. Indicators in the study is the movement and vibration of water particles, the distance between water particles, particle kinetic energy of water, relative atomic mass of water and hydrogen bonding. The results showed an understanding of chemica lmaterial microscopic level is low and spitual attitude as a nurturant effect is high categories.

Short-wavelength plasma turbulence and temperature anisotropy instabilities: recent computational progress

Plasma turbulence consists of an ensemble of enhanced, broadband electromagnetic fluctuations, typically driven by multi-wave interactions which transfer energy in wavevector space via non- linear cascade processes. Temperature anisotropy instabilities in collisionless plasmas are driven by quasi-linear wave–particle interactions which transfer particle kinetic energy to field fluctuation energy; the resulting enhanced fluctuations are typically narrowband in wavevector magnitude and direction. Whatever their sources, short-wavelength fluctuations are those at which charged particle kinetic, that is, velocity-space, properties are important; these are generally wavelengths of the order of or shorter than the ion inertial length or the thermal ion gyroradius. The purpose of this review is to summarize and interpret recent computational results concerning short-wavelength plasma turbulence, short-wavelength temperature anisotropy instabilities and relationships between the two phenomena.