Pattern formation in particle systems driven by color field

The structural evolution of systems with two kinds of particles driven in opposite directions, i.e., driven by a color field, is investigated by molecular dynamics simulations. Gaussian thermostat, a common treatment to restrict the thermal velocity of the particles in the systems, has been used so as to account for the dissipation of heat and allow the system to reach a steady state. It has been found that with the increase of the strength of driving force (F), the system undergoes an obvious structural transition from an initially random mixing state to a state characterized by separate lanes and in each lane only one kind of particles exists. The analysis shows that the reason for the formation of lane structure is not only the increase of F but also the variation of particle friction coefficient. While using Gaussian thermostat the particle friction coefficient becomes a function of F. Increasing F leads to high particle friction coefficient and inevitably results in lane formation for strong enough driving force. When lifting the effect of F on friction coefficient and choosing a constant friction coefficient, our results show that for a given F there always exists a critical value of friction coefficient higher than which the system will develop into lane structure. (c) 2008 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.The structural evolution of systems with two kinds of particles driven in opposite directions, i.e., driven by a color field, is investigated by molecular dynamics simulations. Gaussian thermostat, a common treatment to restrict the thermal velocity of the particles in the systems, has been used so as to account for the dissipation of heat and allow the system to reach a steady state. It has been found that with the increase of the strength of driving force (F), the system undergoes an obvious structural transition from an initially random mixing state to a state characterized by separate lanes and in each lane only one kind of particles exists. The analysis shows that the reason for the formation of lane structure is not only the increase of F but also the variation of particle friction coefficient. While using Gaussian thermostat the particle friction coefficient becomes a function of F. Increasing F leads to high particle friction coefficient and inevitably results in lane formation for strong enough driving force. When lifting the effect of F on friction coefficient and choosing a constant friction coefficient, our results show that for a given F there always exists a critical value of friction coefficient higher than which the system will develop into lane structure. (c) 2008 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved

Prog. Chem.

The mixing of granular materials is an important unit operation in many industries. Due to the complex behaviors of granular flows, general laws and fundamental mechanisms of granular flows in industrial mixers are not completely understood yet. As a detailed numerical approach, the discrete element method (DEM) describes the forces and motions of granular materials at the particle scale, and thus has notable advantages over experimental approaches in the research of mixing mechanisms. With the rapid developments of its models and the computational technologies, this method becomes more and more popular in the simulations of various mixing processes. The effects of particle properties, mixer types, and operating parameters on mixing rate and mixing mechanisms could be investigated comprehensively through DEM, which would be quite valuable for the design and optimization of mixers as well as their optimal operations. Moreover, the high computational cost of industrial-scale simulations could be greatly alleviated by the fast developments of computer hardware, such as the advent of graphics processing unit (GPU). This review summarizes the recent progresses of DEM simulations on mixing, with emphasis on the treatments for non-cohesive particles in different kinds of mixers (rotary and fixed), cohesive particles (fine and wet), non-spherical particles (direct description of shape and multi-sphere method), and large-scale implementations. Finally, future development of the DEM method in mixing simulations is prospected. The mixing of granular materials is an important unit operation in many industries. Due to the complex behaviors of granular flows, general laws and fundamental mechanisms of granular flows in industrial mixers are not completely understood yet. As a detailed numerical approach, the discrete element method (DEM) describes the forces and motions of granular materials at the particle scale, and thus has notable advantages over experimental approaches in the research of mixing mechanisms. With the rapid developments of its models and the computational technologies, this method becomes more and more popular in the simulations of various mixing processes. The effects of particle properties, mixer types, and operating parameters on mixing rate and mixing mechanisms could be investigated comprehensively through DEM, which would be quite valuable for the design and optimization of mixers as well as their optimal operations. Moreover, the high computational cost of industrial-scale simulations could be greatly alleviated by the fast developments of computer hardware, such as the advent of graphics processing unit (GPU). This review summarizes the recent progresses of DEM simulations on mixing, with emphasis on the treatments for non-cohesive particles in different kinds of mixers (rotary and fixed), cohesive particles (fine and wet), non-spherical particles (direct description of shape and multi-sphere method), and large-scale implementations. Finally, future development of the DEM method in mixing simulations is prospected.</p

Removal of antibiotics with different charges in water by graphene oxide membranes

Antibiotics are a large group of emerging organic pollutants with low concentration levels in the water. The presence of antibiotics will affect the ecological environment and human health. The removal of trace organic compounds by graphene oxide (GO) membranes has attracted extensive attention. This study investigated the removal of three differently charged antibiotics by GO membranes and the influence of water quality on the removal of antibiotics. It showed that a crosslinked ethylenediamine-GO (EDA-GO) membrane had better stability and higher antibiotic removal performance than a non-crosslinked GO membrane. Among the three antibiotics, penicillin (PNC) was negatively charged and had the highest removal efficiency due to steric effect and electrostatic repulsion. A low concentration (10 mmol L−1) of Na+ in water could increase the membrane flux but had no significant effect on the removal of antibiotics. Ca2+ could reduce the membrane flux and improve the removal of chloramphenicol (CAP) and PNC. The removal efficiencies of low-concentration antibiotics (500 μg L−1) were higher than those of high-concentration antibiotics (10 mg L−1). Furthermore, the removal of antibiotics under the condition of actual wastewater quality was higher than those in solutions prepared with ultrapure water. The EDA-GO membrane has great potential in the removal of antibiotics in wastewater. HIGHLIGHTS The removal of three differently charged antibiotics by GO membranes was studied.; Crosslinked EDA-GO membrane had higher removal performance and better stability.; The removal of PNC with a negative charge was higher than CAP and ERY.; Ca2+ could reduce the membrane flux and increase the removal of antibiotics.; The removal of antibiotics under the condition of actual wastewater quality was higher.

Numerical investigation of granular flow similarity in rotating drums

The theory of flow similarity has not been well established for granular flows, in contrast to the case for conventional fluids, owing to a lack of reliable and general constitutive laws for their continuum description. A rigorous investigation of the similarity of velocity fields in different granular systems would be valuable to theoretical studies. However, experimental measurements face technological and physical problems. Numerical simulations that employ the discrete element method (DEM) may be an alternative to experiments by providing similar results, where quantitative analysis could be implemented with virtually no limitation. In this study, the similarity of velocity fields is investigated for the rolling regime of rotating drums by conducting simulations based on the DEM and using graphics processing units. For a constant Froude number, it is found that the particle-to-drum size ratio plays a dominant role in the determination of the velocity field, while the velocity field is much more sensitive to some material properties than to others. The implications of these findings are discussed in terms of establishing theoretical similarity laws for granular flows. (C) 2015 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.</p

GPU-based discrete element simulation on a tote blender for performance improvement

The mixing and flow of granular materials in a conical tote blender are investigated using a GPU-based DEM software to explore new approaches to enhance mixing. The structure and dimensions of the blender and other simulation conditions are set according to experimental data from literature. A parametric study on fill level and rotation rate is carried out from which optimum values are found with respect to mixing rate, productivity and energy consumption. It is also found that the standard horizontal installation of the blender results in poor axial mixing, while inclining the blender at a certain angle can enhance mixing effectively. This may be ascribed to the larger mean particles velocity and better velocity distribution under such conditions, which is confirmed to be a consistent character for relatively large-scale systems. Furthermore, the effect of operating conditions for the inclined blender is also examined. It is close to those for the standard blender but has less effect on mixing rate. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved

Characteristics of NE strike-slip fault system in the eastern section of Bachu-Maigaiti area, Tarim Basin and its oil-gas geological significance

Many Ordovician reservoirs discovered in the eastern section of Bachu-Maigaiti area ("Bamai area" for short) in the Tarim Basin are closely related to multi-stage active faults, making it the key to find oil and gas reservoirs in this area by identifying the source faults that cut through Cambrian gypsum-salt layers. Combined with the analysis of fault structure based on a large number of new seismic data and previous studies, the fault system in the eastern section of the Bamai area, especially the distribution and activity characteristics of strike slip faults are reunderstood. The results show that along with the migration and evolution of palaeo-uplift and the activities of large thrust fault zones in Bamai area, a series of high-angle and small-distance NE strike-slip faults that play a role of deformation and regulation are also developed, which together constitute the deformation tectonic system in the area. Two types of strike slip faults are developed in this area. One is superimposed and developed simultaneously or later with the NE and nearly EW Cambrian post-salt decollement zone of bruchfalten, with its strike consistent with that of the thrust fault belt, which is mainly distributed in the boundary and interior of the Hetian paleo-uplift. The other is developed in the compression-shortening zone confined by the large thrust fault belt, intersected with the nearly EW thrust fault belt at a large angle, and mainly distributed in the Hetian palaeo-uplift and Bachu faulted uplift. The former mainly formed in the late Hercynian period with weak local activities in the late Himalayan period, and the latter mainly formed in the late Himalayan period. The strike-slip faults superimposed with the Ordovician carbonate rocks that has experienced karst transformation in the middle and late Caledonian and early Hercynian are more conducive to the formation of effective fracture-karst vug reservoirs. They connect the upper and lower strata of the gypsum-salt layers, and their active period is consistent with the main hydrocarbon generation period of the deep subsalt source rocks, which is more conducive to transporting hydrocarbon source upward to the Ordovician system for accumulation. The large-scale reservoir located above the source and connected with two types of high-angle strike-slip faults is the favorable exploration direction of Ordovician

Quasi-real-time simulation of rotating drum using discrete element method with parallel GPU computing

A single GPU is used to simulate a small model system with about 8000 particles in real-time, and the simulation is then scaled up to industrial scale using more than 200 GPUs in a 1D domain-decomposition parallelization mode. The overall speed is about 1/11 of the real-time

Quasi-real-time simulation of rotating drum using discrete element method with parallel GPU computing

Real-time simulation of industrial equipment is a huge challenge nowadays. The high performance and fine-grained parallel computing provided by graphics processing units (GPUs) bring us closer to our goals. In this article, an industrial-scale rotating drum is simulated using simplified discrete element method (DEM) without consideration of the tangential components of contact force and particle rotation. A single CPU is used first to simulate a small model system with about 8000 particles in real-time, and the simulation is then scaled up to industrial scale using more than 200 GPUs in a 10 domain-decomposition parallelization mode. The overall speed is about 1/11 of the real-time. Optimization of the communication part of the parallel GPU codes can speed up the simulation further, indicating that such real-time simulations have not only methodological but also industrial implications in the near future. (C) 2011 Published by Elsevier B.V. on behalf of Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences