Ping Lin

Influence of geometrical and material parameters on flow rate in simplified ADS dense granular-flow target: a preliminary study

ABSTRACT The spallation target is one of the key components of an accelerator-driven subcritical system (ADS). Following previous designs such as plate targets, rod targets, rotating targets, and liquid metal targets, the gravity-driven dense granular-flow target (DGT), which combines the advantages of solid and liquid metal targets, becomes a new attractive choice. The geometry of DGT consists of a cylindrical hopper and an internal coaxial cylindrical beam pipe. In this paper, using discrete element method simulations on graphics processing units, we research into the relations of the flow rate with the geometrical as well as the material parameters. For geometrical parameters, it is found that the existence of an internal pipe does not influence the flow rate when the distance from the bottom of the pipe to orifice is large enough. The results also reveal how the material parameters influence the flow rate. The whole research is helpful for the design of DGT.

Implementing discrete element method for large-scale simulation of particles on multiple GPUs

Abstract Recently, the use of graphics processing units (GPUs) has become popular in scientific computations due to their low cost, impressive floating-point capabilities, high memory bandwidth, and low electrical power requirements. Discrete element method (DEM), closely related to molecular dynamics (MD), is a widely-accepted method for simulating particle systems, such as powders, bubbles, grains, etc. In this work, we present an efficient implementation of DEM on multiple GPUs. Linked-cell list method is used to accelerate recognition of contacting particles and is beneficial for communications among multiple GPUs. Moreover, asynchronous communication is used to reduce the time costs of communications. Physical validation is performed and parallel efficiency is evaluated, showing that our implementation has high computational efficiency and good scalability. The simulation of a large-scale dense particle system (up to 128,000,000) is achieved with a good parallel efficiency. The speed-up ratio in 16 GPUs vs 128 CPU cores is 10.39.

Preliminary research on flow rate and free surface of the accelerator driven subcritical system gravity-driven dense granular-flow target

A spallation target is one of the three core parts of the accelerator driven subcritical system (ADS), which has already been investigated for decades. Recently, a gravity-driven Dense Granular-flow Target (DGT) is proposed, which consists of a cylindrical hopper and an internal coaxial cylindrical beam pipe. The research on the flow rate and free surface are important for the design of the target whether in Heavy Liquid Metal (HLM) targets or the DGT. In this paper, the relations of flow rate and the geometry of the DGT are investigated. Simulations based on the discrete element method (DEM) implementing on Graphics Processing Units (GPUs) and experiments are both performed. It is found that the existence of an internal pipe doesn’t influence the flow rate when the distance from the bottom of the pipe to orifice is large enough even in a larger system. Meanwhile, snapshots of the free surface formed just below the beam pipe are given. It is observed that the free surface is stable over time. The entire research is meaningful for the design of DGT.

Simulation of Heat Transfer in Granular Systems with DEM on GPUs

Heat transfer in granular system is very important for science studies and industrial designs. Here we developed the code of heat transfer in granular system (including three heat conduction modes and heat radiation between particles) and integrate this code with our previous DEM code on Graphics Processing Units (GPUs). A simple experiment was made and a comparison between numerical results and experiment of heat transfer in granular packs shows a good validity of our code. The scalability test was performed and it shows that the time cost of calculation of heat transfer is acceptable. Therefore, a large-scale simulation of granular system with considering both of dynamic behavior and heat transfer is feasible. This work could be very helpful for design of granular-flow target systems.

Constructing Weighted Gene Correlation Network on GPUs

Here we constructed a weighted gene correlation network in human glioblastoma cells by developing the graphics processing units (GPUs) algorithm. The strength distributions of entire network, housekeeping genes and hubs in protein interaction network were calculated and the differences between them were found. Six definitions of clustering coefficient previously proposed for weighted networks were calculated in this paper and behaved quite differently. Interestingly, the clustering coefficient distributions of housekeeping genes and hubs are similar to that of entire network, as the strengths of them are generally bigger. This work explored how to calculate the network indices in weighted biological networks on GPUs and whether these indices can reflect the characteristics of biological networks.

Evaluation of Influences of Frictions in Hopper Flows Through GPU Simulations

The applicability of general purpose computing on GPUs for scientific and engineering applications has been growing several folds in recent years. Discrete Element method (DEM) is a way to modelling of particles, in which microscopic understanding of millions of particles is studied through simulation of granular materials such as sand or powders. Taking advantage of the highly data parallel nature of such computations, the benefits of executing DEM simulations have been widely spotlighted, and accelerations of computations through heterogeneous many-core environments are expressive. In this work, we present efficient implementations and investigate the applicability of GPUs to DEM used in particle motion simulation. In our implementations, algorithms such as neighbor list generation and pointer-exchange are performed. For the design of granular flow target, the influence of different frictions in hopper flows are investigated and presented here.

Influence of Inclined Angles on the Stability of Inclined Granular Flows Down Rough Bottoms

The inclined granular flow offers the explanations for many phenomenon and is a potential choice as a high-power spallation target. Here we studied about the stability of the inclined granular flows down rough bottoms. Following the previous work, we mainly studied about the influence of inclined angles on the stability of flows. There are some conclusions of this work: (1) the flows with various inclination angles can be divided into five regions. (2) The oscillation flow region can be further divided into three sub-regions according to the oscillation modes. (3) Bagnold profile is valid in disordered flows but not in ordered flows. In ordered flows, there are local maximum values in shear rate profiles. (4) The oscillation flow region is a transition region between ordered and disordered flow region, where the self-organization and dilatant are shown more clearly.