A GPU-accelerated package for simulation of flow in nanoporous source rocks with many-body dissipative particle dynamics

Mesoscopic simulations of hydrocarbon flow in source shales are challenging, in part due to the heterogeneous shale pores with sizes ranging from a few nanometers to a few micrometers. Additionally, the sub-continuum fluid-fluid and fluid-solid interactions in nano- to micro-scale shale pores, which are physically and chemically sophisticated, must be captured. To address those challenges, we present a GPU-accelerated package for simulation of flow in nano- to micro-pore networks with a many-body dissipative particle dynamics (mDPD) mesoscale model. Based on a fully distributed parallel paradigm, the code offloads all intensive workloads on GPUs. Other advancements, such as smart particle packing and no-slip boundary condition in complex pore geometries, are also implemented for the construction and the simulation of the realistic shale pores from 3D nanometer-resolution stack images. Our code is validated for accuracy and compared against the CPU counterpart for speedup. In our benchmark tests, the code delivers nearly perfect strong scaling and weak scaling (with up to 512 million particles) on up to 512 K20X GPUs on Oak Ridge National Laboratory's (ORNL) Titan supercomputer. Moreover, a single-GPU benchmark on ORNL's SummitDev and IBM's AC922 suggests that the host-to-device NVLink can boost performance over PCIe by a remarkable 40\%. Lastly, we demonstrate, through a flow simulation in realistic shale pores, that the CPU counterpart requires 840 Power9 cores to rival the performance delivered by our package with four V100 GPUs on ORNL's Summit architecture. This simulation package enables quick-turnaround and high-throughput mesoscopic numerical simulations for investigating complex flow phenomena in nano- to micro-porous rocks with realistic pore geometries

The Performance Analysis of the Thermal Discrete Element Method Computations on the GPU

The paper presents a GPU implementation of the thermal discrete element method (TDEM) and the comparative analysis of its performance. Several discrete element models for granular flows, the bonded particle model and the TDEM are considered for quantitative comparison of computational performance. The performance measured on NVIDIA(R) Tesla™ P100 GPU is compared with that attained by running the same OpenCL code on Intel(R) Xeon™ E5-2630 CPU with 20 cores. The presented GPU implementation of the TDEM increases the computing time of the bonded particle model only up to 30.6 % of the computing time of the simplest DEM model, which is an acceptable decrease in the performance required for solving coupled thermomechanical problems

Methods and Distributed Software for Visualization of Cracks Propagating in Discrete Particle Systems

Scientific visualization is becoming increasingly important in analyzing and interpreting numerical and experimental data sets. Parallel computations of discrete particle systems lead to large data sets that can be produced, stored and visualized on distributed IT infrastructures. However, this leads to very complicated environments handling complex simulation and interactive visualization on the remote heterogeneous architectures. In micro-structure of continuum, broken connections between neighbouring particles can form complex cracks of unknown geometrical shape. The complex disjoint surfaces of cracks with holes and unavailability of a suitable scalar field defining the crack surfaces limit the application of the common surface extraction methods. The main visualization task is to extract the surfaces of cracks according to the connectivity of the broken connections and the geometry of the neighbouring particles. The research aims at enhancing the visualization methods of discrete particle systems and increasing speed of distributed visualization software. The dissertation consists of introduction, three main chapters and general conclusions. In the first Chapter, a literature review on visualization software, distributed environments, discrete element simulation of particle systems and crack visualization methods is presented. In the second Chapter, novel visualization methods were proposed for extraction of crack surfaces from monodispersed particle systems modelled by the discrete element method. The cell cut-based method, the Voronoi-based method and cell centre-based method explicitly define geometry of propagating cracks in fractured regions. The proposed visualization methods were implemented in the grid visualization e–service VizLitG and the distributed visualization software VisPartDEM. Partial data set transfer from the grid storage element was developed to reduce the data transfer and visualization time. In the third Chapter, the results of experimental research are presented. The performance of e-service VizLitG was evaluated in a geographically distributed grid. Different types of software were employed for data transfer in order to present the quantitative comparison. The performance of the developed visualization methods was investigated. The quantitative comparison of the execution time of local Voronoi-based method and that of global Voronoi diagrams generated by Voro++ library was presented. The accuracy of the developed methods was evaluated by computing the total depth of cuts made in particles by the extracted crack surfaces. The present research confirmed that the proposed visualization methods and the developed distributed software were capable of visualizing crack propagation modelled by the discrete element method in monodispersed particulate media

Modeling asteroid collisions and impact processes

As a complement to experimental and theoretical approaches, numerical modeling has become an important component to study asteroid collisions and impact processes. In the last decade, there have been significant advances in both computational resources and numerical methods. We discuss the present state-of-the-art numerical methods and material models used in "shock physics codes" to simulate impacts and collisions and give some examples of those codes. Finally, recent modeling studies are presented, focussing on the effects of various material properties and target structures on the outcome of a collision.Comment: Chapter to appear in the Space Science Series Book: Asteroids IV. Includes minor correction

Numerical investigation of fracture of polycrystalline ice under dynamic loading

Cohesive zone model is a promising technique for simulating fracture processes in brittle ice. In this work it is applied to investigate the fracture behavior of polycrystalline cylindrical samples under uniaxial loading conditions, four-point beam bending, and L-shaped beam bending. In each case, the simulation results are compared with the corresponding experimental data that was collected by other researchers. The model is based on the implicit finite element method combined with Park-Paulino-Roesler formulation for cohesive potential and includes an adaptive time stepping scheme, which takes into account the rate of damage and failure of cohesive zones. The benefit of the implicit scheme is that it allows larger time steps than explicit integration. Material properties and model parameters are calibrated using available experimental data for freshwater ice and sea ice samples. For polycrystalline ice, granular geometry is generated and cohesive zones are inserted between grains. Simulations are performed for samples with different grain sizes, and the resulting stress–strain and damage accumulation curves are recorded. Investigation of the dependency between the grain size and fracture strength shows a strengthening effect that is consistent with experimental results. The proposed framework is also applied to simulate the dynamic fracture processes in Lshaped beams of sea ice, in which case the cohesive zones are inserted between the elements of the mesh. Evolution of the stress distribution on the surface of the beam is modeled for the duration of the loading process, showing how it changes with progressive accumulation of damage in the material, as well as the development of cracks. An analytical formula is derived for estimating the breaking force based on the dimensions of the beam and the ice strength. Experimental data obtained from the 2014-2016 tests are re-evaluated with the aid of this new analysis. The computation is implemented efficiently with GPU acceleration, allowing to handle geometries with higher resolution than would be possible otherwise. Several technical contributions are described in detail including GPU-accelerated FEM implementation, an efficient way of creation of sparse matrix structure, and comparison of different unloading/reloading relations when using an implicit integration scheme. A mechanism for collision response allows modeling the interaction of fragmented material. To evaluate the collision forces, an algorithm for computing first and second point-triangle distance derivatives was developed. The source code is made available as open-source