ArchSim:A System-Level Parallel Simulation Platform for the Architecture Design of High Performance Computer

High performance computer （HPC） is a complex huge system, of which the architecture design meets increasing difficulties and risks. Traditional methods, such as theoretical analysis, component-level simulation and sequential simulation, are not applicable to system-level simulations of HPC systems. Even the parallel simulation using large-scale parallel machines also have many difficulties in scalability, reliability, generality, as well as efficiency. According to the current needs of HPC architecture design, this paper proposes a system-level parallel simulation platform： ArchSim. We first introduce the architecture of ArchSim simulation platform which is composed of a global server （GS）, local server agents （LSA） and entities. Secondly, we emphasize some key techniques of ArchSim, including the synchronization protocol, the communication mechanism and the distributed checkpointing/restart mechanism. We then make a synthesized test of some main performance indices of ArchSim with the phold benchmark and analyze the extra overhead generated by ArchSim. Finally, based on ArchSim, we construct a parallel event-driven interconnection network simulator and a system-level simulator for a small scale HPC system with 256 processors. The results of the performance test and HPC system simulations demonstrate that ArchSim can achieve high speedup ratio and high scalability on parallel host machine and support system-level simulations for the architecture design of HPC systems.

PARALLEL SIMULATION OF THE ELLIPTIC MILD SLOPE EQUATION WITH A PERSONAL COMPUTER CLUSTER

With the massage passing interface, a parallel solution method was proposedfor the simulation of the elliptic mild slope equation, and implemented numerically on a parallelsystem based on a personal computer cluster, which was constructed by the authors. The wavetransformations over two typical topographies with mild slopes were simulated. Numerical resultsshow that the parallel solution method presented in this paper can not only increase thecomputational efficiency, but also decrease very much the memory storage on a single computer, sothe parallel system based on a PCC can be used to simulate wave transformations over much largerareas.

Parallel Digital Simulation for the Control Problem in Differential Algebraic System

In this paper, a parallel simulation algorithm for the control problem in differential algebraic system is presented. The error of the algorithm is estimated. The stability analysis is made for a model problem and the stability region is given. The numerical example demonstrates that the method is efficient.

Parallel Simulation of 3-D Turbulent Flow Through Hydraulic Machinery

Parallel calculational methods were used to analyze incompressible turbulent flow through hydraulic machinery. Two parallel methods were used to simulate the complex flow field. The space decomposition method divides the computational domain into several sub-ranges. Parallel discrete event simulation divides the whole task into several parts according to their functions. The simulation results were compared with the serial simulation results and particle image velocimetry (PIV) experimental results. The results give the distribution and configuration of the complex vortices and illustrate the effectiveness of the parallel algorithms for numerical simulation of turbulent flows.

PARALLEL SIMULATION OF LARGE-SCALE ARTIFICIAL SOCIETY WITH GPU AS COPROCESSOR

Large-scale artificial societies with millions or billions of agents call for high-performance parallel simulation.Prevailing supercomputers with thousands of CPUs and GPUs make it possible to carry out such simulation.The key is to distribute large-scale agents to massive cores of CPUs and GPUs properly for parallel computing with efficient communication and synchronization.For simplicity and efficiency,a modified discrete event system specification(DEVS)is proposed for large-scale artificial society modeling and parallelism is exploited in agent models because similar agents usually share similar behaviors.Through phased synchronization,a two-tier parallel simulation engine is designed with support of MPI and OpenCL where GPU is used as coprocessor.One-sided communication is used for reflection of remote simulation objects and message passing between processes.A general kernel function prototype is elaborately designed and conditionally compiled for execution on both CPU and GPU.An artificial society for epidemic study is used to test the performance on a supercomputer with 1024 CPU cores and 1792 GPU cores.The speedup reaches 3512 for even 2 billion agents with GPU acceleration which is far over 701 when only CPUs are used.It turns out feasible for parallel simulation of large-scale artificial society with GPU as coprocessor.

A Parallel Multicomputer Simulation System

In this paper, a homogenous parallel simulation system is presented in detail for continuous--system simulation. The system is collstructed by a host computer and I I transputers connected into a topologyof 'Super--Node' which is very suitable for simulation of stiff systems. An automatic software interface runin the host is developed to partition simulation model, either equations or block diagrams, into several equitable segments and then pack them into parallel simulation program to be executed in the parallel system.This interface frees simulation users from parallel programming to focus on their simulation experiments.

PARALLEL ADAPTIVE SIMULATION OF A PLUNGING LIQUID JET

This paper is concerned with three-dimensional numerical simulation of a plunging liquid jet. The transient processes of forming an air cavity around the jet, capturing an initially large air bubble, and the break-up of this large toroidal-shaped bubble into smaller bubbles were analyzed. A stabilized finite element method （FEM） was employed under parallel numerical simulations based on adaptive, unstructured grid and coupled with a level-set method to track the interface between air and liquid. These simulations show that the inertia of the liquid jet initially depresses the pool＇s surface, forming an annular air cavity which surrounds the liquid jet. A toroidal liquid eddy which is subse- quently formed in the liquid pool results in air cavity collapse, and in turn entrains air into the liquid pool from the unstable annular air gap region around the liquid jet.

Parametric Instabilities of Parallel Propagating Circularly Polarized Alfven Waves:One-Dimensional Hybrid Simulations

By performing one-dimensional （l-D） hybrid simulations, we analyze in detail the parametric instabilities of the Alfv^n waves with a spectrum in a low beta plasma. The parametric instabilities experience two stages. In the first stage, the density modes are excited and immediately couple with the pump Alfv6n waves. In the second stage, each pump Alfv^n wave decays into a density mode and a daughter Alfv6n mode similar to the monochromatic cases. Ftlrthermore, the proton velocity beam will also be formed after the saturation of the parametric instabilities. When the plasma beta is high, the parametric decay in the second stage will be strongly suppressed.

Remarks on a benchmark nonlinear constrained optimization problem

Remarks on a benchmark nonlinear constrained optimization problem are made. Due to a citation error, two absolutely different results for the benchmark problem are obtained by independent researchers. Parallel simulated annealing using simplex method is employed in our study to solve the benchmark nonlinear constrained problem with mistaken formula and the best-known solution is obtained, whose optimality is testified by the Kuhn Tucker conditions.

Grid-based internet worm behavior simulator

The traditional network simulator has function and performance limitation when simulating Internet worms,so we designed the grid-based Internet worm behavior simulator (IWBS Grid).IWBS Grid makes use of the real Internet topology,link and routing information,and simulates the worm behavior at the packet event-driven level;and proposes a high-performance Internet worms behavior simulation platform by right of the grid computing capability,resource and task management,and so on.The experimental results show that IWBS grid surpasses the traditional simulator in simulating capability,and the technology to track the worm propagation in packet level can propose the valuable information for the further study on worms.

Numerical and experimental study on coherent beam combining of fibre amplifiers using simulated annealing algorithm

We present the numerical and experimental study on the coherent beam combining of fibre amplifiers by means of simulated annealing （SA） algorithm. The feasibility is validated by the Monte Carlo simulation of correcting static phase distortion using SA algorithm. The performance of SA algorithm under time-varying phase noise is numerically studied by dynamic simulation. It is revealed that the influence of phase noise on the performance of SA algorithm gets stronger with an increase in amplitude or frequency of phase noise; and the laser array that contains more lasers will be more affected from phase noise. The performance of SA algorithm for coherent beam combining is also compared with a widely used stochastic optimization algorithm, i.e., the stochastic parallel gradient descent （SPGD） algorithm. In a proof-of-concept experiment we demonstrate the coherent beam combining of two 1083~nm fibre amplifiers with a total output power of 12~W and 93% combining efficiency. The contrast of the far-field coherently combined beam profiles is calculated to be as high as 95%.

Parallel Numerical Analysis on the Rheology of the Martian Ice-Rock Mixture

The distribution and amount of ground ice on Mars is an important issue to be addressed for the future exploration of the planet.The occurrence of interstitial ice in Martian frozen ground is indicated by landforms,such as fluidized ejecta craters,softened terrain,and fretted channels.How-ever,experimental data on the rheology of ice-rock mixture under Martian physical conditions are sparse,and the amount of ground ice that is required to produce the viscous deformation observed in Martian ice-related landforms is still unknown.In our study,we put forward a three-dimensional non-Newtonian viscous finite element model to investigate the behavior of ice-rock mixtures numeri-cally.The randomly distributed tetrahedral elements are generated in regular domain to represent the natural distribution of ice-rock materials.Numerical simulation results show that when the volume of rock is less than 40%,the rheology of the mixture is dominated by ice,and there is occurrence of a brittle-ductile transition when ice fraction reaches a certain value.Our preliminary results contribute to the knowledge of the determination of the rheology and ice content in Martian ice-rock mixture.The presented model can also be utilized to evaluate the amount of ground ice on Mars.

Hybrid simulation using implicit solver coupling with HLA and FMI

Hybrid systems such as Cyber Physical System(CPS)are becoming increasingly popular,mainly due to the involvement of information technology in different aspects of life.For analysis and verification of hybrid system models,simulation is used extensively.As parts of a common hybrid system may belong to different domains of study,it is sometimes beneficial to use specialized simulation packages(SPs)for each domain.In this case,parts of a system are simulated in different SPs.The idea may seem simple,but coupling more than one simulation component presents challenges related to numerical stability.The presented article suggests an implicit solver coupling technique enhanced to facilitate simulation of hybrid models using multiple simulation components.The technique is developed using two of the most popular simulation interoperability standards,namely,the High Level Architecture and the Functional Mock-up Interface.By using these standards,the developed algorithm will be useful for a large number of practitioners and researchers.The developed algorithm is described using a generic distributed computation model,which makes it reproducible even without using the standards.For the verification of results,the algorithm is tested on two case studies.The results are compared to a monolithic simulator and the proximity of results initiates the validity of the developed algorithm.

PARALLEL MULTI-STAGE & MULTI-STEP METHOD IN ODES

Presents information on a study which discussed the theory of parallel multi-stage and multi-step method, which is a form of combining Runge-Kutta method with linear multi-step method. Basic theory and equations; Applications of the method; Discussion and conclusions.

Fully-Coupled Multi-Physical Simulation with Physics-Based Nonlinearity-Elimination Preconditioned Inexact Newton Method for Enhanced Oil Recovery

In this paper,we introduce a physics-based nonlinear preconditioned Inexact Newton Method(INB)for the multiphysical simulation of fractured reservoirs.Instead of solving the partial differential equations(PDE)exactly,Inexact Newton method finds a direction for the iteration and solves the equations inexactly with fewer iterations.However,when the equations are not smooth enough,especially when lo-cal discontinuities exits,and when proper preconditioning operations are not adopted,the Inexact Newton method may be slow or even stagnant.As pointed out by Keyes et al.[1],multi-physical numerical simulation faces several challenges,one of which is the local-scale nonlinearity and discontinuity.In this work,we have proposed and studied a nonlinear preconditioner to improve the performance of Inexact Newton Method.The nonlinear preconditioner is essentially a physics-based strategy to adaptively identify and eliminate the highly nonlinear zones.The proposed algorithm has been implemented into our fully coupled,fully implicit THM reservoir simulator(Wang et al.[2,3])to study the effects of cold water injection on fractured petroleum reservoirs.The results of this work show that after the implementation of this nonlinear preconditioner,the iterative solver has become significantly more robust and efficient.