Concurrent cell rate simulation of ATM telecommunications network.

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SPICE²: A Spatial, Parallel Architecture for Accelerating the Spice Circuit Simulator

Spatial processing of sparse, irregular floating-point computation using a single FPGA enables up to an order of magnitude speedup (mean 2.8X speedup) over a conventional microprocessor for the SPICE circuit simulator. We deliver this speedup using a hybrid parallel architecture that spatially implements the heterogeneous forms of parallelism available in SPICE. We decompose SPICE into its three constituent phases: Model-Evaluation, Sparse Matrix-Solve, and Iteration Control and parallelize each phase independently. We exploit data-parallel device evaluations in the Model-Evaluation phase, sparse dataflow parallelism in the Sparse Matrix-Solve phase and compose the complete design in streaming fashion. We name our parallel architecture SPICE²: Spatial Processors Interconnected for Concurrent Execution for accelerating the SPICE circuit simulator. We program the parallel architecture with a high-level, domain-specific framework that identifies, exposes and exploits parallelism available in the SPICE circuit simulator. This design is optimized with an auto-tuner that can scale the design to use larger FPGA capacities without expert intervention and can even target other parallel architectures with the assistance of automated code-generation. This FPGA architecture is able to outperform conventional processors due to a combination of factors including high utilization of statically-scheduled resources, low-overhead dataflow scheduling of fine-grained tasks, and overlapped processing of the control algorithms. We demonstrate that we can independently accelerate Model-Evaluation by a mean factor of 6.5X(1.4--23X) across a range of non-linear device models and Matrix-Solve by 2.4X(0.6--13X) across various benchmark matrices while delivering a mean combined speedup of 2.8X(0.2--11X) for the two together when comparing a Xilinx Virtex-6 LX760 (40nm) with an Intel Core i7 965 (45nm). With our high-level framework, we can also accelerate Single-Precision Model-Evaluation on NVIDIA GPUs, ATI GPUs, IBM Cell, and Sun Niagara 2 architectures. We expect approaches based on exploiting spatial parallelism to become important as frequency scaling slows down and modern processing architectures turn to parallelism (\eg multi-core, GPUs) due to constraints of power consumption. This thesis shows how to express, exploit and optimize spatial parallelism for an important class of problems that are challenging to parallelize.</p

Massively parallel split-step Fourier techniques for simulating quantum systems on graphics processing units

The split-step Fourier method is a powerful technique for solving partial differential equations and simulating ultracold atomic systems of various forms. In this body of work, we focus on several variations of this method to allow for simulations of one, two, and three-dimensional quantum systems, along with several notable methods for controlling these systems. In particular, we use quantum optimal control and shortcuts to adiabaticity to study the non-adiabatic generation of superposition states in strongly correlated one-dimensional systems, analyze chaotic vortex trajectories in two dimensions by using rotation and phase imprinting methods, and create stable, threedimensional vortex structures in Bose–Einstein condensates through artificial magnetic fields generated by the evanescent field of an optical nanofiber. We also discuss algorithmic optimizations for implementing the split-step Fourier method on graphics processing units. All computational methods present in this work are demonstrated on physical systems and have been incorporated into a state-of-the-art and open-source software suite known as GPUE, which is currently the fastest quantum simulator of its kind.Okinawa Institute of Science and Technology Graduate Universit

Dynamics in a stellar convective layer and at its boundary: Comparison of five 3D hydrodynamics codes

This is the final version. Available from EDP Sciences via the DOI in this recordOur ability to predict the structure and evolution of stars is in part limited by complex, 3D hydrodynamic processes such as convective boundary mixing. Hydrodynamic simulations help us understand the dynamics of stellar convection and convective boundaries. However, the codes used to compute such simulations are usually tested on extremely simple problems and the reliability and reproducibility of their predictions for turbulent flows is unclear. We define a test problem involving turbulent convection in a plane-parallel box, which leads to mass entrainment from, and internal-wave generation in, a stably stratified layer. We compare the outputs from the codes FLASH, MUSIC, PPMSTAR, PROMPI, and SLH, which have been widely employed to study hydrodynamic problems in stellar interiors. The convection is dominated by the largest scales that fit into the simulation box. All time-averaged profiles of velocity components, fluctuation amplitudes, and fluxes of enthalpy and kinetic energy are within ≲3σ of the mean of all simulations on a given grid (1283 and 2563 grid cells), where σ describes the statistical variation due to the flow’s time dependence. They also agree well with a 5123 reference run. The 1283 and 2563 simulations agree within 9% and 4%, respectively, on the total mass entrained into the convective layer. The entrainment rate appears to be set by the amount of energy that can be converted to work in our setup and details of the small-scale flows in the boundary layer seem to be largely irrelevant. Our results lend credence to hydrodynamic simulations of flows in stellar interiors. We provide in electronic form all outputs of our simulations as well as all information needed to reproduce or extend our study.Science and Technology Facilities Council (STFC)European Research Council (ERC

Turbulence: Numerical Analysis, Modelling and Simulation

The problem of accurate and reliable simulation of turbulent flows is a central and intractable challenge that crosses disciplinary boundaries. As the needs for accuracy increase and the applications expand beyond flows where extensive data is available for calibration, the importance of a sound mathematical foundation that addresses the needs of practical computing increases. This Special Issue is directed at this crossroads of rigorous numerical analysis, the physics of turbulence and the practical needs of turbulent flow simulations. It seeks papers providing a broad understanding of the status of the problem considered and open problems that comprise further steps

A Numerical Investigation Of Turbulence-Driven And Forced Generation Of Internal Gravitywaves In Stratified Mid-Water

Natural and externally-forced excitation of internal gravity waves in a uniformly stratified fluid have been thoroughly investigated by means of highly resolved large eddy simulations. The first part of the thesis focuses on the generation of high frequency internal gravity waves by the turbulent wake of a towed sphere in a uniformly stratified fluid. We have used continuous wavelet transforms to quantify relevant wavelength and frequencies and their spatial and temporal dependence in the near field of the wake. The dependence on Reynolds number and Froude number of the internal wave field wavelengths, frequencies and isopycnal displacements are reported for the first time. The initial wavelengths and decay rates show a dependence on both parameters that can not be explained on the basis of impulsive mass source models. The results also clearly identify Reynolds number as the main driver for the observed selection of a narrow range of wave phase- line-tilt-angles and shed some light on the coupling of the waves and turbulent wake region at high Reynolds number. Finally, the potential for nonlinear interactions, instability and breaking of the waves increases with both Reynolds and Froude numbers. The results of this part of the thesis motivate future theoretical investigations into the underlying generation mechanisms and improved parametrization of the role of small scale processes, such as high frequency internal gravity waves, in large scale circulation models in the ocean and atmosphere. In the second half of the thesis, we have focused on the generation of an internal gravity wavepacket by a vertically localized transient forcing. We have found that the unique combination of strong vertical localization and large wave amplitude, typically not considered in the literature, lead to the formation of strong horizontal mean flow inside the wave forcing region that nonlinearly grows at the expense of a depleted and structurally modified emerging internal wave packet. A novel theoretical analysis is developed which can explain the underlying mechanism for the formation of the mean flow. By appealing to scaling arguments, based on a one way wave-mean flow interaction, we quantify the mean flow dependence on the input parameters. By means of a phase averaging procedure, we offer additional insight on mean flow reduction through horizontal localization of a wavepacket. Finally, mean flow containment techniques that allow the generation of a well-defined wavepacket that preserves its structure near the source and during the propagation towards a remote interaction region are proposed and tested. The efficiency of the techniques is tested in a simulation of internal gravity wave-shear flow interaction near a critical level. The simulations qualitatively agree with previous numerical investigations of such flow