From Physics Model to Results: An Optimizing Framework for Cross-Architecture Code Generation

Starting from a high-level problem description in terms of partial differential equations using abstract tensor notation, the Chemora framework discretizes, optimizes, and generates complete high performance codes for a wide range of compute architectures. Chemora extends the capabilities of Cactus, facilitating the usage of large-scale CPU/GPU systems in an efficient manner for complex applications, without low-level code tuning. Chemora achieves parallelism through MPI and multi-threading, combining OpenMP and CUDA. Optimizations include high-level code transformations, efficient loop traversal strategies, dynamically selected data and instruction cache usage strategies, and JIT compilation of GPU code tailored to the problem characteristics. The discretization is based on higher-order finite differences on multi-block domains. Chemora's capabilities are demonstrated by simulations of black hole collisions. This problem provides an acid test of the framework, as the Einstein equations contain hundreds of variables and thousands of terms.Comment: 18 pages, 4 figures, accepted for publication in Scientific Programmin

Computational fluid dynamics

An overview of computational fluid dynamics (CFD) activities at the Langley Research Center is given. The role of supercomputers in CFD research, algorithm development, multigrid approaches to computational fluid flows, aerodynamics computer programs, computational grid generation, turbulence research, and studies of rarefied gas flows are among the topics that are briefly surveyed

Parallel Anisotropic Unstructured Grid Adaptation

Computational Fluid Dynamics (CFD) has become critical to the design and analysis of aerospace vehicles. Parallel grid adaptation that resolves multiple scales with anisotropy is identified as one of the challenges in the CFD Vision 2030 Study to increase the capacity and capability of CFD simulation. The Study also cautions that computer architectures are undergoing a radical change and dramatic increases in algorithm concurrency will be required to exploit full performance. This paper reviews four different methods to parallel anisotropic grid generation. They cover both ends of the spectrum: (i) using existing state-of-the-art software optimized for a single core and modifying it for parallel platforms and (ii) designing and implementing scalable software with incomplete, but rapidly maturating functionality. A brief overview for each grid adaptation system is presented in the context of a telescopic approach for multilevel concurrency. These methods employ different approaches to enable parallel execution, which provides a unique opportunity to illustrate the relative behavior of each approach. Qualitative and quantitative metric evaluations are used to draw lessons for future developments in this critical area for parallel CFD simulation

Some recent applications of Navier-Stokes codes to rotorcraft

Many operational limitations of helicopters and other rotary-wing aircraft are due to nonlinear aerodynamic phenomena incuding unsteady, three-dimensional transonic and separated flow near the surfaces and highly vortical flow in the wakes of rotating blades. Modern computational fluid dynamics (CFD) technology offers new tools to study and simulate these complex flows. However, existing Euler and Navier-Stokes codes have to be modified significantly for rotorcraft applications, and the enormous computational requirements presently limit their use in routine design applications. Nevertheless, the Euler/Navier-Stokes technology is progressing in anticipation of future supercomputers that will enable meaningful calculations to be made for complete rotorcraft configurations

State-of-the-art in aerodynamic shape optimisation methods

Aerodynamic optimisation has become an indispensable component for any aerodynamic design over the past 60 years, with applications to aircraft, cars, trains, bridges, wind turbines, internal pipe flows, and cavities, among others, and is thus relevant in many facets of technology. With advancements in computational power, automated design optimisation procedures have become more competent, however, there is an ambiguity and bias throughout the literature with regards to relative performance of optimisation architectures and employed algorithms. This paper provides a well-balanced critical review of the dominant optimisation approaches that have been integrated with aerodynamic theory for the purpose of shape optimisation. A total of 229 papers, published in more than 120 journals and conference proceedings, have been classified into 6 different optimisation algorithm approaches. The material cited includes some of the most well-established authors and publications in the field of aerodynamic optimisation. This paper aims to eliminate bias toward certain algorithms by analysing the limitations, drawbacks, and the benefits of the most utilised optimisation approaches. This review provides comprehensive but straightforward insight for non-specialists and reference detailing the current state for specialist practitioners

Primjena automatskog rafiniranja računalne mreže u Numeričkoj mehanici fluida na problemima turbulentnog toka i izmjene topline

Most processes occurring in devices in air-conditioning systems require fluid flow and heat exchange, and the functioning of these devices is crucially dependent on their understanding. Computational Fluid Dynamics is a modern tool which enables development engineers to simulate the physics of processes on a computer. Such simulations may contain errors because the original problem has been replaced by a simplified discrete problem, solved on a mesh of non-overlapping control volumes and assuming certain solution behaviour in every control volume of the modelled domain. This paper presents the advantages of adaptive-mesh refinement which helps engineers get accurate solutions without their intervention by modifying the mesh where higher accuracy is needed. The potential of the method is shown on some examples often found in engineering practice.Strujanje fluida i izmjena topline su važni procesi u klimatizacijskim uređajima, stoga je njihovo funkcioniranje vrlo vezano uz razumijevanje procesa strujanja i izmjene topline. Numerička mehanika fluida (CFD) je moderni alat koji inženjerima omogućuje simuliranje fizike procesa na računalu. No, takve simulacije mogu sadržavati grješke zato jer se sustav parcijalnih diferencijalnih jednadžbi zamjenjuje s pojednostavljenim diskretnim problemom, koji se rješava na mreži ne-preklapajućih kontrolnih volumena, uz pretpostavku ponašanja rješenja u kontrolnom volumenu domene. U ovom članku iznesene su prednosti lokalnog rafiniranja računalne mreže koji omogućava inženjerima dobivanje točnih rješenja matematičkog modela automatski i bez njihove intervencije kroz automatsku modifikaciju računalne mreže na mjestima gdje je potrebna veća točnost. Mogućnosti metode su prikazane na primjerima prisutnima u inženjerskoj praksi