104 research outputs found
Steady State Convergence Acceleration of the Generalized Lattice Boltzmann Equation with Forcing Term through Preconditioning
Several applications exist in which lattice Boltzmann methods (LBM) are used
to compute stationary states of fluid motions, particularly those driven or
modulated by external forces. Standard LBM, being explicit time-marching in
nature, requires a long time to attain steady state convergence, particularly
at low Mach numbers due to the disparity in characteristic speeds of
propagation of different quantities. In this paper, we present a preconditioned
generalized lattice Boltzmann equation (GLBE) with forcing term to accelerate
steady state convergence to flows driven by external forces. The use of
multiple relaxation times in the GLBE allows enhancement of the numerical
stability. Particular focus is given in preconditioning external forces, which
can be spatially and temporally dependent. In particular, correct forms of
moment-projections of source/forcing terms are derived such that they recover
preconditioned Navier-Stokes equations with non-uniform external forces. As an
illustration, we solve an extended system with a preconditioned lattice kinetic
equation for magnetic induction field at low magnetic Prandtl numbers, which
imposes Lorentz forces on the flow of conducting fluids. Computational studies,
particularly in three-dimensions, for canonical problems show that the number
of time steps needed to reach steady state is reduced by orders of magnitude
with preconditioning. In addition, the preconditioning approach resulted in
significantly improved stability characteristics when compared with the
corresponding single relaxation time formulation.Comment: 47 pages, 21 figures, for publication in Journal of Computational
Physic
Real-time lattice boltzmann shallow waters method for breaking wave simulations
We present a new approach for the simulation of surfacebased fluids based in a hybrid formulation of Lattice Boltzmann Method for Shallow Waters and particle systems. The modified LBM can handle arbitrary underlying terrain conditions and arbitrary fluid depth. It also introduces a novel method for tracking dry-wet regions and moving boundaries. Dynamic rigid bodies are also included in our simulations using a two-way coupling. Certain features of the simulation that the LBM can not handle because of its heightfield nature, as breaking waves, are detected and automatically turned into splash particles. Here we use a ballistic particle system, but our hybrid method can handle more complex systems as SPH. Both the LBM and particle systems are implemented in CUDA, although dynamic rigid bodies are simulated in CPU. We show the effectiveness of our method with various examples which achieve real-time on consumer-level hardware.Peer ReviewedPostprint (author's final draft
An MPI-CUDA Implementation for Massively Parallel Incompressible Flow Computations on Multi-GPU Clusters
Modern graphics processing units (GPUs) with many-core architectures have emerged as general-purpose parallel computing platforms that can accelerate simulation science applications tremendously. While multi-GPU workstations with several TeraFLOPS of peak computing power are available to accelerate computational problems, larger problems require even more resources. Conventional clusters of central processing units (CPU) are now being augmented with multiple GPUs in each compute-node to tackle large problems. The heterogeneous architecture of a multi-GPU cluster with a deep memory hierarchy creates unique challenges in developing scalable and efficient simulation codes. In this study, we pursue mixed MPI-CUDA implementations and investigate three strategies to probe the efficiency and scalability of incompressible flow computations on the Lincoln Tesla cluster at the National Center for Supercomputing Applications (NCSA). We exploit some of the advanced features of MPI and CUDA programming to overlap both GPU data transfer and MPI communications with computations on the GPU. We sustain approximately 2.4 TeraFLOPS on the 64 nodes of the NCSA Lincoln Tesla cluster using 128 GPUs with a total of 30,720 processing elements. Our results demonstrate that multi-GPU clusters can substantially accelerate computational fluid dynamics (CFD) simulations
Micro-solid oxide fuel cells running on reformed hydrocarbon fuels
Microâsolid oxide fuel cell (microâSOFC) systems are predicted to have a high energy density and specific energy and are potential power sources for portable electronic devices. A microâSOFC system is under development in the frame of the ONEBAT project [1â3]. In this presentation, we report on the fabrication and characterization of a subâsystem assembly consisting of a startup heater and a microâreformer bonded to a Si chip with electrochemicallyâactive microâSOFC membranes. A functional carrier including fluidic channels for gas feed and integrated heaters was bonded to a microreformer with an overall size of 12.7 mm x 12.7 mm x 1.9 mm [4â7]. As a catalyst, a foamâlike material made of ceriaâzirconia nanoparticles doped with rhodium was used to fill the 58.5 mm3 reformer cavity. This microâreformer allows for high methane and butane conversion of > 90 % with a hydrogen selectivity of > 80 % at 550 °C in the reformer [7, 8]. A silicon chip with 30 freeâstanding microâSOFC membranes (390 ÎŒm x 390 ÎŒm) with a thickness of less than 500 nm was bonded to the carrierâreformer assembly described above. The microâSOFC membrane consisted of an yttriaâ stabilized zirconia thin film electrolyte. Both Ptâbased and ceramicâbased electrode materials were tested regarding the thermal stability and carbon poisoning at temperatures below 600 °C. The functionalâcarrier mircoâreformer microâSOFC assembly was electrochemically tested with hydrocarbon fuel between 300 °C and 600 °C. The fuel cell performance and the microstructural evolution of the anode are discussed as well
Micro-solid oxide fuel cells as power supply for small portable electronic equipment
Micro-solid oxide fuel cell (SOFC) systems are anticipated for powering small, portable electronic devices, such as laptop, personal digital assistant (PDA), medical and industrial accessories. It is predicted that micro-SOFC systems have a 2-4 higher energy density than Li-ion batteries [1]. However, literature mainly focuses on the fabrication and characterization of thin films and membranes for micro-SOFC systems [2-12]; the entire system approach is not yet studied in detail. We will therefore discuss in this paper the entire approach from the fabrication of thin films and membranes up to the complete system, including fuel processing, thermal management and integration
The flora and vegetation of rocky outcrops in three municipalities in the northern region of CearĂĄ, Brazil: phytosociological characterization
Veja material suplementar em <https://doi.org/10.6084/m9.figshare.5915233.v2O presente estudo teve como objetivo identificar a flora e a vegetação dos afloramentos rochosos isolados e
de baixa altitude (lajedos), na vegetação de Caatinga Arbustiva Aberta, que se encontram nos municĂpios de
Sobral, GroaĂras e Santa QuitĂ©ria, no estado do CearĂĄ, Brasil e propor uma classificação fitossociolĂłgica para
estas comunidades xerófilas. Foram definidas cinco åreas de coleta de dados com elevada proporção de rochas
expostas (> 80%) onde as excursĂ”es de campo decorreram em março de 2014 e 2015 (3Âș56âS e 40Âș23âW, 4Âș01âS
e 40Âș05âW, 4Âș07âS e 40Âș08âW, 4Âș09âS e 40Âș09âW e 4Âș03âS e 40Âș00âW). No estudo da vegetação aplicou-se os
métodos TWINSPAN (two-way indicator species analysis) e o clåssico sigmatista de Braun-Blanquet. As åreas
mĂnimas dos inventĂĄrios fitossociolĂłgicos variaram de 8 a 16 m2. Foram coletadas as espĂ©cies vegetais que
crescem em fissuras, fendas e ilhas de vegetação que se encontram em afloramentos rochosos. Foram registradas
88 espĂ©cies, distribuĂdas em 59 gĂȘneros e 30 famĂlias botĂąnicas. Fabaceae foi a famĂlia que se destacou em riqueza
especĂfica (20 spp.), seguida por Poaceae (dez spp.), Euphorbiaceae (sete spp.) e Convolvulaceae (seis spp.).
Quanto ao endemismo foram registradas, em vegetação rupestre, 19 espĂ©cies endĂȘmicas para o Brasil. Na anĂĄlise
fitossociológica da vegetação propÎs-se estudar a comunidade de Pilosocereus gounellei (FA.C.Weber) Byles &
Rowley e Encholirium spectabile Mart. ex Schult. & Schult.f. e a de Crateva tapia L. e Combretum leprosum Martinfo:eu-repo/semantics/publishedVersio
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