J. M. L. M. Palma

Simulation of the Askervein Flow. Part 1: Reynolds Averaged Navier–Stokes Equations (k∈ Turbulence Model)

The neutrally stratified flow over the Askervein Hill was simulatedusing a terrain-following coordinatesystem and a two-equation(k - ∈) turbulence model. Calculations were performed on awide range of numerical grids to assess, among other things, theimportance of spatial discretization and the limitations of theturbulence model. Our results showed that a relatively coarse gridwas enough to resolve the flow in the upstream region of the hill;at the hilltop, 10 m above the ground, the speed-up was 10% lessthan the experimental value. The flows most prominent feature wasa recirculating region in the lee of the hill, which determinedthe main characteristics of the whole downstream flow. This regionhad an intermittent nature and could be fully captured only in the caseof a time-dependent formulation and a third-order discretization ofthe advective terms. The reduction of the characteristic roughnessnear the top of the hill was also taken into account, showing theimportance of this parameter, particularly in the flow close to theground at the summit and in the downstream side of the hill.Calculations involving an enlarged area around the Askervein Hillshowed that the presence of the nearby topography affected the flowneither at the top nor downstream of the Askervein Hill.

On the use of fluorescent dyes for concentration measurements in water flows

An experiment was performed to evaluate the characteristics of various fluorescent dyes used as tracers for concentration measurements in water flows, by laser induced fluorescence. Three common fluorescent dyes (fluorescein, rhodamine B and rhodamine 6G) were used, to select the most suitable fluorescent dye and identify its range of linear response. The results showed that, in terms of the stability of the solution, fluorescein is inferior to either rhodamine B or rhodamine 6G and that for concentrations of rhodamine B less than 0.08 mg/1 the response of fluorescent to the incident light is linear.

High Performance Computing for Computational Science - VECPAR 2006

1: Grid Computing.- An Opportunistic Algorithm for Scheduling Workflows on Grids.- A Service Oriented System for on Demand Dynamic Structural Analysis over Computational Grids.- Scalable Desktop Grid System.- Analyzing Overheads and Scalability Characteristics of OpenMP Applications.- Parallel Fuzzy c-Means Cluster Analysis.- Peer-to-Peer Models for Resource Discovery in Large-Scale Grids: A Scalable Architecture.- 2: Cluster Computing.- JaceV: A Programming and Execution Environment for Asynchronous Iterative Computations on Volatile Nodes.- Aspect Oriented Pluggable Support for Parallel Computing.- Model for Simulation of Heterogeneous High-Performance Computing Environments.- On Evaluating Decentralized Parallel I/O Scheduling Strategies for Parallel File Systems.- Distributed Security Constrained Optimal Power Flow Integrated to a DSM Based Energy Management System for Real Time Power Systems Security Control.- Metaserver Locality and Scalability in a Distributed NFS.- Top-k Query Processing in the APPA P2P System.- Posterior Task Scheduling Algorithms for Heterogeneous Computing Systems.- Design and Implementation of an Environment for Component-Based Parallel Programming.- Anahy: A Programming Environment for Cluster Computing.- DWMiner: A Tool for Mining Frequent Item Sets Efficiently in Data Warehouses.- A Parallel Implementation of the K Nearest Neighbours Classifier in Three Levels: Threads, MPI Processes and the Grid.- On the Use of the MMC Language to Utilize SIMD Instruction Set.- A Versatile Pipelined Hardware Implementation for Encryption and Decryption Using Advanced Encryption Standard.- 3: Numerical Methods.- Combinatorial Scientific Computing: The Enabling Power of Discrete Algorithms in Computational Science.- Improving the Numerical Simulation of an Airflow Problem with the BlockCGSI Algorithm.- EdgePack: A Parallel Vertex and Node Reordering Package for Optimizing Edge-Based Computations in Unstructured Grids.- Parallel Processing of Matrix Multiplication in a CPU and GPU Heterogeneous Environment.- Robust Two-Level Lower-Order Preconditioners for a Higher-Order Stokes Discretization with Highly Discontinuous Viscosities.- The Impact of Parallel Programming Models on the Performance of Iterative Linear Solvers for Finite Element Applications.- Efficient Parallel Algorithm for Constructing a Unit Triangular Matrix with Prescribed Singular Values.- A Rewriting System for the Vectorization of Signal Transforms.- High Order Fourier-Spectral Solutions to Self Adjoint Elliptic Equations.- Multiresolution Simulations Using Particles.- Evaluation of Several Variants of Explicitly Restarted Lanczos Eigensolvers and Their Parallel Implementations.- PyACTS: A High-Level Framework for Fast Development of High Performance Applications.- Sequential and Parallel Resolution of the Two-Group Transient Neutron Diffusion Equation Using Second-Degree Iterative Methods.- Enhancing the Performance of Multigrid Smoothers in Simultaneous Multithreading Architectures.- Block Iterative Algorithms for the Solution of Parabolic Optimal Control Problems.- Evaluation of Linear Solvers for Astrophysics Transfer Problems.- 4: Large Scale Simulations in Physics.- Scalable Cosmological Simulations on Parallel Machines.- Performance Evaluation of Scientific Applications on Modern Parallel Vector Systems.- Numerical Simulation of Three-Phase Flow in Heterogeneous Porous Media.- Simulation of Laser Propagation in a Plasma with a Frequency Wave Equation.- A Particle Gradient Evolutionary Algorithm Based on Statistical Mechanics and Convergence Analysis.- 5: Computing in Biosciences.- A Computational Framework for Cardiac Modeling Based on Distributed Computing and Web Applications.- Triangular Clique Based Multilevel Approaches to Identify Protein Functional Modules.- BioPortal: A Portal for Deployment of Bioinformatics Applications on Cluster and Grid Environments.- Workshop 1: Computational Grids and Clusters.- Adaptive Distributed Metamodeling.- Distributed General Logging Architecture for Grid Environments.- Interoperability Between UNICORE and ITBL.- Using Failure Injection Mechanisms to Experiment and Evaluate a Grid Failure Detector.- Semantic-Based Service Trading: Application to Linear Algebra.- Management of Services Based on a Semantic Description Within the GRID-TLSE Project.- Extending the Services and Sites of Production Grids by the Support of Advanced Portals.- Workshop 2: High-Performance Data Management in Grid Environments.- PSO-Grid Data Replication Service.- Execution Management of Scientific Models on Computational Grids.- Replica Refresh Strategies in a Database Cluster.- A Practical Evaluation of a Data Consistency Protocol for Efficient Visualization in Grid Applications.- Experiencing Data Grids.

Numerical simulation of the atmospheric flow in a mountainous region of the North of Portugal

The present paper discusses the results of a numerical simulation of the wind flow over a mountainous area called Serra das Meadas, located in the North of Portugal, 60xa0km east of Porto, at an altitude of 1000xa0m above sea level. Wind turbines are under installation in this region, where the availability of reliable wind data is crucial for the success of both the economic studies and operation of the windpower station. The mathematical model was based on the solution of the fluid flow (Reynolds averaged) and turbulence model equations (κ–e) using a non-orthogonal three-dimensional grid system. The results showed that it is possible to obtain three-dimensional simulations of the atmospheric flow over complex terrain, within a reasonable amount of computer time. Differences of about 10% of the wind speed measured 30xa0m above the ground could occur as a result of different grid resolution or flow inlet conditions.

High Performance Computing for Computational Science — VECPAR 2002

A methodology to simulate large-scale fluid-structure interaction problems on parallel machines has been developed. Particular emphasis was placed on shock-structure interaction problems. For the fluid, a high-resolution FEM-FCT solver based on unstructured grids is used. The surface motion is handled either by moving, body fitted grids, or via surface embedding. For the structure, a Lagrangean large-deformation finite element code is employed. The coupled system is solved using a loose coupling algorithm, with position and velocity interpolation and force projection. Several examples, run on parallel machines, demonstrate the range of applicability of the proposed methodology.

High Performance Computing for Computational Science - VECPAR 2004

1: Large Scale Computations.- Large Scale Simulations.- Development and Integration of Parallel Multidisciplinary Computational Software for Modeling a Modern Manufacturing Process.- Automatically Tuned FFTs for BlueGene/Ls Double FPU.- A Survey of High-Quality Computational Libraries and Their Impact in Science and Engineering Applications.- A Performance Evaluation of the Cray X1 for Scientific Applications.- Modelling Overhead of Tuple Spaces with Design of Experiments.- Analysis of the Interaction of Electromagnetic Signals with Thin-Wires Structures. Multiprocessing Issues for an Iterative Method.- A Performance Prediction Model for Tomographic Reconstruction in Structural Biology.- 2: Data Management and Data Mining.- Data Management in Large-Scale P2P Systems.- A High Performance System for Processing Queries on Distributed Geospatial Data Sets.- Parallel Implementation of Information Retrieval Clustering Models.- Distributed Processing of Large BioMedical 3D Images.- Developing Distributed Data Mining Applications in the Knowledge Grid Framework.- Scaling Up the Preventive Replication of Autonomous Databases in Cluster Systems.- Parallel Implementation of a Fuzzy Rule Based Classifier.- 3: Grid Computing Infrastructure.- The EGEE European Grid Infrastructure Project.- Grid Technology for Biomedical Applications.- Three-Dimensional Cardiac Electrical Activity Simulation on Cluster and Grid Platforms.- 2DRMP-G: Migrating a Large-Scale Numerical Mathematical Application to a Grid Environment.- Design of an OGSA-Compliant Grid Information Service Using .NET Technologies.- A Web-Based Application Service Provision Architecture for Enabling High-Performance Image Processing.- Influence of Grid Economic Factors on Scheduling and Migration.- Extended Membership Problem for Open Groups: Specification and Solution.- Asynchronous Iterative Algorithms for Computational Science on the Grid: Three Case Studies.- Security Mechanism for Medical Image Information on PACS Using Invisible Watermark.- 4: Cluster Computing.- Parallel Generalized Finite Element Method for Magnetic Multiparticle Problems.- Parallel Model Reduction of Large Linear Descriptor Systems via Balanced Truncation.- A Parallel Algorithm for Automatic Particle Identification in Electron Micrographs.- Parallel Resolution of the Two-Group Time Dependent Neutron Diffusion Equation with Public Domain ODE Codes.- FPGA Implementations of the RNR Cellular Automata to Model Electrostatic Field.- PerWiz: A What-If Prediction Tool for Tuning Message Passing Programs.- Maintaining Cache Coherency for B?+? Tree Indexes in a Shared Disks Cluster.- Message Strip-Mining Heuristics for High Speed Networks.- Analysis of the Abortion Rate on Lazy Replication Protocols.- protoRAID: A User-Level RAID Emulator for Fast Prototyping in Fibre Channel SAN Environment.- Parallel Computational Model with Dynamic Load Balancing in PC Clusters.- Dynamically Adaptive Binomial Trees for Broadcasting in Heterogeneous Networks of Workstations.- 5: Parallel and Distributed Computing.- Parallel Simulation of Multicomponent Systems.- Parallel Boundary Elements: A Portable 3-D Elastostatic Implementation for Shared Memory Systems.- On Dependence Analysis for SIMD Enhanced Processors.- A Preliminary Nested-Parallel Framework to Efficiently Implement Scientific Applications.- Exploiting Multilevel Parallelism Within Modern Microprocessors: DWT as a Case Study.- Domain Decomposition Methods for PDE Constrained Optimization Problems.- Parallelism in Bioinformatics Workflows.- Complete Pattern Matching: Recursivity Versus Multi-threading.- Probabilistic Program Analysis for Parallelizing Compilers.- 6: Linear and Non-Linear Algebra.- Parallel Acceleration of Krylov Solvers by Factorized Approximate Inverse Preconditioners.- Krylov and Polynomial Iterative Solvers Combined with Partial Spectral Factorization for SPD Linear Systems.- Three Parallel Algorithms for Solving Nonlinear Systems and Optimization Problems.- Numerical Integration of the Differential Riccati Equation: A High Performance Computing Approach.- An Efficient and Stable Parallel Solution for Non-symmetric Toeplitz Linear Systems.- Partial Spectral Information from Linear Systems to Speed-Up Numerical Simulations in Computational Fluid Dynamics.- Parallel Newton Iterative Methods Based on Incomplete LU Factorizations for Solving Nonlinear Systems.

The Flow Inside a Model Gas Turbine Combustor: Calculations

The present study assesses the ability of the k-e turbulence model to calculate the flow inside gas turbine combustors. Results of calculations using a cylindrical system of coordinates, hybrid differencing, and a mesh with about 40,000 nodes are compared with velocity measurements of the flow inside a perspex model of can-type gas turbine combustor. The larger discrepancies between measurements and predictions were found in the primary region. The complexity of the flow near the primary jet impingement led to underprediction of the maximum negative axial velocity and turbulence kinetic energy by about 35 and 20 percent, respectively. The calculated results exhibited higher levels of momentum diffusion compared to the experiments and did not show the two contrarotating vortices created between the primary jets; no qualitative agreement with the azimuthal velocity downstream of the primary jets could be achieved. Despite these deficiencies, the model gave acceptable results in other regions of the combustor and correct prediction of the main features of the combustor flow was possible.

High Performance Computing for Computational Science – VECPAR 2010

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The efficiency of alternative pressure-correction formulations for incompressible turbulent flow problems

Abstract Two test cases, one two-dimensional and one three-dimensional, were considered to highlight the convergence characteristics and assess the computational efficiency of three alternative formulations for the pressure-velocity coupling (viz SIMPLE, PISO, and AVPI) in the calculation of incompressible turbulent flows. The results from these test cases showed that the use of the more elaborate pressure-velocity algorithm (PISO), requiring more than one pressure-correction equation, did lead to a reduction of the computing time by about 30% after careful optimization of the numerical parameters. This relatively small reduction occured, however, at the expense of an increased memory requirement and the present test cases did not therefore lend strong support to the use of such algorithms. In addition, our results also showed that, in the calculation of at least some turbulent flows, the overall rate of convergence is dominated by the convergence of the turbulence model equations and the influence of the pressure-correction formulation is not then significant.

Large-eddy simulation of the flow in an S-duct

Large-eddy simulations of the flow in an S-shaped, two-dimensional duct were conducted using a Lagrangian dynamic eddy viscosity subgrid-scale model and a non-orthogonal grid system. The simulations were performed at Re b = 13,800 and 30,800, using up to 13.4 million grid nodes. The results show that two factors affect the boundary layer: the concave or convex wall curvature (which, respectively, enhances or dampens the turbulent motions) and the favourable or adverse pressure gradient in the regions of curvature change, which accelerates or decelerates the boundary layer. In the presence of an adverse pressure gradient the boundary layer can separate intermittently, which also enhances the turbulent motions. The strongest separation occurs between the two curves and affects the flow not only in the following curve but also in the recovery region. The flow near the walls displays a logarithmic behaviour, but its slope and intercept vary with curvature and pressure gradient. Taylor–Görtler vortices are observed near the concave surfaces; they are responsible for strong organization of the streamwise and wall-normal velocity fluctuations, and contribute significantly to the Reynolds stresses. The turbulent kinetic energy budgets show that the production and dissipation are similarly affected by the wall curvature as the turbulent motions: they are increased by the concave wall and decreased by the convex. The mean flow advection transports turbulent kinetic energy from the region with concave curvature to the region with convex curvature.