COLLECTIONS

Documents published in Scipedia

• Parallelizing the construction of indirect access arrays for shared‐memory machines

  J. Tuszynski, R. Lohner

  Comput. Methods Appl. Mech. Engrg., (1998). Vol. 14 (8), pp. 773-781

  
  

  Abstract

  A way has been found to form indirect addressing lists in parallel on shared-memory parallel machines. The maximum possible speed-up for typical tetrahedral grids is approximately 1:23. The algorithm requires an additional scratch array to shift from the serial ‘elements surrounding points’ to the parallel ‘elements surrounding processors surrounding points’ paradigm. The algorithm developed is general in nature, i.e. applicable to all indirect addressing lists. All numerical methods requiring the construction of indirect data structures, such as sparse matrix linear algebra procedures, field and particle solvers operating on unstructured grids, and network flow applications should see a benefit from this algorithm when running on shared-memory parallel machines

  Abstract
  A way has been found to form indirect addressing lists in parallel on shared-memory parallel machines. The maximum possible speed-up for typical tetrahedral grids is approximately [...]

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• Renumbering strategies for unstructured-grid solvers operating on shared-memory, cache-based parallel machines

  R. Lohner

  Comput. Methods Appl. Mech. Engrg., (1998). Vol. 163 (1-4), pp. 95-109

  
  

  Abstract

  Two renumbering strategies for field solvers based on unstructured grids that operate on shared-memory, cache-based parallel machines are described. Special attention is paid to the avoidance of cache-line overwrite, which can lead to drastic performance degradation on this type of machines. Both renumbering techniques avoid cache-misses and cache-line overwrite while allowing pipelining, leading to optimal coding for this type of hardware

  Abstract
  Two renumbering strategies for field solvers based on unstructured grids that operate on shared-memory, cache-based parallel machines are described. Special attention is paid [...]

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• Generalized Meshing Environment for Computational Mechanics

  L. Spradley, R. Lohner, T. Chung

  AIAA Journal (1998). Vol. 36 (9), pp. 1735-1737

  
  

  Abstract

  One of the most time-consuming tasks in performing any discrete analysis the construction of a suitable mesh to represent the computational domain. Mesh generation today remains one of the pacing items in computational mechanics and consumes too many work hours and too many computers resources. This critical need for more progress in three-dimensional resources. This critical need for more progress in three-dimensional mesh generation certainly requires efficient geometry definition systems and advances in meshing methods. However, another major factor toward this progress is efficient methodology and computer software for automation of the meshing process. It is precisely this aspect of meshing that’s is the focus of this Note.   

  Abstract
  One of the most time-consuming tasks in performing any discrete analysis the construction of a suitable mesh to represent the computational domain. Mesh generation today remains [...]

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• Distributed visualization in computational fluid dynamics

  J. Cebral, R. Lohner

  (1998). Computational Fluid Dynamics Review 1998, Part 9, pp. 1097-1112

  
  

  Abstract

  The use of parallel computers and in particular distributed memory architectures imposes a number of requirements on the visualization systems for Computational Fluid Dynamics (CFD). We describe the design and capabilities of our distributed visualization software which can handle parallel multidisciplinary applications, can connect to a running solver for on-line display and steering, supports collaborative visualization and can be used as a tool for the automatic making of movies and animations. This discussion serves as an overview of the current trends and developments in visualization as applied to CFD and other computational sciences.

  Abstract
  The use of parallel computers and in particular distributed memory architectures imposes a number of requirements on the visualization systems for Computational Fluid Dynamics [...]

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• Computation of the 3-D Unsteady Flow Past Deforming Geometries

  R. Ramamurti, R. Lohner, W. Sandberg

  Int. J. Computational Fluid Dynamics (1999). Vol. 13 (1), pp. 83-99

  
  

  Abstract

  A 3-D incompressible unsteady flow solver based on simple finite elements with adaptive remeshing and grid movement for both moving and deforming surfaces is described. We demonstrate the combination of adaptive remeshing techniques with the incompressible flow solver with the computation of flow past an eel in 2-D and a blue-fin tuna in 3-D. The flow past a swimming tuna was computed for two extreme cases of the caudal fin frequency and swimming speed. A grid refinement study was performed and a grid converged solution for the force produced by the caudal fin was obtained.

  Abstract
  A 3-D incompressible unsteady flow solver based on simple finite elements with adaptive remeshing and grid movement for both moving and deforming surfaces is described. We [...]

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• Parallel Advancing Front Grid Generation

  R. Lohner, J. Cebral

  (1999). IMR

  
  

  Abstract

  A parallel advancing front scheme has been developed. The domain to be gridded is rst subdivided spatially using a relatively coarse octree. Boxes are then identiied and gridded in parallel. A scheme that resembles closely the advancing front technique on scalar machines is recovered by only considering the boxes of the active front that generate small elements. The procedure has been implemented on the SGI Origin class of machines using the shared memory paradigm. Timings for a variety of cases show speedups similar to those obtained for ow codes. The procedure has been used to generate grids in excess of a hundred million elements. 

  Abstract
  A parallel advancing front scheme has been developed. The domain to be gridded is rst subdivided spatially using a relatively coarse octree. Boxes are then identiied and gridded [...]

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• Surface triangulation over intersecting geometries

  A. Shostko, R. Lohner, W. Sanderg

  Int. J. Numer. Meth. Engng. (1999). Vol. 44 (9), pp. 1359-1376

  
  

  Abstract

  A method for the rapid construction of meshes over intersecting triangulated shapes is described. The method is based on an algorithm that automatically generates a surface mesh from intersecting triangulated surfaces by means of Boolean intersection/union operations. After the intersection of individual components is obtained, the exposed surface parts are extracted. The algorithm is intended for rapid interactive construction of non‐trivial surfaces in engineering design, manufacturing, visualization and molecular modelling applications. Techniques to make the method fast and general are described. The proposed algorithm is demonstrated on a number of examples, including intersections of multiple spheres, planes and general engineering shapes, as well as generation of surface and volume meshes around clusters of intersecting components followed by the computation of flow field parameters.

  Abstract
  A method for the rapid construction of meshes over intersecting triangulated shapes is described. The method is based on an algorithm that automatically generates a surface [...]

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• The numerical simulation of strongly unsteady flow with hundreds of moving bodies

  R. Lohner, C. Yang, J. Baum, H. Luo, D. Pelessone, C. Charman

  Int. J. Numer. Meth. Fluids (1999). Vol. 31 (1), pp. 113-120

  
  

  Abstract

  A methodology for the simulation of strongly unsteady flows with hundreds of moving bodies has been developed. An unstructured grid, high-order, monotonicity preserving, ALE solver with automatic refinement and remeshing capabilities was enhanced by adding equations of state for high explosives, deactivation techniques and optimal data structures to minimize CPU overheads, automatic recovery of CAD data from discrete data, two new remeshing options, and a number of visualization tools for the preprocessing phase of large runs. The combination of these improvements has enabled the simulation of strongly unsteady flows with hundreds of moving bodies. Several examples demonstrate the effectiveness of the proposed methodology.

  Abstract
  A methodology for the simulation of strongly unsteady flows with hundreds of moving bodies has been developed. An unstructured grid, high-order, monotonicity preserving, ALE [...]

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• A Navier-Stokes/Actuator Disc Simulation of Body-Ducted Propulsor Flow

  C. Kiat Ho, R. Lohner, R. Ramamurti

  (1999). American Physical Society, Division of Fluid Dynamics Meeting

  
  

  Abstract

  The interactions between a cylinder body and a ducted propeller is simulated using a coupled Navier-Stokes and actuator disc approach. The actuator disc approach raises the pressure of the fluid flowing through the propeller disc. Therefore, the finite number of blades, and the production of fluid rotation are ignored. An unstructured grid-based three-dimensional finite element method was used to solve the turbulent hydrodynamic flowfield. A Baldwin-Lomax turbulence model was used. The source strength was determined to match the thrust generated by propeller. The additional momentum due to the actuator disc is treated by a uniform distribution of sources over the propeller disc in momentum equation of Navier-Stokes equations. The three different momentum source strengths were used and the results from these cases and a no-source case are compared. It is shown that the source distribution can induce upstream separation if not properly chosen. (Work Sponsored by DoD HPCMO.)

  Abstract
  The interactions between a cylinder body and a ducted propeller is simulated using a coupled Navier-Stokes and actuator disc approach. The actuator disc approach raises the [...]

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• Surface Gridding from Discrete Data

  R. Lohner

  (1995). Proceedings, 4th International Meshing Roundtable, Sandia National Laboratories, pp.29-44

  
  

  Abstract

  An advancing front gridding technique that operates on discretely defined surfaces is presented. Different aspects that are required to make the procedure reliable for complex geometries are discussed. Notable among these are:   a) the recovery of surface features and discrete surface patches from the discrete data b) filtering based on point and side normals to remove undesirable data close to cusps and corners c) the proper choice of host faces for ridges d) fast interpolation procedures suitable for complex geometries. Post-generation surface recovery or repositioning techniques are discussed. Several examples ranging from academic to industrial demonstrate the utility of the proposed procedure for ab initio surface meshing from discrete data, such as those encountered when the surface description is already given as discrete, the improvement of existing surface triangulations, as well as remeshing applications during runs exhibiting significant change of domain.

  Abstract
  An advancing front gridding technique that operates on discretely defined surfaces is presented. Different aspects that are required to make the procedure reliable for complex [...]

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