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Example Applications Built with the Charm++ ParFUM Framework 1) Parallel Spacetime Discontinuous Galerkin 2) Rocrem : Remeshing a Rocket Isaac Dooley Parallel Programming Lab University Illinois Urbana-Champaign http://charm.cs.uiuc.edu. Parallel Spacetime Discontinuous Galerkin. Overview.

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slide1

Example Applications Built with the

Charm++ ParFUM Framework

1) Parallel Spacetime Discontinuous Galerkin

2) Rocrem: Remeshing a Rocket

Isaac Dooley

Parallel Programming Lab

University Illinois Urbana-Champaign

http://charm.cs.uiuc.edu

overview
Overview
  • My background in parallel programming
  • How the Spacetime Discontinuous Galerkin Method utilizes unstructured meshes.
  • Requirements to parallelize SDG
  • Existing functionality in ParFUM which satisfies some SDG requirements
  • New functionality which has been added to ParFUM to support the rest of the SDG requirements

LACSI 2005

parallel programming lab
Parallel Programming Lab
  • Our focus is parallel programming, especially in frameworks and dynamic or adaptive applications
  • We are not Computational Geometers, nor Mathematicians.
  • We try to build general purpose reusable high performance frameworks
  • Charm++ and AMPI
  • Focus on Migratable Objects and Virtualization
  • Multiple Platforms (Clusters, SMPs, BlueGene/L)

LACSI 2005

spacetime discontinuous galerkin
Spacetime Discontinuous Galerkin
  • Collaboration with:
    • Bob Haber, Jeff Erickson, Mike Garland, …
    • NSF funded center
  • SDG Motivation: Spatial adaptivity is needed in structural dynamics applications. Why shouldn’t we also adapt in the time dimension?

LACSI 2005

spacetime discontinuous galerkin1
Spacetime Discontinuous Galerkin
  • Mesh generation is an advancing front algorithm called Tent Pitcher.
  • Adds a set of new elements called patches to the mesh, then solves them, thus advancing the front.
  • Each patch depends only on inflow elements.

LACSI 2005

1 d mesh generation
1-d Mesh Generation

Unsolved Patches

Time

Tent Pole

Space

LACSI 2005

1 d mesh generation1
1-d Mesh Generation

Unsolved Patches

Time

Solved Patches

LACSI 2005

1 d mesh generation2
1-d Mesh Generation

Refinement

Unsolved Patches

Time

Solved Patches

LACSI 2005

adaptive sdg
Adaptive SDG
  • Method described in
    • Abedi, Zhou, et. al.; Spacetime meshing with adaptive refinement and coarsening; 2004
  • Tent poles are not just pitched above existing space nodes
  • Entire space-time mesh or frontier is built as a mesh. Non-adaptive SDG can store patches as attributes of nodes in original mesh.

LACSI 2005

master slave parallelization of sdg
Master/Slave Parallelization of SDG
  • The first parallelization of the SDG method was based on the observation that each patch could be solved independently.
  • Thus the space mesh is not partitioned, but maintained on one master processor.
  • Workers request patches to solve from the master processor.
  • This method resulted in a bottleneck at the processor holding the entire space mesh.

LACSI 2005

must parallelize the geometry
Must Parallelize the Geometry!
  • Do not want a single processor bottleneck.
  • We have an initial mesh, we’ll partition the geometric space mesh.
  • We need consistent ghost element layer.
  • We need a locking mechanism for updating ghost values at appropriate times to ensure we have a consistent mesh.
  • We will need the ability to incrementally add/remove elements to/from the mesh, maintaining consistency across all processors.

LACSI 2005

required for non adaptive space time meshing
Required for non-adaptive space-time meshingParFUM - New Features
  • Incremental updates to ghost layers of adjacent processors
  • Locking of individual elements or nodes.
  • No global synchronization.
  • New adjacency data structures
    • Element to element
    • Node to node
    • Node to element

LACSI 2005

parfum support for adaptivity
ParFUM Support For Adaptivity
  • Load balancing is required in any efficient framework for adaptive SDG, since mesh partitions can differ in size by orders of magnitude.
  • We have already extended ParFUM to provide parallel incremental mesh modification primitives.
  • The primitives allow simple coding of incremental mesh modification, refinement, coarsening, and repair routines.

LACSI 2005

rocrem remeshing a rocket1
Rocrem: Remeshing a Rocket
  • Old mesh distorted by burning and pressure
  • Create new mesh from old by remeshing
    • Using Simmetrix for sequential tetrahedral meshes
    • Performs variable mesh sizing
  • Repartition new mesh
  • Transfer solution data in parallel from deformed mesh to new mesh
    • Uses accurate conservative transfer (volume-weighted averaging) for cell-centered solution data of Rocflu fluids mesh
    • Uses linear interpolation for node-centered solution data
  • Restart simulation using new mesh and solution data

LACSI 2005

serial remeshing
Serial Remeshing
  • ParFUM: stitch together partitioned surface mesh to form a serial mesh
  • Use Simmetrix to remesh surface and create volume
    • Uses regional sizing
  • Internally coarse volume must be refined

LACSI 2005

parallel solution transfer
Parallel Solution Transfer
  • ParFUM: partition mesh for parallel transfer
  • Collision Detection Library: match up old mesh with overlaid new mesh
  • Data Transfer Library: conservative, accurate volume-to-volume transfer

LACSI 2005

special features
Special Features
  • Scalable parallel solution transfer
  • Supports both node- and cell-centered solution data
  • Supports node- and face-centered boundary conditions
    • Preserved through remeshing and data transfer process
  • Boundary extrusion
  • Complete HDF to HDF conversion with restart files

LACSI 2005

boundary extrusion
Boundary Extrusion
  • After remeshing, new mesh boundary does not perfectly coincide with old mesh boundary
  • Curved surface yields points on new surface beyond surface of old mesh
  • Solution: extrude boundary faces of old mesh to cover new mesh
    • All volumes of new mesh now covered by old mesh
  • Proceed with solution transfer

LACSI 2005

thank you for listening to my talk

Thank-you for listening to my talk!

Questions or Comments?

LACSI 2005