Interoperable Geometry and Mesh Components for SciDAC Applications

1
Interoperable Geometry and Mesh Components
for SciDAC Applications
Enabling shape optimization for future
accelerator designs
The Terascale Simulation Tools Technologies
(TSTT) Center
SLAC/TOPS/TSTT Accelerator Shape Optimization
Collaboration
Purpose Create a new generation of accelerator
modeling optimization capability from SciDAC
computational components, which can be applied
directly for near-term design decisions (e.g.
International Linear Collider Low-Loss cavity)
and to future accelerator designs (RIA, LCLS).
TSTT Role Provide advanced services for
geometry (TSTTG/CGM) and mesh (TSTTM/MOAB,
MESQUITE), linked to accelerator physics and
optimization using core TSTT data model concepts.

• Enabling access to advanced geometry mesh
  representations, tools through common interfaces
• MOAB (SNL) Structured/unstructured FE mesh
• FMDB (RPI) Tri/tet mesh, adaptive mesh
  refinement
• NWGrid (PNNL) Mesh generation for biological
  models
• GRUMMP (UBC, Canada) Tri/tet mesh, mesh
  improvement
• Mesquite (SNL) Optimization-based mesh smoothing
• Frontier (BNL, SUNY-SB) (See X. Lis poster)
• Future extension of approach to
• New components/instances of current interfaces
• New domains (e.g. discretization, fields,
  materials, etc.)
• New applications

Overall Optimization Cycle
Impact Superior accelerator cavities, yielding
better accelerator performance at a lower cost
m?(p)
DDRIV (TSTT)
?(p)
Procedural Geometry Generation
ILC Parameterized Geometry
m?(p)
?(p), E(d)
?(p), g(p)
Mesh Projection/ Smoothing
Design Velocities ?vG/?pi
The TSTT Interfaces
Omega3P Sensitivity (AST/TOPS)

• TSTTR Relations
• Relates entities, sets between geometry, mesh
  interfaces
• Dynamic mapping based on application-defined
  criteria
• Extensible to other (e.g. hierarchical) relations

dp
Optimization (TOPS)
depends on
depends on

• TSTTG Geometry
• BREP-type topological model
• Sub-interfaces for

• TSTTM Mesh
• FE zoo polygons, polyhedra
• Entity- array-based access
• (picture of mesh)

Mesh Projection/Smoothing

• Shape optimization iterations project same mesh
  to new geometric models
• Fixed mesh topology gives continuity in
  optimization allows reuse of matrix
  factorization in Omega3P

Design Velocity Calculation

• Design velocity ?xG/?pi (last term in
  chain-rule expansion of ?f/?pi)
• Computed AUTOMATICALLY using geometry generation
  function
• Communicated to Omega3P as tags on surface mesh
  vertices

Topology Parametric evaluations
Shape Modify
CUBIT Generate mesh
Go
Mo
Iteration 0

• Procecure
• Write original vertex positions as tag on Mk
• Generate new model G(pd) from perturbation pd
• Project/smooth mesh onto affected surfaces in
  G(pd)
• Compute ?xG/?pi using differencing
• Store as tags on mesh vertices

implements-all
implements-all
TSTTB Base
Iteration k
Tags Error class
Sets
?xG/?r2
Qualitative derivative verification using
Paraview
The TSTT Data Model
SNL Geometry, Mesh Tools Supporting Shape
Optimization

• MUST be both simple AND flexible
• 4 Basic Types
• Entity topological entities in a geometry or
  mesh (gvertex, gedge, gface, gregion)
• Entity set Arbitrary combinations of entities
  and of other sets supports parent/child
  relations between sets (! contains)
• Tag arbitrary piece of data which can be written
  to any of the other items created with specified
  name, size, optional type individual values
  assigned to any of the other items
• Interface instance instance of a component
  inside which entities are assumed to be related
  to one another, and which serves as the overall
  container of a components data and as the
  point of reference for those data

Mesh-Oriented datABase (MOAB)
Common Geometry Module (CGM)

• High-efficiency, low memory cost implementation
  of full TSTTM interface

• TSTTG implementation representation,
  modification of solid model-based geometry

Full TSTTG Interface

• Structured unstructured mesh
• FE zoo polygons, polyhedra
• Reads and/or writes CUBIT .cub files
  (w/metadata), ExoII, vtk, etc.
• Geom topology as sets w/parent-child relations
• Various other tools
• Converter (ExoII, vtk, .cub, Ansys, )
• Viz (Qt-, VTK-based)
• Available under LGPL license(http//cubit.sandia.
  gov/MOAB)
• C-based TSTTM interface implementation
  available too

Layered implementation for applicability across
engines
CAD-, facet- based engines
Access times comparable to object-based C
ARIES Compact Stellerator
Tags on vertices used to communicate surface
normals to Mesquite, Omega3P

• Memory efficient
• 25MB/106 hex elements (structured)
• 55MB/106 hex elements (unstructured)

• CGM is the basis for SNLs CUBIT mesh
  generation tool
• LGPL release summer 05 (http//cubit.sandia.gov
  /MOAB)

ITER Simplified Benchmark Model
LASSO (TSTTR)
Mesh Quality Improvement Toolkit (MESQUITE)

• Restore, evaluate data relations between
  interacting components
• Why not bundle components together? Because
  smaller components
• Promote re-usability
• Reduce complexity
• Give applications options/flexibility
• Then why is TSTTR necessary?Because advanced
  applications require interactions between
  components
• Geometry-mesh
• Geometry-materials
• Fields-mesh

Set parent-child relations show geometric model
topology

• Optimization-based mesh smoothing software
  library
• Structured, unstructured, hybrid meshes (most
  element types)
• Multiple state-of-the-art algorithms and solvers
• Multiple application domains
• Deforming domains/meshes,
• r-type adaptivity
• Heterogeneous, anisotropic mesh smoothing
• Arbitrary-Lagrange-Eulerian mesh smoothing
• Mesh fixup (untangle, shape, smoothness)
• Released under LGPL license (http//www.cs.sandia.
  gov/web9200/)

Shape Optimization
Shape Optimization
Viz
Design
TSTTR/ LASSO
TSTTM/ MOAB
TSTTG/CGM
Match, in TSTTG To, in TSTTM
Entity Entity Set
-gtdimension() GEOM_DIMENSIONvalue