GEMS is an object-oriented interactive geometry modeling and 2D/3D multiblock structured mesh generation system, designed as a preprocessor for solving complex flow simulation problems in Computational Fluid Dynamics (CFD) and related fields.
A New Generation of Software
• A state-of-the-art software based on OOP and C++
• Integrated geometry modeling and mesh generation tools
• Multiblock structured grid generation options for surface and volume grids
• Automatic grid generation
• Intelligent topology definition by Case-Based Reasoning/Learning
• Storage and recovery of the mesh generation process at any stage
• Context sensitive help
Figure: Definition of surface geometry by cross sectional cubic spline curves.
Geometry Modeling
• Built in CAD options to create and edit grid boundary curves and surfaces
• Supported curves : Arc, Line, Polyline, B-Spline, Cubic Spline, NURBS
• Surface creation by mapping or interpolation
• Surface intersection curves and surfaces of revolution
• Reading external CAD data (sectional or wire frame) in IGES format
• Specific curve and surface generation and editing options
Figure: Definition of surface geometry by a number of patches (wireframe).
Grid Generation
• Algebraic and elliptic (multigrid or SLOR) grid generation options
• Translating, rotating or sweeping a face to create volume grids
• Interactive control of boundary grid point distribution and orthogonality
• Definition of various boundary conditions by surface patches
• Interactive definition of topology, connectivity and boundary conditions
• Surface and volume grid cell quality checks
• Displaying and saving coarse levels for multigrid
• Rendering, hidden line removal and color map representation
• Overlapping grid cell display
Figure: Surface grids on the FLYER prototype (courtesy of ERG Corp., Ankara)
Automatic Grid Generation
• Macro (script) files to record modeling and generation steps interactively
• Replaying macro files partially or completely to perform repeated tasks
Figure: A six-block H-type grid for the coolant passages of a turbine blade.
Intelligent Topology Definition
• Learning past experiences by Case Based Reasoning / Learning (CBR / CBL)
• User preferences and user evaluation in storing and recovering grid topology
• Case retrieval
- by electing a previous topology or
- by case suggestion utilizing the fitness metric
• Constraint satisfaction based on
- desired number of grid points,
- grid cell quality,
- multigrid levels and
- flow solution method
Figure: Selected block surfaces in an industrial combustion chamber geometry.
Development History
• Originally developed by Dr. Cem Dener in June 1993
• Supported by the Technology Development Fund of Turkey (TTGV)
• TTGV-069 project to extend the capabilities of GEMS (Oct `93 - Dec `94))
- Automatic Grid Generation (AGG) developed by Ms. Esin Koc
- Intelligent Topology Definition (ITD) developed by Mr. Izzet Sirin
Figure: Surface scrolling and surface rendering on space shuttle configuration.
Operating Platform
• GEMS 3.3 : Silicon Graphics with IRIX
• Requirements :
- Min. 32 MB RAM
- Min. 50 MB free space on hard disk
- 1280x1024 pixel resolution display