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| Overview | | Entity Creation | | Grid Generation | | User Interface | | GEMS-SAUNA |

GEMS: Geometrical Exchange and Meshing Software

- the "Customised CAD" solution for Aerodynamics and Engineering Analysis

Grid Generation

GEMS has been designed from the outset to produce the high quality surface grids necessary for engineering analysis, especially CFD, and/or to create large, regular reparameterised surfaces upon which grid generators (including other external applications) can produce the highest quality results.

Structured Grids

For structured grid generation, emphasis is placed upon creation of grids with smooth, regular parametric and physical point distributions that do not need to reflect the underlying topology and parameterisation of the CAD model. This is desirable, since the CAD model is often composed of a patchwork of ill-fitting surfaces, each with their own mutually incompatible parameterisations.

Independence between the grid and the CAD surface parameterisation is established at an early stage. Various techniques are available. Central is the ability to evaluate a series of high quality sections through the CAD model and to distribute points along them. Cases where there are gaps between underlying surfaces are handled without difficulty.

Fine control over the density and distribution of points in both parametric directions is usually a requirement in order to produce the best results from the solver. The distribution may well be driven by the surface curvature, but it also needs to depend on the solver and the characteristics of the variable being solved. Hence the best approach is to empower the GEMS user and provide him with full and fine control over the placement of grid points. A huge variety of point distribution methods are provided, based upon physical arc length. These include cosine, cubic, exponential, power law (all with various bunchings, scales and cut-offs) and local curvature based distributions.

Of central interest to aerodynamicists is analysis of wings and other shapes having aerofoil profiles, usually with smooth leading edges. Grid generation around aerofoil sections is such a common and important requirement that customised functions are available in GEMS to ensure highest quality results. It is often desirable to bunch the grid points symmetrically about the leading edge - but where is the leading edge on a cambered profile? GEMS provides several methods to evaluate leading edge position and subsequently to distribute grid points about it. "Create Wing Grid" handles spanwise, and chordwise distributions about the leading edge, in a single function.


Unstructured Grids


GEMS provides a constrained Delaunay triangulation method for generation of unstructured surface grids. It is edge-point driven; the user specifies one or several trim lines (whose points will lie on a grid boundary). Optionally,any number of internal control lines may also be specified, in order to further control local grid densities.

The import of surface grids from other grid generators is also supported, to enable their integration with the rest of the model.

Operations such as resampling/refinement, creation of grids with a normal offset, reorientation, splitting and merging are all supported (for both structured and unstructured grids).


GEMS is a joint development between Flow Solutions Ltd and QinetiQ


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