Advanced Building Simulation

226 Malkawi
Figure 9.7 Structured grid
showing regular connectivity
(Courtesy: Sun 2003). (See
Plate X.)
Figure 9.8 Unstructured
grid showing irregular connectivity
(Courtesy: Sun
2003). (See Plate XI.)
Figure 9.9 Multi-block
grid showing subdomains
or blocks
(Courtesy: Sun 2003).
(See Plate XII.)
the higher the mesh density, the higher the level of simulation accuracy, which leads
to expensive computation. Five major data structures of meshes or grids are typically
used: (1) structured, (2) unstructured, (3) multi-block or block-structured, (4) hybrid,
and (5) Cartesian.
Structured grids consist of regular connectivity where the points of the grid can be
indexed by two indices in 2D and three indices in 3D, etc. Regular connectivity is provided
by identification of adjacent nodes, Figure 9.7.
Unstructured grids consist of irregular connectivity wherein each point has different
neighbors and their connectivity is not trivial. In unstructured grids, the nodes
and their complex connectivity matrix define the irregular forms, Figure 9.8.
Multi-block approach can break complicated geometry into subdomains or blocks;
structured grids are then generated and governing equations can be solved within
each block independently. These grids can handle complex geometrical shapes and
simultaneously undertake a wide range of numerical analysis (Figure 9.9). Some of the
advantages of multi-block grids are as follows: (a) geometry complexity can be greatly
reduced by breaking the physical domain into blocks; (b) since the gridline across
the blocks are discontinuous, more freedom in local grid refinement is possible;
(c) standard structured flow solvers can be used within each block obviating the need
for complicated data structure, book keeping and complex algorithms; and (d) provides
a natural routine for parallel computing, thereby accelerating the simulation.
Hybrid grids are a combination of structured and unstructured grids and are used
for better results and greater accuracy. High grid density can be designed at locations
where there are sharp features of the boundary (Figure 9.10).
Cartesian grids are mostly hexahedral (right parallelopipeds) and the description of
the surface is no longer needed to resolve both the flow and the local geometry