In finite element analysis, the spatial twist continuum (STC) is a dual representation of a hexahedral mesh that defines the global connectivity constraint.
An analyst has many choices available for creating a mesh that can be used in a CFD or CAE simulation, one is to use a Tetrahedral, Polyhedral, Trimmed Cartesian or Mixed of Hybrid of Hexahedra called hex dominate, these are classified as non-structured meshes, which can all be created automatically, however the CFD and FEA results are both inaccurate and prone to solution divergence, (the simulation fails to solve).
The other option for the analyst is to use an all-hexahedral mesh that offers far greater solver stability and speed as well as accuracy and the ability to run much more powerful turbulence solvers like Large eddy simulation LES in transient mode as opposed to the non-structured meshes that can only run a steady state RANS model.
This is the reason why it is relatively easy to automate a non-structured mesh, the automatic generator only needs to be concerned with the local cell size geometry.
The tradeoffs and relative benefits of using either mesh method to build and solve a CFD or CAE model are best explained by looking at the total work flow.
For large complex geometric models the process of building a hexahedral mesh can take days, weeks and even months depending on the skill level and tool sets available to the analyst.
5) Post processing the results: The time required in this step is highly dependent on the size of the mesh (number of cells).