Objective:
I am conducting a finite element analysis and would like to know how to define an optimal mesh for my problem.
Resolution:
The ideal finite element mesh size will depend on the specific analysis. For example, if the domain size is quite large, the global mesh size will be larger to ensure that solve times are not unreasonable; however, the mesh may need to be constrained (e.g. decreased) in specific parts of the domain where higher gradients (e.g., in water total head, energy, or stress) are present. Areas with higher gradients typically occur adjacent to imposed boundary conditions (e.g., a pumping well flow rate) or near the interface between materials with very different defined material properties.
An initial estimate should be used to set the global element mesh and constrain the mesh in areas where you suspect high gradients will occur. After solving the analysis and reviewing the results, the mesh size should be modified and the analysis re-solved, to see if the results change significantly. If this is the case, further modification of the mesh is necessary to find the optimal size.