The nodes and the elements need to be renumbered before an analysis is performed to minimize the Front Width and Half Band Width in the model. The mesh is renumbered by selecting the Renumber command from the Elements menu after having selected a nodestring. The nodestring is used as a seed to start the renumbering process.
After invoking the Renumber command, the Renumber dialog opens for choosing the renumbering method to used. Currently, only two options are provided. The Band Width option attempts to minimize the half band width, while the Front Width option attempts to minimize the front width.
Upon execution of this command, the nodes and elements are renumbered by a wave that passes through the mesh. This wave proceeds from elements connected to the selected nodestring and continues through the entire mesh. If a section of elements or nodes are disjoint, the wave will not continue and a warning message is given. Disjoint mesh sections are assigned arbitrary numbers, but before running the analysis, there should be no disjoint sections. Nodes which are not connected to any elements can be found and selected automatically.
It is important to realize that after renumbering the finite element mesh, any previous boundary condition file or solution file is no longer valid!
Due to the number of questions that are asked regarding this subject, this section will attempt to describe, in a broad sense, why renumbering is important.
The finite element solvers use an iterative, banded numerical solver to solve the governing differential equations. If the computer had to simultaneously solve the thousands of equations, it would run out of memory. This is why it uses a banded solver. The front width and the half-band width determine the size of the matrix which is used by the finite element solvers. A smaller front width and band width lead to a smaller required matrix. The front width and band width depend on the node and element numbering of the finite element mesh. To minimize the front width and band width, the mesh should be renumbered.
SMS provides an estimate as to how large the front width and half band width may become when running the finite element solver. These estimates are shown in the Mesh Information dialog, which can be opened by performing the File | Get Info command while in the Mesh Module. There is not a single renumbering scheme which always produces the lowest values for these, so it is suggested that you renumber from various locations in the mesh and check the mesh information before deciding which renumbering scheme to use. As a guideline, the mesh should be renumbered using a nodestring which extends across a small section of the mesh, such as a river inflow boundary.