# 6. Elements

This chapter explains how material, geometric, and other properties are associated with element blocks in a mesh file. A mesh file generally contains only topological information about elements. For example, there may be a group of four-noded elements in the mesh file which define a facet in three-dimensional space. These elements could be interpreted as either shells or membranes in the finite element model, based on command lines in the input file. The specifics of a material type associated with these four node facets are also set in the input file.

Most elements can be used in both explicit and implicit calculations. If an element is available for one but not the other, this information will be noted in the relevant element section. In particular there are special element implementations available for explicit calculations in smoothed particle hydrodynamics (SPH). This chapter also includes descriptions of the commands for mass property calculations, element death, and mesh rebalancing (which is available for explicit calculations only). “Element-like” capabilities are also discussed.

Highlights of chapter contents follow. Section 6.1 discusses the `FINITE ELEMENT MODEL` command block, which provides the description of a mesh associated with the elements. Section 6.2 presents the section command blocks that are used to define the different element sections. Next in Section 6.3 are descriptions of command blocks that exhibit element-like functionality. Section 6.3.1 explains the mechanism (explicit only). Section 6.4 describes the `MASS PROPERTIES` command block, which lets the user compute the total mass of the model or the mass of sub-parts of the model once the element blocks are completely defined in terms of geometry and material. Section 6.5 details the `ELEMENT DEATH` command block, which lets the user delete (kill) elements based on various criteria during an analysis. Section 6.6 describes particle embedding (explicit only), which specifies element blocks in which each element is embedded with particles during initialization. A command block for derived quantities that are to be used with transfers or error estimation is discussed in Section 6.7. Section 6.8 presents various options available in explicit calculations for rebalancing of the initial mesh decomposition for parallel runs, which may improve the parallel performance of some problems.

Most of the command blocks and command lines described next appear within the SIERRA scope. There are some exceptions, and these exceptions are noted.