20. Other In-Development Capabilities

This chapter describes other miscellaneous capabilities that are still in development or have limited testing.

20.1. Element Birth (Element Activation)

BEGIN ELEMENT BIRTH <string>birth_name
  BLOCK = <string list>block_names
  BIRTH START TIME = <real>time
  CRITERION IS ELEMENT VALUE OF
    <string>var_name <|<=|=|>=|> <real>tolerance
    [<integer>num_intg INTEGRATION POINTS REMAIN]
  CRITERION IS AVG|MAX|MIN NODAL VALUE OF
    <string>var_name <|<=|=|>=|> <real>tolerance
  CRITERION IS GLOBAL VALUE OF
    <string>var_name <|<=|=|>=|> <real>tolerance
END

A limited element birth/activation capability is provided for the target use cases of additive manufacturing and welds.

Elements are birthed upon an element variable, nodal variable, or global variable criterion. See Element Death section of the Sierra/SM User Manual for tips on properly setting up death/birth criteria based on a registered variable.

This capability is currently implemented for UG Hex8 elements with isotropic hypoelastic materials only.

Element birth works with thermal strains. Inactive elements do not accumulate thermal strains.

Element birth will error if a node is shared between an element birth block and a block involving: contact, force external boundary conditions, and kinetic boundary conditions.

20.2. Initial Particle Conversion

BEGIN CONVERSION TO PARTICLES AT INITIALIZATION <string>name
  BLOCK   = <string list>block_names
  ASSEMBLY   = <string list>assembly_names
  SECTION = <string>section_name
END

The initial particle conversion capability is provided to facilitate the creation of particle meshes for particle based methods—such as smooth particle hydrodynamics (SPH) or reproducing kernel particle method (RKPM)—from an initial mesh of solid elements (e.g., hexes).

At the beginning of the analysis the solid element blocks listed in block_names, or assemblies of solid element blocks listed in assembly_names are converted to spherical particles of the type defined in the particle section section_name. It is important to note that the particle section will thus supersede any section specified in the original solid element block definition (consult Sierra/SM User Manual section on Element Block Parameters).

Note that elements may also be converted to particles via element death (consult Sierra/SM User Manual section on Element Death); however, conversion at initialization should offer more robust creation of particle meshes that are (a) compatible with the original mesh boundary conditions and (b) amenable to the chosen particle formulation methodology.

20.3. Shell Contact Lofting Factor

Warning

The shell contact lofting factor only works with Dash contact.

BEGIN SHELL SECTION <string>shell_section_name
  # ... see the Elements chapter of Sierra/SM User Manual
  CONTACT LOFTING FACTOR = <real>contact_lofting_factor
END [SHELL SECTION <string>shell_section_name]

The CONTACT LOFTING FACTOR line command is available in the SHELL SECTION command block to set a lofting factor specifically for use in contact. This contact lofting factor is used in place of the kinematic lofting factor for creation of the shell lofted geometry in contact. If no contact lofting factor is set, the kinematic lofting factor is used for contact.

The contact lofting factor has no effect on the shell element kinematics, and the LOFTING FACTOR and CONTACT LOFTING FACTOR line commands may be used in combination to independently set the kinematic and contact lofting factors, respectively.

20.4. Discrete Element Method (DEM)

The discrete element method is a particle based element formulation. This method is in early development, experimental, and currently not recommended for use.

BEGIN DEM OPTIONS
  ...
END
BEGIN DEM SECTION
  ...
END

20.5. High Precision Assembly

Summation of floating point values can accumulate rounding errors, which can be unbounded and much larger than machine precision in pathological cases with cancellation. A prototype capability that implements the Kahan-Babushka-Neumair compensated summation algorithm [[1]] for element-wise contribution to nodal fields has been implemented for a restricted set of cases detailed below. The higher precsion assembly is activated in both explicit and implicit regions with the following line command.

HIGH PRECISION ASSEMBLY = ON|OFF (OFF)

The high precision assembly is currently supported for the following use cases:

assembly of nodal force_internal for the UG Hex8 element

20.6. Randomized Mesh Order

The following developer command enables scrambling the input mesh entity orders so that sensitivity to things like bucket-ordering etc. may be investigated. The command is at the region scope.

DEVELOPER COMMAND: SCRAMBLE MESH [SEED]

The default SEED is 0, which will use a random seed. A positive non-zero seed may be used to provide repeatable randomization of the input mesh.