Equations

Equation entities contain mathematical equations that define more complex loads. They are used to define linear constraints in local and global coordinate systems.

Every equation must be organized into one load collector, and therefore are mutually exclusive to a load collector.

Equations are displayed as lines between the dependent node and the independent node(s) with EQ displayed at the dependent node of the equation in the modeling window.

Equations are used in Nastran as MPC (Multipoint Constraint Equation) or in Abaqus as *equation.

Equations are organized into load collectors.

Abaqus Cards

Loads or constraints that are to be used as history data (under *STEP) should be collected into load collectors with the HISTORY card image. These load collectors also need to be added to the corresponding load steps (*STEP). In contrast, loads or constraints for model data should be collected into load collectors with INITIAL_CONDITION card image. They will automatically be written out in the model portion of the Abaqus input deck.

Note: All loads and boundary conditions on sets can be expanded to individual nodes and elements by selecting the Expand load on sets option in the File Options dialog, which is invoked upon importing a solver deck. If a **HMLOAD_SETS_EXPAND comment is found in the input file, all loads and boundary conditions on sets are expanded to individual nodes and elements.

Card	Description
*EQUATION	Define linear multi-point constraints. Note: Explicit node IDs are supported. Node sets are not supported. Equations are considered as loads and therefore, they are collected in load collectors. Upon export, they write to the bulk data portion of the Abaqus deck.

ANSYS Cards

Card	Description
CE	Defines a constraint equation relating to degrees of freedom.

LS-DYNA Cards

Several load types cause three cards to be output for x, y, and z components. During input, these are grouped into one load. Loads cannot be applied to sets, components, or boxes. Load curves are input and output. Use the Card Editor to select load curves. Unless mentioned in the Notes column, load cards cannot be edited.

Card	Description
*CONSTRAINED_LINEAR	Define linear constraint equations between displacements and rotations, which can be defined in a local coordinate system.
*CONSTRAINED_LINEAR_GLOBAL	Define linear constraint equations between displacements and rotations, which can be defined in global coordinate systems.

Nastran Cards

Note: Other loads such as SPCADD, MPCADD, FREQ, FREQ1, EIGR, EIGRL, EIGC, EIGP, EIGB, GRAV, and RFORCE are supported as load collectors.

Card	Description
MPC	Defines a multipoint constraint equation of the form. Note: Individual weight factors can be created on the nodes of an MPC equation using the update functionality in the Equations panel.

OptiStruct Cards

Card	Description
MPC	Defines a multipoint constraint equation of the form. Note: Bulk Data Entry

Permas Cards

Card	Description
$MPC GENERAL	General linear constraint equation.