Importing Abaqus equations

In Abaqus, the *EQUATION keyword lets you define linear multi-point constraints in the form of an equation. You can import an Abaqus model containing *EQUATION keywords. The software imports them as multi-point constraint (MPC) simulation objects.

Equation sets

Every set in an *EQUATION keyword must have either only one node or an equal number of nodes to the other sets in the equation. In other words, if a set has only one node, the software treats it as a set with the repeated node equal to the size of other sets in the equation. Therefore, when the software writes equations, all the sets in the equations have the same size.

For example, four sets are defined as the following in an Abaqus model deck:

Set1 = {a1,a2,a3,a4}  Set2 = {b1}  Set3 = {c1,c2,c3,c4} Set4 = {d1}

The definition of the equation card:

*Equation4Set1, 2, coeff1, Set2, 2, coeff2, Set3, 1, coeff3, Set4, 1, coeff4

is the same as the following:

*Equation 4  a1, 2, coeff1, b1, 2, coeff2, c1, 1, coeff3, d1 , 1, coeff4 4 a2, 2, coeff1, b1, 2, coeff2, c2, 1, coeff3, d1 , 1, coeff4 4 a3, 2, coeff1, b1, 2, coeff2, c3, 1, coeff3, d1 , 1, coeff4 4 a4, 2, coeff1, b1, 2, coeff2, c4, 1, coeff3, d1 , 1, coeff4

Abaqus restricts the data line format. If the first term uses a node label, the following terms must also use node labels. If the first term uses a node set name, the following terms can use either a node set name or a node label.

When importing the equation, the software supports any format of the mixed node set name and node label data. If the node sets to be imported have different total number of nodes, the software takes the minimum total number (greater than one) from all involved node sets. In the example, if you change Set1 to exclude a4, the final imported equation definition is as follows:

*Equation 4 a1, 2, coeff1, b1, 2, coeff2, c1, 1, coeff3, d1 , 1, coeff4 4 a2, 2, coeff1, b1, 2, coeff2, c2, 1, coeff3, d1 , 1, coeff4 4 a3, 2, coeff1, b1, 2, coeff2, c3, 1, coeff3, d1 , 1, coeff4

Node sets and multi-point constraint simulation object creation

The software does not support node sets directly in a multi-point constraint (MPC) simulation objects, which represent equations in Pre/Post. When you import an *EQUATION keyword, the software decomposes each applicable node set, and rebuilds the equation definition into independent node and dependent nodes, which can result in large number of simulation objects and potentially becomes a performance issue.

Where do I find it?

Application	Pre/Post
Prerequisites	A Simulation file as the work part and displayed partAbaqus as the specified solver
Menu	File→Import→Simulation

Learn more

Controlling the import of elements and nodes

Importing Abaqus assembly models

Import support for Abaqus load cases

Importing the Abaqus *NMAP keyword

Combining Abaqus surfaces on import

Controlling the import of element attributes

Controlling the import and export of SPRING2 elements

Compressing node sets when exported

Exporting material definitions

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Abaqus keywords supported for import and export

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Importing Abaqus equations, Simcenter 3D 2021.1 Series

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