Defining constraint equations

Constraints between nodal degrees of freedom are specified in the Interaction module. The form of each equation is

A1⁢u1+A2⁢u2+…+An⁢un=0,

where Ai is the coefficient associated with degree of freedom ui.

Context:

In the crane model the tips of the two trusses are connected together such that degrees of freedom 1 and 2 (the translations in the 1- and 2-directions) of each tip node are equal, while the other degrees of freedom (3–6) are independent. We need two linear constraints, one equating degree of freedom 1 at the two vertices and the other equating degree of freedom 2.

The degrees of freedom associated with the first set defined in an equation are eliminated from the stiffness matrix. Therefore, this set should not appear in other constraint equations, and boundary conditions should not be applied to the eliminated degrees of freedom.

  1. In the Model Tree, double-click the Constraints container. Name the constraint TipConstraint-1, and specify an equation constraint.
  2. In the Edit Constraint dialog box, enter a coefficient of 1.0, the set name Tip-a, and degree of freedom 1 in the first row. In the second row, enter a coefficient of -1.0, the set name Tip-b, and degree of freedom 1. Click OK.

    This defines the constraint equation for degree of freedom 1.

    Note:

    Text input is case-sensitive in Abaqus/CAE.

  3. Click mouse button 3 on the TipConstraint-1 item underneath the Constraints container, and select Copy from the menu that appears. Copy TipConstraint-1 to TipConstraint-2.
  4. Double-click TipConstraint-2 underneath the Constraints container to edit it. Change the degree of freedom on both lines to 2.