Mapdl.irlf(key='', **kwargs)

Specifies that inertia relief calculations are to be performed.

APDL Command: IRLF


Calculation key:

0 - No inertia relief calculations.

1 - Counterbalance loads with inertia relief forces.

  • Precalculate masses for summary printout only (no inertia relief).


The IRLF command specifies that the program is to calculate accelerations to counterbalance the applied loads (inertia relief). Displacement constraints on the structure should be only those necessary to prevent rigid-body motions (3 are needed for a 2-D structure and 6 for a 3-D structure). The sum of the reaction forces at the constraint points will be zero. Accelerations are calculated from the element mass matrices and the applied forces. Data needed to calculate the mass (such as density) must be input. Both translational and rotational accelerations may be calculated.

This option applies only to the static (ANTYPE,STATIC) analysis. Nonlinearities, elements that operate in the nodal coordinate system, and axisymmetric or generalized plane strain elements are not allowed. Symmetry models are not valid for inertia relief analysis. Models with both 2-D and 3-D element types are not recommended.

Loads may be input as usual. Displacements and stresses are calculated as usual.

Use IRLIST to print inertia relief calculation results. The mass and moment of inertia summary printed before the solution is accurate (because of the additional pre-calculations required for inertia relief). See Inertia Relief in the Mechanical APDL Theory Reference for calculation details. See also the Structural Analysis Guide for procedural details.

If the inertia relief calculation is to be performed in the second or later load step, you must specify EMATWRITE,YES in the initial load step for the element matrices needed to perform the calculations to be available.

When a superelement (MATRIX50) is present in the model, any DOF constraints that you need to apply (D) on a degree of freedom (DOF) belonging to the superelement must be applied in the use pass of the MATRIX50 element (not in the generation pass). The command has no effect in the generation pass of a substructure. In the expansion pass, precalculation of masses for summary printout (IRLF,-1) occurs only on elements that are part of the substructure.

This command is also valid in PREP7.