Rigid body motion output variables

This problem contains basic test cases for one or more Abaqus elements and features.

This page discusses:

ProductsAbaqus/Standard

Elements tested

  • B21
  • B21H
  • B22
  • B22H
  • B23
  • B23H
  • B31
  • B31H
  • B32
  • B32H
  • B33
  • B33H
  • C3D4
  • C3D6
  • C3D8
  • C3D10
  • C3D15
  • C3D20
  • CAX3
  • CAX4
  • CAX4R
  • CAX6
  • CAX8
  • CAX8R
  • CPEG3
  • CPEG3H
  • CPEG4
  • CPEG4H
  • CPEG4R
  • CPEG4RH
  • CPEG4I
  • CPEG4IH
  • CPEG6
  • CPEG6H
  • CPEG8
  • CPEG8H
  • CPEG8R
  • CPEG8RH
  • CPE3
  • CPE3H
  • CPE4
  • CPE4H
  • CPE4R
  • CPE4RH
  • CPE4I
  • CPE4IH
  • CPE6
  • CPE6H
  • CPE8
  • CPE8H
  • CPE8R
  • CPE8RH
  • CPS3
  • CPS4
  • CPS4R
  • CPS6
  • CPS8
  • CPS8R
  • ELBOW31
  • ELBOW31B
  • ELBOW31C
  • ELBOW32
  • M3D3
  • M3D4
  • M3D4R
  • M3D6
  • M3D8
  • M3D8R
  • M3D9
  • M3D9R
  • MASS
  • PIPE21
  • PIPE21H
  • PIPE31
  • PIPE31H
  • PIPE32
  • PIPE32H
  • ROTARYI
  • PIPE22
  • PIPE22H
  • S3R
  • S4
  • S4R
  • S4R5
  • S8R
  • S8R5
  • S9R5
  • STRI3
  • STRI65
  • SAX1
  • SAX2
  • SPRING1

Features tested

The following output variables describe the equivalent rigid body motion for any general dynamic motion:

  • current coordinate (XC),

  • displacement of the center of mass UC (URC),

  • equivalent rigid body velocity components VC (VRC),

  • current angular momentum about the center of mass (HC),

  • current angular momentum about the center of origin (HO),

  • current rotary inertia (RI),

  • current mass (MASS), and

  • current volume (VOL).

These output variables are valid only for direct-integration implicit dynamic procedures. The accuracy of these output variables is verified with a test suite that encompasses all elements that have mass and/or rotary inertia.

Problem description

The equivalent rigid body motion output variables are specified in the results (.fil) and data (.dat) files. They can only be requested when using the direct-integration implicit dynamic procedure. These variables are considered whole element set variables, meaning that the quantity requested is summed over the element set specified. If no element set is specified, the quantity is summed over the entire model. The element set specified may contain elements which do not have mass (SPRINGs, DASHPOTs, etc.), but these elements will be ignored during the summation process. Specifying an element set in which all elements have no mass will elicit a warning message from Abaqus.

All of the verification problems below impose a rigid body motion on single element models. Each input file contains separate and distinct single element meshes corresponding to the many specific elements within that element category. For instance, the xrbmcpes.inp input file tests all of the CPE type elements and contains single element meshes for the CPE3, CPE4, CPE4R, CPE6, CPE8, CPE8R elements (and hybrid versions of all these elements). Most of the problems impose a planar 90° rotation about the z-axis; the three-dimensional continuum problem imposes an oblique rotation. Separate output requests to the results file are given for each element set in the model.

Results and discussion

These verification problems all impose a simple rigid body motion. In all cases the magnitude of the rigid body output variables should agree with the imposed motion. For some problems (such as those with an imposed constant velocity) the expected magnitudes of the output variables can be calculated directly from the imposed motion. In other problems the expected output variable magnitudes can be calculated from the imposed motion and the element geometry.

Input files

xrbmaxis.inp

Tests all axisymmetric elements, including axisymmetric shells. A constant z-velocity is imposed (there is no valid rotation in axisymmetric problems).

xrbmbeam.inp

Tests all beam elements (excludes open section beams). A rigid 90° rotation is imposed about the z-axis.

xrbmbepo.inp

Uses results of xrbmbeam.inp to verify the POST OUTPUT option.

xrbmt3ds.inp

Tests all three-dimensional truss elements.

xrbmc3ds.inp

Tests all three-dimensional continuum elements. A rigid rotation is imposed about the direction (.707, .707, 0.0).

xrbmcpeg.inp

Tests all generalized plane strain elements.

xrbmcpes.inp

Tests all plane strain elements.

xrbmcper.inp

Restart of xrbmcpes.inp. Tests RESTART without END STEP.

xrbmcpss.inp

Tests all plane stress elements.

xrbmelbw.inp

Tests all elbow elements.

xrbmmass.inp

Tests the mass element. A constant x-velocity is imposed. Tests are done with and without the TRANSFORM option.

xrbmmemb.inp

Tests all membrane elements. A rigid rotation is imposed about the z-axis. Shell elements overlay the membranes for stability purposes.

xrbmroti.inp

Four separate tests of the rotary inertia element. The first test uses a constant velocity. The second imposes both a translation and rotation. The third is similar to the second, but adds the use of the TRANSFORM option. The fourth test is similar to the second, but adds both TRANSFORM and ORIENTATION.

xrbmshel.inp

Tests all shell elements. A rigid 90° rotation is imposed about the z-axis.

The following tests contain two distinct element types:
xrbmaxb1.inp

This model consists of an axisymmetric solid and a three-dimensional beam element. A constant y-velocity is imposed. A rigid body output request is made for the axisymmetric element, and another is made for the whole model. This tests the format of the printed output. The axisymmetric printed output is limited to specific directions. With the addition of a three-dimensional beam, the whole model output must be given for all directions.

xrbmaxb2.inp

This test is similar to xrbmaxb1.inp, but the order of the element generation is reversed. The printed output should be identical to the output for xrbmaxb1.inp.

xrbmaxb3.inp

This test is similar to xrbmaxb1.inp but uses a two-dimensional beam element. Again, the purpose is to compare the format of the printed output for the axisymmetric element to the output for the whole model.

xrbmsprg.inp

This model consists of a spring and a beam. A rigid body variable request is made for an element set containing only the spring. This should trigger a warning message from Abaqus. Another output request is made for the whole model. The output should agree with the imposed rigid rotation of the beam element.