Products: ABAQUS/Standard ABAQUS/CAE
Benefits: The frequency extraction procedure has been enhanced to include the calculation of residual modes if desired. If you request residual modes, they will be included automatically with the eigenmodes to form the basis for projection and superposition in mode-based procedures. Inclusion of these modes can provide potentially significant gains in accuracy at less cost than simply extracting a larger set of eigenmodes.
Description: A residual mode is representative of the static solution that would be obtained by applying the same loading pattern as is used for the excitation in the mode-based analysis, but orthogonalized with respect to the mass and stiffness matrices against the extracted eigenmodes. Consequently, residual modes effectively compensate for errors introduced when, to reduce cost, higher frequency modes are not extracted in the frequency step and, hence, not included in the basis for the mode-based analysis. The only prerequisite for activating the residual mode calculations is that the loading patterns need to be defined in an immediately preceding static perturbation step. If the static perturbation step includes multiple load cases, one residual mode is calculated for each load case. Although by default all residual modes are included in the basis for the mode-based procedure (like eigenmodes), a subset of the calculated residual modes may be used in a given mode-based analysis. The printed output file clearly identifies which modes are residual modes and which modes are eigenmodes. In terms of use in mode-based procedures ABAQUS/Standard does not distinguish between residual modes and eigenmodes.
Step module: StepCreate: Frequency: Basic: Include residual modes