Real Eigenvalue (Lanczos or Householder) dialog box

Name and description
Name	A descriptive name for this eigenvalue set.
Label	SID field in the EIGRL bulk data entry (or EIGR if using Householder type).The set identification number to identify this eigenvalue set in the Simcenter Nastran bulk data deck.
Description	A long description of this eigenvalue set.
Frequency Options
Frequency Range – Lower Limit and Upper Limit	V1 and V2 fields in the EIGRL bulk data entry (or EIGR if using Householder type).The Frequency Range fields allow you to define a frequency range of interest. This range limits the modes the solver calculates according to the frequency of each mode. For example, if you specify a range from 1 Hz to 1000 Hz, the solver only returns modes with frequencies within that range. Leave these range values blank if you do not want the calculated modes limited by frequency range.The Frequency Range and the Number of Desired Modes values together determine the modes returned by the solver. See the table below for a summary.
Number of Desired Modes	ND field in the EIGRL (or EIGR if using Householder type) bulk data entry.The number of modes you want the solver to return.
Extraction Data
Diagnostic Level	Available for the Lanczos method.MSGLVL field in the EIGRL bulk data entry (or EIGR if using Householder type).Controls the level of diagnostic information returned with the modes (integer value from 0–4). The default value of 0 returns no diagnostic information.
Number of Vectors	Available for the Lanczos method.MAXSET field in the EIGRL bulk data entry (or EIGR if using Householder type).Limits the maximum block size. You can accept the default value (the default value depends on your machine).
Estimate of the First Natural Frequency	Available for the Lanczos method.SHFSCL field in the EIGRL bulk data entry.Accept the default value of blank to allow the software to estimate this frequency.
Method for Normalizing Eigenvectors	Lets you specify the method for normalizing eigenvalues.NORM field in the EIGRL bulk data entry (or EIGR if using Householder type).You can use the default setting of MASS for most situations.AF— (Available for the Householder and Lanczos methods) Scales each mode shape so that the product of the mode shape x with its natural frequency ω is maximally normalized:max {ω
Point Identification Number	Available when Method for Normalizing Eigenvectors is Point.G field in the EIGR bulk data entry.The node or scalar point identification number (integer greater than 0).
Component	Available when Method for Normalizing Eigenvectors is Point.C field in the EIGR bulk data entry.The component number (integer from 1–6).

Frequency Range and Number of Desired Modes interaction

The number and frequency of the modes the software calculates depends on whether you specify a value in the Frequency Range – Upper Limit and Lower Limit boxes and the Number of Desired Modes box.

Frequency Lower Limit	Frequency Upper Limit	Number of Desired Modes	Modes returned
Yes	Yes	Yes	Lowest modes within the number of modes desired, or all modes in frequency range, whichever is smaller.
Yes	Yes	No	All modes in frequency range.
Yes	No	Yes	Lowest modes within the number of modes desired, from the Lower Limit to infinity.
Yes	No	No	Lowest mode from the Lower Limit to infinity.
No	No	Yes	Lowest modes within the number of modes desired, from negative infinity to infinity.If the Lower Limit is blank, all modes less than zero are calculated. Small negative modes are usually computational zeros that indicate rigid-body modes. Finite negative modes are an indication of modeling problems.If the Lower Limit is zero, negative eigenvalues are not calculated.
No	No	No	Lowest mode.
No	Yes	Yes	Lowest modes within the number of modes desired, up to the Upper Limit.
No	Yes	No	All modes below the Upper Limit.

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Defining eigenvalue extraction data for Nastran analyses

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Real Eigenvalue (Lanczos or Householder) dialog box, Simcenter 3D 2021.1 Series

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