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Stiffness-generated rigid-body mode shapes for Lanczos eigensolution with SUPORT DOF by way of a MSC/NASTRAN DMAP alterWhen using all MSC/NASTRAN eigensolution methods except Lanczos, the analyst can replace the coupled system rigid-body modes calculated within DMAP module READ with mass orthogonalized and normalized rigid-body modes generated from the system stiffness. This option is invoked by defining MSC/NASTRAN r-set degrees of freedom via the SUPORT bulk data card. The newly calculated modes are required if the rigid-body modes calculated by the eigensolver are not 'clean' due to numerical roundoffs in the solution. When performing transient structural dynamic load analysis, the numerical roundoffs can result in inaccurate rigid-body accelerations which affect steady-state responses. Unfortunately, when using the Lanczos method and defining r-set degrees of freedom, the rigid-body modes calculated within DMAP module REIGL are retained. To overcome this limitation and to allow MSC/NASTRAN to handle SUPORT degrees of freedom identically for all eigensolvers, a DMAP Alter has been written which replaces Lanczos-calculated rigid-body modes with stiffness-generated rigid-body modes. The newly generated rigid-body modes are normalized with respect to the system mass and orthogonalized using the Gram-Schmidt technique. This algorithm has been implemented as an enhancement to an existing coupled loads methodology.
Document ID
19940024903
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Authors
Abdallah, Ayman A. (Analex Corp. Brook Park, OH., United States)
Barnett, Alan R. (Analex Corp. Brook Park, OH., United States)
Widrick, Timothy W. (Analex Corp. Brook Park, OH., United States)
Manella, Richard T. (NASA Lewis Research Center Cleveland, OH, United States)
Miller, Robert P. (NASA Lewis Research Center Cleveland, OH, United States)
Date Acquired
September 6, 2013
Publication Date
March 1, 1994
Subject Category
Structural Mechanics
Report/Patent Number
E-8676
NAS 1.15:106537
NASA-TM-106537
Meeting Information
Meeting: 1994 MSC World Users'' Conference
Location: Orlando, FL
Country: United States
Start Date: June 20, 1994
End Date: June 24, 1994
Sponsors: MacNeal-Schwendler Corp.
Accession Number
94N29406
Funding Number(s)
CONTRACT_GRANT: NAS3-25776
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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