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TECHNICAL PAPERS

Static Stress Redesign of Structures by Large Admissible Perturbations

[+] Author and Article Information
Michael M. Bernitsas

Dept. of Naval Architecture and Marine Engineering,  University of Michigan, 2600 Draper Road, Ann Arbor, MI 48109-2145 Phone: (734)764-9317, Fax: (734)936-8820.

Bhineka M. Kristanto

Dept. of Naval Architecture and Marine Engineering,  University of Michigan, 2600 Draper Road, Ann Arbor, MI 48109-2145 Phone: (734)764-9317, Fax: (734)936-8820.michaelb@engin.umich.edu

J. Offshore Mech. Arct. Eng 127(2), 122-129 (Jun 19, 2003) (8 pages) doi:10.1115/1.1894414 History: Received June 19, 2003

The LargeE Admissible Perturbation (LEAP) methodology is developed further to solve static stress redesign problems. The static stress general perturbation equation, which expresses the unknown nodal stresses of the objective structure in terms of the baseline structure stresses, is derived first. This equation depends on the redesign variables for each element or group of elements; namely, the cross-sectional area and moment of inertia, and the distance between the neutral axis and the outer fiber of the cross section. This equation preserves the shape of the cross section in the redesign process. LEAP enables the designer to redesign a structure to achieve specifications on modal properties, static displacements, forced response amplitudes, and static stresses. LEAP is implemented in code RESTRUCT which post-processes the FEA results of the baseline structure. Changes on the order of 100% in the above performance particulars and in redesign variables can be achieved without repetitive finite element (FE) analyses. Several numerical applications on a simple cantilever beam and an offshore tower are used to verify the LEAP algorithm for stress redesign.

Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

LEAP Algorithm for stress redesign

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Figure 2

Cantilever beam for structural redesign

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Figure 3

Errors in static stress beam redesign (element #2, node #3)

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Figure 4

Errors in static stress beam redesign (element #4, node #5)

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Figure 5

Change of cross-sectional area for beam redesign using two stress redesign constraints

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Figure 6

Change of moment of inertia for beam redesign using two stress redesign constraints

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Figure 7

Errors in compatible redesign of beam using 4 constraints

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Figure 8

Errors in compatible redesign of beam using 4 constraints

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Figure 9

Changes of redesign variables A and I for beam redesign using 4 constraints

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Figure 10

Errors in incompatible redesign of beam using 4 constraints

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Figure 11

Errors in incompatible redesign of beam using 4 constraints

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Figure 12

Changes of redesign variables A and I for beam redesign using 4 constraints

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Figure 13

Offshore tower (Courtesy of Dr. D. G. Morrison, Shell)

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Figure 14

Errors for static stress redesign of beam-tower using four stress constraints

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Figure 15

Errors in static redesign of beam-tower using two static stress and two displacement constraints

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Figure 16

Errors in static redesign of beam-tower using two static stress and two displacement constraints

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