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Natural sway frequencies and damping ratios of trees: concepts, review and synthesis of previous studies.

Moore, John and Maguire, Douglas A (2004) Natural sway frequencies and damping ratios of trees: concepts, review and synthesis of previous studies. Trees - Structure and Function, 18 (2). pp. 195-203. ISSN 0931-1890

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Abstract/Description

Previous studies that measured the natural frequencies and damping ratios of conifer trees were reviewed and results synthesized. Analysis of natural frequency measurements from 602 trees, belonging to eight different species, showed that natural frequency was strongly and linearly related to the ratio of diameter at breast height to total tree height squared (i.e., DBH/H 2). After accounting for their size, pines (Pinus spp.) were found to have a significantly lower natural frequency than both spruce (Picea spp.) and Douglas-fir (Pseudotsuga spp.). Natural sway frequencies of de-branched trees were significantly higher than those of the same trees with the branches intact, and the difference increased with an increasing ratio of DBH/H 2. Damping mechanisms were discussed and methods for measuring damping ratio were presented. Analysis of available data suggested that internal damping ratios were typically less than 0.05 and were not related to tree diameter. External damping was mainly due to aerodynamic drag on the foliage and contact between the crowns of adjacent trees. Analysis of data from previous wind-tunnel studies indicated that damping due to aerodynamic drag is a nonlinear function of velocity. Damping due to crown contact has been suggested by a previous author to be a function of both the distance to and the size of adjacent trees. Therefore, in uniformly spaced stands it may be possible to model crown contact damping as a function of stand density index (SDI), a common forestry measure which incorporates both of these variables.

Item Type: Article
Print ISSN: 0931-1890
Electronic ISSN: 1432-2285
Uncontrolled Keywords: Coniferous trees; Wind damage; Tree mechanics; Natural frequency; Damping ratio; Stand density;
University Divisions/Research Centres: Faculty of Engineering, Computing and Creative Industries > School of Engineering and the Built Environment
Dewey Decimal Subjects: 600 Technology > 620 Engineering > 620 Engineering & allied operations
500 Science > 580 Plants (Botany) > 582 Plants noted for characteristics & flowers > 582.16 Trees
Library of Congress Subjects: S Agriculture > SD Forestry
T Technology > TA Engineering (General). Civil engineering (General)
Item ID: 1932
Depositing User: RAE Import
Date Deposited: 27 May 2008 10:19
Last Modified: 10 May 2013 15:16
URI: http://researchrepository.napier.ac.uk/id/eprint/1932

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