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Vibrations in lightweight structures - Efficiency and reduction of numerical models

Flodén, Ola LU (2014)
Abstract
Multi-storey wood buildings have been increasing in popularity since a century-old ban on the construction of such buildings was lifted in 1994. Compared to conventional concrete structures, it is more difficult to build lightweight structures in such a way that noise and disturbing vibrations is avoided. To design buildings of high performance regarding sound and vibrations, it is desirable to have tools for predicting the effects of structural modifications prior to construction. The long-term aim of the studies presented in the dissertation is to develop such tools by means of numerical models.



Accurately assessing the dynamic behaviour of multi-storey wood buildings requires use of models representing the geometry in... (More)
Multi-storey wood buildings have been increasing in popularity since a century-old ban on the construction of such buildings was lifted in 1994. Compared to conventional concrete structures, it is more difficult to build lightweight structures in such a way that noise and disturbing vibrations is avoided. To design buildings of high performance regarding sound and vibrations, it is desirable to have tools for predicting the effects of structural modifications prior to construction. The long-term aim of the studies presented in the dissertation is to develop such tools by means of numerical models.



Accurately assessing the dynamic behaviour of multi-storey wood buildings requires use of models representing the geometry in considerable detail, resulting in very large models which easily exceed the limits of computer capacity, at least for computations to be performed within reasonable time. It is therefore desirable to avoid unnecessarily detailed models, while at the same time describing the phenomena of interest accurately. Moreover, the computational efficiency of the models can be improved by employing model order reduction, reducing the size and computational cost of the models without affecting the accuracy appreciably. A common way of employing model order reduction is through substructure modelling, in which full finite element models are divided into smaller parts, or substructures, that are reduced in size and assembled to form reduced global models.



The dissertation includes an investigation into the effect of modelling acoustic media inside cavities of multi-storey wood buildings on the transmission of structural vibrations. Air and insulation inside cavities were modelled as acoustic media in different ways and the resulting finite element models were compared. It was concluded that the acoustic media in cavities close to the source of vibration affect the vibration transmission and that it, therefore, has to be included in the models to some extent.



Furthermore, the efficiency of different methods for reducing substructure models of multi-storey wood buildings are discussed in the dissertation. Comparisons of different methods for model order reduction, applied to substructures of buildings, showed that the frequently employed method of component mode synthesis by Craig & Bampton and the increasingly popular Krylov subspace methods result in efficient reduced order models. In order to improve the efficiency of the reduced order models, interface reduction can be employed. Different methods for interface reduction were found to be the most efficient ones for the interface surfaces of wood components and elastomer materials. Elastomer are used at junctions in wooden buildings in order to reduce the vibration transmission. (Less)
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author
supervisor
organization
publishing date
type
Thesis
publication status
published
subject
pages
129 pages
publisher
Lund University
ISBN
978-91-7473-807-0
language
English
LU publication?
yes
id
d2bd42a9-3dd8-4909-a301-b93bac04cc86 (old id 4376827)
date added to LUP
2014-03-27 13:10:21
date last changed
2016-09-19 08:44:50
@misc{d2bd42a9-3dd8-4909-a301-b93bac04cc86,
  abstract     = {Multi-storey wood buildings have been increasing in popularity since a century-old ban on the construction of such buildings was lifted in 1994. Compared to conventional concrete structures, it is more difficult to build lightweight structures in such a way that noise and disturbing vibrations is avoided. To design buildings of high performance regarding sound and vibrations, it is desirable to have tools for predicting the effects of structural modifications prior to construction. The long-term aim of the studies presented in the dissertation is to develop such tools by means of numerical models.<br/><br>
<br/><br>
Accurately assessing the dynamic behaviour of multi-storey wood buildings requires use of models representing the geometry in considerable detail, resulting in very large models which easily exceed the limits of computer capacity, at least for computations to be performed within reasonable time. It is therefore desirable to avoid unnecessarily detailed models, while at the same time describing the phenomena of interest accurately. Moreover, the computational efficiency of the models can be improved by employing model order reduction, reducing the size and computational cost of the models without affecting the accuracy appreciably. A common way of employing model order reduction is through substructure modelling, in which full finite element models are divided into smaller parts, or substructures, that are reduced in size and assembled to form reduced global models. <br/><br>
<br/><br>
The dissertation includes an investigation into the effect of modelling acoustic media inside cavities of multi-storey wood buildings on the transmission of structural vibrations. Air and insulation inside cavities were modelled as acoustic media in different ways and the resulting finite element models were compared. It was concluded that the acoustic media in cavities close to the source of vibration affect the vibration transmission and that it, therefore, has to be included in the models to some extent.<br/><br>
<br/><br>
Furthermore, the efficiency of different methods for reducing substructure models of multi-storey wood buildings are discussed in the dissertation. Comparisons of different methods for model order reduction, applied to substructures of buildings, showed that the frequently employed method of component mode synthesis by Craig &amp; Bampton and the increasingly popular Krylov subspace methods result in efficient reduced order models. In order to improve the efficiency of the reduced order models, interface reduction can be employed. Different methods for interface reduction were found to be the most efficient ones for the interface surfaces of wood components and elastomer materials. Elastomer are used at junctions in wooden buildings in order to reduce the vibration transmission.},
  author       = {Flodén, Ola},
  isbn         = {978-91-7473-807-0},
  language     = {eng},
  note         = {Licentiate Thesis},
  pages        = {129},
  publisher    = {Lund University},
  title        = {Vibrations in lightweight structures - Efficiency and reduction of numerical models},
  year         = {2014},
}