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| Titel |
A discrete element modelling approach for block impacts on trees |
| VerfasserIn |
David Toe, Franck Bourrier, Ignatio Olmedo, Frédéric Berger |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250102248
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| Publikation (Nr.) |
 EGU/EGU2015-1556.pdf |
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| Zusammenfassung |
| These past few year rockfall models explicitly accounting for block shape, especially
those using the Discrete Element Method (DEM), have shown a good ability to
predict rockfall trajectories. Integrating forest effects into those models still remain
challenging.
This study aims at using a DEM approach to model impacts of blocks on trees and
identify the key parameters controlling the block kinematics after the impact on a
tree. A DEM impact model of a block on a tree was developed and validated using
laboratory experiments. Then, key parameters were assessed using a global sensitivity
analyse.
Modelling the impact of a block on a tree using DEM allows taking into account large
displacements, material non-linearities and contacts between the block and the tree. Tree
stems are represented by flexible cylinders model as plastic beams sustaining normal,
shearing, bending, and twisting loading. Root soil interactions are modelled using a rotation
stiffness acting on the bending moment at the bottom of the tree and a limit bending moment
to account for tree overturning. The crown is taken into account using an additional mass
distribute uniformly on the upper part of the tree. The block is represented by a sphere.
The contact model between the block and the stem consists of an elastic frictional
model.
The DEM model was validated using laboratory impact tests carried out on 41 fresh beech
(Fagus Sylvatica) stems. Each stem was 1,3 m long with a diameter between 3 to 7 cm.
Wood stems were clamped on a rigid structure and impacted by a 149 kg charpy
pendulum.
Finally an intensive simulation campaign of blocks impacting trees was done to identify the
input parameters controlling the block kinematics after the impact on a tree. 20 input
parameters were considered in the DEM simulation model : 12 parameters were related to the
tree and 8 parameters to the block.
The results highlight that the impact velocity, the stem diameter, and the block
volume are the three input parameters that control the block kinematics after impact. |
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