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Title:
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Programs for buckling strength prediction of rotor blades
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Author(s):
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Published by:
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Publication date:
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ECN
Wind Energy
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1-8-2003
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ECN report number:
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Document type:
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ECN-RX--03-050
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Conference Paper
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Number of pages:
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Full text:
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4
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Download PDF
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Presented at: European Wind Energy Conference 2003, Madrid, Spain, 16-19 juni 2003.
Abstract:
The dimensions of large wind turbines under development still increase,which is partly driven by the offshore-requirements of a 'high energy
capture per turbine unit'. The relatively large amount of structural
mass, and the dominating weight loads associated with increasing dimensions
result in a trend towards material-efficient blade design. The consequence
of this trend is that the blade becomes a thin-walled structure that
is sensitive to 'buckling'; the geometric instability of the blade cross-section.
For the design of large size rotor blades it becomes necessary to verify
the resistance against buckling, also called 'buckling strength'. The
verification of the buckling strength can be done with non-linear finite
element packages, FEM. These FEM packages however, require a lot of
structural detail as input which is not always available. For this reason
and also because 'design towards buckling' requires many (fast) analyses
for structural variations,
one may use simpler more dedicated tools, in which the blade is represented
with sectional models. For each of the sectional models it is assumed
that it is part of a long prismatic structure, which is reasonable for
the part of the blade outside of the largest chord. In the past ECN
has been involved in European and Dutch research projects on the development
and verification of buckling-load prediction tools.
A description is given of the so-called 'Design rules' that require
little computational effort. These 'Design rules' are addressed to buckling
of curved composite panels (such as in a rotor blade structure) and
can therefore be applied in the pre-design stage of rotor blades and
of other slender composite structures.
For buckling of complete rotor blade cross-sections, some computer codes
have been developed in the former research projects BUCKBLADE and STARION.
Although these codes work reasonably well, ECN and the Knowledge Centre
WMC planned follow-up research in which these buckling tools will be
improved, and implemented in the rotor-blade design package FOCUS. The
improvements are mainly addressed to the modelling of buckling of sandwich
layup, and the inclusion of shear loading such that the buckling of
shear webs it predicted more realistic. The final aim of these developments
is to bring simple and fast buckling load prediction tools in the design
process. This must allow optimisation of the number of shear webs, and
the location of each shear web.
These tools also help the designer to find the layer-stacking sequence
with the strongest buckling strength, and the (minimum) required stiffness
and thickness of the core of sandwich panels.
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