Environmental Engineering Reference
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model. The discontinuous surfaces are connected by rigid (fi xed) elements. These
rigid elements are capable of transferring all displacements and rotations from one
node to another without deforming.
The combined shell/solid model
is a combined shell/solid model constructed
based on the following surfaces representing the blade section:
Outer aerodynamic surface (outer sandwich skins)
Inner sandwich skins in the leading and trailing part of the blade
Leading and trailing edge
Web sandwich skins
After creating the surfaces, the solids are then created from two opposing surfaces.
The solids represent the following:
Sandwich core in the leading and trailing part of the blade
Box girder caps
Sandwich core in the webs
Layered shell elements are then used to represent the composite laminates on both
sides of the solids. An example is shown in Fig. 17. The combined shell/solid
model provides the highest degree of accuracy.
Adhesive bonds between the aerodynamic shell and the spar
7.1.4 Limitations with shell models
A number of studies have shown that there is limited correlation between the
torsional response obtained by numerical structural models and measurements.
Madsen [55] compared the responses of a beam model and a shell FE model.
Poor correlation was found for predictions of torsional Eigen frequency and Eigen
mode. Larsen [56] compared the response of the numerical models from Madsen
[55] with a number of measured modal modes; the correlation related to torsional
response was limited especially for the higher torsional modes. In predicting tor-
sional behavior, problems associated with the use of offset nodes for layered shell
elements in FE analysis has also been reported by Laird
et al
. [ 57 ].
Figure 17: Meshed part of shell/solid FE model. Solid elements are used for sand-
wich cores and for the adhesive connection between the box girder and the
aerodynamic shell. Shell elements are used for the other structural part.
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