| dc.description.abstract | Offshore wind farm structures may have the potential to affect marine navigation and
communication systems by reflecting radar signals. With ever increasing size of wind
turbines it is necessary to better understand the influence of radar signals on wind
turbine blades in order to minimise the radar reflecting potential. One possible way of
reducing radar reflection is to use radar absorbing materials. In this thesis, epoxy
composite materials reinforced with five different types of nano-size additives: carbon
nanotubes (CNTs), carbon blacks (CBs), silver, tungsten carbide and titanium oxide
are manufactured and tested to investigated their potential as wind turbine blade
material that absorb radar signals.
Nanoadditives/epoxy composites with additives content ranging from 0.05-1 wt. %
were fabricated by a simple cast moulding process. The nanoadditives were dispersed
in the epoxy resin by sonication method. The degree of nanoadditives dispersion was
observed by examining the surface of the composite materials using scanning electron
microscope (SEM). Complex permittivity of the nanoadditives/epoxy composites was
studied using a free wave transmittance only method at a frequency range of 6.5-10.5
GHz. The effect of the percolation threshold of the direct current conductivity on the
composite permittivity was analysed and discussion. In order to get a better insight in
the importance of the results they were compared to existing models (Maxwell-
Garnett, Bruggeman, Bottcher, Lichtenecker and Lichtenecker-Rother). A new model
based rule of mixtures is developed to predict the complex permittivity of the
composite.
A model of wind turbine rotor blade made of the nanoadditives/epoxy composite was
developed using Comsol-multiphysics software. The data obtained from the
experimental work was inputted in to the model to generate result of backscattered
energy verses composite permittivity as a function of nanoadditives content. A
decrease in backscattered energy was noticed with increasing nanoadditives content.
The results demonstrate that radar reflecting signals will be significantly reduced by
incorporating nanoadditives in the composite materials. | en_US |
