In this paper, a local deformation effect in thin-walled box beams is investigated via a finite element modal analysis. The analysis is carried out for single-cell and multi-cell box beam configurations. The single-cell box beam with and without a neck, which mimics a simple wind-turbine blade, is analyzed first. The results obtained by shell elements are compared to those of one-dimensional(1D) beam elements. It is observed that the wall thickness plays a crucial role in the natural frequencies of the beam. The 1D beam analysis deviates from the shell analysis when the wall thickness is either thin or thick. The shell modes(local deformations) are dominant as it becomes thin, whereas the shear deformation effects are significant as it does thick. The analysis is extended to the single-cell box beam with a neck, in which the shell modes are confined to near the neck. Finally the multi-cell box beam with a taper, which is quite similar to real wind-turbine blade configuration, is considered to investigate the local deformation effect. The results reveal that the 1D beam analysis cannot match with the shell analysis due to the local deformation, especially for the lagwise frequencies. There are approximately 5∼7% errors even if the number of segments is increased.

• 이기준(금오공과대학교 기계시스템공학과) | Gi-Jun Lee (Department of Mechanical System Engineering, Kumoh National Institute of Technology, Gumi, 39177, Korea)
• 사진용(금오공과대학교 기계시스템공학과) | Jin-Yong Sa (Department of Mechanical System Engineering, Kumoh National Institute of Technology, Gumi, 39177, Korea)
• 김준식(금오공과대학교 기계시스템공학과) | Jun-Sik Kim (Department of Mechanical System Engineering, Kumoh National Institute of Technology, Gumi, 39177, Korea) Corresponding author