In‐Ho Kim

This study focuses on the performance validation of a wave energy converter (WEC) equipped with resonant frequency adjustment capability. Achieving resonance with the oscillation period of waves is crucial for maximizing the efficiency of wave energy conversion systems. For this purpose, we introduce a variable moment of inertia (VMI) device that allows for tuning of the resonant frequency by adjusting the position of the mass. For validation of the proposed approach, performance verification experiments were conducted using a vibration platform. Through free vibration experiments, we identified the system’s resonant frequency and characteristics. In our forced vibration tests considering the wave frequency band of the coastal area, harmonic vibration experiments were performed over a range of 0.4–0.8 Hz. In these experiments, we considered three separate cases by adjusting the distance from the reel’s center to the mass. As a result, we found that the resonant frequency of the WEC can be adjusted from 0.65 Hz when the mass is furthest away to 0.55 Hz when it is closer. This research confirms the benefits obtained by utilizing VMI to adjust the resonant frequency of WECs without changing the mass or springs. This offers a promising opportunity to enhance the energy conversion efficiency of resonant-type WECs utilizing wave energy.

Since all structures vibrate due to external loads, measuring and analyzing vibration data is a representative method of structural health monitoring. In this paper, we propose a non-contact cable estimation method using a vision sensor mounted on an unmanned aerial vehicle. A target cable among many cables can be identified through marker detection. In addition, the motion of the structure can be quickly captured using the extracted feature points. Although computer vision can be used to transform displacements of multiple axis, in this study, only the vertical displacement is considered to estimate tension. Finally, the cable tension can be estimated via the vibration method using the modal frequencies derived from the cable displacement. To verify the performance of the proposed method, lab-scale experiments were carried out and the results were compared with the conventional method based on the accelerometer. The proposed method showed a 3.54% error compared with the existing method and confirmed that the cable tension force can be estimated quickly at low cost.