PSI - Issue 17

Behzad V. Farahani et al. / Procedia Structural Integrity 17 (2019) 712–717 Behzad V. Farahani et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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Wind turbines convert kinetic energy from wind into usable electrical energy. The wind turbine technology is a very complex technology involving multidisciplinary and broad technical disciplines such as aerodynamics, mechanics, structure dynamics, meteorology as well as electrical engineering addressing the generation, transmission, and integration of wind turbines into the power system. Due to data transmission problems, structural health monitoring (SHM) of wind turbines is generally performed using several accelerometers and strain gauges attached to the nacelle to monitor the gearbox and equipment. Currently, digital image correlation (DIC) and stereo photogrammetry are adopted to measure dynamics of wind turbine blades. These methods usually measure displacement and strain to identify location of defects. Three dimensional point tracking has also been used to measure rotating dynamics of wind turbines. In this regard, Oliveira et al. (Oliveira et al. 2018) developed and implemented a vibration-based monitoring system for a wind turbine. The deployed monitoring system allowed the acquisition of extensive information concerning the evolution of modal parameters of the most important vibration modes of the wind turbine structure throughout the various operating conditions of the turbine. Amongst others, laser-based technologies have received significant attention in the last decades (Kim et al. 2015)(Yoon et al. 2009). Stentoumis et al. (Stentoumis et al. 2015) proposed a system equipped with a 3D laser scanning system, LSS which can recognize and document geometrical changes in civil infrastructures in a single pass. Peji ć (Pejić 2013) designed and optimized a LSS for the geometrical inspection of structural integrity components. Besides, Dilek et al. (Dilek et al. 2019) carried out a study on condition monitoring of wind turbine blades and tower using an automated LSS. In this study, a section of a cylindrical wind tower manufactured from S355J0 steel sheets is considered. Tower fabrication followed the rolling process of sheets and then welding the abutted rolled sheets together. A system was developed which aimed at acquiring the tower interior wall profile using a prototype based on 3D laser scanning technology. During fabrication, the tower might experience some plastic deformation in the welded joints. It might occur due to imperfect welding conditions on joints or the tower ’s own weight. This could result in the residual stress occurrence and the fabricated tower will not be in the perfect geometry. The LSS scans the tower’s interior surface, and it can be possible to detect the geometrical changes and to locate and measure the plastic deformation occurred because of the mentioned reasons. Therefore, this deployed LSS is advantageous and would assist the tower fabrication industry in correcting geometrical changes due to the deformation. 2. Model Definition and 3D LSS system setup A 9-metre-long section of a cylindrical tower was selected as shown in Fig. 1. The inner diameter of the tower was reported by the manufacturer as ≅ 4177 mm . This section has been constructed by three parts, with different length, joined by circular seam welding. In this experiment, the middle part was inspected with a total length of 3000 mm.

Fig. 1: A-9-meter-long cylindrical wind tower.

The geometry acquisition was performed using a 3D LSS consisting of a circular laser module and a camera. The deployed LSS consists of a 2.0 MP (1600×1200) colour camera with a maximum framerate of 30 fps and a green 50