Field evaluation of optical-based three-dimensional dynamic motion measurement system with multiple targets for a floating structure

Recently, optical-based dynamic measurement techniques are becoming more popular owing to the development of high quality and low-price hardware and image processing software. However, there exist several research issues related to these systems including the self-vibration of a capturing device and the optimal threshold value for image processing. From an application point of view, the application area is limited to the two-dimensional flume tank tests and one-dimensional deflection measurement; therefore, it is desirable to extend this application to measuring the three-dimensional motion such as the motion of a real utility-scale structure. In this study, an optical-based dynamic motion measurement technique using multiple targets is proposed to measure the three-dimensional dynamic motion of floating structures. A new scheme is also proposed to determine an appropriate threshold value to discriminate the background by minimizing an estimation error index. The proposed method is applied to field measurement of the dynamic motion of a large concrete floating structure under various wave conditions, and the results are compared with those from a conventional real-time kinematic global positioning system and a motion reference unit (MRU). The results show that the optical-based system is much better than the other two systems for measuring transverse motions, and it is comparable to the MRU device for measuring rotational motions.

► An optical-based motion measurement technique using multiple targets was proposed.
► A new determination method for an optimal threshold value was developed.
► This system was applied to measure the motion of floating structure in field tests.
► This system was better than the RTK-GPS and MRU for measuring transverse motions.
► Optical-based system was comparable to MRU device for measuring rotational motions.