In this paper, a measurement technique which can measure simultaneously the motions of a free-floating structure and the flows around it is introduced.
To investigate the flow field and the motion of the floater, we constructed a measurement system with which analysis on the results of the interactions between fluid flows and structures motions was carried out. The measurement system consists of four cameras, a laser, and a host computer. The laser was used to illuminate the tracer particles. The particles' images were used to reconstruct the 3D measurement volume.
The study focuses on the influences of the fluid viscosity onto the motion of the floating structure. A cylindrical structure (d=30mm, L=100mm) was put over the water surface. The motions of the floating structure was produced by the wave generated in the water channel. The floating structure is made of acrylic and the waves were generated by a DC servo motor which was installed at the top of the channel. 4 wave conditions were generated by the motor rotation speed with 40rpm, 46rpm, 53rpm and 59rpm. The wave height and frequency were measured by a ultrasound-based level sensor(UltraLab ULS 20130).
After confirming the wave generated with the motor speed 40rpm to be optimal to the actual sea condition, the floating model was installed in the water channel.
Simultaneous measurement was performed for the structure's motion and the flow motion around it. For the measurement of the structure's motions, ‘Bidirectional Motion Tracking Algorithm’ was adopted as target tracking method. On the other hand, For the measurement of the flow motion, tomographic flow visualization technique in which MART algorithm was used.
The structure's motions and the flow motions were quantitatively measured by the constructed measurement system, and the their feasibility for the study of viscosity effects of the waves was confirmed.