As an example of Flow-Induced Vibration (FIV), an interaction between a circular cylinder and a surrounding flow is measured by Digital Holographic Particle Tracking Velocimetry (DH PTV). Tracer particles having two different diameters are dispersed in a cylinder and pipe flow. The cylinder, containing dispersed tracer particles, is made of an acrylic transparent resin and is attached to an inner wall of the pipe. In order to suppress a difference in the refractive index between the cylinder and fluid, the acrylic pipe is filled with a refractive-index-matching liquid having the same refractive index as the cylinder (1.49). The holographic pattern of the tracer particles dispersed in both the cylinder and fluid is measured by digital in-line holography. The three-dimensional position of particles is detected by reconstructed holographic patterns at each time step. Three-dimensional velocity of a surrounding flow and three-dimensional vibration of the cylinder are derived by using a Self-Organizing Map (SOM). Vector fields for the vibrating cylinder and surrounding flow are individually identified from the difference in the particle size detected by digital holography.

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