Focused on the velocity of wake after the three dimensional vibrating square prism that changes dynamically and complexly, the systematic structure concerning the fluctuating velocity field of the wake at vortex shedding was evaluated by the POD analysis. The fluctuating velocity field was numerically obtained by the Dynamic PIV system which includes double pulse YAG laser, high speed camera and so on. First three modes look like the distribution shape of standard deviation, and the contribution rate of low level modes at vortex shedding is larger than that at non-vortex shedding. First and second modes seem to play significant roles in correlation between principal coordinate of each mode and deflection of vibrating square prism.
