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The response characteristics and suppression of flow-induced vibrations of rectangular prisms withvarious width-to-depth ratios were experimentally investigated. The prisms were rigid and elastically mounted atof the thre types of flow-induced vibrations generated in a rectangular prism. First, the response characteristicsof torsional vibrations generated in rectangular prisms were investigated by fre-vibration tests. It was found thatthe response characteristics of torsional vibrations generated in rectangular prisms could be classified into sixpatterns depending on the width-to-depth ratio. Next, the response characteristics of torsional vibrationsthre types of flow-induced vibrations, low-speed torsional flutter, vortex excitation and high-speed torsionalflutter, are generated in the rectangular prisms were elucidated on the basis of characteristics of fluid forces andvisualized flow patterns. Experiments were also carried out to establish an effective method for suppressingflow-induced vibrations generated in the rectangular prisms, and it was found that low-speed torsional flutterwhich results in suppression of the alternating rolling-up of the shear layers separating from the leading edgesof the prism. It was also found that vortex excitation could be suppressed by placing a splitter plate downstreamof the prism, which results in suppression of the generation of wake vortices.