Design and fabrication of FIV apparatus for classroom lecture demonstration

Flow induced vibrations (FIVs) of a cylinder commonly occur where a cylindrical body is exposed to a flow. However, their appearance and behavior are widely diverging depending on flow condition and characteristics of cylinder with its supporting structure, making their prediction quite difficult. Hence, many serious accidents have been caused so far for structures and machines. Most typical and well-known FIVs in this category are the Karman vortex induced vibration (KVIV), the galloping and the torsional flutter. In this work, a very simple and convenient apparatus is designed and made to reproduce these three vibrations. This apparatus will be effective in a classroom lecture of fluid mechanics by demonstrating how easily the FIVs can be induced by a simple apparatus, even though their prediction remains to be important but difficult problems to be solved in practical engineering

Suppression of Kármán vortex excitation of a circular cylinder by a second cylinder set downstream in cruciform arrangement

A new technique for suppressing the Kármán vortex excitation of an elastically supported cylinder placed in an otherwise uniform flow is presented in this paper. By placing an another cylinder downstream of it in a cruciform arrangement with a gap s between them, the oscillation of the upstream cylinder can be virtually eliminated in the range of s/d1 < 0.4, where d1 is the diameter of the upstream cylinder. Compared with conventional techniques, this possesses the following advantages: i) it is unnecessary to change the shape of the oscillating body or remodel its supporting structure, and ii) the flow approaching the upstream body is practically undisturbed

Development of robust velocimeter for natural water flow monitoring

The ring-velocimeter coupled with a hot wire/film probe was developed and has been applied to wind and water tunnel experiments in Fluids Engineering Laboratory of Nagaoka University of Technology. In this study, the hot-wire/film probe is replaced by a cantilever attached by a strain gauge to detect the drag acting on the ring. The vortex shedding frequency from the ring is determined from the drag fluctuation by applying the spectrum analysis, and the flow velocity in turn since it is proportional with the vortex shedding frequency. This technique for flow velocity measurement is robust in the sense that it is strong against the noise or decay of the detected signal since the dominant frequency is insensitive to such disturbances, and that the detecting probe is strong against the contaminants or particles/objects carried by the fluid. These advantages, together with its simple and cheap characteristics, make it possible to apply to natural water flow with severe conditions

Blocking of snow/water slurry flow in pipeline caused by compression-strengthening of snow column

In earlier works by the present authors, two systems for sustainable energy were proposed: (i) a system for urban snow removal in winter and storage for air conditioning in summer, applied to Nagaoka City, which suffers heavy snow fall every winter, and (ii) a district cooling system utilizing latent heat of ice to reduce the size of storage reservoir and transportation pipeline system. In these systems, the hydraulic conveying of snow or ice through pump-and-pipeline is the key technique to be developed, since characteristics of snow (ice)/ water slurry is largely different from those of conventional non-cohesive solid particle slurries. In this study, the blocking of pipeline of snow/water slurry is investigated experimentally. While the blocking of conventional slurry occurs due to deposition of heavy particles at low flow velocity or arching of large rigid particles, that of snow/water slurry is caused by a compressed plug of snow formed due to cohesive nature of snow particles. This is because the strength of snow plug formed at a high resistance piping element, such as an orifice, becomes higher when the compression velocity is lower, resulting in a solid-like plug filling the whole channel upstream the elemen