Abstract

This paper presents a discussion of a portable device to demonstrate rigid-cylinder vortex-induced vibration.  It is based on the senior-design project from a group of Mechanical Engineering students at the University of Houston.  The device consists of a variable speed blower, a diffuser, a wind tunnel, and a cylinder, mounted on springs and attached at four points to a rigid frame, subject to air flow from the blower.  The primary mode of vibration in this prototype device is transverse to the direction of fluid flow since there is no restraint or spring stiffness in the in-line direction of the cylinder.          The device has a unique feature that can eliminate vortex-induced vibration once it has begun.  Part of the spring suspension system is made of Smart Memory Alloy springs which have the capability of having their stiffness increased by means of a solid-to-solid phase transition.  A temperature increase in the  SMA springs is all that is necessary to effect the phase change.  This is accomplished by passing an electric current through the springs for a short time, resulting in the necessary temperature increase.  The net result is the elimination of the transverse VIV because of the increased transverse stiffness.

              This particular demonstration device is a prototype that has been constructed to illustrate VIV to students, primarily undergraduates, to aid them in understanding the combined disciplines of fluid dynamics, mechanical vibrations, and materials science.  We are currently modifying this device to also provide in-line stiffness and to include several other features, including a two-cylinder configuration with and without strakes and an airfoil-shaped cylinder (a short fairing) capability.  At the present time, we consider the information contained in the paper to be preliminary because we still have some design and operational problems to solve.  However, the use of the SMA springs to reduce the VIV oscillation of a cylinder is unique and deserves mention in spite of the shortcomings we have identified.