The feasibility of a new current meter based on the well known vortex shedding phenomenon, using a direct approach, is discussed in this paper. The paper briefly presents the results of earlier research and developmental work carried out at the U. of Houston for developing a simple and rugged ocean current meter with long-term deployment capability using the simple hydrodynamic relation offered by the above phenomenon. After developing the necessary theoretical background for the vortex shedding phenomenon, the paper proceeds with utilization of this phenomenon, how this phenomenon can be exploited, and finally, outlines the design procedure adopted in developing this meter. Certain salient features, advantages, and disadvantages also are discussed.
Oceanographic data is of great importance for developing an effective design criteria for offshore structures and pipelines. One such vital parameter is the ocean current data. Over the years, many current meters have been developed. Yet, there is a continuing search for current sensors that are fairly simple and rugged and that provide low-cost, reliable operation with reasonable accuracy.
This paper deals with one such current meter, which has not been introduced on the market yet, but has the potential to be an "optimum" ocean current meter for some purposes.
The current sensor design is based on the vortex shedding phenomenon. The phenomenon, well known to most people involved with fluid flow, causes forced vibration of cylindrical bodies such as cables, submarine periscopes, and marine structures the amplitude of which may become structurally dangerous if the natural frequency of elastic vibration and the vortex shedding frequency are in resonance. The collapse of a suspension bridge near Tacoma, Wash., is attributed to such wind-driven oscillations. The "strumming" of cables or mooring lines caused by this phenomenon is a general experience that may cause fatigue failure. Studies have been carried out to investigate the exact nature of the cause in order to remedy such failures However no real attempt has been made to exploit this phenomenon by utilizing the fluid mechanical relations offered by the very nature of the phenomenon. The vortex shedding phenomenon provides a linear relationship between the fluid flow velocity and the shedding frequency within a certain range of Reynolds number.
Until recently, few attempts have been made to use this relationship in developing flow meters or fluid velocity sources for industrial purposes.
The design of such a meter is conceptually very new, and especially so for oceanic application. J-Tec associates, Inc. has developed a current meter based on this phenomenon. However, they use an acoustical technique to detect the shedding frequency, which makes the instrument complex and perhaps less useful in the hostile environment encountered in the ocean.
This paper deals with a current meter based on this vortex shedding phenomenon, which could become a very useful current meter for oceanic application because of the simplicity and ruggedness of the sensor from a mechanical standpoint and its omnidirectionality and good response characteristic.
