Design and performance evaluation of a wave-driven artificial upwelling device

Abstract

A wave-driven artificial upwelling device, consisting of a floating buoy, an inner water chamber, a long tail pipe, and two flow-controlling valves, was developed for this research. Hydrodynamic performance of the device to pump up nutrient rich deep ocean water is evaluated by mathematical modeling analysis and hydraulic laboratory experiments. The mathematical model of the device is made up of four simultaneous differential equations. The first three equations, which describe the motion of upwelled water inside the device, were formulated based on momentum and mass conservation principles. The fourth equation is the equation of motion of the device in ambient waves. The model is solved numerically by the fourth order Runge-Kutta method. The equation of motion of the device in ambient waves contains several parameters, including added mass ,damping coefficient, wave exciting force and restoring coefficient. Values of these parameters must be determined before the model equations can be solved. In order to determine these variables, a hydrodynamic problem of wave-device interactions must be solved. The boundary element method is used to solve this hydrodynamic problem of radiation and diffraction. Modeling results are verified by a series of hydraulic experiments conducted in a wave basin in the James K. K. Look Laboratory of Oceanographic Engineering at the University of Hawaii. Comparing analytical and experimental results yields some useful information concerning hydrodynamic coefficients under waves of large amplitude. The mathematical model developed in this study was then used to evaluate the effects of five configuration variables on the rate of upwelling flow at the design wave conditions, and to establish design criteria.