A time-domain numerical method to predict in-line dynamics of flexible risers for upwelling deep ocean water has been developed. The analysis method is based on a swing-by-swing technique with symmetrical vortices model, which may estimate instantaneous hydrodynamic forces at low Keulegan-Carpenter Numbers. In this paper, effects of previously separated vortices, which are modeled by the results of flow visualizations, are included in the symmetrical vortices model. Hydrodynamic forces on a harmonically oscillating circular cylinder estimated by the new symmetrical vortices model are compared with measured ones. The results show that the new model may well estimate the hydrodynamic forces with the effects of previously separated vortices. Dynamic analyses of flexible risers for upwelling deep ocean water are also carried out using the new symmetrical vortices model.
Deep ocean water (DOW) has attracted special interest as one of the renewable energy resources with great potential. The worldwide requirements of the renewable energies increase with strengthening the international regulation for CO 2 emission. The DOW has also been focused as an important resource to improve marine primary production. The open ocean mariculture using the large amount of DOW may become a key technology to avoid the food crises. Furthermore, many DOW goods, such as drinks, foods, medicines, cosmetics, etc., have been recently developed in Japan. These may suggest that the demand of the DOW would significantly increase year by year. From the economical point of view, a floating-type DOW upwelling system is advantageous in comparison with a land-based one, because the length of the upwelling pipe (so-called cold water pipe, CWP), whose cost is dominant in the total cost, is much shorter for the floating-type system than that for the land-based one (Vega, 1992).
