A time-domain numerical method for predicting in-line dynamics of flexible deep seawater riser, so-called cold water pipe (CWP), was developed. The analysis method was based on a swing-by-swing technique with symmetrical vortices model. The symmetrical vortices model may accurately estimate instantaneous hydrodynamic forces for Kc lower than eight. To validate the present dynamic analysis method, forced oscillation tests using a CWP model were performed. The results in single sinusoidal oscillation conditions demonstrated that the present method is applicable to the dynamic analysis of CWP. The results in conditions with two different oscillation components showed that the present method may have great potential for analyzing dynamic responses of CWP in irregularly load conditions.
Since "70s, many researches on economics of deep seawater upwelling facilities, mostly ocean thermal energy conversion (OTEC) plants, were carried out (Avery and Wu, 1994). Some of them suggested that the floating-type system is more cost effective than landbased due to the reduction of deep seawater riser (so-called cold water pipe, CWP) length (Vega, 1992). The authors (Bando et al., 1998) evaluated capital costs of land-based and floating-type deep seawater upwelling systems. The results showed that the CWP cost occupies over 65 % of the total cost for the land-based in average, and the cost for the floating-type becomes almost a half of that for the land-based when the amount of upwelling water is of order of 10 million tons per day. As a matter of course, this cost evaluation is on the assumption that the large diameter CWP can be constructed with low cost and high reliability. This would point out that the accurate dynamic analysis of the CWP is one of the most important technical subject for developing commercial size deep seawater upwelling systems.
