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ABSTRACT PIggyback pipeline is defined as a pipeline system be composed of one big pipe and one or several small pipe. Based on the theory of wave-current interaction and physical model test, the hydrodynamic characteristic of submarine piggyback pipeline m wave-current coexisting field (both regular and irregular waves) was investigated. The so-called "modified diameter method" suggested by authors is used for analyzing the in-line hydrodynamic coefficients of such kind pipeline, which is well related to KC number. The comparison of tested data in regular and irregular waves shows that m the region of 9O>KC>20, the results m these two cases can be unified. The effect of water depth was analyzed in detailed. The relationship between Cd, Cm and KC, which is based on the results of present research, may be used as a reference for engineering application.
INTRODUCTION In real engineering practice, submarine pipeline may be combined with a small pipe riding on a big main pipe (or some times several small pipes riding on a big one). We called such kind pipeline system as piggyback pipeline. The flow behaviour around this pipeline are much more complicated than a single submarine pipeline. In the meantime, the natural sea condition is a coexisting field of Irregular waves with currents. Some research was already done in the case of single pipeline in coexisting field of regular waves and currents [Li (1987, 1990), Xing (1990), Beattle(1977), so extended research are expected to meet the need of various engineering application. The main purpose of this study is to know: the hydrodynamic characteristic of submarine piggyback pipeline in random wave and current coexisting field, the effect of small pipe on main pipe, the difference of hydrodynamic characteristic in arious wave conditions, the possibility of the uniformity of hydrodynamic coefficients for various wave conditions and various structures (single pipe or piggyback pipeline).
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