An experimental study is currently being carried out to investigate the hydrodynamic force characteristics produced on vertical multi-cylinder structures when subjected to wave motions. Of particular interest to this study is the modification to the force characteristics attributed to the relative spacing and pattern of a cylinder group on individual members when this loading is in the Morison force regime. Testing is being conducted in the Michell laboratory of the University of Melboume on cylinders with a fixed diameter of 0.02m located in a 1m later depth. A variety of wave types have been used in this program including a range of irregular Pierson Moskowitz waves and sets of both Swept Sine Waves (SSWs) and regular waves of different amplitudes and frequencies. The cylinders in the group include ones that contain are-locatable 0.10m length active segment from which both the in-line and transverse force components are able to be measured simultaneously under test. Results from this study for a two-cylinder and four-cylinder group are provided in this paper that indicate the tendency observed in force coefficients from this interference effect with orientation and distance of separation between the cylinders.
Oil production riser systems used in offshore platforms normally consist of a group of long slender vertical cylindrical pipes that form a pattern which varies with the number and relative spacing of the constituent1members. Because of the proliferation of geometric configurations that have been adopted in the design of riser groups, and the current lack of a good understanding of the wave interaction effects on individual members, it is not possible at this point in time to adequately model the complex realization of the hydrodynamic loading on such members on a theoretical basis.