An offshore structure consisting of slender columns near the free surface and large buoyancy pontoons near the base is considered to be advantageous since the wave force and hence wave induced responses are low when compared to a structure consisting of large diameter columns near the free surface. Since the columns are slender, diffraction of the incident wave field can be considered to be negligible and the wave force can be computed using Morison's equation. For a given sea state, the total force on a structure consisting of a number of such slender cylindrical legs will depend on the relative disposition between cylinders. The effect of this spacing between cylinders on the total force on the structure has been studied. This research has been done to get an insight into the design of an offshore structure that will experience low horizontal force. The sea state considered is one having significant wave height of 6 metres and a mean wave period of 6 seconds since the probability of exceedence of this sea state is low in the west coast of India where the use of this structure is contemplated.

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