DESIGN OF A BUOYANT SYSTEM WITH DISCRETE FORCE DISTRIBUTION

Abstract

The stability and dynamic positioning of any floating structure is essential during offshore or on shore activities. It is therefore necessary to carry out offshore mooring system analysis in order for it to withstand extreme environmental forces of wind, wave, and current that will act on the structures. This project is focused on designing a fit-for-purpose buoyant mooring system to achieve the stability and dynamic positioning of a floating system. This system must provide a discreet non-linear force distribution within a given range. The sea-water depth range at the shore was also provided. For a certain stretch in the mooring line, due to rise in the level of water, the decrement in the required buoyant force was to decrease non-linearly. In order to meet that requirement a mechanism with only one piston-cylinder connected to mooring line was devised. This was the simplest solution that could be achieved for the desired outcome. Any other mechanism, according to observations, increases the complexity of the system, which was to be avoided (as demanded in the problem).Once the string is stretched the piston is pulled downwards. This increases the total volume occupied by the mechanism thus increasing the buoyant force (Archimedes Principle). But there is a linear relationship between the stretch of string and increase of buoyant force. In order to make this relationship non-linear a multi-groove step pulley was used. The mooring line passing over this pulley produced a non-linear pull in the piston (since the radius of the each step changes non-linearly). As a result buoyant force also changes non-linearly for the same stretch of the mooring line. CATIA was used for 3D modeling of the system, and better understanding of the mechanism. The above mentioned mechanism was the simplest which could be achieved, because no complex tools were required for its construction and it also provided the exact values as demanded.