BEHAVIOUR OF SEASTAR TLP IN CASPIAN SEA WAVE CONDITION USING NUMERICAL MODELING

SeaStar platform is a new generation of tensionleg platform, somewhat similar to Spar platform, which in addition to the benefits of Spar, benefits from the positive properties of tension-leg platform. SeaStar platform uses a cylindrical main body with three completely submerged appendages and provides the required Buoyancy for load-bearingdeck and equipment. Pre-stretched cables are connected to these three appendages [1]. Due to this remarkable buoyancy a SeaStar platform can handle up to about 1.8 times its own weight while for a Spar platform this is equal to 0.6. Also, less use of steel in this platform has made it very economical [2]. The movement of SeaStar platform to three degrees offreedom (Surge, Sway, Yaw) is comparative and the natural period is large while it is less in the other three degrees of freedom (Heave, roll, pitch) which are known as the hard movements of the platform [3]. The process results from initial stretching exercise sufficient to control the platform. Sreekumar et al. (2001) using linear diffraction radiation theorystudied the behavior of a mini seastar TLP [4]. In 2006, Tabeshpour and his colleagues analyzed the hydrodynamics of a TLP under the influence of waves [5]. Abaiee et al. conducted numerical and laboratory studies on the seastar TLP platform in 2015 and presented and discussed the results [6]. Substantial benefits of the SeaStar platform as well as proving the existence of huge oil resources in deep waters of the Caspian Sea forced us to analyze this kind of platform and establish a positive step towards enhancing the countrys capacity in the field of oil extraction drilling. In this paper, the behavior of a mini SeaStar platform in deep water of Caspian Sea due to regular waves was investigated using Moses software. The RAO charts of the hard and soft movements of the platform are then estimated in different collision angles.