Tethered floating circular cylinder can be regarded as a typical simplified model in offshore engineering. Such structure is the basic component of TLP. Careful investigation on the dynamic response of this type of cylinder may give a hint on some new nonlinear characteristics of TLP, which have been omitted before. Then the nonlinear dynamic analysis of a tethered cylinder is performed in the time domain. Nonlinearities considered in the analysis include geometric nonlinearity induced by coupled finite translational and rotational displacements of the cylinder, nonlinear hydrostatic and inviscid hydrodynamic forces introduced by the effect of instantaneous wet surface, and the velocity squared viscous drag force (also integrated to instantaneous wet surface). Numerical results are presented which illustrate that rotations exert a significant influence on the dynamic motion responses of the tethered cylinder, and should be dealt with as finite variables instead of infinitesimal.


A typical TLP is a floating structure comprising group of cylinders with taut tether, which allows motions of surge, sway, and yaw in the horizontal plane and heave, pitch, and roll in the vertical plane. Some mathematical models have been presented to analyze the dynamic response of TLP. Ahmad (1996) conducted response analysis considering viscous hydrodynamic force, variable added mass and large excursion. In addition, Ahmad, Islam and Ali (1997) investigate TLP's sensitivity to dynamic effects of the wind. Chandrasekaran and Jain (2002a, b) proposed a triangular configuration TLP, and developed a method to analyze the dynamic behavior of triangular and square TLP. Furthermore, they performed numerical studies to compare the dynamic responses of a triangular TLP with that of a square TLP. Williams and Rangappa (1994) developed an approximate semi-analytical technique to calculate hydrodynamic loads and added mass and damping coefficients for idealized TLP consisting of arrays of circular cylinder.

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