Investigation of nonlinear restoring stiffness in dynamic analysis of tension leg platforms

Shortcomings of the traditional stiffness matrix in dynamic analysis of TLPs, derived by considering equilibrium of forces, are pointed out, as well as dilemma concerning consistency of the recently presented matrix based on energy balance. New stiffness matrix is derived by utilizing both force equilibrium approach, with algebraic averaging and root mean square of tendon forces, and energy balance approach for large surge and sway. Yaw is treated as a small and large displacement. Static numerical analysis is performed for all six cases by imposing surge force and yaw moment. The obtained results are compared with those of FEM analysis, and useful conclusion is drawn, which can be used for improvement of uncoupled mathematical model of TLPs.