<title>Active control of heave motion for TLP-type offshore platform under random waves</title>

In deep waters scenarios Tension Leg Platforms (TLP), under severe sea/wind conditions, may experience large response amplitudes of the hull motion. Large heave amplitudes caused by random dynamic loads appear as one of the most deleterious effects to the structural safety and integrity of the most critical components: mooring system and the handing risers. In a preliminary design reduction of these amplitudes is in general tentatively sought by compromised measures and concurrent design criteria like: high flutuability and deck payload vs. tendons and risers submerged weight; deck hydrodynamic vs. length variation of pretension tendons, etc. This paper shows that active control system may be installed inside the hull to attenuate dynamic amplitudes in heave motion. Optimal control theory are applicated for the idealization of mechanism to reduce the dynamic response amplitude, improving the safety conditions and increasing service life of tendons and risers, insuring the system functioning at all. The uncontrolled and controlled dynamic behaviors of a TLP prototype are investigated by using simplified mathematical models. The numerical results lead to the conclusion that active systems have good performance and efficiency in reducing and controlling the heave motion amplitudes and consequently the stress variations in tendons and risers of a TLP.