This paper presents an active control of coupled dynamic responses of the hull and the tendon of TLP. In a deepwater TLP, the restoring force becomes smaller and the natural frequency of the system decreases with increasing water depth. There is a possibility that the dynamic response of tendon, which is induced by the hull motion, can be significant. Furthermore the motion of TLP due to wave drifting force can be comparable or larger than wave induced motion. This low-frequency response can be controlled by conventional DPS thrusters. The operability is improved and the tendon and the riser are protected from structural damage. The low-frequency motion is induced by small wave drifting force and can be controlled by small control force. The first order wave force is very large and control of this high-frequency response is not practical. The control method is optimal control and the low-frequency hull motion and the bending strain of the tendon are controlled The high-frequency response is removed from the control system by low pass filters. The effectiveness of control is verified by experiment with an 1/100 scale model of JOIA(Japan Ocean Industries Association)-TLP. The hull motion IS measured by an ultrasonic ranging sensor and the control force is generated by two thrusters built in the TLP model. Average control force required for the control is about 1/200 of the hull weight, which is slightly larger than the value of the conventional DPS thrust of a semi-submersible.
A trend observed in the tendon of the deepwater TLP is the increased diameter of the tendon. By this design the payload of the TLP is secured, but the mass of tendon including added mass is increased by thinning the walls and enlarging the diameter of the tendon. The restoring force becomes smaller and the natural frequency of the tendon becomes lower and approaches the frequency range of substantial wave energy.
