ACTIVE CONTROL FOR INSTALLATION OF FLEXIBLE UNDERWATER SLENDER STRUCTURE

This paper presents an installation method for flexible underwater slender structures such as deepwater risers or TLP tendons. In this method, dynamic response and deformation, which structures experience during installation, are controlled to protect them from unexpected disturbances. The control method formulated in this paper is tested experimentally, using two actuators. One is a variable drag type actuator, the opening angle of wing-like appendages is controlled and variable drag force is generated. The other is a variable buoyancy type actuator, buoyancy is varied by changing the volume of air in the actuator drum. An ultrasound ranging sensor is used for measurement of displacement and deformation. Accuracy of this sensor is sufficient (less than 1mm) when used as a deformation sensor. Control experiments are conducted for the upending of a slender structure and for the free fall of a horizontal pipe. The slender structure is supported at one end by a pin joint and upended freely while the deformation is controlled. In the free fall experiment a pipe is laid down on the basin bottom in a straight and horizontal configuration.