Automatic control methods for positioning the lower end of a filiform structure, notably an oil pipe, at sea

An automatic control method for positioning the lower end of an underwater filiform structure in relation to a target located in the water, wherein the following stages are carried out:

• a) holding up the upper end of the filiform structure by means of a floating vessel, the lower end of the filiform structure being free,
• b) determining a mathematical model expressing the position of the lower end as a function of the position of the upper end, the mathematical model being determined from characteristics intrinsic to the filiform structure using a beam model translating the dynamic behaviour of the filiform structure and using a modal decomposition method,
• c) determining a reference path for the lower end, which leads to the target,
• d) from the mathematical model determined in stage b), determining control laws allowing displacement of the lower end of the filiform structure,
• e) applying motions to the upper end so that the position of the lower end follows as closely as possible the reference path determined in stage c), said motions being determined using the control laws determined in stage d), by taking account of the reference path determined in stage c) and by taking account of the positions of the lower and upper ends of the filiform structure.