Selected Applications Related to Control of Offshore Structures
Dynamic analyses of mechanical systems are often considered together with problems related to their control. With traditional ways of operating machines it the operator who decides what the working motions are. In contemporary machines, it is becoming commonplace to support the process of control. Control systems based on microprocessor technology (programmable drivers, onboard computers) are supposed to facilitate human work or even replace it. They enable realization of various strategies unachievable with manual control. Automated control is used also in offshore structures, including cranes. The criteria of control strategies may be different, for example:
■ minimal duration of motion,
■ minimal consumption of energy,
■ accuracy of load positioning, including minimization of oscillations after the motion has ended,
■ minimization of dynamic loads,
■ stabilization of the load’s position,
■ minimization of the influence of sea waves on the device’s dynamics.
The present chapter describes the basics of the method of selecting the drive functions based on dynamic optimization. Control of the drum of a winch of an A-frame type crane allowing it to compensate for vertical movements of the base due to sea waves is presented. For an offshore jib crane, an auxiliary system is proposed enabling the load to be positioned in three directions. In the last part, a concept of active compensation of waves for a drum’s drive of a device for laying pipelines is discussed.
KeywordsGoal Function Auxiliary System Offshore Structure Load Position Vertical Stabilization
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