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Ocean Engineering

Stabilization of Load’s Position in Offshore Cranes

[+] Author and Article Information
A. Maczyński, S. Wojciech

 University of Bielsko-Biała, 2 Willowa Street, 43-309 Bielsko-Biała, Poland

J. Offshore Mech. Arct. Eng 134(2), 021101 (Dec 02, 2011) (10 pages) doi:10.1115/1.4004956 History: Received August 10, 2009; Revised February 03, 2010; Published December 02, 2011; Online December 02, 2011

It is often desirable to keep the load of an offshore crane in a fixed point in space despite the movement of its base. To solve the problem of stabilizing the load’s position, the authors have proposed application of the hoisting winch drum’s drive and an auxiliary system. The auxiliary system enables independent moving of a selected point of the hoisting rope in two perpendicular planes. In this paper, two methods for determining the drive functions of the auxiliary system and the hoisting winch’s drum ensuring stabilization of an offshore crane’s load are presented. Both methods are based on a simplified model of a crane and allow compensation for a pseudo-harmonic base motion. In order to take into account the deviations of base motion from the assumed and avoid over simplifications, the second, more sophisticated model is developed. This model is proposed to be applied in closed-loop control systems with a PID controller. Results of sample numerical simulations are included that proved useful information about the developed methods and models for stabilization of an offshore crane’s load.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 3

External forces and their moments acting on the crane’s base

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Figure 4

Time course of xL coordinate for general motion of the base

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Figure 5

Time course of yL coordinate for general motion

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Figure 6

Time course of zL coordinate for general motion

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Figure 9

Comparison of the hoisting winch drum’s analytic drive function and its initial approximation (4 components)

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Figure 10

Comparison of the θ angle’s analytic drive function and its initial approximation (2 components)

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Figure 11

Comparison of the θ angle’s analytic drive function and its initial approximation (4 components)

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Figure 12

Comparison of the γ angle’s analytic drive function and its initial approximation (2 components)

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Figure 13

Comparison of the γ angle’s analytic drive function and its initial approximation (4 components)

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Figure 14

Block diagram of control systemγO , θO , αO – driver functions determined according the simplified model, γt , θt , αt – input signals determined according the simplified model, γb , θb , αb – current values of controlled signals,, , eα – dynamic errors,, , – output signals,z disturbance.

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Figure 15

Time course of xL coordinate

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Figure 16

Time course of yL coordinate

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Figure 17

Time course of zL coordinate

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Figure 8

Comparison of the hoisting winch drum’s analytic drive function and its initial approximation (2 components)

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Figure 2

Simplified model of an offshore jib crane

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Figure 1

Auxiliary system reducing load oscillations

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Figure 7

Time course of the dynamic coefficient

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