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Ocean Engineering

Control of Fixed Offshore Jacket Platform Using Semi-Active Hydraulic Damper

[+] Author and Article Information
Sudip Paul

ETD, Engineers India Limited, 1 BCP, New Delhi 110066, Indiasudip.rishabh@gmail.com

T. K. Datta

Department of Civil Engineering, IIT-Delhi, New Delhi 110016, Indiatushar_k_datta@yahoo.com

S. Kapuria

Department of Applied Mechanics, IIT-Delhi, New Delhi 110016, Indiakapuria@am.iitd.ac.in

J. Offshore Mech. Arct. Eng 131(4), 041106 (Oct 01, 2009) (10 pages) doi:10.1115/1.3160534 History: Received November 07, 2008; Revised April 09, 2009; Published October 01, 2009

Semi-active control of fixed offshore jacket platforms in shallow water depth using semi-active hydraulic damper (SHD) is presented. The semi-active control uses Bang Bang control algorithm to provide the required control command to the SHDs. In the control strategy, SHDs are installed in the bracings, making it an attractive proposition for the use in jacket structures. Although the main objective of providing semi-active control devices is to control the acceleration response of the deck for smooth operation and comfort condition, the reduction in base shear and displacement are also considered as important. In particular, great reduction in foundation cost can be achieved by base shear control under extreme sea state. The effectiveness of the control scheme is investigated by varying some important parameters such as the damper capacity, the maximum damping coefficient, and the distribution of dampers along the height of the structures under various sea states. A four legged steel jacket platform in a water depth of 122 m is considered as an example problem for finding out the controlled responses. Three wave conditions are considered, namely, operating wave, extreme wave, and irregular sea state. Results of the study indicate that significant control in acceleration response can be achieved by semi-active control using SHDs. Further, considerable reduction in base shear is also possible by providing SHDs of adequate capacity at the bottom-most level of the jacket.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Fixed offshore jacket structure with hydrodynamic force segments and lumped mass model

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Figure 2

Flow diagram of control problem implemented in MATLAB

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Figure 3

Connection of SH Damper with the jacket

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Figure 4

Controlled and uncontrolled top deck displacement for regular operating wave

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Figure 5

Controlled and uncontrolled top deck acceleration for regular operating wave

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Figure 6

Controlled and uncontrolled base shear for regular operating wave

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Figure 7

Controlled and uncontrolled top deck displacement for irregular sea state

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Figure 8

Controlled and uncontrolled top deck acceleration for irregular sea state

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Figure 9

Controlled and uncontrolled base shear for irregular sea state

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Figure 10

(a) Variations in controlled responses with floor damper capacity (operating wave). (b) Variation in total control force with floor damper capacity (operating wave). (c) Variation in % damper capacity utilized with floor damper capacity (operating wave).

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Figure 11

(a) Variations in controlled responses with damper capacity (extreme wave). (b) Variation in total control force with floor damper capacity (extreme wave). (c) Variation in % damper capacity utilized with floor damper capacity (extreme wave).

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Figure 12

(a) Variations in controlled responses with damper capacity (irregular sea state). (b) Variation in total control force with floor damper capacity (irregular sea state). (c) Variation in % damper capacity utilized with floor damper capacity (irregular sea state).

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Figure 13

Variation in base shear control with bottom damper capacity (operating wave)

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Figure 14

Variation in % control of acceleration with maximum damping coefficient for different waves

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