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Keywords: offshore platform, ice load, optimum design, acceleration, pseudo excitation method.

Summary

In the cold region, the ice load is normally the dominant environmental force of engineering structures. The Bohai Gulf, located in the northeast of China with relative high latitude, is an area prone to unpredictable winter conditions that can sometimes cause severe ice load [1]. However, due to lack of the understanding of the dynamic properties of ice load, the current design codes of ice-resistant structure only consider the static ice forces. Moreover, since the oil and natural gas resources in the Bohai Gulf are mainly in marginal oil fields, most of the platforms in service in the Bohai Gulf are economical ice-resistant jacket platforms, which were designed based on the extreme static ice force and did not account for the effects of dynamic properties of ice loading. The full-scale field tests and observations in the Bohai Gulf demonstrated that these platforms underwent severe ice-induced vibrations during winter because of the dynamic interaction between the ice sheet and the structure, which may result in serious consequences such as fatigue failure of tubular joints, human discomfort and gas leaks due to flange failure of pipes [2].

Thus, the evaluation of the dynamic performance of the ice-resistant platforms and their design methodology are the urgent tasks for researchers and engineers, which are beyond the current design codes. Furthermore, how to select the proper design ice loading and the parameters involved is also a difficulty because of the variation of the ice environments and the close dependence of the ice load on the structural properties. In this paper, the optimization technique is employed to achieve an economical and reliable design, and the dynamic performance of the ice-resistant jacket platforms in terms of the deck acceleration is focused on [3]. Considering the randomness of the ice thickness and velocity, we propose a probability-based approach to determine the design ice case by the random ice spectrum [4] and the pseudo excitation method [5]. Finally, an example of acceleration-based optimum design of the ice-resistant jacket platform demonstrates the applicability and feasibility of the proposed method, with both the optimal dynamic performance and the acceptable cost.

References

1: G.J. Yang, "Bohai Sea Ice Condition", Journal of Cold Regions Engineering, 14 (2), 81-92, 2000. doi:10.1061/(ASCE)0887-381X(2000)14:2(54)
2: Q.J. Yue, X.J. Bi, "Ice-Induced Jacket Structure Vibrations in Bohai Sea", Journal of Cold Regions Engineering, 14 (2), 81-92, 2000. doi:10.1061/(ASCE)0887-381X(2000)14:2(81)
3: Q.J. Yue, X.J. Bi, X. Yu, Z.M. Shi, "Ice-induced vibration and ice force function of conical structures", China Civil Engineering Journal, 36(2), 16-19, 2003. (In Chinese).
4: Q.J. Yue, Y. Qu, X.J. Bi, T. Kärnä, "Ice Force Spectrum on Narrow Conical Structures", Cold Regions Science and Technology, 49 (2), 161-169, 2007. doi:10.1016/j.coldregions.2007.02.002
5: J.H. Lin, Y.H. Zhang, "Seismic Random Vibration of Long-Span Structures", in Vibration and Shock Handbook, C.W. de Sila, (Editor), CRC Press., Boca Raton, U.S.A., Chapter 30, 2005.

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Front Page Browse CCP CSETS CTR IJRT Other Authors Search Purchase Guide FAQ Contact us	Civil-Comp Proceedings ISSN 1759-3433 CCP: 88 PROCEEDINGS OF THE NINTH INTERNATIONAL CONFERENCE ON COMPUTATIONAL STRUCTURES TECHNOLOGY Edited by: B.H.V. Topping and M. Papadrakakis Paper 111 Acceleration-Based Optimum Design of Offshore Platforms Subjected to Ice Loading G. Li, X. Liu and G.D. Cheng Department of Engineering Mechanics, State Key Laboratory of Structural Analysis of Industrial Equipment, Dalian University of Technology, China doi:10.4203/ccp.88.111 purchase the full-text of this paper Full Bibliographic Reference for this paper G. Li, X. Liu, G.D. Cheng, "Acceleration-Based Optimum Design of Offshore Platforms Subjected to Ice Loading", in B.H.V. Topping, M. Papadrakakis, (Editors), "Proceedings of the Ninth International Conference on Computational Structures Technology", Civil-Comp Press, Stirlingshire, UK, Paper 111, 2008. doi:10.4203/ccp.88.111 Keywords: offshore platform, ice load, optimum design, acceleration, pseudo excitation method. Summary In the cold region, the ice load is normally the dominant environmental force of engineering structures. The Bohai Gulf, located in the northeast of China with relative high latitude, is an area prone to unpredictable winter conditions that can sometimes cause severe ice load [1]. However, due to lack of the understanding of the dynamic properties of ice load, the current design codes of ice-resistant structure only consider the static ice forces. Moreover, since the oil and natural gas resources in the Bohai Gulf are mainly in marginal oil fields, most of the platforms in service in the Bohai Gulf are economical ice-resistant jacket platforms, which were designed based on the extreme static ice force and did not account for the effects of dynamic properties of ice loading. The full-scale field tests and observations in the Bohai Gulf demonstrated that these platforms underwent severe ice-induced vibrations during winter because of the dynamic interaction between the ice sheet and the structure, which may result in serious consequences such as fatigue failure of tubular joints, human discomfort and gas leaks due to flange failure of pipes [2]. Thus, the evaluation of the dynamic performance of the ice-resistant platforms and their design methodology are the urgent tasks for researchers and engineers, which are beyond the current design codes. Furthermore, how to select the proper design ice loading and the parameters involved is also a difficulty because of the variation of the ice environments and the close dependence of the ice load on the structural properties. In this paper, the optimization technique is employed to achieve an economical and reliable design, and the dynamic performance of the ice-resistant jacket platforms in terms of the deck acceleration is focused on [3]. Considering the randomness of the ice thickness and velocity, we propose a probability-based approach to determine the design ice case by the random ice spectrum [4] and the pseudo excitation method [5]. Finally, an example of acceleration-based optimum design of the ice-resistant jacket platform demonstrates the applicability and feasibility of the proposed method, with both the optimal dynamic performance and the acceptable cost. References 1 G.J. Yang, "Bohai Sea Ice Condition", Journal of Cold Regions Engineering, 14 (2), 81-92, 2000. doi:10.1061/(ASCE)0887-381X(2000)14:2(54) 2 Q.J. Yue, X.J. Bi, "Ice-Induced Jacket Structure Vibrations in Bohai Sea", Journal of Cold Regions Engineering, 14 (2), 81-92, 2000. doi:10.1061/(ASCE)0887-381X(2000)14:2(81) 3 Q.J. Yue, X.J. Bi, X. Yu, Z.M. Shi, "Ice-induced vibration and ice force function of conical structures", China Civil Engineering Journal, 36(2), 16-19, 2003. (In Chinese). 4 Q.J. Yue, Y. Qu, X.J. Bi, T. Kärnä, "Ice Force Spectrum on Narrow Conical Structures", Cold Regions Science and Technology, 49 (2), 161-169, 2007. doi:10.1016/j.coldregions.2007.02.002 5 J.H. Lin, Y.H. Zhang, "Seismic Random Vibration of Long-Span Structures", in Vibration and Shock Handbook, C.W. de Sila, (Editor), CRC Press., Boca Raton, U.S.A., Chapter 30, 2005. purchase the full-text of this paper (price £20) go to the previous paper go to the next paper return to the table of contents return to the book description purchase this book (price £145 +P&P)
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