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Civil-Comp Proceedings
ISSN 1759-3433
CCP: 71
COMPUTATIONAL CIVIL AND STRUCTURAL ENGINEERING
Edited by: G. De Roeck and B.H.V. Topping
Paper I.2

Simulation of Stochastic Response of Offshore Structures Excited by Stationary Drag and Inertia Forces

M. Mashnad+ and M.M. Masud#

+Department of Civil Engineering, New Mexico State University, Las Cruces, New Mexico, United States of America
#Department of Computer Science and Engineering, Bangladesh University of Engineering and Technology, Dhaka, Bangladesh

Full Bibliographic Reference for this paper
M. Mashnad, M.M. Masud, "Simulation of Stochastic Response of Offshore Structures Excited by Stationary Drag and Inertia Forces", in G. De Roeck, B.H.V. Topping, (Editors), "Computational Civil and Structural Engineering", Civil-Comp Press, Edinburgh, UK, pp 11-16, 2000. doi:10.4203/ccp.71.1.2
Abstract
To predict the stochastic response of a single degree of freedom fixed offshore platform to Morison's wave loading, Monte Carlo simulation technique in spectral representation is used. The analysis is based on linear vibration theory, and the assumptions that waves are Gaussian and stationary processes. In this study Pierson Moskowitz gravity spectrum is used as the main input. By multiplying the wave spectrum with appropriate transfer function velocity, acceleration, force, and response spectra were derived. To generate sea surfaces or forces with similar statistics observed in the ocean, theoretically the number of sample N needs to be infinite. However, it is reported that for N = 500 & above the generated process becomes Gaussian. The generation of sample functions was done efficiently by using Inverse Fast Fourier Transformation technique. From the simulated force or deflection some important statistical properties, such as, standard deviation and threshold crossing can be estimated. Simulated response has been compared with the response obtained in a deterministic approach. Although the deterministic approach give useful results, these results cannot predict the response of structures under random excitations. Also simulated response of an offshore platform has been compared with the result obtained in a time domain analysis.

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