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Methods for design and analysis of flexible risers.

DE93721627

Publication Date	1991
Personal Author	Soedahl, N.
Page Count	228
Abstract	The main purpose of this work is to improve existing methods for practical design and analysis of flexible pipes used as fully dynamic risers in floating production systems and contribute to a better understanding of the static and dynamic behavior of flexible risers. The design analysis today are often carried out by stochastic time domain simulations for a given short-term environmental condition by use of the finite element method. The responses of flexible risers are known to be non-Gaussian due to the non-linearities introduced by the hydrodynamic loading and the stiffness properties of the pipe. Rather long simulations will therefore be needed to give a proper statistical response description. An efficient method for including bending stiffeners in the design analyses is presented by splitting the complete system into a local quasi-static response model for the bending stiffener analysed by a shooting technique and a global response model to account for the global dynamic behavior. Several case studies have been carried out to verify the accuracy and computational benefit of the proposed approach. A major part of this study has been concerned with extreme value estimation of non-Gaussian respones by fitting a proposed distribution model to a simulated sample of response maxima or response extremes by use of moment-based estimators. The validity of the proposed methods for extreme value estimation and quantification of statistical uncertainties has been investigated by a case study of a steep wave configuration. It is concluded that the derived expressions give a good description of the statistical uncertainty for extreme values estimated by use of the Weibull and the Weibull-tail distributions. 80 refs., 78 figs., 12 tabs.
Keywords	Marine Risers Pipes Computerized Simulation Design Extreme-Value Problems Finite Element Method Mathematical Models Nonlinear Problems Offshore Platforms Foreign technology EDB/423000 Theses
Source Agency	TIC Foreign Exchange Reports
NTIS Subject Category	47A - Marine Engineering 41 - Manufacturing Technology 94 - Industrial & Mechanical Engineering
Corporate Authors	Norges Tekniske Hoegskole, Trondheim.
Document Type	Thesis
Title Note	Thesis (Dr.ing).
NTIS Issue Number	199307

Methods for design and analysis of flexible risers.

Methods for design and analysis of flexible risers.
DE93721627

Publication Date	1991
Personal Author	Soedahl, N.
Page Count	228
Abstract	The main purpose of this work is to improve existing methods for practical design and analysis of flexible pipes used as fully dynamic risers in floating production systems and contribute to a better understanding of the static and dynamic behavior of flexible risers. The design analysis today are often carried out by stochastic time domain simulations for a given short-term environmental condition by use of the finite element method. The responses of flexible risers are known to be non-Gaussian due to the non-linearities introduced by the hydrodynamic loading and the stiffness properties of the pipe. Rather long simulations will therefore be needed to give a proper statistical response description. An efficient method for including bending stiffeners in the design analyses is presented by splitting the complete system into a local quasi-static response model for the bending stiffener analysed by a shooting technique and a global response model to account for the global dynamic behavior. Several case studies have been carried out to verify the accuracy and computational benefit of the proposed approach. A major part of this study has been concerned with extreme value estimation of non-Gaussian respones by fitting a proposed distribution model to a simulated sample of response maxima or response extremes by use of moment-based estimators. The validity of the proposed methods for extreme value estimation and quantification of statistical uncertainties has been investigated by a case study of a steep wave configuration. It is concluded that the derived expressions give a good description of the statistical uncertainty for extreme values estimated by use of the Weibull and the Weibull-tail distributions. 80 refs., 78 figs., 12 tabs.
Keywords	Marine Risers Pipes Computerized Simulation Design Extreme-Value Problems Finite Element Method Mathematical Models Nonlinear Problems Offshore Platforms Foreign technology EDB/423000 Theses
Source Agency	TIC Foreign Exchange Reports
NTIS Subject Category	47A - Marine Engineering 41 - Manufacturing Technology 94 - Industrial & Mechanical Engineering
Corporate Authors	Norges Tekniske Hoegskole, Trondheim.
Document Type	Thesis
Title Note	Thesis (Dr.ing).
NTIS Issue Number	199307