Non-linear load-deflection models for seafloor interaction with steel catenary risers

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Title: Non-linear load-deflection models for seafloor interaction with steel catenary risers
Author: Jiao, Yaguang
Abstract: The simulation of seafloor -steel catenary interaction and prediction of riser fatigue life required an accurate characterization of seafloor stiffness as well as realistic description of riser load -deflection (P -y ) response . This thesis presents two load -deflection (P -y ) models (non -degradating and degradating models ) to simulate seafloor -riser interaction . These two models considered the seafloor -riser system in terms of an elastic steel pipe supported on non -linear soil springs with vertical motions . These two models were formulated in terms of a backbone curve describing self -embedment of the riser , bounding curves describing P -y behavior under extremely large deflections , and a series of rules for describing P -y behavior within the bounding loop . The non -degradating P -y model was capable of simulating the riser behavior under very complex loading conditions , including unloading (uplift ) and re -loading (downwards ) cycles under conditions of partial and full separation of soils and riser . In the non -degradating model , there was a series of model parameters which included three riser properties , two trench geometry parameters and one trench roughness parameter , two backbone curve model parameters , and four bounding loop model parameters . To capture the seafloor stiffness degradation effect due to cyclic loading , a degradating P -y model was also developed . The degradating model proposes three degradation control parameters , which consider the effects of the number of cycles and cyclic unloading -reloading paths . Accumulated deflections serve as a measure of energy dissipation . The degradating model was also made up of three components . The first one was the backbone curve , same as the non -degradating model . The bounding loops define the P -y behavior of extreme loading deflections . The elastic rebound curve and partial separation stage were in the same formation as the non -degradating model . However , for the re -contact and re -loading curve , degradation effects were taken into the calculation . These two models were verified through comparisons with laboratory basin tests . Computer codes were also developed to implement these models for seafloor -riser interaction response .
URI: http : / /hdl .handle .net /1969 .1 /ETD -TAMU -1279
Date: 2009-05-15

Citation

Non-linear load-deflection models for seafloor interaction with steel catenary risers. Available electronically from http : / /hdl .handle .net /1969 .1 /ETD -TAMU -1279 .

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