Geotechnical Response Models for Steel Compliant Riser in Deepwater Clays

The touchdown zone (TDZ) often proves to be a spot where cyclic bending stresses are the largest and is therefore a critical location for fatigue. Catenary steel compliant pipelines or risers (SCRs) are subject of much ongoing research, particularly with respect to their fatigue life, which is strongly influenced by seabed soil conditions in the TDZ. This chapter reviews the recent publications that might have an impact on the SCR-seabed interaction. The review starts by looking at the SCR general arrangement. Thereafter, the focus moves to the review of the recent research that studied the interactions between deepwater SCRs and the seabed. In addition, the review went over the analysis techniques of the SCR, including the modelling philosophy and models for geotechnical response. The research gap and the need for future research are identified

Sustainable seabed mining: guidelines and a new concept for Atlantis II Deep

The feasibility of exploiting seabed resources is subject to the engineering solutions, and economic prospects. Due to rising metal prices, predicted mineral scarcities and unequal allocations of resources in the world, vast research programmes on the exploration and exploitation of seabed minerals are presented in 1970s. Very few studies have been published after the 1980s, when predictions were not fulfilled. The attention grew back in the last decade with marine mineral mining being in research and commercial focus again and the first seabed mining license for massive sulphides being granted in Papua New Guinea’s Exclusive Economic Zone.Research on seabed exploitation and seabed mining is a complex transdisciplinary field that demands for further attention and development. Since the field links engineering, economics, environmental, legal and supply chain research, it demands for research from a systems point of view. This implies the application of a holistic sustainability framework of to analyse the feasibility of engineering systems. The research at hand aims to close this gap by developing such a framework and providing a review of seabed resources. Based on this review it identifies a significant potential for massive sulphides in inactive hydrothermal vents and sediments to solve global resource scarcities. The research aims to provide background on seabed exploitation and to apply a holistic systems engineering approach to develop general guidelines for sustainable seabed mining of polymetallic sulphides and a new concept and solutions for the Atlantis II Deep deposit in the Red Sea.The research methodology will start with acquiring a broader academic and industrial view on sustainable seabed mining through an online survey and expert interviews on seabed mining. In addition, the Nautilus Minerals case is reviewed for lessons learned and identification of challenges. Thereafter, a new concept for Atlantis II Deep is developed that based on a site specific assessment.The research undertaken in this study provides a new perspective regarding sustainable seabed mining. The main contributions of this research are the development of extensive guidelines for key issues in sustainable seabed mining as well as a new concept for seabed mining involving engineering systems, environmental risk mitigation, economic feasibility, logistics and legal aspects

Reliability-based fatigue analysis of steel catenary riser with seabed interaction

Strathclyde theses - ask staff. Thesis no. : T13456This thesis models a Steel Catenary Riser (SCR) on soft clay subjected to randon waves. SCR-seabead interaftion is modelled using a hysteretic non-linear model in the vertical seabed direction and Coulomb friction model in the lateral direction together with an improved model that includes the breakoutsoil resistance. The influence of the uncertainty in the geotechnical parameters and the development of the trench in the seabead on the dynamic response is determind. The structural behaviour and a probabilistic approach to fatigue performance in the touchdown zone is developed. The probabilistic model can be employed as a risk analysis tool for the SCR assessment, leading to a safer and more cost0effective design of the SCR system. It is noted that confidence in seabed interaction modelling and geotechnical parameter values is needed in order to have confidence in the final numerical analysis results.This thesis models a Steel Catenary Riser (SCR) on soft clay subjected to randon waves. SCR-seabead interaftion is modelled using a hysteretic non-linear model in the vertical seabed direction and Coulomb friction model in the lateral direction together with an improved model that includes the breakoutsoil resistance. The influence of the uncertainty in the geotechnical parameters and the development of the trench in the seabead on the dynamic response is determind. The structural behaviour and a probabilistic approach to fatigue performance in the touchdown zone is developed. The probabilistic model can be employed as a risk analysis tool for the SCR assessment, leading to a safer and more cost0effective design of the SCR system. It is noted that confidence in seabed interaction modelling and geotechnical parameter values is needed in order to have confidence in the final numerical analysis results

Dynamic response of steel catenary riser using a seabed interaction under random loads

It is important to develop better understanding of the Steel Catenary Riser (SCR)–soil interaction mechanism to provide a realistic technique to predict the dynamic response and structural behaviour of the SCR in the Touchdown Zone (TDZ).This paper discusses the significance of SCR–seabed interaction in the design of SCR for deepwater applications and reports the results of an analysis of an SCR on soft clay in 910 m depth of water using the commercial code OrcaFlex for non-linear time domain simulation with a robust meshing technique. In the study reported in this paper, the vertical embedment and large lateral movements of the SCR in the TDZ were investigated. During the simulations the seabed has been modelled using a hysteretic non-linear model in vertical seabed direction, and bilinear and trilinear models in the lateral seabed direction. It has been found that the TDZ responses result in the degradation of the seabed soil stiffness due to cyclic loading. Furthermore, an improved SCR–soil interaction model, with accurate prediction of soil stiffness and riser penetration enables us to more accurately predict global riser dynamic performance in the TDZ

Wave loading fatigue reliability and uncertainty analyses for geotechnical pipeline models

The challenges involved with the fatigue damage assessment of a catenary pipeline in the touchdown zone (TDZ) are primarily because of the non-linear behaviour of pipe-seabed interaction and considerable uncertainty in geotechnical model parameters. The research undertaken in this study investigates the sensitivity of fatigue performance to geotechnical parameters through a parametric study. Furthermore, this paper presents the probability of failure associated with fatigue analysis of a catenary pipeline in the TDZ due to the uncertainty in seabed response model and geotechnical parameters. A first-order reliability method is used for predicting the fatigue safety index. The fatigue analysis results prove that the confounding results indicated by the previous research studies on the catenary pipeline in the TDZ are due to different geotechnical parameters imposed with the soil model. The main benefit of employing a reliability-based fatigue analysis framework is that it enhances the confidence in the steel catenary riser analysis with seabed interaction