Improving the assessment of seismic hazard in the North Sea

The following PhD thesis provides a comprehensive reassessment of probabilistic seismic hazard assessment (PSHA) in the North Sea. PSHA provides probabilistic representations of the expected ground-shaking at sites of interest, which can be used to assess the seismic risk for structures located at (or proximal to) said sites. In the North Sea, the seismic risk for offshore infrastructure including (1) oil and gas platforms and (2) wind turbine facilities must be considered. The seismic risk of this offshore infrastructure is important to consider because certain levels of seismic damage can result in negative impacts upon (1) the environmental health of the North Sea, (2) the personal health of employees on or near the considered infrastructure and (3) the economic health of governments and corporations which are reliant upon this infrastructure. The most recent publicly available North Sea PSHA was undertaken by Bungum et al. (2000). Two decades have passed since this study, since which substantial developments in PSHA have been made, and additional North Sea ground-motion data has been collected. Furthermore, the 2001 Ekofisk earthquake was the first hydrocarbon production induced earthquake in the North Sea to have been deemed of engineering significance for platforms in the region, but was not considered within the Bungum et al. (2000) study. In this investigation, North Sea PSHA is reassessed in several ways. Firstly, a pre-existing ground-motion prediction equation (GMPE) which performs well in the North Sea is identified as a base model for a North Sea GMPE using an additional 20 years of ground motion records available since the Bungum et al. (2000) study. This base model GMPE is then improved incrementally through the constrainment of North Sea path and site effects using novel techniques. Following the development of this North Sea GMPE, the seismogenic source model of Bungum et al. (2000) is updated using an additional two decades of North Sea earthquake observations. The impact of the North Sea GMPE and the updated source model are evaluated using (1) macroseismic earthquake observations and (2) assessment of the seismic risk of offshore infrastructure in the region. The updated PSHA formulation developed within this investigation results in moderate but significant differences in the seismic risk for offshore infrastructure in the North Sea. These seismic risk estimates are potentially more appropriate than those computed using the Bungum et al. (2000) PSHA formulation due to the additional ground-motion data and the PSHA advancements available since the Bungum et al. (2000) PSHA study. Ultimately, the improved seismic hazard estimates potentially help to better assess the structural health of offshore North Sea infrastructure, and subsequently minimise the likelihood of levels of seismic damage which could be detrimental to the North Sea environment or the personnel and/or economies operating within the region.The following PhD thesis provides a comprehensive reassessment of probabilistic seismic hazard assessment (PSHA) in the North Sea. PSHA provides probabilistic representations of the expected ground-shaking at sites of interest, which can be used to assess the seismic risk for structures located at (or proximal to) said sites. In the North Sea, the seismic risk for offshore infrastructure including (1) oil and gas platforms and (2) wind turbine facilities must be considered. The seismic risk of this offshore infrastructure is important to consider because certain levels of seismic damage can result in negative impacts upon (1) the environmental health of the North Sea, (2) the personal health of employees on or near the considered infrastructure and (3) the economic health of governments and corporations which are reliant upon this infrastructure. The most recent publicly available North Sea PSHA was undertaken by Bungum et al. (2000). Two decades have passed since this study, since which substantial developments in PSHA have been made, and additional North Sea ground-motion data has been collected. Furthermore, the 2001 Ekofisk earthquake was the first hydrocarbon production induced earthquake in the North Sea to have been deemed of engineering significance for platforms in the region, but was not considered within the Bungum et al. (2000) study. In this investigation, North Sea PSHA is reassessed in several ways. Firstly, a pre-existing ground-motion prediction equation (GMPE) which performs well in the North Sea is identified as a base model for a North Sea GMPE using an additional 20 years of ground motion records available since the Bungum et al. (2000) study. This base model GMPE is then improved incrementally through the constrainment of North Sea path and site effects using novel techniques. Following the development of this North Sea GMPE, the seismogenic source model of Bungum et al. (2000) is updated using an additional two decades of North Sea earthquake observations. The impact of the North Sea GMPE and the updated source model are evaluated using (1) macroseismic earthquake observations and (2) assessment of the seismic risk of offshore infrastructure in the region. The updated PSHA formulation developed within this investigation results in moderate but significant differences in the seismic risk for offshore infrastructure in the North Sea. These seismic risk estimates are potentially more appropriate than those computed using the Bungum et al. (2000) PSHA formulation due to the additional ground-motion data and the PSHA advancements available since the Bungum et al. (2000) PSHA study. Ultimately, the improved seismic hazard estimates potentially help to better assess the structural health of offshore North Sea infrastructure, and subsequently minimise the likelihood of levels of seismic damage which could be detrimental to the North Sea environment or the personnel and/or economies operating within the region

Performance Guarantee of a Class of Continuous LPV System with Restricted-Model-Based Control

This paper considers the problem of the robust stabilisation of a class of continuous Linear Parameter Varying (LPV) systems under specifications. In order to guarantee the stabilisation of the plant with very large parameter uncertainties or variations, an output derivative estimation controller is considered. The design of such controller that guarantee desired  induced gain performance is examined. Furthermore, a simple procedure for achieving the  norm performance is proved for any all-poles single-input/single-output second order plant. The proof of stability is based on the polytopic representation of the closed loop under Lyapunov conditions and system transformations. Finally, the effectiveness of the proposed method is verified via a numerical example

Novel Approaches for Structural Health Monitoring

The thirty-plus years of progress in the field of structural health monitoring (SHM) have left a paramount impact on our everyday lives. Be it for the monitoring of fixed- and rotary-wing aircrafts, for the preservation of the cultural and architectural heritage, or for the predictive maintenance of long-span bridges or wind farms, SHM has shaped the framework of many engineering fields. Given the current state of quantitative and principled methodologies, it is nowadays possible to rapidly and consistently evaluate the structural safety of industrial machines, modern concrete buildings, historical masonry complexes, etc., to test their capability and to serve their intended purpose. However, old unsolved problematics as well as new challenges exist. Furthermore, unprecedented conditions, such as stricter safety requirements and ageing civil infrastructure, pose new challenges for confrontation. Therefore, this Special Issue gathers the main contributions of academics and practitioners in civil, aerospace, and mechanical engineering to provide a common ground for structural health monitoring in dealing with old and new aspects of this ever-growing research field

Reliability based design of marine risers

PhD ThesisThe harsh environment in which offshore structures must operate, their intended service life and the uncertainties inherent to the load processes, have been the impulse for investigation of their reliability. The method most extensively applied for this purpose during the last two decades was the Structural Systems Reliability, which can not be coupled with the finite element method. Therefore the objectives of the present work are to investigate the applicability of a technique which allows the utilization of the reliability analysis methods with a marine riser modelled by the finite element method, FEM, and revision of the reliability levels associated with this riser, including the fatigue life. For these purposes the response surface methodology was selected, among a number of methods. A response surface approach which requires a low number of experiments with the FEM model was elected, calculations for construction of the response surface are further simplified by the assumption of statistical independence among the basic variables. It is demonstrated in the present study that the response surface is capable of producing an equivalent and explicit limit state function which is used at a second stage with the First Order Reliability Method and the Adaptive Importance Sampling simulation technique. However, it was found that the assumption of independence is not always valid. In this case, a method is proposed in which the correlated variables are implicitly considered at the level of the mechanical model. The reliability of the marine riser was reviewed with the proposed algorithms, finding that the validity of the reliability levels depend on the number of basic variables considered and their statistical properties. The significant reduction in required computing time achieved with the response surface methodology allowed parametric studies to be carried out, in order to investigate the impact of different statistical properties of the basic variables. The fatigue reliability case was also investigated with the S-N approach. The introduction of uncertainty in the fatigue life estimation proved that acceptable levels of deterministic fatigue life may render unacceptablelevels of reliability. The uncertainty associated with the stress range is the most significant variable, though the present fatigue reliability formats consider it in a very simplified manner, therefore an approach is suggested with which the stress uncertainty can be considered in a more detailed fashion. However, the algorithm used here for construction of the response surface was unable to produce the required surface. Therefore it is concluded that though the response surface is capable of handling a large number of structural reliability cases, there are instances in which more research efforts are needed.Consejo Nacional de Ciencia y Tecnologia: CONACYT (National Council for Science and Technology): Mexican Government

MARE-WINT: New Materials and Reliability in Offshore Wind Turbine Technology

renewable; green; energy; environment; law; polic

Advances in Intelligent Robotics and Collaborative Automation

This book provides an overview of a series of advanced research lines in robotics as well as of design and development methodologies for intelligent robots and their intelligent components. It represents a selection of extended versions of the best papers presented at the Seventh IEEE International Workshop on Intelligent Data Acquisition and Advanced Computing Systems: Technology and Applications IDAACS 2013 that were related to these topics. Its contents integrate state of the art computational intelligence based techniques for automatic robot control to novel distributed sensing and data integration methodologies that can be applied to intelligent robotics and automation systems. The objective of the text was to provide an overview of some of the problems in the field of robotic systems and intelligent automation and the approaches and techniques that relevant research groups within this area are employing to try to solve them.The contributions of the different authors have been grouped into four main sections:• Robots• Control and Intelligence• Sensing• Collaborative automationThe chapters have been structured to provide an easy to follow introduction to the topics that are addressed, including the most relevant references, so that anyone interested in this field can get started in the area