Lidija Zdravković

PISA: New Design Methods for Offshore Wind Turbine Monopiles

Improved design of laterally loaded monopiles is central to the development of current and future generation offshore wind farms. Previously established design methods have demonstrable shortcomings requiring new ideas and approaches to be developed, specific for the offshore wind turbine sector. The Pile Soil Analysis (PISA) Project, established in 2013, addresses this problem through a range of theoretical studies, numerical analysis and medium scale field testing. The project completed in 2016; this paper summarises the principal findings, illustrated through examples incorporating the Cowden stiff clay profile, which represents one of the two soil profiles targeted in the study. The implications for design are discussed.

Geotechnical characterization of the Miocene formations at the location of Ivens shaft, Lisbon

The design of complex underground structures in an urban environment requires in the first instance an appropriate characterization and interpretation of the ground conditions and of the mechanical behaviour of soil formations in the ground profile. With such information it is then possible to select and calibrate appropriate soil constitutive models for application in advanced numerical analysis, with the objective of predicting the induced ground movements and the potential damage to existing structures and services. This paper provides an interpretation of the site investigation data collected for the numerical analysis and design of the Ivens shaft excavation in Lisbon, Portugal. For the first time a comprehensive set of interpreted data is obtained for two of the main formations in the Lisbon area, Argilas e Calcários dos Prazeres (AP) and Areolas da Estefânia (AE), improving the understanding of their mechanical behaviour and making the data available for application in most soil constitutive frameworks. It is evident from the results that even with careful testing procedures the data may appear to be inconsistent, requiring further assumptions when deriving soil parameters. Such assumptions are discussed and emphasis is placed on the need to combine data from laboratory and field investigations.

The Effects of Dam–Reservoir Interaction on the Nonlinear Seismic Response of Earth Dams

ABSTRACT The objective of this study is to investigate the effects of dam–reservoir interaction (DRI) on the nonlinear seismic response of earth dams. Although DRI effects have for long been considered as insignificant for earth dams, that conclusion was mainly based on linear elastic investigations which focused only on the acceleration response of the crest without examining the seismic shear stresses and strains within the dam body. The present study explores further the impact of DRI focusing on the nonlinear behavior of earth dams. The effects of reservoir hydrodynamic pressures are investigated in terms of both seismic dam accelerations and nonlinear dynamic soil behavior (seismic shear stresses and strains). It is shown that although dam crest accelerations are indeed insensitive to DRI, the stress and strain development within the dam body can be significantly underestimated if DRI is ignored.

The Implications of Advanced Monopile Design Methodologies in Offshore Wind Turbines

The design of Offshore Wind Turbines (OWT) is a complex process involving several stages: wind turbine selection, tower and sub-structure design, as well as foundation design and installation. A successful design requires close interaction between these components in order to satisfy the main design requirements, namely the capacity and accumulated rotation for the foundation and dynamic response and fatigue for the whole system. Recent research has revealed that the current design methods for laterally loaded piles, when applied to short and stubby OWT monopiles, underestimate their initial stiffness and capacity. Advanced Finite Element (FE) analysis, with realistic modelling of the ground conditions can accurately reproduce soil response around a monopile, and hence improve the design, ultimately leading to cost reduction of monopile foundations. In the present paper, the impact of economies in foundation design on the overall design of a realistic OWT is explored. The NREL 5 MW baseline wind turbine is modelled through FE analysis under several characteristic design load cases. The advantages of using FE analysis when compared to traditional methods, in particular with respect to capacity and dynamic response, are demonstrated and discussed. pitfalls of traditional methods when applied to the design of offshore wind turbine monopiles. To ensure the chosen example is realistic, the main design constraints and realistic sources of information are used, including site conditions, soil characterisation, wind turbine characteristics and industry basis for design. The final objective is to describe a methodology for setting-up integrated models capable of representing the whole wind turbine system. The derived model can then be used for future fatigue assessment and quantification of the response of the wind turbine under varying environmental and operational conditions. Resulting models are able to reproduce accurately the following aspects of the system: the servocontrol of the wind turbine, the dynamic response of the super-structure, hydrodynamic loading and soilstructure interaction.