Final report for WP4.3: Enhancement of design methods ... - Upwind

Summary
The overall aim of the UpWind project is to facilitate the large-scale implementation of offshore wind
farms across the EU. To achieve this aim, offshore wind farm sites must be bigger and also located in
deeper water. The increase in water depth at these sites means that more complex support structures
are required to resist the increased overturning moments; either braced support structures such as
tripods or jackets, or floating platforms. The increase in number of turbines and greater variability in
ground conditions at these sites means that the rapid processing of many design load calculations and
design iterations is required, for detailed and efficient wind farm design and optimisation. Advances are
needed in terms of cost reduction, upscaling of current technology and increases in reliability.
The objectives of Task 4.3 within UpWind Work Package 4 are to enhance the currently available design
tools and methods for the efficient design of large numbers of structures at deep-water sites, and
to actively support the development of dedicated international standards which specify best practice for
the design of offshore wind farms (e.g. site-specific design, aerodynamic and hydrodynamic impact,
low-risk structures, floating concepts). Therefore this report focuses on the development of integrated
design tools, the benchmarking activities performed for these tools, advanced modelling approaches
and techniques for numerical simulation and the development of design requirements and standards.
In terms of cost, enhancing design tools and methods for the modelling of deep-water support structures
is important because it will enable a more accurate and detailed prediction of loads and dynamic
response. Improved accuracy in prediction will lead to more optimised structures and cost savings. In
this report the development of integrated design tools for both bottom-mounted and floating structures
is presented. Benchmarking activities are also presented for these design tools. These are important
for verifying the accuracy of the codes available to the industry. An advanced technique for modelling
joints in braced support structures, the super-element technique, is presented. The way in which joints
are modelled in space-frame support structures such as jackets and tripods can make a significant
difference to frequencies and loads so accurate modeling of these joints is essential. The development
of advanced modelling techniques for the numerical simulation of aerodynamic, hydrodynamic and
mooring line effects for floating wind turbines are also presented.
In terms of upscaling, a greater efficiency in the design process for complex support structures such as
tripods or jackets will assist with the large-scale implementation of wind farms in deep water at large
offshore sites. In this report recommendations are presented for the implementation of a reduced set of
design load cases for the preliminary design of jacket support structures. A design load case parameter
analysis for jacket support structures is also performed, to test the relative influence of a number
of key design load case parameters affecting offshore wind turbine jacket support structure design.
In terms of reliability, it is important that the international design standards are constantly reviewed and
updated to ensure they are in line with industry best practice. In this report a review of the IEC 61400-3
standard is presented, including recommendations for future editions. A reliability-based calibration of
safety factors for the fatigue design of offshore wind turbine support structures is also performed. Finally,
recommendations are presented for possible extensions to the IEC 61400-3 standard to enable
applicability to floating wind turbines, including the implementation of additional/different design load
cases.
Deliverable D4.3.6: Final report for WP4.3: Design methods and standards
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