طراحی تک ستون برای توربین های بادی دریایی
Abstract
1- Introduction
2- Calculation methodology
3- Worked example: design steps using a typical site from the UK
4- Conclusions
References
Abstract
A simplified design procedure for foundations of offshore wind turbines is often useful as it can provide the types and sizes of foundation required to carry out financial viability analysis of a project and can also be used for tender design. This paper presents a simplified way of carrying out the design of monopiles based on necessary data (i.e. the least amount of data), namely site characteristics (wind speed at reference height, wind turbulence intensity, water depth, wave height and wave period), turbine characteristics (rated power, rated wind speed, rotor diameter, cut-in and cut-out speed, mass of the rotor-nacelle-assembly) and ground profile (soil stiffness variation with depth and soil stiffness at one diameter depth). Other data that may be required for final detailed design are also discussed. A flowchart of the design process is also presented for visualisation of the rather complex multi-disciplinary analysis. Where possible, validation of the proposed method is carried out based on field data and references/guidance are also drawn from codes of practice and certification bodies. The calculation procedures that are required can be easily carried out either through a series of spreadsheets or simple hand calculations. An example problem emulating the design of foundations for London Array wind farm is taken to demonstrate the proposed calculation procedure. The data used for the calculations are obtained from publicly available sources and the example shows that the simplified method arrives at a similar foundation to the one actually used in the project.
Introduction
Offshore wind turbines are expected to operate for a lifetime of 20– 30 years, while foundations are often designed for a longer design life. The selection of foundation type and the design is a complex task, which strongly depends not only on the site characteristics, but also on the maturity and track record of different design concepts. As the offshore wind industry is still in an early stage of large scale development, individual projects take a longer time than the rate at which technology advances. As such, it is not uncommon to change the type of turbine and the size/type of foundations during the development phase of a project. Therefore, development consent is typically obtained for a flexible project that allows for optimised detailed design using the most recent technological advances available at the time of final design. Consequently, it is important to have a simplified design procedure that allows for quick design using only limited site and turbine data, and that can be used in the tender design and early design phases of monopile foundations. Naturally, the procedure described in this paper has to be supplemented and refined with more accurate analyses when more information and data about the site conditions (met ocean data, geotechnical conditions) and chosen turbine becomes available. Accordingly, this paper does not aim to provide a methodology for detailed design and optimisation of monopiles but aims to provide a tool for initial design. Most importantly, the paper aims to show the multidisciplinary complex nature of the task. As such, the procedure defines the monopile through a simple geometry that is described by a pile diameter, wall thickness, pile length, and embedded length. Practical issues related to installation and manufacturing are discussed and it may be noted these aspects are beyond the scope of generalised simplified design procedure. However, it is suggested that manufacturing procedures can be taken into account through S-N curves required for typical welds.