University of Surrey

Test tubes in the lab Research in the ATI Dance Research

Closed form solution of Eigen frequency of monopile supported offshore wind turbines in deeper waters incorporating stiffness of substructure and SSI

Bhattacharya, S (2016) Closed form solution of Eigen frequency of monopile supported offshore wind turbines in deeper waters incorporating stiffness of substructure and SSI International Journal of Soil Dynamics and Earthquake Engineering, Volume. pp. 18-32.

[img]
Preview
Text
2016_Eigen_value_SSI_Deepwater.pdf - ["content_typename_Published version (Publisher's proof or final PDF)" not defined]
Available under License : See the attached licence file.

Download (1MB) | Preview
[img]
Preview
PDF (licence)
SRI_deposit_agreement.pdf
Available under License : See the attached licence file.

Download (33kB) | Preview

Abstract

Offshore wind turbines (OWTs) are dynamically loaded structures and therefore the estimation of the natural frequency is an important design calculation to avoid resonance and resonance related effects (such as fatigue). Monopiles are currently the most used foundation type and are also being considered in deeper waters (>30 m) where a stiff transition piece will join the monopile and the tapered tall tower. While rather computationally expensive, high fidelity finite element analysis can be carried to find the Eigen solutions of the whole system considering soil–structure interaction; a quick hand calculation method is often convenient during the design optimisation stage or conceptual design stage. This paper proposes a simplified methodology to obtain the first natural frequency of the whole system using only limited data on the WTG (Wind Turbine Generator), tower dimensions, monopile dimensions and the ground. The most uncertain component is the ground and is characterised by two parameters: type of ground profile (i.e. soil stiffness variation with depth) and the soil stiffness at one monopile depth below mudline. In this framework, the fixed base natural frequency of the wind turbine is first calculated and is then multiplied by two non-dimensional factors to account for the foundation flexibility (i.e. the effect of soil–structure interaction). The theoretical background behind the model is the Euler–Bernoulli and Timoshenko beam theories where the foundation is idealised by three coupled springs (lateral, rocking and cross-coupling). 10 wind turbines founded in different ground conditions from 10 different wind farms in Europe (e.g. Walney, Gunfleet sand, Burbo Bank, Belwind, Barrow, Kentish flat, Blyth, Lely, Thanet Sand, Irene Vorrink) have been analysed and the results compared with the measured natural frequencies. The results show good accuracy (errors below 3.5%). A step by step sample calculation is also shown for practical use of the proposed methodology.

Item Type: Article
Subjects : Civil and Environmental Engineering
Divisions : Faculty of Engineering and Physical Sciences > Civil and Environmental Engineering
Authors :
AuthorsEmailORCID
Bhattacharya, SUNSPECIFIEDUNSPECIFIED
Date : 19 January 2016
Identification Number : 10.1016/j.soildyn.2015.12.011
Additional Information : Copyright 2015 The Authors. Published by Elsevier Ltd. This is an open access article published under the CC BY license.
Depositing User : Symplectic Elements
Date Deposited : 02 Feb 2016 15:49
Last Modified : 02 Feb 2016 15:49
URI: http://epubs.surrey.ac.uk/id/eprint/809822

Actions (login required)

View Item View Item

Downloads

Downloads per month over past year


Information about this web site

© The University of Surrey, Guildford, Surrey, GU2 7XH, United Kingdom.
+44 (0)1483 300800