Offshore wind turbine monopile foundations: Design perspectives

Abstract Perspectives on design of offshore wind turbine (OWT) monopile foundations are provided in this paper by logically adopting optimal analysis choices with a balance between accuracy and computational efficiency. A newly developed analysis framework is used for this purpose. The analysis framework consists of dynamic analysis with linear viscoelastic soil and static analysis with nonlinear elastic soil. The framework is used to show that the Timoshenko beam theory produces most accurate monopile response although the Euler-Bernoulli beam theory produces optimal results maintaining a balance between accuracy and computational efficiency. The rigid beam theory can be used only under very restricted soil and monopile conditions. The analysis further demonstrates that static analysis is sufficient and optimal in producing monopile-soil stiffness values that can be used for determining the natural frequency of vibration of the OWTs. Moreover, nonlinear elastic analysis is sufficiently accurate and quick to produce monopile responses that can be used in design and there is no need for elasto-plastic analysis. The aspect of cyclic degradation of soil stiffness over the design life of monopiles is not considered. Thus, an optimal pathway for monopile design is described using the newly developed analysis framework and demonstrated through a design example.

[1]  Subhamoy Bhattacharya,et al.  Vibrations of wind-turbines considering soil-structure interaction , 2011 .

[2]  Rodrigo Salgado,et al.  A Continuum-Based Model for Analysis of Laterally Loaded Piles in Layered Soils , 2009 .

[3]  B. K. Gupta.  Soil-Structure Interaction Analysis of Monopile Foundations Supporting Offshore Wind Turbines , 2018 .

[4]  B. K. Gupta,et al.  Analysis of laterally loaded short and long piles in multilayered heterogeneous elastic soil , 2017 .

[5]  Byron W. Byrne,et al.  Response of stiff piles to random two-way lateral loading , 2010 .

[6]  Kerstin Lesny,et al.  Design aspects of monopiles in German offshore wind farms , 2005 .

[8]  Subhamoy Bhattacharya,et al.  Experimental validation of soil–structure interaction of offshore wind turbines , 2011 .

[9]  Dan Kallehave,et al.  Optimization of monopiles for offshore wind turbines , 2015, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences.

[10]  Martin Achmus,et al.  Behavior of monopile foundations under cyclic lateral load , 2009 .

[11]  Min Yang,et al.  Numerical study on accumulated deformation of laterally loaded monopiles used by offshore wind turbine , 2018, Bulletin of Engineering Geology and the Environment.

[12]  Vicente Negro,et al.  Offshore Wind Foundation Design: Some Key Issues , 2015 .

[13]  W. D. Liam Finn,et al.  Dynamic elastic analysis of pile foundations using finite element method in the frequency domain , 1997 .

[14]  Domenico Lombardi.  Dynamics of Offshore Wind Turbines , 2010 .

[15]  Paul Doherty,et al.  Laterally loaded monopile design for offshore wind farms , 2012 .

[16]  H. Matlock.  Correlation for Design of Laterally Loaded Piles in Soft Clay , 1970 .

[17]  M. Randolph,et al.  The response of flexible piles to lateral loading , 1981 .

[18]  Ole Hededal,et al.  Effect of load eccentricity and stress level on monopile support for offshore wind turbines , 2014 .

[19]  George Mylonakis,et al.  Elastodynamic model for large-diameter end-bearing shafts , 2001 .

[20]  Garrad Hassan,et al.  THRUST COEFFICIENTS USED FOR ESTIMATION OF WAKE EFFECTS FOR FATIGUE LOAD CALCULATION , 2010 .

[21]  Kul Bhushan,et al.  Closure of "Lateral Load Tests on Drilled Piers in Stiff Clays" , 1979 .

[22]  Søren Peder Hyldal Sørensen,et al.  Effects of Diameter on Initial Stiffness of P-Y Curves for Large-Diameter Piles in Sand , 2010 .

[23]  Subhamoy Bhattacharya,et al.  Design of monopiles for offshore wind turbines in 10 steps , 2017 .

[24]  G. Houlsby,et al.  Rigid pile response to cyclic lateral loading: laboratory tests , 2019, Géotechnique.

[25]  Pablo Cuéllar,et al.  Pile foundations for offshore wind turbines: Numerical and experimental investigations on the behaviour under short-term and long-term cyclic loading , 2011 .

[26]  Milos Novak,et al.  Soil-pile interaction in horizontal vibration , 1977 .

[27]  Bipin K. Gupta,et al.  Analysis of laterally loaded rigid monopiles and poles in multilayered linearly varying soil , 2016 .

[28]  P. R. Vaughan,et al.  Clay-interface shear resistance , 2000 .

[29]  Subhamoy Bhattacharya,et al.  Dynamic Analysis of Wind Turbine Towers on Flexible Foundations , 2012 .

[30]  D. Basu,et al.  Applicability of Timoshenko, Euler–Bernoulli and rigid beam theories in analysis of laterally loaded monopiles and piles , 2017, Géotechnique.

[31]  Byron W. Byrne,et al.  Response of stiff piles in sand to long-term cyclic lateral loading , 2010 .

[32]  K. Gavin,et al.  3D FEM approach for laterally loaded monopile design , 2018, Computers and Geotechnics.

[33]  Masoud Shadlou,et al.  Dynamic stiffness of monopiles supporting offshore wind turbine generators , 2016 .

[34]  Martin Achmus,et al.  Finite Element Modelling of Horizontally Loaded Monopile Foundations for Offshore Wind Energy Converters in Germany , 2005 .

[35]  Bipin K. Gupta,et al.  Response of laterally loaded rigid monopiles and poles in multi-layered elastic soil , 2016 .

[36]  Timoshenko Beam Theory–Based Dynamic Analysis of Laterally Loaded Piles in Multilayered Viscoelastic Soil , 2018, Journal of Engineering Mechanics.

[37]  M. B. Zaaijer,et al.  Foundation modelling to assess dynamic behaviour of offshore wind turbines , 2006 .

[38]  Subhamoy Bhattacharya,et al.  A Critical Review of Serviceability Limit State Requirements for Monopile Foundations of Offshore Wind Turbines , 2015 .

[39]  Varun,et al.  A simplified model for lateral response of large diameter caisson foundations—Linear elastic formulation , 2009 .

[40]  Lidija Zdravković,et al.  New design methods for large diameter piles under lateral loading for offshore wind applications , 2015 .

[41]  Malcolm D. Bolton,et al.  Stiffness of sands through a laboratory test database , 2013 .

[42]  L. Reese,et al.  Analysis of Laterally Loaded Piles in Sand , 1974 .

[43]  Harry G. Poulos,et al.  Pile foundation analysis and design , 1980 .

[44]  G. Cowper.  The Shear Coefficient in Timoshenko’s Beam Theory , 1966 .

[45]  Ren-peng Chen,et al.  Experimental and Analytical Models of Laterally Loaded Rigid Monopiles with Hardening p–y Curves , 2015 .

[46]  E. Alderlieste.  Experimental modelling of lateral loads on large diameter mono-pile foundations in sand , 2011 .

[47]  Martin Achmus,et al.  Minimum Embedded Length of Cyclic Horizontally Loaded Monopiles , 2012 .

[48]  P. J. Vardanega,et al.  Stiffness of clays and silts: Normalizing shear modulus and shear strain , 2013 .