Energy Equipment and Systems

Energy Equipment and Systems

Impact driving-induced stress amplification due to flange waviness in offshore wind turbine monopile foundations

Document Type : Research Paper

Author
Mehdi Shirani
Research Institute for Subsea Science and Technology, Isfahan University of Technology, 8415683111, Isfahan, Iran
10.22059/ees.2025.2054188.1504
Abstract
Impact pile driving is the preferred installation method for offshore wind monopile (MP) foundations. Due to the flange waviness, the MP wall stresses below the waviness apexes are larger during impact pile driving than in other areas. In recent designs of 3XL TP-Less monopiles, the door hole is relocated from the tower to the MP, positioned close to the flange, and the boat landing platform is eliminated. This required the door opening stiffeners and other MP internal attachments to be welded close to the flange. It is generally recommended to avoid positioning the MP wall openings and attachments in the highly stressed areas created by the flange waviness. This study aims to calculate the waviness effects on the MP wall stresses of a 3XL MP and to determine the distance from the flange at which this waviness effect disappears. Pile driving is simulated using the finite element software LS-DYNA, and flange waviness is modelled. It was found that for the studied 3XL MP weighing 2160 tons, at 60 mm below the flange, the MP wall Von Mises stress is 253 MPa at the waviness apex and 140 MPa at the waviness valley, representing an 80% increase. The flange waviness effect on the MP wall stresses gradually decreases as one moves away from the flange and diminishes 2600 mm below the flange.
Keywords
3XL MP
TP-Less Design
Impact Driving
Flatness Tolerance
Flange Waviness
Fatigue
LS-DYNA

Subjects

[1] Kurstjens M, Erents, S, Considerations when moving to tp-less. Pros and cons of tp-less monopiles ;2022.
[2] Memija A, First tp-less monopiles in place at Orsted german offshore wind projects, 2023.
[3] HSD-System, Offnoise-solutions, 2024.
[4] Offshorewind.biz, Hydrohammer s-4000 installs first monopiles, 2016.
[5] Randolph M. Analysis of the dynamics of pile driving.  Advanced geotechnical analyses: CRC Press; 1991. p. 233-82.
[6] Li Y, Li J, Shi W, Li X, Wang B. Analysis of the dynamic characteristics of the top flange pile driving process of a novel monopile foundation without a transition section. Sustainability. 2022;14(10):5950.
[7] Orlando M, Ligthart J, van Wijk J, Raymackers S. PDA measurements: fact or fiction. 11th International Conference on Stress Wave Theory and Design and Testing Methods for Deep Foundations; 2022.
[8] Seidel M, Wegener F, van Dijk I. Influence of flange dimensions and geometrical imperfections on stress concentrations at welded flange necks. Stahlbau. 2020;89(11):932-43.
[9] Jorgensen J, Hodkiewicz M, Cripps E, Hassan GM, editors. An open-source analysis workflow for geometrically imperfect bolted ring-flanges in wind turbine support structures. Journal of Physics: Conference Series; 2024: IOP Publishing.
[10] K. U. MANUAL, Ls-dyna, 1992.
[11] Durstewitz M, Lange B, Schuldt L, Spriestersbach S. Document Control Sheet. 2017.
[12] Bartminn D, Griesshaber T, Lüddecke F, Al Otaibi W, Wirth R. Gerammte Ringflanschverbindungen von Monopfahlgründungen: FE‐basierte Sensitivitätsanalysen im Vergleich mit Messergebnissen während der Installation. Stahlbau. 2016;85(9):591-603.
[13] Seidel M. Tolerance requirements for flange connections in wind turbine support structures. Stahlbau. 2018;87(9):880-7.
[14] Seidel M, Faber T. Zur bemessungs-und fertigungspraxis geschraubter ringflanschverbindungen bei windenergieanlagen. Deutsches Institut für Bautechnik Mitteilungen. 2008;39(3):90.
[15] Dnv G. DNVGL-ST-0126: Support structures for wind turbines. Oslo, Norway: DNV GL. 2016;632.
[16] Orlando M, Ligthart J, Wijk J. V, Schaap M, Pile installation fatigue damage from impact driving records a case study of offshore monopiles, in: Conference on Foundation Decarbonization and Re-use, Amsterdam, 2023.
[17] Ling C, Wang L, Kan C-D, Yang C. Thermal–Electrical–Mechanical Coupled Finite Element Models for Battery Electric Vehicle. Machines. 2024;12(9):596
Energy Equipment and Systems
Volume 13, Issue 4 - Serial Number 4
Autumn 2025
Pages 403-414