Details
| Original language | English |
|---|---|
| Pages (from-to) | 62-73 |
| Number of pages | 12 |
| Journal | Applied Ocean Research |
| Volume | 84 |
| Early online date | 11 Jan 2019 |
| Publication status | Published - Mar 2019 |
Abstract
The eigenfrequency of offshore wind turbine structures is a crucial design parameter, since it determines the dynamic behavior of the structure and with that the fatigue loads for the structural design. For offshore wind turbines founded on monopiles, the rotational stiffness of the monopile-soil system for un- and reloading states strongly affects the eigenfrequency. A numerical model for the calculation of the monopile's behavior under un- and reloading is established and validated by back-calculation of model and field tests. With this model, a parametric study is conducted in which pile geometry, soil parameters and load conditions are varied. It is shown that of course the rotational stiffness varies with mean load and magnitude of the considered un- and reloading span, but that for most relevant load situations the initial rotational stiffness of the monopile system, i.e. the initial slope of the moment-rotation curve for monotonic loading, gives a good estimate of the actual stiffness. Comparisons of different p–y approaches show that the ordinary API approach considerably underestimates the initial stiffness, whereas the recently developed ‘Thieken’ approach and also the ‘Kallehave’ approach give a much better prediction and thus might be used in the design of monopiles in sand.
Keywords
- Eigenfrequency, Monopile, Offshore wind, Stiffness, Un- and reloading
ASJC Scopus subject areas
- Engineering(all)
- Ocean Engineering
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In: Applied Ocean Research, Vol. 84, 03.2019, p. 62-73.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - Un- and reloading stiffness of monopile foundations in sand
AU - Achmus, Martin
AU - Thieken, Klaus
AU - Saathoff, Jann Eike
AU - Terceros, Mauricio
AU - Albiker, Johannes
PY - 2019/3
Y1 - 2019/3
N2 - The eigenfrequency of offshore wind turbine structures is a crucial design parameter, since it determines the dynamic behavior of the structure and with that the fatigue loads for the structural design. For offshore wind turbines founded on monopiles, the rotational stiffness of the monopile-soil system for un- and reloading states strongly affects the eigenfrequency. A numerical model for the calculation of the monopile's behavior under un- and reloading is established and validated by back-calculation of model and field tests. With this model, a parametric study is conducted in which pile geometry, soil parameters and load conditions are varied. It is shown that of course the rotational stiffness varies with mean load and magnitude of the considered un- and reloading span, but that for most relevant load situations the initial rotational stiffness of the monopile system, i.e. the initial slope of the moment-rotation curve for monotonic loading, gives a good estimate of the actual stiffness. Comparisons of different p–y approaches show that the ordinary API approach considerably underestimates the initial stiffness, whereas the recently developed ‘Thieken’ approach and also the ‘Kallehave’ approach give a much better prediction and thus might be used in the design of monopiles in sand.
AB - The eigenfrequency of offshore wind turbine structures is a crucial design parameter, since it determines the dynamic behavior of the structure and with that the fatigue loads for the structural design. For offshore wind turbines founded on monopiles, the rotational stiffness of the monopile-soil system for un- and reloading states strongly affects the eigenfrequency. A numerical model for the calculation of the monopile's behavior under un- and reloading is established and validated by back-calculation of model and field tests. With this model, a parametric study is conducted in which pile geometry, soil parameters and load conditions are varied. It is shown that of course the rotational stiffness varies with mean load and magnitude of the considered un- and reloading span, but that for most relevant load situations the initial rotational stiffness of the monopile system, i.e. the initial slope of the moment-rotation curve for monotonic loading, gives a good estimate of the actual stiffness. Comparisons of different p–y approaches show that the ordinary API approach considerably underestimates the initial stiffness, whereas the recently developed ‘Thieken’ approach and also the ‘Kallehave’ approach give a much better prediction and thus might be used in the design of monopiles in sand.
KW - Eigenfrequency
KW - Monopile
KW - Offshore wind
KW - Stiffness
KW - Un- and reloading
UR - http://www.scopus.com/inward/record.url?scp=85059747875&partnerID=8YFLogxK
U2 - 10.1016/j.apor.2019.01.001
DO - 10.1016/j.apor.2019.01.001
M3 - Article
AN - SCOPUS:85059747875
VL - 84
SP - 62
EP - 73
JO - Applied Ocean Research
JF - Applied Ocean Research
SN - 0141-1187
ER -