Static impedance functions for monopiles supporting offshore wind turbines in nonhomogeneous soils-emphasis on soil/monopile interface characteristics

Abed, Younes; Bouzid, Djillali Amar; Bhattacharya, Subhamoy; Aissa, Mohammed Hemza

doi:10.12989/eas.2016.10.5.1143

Cited by 19 publications

(9 citation statements)

References 24 publications

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“…In this simplified framework a three springs approach (see Figure 8) is suggested to take into account the foundation stiffness following Zaaijer (2006) Abed et al (2016). Figure 8 shows the definition of the foundation stiffness which is shown by (vertical stiffness), (Lateral stiffness) (Rocking stiffness) and (Cross-Coupling).…”

Section: Foundation Stiffness Of Monopilesmentioning

confidence: 99%

Design of monopiles for offshore wind turbines in 10 steps

Arany

Bhattacharya

Macdonald

et al. 2017

Soil Dynamics and Earthquake Engineering

306

157

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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 -upper limit of the 1P frequency range -fixed base (cantilever beam) natural frequency of the tower -characteristic yield strength -gravitational constant -distance from zero shear force location to pile toe -air gap between the highest expected wave crest level and the platform -wave number 0 -equivalent stiffness of first tower mode ℎ -horizontal modulus of subgrade reaction -total structural mass, also strain accumulation exponent 0 -equivalent mass of first tower mode -mass of the pile -mass of the rotor-nacelle assembly -mass of the tower -mass of the transition piece ℎ -horizontal coefficient of subgrade reaction ℎ1 -coefficient of subgrade reaction at the first load cycle ℎ -coefficient of subgrade reaction after N load cycles -shape parameter of Weibull distribution -undrained shear strength of soil , , -time, also degradation parameters degradation model -grout thickness -pile wall thickness -tower wall thickness -wall thickness of the transition piece -transition piece wall thickness -turbulent wind speed component -extreme gust speed ,

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Section: Foundation Stiffness Of Monopilesmentioning

confidence: 99%

Design of monopiles for offshore wind turbines in 10 steps

Arany

Bhattacharya

Macdonald

et al. 2017

Soil Dynamics and Earthquake Engineering

306

157

View full text Add to dashboard Cite

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“…These figures depict the effects of ln(E eq /E s ) and L p /D on K L /(E s D), K LR /(E s D 2 ), and K LR /(E s D 3 ) for steel monopiles, considering t = 0.01D and v s = 0.30 in 3-D version. The results are compared with closed-form solutions from Randolph [13], Shadlou et al [20], Higgins et al [19], and Abed et al [29] presented in Tables 1 and 2.…”

Section: Validation Of the Analysis Compared Against Different Methodsmentioning

confidence: 99%

The Simplified Method of Head Stiffness Considering Semi-Rigid Behaviors of Deep Foundations in OWT Systems

Li,

Wang

et al. 2024

Buildings

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Simplified methods of static free head stiffness of the semi-rigid foundation under lateral loads were limited to flexible or rigid behavior by the critical length of piles. This would lead to errors when predicting the static or dynamic performance of their upper structures in OWT Systems. This paper presents a comprehensive analysis of the head static stiffness of the semi-rigid pile without considering the critical length. Firstly, case studies using the energy-based variational method encompassing nearly twenty thousand cases were conducted. These cases involved different types of foundations, including steel pipe piles and concrete caissons, in three types of soil: homogeneous soil, linearly inhomogeneous soil, and heterogeneous soil. Through the analysis of these cases, a series of polynomial equations of three kinds of head static stiffness, containing the relative stiffness of the pile and soil, the slenderness ratio, and Poisson’s ratio, were developed to capture the semi-rigid behavior of the foundations. Furthermore, the lateral deflection, the rotation for concrete caissons in the bridge projects, and several natural frequencies of three cases about the OWT system considering the SSI effect were carried out. the error of high-order frequency of the OWT system reached 13% after considering the semi-rigid effect of the foundation.

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“…There are several formulations to calculate the stiffness coefficient. 31,58,59 However, all the formulations were verified based on a fundamental natural frequency only. As the primary aim of this study is to investigate higher mode effects, the monopile head stiffness is estimated using the expressions of Gazetas (1991), 31 which have been commonly used in practice.…”

Section: 𝐹 = [𝐾mentioning

confidence: 99%

“…The Lump Spring model is based on the monopile head stiffness at the mudline level. There are several formulations to calculate the stiffness coefficient 31,58,59 . However, all the formulations were verified based on a fundamental natural frequency only.…”

Section: Fem Model Of Owtmentioning

confidence: 99%

Importance of higher modes for dynamic soil structure interaction of monopile‐supported offshore wind turbines

Sah,

Yang

2024

Earthq Engng Struct Dyn

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Offshore wind turbines (OWTs) have emerged as one of the most sustainable and renewable sources of energy. The size of OWTs has been increasing, which creates more challenges in the design of foundations due to the potential higher‐mode effects involved in the dynamic soil‐structure interaction (DSSI) response. Several foundation modeling techniques are available for calculating the OWT fundamental frequency; however, their capability to predict the higher modes by considering real geometric configurations is unclear. The main aim of this study is to perform a rigorous modal analysis of the NREL 5MW reference OWT to investigate the higher mode effects using the 3D finite element method. A detailed parametric analysis is also performed to study the effects of soil inhomogeneity, initial soil modulus, and the monopile dimensions (diameter, thickness, and embedded pile depth) on higher modes' natural frequencies and effective mass participation ratios. The study shows that dynamic soil‐structure interaction has a significant role in modal response and the simplified foundation models are not accurate enough. Given the significant contribution from higher modes, they should not be simply ignored in the OWT design, particularly in earthquake‐prone zones.

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Static impedance functions for monopiles supporting offshore wind turbines in nonhomogeneous soils-emphasis on soil/monopile interface characteristics

Cited by 19 publications

References 24 publications

Design of monopiles for offshore wind turbines in 10 steps

Design of monopiles for offshore wind turbines in 10 steps

The Simplified Method of Head Stiffness Considering Semi-Rigid Behaviors of Deep Foundations in OWT Systems

Importance of higher modes for dynamic soil structure interaction of monopile‐supported offshore wind turbines

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