Seismic responses of monopile-supported offshore wind turbines in soft clays under scoured conditions

Jiang, Wenyu; Lin, Cheng; Sun, Mingyue

doi:10.1016/j.soildyn.2020.106549

Cited by 25 publications

(4 citation statements)

References 54 publications

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“…They naturally occur around structures such as offshore wind turbine foundations, bridges, and piers, compromising their stability and complicating seismic analysis [46]. Scour depth is widely acknowledged as the most significant factor under scoured conditions [69], with limited impacts observed when treating local scour as general scour [70]. Onsite monitoring data (see Figure 5) indicate that a southeastoriented scour hole formed within a 100 m radius of the foundation center, and the scour phenomena were more pronounced within a radius of 36 m. The maximum scour depth relative to the mudline was approximately 6.05 m (0.5 L).…”

Section: Simulation Of Scoured Conditionsmentioning

confidence: 99%

Combined Seismic and Scoured Numerical Model for Bucket-Supported Offshore Wind Turbines

Jia,

Liang,

Shen

et al. 2024

JMSE

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Numerous offshore wind turbines (OWTs) with bucket foundations have been installed in seismic regions. Compared to the relative development of monopiles (widely installed), seismic design guidelines for bucket-supported OWTs still need to be developed. Moreover, scour around bucket foundations induced by water–current actions also creates more challenges for the seismic design of OWTs. In this study, a simplified seismic analysis method is proposed that incorporates the soil–structure interaction (SSI) for the preliminary design of scoured bucket-supported OWTs, aiming to balance accuracy and efficiency. The dynamic SSI effects are represented using lumped parameter models (LPMs), which are developed by fitting impedance functions of the soil–bucket foundation obtained from the four-spring Winkler model. The water–structure interaction is also considered by the added mass in seismic analysis. Based on the OpenSees 3.3.0 platform, an integral model is established and validated using the three-dimensional finite element method. The results indicate that the bucket-supported OWT demonstrates greater dynamic impedance and first-order natural frequency compared to the monopile-supported OWT, which has an increased seismic response. Seismic spectral characteristics and intensities also play an important role in the responses. Additionally, scour can change the bucket impedance functions and the frequency characteristics of the OWT system, leading to a significant alteration in the seismic response. Scour effects may be advantageous or disadvantageous, depending on the spectral characteristics of seismic excitations. These findings provide insights into the seismic response of bucket-supported OWTs under scoured conditions.

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Section: Simulation Of Scoured Conditionsmentioning

confidence: 99%

Combined Seismic and Scoured Numerical Model for Bucket-Supported Offshore Wind Turbines

Jia,

Liang,

Shen

et al. 2024

JMSE

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“…Monopiles in the offshore marine environment are prone to scour. The mechanism is that the soil within a certain area in the vicinity of the pile is washed away by waves and current, reducing the lateral capacity of the pile and changing the structural stiffness and system frequency [3][4][5][6][7][8][9][10][11][12][13][14][15]. Two monopiles at the Robin Rigg wind farm were decommissioned after only six years of operation due to massive unexpected scour, demonstrating the hazard that the active marine environment poses to OWTs [16].…”

Section: Introductionmentioning

confidence: 99%

Scour Effect on the Lateral Bearing Behaviour of Monopiles Considering Different Slenderness Ratios

Li,

Wang,

Gavin

et al. 2024

Water

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Scour leads to the loss of soil around monopile foundations for offshore wind turbines, which affects their structural safety. In this paper, the effect of scour on the lateral behaviour of monopiles was extensively investigated using finite element analysis, and calibration and comparison were undertaken using centrifuge tests. Piles with three slenderness ratios, i.e., 3, 5 and 8, were studied by keeping the diameter constant and varying the embedment length. Three scour types (local narrow, local wide and global) and four scour depths (0.5D, 1D, 1.5D and 2D; D signifies the pile diameter) were considered in this investigation. The results indicate that the lateral resistance of the pile is the greatest in the case of local narrow scour, followed by that in the cases of local wide scour and global scour. When the scour depth is larger than 1D, the influence of the scour type on the pile lateral bearing behaviour is insignificant. The influence of the scour type and scour depth on the pile lateral bearing behaviour is broadly similar for piles with slenderness ratios of 3, 5 and 8. However, the piles featured with smaller embedment lengths show a larger decrease rate in their lateral capacity, which means the effect of scour should cause more concern on small slenderness ratio monopiles.

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“…To meet this requirement, researchers computed the hub-height aerodynamic loads using aero-elastic software and then established a finite element model using the hydro-geotech code USFOS [22,23], where the RNA was also simplified as a concentrated mass. This model has been utilized to investigate the dynamic behavior of OWTs under various loads, such as extreme wind and wave conditions [24], earthquakes [25,26], normal ocean states [27], etc. In summary, rigid blade models have been proposed and improved by researchers.…”

Section: Introductionmentioning

confidence: 99%

Influence of Blade Flexibility on the Dynamic Behaviors of Monopile-Supported Offshore Wind Turbines

Lai,

Li,

et al. 2023

JMSE

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At present, monopole-supported offshore wind turbines (MOWTs) are widely used in offshore wind farms. The influence of blade flexibility on the dynamic behaviors of MOWTs excited by waves and earthquakes was investigated in this study. Numerical analysis models were established for 5 MW and 10 MW MOWTs, incorporating flexible and rigid blade configurations. The modes and natural frequencies of the full system were compared between these two numerical models, and their dynamic responses were evaluated under wave-only and earthquake-only excitations. It was revealed that the influence of blade flexibility on the first- and second-order modes of the system can be neglected. The dynamic response of these MOWTs under wave excitation can be predicted by the rigid blade model, where the maximum relative difference is less than 5%. However, higher-order modes of the system are significantly affected by the blade flexibility. Under high-frequency excitations, these higher-order modes of the system are remarkably stimulated. Additionally, a large relative difference, exceeding 50%, is detected when the rigid blade model is used to predict the seismic response of the two MOWTs. Consequently, the blade flexibility should be adequately modeled when predicting the dynamic response of OWTs.

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Seismic responses of monopile-supported offshore wind turbines in soft clays under scoured conditions

Cited by 25 publications

References 54 publications

Combined Seismic and Scoured Numerical Model for Bucket-Supported Offshore Wind Turbines

Combined Seismic and Scoured Numerical Model for Bucket-Supported Offshore Wind Turbines

Scour Effect on the Lateral Bearing Behaviour of Monopiles Considering Different Slenderness Ratios

Influence of Blade Flexibility on the Dynamic Behaviors of Monopile-Supported Offshore Wind Turbines

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