Deformation Analysis of Large Diameter Monopiles of Offshore Wind Turbines under Scour

Abstract

The displacement of monopile supporting offshore wind turbines needs to be strictly controlled, and the influence of local scour can not be ignored. Using p–y curves to simulate the pile–soil interaction and the finite difference method to calculate iteratively, a numerical frame for analysis of lateral loaded pile was discussed and then verified. On the basis of the field data from Dafeng Offshore Wind Farm in Jiangsu Province, the local scour characteristics of large diameter monopile were concluded, and a new method of considering scour effect applicable to large diameter monopile was put forward. The results show that, for scour of large diameter monopiles, there was no obvious scour pit, but local erosion and deposition. Under the test conditions, the displacement errors between the proposed and traditional method were 46.4%. By the proposed method, the p–y curves of monopile considering the scour effect were obtained through ABAQUS, and the deformation of large diameter monopile under scour was analyzed by the proposed frame. The results show that, with the increase of scour depth, the horizontal displacement of the pile head increases nonlinearly, the depth of rotation point moves downward, and both of the changes are related to the load level. Under the test conditions, the horizontal displacement of the pile head after scour could reach 1.4~3.6 times of that before scour. Finally, for different pile parameters, the pile head displacement was compared, and further, the susceptibility to scour was quantified by a proposed concept of scour sensitivity. The analysis indicates that increasing pile length is a more reasonable way than pile diameter and wall thickness to limit the scour effect on the displacement of large diameter pile.

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

“…Its soil-structure interaction modeling techniques have been reviewed by many scholars and extensively used for the analysis and design of OWTs. 17,25,46,[49][50][51][52][53] Although different modeling techniques require different input parameters, the determination of parameters for each model is based on the procedures widely accepted in engineering practice to represent the same physical problem. Therefore, the common goal of each model is the same.…”

“…2,[18][19][20][21] A largediameter (3−10 m) monopile is a common choice for the foundation of modern offshore wind turbines, but the widely used approach (p-y curve method), as specified in American Petroleum Institute (API) guidelines 22 or Det Norske Veritas (DNV) guidelines, 23 may not be suitable for such large piles. [24][25][26] This is because the p-y, t-z, and q-z curves recommended by API or DNV were calibrated against the response of small-diameter (610 mm) slender piles (length-to-diameter ratio of ∼34) for offshore oil and gas structures. The behavior of large monopiles is like rigid body rotation and displacement, 0.0 0.5 which is different from conventional bending piles.…”

“…The construction of wind turbines is found on different foundation types depending on the depth of water, sea bed condition, and turbine rating; however, more than 80% of offshore wind turbines are constructed on a monopile due to their comparatively easy installation and cost‐effectiveness at shallow to moderate water depths (25–40 m) 2,18–21 . A large‐diameter (3−10 m) monopile is a common choice for the foundation of modern offshore wind turbines, but the widely used approach (p‐y curve method), as specified in American Petroleum Institute (API) guidelines 22 or Det Norske Veritas (DNV) guidelines, 23 may not be suitable for such large piles 24–26 . This is because the p‐y, t‐z, and q‐z curves recommended by API or DNV were calibrated against the response of small‐diameter (610 mm) slender piles (length‐to‐diameter ratio of ∼34) for offshore oil and gas structures.…”

Investigation of Offshore Wind Turbine Structure Deflection Using Experimental Work, Numerical, and Theoretical Approach

“…[16] In 2020, Sajjad tested two fixed-type foundations, one of them is monopile, and the other is a jacket [17]. Using (p-y) curves, in 2020, Zhaoyao Wang et al researched rigorously controlling the displacement of monopile offshore wind turbines, not ignoring the influence of local scour [18]. In 2021, Jianhua Zhang et al suggested a method for the dynamic response of offshore structures by combining segmented responses is proposed, which depends on the pole-residue method to calculate those segmented responses.…”

Bearing Capacity of Single Pile-Friction Wheel Composite Foundation on Sand-over-Clay Deposit under V-H-M Combined Loadings

“…This composite foundation is initiated from the concept of pile caps and embedded retaining walls with stabilizing platforms, in which the addition of the circular wheel increases the shear stress and restoring moment against the lateral deflection [13][14][15]. The combined wheel can also be applied as an effective reinforcement for existing monopiles to provide additional bearing capacities and protections of the seabed from circum-pile scouring [15][16][17].…”