Influence of model parameters on the design of large diameter monopiles for multi‐megawatt offshore wind turbines at 50‐m water depths

Wind Energy ◽  
2019 ◽  
Vol 22 (6) ◽  
pp. 794-812 ◽  
Author(s):  
Wilfried Njomo‐Wandji ◽  
Anand Natarajan ◽  
Nikolay Dimitrov
Keyword(s):  
Wind Turbines ◽  
Large Diameter ◽  
Offshore Wind ◽  
Model Parameters ◽  
Offshore Wind Turbines ◽  
Water Depths

scholarly journals Dynamic Impedances of Offshore Rock-Socketed Monopiles

2019 ◽  
Vol 7 (5) ◽  
pp. 134 ◽  
Author(s):  
Rui He ◽  
Ji Ji ◽  
Jisheng Zhang ◽  
Wei Peng ◽  
Zufeng Sun ◽  
...  
Keyword(s):  
Numerical Model ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Dynamic Stiffness ◽  
Large Diameter ◽  
Offshore Wind ◽  
Offshore Wind Turbines ◽  
Thin Walled ◽  
Rock Parameters ◽  
Radiative Damping

With the development of offshore wind energy in China, more and more offshore wind turbines are being constructed in rock-based sea areas. However, the large diameter and thin-walled steel rock-socketed monopiles are very scarce at present, and both the construction and design are very difficult. For the design, the dynamic safety during the whole lifetime of the wind turbine is difficult to guarantee. Dynamic safety of a turbine is mostly controlled by the dynamic impedances of the rock-socketed monopile, which are still not well understood. How to choose the appropriate impedances of the socketed monopiles so that the wind turbines will neither resonant nor be too conservative is the main problem. Based on a numerical model in this study, the accurate impedances are obtained for different frequencies of excitation, different soil and rock parameters, and different rock-socketed lengths. The dynamic stiffness of monopile increases, while the radiative damping decreases as rock-socketed depth increases. When the weathering degree of rock increases, the dynamic stiffness of the monopile decreases, while the radiative damping increases.

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

2020 ◽  
Vol 10 (21) ◽  
pp. 7579
Author(s):  
Zhaoyao Wang ◽  
Ruigeng Hu ◽  
Hao Leng ◽  
Hongjun Liu ◽  
Yifan Bai ◽  
...  
Keyword(s):  
Wind Turbines ◽  
Wind Farm ◽  
Large Diameter ◽  
Horizontal Displacement ◽  
Local Scour ◽  
Offshore Wind ◽  
Deformation Analysis ◽  
Pile Head ◽  
Offshore Wind Turbines ◽  
Test Conditions

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.

WindFloat: A Floating Foundation for Offshore Wind Turbines—Part I: Design Basis and Qualification Process

2009 ◽  
Author(s):  
Dominique Roddier ◽  
Christian Cermelli ◽  
Alla Weinstein
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Oil And Gas ◽  
Large Diameter ◽  
Offshore Wind ◽  
Site Location ◽  
Offshore Wind Turbines ◽  
Design Basis ◽  
Floating Foundation ◽  
Visual Impacts

This paper and the corresponding hydrodynamic and structural study paper (also in these proceedings) summarize the feasibility study conducted for the WindFloat technology. The WindFloat is a 3-legged floating foundation for very large offshore wind turbines. It is designed to accommodate a wind turbine, 5 MW or larger, on one of the columns of the hull with minimal modifications to the tower, nacelle and turbine. Technologies for floating foundations for offshore wind turbines are evolving. It is agreed by most experts that the offshore wind industry will see a significant increase in activity in the near future. Fixed offshore turbines are limited in water depth to approximately 30∼50m. Market transition to deeper waters is inevitable, provided suitable technologies can be developed. Despite the increase in complexity, a floating foundation offers distinct advantages: • Flexibility in site location. • Access to superior wind resources further offshore. • Ability to locate in coastal regions with limited shallow continental shelf. • Ability to locate further offshore to eliminate visual impacts. • An integrated structure, without a need to redesign the mast foundation connection for every project. • Simplified offshore installation procedures. Anchors are significantly cheaper to install than fixed foundations and large diameter towers. This paper focuses on the design basis for wind turbine floating foundations, and explores the requirements that must be addressed by design teams in this new field. It shows that the design of the hull for a large wind turbine must draw on the synergies with oil and gas offshore platform technology, while accounting for the different design requirements and functionality of the wind turbine.

Pore-Pressure Accumulation and Soil Softening Around Pile Foundations for Offshore Wind Turbines

2012 ◽  
Author(s):  
Pablo Cuéllar ◽  
Matthias Baeßler ◽  
Werner Rücker
Keyword(s):  
Cyclic Loading ◽  
Pore Water ◽  
Wind Turbines ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Large Diameter ◽  
Constitutive Law ◽  
Offshore Wind ◽  
External Loading ◽  
Offshore Wind Turbines

The foundation of offshore wind turbines usually involves the installation of large-diameter steel piles in the seabed, either in monopile or multi-pile configurations (jacket, tripod, etc…), which have to ensure a proper fixity of the turbine during its whole service life-time. However, such foundations raise several challenges and novel questions, partly due to the special characteristics of the offshore environment (for instance, the large numbers of load cycles from wind and waves and the possible influence of transient changes of pore water pressure around the pile) and aggravated by their large diameter, reduced slenderness and elevated ratio of lateral to vertical loads (see Fig. 1). This paper studies the effects of cyclic lateral loading on the offshore piles focusing on the possibility of a progressive accumulation of residual pore water pressure within the saturated embedding soil. As it will be shown, this can lead to significant changes of their behaviour under external loading, which can potentially compromise the foundation’s stability or serviceability. The paper will also analyse some singular effects of an irregular loading (e.g. cyclic loading with variable amplitude), in particular the so-called “order effects” and the phenomena arising during a realistic storm of moderate magnitude, and discuss their potential for transient damages to the foundation’s stiffness. All these phenomena, which can lead to a loss of serviceability of the structure, have been investigated by the authors by means of a coupled bi-phasic analytical model of the offshore foundation featuring a versatile constitutive law suitable for the soil. The constitutive model, in the frame of the theory of Generalized Plasticity, can reproduce some complex features of cyclic soil behaviour such as the tendency for a progressive densification under cyclic loading, which is responsible for the soil liquefaction phenomena in undrained conditions. Finally, some implications of these issues for the practical design of offshore monopiles will be discussed and some specific recommendations for the design procedures will be outlined.

Installation of Monopiles for Offshore Wind Turbines—By Using End-Caps and a Subsea Holding Structure

2011 ◽  
Author(s):  
Arunjyoti Sarkar ◽  
Ove T. Gudmestad
Keyword(s):  
Wind Turbines ◽  
Offshore Wind ◽  
Intermediate Water ◽  
Offshore Wind Turbines ◽  
Correct Location ◽  
End Caps ◽  
Jack Up ◽  
Basic Philosophy ◽  
Water Depths ◽  
Design Challenges

Monopiles are commonly used as foundations for offshore wind turbines at sites with shallow to intermediate water depths (say, up to 40m water depth). The installation of a monopiles is normally carried out by using a bottom supported platform (e.g., a jack-up vessel) which holds the pile at the correct location vertically while driving it into the seabed. In this paper, a methodology for installing a monopile is described which can be applied either by a bottom supported platform or by a floating vessel. The basic philosophy behind this methodology is to support the monopile initially by buoyancy and then by a subsea holding structure. Thus the requirement for a large crane working offshore is eliminated and the marine operation is no longer dependent on the motions of the supporting vessel. Brief geotechnical calculations are presented to support the feasibility of this methodology. Some of the possible design challenges of the installation aids are listed in the conclusion.

scholarly journals Dynamic Response of Articulated Offshore Wind Turbines under Different Water Depths

Energies ◽  
2020 ◽  
Vol 13 (11) ◽  
pp. 2784
Author(s):  
Pei Zhang ◽  
Shugeng Yang ◽  
Yan Li ◽  
Jiayang Gu ◽  
Zhiqiang Hu ◽  
...  
Keyword(s):  
Dynamic Response ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Dynamic Responses ◽  
Wind Pressure ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Offshore Area ◽  
Offshore Wind Turbines ◽  
Water Depths

Focusing on the transitional depth offshore area from 50 m to 75 m, types of articulated foundations are proposed for supporting the NREL 5 MW offshore wind turbine. To investigate the dynamic behaviors under various water depths, three articulated foundations were adopted and numerical simulations were conducted in the time domain. An in-house code was chosen to simulate the dynamic response of the articulated offshore wind turbine. The aerodynamic load on rotating blades and the wind pressure load on tower are calculated based on the blade element momentum theory and the empirical formula, respectively. The hydrodynamic load is simulated by 3D potential flow theory. The motions of foundation, the aerodynamic performance of the wind turbine, and the loads on the articulated joint are documented and compared in different cases. According to the simulation, all three articulated offshore wind turbines show great dynamic performance and totally meet the requirement of power generation under the rated operational condition. Moreover, the comparison is based on time histories and spectra among these responses. The result shows that dynamic responses of the shallower one oscillate more severely compared to the other designs.

scholarly journals Air-Floating Characteristics of Large-Diameter Multi-Bucket Foundation for Offshore Wind Turbines

Energies ◽  
2019 ◽  
Vol 12 (21) ◽  
pp. 4108 ◽  
Author(s):  
Xianqing Liu ◽  
Puyang Zhang ◽  
Mingjie Zhao ◽  
Hongyan Ding ◽  
Conghuan Le
Keyword(s):  
Wind Turbines ◽  
Large Diameter ◽  
Added Mass ◽  
State Equation ◽  
Offshore Wind ◽  
Alternative Form ◽  
Bucket Foundation ◽  
Offshore Wind Turbines ◽  
Damping Characteristics ◽  
Oscillating Motion

In the present study, as a novel and alternative form of foundation for offshore wind turbines, the air-floating characteristics of a large-diameter multi-bucket foundation (LDMBF) in still water and regular waves are investigated. Following the theory of single degree of freedom (DOF)-damped vibration, the equations of oscillating motion for LDMBF are established. The spring or restoring coefficients in heaving, rolling and pitching motion are modified by a dimensionless parameter ϑ related to air compressibility in every bucket with the ideal air state equation. Combined with the 1/25 scale physical model tests and the numerically simulated prototype models by MOSES, the natural periods, added mass coefficients and damping characteristics of the LDMBF in free oscillations and the response amplitude operator (RAO) have been investigated. The results shown that the added mass coefficients between 1.2 and 1.6 is equal to or larger than the recommended values for ship dynamics. The coefficient 1.2 can be taken as the lower limit 1.2 for a large draft and 1.6 can be taken as the upper limit 1.6 for a small draft. The resonant period and maximum amplitudes for heaving and pitching motions decrease with increasing draft. The amplitudes of heaving and pitching movements decrease to a limited extent with decreasing water depth.

scholarly journals Design and Experiment of a Lifting Tool for Hoisting Offshore Single-Pile Foundations

Machines ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 29
Author(s):  
Bo Zhang ◽  
Hexuan Chen ◽  
Tao Wang ◽  
Zhuo Wang
Keyword(s):  
Wind Turbines ◽  
Large Diameter ◽  
Offshore Wind ◽  
Single Pile ◽  
Dynamics Analysis ◽  
Clamping Force ◽  
Force Analysis ◽  
Practical Applications ◽  
Offshore Wind Turbines ◽  
Application Requirements

Experiments with a cam-type clamp tool were carried out to overcome the difficulty of transporting and installing large-diameter mono-piles for offshore wind turbines. Using the experiments method to design a small wedge-type clamping mechanism and using cam teeth made of 40Cr material resulted in the maximum friction for the mechanism. A single clamping design was created for the cam-type clamp tool to hoist mono-piles for offshore wind turbines. Through force analysis and Automatic Dynamics Analysis of Mechanical System (ADAMS) dynamic simulation of the lifting tool, it was calculated that the clamping force of the lifting tool meets application requirements. A prototype was built in order to carry out an experiment in which the lifting tool hoisted a mono-pile. It was concluded from the experiment that the proposed design of the lifting tool is feasible in practical applications.

Implied Reliability Levels in Different Load Models for Offshore Wind Turbines

2014 ◽  
Author(s):  
P. Agarwal ◽  
L. Manuel
Keyword(s):  
Wind Turbines ◽  
Large Diameter ◽  
Offshore Wind ◽  
International Electrotechnical Commission ◽  
Wave Loads ◽  
Support Structures ◽  
Wave Load ◽  
Load Effect ◽  
Offshore Wind Turbines ◽  
Inertia Forces

Assuring uniform reliability levels across various system configurations is the intent of design standards based on the Load and Resistance Factor Design (LRFD) methodology. One such design standard for offshore wind turbines developed by the International Electrotechnical Commission was based on the European experience and may not necessarily represent conditions suited for U.S. waters where several offshore wind energy projects are being planned. It is, hence, of interest to investigate how uniform is the reliability of offshore wind turbines under various levels of wind and wave loads. We assess the reliability of bottom-supported offshore wind turbines in ultimate limit states associated with the fore-aft tower bending moment at the mudline. We compare reliability index estimates for different characteristic load definitions and assumed coefficients of variation for wind and wave loads, as well as for various hydrodynamic to aerodynamic load influences. Effectively, such variations serve to describe different sites and turbine designs. Since large-diameter monopile support structures are dominated by inertia forces, while jacket or tripod support structures with smaller diameter members are dominated by drag forces, we extend an available combined wind-wave load effect model for offshore wind turbines, to include both drag and inertia forces. We show that reasonably uniform reliability levels may be achieved for various combinations of wind and wave loads. Results suggest that drag-dominated wave load cases result in smaller and less uniform reliability estimates than is the case for inertia-dominated wave load cases.

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