scholarly journals The advanced p-y method for analyzing the behaviour of large-diameter monopiles supporting offshore wind turbines

2020 ◽  
Vol 205 ◽  
pp. 12008
Author(s):  
William F Van Impe ◽  
Shin-Tower Wang
Keyword(s):  
Wind Turbine ◽  
Large Diameter ◽  
Offshore Structures ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Response Curves ◽  
Current Design ◽  
Jacket Structures ◽  
Load Tests ◽  
Offshore Industry

The analyses of monopile foundations have been heavily based on the p-y response curves (to represent lateral soil resistances) published by API RP 2GEO (2011) and DNV (2013), which are proven reliable and applicable for piles with smaller diameters that were normally used for jacket structures in the offshore industry. However, concerns have been raised about the validity of semi-empirical p-y criteria for large-diameter piles. Wind turbine monopiles have a significantly larger diameter and smaller length to diameter ratio than typical piles used for offshore structures. The ratio of the length to the diameter for a monopile typically is also significantly smaller than those used in the API load tests. Therefore, the response of a monopile may be more like a rigid rotation, with components of resistance mobilized at the tip and axially along the sides as it rotates. This behaviour is in contrast to long slender piles that respond to lateral loading in bending rather than rotation. The objective of this paper is to analyze the factors that may contribute to the apparent conservatism in the current design practice for large-diameter monopile foundations and to provide improved solutions on how to analyze and design the large-diameter monopiles for offshore wind turbine using the p-y method.

Experimental Investigation on the Dynamic Response of a Three Legged Articulated Type Offshore Wind Tower

2016 ◽  
Author(s):  
Chinsu Mereena Joy ◽  
Anitha Joseph ◽  
Lalu Mangal
Keyword(s):  
Dynamic Response ◽  
Wind Turbine ◽  
Renewable Energy Sources ◽  
Offshore Structures ◽  
Dynamic Responses ◽  
Offshore Wind ◽  
Experimental Investigations ◽  
Offshore Wind Turbine ◽  
Ocean Engineering ◽  
Study Results

Demand for renewable energy sources is rapidly increasing since they are able to replace depleting fossil fuels and their capacity to act as a carbon neutral energy source. A substantial amount of such clean, renewable and reliable energy potential exists in offshore winds. The major engineering challenge in establishing an offshore wind energy facility is the design of a reliable and financially viable offshore support for the wind turbine tower. An economically feasible support for an offshore wind turbine is a compliant platform since it moves with wave forces and offer less resistance to them. Amongst the several compliant type offshore structures, articulated type is an innovative one. It is flexibly linked to the seafloor and can move along with the waves and restoring is achieved by large buoyancy force. This study focuses on the experimental investigations on the dynamic response of a three-legged articulated structure supporting a 5MW wind turbine. The experimental investigations are done on a 1: 60 scaled model in a 4m wide wave flume at the Department of Ocean Engineering, Indian Institute of Technology, Madras. The tests were conducted for regular waves of various wave periods and wave heights and for various orientations of the platform. The dynamic responses are presented in the form of Response Amplitude Operators (RAO). The study results revealed that the proposed articulated structure is technically feasible in supporting an offshore wind turbine because the natural frequencies are away from ocean wave frequencies and the RAOs obtained are relatively small.

scholarly journals Reliability analysis of offshore wind turbine foundations under lateral cyclic loading

2020 ◽  
Vol 5 (4) ◽  
pp. 1521-1535
Author(s):  
Gianluca Zorzi ◽  
Amol Mankar ◽  
Joey Velarde ◽  
John D. Sørensen ◽  
Patrick Arnold ◽  
...  
Keyword(s):  
Cyclic Loading ◽  
Wind Turbine ◽  
Limit State ◽  
Large Diameter ◽  
Probabilistic Approach ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Fe Model ◽  
Foundation Design

Abstract. The design of foundations for offshore wind turbines (OWTs) requires the assessment of long-term performance of the soil–structure interaction (SSI), which is subjected to many cyclic loadings. In terms of serviceability limit state (SLS), it has to be ensured that the load on the foundation does not exceed the operational tolerance prescribed by the wind turbine manufacturer throughout its lifetime. This work aims at developing a probabilistic approach along with a reliability framework with emphasis on verifying the SLS criterion in terms of maximum allowable rotation during an extreme cyclic loading event. This reliability framework allows the quantification of uncertainties in soil properties and the constitutive soil model for cyclic loadings and extreme environmental conditions and verifies that the foundation design meets a specific target reliability level. A 3D finite-element (FE) model is used to predict the long-term response of the SSI, accounting for the accumulation of permanent cyclic strain experienced by the soil. The proposed framework was employed for the design of a large-diameter monopile supporting a 10 MW offshore wind turbine.

Comparison of Cyclic P-Y Methods for Offshore Wind Turbine Monopiles Subjected to Extreme Storm Loading

2015 ◽  
Author(s):  
Wystan Carswell ◽  
Casey Fontana ◽  
Sanjay R. Arwade ◽  
Don J. DeGroot ◽  
Andrew T. Myers
Keyword(s):  
Wind Turbine ◽  
Large Diameter ◽  
Small Diameter ◽  
Design Guidelines ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Extreme Storm ◽  
Design Loads ◽  
Number Of Cycles ◽  
Pile Resistance

Approximately 75% of installed offshore wind turbines (OWTs) are supported by monopiles, a foundation whose design is dominated by lateral loading. Monopiles are typically designed using the p-y method which models soil-pile resistance using decoupled, nonlinear elastic Winkler springs. Because cyclic soil behavior is difficult to predict, the cyclic p-y method accounts for cyclic soil-pile interaction using a quasistatic analysis with cyclic p-y curves representing lower-bound soil resistance. This paper compares the Matlock (1970) and Dunnavant & O’Neill (1989) p-y curve methods, and the p-y degradation models from Rajashree & Sundaravadivelu (1996) and Dunnavant & O’Neill (1989) for a 6 m diameter monopile in stiff clay subjected to storm loading. Because the Matlock (1970) cyclic p-y curves are independent of the number of load cycles, the static p-y curves were used in conjunction with the Rajashree & Sundaravadivelu (1996) p-y degradation method in order to take number of cycles into account. All of the p-y methods were developed for small diameter piles, therefore it should be noted that the extrapolation of these methods for large diameter OWT monopiles may not be physically accurate; however, the Matlock (1970) curves are still the curves predominantly recommended in OWT design guidelines. The National Renewable Energy Laboratory wind turbine analysis program FAST was used to produce mudline design loads representative of extreme storm loading. These design loads were used as the load input to cyclic p-y analysis. Deformed pile shapes as a result of the design load are compared for each of the cyclic p-y methods as well as pile head displacement and rotation and degradation of soil-pile resistance with increasing number of cycles.

scholarly journals Coupled Analysis of Offshore Wind Turbine Jacket Structures with Pile-Soil-Structure Interaction Using FAST v8 and X-SEA

2019 ◽  
Vol 9 (8) ◽  
pp. 1633 ◽  
Author(s):  
Pasin Plodpradit ◽  
Van Dinh ◽  
Ki-Du Kim
Keyword(s):  
Wind Turbine ◽  
Soil Structure ◽  
Offshore Wind ◽  
Coupled Analysis ◽  
Offshore Wind Turbine ◽  
Computationally Efficient ◽  
Time Step ◽  
Support Structure ◽  
Jacket Structures ◽  
Reaction Forces

The coupled analysis between a turbine in operating condition and a complex jacket support structure was formulated in this paper for the reliable evaluation of offshore wind turbine structures including pile-soil-structure interactions (PSSIs). Discussions on the theoretical and simulation aspects of the coupled analysis are presented. The dynamic coupled analysis was implemented in X-SEA program and validated with FAST v8 (fatigue, aerodynamics, structures and turbulence) developed by NREL, USA. By replacing the sub-structural module in the FAST with the component of offshore substructure in the X-SEA, the reaction forces and the turbine loads were calculated in each time step and the results from X-SEA were compared with that from FAST. It showed very good agreement with each other. A case study of a NREL 5MW offshore wind turbine on a jacket support structure was performed. Coupled dynamic analyses of offshore wind turbine and support structures with PSSI were carried out. The results showed that in the coupled analysis, the responses of the structure are significantly less than in the uncoupled analysis. The support structure considering PSSI exhibited decreased natural frequencies and more flexible responses compared to the fixed-support structure. The implemented coupled analysis including PSSI was shown to be more accurate and computationally efficient.

Finite Element Analysis of Large Diameter Grouted Connections

2007 ◽  
Author(s):  
Lars P. Nielsen
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Wind Turbine ◽  
Large Diameter ◽  
Wind Farms ◽  
Element Model ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Joint Research ◽  
Element Analysis

When considering offshore monopile foundations designed for wind turbine support structures, a grouted connection between the monopile and an overlapping transition piece has become the de facto standard. These connections rely on axial loads being carried primarily by the bond between the steel and grout as shear. Given the critical nature of the grouted connection in a system with zero redundancy, the current design verification requirement is that a finite element analysis is performed to ascertain the viability of the connection with respect to combined axial and bending capacity whilst pure axial capacity is handled as a decoupled phenomenon using simple analytical formulas. The present paper addresses the practical modeling aspects of such a finite element model, covering subjects such as constitutive formulations for the grout, mesh density, and steel/grout interaction. The aim of the paper is to discuss different modeling approaches and, to the extent possible, provide basic guidelines for the minimum requirements valid for this type of analysis. This discussion is based on the accumulated experience gained though the independent verification of more than 10 currently operational offshore wind farms that have been certified by DNV, as well as the significant joint research and development with industry captured in the DNV Offshore Standard for Design of Offshore Wind Turbine Structures DNV-OS-J101. Moreover, general observations relating to the basic subjects such as overall geometric extent of the model, inclusion of secondary structures, detail simplification, boundary conditions, load application etc. are presented based on the authors more than 3 year involvement on the subject at DNV.

On the Structural Capacity of Grouted Connections in Offshore Structures

2011 ◽  
Author(s):  
Inge Lotsberg ◽  
Andrzej Serednicki ◽  
Espen Cramer ◽  
Ha˚kon Bertnes ◽  
Per Enggaard Haahr
Keyword(s):  
Large Diameter ◽  
Offshore Structures ◽  
Offshore Wind ◽  
Design Stage ◽  
Design Standards ◽  
Safety Level ◽  
Axial Capacity ◽  
Structural Capacity ◽  
Jacket Structures ◽  
Industry Practice

During the last year, the offshore wind tower structure industry experienced that the design of the grouted connections between the top tower and monopile structure did not necessarily result in an acceptable safety level. A number of wind towers were reported to settle on the monopile structure and the resulting force flow in the structures was different to that intended at the design stage. A joint industry project was therefore carried out to investigate the structural capacity of these connections. It was found that the axial capacity of the grouted connections is a larger function of the diameter and surface tolerances than that accounted for in existing design standards. This paper reviews the industry practice relating to the design of grouted connections in monopile structures. The physical behaviour of the connections is explained and some of the most critical issues related to the design of large diameter grouted connections are assessed. This knowledge is also considered to be of significance for the design of grouted connections in skirt piles in jacket structures subjected to alternating loading.

Risk Assessment of Hoisting Aboard and Installation for Offshore Wind Turbine

2012 ◽  
Author(s):  
Xu Bai ◽  
Liping Sun ◽  
Hai Sun
Keyword(s):  
Risk Assessment ◽  
Wind Turbine ◽  
Failure Modes ◽  
Offshore Structures ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Main Task ◽  
Future Design ◽  
Management Measures ◽  
Operation Process

With the accidents of offshore structures occurring frequently, the significance of risk assessment in the process of transportation, installation and operation is increasing. In this paper, the risk assessment of offshore wind turbine in transportation and installation is presented. Firstly, the main task profiles are identified according to the concrete operation process, the components and risk factors related to the assessment. Secondly, FTA of hoisting aboard and FMEA of installation process are established based on RELEX Studio 2011. The failure modes of task profiles are analyzed and coefficients are assigned according to the principle of As Low As Reasonably Practicable. Finally, using Risk Priority Number method to evaluate their severity rank, and some recommended operations and management measures are given. Risk assessment is applied in offshore wind turbine transportation in this paper and the work has great significance to the evaluation and future design of offshore structures.

On the Adequacy of Existing Foundation Schemes for Offshore Wind Turbines Subjected to Extreme Loading

2017 ◽  
Author(s):  
Rallis Kourkoulis ◽  
Fani Gelagoti ◽  
Irene Georgiou ◽  
Spyros Karamanos ◽  
George Gazetas
Keyword(s):  
Large Diameter ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Mechanical Equipment ◽  
Lateral Loads ◽  
Offshore Wind Turbines ◽  
Energy Demands ◽  
Jacket Structures ◽  
The Common ◽  
Suction Caissons

Dictated by the world’s escalating energy demands, offshore infrastructure is moving beyond the immediate continental shelf into deeper waters. Although the monopile solution has proven its reliability for many years, its feasibility in larger depths is questionable, or even limited, and multi-pod foundations, such as jacket structures, could be regarded as viable alternatives. Their main advantage, compared to the monopile alternative, is that they are able to sustain large lateral loads through axial stressing rather than bending at their supports (usually materialized using piles or suction caissons). Recognizing this reality, the present study attempts to compare the performance of a conventional monopile system with that of a jacket foundation when taking into consideration extreme earthquake loading. Although safety fuses do exist to isolate the mechanical equipment from the direct effects of such loading, our focus in this study is on the irrecoverable deformation at the foundation level which, under circumstances, may render the turbine inoperable. To this end, two foundation alternatives supporting an offshore wind turbine in the Mediterranean Sea are comparatively discussed: the conventional large diameter monopile and a jacket foundation supported by smaller piles or suction caissons. Results show that under expected operational loads the performance of the two systems is practically equivalent. However, extreme loading conditions may significantly alter the response and may, in some cases question the common practice.

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