Optimizing Pile Driving Fatigue for Offshore Foundations in Very Dense Sand: A Case Study

2013 ◽  
Author(s):  
Erdem Ozsu ◽  
An-Ninh Ta ◽  
Bruno Stuyts ◽  
Christophe Jaeck
Keyword(s):  
Rapid Development ◽  
Back Analysis ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Pile Driving ◽  
Optimized Design ◽  
Dense Sand ◽  
Driving Fatigue ◽  
Induced Stresses ◽  
Stress Cycles

With the rapid development of offshore wind energy in Europe, a large number of piled structures are being installed. Driven pipe piles are adopted as a foundation solution for the majority of offshore wind turbine support structures. In soils consisting of very dense sand, pile driving induces large-amplitude stress cycles in pile material, which have to be accounted for in fatigue calculations. These stress cycles can be calculated using one-dimensional wave equation analysis. Different ways of reducing pile driving damage are presented. Depending on the soil surrounding the pile and the target penetration depth, an optimum driving sequence can be established which minimises pile damage. As damage depends more on induced stresses than on the number of hammer blows, reducing the hammer energy at some point during driving can be beneficial for reducing the accumulated damage. In this paper, an optimum driving sequence is developed for a generic soil profile consisting of very dense sand. The pile driving damage calculated with the optimum sequence is compared to the damage calculated when driving close to maximum hammer efficiency. Additionally, using a larger hammer can also be beneficial for reducing induced stresses when keeping the transmitted energy at a similar level. The paper also highlights the advantages of using pile driving monitoring or pile driving back-analysis for verifying the stress levels in the piles during driving. Offshore design standards allow a reduction of the damage fatigue factor for inspected members. This principle may be extended to monitored piles. The differences between data from pile driving monitoring and data from pile driving back-analysis are discussed and the potential impact on the damage fatigue factor is highlighted. Finally, the potential conflict of pile driving fatigue requirements and pile capacity requirements is discussed. Both considerations should eventually lead to an optimized design which satisfies the required design equations.

scholarly journals Evaluation of soil models for improved design of offshore wind turbine foundations in dense sand

Géotechnique ◽  
2020 ◽  
Vol 70 (8) ◽  
pp. 682-699
Author(s):  
Hans Petter Jostad ◽  
Birgitte MISUND Dahl ◽  
Ana Page ◽  
Nallathamby Sivasithamparam ◽  
Hendrik Sturm
Keyword(s):  
Wind Turbine ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Dense Sand ◽  
Improved Design

The Current Situation and Recent Advances of Deep-Water Floating Wind Turbine

2012 ◽  
Vol 226-228 ◽  
pp. 772-775
Author(s):  
Yu Chen ◽  
Chun Li ◽  
Wei Gao ◽  
Jia Bin Nie
Keyword(s):  
Wind Turbine ◽  
Deep Water ◽  
Rapid Development ◽  
Coupled Model ◽  
Wind Farms ◽  
International Standards ◽  
Offshore Wind ◽  
Current Status ◽  
Offshore Wind Turbine ◽  
Floating Wind Turbine

Offshore wind turbine is a novel approach in the field of wind energy technology. With the rapid development of coastal wind farms, it is the trend to move them outward to deep-water district. However, the cost of construction rises significantly with the increase in water depth. Floating wind turbine is one of the efficient methods to solve this problem. The early history, current status and cutting-edge improvements of overseas offshore floating wind turbine as well as the shortcomings shall be presented. The concept designs, international standards, fully coupled model simulations and hydrodynamic experiments will be illustrated and discussed together with the development of the theory and the related software modules. Thus a novel researching method and concept shall be presented to provide reference for future researches

scholarly journals Reliability-Based Serviceability Limit State Design of a Jacket Substructure for an Offshore Wind Turbine

Energies ◽  
2019 ◽  
Vol 12 (14) ◽  
pp. 2751 ◽  
Author(s):  
Jianhua Zhang ◽  
Won-Hee Kang ◽  
Ke Sun ◽  
Fushun Liu
Keyword(s):  
Correlation Analysis ◽  
Reliability Analysis ◽  
Limit State ◽  
Statistical Correlation ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
State Function ◽  
Optimized Design ◽  
Foundation Design ◽  
Serviceability Limit State

The development of a structurally optimized foundation design has become one of the main research objectives for offshore wind turbines (OWTs). The design process should be carried out in a probabilistic way due to the uncertainties involved, such as using parametric uncertainties regarding material and geometric properties, and model uncertainties in resistance prediction models and regarding environmental loads. Traditional simple deterministic checking procedures do not guarantee an optimized design because the associated uncertainties are not fully considered. In this paper, a reliability analysis framework is proposed to support the optimized design of jacket foundations for OWTs. The reliability analysis mainly considers the serviceability limit state of the structure according to the requirements of the code. The framework consists of two parts: (i) an important parameter identification procedure based on statistical correlation analysis and (ii) a finite element-simulation-based reliability estimation procedure. The procedure is demonstrated through a jacket structure design of a 3 MW OWT. The analysis results show that the statistical correlation analysis can help to identify the parameters necessary for the overall structural performance. The Latin hypercube sampling and the Monte Carlo simulation using FE models effectively and efficiently evaluate the reliability of the structure while not relying on a surrogate limit state function. A comparison between the proposed framework and the deterministic design shows that the framework can help to achieve a better result closer to the target reliability level.

Offshore Wind Turbine Mono-Bucket Foundations in Sand

2021 ◽  
Author(s):  
Han Eng Low ◽  
Fangyuan Zhu ◽  
Henning Mohr ◽  
Phillip Watson ◽  
Carl Erbrich ◽  
...  
Keyword(s):  
Wind Turbine ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Large Rotation ◽  
Bucket Foundation ◽  
Dense Sand ◽  
Centrifuge Model ◽  
Centrifuge Tests ◽  
Rotational Response ◽  
Centrifuge Model Tests

Abstract Single (or mono) suction buckets have been put forward by others as possible offshore wind turbine (OWT) foundations. This paper presents a series of centrifuge model tests conducted in dense sand to investigate their monotonic response for a range of drainage conditions. The results from the centrifuge tests suggest that the mono-bucket rotational response at large rotation in dense sand is dependent on drainage conditions but does not seem to be affected by the contact condition between the bucket invert and the seabed. A final comparison between results from an equivalent set of uplift tests suggests, however, that multi-bucket foundation systems are likely to be more efficient foundation solutions, although suggestions are made which might improve mono-bucket foundation response.

Scale Model Investigations on Vibro Pile Driving

2018 ◽  
Author(s):  
Philipp Stein ◽  
Nils Hinzmann ◽  
Jörg Gattermann
Keyword(s):  
Penetration Depth ◽  
Earth Pressure ◽  
Offshore Wind ◽  
Scale Model ◽  
Pile Driving ◽  
Scaled Model ◽  
Dense Sand ◽  
Pressure Transducers ◽  
Vibration Technique ◽  
Force Equilibrium

Monopiles installed by impact driving are the preferred system for the foundation of offshore wind turbines in water depths up to 40 m. The vibration technique as alternative installation method has big advantages regarding piling noise and installation time. Much experience exists for the design and installation of impact driven piles. Within the research project ZykLaMP, the lack of experience concerning vibrated monopiles shall be faced by means of large-scaled model investigations regarding the lateral load-bearing behavior. Therefore, open ended steel pipe piles (L = 2.4 m, Dpile = 0.6 m) are installed into dense sand by means of impact and vibratory pile driving and then subjected to cyclic lateral loading. This paper focusses on pile driving predictions and measurements during the installation process. Pile driving post-predictions were carried out based on a simple force equilibrium approach. Model piles were installed using two different vibro hammers with different eccentric moments and one impact hammer. Measurements of strains and accelerations were carried out to investigate dynamic movements during pile driving. Earth pressure transducers were used to investigate the development of soil stresses due to the installation process. Measurements show that even at high acceleration amplitudes a refusal to vibratory driving may occur at a certain penetration depth. Soil stresses in the vicinity of the pile decrease to about 50 % due to vibratory driving which is one reason for the friction fatigue phenomenon. Drivability studies using the force equilibrium model give rough predictions about whether or not a pile can be driven to a certain penetration depth but are quite sensitive to input parameters. For the model tests, post-predictions gave reasonable results.

scholarly journals Cost effective strategy using Kriging surrogates to compute fatigue at multiple locations of a structure: Application to offshore wind turbine certification

2018 ◽  
Vol 165 ◽  
pp. 17001
Author(s):  
Quentin Huchet ◽  
Cécile Mattrand ◽  
Pierre Beaurepaire ◽  
Nicolas Relun ◽  
Nicolas Gayton
Keyword(s):  
Damage Assessment ◽  
Rapid Development ◽  
Production Capacity ◽  
Cost Effective ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Carbon Reduction ◽  
Wind Energy Development ◽  
Adaptive Kriging ◽  
Numerical Strategy

Offshore wind energy development has experienced a rapid development over the last few years encouraged by the of carbon reduction policy and the energy mix objectives of several countries worldwide. Nowadays, the offshore projects under investigation are composed of tens to hundreds of units reaching impressive dimensions with total rotor diameters from 150 to 220 meters and production capacity of 5 to 12 MW per turbine. Mechanical analyses have to be performed to validate the design regarding the solicitations it may face during its lifetime (20 years). Because of the high number of solicitation cycles the structure is confronted to, an estimation of the cumulated damage is mandatory and has to be carefully assessed. As presented in standards, this verification requires massive computation investments and is usually a challenging task for project engineers. This paper presents the “MultiSite” extension of the AK-DA numerical strategy (“Adaptive Kriging for Damage Assessment”). After being formalized, an illustration of its behaviour and performances is proposed for the validation of a design regarding its cumulated damages at different locations.

scholarly journals Model Tests on the Frequency Responses of Offshore Monopiles

2019 ◽  
Vol 7 (12) ◽  
pp. 430 ◽  
Author(s):  
He ◽  
Zhu
Keyword(s):  
Resonant Frequency ◽  
Water Waves ◽  
Model Tests ◽  
Offshore Wind ◽  
Dynamic Loads ◽  
Soil Conditions ◽  
Offshore Wind Turbine ◽  
Static Loads ◽  
Dense Sand ◽  
Frequency Responses

Monopiles are widely used to support offshore wind turbines as a result of the extensive development of offshore wind energy in coastal areas of China. An offshore wind turbine is a typical high-rise structure sensitive to dynamic loads in ocean environment such as winds, water waves, currents and seismic waves. Most of the existing researches focus on elastic vibration analysis, bearing capacity or cyclic degradation problems. There’re very few studies on vibration of monopiles, especially considering the influence of static loads with different amplitudes, directions, and loading-unloading-reloading processes. In this paper, laboratory-scale 1 g model tests for a monopile in dry sands were carried out to investigate the frequency responses of the monopile under different loading conditions. The bearing capacities of the model monopile were obtained as references, and dynamic loads and static loads with different amplitudes were then applied to the monopile. It was found that (1) the first resonant frequency of the monopile decreases with the increase of dynamic load amplitudes; (2) the first resonant frequency of the monopile steadily increases under the lateral static load and loading-unloading-reloading processes; (3) the frequency responses of the monopile with static loads in different directions are also quite different; (4) damping of the monopile is influenced by the load amplitudes, load frequencies, load directions and soil conditions. Besides, all the tests were conducted in both loose sand and dense sand, and the results are almost consistent in general but more obvious in the dense sand case.

scholarly journals Characterization of impact pile driving signals during installation of offshore wind turbine foundations

2020 ◽  
Vol 147 (4) ◽  
pp. 2323-2333 ◽  
Author(s):  
Jennifer L. Amaral ◽  
James H. Miller ◽  
Gopu R. Potty ◽  
Kathleen J. Vigness-Raposa ◽  
Adam S. Frankel ◽  
...  
Keyword(s):  
Wind Turbine ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Pile Driving

scholarly journals Strength Analysis of a Large-Size Supporting Structure for an Offshore Wind Turbine

2017 ◽  
Vol 24 (s1) ◽  
pp. 156-165 ◽  
Author(s):  
Karol Niklas
Keyword(s):  
Wind Turbine ◽  
Rapid Development ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Strength Analysis ◽  
Support Design ◽  
Nonlinear Buckling ◽  
Basic Part ◽  
Supporting Structure ◽  
Large Size

Abstract The offshore wind power industry is the branch of electric energy production from renewable sources which is most intensively developed in EU countries. At present, there is a tendency to install larger-power wind turbines at larger distances from the seashore, on relatively deep waters. Consequently, technological solutions for new supporting structures intended for deeper water regions are undergoing rapid development now. Various design types are proposed and analysed, starting from gravitational supports (GBS), through monopiles and 3D frame structures (jackets, tripods), and ending with floating and submerged supports anchored to the seabed by flexible connectors, including TLP type solutions. The article presents the results of examination of an untypical large-size gravitational support intended for waters with the depth of up to 40 m. Firstly, a general concept of the new design is presented, while the next basic part of the article describes the support design in detail and provides its strength analysis. The examined support has the form of a large steel container consisting of conical segments. The strength analysis was conducted using the finite element method (FEM), in accordance with the standard DNVGL-ST-0126. Modifications introduced to the most heavily loaded structural node of the support, which was the set of base bottom trusses, is also included. The results of the performed analysis prove that the presented concept of supporting structure for a 7MW turbine meets fundamental strength criteria. The nonlinear buckling analysis was performed to evaluate the critical force acting on the support, which turned out to be 1.44 times as large as the maximum load of the wind turbine. Potentially important issues for further analyses have been identified as those resulting from the asymmetry of basic loads acting on the support.

Scour Assessment and Measurements for Pile-Supported Wind Turbine Foundations

2013 ◽  
Author(s):  
Bruno Stuyts ◽  
David Cathie ◽  
Yi Xie
Keyword(s):  
Wind Turbine ◽  
Time Scale ◽  
Rapid Development ◽  
Element Model ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Scour Depth ◽  
Central Column ◽  
Pile Interaction ◽  
Equilibrium Scour Depth

With the rapid development of offshore wind energy in Europe, a large number of piled structures are being installed. In areas with sandy seabed conditions, erosion of sediment by the actions of wave and current can negatively influence foundation capacity. An accurate prediction model of scour around the piles is therefore required. Well-accepted scour prediction methods exist; both for the equilibrium scour depth and the time scale of scour [1] around single piles. These standard formulas have been combined with metocean data and a hindcasting model to calculate the expected scour depth around piles of wind turbine tripod foundations. Other causes of scour, such as pile-pile interaction, effect of proximity of structural members to the seabed, and seabed mobility were also assessed in order to determine the amount of global scour to be considered. The scour predictions were compared to measurements taken at an offshore wind turbine foundation at Park Alpha Ventus (PAV) in the German North Sea [2]. The data showed very good agreement with the measured scour around the piles. Both the equilibrium scour depth and time scale of scour were well predicted using the hindcasting model. The measured scour below the central column of the tripod structure exceeded expectations; this is believed to be due to a pumping effect during storm episodes. Finally, the effect of scour on the vertical effective stress around the tripod piles was assessed with a finite element model. Local scour had an important effect while scour below the centre of the structure had a much more limited effect. Considering the combined effects of multiple pile interaction, scour below the central column, and making an allowance for seabed mobility, an equivalent global scour depth for pile capacity calculations was established.

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