scholarly journals The impact of scour on the lateral resistance of wind turbine monopiles: an experimental study

2020 ◽  
Author(s):  
Qiang Li ◽  
Amin Askarinejad ◽  
Kenneth Gavin
Keyword(s):  
Numerical Models ◽  
Large Diameter ◽  
Offshore Wind ◽  
Soil Reaction ◽  
Pile Capacity ◽  
Moment Capacity ◽  
Scour Hole ◽  
Waves And Currents ◽  
Laterally Loaded ◽  
The Impact

The majority of offshore wind structures are supported on large-diameter, rigid monopile foundations. These piles may be subjected to scour due to the waves and currents that causes a loss of soil support and consequently decreases the pile capacity and system stiffness. The results of numerical models suggest that the shape of the scour-hole affects the magnitude of pile capacity loss, however, there is a dearth of experimental test data that quantify this effect. This paper presents a series of centrifuge model tests on an instrumented model pile that investigates the effects of scour-hole geometry on the response of a laterally loaded pile embedded in sand. The pile instrumentation allowed load-displacement and p-y (soil reaction-displacement) curves to be derived. Three scour geometries (global, local wide and local narrow) and three scour depths (1D, 1.5D and 2D; where D is pile diameter) were modelled. For all three scour types, pile moment capacity decreased almost linearly with increase of scour depth. Simple empirical relations were proposed to evaluate the detrimental influence of scour on the pile moment capacity. A new method has been developed to allow designers to quantify the effect of scour-hole shape and severity of scour on the pile response.

scholarly journals Large-Scale Experiments to Improve Monopile Scour Protection Design Adapted to Climate Change—The PROTEUS Project

Energies ◽  
2019 ◽  
Vol 12 (9) ◽  
pp. 1709 ◽  
Author(s):  
Carlos Emilio Arboleda Chavez ◽  
Vasiliki Stratigaki ◽  
Minghao Wu ◽  
Peter Troch ◽  
Alexander Schendel ◽  
...  
Keyword(s):  
Climate Change ◽  
Wind Turbine ◽  
Large Scale ◽  
Scale Effects ◽  
Numerical Models ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Waves And Currents ◽  
Combined Action ◽  
Scour Protection

This study aims to improve the design of scour protection around offshore wind turbine monopiles, as well as future-proofing them against the impacts of climate change. A series of large-scale experiments have been performed in the context of the European HYDRALAB-PLUS PROTEUS (Protection of offshore wind turbine monopiles against scouring) project in the Fast Flow Facility in HR Wallingford. These experiments make use of state of the art optical and acoustic measurement techniques to assess the damage of scour protections under the combined action of waves and currents. These novel PROTEUS tests focus on the study of the grading of the scour protection material as a stabilizing parameter, which has never been done under the combined action of waves and currents at a large scale. Scale effects are reduced and, thus, design risks are minimized. Moreover, the generated data will support the development of future scour protection designs and the validation of numerical models used by researchers worldwide. The testing program objectives are: (i) to compare the performance of single-layer wide-graded material used against scouring with current design practices; (ii) to verify the stability of the scour protection designs under extreme flow conditions; (iii) to provide a benchmark dataset for scour protection stability at large scale; and (iv) to investigate the scale effects on scour protection stability.

scholarly journals Seismic Analysis of 10-MW Off Shore Wind Turbine with Large-Diameter Monopile in Consideration of Seabed Liquefaction

2021 ◽  
Author(s):  
Jian Zhang ◽  
Songye Zhu ◽  
Guo-Kai Yuan ◽  
Quan Gu ◽  
Shitang Ke ◽  
...  
Keyword(s):  
Wind Turbines ◽  
Large Scale ◽  
Seismic Analysis ◽  
Large Diameter ◽  
Soil Liquefaction ◽  
Dynamic Responses ◽  
Offshore Wind ◽  
Wind Loading ◽  
Geological Conditions ◽  
The Impact

Abstract With the increasing construction of large-scale wind turbines in seismically active coastal areas, the survivability of these high-rated power offshore wind turbines (OWTs) in marine and geological conditions becomes extremely important. Although research on the dynamic behaviors of OWTs under earthquakes has been conducted in consideration of soil-structure interaction, attention paid to the impact of earthquake-induced seabed liquefaction on OWTs supported by large-diameter monopiles is limited. In view of this research gap, this study carries out dynamic analyses of a 10-MW OWT under the combined wind, wave, and earthquake loadings. This study uses a pressure-dependent multi-surface elastoplastic constitutive model to simulate the soil liquefaction phenomenon. Results indicate that the motion of the large-diameter monopile leads to more extensive soil liquefaction surrounding the monopile, specifically in the zone near the pile toe. Moreover, compared with earthquake loading alone, liquefaction becomes more severe under the coupled wind and earthquake loadings. Accordingly, the dynamic responses of the OWT are apparently amplified, demonstrating the importance of considering the coupling loadings. Compared with wind loading, the effect of wave loading on the dynamic response and liquefaction potential is relatively insignificant.

Upper bound analysis of laterally loaded rigid monopiles in clay with linearly increasing strength

2020 ◽  
Author(s):  
Jian Yu ◽  
Hongyu Wang ◽  
Maosong Huang ◽  
Chun Fai Leung
Keyword(s):  
Failure Mechanism ◽  
Upper Bound ◽  
Wind Waves ◽  
Wind Farms ◽  
Offshore Wind ◽  
Pile Capacity ◽  
Offshore Wind Farms ◽  
Failure Patterns ◽  
Wedge Failure ◽  
Waves And Currents

Monopiles supporting offshore wind farms are often subject to severe lateral environmental loads due to wind, waves, and currents. Previous studies reported various failure patterns for such rigid monopiles in clay; hence predicting lateral pile capacity of widely different magnitudes. In this study, both single-sided wedge failure mechanism involving passive soil failure only and two-sided wedge failure mechanism with simultaneous active and passive soil failures are proposed. The single wedge mechanism is found to be applicable if the soil behind the pile does not move together with pile resulting in a gap between the soil and the pile upon loading. On the other hand, the two-sided wedge is found appropriate for the soil behind the pile moves together with the pile upon loading. Two formulations are then derived from the two upper-bound failure mechanisms. The lateral pile capacity can be determined, and the corresponding failure mechanism identified based on the formulation which yields the lower capacity magnitude. In addition, the reliability of the formulations is verified against reported finite element methods as well as existing experimental and field test results.

scholarly journals Centrifuge and Numerical Modeling of Monopiles for Offshore Wind Towers Installed in Clay

2015 ◽  
Author(s):  
Madhuri Murali ◽  
Francisco Grajales ◽  
Ryan D. Beemer ◽  
Giovanna Biscontin ◽  
Charles Aubeny
Keyword(s):  
Aspect Ratio ◽  
Oil And Gas ◽  
Numerical Models ◽  
Large Diameter ◽  
Oil And Gas Industry ◽  
Rensselaer Polytechnic Institute ◽  
Offshore Wind ◽  
Geotechnical Centrifuge ◽  
Low Aspect Ratio ◽  
Centrifuge Tests

Offshore wind power has gained momentum as a means to diversify the world’s energy infrastructure; however, little is still known of the global stiffness behavior of the large diameter low aspect ratio monopiles which have become the foundation of choice for offshore wind towers. Traditionally, offshore foundations have been associated with gravity structures for the oil and gas industry, which in general need to resist large vertical loads with limited lateral and moment loading. However, wind towers are purposely designed to be subjected to large lateral and moment loads from the wind and waves in order to maximize power generation. Geotechnical centrifuge tests were conducted and numerical models are being developed to examine the behavior of low aspect ratio piles in clayey soils. Monopiles with aspect ratio of two are being tested in the the 150g-ton centrifuge at Rensselaer Polytechnic Institute. Initial results include momenttheta and force-displacement for various loading conditions. Numerical studies consist of finite element (FE) simulations in order to predict capacities and permanent deformations. The comparisons are to be performed in terms of the total resistance that is exerted by the soil on the caisson. FE studies allow to model capacity for different displacement fields and also to compute interactions between different loading modes. This paper outlines our progress to date including both numerical and experimental results.

scholarly journals OC6 Phase Ib: Floating Wind Component Experiment for Difference-Frequency Hydrodynamic Load Validation

Energies ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 6417
Author(s):  
Amy Robertson ◽  
Lu Wang
Keyword(s):  
Numerical Models ◽  
Department Of Energy ◽  
Difference Frequency ◽  
Offshore Wind ◽  
Wind Component ◽  
Ocean Engineering ◽  
Component Level ◽  
Frequency Wave ◽  
Hydrodynamic Loading ◽  
The Impact

A new validation campaign was conducted at the W2 Harold Alfond Ocean Engineering Laboratory at the University of Maine to investigate the hydrodynamic loading on floating offshore wind substructures, with a focus on the low-frequency contributions that tend to drive extreme and fatigue loading in semisubmersible designs. A component-level approach was taken to examine the hydrodynamic loads on individual parts of the semisubmersible in isolation and then in the presence of other members to assess the change in hydrodynamic loading. A variety of wave conditions were investigated, including bichromatic waves, to provide a direct assessment of difference-frequency wave loading. An assessment of the impact of wave uncertainty on the loading was performed, with the goal of enabling validation with this dataset of numerical models with different levels of fidelity. The dataset is openly available for public use and can be downloaded from the U.S. Department of Energy Data Archive and Portal.

scholarly journals Installation of Large-Diameter Monopiles: Introducing Wave Dispersion and Non-Local Soil Reaction

2021 ◽  
Vol 9 (3) ◽  
pp. 313
Author(s):  
Athanasios Tsetas ◽  
Apostolos Tsouvalas ◽  
Andrei V. Metrikine
Keyword(s):  
Numerical Study ◽  
Large Diameter ◽  
Small Diameter ◽  
Wave Dispersion ◽  
Offshore Wind ◽  
Soil Reaction ◽  
Pile Driving ◽  
New Model ◽  
Local Soil ◽  
Non Local

During the last decade the offshore wind industry grew ceaselessly and engineering challenges continuously arose in that area. Installation of foundation piles, known as monopiles, is one of the most critical phases in the construction of offshore wind farms. Prior to installation a drivability study is performed, by means of pile driving models. Since the latter have been developed for small-diameter piles, their applicability for the analysis of large-diameter monopiles is questionable. In this paper, a three-dimensional axisymmetric pile driving model with non-local soil reaction is presented. This new model aims to capture properly the propagation of elastic waves excited by impact piling and address non-local soil reaction. These effects are not addressed in the available approaches to predict drivability and are deemed critical for large-diameter monopiles. Predictions of the new model are compared to those of a one-dimensional model typically used nowadays. A numerical study is performed to showcase the disparities between the two models, stemming from the effect of wave dispersion and non-local soil reaction. The findings of this numerical study affirmed the significance of both mechanisms and the need for further developments in drivability modeling, notably for large-diameter monopiles.

scholarly journals Influence of Vertical Loading on Behavior of Laterally Loaded Foundation Piles: A Review

2020 ◽  
Vol 8 (12) ◽  
pp. 1029
Author(s):  
Qiang Li ◽  
Luke J. Prendergast ◽  
Amin Askarinejad ◽  
Ken Gavin
Keyword(s):  
Large Diameter ◽  
Offshore Wind ◽  
Pile Foundations ◽  
Future Research ◽  
Gravitational Acceleration ◽  
Lateral Loads ◽  
Vertical Loading ◽  
Lateral Response ◽  
Current Design ◽  
Laterally Loaded

The majority of installed offshore wind turbines are supported on large-diameter, open-ended steel pile foundations, known as monopiles. These piles are subjected to vertical and lateral loads while in service. In current design practice, interaction of vertical and lateral loads are not considered, rather piles are designed to resist vertical and lateral loads independently. Whilst interaction effects are widely studied for shallow foundations, the limited research on this topic for pile foundations often produces conflicting results. This paper reviews the research of the influence of vertical loading on the lateral response of pile foundations under combined loads, from the perspective of analytical research, numerical research, and experimental research from tests performed on 1-g (gravitational acceleration) model, centrifuge, and full-scale piles. The potential reasons for the differences among the results of previous research are discussed. Some guidance for future research on the effect of vertical loads on the lateral response of piles is provided.

Cyclic Loading of Piles Using the P-Y Method

2019 ◽  
Vol 13 (2) ◽  
Author(s):  
Matt Bristow
Keyword(s):  
Cyclic Loading ◽  
Soil Depth ◽  
Large Diameter ◽  
Reference Conditions ◽  
Numerical Procedure ◽  
New Method ◽  
Shear Stresses ◽  
Applied Loading ◽  
Cyclic Degradation ◽  
Laterally Loaded

A new analytical method is presented to determine the effects of cyclic loading on laterally loaded piles. The method uses a new numerical procedure to quantify the effects of the cyclic loading at each soil depth and convert that to a set of cyclic p-y modifiers. The reduced foundation stiffness associated with the cyclic loading can be determined, including the residual static capacity and an estimate of the accumulated displacement. The new method introduces the concept of cyclic degradation damage, which is defined as sum of the cyclic degradation that is occurring at each soil depth. Cyclic degradation calculations are based on the shear stresses in the soil. Consequently, anything that causes the shear stresses to change (e.g. pile length, pile diameter, applied loading, etc.) will automatically be included in the calculation of cyclic p-y modifiers. The method has been validated by comparing the cyclic p-y curves produced using the new method with established cyclic p-y curves derived from fielding testing. The new method has also been used to investigate what happens to the cyclic p-y modifiers as one moves away from the reference conditions used to determine the established cyclic p-y curves in API RP2A (2000). The new method shows that every application (e.g. combination of cyclic loading, pile properties, and soil characteristics) has its own unique set of cyclic p-y curves, though most p-y curves fit within an upper and lower bound range. Examples are provided for large diameter monopiles.

scholarly journals A Rational Numerical Method for Simulation of Drop-Impact Dynamics of Oleo-Pneumatic Landing Gear

2021 ◽  
Vol 11 (9) ◽  
pp. 4136
Author(s):  
Rosario Pecora
Keyword(s):  
Numerical Method ◽  
Initial Conditions ◽  
Impact Load ◽  
Numerical Models ◽  
Landing Gear ◽  
Design Stage ◽  
Impact Dynamics ◽  
State Variables ◽  
Adopted Model ◽  
The Impact

Oleo-pneumatic landing gear is a complex mechanical system conceived to efficiently absorb and dissipate an aircraft’s kinetic energy at touchdown, thus reducing the impact load and acceleration transmitted to the airframe. Due to its significant influence on ground loads, this system is generally designed in parallel with the main structural components of the aircraft, such as the fuselage and wings. Robust numerical models for simulating landing gear impact dynamics are essential from the preliminary design stage in order to properly assess aircraft configuration and structural arrangements. Finite element (FE) analysis is a viable solution for supporting the design. However, regarding the oleo-pneumatic struts, FE-based simulation may become unpractical, since detailed models are required to obtain reliable results. Moreover, FE models could not be very versatile for accommodating the many design updates that usually occur at the beginning of the landing gear project or during the layout optimization process. In this work, a numerical method for simulating oleo-pneumatic landing gear drop dynamics is presented. To effectively support both the preliminary and advanced design of landing gear units, the proposed simulation approach rationally balances the level of sophistication of the adopted model with the need for accurate results. Although based on a formulation assuming only four state variables for the description of landing gear dynamics, the approach successfully accounts for all the relevant forces that arise during the drop and their influence on landing gear motion. A set of intercommunicating routines was implemented in MATLAB® environment to integrate the dynamic impact equations, starting from user-defined initial conditions and general parameters related to the geometric and structural configuration of the landing gear. The tool was then used to simulate a drop test of a reference landing gear, and the obtained results were successfully validated against available experimental data.

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