On the Use of Scaled Model Tests for Analysis and Design of Offshore Wind Turbines

2018 ◽  
pp. 107-129 ◽  
Author(s):  
Subhamoy Bhattacharya ◽  
Georgios Nikitas ◽  
Saleh Jalbi
Keyword(s):  
Wind Turbines ◽  
Model Tests ◽  
Offshore Wind ◽  
Scaled Model ◽  
Analysis And Design ◽  
Offshore Wind Turbines

Model Tests on the Long-Term Dynamic Performance of Offshore Wind Turbines Founded on Monopiles in Sand

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
Zhen Guo ◽  
Luqing Yu ◽  
Lizhong Wang ◽  
S. Bhattacharya ◽  
G. Nikitas ◽  
...  
Keyword(s):  
Dynamic Response ◽  
Wind Turbines ◽  
Model Tests ◽  
Offshore Wind ◽  
Frequency Change ◽  
Test Results ◽  
Scaled Model ◽  
Structural Dynamic ◽  
Offshore Wind Turbines

The dynamic response of the supporting structure is critical for the in-service stability and safety of offshore wind turbines (OWTs). The aim of this paper is to first illustrate the complexity of environmental loads acting on an OWT and reveal the significance of its structural dynamic response for the OWT safety. Second, it is aimed to investigate the long-term performance of the OWT founded on a monopile in dense sand. Therefore, a series of well-scaled model tests have been carried out, in which an innovative balance gear system was proposed and used to apply different types of dynamic loadings on a model OWT. Test results indicated that the natural frequency of the OWT in sand would increase as the number of applied cyclic loading went up, but the increasing rate of the frequency gradually decreases with the strain accumulation of soil around the monopile. This kind of the frequency change of OWT is thought to be dependent on the way how the OWT is cyclically loaded and the shear strain level of soil in the area adjacent to the pile foundation. In this paper, all test results were plotted in a nondimensional manner in order to be scaled up to predict the consequences for prototype OWT in sandy seabed.

scholarly journals Comparative Modal Analysis of Monopile and Jacket Supported Offshore Wind Turbines including Soil-Structure Interaction

2020 ◽  
Vol 20 (10) ◽  
pp. 2042016
Author(s):  
A. Abdullahi ◽  
Y. Wang ◽  
S. Bhattacharya
Keyword(s):  
Wind Turbines ◽  
Soil Structure ◽  
Natural Frequencies ◽  
Model Updating ◽  
Offshore Wind ◽  
Fe Model ◽  
Analysis And Design ◽  
Offshore Wind Turbines ◽  
Future Design ◽  
Wide Range

Offshore wind turbines (OWTs) have emerged as a reliable source of renewable energy, witnessing massive deployment across the world. While there is a wide range of support foundations for these structures, the monopile and jacket are most utilized so far; their deployment is largely informed by water depths and turbine ratings. However, the recommended water depth ranges are often violated, leading to cross-deployment of the two foundation types. This study first investigates the dynamic implication of this practice to incorporate the findings into future analysis and design of these structures. Detailed finite element (FE) models of Monopile and Jacket supported OWTs are developed in the commercial software, ANSYS. Nonlinear soil springs are used to simulate the soil-structure interactions (SSI) and the group effects of the jacket piles are considered by using the relevant modification factors. Modal analyzes of the fixed and flexible-base cases are carried out, and natural frequencies are chosen as the comparison parameters throughout the study. Second, this study constructs a few-parameters SSI model for the two FE models developed above, which aims to use fewer variables in the FE model updating process without compromising its simulation quality. Maximum lateral soil resistance and soil depths are related using polynomial equations, this replaces the standard nonlinear soil spring model. The numerical results show that for the same turbine rating and total height, jacket supported OWTs generally have higher first-order natural frequencies than the monopile supported OWTs, while the reverse is true for the second-order vibration modes, for both fixed and flexible foundations. This contributes to future design considerations of OWTs. On the other hand, with only two parameters, the proposed SSI model has achieved the same accuracy as that using the standard model with seven parameters. It has the potential to become a new SSI model, especially for the identification of soil properties through the model updating process.

Hybrid Model Tests for Floating Offshore Wind Turbines

2019 ◽  
Author(s):  
Maxime Thys ◽  
Alessandro Fontanella ◽  
Federico Taruffi ◽  
Marco Belloli ◽  
Petter Andreas Berthelsen
Keyword(s):  
Wind Tunnel ◽  
Real Time ◽  
Hybrid Model ◽  
Wind Turbines ◽  
Ocean Basin ◽  
Model Testing ◽  
Model Tests ◽  
Offshore Wind ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines

Abstract Model testing of offshore structures has been standard practice over the years and is often recommended in guidelines and required in certification rules. The standard objectives for model testing are final concept verification, where it is recommended to model the system as closely as possible, and numerical code calibration. Model testing of floating offshore wind turbines is complex due to the response depending on the aero-hydro-servo-elastic system, but also due to difficulties to perform model tests in a hydrodynamic facility with correctly scaled hydrodynamic, aerodynamic and inertial loads. The main limitations are due to the Froude-Reynolds scaling incompatibility, and the wind generation. An approach to solve these issues is by use of hybrid testing where the system is divided in a numerical and a physical substructure, interacting in real-time with each other. Depending on the objectives of the model tests, parts of a physical model of a FOWT can then be placed in a wind tunnel or an ocean basin, where the rest of the system is simulated. In the EU H2020 LIFES50+ project, hybrid model tests were performed in the wind tunnel at Politecnico di Milano, as well as in the ocean basin at SINTEF Ocean. The model tests in the wind tunnel were performed with a physical wind turbine positioned on top of a 6DOF position-controlled actuator, while the hydrodynamic loads and the motions of the support structure were simulated in real-time. For the tests in the ocean basin, a physical floater with tower subject to waves and current was used, while the simulated rotor loads were applied on the model by use of a force actuation system. The tests in both facilities are compared and recommendations on how to combine testing methodologies in an optimal way are discussed.

Using Nonlinear Wave Kinematics to Estimate the Loads on Offshore Wind Turbines in 3-Hour Sea States

2018 ◽  
Author(s):  
Tim Bunnik ◽  
Erik-Jan de Ridder
Keyword(s):  
Wind Turbine ◽  
Nonlinear Wave ◽  
Wind Turbines ◽  
Wave Model ◽  
Breaking Waves ◽  
Model Tests ◽  
Offshore Wind ◽  
Wave Loads ◽  
Offshore Wind Turbines ◽  
Wave Basin

The effects of operational wave loads and wind loads on offshore mono pile wind turbines are well understood. For most sites, however, the water depth is such that breaking or near-breaking waves will occur causing impulsive excitation of the mono pile and consequently considerable stresses, displacements and accelerations in the monopile, tower and turbine. As has been shown in earlier, recent publications, Computational Fluid Dynamics (CFD) can be used to accurately analyze wave impacts on offshore wind turbines. However, it is not yet well suited to study the statistical variability of wave impact loads in long-duration sea states, and thus estimate the ULS and ALS loads for which a wind turbine has to be designed. An alternative, simplified approach, is the use of a Morison model in which the kinematics (water particle velocities and accelerations) from a nonlinear wave model are used. For long-crested waves the nonlinear wave model can be run in a 2D mode and is therefore relatively cheap. In this paper model tests for steep and breaking waves on an offshore wind turbine are compared with results from the Morison model. First, a deterministic comparison is made between the wave loads from the model tests and the simulation model (simulating the same 3-hour wave realization as in the basin), which turns out to be difficult because of differences between wave reflections in the wave basin (a physical beach) and the numerical wave model (absorbing boundary condition). Second, a statistical comparison is made by comparing with different wave realizations measured in the wave basin.

scholarly journals Offshore Wind Turbines – Research and Development

2018 ◽  
Vol 2 (Special edition 2) ◽  
pp. 59-70
Author(s):  
Neven Hadžić ◽  
Ivan Ćatipović ◽  
Marko Tomić ◽  
Nikola Vladimir ◽  
Hrvoje Kozmar
Keyword(s):  
Research And Development ◽  
Wind Turbines ◽  
Offshore Wind ◽  
Response Analysis ◽  
Energy Potential ◽  
Analysis And Design ◽  
Offshore Wind Turbines ◽  
Design Procedures ◽  
Sea Current ◽  
Current Loading

The purpose of the present study is to review the state-of-the-art in research and development of offshore wind turbines in order to address the latest findings and trends in structural design and response analysis. This could enhance a development of sophisticated offshore wind turbines. To complete such a task, a detailed review of offshore wind renewable energy potential, wind, wave and sea current loading as well as structural analysis and design procedures and experimental work are presented.

scholarly journals Seismic Design of Offshore Wind Turbines: Good, Bad and Unknowns

Energies ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3496
Author(s):  
Subhamoy Bhattacharya ◽  
Suryakanta Biswal ◽  
Muhammed Aleem ◽  
Sadra Amani ◽  
Athul Prabhakaran ◽  
...  
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Large Scale ◽  
Wind Farms ◽  
Offshore Wind ◽  
Future Research ◽  
Offshore Wind Farms ◽  
Analysis And Design ◽  
Offshore Wind Turbines ◽  
Floating Systems

Large scale offshore wind farms are relatively new infrastructures and are being deployed in regions prone to earthquakes. Offshore wind farms comprise of both offshore wind turbines (OWTs) and balance of plants (BOP) facilities, such as inter-array and export cables, grid connection etc. An OWT structure can be either grounded systems (rigidly anchored to the seabed) or floating systems (with tension legs or catenary cables). OWTs are dynamically-sensitive structures made of a long slender tower with a top-heavy mass, known as Nacelle, to which a heavy rotating mass (hub and blades) is attached. These structures, apart from the variable environmental wind and wave loads, may also be subjected to earthquake related hazards in seismic zones. The earthquake hazards that can affect offshore wind farm are fault displacement, seismic shaking, subsurface liquefaction, submarine landslides, tsunami effects and a combination thereof. Procedures for seismic designing OWTs are not explicitly mentioned in current codes of practice. The aim of the paper is to discuss the seismic related challenges in the analysis and design of offshore wind farms and wind turbine structures. Different types of grounded and floating systems are considered to evaluate the seismic related effects. However, emphasis is provided on Tension Leg Platform (TLP) type floating wind turbine. Future research needs are also identified.

scholarly journals Assessment of Practical Methods to Predict Accumulated Rotations of Monopile-Supported Offshore Wind Turbines in Cohesionless Ground Profiles

Energies ◽  
2020 ◽  
Vol 13 (15) ◽  
pp. 3915
Author(s):  
Saleh Jalbi ◽  
Joseph Hilton ◽  
Luke Jacques
Keyword(s):  
Wind Turbines ◽  
Time History ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Complex Nature ◽  
Scaled Model ◽  
Offshore Wind Turbines ◽  
Applied Loading ◽  
Number Of Cycles

Monopiles supporting offshore wind turbines can experience permanent non-recoverable rotations (or displacements) during their lifetime due to the cyclic nature of hydrodynamic and aerodynamic loading exerted on them. Recent studies in the literature have demonstrated that conventional cyclic p–y curves recommended in different codes of practice (API-RP-2GEO and DNVGL-RP-C212) may not capture the effects of long-term cyclic loads as they are independent of the loading profile and the number of applied cycles. Several published methodologies based on laboratory scaled model tests (on sands) exist to determine the effect of cyclic lateral loads on the long-term behaviour of piles. The tests vary in terms of the pile behaviour (rigid or flexible pile), number of applied loading cycles, and the load profile (one-way or two-way loading). The best-fit curves provided by these tests offer practical and cost-efficient methods to quantify the accumulated rotations when compared to Finite Element Method. It is therefore desirable that such methods are further developed to take into account different soil types and the complex nature of the loading. The objective of this paper is to compare the performance of the available formulations under the actions of a typical 35-h (hour) storm as per the Bundesamt für Seeschifffahrt und Hydrographie (BSH) recommendations. Using classical rain flow counting, the loading time-history is discretized into load packets where each packet has a loading profile and number of cycles, which then enables the computation of an equivalent number of cycles of the largest load packet. The results show that the loading profile plays a detrimental role in the result of the accumulated rotation. Furthermore, flexibility of the pile also has an important effect on the response of the pile where predictions obtained from formulations based on flexible piles resulted in a much lower accumulated rotation than tests based on rigid piles. Finally, the findings of this paper are expected to contribute in the design and interpretation of future experimental frameworks for Offshore Wind Turbine (OWT) monopiles in sands, which will include a more realistic loading profile, number of cycles, and relative soil to pile stiffness.

scholarly journals Experimental Validation of Aero-Hydro-Servo-Elastic Models of a Scaled Floating Offshore Wind Turbine

2019 ◽  
Vol 9 (6) ◽  
pp. 1244 ◽  
Author(s):  
Kasper Jessen ◽  
Kasper Laugesen ◽  
Signe M. Mortensen ◽  
Jesper K. Jensen ◽  
Mohsen N. Soltani
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Experimental Validation ◽  
Numerical Models ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Scaled Model ◽  
Floating Offshore Wind Turbine ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines

Floating offshore wind turbines are complex dynamical systems. The use of numerical models is an essential tool for the prediction of the fatigue life, ultimate loads and controller design. The simultaneous wind and wave loading on a non-stationary foundation with a flexible tower makes the development of numerical models difficult, the validation of these numerical models is a challenging task as the floating offshore wind turbine system is expensive and the testing of these may cause loss of the system. The validation of these numerical models is often made on scaled models of the floating offshore wind turbines, which are tested in scaled environmental conditions. In this study, an experimental validation of two numerical models for a floating offshore wind turbines will be conducted. The scaled model is a 1:35 Froude scaled 5 MW offshore wind turbine mounted on a tension-leg platform. The two numerical models are aero-hydro-servo-elastic models. The numerical models are a theoretical model developed in a MATLAB/Simulink environment by the authors, while the other model is developed in the turbine simulation tool FAST. A comparison between the numerical models and the experimental dynamics shows good agreement. Though some effects such as the periodic loading from rotor show a complexity, which is difficult to capture.

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