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.

Physical Model Testing of the TetraSpar Demo Floating Wind Turbine Prototype

2019 ◽  
Author(s):  
Michael Borg ◽  
Anthony Viselli ◽  
Christopher K. Allen ◽  
Matthew Fowler ◽  
Christoffer Sigshøj ◽  
...  
Keyword(s):  
Wind Turbine ◽  
Numerical Models ◽  
Model Testing ◽  
Offshore Wind ◽  
Scale Model ◽  
Test Facility ◽  
Hydrodynamic Characteristics ◽  
Ocean Engineering ◽  
Floating Wind Turbine ◽  
Floating Offshore Wind Turbines

Abstract As part of the process of deploying new floating offshore wind turbines, scale model testing is carried out to de-risk and verify the design of novel foundation concepts. This paper describes the testing of a 1:43 Froude-scaled model of the TetraSpar Demo floating wind turbine prototype that shall be installed at the Metcentre test facility, Norway. The TetraSpar floating foundation concept consists of a floater tetrahedral structure comprising of braces connected together through pinned connections, and a triangular keel structure suspended below the floater by six suspension lines. A description of the experimental setup and program at the Alfond W2 Ocean Engineering Lab at University of Maine is given. The objective of the test campaign was to validate the initial design, and contribute to the development of the final demonstrator design and numerical models. The nonlinear hydrodynamic characteristics of the design are illustrated experimentally and the keel suspension system is shown to satisfy design criteria.

Experimental Investigation of Ice Mass Hydrodynamic Interaction With Offshore Structure in Close Proximity

2015 ◽  
Author(s):  
Tanvir Mehedi Sayeed ◽  
Bruce Colbourne ◽  
Heather Peng ◽  
Benjamin Colbourne ◽  
Don Spencer
Keyword(s):  
Hydrodynamic Interaction ◽  
Impact Load ◽  
Numerical Study ◽  
Numerical Models ◽  
Offshore Structures ◽  
Ocean Engineering ◽  
Offshore Structure ◽  
Area Of Interest ◽  
Close Proximity ◽  
The Impact

Iceberg/bergy bit impact load with fixed and floating offshore structures and supply ships is an important design consideration in ice-prone regions. Studies tend to divide the iceberg impact problem into phases from far field to contact. This results in a tendency to over simplify the final crucial stage where the structure is impacted. The authors have identified knowledge gaps and their influence on the analysis and prediction of iceberg impact velocities and loads (Sayeed et. al (2014)). The experimental and numerical study of viscous dominated very near field region is the main area of interest. This paper reports preliminary results of physical model tests conducted at Ocean Engineering Research Center (OERC) to investigate hydrodynamic interaction between ice masses and fixed offshore structure in close proximity. The objective was to perform a systematic study from simple to complex phenomena which will be a support base for the development of subsequent numerical models. The results demonstrated that hydrodynamic proximity and wave reflection effects do significantly influence the impact velocities at which ice masses approach to large structures. The effect is more pronounced for smaller ice masses.

The POWER Experiment: Impact of Assimilation of a Network of Coastal Wind Profiling Radars on Simulating Offshore Winds in and above the Wind Turbine Layer

2016 ◽  
Vol 31 (4) ◽  
pp. 1071-1091 ◽  
Author(s):  
Irina V. Djalalova ◽  
Joseph Olson ◽  
Jacob R. Carley ◽  
Laura Bianco ◽  
James M. Wilczak ◽  
...  
Keyword(s):  
New England ◽  
Gulf Of Maine ◽  
Negative Impact ◽  
Positive Impact ◽  
Weather Prediction ◽  
Department Of Energy ◽  
Offshore Wind ◽  
Model Skill ◽  
Nwp Model ◽  
The Impact

Abstract During the summer of 2004 a network of 11 wind profiling radars (WPRs) was deployed in New England as part of the New England Air Quality Study (NEAQS). Observations from this dataset are used to determine their impact on numerical weather prediction (NWP) model skill at simulating coastal and offshore winds through data-denial experiments. This study is a part of the Position of Offshore Wind Energy Resources (POWER) experiment, a Department of Energy (DOE) sponsored project that uses National Oceanic and Atmospheric Administration (NOAA) models for two 1-week periods to measure the impact of the assimilation of observations from 11 inland WPRs. Model simulations with and without assimilation of the WPR data are compared at the locations of the inland WPRs, as well as against observations from an additional WPR and a high-resolution Doppler lidar (HRDL) located on board the Research Vessel Ronald H. Brown (RHB), which cruised the Gulf of Maine during the NEAQS experiment. Model evaluation in the lowest 2 km above the ground shows a positive impact of the WPR data assimilation from the initialization time through the next five to six forecast hours at the WPR locations for 12 of 15 days analyzed, when offshore winds prevailed. A smaller positive impact at the RHB ship track was also confirmed. For the remaining three days, during which time there was a cyclone event with strong onshore wind flow, the assimilation of additional observations had a negative impact on model skill. Explanations for the negative impact are offered.

scholarly journals Uncertainty Assessment of CFD Investigation of the Nonlinear Difference-Frequency Wave Loads on a Semisubmersible FOWT Platform

2020 ◽  
Vol 13 (1) ◽  
pp. 64
Author(s):  
Lu Wang ◽  
Amy Robertson ◽  
Jason Jonkman ◽  
Yi-Hsiang Yu
Keyword(s):  
Low Frequency ◽  
Uncertainty Assessment ◽  
Difference Frequency ◽  
Offshore Wind ◽  
Wave Loads ◽  
Wave Excitation ◽  
Wave Load ◽  
Frequency Wave ◽  
Floating Offshore Wind Turbines ◽  
Frequency Excitation

Current mid-fidelity modeling approaches for floating offshore wind turbines (FOWTs) have been found to underpredict the nonlinear, low-frequency wave excitation and the response of semisubmersible FOWTs. To examine the cause of this underprediction, the OC6 project is using computational fluid dynamics (CFD) tools to investigate the wave loads on the OC5-DeepCwind semisubmersible, with a focus on the nonlinear difference-frequency excitation. This paper focuses on assessing the uncertainty of the CFD predictions from simulations of the semisubmersible in a fixed condition under bichromatic wave loading and on establishing confidence in the results for use in improving mid-fidelity models. The uncertainty for the nonlinear wave excitation is found to be acceptable but larger than that for the wave-frequency excitation, with the spatial discretization error being the dominant contributor. Further, unwanted free waves at the difference frequency have been identified in the CFD solution. A wave-splitting and wave load-correction procedure are presented to remove the contamination from the free waves in the results. A preliminary comparison to second-order potential-flow theory shows that the CFD model predicted significantly higher difference-frequency wave excitations, especially in surge, suggesting that the CFD results can be used to better calibrate the mid-fidelity tools.

Investigation of Nonlinear Difference-Frequency Wave Excitation on a Semisubmersible Offshore-Wind Platform With Bichromatic-Wave CFD Simulations

2021 ◽  
Author(s):  
Lu Wang ◽  
Amy Robertson ◽  
Jason Jonkman ◽  
Yi-Hsiang Yu ◽  
Arjen Koop ◽  
...  
Keyword(s):  
Potential Flow ◽  
Low Frequency ◽  
Flow Theory ◽  
Second Order ◽  
Difference Frequency ◽  
Offshore Wind ◽  
Viscous Drag ◽  
Cfd Simulations ◽  
Frequency Wave ◽  
Potential Flow Theory

Abstract The natural surge and pitch frequencies of semisubmersible offshore wind platforms are typically designed to be below the wave frequencies to avoid direct excitation. However, surge or pitch resonance can be excited by the nonlinear low-frequency loads generated by irregular incident waves. Second-order potential-flow models with added Morison drag have been found to underpredict this low-frequency excitation and response. As part of the OC6 project1, the authors performed computational fluid dynamics (CFD) simulations to enable a better understanding of the low-frequency loads and the limitations of lower-fidelity models. The focus of this paper is to set up a computationally cost-effective CFD simulation of a fixed semisubmersible platform to investigate nonlinear difference-frequency loads and establish the corresponding uncertainty in the results. Because of the high computing cost, CFD simulations of irregular waves can be challenging. Instead, simulations were performed with bichromatic waves having a shorter repeat period. A preliminary comparison with quadratic transfer functions from second-order potential-flow theory shows that CFD models consistently predict higher nonlinear wave loads at the difference frequency, likely because of flow separation and viscous drag not accounted for in potential-flow theory.

scholarly journals Comparison of Nonlinear Wave-Loading Models on Rigid Cylinders in Regular Waves

Energies ◽  
2019 ◽  
Vol 12 (21) ◽  
pp. 4022 ◽  
Author(s):  
Agota Mockutė ◽  
Enzo Marino ◽  
Claudio Lugni ◽  
Claudio Borri
Keyword(s):  
Second Harmonic ◽  
Numerical Models ◽  
Finite Depth ◽  
Offshore Wind ◽  
Intermediate Water ◽  
Wave Loading ◽  
Wave Kinematics ◽  
Hydrodynamic Loading ◽  
Numerical Wave ◽  
Steep Waves

Monopiles able to support very large offshore wind turbines are slender structures susceptible to nonlinear resonant phenomena. With the aim to better understand and model the wave-loading on these structures in very steep waves where ringing occurs and the numerical wave-loading models tend to lose validity, this study investigates the distinct influences of nonlinearities in the wave kinematics and in the hydrodynamic loading models. Six wave kinematics from linear to fully nonlinear are modelled in combination with four hydrodynamic loading models from three theories, assessing the effects of both types of nonlinearities and the wave conditions where each type has stronger influence. The main findings include that the nonlinearities in the wave kinematics have stronger influence in the intermediate water depth, while the choice of the hydrodynamic loading model has larger influence in deep water. Moreover, finite-depth FNV theory captures the loading in the widest range of wave and cylinder conditions. The areas of worst prediction by the numerical models were found to be the largest steepness and wave numbers for second harmonic, as well as the vicinity of the wave-breaking limit, especially for the third harmonic. The main cause is the non-monotonic growth of the experimental loading with increasing steepness due to flow separation, which leads to increasing numerical overpredictions since the numerical wave-loading models increase monotonically.

Importance of Second-Order Difference-Frequency Wave-Diffraction Forces in the Validation of a FAST Semi-Submersible Floating Wind Turbine Model

2013 ◽  
Author(s):  
Alexander J. Coulling ◽  
Andrew J. Goupee ◽  
Amy N. Robertson ◽  
Jason M. Jonkman
Keyword(s):  
Wind Turbine ◽  
Wave Diffraction ◽  
Second Order ◽  
Difference Frequency ◽  
Offshore Wind ◽  
Wave Forces ◽  
Global Response ◽  
Frequency Wave ◽  
Order Difference ◽  
Floating Wind Turbine

To better access the abundant offshore wind resource, efforts are being made across the world to develop and improve floating offshore wind turbine technologies. A critical aspect of creating reliable, mature floating wind turbine technology is the development, verification, and validation of efficient computer-aided-engineering (CAE) tools. The National Renewable Energy Laboratory (NREL) has created FAST, a comprehensive, coupled analysis CAE tool for floating wind turbines, which has been verified and utilized in numerous floating wind turbine studies. Several efforts are underway to validate the floating platform functionality of FAST to complement its already validated aerodynamic and structural simulation capabilities. The research employs the 1/50th-scale DeepCwind wind/wave basin model test dataset, which was obtained at the Maritime Research Institute Netherlands (MARIN) in 2011. This paper describes further work being undertaken to continue this validation. These efforts focus on FAST’s ability to replicate global response behaviors associated with dynamic wind forces and second-order difference-frequency wave-diffraction forces separately and simultaneously. The first step is the construction of a FAST numerical model of the DeepCwind semi-submersible floating wind turbine that includes alterations for the addition of second-order difference-frequency wave-diffraction forces. The implementation of these second-order wave forces, which are not currently standard in FAST, are outlined and discussed. After construction of the FAST model, the calibration of the FAST model’s wind turbine aerodynamics, tower-bending dynamics, and platform hydrodynamic damping using select test data is discussed. Subsequently, select cases with coupled dynamic wind and irregular wave loading are simulated in FAST, and these results are compared to test data. Particular attention is paid to global motion and load responses associated with the interaction of the wind and wave environmental loads. These loads are most prevalent in the vicinity of the rigid-body motion natural frequencies for the DeepCwind semi-submersible, with dynamic wind forces and the second-order difference-frequency wave-diffraction forces driving the global system response at these low frequencies. Studies are also performed to investigate the impact of neglecting the second-order wave forces on the predictive capabilities of the FAST model. The comparisons of the simulation and test results highlight the ability of FAST to accurately capture many of the important coupled global response behaviors of the DeepCwind semi-submersible floating wind turbine.

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 Response of the International Energy Agency (IEA) Wind 15 MW WindCrete and Activefloat floating wind turbines to wind and second-order waves

2021 ◽  
Vol 6 (3) ◽  
pp. 867-883
Author(s):  
Mohammad Youssef Mahfouz ◽  
Climent Molins ◽  
Pau Trubat ◽  
Sergio Hernández ◽  
Fernando Vigara ◽  
...  
Keyword(s):  
Wind Turbines ◽  
Numerical Models ◽  
International Energy Agency ◽  
Second Order ◽  
Offshore Wind ◽  
Wave Forces ◽  
Energy Agency ◽  
Frequency Wave ◽  
Floating Offshore Wind Turbines ◽  
Floating Platforms

Abstract. The EU Horizon 2020 project COREWIND (COst REduction and increase performance of floating WIND technology) has developed two floating platforms for the new International Energy Agency (IEA) Wind 15 MW reference wind turbine. One design – “WindCrete” – is a spar floater, and the other – “Activefloat” – is a semi-submersible floater; both designs are made of concrete. In this work the design of the floaters is introduced with their aero–hydro–servo-elastic numerical models, and the responses of both floaters in both static and dynamic simulations are investigated. The static displacements and natural frequencies are simulated and discussed. Additionally, the effects of the mean wave drift forces and second-order difference-frequency wave forces on the systems' responses are presented. The increase in the turbine's power capacity to 15 MW in IEA Wind model leads to an increase in inertial forces and aerodynamic thrust force when compared to similar floating platforms coupled to the Technical University of Denmark (DTU) 10 MW reference model. The goal of this work is to investigate the floaters' responses for different load cases. The results in this paper suggest that at mild wave loads the motion responses of the 15 MW floating offshore wind turbines (FOWTs) are dominated by low-frequency forces. Therefore, motions are dominated by the wind forces and second-order wave forces rather than the first-order wave forces. After assessing and understanding the models' responses, the two 15 MW FOWT numerical reference models are publicly available to be used in the research and development of floating wind energy.

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