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.

Hydrodynamic Modeling of Large-Diameter Bottom-Fixed Offshore Wind Turbines

2015 ◽  
Author(s):  
Erin E. Bachynski ◽  
Harald Ormberg
Keyword(s):  
Wind Turbines ◽  
Environmental Conditions ◽  
Limit State ◽  
Second Order ◽  
Offshore Wind ◽  
Stokes Wave ◽  
Intermediate Water ◽  
Hydrodynamic Loads ◽  
Offshore Wind Turbines ◽  
Wave Kinematics

For shallow and intermediate water depths, large monopile foundations are considered to be promising with respect to the levelized cost of energy (LCOE) of offshore wind turbines. In order to reduce the LCOE by structural optimization and de-risk the resulting designs, the hydrodynamic loads must be computed efficiently and accurately. Three efficient methods for computing hydrodynamic loads are considered here: Morison’s equation with 1) undisturbed linear wave kinematics or 2) undisturbed second order Stokes wave kinematics, or 3) the MacCamy-Fuchs model, which is able to account for diffraction in short waves. Two reference turbines are considered in a simplified range of environmental conditions. For fatigue limit state calculations, accounting for diffraction effects was found to generally increase the estimated lifetime of the structure, particularly the tower. The importance of diffraction depends on the environmental conditions and the structure. For the case study of the NREL 5 MW design, the effect could be up to 10 % for the tower base and 2 % for the monopile under the mudline. The inclusion of second order wave kinematics did not have a large effect on the fatigue calculations, but had a significant impact on the structural loads in ultimate limit state conditions. For the NREL 5 MW design, a 30 % increase in the maximum bending moment under the mudline could be attributed to the second order wave kinematics; a 7 % increase was seen for the DTU 10 MW design.

Numerical and Experimental Investigation of the Wave Loading on a Three-Legged Offshore Wind Turbine Jacket Platform

2018 ◽  
Author(s):  
Ioannis K. Chatjigeorgiou ◽  
Konstantinos Chatziioannou ◽  
Vanessa Katsardi ◽  
Apostolos Koukouselis ◽  
Euripidis Mistakidis
Keyword(s):  
Wave Structure ◽  
Element Model ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Wave Forces ◽  
Intermediate Water ◽  
Wave Loads ◽  
Wave Loading ◽  
Scaled Model ◽  
The Time Domain

The purpose of this work is to examine a three-legged jacket tower support system subjected to wave loading. To this end, linear as well as nonlinear wave scenarios are investigated. The structure was designed for offshore wind turbines installed in intermediate water depths. The phenomenon of the wave-structure interaction is examined experimentally with a 1:18 scaled model as well as numerically with the use of Finite Element Model (FEM). The structural calculations were performed using the structural analysis software SAP2000, which was enhanced by a special programming interface that was developed to calculate the wave loading and to directly apply the wave loads on the structural members. The FEM model in combination with the key parameters that are taken into account, provides a good correlation with the experimental results. The wave theories of Airy and Stokes 5th are employed for the calculation of the wave particle kinematics. The resulting wave forces are examined both in the frequency and in the time domain.

scholarly journals Validation of Hydrodynamic Loads on a Large-Diameter Monopile in Regular Waves

2019 ◽  
Author(s):  
Fatemeh H. Dadmarzi ◽  
Maxime Thys ◽  
Erin E. Bachynski
Keyword(s):  
Second Harmonic ◽  
Large Diameter ◽  
Offshore Wind ◽  
Wave Loads ◽  
Hydrodynamic Load ◽  
Regular Waves ◽  
Third Harmonic ◽  
Offshore Wind Turbines ◽  
Load Models ◽  
Steep Waves

Abstract Validated hydrodynamic load models for large-diameter support structures are increasingly important as the industry moves towards larger offshore wind turbines. Experiments at 1:50 scale with stiff, vertical, bottom-fixed, extra-large (9m and 11m diameter full-scale) monopiles in steep waves are conducted. The tests are carried out at two water depths, 27 m and 33 m. A range of regular waves, with varying period and amplitude, are used. The first, second, and third harmonics of the total wave loads, where measurements are available, are calculated with different methods. For the first harmonic of the force (and consequently the mudline moment), MacCamy-Fuchs gives the best agreement with experiments, especially for the larger diameter model. For the second harmonic, for the shortest waves the generalized FNV theory and Morison equation overpredict the forces, while for the longest (and largest) waves, the opposite is observed. The third harmonic of the force is generally overpredicted by the calculations.

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 Effect of Roughness of Mussels on Cylinder Forces from a Realistic Shape Modelling

2021 ◽  
Vol 9 (6) ◽  
pp. 598
Author(s):  
Antoine Marty ◽  
Franck Schoefs ◽  
Thomas Soulard ◽  
Christian Berhault ◽  
Jean-Valery Facq ◽  
...  
Keyword(s):  
Marine Species ◽  
Offshore Structures ◽  
Offshore Wind ◽  
Mooring Lines ◽  
Shape Modelling ◽  
Offshore Wind Turbines ◽  
Specific Effects ◽  
Hydrodynamic Loading ◽  
Floating Offshore Wind Turbines ◽  
Realistic Shape

After a few weeks, underwater components of offshore structures are colonized by marine species and after few years this marine growth can be significant. It has been shown that it affects the hydrodynamic loading of cylinder components such as legs and braces for jackets, risers and mooring lines for floating units. Over a decade, the development of Floating Offshore Wind Turbines highlighted specific effects due to the smaller size of their components. The effect of the roughness of hard marine growth on cylinders with smaller diameter increased and the shape should be representative of a real pattern. This paper first describes the two realistic shapes of a mature colonization by mussels and then presents the tests of these roughnesses in a hydrodynamic tank where three conditions are analyzed: current, wave and current with wave. Results are compared to the literature with a similar roughness and other shapes. The results highlight the fact that, for these realistic roughnesses, the behavior of the rough cylinders is mainly governed by the flow and not by their motions.

Validation of Wave Propagation in Numerical Wave Tanks

2005 ◽  
Author(s):  
Tim Bunnik ◽  
Rene´ Huijsmans
Keyword(s):  
Shallow Water ◽  
Model Test ◽  
Water Depth ◽  
Linear Potential ◽  
Intermediate Water ◽  
Numerical Wave Tank ◽  
Wave Tank ◽  
Type Wave ◽  
Wave Generator ◽  
Numerical Wave

During the last few years there has been a strong growth in the availability and capabilities of numerical wave tanks. In order to assess the accuracy of such methods, a validation study was carried out. The study focuses on two types of numerical wave tanks: 1. A numerical wave tank based a non-linear potential flow algorithm. 2. A numerical wave tank based on a Volume of Fluid algorithm. The first algorithm uses a structured grid with triangular elements and a surface tracking technique. The second algorithm uses a structured, Cartesian grid and a surface capturing technique. Validation material is available by means of waves measured at multiple locations in two different model test basins. The first method is capable of generating waves up to the break limit. Wave absorption is therefore modeled by means of a numerical beach and not by mean of the parabolic beach that is used in the model basin. The second method is capable of modeling wave breaking. Therefore, the parabolic beach in the model test basin can be modeled and has also been included. Energy dissipation therefore takes place according to physics which are more related to the situation in the model test basin. Three types of waves are generated in the model test basin and in the numerical wave tanks. All these waves are generated on basin scale. The following waves are considered: 1. A scaled 100-year North-Sea wave (Hs = 0.24 meters, Tp = 2.0 seconds) in deep water (5 meters). 2. A scaled operational wave (Hs = 0.086 meters, Tp = 1.69 seconds) at intermediate water depth (0.86 meters) generated by a flap-type wave generator. 3. A scaled operational wave (Hs = 0.046 meters, Tp = 1.2 seconds) in shallow water (0.35 meters) generated by a piston-type wave generator. The waves are generated by means of a flap or piston-type wave generator. The motions of the wave generator in the simulations (either rotational or translational) are identical to the motions in the model test basin. Furthermore, in the simulations with intermediate water depth, the non-flat contour of the basin bottom (ramp) is accurately modeled. A comparison is made between the measured and computed wave elevation at several locations in the basin. The comparison focuses on: 1. Reflection characteristics of the model test basin and the numerical wave tanks. 2. The accuracy in the prediction of steep waves. 3. Second order effects like set-down in intermediate and shallow water depth. Furthermore, a convergence study is presented to check the grid independence of the wave tank predictions.

scholarly journals VERIFICATION OF NUMERICAL WAVE PROPAGATION MODELS IN TIDAL INLETS

1988 ◽  
Vol 1 (21) ◽  
pp. 30 ◽  
Author(s):  
J.A. Vogel ◽  
A.C. Radder ◽  
J.H. De Reus
Keyword(s):  
Wave Propagation ◽  
Numerical Models ◽  
River Estuary ◽  
Regular Grid ◽  
Local Wind ◽  
Tidal Inlets ◽  
Propagation Models ◽  
Dutch Coast ◽  
Model Based ◽  
Numerical Wave

The performance of two numerical wave propagation models has been investigated by comparison with field data. The first model is a refractiondiffraction model based on the parabolic equation method. The second is a refraction model based on the wave action equation, using a regular grid. Two field situations, viz. a tidal inlet and a river estuary along the Dutch coast, were used to determine the influence of the local wind on waves behind an island and a breaker zone. It may be concluded from the results of the computations and measurements that a much better agreement is obtained when wave growth due to wind is properly accounted for in the numerical models. In complicated coastal areas the models perform well for both engineering and research purposes.

scholarly journals Characterization of the unsteady aerodynamic response of a floating offshore wind turbine

2020 ◽  
Author(s):  
Simone Mancini ◽  
Koen Boorsma ◽  
Marco Caboni ◽  
Marion Cormier ◽  
Thorsten Lutz ◽  
...  
Keyword(s):  
Numerical Models ◽  
Aerodynamic Performance ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
High Fidelity ◽  
Aerodynamic Damping ◽  
Unsteady Aerodynamic ◽  
Future Work ◽  
Good Agreement

Abstract. The disruptive potential of floating wind turbines has attracted the interest of both industry and scientific community. Lacking a rigid foundation, such machines are subject to large displacements whose impact on the aerodynamic performance is not yet fully acknowledged. In this work, the unsteady aerodynamic response to an harmonic surge motion of a scaled version of the DTU10MW turbine is investigated in detail. The imposed displacements have been chosen representative of typical platform motions. The results of different numerical models are validated against high fidelity wind tunnel tests specifically focused on the aerodynamics. Also a linear analytical model, relying on the quasi-steady assumption, is presented as a theoretical reference. The unsteady responses are shown to be dominated by the first surge harmonic and a frequency domain characterization, mostly focused on the thrust oscillation, is conducted involving aerodynamic damping and mass parameters. A very good agreement among codes, experiments and quasi-steady theory has been found clarifying some literature doubts. A convenient way to describe the unsteady results in non-dimensional form is proposed, hopefully serving as reference for future work.

Consistent Modal Calibration of a Pendulum-Type Vibration Absorber

2022 ◽  
Author(s):  
J. Høgsberg
Keyword(s):  
Wind Turbines ◽  
Offshore Wind ◽  
Vibration Absorber ◽  
Wave Loading ◽  
Offshore Wind Turbines ◽  
Stiffness And Damping

Abstract. Pendulum absorbers are installation in offshore wind turbines to mitigate excessive vibration amplitudes from wind and wave loading. The pendulum damper is placed inside the tower and attached to the structure at two distinct points: The tower top, where the pendulum arm is fixated, and at the position of the pendulum mass, which is connected to the tower wall by the damper. The present paper derives a modal calibration principle, which consistently accounts for different points of attachment for the absorber stiffness and damping.

Cable JIP: A Research Project to Assess the Feasibility of a Semi-Static Electrical Subsea Cable for the Power Take-off from a TLP-type Floating Offshore Wind Turbine

2021 ◽  
Author(s):  
J. J. de Wilde ◽  
C. G. J. M. van der Nat ◽  
L.. Pots ◽  
L. B. de Vries ◽  
Q.. Liu
Keyword(s):  
Wind Turbine ◽  
Numerical Models ◽  
Electrical Power ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Power Cable ◽  
Test Case ◽  
Research Project ◽  
Floating Offshore Wind Turbine ◽  
Cost Of Energy

Abstract CABLE JIP research project in 2017-2019 was initiated with the aim of studying the feasibility of deploying a novel semi-static electrical cable for the power take-off from a TLP-type Floating Offshore Wind Turbine (FOWT). Today, expensive dynamic electrical cables are mainly used for the power take-off from demonstrator project FOWTs or from new FOWTs on the drawing board. For a TLP-type FOWT, the use of a semi-static electrical power cable instead of a fully dynamic electrical power cable (umbilical) is an attractive option to reduce the levelized cost of energy (LCoE). However, the electrical power cable in a dynamic offshore environment is vulnerable to failure, either at the floater side or at the seabed touchdown area. Moreover, the electrical power cable for power take-off is typically non-redundant, while the availability of the turbine(s) highly depends on this critical component to transport the produced power to the substation. The paper discusses the results of the CABLE JIP research project, with focus on the verification and calibration of the numerical models for the ULS and FLS assessment of the electrical power inter-array cable for a harsh weather test case with a TLP-type floating offshore wind turbine in 96.5 m water depth.

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