scholarly journals Concept Research of a Countermeasure Device for Preventing Scour around the Monopile Foundations of Offshore Wind Turbines

Energies ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 2593 ◽  
Author(s):  
Wenxian Yang ◽  
Wenye Tian
Keyword(s):  
Shear Stress ◽  
Wind Turbines ◽  
Surface Profile ◽  
Offshore Wind ◽  
Optimal Size ◽  
Offshore Wind Turbines ◽  
Service Period ◽  
Horseshoe Vortices ◽  
Calculation Results ◽  
The Impact

Scouring has long been considered to be a major issue affecting the reliability of the monopile foundations of offshore wind turbines (OWTs) on sandy seabeds. To reduce the impact of scouring, several tons of rock/stone are usually placed around the foundations shortly after the installation of them. Such a measure is costly. Moreover, rock and stone may spread widely on the seabed during the long-term service period of OWTs. It has no doubt that recycling these rock and stone on the seabed is quite difficult in future decommission. For this reason, a new scour-countermeasure device (SEMCD) is proposed and studied in this paper. Considering that the major driver of scouring is horseshoe vortices around the monopile foundation, a hollow horn-like SEMCD with an arc surface profile is designed for weakening the horseshoe vortices. The SEMCD is made of either cement or other kinds of corrosion resistant materials. It is light in weight, and easy to install and decommission. In the paper, the working mechanism of the SEMCD is first explained. Then, its scouring mitigation effect (SME), i.e., its contribution to the reduction of horseshoe vortices and the mitigation of seabed erosion around the foundation, is studied through investigating its influences on down/up-flow and seabed shear stress. Finally, the optimal size of the SEMCD is discussed through investigating the impact of its size on the speeds of up and down flows and the shear stress on seabed surface. The calculation results have shown that the proposed SEMCD has great potential to prevent scouring and seabed erosion, so that it is of significance to improve the reliability of the monopile foundations of OWTs.

How to Detect Local Out-of-Plane Vibrations in Jacket Support Structures for Offshore Wind Turbines

2014 ◽  
Author(s):  
Sebastian Schafhirt ◽  
John M. Hembre ◽  
Michael Muskulus
Keyword(s):  
Fatigue Damage ◽  
Wind Turbines ◽  
Sequential Analysis ◽  
Offshore Wind ◽  
Support Structures ◽  
Local Vibration ◽  
Offshore Wind Turbines ◽  
Simulation Based ◽  
Out Of Plane ◽  
The Impact

There has been an ongoing debate whether local out-of-plane vibrations of braces exist in jacket support structures for wind turbines. The issue has been raised with the sequential analysis of offshore wind turbines, where increased fatigue damage for bracings was observed. Local vibration modes, excited by rotor harmonics, were detected as a reason for it. A methodology to remove global motion of the jacket from the displacements of the central joint in a brace is presented and the amplitude of local out-of-plane displacements is analyzed, using an integrated wind turbine simulation based on a flexible multibody solver. Finally, the impact on fatigue damage is calculated. Results indicate that the extent of local vibrations is much less than previously thought or predicted in other studies.

Experimental Investigations of Breaking Wave Impact Forces on a Monopile Substructure for Offshore Wind Turbines Under Regular Breaking Waves

2017 ◽  
Author(s):  
Vipin Chakkurunni Palliyalil ◽  
Panneer Selvam Rajamanickam ◽  
Mayilvahanan Alagan Chella ◽  
Vijaya Kumar Govindasamy
Keyword(s):  
Circular Cylinder ◽  
Wind Turbines ◽  
Breaking Waves ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Breaking Wave ◽  
Wave Impact ◽  
Offshore Wind Turbines ◽  
Impact Forces ◽  
The Impact

The main objective of the paper is to investigate wave impact forces from breaking waves on a monopile substructure for offshore wind turbine in shallow waters. This study examines the load assessment parameters relevant for breaking wave forces on a vertical circular cylinder subjected to breaking waves. Experiments are conducted in a shallow water flume and the wave generation is based on piston type wave maker. The experiments are performed with a vertical circular cylinder with diameter, D = 0.20m which represents a monopile substructure for offshore wind turbines with regular waves of frequencies around 0.8Hz. The experimental setup consists of a 1/10 slope followed by a horizontal bed portion with a water depth of 0.8m. Plunging breaking waves are generated and free surface elevations are measured at different locations along the wave tank from wave paddle to the cylinder in order to find the breaking characteristics. Wave impact pressures are measured on the cylinder at eight different vertical positions along the height of the cylinder under breaking waves for different environmental conditions. The wave impact pressures and wave surface elevations in the vicinity of the cylinder during the impact for three different wave conditions are presented and discussed.

Comparison of Epoxy Coating Degradations Under Impingement Flow and Stationary Immersion

2020 ◽  
Author(s):  
Amin Vedadi ◽  
M. Subbir Parvej ◽  
Xinnan Wang ◽  
Yechun Wang
Keyword(s):  
Wind Turbines ◽  
Sea Water ◽  
Electrochemical Impedance ◽  
Epoxy Coating ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Corrosive Environment ◽  
Nacl Solution ◽  
Offshore Wind Turbines ◽  
The Impact

Abstract Offshore wind turbines are considered as a reliable source of electricity generation. However, due to the large cost of the construction and installation of offshore wind turbines, most wind turbines are designed to operate for more than 20 years. One of the biggest issues which causes a severe damage to the construction of wind turbines is the existence of a very corrosive environment including large mechanical loads applied to the construction by the waves and the high concentration of salt and other chemicals in the sea water. The construction of offshore wind turbine can be divided into four main regions based on the types of exposure to the water and the corrosive environment, including submerged zone, tidal zone, splash zone, and atmospheric zone. In this study, experiments were conducted to compare the impact of impingement flow of 3.5 w.t.% NaCl solution on the epoxy coating samples to the exposure of the same type of samples to a stationary 3.5 w.t.% NaCl solution. Those two exposure conditions correspond to the environments at the top and the bottom part of the submerged zone of offshore wind turbines respectively. Electrochemical Impedance Spectroscopy (EIS) method was used to monitor the degradation of organic coatings. The surface roughness was measured by Atomic Force Microscope (AFM). The roughness of the coated surfaces before and after the exposure was compared. For the two different flow conditions, i.e. impingement flow and stationary immersion, significant differences have been discovered from the EIS results and AFM results. We observed a more severe degradation in the epoxy coatings in impingement flow, and a rougher surface is formed for coating samples subjected to impingement flow.

Floating Offshore Wind Turbines

2008 ◽  
Vol 42 (2) ◽  
pp. 39-43 ◽  
Author(s):  
Paul Sclavounos
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Research Effort ◽  
Wind Farms ◽  
Offshore Wind ◽  
Response Dynamics ◽  
Offshore Wind Farms ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines ◽  
The Impact

Wind is a rapidly growing renewable energy source, increasing at an annual rate of 30%, with the vast majority of wind power generated from onshore wind farms. The growth of these facilities, however, is limited by the lack of inexpensive land near major population centers and the visual impact caused by large wind turbines.Wind energy generated from floating offshore wind farms is the next frontier. Vast sea areas with stronger and steadier winds are available for wind farm development and 5 MW wind turbine towers located 20 miles from the coastline are invisible. Current offshore wind turbines are supported by monopoles driven into the seafloor or other bottom mounted structures at coastal sites a few miles from shore and in water depths of 10-15 m. The primary impediment to their growth is their prohibitive cost as the water depth increases.This article discusses the technologies and the economics associated with the development of motion resistant floating offshore wind turbines drawing upon a seven-year research effort at MIT. Two families of floater concepts are discussed, inspired by developments in the oil and gas industry for the deep water exploration of hydrocarbon reservoirs. The interaction of the floater response dynamics in severe weather with that of the wind turbine system is addressed and the impact of this coupling on the design of the new generation of multi-megawatt wind turbines for offshore deployment is discussed. The primary economic drivers affecting the development of utility scale floating offshore wind farms are also addressed.

scholarly journals Application of a Monte Carlo Procedure for Probabilistic Fatigue Design of Floating Offshore Wind Turbines

2017 ◽  
Author(s):  
Kolja Müller ◽  
Po Wen Cheng
Keyword(s):  
Monte Carlo ◽  
Wind Turbines ◽  
Environmental Conditions ◽  
Measurement Data ◽  
Monte Carlo Integration ◽  
Offshore Wind ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines ◽  
Sampling Procedures ◽  
The Impact

Abstract. Fatigue load assessment of floating offshore wind turbines poses new challenges on the feasibility of numerical procedures. Due to the increased sensitivity of the considered system with respect to the environmental conditions from wind and ocean, the application of common procedures used for fixed-bottom structures results in either inaccurate simulation results or hard-to-quantify conservatism in the system design. Monte Carlo based sampling procedures provide a more realistic approach to deal with the large variation of the environmental conditions, although basic randomization has shown slow convergence. Specialized sampling methods allow efficient coverage of the complete design space, resulting in faster convergence and hence a reduced number of required simulations. In this study, a quasi-random sampling approach based on Sobol’ sequences is applied to select representative events for the determination of the lifetime damage. This is calculated applying Monte-Carlo integration, using subsets of a resulting total of 16 200 coupled time-domain simulations performed with the simulation code FAST. The considered system is the DTU 10 MW reference turbine installed on the LIFES50+ OO-Star Wind Floater Semi 10 MW floating platform. Statistical properties of the considered environmental parameters (i.e. wind speed, wave height and wave period) are determined based on the measurement data from Gulf of Maine, USA. Convergence analyses show that it is sufficient to perform around 200 simulations in order to reach less than 10 % uncertainty of lifetime fatigue damage equivalent loading. Complementary in-depth investigation is performed focusing on the load sensitivity and the impact of outliers. Recommendations for the implementation of the proposed methodology in the design process are also provided.

scholarly journals Application of a Monte Carlo procedure for probabilistic fatigue design of floating offshore wind turbines

2018 ◽  
Vol 3 (1) ◽  
pp. 149-162 ◽  
Author(s):  
Kolja Müller ◽  
Po Wen Cheng
Keyword(s):  
Monte Carlo ◽  
Wind Turbines ◽  
Environmental Conditions ◽  
Measurement Data ◽  
Monte Carlo Integration ◽  
Offshore Wind ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines ◽  
Sampling Procedures ◽  
The Impact

Abstract. Fatigue load assessment of floating offshore wind turbines poses new challenges on the feasibility of numerical procedures. Due to the increased sensitivity of the considered system with respect to the environmental conditions from wind and ocean, the application of common procedures used for fixed-bottom structures results in either inaccurate simulation results or hard-to-quantify conservatism in the system design. Monte Carlo-based sampling procedures provide a more realistic approach to deal with the large variation in the environmental conditions, although basic randomization has shown slow convergence. Specialized sampling methods allow efficient coverage of the complete design space, resulting in faster convergence and hence a reduced number of required simulations. In this study, a quasi-random sampling approach based on Sobol sequences is applied to select representative events for the determination of the lifetime damage. This is calculated applying Monte Carlo integration, using subsets of a resulting total of 16 200 coupled time–domain simulations performed with the simulation code FAST. The considered system is the Danmarks Tekniske Universitet (DTU) 10 MW reference turbine installed on the LIFES50+ OO-Star Wind Floater Semi 10 MW floating platform. Statistical properties of the considered environmental parameters (i.e., wind speed, wave height and wave period) are determined based on the measurement data from the Gulf of Maine, USA. Convergence analyses show that it is sufficient to perform around 200 simulations in order to reach less than 10 % uncertainty of lifetime fatigue damage-equivalent loading. Complementary in-depth investigation is performed, focusing on the load sensitivity and the impact of outliers (i.e., values far away from the mean). Recommendations for the implementation of the proposed methodology in the design process are also provided.

Hurricane Risk Considerations for Offshore Wind Turbines on the Atlantic Coast

2015 ◽  
Author(s):  
V. Valamanesh ◽  
K. Wei ◽  
A. T. Myers ◽  
S. R. Arwade ◽  
W. Pang
Keyword(s):  
Wind Turbines ◽  
Renewable Energy Sources ◽  
Atlantic Coast ◽  
Offshore Structures ◽  
Parametric Models ◽  
Offshore Wind ◽  
Offshore Wind Turbines ◽  
Wave Measurements ◽  
Hurricane Activity ◽  
The Impact

The development of renewable energy sources is a critical global need. The Atlantic coast and Gulf of Mexico of the U.S., with large wind resources and proximity to major population centers, are natural places for such development; however, these regions are also at considerable risk from severe hurricanes or tropical cyclones. Current international guidelines for the design of offshore wind turbines (OWTs) do not explicitly consider loading under hurricane conditions, however subsequent editions are anticipated to include language specific to hurricanes. Variability in extreme loads is greater in areas where hurricanes are likely and the design loads and risk profile of offshore structures installed in such areas are expected to be strongly influenced by hurricanes. For many offshore structures, environmental conditions at design recurrence periods and beyond are often estimated through extrapolation of long-term (i.e. multiple decades) wind and wave measurements from buoys, however, for offshore structures located at areas exposed to hurricanes, it is accepted practice to use physics-based models to augment the historical record of Atlantic hurricane activity and generate a stochastic catalog of synthetic hurricanes that provides tens of thousands of realizations for one year of potential hurricane activity. Once a stochastic catalog has been established, appropriate hazard intensity measures (e.g. the one-minute sustained wind speed, the significant wave height, and the peak spectral wave period) can be estimated for each storm at any site using well-known wind and wave parametric models. In this study, we consider several sites along the Atlantic coast and quantify the impact of estimating hazard for design recurrence periods and beyond for three different methods. The first is based on an extrapolation of wind and wave measurements from buoys, and the second and third are based on a stochastic catalog of synthetic hurricanes with wind and wave intensities estimated based on deterministic and probabilistic relationships.

Pitch Angle Control of Floating Offshore Wind Turbines by H∞ Control

2014 ◽  
Vol 134 (8) ◽  
pp. 1096-1103 ◽  
Author(s):  
Sho Tsujimoto ◽  
Ségolène Dessort ◽  
Naoyuki Hara ◽  
Keiji Konishi
Keyword(s):  
Wind Turbines ◽  
Pitch Angle ◽  
Offshore Wind ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines
Sign in / Sign up

Export Citation Format

Share Document