Category Archives: Wind

Computationally efficient modelling of dynamic soil-structure interaction of offshore wind turbines on gravity footings


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M. Damgaard, L.V. Andersen, and L.B. Ibsen – Renewable Energy, August 2014

Abstract

The formulation and quality of a computationally efficient model of offshore wind turbine surface foundations are examined. The aim is to establish a model, workable in the frequency and time domain, that can be applied in aeroelastic codes for fast and reliable evaluation of the dynamic structural response of wind turbines, in which the geometrical dissipation related to wave propagation into the subsoil is included. Based on the optimal order of a consistent lumped-parameter model obtained by the domain-transformation method and a weighted least-squares technique, the dynamic vibration response of a 5.0 MW offshore wind turbine is evaluated for different stratifications, environmental conditions and foundation geometries by the aeroelastic nonlinear multi-body code HAWC2. Analyses show that a consistent lumped-parameter model with three to five internal degrees of freedom per displacement or rotation of the foundation is necessary in order to obtain an accurate prediction of the foundation response in the frequency and time domain. In addition, the required static bearing capacity of surface foundations leads to fore–aft vibrations during normal operation of a wind turbine that are insensitive to wave propagating in the subsoil—even for soil stratifications with low cut-in frequencies. In this regard, utilising discrete second-order models for the physical interpretation of a rational filter puts special demands on the Newmark β-scheme, where the time integration in most cases only provides a causal response for constant acceleration within each time step.

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Assessing the China Sea wind energy and wave energy resources from 1988 to 2009


C-W Zheng, J. Pan, J-X Li – Ocean Engineering, June, 2013

Abstract

In this study, the wave field in the China Sea was simulated over the period from 1988 to 2009 using the third-generation wave model WAVEWATCH-III (WW3), with Cross-Calibrated, Multi-Platform (CCMP) wind field as the driving field. The China Sea wind energy density and wave energy density were calculated using the CCMP wind and WW3 model simulation results. The China Sea wind energy and wave energy resource were analyzed, synthetically considering the value of energy density, probability of exceedance of energy density level, exploitable wind speed and exploitable significant wave height (SWH), the stability of energy density, total storage and exploitable storage of energy resources, thus providing the guidance for the location of wind and wave power plants. Our results show that most of the China Sea contains abundant wave energy and offshore wind energy resources, with wind energy density above 150 W/m2, wave energy density above 2 kW/m, high occurrence of exploitable wind and wave energy in large scale waters, wind energy storage above 2×103 kW h m−2, wave energy storage above 4×104 kW h m−1. The richest area is in the northern South China Sea (wind energy density 350–600 W/m2, wave energy density 10–16 kW/m, wind energy storage 3×103–5×103 kW h m−2, wave energy storage 8×104–16×104 kW h m−1), followed by southern South China Sea and the East China Sea (wind energy density 150–450 W/m2, wave energy density 4–12 kW/m, wind energy storage 2×103–4×103 kW h m−2, wave energy storage 4×104–12×104 kW h m−1). The Yellow Sea and Bohai Sea resources are relatively poorer (wind energy density below 300 W/m2, wave energy density below 4 kW/m, wind energy storage below 2.5×103 kW h m−2, wave energy storage below 6×104 kW h m−1).

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Filed under Resource Assessment, Resource Characterization, Wind

Offshore wind turbine risk quantification/evaluation under extreme environmental conditions


A.A. Taflanidis, E. Loukogeorgaki, and D.C. Angelides – Reliability Engineering & System Safety, February, 2013

Abstract

A simulation-based framework is discussed in this paper for quantification/evaluation of risk and development of automated risk assessment tools, focusing on applications to offshore wind turbines under extreme environmental conditions. The framework is founded on a probabilistic characterization of the uncertainty in the models for the excitation, the turbine and its performance. Risk is then quantified as the expected value of the risk consequence measure over the probability distributions considered for the uncertain model parameters. Stochastic simulation is proposed for the risk assessment, corresponding to the evaluation of the associated probabilistic integral quantifying risk, as it allows for the adoption of comprehensive computational models for describing the dynamic turbine behavior. For improvement of the computational efficiency, a surrogate modeling approach is introduced based on moving least squares response surface approximations. The assessment is also extended to a probabilistic sensitivity analysis that identifies the importance of each of the uncertain model parameters, i.e. risk factors, towards the total risk as well as towards each of the failure modes contributing to this risk. The versatility and computational efficiency of the advocated approaches is finally exploited to support the development of standalone risk assessment applets for automated implementation of the probabilistic risk quantification/assessment.

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Calculating the offshore wind power resource: Robust assessment methods applied to the U.S. Atlantic Coast


B Sheridan, SD Baker, NS Pearre, J Firestone, W Kempton- Renewable Energy, July 2012

Highlights
► Power potential methodology improves upon existing offshore resource assessments. ► Includes bathymetry delineations based on technology advancements. ► Acknowledges previously unaddressed, potential conflict with commercial shipping. ► Presents previously un-quantified offshore wind potential for Maryland. ► Results are presented in terms useful for energy planners and policy makers.

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A simplified method for coupled analysis of floating offshore wind turbines


M Karimirad T Moan – Marine Structures, July 2012

Highlights
► Simplified approach for dynamic response analysis of floating wind turbines. ► Idea is to minimize the computational time while maintaining acceptable accuracy. ► Method is validated against a comprehensive aero-hydro-servo-elastic approach. ► The codes agree for the wave-only cases and for the wave- and wind-induced cases. ► Two floating wind turbines are considered to perform sensitivity study.

 

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Study on the Dynamic Characteristic for Spar Type Floating Foundation of Offshore Wind Turbine


RY Zhang, CH Chen, Y Tang – Applied Mechanics and Materials, May 2012

Abstract
In this paper, the dynamic behaviors are studied for Spar type floating foundation of a 3kW in the 10m deep water considering the coupled wind turbine-tower-floating foundation and mooring lines and ocean environment load effects. The paper focus on the key issues of design of floating foundation, such as coupling dynamic analysis model and calculating method. The finite element models are established and dynamic responses of floating wind turbine system under different combinations of turbulent wind, constant current and irregular wave are calculated in frequency and time domain with SESAM software. The motion performance and lines’ tension are investigated, and some valuable conclusions are drawn. The results show that the Spar type floating foundation and mooring system can work in the ocean environment which significant wave height less than 2m, the designed large water-entrapment plate can minimized the motion of floating foundation obviously.

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Research of Offshore Wind Power Generation Technology


YN Guo, Y Zhang, J Wang, Y Huang – Advanced Materials Research, May 2012

Abstract
Offshore wind farm development direction is from shallow sea to sea . In this paper, according to the current on the wind power base also can not meet the requirements of the problem deep, analysed the base cost will not be particularly high reason. In view of the Hainan offshore wind power, put forward the design train of thought, the analysis obtained an ideal design model.

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Analysis of Environmental Characteristics and Operational Reports of Small and Medium Turbines


AMS Florescu, G Bandoc, M Degeratu – Applied Mechanics and Materials, May 2012

Abstract
Application of environmental policies to prevent climate change, mitigation of climate change, the progressive reduction of emissions of greenhouse gases under commitments, encourage reducing energy consumption by using technologies that are efficient and support production of cheap and clean energy sources should be a priority for contemporary society. Given the above goals, the application presented in this article represents a model of how we addressed the question of the correct size of local wind turbines to provide energy coverage of a community. This method involves an analysis of environmental factors, followed by the analysis of wind in the area and continued to calculate the energy potential of the area and capable energy and wind turbines provided consumer choice.

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Offshore reliability


G Marsh – Renewable Energy Focus, May 2012

Summary
Offshore turbines need to be more reliable than their onshore counterparts. How is this creating divergence in approach as the offshore turbine industry evolves?

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Study on the marine growth effect on the dynamic response of offshore wind turbines


W Shi, HC Park, JH Baek, CW Kim, YC Kim, HK Shin – International Journal of Precision Engineering and Manufacturing, April 2012

Abstract
Jacket foundation is regarded as a suitable solution for wind turbines in the intermediate water depths ranging from 30 to 80 m. Numerous types of marine fouling organisms may be found on the submerged members of jacket. Marine growth is found to influence loading of offshore structures by increasing tube diameters, drag coefficient, mass and hydrodynamic added mass and structural weight. In this paper, the types and distribution of marine growth are mentioned. We aimed to investigate the effects of marine growth with different thicknesses, densities and hydrodynamic coefficients values on characteristics of an offshore wind turbine with jacket foundation. The eigen analysis shows that the marine growth has a little effect on the first order natural frequencies while it has higher effect on second and third order natural frequencies of the support structure. Thickness and density have a strong effect on hydrodynamic loads. To obtain the properties of marine growth and hydrodynamic coefficients in the design of offshore wind turbines, full-scale measurements are needed.

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