The industry standard for analysis of monopile foundations is inaccurate, and alternative models for foundation behavior are needed. This study investigates how four different soil-foundation models affect the fatigue damage of an offshore wind turbine with a monopile foundation. Stiffness and damping properties have a noticeable effect, in particular for idling cases. At mud-line, accumulated fatigue damage varied up to 22 % depending on the foundation model used.
Predicting the 50-year extreme loads for wind turbines requires a tremendous computational effort. Therefore, designers often have to extrapolate from relatively small data sets and have to settle for some degree of uncertainty. We investigated the impact of this uncertainty on practical design problems by drawing subsets from a 96-year load data set and using a crude Monte Carlo method to find the 50-year load. The results show that designers have to be careful with selecting sample sizes.
This paper presents the idea of centralized electricity production in a wind farm by means of water technology. A new way of generating and transmitting wind energy is explored with no intermediate electrical conversion until the energy has reached the central offshore platform. This work includes the modelling and simulations of a hypothetical hydraulic wind farm, where results indicate good performance despite the turbulent wind conditions and wake effects.
The majority of the wind turbine market is focused on large pitch-regulated machines, but small stall-regulated are still attractive because of their simplicity and robustness. This work focuses on aerodynamic section design for these machines and its impact on overall performance. The big challenge faced was that, beside the need to maximise the energy produced, the control of the machine depends on the section design. The results, however, showed a large performance gain and machine control.
In the paper, rotor stability in slow idling operation is assessed on the basis of nonlinear time domain and linear eigenvalue analyses. A consistent and computationally cost effective modeling environment has been presented for the analysis of parked or idling rotors. The analysis shows that the lowest damped modes of a 10 MW idling rotor are out-of-plane modes (symmetric and asymmetric).
Recently, the concept of intentional derating of single wind turbines in order to increase the energy yield of a wind farm has been studied intensively. Although the potential seems promising, the effects of atmospheric conditions need to be understood in greater detail. This study shows a strong influence of vertical velocity gradients on the power output of two model wind turbines, whereas the upstream turbine is derated by an intentional misalignment of the rotor and the inflow.
This paper presents a validation and code-to-code verification of the U.S. Dept of Energy/NREL wind turbine aeroelastic code, FAST v8, on a 2.3 MW wind turbine. Model validation is critical to any model-based research and development activity, and validation efforts on large turbines, as the current one, are extremely rare, mainly due to the scale. This paper, which was a collaboration between NREL and Siemens Wind Power, successfully demonstrates and validates the capabilities of FAST.
The first larger offshore wind farms are reaching a mature age. Operators have to take actions for monitoring now in order to have accurate knowledge on structural reserves later. This knowledge is important to make decisions on lifetime extension. Many offshore wind turbines have one set of strain gauges already installed at the transition piece. We present a simple and robust method to extrapolate these measurements to other locations of the monopile without need of additional instrumentation.
Stability classification is usually based on measurements from met masts, buoys or lidars. The objective of this paper is to find a classification for stability based on wind turbine supervisory control and data acquisition measurements in order to fit engineering wake models better to the current ambient conditions. The proposed signal is very sensitive to increased turbulence. It allows us to distinguish between conditions with different magnitudes of wake effects.
For the design of offshore wind turbines, the knowledge of environmental conditions is important. However, real high-quality data are rare. This is why a comprehensive database of environmental conditions at wind turbine locations in the North and Baltic Sea is derived using real data. The main purpose of this work is to collect realistic data for probabilistic approaches. Hence, all results are freely available.
We present an engineering model of 3-D turbulent wind inflow which reduces the number of random variables required from tens of thousands to ~ 20. This new model is a vital step towards stochastic modelling of wind turbines. Such models can quickly assess turbine lifetime loads and fluctuating power output and thus can be used to design better turbines. However, stochastic models are only viable when the input is expressed with very few random variables, hence the new wind model presented here.
Current fast aeroelastic wind turbine codes suitable for certification lack an induction model for standstill conditions. A near-wake model for wind turbines in operation is extended to cover these conditions. The model is validated in aerodynamic simulations of the NREL/NASA Ames Phase VI rotor. Good agreement with the experiments has been obtained in attached flow and beginning separation. Aeroelastic simulations of the DTU 10 MW turbine in standstill indicate a minor impact of the model.
Low-level jets (LLJ) are fast flows in the low atmosphere, usually seen at night, with a wind speed peak between 100–1000 m above the ground. More wind energy can be captured if an LLJ is present. The positive wind shear below the peak augments the damage to wind turbines. However, our results show that the negative shears above decrease the mechanical loading. Therefore, reaching negative shears more often reduces the LLJs' adverse impacts and makes it more feasible to harness their power.
This paper presents an alternative method to evaluate power performance and loads on wind turbines using a blade-mounted flow sensor. A high correlation is found between the wind speed measured at the blades and the power/loads, and simulations indicate that it is possible to reduce the time required for power and load assessment considerably. This result, however, cannot be confirmed from the full-scale measurement study due to practical circumstances.
The wakes of wind turbines cause losses in the energy production of a wind farm. The accuracy of models applied to predict wake losses is a key factor for new wind projects. This paper presents an engineering wake model that can simulate merging wakes on the basis of physical principles. We used high-fidelity simulations of merging wakes to assess this model and found a better agreement with the reference than commonly used models implementing the superposition of individual wakes.
A model chain to simulate changing atmospheric conditions at the location of an offshore wind farm is introduced and validated. The methodology is used to simulate the wind flow upstream and downstream of an offshore wind turbine of the German wind farm Alpha ventus. The model results show a good agreement with wind measurements from the met mast that is located at the wind farm and with remote sensing measurements of the horizontal wind field.
The rotor of a wind turbine is used to determine some important parameters of the wind, including the direction of the wind vector relative to the rotor disk and horizontal and vertical shears. The method works by using measurements provided by existing onboard load sensors. The observed wind characteristics can be used to implement advanced features in smart wind turbine and wind farm controllers.
Given the rapid growth and large scale of wind turbines, it is important that wind farms achieve maximum availability by reducing downtime due to maintenance and failures. The Blade Reliability Collaborative, led by Sandia National Laboratories and sponsored by the US DOE, was formed to address this issue. A comprehensive study to characterize and understand the manufacturing flaws common in blades, and their impact on blade life, was performed by measuring and testing commonly included defects.
The Blade Reliability Collaborative was formed to address wind turbine blade reliability. To better understand and predict these effects, various progressive damage modeling approaches, built upon the characterization previously addressed, were investigated. The results indicate that a combined continuum–discrete approach provides insight into reliability with known defects when used in conjunction with a probabilistic flaw framework.
Floating platform wind turbines present a challenge for engineers to simulate. This paper explores some better methods for simulating the aerodynamics of wind turbines as they move about on a floating platform. We also derived a new way of investigating whether the aerodynamics of the wind turbine rotor help it stay stable.