1 - 10 of 518
-
PublicationDetection of electrocatalytical and -chemical processes by means of in situ flow NMR spectroscopy( 2024-06)In situ studies of electrochemical processes using NMR offer valuable information on reaction mechanisms, kinetics, and species identification, making it a powerful tool in electrochemistry research. In this study, we present the design of an in situ redox-flow NMR cell that allows for a continuous flow of liquid (electrolyte) or gas, application of electrical voltage, and recording of NMR signals. The utility of this setup is demonstrated through two case studies: electrochemical copper deposition on a gold electrode and the electrochemical conversion of carbon dioxide into hydrocarbon products. Specifically, the presence of multicarbon products containing C–C bonds generated during the electrochemical reduction reaction is confirmed in the 2H NMR spectra in the latter example. These findings highlight the ability of the in situ redox-flow NMR cell to directly monitor reaction intermediates and products, thereby enabling the elucidation of reaction mechanisms for the efficient and selective production of valuable hydrocarbon products through the conversion of CO2 into value-added chemicals. In contrast to other reported in situ NMR cells, the presented cell is suitable for multiple uses, and allows detecting NMR signals not only from exhaust products but also from those formed on the catalyst surface.
-
PublicationAn Ontology for Describing Wind Lidar Concepts( 2024-05-31)This article reports on an open-source ontology that has been developed to establish an industry-wide consensus on wind lidar concepts and terminology. The article provides an introduction to wind lidar ontology, provides an overview of its development, and provides a summary of its aims and achievements. The ontology serves both reference and educational purposes for wind energy applications and lidar technology. The article provides an overview of the creation process, the outcomes of the project, and the proposed uses of the ontology. The ontology is available online and provides standardisation of terminology within the lidar knowledge domain. The open-source framework provides the basis for information sharing and integration within remote sensing science and fields of application.
-
PublicationMulti-physics system modelling based on bond graph theory for offshore hydrogen production( 2024-05-28)
-
PublicationIntermittency, an inevitable feature for faster convergence of large eddy simulations( 2024-05-22)Gaussian and intermittent synthetically generated turbulences are investigated as initial conditions for high-resolution numerical simulations. Turbulent fields, namely the Mann and the intermittent Time-mapped Mann model, are injected into large eddy simulations, and subsequently their convergences are investigated. In addition to the usual one-point and two-point characterizations, the higher moments of the velocity increments are addressed to grasp the intermittency. Here, we show that independent of the initial conditions, the evolving turbulence converges to a common state, which is well represented by the classical intermittent turbulence of Kolmogorov. The findings reveal that if the intermittency parameters of the inflow field are adjusted to those of the common state, the convergence behavior is much faster.
-
PublicationDevelopment of a Load Model Validation Framework Applied to Synthetic Turbulent Wind Field Evaluation( 2024-04)The validation of aeroelastic load models used for load calculations on wind turbines substantially increases the confidence in the accuracy and correctness of these models. In this contribution, we introduce a framework for the validation of these models, integrating a normalized area metric as an objective, quantifiable validation metric that considers the entire statistical distribution of a model and a benchmark and additionally enables a comparison of model accuracy between sensors of different physical units. The framework is applied to test cases that evaluate varying synthetic turbulent wind fields. Two test cases with a focus on turbulence parameters and abnormal shear conditions based on comprehensive wind measurements at the Testfeld Bremerhaven are used to demonstrate the workflow with four different members using IEC-compliant and measurement-derived wind field parameters, respectively. Along with these measurements, an uncertainty model for synthetic wind fields is introduced to quantify propagated wind measurement uncertainties associated with the measured boundary conditions during a validation campaign. The framework is presented as a straightforward and concise methodology to not only find but also quantify mismatches of load models. Major mismatches are found for wind fields associated with larger uncertainties in the mean wind field due to a reduced spatial resolution of measurements.
-
PublicationInfluence of rotor blade flexibility on the near-wake behavior of the NREL 5 MW wind turbine( 2024-01-22)High-fidelity computational fluid dynamics (CFD) simulations of the National Renewable Energy Laboratory (NREL) 5 MW wind turbine rotor are performed, comparing the aerodynamic behavior of flexible and rigid blades with respect to local blade quantities as well as the wake properties. The main focus has been set on rotational periodic quantities of blade loading and fluid velocity magnitudes in relation with the blade tip vortex trajectories describing the development of those quantities in the near wake. The results show that the turbine loading in a quasi-steady flow field is mainly influenced by blade deflections due to gravitation. Deforming blades change the aerodynamic behavior, which in turn influences the surrounding flow field, leading to non-uniform wake characteristics with respect to speed and shape.
-
-
PublicationDeep Learning Enabled Data-Driven Detection of Wind Turbine Operating Conditions Using Transformer Networks( 2024-01-17)Test data (1min) Test data (10min) Test data (30min) Training data (1min) Training data (10min) Training data (30min) Precision Recall F1 (calibrated) Prevalence
-
PublicationResults of wear endurance runs of wind turbine pitch bearings( 2024)Pitch bearings of wind turbines connect the rotor blade and the rotor hub. They have to cope with highly dynamic and stochastic loads and oscillating movements for lifetimes of 20 years and more. While several test rigs for pitch bearings are in operation, only very limited data is publicly accessible. Oscillating bearings typically suffer from wear, and this work covers the results of wear endurance tests of full-scale pitch bearings. Four bearings were tested approximately 120 days each under realistic conditions which included dynamic loads in five degrees of freedom. The bearings did not show any or very limited signs of raceway wear, in contrast to results of small-scale tests and short-term tests under worst-case conditions.
-
PublicationAdaptive Anti-Saturation Control Design of Transformers in Converter-Based Grid Emulators( 2024)Transformer saturation is a common issue in megawatt converter-based grid emulators (GEs) when emulating grid faults. This problem necessitates the use of anti-saturation control (ASC) with GEs. However, conventional ASC methods tend to distort the emulated grid voltage or even interact with the voltage control (VC) of GEs, causing instability in the system. This article, thus, proposes an adaptive ASC method and superimposes its output command to both modulation and VC references, which not only alleviate transformer saturation with the lower output voltage distortion, but mitigate its adverse interaction with the VC of converter-based GEs. Experimental results confirm the effectiveness of the adaptive ASC.
