12 research outputs found
A study on the propagation of aero and wind uncertainties and their effect on the dynamic loads of a wind turbine
No full textThis work is concerned with the quantification of uncertainties associated with wind turbines. A part form the understanding of the Effects of uncertainties per se, the efficient propagation of uncertainties is necessary for the implementation of robust design optimization methods, which is one of our future goals. Among all possible sources of uncertainties, here uncertainties related to the incoming wind and to the aerodynamic characteristics of the blades are propagated throughout a high-fidelity multibody aeroservoelastic tool. Different techniques, which could all be used for propagating uncertainties other than the ones considered here, are tested and compared. These include different formulations from the family of Non-Intrusive Polynomial Chaos Expansion, as well as Ordinary and Universal Kriging. By running a reduced subset of standard design load cases, a comparison among the various methods is drawn in terms of accuracy and computational efficiency with respect to a standard Monte Carlo approach. It is concluded that, for the uncertain- ties considered here, all approaches lead to a significantly higher performance compared to Monte Carlo, with Universal Kriging slightly standing out. It is also observed that the output parameters exhibit significant variations, and this highlights the importance of a comprehensive framework for the quantification and propagation of uncertainties in wind energy systems
Turbulence modeling using a lagged eddy viscosity model for subsonic separated flows over wind turbine airfoils
No full textThe objective of this research work is to assess the capability of the lagged eddy viscosity model in predicting separated flows over wind turbine airfoils at subsonic flow conditions. Pressure driven flow separation is an important category of flows and many aerodynamic devices are required to operate on the verge of boundary layer separation to maximize efficiency. Current one- and two-equation turbulence models do not capture all the relevant physics associated with flow separation and, hence, result in erroneous predictions. The lagged eddy viscosity turbulence model is a new model proposed as an improvement over existing two-equation based models. In this model an additional transport equation is solved to account for history effects, which become predominant for non-equilibrium flows, such as separated flows. This model was implemented in the NASA CFD code, OVERFLOW, and has shown promising results in predicting separated flows under high speed or supersonic flow conditions. In the current study, the lagged eddy viscosity turbulence model is implemented in the commercial CFD software FLUENT and CFX. An additional transport equation for the non-equilibrium eddy viscosity is solved using user defined functions in FLUENT and through expressions in CFX. Compared to FLUENT, CFX has the option of an additional turbulence model (EARSM) and also allows the option of simulating natural transition flows by lagging the eddy viscosity of the four-equation SST transition model. Hence, CFX was used for all the flow computations. To ensure proper implementation of the lagged eddy viscosity model, zero pressure gradient flow over a flat plate and flow inside an asymmetric diffuser are computed using the standard k– ω, SST k– ω and EARSM models and compared to computations using the lagged eddy viscosity model and results from experiments. Airfoils with thickness to chord ratios of 18% (DU96-W-180) and 25% (DU91-W2-250) were considered for this study. The standard k– ω and SST k– ω models predicted a delayed separation and stall. EARSM, although it performed better than SST k– ω, did not predict stall to the desired level of accuracy. The lagged eddy viscosity model with the original parameters for σ kA and a0 as recommended by Olsen behaved similarly to SST k- ω; however, the lag model showed significantly improved separated flow prediction capability for modified parameter values for σ kA and a0
Numerical Validation of Empirical Formula for Estimating Airfoil Drag Coefficient at Extreme Angles of Attack in Wind Turbine Applications
No full textNumerical Study on the Effect of Limiting Eddy Viscosity on Flow Separation Prediction for Airfoils in Wind Energy Applications
No full text
Impact of Shared Electric Vehicles Availability to Provide Peak Reduction through Vehicle-to-Grid. A Case Study
No full textThis paper presents a Mix Integer Linear Programming (MILP) optimization approach to reduce peak demand and maximize revenue in a grid-connected building with a PV-equipped charging station for Shared EVs. The study investigates the impact of EV availability on the effectiveness of the system by comparing the results for different connection times of a fleet of Shared EVs, a private EV used for commuting, and a stationary battery. Results from the case study conducted in The Netherlands demonstrate that not only the duration but also the timing of EV connection significantly influence system effectiveness, emphasizing the need for accurate availability estimation. The trade-off between peak reduction and Peak-to-Average Ratio (PAR) reduction is also highlighted, underscoring the importance of considering both factors for optimizing charging station usage. These findings provide valuable insights for optimizing energy management, reducing peak loads, and increasing the utilization of renewable energy sources in the context of Shared EVs and V2G technology.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.DC systems, Energy conversion & Storag
Semiconductor Polymer Carbon Composite Coated Fabric for Warm Beds in Hospital
No full textPatients suffering from diseases that occur due to spreading of virus like fever and cold will have decrease in body temperature. They feel cold in the normal body and room temperature conditions. For the comfort of these patients, an electric under blanket is designed which warms up the patient to maintain the normal body temperature. The heated under body supports include a heater assembly and a layer of compressible support material. The heater assembly includes a flexible heating element, multiplex polyester, and a temperature sensor. The flexible heater element may include a fabric, which coated with a conductive or semiconductive polymer. The heated under body support may also include a water resistant shell, whereas it may encase the heater assembly and the compressible support material. The material used for outer shell and inner heating element has simulated in COMSOL tool for analyzing the heat transfer between them. The proto type model has simulated in PROTEUS software, which includes Arduino UNO and thermistor. This analysis will give the result whether the material can be used as the under garment for warming the patient
Keys under doormats - mandating insecurity by requiring government access to all data and communications
No full textAbstract
Twenty years ago, law enforcement organizations lobbied to require data and communication services to engineer their products to guarantee law enforcement access to all data. After lengthy debate and vigorous predictions of enforcement channels “going dark,” these attempts to regulate the emerging Internet were abandoned. In the intervening years, innovation on the Internet flourished, and law enforcement agencies found new and more effective means of accessing vastly larger quantities of data. Today we are again hearing calls for regulation to mandate the provision of exceptional access mechanisms. In this report, a group of computer scientists and security experts, many of whom participated in a 1997 study of these same topics, has convened to explore the likely effects of imposing extraordinary access mandates.
We have found that the damage that could be caused by law enforcement exceptional access requirements would be even greater today than it would have been 20 years ago. In the wake of the growing economic and social cost of the fundamental insecurity of today’s Internet environment, any proposals that alter the security dynamics online should be approached with caution. Exceptional access would force Internet system developers to reverse “forward secrecy” design practices that seek to minimize the impact on user privacy when systems are breached.
The complexity of today’s Internet environment, with millions of apps and globally connected services, means that new law enforcement requirements are likely to introduce unanticipated, hard to detect security flaws. Beyond these and other technical vulnerabilities, the prospect of globally deployed exceptional access systems raises difficult problems about how such an environment would be governed and how to ensure that such systems would respect human rights and the rule of law
