56 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
Extracellular Matrix Dynamics in Biology, Bioengineering, and Pathology
No full textThis eBook is a collection of articles from a Frontiers Research Topic. Frontiers Research Topics are very popular trademarks of the Frontiers Journals Series: they are collections of at least ten articles, all centered on a particular subject. With their unique mix of varied contributions from Original Research to Review Articles, Frontiers Research Topics unify the most influential researchers, the latest key findings and historical advances in a hot research area! Find out more on how to host your own Frontiers Research Topic or contribute to one as an author by contacting the Frontiers Editorial Office: frontiersin.org/about/contac
The Impact of micro-tunnelling on adjacent pile foundations: Numerical modelling of micro-tunnel excavation in PLAXIS
No full textA series of finite element simulations via PLAXIS were carried out to investigate the effects of micro- tunnelling on nearby pile foundations. A numerical model concerning the large diameter tunnel boring machine was first established based on identical properties of the centrifuge experiment executed by Loganathan et al. (2000). Results from numerical simulation were validated by measured data from the centrifuge test. After the validation of the numerical modelling method, the model was adjusted to match the case of micro-tunnel and a new model regarding the micro-tunnelling procedure was generated based on geotechnical conditions of the North/South Metro Line Amsterdam. The Hardening Soil constitutive model was chosen for all soil layers. In the model, the condition of single bored pile with working load was activated in the greenfield condition before the simulation of micro- tunnel. Advancement procedure of the micro-tunnel was simulated, and pile responses were collected under the plane strain condition. Based on the study of the model, two load transfer mechanisms of piles during tunnel-pile interaction process were identified. Impact of tunnel advancement on adjacent piles was also interpreted. A set of parametric studies were implemented to study changes of pile settlement and bearing capacity with increasing volume loss. An influence zone around the micro- tunnel respecting the potential of pile critical movements was established. Although the lack of field data makes the validation of results hard, comparison with analytical prediction and measured data from the centrifuge test shows good agreements for soil movements and pile responses. The results of this research remain to be validated by field data but it can provide insights into the problem of the impact of micro-tunnelling on piles.Geo-Engineerin
Soft magnetic materials for aerospace applications
No full textThis author collated and reviewed existing literature regarding soft magnetic materials, to better
understand the materials suited for aerospace applications and compare the functionality and
characteristics of these given materials. It is quickly clear that Fe-Co alloys are the most
attractive candidates for usage in an electric engine, and review was narrowed to a focus on the
aforementioned material. The consensus that followed was the observation that the Fe-Co-V
ternary alloy would exhibit the most suitable attributes for the given application. This report then
follows the different routes taken to improve the Fe-Co-V alloy and comparatively analyse the
effectiveness of the different alloying elements and processing methods suggested in the relevant
literature.Bachelor of Engineering (Materials Engineering
The implementation of a risk based maintenance policy to a power plant
No full textThe unexpected failures, the down time (outage) associated with such failures, the loss of production of power and, the higher maintenance costs are major problems in operation of thermal power plants. The unexpected failure of an equipments and systems causes economic risk and can be minimized using an effective maintenance strategy. The risk based approach ensures a strategy, which is cost effective. Such an approach uses the information obtained from the study of failure modes and their consequences. -- The purpose of the thesis is to develop and show how to implement a risk based maintenance (RBM) policy to a power plant. This quantitative approach will provide a basis for selection of the best alternative strategy to minimize the risk resulting from breakdowns or failures. -- The proposed methodology is comprised of three modules: risk assessment, risk evaluation, and maintenance planning. This work presents a mechanism for the study of the occurrence of failures and functional failures in equipment and the severity of their consequences, known as risk. Maintenance of equipment is prioritized based on the risk, and the reduction in overall risk of the plant is accomplished by focusing on the maintenance of high-risk items first. To the author's knowledge this quantitative approach has not been developed before. -- The study is conducted for Newfoundland and Labrador Hydro, Holyrood thermal power generation plant. Failure data is collected from the existing power station (Unit 3-150 MW) over a period of twelve years. The data is modeled using Weibull and Exponential distributions to estimate the parameters. A probabilistic risk analysis is performed to quantify the risk at the plant. An acceptable risk criterion is determined and the major systems and subsystems that are found to have a risk higher than acceptable risk are identified. The maintenance interval is calculated by reverse or target probability analysis for reducing the level or risk resulting from the failure of a system. -- To conclude, the risk based maintenance strategy can be employed to prioritize the systems for maintenance planning, and to improve the existing maintenance policies. In addition, this strategy provides cost-effective means for maintenance as well it minimizes the consequences (safety, economic and environment) related to a system failure.Bibliography: leaves 88-91
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