1,721,003 research outputs found
Large-eddy Simulations of Microscale Turbulent Winds over Arbitrarily Complex Terrain
No full textAs the percentage of wind energy continues to increase in the overall energy portfolio, two essential components of integrating wind energy are designing wind turbines to withstand the forces created by the wind and correctly predicting the power production from wind farms. Accurate wind modeling over complex terrain is paramount to both applications. Existing wind forecasting techniques use computational resolutions on the order of a kilometer, whether the terrain be flat or complex. In this dissertation, a computational framework that applies the large-eddy simulation (LES) technique with resolutions on the order of 10 m is developed to improve predictions of turbulent winds over complex terrain. LES is a computationally expensive technique and a distinguishing aspect of the proposed framework is that the entire simulation is developed for massive-parallelism using clusters of graphics process units (GPUs). To reduce the near-wall resolution requirements, Reynolds-averaged Navier-Stokes (RANS) is used in tandem with LES as a wall-model. The hybrid use of RANS and LES leads to modeling artifacts such as a mismatch in the theoretical logarithmic law-of-the wall. A forcing technique that splits the driving mean pressure gradient based on conservation of mass principle is proposed. The split-forcing approach was found to reduce the modeling artifacts on coarse grids. A new turbulent inflow condition based on buoyancy perturbations is proposed for both smooth-wall-engineering and complex-terrain flows. For complex terrain winds, an improved immersed-boundary method is developed based on the equilibrium assumptions in the atmospheric surface layer, along with a pre-processor to process terrain geometry. The computational framework and individual components are thoroughly tested and validated using well-known benchmark cases. Finally, the computational framework is applied to study the feasibility of dynamic line-rating concept over complex terrain. Potential avenues of further research are also recommended.Thesis (Ph.D., Mechanical Engineering) -- University of Idaho, 201
Application of a Bayesian Inference Method to Reconstruct Short-Range Atmospheric Dispersion Events
Get PDFIn the event of an accidental or intentional release of chemical or biological (CB) agents into the atmosphere, first responders and decision makers need to rapidly locate and characterize the source of dispersion events using limited information from sensor networks. In this study the stochastic event reconstruction tool (SERT) is applied to a subset of the Fusing Sensor Information from Observing Networks (FUSION) Field Trial 2007 (FFT 07) database. The inference in SERT is based on Bayesian inference with Markov chain Monte Carlo (MCMC) sampling. SERT adopts a probability model that takes into account both positive and zero-reading sensors. In addition to the location and strength of the dispersion event, empirical parameters in the forward model are also estimated to establish a data-driven plume model. Results demonstrate the effectiveness of the Bayesian inference approach to characterize the source of a short range atmospheric release with uncertainty quantification
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Interfacial dynamics-based modelling of turbulent cavitating flows, part-2: Time-dependent computations
No full textThe interfacial dynamics-based cavitation model, developed in Part-1, is further employed for unsteady flow computations. The pressure-based operator-splitting algorithm (PISO) is extended to handle the time-dependent cavitating flows with particular focus on the coupling of the cavitation and turbulence models, and the large density ratio associated with cavitation. Furthermore, the compressibility effect is important for unsteady cavitating flows because in a water-vapour mixture, depending on the composition, the speed of sound inside the cavity can vary by an order of magnitude. The implications of the issue of the speed of the sound are assessed with alternative modelling approaches. Depending on the geometric confinement of the nozzle, compressibility model and cavitation numbers, either auto-oscillation or quasi-steady behaviour is observed. The adverse pressure gradient in the closure region is stronger at the maximum cavity size. One can also observe that the mass transfer process contributes to the cavitation dynamics. Compared to the steady flow computations, the velocity and vapour volume fraction distributions within the cavity are noticeably improved with time-dependent computations.</p
Stochastic Reconstruction of Multiple Source Atmospheric Contaminant Dispersion Events
Get PDFReconstruction of intentional or accidental release of contaminants into the atmosphere using concentration measurements from a sensor network constitutes an inverse problem. An added complexity arises when the contaminant is released from multiple sources. Determining the correct number of sources is critical because an incorrect estimation could mislead and delay response efforts. We present a Bayesian inference method coupled with a composite ranking system to reconstruct multiple source contaminant release events. Our approach uses a multi-source data-driven Gaussian plume model as the forward model to predict the concentrations at sensor locations. Bayesian inference with Markov chain Monte Carlo (MCMC) sampling is then used to infer model parameters within minutes on a conventional processor. The composite ranking system enables the estimation of the number of sources involved in a release event. The ranking formula allows plume model results to be evaluated based on a combination of error (scatter), bias, and correlation components. We use the 2007 FUSION Field Trial concentration data resulting from near-ground-level sources to test the multi-source event reconstruction tool (MERT). We demonstrate successful reconstructions of source parameters, as well as the number of sources involved in a release event with as many as three sources
A Best Practices Guide to CFD Education in the Undergraduate Curriculum
No full textThe AIAA Fluid Dynamics Technical Committee formed a working group in 2010 to explore how to include computational fluid dynamics (CFD) in undergraduate education. The following article is the best practices guide resulting from that working group, and is intended to guide the development of CFD instructional content in undergraduate aerospace and mechanical engineering curricula. The article addresses a growing need for new engineers to become \u27intelligent users\u27 of CFD: that is, to be able to obtain a solution of a flow, and to critically assess the quality of the result. The article distils the concepts of CFD into curricular elements, and establishes reasonable expected outcomes for undergraduate-level instruction of these concepts. It then provides numerous case studies of existing CFD courses, presented in a hierarchy of various \u27profiles\u27 - from CFD light to CFD heavy - for inclusion in courses with lecture, laboratory or design formats. Specific needs of mechanical engineering programmes are also discussed. Hardware, software, and textbook resources are also briefly reviewed
The Search for Strategies to Prevent Persistent Misconceptions
No full textResearch shows that it may be too late to repair misconceptions of fundamental science and engineering concepts by the time students reach core engineering courses. Therefore, we need to focus on preventing such misconceptions. This paper reports the Stage One outcomes of a larger study: A synergistic approach to prevent persistent misconceptions with first-year engineering students. It addresses the following two aspects: (1) misconception repair strategies have had weak results, and (2) a synergistic approach that focuses on preventing/eliminating misconceptions. This paper has implications for new direction and effort in studying student misconceptions and promoting conceptual changes, which is to focus on preventing misconceptions from forming
Interfacial dynamics-based modelling of turbulent cavitating flows, part-1: Model development and steady-state computations
No full textThe merits of transport equation-based models are investigated by adopting an enhanced pressure-based method for turbulent cavitating flows. An analysis of the mass and normal-momentum conservation at a liquid-vapour interface is conducted in the context of homogeneous equilibrium flow theory, resulting in a new interfacial dynamics-based cavitation model. The model offers direct interpretation of the empirical parameters in the existing transport-equation-based models adopted in the literature. This and three existing cavitation models are evaluated for flows around an axisymmetric cylindrical body and a planar hydrofoil, and through a convergent-divergent nozzle. Although all models considered provide qualitatively comparable wall pressure distributions in agreement with the experimental data, quantitative differences are observed in the closure region of the cavity, due to different compressibility characteristics of each cavitation model. In particular, the baroclinic effect of the vorticity transport equation plays a noticeable role in the closure region of the cavity, and contributes to the highest level of turbulent kinetic energy there.</p
Computations of unsteady cavitation with a pressure-based method
No full textA computational approach based on the conservative form of the Favre-averaged Navier-Stokes equations, transport equation-based turbulent cavitation models and a pressure-based operator-splitting algorithm is applied to study turbulent cavitating flows through convergent-divergent nozzles. The implications of the compressibility effect, reflected via the speed of sound definition in the two-phase mixture, are assessed with two modeling approaches. Depending on the geometric confinement of the nozzle, compressibility model, and cavitation numbers, auto-oscillations and quasi-steady behaviors are observed. Detailed flow structures and cavitation dynamics are highlighted, and implications of the cavitation model discussed.</p
- …
