1,721,000 research outputs found
A Review on the Meandering of Wind Turbine Wakes
No full textMeandering describes the large-scale, low frequency motions of wind turbine wakes, which could determine wake recovery rates, impact the loads exerted on turbine structures, and play a critical role in the design and optimal control of wind farms. This paper presents a comprehensive review of previous work related to wake meandering. Emphasis is placed on the origin and characteristics of wake meandering and computational models, including both the dynamic wake meandering models and large-eddy simulation approaches. Future research directions in the field are also discussed
High-fidelity simulations and field measurements for characterizing wind fields in a utility-scale wind farm
No full textCharacterizing wind farm flow fields at high temporal and spatial resolutions is critical prerequisite for the optimal design and operation of utility-scale wind farms and for reducing the levelized cost of energy. However, due to the large disparity of underlying scales, measurements or simulations alone cannot provide high resolution wind fields, which are informed by and account for the effect of both large scale (i.e. hour, day, month and year) and small scale (i.e. second and minute) site-specific variations in the atmosphere. We explore the feasibility of integrating field measurements and high-fidelity large-eddy simulation (LES) to characterize the wind field in a utility-scale wind farm while accounting for flow phenomena across multiple temporal scales. Specifically, we employ field measurements to characterize the monthly wind speed and wind direction distributions and investigate the wind characteristics in turbine wakes. It was found that the probability density function (PDF) of the wind speed in turbine wakes can be reasonably represented using the Weibull distribution but with shape factors smaller than those not in the wake. LES of the wind farm under statistically steady inflow is subsequently carried out for one wind direction. The LES predictions are compared with the measured data conditionally averaged based on the wind speed, wind direction and the root-mean-square of wind speed fluctuations over time intervals of 30 min. Good agreement is obtained for both mean wind speed and turbulence intensity. The present work shows the possibility of integrating field measurements and high-fidelity simulations for improved characterization of the site-specific wind fields in utility-scale wind farms
Scaled Hydrokinetic Turbine Array installed in a laboratory channel and flood-like sediment transport conditions: topography, flow velocity and array model performance
No full textPlease see Readme files included in every data folder.The data represent sediment flux, spatio-temporally resolved topographic scans, flow velocity and voltage from the hydrokinetic turbine array experiments presented in the referenced scientific article published on Nature Energy (see reference). Hydrokinetic Energy represents a viable source of renewable energy that harness the kinetic energy of natural currents. Our experiments show that this technology can be deployed efficiently in large sandy rivers (e.g. Mississippi River), without compromising the geomorphic equilibrium of the stream and the structural safety of the turbine foundation, even in the presence of large migrating dunes.National Science Foundation CAREER: Geophysical Flow Control (award ID 13513013)Institute on the Environment (IonE), University of MinnesotaMusa, Mirko; Hill, Craig; Sotiropoulos, Fotis; Guala, Michele. (2019). Scaled Hydrokinetic Turbine Array installed in a laboratory channel and flood-like sediment transport conditions: topography, flow velocity and array model performance. Retrieved from the University Digital Conservancy, https://doi.org/10.13020/353t-xm19
Using Virtual Reality Environments for Medical Devices Design
No full textThere is an urgent need for improved design methodologies and tools that give designers meaningful and accurate feedback early in the design process; virtual reality can be used to fill this need. Virtual reality provides a highly engaging environment that allows user to experience and comprehend abstract concepts. It can allow designers to broadly explore the space of potential design alternatives, and to expand the boundaries of complex designs that are possible given today's computer assisted tools.
Medical device researchers seek to better understand the complexities of cardiac anatomy, visualize how surrounding structures affect device function and deployment, and ultimately design more effective devices. Virtual representation combines visual graphics, virtual reality applications, finite element analysis based on the architecture of a 3D model. Introducing virtual reality based tools into the process of medical device design can significantly improve the process.
We present our initial work aimed at developing new immersive visualization and interactive design tools for improving the medical device design process. Our initial work focuses on developing 3-dimensional visualizations of simulated blood flow through mechanical heart valves. Our goal is to develop 3D user interfaces for refining medical device designs within the context of patient-specific anatomy and simulated flow data.Konchada, Vamsi; Coffey, Dane; Borazjani, Iman; Sotiropoulos, Fotis; Erdman, Arthur; Interrante, Victoria; Keefe, Daniel F.. (2009). Using Virtual Reality Environments for Medical Devices Design. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/58248
Wake Statistics of Different-Scale Wind Turbines under Turbulent Boundary Layer Inflow
No full textSubscale wind turbines can be installed in the field for the development of wind technologies, for which the blade aerodynamics can be designed in a way similar to that of a full-scale wind turbine. However, it is not clear whether the wake of a subscale turbine, which is located closer to the ground and faces different incoming turbulence, is also similar to that of a full-scale wind turbine. In this work we investigate the wakes from a full-scale wind turbine of rotor diameter 80 m and a subscale wind turbine of rotor diameter of 27 m using large-eddy simulation with the turbine blades and nacelle modeled using actuator surface models. The blade aerodynamics of the two turbines are the same. In the simulations, the two turbines also face the same turbulent boundary inflows. The computed results show differences between the two turbines for both velocity deficits and turbine-added turbulence kinetic energy. Such differences are further analyzed by examining the mean kinetic energy equation
Numerical simulation of unsteady three dimensional incompressible flows in complex geometries
No full textPh.D
On the structure of vortex rings from inclined nozzles
No full textWe carry out numerical simulations to investigate the vortex dynamics of laminar, impulsively driven flows through inclined nozzles in a piston-cylinder apparatus. Our simulations are motivated by the need to provide a complete description of the intricate vortical structures and governing mechanisms emerging in such flows as documented in the experiments of Webster & Longmire (Phys. Fluids, vol. 10, 1998, pp. 400-416) and Troolin & Longmire (Exp. Fluids, vol. 48, 2010, pp. 409-420). We show that the flow is dominated by the interaction of two main vortical structures: the primary inclined vortex ring at the nozzle exit and the secondary stopping ring that arises due to the entrainment of the flow into the cylinder when the piston stops moving. These two structures are connected together with pairs of vortex tubes, which evolve from the continuous vortex sheet initially connecting the primary vortex ring with the interior cylinder wall. In the exterior of the nozzle the key mechanism responsible for the breakup of the vortical structure is the interaction of the stronger inclined primary ring with the weaker stopping ring near the longest lip of the nozzle. In the interior of the nozzle the dynamics is governed by the axial stretching of the secondary ring and the ultimate impingement of this ring on the cylinder wall. Our simulations also clarify the kinematics of the azimuthal flow along the core of the primary vortex ring documented in the experiments by Lim (Phys. Fluids, vol. 10, 1998, pp. 1666-1671). We show that the azimuthal flow is characterized by a pair of two spiral saddle foci at the long and short lips of the nozzle through which ambient flow enters and exits the primary vortex core.We would like to thank Professor D. R. Webster and Dr D. R. Troolin for providing us their PIV and V3V experimental data. We are also grateful to Professor E. K. Longmire for many helpful discussions about the experimental set-up and the physics of the flow. This work was supported by NIH grant number RO1-HL-07262 and a fellowship from the Vietnam Education Foundation to the first author. Computational resources were provided by the Minnesota Supercomputing Institute
Computational study and modeling of turbine spacing effects in infinite aligned wind farms
No full textWe study the turbine spacing effects in infinite, aligned wind-turbine arrays using large-eddy simulation (LES) with the wind turbine rotors parameterized as actuator disks. A series of simulations is carried out to systematically investigate the different effects of streamwise and spanwise turbine spacings on the array power output and turbulence intensities. We show that for the same turbine density, increasing the streamwise spacing is more beneficial than increasing the spanwise spacing. Larger streamwise turbine spacing increases the power extraction and lowers the turbulence intensity at each turbine more efficiently than when the spanwise turbine spacing is increased. The reason for the different effects of streamwise and spanwise turbine spacings on wind farm performance is that the wake recovery of wind turbines in infinite arrays depends on the area influenced by the wind-turbine wakes, rather than the land area occupied by each turbine. Based on this idea, an improved effective roughness height model is proposed, which can account for the different effects of streamwise and spanwise turbine spacings in infinite aligned wind farms. The predictive capabilities of the new model are demonstrated via extensive comparisons with results obtained from the LES and previously proposed roughness height models.This work was supported by the US Department of Energy (DOE) (DE-EE0002980 and DE-EE0005482) and Xcel Energy through the Renewable Development Fund (Grant No. RD3-42).Computational resources were provided by the University of Minnesota Supercomputing Institute
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
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