Browsing by Subject "Wind energy"
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Item Aerodynamic wake study: oscillating model wind turbine within a turbulent boundary layer(2015-03) Feist, Christopher JamesAn experimental investigation on the aerodynamic wake behind a pitching and/or heaving model wind turbine was performed. The study was split into two quasi-coupled phases; the first phase characterized the motion of an offshore floating wind turbine subjected to linear wave forcing, the second phase replicated specific motion cases, which were driven by results from phase I, on a model wind turbine within a turbulent boundary layer. Wake measurements were made in an effort to quantify fluctuations in the flow associated with the motion of the turbine. Weak differences were observed in the mean, streamwise velocity and turbulent fluctuations between the static and oscillating turbine cases. These weak differences were a result of opposing trends in the velocity quantities based on turbine motion phases. The wake oscillations created by the turbine motion was characteristic of a 2D wave (with convection in the x plane and amplitude in the z plane) with a relatively small amplitude as compared to u_rms.Item Assessing bat and bird fatality risk at wind farm sites using acoustic detectors(2014-08) Heist, Kevin W.Wind power is a promising and rapidly growing clean energy technology. Despite its environmentally friendly reputation, industrial wind energy generation can have serious impacts on wildlife. Bat and bird collision fatality rates have been alarmingly high at some wind farms. Proper siting of wind facilities may help minimize collision impacts; however, there is no reliable method for assessing risks prior to development. My goal was to develop a method for predicting fatality rates at prospective wind energy sites by monitoring acoustic activity of bats and birds. I monitored bat and bird activity using ultrasonic-acoustic detectors at 160 locations, in a variety of landscape settings to: 1) examine the utility of the detectors for monitoring bat and bird activity for pre-construction site assessment, 2) evaluate the ability of an automated bat call identification program to identify the species of recorded calls, 3) determine how pass rates relate to fatality rates, 4) examine how pass rates vary with respect to specific landscape features, 5) examine how activity differs before versus after a wind facility is built, and 6) investigate whether bat activity levels are elevated near turbines. Ground-based recording was found to be useful for studying near-ground bat activity patterns at multiple scales, but patterns of bird activity were apparent only at the coarsest geographic scale. The bat call identification program produced mixed results among species and regions. No relations between bat pass rates and fatality rates among wind farms were found. Large differences in bat and bird activity among geographic regions were found, with highest levels near Great Lakes coastlines. Also, bat and bird activity was elevated near edges of forested river corridors, relative to distances farther from the edge. Distance to water, distance to trees, and ecoregion were found to be good predictors of bat activity levels. Models of bird activity were of limited usefulness in explaining spatial variation in pass rates. Ground-based acoustic recorders were not found to be a good predictor of bat fatalities; however, they did reveal local and regional patterns that may be useful for siting wind energy facilities in low-impact areas.Item The Cost Effectiveness of Using Wind Energy to Generate Electricity and Abate CO2 Emissions(Hubert H. Humphrey Institute of Public Affairs, 2009-11-14) Paine, NathanThis paper also investigates the costs and benefits of wind energy and fossil fuel technologies. To decide whether to meet demand for electricity with wind power, I investigate the cost effectiveness of wind power under a range of emissions prices and take into account the need for back up power. In the long-run, innovative pollution abatement technologies will impact the costs and benefits of various generation types. The installation of large-scale wind power is also expected to create economies of scale and learning-by-doing is expected to drive down the costs of wind technology. I also investigate the transmission costs associated with the injection of large-scale wind power into the transmission grid.Item Design and analysis of optimal ascent trajectories for stratospheric airships(2013-08) Mueller, Joseph BernardStratospheric airships are lighter-than-air vehicles that have the potential to provide a long-duration airborne presence at altitudes of 18-22 km. Designed to operate on solar power in the calm portion of the lower stratosphere and above all regulated air traffic and cloud cover, these vehicles represent an emerging platform that resides between conventional aircraft and satellites. A particular challenge for airship operation is the planning of ascent trajectories, as the slow moving vehicle must traverse the high wind region of the jet stream. Due to large changes in wind speed and direction across altitude and the susceptibility of airship motion to wind, the trajectory must be carefully planned, preferably optimized, in order to ensure that the desired station be reached within acceptable performance bounds of flight time and energy consumption. This thesis develops optimal ascent trajectories for stratospheric airships, examines the structure and sensitivity of these solutions, and presents a strategy for onboard guidance. Optimal ascent trajectories are developed that utilize wind energy to achieve minimum-time and minimum-energy flights. The airship is represented by a three-dimensional point mass model, and the equations of motion include aerodynamic lift and drag, vectored thrust, added mass effects, and accelerations due to mass flow rate, wind rates, and Earth rotation. A representative wind profile is developed based on historical meteorological data and measurements. Trajectory optimization is performed by first defining an optimal control problem with both terminal and path constraints, then using direct transcription to develop an approximate nonlinear parameter optimization problem of finite dimension. Optimal ascent trajectories are determined using SNOPT for a variety of upwind, downwind, and crosswind launch locations. Results of extensive optimization solutions illustrate definitive patterns in the ascent path for minimum time flights across varying launch locations, and show that significant energy savings can be realized with minimum-energy flights, compared to minimum-time time flights, given small increases in flight time. The performance of the optimal trajectories are then studied with respect to solar energy production during ascent, as well as sensitivity of the solutions to small changes in drag coefficient and wind model parameters. Results of solar power model simulations indicate that solar energy is sufficient to power ascent flights, but that significant energy loss can occur for certain types of trajectories. Sensitivity to the drag and wind model is approximated through numerical simulations, showing that optimal solutions change gradually with respect to changing wind and drag parameters and providing deeper insight into the characteristics of optimal airship flights. Finally, alternative methods are developed to generate near-optimal ascent trajectories in a manner suitable for onboard implementation. The structures and characteristics of previously developed minimum-time and minimum-energy ascent trajectories are used to construct simplified trajectory models, which are efficiently solved in a smaller numerical optimization problem. Comparison of these alternative solutions to the original SNOPT solutions show excellent agreement, suggesting the alternate formulations are an effective means to develop near-optimal solutions in an onboard setting.Item Development of a Comprehensive Conservation Strategy for the North Shore Highlands Region of Minnesota in the Context of Future Wind Power Development(University of Minnesota Duluth, 2012) Peterson, Anna; Niemi, Gerald JEach autumn, millions of birds migrate from their breeding grounds in the northern hemisphere to wintering areas in the continental United States, Mexico, Central America, and South America (Rich 2004, Bildstein 2006). The North Shore Highlands parallels the Lake Superior shoreline from Duluth through Grand Portage, Minnesota to the US border with Canada. This region’s prominent ridgelines and Lake Superior coastline funnel migrating birds into this migration corridor (Hofslund 1966, Mueller and Berger 1967, Bildstein 2006). As a result, the North Shore Highlands hosts the largest migratory route for birds of prey in Minnesota and is among the highest in the US. In addition, recent data suggest that the numbers of non-raptor bird species moving along the north shore of Lake Superior are orders of magnitude larger than those for raptors. Migration periods constitute a critical life-stage for these birds as mortality rates may be higher during migration than during breeding or over wintering periods (Sillett and Holmes 2002, Smith and Moore 2003). Large bodies of water and other major topographical features cause a nonrandom distribution of migrating birds on the landscape in both periods of active flight and rest (Goodrich and Smith 2008). Landscape features that define the North Shore Highlands (Lake Superior, ridgelines, river valleys) result in a major congregation of migratory birds (raptors and passerines) that are both actively flying and resting within the region. With the current emphasis on renewable energy (Great Lakes Commission 2011), the North Shore Highlands region has become a focal point for potential wind power, with many plans already in progress (Mageau et al. 2008). Besides wind turbines there is also increased activity in the development of communication towers in the region. The North Shore Highlands region is recognized as one of the top tourist destinations in Minnesota and the upper Midwestern US. Over the past twenty years, the area has experienced increased developmental pressure from recreation, tourism, and exurban housing (MNDNR 2006). Conservation strategies aimed at the protection of migratory birds are incomplete without the focus on migratory bird flyway and stopover habitat preservation (Petit 2000, Mehlman et al. 2005). To develop conservation strategies to protect en route migratory birds within this region, there is a need to understand the cues by which migrants choose migratory flight paths and stopover habitats (Ewert et al. 2011, Buler et al. 2007, Bonter et al. 2009). Our overall goal is to provide data and mapping products that will contribute to a comprehensive conservation plan for migratory birds highlighting the potential risks of wind energy development within the North Shore Highlands region. We have worked closely with several community groups in the region (e.g., Grand Portage Indian Reservation, Cook County Local Energy Project, and Lutsen Mountains Resort) who have expressed an interest in wind energy development. Our purpose will be to eliminate or minimize interactions with migratory birds if wind turbines are placed in the North Shore Highlands region.Item North Shore bat activity and habitat use(University of Minnesota Duluth, 2011) Abel, Rebecca; Moen, RonaldWind power development is an emerging issue in northeastern Minnesota. A recent Coastal Zone Management Program (CZMP) study showed strong potential for wind energy along the North Shore, even though wind speed maps indicate that northeastern Minnesota has less wind potential than other parts of the state. There are seven bat species in Minnesota, and all of them could be affected by wind power development. Baseline data on bat distribution and habitat use is essential for bat conservation. Little information exists on bats in the southern boreal forests of the Midwest. We measured summer bat habitat use and foraging activity at aquatic, linear corridor, and interior forest sites with bat detectors in deciduous, mixed-wood, and coniferous forests in northeastern Minnesota. We used three common acoustic bat activity indices to quantify acoustic bat data and examined the indices to determine how differences among activity indices influence statistical inferences of bat activity. We measured the effects of relative insect abundance and degree of vegetation density on bat activity. Bat detectors recorded 7,666 identifiable bat calls during 1,440 detector hours in 2009 and 8,554 bat calls during 930 detector hours in 2010. Bat activity was dominated by Myotis species (Myotis lucifugus and M. septentrionalis) and Lasionycteris noctivagans. Activity was concentrated at aquatic and linear corridor microsites, regardless of forest cover type. However, bats foraged at similar rates in each microsite type. Bat activity and foraging activity occurred earlier at night at interior forest sites relative to aquatic and linear corridor sites, suggesting that interior forest is used by bats to forage as they leave day roosts. The three acoustic activity indices we used resulted in similar conclusions of habitat use by bats, despite different biases of each. Bats would generally be flying in low wind conditions, especially when foraging. If wind turbines were deployed along the North Shore, we recommend monitoring bat activity to document potential effects at the site(s). However, because all bat species were present along the entire north shore of Lake Superior inland throughout the Coastal Zone area, wind turbines are unlikely to have a population level effect on bats unless many are installed.Item Real-time strategies for enhancing aircraft performance in wind.(2012-08) Turkoglu, KamranThis thesis presents real-time guidance strategies for unmanned aerial vehicles (UAVs) that can be used to enhance their flight endurance by utilizing in-situ measurements of wind speeds and wind gradients. In these strategies, periodic adjustments can be made in the airspeed and/or heading angle command for the UAV to minimize a projected power requirement at some future time. In this thesis, UAV flights are described by a three-dimensional dynamic point-mass model. A stochastic wind field model has been developed not only to reflect the mean wind magnitude behaviour in both vertical and horizontal axis, but also has it been extended to characterize wind direction behaviour as well. Proposed wind field model is assumed that it is consisted of a constant term plus terms that vary sinusoidally with respect to the location and time. Onboard closed-loop trajectory tracking logics that follow airspeed vector commands are modeled using the method of feedback linearization. To evaluate the benefits of these strategies in enhancing UAV flight endurance, a reference strategy is introduced in which the UAV would follow the optimal airspeed command in a steady level flight under zero wind conditions. A performance measure is defined as the average power consumption both over a specified time interval and over different initial heading angles of the UAV. A relative benefit criterion is then defined as the percentage improvement in the performance measure of a proposed strategy over that of the reference strategy. Extensive numerical simulations are conducted to show efficiency and applicability of the proposed algorithms. Results demonstrate the efficiency, benefits and trends of power savings of the proposed real-time guidance strategies in level flights.Item Reduced-Order Modeling and Data-driven Techniques for Control of Grid-Connected Wind Farms(2022-04) Vijayshankar, SanjanaThis thesis focuses on improving the commercial viability of wind energy systems through modeling, control, and analysis. In the area of modeling, we propose computationally scalable mathematical models that are suitable for real-time control applications. These models are then utilized to systematically analyze the effects of high wind penetration on the grid. Additionally, recognizing the importance of wind energy in providing ancillary services, we propose a control platform that integrates forecasting tools with economic and aerodynamic models to maximize energy value streams. The research presented in this thesis has the potential to enhance the performance and profitability of wind energy systems, contributing to the growth and sustainability of renewable energy sources.Item Wake dynamics in the atmospheric boundary layer over complex terrain(2013-08) Markfort, Corey D.The goal of this research is to advance our understanding of atmospheric boundary layer processes over heterogeneous landscapes and complex terrain. The atmospheric boundary layer (ABL) is a relatively thin (∼ 1 km) turbulent layer of air near the earth's surface, in which most human activities and engineered systems are concentrated. Its dynamics are crucially important for biosphere-atmosphere couplings and for global atmospheric dynamics, with significant implications on our ability to predict and mitigate adverse impacts of land use and climate change. In models of the ABL, land surface heterogeneity is typically represented, in the context of Monin-Obukhov similarity theory, as changes in aerodynamic roughness length and surface heat and moisture fluxes. However, many real landscapes are more complex, often leading to massive boundary layer separation and wake turbulence, for which standard models fail. Trees, building clusters, and steep topography produce extensive wake regions currently not accounted for in models of the ABL. Wind turbines and wind farms also generate wakes that combine in complex ways to modify the ABL. Wind farms are covering an increasingly significant area of the globe and the effects of large wind farms must be included in regional and global scale models. Research presented in this thesis demonstrates that wakes caused by landscape heterogeneity must be included in flux parameterizations for momentum, heat, and mass (water vapor and trace gases, e.g. CO2 and CH4) in ABL simulation and prediction models in order to accurately represent land-atmosphere interactions. Accurate representation of these processes is crucial for the predictions of weather, air quality, lake processes, and ecosystems response to climate change. Objectives of the research reported in this thesis are: 1) to investigate turbulent boundary layer adjustment, turbulent transport and scalar flux in wind farms of varying configurations and develop an improved modeling framework for wind farm - atmosphere interaction, 2) to determine how heterogeneous patches of forest affect the structure of the ABL and its interactions with clearings and water bodies, 3) to investigate how landscape heterogeneity, including wakes, may be parameterized in regional-scale weather and climate models to improve the representation of surface fluxes, e.g. from lakes/wetlands and forest clearings. To achieve these objectives, this research employs an interdisciplinary strategy, utilizing concepts and methods from fluid mechanics, micrometeorology, ecosystem ecology and environmental sciences, and combines laboratory and field experiments. In particular, a) wind tunnel experiments of flow through and over model wind farms and model forest canopies were used to improve our fundamental understanding of how wakes affect land-atmosphere coupling, including surface fluxes, after wind farm installation and for heterogeneous landscapes of canopies and clearings or lakes, and b) extensive field studies over lakes and wetlands were undertaken to study the effects of wakes downwind of forest canopies and the effect of wind sheltering on lake stratification dynamics and gas fluxes. These experiments were also used to improve and validate numerical simulation techniques for the atmospheric boundary layer, specifically the large eddy simulation technique, which is used to simulate flow in wind farms and flow over heterogeneous terrain.