Browsing by Author "Thornton, Christopher, committee member"
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Item Open Access Application of large-scale particle image velocimetry at the Hydraulics Laboratory of Colorado State University(Colorado State University. Libraries, 2018) Chen, Kaiwei, author; Ettema, Robert, advisor; Thornton, Christopher, committee member; Nelson, Peter, committee member; Landers, Stuart, committee memberLarge-scale particle image velocimetry (LSPIV) is a nonintrusive technique used to measure free-surface velocities of water flow in a manner that produces a two-dimensional vector field of flow velocity. LSPIV is gradually becoming quite widely used as a technique for measuring flow velocities in a range of flow areas. This study used readily available material and devices, and software, to apply LSPIV to flow fields in two laboratory flumes at the Hydraulics Laboratory of Colorado State University; LSPIV had not been used in this laboratory before this study. The applications used pieces of paper as tracer floats in the flow field, and employed a standard iPhone 6s to record video of the tracers moving in the flow field. The video record of tracer movements was then analyzed using Fudaa LSPIV software and Tecplot 360 software to calculate and present the flow velocity data. The applications demonstrated the utility of the LSPIV technique for determining the free-surface flow patterns, and their variations, in experiments done at the Hydraulics Laboratory. Additionally, this study examined the relationship between the tracer size and LSPIV accuracy with the objective of identifying an optimal width of tracer relative to the width of the flow field and its features. Five sizes of tracer were used in measuring the water-surface flow field through a series of contractions and expansions. It was found that the best tracer size is about from 3.80% to 6.33% of the wide of the channel.Item Open Access Application of large-scale particle image velocimetry to entrance flows(Colorado State University. Libraries, 2021) Fakhri, Alireza, author; Ettema, Robert, advisor; Thornton, Christopher, committee member; Bond, Laurel, committee memberThis thesis presents the findings of the application of Large-Scale Image Velocimetry (LSPIV) to illuminate three entrance flows. LSPIV is an image-based method that non-invasively measures two-dimensional instantaneous free-surface velocities of water flow using video equipment. Three different applications used in this study are a flume study with three different contraction ratios, flow through and over spillways in hydraulic models for Gross Dam and Los Vaqueros Dams. For the first application, large-scale-particle velocimetry (LSPIV) was applied to estimate the top-width of the vena contracta formed by an approach open-channel flow entering a contraction of the channel. The experiments investigated the requisite dimensions of two essential LSPIV components: the Search Area and Interrogation Area, to establish the optimum range of these components for use in LSPIV application to contractions of open-channel flows. Of practical concern (e.g., bridge hydraulics) is flow contraction and contraction scour that can occur in the vena contracta region. The thesis showed that optimum values for the Search Area (SA) and Interrogation Area (IA) were 10 and 60 pixels, respectively. Also, the study produced a curve indicating a trend for vena-contracta width narrowing with a variable ratio of approach-channel and contracted-channel widths and varying bed shear stress of approach flow. For the other two applications, the hydraulic models of the spillways for Gross Dam and Los Vaqueros Dam, LSPIV was applied to assess the robustness of LSPIV on mapping the streamlines through and over spillways.Item Open Access Computational fluid dynamics models of Rio Grande bends fitted with rock vanes or bendway weirs(Colorado State University. Libraries, 2019) Siefken, Seth, author; Ettema, Robert, advisor; Thornton, Christopher, committee member; McGrath, Daniel, committee memberRock vanes (also known as stream barbs) and bendway weirs are two types of transverse rock structures used to modify the flow field in river bends. This study examines the effectiveness of the two types of structures at reducing velocity along the outer bank of river bends to protect the bank from erosion. A numerical model using the commercially available FLOW-3D software was used to evaluate the effect of various rock vane and bendway weir configurations on the flow field through two river bends typical of the Middle Rio Grande. The model was calibrated and validated using data from a previous physical model study of rock vanes. 33 different rock vane configurations were tested in the numerical model to evaluate the effect of altering planform angle, crest slope, projected length, and structure spacing. In addition, 14 different bendway weir configurations were tested to provide a comparison of the relative performance of bendway weirs and rock vanes. The numerical modeling results indicate that rock vanes are more effective at reducing the velocity along the outer bank of a bend than bendway weirs. Modelling showed that the completely submerged crest of bendway weirs allows a substantial amount of flow to pass over the crest, limiting their effectiveness in reducing velocity along the bank. In contrast, rock vanes, with a sloped crest intersecting the waterline at the design flow rate, directed more flow around the tip of the structure rather than over the crest and were much more effective at reducing velocity along the bank. Based on the modeling results, it is recommended that bendway weirs not be installed for the purpose of erosion protection along riverbanks. The reduction in velocity along the bank produced by the various rock vane configurations varied considerably with the geometry of the configuration. Based on the results, the following conclusions are made regarding rock vane geometry: (1) Rock vanes should be installed at a planform angle between 45° and 90° to the river bank. (2) There exists an optimal projected length of rock vane, which lies in the neighborhood of 1/5 to 1/3 of the channel top-width. (3) Rock vanes with a 10% crest slope perform well, although decreasing the crest slope will decrease the velocity along the outer bank and vice versa. (4) Decreasing the spacing of rock vanes decreases the velocity along the outer bank, up to a limit. A design equation was developed to predict the velocity reduction along the bank of a river bend produced by a given configuration of rock vanes, based on the geometry of the rock vanes and the river channel. The equation provided good predictions for the range of configurations tested, having a coefficient of determination r2 = 0.83 and predicting the velocity reduction along the outer bank to within 15 percentage points for all of the tested configurations.Item Open Access Effect of spillway-ogee location on flow uniformity and turbulence at the crest of an ogee weir(Colorado State University. Libraries, 2023) Alsultan, Faisal Abdulaziz, author; Ettema, Robert, advisor; Thornton, Christopher, committee member; Conrad, Steve, committee memberThis study investigated the effect of spillway-crest location relative to spillway entrance, and spillway-abutment shape, on uniformity of flow distribution and turbulence intensity of flow, over the ogee crest of a spillway. These issues are especially of concern for spillways for which the approach flow to the ogee weir is relatively shallow. Circular and elliptical shapes of abutments were used. These abutment forms, and the bathymetry of the reservoir approach to the spillway, cause the approach flow to the ogee weir to be non-uniformly distributed and turbulent for part of the ogee weir. Turbulence can be generated by flow separation from an abutment or by the manner whereby the flow approaches the spillway. In the latter case, the reservoir bathymetry at the spillway entrance is important, as it affects flow distribution at the spillway entrance. The base spillway used for the study was a hydraulic model used to assist in the design of the new spillway for Los Vaqueros Dam on Kellogg Creek near Brentwood, California. The flow approach to this spillway is typical of many, relatively shallow over-flow spillways that involve an ogee crest. As often is the case for spillways associated with embankment dams, the spillway is built on an abutment of the dam itself and must deal with non-uniform and turbulent approach flow from the reservoir retained by the dam to the spillway's location at the side of the dam. Consequently, the approach flow was non uniform and turbulent, and design questions arise as to where to place the ogee crest for the spillway and what shape to use for a spillway. Though the investigation used the spillway just mentioned, the results have general application. The experiments were performed using a spillway flume with a rectangular cross-section, a circular abutment intake and a controllable spillway crest with changing the crest location to five locations (one downstream of the selected location and three upstream of that location). Measurements included water profiles, velocity across transects downstream of the spillway's entrance. These measurements were made for a circular spillway-abutment and for an elliptical spillway-abutment. The results show that changing the crest location significantly affects flow uniformity and possible shed-vortex formation from the intake abutment. Therefore, the results also indicate that spillway crest location has a direct impact on the hydraulic performance of the spillway. Suitable selection of crest location can be used to minimize non-uniformity and vortex-related problems in spillway design. The present study recommends that the ogee crest face be placed at least 1.5 crest widths from the entrance of the spillway. This position enables the flow to the crest to become suitably uniform and turbulence of flow within the entrance to extensively (though not entirely) decay. The findings from this study are significant for engineers and researchers involved in spillway design and generally in many aspects of hydraulic engineering design. The findings also demonstrate the importance of careful consideration of crest location in spillway design to mitigate problems related to vortex formation. Overall, this study adds to the knowledge base regarding spillways and their design. Spillways have been used for hundreds of years but there are many aspects of these hydraulic structures requiring continued research.Item Open Access Feasibility assessment of magnetic sensors for measurement of Hall current induced changes to the static magnetic field nearby a Hall thruster(Colorado State University. Libraries, 2013) Morozko, Zoe, author; Williams, John, advisor; Stansloski, Mitchell, committee member; Thornton, Christopher, committee memberA Hall thruster is an electric propulsion device that produces thrust electrostatically by accelerating propellant to velocities 5 to 10 times higher than is achievable using conventional chemical thrusters. This is accomplished through the application of static, crossed electric and magnetic fields that are concentrated in a region close to the exit plane of the thruster. During operation an azimuthal plasma-electron current develops in the region where the electric and magnetic fields are concentrated. This embedded plasma current is referred to as the Hall current. The thrust produced from accelerating the propellant is transferred to a satellite or spacecraft through interaction between the Hall current and the magnetic coils used to produce the static magnetic field within the thruster. The Hall current can be calculated and the thrust can be determined in real time by measuring the magnetic field produced by the Hall current using sensors located external to the thruster. This work investigates the feasibility of placing magnetic sensors in the regions close to the exit of the thruster to measure the external magnetic field and correlate it to the Hall current. A finite element magnetic solver was used to identify several locations outside of the thrust plume and near the pole piece where the magnetic field magnitude changes by several Gauss in a background field level of ~50 Gauss. Magnetic sensors based on the giant magnetoresistive effect were identified as acceptable with regard to sensitivity, and measurements made with these sensors in a simulated high background magnetic field environment demonstrated that changes of 0.5 Gauss could be easily measured. This work also presents the development of a thrust stand that will be useful in future work to demonstrate the overall concept. Special focus was directed to the design of the data acquisition system and in-vacuum calibration system used to make measurements with the thrust stand.Item Open Access Floodwave and sediment transport assessment along the Doce River after the Fundão Tailings Dam collapse (Brazil)(Colorado State University. Libraries, 2019) Palu, Marcos Cristiano, author; Julien, Pierre, advisor; Thornton, Christopher, committee member; Ettema, Robert, committee member; Rathburn, Sara, committee memberThe collapse of the Fundão Tailings Dam in November 2015 spilled 32 Mm3 of mine waste, causing a substantial socio-economic and environmental damage within the Doce River basin in Brazil. Approximately 90% of the spilled volume deposited over 118 km downstream of Fundão Dam on floodplains. Nevertheless, high concentration of suspended sediment (≈ 400,000 mg/l) reached the Doce River, where the floodwave and sediment wave traveled at different velocities over 550 km to the Atlantic Ocean. The one-dimensional advection-dispersion equation with sediment settling was solved to determine, for tailing sediment, the longitudinal dispersion coefficient and the settling rate along the river and in the reservoirs (Baguari, Aimorés and Mascarenhas). The values found for the longitudinal dispersion coefficient ranged from 30 to 120 m2/s, which are consistent with those in the literature. Moreover, the sediment settling rate along the whole extension of the river corresponds to the deposition of finer material stored in Fundão Dam, which particle size ranged from 1.1 to 2 μm. The simulation of the flashy hydrographs on the Doce River after the dam collapse was initially carried out with several widespread one-dimensional flood routing methods, including the Modified Puls, Muskingum-Cunge, Preissmann, Crank Nicolson and QUICKEST. All of these methods presented unsatisfactory results, with prediction errors in peak discharge up to 44%, and differences in timing to peak up to 5 hours. A new and more accurate one-dimensional flood routing approach was then used, solving the full dynamic equation into an equivalent diffusive wave format and reformulating the hydraulic diffusion coefficient in terms of the Froude number and floodwave celerity. The numerical solution to this new approach was implemented using Crank Nicolson and QUICKEST schemes. The error in predicted peak discharge along the Doce River was reduced to 2%, and the maximum difference found in time to peak was about 1 hour. Regarding sediment transport, a comprehensive one-dimensional numerical model is developed, coupling the new floodwave propagation algorithm with the numerical solution for advective sediment transport and settling. One of the main features of this model is the ability to simulate the propagation of the floodwave and sediment through the entire Doce River extension with or without reservoirs. A sensitivity analysis showed that a hypothetical decrease in water temperature from 30°C to 5°C would have resulted in a concentration 13 times higher at the outlet. In addition, without the presence of hydropower reservoirs on the Doce River, the sediment concentration at the basin outlet would have been 70,000 mg/l instead of the observed 1,600 mg/l. Finally, a simplified numerical model based on the Doce River measurements can simulate the hypothetical collapse of 56 tailings dams in the Doce River basin to estimate the potential impact on the water supply for the towns along the river. Those simulation results show that tailings dams located in the Piracicaba basin, a Doce River sub-basin, have the highest potential to adversely impact the water supply of the downstream towns due the volume stored and proximity with populated towns. Ultimately, the collapse of the biggest dams in this sub-basin could affect approximately 1,000,000 people for several days.Item Open Access Geomorphic analysis of the Middle Rio Grande - Elephant Butte Reach, New Mexico(Colorado State University. Libraries, 2012) Owen, Tracy Elizabeth, author; Julien, Pierre, advisor; Thornton, Christopher, committee member; Rathburn, Sara, committee memberThe Elephant Butte Reach spans about 30 miles, beginning from the South Boundary of the Bosque del Apache National Wildlife Refuge (River Mile 73.9) to the "narrows" of the Elephant Butte Reservoir (River Mile 44.65), in central New Mexico. Sediment plugs occasionally form along the Middle Rio Grande, completely blocking the main channel of the river. In 1991, 1995, and 2005, the Tiffany Plug was initiated at the upstream end of the Elephant Butte Reach. In 2008, the Bosque del Apache Plug formed just upstream of the Elephant Butte Reach. Sediment plugs occur at the location of a constriction or channel aggradation (Burroughs 2011). As aggradation within the Elephant Butte Reach is known to contribute to a decrease in channel capacity (Reclamation 2007), it is important to understand the influences of Elephant Butte Reservoir levels on channel aggradation/degradation in order to decrease the potential for future sediment plug formation. Further understanding of the historical and spatial changes within Elephant Butte Reach, along with a better understanding of the influences of Elephant Butte Reservoir levels on channel aggradation/degradation, are essential for improvement in future river management practices along the Middle Rio Grande. Using aerial photographs, survey data, reservoir water surface elevation data, and bed material data, the following objectives are addressed in this study: 1. Quantify temporal changes in channel widths and sinuosity from 1935 to 2010. 2. Quantify change in channel slope temporally. 3. Quantify rate of aggradation/degradation in response to a change in base-level (i.e., change in reservoir water surface elevation). 4. Quantify aggradation/degradation wave propagation upstream. 5. Quantify spatial and temporal trends in bed material grain size. From 1935 to 2010, channel widths and sinuosity decrease over time. The majority of the Reach's channel slope decreases from 1935 to 2010; the downstream-most stretch of the channel, closest to Elephant Butte Reservoir, alternates between increasing and decreasing channel slopes. As the Elephant Butte Reservoir level (base-level) increases, the channel aggrades in response. As the base-level decreases, the channel degrades. The rates of aggradation and degradation vary between different periods of base-level changes, and are quantified within the report. When the base-level changes a wave of aggradation/degradation travels upstream. The rate of wave propagation upstream varies relative to the rate of base-level change, and is quantified within the report for four sets of aggradation/degradation waves. Bed material samples obtained from cross-section surveys and at the San Acacia and San Marcial gauges showed a coarsening at a rate of about 0.03 mm/year. In the downstream direction, bed material became slightly finer. The median bed material grain size ranged from 0.11 mm to 0.26 mm.Item Open Access Mitigation measures for barriers to Great Plains fish migration(Colorado State University. Libraries, 2015) Ficke, Ashley D., author; Myrick, Christopher, advisor; Bestgen, Kevin, committee member; Fausch, Kurt, committee member; Thornton, Christopher, committee memberTo view the abstract, please see the full text of the document.Item Open Access Nonlinear internal wave - topographic interaction and turbulent mixing using numerical simulations(Colorado State University. Libraries, 2021) Klema, Matthew Roy, author; Venayagamoorthy, Subhas Karan, advisor; Nelson, Peter, committee member; Rathburn, Sarah, committee member; Thornton, Christopher, committee memberTo view the abstract, please see the full text of the document.Item Open Access The effects of scour on the flow field at a bendway weir(Colorado State University. Libraries, 2019) Garfield, Mason, author; Ettema, Robert, advisor; Thornton, Christopher, committee member; Wohl, Ellen, committee memberBendway weirs (BWs) are rock structures commonly used for controlling the thalweg location in alluvial channels, especially bends. Although there are many studies analyzing the effect of BWs on bend flow fields, there is little known about the effects of scour on the modified flow field. Many physical and numerical models of BWs use a fixed bed with the existing river bathymetry, assuming that the effects of scour are negligible. This study analyzed the effects of the scour on the flow field using SRH-2D, a 2-dimensional numerical model solving the full St. Venant equation (also termed the dynamic wave equation). In addition, the study used small scale and large scale hydraulic models and a 3-dimensional numerical model, FLOW-3D, to validate and calibrate the 2-D model. Using FLOW-3D, the 3-dimensional flow field was used to identify areas where SRH-2D was accurate and where it was lacking. The small scale hydraulic model was used to determine the effect of streamwise blockage on scour using plates. Results from the small scale hydraulic model indicate that when the degree of streamwise blockage (L/B where L is the width of the plate and B is the width of the flume) and submergence (Y/H where Y is the flow depth and H is the height of the plate) remained the same, but the acute angle to the flume wall varied (α), the maximum scour depth did not change significantly. Accordingly, the scour morphology from the tests with α = 90° could be applied to tests with α = 30° and 60° using the 2-D model. When comparing the flow field using SRH-2D to FLOW-3D, it was found that the maximum depth-averaged velocity was closer to FLOW-3D's when Y/H = 1.25 than when Y/H = 2.0. This finding likely results from the greater effect of blockage directing the flow around the BW than the deeper case, where the flow has a higher vertical velocity over the top of the BW. The 2-D model cannot take this into account, leading to error. The pre- and post-scour maximum velocity magnitude and locations were compared to determine the effect of scour on the flow field using the 2-D model. A deep flow depth (Y/H = 2.0) and a shallower flow depth (Y/H = 1.25) were run for different BW orientations, (α=30°,60°,and 90°) to determine the applicability of the effect of scour on the flow field. The analysis found that, when Y/H = 2.0, the difference in the maximum velocity magnitude and location between pre-and post-scour were fairly negligible for all orientations, whereas when Y/H =1.25, the effects of the scour on the flow field were more prominent. Overall it was found that the scour morphology is important to take into consideration for a fixed bed numerical or physical model when analyzing flow depths slightly overtopping the BW, but has little effect when the flow is twice the size of the BW.