Browsing by Author "Musa, Mirko"

Now showing 1 - 6 of 6
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    A bedform tracking tool coupled with Fast Fourier Transform decomposition
    (2021-02-12) Lee, Jiyong; Musa, Mirko; Guala, Michele; lee02291@umn.edu; Lee, Jiyong; Turbulent Boundary Layer plus research team
    Quantifying bedform characteristics is crucial because bedforms are omnipresent and play an important role in fluvial environments. Bedforms induce form drag against flows and can significantly alter water depth, flow velocity, and sediment transport rate (i.e. the hydraulic roughness of channels can be parameterized with bedforms). In addition, ship navigation can be constrained by the presence and distributions of bedform crests; and localized scour within bedform troughs can deteriorate performance of fluvial infrastructures (e.g. containment walls, embedded pipes, or groynes). Despite of its importance, characterizing bedforms has been challenges due to inherent multi-scale features observed in channel bathymetries in both natural rivers and laboratory flumes. To tackle such challenges, we developed a bedform tracking tool coupled with Fast Fourier Transform (FFT) decomposition. A key advantage of the presented bedform tracking method is that bedform characteristics (morphology and kinematics) can be quantified in a wider range of scales.
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    Hydrokinetic turbine array performance and geomorphic effects under different siting strategies and sediment transport conditions: topography, flow velocity and array performance measurements
    (2019-06-27) Musa, Mirko; Hill, Craig; Guala, Michele; mguala@umn.edu; Guala, Michele; Saint Anthony Falls Laboratory, CEGE, University of Minnesota
    Hydrokinetic energy can be extracted efficiently from naturally occurring water flows. Although representing a continuous and ubiquitous source of kinetic energy, rivers in particular are delicate environments, sensitive to external disturbances. Asymmetric installation of in-stream hydrokinetic energy converters have proven to actively interact with sediment transport and bedforms characteristics, triggering non-local geomorphic effects that resemble river instabilities known as forced-bars. This data-set comprises a series of measurements of channel topography evolution, flow velocity around the turbines and array performance under different configurations.
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    Local and Non-local Geomorphic Effects of Hydrokinetic Turbines: Bridging Renewable Energy and River Morphodynamics
    (2019-06) Musa, Mirko
    Marine and Hydrokinetic (MHK) energy is an emerging renewable and sustainable technology which harnesses kinetic energy of natural water flows such as tides, rivers and ocean currents. In particular, rivers are currently an overlooked source of local and continuous kinetic energy that can be exploited using the available in-stream converters technology. The uncertainties regarding the interaction between these devices and the surrounding environment complicate the regulatory permitting processes, slowing down the expansion of MHK industry. A crucial issue that needs further attention is the interaction between these devices and the physical fluvial environment such as the bathymetry, sediment transport, and the associated morphodynamic processes. Analytical and experimental research conducted at Saint Anthony Falls Laboratory (SAFL) addressed this topic, unveiling the local and non-local (far from the device location) effects of hydrokinetic turbines on channel bathymetry and morphology. A theoretical model framework based on the phenomenology of turbulence was derived to predict the scour at the base of MHK device. Asymmetric installations of turbine array models within multi-scale laboratory channels were observed to trigger river instabilities known as forced-bars. Results suggest that the amplitude of these instabilities might be reduced by limiting the power plant lateral obstruction within the channel cross-section. A 12-turbine staggered array also proved to be resilient to intense flooding conditions, encouraging the expansion of this technology to large sandy rivers. Current research is investigating how hydrokinetic technology can be synergistically integrated in rivers, not only minimizing the environmental costs but also providing a positive feedback on the channel. Experiments suggest that turbines strategically installed in the river (i.e. at the side bank in yawed condition or in a vane-shaped array) could be used as stream bank protection systems and, eventually, be integrated in stream restoration projects.
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    Measurements of spatio-temporal fluvial channel bed evolution in an array of yawed porous vanes at the Saint Anthony Falls Laboratory (SAFL) main channel
    (2024-04-11) Lee, Jiyong; Tseng, Chien-Yung; Musa, Mirko; Guala, Michele; mguala@umn.edu; Guala, Michele; Turbulent Boundary Layer plus research team
    Controlling lateral sediment flux and bed surface elevation distributions is important engineering solutions for sustainable river management. However, quantification of the lateral sediment flux has posed great challenges for river engineers for decades due to difficulties in measuring high resolution 2D spatio-temporal bed surface evolution data, \eta(x,y,t), when lateral sediment flux control is imposed by hydraulic structures. Here, \eta is bed surface elevation. Dimensions x and y are stream- and span-wise directions, and t is time. We conducted two sets of open channel experiments, in which \eta(x,y,t) was monitored using the state-of-the-art laser scanning data acquisition system. The first experiment was carried out without hydraulic structures, namely baseline case. The second experiment was conducted under the same hydraulic condition with an array of yawed porous vanes that were installed at the one-half of the channel width, imposing asymmetric lateral sediment flux. By comparing results from these two sets of experiments, the effects of an array of yawed porous vanes on the lateral sediment flux were quantified. We found that an array of porous yawed vanes can effectively direct sediment flux in the lateral direction by 9-18% of the averaged streamwise sediment flux under the current array configurations and hydraulic conditions.
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    Predictive model for local scour downstream of hydrokinetic turbines in erodible channels
    (American Physical Society, 2018-02-22) Musa, Mirko; Heisel, Michael; Guala, Michele
    A modeling framework is derived to predict the scour induced by marine hydrokinetic turbines installed on fluvial or tidal erodible bed surfaces. Following recent advances in bridge scour formulation, the phenomenological theory of turbulence is applied to describe the flow structures that dictate the equilibrium scour depth condition at the turbine base. Using scaling arguments, we link the turbine operating conditions to the flow structures and scour depth through the drag force exerted by the device on the flow. The resulting theoretical model predicts scour depth using dimensionless parameters and considers two potential scenarios depending on the proximity of the turbine rotor to the erodible bed. The model is validated at the laboratory scale with experimental data comprising the two sediment mobility regimes (clear water and live bed), different turbine configurations, hydraulic settings, bed material compositions, and migrating bedform types. The present work provides future developers of flow energy conversion technologies with a physics-based predictive formula for local scour depth beneficial to feasibility studies and anchoring system design. A potential prototype-scale deployment in a large sandy river is also considered with our model to quantify how the expected scour depth varies as a function of the flow discharge and rotor diameter.
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    Scaled Hydrokinetic Turbine Array installed in a laboratory channel and flood-like sediment transport conditions: topography, flow velocity and array model performance
    (2019-06-26) Musa, Mirko; Hill, Craig; Sotiropoulos, Fotis; Guala, Michele; mguala@umn.edu; Guala, Michele; Saint Anthony Falls Laboratory, CEGE, University of Minnesota
    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.