Theses and Dissertations at Montana State University (MSU)
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Item Underwater acoustic propagation modeling and utilization for marine hydrokinetic devices(Montana State University - Bozeman, College of Engineering, 2024) Hafla, Erin Christine; Chairperson, Graduate Committee: Erick JohnsonOver the last two decades, there has been growing concern surrounding the increase in underwater anthropogenic sounds as expanding human populations interact with marine life and look for alternative energy production methods. That concern has led to a significant push worldwide to understand how propagated sound interacts with the surrounding marine environment. Marine hydrokinetic (MHK) devices are an alternative source of renewable energy available, which generate electricity from the motion of tidal and ocean currents, as well as ocean waves. Sounds produced by MHKs tend to overlap the frequency range common to both marine fauna communication and behavior. Preliminary measurements indicate that sound level values fall near the total sound decibel limitations presented by regulatory bodies. To date, the power optimization of MHK arrays has been prioritized over how its sound is produced, directed, and may impact the marine soundscape. There is a gap in knowledge regarding how marine fauna may respond to these sounds and what their physical and behavioral impact may be, and an absence in measured levels from insitu MHK deployments. A model for predicting the propagation of sound from an array of MHK sources in a real environment is essential for understanding potential impacts on a surrounding system. This work presents a fully three-dimensional solution to a set of coupled, linearized velocity-pressure equations in the time-domain as applied to underwater systems, and is an alternative sound propagation model to the Helmholtz and wave equation methods. The model is validated for a single source located within a series of increasingly complex two-dimensional and three-dimensional shallow water environments and compared against analytical solutions, examples from literature, and recorded sound pressure levels collected from Sequim Bay, WA. An uncertainty analysis for an array of MHK devices is presented to further understand how multiple turbine signals interact with one another in increasingly complex systems. This research presents a novel use of the velocity-pressure equations to analyze the variability associated with sound sources as sound propagates through a selected environment to inform the design and deployment of a MHK device or array of devices to minimize potential future impacts.Item Aggregate piers: stress transfer mechanism and construction effect(Montana State University - Bozeman, College of Engineering, 2022) Gamboa, William; Chairperson, Graduate Committee: Mohammad KhosraviThis thesis is a compilation of two different papers based on the behavior of aggregate piers which is a soil improvement method used to increase the bearing capacity and reduce the expected settlements of soils in which different types of structures are supported. The first paper describes the results of two modulus load tests and a dimensional finite difference analysis (FDA) conducted to evaluate the load-displacement response of isolated aggregate piers. Load test aggregate piers were constructed with two different materials: the first one with 38 mm base coarse and the second one with 75 mm subbase coarse materials. The numerical analyses provided reasonable predictions of the load-displacement response of the isolated aggregate piers. Parametric analyses using the validated numerical model illustrate that the lateral stress increment on the soil around the pier during the installation process of the pier should be considered in the numerical analysis, otherwise the settlement can be overestimated. The second paper is based on two full-scale load tests that were conducted to examine the load transfer mechanisms of end-bearing single and group aggregate piers. The first included a load test on a 0.76 m diameter isolated aggregate pier. The length of the aggregate pier was 4.3 m. The second test included a 2.1 m square reinforced concrete footing supported by four 0.76 m diameter aggregate piers of 4.3 m long. The soil consists of soft to medium stiff layers of sandy and clayey silt overlain by a 2-m-thick, softer silty clay layer. At the bottom, weathered rock was found. The load transfer mechanism within the length of the piers was examined using a series of load cells and tell-tale reference plates installed at different depths of the aggregate piers. Additionally, the installation effect was investigated using Cone Penetration Tests (CPT) conducted prior and after construction of the aggregate piers and inclinometers installed at multiple locations around the aggregate piers. The results of the experiments were compared with those in the literature to provide insights on the performance of aggregate piers with different configurations (single vs. group) and depths (floating vs end-bearing) in different soil profiles.Item Separating the EPS in a biofilm : models and simulations of movement of the EPS within(Montana State University - Bozeman, College of Letters & Science, 2016) McClanahan, Nathan James; Chairperson, Graduate Committee: Tianyu ZhangIn this dissertation two models are investigated for describing movement of different components within a biofilm. The first model uses a single fluid three component formulation of the biofilm to model the movement within the biofilm in 1D. This is done using a system partial differential equations to model the expansion or contraction of the biofilm in order for the three components to reach an ideal concentration. The model is further refined to include separate velocities for each component as well as using zeroth order kinetics for the growth. In order to solve this system of partial differential equations a finite difference method with an upwind scheme was used to solve the system numerically. The second model is an energy based approach done in both 1D and 2D. An energy, in the case the Flory-Huggins free energy density, is used to describe the interactions of different components within the biofilm. The Cahn-Hilliard equation with the Flory-Huggins free energy density is used to model the separation of the biofilm into two phases. A brief derivation of both the Flory-Huggins equation and the Cahn-Hilliard equation is given using a lattice model and thermodynamic properties. The Flory-Huggins equation is modified slightly for simplicity. A movement energy is also added to the Flory-Huggins equation in order to allow the polymers within the biofilm to move around the domain. In the 1D case the numerical solution was found using finite differences with an upwind scheme similar to the first model. The 2D case is more difficult to solve due to the extra dimension. Due to this the projection method was used to solve part of the system of equations and finite difference using central difference instead of upwind is used to solve the rest.Item An adaptive stencil finite difference method for first order linear hyperbolic systems(Montana State University - Bozeman, College of Letters & Science, 1995) Hoar, Robert HenryItem Numerical modeling of the deflection of an electrostatically actuated circular membrane mirror(Montana State University - Bozeman, College of Engineering, 2011) Moog, Eric John; Chairperson, Graduate Committee: Steven R. Shaw; David L. Dickensheets (co-chair)This thesis outlines a numerical modeling method to describe the deflection behavior and investigate control schemes for an electrostatically actuated deformable membrane mirror, with application to focus control and aberration correction in micrelectromechanical systems. The physics of the membrane are approximated using a finite difference approach with parameters obtained from measurements of a physical device. The model is validated by comparison of simulated and measured mirror position under static and dynamic conditions. This thesis provides simulation results for control schemes that would be difficult or potentially destructive if implemented using real devices. We suggest that the model may be useful for the development of future control strategies and in refining device design. Finally, a number of capacitive sensing circuits are presented as position feedback mechanisms and the capabilities and limitations of each are examined.