Scholarship & Research
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Item Evaluation of pitch control techniques for a cross-flow water turbine(Montana State University - Bozeman, College of Engineering, 2017) Gauthier, Timothy Andrew; Chairperson, Graduate Committee: Erick JohnsonCross-flow water turbines are complex devices that have yet to see large-scale implementation relative to conventional horizontal-axis wind turbines. While wind energy was the primary target of past investigations, water energy follows most of the same dynamic principles. However, water currents tend to be much more stable than their wind current counterparts, and many water currents exist in channels that favor the compact shape of the cross-flow turbine. These advantages have rejuvenated interest in cross-flow turbine design for marine energy generation. Computational models give engineers the ability to accurately estimate what designs work best to avoid costly field maintenance and downtime. Specifically, computational fluid dynamics uses the Navier-Stokes equations, a set of differential equations that describe the pressure and velocity fields in a fluid domain. The Reynold-Averaged Navier-Stokes turbulence model described in this work examines how controlling the pitch of water turbine blades can improve system performance and reliability. Pitch means that the blade noses up or down about the chord line which runs from leading edge to trailing edge relative to the inflow. Pitch control was originally developed for helicopter blades and is commonly used by conventional wind turbines, but pitch control for water turbines is a relatively new research area. Initial results suggest significant incremental gain in power output with pitch control up to 149%, as compared to a no-pitch case, based on a to-scale representation of the cross-flow water turbine in the Fluids and Computations Laboratory at Montana State University. Simultaneous reliability gain is observed as the force transmitted by the water to the blades is reduced by 135%; this may allow for lower cost turbine structures and streamlined hydrofoil design. Additionally, turbine wake profile visualization and blade pressure coefficient curves describe the viscous interaction both quantitatively and qualitatively. Cross-flow water turbines have the potential to become a significant worldwide energy source, with performance optimization studies such as these a necessary prerequisite.Item Exploring the effects of fiber angle and stacking sequence on the static strength and acoustic emission signature of epoxy-fiberglass composites in marine environments(Montana State University - Bozeman, College of Engineering, 2017) Nunemaker, Jake Douglas; Chairperson, Graduate Committee: David A. MillerMarine Hydro-Kinetic (MHK) devices encompass promising new technologies designed to harness energy from ocean currents and tides. However, there are unique challenges to successful implementation of MHK devices. Material selection and characterization are crucial steps in the design process as the marine environment can be extremely detrimental to many materials systems. Epoxy-fiberglass composites, the premier material in wind turbine blades are being studied for use in MHK due to desirable price and durability. Preliminary research has shown a significant drop in ultimate strength due to moisture absorption in unidirectional laminates. This research extends these studies by exploring these effects on balanced and unbalanced off-axis fiber angles for a common epoxy-fiberglass material system. Ply by ply analysis is completed to explore the efficacy of a strength reduction prediction method for off-axis laminates. It also extends the study to include acoustic emission analysis to further investigate the material degradation at a micromechanical level. Partial saturation strength reduction in symmetric laminates is also studied.Item A fundamental study of hot corrosion and interdiffusion of chromium, aluminum, and silicon coatings on a nickel-201 substrate(Montana State University - Bozeman, College of Engineering, 2014) Gill, Zachery Edward; Co-chairpersons, Graduate Committee: Paul E. Gannon and Roberta AmendolaModern turbine engine systems require increased efficiency and durability. To achieve these goals, high-temperature materials with high-strength, low-cost and non-strategic compositions are needed. In advanced turbine applications, combustor liners, blades and vanes are exposed to corrosive combustion byproducts, such as alkali salts, at temperatures up to ~1700°C with high gas velocities, entrained particulates, and other foreign objects at pressures of up to 3 MPa (30 atm). These extreme conditions can drive a dangerous phenomenon known as "hot corrosion", an accelerated form of oxidation that occurs when metals and metal alloys are heated in the temperature range 700-900°C in the presence of alkali salts. An increased understanding of the fundamental behaviors of common high temperature alloys and their degradation mechanisms is therefore critical for the production of reliable components. In this study a model substrate, Nickel 201, was coated on one side with Cr, Al, or Si thin films (~1 micron) via magnetron sputtering physical vapor deposition (PVD). Uncoated and PVD coated samples were then exposed to laboratory air at 700°C and 900°C and to an environment similar in composition to atmospheres found in post combustion turbine systems, comprised of air/SO 2 gas mixture, at 700°C. The exposures were conducted over time intervals observing coating-substrate interactions and surface oxide development. Identical samples were subjected to the same exposures with addition of a deposit of sodium sulfate (Na 2SO 4), a model alkali salt. Sample mass gains were recorded and resulting oxide compositions assessed as a function of exposure time using microscopy techniques on sample surfaces and cross sections. The development of intermetallic species was determined by X-ray diffraction. At 700°C, coated and uncoated samples displayed different oxidation behaviors. Under laboratory air, no hot-corrosion occurred. While at 700°C in air/SO 2 exposures, evidence for hot corrosion on deposited samples was observed. When sodium sulfate was introduced at 900°C, coated and uncoated samples displayed rapid corrosion consistent with hot corrosion. The oxidation processes and coating/substrate inter-diffusion phenomena are presented and discussed in the context of establishing basic approaches to improve the fundamental understanding of hot corrosion, and the protection mechanisms of high temperature materials.Item Development of reliability program for risk assessment of composite structures treating defects as uncertainty variables(Montana State University - Bozeman, College of Engineering, 2013) Riddle, William Wilson, III; Chairperson, Graduate Committee: Douglas S. CairnsIt has been reported that a leading cause of repairs and failures in wind turbine blades is attributable to manufacturing defects. The size, weight, shape and economic considerations of wind turbine blades have dictated the use of low cost composite materials. Composite structure manufacturing quality is a critical issue for reliability. While significant research has been performed to better understand what is needed to improve blade reliability, a comprehensive study to characterize and understand the manufacturing flaws commonly found in blades has not been performed. The work presented herein is focused on performing mechanical testing of flawed composite specimen and developing probabilistic models to assess the reliability of a wind blade with defects. The analysis postulates that one should assess defects as a design parameter in a parametric probabilistic analysis. A consistent framework has been established and validated for quantitative categorization and analysis of flaws. Results from this effort have shown that the probability of failure of a wind turbine blade with defects, can be adequately described through the use of Monte Carlo simulation. The two approaches detailed in this analysis have shown that, by treating defects as random variables, one can reduce the design conservatism of a wind blade in fatigue. Reduction in the safe operating lifetime of a blade with defects, compared to one without has shown that the inclusion of defects is critical for proper reliability assessment. If one assumes that defects account for some of the uncertainty in the blade design and these defects are analyzed with application specific data, then safety factors can be reduced. It has been shown that characterization of defects common to wind turbine blades and reduction of design uncertainty is possible. However, it relies on accurate and statistically significant data.Item A comparison of continuum and discrete modeling techniques of the effects of manufacturing defects common to composite structures(Montana State University - Bozeman, College of Engineering, 2013) Nelson, Jared William; Chairperson, Graduate Committee: Douglas S. CairnsApplication of different damage modeling approaches for use with composite materials and composite material structures has grown with increasing computational ability. However, assumptions are often made for "worst case" scenarios with these modeling techniques resulting in approximating defects as a hole or notch in a plate instead of modeling actual flaw geometry. These analytical tools have helped bound composite material and structure capabilities, but do not allow for comprehensive understanding of the effects of defects as the characteristic parameters of the defects vary. In order to develop a tool that will allow for accurate analysis of a complete structure, including defects of different parameters, modeling approaches must be optimized. It was the optimization of these approaches that was investigated herein with specific application toward establishing a protocol to understand and quantify the effects of defects in composite wind turbine blades. A systematic, three-round study of increasing complexity was performed to understand the effects of three typical blade manufacturing defects while investigating continuum, discrete, and combined damage modeling. Through the three rounds of the benchmark material testing, significant coupon level testing was performed to generalize the effects of these defects. In addition, material properties and responses were analyzed and then utilized as material inputs and correlation criteria for each analytical technique. Parallel to the material testing, each of the three rounds increased in analytical complexity to ensure that models were only as complex as necessary to achieve acceptable correlation. Correlation was compared both qualitatively and quantitatively for an initial case and other cases were investigated only if initial correlation was acceptable. While each modeling type offered certain attributes, a combined approach yielded the most accurate analytical/experimental correlation. Thus, a unique comparison of several different analytical approaches to composites with respect to manufacturing for consistency, accuracy, and predictive capability allowing for improved blade reliability and composite structural assessment.Item Manufacturing process modeling for composite materials(Montana State University - Bozeman, College of Engineering, 2013) Guest, Daniel Aaron; Chairperson, Graduate Committee: Douglas S. CairnsThe increased use and interest in wind energy over the last few years has necessitated an increase in the manufacturing of wind turbine blades. This increase in manufacturing has in many ways out stepped the current understanding of not only the materials used but also the manufacturing methods used to construct composite laminates. The goal of this study is to develop a list of process parameters which influence the quality of composite laminates manufactured using vacuum assisted resin transfer molding and to evaluate how they influence laminate quality. Known to be primary factors for the manufacturing process are resin flow rate and vacuum pressure. An incorrect balance of these parameters will often cause porosity or voids in laminates that ultimately degrade the strength of the composite. Fiber waviness has also been seen as a major contributor to failures in wind turbine blades and is often the effect of mishandling during the lay-up process. Based on laboratory tests conducted, a relationship between these parameters and laminate quality has been established which will be a valuable tool in developing best practices and standard procedures for the manufacture of wind turbine blade composites.