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Characterization of adhesives at room and elevated temperaturesNedukanjirathingal, Santhosh Kumar 07 1900 (has links)
Recent interest in advanced materials has paved the way for exploring joining options besides the traditional mechanical or thermal methods such as riveting or welding. Because of the availability of highly advanced materials, mass production rates and demands for more aesthetic products, adhesive bonding is being used in more applications. Today, interstate signs, semitrailer panels, aircraft structures, and many other commonly used products are adhesively bonded. Some of the common misconceptions about adhesives are that they are inherently weak, require high operator skill, and are too expensive for production. However, these assumptions are true only when the adhesive joint design is faulty and/or the bonding process is performed incorrectly. This report includes testing, using single lap joints, of some adhesives both at room and elevated temperatures. Experimental setups for performing the tests are discussed. The shear strengths of various adhesives are determined with titanium adherents. A methodology was developed to determine the approximate value of shear modulus of the adhesive using finite element modeling (FEM) from the ASTM D 3165 test. This was completed in conjunction with experiments using a laser extensometer. Later in the report, correction factors that are used with the laser extensometer data to determine the shear moduli are determined. / Thesis (M.S.)Wichita State University, Dept. of Aerospace Engineering. / "July 2006." / Includes bibliographic references (leaves 8789)

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The analysis of horizontal axis wind turbine aerodynamics using wavelet theory, spectral and time series methodsSlepski, Jonathon Edward 01 January 1996 (has links)
The study of wind turbine blade aerodynamics during full operation has only recently received attention, due to the high cost of conducting such experiments. Data used in this dissertation was received from the National Renewable Energy Laboratory. Such unsteady aerodynamic processes as dynamic stall, boundary layer separation, and turbulent inflow will contribute to increased blade loadings and reduced machine life. The research presented in this dissertation utilizes time series, spectral, and wavelet techniques to analyse wind turbine aerodynamics. In particular, the tower shadow event at 30, 47, and 63% span is linked to rapid reattachment, followed by detachment of the boundary layer. It is also shown that the intensity of these events may be reduced by operating at a slight yaw error, between $$4 and $$10 degrees. Furthermore, a unique wavelet analysis technique has been developed to study a 2p effect seen in pressure and lift coefficient data. This wavelet technique is used to show that 2p results from the splitting of the signal time series into two halves by intense tower shadow spikes. Through careful analysis of C$\rm\sb{p}$ plots, the blade section boundary at 30, 47, and 63% span was seen to be detached in 90% of the revolutions studied. Boundary layer transition to separated conditions occurs when the attack angle surpasses 18 degrees, indicating a stall delay of about 8 degrees. Dynamic stall vortex shedding rarely occurs for the conditions seen in the data set analysed in this dissertation. Slight yaw error, as well as the three dimensional effect of rotation, appears to be beneficial for maintaining a slight favorable pressure gradient at inboard blade section during deep stall operation, thereby reducing the potential for vortex growth.

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Sequential experimental design approaches to helicopter rotor tuningWang, Shengda 01 January 2005 (has links)
Two different approaches based on sequential experimental design concepts have been studied for helicopter rotor tuning, which is the process of adjusting the rotor blades so as to reduce the aircraft vibration and the spread of rotors. One uses an interval model adapted sequentially to improve the search for the blade adjustments. The other uses a probability model to search for the blade adjustments with the maximal probability of success. In the first approach, an interval model is used to represent the range of effect of blade adjustments on helicopter vibration, so as to cope with the nonlinear and stochastic nature of aircraft vibration. The coefficients of the model are initially defined according to sensitivity coefficients between the blade adjustments and helicopter vibration, to include the expert knowledge of the process. The model coefficients are subsequently transformed into intervals and updated after each tuning iteration to improve the model's estimation accuracy. The search for the blade adjustments is performed according to this model by considering the vibration estimates of all of the flight regimes so as to provide a comprehensive solution for rotor tuning. The second approach studied uses a probability model to maximize the likelihood of success of the selected blade adjustments. The underlying model in this approach consists of two segments: a deterministic segment to include a linear regression model representing the relationships between the blade adjustments and helicopter vibration, and a stochastic segment to comprise probability densities of the vibration components. The blade adjustments with the maximal probability of generating acceptable vibration are selected as recommended adjustments. The effectiveness of the proposed approaches is evaluated in simulation based on a series of neural networks trained with actual vibration data. To incorporate the stochastic behavior of the helicopter vibration and better simulate the tuning process, the probability density function of the prediction error is used to simulate noise. Due to the stochastics of the helicopter vibration, the proposed approaches cannot be evaluated by deterministic measures. Therefore, several performance measures have been devised to represent the various aspects of helicopter rotor tuning as the evaluation criteria.

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Hinged blade model dynamics for a horizontal axis wind turbineKendall, David Arthur 01 January 2003 (has links)
This dissertation describes fundamental extensions to the hingespring model used to simulate the first mode of blade vibration in wind turbine dynamics. Complete equations of motion are developed while allowing for both bending of the blade perpendicular to its chord and overall motion of the rotor in azimuth and yaw. The model examines the relationship between the natural rotation frequency of the rotor ω and the fundamental natural bending frequency of the blades without including the bending frequency of the tower. In the case of no yaw motion, perturbation analysis and iteration lead to analytical solutions for the bending and azimuth equations of motion that involve as little simplification of these equations as possible. The natural bending frequency is “stiffened” by the rotor rotation and is expressed as a multiple of the rotor rotation, ω∗ ω. While the bending frequency is used in models using the hinged blade, the solutions found in this work contain more detail than can be found in prior investigations. These analytical solutions reveal that the harmonics with frequencies Nω∗ω (ω ∗ + 1)ω and (ω∗ − 1)ω are involved with the coupling between bending motion and azimuth motion with N = 1, 2, 3,…. Subsequent derivation of the power output for the condition of a relatively large amplitude of blade vibration predicts a noticeable contribution to power generation for the ω∗ ω response, which is verified in the data. Glauret's momentum transfer theory as extended by Wilson and Lissaman [1974] and de Vries [1979] is modified to allow for blade bending, variations of wind speed with time and position, and variations in wind direction with time. No vertical wind is considered. It is concluded that: (1) the bending frequency and linear combinations with the rotor rotation frequency provide an important contribution under at least some of the expected operating conditions of the turbine, (2) the dynamic mass imbalance produced by the effects of blade bending is not important for an otherwise balanced rotor, and (3) modest nonsymmetric effects to the dynamics such as basic wind shear or changing wind speed and direction enhance the Nω frequencies much more readily than the Nω∗ω frequencies.

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Radiation characteristics of dualpolarized notch antenna arraysWunsch, Gregory Joseph 01 January 1997 (has links)
Investigation of endfire slotline antennas, such as notch or Vivaldi antennas, has been progressing over the last few decades. The physics of these antennas is as yet not well understood. Simple models do not predict their behavior accurately, and experimental data is expensive and time consuming to obtain, therefore full wave computer simulations, (finite element and moment method) are used extensively to model their behavior. Dualpolarized arrays of these elements is the main topic of this work. A moment method analysis is developed to analyze these arrays. Many previously unknown results pertaining to their radiation and polarization characteristics are presented. With two orthogonally polarized elements, virtually any arbitrary polarization of wave can be transmitted provided (1) amplitude and phase control is used and (2) neither antenna is blind at the operating frequency and scan angle. Also, an unexpected asymmetry of the radiation was discovered and traced to the stripline feed. Amplitude and phase control can be expensive to implement and may reduce the efficiency of the amplifiers, however. As an alternative, the use of phaseonly control is investigated. This works well for generating a reduced set of antenna polarizations, namely, the left and right hand circular polarization, $\pm$45$\sp\circ$ slant linear polarization. Horizontal and vertical polarization can be generated as well if the amplifiers are switched on and off. A new class of resonance was discovered for the dualpolarized array. The physical mechanism is identified and studies are performed showing the variation of resonant frequency with antenna shape, dielectric constant of the substrate and array depth. A new class of singlepolarized arrays is also studied. Full and partial crosswalls are shown to alter the Eplane patterns in a variety of useful ways.

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Degradation of glycol based aircraft deicing fluids under anaerobic methanogenic conditionsVeltman, Shawn Herbert 01 January 2000 (has links)
Large quantities of aircraft deicing fluid (ADF) comprised mainly of ethylene glycol (EG) and propylene glycol (PG) are used for aircraft deicing/antiicing during cold weather operations at airports throughout the world. Several different formulations of ADF have been developed and are used. Type I solutions are commonly employed to remove snow and ice from aircraft surfaces (deicing), and Type IV solutions are commonly applied to prevent ice from reforming (antiicing). The runoff from aircraft deicing operations is known to have a high oxygen demand. As a consequence, deicing wastes are often collected at airports for treatment. ADF products also contain small amounts of colorants, corrosion inhibitors, and thickeners, and these compounds may pose a greater environmental concern than oxygen depletion. Several studies have been completed to compare the relative toxicity of the pure glycols (EG and PG) vs. ADF using Microtox ® assays and other aquatic tests, and it has been reported that ADF is significantly more inhibitory than the pure glycols. With growing concern over the environmental consequences of deicing there has been interest in developing anaerobic technology to treat deicing waste. In this dissertation a survey, a deicing waste characterization study, and research efforts employing serum bottles and bench scale laboratory reactors were used to demonstrate that ADF may be degraded effectively and efficiently in an anaerobic methanogenic environment. The factors that may affect this degradation are examined and discussed.

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Additive Manufacturing of Oxide Dispersion Strengthened Multi Principle Element Alloys for Future Aerospace ApplicationsWilson, Laura G. 26 May 2023 (has links)
No description available.

18 
Residual Stresses Mapping in Laser Additive Manufacturing of IN 718: An XRay Diffraction StudyRamineni, Lakshmi Prathusha January 2022 (has links)
No description available.

19 
An experimental investigation of the effect of vortex generators on the aerodynamic characteristics of a NACA 0021 airfoil undergoing large amplitude pitch oscillationsRueger, Mathew Lee January 1988 (has links)
No description available.

20 
Experimental Approach to the Feasibility of an AxiallyStacked Propeller SystemNichols, Schuyler R. January 2014 (has links)
No description available.

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