This thesis studies the basic concept of doubly-fed induction generators (DFIG) and develops a laboratory model to simulate DFIG wind turbine generators (WTG). “Doubly-fed” refers to the three-phase stator and rotor windings, both of which have electric power exchange with the ac power system. Different from synchronous generators installed in coal, oil, gas, hydro, and nuclear power plants, asynchronous DFIG generators are widely used for wind energy conversion because of the diversity of wind power. Through the control of back-to-back PWM converters connected between the DFIG rotor and power system, a DFIG can operate at variable speed but constant stator frequency. Below rated wind speed, the DFIG controls the torque on the turbine shaft to track the best operating point (i.e. at best tip-speed ratio). Above rated wind speed, the pitch angle of the turbine blades is adjusted to limit the power captured from the wind. DFIG can provide power factor regulation by controlling the reactive power exchange with the grid. In this laboratory DFIG experiment, a DC motor is open-loop controlled as a prime mover with variable mechanical power output. A wound-rotor induction motor is mechanically coupled to the DC motor and operated as a DFIG. An IGBT inverter is connected to a variable DC voltage source in order to provide a controllable three-phase voltage applied to the rotor windings. The reactive power output is controlled by setting the magnitude of the rotor excitation voltage. The active power (torque), reactive power output and speed can be controlled by setting the frequency of the rotor excitation voltage. Through manually adjusting the DC input and rotor excitation voltage, the laboratory DFIG is able to operate at a variable simulated wind speed (4 – 25 m/s) with desired power output following the GE 1.5 MW WTG. As an advanced control strategy, decoupled d-q vector control for DFIG using back-to-back converters is studied. Under a stator-flux oriented reference frame, for the rotor-side converter, the rotor d- component (i.e. vrd, ird) controls the stator reactive power (rotor excitation current), while the rotor q- component (i.e. vrq, irq) controls the stator active power (electrical torque); for the supply-side converter, the d- component (i.e. vd, id) controls the DC-link voltage, while the q- component (i.e. vq, iq) controls the reactive power. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Electrical Engineering and Computer Science.

An investigation was conducted to develop low Z-force (normal/forge load) friction stir spot welds (FSSWs) using conventional tooling and process development approaches. Low Z-forces can be achieved by studying the relationship between pin tool features, geometries, processing parameters, and resultant strength of coupons produced by friction stir spot welding (FSSW). The effects of geometrical and feature changes of pin tool designs—including shoulder diameters, shoulder features, probe diameters, probe shapes, and probe features—on the joint properties of 0.040-inch-thick bare 2024-T3 aluminum alloy were evaluated. Welding tools included Psi™, Counterflow™, Modified Trivex™, and V-flute™ pin tools. A Box-Behnken design of experiments (DOE) approach was used to investigate the effects of three process parameters: spindle speed, Z-force (forge load), and travel speed. The goal of the investigation was to maintain the ultimate tensile load (UTL) in unguided lap shear coupons tested in tension while reducing the Z-force required for producing a sound joint. This goal was achieved on a specially built MTS Systems Corporation ISTIR PDS FSW gantry system. In addition to single-spot unguided lap shear tests, the performance of low Z-force FSSW joints was evaluated by optical metallographic cross-section analyses, which were then correlated with process parameters, UTL, and pin tool designs. The maximum Z-force spikes encountered during the initial plunge were reduced by an order of magnitude, and the Z-force processing loads were reduced by half for Octaspot™ swept FSSW, most effectively by controlling the plunge rate under force control. Additional reductions in Z-force were achieved by refining the conventional FSSW tool shoulder and probe designs. Therefore, it was demonstrated that weld forces can be reduced to the point where it would be feasible to perform robotic low Z-force FSSW for at least some applications. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Mechanical Engineering.

Aircraft regulations for seat certification are adapting to new crashworthiness exigencies. However, the use of the forty year old Hybrid II Anthropomorphic Test Device (ATD) for seat certification has remained invariable in the aircraft community (manufacturers, regulators and researchers) for decades. Although the community has had the improved FAA Hybrid III 50th ATD (FAA HIII) from more than ten years is still scarcely used for seat certification. Possible reasons of the unpopularity of the FAA HIII might be: (1) concern with rumored more stringent biomechanic responses, which might make it more difficult for seat certification and (2) poor literature available for the FAA HIII in comparison to the Hybrid II ATD (HII). This Thesis deals with a research effort to expand the scarce information available on the FAA Hybrid III 50th male ATD, focusing in the lumbar-pelvis responses for different aircraft vertical loading conditions. The results from this Thesis research indicate that the FAA Hybrid III 50th ATD has achieved high degree of repeatability and linearity for lumbar-pelvis responses for Parts 23 and 25 Section 562 Emergency Landing Conditions. The demonstrated FAA HIII´s characteristics can help aircraft seat community to predict potential spine responses for different dynamic test configurations and for instance answer “what if” questions at the beginning of the seat design phase. Thus, the biofidelic improvements of the FAA HIII as well as reliable lumbar-pelvis responses can be sufficient enough reasons for replacing the old Hybrid II for seat certification purposes leading in safer designs. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Mechanical Engineering

Vacuum-Assisted Resin Transfer Molding (VARTM) has become a widly used and rapidly growing manufacturing process for wind turbine blades. However, in the case of complex geometries, resin flow pattern during the VARTM process tends to be unpredictable. In addition, increasing the size and thickness of the blades is expected to result in additional technical difficulties. Therefore, use of flow pattern simulation tools has become a necessity in order to avoid costly and time-consuming trial-and-error procedures during manufacturing. In this thesis, a 3-D non-isothermal framework for modeling the VARTM process for a wind turbine blade was developed. The model was utilized in a case study optimizing inlet gate arrangement, resin temperature, and mold temperature to shorten the filling time. Sequential filling scheme was assumed and different inlet gate arrangements and activation times were used in the first phase of the study. It was observed that, although increasing the number of the inlet gates tends to shorten the filling process, its effectiveness kept decreasing monotonically. The generally observed filling issue was the formation of dry spots in the sandwich region at the bottom of the part. In the sandwich region, the core splits the flow and forms two flow fronts, one on the top and another at the bottom of the sandwich region. The two flow fronts converge right after the core. For some cases, the slow moving flow front beneath the core was not able to reach its way out and converge with the flow front on the top of the core. To overcome the problem, activation of the auxiliary inlet gates located on the top of the core was postponed. In the second phase of the study, different resin temperatures were used. Increasing the temperature up to 325°K resulted in shorter filling durations while increasing the temperature further produced dry spots beneath the core. From the flow pattern results in non-sandwich areas, it was concluded that resolving the issue of slow moving flow front at the bottom of the core vii makes it possible to decrease the filling time by 17% through increasing the resin temperature by 20°C. The effect of different mold temperatures on the filling time was examined in the third phase of the study. Increasing the mold temperature from the initial value (330°K) did not result in shorter filling times. To investigate the necessity of employing 3-D non-isothermal model, a 2.5-D non-isothermal model and a 3-D isothermal model were developed and their results were compared to the results of the 3-D non-isotheral model. The 2.5-D non-isothermal model was unable to accurately predict the flow behavior in the sandwich region. In addition, although the same inlet arrangement and activation times were used for all simulations, the predicted filling time using the 2.5-D model was 30% shorter than the filling time using the 3-D non-isothermal model. On the other hand, the predicted flow pattern for the 3-D isothermal model was very similar to that for 3-D non-isothermal model and the difference between the filling times was relatively small. However, since the model does not keep track of the temperature variations and curing during filling, the simulation of cure after the filling would not provide accurate results. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Mechanical Engineering.

Without a ligand, Germ Cell Nuclear Factor (GCNF) binds to and represses genes. Targets include Oct4 (involved in the pluripotency of embryonic and germ cells), CRIPTO-1 (found in undifferentiated stem cells), and reproductive genes in both the male and female including GDF-9 and BMP-15. Previous studies using qRtPCR suggest that GCNF is involved in cell growth proliferation. It was theorized that higher concentrations of GCNF would be found in growing tissues, for instance in embryonic and neonatal tissues, and lower concentrations in fully developed tissues. Tests were conducted by isolating total RNA from hamster tissue samples, reverse transcribing it, and then followed up by RtPCR. Standard curves from isolated ds DNA GCNF PCR product were created to allow the formation of a database monitoring changes in hamster tissue GCNF mRNA levels using ds DNA PCR product. Linearity of the GCNF qRtPCR was reproducible over a broad range of DNA levels. However, it was found that the sample tissues contained extremely low amounts of GCNF mRNA that could not be measured accurately or reproduced easily even by qRtPCR. GCNF 351 primers were found to work better than the GCNFRT primers due to possible alternate splicing occurring in the mRNA not allowing GCNRT primers to bind. The overall conclusion does not support the hypothesis that GNCF mRNA expression is greater in growing versus non-growing adult tissues. / Thesis (M.S.)--Wichita State University, College of Liberal Arts and Sciences, Dept. of Biological Sciences

It is well known that the mechanical performance and fracture behavior of a thermosetting composite is inherently determined by the properties and characteristics of its constituents. However, the performance and behavior is also drastically influenced by the viscoelastic properties and status of the material during the cure process. This brings about a need to possess knowledge of the cure history of any composite product. Such knowledge is attainable by monitoring the material response to temperature and pressure cycles throughout the cure process. Nevertheless, changes to the cure and, equivalently, the manufacturing process influences the final cost of a composite product, thus, making it crucial to select an optimum cure profile conducive to both the desired thermo-mechanical properties as well as minimum cost. The present work investigates the cure kinetics and process behavior of a commercial carbon-fiber thermoplastic-toughened epoxy resin prepreg, IM7/977-2 UD. Experimental data and theoretical models are mostly demonstrated in the form of cure time and temperature functions, f(t,T). A comprehensive cure map is constructed based on this data in order to provide all the necessary information for design of an optimum cure profile. Material properties are measured over a broad range of isothermal cure profiles using advanced analytical techniques such as shear rheometry and Differential Scanning Calorimetry (DSC). Shear rheometry is utilized to quantify some important viscoelastic properties, such as complex viscosity (η*), shear storage modulus (G′), and shear loss modulus (G″), as well as to identify important cure transitions like gelation and vitrification. Thermal properties are obtained using DSC. These include heat flow (dH/dt), glass transition temperature (Tg), and degree of conversion (α). Before performing DSC experiments it is necessary to know a material’s decomposition temperature, and this is obtained through the use of Thermogravimetric Analysis (TGA). Since the material studied in this work is a thermoplastic-toughened epoxy prepreg, a variety of discrepancies in comparison to the kinetics of neat epoxies are observed. These inconsistencies invariably show up as variations in the values of Tg, ultimate heat of reaction (HU), and rate of reaction (dα/dt). For the 977-2 material, it is concluded that the addition of the thermoplastic agent to the epoxy significantly affects the progress of chemical reactions in addition to imparting a step transition in the progress of Tg at elevated isothermal cure temperatures (Tcure ≥ 180 °C). Furthermore, it is concluded that the existence of fibers among the polymer monomers alter the flow-ability of resin molecules throughout the cure process, resulting in early vitrification and lower HU over the entire range of Tcure. The variations observed in the values of HU at various Tcure may result in either under- or overestimation of α regardless of the relationship utilized to calculate it. In addition, a unique one-to-one relationship is established between Tg and α. Regarding the uncertainties present in the calculation of α, it is concluded that Tg is a better estimate of the state of the material at every desired stage of cure. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Mechanical Engineering.

With the rapid development of wireless technology and the wide availability of low cost wireless devices, the domain of mobile computer networks has expanded in the recent past. Mobile ad-hoc networks promise to be the feature of wireless networking technology, which opens up new frontiers of research and continuous development. One such frontier is VANET – Vehicular ad-hoc network. VANET is a type of mobile ad-hoc network that is formed between and among the nearby vehicles. It enables them to communicate among themselves and with the fixed unit or access point called the roadside unit. The nearby vehicles exchange safety messages among themselves and with the roadside units. The safety messages are broadcasted, which ensures that all the mobile nodes receive the safety message being sent out. This creates several issues such as broadcast storms, collisions and contention among the neighboring nodes or vehicles, which is referred as the broadcast problem. The main objective of this thesis is to propose an efficient scheme, that will greatly reduce or possibly eliminate the broadcast problem in VANET`s and to put forth a safety application called as Remote Chase Ender (RCE). This would aid the police officers to end vehicle chases. To address the issue of broadcast problem in VANET`s, we propose a broadcast scheme known as i-broadcast and evaluate its performance. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Electrical Engineering and Computer Science

The study of three-dimensional open cavity flow with and without cover plates at the edges of the cavity at freestream Mach number of 0.85 was performed. Such open cavities find their application in landing gear wells, bomb bay of an airplane and sunroof or window of an automobile. The aerodynamic noise and the flow field together in the above mentioned cavities lead to self-sustaining flow oscillations. These self-sustaining flow oscillations results in the structural failure in the surrounding of the cavity due to resonance phenomenon in the aircrafts and lead to loud and unbearable noise both in aircrafts and automobiles. Understanding this aeroacoustic phenomenon helps us in reducing the noise, increase the component stability and passenger comfort. Therefore, this problem has become an important topic of research for several decades in aerospace and automobile fields. In this thesis an effort was made to investigate the fully developed turbulent flow over an open cavity and to evaluate the effect of cover plates numerically using the detached eddy simulation (DES) formulation. For this purpose, computational fluid dynamics approach was utilized on the M219 cavity at Mach 0.85 using DES with the Spalart-Allmaras (S-A) turbulence model. Two cavity cases were modeled. The test case 1 is a three-dimensional open cavity without cover plates and the test case 2 is a three-dimensional open cavity with cover plates at the edges of the cavity. Furthermore, three variants of DES were considered for the test case 2 cavity namely Spalart- Allmaras, k-ω-SST and realizable k-ε model, whereas for the test case 1 cavity only the DES S-A model was employed. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Aerospace Engineering

This master’s-level thesis work had focused on the boundary treatments for computational fluid dynamics problems, especially those with unbounded domains. Therefore, it involved a rigorous literature survey on boundary treatment techniques. The primary interest in this effort was on one of the emerging concepts of boundary treatment for numerical schemes, namely the perfectly matched layer (PML) absorbing technique. PML equations were constructed in both Cartesian and generalized coordinate systems to widen its application in uniform and non-uniform grid structures. Throughout the study, Euler equations for perturbation equations linearized about a uniform mean flow were utilized, and flow that is parallel to an axis and flow that is at an arbitrary direction were considered. The PML formulation was validated and PML cases were simulated for a combination of absorbing coefficients and layer thickness in order to find the optimum performance of the technique. The results were analyzed, and the issues were documented. Furthermore, PML equations were constructed by splitting the velocity into three components. Discussion is provided on the need for a proper spacetime transformation, based on the literature study. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Aerospace Engineering.

Birdstrikes on aircraft pose a major threat to human life and there is a need to devolop structures which have high resistance towards these structures. According to the Federal Aviation Regulation (FAR 25.571) on Damage-tolerance and fatigue evaluation of structure (Amdt.25-96), an airplane must be capable of successfully completing the flight during which likely structural damage might occur as a result of impact with 4-lb bird at cruise velocity at sea level or 0.85 cruise velocity at 8000 feet. The aim of the research is to develop a methodology which can be utilized to certify an aircraft for birdstrike using computational techniques since the physical testing of birdstrike is expensive, time consuming, cumbersome and for sanitary purpose. The simulations are carried out in the LS Dyna, non-linear finite element analysis code, in which the bird is modeled using the Smooth Particle Hydrodynamics (SPH) technique. Initially to validate the bird model in the LS Dyna, the birdstrike is carried out on rigid and deformable plates. The results including displacement, Von-Mises stresses, forces, impulse, squash time and rise time are obtained from the simulation. Then the non-dimensional plots of force, impulse and rise time are plotted and compared with results from experimental test data. The detailed CAD geometry of the leading edge is modeled in CATIA V5. Meshing, connections and material properties are then defined in the Altair Hypermesh 9.0. The validated SPH bird model is impacted at the leading edge. The results obtained from the simulation are compared with the data from the experiments, and the process is validated. The parametric studies are carried out by designing the leading edge for different values of nose radius and by vii assigning appropriate thickness values for leading edge components. Then the SPH bird model is impacted at varying impact velocites and results are compared with test data. It is proposed that the results obtained from simulation can be utilized in the initial design stages as well as for certification of an aircraft for birdstrike requirements as per federal regulations. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Mechanical Engineering.