This research attempted to determine the practicality of the integration of electrospun polyaniline nanofiber as the main sensing component into interdigitated gold microelectrodes to develop a biosensor platform for sensitive, selective, and label-free detection the of Cyclooxygenase-2 (COX-2) biomarker from pure and human serum samples. COX-2 is an important enzyme in pain biomarkers, inflammation and cancer cell proliferation, so it is necessary to develop a reliable biosensor that can sensitively and objectively quantify COX-2 enzyme expression for clinical diagnosis. Polyaniline nanofibers were prepared at four different diameters using electrospinning performed at four different flow rates. The performance of the electrospun polyaniline nanofiber based biosensor was evaluated in comparison with a plain control biosensor using electrochemical impedance spectroscopy. Significant improvement was observed in the sensitivity of the electrospun polyaniline nanofiber based biosensor revealing the remarkable capability of electrospun polyaniline nanofiber in robust and rapid detection of the COX-2 biomarker. This improvement was attributed to the large specific surface area of electrospun polyaniline nanofiber as well as its highly porous structure which enhances size-matched confinement, transduction and signal strength, thus increasing the sensitivity of the biosensor significantly. The fabricated nanofiber based biosensor was able to detect the target antigen with concentrations as low as 0.01pg/ml and 10fg/ml in pure and human serum samples, respectively, as well as remarkable selectivity towards Human Serum Albumin suggesting the significant contribution of this nanofiber based platform to the enhanced strength and sensitivity in COX-2 analyte detection. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Mechanical Engineering

Tremendous advances in high performance sensing and signal processing technology enable the development of condition monitoring systems (CMS) for complex engineered systems to detect, diagnose, and predict the system-wide effects of failure events. Although employing CMS in preventing catastrophic system failures and reducing the operation and maintenance (O&M) costs have been acknowledged, the cost and benefit of CMS have not been well studied and further the advantages of CMS have not been fully recognized for the optimal maintenance decision making, mainly due to the lack of valid theoretical modeling addressing the interrelationship between the CMS effectiveness and system downtime due to system failures. In this study, a Poisson Process model will be developed for the modeling of occurrence of the system-wide failure events and study the potential benefits provided by the CMS in preventing these failure events. With the developed Poisson process model, the cost benefit analysis (CBA) will then be implemented by considering the CMS system reliability and costs varying with its failure detection effectiveness presented by the probabilistic detectability measure. Facilitated by CBA of the CMS, break-even points (BEP) between expected lifecycle benefits and the required CMS detectability level can be found to select optimal CMS for different system failure modes. Moreover, with the help of the CBA results, optimal maintenance strategies can be determined to minimize the O&M costs. The presented CBA methodology for the CMS systems will be demonstrated with an aircraft maintenance case study and the efficacy will be validated. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Industrial and Manufacturing Engineering

In intermittently connected sensor networks, the data generated may have different importance and priority. Different types of data will help scientists analyze the physical environment differently. In a challenging environment, wherein sensor nodes are not always connected to the base station with a communication path, and not all data may be preserved in the network. Under such circumstances, due to the severe energy constraint in the sensor nodes and the storage limit, how to preserve data with the maximum priority is a new and challenging problem. In this thesis, we will study how to preserve data to produce the maximum total priority under the constraints of the limited energy level and storage capacity of each sensor node. We have designed an efficient optimal algorithm, and prove it is optimal. The core of the problem is Maximum weighted flow problems, which is in order to maximize the total weight of the flow network, taking into account the different flows having different weights. The maximum weighted flow is a generalization of the classical maximum flow problem, characterized in that each unit of flow has the same weight. To the best of our knowledge, our work first study and solve the maximum weighted flow problems. We also propose a more efficient heuristic algorithm. Through simulation, we show that it performs comparably to the optimal algorithm, and perform better than the classical maximum flow algorithm, which does not consider the data priority. Finally, we design a distributed data preservation algorithm based on the push-relabel algorithm and analyze its time and message complexity, experience has shown that it is superior to push-relabel distributed maximum flow algorithm according to total preserved priorities. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Electrical Engineering and Computer Science

Over the last two decades, extensive work has been conducted to study the dynamic effect of the joint clearances in multibody mechanical systems. In contrast, little work has been devoted to optimize the performance of these systems. In this study, analysis of revolute joint clearance is formulated in terms of a Hertzian-based contact force model. For illustration, the classical slider-crank mechanism with a revolute clearance joint at the piston pin is presented, and a simulation model has been built through the analysis/design code MSC.ADAMS. The clearance is modeled as a pin-in-a-hole surface-to-surface dry contact, with appropriate contact force model between the journal and the bearing surfaces. Different simulations are performed to demonstrate the influence of the joint clearance size and the input crank speed on the dynamic behavior of the system with the clearance joint. An innovative DOE-based method for optimizing the performance of a mechanical system with the revolute joint clearance for different range of design parameters is then proposed. Based on the simulation modeling results from sample points, which are selected by a Latin hypercube sampling method, a polynomial function Kriging meta-model is established instead of the actual simulation model. The reason to build the meta-model is to bypass a compute-intensive simulation computer model for different values of design parameters to a more efficient and cost-effective mathematical model. Finally, numerical results obtained from two application examples, considering the different design parameters, including the joint clearance size, crank speed and contact stiffness, are presented for further analyzing and optimizing the dynamics of the revolute clearance joint in a mechanical system, thus accurately predicting the influence of the design parameters changes for the purpose of minimizing the contact forces, accelerations, and power requirements due to the clearance. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Mechanical Engineering

This research investigates the effect of pressure gradient on wall-pressure fluctuations in turbulent boundary layers using a delayed detached eddy simulation (DDES) turbulence scheme. The results are compared to Goody's and Efimtsov's empirical single-point wall-pressure spectrum models. Three different types of pressure gradient conditions were investigated numerically: zero pressure gradient (Flat Plate as a baseline model), favorable pressure gradient (Convex 10 , 20 , and 40 Plates), and adverse pressure gradient (Concave 10 , 20 , and 40 Plates). The numerical results were subsequently compared with each other. For the zero pressure gradient case, results compared well with empirical solutions. It was observed that, for cases with adverse pressure gradients, the pressure fluctuations were more chaotic than for the favorable pressure gradient models. In contrast, the favorable pressure gradient models induced lower frequency noise relative to adverse pressure gradient models. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Aerospace Engineering

Approximate Dynamic Programming (ADP) offers a systematic method of optimal control design for nonlinear systems. Of the many architectures based on ADP, Adaptive Critic (AC) is the most popular. An AC consists of two neural networks that interactively train each other to arrive at the optimal control solution. Single Network Adaptive Critic (SNAC) is an improvement over the AC. As the name suggests, it consists of only one network but, at the same time, achieves faster convergence to the optimal solution. The advantages of SNAC have been harnessed very well in optimal state regulation applications. However, literature concerning the direct use of SNAC in command following applications seems sparse. This is probably because of the fact that it is practically difficult to anticipate a proper training domain to train the SNAC neural network when the commands are not known a-priori. Nonlinear Dynamic Inversion (NDI) is a sub-optimal, nonlinear control design method that offers a closed form solution. The ease of implementation and the ability to use NDI control readily for regulating and command following applications make it a very popular control design method in a wide area of applications. However, it lacks the formalism and advantages of optimal control design principles. In this dissertation, we present a novel hybrid technique of nonlinear design that retains the advantages of both SNAC and NDI and, at the same time, makes SNAC extendable to command following applications to achieve near-optimal responses and relates NDI to optimal control design principles. We also present in this dissertation an extended architecture that adapts online to system inversion errors, parameter estimation error and reduced control effectiveness. The versatility of the new technique is demonstrated by considering five nonlinear systems of increasing complexity, including the longitudinal aircraft system. / Thesis (Ph.D.)--Wichita State University, College of Engineering, Dept. of Electrical Engineering and Computer Science

Crashworthiness has become an important aspect in vehicle design due to the stringent requirements on occupant safety under survivable accident scenarios. The uses of composite materials have increased due to their tailorability and high specific strength and stiffness. Variety of energy absorption devices have been investigated for their energy absorption characteristics. Literature suggests that corrugated beam geometry promotes stable crushing behavior and has the highest energy absorption capability. But a lack of consensus on the rate sensitivity of these devices exists and is mainly attributed to different material systems, specimen geometries, test apparatus used, etc. This experimental study addresses the progressive crushing of Newport NB321/7781 E-glass and Toray T700G/3900 plain weave fabric prepreg fiber-reinforced corrugated panel. The progressive crushing behavior is studied at quasi-static rates as well as dynamic loading rates up to 100in/s. Load rate effects, stacking sequence effects and laminate gross thickness effects on energy absorption of corrugated beams were investigated. The test data indicates that the specific energy absorption of corrugated beams is rate sensitive. Besides, modes of failure of corrugated beams were observed to be sensitive to test speed. Furthermore, stacking sequences of [0]n are superior in energy absorption compared to [45]n and thickness of the laminates were observed to affect the specific energy absorption. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Aerospace Engineering

Tests of Mode-I delamination in Double Cantilever Beam (DCB) specimens were modeled with the finite element solver, LS-DYNA, to simulate the behavior of composite materials at high speed loading rates (between 2 in/s and 100 in/s). Cohesive elements were used to model the crack growth behavior. The investigation examines the dynamic effects of the loading block or loading hinge on the simulations. Recommendations are made for which material models, boundary conditions, and other modeling techniques to use for best results. A factor for strain energy release rate is also introduced to account for reductions in GIc at high loading rates. The adjustment factor would apply to a test-derived value of GIc and would result in a reduction ranging from 1.6% at 2 in/s to 87% at 100 in/s. The implications of the finding are that testing would need to indicate a power-law increase in the apparent GIc value in order to maintain a constant actual GIc. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Aerospace Engineering.

An experimental investigation was conducted to study the behavior of an edge chamfer on the resulting crushing response of flat laminated composite strips. The effects of variables such as chamfer angle, stacking sequence and material system were addressed. In the present study the material systems used was Newport NB 321/7781 fiberglass/epoxy and Toray T700G-12K-PW/3900 carbon-fiber/epoxy. Chamfer angles of 30°, 45° and 60° were used in the present study to simulate the trigger mechanism. Laminate stacking sequences of [0º]N, [±45º]N (N=4,8 and 12), were studied using Newport NB 321/7781 fiberglass/epoxy and Toray T700G-12K-PW/3900 carbon-fiber/epoxy. In addition Newport NB 321/7781 fiberglass/epoxy specimens were fabricated with a [0Nº/±45ºN]S stacking sequence and tested. Monotonic and cyclic load-unload tests were conducted on an MTS electromechanical machine at a quasi-static stroke rate of 10-3 in/s. Monotonic tests were also conducted at stroke rates of 10-1 in/s, but restricted to the specimens with 45° chamfer specimen. Failure modes observed in [0º]N, [±45º]N, [0Nº/±45ºN]S specimens included delamination induced lamina/ sub-laminate bending mode, laminate bending mode, brittle fracture mode, catastrophic failure mode, and mixed mode failures. Lamina/sub-laminate bending mode and brittle fracture mode were observed to be the most dominant failure modes, with corresponding high energy absorption. The amount of energy absorption through delamination in cyclic load-unload test was investigated using image analysis and geometry calculations. With an increase in chamfer angle, the peak load, in the load-displacement curve, increased for the 12 and 8 ply laminates, while no significant differences were observed in the 4 viii ply laminates. The load eccentricity due to chamfering forced a global bending dominated failure mode in 4 ply laminates, which resulted in the observed apparent insensitivity to chamfer angle. Due to the 0° fiber orientation in [0º]N stacking sequence, a higher load carrying capacity was observed in comparison to [±45º]N, [0Nº/±45ºN]S. However, the energy absorption in [±45º]N was higher owing to the crushing mode of failure rather than the delamination induced splaying/bending mode observed in [0º]N laminates. Results from the load-displacement curve showed that the Newport NB 321/7781 fiberglass/epoxy had a higher load carrying capacity than carbon-fiber/epoxy, and this was attributed to the crushing mode being dominant in the fiberglass/epoxy specimens. Although, both fiberglass and carbon-fiber are brittle by nature, there was a shift in the initial load response from linear to non-linear behavior in the load-displacement curve of the [±45º]N stacking sequence. The sustained crush region of the load-displacement curves for the [0º]N laminates exhibited high serrations typically associated with load oscillations in brittle failure. Cyclic load tests revealed the sequence of failure mechanisms in chamfered laminates. While delamination was observed to be the primary driving mechanism, the estimation of energy dissipated due to the same was observed to be small in comparison to the overall energy absorbed. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Aerospace Engineering.

The crack arrest capabilities and the load bearing characteristic of a stiffened and unstiffened panel subjected to remote tension loading is examined in this work. We make use of cohesive interface elements to predict the behavior of the center crack stiffened and unstiffened panels using a nonlinear traction-separation relationship. This thesis describes an application of traction-separation model on a four stringer stiffened wide panel with and without a disbond, and also an unstiffened panel with a center crack and compare their residual strengths. Aluminum 2024-T3 alloy panels were tested as a part of another study and the measured values were used to compare the numerical results. The predicted crack growth and residual predictions shows fair convergence with experimental values. The strength of the stiffened panel was observed to be much higher (55%) than that of that unstiffened panel. Moreover the presence of the disbond of 1” caused a 9% drop in the residual strength and disbond lesser than 1” does not lead to a drop in strength. The stiffened panel readily supported the transfer of load from the plate to the stiffener, thus aiding in the crack growth arrest. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Aerospace Engineering