Browsing by Author "Dr. Mohammed A. Zikry, Committee Member"

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Design and Manufacture of a Second Generation Switch-operated Window Wall
(2006-09-07) Butterfield, Matthew Paul; Dr. Larry M. Silverberg, Committee Chair; Dr. Mohammed A. Zikry, Committee Member; Dr. M. K. Ramasubramanian, Committee Member
A new system of horizontal window blinds that operates by means of electrostatic induction, called the powerblind, was developed at North Carolina State University. The blinds can be opened and closed with a simple switch. An evaluation of the first-generation system was conducted to determine the features that needed improvement before a second-generation model could be constructed. The problems inherent to the previous powerblind model were resolved after redesigning several parts. Eight new, fully operational powerblind units were assembled and installed in a boardroom of the Talley Student Center at North Carolina State University in July 2006. They replaced the defective first-generation units previously located in the boardroom. A set of instructions for all the assembly and manufacturing processes was also created to facilitate the construction of additional second-generation windows. With the improvements made to the design and to the manufacturing process, it was concluded that commercial production would be possible at this stage of the project. The powerblind windows remain cost effective, when compared to the combination of standard window blinds and insulated glass. The ability to quickly and easily control the amount of light entering a room makes these windows desirable for many applications.
Finite Element Formulation for Self-Writing of Polymer Optical Fiber Sensors
(2008-05-08) Anderson, Aliesha Dawn; Dr. Greg D. Buckner, Committee Member; Dr. Mohammed A. Zikry, Committee Member; Dr. Kara J. Peters, Committee Chair
This thesis presents a multi-physics finite element model of the self-writing process of photopolymerization in photosensitive gels in order to better predict the self-generation of polymer optical fiber sensors. The finite element model incorporates the electromagnetic, chemical and mechanical physics of this photonic reaction. The output of the model is thus the dynamics of photopolymerization and self-focusing including densification and the induced index of refraction change. An experimentally verifiable benchmark trial of a UV light source focused into UV curable resin was modeled using COMSOL Multiphysics, to develop a basis for calibration of different photosensitive gels. This model was then extrapolated to demonstrate the effects of photopolymerization when a single fiber is focused into an epoxy resin as well as the effects of curing an epoxy-filled gap between two aligned fibers. Results were obtained for linear and saturation models of the change in the index of refraction. These models are applied to single and two fiber benchmark examples. The saturating effects are consistent with previous experimental research showing a 2% change in refractive index with similar lightwave confinement within the cured portion of the resin. The confinement achieved with this model has also verified the ability to predict self-focusing and tapering effects that are also seen in previous experimental studies. The effect of densification within the sample and how this is affected by the geometric constraints on the system are demonstrated as well. This thesis provides a versatile finite element model for predicting the dynamics of the photopolymerization process for a variety of resins and experimental geometries and has presented an effective tool for use in determining the response of a polymer sensing element cured using the photopolymerization process.
Low Power Valve Actuation Using Trans-Permanent Magnetics
(2003-11-21) Duval, Luis Denit; Dr. Richard F. Keltie, Committee Member; Dr. Mohammed A. Zikry, Committee Member; Dr. Lawrence M. Silverberg, Committee Chair; Dr. Gregory D. Buckner, Committee Member
The subject of magnetic actuators is very broad, and encompasses a wide range of technologies, magnetic circuit topologies, and performance characteristics for an ever-increasing spectrum of applications. As a consequence of recent advances in soft and hard magnetic materials and developments in power electronics, microprocessors and digital control strategies, and the continuing demand for higher performance motion control systems, there appears to be more research and development activity in magnetic actuators for applications spanning all market sectors than at any time. Thus many actuator types and topologies are emerging with widely varying operational characteristics, in terms of displacement (rotary or linear), speed of response, position accuracy and duty cycle. In this dissertation, a rational approach for switching the states of permanent magnets through an on-board magnetization process is presented. The resulting dynamic systems are referred to as trans-permanent magnetic systems (T-PM). The first part of this research focuses on the governing equations needed for the analysis of trans-permanent magnetic systems. Their feasibility is demonstrated experimentally. In doing so, a method that has the potential of leading to new ultra-low power designs for electromechanical devices is introduced. In the second part of this research, the aforementioned developments in T-PM are applied to the problem of low power valves. Whereas alternate approaches to low power valve control may utilize latching to maintain valve position during inactive periods, an approach that eliminates the need for latching mechanisms is presented. Instead, the principles of T-PM are employed to switch the states of permanent magnets; the used of permanent magnets instead of electromagnets eliminates power consumption during inactive periods, thereby reducing power consumption to ultra-low levels. The magnets in a T-PM actuator are configured in a stack. The relationships between the strength and number of magnets in the stack and the stroke and resolution of the actuator are developed. This dissertation reports on the design and testing of a prototype valve actuator that uses a stack pf T-PM with alternating polarity. It is shown that this stack is well suited for discrete state process valves having a small number of states. It is concluded that the trans-permanent valve represents a promising valve actuation technology.
Unified Constitutive Modeling for Proportional and Nonproportional Cyclic Plasticity Responses
(2009-04-23) Krishna, Shree; Dr. Tasnim Hassan, Committee Chair; Dr. Kerry S. Havner, Committee Member; Dr. Shamim M. Rahman, Committee Member; Dr. Murthy N Guddati, Committee Member; Dr. Mohammed A. Zikry, Committee Member
Several features of cyclic plasticity, e.g. cyclic hardening/softening, ratcheting, relaxation, and their dependence on strain range, nonproportionality of loading, time, and temperature determine the stress-strain responses of materials under cyclic loading. Numerous efforts have been made in the past decades to characterize and model these responses. Many of these responses can be simulated reasonably by the existing constitutive models, but the same models would fail in simulating the structural responses, local stress-strain or global deformation. One of the reasons for this deficiency is that the constitutive models are not robust enough to simulate the cyclic plasticity responses when they interact with each other. This deficiency can be understood better or resolved by developing and validating constitutive models against a broad set of experimental responses and two or more of the responses interacting with each other. This dissertation develops a unified constitutive model by studying the cyclic plasticity features in an integrated manner and validating the model by simulating a broad set of proportional and nonproportional cyclic plasticity responses. The study demonstrates the drawbacks of the existing nonlinear kinematic hardening model originally developed by Chaboche and then develop and incorporate novel ideas into the model for improving its cyclic response simulations. The Chaboche model is modified by incorporating strain-range dependent cyclic hardening/softening through the kinematic hardening rule parameters, in addition to the conventional method of using only the isotropic hardening parameters. The nonproportional loading memory parameters of Tanaka and of Benallal and Marquis are incorporated to study the influence of nonproportionality. The model is assessed by simulating hysteresis loop shape, cyclic hardening-softening, cross-effect, cyclic relaxation, subsequent cyclic softening, and finally a series of ratcheting responses under uniaxial and biaxial loading responses. Next, it is demonstrated that the hysteresis loop shape and width can be improved by incorporation of time dependence (visco-effect) and a novel modeling scheme of backstress shift. Overall, this dissertation demonstrates a methodical and systematic development of a constitutive model for simulating a broad set of low-cycle fatigue responses. However, more modification would be needed before claiming that the model would simulate structural responses acceptably.