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Articles 1 - 17 of 17
Full-Text Articles in Engineering
Electrical Properties Of Srbi₂Ta₂O₉ Ferroelectric Thin Films At Low Temperature, Pingxiong Yang, David L. Carroll, John Ballato, Robert W. Schwartz
Electrical Properties Of Srbi₂Ta₂O₉ Ferroelectric Thin Films At Low Temperature, Pingxiong Yang, David L. Carroll, John Ballato, Robert W. Schwartz
Mechanical and Aerospace Engineering Faculty Research & Creative Works
The temperature dependence of electrical properties for SrBi2Ta2O9 thin film capacitors with platinum electrodes (Pt/SBT/Pt) on silicon wafers was studied from 10 to 300 K. with a decrease in temperature from 300 to 200 K, the remanent polarization of the thin films shows about an 11% reduction from its 300 K value; however, it is reduced by about 87% reduction from its 200 K value when the temperature drops from 200 to 100 K. with a decrease to 200 K, the polarization fatigue was significant, and the capacitor shows an approximate 29% reduction in polarization from its initial value following …
Photoreflectance Spectroscopy Of Strained (In)Gaasn/Gaas Multiple Quantum Wells, J. B. Heroux, Xiaodong Yang, W. I. Wang
Photoreflectance Spectroscopy Of Strained (In)Gaasn/Gaas Multiple Quantum Wells, J. B. Heroux, Xiaodong Yang, W. I. Wang
Mechanical and Aerospace Engineering Faculty Research & Creative Works
The effect of a variation of the indium and nitrogen concentrations in Inᵪ Ga1-x As1-y Ny /GaAs multiquantum wells grown by molecular beam epitaxy is studied systematically by room temperature photoreflectance spectroscopy. The band gap redshift caused by a nitrogen fraction of 1.5% decreases by as much as 30% as the indium fraction increases from 0% to 20%. A moderate increase of electron effective mass (Δmₑ ~ 0.03m₀) is found in all samples containing nitrogen (y ≳ 1%). In compressively strained quantum wells, the energy separation between the first confined heavy and light hole energy levels decreases …
Composite Structures Using Asphalt Based Roofing Scrap Materials: Eiera -- Final Report, V. J. Flanigan, K. Chandrashekhara, Susan L. Murray
Composite Structures Using Asphalt Based Roofing Scrap Materials: Eiera -- Final Report, V. J. Flanigan, K. Chandrashekhara, Susan L. Murray
Mechanical and Aerospace Engineering Faculty Research & Creative Works
The uses of recycled materials in composites provide the potential for large cost savings and a solution to the ever-growing disposal problem. Shingles contain petroleum based binders and fillers, which used as a valuable resource in composite production. Composites offer inherent advantages over traditional materials in regard to corrosion resistance, design flexibility and extended service life. Use of scrap-roofing shingles as a core material in glass fiber reinforced composite materials offer potential low cost composite products such as sound barrier system, railroad ties and other building materials including blocks. In the present work, processes have been developed for shredding scrap …
Investigation Of Part Accuracy And Surface Roughness In Rapid Freeze Prototyping Based Investment Casting, Qingbin Liu, Ming-Chuan Leu, Stephen M. Schmitt
Investigation Of Part Accuracy And Surface Roughness In Rapid Freeze Prototyping Based Investment Casting, Qingbin Liu, Ming-Chuan Leu, Stephen M. Schmitt
Mechanical and Aerospace Engineering Faculty Research & Creative Works
The study as described in this paper is aimed at investigating the dimensional accuracy and surface finish of metal parts made by investment casting with ice patterns generated by rapid freeze prototyping. The process of investment casting with ice patterns is described and contrast with conventional investment casting with wax patterns is made. The selection of binder material for ceramic slurries and the need for an interface agent to separate the ice pattern from the ceramic slurry in the mold making process are discussed. The accuracy and surface finish of ice patterns and of the metal castings are presented and …
Object-Oriented Modeling And Fault Detection Of A Powder Feeder For A Laser Metal Deposition System, Robert G. Landers, Michael Gene Hilgers, Frank W. Liou, Bruce M. Mcmillin
Object-Oriented Modeling And Fault Detection Of A Powder Feeder For A Laser Metal Deposition System, Robert G. Landers, Michael Gene Hilgers, Frank W. Liou, Bruce M. Mcmillin
Mechanical and Aerospace Engineering Faculty Research & Creative Works
One of the most critical components of a laser metal deposition system is the powder feeder unit. Techniques are required to efficiently design and analyze these systems and to ensure fault tolerance during the operation. In this paper, a model of the powder feeder unit, based on object-oriented abstractions of it components, is developed. This model is modular in that specific components can be efficiently updated or replaced with components that perform a similar function. In addition, the model can be used for simulation allowing for efficient design and analysis. Assurance of the correctness of the powder feeder system is …
Laser Aided Part Repair -- A Review, Jinglei Wang, Sashikanth Prakash, Yashodhan Joshi, Frank W. Liou
Laser Aided Part Repair -- A Review, Jinglei Wang, Sashikanth Prakash, Yashodhan Joshi, Frank W. Liou
Mechanical and Aerospace Engineering Faculty Research & Creative Works
Laser aided part-repair is an emerging trend that has great potential for future industrial applications. Part-repair technologies are currently used in repairing military and civilian equipment. The focus of this paper is to review the current repair processes, which use the laser-aided metal deposition technology. Many metal parts, which are worn by continual use, can be restored to working condition by the deposition of metal with a laser and machining. This not only extends the life of the part, but also, saves on cost. A comparison between various processes, their parameters, efficiency, cost, and etc. are also presented. The process …
Object-Oriented Modeling And Fauly Detection Of A Powder Feeder For A Laser Metal Deposition System, Robert G. Landers, Michael Gene Hilgers, Frank W. Liou, Bruce M. Mcmillin
Object-Oriented Modeling And Fauly Detection Of A Powder Feeder For A Laser Metal Deposition System, Robert G. Landers, Michael Gene Hilgers, Frank W. Liou, Bruce M. Mcmillin
Mechanical and Aerospace Engineering Faculty Research & Creative Works
One of the most critical components of a laser metal deposition system is the powder feeder unit. Techniques are required to efficiently design and analyze these systems and to ensure fault tolerance during the operation. In this paper, a model of the powder feeder unit, based on object- oriented abstractions of it components, is developed. This model is modular in that specific components can be efficiently updated or replaced with components that perform a similar function. In addition, the model can be used for simulation allowing for efficient design and analysis. Assurance of the correctness of the powder feeder system …
A Study On Effects Of Process Parameters In Rapid Freeze Prototyping, Frances D. Bryant, Guanghua Sui, Ming-Chuan Leu
A Study On Effects Of Process Parameters In Rapid Freeze Prototyping, Frances D. Bryant, Guanghua Sui, Ming-Chuan Leu
Mechanical and Aerospace Engineering Faculty Research & Creative Works
Rapid Freeze Prototyping (RFP) is a relatively new solid freeform fabrication process, which builds a three-dimensional part according to a CAD model by depositing and freezing water droplets layer by layer. A study on the effects of RFP process parameters including the nozzle scanning speed, droplet size, and droplet frequency in building ice parts with a single-nozzle work head is made. Presented in this paper are the results of this study which indicate that these process parameters determine the ice layer thickness and ice line width, which in turn determine the surface roughness and the waiting time required after depositing …
System Integration And Real-Time Control Architecture Of A Laser Aided Manufacturing Process, Mallikharjuna R. Boddu, Robert G. Landers, Srinivas Musti, Sanjeev Agarwal, Jianzhong Ruan, Frank W. Liou
System Integration And Real-Time Control Architecture Of A Laser Aided Manufacturing Process, Mallikharjuna R. Boddu, Robert G. Landers, Srinivas Musti, Sanjeev Agarwal, Jianzhong Ruan, Frank W. Liou
Mechanical and Aerospace Engineering Faculty Research & Creative Works
This paper discusses a hybrid deposition–removal manufacturing system being developed at the University of Missouri--Rolla. The system consists of a laser system, five-axis CNC machining center, and powder feeder system. A description of the control software, real-time control architecture, and integration of various subsystems to build the hybrid system is given. The interaction of the real-time controller with various sensors and subsystems to monitor and regulate the process is presented. The communication between integrated process planning for the system and real–time control is also discussed in this paper.
Optical Limiting In Srbi₂Ta₂O₉ And Pbzrxti₁₋ₓo₃ Thin Films, Pingxiong Yang, Jianfeng Xu, Robert W. Schwartz, David L. Carroll, John Ballato
Optical Limiting In Srbi₂Ta₂O₉ And Pbzrxti₁₋ₓo₃ Thin Films, Pingxiong Yang, Jianfeng Xu, Robert W. Schwartz, David L. Carroll, John Ballato
Mechanical and Aerospace Engineering Faculty Research & Creative Works
Optical limiting effects in SrBi2Ta2O9 (SBT) and PbZrxTi1-xO3 (PZT) ferroelectric thin films have been observed with nanosecond laser pulses at 1.064 µm. Limiting thresholds were found to be 5.84 J/cm2 for SBT and between 4.53 and 5.93 J/cm2 for PZT, depending on composition, whereas saturation thresholds for the films were about 2.92 J/cm2 and between 2.27 J/cm2 to 2.97 J/cm2, respectively. Damage thresholds around 10.0 J/cm2 and between 10.37 J/cm2 to 10.54 J/cm2, respectively for SBT and PZT, were also determined. A possible mechanism for the observed limiting, nonlinear optical scattering from the ferroelectric domains, is discussed. These results elucidate …
Energy Conservation Using The Closed Water Loop Heat Pump, Harry J. Sauer, Guruprasad Rao
Energy Conservation Using The Closed Water Loop Heat Pump, Harry J. Sauer, Guruprasad Rao
Mechanical and Aerospace Engineering Faculty Research & Creative Works
The closed water loop heat pump (CWLHP) system has been shown to be an energy conserving building heating and cooling system. Such systems are most applicable where simultaneous heating and cooling needs occur. In these systems, internally generated space heat is used to meet heating needs before external heat is provided from a heating plant. The water loop is the transport system moving heat from where it is not wanted to where it is required. Addition of water storage gives an option to store thermal energy for later use. In the common arrangement for the closed water loop heat pump …
Analytical Derivation Of A Coupled-Circuit Model Of A Claw-Pole Alternator With Concentrated Stator Windings, Hua Bai, Steven Pekarek, Jerry L. Tichenor, Walter Eversman, Duane J. Buening, Gregory R. Holbrook, Michael L. Hull, Ronald J. Krefta, Steven J. Shields
Analytical Derivation Of A Coupled-Circuit Model Of A Claw-Pole Alternator With Concentrated Stator Windings, Hua Bai, Steven Pekarek, Jerry L. Tichenor, Walter Eversman, Duane J. Buening, Gregory R. Holbrook, Michael L. Hull, Ronald J. Krefta, Steven J. Shields
Mechanical and Aerospace Engineering Faculty Research & Creative Works
A lumped-parameter coupled-circuit model of a claw-pole alternator is derived. To derive the model, analytical techniques are used to define a three-dimensional (3-D) Fourier-series representation of the airgap flux density. Included in the series expansion are the harmonics introduced by rotor saliency, concentrated stator windings, and stator slots. From the airgap flux density waveform, relatively simple closed-form expressions for the stator and rotor self- and mutual-inductances are obtained. The coupled-circuit model is implemented in the simulation of an alternator/rectifier system using a commercial state-model-based circuit analysis program. Comparisons with experimental results demonstrate the accuracy of the model in predicting both …
A New Method For Suboptimal Control Of A Class Of Nonlinear Systems, Ming Xin, S. N. Balakrishnan
A New Method For Suboptimal Control Of A Class Of Nonlinear Systems, Ming Xin, S. N. Balakrishnan
Mechanical and Aerospace Engineering Faculty Research & Creative Works
In this paper, a new nonlinear control synthesis technique (θ - D approximation) is presented. This approach achieves suboptimal solutions to nonlinear optimal control problems in the sense that it solves the Hamilton-Jacobi-Bellman (HJB) equation approximately by adding perturbations to the cost function. By manipulating the perturbation terms both semi-globally asymptotic stability and suboptimality properties can be obtained. The convergence and stability proofs are given. This method overcomes the large control for large initial states problem that occurs in some other Taylor expansion based methods. It does not need time-consuming online computations like the state dependent Riccati equation (SDRE) technique. …
A New Filtering Technique For A Class Of Nonlinear Systems, Ming Xin, S. N. Balakrishnan
A New Filtering Technique For A Class Of Nonlinear Systems, Ming Xin, S. N. Balakrishnan
Mechanical and Aerospace Engineering Faculty Research & Creative Works
In this paper, a new nonlinear filtering technique (θ-D filter) is presented. This filter is derived by constructing the dual of a new nonlinear regulator control technique, θ-D approximation which involves approximate solution to the Hamilton-Jacobi-Bellman equation. The structure of this filter is similar to the state dependent riccati equation filter (SDREF). However, this method does not need time-consuming online computation of the algebraic Riccati equation at each sample time compared with the SDREF. By manipulating the perturbation terms both the asymptotic stability and optimality properties can be obtained. A simple pendulum problem is investigated to demonstrate the effectiveness of …
State-Constrained Agile Missile Control With Adaptive-Critic-Based Neural Networks, Dongchen Han, S. N. Balakrishnan
State-Constrained Agile Missile Control With Adaptive-Critic-Based Neural Networks, Dongchen Han, S. N. Balakrishnan
Mechanical and Aerospace Engineering Faculty Research & Creative Works
In this study, we develop an adaptive-critic-based controller to steer an agile missile that has a constraint on the minimum flight Mach number from various initial Mach numbers to a given final Mach number in minimum time while completely reversing its flightpath angle. This class of bounded state space, free final time problems is very difficult to solve due to discontinuities in costates at the constraint boundaries. We use a two-neural-network structure called "adaptive critic" in this study to carry out the optimization process. This structure obtains an optimal controller through solving optimal control-related equations resulting from a Hamiltonian formulation. …
Proper Orthogonal Decomposition Based Feedback Optimal Control Synthesis Of Distributed Parameter Systems Using Neural Networks, Radhakant Padhi, S. N. Balakrishnan
Proper Orthogonal Decomposition Based Feedback Optimal Control Synthesis Of Distributed Parameter Systems Using Neural Networks, Radhakant Padhi, S. N. Balakrishnan
Mechanical and Aerospace Engineering Faculty Research & Creative Works
A new method for optimal control design of distributed parameter systems is presented in this paper. The concept of proper orthogonal decomposition is used for the model reduction of distributed parameter systems to form a reduced order lumped parameter problem. The optimal control problem is then solved in the time domain, in a state feedback sense, following the philosophy of ''adaptive critic'' neural networks. The control solution is then mapped back to the spatial domain using the same basis functions. Numerical simulation results are presented for a linear and nonlinear one-dimensional heat equation problem in an infinite time regulator framework.
Experimental Implementation Of Adaptive-Critic Based Infinite Time Optimal Neurocontrol For A Heat Diffusion System, Prashant Prabhat, S. N. Balakrishnan, Dwight C. Look
Experimental Implementation Of Adaptive-Critic Based Infinite Time Optimal Neurocontrol For A Heat Diffusion System, Prashant Prabhat, S. N. Balakrishnan, Dwight C. Look
Mechanical and Aerospace Engineering Faculty Research & Creative Works
Recently the synthesis methodology for the infinite time optimal neuro-controllers for PDE systems in the framework of adaptive-critic design has been developed. In this paper, first we model an experimental setup representing one dimensional heat diffusion problems. Then we synthesize and implement an adaptive-critic based neuro-controller for online temperature profile control of the experimental setup.