This paper describes a high-rel transformer design and the design iterations required to meet the severe environments of military grade transformers. It describes a method of reducing the mechanical stress caused when a ferrite pot core is encapsulated in a rigid epoxy. Stresses are due to differences in coefficient of thermal expansion between the two materials. The mechanical design optimization of a small flyback transformer designed to charge an energy storage capacitor up to 6 kV from a low voltage source is described. The basic design uses a 2616 manganese zinc ferrite pot core. The goal was to eliminate the core cracking problem. The purpose for writing and presenting this paper is to document a proven process that evolved out of necessity, and to present to the industry a method which reduces stresses on the core, eliminates cracking of the core and provides the insulation necessary for small high voltage transformers.
Organic polymer materials are used frequently in structures and transportation systems. Polymer materials may provide fuel for a fire or be damaged catastrophically due to an incident heat flux. Modeling the response of such structures and systems in fire environments has important applications in safety and vulnerability analyses. The decomposition chemistry of the organic polymer materials is an important factor in many analyses. To provide input to numerical models for hazard and vulnerability analyses, the thermal decomposition chemistry of organic polymers is being experimentally investigated using TGA-FTIR, GC-FTIR, infrared microprobe (IRMP), and DSC Both TGA-FTIR and DSC experiments are done with unconfined and partially confined samples. Unconfined samples are used to examine initial decomposition reactions. Partially confined samples are used to examine reversible and secondary reactions. This paper discusses phenomena pertinent to using the aforementioned techniques to develop rate expressions for polymer decomposition reactions, and a specific example illustrating development of rate expressions for decomposition of PMMA is given.
Decomposition of PGN (Poly Glycidyl Nitrate) has been investigated using TJump/ FTIR (Fourier Transform Infrared Spectroscopy) and STMBMS (Simultaneous Thermogravimetric Modulated Beam Mass Spectrometry) in an effort to understand the effects of hydroxyl end-modification and isocyanate curing of PGN. T-Jump/FTIR allows real-time determination and quantification of decomposition gas products as samples are heated very fast (20°C/s) to simulate deflagration conditions. Our results identify decomposition gas products including: CH2O, H2O, CO2, CO, N2O, NO, NO2, HCN and HONO. PGN deflagration kinetic rates relative to CO2 formation and preliminary results on the effects of hydroxyl end-capping are presented. Slow heating, STMBS experiments aid in discerning possible mechanistic pathways by temporally separating decomposition gas products as they evolve. These results show that thermal decomposition of PGN is controlled by a three step reaction process: (I) decomposition of the CH2-ONO2 functional moiety, (II) reactions of initial low-molecular-weight species with each other, and (III) reactions of lowmolecular-weight species with the polymer backbone. While this work focuses only on ncured PGN prepolymer, future results will include the effects of isocyanate curing on standard and end-modified PGN.
The development of tools and techniques for security testing and performance testing of Process Control Systems (PCS) is needed since those systems are vulnerable to the same classes of threats as other networked computer systems. In practice, security testing is difficult to perform on operational PCS because it introduces an unacceptable risk of disruption to the critical systems (e.g., power grids) that they control. In addition, the hardware used in PCS is often expensive, making full-scale mockup systems for live experiments impractical. A more flexible approach to these problems can be provided through test beds that provide the proper mix of real, emulated, and virtual elements to model large, complex systems such as critical infrastructures. This paper describes a "Virtual Control System Environment" that addresses these issues.
Removable polymer coatings were evaluated as a means to suppress dehydration of Alodine chromate conversion coatings during thermal aging and thereby retain the corrosion protection afforded by Alodine. Two types of polymer coatings were applied to Alodine-treated panels of aluminum alloys 7075-T73 and 6061-T6 that were subsequently aged for 15 to 50 hours at temperatures between 135 F to 200 F. The corrosion resistance of the thermally aged panels was evaluated, after stripping the polymer coatings, by exposure to a standard salt-fog corrosion test and the extent of pitting of the polymer-coated and untreated panels compared. Removable polymer coatings mitigated the loss of corrosion resistance due to thermal aging experienced by the untreated alloys. An epoxide coating was more effective than a fluorosilicone coating as a dehydration barrier.
TufFoam™ is a TDI-free, water-blown, closed-cell, rigid polyurethane foam (PU) initially formulated as an electronics encapsulant to mitigate the effects of harsh mechanical environments. Because it contains no TDI, the handling hazards and chemical sensitization associated with exposure during processing of common, commercial PU foams are obviated. The mechanical properties of TufFoam™ have been found to be comparable or superior to conventional TDI-based foams. Beyond its original intent, it has since found use in a variety of additional applications, including as a structural material and as a thermal and electrical insulating material. TufFoam™ constituents are commercially available in commodity quantities and batch processing schedules have been developed for its preparation at densities ranging from 0.03 to 0.70 g/cc (2 to 40 pcf). TufFoam™ has a uniform, fine cell structure over the entire range of density explored. Its Tg is somewhat dependant on the cure temperature, but is approximately 127°C when cured at 65°C. The coefficient of thermal expansion (CTE) is 7x10 -5 °C -1. TufFoam™ is electrically insulating with a volume resistivity of 3x10 17 ohm-cm at a density of 0.1 g/cc.
Frictional contact results in surface and subsurface damage that could influence the performance, aging, and reliability of moving mechanical assemblies. Changes in surface roughness, hardness, grain size and texture often occur during the initial run-in period, resulting in the evolution of subsurface layers with characteristic microstructural features that are different from those of the bulk. The objective of this LDRD funded research was to model friction-induced microstructures. In order to accomplish this objective, novel experimental techniques were developed to make friction measurements on single crystal surfaces along specific crystallographic surfaces. Focused ion beam techniques were used to prepare cross-sections of wear scars, and electron backscattered diffraction (EBSD) and TEM to understand the deformation, orientation changes, and recrystallization that are associated with sliding wear. The extent of subsurface deformation and the coefficient of friction were strongly dependent on the crystal orientation. These experimental observations and insights were used to develop and validate phenomenological models. A phenomenological model was developed to elucidate the relationships between deformation, microstructure formation, and friction during wear. The contact mechanics problem was described by well-known mathematical solutions for the stresses during sliding friction. Crystal plasticity theory was used to describe the evolution of dislocation content in the worn material, which in turn provided an estimate of the characteristic microstructural feature size as a function of the imposed strain. An analysis of grain boundary sliding in ultra-fine-grained material provided a mechanism for lubrication, and model predictions of the contribution of grain boundary sliding (relative to plastic deformation) to lubrication were in good qualitative agreement with experimental evidence. A nanomechanics-based approach has been developed for characterizing the mechanical response of wear surfaces. Coatings are often required to mitigate friction and wear. Amongst other factors, plastic deformation of the substrate determines the coating-substrate interface reliability. Finite element modeling has been applied to predict the plastic deformation for the specific case of diamond-like carbon (DLC) coated Ni alloy substrates.
Electroluminescence from self-assembled InAs quantum dots in cascade-like unipolar heterostructures is demonstrated. Initial results show weak luminescence signals in the mid-infrared from such structures, though more recent designs exhibit significantly stronger luminescence with improved designs of the active region of these devices. Further studies of mid-infrared emitting quantum dot structures have shown anisotropically polarized emission at multiple wavelengths. A qualitative explanation of such luminescence is developed and used to understand the growth morphology of buried quantum dots grown on AlAs layers. Finally, a novel design for future mid-infrared quantum dot emitters, intended to increase excited state scattering times and, at the same time, more efficiently extract carriers from the lowest states of our quantum dots, is presented,.
Genetic expression and control pathways can be successfully modeled as electrical circuits. To tackle large multicellular and genome scale simulations, the massively-parallel, electronic circuit simulator, Xyce™ [11], was adapted to address biological problems. Unique to this bio-circuit simulator is the ability to simulate not just one or a set of genetic circuits in a cell, but many cells and their internal circuits interacting through a common environment. Additionally, the circuit simulator Xyce can couple to the optimization and uncertainty analysis framework Dakota [2] allowing one to find viable parameter spaces for normal cell functionality and required parameter ranges for unknown or difficult to measure biological constants. Using such tools, we investigate the Drosophila sp. segmental differentiation network's stability as a function of initial conditions.
The probability of a laser caused ocular injury, to the aircrew of an undetected aircraft entering the exclusion zone about the AURA LIDAR airborne platform with the possible violation of the Laser Hazard Zone boundary, was investigated and quantified for risk analysis and management.
Dargaville, Tim R.; Elliott, Julie M.; Jones, Gary D.; Celina, Mathias C.
Piezoelectric polymers based on polyvinylidene fluoride (PVDF) are of interest as smart materials for novel space-based telescope applications. Dimensional adjustments of adaptive thin polymer films are achieved via controlled charge deposition. Predicting their long-term performance requires a detailed understanding of the piezoelectric property changes that develop during space environmental exposure. The overall materials performance is governed by a combination of chemical and physical degradation processes occurring in low Earth orbit as established by our past laboratory-based materials performance experiments (see report SAND 2005-6846). Molecular changes are primarily induced via radiative damage, and physical damage from temperature and atomic oxygen exposure is evident as depoling, loss of orientation and surface erosion. The current project extension has allowed us to design and fabricate small experimental units to be exposed to low Earth orbit environments as part of the Materials International Space Station Experiments program. The space exposure of these piezoelectric polymers will verify the observed trends and their degradation pathways, and provide feedback on using piezoelectric polymer films in space. This will be the first time that PVDF-based adaptive polymer films will be operated and exposed to combined atomic oxygen, solar UV and temperature variations in an actual space environment. The experiments are designed to be fully autonomous, involving cyclic application of excitation voltages, sensitive film position sensors and remote data logging. This mission will provide critically needed feedback on the long-term performance and degradation of such materials, and ultimately the feasibility of large adaptive and low weight optical systems utilizing these polymers in space.
Four Well-Characterized Open Pool fires were conducted by Fire Science and Technology Department. The focus of the Well-Characterized Open Pool fire series was to provide environmental information for open pool fires on a physics first principal basis. The experiments measured the burning rate of liquid fuel in an open pool and the resultant heat flux to a weapon-sized object and the surrounding environment with well-characterized boundary and initial conditions. Results presented in this report include a general description of test observation (pre- and post-test), wind measurements, fire plume topology, average fuel recession and heat release rates, and incident heat flux to the pool and to the calorimeters. As expected, results of the experiments show a strong correlation between wind conditions, fuel vaporization (mass loss) rate, and incident heat flux to the fuel and ground surface and calorimeters. Numerical fire simulations using both temporally- and spatially-dependant wind boundary conditions were performed using the Vulcan fire code. Comparisons of data to simulation predictions showed similar trends; however, simulation-predicted incident heat fluxes were lower than measured.
This report examines the localization of time harmonic high frequency modal fields in two dimensional cavities along periodic paths between opposing sides of the cavity. The cases where these orbits lead to unstable localized modes are known as scars. This paper examines the enhancements for these unstable orbits when the opposing mirrors are both convex and concave. In the latter case the construction includes the treatment of interior foci.
Establishing a Cartesian coordinate reference system for an existing Compact Antenna Range using the parabolic reflector is presented. A SMX (Spatial Metrix Corporation) M/N 4000 laser-based coordinate measuring system established absolute coordinates for the facility. Electric field characteristics with positional movement correction are evaluated. Feed Horn relocation for alignment with the reflector axis is also described. Reference points are established for follow-on non-laser alignments utilizing a theodolite.
Recent amendments to the Safe Drinking Water Act emphasize efforts toward safeguarding our nation's water supplies against attack and contamination. Specifically, the Public Health Security and Bioterrorism Preparedness and Response Act of 2002 established requirements for each community water system serving more than 3300 people to conduct an assessment of the vulnerability of its system to a terrorist attack or other intentional acts. Integral to evaluating system vulnerability is the threat assessment, which is the process by which the credibility of a threat is quantified. Unfortunately, full probabilistic assessment is generally not feasible, as there is insufficient experience and/or data to quantify the associated probabilities. For this reason, an alternative approach is proposed based on Markov Latent Effects (MLE) modeling, which provides a framework for quantifying imprecise subjective metrics through possibilistic or fuzzy mathematics. Here, an MLE model for water systems is developed and demonstrated to determine threat assessments for different scenarios identified by the assailant, asset, and means. Scenario assailants include terrorists, insiders, and vandals. Assets include a water treatment plant, water storage tank, node, pipeline, well, and a pump station. Means used in attacks include contamination (onsite chemicals, biological and chemical), explosives and vandalism. Results demonstrated highest threats are vandalism events and least likely events are those performed by a terrorist.
Three dimensional finite element analyses were performed to evaluate the structural integrity of the caverns located at the Bayou Choctaw (BC) site which is considered a candidate for expansion. Fifteen active and nine abandoned caverns exist at BC, with a total cavern volume of some 164 MMB. A 3D model allowing control of each cavern individually was constructed because the location and depth of caverns and the date of excavation are irregular. The total cavern volume has practical interest, as this void space affects total creep closure in the BC salt mass. Operations including both cavern workover, where wellhead pressures are temporarily reduced to atmospheric, and cavern enlargement due to leaching during oil drawdowns that use water to displace the oil from the caverns, were modeled to account for as many as the five future oil drawdowns in the six SPR caverns. The impacts on cavern stability, underground creep closure, surface subsidence, infrastructure, and well integrity were quantified.
Monroe, Justin; Tang, Zhong; Gu, Xuehong; Dong, Junhang; Weinkauf, Donald; Nenoff, Tina M.
Hydrogen production from biomass has been paid more attention for years. Processes suggested for production of hydrogen from biomass are often involved in high-temperature pyrolysis[1-2], catalytic steam reforming [3] or enzymatic biosynthesis[4]. These strategies, however, encounter problems of high consumption of energy, low catalyst efficiency and very limited productivity. Group VIII metals such as Pt, Ni and Ru are more likely to be effective catalysts for reforming of oxygenated hydrocarbons (the main component in biomass), and among which, only Pt and Pd show both high activities and high selectivity for production of H 2[5-7]. Although lots of catalysts have been screened for this aqueous-phase reforming, the catalysts with high loadings noble metal such as platinum has to be used even when conducting at low feed concentration of 1 wt%[8]. Therefore, highly active catalytic materials need to be developed in order to render the process practical.