An experiment to measure surface pressure data on a series of three stainless steel simulated parachute ribbons was conducted. During the first phase of the test, unsteady pressure measurements were made on the windward and leeward sides of the ribbons to determine the statistical properties of the surface pressures. Particle Image Velocimetry (PIV) measurements were simultaneously made to establish the velocity field in the wake of the ribbons and its correlation with the pressure measurements. In the second phase of the test, steady-state pressure measurements were made to establish the pressure distributions. In the third phase, the stainless steel ribbons were replaced with nylon ribbons and PIV measurements were made in the wake. A detailed error analysis indicates that the accuracy of the pressure measurements was very good. However, an anomaly in the flow field caused the wake behind the stainless steel ribbons to establish itself in a stable manner on one side of the model. This same stability was not present for the nylon ribbon model although an average of the wake velocity data indicated an apparent 2{degree} upwash in the wind tunnel flow field. Since flow angularity upstream of the model was not measured, the use of the data for code validation is not recommended without a second experiment to establish that upstream boundary condition.
In support of two major SNL programs, the Long-term Inflow and Structural Test (LIST) program and the Blade Manufacturing Initiative (BMI), three Micon 65/13M wind turbines have been erected at the USDA Agriculture Research Service (ARS) center in Bushland, Texas. The inflow and structural response of these turbines are being monitored with an array of 60 instruments: 34 to characterize the inflow, 19 to characterize structural response and 7 to characterize the time-varying state of the turbine. The primary characterization of the inflow into the LIST turbine relies upon an array of five sonic anemometers. Primary characterization of the structural response of the turbine uses several sets of strain gauges to measure bending loads on the blades and the tower and two accelerometers to measure the motion of the nacelle. Data are sampled at a rate of 30 Hz using a newly developed data acquisition system. The system features a time-synchronized continuous data stream and telemetered data from the turbine rotor. This paper documents the instruments and infrastructure that have been developed to monitor these turbines and their inflow.
Numerical methods may require derivatives of functions whose values are known only on irregularly spaced calculation points. This document presents and quantifies the performance of Moving Least-Squares (MLS), a method of derivative evaluation on irregularly spaced points that has a number of inherent advantages. The user selects both the spatial dimension of the problem and order of the highest conserved moment. The accuracy of calculations is maintained on highly irregularly spaced points. Not required are creation of additional calculation points or interpolation of the calculation points onto a regular grid. Implementation of the method requires the use of only a relatively small number of calculation points. The method is fast, robust and provides smooth results even as the order of the derivative increases.
Meso-scale manufacturing processes are bridging the gap between silicon-based MEMS processes and conventional miniature machining. These processes can fabricate two and three-dimensional parts having micron size features in traditional materials such as stainless steels, rare earth magnets, ceramics, and glass. Meso-scale processes that are currently available include, focused ion beam sputtering, micro-milling, micro-turning, excimer laser ablation, femtosecond laser ablation, and micro electro discharge machining. These meso-scale processes employ subtractive machining technologies (i.e., material removal), unlike LIGA, which is an additive meso-scale process. Meso-scale processes have different material capabilities and machining performance specifications. Machining performance specifications of interest include minimum feature size, feature tolerance, feature location accuracy, surface finish, and material removal rate. Sandia National Laboratories is developing meso-scale mechanical components and actuators which require meso-scale parts fabricated in a variety of materials. Subtractive meso-scale manufacturing processes expand the functionality of meso-scale components and complement silicon based MEMS and LIGA technologies.
This technical report presents the initial proposal and renewable proposals for an LDRD project whose intended goal was to enable applications to take full advantage of the hardware available on Sandia's current and future massively parallel supercomputers by analyzing various ways of combining distributed-memory and shared-memory programming models. Despite Sandia's enormous success with distributed-memory parallel machines and the message-passing programming model, clusters of shared-memory processors appeared to be the massively parallel architecture of the future at the time this project was proposed. They had hoped to analyze various hybrid programming models for their effectiveness and characterize the types of application to which each model was well-suited. The report presents the initial research proposal and subsequent continuation proposals that highlight the proposed work and summarize the accomplishments.
This paper studies the implementation of polar format, synthetic aperture radar image formation in modern Field Programmable Gate Arrays (FPGA's). The polar format algorithm is described in rough terms and each of the processing steps is mapped to FPGA logic. This FPGA logic is analyzed with respect to throughput and circuit size for compatibility with airborne image formation.
The progress in the fabrication of high voltage GaN and AlGaN rectifiers, GaN/AlGaN HBT and GaN MOSFET is reviewed. Improvements in epitaxial layer quality are studied. The advances in fabrication techniques that led to the improvement of device performance are discussed.
This paper documents work performed to convert scanned range data to CAD solid model representation. The work successfully developed surface fitting algorithms for quadric surfaces (e.g. plane, cone, cylinder, and sphere), and a segmentation algorithm based entirely on surface type, rather than on a differential metric like Gaussian curvature. Extraction of all CAD-required parameters for quadric surface representation was completed. Approximate face boundaries derived from the original point cloud were constructed. Work to extrapolate surfaces, compute exact edges and solid connectivity was begun, but left incomplete due to funding reductions. The surface fitting algorithms are robust in the face of noise and degenerate surface forms.
As part of a project with SEMATECH, detailed chemical reaction mechanisms have been developed that describe the gas-phase and surface chemistry occurring during the fluorocarbon plasma etching of silicon dioxide and related materials. The fluorocarbons examined are C{sub 2}F{sub 6}, CHF{sub 3} and C{sub 4}F{sub 8}, while the materials studied are silicon dioxide, silicon, photoresist, and silica-based low-k dielectrics. These systems were examined at different levels, ranging from in-depth treatment of C{sub 2}F{sub 6} plasma etch of oxide, to a fairly cursory examination of C{sub 4}F{sub 8} etch of the low-k dielectric. Simulations using these reaction mechanisms and AURORA, a zero-dimensional model, compare favorably with etch rates measured in three different experimental reactors, plus extensive diagnostic absolute density measurements of electron and negative ions, relative density measurements of CF, CF{sub 2}, SiF and SiF{sub 2} radicals, ion current densities, and mass spectrometric measurements of relative ion densities.
As computers become faster, have more memory, and use multiple parallel processors, large, complex codes that more accurately simulate physical phenomena have emerged to utilize this capability. Most problems can benefit from this approach and many require it. But not all! There are problems for which simpler methods on more modest computers still work. The trick is to identify those problems, write the codes, and make their implementation sufficiently simple that they can be used conveniently by those who could profit from them. A Simple Plasma Code has been written with this philosophy in mind. It retains just enough physics to allow realistic simulations to be formulated and run quickly, even on a personal computer. This paper describes the physical model, its numerical implementation, and presents a sample simulation.
Window and free surface interfaces perturb the flow in compression wave experiments. The velocity of these interfaces is routinely measured in shock-compression experiments using interferometry (i.e., VISAR). Interface perturbations often must be accounted for before meaningful material property results can be obtained. For shockless experiments when stress is a single valued function of strain, the governing equations of motion are hyperbolic and can be numerically integrated forward or backward in either time or space with assured stability. Using the VISAR results as ''initial conditions'' the flow fields are integrated backward in space to the interior of the specimen where the VISAR interface has not perturbed the flow at earlier times and results can be interpreted as if the interface had not been present. This provides a rather exact correction for free surface perturbations. The method can also be applied to window interfaces by selecting the appropriate initial conditions. Applications include interpreting Z-accelerator ramp wave experiments. The method applies to multiple layers and multiple reverberations. For an elastic-plastic material model the flow is dissipative and the governing equations are parabolic. When the parabolic terms are small, the equations also can be successfully integrated backward in space. This is verified by using a traditional elastic-plastic wave propagation code with a backward-derived stress history as the boundary condition for a forward calculation. Calculated free surface histories match the starting VISAR record verifying that the backward method produced an accurate solution to the governing equations. With our cooperation, workers at Los Alamos have successfully applied the Sandia-developed backward technique for the time-dependent quasielastic material model and are analyzing stress histories at a spall plane using the VISAR free surface velocity measurement from a ''pullback'' experiment.
Superresolution concepts offer the potential of resolution beyond the classical limit. This great promise has not generally been realized. In this study we investigate the potential application of superresolution concepts to synthetic aperture radar. The analytical basis for superresolution theory is discussed. The application of the concept to synthetic aperture radar is investigated as an operator inversion problem. Generally, the operator inversion problem is ill posed. A criterion for judging superresolution processing of an image is presented.
This report is a supplement to ''The Unique Signal Concept for Detonation Safety in Nuclear Weapons,'' SAND91-1269, which provides a prerequisite fundamental background on the unique signal (UQS) concept. The UQS is one of the key constituents of Enhanced Nuclear Detonation Safety (ENDS), as outlined in Section 1 of that report. There have been many documents written over the past quarter of a century describing various aspects of the UQS, but none of these emphasized the mathematical approaches that help explain why the UQS is effective in resisting inadvertent pre-arming, even in abnormal environments and how UQS implementations can be quantitatively assessed. The intent of this report is to describe various pertinent mathematical methodologies (many of which have not been previously reported) without duplicating, any more than necessary, background information available in other reports. Mathematical UQS analysis is needed because of quantitative requirements associated with ENDS, and because limited comparisons of various implementation approaches can be quantified under mathematical modeling assumptions. Some of the mathematics-based results shown in this report are presented to explain: (1) The reasons that the UQS methodology can provide greater protection against accident environments than could combinational techniques (Sections 2.1 through 2.4); (2) The reason that the probability of inadvertently duplicating a UQS comprising n bivalued events cannot be estimated as low as (1/2) inches (Section 2.4); (3) The value of, and the Sandia National Laboratories policy on independent sequential communication of UQS events (Section 3.4); and (4) The care that must be exercised if any signal processing is necessary (Section 4). There are also numerous examples (e.g., in Appendices A and B) of ill-advised deviations from UQS methodology that can seriously degrade safety. These examples help demonstrate that the UQS methodology should not be compromised.
Dual control volume molecular dynamics was employed to study the flux of methane through channels of thin silicalite membranes. The DCANIS force field was analyzed to describe the adsorption isotherms of methane and ethane in silicalite. The alkane parameters and silicalite parameters were determined by fiiting the DCANIS force field to single-component vapor-liquid coexistence curves (VLCC) and adsorption isotherms respectively. The adsorption layers on the surfaces of thin silicalite membranes showed a sifnificant resistance to the flux of methane. The results depicted the insensitivity of permeance to both the average pressure and pressure drop.
For highly cross-linked polymer networks bonded to a solid surface, the effect of interfacial bond density and system size on interfacial fracture is studied using molecular dynamics simulations. Results for tensile and shear mode simulations are given. The correspondence between the stress-strain curve and the sequence of molecular deformations is obtained. The failure strain for a fully bonded surface is equal to the strain necessary to make taut the average of the minimal paths through the network from a bonded site on the bottom solid surface to a bonded site on the top surface. At fractional interfacial bond densities, cavities form above the nonbonded surface, yielding an inhomogeneous strain profile and a smaller failure strain. The failure strain and stress are linearly proportional to the number of bonds at the interface except in the tensile mode when number of bonds is so few that van der Waals interactions dominate. The failure mode is successfully constructed to be interracial by limiting the interfacial bond density to be less than the bulk bond density.
Advanced thin-film processing and packaging technologies are employed in the fabrication of new planar thin-film multijunction thermal converters (MJTCs). The processing, packaging, and design features build on experience gained from prior NIST demonstrations of thin-film converters and are optimized for improved sensitivity, bandwidth, manufacturability, and reliability.
This case study describes a success in technology transfer out of Sandia National Laboratories that resulted in commercialization supporting both the laboratories' national security mission and economic development. This case exemplifies how the process of technology innovation stretches from national legislation to laboratory management to entrepreneurs, and then out into the community where the technology must be developed and commercialized if innovation is to occur. Two things emerged from the research for this case study that have implications for technology transfer and commercialization from other national laboratories and may also be relevant to technology commercialization out of other federal laboratories and universities. The first is the very clear theme that partnerships were critical to the ultimate successful commercialization of the technology--partnerships between public and private research groups as well as between business development groups. The second involves identifiable factors that played a role in moving the process forward to successful commercialization. All of the factors, with two significant exceptions, focused on technology and business development directly related to creating research and business partnerships. The two exceptions, a technology with significant market applications, and entrepreneurs willing and able to take the risks and accomplish the hard work of technology innovation, were initiating requirements for the process.
The Sandia Photovoltaic Program conducted research in crystalline-silicon solar cells between 1986 and 2000 for the U.S. Department of Energy. This period saw rapid improvements in the fundamental understanding of c-Si materials and devices, improvements in c-Si PV manufacturing and control, and a rapid expansion of c-Si PV manufacturing capacity. Crystalline-silicon technology has provided the basis for PV to emerge as a serious option for global energy needs. The c-Si cell research at Sandia examined c-Si materials, devices, processing, and process integration. This report summarizes research conducted in this program over the past 15 years.
Despite the end of the Cold War, the US and Russia continue to maintain their ICBMs and many SLBMs in a highly alerted state--they are technically prepared to launch the missiles within minutes of a command decision to do so. Some analysts argue that, particularly in light of the distressed condition of the Russian military, these high alert conditions are tantamount to standing on the edge of a nuclear cliff from which we should now step back. They have proposed various bilateral ''de-alerting'' measures, to be taken prior to and outside the context of the formal strategic arms reduction treaty (START) process. This paper identifies several criteria for a stable de-alerting regime, but fails to find de-alerting measures that convincingly satisfy the criteria. However, some de-alerting measures have promise as de-activation measures for systems due for elimination under the START II and prospective START III treaties. Moreover, once these systems are deactivated, a considerable part of the perceived need to keep nuclear forces on high alert as a survivability hedge will be reduced. At the same time, the U.S. and Russia could consider building on their earlier cooperative actions to reduce the risk of inadvertent nuclear war by enhancing their communications links and possibly joining in efforts to improve early warning systems.
The authors have developed novel metal-assisted texturing processes that have led to optically favorable surfaces for solar cells. Large area ({approximately} 200 cm{sup 2}) uniform texturing has been achieved. The physical dimensions of the chamber limited texturing of even larger wafers. Surface contamination and residual RIE-induced damage were removed by incorporation of a complete RCA clean process followed by wet-chemical etching treatments. RIE-textured solar cells with optimized profiles providing performance comparable to the random, wet-chemically etched cells have been demonstrated. A majority of the texture profiles exhibit an enhanced IQE response in the near IR region.using scanning electron microscope measurements, they carried out a detailed analysis of the microstructure of random RIE-textured surfaces. The random microstructure represents a superposition of sub-{micro}m grating structures with a wide distribution of periods, depths, and profiles as determined by the SEM measurements. These structures were modeled using GSOLVER{trademark} software for periodic patterns. The enhanced IR response from random, RIE-textured surfaces is attributed to enhanced coupling of light into the transmitted diffraction orders. These obliquely propagating diffraction orders generate electron-hole pairs closer to the surface, thus, reducing bulk recombination losses relative to a non-scattering, planar surface with identical hemispherical reflection. The optimized texture and damage removal processes have been applied to large area (100--132 cm{sup 2}) multi-crystalline wafers. initial results have demonstrated improved performance relative to planar, control wafers. However, the texture and solar cell fabrication processes require further optimization in the RCA clean, DRE treatments, and emitter formation in order to fully realize the benefits of the low-reflection ({approximately}1-2%) textured surfaces.
