Virginia Space Grant Consortium
Student Research Conference - April 16, 2007
Hosted by The College of William and Mary, Williamsburg, Virginia
Aerospace Graduate Research Fellows Research Papers and Presentations
Aerospace Systems Concepts and Analysis
Flow and Thermal Performance of a Leading Edge Airfoil-Endwall Fillet for a Gas Turbine Nozzle Guide Vane ( Presentation)
Stephen Lynch, Virginia Tech
Gas turbine engines have a high power-to-weight ratio, making them ideal for generation of aircraft thrust, and can have excellent electrical power generation efficiencies when used in a combined cycle power plant. The efficiency and power output of a turbine engine can be increased by raising the combustion temperature. However, a complex swirling flow present near the junction of the nozzle guide vane airfoil and its casing (endwall) tends to decrease aerodynamic efficiency and increase metal temperatures. Past research indicates a large fillet at the endwall-airfoil junction can reduce aerodynamic losses and endwall heat transfer. Also, leakage flow through inherent gaps between individually manufactured turbine components can interfere with the endwall vortical flow.
This research discusses the combined effect of a leading edge endwall-airfoil fillet and leakage flow from a two-dimensional slot simulating the combustor-turbine gap. High-resolution measurements of endwall friction coefficients, heat transfer coefficients, and adiabatic cooling effectiveness of gap leakage flow were obtained in a large-scale cascade at engine Reynolds number conditions. Results indicate that the addition of a fillet to the endwall-airfoil junction slightly increases wall friction at the throat of the vane passage; however, the overturning of the near-wall flow associated with the complex vortical structure is reduced. Cool leakage flow from a combustor-turbine interface gap upstream of the endwall causes increased heat transfer coefficients, but also cooler wall temperatures. A fillet in the presence of upstream leakage flow displaces the coolant, but also reduces the heat transfer coefficient augmentation caused by the leakage flow.
Development of a Simple Design Rule for Subsonic Axial-flow Compressor Blades
Jonathan McGlumphy, Virginia Tech
Tandem-airfoils have demonstrated the ability to provide more work per blade row than a conventional airfoil while not suffering from higher losses. Tandem blades are employed as stators in production axial-flow compressors, but not as rotors. By making several simplifying assumptions, a design rule has been developed that allows the designer to choose the best geometric parameters for each blade (i.e. camber, metal angles) prior to performing time-consuming CFD analysis. The goal is to ensure that both blades are producing minimum aerodynamic loss. The design rule has been compared to both CFD and experimental data, and has demonstrated the ability to capture tandem blade performance trends.
Cognitive Radio Engine for IEEE 802.22 WRAN (Presentation)
Lizdabel Morales-Tirado, Virginia Tech
Cognitive radio (CR) is a promising tool in the field of wireless communication research. Although algorithms and techniques envisioned in CR research can reside in any of the layers of the protocol stack, current investigations in CR have been focused on the physical layer functionality. Research in radio resource management (RRM) of a distributed, decentralized CR network has begun only recently. IEEE 802.22 WRAN system claims to be the first wireless communication standard adopting cognitive radio functionalities. However, current specifications seem to be more like “a frequency agile radio” system. In order to be a cognitive radio system, the system needs to have the capabilities of recognizing its system operating scenarios on top of its awareness of surrounding environment, choosing intelligently efficient strategies and algorithms under, supporting coexistence of other CR systems, and learning from its experiences and predefined rules.
During the last year, we investigated and developed a cognitive engine, which is the first application of cognitive radio concept to more efficient radio resource management (RRM) in a centralized network. We have designed the architecture of a cognitive engine (CE) which is generic and flexible so that it can be applied to general cognitive radio systems. Along with a general framework that will allow for future design, development, and testing of more enhanced cognitive engine, we have implemented a cognitive engine which provides means for 802.22 base stations to have scenario-classification and optimization capability by tailoring the developed CE architecture to fit 802.22 base station operation scenarios.
Attitude Control Investigation Using Spacecraft Hardware-In-The-Loop Simulator (Presentation)
Scott A. Kowalchuk, Virginia Tech
The Distributed Spacecraft Attitude Control System Simulator (DSACSS) testbed at Virginia Polytechnic
Institute and State University facilitates investigation of various control strategies for single and multiple spacecraft. DSACSS is comprised of two independent hardware-in-the-loop simulators and one software spacecraft simulator. The two hardware-in-the-loop spacecraft simulators have similar subsystems as flight-ready spacecraft, mounted on independent spherical air-bearing platforms. The nonlinear attitude control investigation uses one hardware-in-the-loop simulator with three reaction wheels as the actuator for attitude control. A Lyapunov based angular rate controller and Modified Rodrigues Parmater (MRP) attitude controller are evaluated using the hardware simulator. The angular rate controller successfully drives the angular rates of the simulator to zero. The MRP attitude controller successfully drives the angular rates and MRP attitude vector of the simulator to zero. The angular rate and MRP controllers demonstrate the capability of investigating nonlinear attitude control strategies in real-time with hardware similar to flight-ready spacecraft.
Code Analysis and The CS-XML
Kara Olson, Old Dominion University
The automated analysis of model specifications is an area that historically receives little attention in the simulation research community but which can offer significant benefits in time and cost savings to model development efforts as well as additional insights into the models themselves. The Condition Specification (CS) 1 represents one of the model specification forms that is amenable to useful and informative analysis. In addition, current Web-based technologies such as XML offer exciting new approaches to extend our knowledge in this and other areas of simulation research. This paper discusses the motivations for and the creation of an XML Schema for the Condition Specification; a translator for the CS grammar into an XML-based Condition Specification (CS-XML); and a translator for the CS-XML into a fully-executable C/C++ program. It also proposes immediate future work of using CodeSurfer 2, a software static analysis tool, for model analysis. In conclusion, it is argued that the CS-XML can provide an essential foundation for Web Services that support the analysis of discrete-event simulation models.
System Identification Methods Based on the Proper Orthogonal Decomposition
Tim Allison, Virginia Tech
The proper orthogonal decomposition is a powerful engineering analysis tool that has historically been used to reduce the dimension of large finite element models. The usefulness of this approach is limited because it requires the construction of a full-order finite element model. This research outlines a method for using experimental data to construct a system model that can be used to simulate a system’s response to various initial conditions without requiring a finite element model. This modeling approach is particularly powerful because it may even be applied to a nonlinear system to obtain the optimal linear model for the system. Sample models were created using this method for both linear and nonlinear beams and the responses to various initial conditions are compared with the response generated by full-order finite element models.
Investigation of Shock Wave Interaction Using Laser-Induced Iodine Fluorescence
Eric Cecil, University of Virginia
Shock wave interference occurs when the bow shock of a supersonic vehicle impinges on the bow shock formed on an appendage such as a wing, fin, or cowling. Such interactions result in high localized heat transfer rates and peak surface pressures on the appendage near the impingement, with the details depending the configuration of the shock waves. In the present work, detailed measurements of flow behavior have been taken in a rarefied ‘slip-flow’ regime hypersonic flow (Mach 12) over a sharp edged flat plate with a circular cylindrical appendage. The flat plate is presented parallel to the wind tunnel freestream to generate a weak shock which impinges on the nearly-normal cylinder bow shock wave. The tests were conducted in a ‘cold’ free jet wind tunnel facility, using nitrogen gas expanded from ambient temperature. Detailed velocity measurements were made from the Doppler shift of the iodine B-X absorption spectra produced by laser-induced fluorescence (LIF) of a trace amount of iodine seeded in the gas. A planar grid of local velocity with a resolution on the order of one mean-free-path in the flow free stream was obtained using a wide sheetbeam from a frequency-tunable multi-watt argon laser to excite LIF and a low-noise CCD camera to record multiple images. In addition to the velocity measurements, these spectra provide information on the local translational and rotational temperature in the flow.
Kinematics of Dwarf Galaxies and Their Remnants in the Milky Way Halo
Jeffrey L. Carlin, University of Virginia
Dwarf spheroidal (dSph) galaxies represent the low-mass end of the dark matter halo distribution, making them key discriminators between models of cosmological structure formation in the universe. Recent e_orts have uncovered a few low-luminosity dSphs, as well as numerous stellar tidal streams (remnants of accreted, tidally disrupted dwarf galaxies) in the Milky Way halo, helping to explain the perceived de_cit of observed dSphs relative to model predictions. To explore the reasons some halos survive intact, while others are tidally disrupted, orbital information is needed. To date, most kinematic studies of the dwarfs themselves, as well as known tidal features, have been limited to radial velocity programs, providing only one dimension of the full space motions. In the work described here, we measure tangential velocities (\proper motions") of individual stars in these systems, which can be combined with the radial component to derive orbits. The dynamical information of the dSphs and known tidal streams can then be used to look for orbital associations, as well as to constrain the shape of the Milky Way dark matter halo. We report here work in progress on the absolute proper motion of the Carina dSph, as well as a proper motion survey of, among others, the Sagittarius and Monoceros tidal streams.
The Origin of the Magellanic Stream
David L. Nidever, University of Virginia
According to current theories of galaxy formation, large galaxies like our own Milky Way grow by absorbing smaller galaxies. This phenomenon of “galaxy accretion” continues today, and our Galaxy is known to be cannibalizing two of its satellite galaxies, as is evident by the Magellanic Stream; a stream of hydrogen gas stretching 100 degrees across the sky and originating in the Magellanic Clouds. We have discovered that one of the Magellanic Stream filaments and the Leading Arm can be traced back to the 30 Doradus star forming region of the Large Magellanic Cloud. This is contrary to previous suggestions that these features originate in the Small Magellanic Cloud and the Magellanic Bridge. Furthermore, there is evidence that gas outflow from supergiant shells in the 30 Doradus region are creating the Magellanic Stream and Leading Arm. Gas blowout provides a new and previously unexplored potential mechanism for creating the Magellanic Stream.
Spitzer Infrared Spectrograph Observations of Class I Sources In Taurus: Composition, Temperature, and Thermal History of Circumstellar Ices
Gail Zasowski, University of Virginia
We present observations of Class I protostars in Taurus obtained with the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope. The mid-infrared spectra (5 to 37 microns) are excellent diagnostics of the properties of the material found in the circumstellar disks and envelopes. We find that the 16 protostellar sources in our sample show features due to the expected ices in absorption, most notably carbon dioxide ice at 15.2um, but also water ice as well as blends with a variety of organic ices. An inventory of the ice features observed is presented. Using publicly available mid-infrared laboratory spectra, we utilize the optical depths in the IRS features to derive the range of ice compositions and temperatures seen around these stars. Furthermore, we demonstrate full spectral fitting of some of the ice features and suggest candidates for the as-yet-unidentified components. We are able to constrain the composition, temperature, and thermalization history of ices around the varied protostars. By adding a finer level of detail to current full-scale models of Class I protostellar systems, these results will contribute to the growing pool of evidence on how solar systems, including those like our own, are formed.
The Birth of Super Star Clusters
Amy E. Reines, University of Virginia
Star formation is arguably the most important process in the universe, with implications from galaxy evolution to planet formation and the origin of life. Super star clusters (SSCs) are the most massive and dense of all stellar clusters and are consistent with being young analogues of the ancient globular clusters we see today around massive galaxies like our own Milky Way. I present a study of the irregular starburst galaxy NGC 4449 in which I find ~37 newborn stellar clusters. Using a combination of data at radio and optical wavelengths from the Very Large Array and the Hubble Space Telescope, I determine the physical properties such as ages, masses and extinctions of the young clusters. Studying the formation and evolution of local super star clusters as they emerge from their dusty birth cocoons will shed light on an extreme mode of star formation that was prevalent in the early universe and continues to have a major impact on the evolution of galaxies.
Simulating Europa’s Tenuous Atmosphere
Timothy A. Cassidy, University of Virginia
During my 2006-2007 VSGC fellowship, I modeled the O2 atmosphere of Jupiter’s moon Europa. By assuming that atmospheric O2 can react with species contained in portions of Europa’s surface, my coauthors and I have been able to reproduce the O2 density variations seen by a previously-unexplained HST observation. This work included further refinements to a regolith model that I published previous to the fellowship. Ongoing work is focused on modeling other atmospheric constituents to analyze recent Europa observations by the New Horizons spacecraft and in preparation for a possible future Europa mission, along with continued work on the O2 model and its implications for the evolution of Europa’s surface. The talk will include a brief introduction to tenuous atmospheres throughout the solar system.
Nonlinear Acoustic Concealed Weapons Detector
Kevin Rudd, The College of William and Mary
A Nonlinear Acoustic Concealed Weapons Detector uses sound waves to inspect a person for concealed weapons and explosives at large standoff distances. A parametric array exploits the complex propagation of nonlinear acoustics to create a very narrow sound beam that is directed onto a person. The sound beam interacts with a person’s clothing, body, and any concealed objects. The backscattered sound waves are recorded and analyzed to determine if the person is concealing any weapons. In this talk, we will present a 3D acoustic simulation method along with examples of nonlinear sound beam scattering from humans and weapons. We will also show promising but preliminary experimental results.
Electromagnetic Scattering from Perturbed Surfaces
Katharine Ott, University of Virginia
This work is concerned with the study of scattering of electromagnetic waves from a (local) perturbation of a fixed surface, the boundary of a given obstacle in three dimensions. The goal is to produce an algorithm for solving boundary value problems in the exterior of the perturbed domain solely based on the knowledge of the Green function for the original surface. This is done by solving a boundary integral equation which only involves the perturbed portion of the boundary.
Structural Health Monitoring and a Resonance Study
Pablo A. Tarazaga, Virginia Tech
Impedance-based structural health monitoring uses collocated piezoelectric transducers to locally excite a structure at high frequencies. The response of the structure is measured by the same transducer. Changes in this response indicate damage. Frequency range selection for monitoring with impedance-based structural health monitoring has, in the past, been done by trial and error methods, or been selected after analysis by engineers familiar with the method. For future applications it is desirable to be able to automatically select frequency ranges, perhaps even before installing the system. In this study, analysis of the measurement change through a damage metric is examined and related to characteristics of the measurement. Specifically, an outlier detection framework was used to statistically evaluate the sensing ability of the transducers at various frequency ranges. The variation in undamaged measurements is compared to the amount of change in the measurement upon various levels of damage. Testing was performed with both solid piezoceramic transducers and macro-fiber composite (MFC) piezoelectric devices of different sizes bonded to aluminum and fiber reinforced composite structures. The results indicate that frequency ranges containing a resonance of the actuator are more suited for structural health monitoring.
Sensitivity of MicroMAPS Carbon Monoxide Retrieval Algorithm to Surface Temperature
Patrick E. Hopkins, University of Virginia
The scientific goal of the Micro Measurement of Air Pollution from Satellites (mMAPS) project is to measure carbon monoxide (CO) mixing ratios in the middle troposphere from an airborne platform. Recent work has focused on the development of a data processing algorithm to determine precise scientific total column amounts of carbon monoxide from mMAPS flights. The data processing algorithm uses flight signals to infer surface temperature then uses the inferred surface temperature in calculating CO mixing ratios. In this paper, the sensitivity of this data processing algorithm to surface temperature is studied. MicroMAPS data is used from Proteus flights over the mid-Atlantic and South Pacific. Synthetic and measured surface temperature profiles are used to calculate CO mixing ratios with the mMAPS data retrieval algorithm. These results are compared to CO mixing ratios calculated from the inferred surface temperature from the mMAPS algorithm and CO mixing ratios measured from other instruments.
Remote Pulsed-laser Raman Spectroscopy System for Mineral Analysis on Planetary Surfaces
Christopher S. Garcia, Old Dominion University
Recent and future explorations of Mars and lunar surfaces through rovers and landers have spawned great interest in developing an instrument that can perform in- situ analysis of minerals on planetary surfaces. Several research groups have anticipated that for such analysis, Raman spectroscopy is the best suited because it can unambiguously provide the composition and structure of a material. A remote pulsed Raman spectroscopy system for analyzing minerals was developed at NASA Langley Research Center. This system utilizes a 532 nm pulsed laser as an excitation wavelength, and a telescope with a 4-inch aperture for collecting backscattered radiation. A spectrograph equipped with a super notch filter for attenuating the strong Rayleigh scattering is used to analyze the scattered signal. To form the Raman spectrum, the spectrograph utilizes a holographic transmission grating that simultaneously disperses two spectral tracks on the detector for increased spectral range. The spectrum is recorded on an intensified charge-coupled device (ICCD) camera system, which provides high gain to allow detection of inherently weak Stokes lines. The system was used to analyze various rocks and mineral samples. It was also used to detect ice, water, and hydrous minerals.
Structures and Materials
A Dynamic Equilibrium Analysis of a Leading Edge Thermal Heat Spreader Using a Cubic Equation Of State
Scott D. Kasen, University of Virginia
A new thermodynamic model for calculating the steady state behavior of a leading edge thermal heat spreader, which operates upon the principles of evaporation, convection, and condensation of a working fluid, is presented. The intense, localized impinging heat flux is balanced with the thermal capacitance of the container walls and working fluid. The thermophysical properties of the vapor-liquid equilibrium are modeled using the Patel-Teja cubic equation of state. Adiabatic operating temperatures and pressures of the leading edge are presented, and are found to agree well with thermodynamic tabular data. Correlation to
experimental testing is planned.
Evaluating the Failure Pressure of Bilayer Lipid Membranes Using an Automated Pressurization Test Apparatus
David Hopkinson, Virginia Tech
A new methodology has been developed to measure the mechanical integrity of a bilayer lipid membrane (BLM) formed over porous substrates. A custom test fixture was fabricated in which a stepper motor linear actuator drives a piston in order to apply pressure to a BLM in very fine increments. The pressure, monitored with a pressure transducer, is observed to increase until the BLM reaches its failure pressure, and then drop. This experiment was performed on 1-Stearoyl-2-Oleoyl-sn-Glycero-3-Phosphocholine (SOPC) lipid bilayers formed over porous polycarbonate substrates with various pore sizes ranging from 0.05 - 10 m in diameter. A trend of increasing failure pressure with decreasing pore size was observed. The same set of experiments was repeated for BLMs that were formed from a mixture of SOPC and cholesterol (CHOL) at a cholesterol concentration of 50 mol%. The presence of cholesterol was found to increase the failure pressure of the BLMs by 1.5 times on average. A model of the characteristic pressure curve from this experiment was developed based on an initially closed fluid system in which pressure increases as it is loaded by a moving piston, and which upon reaching a critical failure pressure allows pressure to decrease as fluid escapes through a porous medium. Since the BLM is formed over many pores, this model assumes that the failure pressure for each micro-BLM follows a normal distribution over all pores. The model is able to accurately predict the major trends in the pressurization curves by curve-fitting a few statistical parameters.
Uniqueness Results For Nonlinear Structural Acoustic Interactions
Inger M. Daniels, University of Virginia
We consider a coupled system of nonlinear partial differential equations arising in structural acoustic interactions. A linear wave equation, defined on three dimensional Ω, is coupled with a nonlinear plate equation defined on a subset Γ0 of the two dimensional smooth boundary ðΩ. We demonstrate existence and uniqueness of a weak, finite energy solution pertaining to the system. In this effort, the research has established a special trace estimate for the solution to the wave component. Also, the research has established and employed a generalized version of a well known method for establishing uniqueness.
Inflation of Strain-Stiffening Rubber-Like Thin Spherical Shells
Landon M. Kanner, University of Virginia
This paper is concerned with the investigation of the predictions of several widely used strain-stiffening phenomenological constitutive models for the classical limit point instability that is well-known to occur in the inflation of internally pressurized rubber-like spherical thin shells (balloons). The shells are composed of incompressible isotropic nonlinearly elastic materials. For a variety of specific strain-energy densities that give rise to strain-stiffening in the stress-stretch response, the inflation pressure versus stretch relations are given explicitly and the monotonicity, or lack thereof, of the inflation curves is examined. While such results are known for constitutive models that exhibit a gradual stiffening (e.g. exponential and power-law models), our primary focus is on materials that undergo severe strain-stiffening in the stress-stretch response. In particular, we consider two recently developed constitutive models that reflect limiting chain extensibility at the molecular level. Results for classical models are also presented for comparison. It is shown that for materials with sufficiently low extensibility no limit point instability occurs and so stable inflation is then predicted for such materials. The results have a variety of aerospace applications, e.g. to deployable space structures and NASA Weather Balloons.
Feasibility Study: Housing NASA’s MicroMAPS Instrument in a Self-Sustained Pod
Charles Walston, Virginia Tech
The MicroMAPS instrument is currently housed on the Proteus research aircraft and measures the amount of carbon monoxide in the atmosphere. One of the bigger problems with the instrument is its extreme sensitivity to changes in temperature. The goal of this research is to determine if it is possible to house the instrument in a thermally insulated pod that could be attached to the external hardpoints of various aircraft. This would result in an increase in the amount of data that can be collected, less time needed for data reduction, and less dependence on the availability of a single aircraft. Simulations were run using the thermal software package within ANSYS for a number of configurations. The initial results indicate that the pod would fall short of being completely autonomous, as it would need extra power, and the desired thermal regulation would be difficult.
Guided Wave Interpretation for Integrated Vehicle Health Management Sensors
Jill Bingham, The College of William and Mary
Integrated Vehicle Health Management (IVHM) combines the use of onboard sensors with artificial intelligence algorithms to automatically identify and monitor structural health issues. A fully integrated approach to IVHM systems demands an understanding of the sensor output relative to the structure, along with sophisticated prognostic systems that automatically draw conclusions about structural integrity issues. Ultrasonic guided wave methods allow us to examine the interaction of multiphysics signals within key structural components. Since they propagate relatively long distances within plate- and shell-like structures, guided waves allow inspection of greater areas with fewer sensors. In order to interpret the signals that we receive from transducers we look not only at the wave mechanics but also the signal processing using the dynamic wavelet fingerprinting technique to deliver the information in a form that does not require extensive knowledge of the guided wave physics.
Impedance-based Structural Health Monitoring of Thermal Protection Systems
Benjamin L. Grisso, Virginia Tech
Thermal protection systems (TPS) on spacecraft are crucial for the survival of the vehicle during Earth reentry. The complex nature of thermal protection systems and extreme reentry temperatures and do not allow for easy access to monitor the condition of the external surface of the spacecraft, and the impedance method has not been previously used to interrogate components used for thermal protection. Impedance-based health monitoring techniques utilize small piezoceramic patches attached to a structure as self-sensing actuators to both excite the structure with high-frequency excitations and monitor any changes in structural mechanical impedance. In this study, structures are fabricated to represent typical thermal protections systems. The replicas are designed to simulate actual protection systems in use. Observations are made into the verification of the impedance method in effectively monitoring complex thermal protection systems from non-optimal sensor placement locations. The thermal protections systems are damaged in a way to represent typical damage mechanisms. The sensitivity of the impedance method to various types of damage in representative structures will also be discussed. Different operational conditions, including high temperatures, are also included in the experimentation.
Ionic Inhibition of Environmental Fatigue Crack Growth In 7075-T6
Jenifer S. Warner, University of Virginia
The objective of this study is to quantify and understand the effectiveness of a hexavalent chrome replacement ion to inhibit environmentally assisted fatigue crack propagation (EFCP) in high strength aluminum alloys. Because of dynamic-cyclic stress (or strain) loading, fatigue degradation occurs at stress levels considerably lower than the tensile or yield strength; degradation is exacerbated when paired with a corrosive environment. Because CrO4-2 is carcinogenic and the hexavalent ionic state is not produced by oxidation of a metallic film in service, necessary for a “smart-coating” damage mitigation strategy, an effective replacement must be identified. Addition of molybdate (MoO42-) to bulk-low chloride solution effectively inhibits EFCP in peak aged 7075, an Al-Zn-Mg-Cu alloy; comparable to that of CrO42-. The effectiveness of inhibition depends strongly on loading variables: ΔK (stress intensity maximum – stress intensity minimum), R (stress intensity ratio), and loading frequency as explained qualitatively by mechanical instability of a crack tip passive film that hinders production and uptake of embrittling hydrogen. For low R loading only, the critical loading frequency below which film stability and inhibition occur increases with increasing inhibitor concentration. Molybdate could be a beneficial replacement for chromate and a candidate for inhibitor release from a coating.
Central Patter Generator Control of a Tensegrity Morphing Structure for Biomimetic Applications
Thomas Bliss, University of Virginia
The manta ray, Manta birostris, is an amazing creature, propelling itself through the water with the elegant and complex flapping of its wings. This animal is of interest for morphing structures applications, achieving outstanding efficiency and speed even with the enormous span of over five meters. This project aims at integrating biomimetic control systems with morphing structures to harness what years of evolution have created. Synthetic central pattern generators (CPG), the fundamental neural control mechanisms for rhythmic motion in animals, are applied to actuation control of morphing tensegrity structures. Current results illustrate successful integration of biomimetic control and structures to achieve efficient underwater propulsion.
Nuclear Magnetic Resonance Chemical Shielding Calculations of Piezoelectric Materials
Daniel Pechkis, The College of William and Mary
The local atomic structure of high performance piezoelectric materials is currently being investigated computationally. These materials are expected to play an important role in the next generation of sensors and actuators, used for example, in aircraft for active vibration and noise control. Many sensors and actuators are composed of piezoelectric materials, since they can transform mechanical to electrical energy (and vice versa). The goal of this study is to understand how the local atomic structure is related to piezoelectric properties. For example, B-site alloys with the perovskite structure ABO3 such as Pb(Zr,Ti)O3 and Pb(Mg,Nb)O3 have extremely different piezoelectric characteristics. Nuclear magnetic resonance (NMR) has been shown to be a sensitive experimental probe of the local structure, but it is difficult to interpret the measurements without theoretical modeling. This study uses first-principle quantum mechanical calculations to determine the NMR chemical shielding tensor in order to replicate the NMR spectrum. Recent progress in performing these calculations will be discussed. The methodology was first tested on simple systems, MgO and CaO, which are well understood. Preliminary results for PbTiO3 will be presented.
Active Materials: Spacecraft to Houseplants
Stephen A. Sarles, Virginia Tech
An active approach for initiating rigidization in carbon-fiber reinforced polymer (CFRP) composites unites electrical resistivity to mechanical stiffening. In efforts to develop an active method for composite rigidization of ultra-lightweight and gossamer space structures, temperature-controlled resistive heating is used to create on-command rigidizable materials. As required by the on-orbit conditions in space, flexible, rigidizable structures demand stable and space-survivable materials that incorporate techniques for providing shape control and structural stiffening. Current methods for achieving mechanical hardening include mostly passive techniques: UV curing, sub-Tg curing, solar heating, hydro-gel evaporation. The benefits of a passive system (simplicity and minimal energy demand) are offset by their inherent lack of control, which can lead to long curing times and structural weak spots due to uneven curing. In efforts to reduce the curing time of the composite from a structurally vulnerable state to a fully rigidized shape and to increase control of the curing process, we present an active approach. Specifically, PID feedback control during internal resistive (Joule) heating establishes an electrically-controlled, thermally-activated material. This research examines how selective temperature control is applied to the resistive heating of novel CFRP materials. Precise temperature tracking (less than 1˚C error at steady state) was achieved for controlled sample heating tests. The rigidization of these materials was quantified and compared for different curing profiles by measuring the increase in bending stiffness as well as verifying resin cure completion with DSC. Small samples of carbon-fiber tow coated with toughened epoxy Unyte® powder resin (Hydrosize Technologies) were successfully rigidized (15-20 times stiffer than the flexible, uncured material) and fully-cured through resistive heating that occurred in only 24 minutes and required less than 0.1 W-hr/cm of electrical energy. Experimental studies on how the prescribed curing profiles (including curing temperature and time) affect consolidation and curing were performed and methods for reducing the curing time and energy were investigated. Active rigidization via internal resistive heating was demonstrated on a small, “inflatable” structure.
Can Organic-Walled Microfossils Survive High-Temperature Metamorphic Heating? Characterization of Experimentally-Heated Acritarchs Using Raman Spectroscopy, Scanning Electron Microscopy, And Taphonomic Analysis
James D.Schiffbauer, Virginia Tech
Metamorphic shearing and heating are generally perceived as destructive processes in fossil preservation and thus highly metamorphosed rocks have not been a target of paleontological exploration. However, the potential for microfossil preservation in high-grade metamorphic rocks has not been extensively tested. From Late Archean-Early Paleoproterozoic (~2.5 billion years old – or Ga) high metamorphic grade carbonaceous quartzites collected in North China, we have extracted circular graphite discs characterized by features related to graphitization as well as distinct biological morphologies (i.e. circular to elliptical shapes, marginal concentric folds, surficial wrinkles, and complex nanostructures). These discs are interpreted as graphitized, compressed organic-walled vesicles (acritarchs). To experimentally examine whether acritarchs graphitize and retain biological morphology during metamorphic heating, Mesoproterozoic (~1.5 Ga) Ruyang Group rock samples containing dense populations of acritachs (i.e. Dictyosphaera delicata and Shiuyousphaeridium macroreticulatum) have been heated to 500°C (± 2.5°C) in both oxic and anoxic conditions, under 1 atm isotropic pressure, for varying lengths of time ranging from 1 day to 250 days. These samples were subsequently macerated, and extracted acritarchs were examined via standard optical microscopy with both transmitted and reflected light sources, Raman spectroscopy, and scanning electron microscopy (SEM).
Thus far, the analyses have yielded the following conclusions: 1. The presence of oxygen has noticeably damaging effects on the acritarchs within the heating system, while morphologies of heated, anoxic-preparation acritarchs are retained; 2. Raman analyses illustrate a less ordered carbonaceous composition of heated acritarchs from both oxic- and anoxic-preparation methods as compared to the composition of unheated acritarchs; 3. Taphonomic scoring analysis shows increasing opacity of the acritarchs prepared in anoxic conditions and decreasing opacity of those prepared in oxic conditions; and 4. SEM analysis of oxic-preparation versus anoxic-preparation acritarch microstructures clearly illustrates surficial disarticulation of acritarchs from the oxic system but intact acritarchs from the anoxic system. The effects of pressure and directional shearing on fossil preservation have not been investigated in our experiments.
Irradiation Promoted Dissolution of Olivine
Elizabeth Cantando, University of Virginia
Recent laboratory simulations of ion irradiation effects on planetary minerals show changes in the surface composition of surfaces that are different depending on whether the analysis is done in-situ (without removing the sample from vacuum) or ex-situ using an electron microscope. We found that olivine samples that have been irradiated by keV ions show preferential loss of magnesium when exposed to water. Irradiations were done with 4 keV argon ions to fluences between 1015 and 1018 ions/cm2. Soak times in high purity water ranged from minutes to days, and exhibit the same degree of Mg depletion, independent of soak time. The concentration of magnesium on the surface of irradiated natural olivine decreases by 40% upon contact with water, as measured with x-ray photoelectron spectroscopy. This finding is important for laboratory simulations of regolith processes and for establishing procedures for the handling of irradiated samples, including those from sample return missions.
Double Electric Layer in the Stationary Shock Wave Structures of a Supersonic Flow
D. Janette Drake, Old Dominion University
Study of the interaction between a weakly ionized gas and a shock wave is important for detailed understanding of the conditions of planetary atmospheric entry. This interaction can manifest itself in the form of a localized increase of electron temperature, plasma induced shock dispersion and acceleration, optical emission enhancement, or double electric layers. In our work, a microwave generator was combined with an evacuated quartz tube and a de Laval nozzle to sustain a supersonic discharge downstream of the microwave cavity. Excited state populations of the argon (4p-4s) spectral line were measured employing absolute emission spectroscopy. We compared measured intensity in the subsonic and the supersonic regions of the flow and observed dispersion effects in the form of a double-peak distribution. Interpretation of results will be given at conference.
Development of an Acoustic Measurement Capability for Automotive Testing in Open-Jet Wind Tunnels
Brianne Williams, Old Dominion University
Automobile aeroacoustics are still in their beginning stages of understanding and control of the noise sources using mainly exploratory experimental methods and idealized models. The difficulty lies in the mechanisms that generate noise. Sound sources are generated from unsteady aerodynamics which arises from turbulent boundary layers and from regions of separated flow over the vehicle. These regions are subjected to unsteady pressures which are interpreted by the driver as undesirable noise. In order to reduce the noise around an automobile the individual sources are best identified by performing full-scale wind tunnel testing. This can be achieved by deploying a microphone phased array in a suitable configured wind tunnel test section. A microphone phased array permits discrimination of low-level sources in the presence of diffuse background noise by means of strong spatial variations in array sensitivity. The aim of this study is to demonstrate the technology for microphone phased arrays for source localization in the NASA Langley Research Center 14 by 22 wind tunnel in order to permit suppression of undesirable noises by design changes and improve the acoustic measurement capability for automobile testing.
Robust Design of a Low-Boom Supersonic Aircraft
Daniel Le, University of Virginia
The deployment of supersonic aircraft over land has been limited by the intensity of the sonic boom generated during flight. Shock propagation has been studied extensively by Whitman, Walken, and many others. The audible sonic boom is a result of the shock and expansion waves generated from various parts of the aircraft, i.e. the nose and wing leading edge. The waves coalesce such that a distinct pressure signature is generated. The sudden increase in pressure results in the sonic boom. Investigations
have found that sonic boom reduction can be achieved through specific aircraft design features such as swept wings, sharp leading edge nose, etc. However, aircraft design must not only account for sonic boom generation but must also provide good aerodynamic performance. The focus of this investigation is to increase the design capability for supersonic aircraft. Thus, this research has several objectives. The first objective will be to use ModelCenter to provide a multidisciplinary analysis of supersonic concepts. Second, importance will be given to the development of the design methodology. Finally, optimization and probabilistic analysis techniques will be applied to assess aerodynamic concepts.
Passenger Effects on Electromagnetic Propagation Prediction Inside Airport Cabins
Mennatoallah Youssef, University of Virginia
The passenger effect on power propagation was examined in a Canada Region Jet 200. Using Wireless Insite as the modeling program multiple frequencies were studied for potential use in aircraft cabins. Cabin models were created and assigned material properties to ensure accuracy in modeling. The results were graphed and grided. It was concluded that passenger have an adverse effect on power propagation. As the frequency increases, the signal decays rapidly.