NASA Technical Report Research Articles

Synthesis, crystal structure and thermal properties of a new polymorphic modification of diisothiocyanatotetrakis(4-methylpyridine)cobalt(II)

The title compound, [Co(NCS)2(C6H7N)4] or Co(NCS)2(4-methylpyridine)4, was prepared by the reaction of Co(NCS)2 with 4-methylpyridine in water and is isotypic to one of the polymorphs of Ni(NCS)2(4-methylpyridine)4 [Kerr & Williams (1977). Acta Cryst. B33, 3589–3592 and Soldatov et al. (2004). Cryst. Growth Des. 4, 1185–1194]. Comparison of the experimental X-ray powder pattern with that calculated from the single-crystal data proves that a pure phase has been obtained. The asymmetric unit consists of one CoII cation, two crystallographically independent thiocyanate anions and four independent 4-methylpyridine ligands, all located in general positions. The CoII cations are sixfold coordinated to two terminally N-bonded thiocyanate anions and four 4-methylpyridine coligands within slightly distorted octahedra. Between the complexes, a number of weak C—H...N and C—H...S contacts are found. This structure represent a polymorphic modification of Co(NCS)2(4-methylpyridine)4 already reported in the CCD [Harris et al. (2003). NASA Technical Reports, 211890]. In contrast to this form, the crystal structure of the new polymorph shows a denser packing, indicating that it is thermodynamically stable at least at low temperatures. Thermogravimetric and differential thermoanalysis reveal that the title compound starts to decomposes at about 100°C and that the coligands are removed in separate steps without any sign of a polymorphic transition before decomposition.

Strategies, Research Priorities, and Challenges for the Exploration of Space Beyond Low Earth Orbit

Abstract NASA's recent emphasis on human exploration of the Moon and, ultimately, Mars necessitates a transition from a focus of its research in the biological sciences from Low Earth Orbit (LEO) to platforms beyond LEO. Fundamental research questions need to be addressed to enable humans to thrive in deep space. Work beyond LEO necessitates a shift in technology and the utilization of organisms in autonomous experiments, especially in the near term. The Beyond LEO Instrumentation & Science Series Science Working Group (BLISS-SWG) was established to provide NASA's Space Biology Program input on its strategy for developing research priorities and tools for exploration beyond LEO. Here, we present an abridged version of the first annual report of the BLISS-SWG, which is publicly available on the NASA Technical Reports Server. Seven priority areas and pertinent research questions were identified for research beyond LEO in the coming 2–5 years. Appropriate experimental organisms and technology development needs for research addressing these questions are summarized. The BLISS-SWG aims for this review to serve as a resource for the space biology and science and engineering communities as they develop research to understand risks and mitigation strategies for deep-space stressors on human crew, plants, and their microbiomes.

Matrix metalloproteinases in extracellular matrix remodeling: molecular, cellular and tissue aspects

Matrix metalloproteinases are an integral component of the organ-specific tissue microenvironment, primarily participating in the regulation of the state of the integrative-buffer metabolic environment, tissue remodeling, morphogenesis and immunogenesis, and the genesis of pathological vascular diseases. Therefore, issues related to regulation of matrix metalloproteinase activity under altered gravity are a matter of high urgency for space biomedicine. The review highlights aspects of regulation of matrix metalloproteinase activity under altered gravity. The study results included in the current systematic review were searched for in independent literature sources in the PubMed and Cochrane databases, Google Scholar and the NASA Technical Reports Server. A variety of stress factors associated with space flights, in particular, exposure to radiation, enhances the expression of transforming growth factor beta and matrix metalloproteinases-2. Experimental data obtained during several flights demonstrate that microgravity affects the architecture of cells and increases the expression of matrix metalloproteinases-1 and interleukin-6. Microgravity reduces the expression of collagen I, and the level of fibrillar collagen, which affects the mechanical properties of the intracellular matrix. Matrix metalloproteinases -1, -3, -10 demonstrated an increased activity in flight samples of 16-week-old female C57BL/6J mice (n = 8) during 15 days aboard the Space Shuttle Discovery, the STS-131 mission, compared to ground control (12.94; 2.98 and 16.85 times, respectively, P<0.05), while matrix metalloproteinases inhibitors – tissue metalloproteinase inhibitors-1, -2, and -3, demonstrated no statistically significant changes in gene expression. There were determined significant differences in the gene expression profiles in the lungs of animals of the space flight and ground control groups. The genes that revealed more than doubled expression were CTGF, MMP-2, NACM1, SPARC, SPOCK1 and TIMP-3, while the genes with the greatest decrease in expression were LAMA1, MMP-3, MMP-7, MMP-13, VCAM-1, and SELE.

Modeling and Cycle Parameter Matching of a High-Speed Variable Cycle Turbofan-Ramjet Engine

AbstractVariable cycle turbofan-ramjet (VCTR) engine is a promising propulsion system candidate for future Mach 4+ vehicles. Compared with conventional turbine engines, the VCTR engine has a higher thrust-to-weight ratio, a smaller diameter and a more compact structure. A component-based simulation model is developed to explore the operating characteristics of a high-speed VCTR concept. Modeling methods of variable-geometry components are characterized in this paper, and then, the way to build the VCTR model solver is described. The VCTR engine simulation model is validated by the numerical and experimental results of double bypass (DB) variable cycle engines from NASA technical reports. Performance and control law of the VCTR engine along the flight trajectory with flight Mach number varying from 0.5 to 4.0 are obtained to maximize net thrust and compared with that of a conventional two-spool afterburning mixed-flow turbofan (MFTF). Results show that the VCTR's performance is highly dependent on the fan characteristics and limited by various operating constraints, such as fan surge margin, turbine inlet temperature, and compressor discharge temperature. In addition, the thrust level of the MFTF with the variable-area low-pressure turbine is close to the VCTR engine.

Bone strength and composition in spacefaring rodents: systematic review and meta-analysis

Studying the effects of space travel on bone of experimental animals provides unique advantages, including the ability to perform post-mortem analysis and mechanical testing. To synthesize the available data to assess how much and how consistently bone strength and composition parameters are affected by spaceflight, we systematically identified studies reporting bone health in spacefaring animals from Medline, Embase, Web of Science, BIOSIS, and NASA Technical reports. Previously, we reported the effect of spaceflight on bone architecture and turnover in rodents and primates. For this study, we selected 28 articles reporting bone strength and composition in 60 rats and 60 mice from 17 space missions ranging from 7 to 33 days in duration. Whole bone mechanical indices were significantly decreased in spaceflight rodents, with the percent difference between spaceflight and ground control animals for maximum load of −15.24% [Confidence interval: −22.32, −8.17]. Bone mineral density and calcium content were significantly decreased in spaceflight rodents by −3.13% [−4.96, −1.29] and −1.75% [−2.97, −0.52] respectively. Thus, large deficits in bone architecture (6% loss in cortical area identified in a previous study) as well as changes in bone mass and tissue composition likely lead to bone strength reduction in spaceflight animals.

Craniofacial Bones and Teeth in Spacefarers: Systematic Review and Meta-analysis.

Estimating the risk of dental problems in long-duration space missions to the Moon and Mars is critical for avoiding dental emergencies in an environment that does not support proper treatment. Previous risk estimates were constructed based on the experience in short-duration space missions and isolated environments on Earth. However, previous estimates did not account for potential changes in dental structures due to space travel, even though bone loss is a known problem for long-duration spaceflights. The objective of this study was to systematically analyze the changes in hard tissues of the craniofacial complex during spaceflights. Comprehensive search of Medline, Embase, Scopus, the NASA Technical Report Server, and other sources identified 1,585 potentially relevant studies. After screening, 32 articles that presented quantitative data for skull in humans (6/32) and for calvariae, mandible, and lower incisors in rats (20/32) and mice (6/32) were selected. Skull bone mineral density showed a significant increase in spacefaring humans. In spacefaring rodents, calvariae bone volume to tissue volume (BV/TV) demonstrated a trend toward increasing that did not reach statistical significance, while in mandibles, there was a significant decrease in BV/TV. Dentin thickness and incisor volume of rodent incisors were not significantly different between spaceflight and ground controls. Our study demonstrates significant knowledge gaps regarding many structures of the craniofacial complex such as the maxilla, molar, premolar, and canine teeth, as well as small sample sizes for the studies of mandible and incisors. Understanding the effects of microgravity on craniofacial structures is important for estimating risks during long-duration spaceflight and for formulating proper protocols to prevent dental emergencies. Avoiding dental emergencies in long-duration spaceflights is critical since this environment does not support proper treatment. Prior risk estimates did not account for changes in dental structures due to space travel. We reviewed and synthesized the literature for changes in craniofacial complex associated with spaceflight. The results of our study will help clinicians and scientists to better prepare to mitigate potential oral health issues in space travelers on long-duration missions.

Bone health in spacefaring rodents and primates: systematic review and meta-analysis

Animals in space exploration studies serve both as a model for human physiology and as a means to understand the physiological effects of microgravity. To quantify the microgravity-induced changes to bone health in animals, we systematically searched Medline, Embase, Web of Science, BIOSIS, and NASA Technical reports. We selected 40 papers focusing on the bone health of 95 rats, 61 mice, and 9 rhesus monkeys from 22 space missions. The percentage difference from ground control in rodents was –24.1% [Confidence interval: −43.4, −4.9] for trabecular bone volume fraction and –5.9% [−8.0, −3.8] for the cortical area. In primates, trabecular bone volume fraction was lower by –25.2% [−35.6, −14.7] in spaceflight animals compared to GC. Bone formation indices in rodent trabecular and cortical bone were significantly lower in microgravity. In contrast, osteoclast numbers were not affected in rats and were variably affected in mice. Thus, microgravity induces bone deficits in rodents and primates likely through the suppression of bone formation.

Lateral Sloshing Analysis by CFD and Experiment for a Spherical Tank

Propellant sloshing is one of the potential sources of disturbance which affects the stability and structural integrity of space vehicles. In this study, using a small scale model of the first Korean lunar orbiter fuel tank, which is partially filled with liquid fuel, the dynamic lateral sloshing has been simulated by CFD analysis for various fill-levels. Spherical tank geometry was assumed, because it is one of the options for the fuel tank. After applying an accelerated motion to the fuel tank, the dynamic sloshing forces exerted on the tank wall in lateral directions during a free sloshing motion were measured and analyzed to identify the sloshing frequencies. The results show very good consistency with the mathematical and experimental studies from available sources in NASA technical reports. A simple inexpensive experimental work was also performed successfully to verify the fundamental slosh frequency. The methodology developed here would be useful for understanding the slosh dynamics and for modeling of the propellant sloshing in a fuel tank of an arbitrary geometry.

A systematic review and meta-analysis of bone loss in space travelers

Bone loss in space travelers is a major challenge for long-duration space exploration. To quantify microgravity-induced bone loss in humans, we performed a meta-analysis of studies systematically identified from searching Medline, Embase, Web of Science, BIOSIS, NASA Technical reports, and HathiTrust, with the last update in November 2019. From 25 articles selected to minimize the overlap between reported populations, we extracted post-flight bone density values for 148 individuals, and in-flight and post-flight biochemical bone marker values for 124 individuals. A percentage difference in bone density relative to pre-flight was positive in the skull, +2.2% [95% confidence interval: +1.1, +3.3]; neutral in the thorax/upper limbs, −0.7% [−1.3, −0.2]; and negative in the lumbar spine/pelvis, −6.2 [−6.7, −5.6], and lower limbs, −5.4% [−6.0, −4.9]. In the lower limb region, the rate of bone loss was −0.8% [−1.1, −0.5] per month. Bone resorption markers increased hyperbolically with a time to half-max of 11 days [9, 13] and plateaued at 113% [108, 117] above pre-flight levels. Bone formation markers remained unchanged during the first 30 days and increased thereafter at 7% [5, 10] per month. Upon landing, resorption markers decreased to pre-flight levels at an exponential rate that was faster after longer flights, while formation markers increased linearly at 84% [39, 129] per month for 3–5 months post-flight. Microgravity-induced bone changes depend on the skeletal-site position relative to the gravitational vector. Post-flight recovery depends on spaceflight duration and is limited to a short post-flight period during which bone formation exceeds resorption.

Intelligent checking model of Chinese radiotelephony read-backs in civil aviation air traffic control

Federal Aviation Administration (FAA) and NASA technical reports indicate that the misunderstanding in radiotelephony communications is a primary causal factor associated with operation errors, and a sizable proportion of operation errors lead to read-back errors. We introduce deep learning method to solve this problem and propose a new semantic checking model based on Long Short-Time Memory network (LSTM) for intelligent read-back error checking. A mean-pooling layer is added to the traditional LSTM, so as to utilize the information obtained by all the hidden activation vectors, and also to improve the robustness of the semantic vector extracted by LSTM. A MultiLayer Perceptron (MLP) layer, which can maintain the information of different regions in the concatenated vectors obtained by the mean-pooling layer, is applied instead of traditional similarity function in the new model to express the semantic similarity of the read-back pairs quantitatively. The K-Nearest Neighbor (KNN) classifier is used to verify whether the read-back pairs are consistent in semantics according to the output of MLP layer. Extensive experiments are conducted and the results show that the proposed model is more effective and more robust than the traditional checking model to verify the semantic consistency of read-backs automatically.

FR-18 HOW DO ASTRONAUTS URINATE? THE HISTORY OF INNOVATIONS ENABLING VOIDING IN THE VOID

You have accessJournal of UrologyHistory Forum1 Apr 2018FR-18 HOW DO ASTRONAUTS URINATE? THE HISTORY OF INNOVATIONS ENABLING VOIDING IN THE VOID Kimberly A Maciolek and Sara L Best Kimberly A MaciolekKimberly A Maciolek More articles by this author and Sara L BestSara L Best More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2018.02.3038AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Astronauts require significant technological assistance for essential daily activities, and urination is no exception. We sought to discover the history of device innovation to enable urination in space. METHODS We searched NASA technical reports, Google, and PubMed for media and articles describing technology for waste management in space from the first manned missions to modern day space travel. RESULTS Urine collection was an oversight in early manned space travel. Alan Shepard, the first American in space in 1961, had no option but to urinate in his pressure suit after significant flight delays. He avoided electrocuting himself but short circuited his biosensors. The second Mercury astronaut, Gus Grissom, wore a urine collection device (UCD) in his suit in 1962. UCDs were modified versions of condom catheters with a belt-like collection bag. UCDs persisted until Apollo missions into the 1970′s. UCDs were prone to leakage and incompatible with female anatomy. These design flaws drove the use of high absorbency adult diapers, or Disposable Absorption Containment Trunks (DACTs), during the 1983 Challenger mission. DACTs were replaced with disposable, moisture-wicking and superabsorbent shorts, called Maximal Absorptive Garments (MAGs), in 1988 to avoid skin irritation. Outside the confines of a pressure suit, urine collection has been enabled by vacuum-assisted devices. Astronauts in a space shuttle void into various male or female-specific funnels attached to a flexible hose. The cumbersome nature of these devices and the time required to use them often caused astronauts to decrease oral intake. The first American space station, Skylab, included the first toilet. Astronauts are required to practice using the toilet as well as timed voiding to reduce risk of urinary stasis, infection, and retention, all of which are risks in a microgravity environment. Improvements upon this basic Skylab design to allow voiding procedures most similar to that on Earth were used for the International Space Station (ISS). Technology on the ISS has allowed processing of urine into drinking water since 2008 and new prototypes are harnessing urine waste products as fuel for longer missions. CONCLUSIONS Early space missions showed that microgravity posed both a physiologic challenge for urination as well as a design challenge for urine containment and disposal, especially for female astronauts. These challenges were not expected for some of the earliest manned space missions but since then has been a considerable focus for innovation and astronaut quality of life. © 2018FiguresReferencesRelatedDetails Volume 199Issue 4SApril 2018Page: e1247-e1248 Advertisement Copyright & Permissions© 2018MetricsAuthor Information Kimberly A Maciolek More articles by this author Sara L Best More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

A Spreadsheet Tool for the AERODAS Model for Calculating Airfoil Pre-Stall and Post-Stall Lift and Drag Characteristics

In this study a spreadsheet tool with visual graphs is presented. The spreadsheet tool uses the AERODAS model developed by Spera ( NASA Technical Report, NASA/CR-2008-215434 ) to predict airfoil pre-stall and post-stall characteristics that is needed as an input for a Blade Element Momentum theory simulation of a wind turbine blade. The spreadsheet tool uses simple up and down buttons to adjust some parameters needed for the AERODAS model with the help of visual graphs. With the presented spreadsheet tool predicting the airfoil polar characteristics in the pre-stall and post-stall regimes using AERODAS model becomes very easy and efficient. The spreadsheet tool is freely available for the scientific community to download. The usage and the efficiency of the presented spreadsheet tool is presented for various applications.

A Complexity Measure for System Safety Assurance

AbstractThis paper describes a two‐year research effort to define complexity measures for avionics systems in order to help the FAA identify when systems are too complex to be able to assure their safety. The research project developed a measure of complexity related to the number of ways that an avionics system error (fault) could propagate from one element to another. Since each potential propagation requires another sub‐argument in the safety case, the number of such arguments should be proportional to certification effort. Thus, the ability to show that the system is safe, through the certification process, should depend on whether a system has low enough complexity (number of ways for errors to propagate).Our results include a formula for estimating the “error‐propagation complexity” from a system design, the results of using that formula on small and medium systems, and steps for using the formula. The test of the formula was performed by repeating that calculation on a second design for the first system and briefly on a larger design identified by the FAA, from a NASA technical report.

Multiaxial Fatigue Damage Prediction and Life Estimation of a Centrifugal Impeller for a Turboshaft Engine

The rotating gas turbine engine component such as centrifugal compressor is subjected to various static and dynamic loads during service. These service loads introduce multiaxial stress-strain states and inflict severe structural damage and hence reduce compressor efficiency and service life. In many cases, the service loads are non-proportional which introduces additional cyclic hardening depending on the loading path and the material used (Wu et al., Int J Fatigue 59:170–175, 2014). Studies have revealed that fatigue life is drastically reduced as a result of this additional cyclic hardening phenomenon. In recent decades, numerous multiaxial fatigue damage theories (which are strain based) have been developed taking into account the factors influencing fatigue like operating temperature, anisotropy, microstructure, nature of loading (proportional or non-proportional), and environmental effects. In general, these theories envisage crack nucleation and propagation to take place at a critical plane, but differ from one another the way critical planes are defined and damage parameters are proposed. To estimate the fatigue life under the multiaxial loading conditions, these theories relate multiaxial stress-strain components to uniaxial fatigue properties obtained from test data. But, it is observed that most of these theories are limited in application to a particular material or loading conditions. No general consensus is available on the best available fatigue damage theory for a particular application. Further, literature shows that most of these theories are applied and compared on tubular and notched test specimens under proportional and non-proportional loading conditions. Literatures are seldom available which compares these theories at the application level and validate through experiments. The objective of this paper is to estimate the low-cycle fatigue life of a centrifugal impeller used in a gas turbine application using different multiaxial fatigue damage models in the literature and propose a methodology which closely fits the experimental results. For applications such as gas turbine engines, the margin of safety (with respect to 0.2% PS) varies in the range of 1.05 to 1.15 (Stephens et al. in Metal fatigue in engineering. Wiley, New York, 2001). For this, it is extremely important to estimate the life and damage mechanism affecting the life of the components accurately to ensure the flight safety, reliability, and total service life of the gas turbine engine. The centrifugal impeller was designed for a pressure ratio of 3.2 and maximum rotational speed of 52,500 rpm. The titanium alloy Ti6Al4V was chosen as the possible material for the impeller as it has high strength and stiffness to weight ratio and is widely used in aerospace application (Wu et al., Int J Fatigue 44(12):14–20, 2012). The entire analysis can be divided into three main modules. Firstly, the stress and strain history on the centrifugal impeller was determined under actual operating condition. Finite element structural analysis packages were used for this purpose. Secondly, the stress-strain histories obtained from FE analysis were post-processed using several multiaxial fatigue damage models like Maximum von Mises strain model (Kalluri and Bonacuse in In-Phase and Out-of-Phase Axial-Torsional Fatigue Behavior of Haynes 188 at 760 °C. NASA Technical Report 1991, 91-C-046, 1991), which is based on the equivalent strain and the Smith-Watson-Topper (SWT) model (Shamsaei and McKelvey, Int J Fatigue 59:170–175, 2014), Kandil-Brown-Miller (KBM) model (Kandil et al., Met Struct 280:203–210, 1988), Fatemi and Socie (FS) model (Fatemi and Socie, Fatigue Fract Eng Mater 11(3):149–166, 1987), which are based on the critical plane approach to obtain the fatigue life. Finally, a prototype of the centrifugal impeller was made and tested at our sophisticated cyclic spin test facility to validate the Low-Cycle Fatigue life.

Exogenic olivine on Vesta from Dawn Framing Camera color data

In this paper we present the results of a global survey of olivine-rich lithologies on (4) Vesta. We investigated Dawn Framing Camera (FC) High Altitude Mapping Orbit (HAMO) color cubes (∼60m/pixel resolution) by using a method described in Thangjam et al. (Thangjam, G., Nathues, A., Mengel, K., Hoffmann, M., Schäfer, M., Reddy, V., Cloutis, E.A., Christensen, U., Sierks, H., Le Corre, L., Vincent, J.-B, Russell, C.T. [2014b]. Meteorit. Planet. Sci. arXiv:1408.4687 [astro-ph.EP]). In total we identified 15 impact craters exhibiting olivine-rich (>40wt.% ol) outcrops on their inner walls, some showing olivine-rich material also in their ejecta and floors. Olivine-rich sites are concentrated in the Bellicia, Arruntia and Pomponia region on Vesta’s northern hemisphere. From our multi-color and stratigraphic analysis, we conclude that most, if not all, of the olivine-rich material identified is of exogenic origin, i.e. remnants of A- or/and S-type projectiles. The olivine-rich lithologies in the north are possibly ejecta of the ∼90km diameter Albana crater. We cannot draw a final conclusion on their relative stratigraphic succession, but it seems that the dark material (Nathues, A., Hoffmann, M., Cloutis, E.A., Schäfer, M., Reddy, V., Christensen, U., Sierks, H., Thangjam, G.S., Le Corre, L., Mengel, K., Vincent, J.-B., Russell, C.T., Prettyman, T., Schmedemann, N., Kneissl, T., Raymond, C., Gutierrez-Marques, P., Hall, I. Büttner, I. [2014b]. Icarus (239, 222--237)) and the olivine-rich lithologies are of a similar age. The origin of some potential olivine-rich sites in the Rheasilvia basin and at crater Portia are ambiguous, i.e. these are either of endogenic or exogenic origin. However, the small number and size of these sites led us to conclude that olivine-rich mantle material, containing more than 40wt.% of olivine, is basically absent on the present surface of Vesta. In combination with recent impact models of Veneneia and Rheasilvia (Clenet, H., Jutzi, M., Barrat, J.-A., Gillet, Ph. [2014]. Lunar Planet Sci. 45, #1349; Jutzi, M., Asphaug, E., Gillet, P., Barrat, J.-A., Benz, W. [2013]. Nature 494, 207–210), which predict an excavation depth of up to 80km, we are confident that the crust–mantle depth is significantly deeper than predicted by most evolution models (30km; Mittlefehldt, D.W. [2014]. Asteroid 4 Vesta: A Fully Differentiated Dwarf Planet. NASA Technical Reports Server (20140004857.pdf)) or, alternatively, the olivine-content of the (upper) mantle is lower than our detection limit, which would lead to the conclusion that Vesta’s parent material was already depleted in olivine compared to CI meteorites.

The Public Domain, the National Interest, and the Fate of the NASA Technical Reports Server

On March 20, 2013, the NASA Technical Reports Server was taken off line. This vital repository of aerospace knowledge has become a focal point for a discussion on the public dissemination of technical information: it raises questions as to what is the true meaning of the "Public Domain." NASA Administrator Charles F. Bolden, prompted by Rep. Frank R. Wolf (R-Va), directed a thorough reevaluation of the contents of NASA public servers. At the time of this writing, only a fraction of the original data repository has been made generally accessible again. This manuscript introduces and reviews modern legal theories governing intellectual property law. It seeks to find policy positions whereby historical, but competitively sensitive information can be restricted from world-wide dissemination but once again be made available to hard-working U.S. nationals who further the progress of science and useful arts through their scholarship in aeronautics and space. Precedent for new law may be found in the Semiconductor Protection Act of 1984.

The real first weather satellite picture

The real first weather satellite picture

Open-loop control of compressible afterbody flows using adjoint methods

The flow past an axisymmetric body is generically unstable to a steady and a time-periodic global instability, the latter being thought to lead the low-frequency unsteadiness of the wake even at larger Reynolds numbers. The present paper examines how the growth rate of the oscillatory unstable mode developing in the wake of bullet-shaped objects can be reduced by a steady forcing, whose effect is to modify the base flow. The use of the compressible Navier–Stokes equations allows to consider control through steady mass, momentum, and heat forcing applied in the bulk and at the wall. To do so, we extend to compressible flows and axisymmetric geometries the method first proposed by Hill (NASA Technical Report No. 103858, 1992) to analyze the control of the two-dimensional mode of the incompressible cylinder wake. This method aims at evaluating the sensitivity of one particular eigenvalue to forcing by resolution of adjoint equations. Considering control at the wall, it allows to compute directly the eigenvalue gradient with respect to the wall variables. We show that the oscillating mode can be stabilized by a steady blowing at the wall (the so-called base-bleed control). Expressing the gradient as a sum of production, streamwise advection, and cross-stream advection terms, we show that this stabilizing effect is due to cross-stream advection, in contradiction with the up to now accepted interpretation based on the local absolute and convective instability analysis of parallel profiles. The same technique allows to compute the gradient of the oscillatory eigenvalue to bulk mass, momentum, and heat sources. Momentum control can be achieved by placing a small ring in the lee of the afterbody. Similar to the two-dimensional case studied by Hill, the effect of such a ring is twofold, as it induces a steady drag force which modifies the base flow and a fluctuating drag force proportional to the perturbation momentum at the ring location. We show that the efficiency of the control can be improved by heating the ring, which then acts as an additional heat source.

NTRS: NASA Technical Reports Server

NTRS: NASA Technical Reports Server

OAI and NASA’s scientific and technical information

The Open Archives Initiative Protocol for Metadata Harvesting (OAI‐PMH) is an evolving protocol and philosophy regarding interoperability for digital libraries (DLs). Previously, “distributed searching” models were popular for DL interoperability. However, experience has shown distributed searching systems across large numbers of DLs to be difficult to maintain in an Internet environment. The OAI‐PMH is a move away from distributed searching, focusing on the arguably simpler model of “metadata harvesting”. We detail NASA’s involvement in defining and testing the OAI‐PMH and experience to date with adapting existing NASA distributed searching DLs (such as the NASA Technical Report Server) to use the OAI‐PMH and metadata harvesting. We discuss some of the entirely new DL projects that the OAI‐PMH has made possible, such as the Technical Report Interchange Project. We explain the strategic importance of the OAI‐PMH to the mission of NASA’s Scientific and Technical Information Program.