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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

Design of intelligent mesoscale periodic array structures utilizing smart hydrogel

Mesoscale Periodic Array Structures (MPAS, also known as crystalline colloidal arrays), composed of aqueous or nonaqueous dispersions of self-assembled submicron colloidal spheres are emerging toward the development of advanced optical devices for technological applications. This is because of their unique optical diffraction properties and the ease with which these intriguing properties can be modulated experimentally. Moreover our recent advancements in this area which include 'locking' the liquid MPAS into solid or semisolid polymer matrices for greater stability with longer life span, and incorporation of CdS quantum dots and laser dyes into colloidal spheres to obtain nonlinear optical (NLO) responses further corroborate the use of MPAS in optical technology. Our long term goal is fabrication of all-optical and electro-optical devices such as spatial light modulators for optical signal processing and flat panel display devices by utilizing intelligent nonlinear periodic array structural materials. Here we show further progress in the design of novel linear MPAS which have the ability to sense and respond to an external source such as temperature. This is achieved by combining the self-assembly properties of polymer colloidal spheres and thermoshrinking properties of smart polymer gels. At selected temperatures the periodic array efficiently Bragg diffracts light and transmits most of the light at other temperatures. Hence these intelligent systems are of potential use as fixed notch filters optical switches or limiters to protect delicate optical sensors from high intensity laser radiation.

Sunkara, H. B.↗
NASA NTRS1996

Thermoacoustic Effects at a Solid-Fluid Boundary: The Role of a Second-Order Thermal Expansion Coefficient

Analytical and numerical studies are to be carried out to examine time-averaged thermal effects which are induced by the interaction of strong acoustic fields with a rigid boundary (thermoacoustic streaming). Also of interest is the significance of a second-order thermal expansion coefficient that emerges from this analysis. The model problem to be considered is that of a sphere that is acoustically levitated such that it is effectively isolated in a high-intensity standing acoustic field. The solution technique involves matched asymptotic analysis along with numerical solution of the boundary layer equations. The objective of this study is to predict the thermoacoustic streaming behavior and fully understand the role of the associated second-order thermodynamic modulus.

Gopinath, Ashok↗
NASA NTRS1996

Acoustic Streaming and Heat and Mass Transfer Enhancement

A second order effect associated with high intensity sound field, acoustic streaming has been historically investigated to gain a fundamental understanding of its controlling mechanisms and to apply it to practical aspects of heat and mass transfer enhancement. The objectives of this new research project are to utilize a unique experimental technique implementing ultrasonic standing waves in closed cavities to study the details of the generation of the steady-state convective streaming flows and of their interaction with the boundary of ultrasonically levitated near-spherical solid objects. The goals are to further extend the existing theoretical studies of streaming flows and sample interactions to higher streaming Reynolds number values, for larger sample size relative to the wavelength, and for a Prandtl and Nusselt numbers parameter range characteristic of both gaseous and liquid host media. Experimental studies will be conducted in support to the theoretical developments, and the crucial impact of microgravity will be to allow the neglect of natural thermal buoyancy. The direct application to heat and mass transfer in the absence of gravity will be emphasized in order to investigate a space-based experiment, but both existing and novel ground-based scientific and technological relevance will also be pursued.

Trinh, E. H.↗
NASA NTRS1997

Investigation of Fiber Optics Based Phased Locked Diode Lasers

Optical power beaming requires a high intensity source and a system to address beam phase and location. A synthetic aperture array of phased locked sources can provide the necessary power levels as well as a means to correct for phase errors. A fiber optic phase modulator with a master oscillator and power amplifier (MOPA) using an injection-locking semiconductor optical amplifier has proven to be effective in correcting phase errors as large as 4pi in an interferometer system. Phase corrections with the piezoelectric fiber stretcher were made from 0 - 10 kHz, with most application oriented corrections requiring only 1 kHz. The amplifier did not lose locked power output while the phase was changed, however its performance was below expectation. Results of this investigation indicate fiber stretchers and amplifiers can be incorporated into a MOPA system to achieve successful earth based power beaming.

Burke, Paul D.↗
NASA NTRS1998

Directional Electrostatic Accretion Process Employing Acoustic Droplet Formation

The present invention is directed to an apparatus for manufacturing a free standing solid metal part. In the present invention, metal droplets are ejected in a nozzleless fashion from a free surface pool of molten metal by applying focused acoustic radiation pressure. The acoustic radiation pressure is produced by high intensity acoustic tone bursts emitted from an acoustic source positioned at the bottom of the pool which directs the acoustic energy at the pool surface. The metal droplets are electrostatically charged so their trajectory can be controlled by electric fields that guide the droplets to predetermined points on a target. The droplets impinge upon the target and solidify with the target material. The accretion of the electrostatically directed solidified droplets forms the free standing metal part.

Oeftering, Richard↗
NASA NTRS1961

Sputtering of Metals by Mass-Analyzed N2(+) and N(+)

Low-energy sputtering studies were conducted with the help of a specially designed ion accelerator. A high-intensity rf ion source was developed for use in conjunction with electrostatic acceleration and magnetic mass separation of ion beams in the 0 to 8 kev energy range. Beams of N(+) or N2(+) ions have been produced with intensities of 200 to 500 micro-a (approx. 1 sq cm in cross section) and energy half-widths of about 20 ev. The sputtering yields of five metals (Cu, Ni, Fe, Mo, and W) were obtained as a function of energy (0-8 kev), bombarding ion (N(+) and N2(+)), and angle of incidence (normal and 450). Results are presented and some of their theoretical implications are discussed.

Bader, Michel↗
NASA NTRS1998

Signal-Induced Noise Effects in a Photon Counting System for Stratospheric Ozone Measurement

Signal-induced noise (SIN) is a common effect resulting when a photomultiplier tube (PMT) is saturated, for a brief moment, with a high intensity light pulse. After the laser pulse is sent into the atmosphere a very large light return, from either the near-field or a cloud, causes the PMT to momentarily saturate. The PMT is gated off at this time so no signal is seen at the anode. When the PMT gate is turned on, the far-field light return from the atmosphere is observed. This signal is distorted, however because of the addition of SIN to the received light signal causing a slower than expected decay of the atmospheric signal return. We have characterized SIN responses to varying parameters of the incident light on the PMT. These varied parameters included incident wavelength, PMT voltage, incident intensity, and tube type. We found that only the amplitude of the SIN was effected by varying PMT voltages and light intensities. The amplitude increased linearly as input light intensity increased. Different incident wavelengths at the same intensity did not effect the amplitude or the temporal behavior of the SIN response. Finally, different PMT tubes with similar physical structures exhibited similar SIN responses although with different amplitudes. The different amplitudes can be attributed to the different gains and operating voltages of each tube. These results suggest that SIN is caused by photocathode electron dynamics such as charge accumulation on internal PMT surfaces. These surfaces then emit the electrons slowly resulting in a long decay noise signal. With the SIN responses characterized we can now try to develop a method to reduce or eliminate SIN in DIAL systems.

Harper, David B.↗
NASA NTRS1997

A study of the evolutionary stages of IRAS sources and outflows in the Mon OB1 dark cloud

An ongoing project aiming to relate the evolutionary stages of the Infrared Astronomy Satellite (IRAS) sources in the Mon OB1 dark cloud to the morphology and energetics of outflows associated with some of these sources, is reported on. Previous evolutionary classifications of IRAS sources are refined and potential class O objects are identified. The fully-sampled CO maps of the outflows in this cloud are presented. These observations yield information on outflow structure, kinematics and excitation conditions. Low-intensity, high velocity gas is observed in the youngest outflows. This emission is characterized by relatively flat line wings at the highest velocities in spectral line profiles obtained at the peaks of the outflow emission.

Wolf-Chase, G.↗
NASA NTRS1998

Signal Analysis of Helicopter Blade-Vortex-Interaction Acoustic Noise Data

Blade-Vortex-Interaction (BVI) produces annoying high-intensity impulsive noise. NASA Ames collected several sets of BVI noise data during in-flight and wind tunnel tests. The goal of this work is to extract the essential features of the BVI signals from the in-flight data and examine the feasibility of extracting those features from BVI noise recorded inside a large wind tunnel. BVI noise generating mechanisms and BVI radiation patterns an are considered and a simple mathematical-physical model is presented. It allows the construction of simple synthetic BVI events that are comparable to free flight data. The boundary effects of the wind tunnel floor and ceiling are identified and more complex synthetic BVI events are constructed to account for features observed in the wind tunnel data. It is demonstrated that improved recording of BVI events can be attained by changing the geometry of the rotor hub, floor, ceiling and microphone. The Euclidean distance measure is used to align BVI events from each blade and improved BVI signals are obtained by time-domain averaging the aligned data. The differences between BVI events for individual blades are then apparent. Removal of wind tunnel background noise by optimal Wiener-filtering is shown to be effective provided representative noise-only data have been recorded. Elimination of wind tunnel reflections by cepstral and optimal filtering deconvolution is examined. It is seen that the cepstral method is not applicable but that a pragmatic optimal filtering approach gives encouraging results. Recommendations for further work include: altering measurement geometry, real-time data observation and evaluation, examining reflection signals (particularly those from the ceiling) and performing further analysis of expected BVI signals for flight conditions of interest so that microphone placement can be optimized for each condition.

Rogers, James C.↗
NASA NTRS1995

Optical Systems Design for a Stratospheric Lidar System

The optical systems for the transmitter and receiver of a high-power lidar for stratospheric measurements have been designed and analyzed. The system requirements and design results are presented and explained. An important and driving factor of this design was the requirement for a small image diameter in the plane of an optical chopper to allow the high-intensity lidar returns from the lower atmosphere to be shielded from the detection system. Some results relevant to the optical performance of the system are presented. The resulting system has been constructed and is now in operation at the Mauna Loa Observatory, Hawaii, and is making regular measurements of stratospheric ozone, temperature, and aerosol profiles.

McDermid, I. Stuart↗
NASA NTRS1999

Carotid Baroreflex Function During Prolonged Exercise

Astronauts are often required to work (exercise) at moderate to high intensities for extended periods while performing extra-vehicular activities (EVA). Although the physiologic responses associated with prolonged exercise have been documented, the mechanisms involved in blood pressure regulation under these conditions have not yet been fully elucidated. An understanding of this issue is pertinent to the ability of humans to perform work in microgravity and complies with the emphasis of NASA's Space Physiology and Countermeasures Program. Prolonged exercise at a constant workload is know to result in a progressive decrease in mean arterial pressure (MAP) concomitant with a decrease in stroke volume and a compensatory increase in heart rate. The continuous decrease in MAP during the exercise, which is related to the thermoregulatory redistribution of circulating blood volume to the cutaneous circulation, raises the question as to whether there is a loss of baroreflex regulation of arterial blood pressure. We propose that with prolongation of the exercise to 60 minutes, progressive increases on central command reflect a progressive upward resetting of the carotid baroreflex (CBR) such that the operating point of the CBR is shifted to a pressure below the threshold of the reflex rendering it ineffectual in correcting the downward drift in MAP. In order to test this hypothesis, experiments have been designed to uncouple the global hemodynamic response to prolonged exercise from the central command mediated response via: (1) continuous maintenance of cardiac filling volume by intravenous infusion of a dextran solution; and (2) whole body surface cooling to counteract thermoregulatory cutaneous vasodialation. As the type of work (exercise) performed by astronauts is inherently arm and upper body dependent, we will also examine the physiologic responses to prolonged leg cycling and arm ergometry exercise in the supine positions with and without level lower body negative pressure (-10 torr) to mimic spaceflight- related decreases in cardiac filling volumes.

Raven, P. B.↗
NASA NTRS1999

Radiation Effects: Core Project

The risks to personnel in space from the naturally occurring radiations are generally considered to be one of the most serious limitations to human space missions, as noted in two recent reports of the National Research Council/National Academy of Sciences. The Core Project of the Radiation Effects Team for the National Space Biomedical Research Institute is the consequences of radiations in space in order to develop countermeasure, both physical and pharmaceutical, to reduce the risks of cancer and other diseases associated with such exposures. During interplanetary missions, personnel in space will be exposed to galactic cosmic rays, including high-energy protons and energetic ions with atomic masses of iron or higher. In addition, solar events will produce radiation fields of high intensity for short but irregular durations. The level of intensity of these radiations is considerably higher than that on Earth's surface, and the biological risks to astronauts is consequently increased, including increased risks of carcinogenesis and other diseases. This group is examining the risk of cancers resulting from low-dose, low-dose rate exposures of model systems to photons, protons, and iron by using ground-based accelerators which are capable of producing beams of protons, iron, and other heavy ions at energies comparable to those encountered in space. They have begun the first series of experiments using a 1-GeV iron beam at the Brookhaven National Laboratory and 250-MeV protons at Loma Linda University Medical Center's proton synchrotron facility. As part of these studies, this group will be investigating the potential for the pharmaceutical, Tamoxifen, to reduce the risk of breast cancer in astronauts exposed to the level of doses and particle types expected in space. Theoretical studies are being carried out in a collaboration between scientists at NASA's Johnson Space Center and Johns Hopkins University in parallel with the experimental program have provided methods and predictions which are being used to assess the levels of risks to be encountered and to evaluate appropriate strategies for countermeasures. Although the work in this project is primarily directed toward problems associated with space travel, the problem of protracted exposures to low-levels of radiation is one of national interest in our energy and defense programs, and the results may suggest new paradigms for addressing such risks.

Dicello, John F.↗
NASA NTRS1999

System for Manipulating Drops and Bubbles Using Acoustic Radiation Pressure

The manipulation and control of drops of liquid and gas bubbles is achieved using high intensity acoustics in the form of and/or acoustic radiation pressure and acoustic streaming. generated by a controlled wave emission from a transducer. Acoustic radiation pressure is used to deploy or dispense drops into a liquid or a gas or bubbles into a liquid at zero or near zero velocity from the discharge end of a needle such as a syringe needle. Acoustic streaming is useful in manipulating the drop or bubble during or after deployment. Deployment and discharge is achieved by focusing the acoustic radiation pressure on the discharge end of the needle, and passing the acoustic waves through the fluid in the needle. through the needle will itself, or coaxially through the fluid medium surrounding the needle. Alternatively, the acoustic waves can be counter-deployed by focusing on the discharge end of the needle from a transducer axially aligned with the needle, but at a position opposite the needle, to prevent premature deployment of the drop or bubble. The acoustic radiation pressure can also be used for detecting the presence or absence of a drop or a bubble at the tip of a needle or for sensing various physical characteristics of the drop or bubble such as size or density.

Oeftering, Richard C.↗
NASA NTRS2000

Thermographic Analysis of Composite Cobonds on the X-33

During the manufacture of the X-33 liquid hydrogen (LH2) Tank 2, a total of thirty-six reinforcing caps were inspected thermographically. The cured reinforcing sheets of graphite/epoxy were bonded to the tank using a wet cobond process with vacuum bagging and low temperature curing. A foam filler material wedge separated the reinforcing caps from the outer skin of the tank. Manufacturing difficulties caused by a combination of the size of the reinforcing caps and their complex geometry lead to a potential for trapping air in the bond line. An inspection process was desired to ensure that the bond line was free of voids before it had cured so that measures could be taken to rub out the entrapped air or remove the cap and perform additional surface matching. Infrared thermography was used to perform the precure "wet bond" inspection as well as to document the final "cured" condition of the caps. The thermal map of the bond line was acquired by heating the cap with either a flash lamp or a set of high intensity quartz lamps and then viewing it during cool down. The inspections were performed through the vacuum bag and voids were characterized by localized hot spots. In order to ensure that the cap had bonded to the tank properly, a post cure "flash heating" thermographic investigation was performed with the vacuum bag removed. Any regions that had opened up after the preliminary inspection or that were hidden during the bagging operation were marked and filled by drilling small holes in the cap and injecting resin. This process was repeated until all critical sized voids were filled.

Russell, Samuel S.↗
NASA NTRS2001

Modeling of Fillets in Thin-Walled Structures for Dynamic Analysis

Relatively new developments in manufacturing methods have made it possible to produce machined parts with a wall thickness of less than 0.010". While the parts are being machined. Fillets of relatively large radius to thickness ratios are created by the milling tool. This paper discusses an accurate new technique for finite-element modeling of fillets for dynamic and stiffness analysis using efficient plate elements rather than more computationally intensive, high density solid meshes, A simple filleted cantilever beam of 0.040" thickness, 1.6" length, 1" depth, and 0.250" radius in the corner was modeled using both solid elements and several different plate element geometries. The finite element results were then compared with static and modal testing of a machined sample. The highest-scoring plate element technique uses a bridge of elements that is constructed through the tangent point of the Fillet radius such that the thickness of the element matches tile volume of the fillet. This model produces errors of less than 4.6 percent for static loading and less than 7.4 percent for modal analysis. This simple plate element technique will prove critical for efficient, timely, and accurate dynamic analysis of complex thin-walled structures.

Seugling, Richard M.↗
NASA NTRS2001

Flight Test Analysis of the Forces and Moments Imparted on a B737-100 Airplane During Wake Vortex Encounters

Aircraft travel has become a major form of transportation. Several of our major airports are operating near their capacity limit, increasing congestion and delays for travelers. As a result, the National Aeronautics and Space Administration (NASA) has been working in conjunction with the Federal Aviation Administration (FAA), airline operators, and the airline industry to increase airport capacity without sacrificing public safety. One solution to the problem is to increase the number of airports and build new. runways; yet, this solution is becoming increasingly difficult due to limited space. A better solution is to increase the production per runway. This solution increases the possibility that one aircraft will encounter the trailing wake of another aircraft. Hazardous wake vortex encounters occur when an aircraft encounters the wake produced by a heavier aircraft. This heavy-load aircraft produces high-intensity wake turbulence that redistributes the aerodynamic loads of trailing smaller aircraft. This situation is particularly hazardous for smaller aircraft during takeoffs and landings. In order to gain a better understanding of the wake-vortex/aircraft encounter phenomena, NASA Langley Research Center conducted a series of flight tests from 1995 through 1997. These tests were designed to gather data for the development a wake encounter and wake-measurement data set with the accompanying atmospheric state information. This data set is being compiled into a database that can be used by wake vortex researchers to compare with experimental and computational results. The purpose of this research is to derive and implement a procedure for calculating the wake-vortex/aircraft interaction portion of that database by using the data recorded during those flight tests. There were three objectives to this research. Initially, the wake-induced forces and moments from each flight were analyzed based on varying flap deflection angles. The flap setting alternated between 15 and 30 degrees while the separation distance remained constant. This examination was performed to determine if increases in flap deflection would increase or decrease the effects of the wake-induced forces and moments. Next, the wake-induced forces and moments from each flight were analyzed based on separation distances of 1-3 nautical miles. In this comparison, flap deflection was held constant at 30 degrees. The purpose of this study was to determine if increased separation distances reduced the effects of the wake vortex on the aircraft. The last objective compared the wake-induced forces and moments of each flight as it executed a series of maneuvers through the wake-vortex. This analysis was conducted to examine the impact of the wake on the B737 as it traversed the wake horizontally and vertically. Results from the first analysis indicated that there was no difference in wake effect at flap deflections of 15 and 30 degrees. This conclusion is evidenced in the cases of the wake-induced sideforce, rolling moment, and yawing moment. The wake-induced lift, drag, and pitching moment cases yielded less conclusive results. The second analysis compared the wake-induced forces and moments at separation distances of 1-3 nautical miles. Results indicated that there was no significant difference in the wake-induced lift, drag, sideforce, or yawing moment coefficients. The analysis compared the wake-induced forces and moments based on different flight maneuvers. It was found that the wake-induced forces and moments had the greatest impact on out-to-in and in-to-out maneuvers.

Roberts, Chistopher L.↗
NASA NTRS1999

Modeling of Wake-vortex Aircraft Encounters

There are more people passing through the world's airports today than at any other time in history. With this increase in civil transport, airports are becoming capacity limited. In order to increase capacity and thus meet the demands of the flying public, the number of runways and number of flights per runway must be increased. In response to the demand, the National Aeronautics and Space Administration (NASA), in conjunction with the Federal Aviation Administration (FAA), airport operators, and the airline industry are taking steps to increase airport capacity without jeopardizing safety. Increasing the production per runway increases the likelihood that an aircraft will encounter the trailing wake-vortex of another aircraft. The hazard of a wake-vortex encounter is that heavy load aircraft can produce high intensity wake turbulence, through the development of its wing-tip vortices. A smaller aircraft following in the wake of the heavy load aircraft will experience redistribution of its aerodynamic load. This creates a safety hazard for the smaller aircraft. Understanding this load redistribution is of great importance, particularly during landing and take-off. In this research wake-vortex effects on an encountering 10% scale model of the B737-100 aircraft are modeled using both strip theory and vortex-lattice modeling methods. The models are then compared to wind tunnel data that was taken in the 30ft x 60ft wind tunnel at NASA Langley Research Center (LaRC). Comparisons are made to determine if the models will have acceptable accuracy when parts of the geometry are removed, such as the horizontal stabilizer and the vertical tail. A sensitivity analysis was also performed to observe how accurately the models could match the experimental data if there was a 10% error in the circulation strength. It was determined that both models show accurate results when the wing, horizontal stabilizer, and vertical tail were a part of the geometry. When the horizontal stabilizer and vertical tail were removed there were difficulties modeling the sideforce coefficient and pitching moment. With the removal of only the vertical tail unacceptable errors occurred when modeling the sideforce coefficient and yawing moment. Lift could not be modeled with either the full geometry or the reduced geometry attempts.

Smith, Sonya T.↗