Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Beam Simulations”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 901 records · Page 50
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

Characteristics of a Linearly Tapered Slot Antenna (LTSA) Conformed Longitudinally Around a Cylinder

The family of tapered slot antennas (TSA s) is suitable for numerous applications. Their ease of fabrication, wide bandwidth, and high gain make them desirable for military and commercial systems. Fabrication on thin, flexible substrates allows the TSA to be conformed over a given body, such as an aircraft wing or a piece of clothing for wearable networks. Previously, a Double Exponentially Tapered Slot Antenna (DETSA) was conformed around an exponential curvature, which showed that the main beam skewed towards the direction of curvature. This paper presents a Linearly Tapered Slot Antenna (LTSA) conformed longitudinally around a cylinder. Measured and simulated radiation patterns and the direction of maximum H co-polarization (Hco) as a function of the cylinder radius are presented.

Jordan, Jennifer L.↗
NASA NTRS2007

Laboratory Measurements of Charging of Apollo 17 Lunar Dust Grains by Low Energy Electrons

It is well recognized that the charging properties of individual micron/sub-micron size dust grains by various processes are expected to be substantially different from the currently available measurements made on bulk materials. Solar UV radiation and the solar wind plasma charge micron size dust grains on the lunar surface with virtually no atmosphere. The electrostatically charged dust grains are believed to be levitated and transported long distances over the lunar terminator from the day to the night side. The current models do not fully explain the lunar dust phenomena and laboratory measurements are needed to experimentally determine the charging properties of lunar dust grains. An experimental facility has been developed in the Dusty Plasma Laboratory at NASA Marshall Space Flight Center MSFC for investigating the charging properties of individual micron/sub-micron size positively or negatively charged dust grains by levitating them in an electrodynamic balance in simulated space environments. In this paper, we present laboratory measurements on charging of Apollo 17 individual lunar dust grains by low energy electron beams in the 5-100 eV energy range. The measurements are made by levitating Apollo 17 dust grains of 0.2 to 10 micrometer diameters, in an electrodynamic balance and exposing them to mono-energetic electron beams. The charging rates and the equilibrium potentials produced by direct electron impact and by secondary electron emission processes are discussed.

Abbas, Mian M.↗
NASA NTRS2011

Development of Benchmark Examples for Delamination Onset and Fatigue Growth Prediction

An approach for assessing the delamination propagation and growth capabilities in commercial finite element codes was developed and demonstrated for the Virtual Crack Closure Technique (VCCT) implementations in ABAQUS. The Double Cantilever Beam (DCB) specimen was chosen as an example. First, benchmark results to assess delamination propagation capabilities under static loading were created using models simulating specimens with different delamination lengths. For each delamination length modeled, the load and displacement at the load point were monitored. The mixed-mode strain energy release rate components were calculated along the delamination front across the width of the specimen. A failure index was calculated by correlating the results with the mixed-mode failure criterion of the graphite/epoxy material. The calculated critical loads and critical displacements for delamination onset for each delamination length modeled were used as a benchmark. The load/displacement relationship computed during automatic propagation should closely match the benchmark case. Second, starting from an initially straight front, the delamination was allowed to propagate based on the algorithms implemented in the commercial finite element software. The load-displacement relationship obtained from the propagation analysis results and the benchmark results were compared. Good agreements could be achieved by selecting the appropriate input parameters, which were determined in an iterative procedure.

Krueger, Ronald↗
NASA NTRS2012

Reconfigurable Wave Velocity Transmission Lines for Phased Arrays

This presentation discussed a novel phased array with an emphasis to simplify the array feed. Specifically, we will demonstrate a simple, low cost feeding approach by mechanically controlling the substrate thickness. The array feed lines are constructed from parallel plate transmission lines whose thickness are adjusted to control their effective dielectric constant (Epsilon_eff). As a result the phase delay/excitation at each array element will be adjusted per desired beam direction. The proposed antenna elements will be overlapping dipoles operating over a 2:1 bandwidth in the Ku-Band spectrum. Preliminary simulation and experimental demonstration of such an array will be presented.

Host, Nicholas Keith↗
NASA NTRS2016

Use and Protection of GPS Sidelobe Signals for Enhanced Navigation Performance in High Earth Orbit

The application of the Global Positioning System (GPS) for navigation of spacecraft in High and Geosynchronous Earth Orbit (HEO/GEO) has crossed a threshold and is now being employed in operational missions. Utilizing advanced GPS receivers optimized for these missions, space users have made extensive use of the sidelobe transmissions from the GPS satellites to realize navigation performance that far exceeds that predicted by pre-launch simulations. Unfortunately, the official specification for the GPS Space Service Volume (SSV), developed in 2006, assumes that only signals emanating from the main beam of the GPS transmit antenna are useful for navigation, which greatly under-estimates the number of signals available for navigation purposes. As a result, future high-altitude space users may be vulnerable to any GPS design changes that suppress the sidelobe transmissions, beginning with Block III space vehicles (SVs) 11-32. This paper presents proposed changes to the GPS system SSV requirements, as informed by data from recent experiments in the SSV and new mission applications that are enabled by GPS navigation in HEO/GEO regimes. The NASA/NOAA GOES-R series satellites are highlighted as an example of a mission that relies on this currently-unspecified GPS system performance to meet mission requirements.

Navigation↗
NASA NTRS2015

Technology Advancement for Active Remote Sensing of Carbon Dioxide from Space Using the ASCENDS CarbonHawk Experiment Simulator: First Results

The ASCENDS CarbonHawk Experiment Simulator (ACES) is a newly developed lidar developed at NASA Langley Research Center and funded by NASA's Earth Science Technology Office (ESTO) Instrument Incubator Program (IIP) that seeks to advance technologies critical to measuring atmospheric column carbon dioxide (CO2) mixing ratios in support of the NASA Active Sensing of CO2 Emissions over Nights, Days, and Seasons (ASCENDS) mission. The technology advancements targeted include: (1) increasing the power-aperture product to approach ASCENDS mission requirements by implementing multi-aperture telescopes and multiple co-aligned laser transmitters; (2) incorporating high-efficiency, high-power Erbium-Doped Fiber Amplifiers (EDFAs); (3) developing and incorporating a high-bandwidth, low-noise HgCdTe detector and transimpedence amplifier (TIA) subsystem capable of long-duration autonomous operation on Global Hawk aircraft, and (4) advancing algorithms for cloud and aerosol discrimination. The ACES instrument architecture is being developed for operation on high-altitude aircraft and will be directly scalable to meet the ASCENDS mission requirements. These technologies are critical towards developing not only spaceborne instruments but also their airborne simulators, with lower platform requirements for size, mass, and power, and with improved instrument performance for the ASCENDS mission. ACES transmits five laser beams: three from commercial EDFAs operating near 1.57 microns, and two from the Exelis oxygen (O2) Raman fiber laser amplifier system operating near 1.26 microns. The three EDFAs are capable of transmitting up to 10 watts average optical output power each and are seeded by compact, low noise, stable, narrow-linewidth laser sources stabilized with respect to a CO2 absorption line using a multi-pass gas absorption cell. The Integrated-Path Differential Absorption (IPDA) lidar approach is used at both wavelengths to independently measure the CO2 and O2 column number densities and retrieve the average column CO2 mixing ratio. The ACES receiver uses three fiber-coupled 17.8-cm diameter athermal telescopes. The transmitter assembly consists of five fiber-coupled laser collimators and an associated Risley prism pair for each laser to co-align the outgoing laser beams and to align them with the telescope field of view. The backscattered return signals collected by the three telescopes are combined in a fiber bundle and sent to a single low noise detector. The detector/TIA development has improved the existing detector subsystem by increasing its bandwidth to 4.7 MHz from 500 kHz and increasing the duration of autonomous, service-free operation periods from 4 hours to >24 hours. The new detector subsystem enables the utilization of higher laser modulation rates, which provides greater flexibility for implementing advanced thin-cloud discrimination algorithms as well as improving range-determination resolution and error reduction. The cloud/aerosol discrimination algorithm development by Langley and Exelis features a new suite of algorithms for the minimization/elimination of bias errors in the return signal induced by the presence of intervening thin clouds. Multiple laser modulation schemes are being tested in an effort to significantly mitigate the effects of thin clouds on the retrieved CO2 column amounts. Full instrument development concluded in the spring of 2014. After ground range tests of the instrument, ACES successfully completed six test flights on the Langley Hu-25 aircraft in July, 2014, and recorded data at multiple altitudes over land and ocean surfaces with and without intervening clouds. Preliminary results from these test flights will be presented in this paper.

Obland, Michael D.↗
NASA NTRSDate not supplied

TPSAS-NF1676L-13122-DND

An approach for assessing the delamination propagation and growth capabilities in commercial finite element codes was developed and demonstrated for the Virtual Crack Closure Technique (VCCT) implementations in ABAQUS?. The Double Cantilever Beam (DCB) specimen was chosen as an example. First, benchmark results to assess delamination propagation capabilities under static loading were created using models simulating specimens with different delamination lengths. Second, starting from an initially straight front, the delamination was allowed to propagate based on the algorithms implemented in the commercial finite element software. The load-displacement relationship obtained from the propagation analysis results and the benchmark results were compared. Good agreements could be achieved by selecting the appropriate input parameters, which were determined in an iterative procedure. A benchmark case to assess the fatigue growth prediction capabilities was also created. Input control parameters were varied to study the effect on the computed delamination growth. The benchmarks enabled the selection of the appropriate input parameters that yielded good agreements between the results obtained from the automated analysis and the benchmark results. Overall, the results are encouraging but further assessment for mixed-mode delamination is required.

Ronald Krueger↗
NASA NTRS1991

Far-field pattern of a coherently combined beam from large-scale laser diode arrays

The far-field pattern of a large-scale amplifier array (LSAA) consisting of a large number (2000) of diode laser amplifiers is numerically simulated, and the power collection efficiencies are determined. Random distributions of phase mismatches, misorientations, and element failures in the LSAA system are considered. Phase mismatches and misorientations of the element amplifiers are found to be the most critical parameters of those affecting the power-collection efficiency. Errors of 0.2 wavelength and 25 percent for phase and diffraction angle, respectively, cause a 10 percent reduction in power-collection efficiency. The results are used to evaluate the concept of space-laser power transmission. It is found that an overall transmission efficiency of 80 percent could be realized with a 5-m-diam. receiver at a distance of 10,000 km when an LSAA transmitter 6 m in diam. is aimed with state-of-the-art pointing accuracy.

Kwon, Jin H.↗
NASA NTRS1987

Characterization of ion beam modified ceramic wear surfaces using Auger electron spectroscopy

An investigation of the surface chemistry and morphology of the wear surfaces of ceramic material surfaces modified by ion beam mixing has been conducted using Auger electron spectroscopy and secondary electron microscopy. Studies have been conducted on ceramic/ceramic friction and wear couples made up of TiC and NiMo-bonded TiC cermet pins run against Si3N4 and partially stabilized zirconia disc surfaces modified by the ion beam mixing of titanium and nickel, as well as ummodified ceramic/ceramic couples in order to determine the types of surface changes leading to the improved friction and wear behavior of the surface modified ceramics in simulated diesel environments. The results of the surface analyses indicate that the formation of a lubricating oxide layer of titanium and nickel, is responsible for the improvement in ceramic friction and wear behavior. The beneficial effect of this oxide layer depends on several factors, including the adherence of the surface modified layer or subsequently formed oxide layer to the disc substrate, the substrate materials, the conditions of ion beam mixing, and the environmental conditions.

Wei, W.↗
NASA NTRS2022

Simulated 8x8 Ku-Band Array Antenna Performance on Airplane Door

An 8x8, Ku-band antenna array composed of circular patches was simulated both on an infinite ground plane and mounted on an airplane door. The radiated far field was calculated for both cases to determine the effect of mounting the antenna on the side of the airplane. It was found that the main beam was relatively unaffected, while the sidelobes were increased by 15 to 20 dB at angles more than 30° off boresight..

array antenna↗
NASA NTRS2020

Formation and Topology of Foreshock Bubbles

We use global and local hybrid (kinetic ions and fluid electrons) simulations to investigate the conditions under which foreshock bubbles (FBs) form and how their topology changes with solar wind conditions. FBs form as a result of the interaction between solar wind discontinuities and backstreaming ion beams in the foreshock. They consist of an outer shock and its associated sheath plasma and a low density high temperature core with low magnetic field strength. The structure of FBs is determined by the angle between the interplanetary magnetic field and the normal to the solar wind discontinuity. We show that interaction of rotational discontinuities with the foreshock during small angles between the interplanetary magnetic field and discontinuity normal results in the formation of a nearly spherical bubble with a radius that scales with the width of the foreshock. As this angle increases, FBs become more elongated and eventually become nearly planar structures with dimensions that scale with the length of the foreshock. Despite this transformation, the signatures of FBs in spacecraft time series data remain the same in agreement with the observations. Global simulation results show that FBs form when the solar wind flow speed corresponds to high or intermediate Alfvén Mach numbers (approximately >7 MA). In general, this is tied to the relative speed between the solar wind and ion beams and drop in density of the back streaming ions.

Nick Omidi↗
NASA NTRS1987

Dynamic testing of a two-dimensional box truss beam

Testing to determine the effects of joint freeplay and pretensioning of diagonal members on the dynamic characteristics of a two-dimensional box truss beam was conducted. The test article was ten bays of planar truss suspended by long wires at each joint. Each bay measured 2 meters per side. Pins of varying size were used to simulate various joint freeplay conditions. Single-point random excitation was the primary method of test. The rational fraction polynomial method was used to extract modal characteristics from test data. A finite element model of the test article was generated from which modal characteristics were predicted. These were compared with those obtained from tests. With the exception of the fundamental mode, correlation of theoretical and experimental results was poor, caused by the resonant coupling of local truss member bending modes with global truss beam modes. This coupling introduced many modes in the frequency range of interest whose frequencies were sensitive to joint boundary conditions. It was concluded that local/global coupling must be avoided in the frequency range where accurate modal characteristics are required.

White, Charles W.↗
NASA NTRSDate not supplied

Sidelobe Reduction and Mode-Purity Enhancement of Vortex Beams from a Programmable, Rectangular Phased Array Antenna

Tapering the magnitude of the electric field excitation of a programmable, rectangular phased array has been employed to achieve sidelobe reduction and enhancement of mode purity in vortex beams, which carry non-zero orbital angular momentum. Far-field radiation patterns pertaining to a commercial-off-the-shelf, 256-element antenna were generated via electromagnetic simulation. The patterns were decomposed into weighted sums of Laguerre-Gaussian modes. The extracted coupling coefficients were used to gauge mode purity. In comparison to a uniform excitation of the phased array elements, our studies indicate that employing a tapering technique can result in a 10.7 dB reduction of sidelobe power and a 7.22 dB improvement in worst-case, mode-to-mode cross-talk.

orbital angular momentum, phased array, beamformin↗
NASA NTRS2012

Kinetic and Potential Sputtering Enhancements of Lunar Regolith Erosion: The Contribution of the Heavy Multicharged (Minority) Solar Wind Constituents

We report preliminary results for H+, Ar+1, Ar+6 and Ar+9 ion sputtering of JSC-1A lunar regolith simulant at solar wind velocities, obtain ed at the ORNL Multicharged Ion Research Facility using quadrupole ma ss spectrometry. The multi-charged Ar ions were used as proxies for i ntermediate mass solar wind multicharged ions. Prior to the Ar beam e xposures, the sample was exposed to high fluence H+ irradiation to si mulate H-loading due to the dominant solar wind constituent. A x80 en hancement of oxygen sputtering by Ar+ over same velocity H+ was measu red and an additional x2 increase for Ar+9 over same velocity Ar+ was demonstrated, giving clear evidence of the importance of potential s puttering by multicharged ions. This enhancement was observed to pers ist to the maximum fluences investigated (approx 10(exp 16)/sq cm). As discussed in a companion abstract by N. Barghouty, such persistent s puttering enhancement has significant implications on weathering and aging of lunar regolith. In addition, XPS measurements showed strong evidence of Fe reduction for those target areas that had been exposed to high fluence Ar+ and Ar+8 beams. Preferential oxidation of the Fe -reduced beam-exposed regions during transfer to the XPS system led t o enhanced O concentrations in those regions as well. On the basis of these very promising preliminary results, a NASA-LASER project on mo re extensive measurements was recently selected for funding. The prop osal expands the collaboration with NASA-MSFC for the simulation effort, and adds a new collaboration with NASA-GSFC for lunar mission-rele vant measurements.

Meyer, F. W.↗
NASA NTRS2000

Simulation of Aluminum Micro-mirrors for Space Applications at Cryogenic Temperatures

Closed form and finite element models are developed to predict the device response of aluminum electrostatic torsion micro-mirrors fabricated on silicon substrate for space applications at operating temperatures of 30K. Initially, closed form expressions for electrostatic pressure arid mechanical restoring torque are used to predict the pull-in and release voltages at room temperature. Subsequently, a detailed mechanical finite element model is developed to predict stresses and vertical beam deflection induced by the electrostatic and thermal loads. An incremental and iterative solution method is used in conjunction with the nonlinear finite element model and closed form electrostatic equations to solve. the coupled electro-thermo-mechanical problem. The simulation results are compared with experimental measurements at room temperature of fabricated micro-mirror devices.

Kuhn, J. L.↗
NASA NTRS2004

Role of shielding in modulating the effects of solar particle events: Monte Carlo calculation of absorbed dose and DNA complex lesions in different organs

Distributions of absorbed dose and DNA clustered damage yields in various organs and tissues following the October 1989 solar particle event (SPE) were calculated by coupling the FLUKA Monte Carlo transport code with two anthropomorphic phantoms (a mathematical model and a voxel model), with the main aim of quantifying the role of the shielding features in modulating organ doses. The phantoms, which were assumed to be in deep space, were inserted into a shielding box of variable thickness and material and were irradiated with the proton spectra of the October 1989 event. Average numbers of DNA lesions per cell in different organs were calculated by adopting a technique already tested in previous works, consisting of integrating into "condensed-history" Monte Carlo transport codes--such as FLUKA--yields of radiobiological damage, either calculated with "event-by-event" track structure simulations, or taken from experimental works available in the literature. More specifically, the yields of "Complex Lesions" (or "CL", defined and calculated as a clustered DNA damage in a previous work) per unit dose and DNA mass (CL Gy-1 Da-1) due to the various beam components, including those derived from nuclear interactions with the shielding and the human body, were integrated in FLUKA. This provided spatial distributions of CL/cell yields in different organs, as well as distributions of absorbed doses. The contributions of primary protons and secondary hadrons were calculated separately, and the simulations were repeated for values of Al shielding thickness ranging between 1 and 20 g/cm2. Slight differences were found between the two phantom types. Skin and eye lenses were found to receive larger doses with respect to internal organs; however, shielding was more effective for skin and lenses. Secondary particles arising from nuclear interactions were found to have a minor role, although their relative contribution was found to be larger for the Complex Lesions than for the absorbed dose, due to their higher LET and thus higher biological effectiveness. c2004 COSPAR. Published by Elsevier Ltd. All rights reserved.

Non-NASA Center↗
NASA NTRS1974

A low cost ""Air Mass 2'' solar simulator

Tungsten halogen projection lamps have integral ellipsoidal reflector, and hexagonal shaped plastic Fresnel lenses. Reflector is dichroic coated to reduce infrared content of reflected radiation. Array of lamps and lenses produces uniform collimated beam having near AM2 spectrum and intensity that can be used for testing flat plate solar collectors.

Yass, K.↗
NASA NTRS2004

Evaluation of Training Samples Manually Welded With the Universal Handtool in a Space Simulation Chamber

The international space welding experiment was designed to evaluate the universal handtool (UHT) functions as a welding, brazing, coating, and cutting tool for in-space operations. The UHT is an electron beam welding system developed by the Paton Welding Institute (PWI), Kiev, Ukraine, and operated a 8 kV with up to 1 kW of power. In preparation for conducting the space welding experiment, cosmonauts were trained to properly operate the UHT and correctly process samples. This Technical Memorandum presents the results of the destructive and nondestructive evaluation of the training samples made in Russia in 1998. It was concluded that acceptable welds can be made with the UHT despite the constraints imposed by a space suit. The lap joint fillet weld configuration was more suitable than the butt joint configuration for operators with limited welding experience. The tube braze joint configuration designed by the PWI was easily brazed in a repeatable manner.

Russell, C. K.↗