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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS2013

A Comparative Study of Four Impedance Eduction Methodologies Using Several Test Liners

A comparative study of four commonly used impedance eduction methods is presented for a range of liner structures and test conditions. Two of the methods are restricted to uniform flow while the other two accommodate both uniform and boundary layer flows. Measurements on five liner structures (a rigid-wall insert, a ceramic tubular liner, a wire mesh liner, a low porosity conventional liner, and a high porosity conventional liner) are obtained using the NASA Langley Grazing Flow Impedance Tube. The educed impedance of each liner is presented for forty-two test conditions (three Mach numbers and fourteen frequencies). In addition, the effects of moving the acoustic source from upstream to downstream and the refractive effects of the mean boundary layer on the wire mesh liner are investigated. The primary conclusions of the study are that: (1) more accurate results are obtained for the upstream source, (2) the uniform flow methods produce nearly identical impedance spectra at and below Mach 0.3 but significant scatter in the educed impedance occurs at the higher Mach number, (3) there is better agreement in educed impedance among the methods for the conventional liners than for the rigid-wall insert, ceramic, or wire mesh liner, and (4) the refractive effects of the mean boundary layer on the educed impedance of the wire mesh liner are generally small except at Mach 0.5.

Watson, Willie R.↗
NASA NTRS1977

Leading edge protection for composite blades

A laminated filament composite structure, such as an airfoil for use in an environment in which it is subjected to both foreign object impact and bending is provided with improved leading edge protection. At least one fine wire mesh layer is partially bonded within the composite structure along its neutral bending axis. A portion of the wire mesh layer extends beyond the neutral bending axis and partially around the leading edge where it is bonded to the outer periphery of the primary composite structure. The wire mesh is clad with a metal such as nickel to provide an improved leading edge protective device which is firmly anchored within the composite structure. Also described is a novel method of constructing a composite airfoil so as to further minimize the possibility of losing the leading edge protective device due to delamination caused by impact and bending.

Brantley, J. W.↗
NASA NTRS2009

The Development of Wheels for the Lunar Roving Vehicle

The Lunar Roving Vehicle (LRV) was developed for NASA s Apollo program so astronauts could cover a greater range on the lunar surface, carry more science instruments, and return more soil and rock samples than by foot. Because of the unique lunar environment, the creation of flexible wheels was the most challenging and time consuming aspect of the LRV development. Wheels developed for previous lunar systems were not sufficient for use with this manned vehicle; therefore, several new designs were created and tested. Based on criteria set by NASA, the choices were narrowed down to two: the wire mesh wheel developed by General Motors (GM), and the hoop spring wheel developed by the Bendix Corporation. Each of these underwent intensive mechanical, material, and terramechanical analyses, and in the end, the wire mesh wheel was chosen for the LRV. Though the wire mesh wheel was determined to be the best choice for its particular application, it may be insufficient towards achieving the objectives of future lunar missions that could require higher tractive capability, increased weight capacity, or extended life. Therefore lessons learned from the original LRV wheel development and suggestions for future Moon wheel projects are offered.

Asnani, Vivake↗
NASA NTRS2001

Retention of Sputtered Molybdenum on Ion Engine Discharge Chamber Surfaces

Grit-blasted anode surfaces are commonly used in ion engines to ensure adherence of sputtered coatings. Next generation ion engines will require higher power levels, longer operating times, and thus there will likely be thicker sputtered coatings on their anode surfaces than observed to date on 2.3 kW-class xenon ion engines. The thickness of coatings on the anode of a 10 kW, 40-centimeter diameter thruster, for example, may be 22 micrometers or more after extended operation. Grit-blasted wire mesh, titanium, and aluminum coupons were coated with molybdenum at accelerated rates to establish coating stability after the deposition process and after thermal cycling tests. These accelerated deposition rates are roughly three orders of magnitude more rapid than the rates at which the screen grid is sputtered in a 2.3 kW-class, 30-centimeter diameter ion engine. Using both RF and DC sputtering processes, the molybdenum coating thicknesses ranged from 8 to 130 micrometers, and deposition rates from 1.8 micrometers per hour to 5.1 micrometers per hour. In all cases, the molybdenum coatings were stable after the deposition process, and there was no evidence of spalling of the coatings after 20 cycles from about -60 to +320 C. The stable, 130 micrometer molybdenum coating on wire mesh is 26 times thicker than the thickest coating found on the anode of a 2.3 kW, xenon ion engine that was tested for 8200 hr. Additionally, this coating on wire mesh coupon is estimated to be a factor of greater than 4 thicker than one would expect to obtain on the anode of the next generation ion engine which may have xenon throughputs as high as 550 kg.

Sovey, James S.↗
NASA NTRS2023

Partition Thickness Considerations for Additively Manufactured Acoustic Liners

Three types of uniform-depth liners are evaluated to explore the effects of partition thickness on the surface impedance achieved with additively manufactured liners. A transmission line code is used to predict the effects of sound transmission through empty chambers and wire mesh facesheets, and is combined with the Motsinger and Kraft model to account for sound transmission through perforated facesheets. The inclusion of partitions causes a blockage effect, i.e., a portion of the surface is ‘blocked’ (nonactive surface). For liners with no facesheet, these blockage effects are incorporated simply by accounting for the change in cross sectional area between the individual chamber and the unit cell that includes half of a partition thickness around the perimeter of this chamber. Comparison of impedances predicted in this manner with data acquired in the NASA Langley Normal Incidence Tube (NIT) confirms the efficacy of this modeling approach. Two approaches are considered to account for the inclusion of a wiremesh or perforated plate facesheet on these same cores. The first accounts for the effects of partition thickness before including the transfer impedance across the facesheet, while the second reverses these steps. A comparison of data acquired in the NASA NIT with modeled impedances suggests the first approach is best when the facesheet is a wire mesh, but the second approach is preferred when a perforated plate facesheet is used. It is hypothesized that this is due to the fact that a lumped element model is used to compute the transfer impedance across a wire mesh, while the corresponding transfer impedance across a perforated sheet explicitly incorporates the efffects of the liner core. However, comparisons of data acquired in the NASA Langley Grazing Flow Impedance Tube with modeled impedances seem slightly better when the first approach is employed with a perforated plate facesheet. Thus, the effects of partition thickness on liners with perforated sheets subjected to grazing incidence sound require further review

acoustic↗
NASA NTRSDate not supplied

Design and Analysis of Shape Memory Spring Tires for Martian and Lunar Rover Vehicles

Shape memory alloys (SMAs) have played an important role in various innovative engineering and medical applications, such as aerospace actuators, vibration damping devices, and coronary stents. In applications, shape memory alloys are commonly utilized in two fundamentally different ways: (i) making use of the superelasticity/ pseudoelasticity (SE/PE) phenomena, as in applications in biomedical engineering, and (ii) taking advantages of the shape memory effect (SME), as is used for actuators. Their ability to act in such vastly different capacities is mainly due to their unique capability to recover large amounts of deformation produced by either applied stresses or temperature changes. One recent emerging application in use of SMAs has been in the area of non-pneumatic tire designs for Martian or Lunar roving vehicles. These vehicles require tires that are capable of traversing rugged terrain while withstanding extreme temperatures and atmospheric conditions. Inspired by the flexible wire mesh tires used on three Lunar Roving Vehicle (LRV) missions to the Moon on Apollo 15, 16, and 17, a new compliant tire technology was developed by the NASA Glenn Research Center (GRC) and Goodyear Tire & Rubber, known as the Spring Tire. The Spring Tire consists of several hundred coiled springs woven into a flexible mesh and formed into the shape of a tire. Like the LRV wire mesh tires, the original Spring Tires were made from spring steel and were prone to permanent deformation when undergoing high localized loads. Later, a new iteration of this technology was invented, known as the ‘Superelastic Tire’. This new technology incorporated the use of superelastic SMA springs, which could effectively undergo approximately 30 times more reversible deformation than the steel spring. It also provided even greater durability and allowed for more flexibility in design, such as the use of other structural forms to reduce mass or increase load carrying capacity. Because of the unique nature of both the SMA material and the complex interactions between the springs, designing Spring Tires for a specific application requires extensive effort. Historically, design decisions have relied on full-scale empirical testing; however, this is very expensive and time consuming, especially when multiple iterations are needed. Therefore, developing a large-scale, robust, and predictive numerical model entailing complex spring interactions and the shape memory material behavior within a tire construct is the first essential step towards a successful design program. The current work focuses on implementation of the user-defined Shape Memory Alloy (SMA) model, otherwise known as SMA-GVIPs, in the Finite Element analysis (FEA) program ABAQUS for large-scale simulations of the GRC-developed Spring Tires made of SMA. The novelty of this work lies in the thorough, detail-oriented, and computationally efficient finite element analysis of full-scale SMA tires. A well-thought material characterization plan followed by model validation and a systemic sensitivity study on SMA tires has never been reported in the previous literature. The main objective of this study is to help the team improve and optimize the structural design of the SMA tires through in-depth numerical analysis and sensitivity studies. Various design variables (wire diameter, coil diameter, pitch, bead angle, and number of springs) were varied to study their influence on the global load-displacement response of the tire construct. A detailed investigation of the three-dimensional stress states was also carried out to enhance our understanding of the local changes as the tire goes through global deformation. It was concluded that a robust numerical model with a good predictive capability, together with a thoughtfully crafted sensitivity study can result in improved design iterations required to reach a desired tire performance while, significantly reducing manufacturing, labor and testing expenses. A summary of the Finite Element (FE) model construction will be presented together with a description of the user-defined SMA model, characterization process, experimental results, model validation, and numerical sensitivity study results.

shape memory alloys↗
NASA NTRS1979

Automated inspection of wire-frame assemblies

System improves accuracy of measurement between spaces of wire mesh and other wire frame assemblies while significantly reducing inspection time. Device operates automatically producing printout of measured spacings through use of optical scanner.

Etzel, J. G.↗
NASA NTRS1989

Measured and predicted root-mean-square errors in square and triangular antenna mesh facets

Deflection shapes of square and equilateral triangular facets of two tricot-knit, gold plated molybdenum wire mesh antenna materials were measured and compared, on the basis of root mean square (rms) differences, with deflection shapes predicted by linear membrane theory, for several cases of biaxial mesh tension. The two mesh materials contained approximately 10 and 16 holes per linear inch, measured diagonally with respect to the course and wale directions. The deflection measurement system employed a non-contact eddy current proximity probe and an electromagnetic distance sensing probe in conjunction with a precision optical level. Despite experimental uncertainties, rms differences between measured and predicted deflection shapes suggest the following conclusions: that replacing flat antenna facets with facets conforming to parabolically curved structural members yields smaller rms surface error; that potential accuracy gains are greater for equilateral triangular facets than for square facets; and that linear membrane theory can be a useful tool in the design of tricot knit wire mesh antennas.

Fichter, W. B.↗
NASA NTRS2011

Investigation of Flow Conditioners for Compact Jet Engine Simulator Rig Noise Reduction

The design requirements for two new Compact Jet Engine Simulator (CJES) units for upcoming wind tunnel testing lead to the distinct possibility of rig noise contamination. The acoustic and aerodynamic properties of several flow conditioner devices are investigated over a range of operating conditions relevant to the CJES units to mitigate the risk of rig noise. An impinging jet broadband noise source is placed in the upstream plenum of the test facility permitting measurements of not only flow conditioner self-noise, but also noise attenuation characteristics. Several perforated plate and honeycomb samples of high porosity show minimal self-noise but also minimal attenuation capability. Conversely, low porosity perforated plate and sintered wire mesh conditioners exhibit noticeable attenuation but also unacceptable self-noise. One fine wire mesh sample (DP450661) shows minimal selfnoise and reasonable attenuation, particularly when combined in series with a 15.6 percent open area (POA) perforated plate upstream. This configuration is the preferred flow conditioner system for the CJES, providing up to 20 dB of broadband attenuation capability with minimal self-noise.

Doty, Michael J.↗
NASA NTRS2022

Mars 2020 Perseverance Rover SHERLOC Instrument Isolation System

The NASA Jet Propulsion Laboratory (JPL) successfully landed the Mars 2020 Perseverance Rover at Jezero Crater on the Martian surface. Perseverance’s main mission objective is to cache Martian rock and regolith samples in hermetically sealed tubes to be brought back to Earth by future missions. To achieve this goal the rover is equipped with a 2-meter-long Robotic Arm (RA) which manipulates the Turret to interact with the surface. The Turret is comprised of science instruments and tools that enable surface sampling and science. The backbone of the Turret hardware is the Rotary Percussive Coring Drill. The science instruments, which are directly mounted to the structural housing of this drill, must be able to withstand not only the launch and entry, descent and landing (EDL) loads of the vehicle but also the dynamic percussive environment, induced by the drill throughout surface operations. This paper discusses the technical hardware design, development and testing of a vibration isolation system to protect the Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) Instrument from these dynamic environments. The hardware design aspect of this problem was limited by both size and mass constraints. The Turret is tightly configured and the physical space in which hardware can reside is restricted due to multiple axes of surface interaction points. Another driving requirement is the extreme range of thermal non-operational environment from -135C to +90C. This, in addition to SHERLOC being a heavier instrument than previously integrated on a turret, made the use of isolation systems employed on previous rover missions problematic. The final design incorporates custom wire mesh springs preloaded within titanium hexapod struts equipped with flexure ends. Custom versions of commercially available wire mesh springs were designed and tested. These custom springs differed in dimension, density and stiffness from the off the shelf options. The newly designed springs went through various stages of flight acceptance testing. Detailed physics-based modeling to understand what loads the isolation system would experience was used to define the test conditions for the springs and entire isolation subsystem. The testing program developed around this was extensive to fully characterize the isolation performance over cleanliness levels, temperature and life. Another major aspect of this work was developing a method of replicating the drill’s percussive environment for performance and life testing of Turret mounted hardware. Attaching the instrument to an operating drill for testing was not a viable option. A method of using a Highly Accelerated Life Test (HALT) table was developed and applied across the project as the most representative and tunable option to physically simulate this new environment. This method, along with launch environment random vibration testing, was used to build an entire dynamic qualification and flight hardware test program. The results of the design, modeling, testing and analysis of the SHERLOC Isolation System is described throughout the following paper.

Krafchak, Todd↗
NASA NTRS1980

Installing fiber insulation

A method for installing fragile, high temperature insulation batting in an elongated cavity or in a resilient wire sleeve to form a resilient seal. The batting is preformed to rough dimensions and wrapped in a plastic film, the film being of a material which is fugitive at a high temperature. The film is heat sealed and trimmed to form a snugly fit skin which overlaps at least at one end to permit attachment of a pull cord. The film absorbs the tensile force of pulling the film enclosed batting through the cavity or wire mesh sleeve and is subsequently driven off by high temperature baking, leaving only the insulation in the cavity or wire mesh sleeve.

Wang, D. S.↗
NASA NTRS1992

AXAF VETA-I mirror encircled energy measurements and data reduction

The AXAF VETA-I mirror encircled energy was measured with a series of apertures and two flow gas proportional counters at five X-ray energies ranging from 0.28 to 2.3 keV. The proportional counter has a thin plastic window with an opaque wire mesh supporting grid. Depending on the counter position, this mesh can cause the X-ray transmission to vary as much as +/-9 percent, which directly translates into an error in the encircled energy. In order to correct this wire mesh effect, window scan measurements were made, in which the counter was scanned in both horizontal (Y) and vertical (Z) directions with the aperture fixed. Post VETA measurement of the VXDS setup were made to determine the exact geometry and position of the mesh grid. Computer models of the window mesh were developed to simulate the X-ray transmission based on this measurement. The window scan data were fitted to such mesh models and corrections were made. After this study, the mesh effect was well understood and the final results of the encircled energy were obtained with an uncertainty of less than 0.8 percent.

Zhao, Ping↗
NASA NTRS1993

AXAF VETA-I mirror encircled energy measurements and data reduction

The AXAF VETA-I mirror encircled energy was measured with a series of apertures and two flow gas proportional counters at five X-ray energies ranging from 0.28 to 2.3 keV. The proportional counter has a thin plastic window with an opaque wire mesh supporting grid. Depending on the counter position, this mesh can cause the X-ray transmission to vary as much as +/- 9 percent, which directly translates into an error in the encircled energy. In order to correct this wire mesh effect, window scan measurements were made, in which the counter was scanned in both horizontal (Y) and vertical (Z) directions with the aperture fixed. Post VETA measurement of the VXDS setup were made to determine the exact geometry and position of the mesh grid. Computer models of the window mesh were developed to simulate the X-ray transmission based on this measurement. The window scan data were fitted to such mesh models and corrections were made. After this study, the mesh effect was well understood and the final results of the encircled energy were obtained with an uncertainty of less than 0.8 percent.

Zhao, Ping↗
NASA NTRS1970

Design and Manufacture of Wheels for A Dual-Mode (Manned - Automatic) Lunar Surface Roving Vehicle. Volume 1: Detailed Technical Report

The concept development, testing, evaluation, and the selection of a final wheel design concept for a dual-mode lunar surface vehicle (DLRV) is detailed. Four wheel configurations were fabricated (one open wheel and three closed wheel) (and subjected to a series of soft soil, mechanical, and endurance tests. Results show that the open wheel has lower draw-bar pull (slope climbing) capability in loose soil due to its higher ground pressure and tendency to dig in at high wheel slip. Endurance tests indicate that a double mesh, fully enclosed wheel can be developed to meet DLRV life requirements. There is, however, a 1.0 to 1.8 lb/wheel weight penalty associated with the wheel enclosure. Also the button cleats used as grousers for the closed-type wheels result in local stress concentration and early fatigue failure of the wire mesh. Load deflection tests indicate that the stiffness of the covered wheel increased by up to 50% after soil bin testing, due to increased friction between the fabric and the wire mesh caused by the sand. No change in stiffness was found for the open wheel. The single woven mesh open wheel design with a chevron tread is recommended for continued development

Source record↗
NASA NTRSDate not supplied

Benchmark Data for Evaluation of NASA Impedance Eduction Methods

Results achieved with three acoustic liner configurations are used to evaluate the effects of recent modifications to the NASA Normal Incidence Tube and Grazing Flow Impedance Tube. These include a calibration liner, a wire mesh liner, and a perforate liner. The effects of source type, source level, and mean flow Mach number on the impedances educed with these liners are explored. Existing models are used to predict the impedance for each test condition and are compared with educed impedance spectra to determine their validity. The results suggest that educed impedances are similar for either a stepped sine or swept sine source. The predicted models are acceptable for the perforate liner and are quite good for the calibration and wire mesh liners.

acoustic↗
NASA NTRSDate not supplied

Benchmark Data for Evaluation of NASA Impedance Eduction Methods

Results achieved with three acoustic liner configurations are used to evaluate the effects of recent modifications to the NASA Normal Incidence Tube and Grazing Flow Impedance Tube. These include a calibration liner, a wire mesh liner, and a perforate liner. The effects of source type, source level, and mean flow Mach number on the impedances educed with these liners are explored. Existing models are used to predict the impedance for each test condition, and are compared with educed impedance spectra to determine their validity. The results suggest that educed impedances are similar for either a stepped sine or swept sine source. The predicted models are acceptable for the perforate liner, and are quite good for the calibration and wire mesh liners.

acoustic↗
NASA NTRS1989

The divergence characteristics of constrained-sheath optics systems for use with 5-eV atomic oxygen sources

The potential usefulness of the constrained sheath optics concept as a means of controlling the divergence of low energy, high current density ion beams is examined numerically and experimentally. Numerical results demonstrate that some control of the divergence of typical ion beamlets can be achieved at perveance levels of interest by contouring the surface of the constrained sheath properly. Experimental results demonstrate that a sheath can be constrained by a wire mesh attached to the screen plate of the ion optics system. The numerically predicted beamlet divergence characteristics are shown to depart from those measured experimentally, and additional numerical analysis is used to demonstrate that this departure is probably due to distortions of the sheath caused by the fact that it attempts to conform to the individual wires that make up the sheath constraining mesh. The concept is considered potentially useful in controlling the divergence of ion beamlets in applications where low divergence, low energy, high current density beamlets are being sought, but more work is required to demonstrate this for net beam ion energies as low as 5 eV.

Anderson, John R.↗
NASA NTRS1984

Hy-wire measurements of atmospheric potential

A method for directly measuring the electric potential drop across the lowest portion of the atmosphere by using an apparatus called Hy-wire is described. The Hy-wire system consists of a long, high-voltage, insulated conductor connected at the top to a wire-mesh braid and terminated at the bottom inside a large-diameter corona ball mounted on 1 m Teflon legs. The system impedance is near 10 billion ohms, while the grounded mode, Hy-wire draws about 10 micro-a at 500 m altitude. Around-the-clock measurements with characteristic peaks near 1530 and 1900 UT of potentials near 125,000 volts are presented, with total daily average potential near 90,000 volts at 507 m altitude. The experimental weather conditions varied from clear to local fog, except that there was only trace precipitation. The data have been interpreted in terms of the possible source of the potential variations; neither a local nor a global source is clearly indicated.

Holzworth, R. H.↗