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A matrix Fredholm integral equation of neuronal networks is transformed into a Cauchy system suited for numerical and analytical studies. A special case is discussed, and a connection with the classical renewal integral equation of stochastic point processes is presented.
Current emphasis in the aircraft industry toward reducing manufacturing cost has created a renewed interest in integrally stiffened structures. Crack turning has been identified as an approach to improve the damage tolerance and fail-safety of this class of structures. A desired behavior is for skin cracks to turn before reaching a stiffener, instead of growing straight through. A crack in a pressurized fuselage encounters high T-stress as it nears the stiffener--a condition favorable to crack turning. Also, the tear resistance of aluminum alloys typically varies with crack orientation, a form of anisotropy that can influence the crack path. The present work addresses these issues with a study of crack turning in two-dimensions, including the effects of both T-stress and fracture anisotropy. Both effects are shown to have relation to the process zone size, an interaction that is central to this study. Following an introduction to the problem, the T-stress effect is studied for a slightly curved semi-infinite crack with a cohesive process zone, yielding a closed form expression for the future crack path in an infinite medium. For a given initial crack tip curvature and tensile T-stress, the crack path instability is found to increase with process zone size. Fracture orthotropy is treated using a simple function to interpolate between the two principal fracture resistance values in two-dimensions. An extension to three-dimensions interpolates between the six principal values of fracture resistance. Also discussed is the transition between mode I and mode II fracture in metals. For isotropic materials, there is evidence that the crack seeks out a direction of either local symmetry (pure mode I) or local asymmetry (pure mode II) growth. For orthotropic materials the favored states are not pure modal, and have mode mixity that is a function of crack orientation.
The National Aeronautics and Space Administration (NASA) is working towards developing and demonstrating new technologies, capabilities, and business approaches that are needed for future human deep space exploration missions. This includes collaborating with commercial and international partners to establish the first long-term presence on the Moon under the Artemis mission. Artemis lunar surface operations begin with robotically exploring the lunar south polar region for locations suitable for harvesting lunar surface resources. Over time, activities will expand beyond robotic operations, increasing the need for highly reliable and available electrical power. Beyond Artemis, there are interests in full commercial lunar surface activities. A lunar microgrid is being proposed to deliver highly reliable and available electrical power on the lunar surface and meet the power needs. Microgrids are of interest in terrestrial applications due to their ability to integrate a variety of renewable power sources. A similar approach can be taken for the lunar surface. A lunar microgrid would offer the ability to integrate various power sources to maximize power availability, including nuclear, solar arrays, batteries, and regenerative fuel cells. Microgrids are flexible and can be designed to allow for islanded operation, where power is utilized near the loads to minimize power distribution losses, or in a power sharing mode where power is transmitted longer distances. This capability is crucial during failures where overall power availability is reduced. Microgrids will also allow for the power system to grow and evolve over time, meeting the need to expand beyond initial lunar surface activities.
In line with the Sustainable D.C. 2.0 plan to combat climate change, Washington D.C. aims to decrease its greenhouse gas emissions by 100% by 2050. As solar energy is a clean, renewable energy form, its integration into the region’s power grids lowers energy costs and incentivizes sustainable development. We partnered with the Washington D.C. Department of Energy & Environment (DOEE) to determine how urban areas surrounding D.C. can better be incorporated into decisions regarding renewable energy policy. The team used NASA’s Prediction of Worldwide Energy Resources (POWER) solar data and a Light Detection and Ranging (LiDAR) derived digital surface model, to estimate and visualize rooftop solar potential for Maryland’s Prince George’s and Montgomery counties. POWER provided solar irradiance data adjusted for tilt angle while the digital surface model contributed aspect and slope data. This methodology factored out areas that were unsuitable for solar panel installation while displaying areas that possess a high potential for energy return. The team found the total rooftop solar potential for the study area to be almost 32 million kW, which is equivalent to roughly 660 kW per building. The methodology used to generate the solar potential maps can be applied to other regions of the country seeking to efficiently utilize solar energy. The end users at the DOEE can use our resulting solar potential map and data table to effectively target buildings that have the highest potential to generate solar energy.
Integrating CO2 utilization and renewable energy delivery/storage, the rechargeable Li–CO2 battery has been considered as a promising candidate for next-generation secondary batteries. However, high-performance catalyst(s) for efficient formation and decomposition of the discharge product, Li2CO3, are an imperative part of a Li–CO2 battery. The development of flexible Li–CO2 batteries extends their applications into compliant and wearable devices/systems, but at the same time imposes a big challenge for battery fabrication and lifetime enhancement. In this study, a rechargeable quasi-solidus flexible Li–CO2 battery was designed and fabricated using highly active N,S-doped carbon nanotubes (N,S-doped CNTs) as the cathode catalyst, and a smart polymer gel as the flexible electrolyte. This newly-developed flexible Li–CO2 battery exhibited a capacity as high as 23560 mAh g−1 based on the catalyst mass and an ultra-long lifetime of up to 538 cycles with excellent mechanical flexibility. This work provides a platform for the design and development of high-performance flexible Li–CO2 batteries from low-cost, earth-abundant, carbon-based multifunctional cathode catalysts.
The continual need to reduce airframe cost and the emergence of high speed machining and other manufacturing technologies has brought about a renewed interest in large-scale integral structures for aircraft applications. Applications have been inhibited, however, because of the need to demonstrate damage tolerance, and by cost and manufacturing risks associated with the size and complexity of the parts. The Integral Airframe Structures (IAS) Program identified a feasible integrally stiffened fuselage concept and evaluated performance and manufacturing cost compared to conventional designs. An integral skin/stiffener concept was produced both by plate hog-out and near-net extrusion. Alloys evaluated included 7050-T7451 plate, 7050-T74511 extrusion, 6013-T6511 extrusion, and 7475-T7351 plate. Mechanical properties, structural details, and joint performance were evaluated as well as repair, static compression, and two-bay crack residual strength panels. Crack turning behavior was characterized through panel tests and improved methods for predicting crack turning were developed. Manufacturing cost was evaluated using COSTRAN. A hybrid design, made from high-speed machined extruded frames that are mechanically fastened to high-speed machined plate skin/stringer panels, was identified as the most cost-effective manufacturing solution. Recurring labor and material costs of the hybrid design are up to 61 percent less than the current technology baseline.
Renewable energy sources and their integration with other power sources to support remote communities is of interest for Mars applications as well as Earth communities. The National Science Foundation (NSF), NASA, and the Department of Energy (DOE) have been jointly supporting development of a 100 kW cold weather wind turbine through grants and SBIRs independently managed by each agency but coordinated by NASA. The NSF grant addressed issues associated with the South Pole application and a 3 kW direct drive unit is being tested there in anticipation of the 100 kW unit operation. The DOE-NREL contract focused on development of the 100 kW direct drive generator. The NASA SBIR focused on the development of the 100 kW direct drive wind turbine. The success of this effort has required coordination and team involvement of federal agencies and the industrial partners. Designs of the wind turbine and component performance testing results will be presented. Plans for field testing of wind turbines, based on this design, in village energy systems in Alaska and in energy production at the South Pole Station will be discussed. Also included will be a discussion of terrestrial and space use of hybrid energy systems, including renewable energy sources, such as the wind turbine, to support remote communities.
The primary purpose of this project was to evaluate and improve models for the bulk-skin temperature difference to the point where they could accurately and reliably apply under a wide variety of environmental conditions. To accomplish this goal, work was conducted in three primary areas. These included production of an archive of available data sets containing measurements of the skin and bulk temperatures and associated environmental conditions, evaluation of existing skin layer models using the compiled data archive, and additional theoretical work on the development of an improved model using the data collected under diverse environmental conditions. In this work we set the basis for a new physical model of renewal type, and propose a parameterization for the temperature difference across the cool skin of the ocean in which the effects of thermal buoyancy, wind stress, and microscale breaking are all integrated by means of the appropriate renewal time scales. Ideally, we seek to obtain a model that will accurately apply under a wide variety of environmental conditions. A summary of the work in each of these areas is included in this report. A large amount of work was accomplished under the support of this grant. The grant supported the graduate studies of Sandra Castro and the preparation of her thesis which will be completed later this year. This work led to poster presentations at the 1999 American Geophysical Union Fall Meeting and 2000 IGARSS meeting. Additional work will be presented in a talk at this year's American Meteorological Society Air-Sea Interaction Meeting this May. The grant also supported Sandra Castro during a two week experiment aboard the R/P Flip (led by Dr. Andrew Jessup of the Applied Physics Laboratory) to help obtain additional shared data sets and to provide Sandra with a fundamental understanding of the physical processes needed in the models. In a related area, the funding also partially supported Dr. William Emery and Daniel Baldwin in the preparation of their publication "Accuracy of in situ sea surface temperatures used to calibrate infrared satellite measurements". The remainder of this report is drawn from these publications and presentations.
Detailed characterization of neotectonics evolution of the Valle de San Felipe and Arroyo Grande regions in northern Baja California. Reoccupied GEOMEX GPS sites, and occupied a regional GPS (Global Positioning System) network. The Baja California peninsula in Mexico offers a unique setting for studying the kinematic evolution of a complex, active strike-slip/rift plate boundary. We are currently conducting remote sensing, geologic, and geodetic studies of this boundary. The combined data sets will yield instantaneous and time integrated views of its evolution. This proposal solicits renewed funding from NASA to support remote sensing and geologic studies. During the late Cenozoic, Baja California has been the locus of changing fault geometry that has accommodated components of the relative motion between the North America and Pacific plates. Contemporary slip between the two plates occurs in a broad zone that encompasses much of southern California and the Baja California Peninsula. The transfer of slip across this zone in southern California is relatively well understood. South of the border, the geometry and role of specific faults and structural provinces in transferring plate margin deformation across the peninsula is enigmatic. Results We use Landsat Thematic Mapper imagery of the Baja California Peninsula to identify recent and active faults, and then conduct field studies that characterize the temporal and spatial structural evolution of the plate margin. These data address questions concerning the neotectonic development of the Gulf of California, the Baja California Peninsula, and their role in evolution of the post-Miocene Pacific - North American plate boundary. Moreover, these studies provide constraints on the geometry of active faults, allowing more exact understanding of the results of ongoing NASA-supported geodetic experiments. In addition, anticipated publication of the TM scenes will provide a widely available geological data base for relatively little-known peninsula California. Achievements include development of an ArcInfo data base of Landsat and SPOT imagery, detailed field studies of Neogene structures in northeastern Baja California, and new constraint on Pacific - North America plate motion at Baja California latitudes. These results are reported in maps, manuscripts and data products which are published or near completion.
The Hybrid-Laminar Flow Control (HLFC) Crossflow Experiment, completed in 1995. generated a large database of boundary layer stability and transition data that was only partially analyzed before data analysis was abruptly ended in the late 1990's. Renewed interest in laminar flow technologies prompted additional data analysis, to integrate all data, including some post-test roughness and porosity measurements. The objective is to gain new insights into the effects of suction on boundary layer stability. A number of challenges were encountered during the data analysis, and their solutions are discussed in detail. They include the effect of the probe vibration, the effect of the time-varying surface temperature on traveling crossflow instabilities, and the effect of the stationary crossflow modes on the approximation of wall location. Despite the low turbulence intensity of the wind tunnel (0.01 to 0.02%), traveling crosflow disturbances were present in the data, in some cases at amplitudes up to 1% of the freestream velocity. However, the data suggests that transition was dominated by stationary crossflow. Traveling crossflow results and stationary data in the presence of suction are compared with linear parabolized stability equations results as a way of testing the quality of the results.
Declining supplies of domestic oil and gas and the increased cost of energy resulted in a renewed emphasis in utilizing available resources in the most efficient manner possible. This, in turn, brought about a reassessment of a number of methods for converting fossil fuels to end uses at the highest practical efficiency. One of these is the on-site integrated energy system (OS/IES). This system provides electric power from an on-site power plant and recovers heat from the power plant that would normally be rejected to the environment. An OS/IES is potentially useful in any application that requires both electricity and heat. Several OS/IES are analyzed for a residential complex. The paper is divided into two sections; the first compares three energy supply systems, the second compares various designs for fuel cell OS/IES.
The US National Research Council (NRC) recommended that: "The U.S. government, working in concert with the private sector, academe, the public, and its international partners, should renew its investment in Earth-observing systems and restore its leadership in Earth science and applications." in response to the NASA Earth Science Division's request to prioritize research areas, observations, and notional missions to make those objectives. In this presentation, we will discuss our approach to connect remote sensing science to decision support applications by establishing a framework to integrate direct measurements, earth system models, inventories, and other information to accurately estimate fresh water resources in global, regional, and local scales. We will discuss our demonstration projects and lessons learned from the experience. Deploying a monitoring system that offers sustained, accurate, transparent and relevant information represents a challenge and opportunity to a broad community spanning earth science, water resource accounting and public policy. An introduction to some of the scientific and technical infrastructure issues associated with monitoring systems is offered here to encourage future treatment of these topics by other contributors as a concluding remark.
Interest in inward-turning supersonic inlets renewed during NASA’s Commercial Supersonic Technology Project, as a means of reducing disturbances caused by propulsion integration. Inward-turning designs have the potential to greatly reduce the strength of shock waves emanating outward from the nacelle, and therefore their contribution to the overall sonic boom signature. For top-mounted, or over-wing installations, disturbances to aircraft aerodynamics are reduced. The nature of the inward-turning geometry results in a boundary-layer thickening effect, opposite that of the familiar thinning of an outward-turning cone boundary-layer. The application of a small amount of boundary-layer bleed at the throat has been shown to alleviate the negative effects of the boundary-layer on subsonic diffuser performance. Boundary-layer bleed, however, comes at the expense of increased complexity, and external disturbances at bleed exits that would partially defeat the purpose of the inward-turning scheme. Vortex generators were proposed as an alternative to bleed, and an initial CFD study of their effectiveness in this application forms the basis of the present work. A source-term model in the Wind-US CFD code was used to model the effects of an array of vortex generators placed at the entrance to the subsonic diffuser. Baseline results with no vortex generators compared favorably to previously reported results with no bleed at back-pressures near the design point, but stability margin in the present case was limited by a curious non-linear phenomena similar to unstart in mixed-compression inlets. While some improvement was noted with vortex generators, their effectiveness was diminished by the limited stability margin. A time-accurate calculation was subsequently performed to better understand this process. Results of this calculation are presented and instantaneous solutions compared with steady-state, subcritical results previously reported. The stability margin limitation is attributed to the use of a constant-pressure outflow boundary condition, which differed from that used in the prior simulations.
Space Geodesy Satellite Laser Ranging (SGSLR) is a component of NASA’s Space Geodesy Project. It is an initiative to renew and expand NASA’s Geodetic Network. SGSLR at Ny-Ålesund is being developed, deployed, and integrated into the NASA Network by KBR Wyle, in partnership between NASA and Kartverket.
There is a large gap between the production and demand for energy from alternative fuel and alternative renewable energy sources. The NASA Glenn Research Center (GRC) has initiated a laboratory-pilot study that concentrates on using biofuels as viable alternative fuel resources for the field of aviation, as well as, utilizing wind and solar technologies as alternative renewable energy resources, and in addition, the use of pumped water for storage of energy that can be retrieved through hydroelectric generation. This paper describes the GreenLab Research Facility and its power and energy sources with .recommendations for worldwide expansion and adoption of the concept of such a facility
A receiver autonomous integrity monitoring (RAIM) scheme has been implemented in a real time, prototype hybrid GPS/LORAN receiver. A four-channel GPS receiver and an eight-channel LORAN-C receiver are used to obtain raw GPS and LORAN pseudorange measurements. The measurement data is sent to a microcomputer for position and integrity determination. Navigation data is presented to the pilot on a standard course deviation indicator with a data renewal rate of up to one update per second. Provisions are made to simulate signal malfunctions in real time by injecting step or ramp failures in the pseudorange measurements. A least-squares fault detection algorithm is presented for the detection of slowly growing measurement errors. The performance of the hybrid GPS/LORAN receiver has been demonstrated through actual flight tests. One of the flight tests is summarized in the paper.
Currently, when the Reynolds-Averaged Navier-Stokes (RANS) equations are solved using turbulence modeling, most often the one-equation model of Spalart and Allmaras is used. Then, it is only necessary to solve the RANS equations in conjunction with a single transport equation for modeling turbulence. For this model, considerable assessment and analysis has been performed, allowing the possibility of a reliable solution method for an eddy viscosity required to compute the Reynolds stresses in the RANS equations. Such evaluation along with analysis has not been achieved to realize similar performance with two-equation models of the k-w type. The primary objective of this paper is to present and discuss the components of an effective numerical algorithm for solving the RANS equations and the two transport equations of k-w type turbulence models. All the important details of the turbulence model as actually implemented are given, which is sometimes not done in various papers considering such modeling. The viability and effectiveness of this solution algorithm are demonstrated by solving both two-dimensional and three-dimensional aerodynamic flows. In all applications, a linear rate of convergence without oscillations or other evidence of unstable behavior is observed. This behavior is also particularly true when the proposed algorithm is applied to systematically renewed mesh sequences, which is generally not observed with algorithms solving more than one transport equation. Thus, numerical integration errors are systematically reduced, allowing for a significantly more reliable assessment of the effectiveness of the turbulence model. Additionally, in this paper, analysis of the solution algorithm, including linear stability, is also performed for a particular flow problem.
Power system selection for outer planet destinations, such as Jupiter, Saturn, and Uranus and beyond, is complex, involving and dependent on many interdisciplinary factors such as power system mass, specific power, cost, mechanical and electrical integration, and natural radiation environment. Low solar irradiance at Jupiter, Saturn, and Uranus systems (i.e., 50, 15, and 4 W/m2 , respectively) makes solar power systems challenging in mechanical / electrical integration and accommodating radiation environments. More costly radioisotope thermoelectric generator (RTG) systems can help proposed missions overcome radiation environment and spacecraft control challenges at Jupiter, Saturn, and Uranus. NASA’s Jet Propulsion Laboratory (JPL) has recently made significant strides in demonstrating high-efficiency, radiation-hard solar cell technologies for low-irradiance, low-temperature (LILT) applications, and high-efficiency thermoelectric (TE) materials and modules for higher-specific-power RTGs. Stateof-art multi-junction solar cells now routinely demonstrate high efficiencies of 30-34% at LILT (9.5AU and -165°C), making solar arrays a viable option for many near-term Saturn mission concepts. Emerging technologies like LILToptimized solar cells have recently demonstrated even higher efficiencies of 37% at 9.5AU and -165°C and 30% lower mass than the state-of-art, offering the prospect of ~3W/kg array-level, end-of-life specific powers under Saturn conditions. Having already demonstrated the tremendous utility of RTGs on Mars and in deep-space missions (e.g., Galileo at Jupiter, New Horizons at Pluto), NASA is now developing and demonstrating new TE materials and modules (e.g., skutterudites, La3-x Te4, and Zintls) for increasing RTG specific power (up to >8.5 W/kg), which strongly impacts an RTG’s mass, fuel utilization, and modularity in the power system trade domain. New accomplishments in both areas highlight the renewed requisite for updated comparisons and trade-offs in power output, specific power and mass, cost, mechanical and electrical integration, new technology timelines, and natural radiation impacts between new LILT-optimized photovoltaic technologies and next-generation RTG technologies. This work discusses and demonstrates how new LILT-based technologies are now allowing one to consider and design solar power systems for Saturn orbit and beyond, and are changing the potential cost-mass trade-offs between emerging solar power technologies and newly-envisioned RTG technologies. Key updated system mass and cost trade-offs between high-performance LILT solar technologies and new RTG technologies are presented, reinforcing and refining power selection criteria supporting possible future NASA deep-space science and exploration missions to Mars, the Jupiter system (Europa, Ganymede), the Saturn system (Titan, Enceladus), Uranus, and beyond. Key trade-offs in other above-mentioned interdisciplinary factors between these two power technologies are also discussed.