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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 487 records · Page 27

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NASA NTRS1990

Satellite range delay simulator for a matrix-switched time division multiple-access network simulation system

The Systems Integration, Test, and Evaluation (SITE) facility at NASA Lewis Research Center is presently configured as a satellite-switched time division multiple access (SS-TDMA) network simulator. The purpose of SITE is to demonstrate and evaluate advanced communication satellite technologies, presently embodied by POC components developed under NASA contracts in addition to other hardware, such as ground terminals, designed and built in-house at NASA Lewis. Each ground terminal in a satellite communications system will experience a different aspect of the satellite's motion due mainly to daily tidal effects and station keeping, hence a different duration and rate of variation in the range delay. As a result of this and other effects such as local oscillator instability, each ground terminal must constantly adjust its transmit burst timing so that data bursts from separate ground terminals arrive at the satellite in their assigned time slots, preventing overlap and keeping the system in synchronism. On the receiving end, ground terminals must synchronize their local clocks using reference transmissions received through the satellite link. A feature of the SITE facility is its capability to simulate the varying propagation delays and associated Doppler frequency shifts that the ground terminals in the network have to cope with. Delay is ahcieved by means of two NASA Lewis designed and built range delay simulator (RDS) systems, each independently controlled locally with front panel switches or remotely by an experiment control and monitor (EC/M) computer.

Nagy, Lawrence A.↗

NASA NTRS1973

Bayesian estimation of life parameters in the Weibull distribution.

Development of a Bayesian analysis of the scale and shape parameters in the Weibull distribution and the corresponding reliability function with respect to the usual life-testing procedures. For the scale parameter theta, Bayesian estimates of theta and reliability are obtained for the uniform, exponential, and inverted gamma prior probability densities. Bhattacharya's results (1967) for the one-parameter exponential life-testing distribution are reduced to a special case of these results. A fully Bayesian analysis of both the scale and shape parameters is developed by assuming independent prior distributions; since in the latter case, analytical tractability is not possible, Bayesian estimates are obtained through a conjunction of Monte Carlo simulation and numerical-integration techniques. In both cases, a computer simulation is carried out, and a comparison is made between the Bayesian and the corresponding minimum-variance unbiased, or maximum likelihood, estimates. As expected, the Bayesian estimates are superior.

Canavos, G. C.↗

NASA NTRS1987

Performance limitations in parallel processor simulations

A jet-engine model is partitioned and simulated on a parallel processor system consisting of five 8086/8087 floating-point computers. The simulation uses Heun's integration method. A near-optimal parallel simulation (in the sense of minimum execution time) achieves speedup of only 2.13 and efficiency of 42.6 percent, in effect wasting 57.4 percent of the available processing power. A detailed analysis identifies and graphically demonstrates why the system fails to achieve ideal performance (viz., speedup of 5 and efficiency of 100 percent). Inherent characteristics of the problem equations and solution algorithm account for the loss of nearly half of the available processing power. Overheads associated with interprocessor communication and processor synchronization account for only a small fraction of the lost processing power. The effects of these and other factors which limit parallel processor performance are illustrated through real-time timing-analyzer tracers describing the run/idle status of the parallel processors during the simulation.

O'Grady, E. Pearse↗

NASA NTRS2010

Post2 End-to-End Descent and Landing Simulation for ALHAT Design Analysis Cycle 2

The ALHAT project is an agency-level program involving NASA centers, academia, and industry, with a primary goal to develop a safe, autonomous, precision-landing system for robotic and crew-piloted lunar and planetary descent vehicles. POST2 is used as the 6DOF descent and landing trajectory simulation for determining integrated system performance of ALHAT landing-system models and lunar environment models. This paper presents updates in the development of the ALHAT POST2 simulation, as well as preliminary system performance analysis for ALDAC-2 used for the testing and assessment of ALHAT system models. The ALDAC-2 POST2 Monte Carlo simulation results have been generated and focus on HRN model performance with the fully integrated system, as well performance improvements of AGNC and TSAR model since the previous design analysis cycle

Davis, Jody L.↗

NASA NTRS2023

Space Weathering at the Moon

In this paper we summarize the substantial recent progress in understanding space weathering that has occurred through technical innovations in the laboratory and in space, including employment of ultra-high-resolution imaging of lunar samples, a wave of new remote sensing observations, samples returned from asteroid regolith, and new methods for simulating space weathering to gain insight into its mechanisms. The paper begins with a summary of space weathering processes and their observed effects on lunar samples (Section 2). It then describes new insights gleaned from remote sensing at a broadened range of wavelengths (Section 3.1) and from observations of special lunar environments where space weathering inputs vary, such as the intensity of solar wind at lunar swirls or in permanent shadow in polar regions (Section 3.2). We then outline how laboratory simulations have informed the understanding of space weathering mechanisms and rates (Section 4). Finally, we discuss the integrated observations and simulations and the current state of our knowledge (Section 5) and make suggestions for future investigations (Section 6).

moon↗

NASA NTRS2003

Development of an Output-based Adaptive Method for Multi-Dimensional Euler and Navier-Stokes Simulations

The use of computational simulations in the prediction of complex aerodynamic flows is becoming increasingly prevalent in the design process within the aerospace industry. Continuing advancements in both computing technology and algorithmic development are ultimately leading to attempts at simulating ever-larger, more complex problems. However, by increasing the reliance on computational simulations in the design cycle, we must also increase the accuracy of these simulations in order to maintain or improve the reliability arid safety of the resulting aircraft. At the same time, large-scale computational simulations must be made more affordable so that their potential benefits can be fully realized within the design cycle. Thus, a continuing need exists for increasing the accuracy and efficiency of computational algorithms such that computational fluid dynamics can become a viable tool in the design of more reliable, safer aircraft. The objective of this research was the development of an error estimation and grid adaptive strategy for reducing simulation errors in integral outputs (functionals) such as lift or drag from from multi-dimensional Euler and Navier-Stokes simulations. In this final report, we summarize our work during this grant.

Darmofal, David L.↗

NASA NTRS2010

Test Results from a Direct Drive Gas Reactor Simulator Coupled to a Brayton Power Conversion Unit

Component level testing of power conversion units proposed for use in fission surface power systems has typically been done using relatively simple electric heaters for thermal input. These heaters do not adequately represent the geometry or response of proposed reactors. As testing of fission surface power systems transitions from the component level to the system level it becomes necessary to more accurately replicate these reactors using reactor simulators. The Direct Drive Gas-Brayton Power Conversion Unit test activity at the NASA Glenn Research Center integrates a reactor simulator with an existing Brayton test rig. The response of the reactor simulator to a change in Brayton shaft speed is shown as well as the response of the Brayton to an insertion of reactivity, corresponding to a drum reconfiguration. The lessons learned from these tests can be used to improve the design of future reactor simulators which can be used in system level fission surface power tests.

Hervol, David S.↗

NASA NTRS1982

Computer simulations of postural change, water immersion and bedrest - An integrative approach for understanding the spaceflight response

Mathematical modeling techniques were used to simulate the fluid electrolyte (F-E) responses during gravity unloading. It is shown that the response to weightlessness can best be understood by separately examining the acute (hours to days) and chronic (days to weeks) phases, and assuming the presence of normal, although complex, feedback regulatory processes. Headward shifts of fluid are shown to be primarily responsible for acute body losses of extracellular F-E. Losses of body water are closely related to the volume of fluid shifts from the legs. A diuresis is predicted within the first several hours of hypogravity, and this may be obscured by a reduced F-E intake; on Skylab, early F-E losses occurred primarily by deficit intake.

Leonard, J. I.↗

NASA NTRS1991

A stochastic regulator for integrated communication and control systems. I - Formulation of control law. II - Numerical analysis and simulation

A state feedback control law for integrated communication and control systems (ICCS) is formulated by using the dynamic programming and optimality principle on a finite-time horizon. The control law is derived on the basis of a stochastic model of the plant which is augmented in state space to allow for the effects of randomly varying delays in the feedback loop. A numerical procedure for synthesizing the control parameters is then presented, and the performance of the control law is evaluated by simulating the flight dynamics model of an advanced aircraft. Finally, recommendations for future work are made.

Liou, Luen-Woei↗

NASA NTRS2011

Integration of Weather Avoidance and Traffic Separation

This paper describes a dynamic convective weather avoidance concept that compensates for weather motion uncertainties; the integration of this weather avoidance concept into a prototype 4-D trajectory-based Airborne Separation Assurance System (ASAS) application; and test results from a batch (non-piloted) simulation of the integrated application with high traffic densities and a dynamic convective weather model. The weather model can simulate a number of pseudo-random hazardous weather patterns, such as slow- or fast-moving cells and opening or closing weather gaps, and also allows for modeling of onboard weather radar limitations in range and azimuth. The weather avoidance concept employs nested "core" and "avoid" polygons around convective weather cells, and the simulations assess the effectiveness of various avoid polygon sizes in the presence of different weather patterns, using traffic scenarios representing approximately two times the current traffic density in en-route airspace. Results from the simulation experiment show that the weather avoidance concept is effective over a wide range of weather patterns and cell speeds. Avoid polygons that are only 2-3 miles larger than their core polygons are sufficient to account for weather uncertainties in almost all cases, and traffic separation performance does not appear to degrade with the addition of weather polygon avoidance. Additional "lessons learned" from the batch simulation study are discussed in the paper, along with insights for improving the weather avoidance concept. Introduction

Consiglio, Maria C.↗

NASA NTRS2016

Integrated Turbine Tip Clearance and Gas Turbine Engine Simulation

Gas turbine compressor and turbine blade tip clearance (i.e., the radial distance between the blade tip of an axial compressor or turbine and the containment structure) is a major contributing factor to gas path sealing, and can significantly affect engine efficiency and operational temperature. This paper details the creation of a generic but realistic high pressure turbine tip clearance model that may be used to facilitate active tip clearance control system research. This model uses a first principles approach to approximate thermal and mechanical deformations of the turbine system, taking into account the rotor, shroud, and blade tip components. Validation of the tip clearance model shows that the results are realistic and reflect values found in literature. In addition, this model has been integrated with a gas turbine engine simulation, creating a platform to explore engine performance as tip clearance is adjusted. Results from the integrated model explore the effects of tip clearance on engine operation and highlight advantages of tip clearance management.

aerothermodynamics↗

NASA NTRS2016

Integrated Turbine Tip Clearance and Gas Turbine Engine Simulation

gas path dynamics↗

NASA NTRS1989

Applications of a general thermal/hydraulic simulation tool

The analytic techniques, sample applications, and development status of a general-purpose computer program called SINDA '85/FLUINT (for systems improved numerical differencing analyzer, 1985 version with fluid integrator), designed for simulating thermal structures and internal fluid systems, are described, with special attention given to the applications of the fluid system capabilities. The underlying assumptions, methodologies, and modeling capabilities of the system are discussed. Sample applications include component-level and system-level simulations. A system-level analysis of a cryogenic storage system is presented.

Cullimore, B. A.↗

NASA NTRS1994

Modification of ACSYNT aircraft computer program for preliminary design

This paper presents the development of a computer simulation of agility flight test techniques. Its purpose is to evaluate the agility of aircraft configurations early in the preliminary design phase. The simulation module is integrated into the NASA Ames aircraft synthesis design code. Trade studies using the agility module embedded within the design code to simulate the combat cycle time agility metric are illustrated using a Northrop F-20 aircraft model. Results show that the agility module is effective in analyzing the influence of common parameters such as thrust-to-weight ratio and wing loading on agility criteria. The module can also compare the agility potential between different configurations and has the capability to optimize agility performance early in the design process.

Biezad, Daniel J.↗

NASA NTRS1997

A Flight Deck Perspective of Self-Separation

I will be participating on a Free Flight Human Factors Panel at the Ninth International Symposium on Aviation Psychology in Columbus, Ohio. My representation is related to the work that our group has conducted on flight deck issues associate with free flight. Our group completed a full-mission simulation study investigating procedural issues associated with airborne self-separation. Ten crews flew eight scenarios each in the B747-400 simulator at Ames. Each scenario had a representation of different conflict geometries with intruder aircraft. New alerting logic was created and integrated into the simulator to enable self-separation. In addition, new display features were created to help provide for enhanced information to the flight crew about relevant aircraft, The participants were asked to coordinate maneuvers for self-separation with the intruder aircraft. Data analyses for the many of the crew procedures have been completed.

Lozito, Sandra↗

NASA NTRS1980

An integrative approach to space-flight physiology using systems analysis and mathematical simulation

An approach was developed to aid in the integration of many of the biomedical findings of space flight, using systems analysis. The mathematical tools used in accomplishing this task include an automated data base, a biostatistical and data analysis system, and a wide variety of mathematical simulation models of physiological systems. A keystone of this effort was the evaluation of physiological hypotheses using the simulation models and the prediction of the consequences of these hypotheses on many physiological quantities, some of which were not amenable to direct measurement. This approach led to improvements in the model, refinements of the hypotheses, a tentative integrated hypothesis for adaptation to weightlessness, and specific recommendations for new flight experiments.

Leonard, J. I.↗

NASA NTRS2000

Free Flight Simulation: An Initial Examination of Air-Ground Integration Issues

The concept of "free flight" is intended to emphasize more flexibility for operators in the National Airspace System (RTCA, 1995). This may include the potential for aircraft self-separation. The purpose of this simulation was to begin examining some of the communication and procedural issues associated with self-separation in an integrated air-ground environment. Participants were 10 commercial U.S. flight crews who flew the B747-400 simulator and 10 Denver ARTCC controllers who monitored traffic in an ATC simulation. A prototypic airborne alerting logic and flight deck display features were designed to allow for increased traffic and maneuvering information. Eight different scenarios representing different conflict types were developed. The effects of traffic density (high and low) and different traffic convergence angles (obtuse, acute, and right) were assessed. Conflict detection times were found to be lower for the flight crews in low density compared to high density scenarios. For the controllers, an interaction between density and convergence angle was revealed. Analyses on the controller detection times found longer detection times in the obtuse high density compared to obtuse low density, as well as the shortest detection times in the high density acute angle condition. Maneuvering and communication events are summarized, and a discussion of future research issues is provided.

Lozito, Sandra↗

NASA NTRS1977

Nonaxisymmetric nozzle technology program - An overview

Nonaxisymmetric nozzles, with in-flight thrust vectoring and/or reversing capabilities, provide the potential for substantial gains in fighter aircraft performance, maneuvering, survivability and ground handling. This paper presents an overview of some of the current programs to develop nonaxisymmetric nozzle technology for future aircraft applications. The initial phase of this program, which consists of a series of subscale model tests, engine/nozzle studies, system integration studies and simulation studies, has been initiated. Successful completion of this program will allow designers of future aircraft to consider, with high confidence, the integration of nonaxisymmetric nozzle concepts to improve aircraft mission performance effectiveness, survivability and cost.

Berrier, B. L.↗