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At least 955 records · Page 53

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NASA NTRS1992

Phase II simulation evaluation of the flying qualities of two tilt-wing flap control concepts

A simulation study was initiated to investigate alternative wing and flap controls for tilt-wing aircraft. The initial phase of the study compared the flying qualities of both a conventional (programmed) flap and an innovative geared flap. The second phase of the study, reported in this paper, introduced an alternate method for pilot control of the geared flap and further studied the flying qualities of the programmed flap, and two geared flap configurations. The results showed little difference among the three flap control configurations except during a longitudinal reposition task where the programmed flap configuration was the best. The addition of pitch attitude stabilization greatly enhanced the aircraft handling qualities. This paper describes the tilt-wing aircraft and the flap control concepts, and presents the results of the second simulation experiment.

Birckelbaw, Lourdes G.↗

NASA NTRS1993

Profile negotiation: An air/ground automation integration concept for managing arrival traffic

NASA Ames Research Center and NASA Langley Research Center conducted a joint simulation study to evaluate a profile negotiation process (PNP) between a time-based air traffic control ATC system and an airplane equipped with a four dimensional flight management system (4D FMS). Prototype procedures were developed to support the functional implementation of this process. The PNP was designed to provide an arrival trajectory solution that satisfies the separation requirements of ATC while remaining as close as possible to the airplane's preferred trajectory. The Transport Systems Research Vehicle cockpit simulator was linked in real-time to the Center/TRACON Automation System (CTAS) for the experiment. Approximately 30 hours of simulation testing were conducted over a three week period. Active airline pilot crews and active Center controller teams participated as test subjects. Results from the experiment indicate the potential for successful incorporation of airplane preferred arrival trajectories in the CTAS automation environment. Controllers were able to consistently and effectively negotiate nominally conflict-free trajectories with pilots flying a 4D-FMS-equipped airplane. The negotiated trajectories were substantially closer to the airplane's preference than would have otherwise been possible without the PNP. Airplane fuel savings relative to baseline CTAS were achieved in the test scenarios. The datalink procedures and clearances developed for this experiment, while providing the necessary functionality, were found to be operationally unacceptable to the pilots. Additional pilot control and understanding of the proposed airplane-preferred trajectory and a simplified clearance procedure were cited as necessary for operational implementation of the concept. From the controllers' perspective, the main concerns were the ability of the 4D airplane to accurately track the negotiated trajectory and the workload required to support the PNP as implemented in this study.

Williams, David H.↗

NASA NTRS2014

Effect of Traffic Position Accuracy for Conducting Safe Airport Surface Operations

The Next Generation Air Transportation System (NextGen) concept proposes many revolutionary operational concepts and technologies, such as display of traffic information and movements, airport moving maps (AMM), and proactive alerts of runway incursions and surface traffic conflicts, to deliver an overall increase in system capacity and safety. A piloted simulation study was conducted at the National Aeronautics and Space Administration (NASA) Langley Research Center to evaluate the ability to conduct safe and efficient airport surface operations while utilizing an AMM displaying traffic of various position accuracies as well as the effect of traffic position accuracy on airport conflict detection and resolution (CD&R) capability. Nominal scenarios and off-nominal conflict scenarios were conducted using 12 airline crews operating in a simulated Memphis International Airport terminal environment. The data suggest that all traffic should be shown on the airport moving map, whether qualified or unqualified, and conflict detection and resolution technologies provide significant safety benefits. Despite the presence of traffic information on the map, collisions or near collisions still occurred; when indications or alerts were generated in these same scenarios, the incidences were averted.

Jones, Denise R.↗

NASA NTRS1974

Computer simulation of the threshold sensitivity determinations

A computer simulation study was carried out to evaluate various methods for determining threshold stimulus levels for impact sensitivity tests. In addition, the influence of a number of variables (initial stimulus level, particular stimulus response curve, and increment size) on the apparent threshold values and on the corresponding population response levels was determined. Finally, a critical review of previous assumptions regarding the stimulus response curve for impact testing is presented in the light of the simulation results.

Gayle, J. B.↗

NASA NTRS1978

Control system studies for thermionic reactors

In core thermionic reactor concepts are of interest for space missions that require electrical power in the range of a few tens of kilowatts up to several megawatts. The physical principle involved--thermionic direct conversion of heat to electricity at net efficiencies up to 15 percent--offers potential advantages when compared to other nuclear powerplant concepts. However, the integration of the thermionic diode electrode structure with high-temperature nuclear fuel materials presents new design problems and new reactor physical constraints. Among the topics that must be investigated are those associated with the control system. The results of analytical and simulation studies of thermionic reactor control performed at the Jet Propulsion Laboratory are discussed.

Hermsen, R. J.↗

NASA NTRS2009

Particle Acceleration and Associated Emission from Relativistic Shocks

Five talks consist of a research program consisting of numerical simulations and theoretical development designed to provide an understanding of the emission from accelerated particles in relativistic shocks. The goal of this lecture is to discuss the particle acceleration, magnetic field generation, and radiation along with the microphysics of the shock process in a self-consistent manner. The discussion involves the collisionless shocks that produce emission from gamma-ray bursts and their afterglows, and producing emission from supernova remnants and AGN relativistic jets. Recent particle-in-cell simulation studies have shown that the Weibel (mixed mode two-stream filamentation) instability is responsible for particle (electron, positron, and ion) acceleration and magnetic field generation in relativistic collisionless shocks. 3-D RPIC code parallelized with MPI has been used to investigate the dynamics of collisionless shocks in electron-ion and electron-positron plasmas with and without initial ambient magnetic fields. In this lecture we will present brief tutorials of RPIC simulations and RMHD simulations, a brief summary of recent RPIC simulations, mechanisms of particle acceleration in relativistic shocks, and calculation of synchrotron radiation by tracing particles. We will discuss on emission from the collisionless shocks, which will be calculated during the simulation by tracing particle acceleration self-consistently in the inhomogeneous magnetic fields generated in the shocks. In particular, we will discuss the differences between standard synchrotron radiation and the jitter radiation that arises in turbulent magnetic fields.

Nishkawa, Ken-Ichi↗

NASA NTRS1974

A STOL airworthiness investigation using a simulation of an augmentor wing transport. Volume 1: Summary of results and airworthiness implications

A simulator study of STOL airworthiness criteria was conducted using a model of an augmentor wing transport. The approach, flare and landing, go-around, and takeoff phases of flight were investigated. The results are summarized and possible implications with regard to airworthiness criteria are discussed. The results provide a data base for future STOL airworthiness requirements and a preliminary indication of potential problem areas. The results are also compared to the results from an earlier simulation of the Breguet 941S. Where possible, airworthiness criteria are proposed for consideration.

Stapleford, R. L.↗

NASA NTRS1977

NASA ground-based and space-based laser ranging systems

The development of NASA laser ranging systems is discussed with reference to applications such as orbit determination, gravity-field studies, and analyses of polar motion, earth tides, and tectonic plate motion. Several laser ranging designs are described noting the first satellite laser ranging experiment, the Moblas II and III systems, and the laser ranging satellites presently in orbit. Primary error sources are identified as atmospheric delay, optical signal-to-noise ratios, the electron multiplier, time-interval measurements, and target noise. Plans for Shuttle-based laser ranging systems are reviewed noting simulation studies of 12-day Shuttle missions.

Fitzmaurice, M. W.↗

NASA NTRS1985

Space-flight simulations of calcium metabolism using a mathematical model of calcium regulation

The results of a series of simulation studies of calcium matabolic changes which have been recorded during human exposure to bed rest and space flight are presented. Space flight and bed rest data demonstrate losses of total body calcium during exposure to hypogravic environments. These losses are evidenced by higher than normal rates of urine calcium excretion and by negative calcium balances. In addition, intestinal absorption rates and bone mineral content are assumed to decrease. The bed rest and space flight simulations were executed on a mathematical model of the calcium metabolic system. The purpose of the simulations is to theoretically test hypotheses and predict system responses which are occurring during given experimental stresses. In this case, hypogravity occurs through the comparison of simulation and experimental data and through the analysis of model structure and system responses. The model reliably simulates the responses of selected bed rest and space flight parameters. When experimental data are available, the simulated skeletal responses and regulatory factors involved in the responses agree with space flight data collected on rodents. In addition, areas within the model that need improvement are identified.

Brand, S. N.↗

NASA NTRS1996

Experimental study of vortex breakdown in a cylindrical, swirling flow

The stability of a steady, vortical flow in a cylindrical container with one rotating endwall has been experimentally examined to gain insight into the process of vortex breakdowwn. The dynamics of the flow are governed by the Reynolds number (Re) and the aspect ratio of the cylinder. Re is given by Omega R(sup 2)/nu, where Omega is the speed of rotation of the endwall, R is the cylinder radius, and nu is the kinematic viscosity of the fluid filling the cylinder. The aspect ratio is H/R, where H is the height of the cylinder. Numerical simulation studies disagree whether or not the steady breakdown is stable beyond a critical Reynolds number, Re(sub c). Previous experimental researches have considered the steady and unsteady flows near Re(sub c), but have not explored the stability of the steady breakdown structures beyond this value. In this investigation, laser induced fluorescence was utilized to observe both steady and unsteady vortex breakdown at a fixed H/R of 2.5 with Re varying around Re(sub c). When the Re of a steady flow was slowly increased beyond Re(sub c), the breakdown structure remained steady even though unsteadiness was possible. In addition, a number of hysteresis events involving the oscillation periods of the unsteady flow were noted. The results show that both steady and unsteady vortex breakdown occur for a limited range of Re above Re(sub c). Also, with increasing Re, complex flow transformations take place that alter the period at which the unsteady flow oscillates.

Stevens, J. L.↗

NASA NTRS1985

Evolution and interaction of interplanetary shocks

Whang's unsteady, one-dimensional, one-fluid MHD model is used to carry out a simulation study of the evolution of the solar wind based on two shock events over a distance of the order of 10 AU in the outer heliosphere. The study is based on the observation of two events, each observed by two or more spacecraft. The results show that the shock process, including the formation, collision, and merging of shocks, dominates the dynamical evolution of large-scale solar wind structures. In the outer heliosphere, the large-scale solar wind and magnetic field evolve into a much simpler structure, and MHD shocks are present as a principal component of the solar wind. The simulation results shed new light on the interaction and evolution of large interplanetary streams.

Whang, Y. C.↗

NASA NTRS1983

Scan angle dependence of radiance recorded by the NOAA-AVHRR

NOAA-AVHRR data is being used to monitor global vegetation type and condition and to study various environmental factors in addition to performance of meteorological functions. The AVHRR instrument has + or - 54 deg as maximum scan angle limits and it is necessary to be aware of the effects of sun-target-sensor geometry at extreme scan angles to be able to properly interpret the satellite images. In order to interpret the images for vegetation type and condition analysis, it is necessary to calibrate back to the nadir view position. Both simulation studies and empirical investigations with digital scanner data have been performed in order to sufficiently understand the effects of scan angle and sun angle, as well as the effects of atmospheric scattering, to eventually perform adequate calibrations. Not surprisingly, the effects are large and studies are continuing to provide improved calibrations.

Duggin, M. J.↗

NASA NTRS1990

Cockpit display of hazardous weather information

Information transfer and display issues associated with the dissemination of hazardous weather warnings are studied in the context of windshear alerts. Operational and developmental windshear detection systems are briefly reviewed. The July 11, 1988 microburst events observed as part of the Denver Terminal Doppler Weather Radar (TDWR) operational evaluation are analyzed in terms of information transfer and the effectiveness of the microburst alerts. Information transfer, message content and display issues associated with microburst alerts generated from ground based sources are evaluated by means of pilot opinion surveys and part task simulator studies.

Hansman, R. John, Jr.↗

NASA NTRS1995

A study of space-rated connectors using a robot end-effector

The main research activities have been directed toward the study of the Robot Operated Materials Processing System (ROMPS), developed at GSFC under a flight project to investigate commercially promising in-space material processes and to design reflyable robot automated systems to be used in the above processes for low-cost operations. The research activities can be divided into two phases. Phase 1 dealt with testing of ROMPS robot mechanical interfaces and compliant device using a Stewart Platform testbed and Phase 2 with computer simulation study of the ROMPS robot control system. This report provides a summary of the results obtained in Phase 1 and Phase 2.

Nguyen, Charles C.↗

NASA NTRS2016

Sensitivity Analysis of the Integrated Medical Model for ISS Programs

Sensitivity analysis estimates the relative contribution of the uncertainty in input values to the uncertainty of model outputs. Partial Rank Correlation Coefficient (PRCC) and Standardized Rank Regression Coefficient (SRRC) are methods of conducting sensitivity analysis on nonlinear simulation models like the Integrated Medical Model (IMM). The PRCC method estimates the sensitivity using partial correlation of the ranks of the generated input values to each generated output value. The partial part is so named because adjustments are made for the linear effects of all the other input values in the calculation of correlation between a particular input and each output. In SRRC, standardized regression-based coefficients measure the sensitivity of each input, adjusted for all the other inputs, on each output. Because the relative ranking of each of the inputs and outputs is used, as opposed to the values themselves, both methods accommodate the nonlinear relationship of the underlying model. As part of the IMM v4.0 validation study, simulations are available that predict 33 person-missions on ISS and 111 person-missions on STS. These simulated data predictions feed the sensitivity analysis procedures. The inputs to the sensitivity procedures include the number occurrences of each of the one hundred IMM medical conditions generated over the simulations and the associated IMM outputs: total quality time lost (QTL), number of evacuations (EVAC), and number of loss of crew lives (LOCL). The IMM team will report the results of using PRCC and SRRC on IMM v4.0 predictions of the ISS and STS missions created as part of the external validation study. Tornado plots will assist in the visualization of the condition-related input sensitivities to each of the main outcomes. The outcomes of this sensitivity analysis will drive review focus by identifying conditions where changes in uncertainty could drive changes in overall model output uncertainty. These efforts are an integral part of the overall verification, validation, and credibility review of IMM v4.0.

medical equipment↗

NASA NTRS1974

A STOL airworthiness investigation using a simulation of a deflected slipstream transport. Volume 1: Summary of results and airworthiness implications

A simulator study of short takeoff and landing (STOL) aircraft was conducted using a model of a deflected slipstream transport aircraft. The subjects considered are: (1) the approach, (2) flare and landing, (3) go-around, and (4) takeoff phases of flight. The results are summarized and possible implications with regard to airworthiness criteria are discussed. A data base is provided for future STOL airworthiness requirements and a preliminary indication of potential problem areas is developed. Comparison of the simulation results with various proposed STOL criteria indicates significant deficiencies in many of these criteria.

Stapleford, R. L.↗

NASA NTRS1993

Low bandwidth robust controllers for flight

Through throttle manipulations, engine thrust can be used for emergency flight control for multi-engine aircraft. Previous study by NASA Dryden has shown the use of throttles for emergency flight control to be very difficult. In general, manual fly-by-throttle is extremely difficult - with landing almost impossible, but control augmentation makes runway landings feasible. Flight path control using throttles-only to achieve safe emergency landing for a large jet transport airplane, Boeing 720, was investigated using Quantitative Feedback Theory (QFT). Results were compared to an augmented control developed in a previous simulation study. The control augmentation corrected the unsatisfactory open-loop characteristics by increasing system bandwidth and damping, but increasing the control bandwidth substantially proved very difficult. The augmented pitch control is robust under no or moderate turbulence. The augmented roll control is sensitive to configuration changes.

Biezad, Daniel J.↗

NASA NTRS1993

Low Bandwidth Robust Controllers for Flight

Biezad, Daniel J.↗