Results for “coordination number” — Page 21

NASA NTRS1984

An empirical method for predicting the mixing noise levels of subsonic circular and coaxial jets

An empirical method for predicting the static free field source noise levels of subsonic circular and coaxial jet flow streams is presented. The method was developed from an extensive data base of 817 jet tests obtained from five different government and industry sources in three nations. The prediction method defines the jet noise in terms of four components which are overall power level, power spectrum level, directivity index, and relative spectrum level. The values of these noise level components are defined on a grid consisting of seven frequency parameter values (Strouhal numbers) and seven directivity angles. The value of the noise level at each of these grid points is called a noise level coordinate and was defined as a function of five jet exhaust flow state parameters which are equivalent jet velocity, equivalent jet total temperature, the velocity ratio (outer stream to inner stream), temperature ratio, and area ratio. The functions were obtained by curve fitting in a least squares sense the noise level coordinates from the data base in a five dimensional flow state space using a third order Taylor series. The noise level coordinates define the component noise levels for all frequencies and directivities through a bicubic spline function.

Russell, J. W.↗

NASA NTRS1993

Navier-Stokes analysis of three-dimensional S-ducts

Full 3D Navier-Stokes computational results are presented for compressible flows within nondiffusing and diffusing S-ducts. The present study provides an understanding of the performance characteristics of typical S-ducts with attached and separated flows and provides a frame of reference for future computational fluid dynamic studies of internal flows with strong secondary flows. The predicted results, which were obtained using both H- and O-grids, are compared with the experimental wall pressures, static and total pressure fields, and velocity vectors. In addition, computed boundary-layer thickness, velocity profiles in wall coordinates and skin friction values are presented. The inviscid contributions to the secondary flows are quantified. The S-duct entrance Mach number was 0.6, and the Reynolds number was 1.76 x 10 exp 6 based on the upstream duct diameter.

Harloff, G. J.↗

NASA NTRS1995

Flow in serpentine coolant passages with trip strips

Under the subject contract, an effort is being conducted at Scientific Research Associates, Inc. (SRA) to obtain flow field measurements in the coolant passage of a rotating turbine blade with ribbed walls, both in the stationary and rotating frames. The data obtained will be used for validation of computational tools and assessment of turbine blade cooling strategies. The configuration of the turbine blade passage model is given, and the measuring plane locations are given. The model has a four-pass passage with three 180 turns. This geometry was chosen to allow analyses of the velocity measurements corresponding to the heat transfer results obtained by Wagner. Two passes of the passage have a rectangular cross-section of 1.0 in x 0.5 in. Another two passes have a square cross-section of 0.5 in x 0.5 in. Trips with a streamwise pitch to trip height (P/e) = 5 and trip height to coolant passage width (e/Z) = 0.1, were machined along the leading and trailing walls. These dimensions are typical of those used in turbine blade coolant passages. The trips on these walls are staggered by the half-pitch. The trips are skewed at +/- 45 deg, and this allows the effect of trip orientation to be examined. Experiments will be conducted with flow entering the model through the 1.0 in x 0.5 in rectangular passage (Configuration C) and the 0.5 in x 0. 5 in square passage (Configuration D) to examine the effect of passage aspect ratio. Velocity measurements were obtained with a Reynolds number (Re) of 25,000, based on the hydraulic diameter of and bulk mean velocity in the half inch square passage. The coordinate system used in presenting the results for configurations C and D, respectively, is shown. The first, second and third passes of the passage will be referred to as the first, second and third passages, respectively, in later discussion. Streamwise distance (x) from the entrance is normalized by the hydraulic diameter (D). Vertical (y) and tangential (z) distances are normalized by the half passage height (H) and width (Z), respectively. The x coordinate and U component are positive in the streamwise direction. The y coordinate and V component are positive against gravity. The z coordinate and W component are positive in the direction of rotation. The velocities are normalized by the bulk mean velocity (Ub) of 3.44 m/s based on the half-inch square passage. The contours of the 1.0 in x 0.5 in and 0.5 in x 0.5 in passages were evaluated from 11 x 30 and 9 x 30 measurement grids, respectively.

Tse, D. G.-N.↗

NASA NTRS2003

Effect of Above Real Time Training and Post Flight Feedback in Training of Novice Pilots in a PC-Based Flight Simulator

The use of Post-Flight Feedback (PFFB) and Above Real-Time Training (ARTT) while training novice pilots to perform a coordinated level turn on a PC-based flight simulator was investigated. One group trained at 1.5 ARTT followed by an equal number of flights at 2.0 ARTT; the second group experienced Real Time Training (RTT). The total number of flights for both groups was equal. Each group was further subdivided into two groups one of which was provided PFFB while the other was not. Then, all participants experienced two challenging evaluation missions in real time. Performance was assessed by comparing root-mean-square error in bank-angle and altitude. Participants in the 1.512.0 ARTT No-PFFB sequence did not show improvement in performance across training sessions. An ANOVA on performance in evaluation flights found that the PFFB groups performed significantly better than those with No-PFFB. Also, the RTT groups performed significantly better than the ARTT groups. Data from two additional groups trained under a 2.011.5 ARTT PFFB and No-PFFB regimes were collected and combined with data from the previously Trainers, Real-time simulation, Personal studied groups and reanalyzed to study the computers, Man-in-the-loop simulation influence of sequence. An ANOVA on test trials found no significant effects between groups. Under training situations involving ARTT we recommend that appropriate PFFB be provided.

Khan, M. Javed↗

NASA NTRS2010

Beijing Lunar Declaration 2010: B) Technology and Resources; Infrastructures and Human Aspects; Moon, Space and Society

We report on the Beijing Lunar Declaration endorsed by the delegates of the Global Lunar Conference/11th ILEWG Conference on Exploration and Utilisation of the Moon, held at Beijing on 30 May- 3 June 2010. Specifically we focus on Part B:Technologies and resources; Infrastructures and human aspects; Moon, Space, Society and Young Explorers. We recommend continued and enhanced development and implementation of sessions about lunar exploration, manned and robotic, at key scientific and engineering meetings. A number of robotic missions to the Moon are now undertaken independently by various nations, with a degree of exchange of information and coordination. That should increase towards real cooperation, still allowing areas of competition for keeping the process active, cost-effective and faster. - Lunar landers, pressurized lunar rover projects as presented from Europe, Asia and America are important steps that can create opportunities for international collaboration, within a coordinated village of robotic precursors and assistants to crew missions. - We have to think about development, modernization of existing navigation capabilities, and provision of lunar positioning, navigation and data relay assets to support future robotic and human exploration. New concepts and new methods for transportation have attracted much attention and are of great potential.

Arvidson, R.↗

NASA NTRSDate not supplied

Effects of Communication Modality on Pilot-Controller Coordination during a Simulated m:N Operation

The last decade or so has seen growing interest in new control paradigms and concepts of operation for uncrewed aircraft systems (UAS) in which multiple aircraft are piloted remotely by a single or relatively small number of people. Referred to as “one-to-many” and “many-to- many” (alternatively, “multi-operator, multi-vehicle”)—and frequently expressed as the corresponding ratios, 1:N and m:N—such novel configurations of aircraft and the people who manage them are seen as critical to the path to future operations involving UAS. Examples of industry domains interested in these control paradigms are small package delivery services utilizing small UAS and passenger-carrying, short-range “Urban Air Mobility” (UAM) operations. Stakeholders in such operations have identified communication and coordination of flight activity with air traffic controllers (ATC) as a barrier to operations. In contrast to present-day flight operations, in which a pilot communicates with one ATC on one radio frequency for one aircraft, multi-vehicle operations potentially entail a significant increase in pilot task load for management of comms. New concepts, such as UAS Service Suppliers (USSs) and Providers of Services to UAM (PSUs), have been proposed to address the known bottleneck for Air Traffic Management (ATM) presented by multi-vehicle operations. While progress has been steadily made over years developing USSs and PSUs, it is generally expected that initial UAM operations will rely on traditional voice-over-radio communication with ATC for purposes of ATM. The current study was a human-in-the-loop simulation that had participants, each possessing a Private Pilot License, act as the ground-based pilot-in- command for multiple vehicles in a hypothetical UAM service in the San Francisco Bay Area. The experiment utilized a 2-by-3, within-subjects design in which the pilot’s Vehicle Load (4 vs. 12) and Comm System (Voice, Datalink, and a Hybrid) were manipulated. The task given to pilots was to use the Comm System to coordinate flight activity for all aircraft with appropriate controllers, having to obtain departure and arrival clearances at “vertiport” facilities and transition clearances for any intermediate airspaces along the route. Pilots were additionally responsible for compliance with vectoring instructions issued by ATC. Subjective workload questionnaires (NASA-TLX) were administered following each experimental trial. Screen recordings of the pilot’s Ground Control Station (GCS) and audio recordings of trials were subsequently coded to obtain performance metrics: response times and error rates. Presented in this paper are results related to pilot responses to vectoring instructions issued by ATC. Workload was found to be significantly higher in the 12-Vehicle condition compared to the 4-Vehicle condition, nearly maxing out the NASA-TLX overall workload scale. There was no significant difference made by the Comm System on workload ratings. Pilots’ response times to communications were fastest in the Voice condition, although overall “service time” for compliance was shorter in Datalink and Hybrid conditions in most cases. Errors by pilots were frequent in both Vehicle Load conditions, most perniciously when using the Voice system. The results of this study suggest tradeoffs in advantages and disadvantages of the three comm systems. Recommendations for communication system design are provided taking the tradeoffs into account.

Garrett G Sadler↗

NASA NTRSDate not supplied

Effects of Communication Modality on Pilot-Controller Coordination during a Simulated m:N Operation

The last decade or so has seen growing interest in new control paradigms and concepts of operation for uncrewed aircraft systems (UAS) in which multiple aircraft are piloted remotely by a single or relatively small number of people. Referred to as “one-to-many” and “many-to- many” (alternatively, “multi-operator, multi-vehicle”)—and frequently expressed as the corresponding ratios, 1:N and m:N—such novel configurations of aircraft and the people who manage them are seen as critical to the path to future operations involving UAS. Examples of industry domains interested in these control paradigms are small package delivery services utilizing small UAS and passenger-carrying, short-range “Urban Air Mobility” (UAM) operations. Stakeholders in such operations have identified communication and coordination of flight activity with air traffic controllers (ATC) as a barrier to operations. In contrast to present-day flight operations, in which a pilot communicates with one ATC on one radio frequency for one aircraft, multi-vehicle operations potentially entail a significant increase in pilot task load for management of comms. New concepts, such as UAS Service Suppliers (USSs) and Providers of Services to UAM (PSUs), have been proposed to address the known bottleneck for Air Traffic Management (ATM) presented by multi-vehicle operations. While progress has been steadily made over years developing USSs and PSUs, it is generally expected that initial UAM operations will rely on traditional voice-over-radio communication with ATC for purposes of ATM. The current study was a human-in-the-loop simulation that had participants, each possessing a Private Pilot License, act as the ground-based pilot-in- command for multiple vehicles in a hypothetical UAM service in the San Francisco Bay Area. The experiment utilized a 2-by-3, within-subjects design in which the pilot’s Vehicle Load (4 vs. 12) and Comm System (Voice, Datalink, and a Hybrid) were manipulated. The task given to pilots was to use the Comm System to coordinate flight activity for all aircraft with appropriate controllers, having to obtain departure and arrival clearances at “vertiport” facilities and transition clearances for any intermediate airspaces along the route. Pilots were additionally responsible for compliance with vectoring instructions issued by ATC. Subjective workload questionnaires (NASA-TLX) were administered following each experimental trial. Screen recordings of the pilot’s Ground Control Station (GCS) and audio recordings of trials were subsequently coded to obtain performance metrics: response times and error rates. Presented in this paper are results related to pilot responses to vectoring instructions issued by ATC. Workload was found to be significantly higher in the 12-Vehicle condition compared to the 4-Vehicle condition, nearly maxing out the NASA-TLX overall workload scale. There was no significant difference made by the Comm System on workload ratings. Pilots’ response times to communications were fastest in the Voice condition, although overall “service time” for compliance was shorter in Datalink and Hybrid conditions in most cases. Errors by pilots were frequent in both Vehicle Load conditions, most perniciously when using the Voice system. The results of this study suggest tradeoffs in advantages and disadvantages of the three comm systems. Recommendations for communication system design are provided taking the tradeoffs into account.

urban air mobility↗

NASA NTRS1976

Three dimensional supersonic flows with subsonic axial Mach numbers

A numerical approach is presented for the computation of flows in which the component of velocity in the selected marching direction is subsonic although the total velocity is supersonic. A local coordinate rotation procedure is employed together with an implicit differencing scheme. Complex coordinate transformations and time-consuming iterations are avoided. The implementation of the described approach is illustrated with the aid of a two-dimensional problem. An application in the case of three-dimensional flows is also discussed.

Marconi, F.↗

NASA NTRS1979

A hybridized method for computing high-Reynolds-number hypersonic flow about blunt bodies

A hybridized method for computing the flow about blunt bodies is presented. In this method the flow field is split into its viscid and inviscid parts. The forebody flow field about a parabolic body is computed. For the viscous solution, the Navier-Stokes equations are solved on orthogonal parabolic coordinates using explicit finite differencing. The inviscid flow is determined by using a Moretti type scheme in which the Euler equations are solved, using explicit finite differences, on a nonorthogonal coordinate system which uses the bow shock as an outer boundary. The two solutions are coupled along a common data line and are marched together in time until a converged solution is obtained. Computed results, when compared with experimental and analytical results, indicate the method works well over a wide range of Reynolds numbers and Mach numbers.

Weilmuenster, K. J.↗

NASA NTRS2004

Autonomous Multi-Sensor Coordination: The Science Goal Monitor

Many dramatic earth phenomena are dynamic and coupled. In order to fully understand them, we need to obtain timely coordinated multi-sensor observations from widely dispersed instruments. Such a dynamic observing system must include the ability to Schedule flexibly and react autonomously to sciencehser driven events; Understand higher-level goals of a sciencehser defined campaign; Coordinate various space-based and ground-based resources/sensors effectively and efficiently to achieve goals. In order to capture transient events, such a 'sensor web' system must have an automated reactive capability built into its scientific operations. To do this, we must overcome a number of challenges inherent in infusing autonomy. The Science Goal Monitor (SGM) is a prototype software tool being developed to explore the nature of automation necessary to enable dynamic observing. The tools being developed in SGM improve our ability to autonomously monitor multiple independent sensors and coordinate reactions to better observe dynamic phenomena. The SGM system enables users to specify what to look for and how to react in descriptive rather than technical terms. The system monitors streams of data to identify occurrences of the key events previously specified by the scientisther. When an event occurs, the system autonomously coordinates the execution of the users' desired reactions between different sensors. The information can be used to rapidly respond to a variety of fast temporal events. Investigators will no longer have to rely on after-the-fact data analysis to determine what happened. Our paper describes a series of prototype demonstrations that we have developed using SGM and NASA's Earth Observing-1 (EO-1) satellite and Earth Observing Systems' Aqua/Terra spacecrafts' MODIS instrument. Our demonstrations show the promise of coordinating data from different sources, analyzing the data for a relevant event, autonomously updating and rapidly obtaining a follow-on relevant image. SGM was used to investigate forest fires, floods and volcanic eruptions. We are now identifying new Earth science scenarios that will have more complex SGM reasoning. By developing and testing a prototype in an operational environment, we are also establishing and gathering metrics to gauge the success of automating science campaigns.

Koratkar, Anuradha↗

NASA NTRS1978

The stability of an asymmetric rotor in damped supports

A general-purpose method of evaluating the stability of an asymmetric flexible rotor, mounted in symmetric damped bearings, is defined. This method evaluates the complex eigenvalues of the rotor system by solving the equations of motion in a rotating coordinate frame. The application of this method to a rotor mounted in tilting-pad bearings is demonstrated. The observed behavior of a number of different rotor configurations is compared with corresponding predictions of stability. For the configurations predicted to be unstable, a distinct and unnegotiable threshold of instability is encountered. The sharpness of this threshold is emphasized by careful balancing at speeds fractionally below the threshold. In a final configuration predicted to be marginally stable, lightly damped resonant behavior, negotiable by balancing, is encountered in the region of the first critical speed.

Smalley, A. J.↗

NASA NTRS1982

Numerical methods and calculations for droplet flow, heating and ignition

A numerical method was devised and employed to solve a variety of problems related to liquid droplet combustion. The basic transport equations of mass, momentum and energy were formulated in terms of generalized nonorthogonal coordinates, which allows for adaptive griding and arbitrary particle shape. Example problems are solved for internal droplet heating, droplet ignition and high Reynolds number flow over a droplet.

Dwyer, H. A.↗

NASA NTRS1982

AGARD three-dimensional aeroelastic configurations

The calculation of unsteady aerodynamic forces in the critical transonic speed regime is investigated. The development of such methods is be enhanced by the availability of a limited number of test cases for the comparison of competing methods. Test cases for five clean, isolated wings are presented. Wing geometric descriptions, airfoil coordinates, and suggested aerodynamic conditions for each are included.

Bland, S. R.↗

NASA NTRS1989

Vibration analysis of rotor systems using reduced subsystem models

A general impedance method using reduced submodels has been developed for the linear dynamic analysis of rotor systems. Formulated in terms of either modal or physical coordinates of the subsystems, the method enables imbalance responses at specific locations of the rotor systems to be efficiently determined from a small number of 'master' degrees of freedom. To demonstrate the capability of this impedance approach, the Space Shuttle Main Engine high-pressure oxygen turbopump has been investigated to determine the bearing loads due to imbalance. Based on the same formulation, an eigenvalue analysis has been performed to study the system stability. A small 5-DOF model has been utilized to illustrate the application of the method to eigenvalue analysis. Because of its inherent characteristics of allowing formulation of reduced submodels, the impedance method can significantly increase the computational speed.

Fan, Uei-Jiun↗

NASA NTRS1992

Information processing in the primate visual system - An integrated systems perspective

The primate visual system contains dozens of distinct areas in the cerebral cortex and several major subcortical structures. These subdivisions are extensively interconnected in a distributed hierarchical network that contains several intertwined processing streams. A number of strategies are used for efficient information processing within this hierarchy. These include linear and nonlinear filtering, passage through information bottlenecks, and coordinated use of multiple types of information. In addition, dynamic regulation of information flow within and between visual areas may provide the computational flexibility needed for the visual system to perform a broad spectrum of tasks accurately and at high resolution.

Van Essen, David C.↗

NASA NTRS1993

Wigner functions for nonclassical states of a collection of two-level atoms

The general theory of atomic angular momentum states is used to derive the Wigner distribution function for atomic angular momentum number states, coherent states, and squeezed states. These Wigner functions W(theta,phi) are represented as a pseudo-probability distribution in spherical coordinates theta and phi on the surface of a sphere of radius the square root of j(j +1) where j is the total angular momentum.

Agarwal, G. S.↗

NASA NTRS1994

System concept definition of the Grumman superconducting Electromagnetic Suspension (EMS) Maglev design

Grumman, under contract to the Army Corps of Engineers, completed a System Concept Definition (SCD) study to design a high-speed 134 m/s (300 m.p.h.) magnetically levitated (Maglev) transportation system. The primary development goals were to design a Maglev that is safe, reliable, environmentally acceptable, and low-cost. The cost issue was a predominant one, since previous studies have shown that an economically viable Maglev system (one that is attractive to investors for future models of passenger and/or freight transportation) requires a cost that is about $12.4 M/km ($20 Million per mile). The design is based on the electromagnetic suspension (EMS) system using superconducting iron-core magnets mounted along both sides of the vehicle. The EMS system has several advantages compared to the electrodynamic suspension (EDS) Maglev systems such as low stray magnetic fields in the passenger cabin and the surrounding areas, uniform load distribution along the full length of the vehicle, and small pole pitch for smoother propulsion and ride comfort. It is also levitated at all speeds and incorporates a wrap-around design of safer operation. The Grumman design has all the advantages of an EMS system identified above, while eliminating (or significantly improving) drawbacks associated with normal magnet powered EMS systems. Improvements include larger gap clearance, lighter weight, lower number of control servos, and higher off line switching speeds. The design also incorporates vehicle tilt (plus or minus 9 deg) for higher coordinated turn and turn out speed capability.

Proise, M.↗

NASA NTRS1994

Noise Radiation by Instability Waves in Coaxial Jets

In this paper predictions are made for the noise radiation from supersonic coaxial jets. The noise in the downstream arc of a supersonic jet is dominated by highly directional radiation from the supersonically convecting large scale structures in the jet mixing layer. Since the mean flow is not described easily in terms of simple analytic functions, a numerical prediction is made for its development. The compressible Reynolds-averaged boundary layer equations in cylindrical polar coordinates are solved. A mixing length turbulence model is used. Empirical correlations are developed the effects of velocity and temperature ratio and Mach number. Both normal and inverted velocity profiles are considered. Comparisons with measurements for both single and coaxial jets show good agreement. The large scale structures are modeled as instability waves. The noise radiation generated by the instability waves is determined by a matching between the inner instability wave solution and the outer acoustic solution. Predictions are made for the differences between the noise radiated by coaxial jets with different operating conditions and a single equivalent jet with the same exit area, thrust, and mass-flow.

Dahl, Milo D.↗