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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

The use of satellite data in understanding and predicting convective and large-scale dynamical processes

Mesoscale convective processes and how they affect and interact with mid-latitude cyclones were studied. The ageostrophic and associated vertical motion field was calculated using a highly accurate iterative method of solving the semigeostrophic omega equation. The tendencies for convective destabilization in the 850-750 mb layer due to differential geostrophic and ageostrophic advection and differential moist adiabatic ascent, were found. The spectral models of the index oscillation, one barotropic and the other baroclinic, were developed. Theoretical and observational studies of cloud streets were conducted.

Dutton, J. A.↗
NASA NTRS1984

Utilization of satellite cloud information to diagnose the energy state and transformations in extratropical cyclones

A study of the contribution of latent heat release to the synoptic scale vertical motions in the Jan. 9-11, 1975 extratropical cyclone case study was completed. Results indicate that early cyclone development was dominated by dry dynamical forcing. However, as the cyclone matured, the influence of latent heating became more significant. This influence appeared to be of two types, (1) the direct impact of heating causing a lowering of surface pressures, and (2) an indirect role in which the heating altered thermal and vorticity gradients and lead to subsequent increases in dry dynamical forcing. The kinetic energy budget was completed and extended to include an available potential energy budget. Focusing on the eddy component of the budgets, results indicate that kinetic energy increased throughout the cyclone's development, with the increase being most pronounced after the onset of significant latent heat release. Latent heating played a strong role not only in generating available potential energy, but also in forcing baroclinic release of potential energy.

Smith, P. J.↗
NASA NTRS1983

The response of stationary planetary waves to tropospheric forcing

The lower boundary forcing of airflow over topography, and the internal forcing that results from the geographical distribution of diabatic heating, are studied in light of a steady state, linear, quasi-geostrophic model of stationary waves on a sphere. The lower boundary vertical motions forced by airflow over topography depend on whether the horizontal deflection of airflow around topographic features is taken into account, the level of the wind profile at which flow over topography is assumed to take place, and the topographic data set that was used in the forcing formulation. The lower boundary forcing is taken to be given by the observed stationary planetary wave in lower boundary geopotential height, and the internal forcing is computed using the planetary wave propagation equation on the observed wave structure.

Alpert, J. C.↗
NASA NTRS1983

Short-range quantitative precipitation forecasts using a divergent initialization

Data simulations and real data tests indicate that the treatment of the initial divergence field in a mesoscale weather prediction model strongly influences the quality of the first 6 hours of a rainfall forecast. Of the procedures tested for determining the initial divergence field for the predictions, the best technique is found to be the Tarbell et al. (1981) diagnostic procedure, where a diabatic form of the omega equation is used to obtain a three-dimensional vertical motion field that in turn can be used in conjunction with a continuity equation to obtain the horizontal divergence fields.

Salmon, E. M.↗
NASA NTRS1984

The Presidents' Day cyclone of 18-19 February 1979 - Synoptic overview and analysis of the subtropical jet streak influencing the pre-cyclogenetic period

A detailed examination is undertaken of the subtropical jet (STJ) streak revealed by an analysis of the Presidents' Day cyclone of February 18-19, 1979. During its 24 h period, the STJ's flow became increasingly supergeostrophic and apparently unbalanced, while ageostrophic wind speeds increased to more than 30 m/sec in association with a significant cross-contour component, directed toward lower values of the Montgomery streamfunction, as the flow along the STJ became more divergent with time. These phenomena are linked to the increasing confluence in the entrance region of the jet streak and the decreasing wavelength of the trough-ridge system in which the jet streak was embedded. The upper level divergence and upward vertical motion near the axis of the STJ are found to be important factors in the development of the cyclone's first area of heavy snow.

Uccellini, L. W.↗
NASA NTRS1984

Cloud distributions in a Bay of Bengal monsoon depression

Much of the volume of a monsoon depression studied over the Bay of Bengal on July 7, 1979 featured thin, fragmentary layers of stratus, implying an absence of strong vertical motion. Coverage by cumulus updrafts was about 20 times less than coverage by inert cumulus remnants, and a great number density of humilis was found moistening the central area, following subsidence and drying. Detailed observations were made of a cloud line growing out of the southwesterly flow south of the center of the depression, which propagated faster than the low level winds. Aircraft altimetry showed an abrupt height drop from 6097 to 6090 m at 483 hPa, over a distance of 50 km from southeast to northwest through the line. Southwesterly momentum was lifted from 900 to 600 hPa and from southeast to northwest through the line. Other colocated singularities in convection and wind fields were found.

Warner, C.↗
NASA NTRS1984

Numerical simulations of the Ross Sea tides

Tidal currents below the floating Ross Ice shelf are reconstructed by using a numerical tidal model. They are predominantly diurnal, achieve maximum strength in regions near where the ice shelf runs aground, and are significantly enhanced by topographic Rossby wave propagation along the ice front. A comparison with observations of the vertical motion of the ice shelf surface indicates that the model reproduces the diurnal tidal characteristics within 20 percent. Similar agreement for the relatively weak semidiurnal tides was not obtained, and this calls attention to possible errors of the open boundary forcing obtained from global-ocean tidal simulations and to possible errors in mapping zones of ice shelf grounding. Air-sea contact below the ice shelf is eliminated by the thick ice cover. The dominant sub-ice-shelf circulation may thus be tidally induced. A preliminary assessment of sub-ice-shelf conditions based on the numerical tidal simulations suggests that (1) strong barotropic circulation is driven along the ice front and (2) tidal fronts may form in the sub-ice-shelf cavity where the water column is thin and where the buoyancy input is weak.

Macayeal, D. R.↗
NASA NTRS1983

Handling characteristics of a simulated twin tilt nacelle V/STOL aircraft

The first government-conducted piloted flight simulation of the Grumann-designed twin turbofan-powered tilt-engine V/STOL aircraft (design 698) was conducted at NASA Ames Research Center. The aircraft is discussed with an emphasis on its unique hover characteristics. These chracteristics include the adverse nonminimum phase that occurs in lateral and longitudinal translation, and the large attitude control power available. Both of these features are attributes of the control vanes (a Grumman-patented concept) buried in the fan exhaust flow. The simulation used the following NASA Ames Research Center facilities: the Vertical Motion Simulator with the interchangeable cab, the Sigma 8 computer, and the Computer-Generated Image system with a four-window display.

Wilson, S. B., III↗
NASA NTRS1984

The structures and energetics of fully nonlinear symmetric baroclinic waves

Rotating baroclinic flow for Richardson number lower than about 1 is studied by means of a finite difference Navier-Stokes model assuming no variations except in the vertical plane that completely contains the density gradient vector. The horizontally infinite channel to which attention is given further assumes periodic boundary conditions at the vertical computational boundaries and no-slip conducting horizontal boundaries. Two configurations are considered. Symmetric baroclinic waves developed in the flows in a manner consistent with linear theory, and it is noted that the structures and energetics of the fully developed waves were dependent on the Prandtl number Pr. For Pr greater than 1, the conversion from potential energy to wave kinetic energy was direct, via temperature and vertical motion correlation, while for Pr of less than 1, conversion proceeded from potential energy to average kinetic energy by means of an induced meridional flow, and then to wave kinetic energy.

Miller, T. L.↗
NASA NTRS1984

Ground-simulation investigation of VTOL instrument flight rules airworthiness criteria

A two-part ground-simulation investigation of VTOL terminal-area operations, conducted as part of a joint NASA/FAA program to develop airworthiness criteria for this class of vehicle, is described. The baseline vehicle selected for the simulations was a generalized version of the XV-15 tilt-rotor mathematical model, which was modified to permit generic variations in forces or moments or both with power or configuration changes. Additionally, changes to wing area and rotor-blade chord were considered as a means of modifying the allowable thrust-angle versus speed relationships (the conversion corridor). The Vertical Motion Simulator at Ames Research Center was used in the experiment. Four engineering test pilots conducted over 200 piloted evaluations examining the influence of the experimental variables on their ability to perform terminal-area operations.

Lebacqz, J. V.↗
NASA NTRS1984

Numerical Prediction of the President's Day Cyclone

Numerical-diagnostic studies of major anomalous weather events are being conducted in order to investigate the relevant physical processes associated with the events and the role of satellite observing systems in the analysis and prediction of these phenomena. One component of this study is concerned with the numerical prediction of intense coastal and oceanic cyclogenesis. The specific objectives of this research are: (1) to assess the accuracy of Goddard Laboratory for Atmospheric Sciences model predictions of cyclogenesis, (2) to determine the importance of large scale dynamical processes and diabatic heating to the prediction, and (3) to evaluate the sensitivity of the model predictions to the initial conditions. It was shown that diabatic heating resulting from oceanic fluxes significantly contributed to the generation of low level cyclonic vorticity and the intensification and slow rate movement of an upper level ridge over the western Atlantic. As an upper level short-wave trough approached this ridge, diabatic heating associated with the release of latent heat intensified, and the gradient of vorticity, vorticity advection, upper level divergence, and upward vertical motion in advance of the trough were greatly increased, providing strong large-scale forcing for the surface cyclogenesis.

Atlas, R.↗
NASA NTRS1984

A Control Model: Interpretation of Fitts' Law

The analytical results for several models are given: a first order model where it is assumed that the hand velocity can be directly controlled, and a second order model where it is assumed that the hand acceleration can be directly controlled. Two different types of control-laws are investigated. One is linear function of the hand error and error rate; the other is the time-optimal control law. Results show that the first and second order models with the linear control-law produce a movement time (MT) function with the exact form of the Fitts' Law. The control-law interpretation implies that the effect of target width on MT must be a result of the vertical motion which elevates the hand from the starting point and drops it on the target at the target edge. The time optimal control law did not produce a movement-time formula simular to Fitt's Law.

Connelly, E. M.↗
NASA NTRS1984

The Sternberg Task as a Workload Metric in Flight Handling Qualities Research

The objective of this research was to determine whether the Sternberg item-recognition task, employed as a secondary task measure of spare mental capacity for flight handling qualities (FHQ) simulation research, could help to differentiate between different flight-control conditions. FHQ evaluations were conducted on the Vertical Motion Simulator at Ames Research Center to investigate different primary flight-control configurations, and selected stability and control augmentation levels for helicopers engaged in low-level flight regimes. The Sternberg task was superimposed upon the primary flight-control task in a balanced experimental design. The results of parametric statistical analysis of Sternberg secondary task data failed to support the continued use of this task as a measure of pilot workload. In addition to the secondary task, subjects provided Cooper-Harper pilot ratings (CHPR) and responded to a workload questionnaire. The CHPR data also failed to provide reliable statistical discrimination between FHQ treatment conditions; some insight into the behavior of the secondary task was gained from the workload questionnaire data.

Hemingway, J. C.↗
NASA NTRS1985

Piloted simulation of one-on-one helicopter air combat at NOE flight levels

A piloted simulation designed to examine the effects of terrain proximity and control system design on helicopter performance during one-on-one air combat maneuvering (ACM) is discussed. The NASA Ames vertical motion simulator (VMS) and the computer generated imagery (CGI) systems were modified to allow two aircraft to be independently piloted on a single CGI data base. Engagements were begun with the blue aircraft already in a tail-chase position behind the red, and also with the two aircraft originating from positions unknown to each other. Maneuvering was very aggressive and safety requirements for minimum altitude, separation, and maximum bank angles typical of flight test were not used. Results indicate that the presence of terrain features adds an order of complexiaty to the task performed over clear air ACM and that mix of attitude and rate command-type stability and control augmentation system (SCAS) design may be desirable. The simulation system design, the flight paths flown, and the tactics used were compared favorably by the evaluation pilots to actual flight test experiments.

Lewis, M. S.↗
NASA NTRS1985

The effect of finite-amplitude baroclinic waves on passive, low-level, atmospheric constituents, with applications to comma cloud evolution

The redistribution of a low-level, passive constituent of the atmosphere under the influence of a growing baroclinic wave is examined by a series of analytical calculations based on a two-level, highly truncated model. It is shown that a constituent confined to the lower half of the atmosphere, and initially homogeneous in the horizontal, will tend to achieve maximum concentration in the low pressure/warm sector portion of the wave and minimum concentration in the high pressure/cold outbreak region with sharpest gradient between the maxima and minima roughly coinciding with the cold front. This distribution is further accentuated if an initial meridional gradient of the constituent exists. Assuming as a rough first approximation, that water vapor can be considered to be such a passive constituent, it is shown that the implied relative humidity field and cloud distribution will tend to evolve into the comma-type form commonly observed on satellite images of mid-latitude cyclone waves. Moreover, the solution is shown to replicate the complex flow regime associated with the comma formation, elucidating the dynamical roles of vertical motion and advection in the cloud evolution.

Saltzman, B.↗
NASA NTRS1983

Low-level microburst wind structure using Doppler radar and PAM data

The Joint Airport Weather Studies (JAWS) observation network used at an airport in Denver, CO consisted of one S-band and two C-band radars, together with 27 Portable Automated Mesonet (PAM) stations. Each of the three microburst case studies observed during the JAWS experiment occurred within the surface PAM network, and these surface data were compared with the radar analyses. It emerges that if microburst vertical motions are to be accurately resolved, the spacing of the surface stations must be considerably less than 4 km.

Kessinger, C.↗
NASA NTRS1984

Assessment of simulation fidelity using measurements of piloting technique in flight

The U.S. Army and NASA have undertaken the systematic validation of a ground-based piloted simulator for the UH-60A helicopter. The results of previous handling quality and task performance flight tests for this helicopter have been used as a data base for evaluating the fidelity of the present simulation, which is being conducted at the NASA Ames Research Center's Vertical Motion Simulator. Such nap-of-the-earth piloting tasks as pop-up, hover turn, dash/quick stop, sidestep, dolphin, and slalom, have been investigated. It is noted that pilot simulator performance is significantly and quantifiable degraded by comparison with flight test results for the same tasks.

Ferguson, S. W.↗
NASA NTRS1985

Global transport of atmospheric smoke following a major nuclear exchange

A fully interactive zonally symmetric general circulation model is used to simulate the transport and evolution of a massive smoke cloud that is likely to form in the atmosphere following a major nuclear war. The presence of such a cloud significantly alters the simulated circulation and the subsequent transport of the smoke particles themselves. While the model indicates a tendency for interhemispheric exchange, the most immediate effect is that the radiatively active particles are carried into the stratosphere by the generation of strong vertical motions and intense convection regardless of their initial injection altitudes.

Haberle, R. M.↗