55,411 research outputs found
3D Dune Skeleton Model as a Coupled Dynamical System of 2D Cross-Sections
To analyze theoretically the stability of the shape and the migration process
of transverse dunes and barchans, we propose a {\it skeleton model} of 3D dunes
described with coupled dynamics of 2D cross-sections. First, 2D cross-sections
of a 3D dune parallel to the wind direction are extracted as elements of a
skeleton of the 3D dune, hence, the dynamics of each and interaction between
them is considered. This model simply describes the essential dynamics of 3D
dunes as a system of coupled ordinary differential equations. Using the model
we study the stability of the shape of 3D transversal dunes and their
deformation to barchans depending on the amount of available sand in the dune
field, sand flow in parallel and perpendicular to wind direction.Comment: 6 pages, 6 figures, lette
Investigation of Air Transportation Technology at Princeton University, 1989-1990
The Air Transportation Technology Program at Princeton University proceeded along six avenues during the past year: microburst hazards to aircraft; machine-intelligent, fault tolerant flight control; computer aided heuristics for piloted flight; stochastic robustness for flight control systems; neural networks for flight control; and computer aided control system design. These topics are briefly discussed, and an annotated bibliography of publications that appeared between January 1989 and June 1990 is given
Aerodynamics, Stability and Control of the 1903 Wright Flyer
The Los Angeles Chapter of the American Institute of Aero and
Astronautics is building two replicas of the 1903 Wright Flyer airplane;
one to wind-tunnel test and display, and a modified one to fly. As part
of this project the aerodynamic characteristics of the Flyer are being
analyzed by modern wind-tunnel and analytical techniques. Tnis paper
describes the Wright Flyer Project, and compares key results from
small-scale wind-tunnel tests and from vortex-lattice computations for
this multi-biplane canard configuration. Analyses of the stability and
control properties are summarized and their implications for closed-loop
control by a pilot are derived using quasilinear pilot-vehicle analysis
and illustrated by simulation time histories.
It is concluded that, although the Wrights were very knowledgeable
and ingenious with respect to aircraft controls and their interactions
(e.g., the good effects of their wing-warp-to-rudder linkage are
validated), they were largely ignorant of dynamic stability
considerations. The paper shows that the 1903 Flyer was readily
controllable about all axes but was intrinsically unstable in pitch and
roll, and it could barely be stabilized by a skilled pilot
Stability of transverse dunes against perturbations; a theoretical study using dune skeleton model
The dune skeleton model is a reduced model to describe the formation process
and dynamics of characteristic types of dunes emerging under unidirectional
steady wind. Using this model, we study the dependency of the morphodynamics of
transverse dunes on the initial random perturbations and the lateral field
size. It was found that i) an increase of the lateral field size destabilizes
the transverse dune to cause deformation of a barchan, ii) the initial random
perturbations decay with time by the power function until a certain time;
thereafter, the dune shapes change into three phases according to the amount of
sand and sand diffusion coefficient, iii) the duration time, until the
transverse dune is broken, increases exponentially with increasing the amount
of sand and sand diffusion coefficient. Moreover, under the condition without
the sand supply from windward ground, the destabilization of transverse dune in
this model qualitatively corresponds to the subaqueous dunes in water tank
experiments.Comment: 7pages, 8figure
Evaluation of the gust-alleviation characteristics and handling qualities of a free-wing aircraft
Dynamic characteristics of aircraft with wings free to pivot spanwise axi
Applications of flight control system methods to an advanced combat rotorcraft
Advanced flight control system design, analysis, and testing methodologies developed at the Ames Research Center are applied in an analytical and flight test evaluation of the Advanced Digital Optical Control System (ADOCS) demonstrator. The primary objectives are to describe the knowledge gained about the implications of digital flight control system design for rotorcraft, and to illustrate the analysis of the resulting handling-qualities in the context of the proposed new handling-qualities specification for rotorcraft. Topics covered in-depth are digital flight control design and analysis methods, flight testing techniques, ADOCS handling-qualities evaluation results, and correlation of flight test results with analytical models and the proposed handling-qualities specification. The evaluation of the ADOCS demonstrator indicates desirable response characteristics based on equivalent damping and frequency, but undersirably large effective time-delays (exceeding 240 m sec in all axes). Piloted handling-qualities are found to be desirable or adequate for all low, medium, and high pilot gain tasks; but handling-qualities are inadequate for ultra-high gain tasks such as slope and running landings
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