5,898 research outputs found
Propagating and evanescent internal waves in a deep ocean model
We present experimental and computational studies of the propagation of
internal waves in a stratified fluid with an exponential density profile that
models the deep ocean. The buoyancy frequency profile (proportional to
the square root of the density gradient) varies smoothly by more than an order
of magnitude over the fluid depth, as is common in the deep ocean. The
nonuniform stratification is characterized by a turning depth , where
is equal to the wave frequency and .
Internal waves reflect from the turning depth and become evanescent below the
turning depth. The energy flux below the turning depth is shown to decay
exponentially with a decay constant given by , which is the horizontal
wavenumber at the turning depth. The viscous decay of the vertical velocity
amplitude of the incoming and reflected waves above the turning depth agree
within a few percent with a previously untested theory for a fluid of arbitrary
stratification [Kistovich and Chashechkin, J. App. Mech. Tech. Phys. 39,
729-737 (1998)].Comment: 13 pages, 4 figures, 4 table
INVESTIGATION OF ADHESION AND COHESION OF METALS IN ULTRAHIGH VACUUM.
Adhesion and cohesion of metals in ultrahigh vacuu
MAST flight system dynamic performance
The MAST Flight System as a test bed for large space structure control algorithms is discussed. An overview is given of the control system architecture. The actuators, the sensors, the control computer, and the baseline damping algorithm are discussed
Report of the Secretary, 1942-45, inclusive
Detailed reports of the annual spring meetings of the Arkansas Academy of Science have been sent out to all members. Therefore, only a summary of Academy activities for a more permanent record will be reviewed. Further secretarial information will be found in tabular forms elsewhere. While the period under discussion has never been equaled before in history, the Academy has held meetings each spring, though on a smaller scale. In the meantime new evidence that the people of our part of the country sense the importance of research in industry may be seen in the new research organizations such as the University Bureau of Research, The Southern Association of Science and Industry, The Gulf of Southwest Industrial and Agricultural Conference, Inc. and the Midwest Research Institute
Wind Tunnel Generation of Sinusoidal Lateral and Longitudinal Gusts by Circulation of Twin Parallel Airfoils
A gust generator capable of producing sinusoidal lateral and longitudinal gusts was developed for the purpose of studying the gust response of a model rotor-propeller in a wind tunnel. The gust generator utilized harmonic circulation control of twin parallel airfoils to achieve the harmonic lift variation required for gust generation. The gust generator design, construction, and testing is described. Typical test results are presented in the form of lateral and longitudinal gust perturbation velocities as a function of generator reduced frequency
Aerodynamic interference effects on tilting proprotor aircraft
The Green's function method was used to study tilting proprotor aircraft aerodynamics with particular application to the problem of the mutual interference of the wing-fuselage-tail-rotor wake configuration. While the formulation is valid for fully unsteady rotor aerodynamics, attention was directed to steady state aerodynamics, which was achieved by replacing the rotor with the actuator disk approximation. The use of an actuator disk analysis introduced a mathematical singularity into the formulation; this problem was studied and resolved. The pressure distribution, lift, and pitching moment were obtained for an XV-15 wing-fuselage-tail rotor configuration at various flight conditions. For the flight configurations explored, the effects of the rotor wake interference on the XV-15 tilt rotor aircraft yielded a reduction in the total lift and an increase in the nose-down pitching moment. This method provides an analytical capability that is simple to apply and can be used to investigate fuselage-tail rotor wake interference as well as to explore other rotor design problem areas
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