Engineering topics

Murphy, J. R.

Publications and source records attributed to Murphy, J. R..

22 records · Page 2

NASA NTRS1992

Astronomical variation experiments with a Mars general circulation model

In time scales of a hundred thousand to a million years, the eccentricity of Mars orbit varies in a quasi-periodic manner between extremes as large as 0.14 and as small as 0 and the tilt of its axis of rotation with respect to the orbit normal also varies quasi-periodically between extremes as large as 35 deg and as small as 15 deg. In addition, the orientation of the axis precesses on comparable time scales. These astronomical variations are much more extreme than those experienced by the Earth. These variations are thought to have strongly modulated the seasonal cycles of dust, carbon dioxide, and water. One manifestation of the induced quasiperiodic climate changes may be the layered terrain of the polar regions, with individual layers perhaps recording variations in the absolute and/or relative deposition rates of dust and water in the polar regions, most likely in association with the winter time deposition of carbon dioxide ice. In an attempt to understand the manner in which atmospheric temperatures and winds respond to the astronomical forcings, we have initiated a series of numerical experiments with the NASA/Ames general circulation model of the Martian Atmosphere.

Pollack, J. B.↗

NASA NTRS1992

Mars dust storm simulations: Analysis of surface stress

The primary mechanism by which dust is inserted into the Martian atmosphere is the interaction of low-level atmospheric motions with the planet's surface. Near-surface winds exert a shear stress upon dust particles resting on the Martian surface, and at some lower threshold limit of stress magnitude, approximately 0.04 N-m(exp -2), particles are set into motion. Wind tunnel studies indicate that the first particles are too large to remain in suspension in the Martian atmosphere, but their impact back upon the surface can set smaller suspendable particles into motion. This process is termed saltation. Numerical simulations of Martian dust storms were carried out via the interactive coupling of the NASA Ames Mars general circulation Model with an aerosol transport/microphysical model.

Murphy, J. R.↗

NASA NTRS1992

Dust transport into Martian polar latitudes

The presence of suspended dust in the Martian atmosphere, and its return to the planet's surface, is implicated in the formation of the polar layered terrain and the dichotomy in perennial CO2 polar cap retention in the two hemispheres. A three dimensional model was used to study Martian global dust storms. The model accounts for the interactive feedbacks between the atmospheric thermal and dynamical states and an evolving radiatively active suspended dust load. Results from dust storm experiments, as well as from simulations in which there is interest in identifying the conditions under which surface dust lifting occurs at various locations and times, indicate that dust transport due to atmospheric eddy motions is likely to be important in the arrival of suspended dust at polar latitudes. The layered terrain in both polar regions of Mars is interpreted as the reality of cyclical episodes of volatile (CO2, H2O) and dust deposition.

Murphy, J. R.↗

NASA NTRS1968

Advances in light-gas gun technology

Constant-area accelerator used with light-gas guns increases the velocity of accelerating projectiles. A disposable accelerator on the muzzle of the gun uses the energy and momentum of a primary projectile, launched by the gun, to achieve high velocities of a light secondary projectile accelerated from rest in the accelerator.

Cowan, P. L.↗