Engineering topics

Hsui, A. T.

Publications and source records attributed to Hsui, A. T..

8 records

NASA NTRS1980

Thermal evolution of Ganymede and Callisto - Effects of solid-state convection and constraints from Voyager imagery

The imaging experiments of the Voyager 1 and 2 fly-by missions have provided a large amount of information about the nature of the surfaces of the Galilean satellites. The present investigation is concerned with the development of models regarding the thermal evolution of Ganymede and Callisto, taking into account the approach of parameterized convection. Attention is given to the physical, chemical, and geological data which are available as constraints on the thermal evolution of Ganymede and Callisto. Both satellites appear to possess surfaces composed of silicates and ice. However, their surface features are distinctly different from each other. In the discussion of thermal evolution models, attention is given to ice-dominant rheology, silicate-dominant rheology, and aspects of phase changes and solid-state convection.

Thurber, C. H.↗

NASA NTRS1979

The bounds of the heat production rate within the moon

A new approach is proposed to the evaluation of the lower and upper bounds of the global heat production rate within planetary interiors. The approach is based on the relationship between the internal energy change and the volume change of a planetary object. For illustration, the approach is applied to the moon. Using an average global surface heat flux of 18 erg/sq cm-sec, and assuming constancy of the lunar radius during the past 3.2 billion years. the lunar heat release within the past 3.2 billion years is estimated at (30 to 40) x 10 to the tenth erg/cu cm. This is equivalent to the present day uranium concentration of 35 to 50 ppb provided the radiogenic isotopes are of the same proportion as that given by Toksoz et al. (1978).

Hsui, A. T.↗

NASA NTRS1978

Thermal history and evolution of Mars

A thermal history of Mars is developed on the basis of available geophysical and geological data, including information obtained by the Viking missions. Specification of initial temperatures, composition and heat sources takes into account conduction and subsolidus mantle convection. Four phases in the Martian thermal history are distinguished. Core formation and crust differentiation occur during the first billion years. Partial melting, differentiation and outgassing of the mantle have taken place by the end of 3 billion years. In the 3- to 4-billion year epoch, the lithosphere thickens and the partial melt zone becomes deeper. By 4.6 billion years after commencement of evolution, volcanic activity has subsided, while the partial melt zone continues to shrink.

Toksoz, M. N.↗

NASA NTRS1978

Thermal evolutions of the terrestrial planets

Theoretical models are formulated for the thermal evolution of the moon, Mercury, Mars, Venus, and hypothetical minor planets, with consideration of conduction, solid-state convection, and differentiation. A variety of geological, geochemical and geophysical data is used to constrain both the present-day temperatures and the thermal histories of the planetary interiors. The data imply that the planets were heated during or shortly after formation and that all the terrestrial planets started differentiating early in their history. The size of the planet is the primary factor in determining its present-day thermal state. A planetary body with radius less than 1000 km is unlikely to reach melting, given heat source concentrations similar to terrestrial values and in the absence of intensive early heating.

Toksoz, M. N.↗

NASA NTRS1977

Thermal evolution of planetary size bodies

The size dependence of planetary thermal evolution is investigated through calculations which take into account the effects of heat source differentiation and convection. The theoretical computations make use of hypothetical bodies for minor planets; Mercury, Venus and Mars are employed to represent the size spectrum of the inner planets. If started at a cold initial condition, an object with a radius less than 1000 km is unlikely to reach melting. Accretional heating, inductive heating and short half-life radioactive heating are among the mechanisms which may produce early melting and differentiation in larger planets. Core formation in Mercury and Venus is also discussed.

Hsui, A. T.↗

NASA NTRS1973

Convection in the earth's mantle

The computer is used to solve for thermal convection within the earth's mantle. A review of the knowledge of surface displacements and of the present understanding of the mantle and its relevant physical and chemical properties is contained in the paper. Applicable equations assume a Newtonian fluid layer heated from below and within, with gravity acting downward. The numerical method employs finite differences and was constructed with a view toward the faithful simulation of coupling mechanisms. It enables surveying the effect of a parameter using a relatively coarse computing mesh. Some of the results obtained are presented.

Turcotte, D. L.↗

NASA NTRS1972

Thermal structure of the moon.

Numerical calculations for the structure of convection cells within a self-gravitating, fluid sphere are used to determine the temperature distribution within the moon. The distribution of surface heat flux is also given. The results are compared with the temperatures deduced from magnetic induction within the moon and with the surface heat flow measurement carried out on Apollo 15.

Turcotte, D. L.↗

NASA NTRS1972

Finite-amplitude thermal convection within a self-gravitating fluid sphere.

Finite-difference calculations have been carried out to determine the structure of finite-amplitude thermal convection within a self-gravitating fluid sphere with uniform heat release. For a fixed-surface boundary condition, single-cell convection breaks up into double-cell convection at a Rayleigh number of 30,000, at a Rayleigh number of 500,000 four-cell convection is observed. With a free-surface boundary condition only single cell convection is obtained up to a Rayleigh number of 5,000,000.

Hsui, A. T.↗