摘要:

The numerical modeling of viscous drops and films have been restrictive due to the difficulty in solving the full transport equations where the location of the boundary is not knowna priori, and also due to the perplexity in calculating an accurate surface curvature. In this paper we combine an advanced numerical algorithm (FLAIR) with a newly presented and accurate curvature calculation scheme, to study the dynamics of viscous drops and films. It is demonstrated that this technique can resolve the complex flow fields and large surface deformations of the type which are common in studies of viscous liquid drops and films. The evolution of the shape and internal flow field of an initially elliptic, infinitely long, viscous liquid cylinder and a liquid film with both symmetric and asymmetric large amplitude sinusoidal surface disturbances are calculated numerically.

ISSN:0094-243X    

DOI:10.1063/1.38960

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Over the past decade, the significant advancements that have been made in the development of computational tools and numerical techniques have allowed astrophysicists to begin to model accurately the nonlinear growth of gravitational instabilities in a variety of physical systems. The fragmentation or rotationally driven fission of dynamically evolving, self‐gravitating ‘‘drops and bubbles’’ is now routinely modeled in full three‐dimensional generality as we attempt to understand the behavior of protostellar clouds, rotating stars, galaxies, and even the primordial soup that defined the birth of the universe. A brief review is presented here of the general insights that have been gained from studies of this type, followed by a somewhat more detailed description of work, currently underway, that is designed to explain the process of binary star formation. A short video animation sequence, developed in conjunction with some of the research being reviewed, illustrates the basic‐nature of the fission instability in rotating stars and of an instability that can arise in a massive disk that forms in a protostellar cloud.

ISSN:0094-243X    

DOI:10.1063/1.38961

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

In a continuation of the long‐standing effort of the nuclear physics community to model atomic nuclei as droplets of a specialized nuclear fluid, we have developed a hydrodynamic model for simulating the collisions of heavy nuclei at relativistic speeds. Our model couples ideal relativistic hydrodynamics with a new Monte Carlo treatment of dynamic pion production and tracking. The collective flow for low‐energy (200 MeV/N) collisions predicted by this model compares favorably with results from earlier hydrodynamic calculations which used quite different numerical techniques. Our pion predictions at these lower energies appear to differ, however, from the experimental data on pion multiplicities. In the case of ultra‐relativistic (200 GeV/N) collisions, our hydrodynamic model has produced baryonic matter distributions which are in reasonable agreement with recent experimental data. These results may shed some light on the sensitivity of relativistic collision data to the nuclear equation of state.

ISSN:0094-243X    

DOI:10.1063/1.38962

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The equation describing the dynamics of rotating, self‐gravitating fluid masses are formulated, with particular emphasis on quasi‐steady approximations needed to resolve the problem of ‘‘stiffness’’ due to the presence of widely separated timescales. The solutions of the quasi‐steady system need to be tested separately for stability on the shortest timescale, and the essentially Lagrangian, or Hamiltonian, nature of that stabilitiy problem is indicated. Application is made to the classical ellipsoidal figures, and recent progress toward understanding the fission process of binary‐star formation is described in this context.

ISSN:0094-243X    

DOI:10.1063/1.38963

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Light scattered from spheroidal drops produces a variety of complicated diffraction patterns which are examples of optical catastrophes. These patterns decorate caustics in the outgoing rays which have been refracted by (and internally reflected from) the drop’s surface. Near the rainbow scattering angle, hyperbolic umbilic, cusp, and other catastrophes have been observed with laser and white light illumination. Lips caustics in the backscattering pattern have also been obseved. Calculations of caustic parameters (from generalized ray tracing) and wavefields are summarized.

ISSN:0094-243X    

DOI:10.1063/1.38964

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The undercooling of liquids is observed often, but is restricted by the catalysis of heterogeneous nucleation sites in contact with the liquid. Containerless liquid processing and liquid dispersal into fine droplets yields an effective nucleant isolation which permits a deep undercooling approaching 0.3–0.4Tmbefore the onset of solidification. At high undercooling the nucleation of an equilibrium phase may be superseded by metastable product structures. Often processing variable such as melt superheat, liquid surface films, powder size and cooling rate can be used to control the undercooling and produce a transition in phase selection kinetics. In this case the use of metastable phase diagrams is important for the interpretation and prediction of solidification products such as supersaturated solutions, metastable intermediate phases and glasses. At the same time a consideration of the competitive nucleation and growth kinetics and solidification thermal history is essential in the analysis of solidification microstructure. These features highlight a number of solidifcation reaction paths and new opportunities for the development of microstructure control.

ISSN:0094-243X    

DOI:10.1063/1.38965

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

By utilizing electromagnetic levitation, it is possible to control both the degree of superheating and, more importantly, the degree of supercooling of a melt prior to splat‐quenching. This allows some control over the resulting microstructure. For the case of Ni3Al‐Cr alloys, this enabled us to control the antiphase domain size relative to the grain size. Subsequent annealing treatment were used to modify these microstructural features. Miniature tensile tests were performed on the resulting material in order to test current theories of ductility in these ordered alloys. Conducive to the testing of such theories is the ability to solidify the various alloys at different degrees of undercooling, which is conveniently done with containerless processing.

ISSN:0094-243X    

DOI:10.1063/1.38967

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

This paper reviews the theoretical and experimental advances in droplet combustion since the 1982 Second International Colloquium on Drops and Bubbles. Specific topics discussed include multicomponent droplet combustion and microexplosion, convection droplet combustion, the combustion of slurries, propellants and hazardous wastes, soot formation in droplet burning, and several miscellaneous subjects. Areas of further research are suggested.

ISSN:0094-243X    

DOI:10.1063/1.38968

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

This paper presents recent results from a continuing study on the burning characteristics of pure, single component fuel droplets in a microgravity environment. A new, economical, microprocessor‐based, computer imaging and data analysis method for determining the diameter and the position of the burning droplet from photographic records is described and demonstrated using experimental data previously obtained on the combustion of n‐decane droplets in air. Initial observations on the combustion of methanol droplets in air are also reported.

ISSN:0094-243X    

DOI:10.1063/1.38986

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A Droplet Burning Facility which allows the investigation of droplet vaporization and burning under various dynamic and thermal conditions has been constructed. The system has been operated during the parabolic flights of the NASA KC135 aircraft. An important set of data has been collected on the low temperature turbulent vaporization and envelope burning of suspended n‐heptane droplets at ground and reduced gravity conditions. From digitized images obtained by a rapid video camera, the time evolution of the droplet and the flame dimensions are determined with great accuracy. The information is used to deduce the vaporization rate constant, the flame diameter and the flame standoff ratio under various conditions.

ISSN:0094-243X    

DOI:10.1063/1.38969

出版商:AIP    

年代:1990

数据来源: AIP