Hydrostatic equilibrium

About: Hydrostatic equilibrium is a research topic. Over the lifetime, 2451 publications have been published within this topic receiving 62172 citations.

Robe's restricted three-body problem revisited

Abstract: Robe's restricted three-body problem is reanalyzed with a view to incorporate a new assumption, namely that the configuration of the fluid body is that described by an hydrostatic equilibrium figure (Roche's ellipsoid). In the concomitant gravitational field a full treatment of the buoyancy force is given. The pertinent equations of motion are derived, the linear stability of the equilibrium solution is studied and the connection between the effect of the buoyancy forces and a perturbation of the Coriolis force is pointed out.

Atmospheres for hot, high-gravity stars. II. Pure helium models

Abstract: We present an extensive grid of pure helium stellar model atmosphere calculations for hot, high-gravity stars. These models are intended to help elucidate the nature and characteristics of the progenitors of the DB white dwarfs. The surface gravity in the model grid ranges from log g = 6.0 (1.0) 9.0, and the effective temperature ranges from T/sub e/ = 25,000 K at log g = 6.0 and 8.0 (T/sub e/ = 40,000 K at log g = 7.0 and 9.0) up to temperatures close to the Eddington limit at each gravity. All our models assume hydrostatic equilibrium, steady-state statistical equilibrium, pure helium composition, and plane-parallel geometry. Most of our models are unblanketed and in LTE, and include convective energy transport. In addition to these, smaller preliminary grids of NLTE models (assuming detailed radiative balance in the helium lines) and of LTE, helium-line--blanketed models (including convective energy transport) were computed to assess the importance of these effects.

Continentality and the gravitational field of the Earth

Abstract: Satellite observations provide some information about zonal harmonics J2, J3, … J6 of the gravitational field. For a hydrostatic earth (all surfaces of equal density are level), odd harmonics vanish and even harmonics can be computed from precession and geophysical data. We have compared the nonhydrostatic (observed minus hydrostatic) harmonics with those calculated for the known distribution of continents and some reasonable assumptions about density in the crust. The two sets of values do not agree, and this raises the possibility that density variations in the mantle, perhaps unrelated to the distribution of continents, are the important factor in determining the gravitational coefficients of low order.

Time scales of relaxation dynamics during transient conditions in two-phase flow

Abstract: The relaxation dynamics towards a hydrostatic equilibrium after a change in phase saturation in porous media is governed by fluid reconfiguration at the pore scale. Little is known whether a hydrostatic equilibrium in which all interfaces come to rest is ever reached and which microscopic processes govern the time scales of relaxation. Here we apply fast synchrotron-based X-ray tomography (X-ray CT) to measure the slow relaxation dynamics of fluid interfaces in a glass bead pack after fast drainage of the sample. The relaxation of interfaces triggers internal redistribution of fluids, reduces the surface energy stored in the fluid interfaces and relaxes the contact angle towards the equilibrium value while the fluid topology remains unchanged. The equilibration of capillary pressures occurs in two stages: (i) a quick relaxation within seconds in which most of the pressure drop that built up during drainage is dissipated, a process that is to fast to be captured with fast X-ray CT, and (ii) a slow relaxation with characteristic time scales of 1-4 h which manifests itself as a spontaneous imbibition process that is well described by the Washburn equation for capillary rise in porous media. The slow relaxation implies that a hydrostatic equilibrium is hardly ever attained in practice when conducting two-phase experiments in which a flux boundary condition is changed from flow to no-flow. Implications for experiments with pressure boundary conditions are discussed.