Hydrostatic equilibrium

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

Experimental equipment for measuring physical properties of the annular hydrostatic thrust bearing

Abstract: The hydraulic circuit, through which the mineral oil is brought, is an important part of hydrostatic bearings. The annular hydrostatic thrust bearing consists of two sliding plates divided by a layer of mineral oil. In the lower plate, there are oil grooves which distribute the liquid between the sliding areas. The hydraulic circuit is made of two basic parts: the energy source and the controlling part. The hydraulic pump, which brings the liquid into the sliding bearing, is the source of the pressure energy. The sliding bearing is weighted down by axial force, which can be changed during the process. That´s why in front of the particular oil grooves control components adjusting pressure and flow size are located. This paper deals with a project of a hydraulic circuit for regulation of fluid layer in the annular hydrostatic thrust bearing and the testing equipment for measuring its physical properties. It will include the issue of measuring loading capacity and height of the fluid layer in the annular hydrostatic thrust bearing.

Cosmic snow clouds: self-gravitating gas spheres manifesting hydrogen condensation

Abstract: We present hydrostatic equilibrium models of spherical, self-gravitating clouds of helium and molecular hydrogen, focusing on the cold, high-density regime where solid- or liquid-hydrogen can form. The resulting structures have masses from 0.1 Msun down to several x 1.e-8 Msun, and span a broad range of radii: 1.e-4 < R(AU) < 1.e7. Our models are fully convective, but all have a two-zone character with the majority of the mass in a small, condensate-free core, surrounded by a colder envelope where phase equilibrium obtains. Convection in the envelope is unusual in that it is driven by a mean-molecular-weight inversion, rather than by an entropy gradient. In fact the entropy gradient is itself inverted, leading to the surprising result that envelope convection transports heat inwards. In turn that permits the outer layers to maintain steady state temperatures below the cosmic microwave background. Amongst our hydrostatic equilibria we identify thermal equilibria appropriate to the Galaxy, in which radiative cooling from H2 is balanced by cosmic-ray heating. These equilibria are all thermally unstable, albeit with very long thermal timescales in some cases. The specific luminosities of all our models are very low, and they therefore describe a type of baryonic dark matter. Consequently such clouds are thermally fragile: when placed in a harsh radiation field they will be unable to cool effectively and disruption will ensue as heat input drives a secular expansion. Disrupting clouds should leave trails of gas and H2 dust in their wake, which might make them easier to detect. Our models may be relevant to the cometary globules in the Helix Nebula, and the G2 cloud orbiting Sgr A*.

A Non-Hydrostatic Depth-Averaged Model for Hydraulically Steep Free-Surface Flows

Abstract: This study describes the results of a numerical investigation aimed at developing and validating a non-hydrostatic depth-averaged model for flow problems where the horizontal length scales close to flow depth. For such types of problems, the steep-slope shallow-water equations are inadequate to describe the two-dimensional structure of the curvilinear flow field. In the derivation of these equations, the restrictive assumptions of negligible bed-normal acceleration and bed curvature were employed, thus limiting their applicability to shallow flow situations. Herein, a Boussinesq-type model is deduced from the depth-averaged energy equation by relaxing the weakly-curved flow approximation to deal with the non-hydrostatic steep flow problems. The proposed model is solved with an implicit finite difference scheme and then applied to simulate steady free-surface flow problems with strong curvilinear effects. The numerical results are compared to experimental data, resulting in a reasonable overall agreement. Further, it is shown that the discharge characteristics of free flow over a round-crested weir are accurately described by using a Boussinesq-type approximation, and the drawbacks arising from a standard hydrostatic approach are overcome. The suggested numerical method to determine the discharge coefficient can be extended and adopted for other types of short-crested weirs.