Hydrostatic equilibrium

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

Pressure distribution in hydrostatic extrusion dies

Abstract: To be able to understand the detailed mechanics of plastic flow and lubrication during hydrostatic extrusion it is very desirable to be able to measure the precise pressure distribution along the length of the die.In the present work, experiments have been developed which enable this pressure distribution to be measured indirectly with reasonable accuracy and comparison is made between the distribution obtained experimentally during slow-speed hydrostatic extrusion of annealed copper and the distribution predicted by theoretical analysis. Very good agreement was obtained for the single geometry investigated.

Hydrostatic Experiments up to Ultrahigh Pressures

Abstract: The development of the diamond-anvil-cell technology has enabled us to conduct in situ experiments at ultrahigh pressures. The current pressure limit reaches well beyond 200 GPa. The stress environment in such experiments is in general highly nonhydrostatic, and one has to be careful in evaluating the obtained data. Nonhydrostaticity affects the phase stability, transition pressures, equation of state, and various lattice properties. For detailed discussion of the change in physical properties with pressure, we have to realize hydrostatic or quasihydrostatic conditions. I describe our present understanding of the stress state of a sample compressed in a diamond-anvil cell, together with recent efforts for extending the pressure limit of hydrostatic experiments.

Detection of a Bipolar Molecular Outflow Driven by a Candidate First Hydrostatic Core

Abstract: We present new 230 GHz Submillimeter Array observations of the candidate first hydrostatic core Per-Bolo 58. We report the detection of a 1.3 mm continuum source and a bipolar molecular outflow, both centered on the position of the candidate first hydrostatic core. The continuum detection has a total flux density of 26.6 +/- 4.0 mJy, from which we calculate a total (gas and dust) mass of 0.11 +/- 0.05 Msun and a mean number density of 2.0 +/- 1.6 X 10^7 cm-3. There is some evidence for the existence of an unresolved component in the continuum detection, but longer-baseline observations are required in order to confirm the presence of this component and determine whether its origin lies in a circumstellar disk or in the dense inner envelope. The bipolar molecular outflow is observed along a nearly due east-west axis. The outflow is slow (characteristic velocity of 2.9 km/s), shows a jet-like morphology (opening semi-angles ~8 degrees for both lobes), and extends to the edges of the primary beam. We calculate the kinematic and dynamic properties of the outflow in the standard manner and compare them to several other protostars and candidate first hydrostatic cores with similarly low luminosities. We discuss the evidence both in support of and against the possibility that Per-Bolo 58 is a first hydrostatic core, and we outline future work needed to further evaluate the evolutionary status of this object.

A weakly non-hydrostatic shallow model for dry granular flows

Abstract: A non-hydrostatic depth-averaged model for dry granular flows is proposed, taking into account vertical acceleration. A variable friction coefficient based on the $\mu(I)$ rheology is considered. The model is obtained from an asymptotic analysis in a local reference system, where the non-hydrostatic contribution is supposed to be small compared to the hydrostatic one. The non-hydrostatic counterpart of the pressure may be written as the sum of two terms: one corresponding to the stress tensor and the other to the vertical acceleration. The model introduced here is weakly non-hydrostatic, in the sense that the non-hydrostatic contribution related to the stress tensor is not taken into account due to its complex implementation. A simple and efficient numerical scheme is proposed. It consists of a three-step splitting procedure, and it is based on a hydrostatic reconstruction. Two key points are: (i) the friction force has to be taken into account before solving the non-hydrostatic pressure. Otherwise, the incompressibility condition is not ensured; (ii) both the hydrostatic and the non-hydrostatic pressure are taken into account when dealing with the friction force. The model and numerical scheme are then validated based on several numerical tests, including laboratory experiments of granular collapse. The influence of non-hydrostatic terms and of the choice of the coordinate system (Cartesian or local) is analyzed. We show that non-hydrostatic models are less sensitive to the choice of the coordinate system. In general, the non-hydrostatic model introduced here much better reproduces granular collapse experiments compared to hydrostatic models. An important result is that the simulated mass profiles up to the deposit and the front velocity are greatly improved. As expected, the influence of the non-hydrostatic pressure is shown to be larger for small values of the slope.