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Hydrostatic equilibrium

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


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Patent
08 Jan 1975
TL;DR: In this article, a transmission mechanism adapted especially for agricultural and industrial tractors and for heavy construction vehicles comprising a pair of hydrostatic pump-and-motor units arranged in a closed hydrostatic fluid flow circuit, a planetary gear unit and geared connections between separate elements of the gear units and the rotor for each hydrostatic unit, each geared connection having its characteristic speed ratio, defining multiple speed ranges within which an infinite torque ratio variation was achieved.
Abstract: A transmission mechanism adapted especially for agricultural and industrial tractors and for heavy construction vehicles comprising a pair of hydrostatic pump-and-motor units arranged in a closed hydrostatic fluid flow circuit, a planetary gear unit and geared connections between separate elements of the gear unit and the rotor for each hydrostatic unit, each geared connection having its characteristic speed ratio thereby defining multiple speed ranges within which an infinite torque ratio variation is achieved.

31 citations

Journal ArticleDOI
TL;DR: In this article, the authors compare isothermal models to models including cooling with a simple but self-consistent treatment of the coupling between gas, grains and radiation field temperatures, and show that isothermal model fails to account for the innermost slow infall motions observed, even with the most hydrostatic initial conditions.
Abstract: We compute numerical simulations of spherical collapse triggered by a slow increase in external pressure. We compare isothermal models to models including cooling with a simple but self-consistent treatment of the coupling between gas, grains and radiation field temperatures. The hydrostatic equilibrium appears to hold past the marginally stable state, until the collapse proceeds. The last hydrostatic state before collapse has a lower central gas temperature in the centre due to the enhanced coupling between gas, grains and radiation field. This results in slightly lower pressure gradients in the bulk of the envelope which is hence slightly more extended than in the isothermal case. Due to the sensitivity of the collapse on these initial conditions, protostellar infall velocities in the envelope turn out to be much slower in the case with cooling. Our models also compute the radiative transfer and a rather large chemical network coupled to gas dynamics. However, we note that the steady-state chemisorption of CO is sufficient to provide an accurate cooling function of the gas. This justifies the use of post-processing techniques to account for the abundance of observed molecules. Existing observations of infall signatures put very stringent constraints on the kinematics and temperature profile of the class 0 protostar IRAM 04191+1522. We show that isothermal models fail to account for the innermost slow infall motions observed, even with the most hydrostatic initial conditions. In contrast, models with cooling reproduce the general shape of the temperature profile inferred from observations and are in much better agreement with the infall signatures in the inner 3000 AU.

31 citations

Journal ArticleDOI
TL;DR: In this article, the results of a layer-by-layer analysis of a cross-ply graphite-epoxy cylinder subjected to external hydrostatic pressure were presented. But the analysis was performed away from the surface of the cylinder.
Abstract: This study discusses the results of a layer-by-layer analysis of a thick-walled cross-ply graphite-epoxy cylinder subjected to external hydrostatic pressure. The analysis, which is valid away from ...

31 citations

Journal ArticleDOI
TL;DR: In this paper, it was shown that nonmonotone saturation profiles might occur even at zero flux, when both fluids are at rest, and that hysteresis suffices to explain the effect.
Abstract: Nonmonotonic saturation profiles (saturation overshoot) occur as travelling waves in gravity driven fingering. They seem important for preferential flow mechanisms and have found much attention recently. Here, we predict them even for hydrostatic equilibrium when all velocities vanish. We suggest that hysteresis suffices to explain the effect. Recently, the observation of nonmonotonicity of traveling wave solutions for saturation profiles during constant-flux infiltration experiments has highlighted the shortcomings of the traditional, seventy year old mathematical model for immiscible displacement in porous media. Several recent modifications have been proposed to explain these observations. The present paper suggests that nonmonotone saturation profiles might occur even at zero flux. Specifically, nonmonotonicity of saturation profiles is predicted for hydrostatic equilibrium, when both fluids are at rest. It is argued that in traditional theories with the widely used single-valued monotone constitutive functions, nonmonotone profiles should not exist in hydrostatic equilibrium. The same applies to some modifications of the traditional theory. Nonmonotone saturation profiles in hydrostatic equilibrium arise within a generalized theory that contains the traditional theory as a special case. The physical origin of the phenomenon is simultaneous occurrence of imbibition and drainage. It is argued that indications for nonmonotone saturation profiles in hydrostatic equilibrium might have been observed in past experiments and could become clearly observable in a closed column experiment.

31 citations

Journal ArticleDOI
Hao Su1, Lihua Lu1, Yingchun Liang1, Qiang Zhang1, Yazhou Sun1 
TL;DR: In this paper, an integrated heat-fluid-solid coupling model of the hydrostatic spindle system is built to simulate the heat generation process and the fluid-structure conjugate heat transfer.
Abstract: The temperature rise of an ultra-precision machine tool has a great impact on machining accuracy. Meanwhile, the hydrostatic spindle system is the main internal heat source of the machine tool, which consists of a hydrostatic spindle and a direct current motor. Therefore, it is very significant to study the thermal behaviors of the hydrostatic spindle system. In this paper, an integrated heat-fluid–solid coupling model of the hydrostatic spindle system is built to simulate the heat generation process and the fluid–structure conjugate heat transfer. Then a finite volume element method (FVEM) is proposed by combining the advantages of the finite volume method (FVM) and the finite element method (FEM) with consideration of the interaction of the temperature field, thermal deformation, and eccentricity. Based on the proposed model and method, the thermal characteristics of the hydrostatic spindle system are studied by the two-way heat-fluid–solid coupling analysis. The temperature variations obtained by the simulation agree well with the experimental results, which validate the proposed model and method.

31 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023282
2022708
202167
202089
201998
201893