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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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Journal ArticleDOI
17 Oct 2014-Science
TL;DR: The precise difference between rotational and orbital periods suggests an unexpected interior for one of Saturn’s moons, and it is argued that the satellite has either a large nonhydrostatic interior, or a hydrostatic one with an internal ocean beneath a thick icy shell.
Abstract: Like our Moon, the majority of the solar system’s satellites are locked in a 1:1 spin-orbit resonance; on average, these satellites show the same face toward the planet at a constant rotation rate equal to the satellite’s orbital rate In addition to the uniform rotational motion, physical librations (oscillations about an equilibrium) also occur The librations may contain signatures of the satellite’s internal properties Using stereophotogrammetry on Cassini Image Science Subsystem (ISS) images, we measured longitudinal physical forced librations of Saturn’s moon Mimas Our measurements confirm all the libration amplitudes calculated from the orbital dynamics, with one exception This amplitude depends mainly on Mimas’ internal structure and has an observed value of twice the predicted one, assuming hydrostatic equilibrium After considering various possible interior models of Mimas, we argue that the satellite has either a large nonhydrostatic interior, or a hydrostatic one with an internal ocean beneath a thick icy shell

74 citations

Journal ArticleDOI
TL;DR: In this article, a simple cyclic process is proposed to explain why major strike-slip fault zones, including the San Andreas, are weak, and the cycle adjusts so that no net porosity is created (if the fault zone remains constant width).
Abstract: A simple cyclic process is proposed to explain why major strike-slip fault zones, including the San Andreas, are weak. Field and laboratory studies suggest that the fluid within fault zones is often mostly sealed from that in the surrounding country rock. Ductile creep driven by the difference between fluid pressure and lithostatic pressure within a fault zone leads to compaction that increases fluid pressure. The increased fluid pressure allows frictional failure in earthquakes at shear tractions far below those required when fluid pressure is hydrostatic. The frictional slip associated with earthquakes creates porosity in the fault zone. The cycle adjusts so that no net porosity is created (if the fault zone remains constant width). The fluid pressure within the fault zone reaches long-term dynamic equilibrium with the (hydrostatic) pressure in the country rock. One-dimensional models of this process lead to repeatable and predictable earthquake cycles. However, even modest complexity, such as two parallel fault splays with different pressure histories, will lead to complicated earthquake cycles. Two-dimensional calculations allowed computation of stress and fluid pressure as a function of depth but had complicated behavior with the unacceptable feature that numerical nodes failed one at a time rather than in large earthquakes. A possible way to remove this unphysical feature from the models would be to include a failure law in which the coefficient of friction increases at first with frictional slip, stabilizing the fault, and then decreases with further slip, destabilizing it.

74 citations

Journal ArticleDOI
TL;DR: In this article, the most widely used values computed by Nakiboglu need to be updated for two reasons: the difference between the polar and equatorial radii appears to be 113 ± 1 m (instead of 98 m) larger than the hydrostatic value.
Abstract: SUMMARY The knowledge of the gravitational potential coefficients J2 and J4 of a hydrostatic Earth model is necessary to deal with non-hydrostatic properties of our planet. They are indeed fundamental parameters when modelling the 3-D density structure or the rotational behaviour of our planet. The most widely used values computed by Nakiboglu need to be updated for two reasons. First, we have noted a mistake in one of his formulae. Secondly, the value of the inertia ratio I/MR2 chosen at the time of prem is not any more the best estimate. Both corrections slightly but significantly reduce the hydrostatic J2 value: the dynamical flattening of the Earth is even further from hydrostaticity than previously thought. The difference between the polar and equatorial radii appears to be 113 ± 1 m (instead of 98 m) larger than the hydrostatic value. Moreover, uncertainties upon the hydrostatic parameters are estimated.

72 citations

Journal ArticleDOI
TL;DR: In this paper, a two-column radiative-convective model with an explicit hydrological cycle that uses clear-sky conditions in the radiation calculation is considered, and a flow field is calculated by the linearized, hydrostatic equations of motion in a non-rotating frame of reference.
Abstract: Interaction between steady, large-scale atmospheric circulations and a radiative-convective environment is considered. As a model tool, we use a two-column radiative-convective model with an explicit hydrological cycle that uses clear-sky conditions in the radiation calculation. A flow field is calculated by the linearized, hydrostatic equations of motion in a non-rotating frame of reference. Mechanical damping is represented by vertical diffusion of momentum and surface drag. the flow advects heat and moisture, and thereby modifies the local radiative-convective equilibrium. A dynamically passive ocean mixed layer is situated below the model atmosphere. All externally specified parameters are identical in the two columns, implying that local radiative-convective equilibrium is a steady solution. For weak mechanical damping (or small column length), the local equilibrium is generally unstable due to a positive feedback between large-scale subsidence and infrared cooling, which operates via advective drying. A circulating equilibrium, in which the air ascends in one column and descends in the other, is attained. Due to a reduced content of clear-sky water vapour, which is the major infrared absorber in the model, the circulating equilibrium can emit the absorbed solar radiation at a significantly lower surface temperature than the corresponding local equilibrium. In the limit of a nearly inviscid atmosphere, the intensity of the large-scale circulation is controlled chiefly by the mid-tropospheric radiative cooling in the downdraught column. In this regime, we find two distinct equilibria with circulation that are distinguished by the features of the downdraught column: one branch with deep convection but where the integrated convective heating vanishes due to evaporation of precipitation; and one branch with shallow (or no) convection where the surface boundary layer is disconnected from the free atmosphere.

72 citations

Journal ArticleDOI
TL;DR: In this paper, the deformational behavior of a granular soil under hydrostatic compressive stress is studied and a theoretical model consisting of regular arrays of uniform spherical spheres, but with a probabilistic distribution of holes in the arrays, is postulated.
Abstract: The deformational behavior of a granular soil under hydrostatic compressive stress is studied. A theoretical model consisting of regular arrays of uniform spheres, but with a probabilistic distribution of holes in the arrays, is postulated. When Hertzian behavior at the points of contact between the spheres is assumed and the holes are made to close under increasing pressure, a theoretical hydrostatic stress-strain relationship is derived. The theory is used to predict the compression of an Ottawa sand at various densities, and is found to give good agreement with the measurements obtained by testing the soil in a new apparatus. The behavior is found to be nonlinear but almost completely elastic.

72 citations


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