Hydrostatic equilibrium

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

Corrections to Solar Thermal Structure when a Turbulent Magnetic Field is Included

Abstract: Correction of non-ideal effect due to a magnetic fluctuating tensor is derived from the ideal MHD equations. The inclusion of a magnetic turbulent field leads to modifications of the hydrostatic equilibrium equation and thermodynamical variables such as the temperature T, the adiabatic exponent gamma, the adiabatic temperature gradient del(ad) and the temperature gradient del. In particular, the modifications in the adiabatic and radiative temperature gradients will result in a change in the Schwarzchild criterion, hence in the location of the base of the convective zone. Incorporating the modifications, we construct a modified thermodynamical equilibrium structure of the Sun.

Atmospheric physics and Atmospheres of Solar-System bodies

Abstract: The physical principles governing the planetary atmospheres are briefly introduced in the first part of this chapter, moving from the examples of Solar System bodies. Namely, the concepts of collisional regime, balance equations, hydrostatic equilibrium and energy transport are outlined. Further discussion is also provided on the main drivers governing the origin and evolution of atmospheres as well as on chemical and physical changes occurring in these systems, such as photochemistry, aerosol condensation and diffusion. In the second part, an overview about the Solar System atmospheres is provided, mostly focussing on tropospheres. Namely, phenomena related to aerosol occurrence, global circulation, meteorology and thermal structure are described for rocky planets (Venus and Mars), gaseous and icy giants and the smaller icy bodies of the outer Solar System.

Nonlinear Coupled Hydrostatics of Floating Conical Platforms

Abstract: The increased exploration of deeper Arctic waters motivates the designs of new floating structures to operate under harsh Arctic conditions. Based on several model tests and investigations, structures with conical sections at the waterline have been shown to be a good design for waters where drifting ice is present, because the approaching ice fails in bending which induces smaller loads than crushing failure. However, in most Arctic waters ice features are only present parts of the year and a large portion of the operation time of these structures will be in open water. Therefore, the floating structures must perform well in both these conditions. Conical sections at the waterline will induce nonlinear coupling in the hydrostatic restoring forces and moments. It is important to understand how this affects the behaviour in both ice and open water conditions. In order to investigate the nonlinear coupled hydrostatic restoring forces, an exact analytic expression for the metacentric height of a regular cone is presented. This is further derived to a frustum cone that can be used to develop an exact analytic expression for the hydrostatic restoring forces and moments for any conical body. A platform of the shallow draught-type is used as a basis for the discussion and the effect of the coupled nonlinear restoring forces is illustrated by two-degrees-of-freedom (2DOF) pitch-heave time domain simulations.Copyright © 2009 by ASME

A note on instabilities of a Kelvin-Helmholtz velocity profile in different approximations

Abstract: The Kelvin-Helmholtz problem deals with the stability of superposed fluids in relative motion. For a basic discontinuity in the velocity of 2U and a constant Brunt-Vaisala frequencyN it has been found that in the Boussinesq approximation small perturbations with a horizontal wavenumberk, such thatk 2>N 2/2U 2, are unstable. When the fluid is assumed to be compressible and taking into account the variation of the density in all the equations we find that there are also instabilities fork 2

Synthetic observations of first hydrostatic cores in collapsing low-mass dense cores. I. Spectral energy distributions and evolutionary sequence

Abstract: The low-mass star formation evolutionary sequence is relatively well-defined both from observations and theoretical considerations. The first hydrostatic core is the first protostellar equilibrium object that is formed during the star formation process. Using state-of-the-art radiation-magneto-hydrodynamic 3D adaptive mesh refinement calculations, we aim to provide predictions for the dust continuum emission from first hydrostatic cores. We investigate the collapse and the fragmentation of magnetized one solar mass prestellar dense cores and the formation and evolution of first hydrostatic cores using the RAMSES code. We use three different magnetization levels for the initial conditions, which cover a large variety of early evolutionary morphology, e.g., the formation of a disk or a pseudo-disk, outflow launching, and fragmentation. We post-process the dynamical calculations using the 3D radiative transfer code RADMC-3D. We compute spectral energy distributions and usual evolutionary stage indicators such as bolometric luminosity and temperature. We find that the first hydrostatic core lifetimes depend strongly on the initial magnetization level of the parent dense core. We derive, for the first time, spectral energy distribution evolutionary sequences from high-resolution radiation-magneto-hydrodynamic calculations. We show that under certain conditions, first hydrostatic cores can be identified from dust continuum emission at 24 microns and 70 microns. We also show that single spectral energy distributions cannot help to distinguish between the formation scenarios of the first hydrostatic core, i.e., between the magnetized and non-magnetized models. Spectral energy distributions are a first useful and direct way to target first hydrostatic core candidates but high-resolution interferometry is definitively needed to determine the evolutionary stage of the observed sources.