Hydrostatic equilibrium

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

Slow magnetohydrodynamic waves in stratified and viscous plasmas

Abstract: The propagation of slow magnetohydrodynamic waves in vertical thin flux tubes embedded in a vertically stratified plasma in the presence of viscosity is shown here to be governed by the Klein-Gordon-Burgers (KGB) equation, which is solved in two limiting cases assuming an isothermal medium in hydrostatic equilibrium surrounded by a quiescent environment. The results presented here can be applied to, e.g., study the propagation of slow magnetohydrodynamic waves generated by the granular buffeting motion in thin magnetic photospheric tubes. When the variation in the reduced velocity occurs over typical lengths much larger than the gravitational scale height, the KGB equation can be reduced to a Klein-Gordon equation describing the propagation of an impulse followed by a wake oscillating with the frequency reduced by viscosity and the solution has no spatial or temporal decay. However, in the other limiting case, i.e., typical variations in the reduced velocity occur over characteristic lengths much smaller than the gravitational scale height, waves have a temporal and spatial decay.

Linear dynamics of hydrostatic adjustment to horizontally homogeneous heating

Abstract: The process of hydrostatic adjustment to horizontally homogeneous heating in a stably stratifiedatmosphere of arbitrary thermal structure is investigated in the limit of small perturbations. Alinear differential equation is derived for the vertical pressure distribution in the final balancedstate. Solutions of this equation are compared with the time dependent solution which is foundby numerically integrating the equations in time. During the process of hydrostatic adjustmentacoustic-buoyancy oscillations are generated. The amplitudes of these oscillations become sogreat that static instability is generated at heights above 100 km, depending on where and howabruptly the heat is added. As a crude representation of the unstable breakdown and dampingof these waves, Rayleigh damping is introduced. If the associated damping coefficient in theupper atmosphere is sufficiently large (greater than the Brunt Vaisala frequency), the oscillationsvanish. Below a height of about 50 km the steady state predicted by the above mentioneddifferential equation is reached approximately in 10 min. DOI: 10.1034/j.1600-0870.2000.00063.x

Numerical Simulation of Static Seal Contact Mechanics Including Hydrostatic Load at the Contacting Interface

Abstract: A finite element model of a static seal assembled in its housing has been built and is utilized to study how the seal deforms under varying loading conditions. The total contact load on the sealing surface is balanced by the sealed fluid pressure and the friction between the seal and the housing sidewall perpendicular to the sealing surface. The effect of the sealed fluid pressure between the sealing surfaces was investigated and the simulation showed that the surface profile is distorted due to the hydrostatic pressure. We study the distorted contact profile with varying sealed fluid pressure and propose five parameters to describe the corresponding contact pressure profile. One of these parameters, overshoot pressure, a measure of the difference between maximum contact pressure and the sealed fluid pressure, is an indicator of sealing performance. The simulations performed show different behaviors of the overshoot pressure with sealed fluid pressure for cosinusoidal and parabolic surfaces with the same peak to valley (PV) value.

Gravothermal instability of anisotropic self-gravitating gas spheres : singular equilibrium solution

Abstract: A re-investigation of linear perturbation theory is presented, which examines the hydrostatic re-adjustment of an isolated self-gravitating gas sphere to a redistribution of energy. Such a model describes a stellar system by the common equations of gas in hydrostatic equilibrium but with the effect of the anisotropic velocity distribution on the pressure gradient. We take as equilibrium models the singular isothermal solution with and without anisotropy. The total variation of the Boltzmann entropy resulting from a perturbation of the system caused by a redistribution of heat (i.e. rms kinetic energy of the stars) is calculated for anisotropic solutions to first order as well as to second order for the isotropic equilibrium