Showing papers on "Hydrostatic equilibrium published in 1984"

Analytical surface pressure and drag for linear hydrostatic flow over three-dimensional elliptical mountains

Abstract: A linear hydrostatic model of the flow of stably stratified air over a three-dimensional mountain with an elliptical horizontal cross section is considered. Analytical expressions for the surface pressure perturbation are used to study the differences between two- and three-dimensional flows. The horizontal divergence and lateral streamline deflection associated with the velocity component perpendicular to the mean flow are also considered. The force exerted on the mountain by the incoming airstream is determined as a function of the barrier eccentricity and orientation. If the upstream flow is not parallel to a symmetry axis of the terrain, there is a transverse force on the air which can be an appreciable fraction of the drag force acting in the direction opposite to the mean wind.

Effects of the pressure perturbation field in numerical models of unidirectionally sheared thunderstorm convection - Two versus three dimensions

Abstract: The physical roles of 'buoyant' and 'dynamic' pressure components, and the distinction between buoyant and hydrostatic pressure perturbations, are aspects of the pressure perturbation field in strongly sheared convective storms studied by means of two- and three-dimensional anelastic numerical modeling experiments with common environmental profiles. The pressure analysis clarifies the differences between two- and three-dimensional storms. In the main updraft, strong midlevel thermal buoyancy is partly opposed by a downward-perturbed vertical pressure gradient force. This, however, occurs to a much greater extent in two dimensions than in three, contributing to smaller net upward accelerations. While the buoyant and hydrostatic fields are intimately related to the total buoyancy distribution, the buoyant pressure perturbation is smoother and of lower amplitude than its hydrostatic counterpart. For the model experiments, this distinction is far greater in three dimensions than in two, in association with the smaller scale of the active convection in three dimensions.

Numerical Analysis for Hydrostatic and Nonhydrostatic Equations of Inertial-Internal Gravity Waves

Abstract: A modified forward-backward scheme applied to the anelastic system is proposed. This modified scheme not only retains all the advantages of the conventional forward-backward scheme but also is more consistent with the original differential equations. This scheme is used to investigate inertial waves and internal gravity waves in three different lattices. It is found that the lattice C proposed by Deardorff is better than either lattice A or lattice B when applied to internal gravity waves and thermal convection in the atmosphere. The difference between a hydrostatic system and a nonhydrostatic system is also discussed in detail in this paper. Here we propose to apply Shuman's smoothing on a hydrostatic system to filter out the undesirably, highly oscillatory short waves, or stroll small-scale convection, so that we may produce reasonable results compared with those of a nonhydrostatic system. The validity of this method has been proved by the numerical results of a study on the mesoscale cloud ba...

Vertical Accelerations in Prestressed Concrete Tanks

Abstract: Vertical accelerations of circular cylindrical tanks and their contents cause hoop forces in the tank walls. The hoop forces caused by hydrodynamic fluid pressure are additive to those caused by hydrostatic fluid pressure; earthquake-resistant design of tanks should therefore consider the combined fluid pressure. The design of a prestressed concrete tank wall must be such that under combined hydrostatic and earthquake-induced hoop forces either; (1) the concrete does not crack (if leaking is not permitted); or (2) the stress in the prestressing wires remains below 0.7f\dp\du(if minor leaking during the earthquake is permitted). Since under both of these criteria the tank wall materials remain practically elastic, the earthquake-induced hoop forces should be based on elastic acceleration response spectra. This paper presents a normal mode solution for a neoprene pad supported, cylindrical, prestressed concrete tank filled with an inviscid and incompressible liquid subjected to vertical accelerations. The solution, which gives the natural modes and frequencies and the load participation factors, is used to compute the hoop forces caused by the hydrodynamic fluid pressure.

A Numerical Investigation of Mechanisms Linking Glaciation of the Ice-Phase to the Boundary Layer

Abstract: Nine clouds are simulated by perturbing Florida Area Cumulus Experiment (FACE) field soundings employing the Colorado State University cloud model. After a cloud similar in size to the one observed is initiated, glaciation is simulated in experiments designed to study the mechanisms by which glaciation is communicated to the subcloud boundary layer. Numerical model results show that the vertical pressure mechanism consisting of hydrostatic and dynamic pressure gradient force and “pressure buoyancy” is present, as is the downdraft mechanism, but they are secondary to loading, temperature buoyancy, water vapor buoyancy and the horizontal dynamic forces on the scale of a single deep convective cloud. The communication mechanism that has the most sustained and coherent influence upon the subcloud layer is the settling and evaporation of precipitation. A clear implication of this study to weather modification is that for dynamic seeding to have a significant influence upon the upscale growth of a clou...

A Vertical Finite-Difference Scheme for Hydrostatic and Nonhydrostatic Equations

Abstract: Vertical finite-differences schemes that preserve the important integral properties of the continuum equations are derived for the basic hydrodynamic and thermodynamic equations governing the atmosphere. The vertical coordinate is altitude. The first scheme applies in fully nonhydrostatic cases and therefore can be used to study smaller motion when the hydrostatic approximation cannot be justified. The finite-difference equations are then reduced to a hydrostatic set that continues to satisfy the integral constraints. In this simplified form, the vertical difference scheme guarantees local compliance with hydrostatic balance, in contrast to some sigma-coordinate models in which nonlocal treatments of this approximation may be required.

Secular Love numbers and hydrostatic equilibrium of planets

Abstract: The secular Love numbers of planets and of the Moon have been computed by use of the recent satellite data. It has been demonstrated that Venus, Mercury, and the Moon are far from the ideal hydrostatic equilibrium; the angular velocities (rotation periods) which correspond to the hydrostatic equilibrium have been computed.

Bifurcations of the modal structure of internal waves in a fluid induced by a spatially periodical variation of the hydrostatic stability parameter

Abstract: The dispersion law of internal gravity waves in a stratified fluid at rest is investigated: it is shown that the introduction of an oscillating component of the stratification parameter along the vertical direction introduces an infinite number of branches of the dispersion relation. The importance of this effect for the estimate of the triadic nonlinear interaction between internal waves is suggested as one of the most relevant consequences of the results reported.

Dynamic characteristics of a hydrostatic gas bearing driven by oscillating exhaust pressure

Abstract: Vibration of a statically loaded, inherently compensated hydrostatic journal bearing due to oscillating exhaust pressure is investigated. Both angular and radial vibration modes are analyzed. The time-dependent Reynolds equation governing the pressure distribution between the oscillating journal and sleeve is solved together with the journal equation of motion to obtain the response characteristics of the bearing. The Reynolds equation and the equation of motion are simplified by applying regular perturbation theory for small displacements. The numerical solutions of the perturbation equations are obtained by discretizing the pressure field using finite-difference aproximations with a discrete, nonuniform line-source model which excludes effects due to feeding hole volume. An iterative scheme is used to simultaneously satisfy the equations of motion for the journal. The results presented include Bode plots of bearing-oscillation gain and phase for a particular bearing configuration for various combinations of parameters over a range of frequencies, including the resonant frequency.

Matter Distributions of Various Components in the Coma Cluster

Abstract: Making use of the hydrostatic equilibrium equation observed density and velocity dispersion profiles of galaxies lead to obtain the distribution of total matter responsible for the gravitational potential. Applied to ICM the equivalent equation gives its temperature and density from the X-ray surface brightness profile.