Hydrostatic equilibrium

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

Simulation of dynamic effects on hydrostatic bearings and membrane restrictors

Abstract: Hydrostatic bearings have an excellent static and dynamic behavior and are used for different kinds of application. Application of hydrostatic bearings is limited by friction and therewith by velocity. Typical characteristics of the hydrostatic system (load, stiffness, flow) are calculated without a velocity dependency. The geometry of the hydrostatic bearing pockets and their restrictors are optimized by using time continuous pressure distribution at the bearing pocket, laminar flow behavior as well as constant velocity of the bearing. The dynamic effects of the flow at high velocities are not considered. The paper reflects the common design and calculation methods and shows their limitations in regard to the calculation of hydrostatic bearings at high velocities. It analyzes the results of complex dynamic flow simulations of hydrostatic bearings and presents a new design and optimization concept of hydrostatic bearings. This concept analyses the oil flow at high bearing velocities and it optimizes the bearing geometry, the restrictor geometry as well as the geometry of the main mechanical components.

Defining constants, equations, and abbreviated tables of the 1975 US Standard Atmosphere

Abstract: The U.S. Standard Atmosphere, 1975 (COESA, 1975) is an idealized, steady-state representation of the earth's atmosphere from the surface of the earth to 1000-km altitude, as it is assumed to exist in a period of moderate solar activity. From 0 to 86 km, the atmospheric model is specified in terms of the hydrostatic equilibrium of a perfect gas, with that portion of the model from 0 to 51 geopotential kilometers being identical with that of the U.S. Standard Atmosphere, 1962 (COESA, 1962). Between 51 and 86 km, the defining temperature-height profile has been modified from that of the 1962 Standard to lower temperatures between 51 and 69.33 km, and to greater values between 69.33 and 86 km. Above 86 km, the model is defined in terms of quasi-dynamic considerations involving the vertical component of the flux of molecules of individual gas species. These conditions lead to the generation of independent number-density distributions of the major species, N2, O2, O, Ar, Ne, and H, consistent with observations. The detailed definitions of the model are presented along with graphs and abbreviated tables of the atmospheric properties of the 1975 Standard.

Thermal relaxation oscillations in a two-zone model.

Abstract: We simulate the behavior of stars in those advanced evolutionary phases in which thermal cycles have been reported. To this end we consider a two-zone stellar model in hydrostatic equilibrium, consisting of a thin energy-generating shell and a buffer zone on top of it with the rest of the star acting as boundary conditions. Under the conditions apposite to thin-shell helium burning we show that this model can exhibit rigorous thermal limit cycle oscillations. By the same token our result implies that the two-time asymptotic method may be used to bridge such otherwise inaccessible evolutionary phases.

The prediction of the elastic critical load of submerged elliptical cylindrical shell based on the vibro-acoustic model

Abstract: Based on the vibro-acoustical model, an effective new approach to nondestructively predict the elastic critical hydrostatic pressure of a submerged elliptical cylindrical shell is presented in this paper. Based on the Goldenveizer–Novozhilov thin shell theory, the vibration equations considering hydrostatic pressures of outer fluid are written in the form of a matrix differential equation which is obtained by using the transfer matrix of the state vector of the shell. The fluid-loading term is represented as the form of Mathieu function. The data of the fundamental natural frequencies of the various elliptical cylindrical shells with different hydrostatic pressure and boundary conditions are obtained by solving the frequency equation using Lagrange interpolation method. The curve of the fundamental natural frequency squared versus hydrostatic pressure is drawn, which is approximately straight line. The elastic critical hydrostatic pressure is therefore obtained while the fundamental natural frequency is assumed to be zero according to the curve. The results obtained by the present approach show good agreement with published results.

Preliminary design of dynamic framework for global non-hydrostatic spectral model

Abstract: Based on the global hydrostatic spectral model for operational run,referring to the upgrade and design idea of ECMWF from hydrostatic spectral model to the non-hydrostatic one,a preliminary dry dynamic framework is designed for global non-hydrostatic spectral model,with the consideration of the selection of the model equations,the linearization of the model equations,spectral representation in horizontal,finite difference in vertical,the scheme of integral in time,and the solution of the derived Helmholtz systems.The framework is provided for atmosphere with shallow approximation,and the Euler convection is exploited.Further,for the solution of the Helmholtz equations,a new computational scheme is provided based on the convection to the linear equations of block tri-diagonal form.The new scheme is clearly superior to the current one used in ECMWF for efficiency.