Hydrostatic equilibrium

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

Determination of High Precision Underground Equipotential Profiles for the Alignment of a Future Linear Collider

Abstract: The alignment challenge presented by the Compact Linear Collider (CLIC) project requires us to look closely at the ultra-high frequencies ( < 1 km) of the gravity field and our ability to model or determine underground equipotential profiles at a very high level of precision. This is of particular importance in the context of an alignment system based on Hydrostatic Levelling System (HLS) and other instruments dependent on gravity. In the first part of this paper, the theoretical formulation of the gravity field, Astronomical Levelling and a misalignment operator are presented. Then, the error propagation model of Astronomical Levelling is revisited and adapted to the specifications of accelerator alignment. Afterwards, numerical gravity field simulations, based on sinusoidal anomalies of varying geometry and density, give the first orders of magnitude of the signals in the equipotential and in the observation space which can be expected at ultra-high frequencies. Finally, a measurement campaign based around a tunnel, 850 m in length, at a depth of 80 m, that include deflections of the vertical and gravimetric measurements is presented.

Mixed Lubrication of Hydrostatic Thrust Bearings. 2nd Report. Experiment.

Abstract: It is strongly desired to clarify performances of hydrostatic bearings under mixed lubrication conditions because seldom there is information available on them. Therefore, in a previous paper, we calculated the performances of friction, leakage flow rate and power losses under conditions ranging from mixed to fluid film lubrication and clarified numerically the effects of surface roughness, the eccentric loads (moment loads), the supply pressure and the speed of rotation. In this paper, by the use of an apparatus featuring circular hydrostatic thrust bearings acting on concentric loads, we measure the frictional force and leakage flow rate under a lubrication range from mixed to fluid film. The surface roughness, the supply pressure, the loads, the speed of rotation and the restrictors are selected as main experimental parameters. We evaluate the coefficient of friction, the leakage flow rate and power losses for the bearing-modulus and the ratios of hydrostatic balance. Furthermore, these experimental results are compared with the theoretical ones. The conclusions are as follows : 1) the minimum power losses are given by the ratio of hydrostatic balance being close to unity independent of the surface roughness, the loads, and the speed of rotation; 2) the coefficient of friction of hydrostatic bearings can be clarified generally versus a bearing-modulus by use of the load carrying capacity due to asperities; 3) a larger surface roughness, causes a larger leakage flow rate in mixed lubrication; 4) the larger the supply pressure, the larger the power losses in fluid film and under mixed lubrication; 5) the larger the speed of rotation, the larger are the proportional power losses under mixed lubrication; 6) the size of restrictors seldom have any effects under mixed lubrication conditions.

Dynamical tides in Jupiter and other rotationally flattened planets and stars with stable stratification

Abstract: We develop a numerical method for directly computing the dissipative dynamical tidal response of rapidly rotating, oblate stars and gaseous planets with realistic internal structures. Applying these calculations to neutrally and stably stratified polytropes, we identify the most relevant resonances in models with rotation rates up to nearly the mass-shedding limit. We then compute the dynamical tidal response for Jupiter interior models including both stably stratified and convective regions. These calculations show that resonances involving mixed waves with both gravito-inertial and purely inertial character are capable of explaining a discrepancy between observations and hydrostatic calculations of Jupiter’s response to tidal forcing by Io. This result contrasts with recent work that excluded Jupiter’s rotational flattening, and opens the door to resonances involving a wider range of internal oscillation modes than previously considered.

Small-Scale Modeling of Flexible Barriers. I: Mechanical Similitude of the Structure

Abstract: : Flexible barriers can be used to trap woody debris or debris flows. However, their small scale modelling is challenging because of their possible deformation. This article addresses how to meet the partial mechanical similitude of manufactured flexible barriers. Relevant dimensionless parameters are defined from flow velocity, barrier geometry, and component mechanical properties. These similitude criteria are validated using numerical simulations of barriers exposed to a hydrodynamic loading at various scales. The simulations also confirm the importance of accounting for the mechanical characteristics of the barrier components when designing model barriers in view of achieving realistic deformations. Next, a real barrier with complex features is scaled to conduct flume experiments. This scaled barrier is 3D-printed with material selected to achieve the mechanical similitude criterion. Another validation of this approach is performed considering hydrostatic loading and checking that simulated and measured deformations are similar. As an application case, the deformations measured during the experiments performed with woody debris are also compared to the hydrostatic loading. DOI: 10.1061/JHEND8.HYENG-13070. This work is made available under the terms of the Creative Commons Attribution 4.0 International license, https://creativecommons.org/licenses/by/4.0/.