Quasi-stationary Pressure Research Articles

Rogue wave formation under the action of quasi-stationary pressure

The process of rogue wave formation on deep water is considered. A wave of extreme amplitude is born against the background of uniform waves (Gerstner waves) under the action of external pressure on free surface. The pressure distribution has a form of a quasi-stationary “pit”. The fluid motion is supposed to be a vortex one and is described by an exact solution of equations of 2D hydrodynamics for an ideal fluid in Lagrangian coordinates. Liquid particles are moving around circumferences of different radii in the absence of drift flow. Values of amplitude and wave steepness optimal for rogue wave formation are found numerically. The influence of vorticity distribution and pressure drop on parameters of the fluid is investigated.

On the accuracy of atmospheric forcing for extra-tropical storm surge prediction

The ability of the SMARA storm surge numerical prediction system to reproduce local effects in estuarine and coastal winds was recently improved by considering one-way coupling of the air-sea momentum exchange through the wave stress, and best forecasting practices for downscaling. The inclusion of long period atmospheric pressure forcing in tide and tide/surge calculations corrected a systematic error in the surge, produced by the South Atlantic Ocean quasi-stationary pressure patterns. The maximum forecast range for the storm surge at Buenos Aires provided by the real-time use of water level observations is approximately 12 h. The best available water level prediction is the 6-h forecast (nowcast) based on the closest water level observations. The 24-h forecast from the numerical models slightly improves this nowcast. Although the numerical forecast accuracy degrades after the first 48 h, the improvement to the full range observation-based prediction is maintained at the inner Rio de la Plata area and extends to the first 3 days at the intermediate navigation channels.

Drying of glassy polymer varnishes: A quartz resonator study

We report on desorption measurements on polymeric thin films coated onto quartz crystal resonators. Due to the high sensitivity of quartz crystal microbalances, the experiments can be performed on very thin films, which have small diffusion time constants even in the glassy state. When drying is performed slowly enough, diffusion equilibrium can be maintained through the whole process of desorption, including the glassy domain. From these quasi-stationary pressure ramps, we derived the solvent chemical potential as a function of polymer volume fraction μ(o). The results fit well to a model recently proposed by Leibler and Sekimoto. 1 In addition, we have derived the mutual diffusion coefficient D(o) from pressure step experiments. We observe a strong decrease of D(o) for high polymer concentrations typical of hypodiffusive systems like polymers. We investigated the drying of an industrial varnish that is a blend of 2 copolymers as well as the drying of its components separately. Both the solvent chemical potential μ(o) and the mutual diffusion coefficient D(o) of the blend interpolate between the respective quantities of the components.

Acoustical finite-difference time-domain simulations of subwavelength geometries

Accurate simulation of wave propagation around subwavelength geometries using standard finite-difference time-domain (FDTD) techniques require a fine spatial and temporal sampling resulting in high computational costs. In this paper an extension to this standard FDTD technique is proposed by means of quasi-stationary solutions on a subwavelength scale. The FDTD equations in the region near the subwavelength geometry are extended with some correction terms of which the magnitude is extracted from the quasi-stationary pressure distribution around these geometries. These pressure distributions can be calculated from the Laplace equation. Using this new technique, FDTD simulations can be based on a more coarse grid, thus reducing computational cost considerably. The accuracy of this technique is mainly determined by the accuracy of the Laplace solutions. This technique was tested with success on the simulation of resonators. It was also shown that the new FDTD equations can be extended to include viscosity effects.

Hydrodynamic processes in dynamic bubble pressure experiments: 2. Slow meniscus oscillations

The physical mechanisms of processes taking place immediately after a bubble separates from a capillary are discussed. The decreased pressure inside a separating bubble and at the orifice of the capillary cause the movement of liquid into the capillary. The depth of this displacement is limited by the kinetics of changes in gas pressure along the capillary. When the gas pressure becomes equal to the meniscus capillary pressure, the meniscus starts to move back to the capillary tip. Equations are derived which describe the restoration process of a quasistationary pressure distribution along the capillary. A solution of these equations is obtained which describes the evolution of pressure distribution along the capillary with time. Even in the ms time range, the characteristic time of quasistationary pressure distribution re-establishment along the capillary is shown to be shorter than the time necessary to overcome the maximum bubble pressure. The existence of fast oscillations in gas pressure in short capillaries is also predicted. In this case, the characteristic time is found to be comparable to the hydrodynamic relaxation time.

The use of a subgrid-scale quasi-stationary approximation in finite-difference time-domain simulations to calculate the absorption by Helmholtz resonators

To calculate Helmholtz resonators using a finite-difference time-domain (FDTD) simulation technique, one has to deal with two important difficulties. First, the determining structures of a Helmholtz resonator are typically subwavelength geometries with dimensions that are smaller than the FDTD cell size normally used for the wavelengths of interest. Therefore, the FDTD cell size should be reduced, resulting in a very high computational cost. On the other hand, the viscous absorption in the resonator neck influences the resonator behavior a lot and has to be included in the calculation. The first problem was solved by using a coarse FDTD grid but applying detailed simulated quasistationary pressure distribution to modify the FDTD equations in the neighborhood of the resonator neck. For the second problem the analytical solution for viscous boundary layer absorption was introduced into the FDTD equations. However, this solution is only correct for the viscous absorption near an infinite plate. Therefore, the calculated quasi-stationary solutions were applied to correct for the nonuniform velocity distribution in the resonator neck. The results are compared with both analytical solutions and with experimental results.

Meso-α and meso-β network analyses of a severe storm complex during SESAME-AVE-V

Presented in this paper are meso-α and meso-β network analyses of thermodynamics and kinematics related to the formation of a severe storm complex on 20 May 1979 during SESAME-AVE-V. The storm organizes in the mesonetwork by mid-afternoon ahead of a nearly east-west-aligned quasistationary pressure trough. By mid-morning a tongue of high mixing ratios develops south of the trough in northern Texas and southern Oklahoma. In response to strong differential solar heating and the moist tongue, a pronounced low-level ϑe maximum appears in this region. Convective activity to the south of the trough is inhibited by a low-level stable layer in the region. Sinking motion aloft enhances the stable layer. At midday the pressure trough accelerates southward and intensifies, strengthening low-level convergence, which in turn induces a well-defined vertical circulation in the meso-β network. The vertical motion in the circulation pushes the air to its lifting condensation level, and the convective instability is released.

The Katabatic Winds of Adélie Land and King George V Land

The principle features of the katabatic wind in the neighbourhood of Commonwealth Bay, Antarctica, are described with particular emphasis on the sudden onsets and cessations of the wind. The unusual features are explained on the hypothesis that a quasistationary pressure jump line, forming a sharp boundary between the strong katabatic winds of the ice slope and the comparitively calm conditions over the sea, occurs near the coast. Movement of this pressure jump line across the causes a sudden change in wind conditions there. Quantitative predictions on this hypothesis are of the correct magnitude. DOI: 10.1111/j.2153-3490.1957.tb01874.x

The Katabatic Winds of Adélie Land and King George V Land

The principle features of the katabatic wind in the neighbourhood of Commonwealth Bay, Antarctica, are described with particular emphasis on the sudden onsets and cessations of the wind. The unusual features are explained on the hypothesis that a quasistationary pressure jump line, forming a sharp boundary between the strong katabatic winds of the ice slope and the comparitively calm conditions over the sea, occurs near the coast. Movement of this pressure jump line across the causes a sudden change in wind conditions there. Quantitative predictions on this hypothesis are of the correct magnitude.