인공고관절의 세라믹 볼 헤드의 기계적 안정성 평가를 위한 3 차원 유한요소 해석

To improve the performance of particle image velocimetry in measuring instantaneous velocity fields, direct cross-correlation of image fields can be used in place of auto-correlation methods of interrogation of double- or multiple-exposure recordings. With improved speed of photographic recording and increased resolution of video array detectors, cross-correlation methods of interrogation of successive single-exposure frames can be used to measure the separation of pairs of particle images between successive frames. By knowing the extent of image shifting used in a multiple-exposure and by a priori knowledge of the mean flow-field, the cross-correlation of different sized interrogation spots with known separation can be optimized in terms of spatial resolution, detection rate, accuracy and reliability.

Theory of cross-correlation analysis of PIV images : Image analysis as measuring technique in flows

Quantifying air–sea exchanges of enthalpy and momentum is important for understanding and skillfully predicting tropical cyclone intensity, but the magnitude of the corresponding wind speed–dependent bulk exchange coefficients is largely unknown at major hurricane wind speeds greater than 50 m s−1. Since direct turbulent flux measurements in these conditions are extremely difficult, the momentum and enthalpy fluxes were deduced via absolute angular momentum and total energy budgets. An error analysis of the methodology was performed to quantify and mitigate potentially significant uncertainties resulting from unresolved budget terms and observational errors. An analysis of six missions from the 2003 Coupled Boundary Layers Air–Sea Transfer (CBLAST) field program in major hurricanes Fabian and Isabel was conducted using a new variational technique. The analysis indicates a near-surface mean drag coefficient CD of 2.4 × 10−3 with a 46% standard deviation and a mean enthalpy coefficient CK of 1.0 × 1...

Air–Sea Enthalpy and Momentum Exchange at Major Hurricane Wind Speeds Observed during CBLAST

[1] The laboratory experiments on investigation of aerodynamic resistance of the waved water surface under severe wind conditions (up to U10 ≈ 40 m s−1) were carried out, complemented by measurements of the wind-wave spectra. The tendency to saturation of the surface drag was observed for wind speeds exceeding 25 m s−1, accompanied by the saturation of wind-wave slopes. The effect of surface drag saturation can be explained quantitatively within the quasi-linear model of the air boundary layer above the waved water surface, when the contribution of the short-wave part of the wind-wave spectrum to aerodynamic resistance of the water surface is taken into account.

Laboratory and theoretical modeling of air-sea momentum transfer under severe wind conditions

http://radiometrics.com/data/uploads/2012/11/Tretyakova_JMS_05.pdf

60-GHz oxygen band: precise broadening and central frequencies of fine-structure lines, absolute absorption profile at atmospheric pressure, and revision of mixing coefficients

This paper describes the results of an experimental and theoretical investigation into the mechanisms by which spume droplets are generated by high winds. The experiments were performed in ...

The ``Bag Breakup'' Spume Droplet Generation Mechanism at High Winds. Part I: Spray Generation Function

Showing the record strengths and growth-rates, recent hurricanes have highlighted needs for improving forecasts of tropical cyclone intensities most sensitive to models of the air-sea interaction. Especially challenging is the nature of sea-spray supposed to strongly affecting the momentum- and energy- air-sea fluxes at strong winds. Even the spray-generation mechanisms in extreme winds remained undetermined. Basing on high-speed video here we identify it as the bag-breakup mode of fragmentation of liquid in gaseous flows known in a different context. This regime is characterized by inflating and consequent bursting of the short-lived objects, bags, comprising sail-like water films surrounded by massive liquid rims then fragmented to giant droplets with sizes exceeding 500 micrometers. From first principles of statistical physics we develop statistical description of these phenomena and show that at extreme winds the bag-breakup is the dominant spray-production mechanism. These findings provide a new basis for understanding and modeling of the air-sea exchange processes at extreme winds.

/pdf/bag-breakup-fragmentation-as-the-dominant-mechanism-of-sea-3kk5onhs1o.pdf

Bag-breakup fragmentation as the dominant mechanism of sea-spray production in high winds.

Line Broadening and Shifting Studies of the J=5←4 Transition of Carbon Monoxide Perturbed by CO, N2, and O2

A turbulent airflow with a centerline velocity of 4 m s−1 above 2.5-Hz mechanically generated gravity waves of different amplitudes has been studied in experiments using the particle image velocimetry (PIV) technique. Direct measurements of the instantaneous flow velocity fields above a curvilinear interface demonstrating flow separation are presented. Because the airflow above the wavy water surface is turbulent and nonstationary, the individual vector fields are conditionally averaged sampled on the phase of the water elevation. The flow patterns of the phase-averaged fields are relatively smooth. Because the averaged flow does not show any strongly nonlinear effects, the quasi-linear approximation can be used. The parameters obtained by the flow averaging are compared with the theoretical results obtained within the theoretical quasi-linear model of a turbulent boundary layer above the wavy water surface. The wave-induced pressure disturbances in the airflow are calculated using the retrieved s...

Daniil Sergeev

Papers

Laboratory and theoretical modeling of air-sea momentum transfer under severe wind conditions

The ``Bag Breakup'' Spume Droplet Generation Mechanism at High Winds. Part I: Spray Generation Function

Bag-breakup fragmentation as the dominant mechanism of sea-spray production in high winds.

Line Broadening and Shifting Studies of the J=5←4 Transition of Carbon Monoxide Perturbed by CO, N2, and O2

Statistical Parameters of the Air Turbulent Boundary Layer over Steep Water Waves Measured by the PIV Technique