Function Of Air Density Research Articles

A New Erosion Model for Wind‐Induced Structural Vibrations

In recent years, computational fluid dynamics (CFD) method has been widely utilized in simulating wind‐induced snow drifting. In the simulating process, the erosion flux is the main controlling factor which can be calculated by the product of erosion coefficient and the differences between the flow stress and threshold stress. The erosion coefficient is often adopted as an empirical constant which is believed not to change with time and space. However, in reality, we do need to consider the influences of snow diameter, density, and wind speed on the erosion coefficient. In this technical note, a function of air density, sow particle density, snow particle radius, and snow particle strength bond is proposed for the erosion coefficient. Based on an experiment study, the effects of these parameters in erosion coefficient is analyzed and discussed. The probability distribution and value range of erosion coefficient are also presented in this technical note. The applicability of this approach is also demonstrated in a numerical study for predicting the snow distributions around a cube structure. The randomness of the structural vibrations is studied with details.

Effects of temperature and pressure change on positive corona and sparkover under direct voltage in short airgaps

Measurements are reported of breakdown voltage values and pre-breakdown voltage–current characteristics as a function of air density in a simple rod–plane electrode gap 50 mm in length. Pressure has been reduced and temperature raised from normal atmospheric values, independently of each other, to give the relative air densities in a common range less than unity. The effects of different diameters of rod have been studied. The results allow a comparison of the characteristics at equal relative air densities attained by either pressure or temperature adjustment. It is shown that at common relative air densities, breakdown is temperature- and geometry-dependent and that there is a temperature dependence of the pre-breakdown glow currents. The density-dependent relationship between the pre-breakdown glow discharge currents and breakdown voltages is discussed.

High-order averaging of eccentric artificial satellites perturbed by the Earth'potential and air-drag terms

This paper deals with an analytical approach to the Earth'satellite problem where the perturbation includes the effects of the zonal harmonics and a specific function of air density well suited for...

Implementation of Optimal Guidance Laws Using Predicted Missile Velocity Profiles

A class of weighted control-effort minimizing guidance laws are derived for missiles of varying velocity. As a practical weighting function, we consider a function of air density and missile velocity parameterized by positive real numbers. The resulting optimal guidance problem can be interpreted as the drag minimization problem for subsonic or supersonic missiles, depending on what parameters are used. This approach is extended easily to solve the drag minimization of a typical antiaircraft missile system with an arbitrary velocity proe le and arbitrary drag characteristics, as demonstrated by a simulation study. We also present analytical results on how the guidance gain of the optimal law varies according to the values of the parameters. Because the optimal guidance laws make use of the future missile velocity proe le, one critical issue is how to implement the laws. To avoid the dife culty that an inaccurately predicted missile velocity proe le causes the guidance command to blow up in the last part of the engagement, we suggest two simple on-line velocity-proe le updating schemes, which considerably alleviate the problem.

Coherent Ion Plasma Oscillations in a DC Corona Discharge in Rarefied Air

Stable, nearly sinusoidal, phase-coherent ion plasma oscillations have been consistently observed superimposed on the dc levels of positive coaxial corona discharges at air pressures of the order of a few torr. The frequency of these oscillations, typically several hundred kilohertz, has been found to be a function of air density and dependent on the presence and concentration of gaseous trace contaminants. Various characteristics of these oscillations, a simplified theoretical model, and possible applications are discussed.

Coherent ion plasma oscifiations in a d.c. corona discharge in rarefied air

Stable, phase coherent ion plasma oscillations are found superimposed on the d.c. potential and current of positive coaxial corona discharges in air at pressures of the order of 1/100 of one atmosphere. The frequency of these oscillations, typically several hundred kHz, is a function of air density, and varies with the concentration of gaseous trace contaminants.

Influence of air density on electrical strength of air gaps at 50Hz

50Hz breakdown voltages have been measured for rod-rod gaps of 0.1–1.5m, and for point-point gaps of 0.1–0.4m, at different air temperatures and at about atmospheric pressure. The density-correction factor K derived from the measurements is a linear function of air density at a constant gap length. For a constant air density, K is larger for a greater gap length; K is also larger for a point-point gap than for a rod-rod gap of the same gap length.