METHOD OF HYSTERESIS CALCULATION IN A HYSTERESIS CONTROL CURRENT REGULATOR WITH CURRENT REFERENCE ADAPTATION

In this paper hysteresis adaptation method is presented. It provides the algorithm to calculate hysteresis value equal to the maximum pulsation of current. This allows decrease disadvantage of hysteresis regulator with clocked commutation in application with variable reference.

Flow-Induced Pulsations in Closed Side Branches With Wet Gas

In a recent paper it has been shown that the presence of liquid has an influence on Flow Induced Pulsations (FIPs) in closed side branches. Even larger effects of liquid in case of whistling in corrugated pipes were reported. For this experimental study, the “Tandem configuration” with two closed side branches along a main pipe is considered. It is characterized by the distance between the two closed side branches equal to the double of their acoustic length. The experiments reported in this paper aim at investigating the effect of the mixture water/gas on FIPs measured at the closed end of the two closed side branches. Different water flow rates are injected in the flow to obtain a mass factor rate in the range 0–10−4 m3/s. Furthermore, the relation between the multiphase flow pattern in the main pipe and the trend in the pulsation amplitude and Strouhal number is discussed, by comparison with the test for dry gas. To understand the effect of the type of flow, tests are performed with the injector far from and close to the upstream side branch. For the far configuration, at both low and high injection rates, pulsations decrease for increasing injection rates. However, in the intermediate region, an increase of pulsations is observed. These different ranges can be attributed to different (multiphase) flow regimes. Concerning the close configuration, only a decrease of the pulsations is observed over the full range. Furthermore, a decrease of the Strouhal number corresponding to the maximum pulsation level is observed.

Magnetic Properties of Rapidly Oscillating Ap Stars

Rapidly oscillating Ap stars generally pulsate in multiple modes, characterized by different frequencies. The amplitudes of these modes may furthermore be modulated with the rotation frequency of the star. For the two roAp stars whose magnetic fields have been sufficiently studied, the maximum pulsation amplitude coincides in phase with one of the extrema of the mean longitudinal magnetic field. Two interpretations of this property have been proposed: the oblique pulsator model, according to which the pulsation modes are aligned with the magnetic axis of the star, and the spotted pulsator model, which assumes that the pulsation modes are symmetric about the rotation axis of the star, and that pulsation amplitude modulation is due to the inhomogeneity of the stellar surface (which, itself, is related to the magnetic field geometry). At present, no definite choice between these two models can be made, though the oblique pulsator model is often preferred.

Increased milking vacuum in teatcups fitted with non-return valves

SummaryAn experimental non-return valve was fitted in the short milk tube so that flow was permitted only in one direction, away from the teat. Liner movement was minimal because no air admission to the liner above the valve was provided. The extent of liner opening therefore depended on the amount of milk extracted within a pulsation cycle and on any air leakage past the liner mouthpiece. Milking experiments using four cows showed that the mean vacuum level in nominally open liners of valved teatcups during peak milk flow was 8·6 kPa higher than in conventional teatcups. Bench tests showed that the increase in liner vacuum (LV) depended on the nominal plant vacuum level, the pressure difference between initial LV and maximum pulsation chamber vacuum, the liner elasticity and mounting tension. The main source of energy available to raise LV above the nominal plant vacuum is the release of strain energy, stored within the liner during the collapse phase of each pulsation cycle.