High-frequency instabilities

Similarly, the majority of the investigations reported conclude that for both rectangular and cylindrical columns the high frequency instabilities are 3D and have to be resolved by the use of 3D models. Nevertheless, in a few recent papers [5, 6, 21] it has been shown that 2D mixture model formulations can be used to reproduce the time-dependent flow behavior of 2D bubble... 

High-frequency instabilities occurring faster than the frequency of screw rotation... 

High-frequency instabilities are often associated with die flow instabilities, such as melt fracture, shark skin, or draw resonance. They can also be caused by drive problems, melt temperature non-uniformities, or vibration. 

Thus, to date we have three theoretically predicted modes for a high-frequency instability caused by the Carr-Helfrich anisotropic mechanism. They are the conductance and dielectric regimes and the inertia mode. Two of these (the conducting regime and the inertia mode) correspond to the steady-state motion of the liquid and the stationary deviations of the... 

You can add restraints to any molecular mechanics calculation (single point, optimization or dynamics). These might be NMR restraints, for example, or any situation where a length, angle, or torsion is known or pre-defined. Restraints with large force constants result in high frequency components in a molecular dynamics calculation and can result in instability under some circumstances. 

Acoustic instabilities involve the interactions of acoustic waves with the combustion processes. These instabilities are of high frequency and can be significant in certain situations but can successfully be avoided by suitable design (11,24). 

What are the reasons for clock instability High-frequency noise is always generated at turn-on and turnoff in any switcher. This noise can infiltrate into the IC via various pins. It can be very hard to filter out and control. You may need to ultimately simply avoid turning the Fet OFF too dramatically. In most switchers, the turn-on transition is traditionally delayed (or slowed) just a little, so as to allow the output/catch diodes to recover... 

Peskin and Raco (P3) have given a theoretical analysis of both ultrasonic and electrostatic atomization from the point of view of liquid instability. They conclude that atomization with low frequency ac will require about twice the field strength as dc but that, by going to high frequency, lower fields are possible with conducting liquids. The value for the critical field for atomization given by these authors for a dc field is, however, smaller than that which would be calculated from Eq. (39) by a factor of (1/32)1/2. This presumably reflects the simplified one-dimensional model used in their derivation. 

When an energetic material burns in a combustion chamber fitted with an exhaust nozzle for the combustion gas, oscillatory combustion occurs. The observed frequency of this oscillation varies widely from low frequencies below 10 Hz to high frequencies above 10 kHz. The frequency is dependent not only on the physical and chemical properties of the energetic material, but also on its size and shape. There have been numerous theoretical and experimental studies on the combustion instability of rocket motors. Experimental methods for measuring the nature of combustion instability have been developed and verified. However, the nature of combustion instability has not yet been fully understood because of the complex interactions between the combustion wave of propellant burning and the mode of acoustic waves. 

Combustion of a propellant in a rocket motor accompanied by high-frequency pressure oscillation is one of the most harmful phenomena in rocket motor operation. There have been numerous theoretical and experimental studies on the acoustic mode of oscillation, concerning both the medium-frequency range of 100 Hz-1 kHz and the high-frequency range of 1 kHz-30 kHz. The nature of oscillatory combustion instability is dependent on various physicochemical parameters, such... 

Check Valves These valves are used to prevent reversal of flow. They must be located where flow turbulence or instability does not resmt in chatter (high-frequency opening and closing of the valve) and in systems designed to prevent sudden high-velocity flow reversal which results in slamming upon closure. Many valve manufacturers can provide application aoMce. 

D.W. Rice, CombstnFlame 8(1), 21-8 (1964) CA 60, 14325 (1964) (Effect of compositional variables upon oscillatory combustion of solid rocket propellants) N ) R.W. Hart F.T. McClure, "Theory of Acoustic Instability in Solid Propellant Rocket Combustion , lOthSympCombstn (1965), pp 1047-65 N2) E.W. Price, "Experimental Solid Rocket Combustion Instability , Ibid, pp 1067-82 Qi) R.S. Levine, "Experimental Status of High Frequency Liquid Rocket Combustion Instability , Ibid, pp 1083-99 O2) L. Crocco,... 

Levine (Ref 22, p 1083) has studied high frequency combustion instability of LP via high speed... 

Under certain conditions, propellants may exhibit high frequency vibratory combustion. Such vibration can cause extensive hardware damage and/or a mission abort. In most instances, however, combustion instability is related principally to the physical design of the combustion chamber rather than the chemical properties of the propellants. 

High Frequency Combustion Instability in Rockets with Distributed Combustion , in 4th Symposium on Combustion, Williams Wilkins,... 

This obiously does not exclude the possibility of oscillation phenomena such as ionization waves, etc., which are among the most frequently observed instabilities in d.c. glow discharges49. Any allowance for these phenomena in the theoretical treatment of chemical processes would introduce major complications and, we shall therefore ignore them in the first approximation. Such a simplification is justified, because the relaxation processes related to the ionization waves are usually much faster than chemical processes. Therefore, the oscillations take place on a time scale which is different from that of the chemistry. Moreover, the waves arise in a d.c. discharge rather than in a high frequency discharge, which was used in most experiments on chemical transport. 

A high-resolution spectrum of the clock transition is shown in Fig. 2. The clock-laser power was reduced to 30 nW to avoid saturation broadening. The fit with a lorentzian curve results in a linewidth of 170 Hz (FWHM), corresponding to a fractional resolution bv/v of 1.3 10-13. A spectral window of 200 Hz width contains 50% of all excitations. According to our present experimental control of the ion temperature, electromagnetic fields and vacuum conditions, no significant Doppler, Zeeman, Stark or collisional broadening of the absorption spectrum of the ion is expected beyond the level of 1 Hz. The linewidth is determined by the frequency instability of the laser and the lineshape is not exactly lorentzian... 

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