Range Of Disturbance Frequencies Research Articles

Adaptive state regulation in the presence of disturbances of known frequency range

Adaptive state regulation via adaptive observation and asymptotic feedback matrix synthesis in the presence of bounded disturbances of known frequency range is considered. The adaptive observer uses a filtered output error to adapt parameter and state estimates. The filter is designed to attenuate in the disturbance frequency range. It is shown that, with persistent excitation, parameter and feedback gain errors are bounded by a quantity which is proportional directly to the attenuated disturbance magnitudes and inversely to the degree of persistent excitation. Closed-loop stability is proven when the ratio of filtered disturbance magnitude to degree of persistent excitation is sufficiently small. A computer simulation demonstrates the method.

Criterion Functions and Their Control Characteristics for Active Vibration Control

In optimal vibration control, the control characteristics of vibration depend on the criterion function and the coordinate system in the modelling, since the objective function is not necessarily described by the state variables. In this study, the relationships between the control characteristics and the criterion functions were investigated for the two cases of ignoring the dynamics of disturbance and restricting the frequency range of disturbance in the optimal control with the feedforward control due to lack of knowledge of the dynamics of disturbance. By carrying out numerical calculations, it was clarified that the optimization of the objective function can be given by feedforward control restricting the frequency range of disturbance, and that the same control effectiveness as the sky-hook damper can be obtained by choosing the absolute velocity as the objective function.

Monosize droplet stream generator

A simple low‐cost, uniform‐sized liquid droplet generator is described. The generator is based on the breakup phenomenon of a liquid jet flowing out of a capillary by imposing mechanical disturbances on it. The generator enables the injection of droplets into systems where injection is difficult, with minimum disturbance. It has been shown, theoretically and experimentally, that scattering of the droplets around the mean trajectory due to capillary vertical vibrations is negligible over a wide range of disturbance frequencies. The performance of the droplet generator is considerably deteriorated around the resonance frequencies of the capillary.

Acoustic Interaction with a Turbulent Plane Jet: Effects on Mean Flow

The effects of pure tone acoustic fields upon the mean flow in a low Reynolds number turbulent plane jet were investigated experimentally. It was found that the main region flow can be altered by moderate level disturbances over a range of disturbance frequencies. The effects were observed to extend to distances of 80 nozzle widths downstream of the nozzle, while decaying with downstream distance, and to be linked to the turbulence behavior of the initial region shear layers.

Stability of the Lithium “Waterfall” First Wall Protection Concept for Inertial Confinement Fusion Reactors

Uncertainties regarding the feasibility of using an annular ''waterfall'' of liquid lithium to protect the first wall in inertial confinement fusion reactor cavities have prompted a theoretical investigation of annular jet stability. Infinitesimal perturbation techniques are applied to an idealized model of the jet with disturbances acting upon either or both of the free surfaces. Dispersion relations are derived that predict the range of disturbance frequencies leading to instability, as well as the perturbation growth rates and jet breakup length. The results are extended to turbulent annular jets and are evaluated for the lithium waterfall design. It is concluded that inherent instabilities due to turbulent fluctuations will not cause the jet to break up over distances comparable to the height of the reactor cavity.

On the Stability of a Poppet Valve with an Elastic Support : 1st Report, Considering the Effect of the Inlet Piping System

A conical type hydraulic poppet valve with an elastic support (e.g. a helical spring) builds up a complex vibration system with the inlet and outlet piping, and often induces a violent vibration making noise and leading the whole system into unstable conditions. In this report, the author derives the characteristic equation of the whole system including a poppet valve and inlet and outlet pipings. Some theoretical considerations are developed neglecting the outlet piping. The effect of the nonlinearity of the system is also discussed. Some experiments were conducted without outlet piping and varying the length of the inlet piping, spring constant, inlet pressure and other parameters. The experimental results agree fairly well with the theory. The conditions determining the disturbance frequency range in which instability occurs are obtained as a function of length of inlet piping, spring constant, inlet pressure, valve lift, valve shape and Reynolds number.

The Response of an Unbounded Atmosphere to Point Disturbances. I. Time-Harmonic Disturbances

The response of an unbounded and isothermal atmosphere to time-harmonic point disturbances of force is studied. The exact solution is obtained in the whole frequency range of disturbances, including the frequency ranges of acoustic waves, trapped oscillations, and gravity waves. For disturbances whose frequencies are Just above the lower characteristic frequency of the atmosphere, ,,,3( = [ y - 1j3/3 g/c), the atmosphere responds very efficiently, especially to vertically oscillating disturbances. Furthermore the response is sharply restricted to regions above the source, and the velocity field in that region consists' mainly of a vertical one. These characteristics of the response persist into the frequency range of acoustic waves if the atmosphere is sufficiently stable to convection.