Stability diagrams and time responses of the feedback control for vertical instability are obtained in the JFT-2M tokamak. The experimental results are in good agreement with a feedback theory based on the filament current plasma model taking account of the non-axisymmetric effect of the vacuum vessel. The vertical instability, with a growth rate of about 500 s" 1 , is successfully stabilized by feedback control of the plasma position with ordinary 12-phase thyristor power supplies; the elongation factor achieved amounts to up tOK = 1.7.
Stability of a flat or buckled panel exposed to an incompressible flow has been reanalyzed as the analyses on this problem by other investigators have errors in the fluid forces used. The deflection of the panel in an oscillatory motion is assumed in such a way that there occurs no change in the fluid volume in a control surface enclosing the panel. The nonlinear equation of motion of the panel on a continuous elastic spring is solved by using the Galerkin method and the generalized fluid forces which are derived in the author’s previous paper. The stability of the flat and buckled configuration in static equilibrium is examined against small disturbances. Existence of the limit cycle oscillation is studied by applying the harmonic balance method. Numerical results are compared with those of the analysis on a two-dimensional finite elastic channel conveying an almost incompressible flow.
This paper examines the dynamic behavior of a two-dimensional channel whose upper and lower walls deform symmetrically with respect to the center line of the channel. Unsteady fluid dynamic forces acting on the internal wall are analytically evaluated on the basis of a linearized compressible potential flow theory. The effects of distributed springs outside the channel and an internal pressure on the stability characteristics are studied by considering small disturbances about flat and buckled equilibrium configurations of the wall. The analytic methods indicate that no flutter of the flat or buckled wall is predicted when the Mach number is small and the viscous damping coefficient is positive. Numerical results by the Runge-Kutta-Gill method suggest that nonlinear effect of flow should be taken into account to fully examine the dynamic characteristics of the channel conveying a flow.
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