Selectivity of electromagnetic influence on the oscillations of a heavy conductive liquid in a channel

Under consideration is the MHD problem of oscillations of a heavy conductive liquid inside a channel with vertical walls in presence of an external horizontal electromagnetic field. We show that the standing surface waves are not damped in the case of symmetric position (with respect to the mid-channel) of the segment affected by a magnetic force. In the case of nonsymmetric position of the active segment, the magnetic force acts selectively on different standing waves. The selectivity condition for each standing wave depends on the width and position of the active segment. We obtain the general conditions for the absence of electromagnetic influence and inspect various special cases.