Digital vibration control of a flexible cantilever beam using a thermal bending mo ment caused by the temperature gradient across the section of the beam is attained both by experi ments and simulations. Foil strain gauges bonded on the surfaces of the beam are used as an actuator which is capable of producing a thermal gradient. Thermal bending moments are applied in the proper sense to a flexible cantilever beam having very low natural frequency so that active control of the first mode bending vibration is realized. Experimental results show that the damping ratio is increased by about ten times. Simulations are based on the theoretical analysis in which the equation of state is derived from the equation of bending vibration for the beam, considering the heat flow on both upper and lower surfaces. A linear control law is determined based on the digital optimal regulator theory. A minimal order state observer is used to estimate a state variable which is not available in the measurements. Experimental results are consistent with the simulated ones.

Long extendible spacecraft boom subjected to solar radiant heating is modeled as a thin-walled long cylinder of split non-overlapping section. Tip mass is attached to one end which is free to warp and other is fixed. The boom is heated by the unidirectional solar radiation assumed to be normal to its longitudinal axis. The equation of thermallyinduced torsional vibration of this system is formulated by considering the coupling effect of mechanical and thermal phenomena as one-degreeof-freedom system. The characteristic equation is evaluated using the Routh-Hurwitz stability criterion and it is found that the stability characteristics are dependent upon, along with three system parameters, the direction of radiant heating. The boundary curves, which divide the parameter plane into regions of stability and instability according to a direction of radiation, and some typical responses based on the closed-form solution are also included.

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