Previous studies of strumming induced dynamic tensions in long cables have been extended to include the effects of axial strain and end mass. Large increases in dynamic tension and phase reversal between tensions and lateral response are predicted when twice the strumming frequency is in the vicinity of the cable's axial natural frequency. The theory also predicts that the presence of an end mass reduces the effective damping of the system. The theory was verified by experiments in air with a cable composed of rubber tubing. The theory predicts that for typical wire cables with no attached masses, fundamental mode resonant conditions would exist and large dynamic tensions might result for Iengtbs ranging from 100 to 500 ft, depending on cable diameter and tow speed. The addition or an end mass would lower this length, but would at the same time also reduce the effective damping and increase the potential for larger amplitude dynamic tensions. A simple dynamic tension formula which approximates the exact solution and includes the effects of axial strain is presented.
In tow tank experiments reported last year, it was shown that cable strumming of short, fixed-free ended cables resulted in dynamic tensions at twice the strumming frequency (Welch & Tulin, 1992). The amplitude and phase of these dynamic tensions may be calculated from the motion of the cable mass center. In the present work we extend the previous analysis to include the effect of axial strain and end mass, thus permitting the above result for the short cables used in the earlier tow tests and predictions of dynamic tensions for longer cables with an attached end mass. We find an exact solution of the dynamic equations. Predictions are compared with experimental results obtained by shaking a long rubber tube in air.
