Dynamic Stability of Cylindrical Shells under Moving Loads by Applying Advanced Controlling Techniques Part I—Using Periodic Stiffeners

The load acting on a cylindrical shell, with added periodic stiffeners,under a transient pressure pulse propelling a pullet (gun case) has been experimentallystudied. This study is based on two modes of velocities, the first is subcritical mode andthe second is supercritical mode. The stiffeners are added to the gun tube of anexperimental gun facility, of 14 mm bore diameter. The radial strains are measured byusing high-frequency strain gage system in phase with a laser beam detection system.Time-resolved strain measurement of the wall response is obtained and both precursorand transverse hoop strains have been resolved. The time domain analysis has been done using “wavelet transform package” in order to determine the frequency domainmodes of vibrations and detect the critical frequency mode. A complete comparisonof the dynamic behavior of the shell tube before and after adding periodic stiffeners has been done, which indicated that a significant damping effect reaches values between 61.5and 38% for subcritical and critical modes. The critical frequency of the stiffened shellis increased, so the supercritical mode is changed to subcritical mode. The amplificationand dispersion factors are determined and constructed; there is a reduction in thecorresponding speed frequencies by about 10%. Also the radial-bending vibrations andtube muzzle motions are detected at muzzle velocity ratio of 0.99%, the results indicatedthat there is a significant improvement in increasing the number of rounds per second byabout 36% and increasing the pointing precision by about 47%