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Fig. 25g Two views of the seventh vibration mode from the STAGS model. The modal vibration frequency predicted by STAGS is 16.25 Hz. This mode is a combination of shell deformation with m = 2 axial half-waves and mostly pitching motion of the propellant tank approximately as a rigid body with significant tension and compression in the supporting struts. The GENOPT/BIGBOSOR4 model predicts mostly pitching tank motion with a modal vibration frequency equal to 15.284 Hz, as displayed in Fig. 16a(D). Shell deformation modes with m greater than one-half axial wave were not computed for the GENOPT/BIGBOSOR4 model.
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