7 .B2 presented. During spin-up, spin rate adjustment, pressurization, and docking, the hull will be subjected to forces which will excite vibrations of several forms. As illustrated in Figure 7.Bl, there are four basic modes of which bending and torsion appear the most significant. It is important to establish the frequency of the lowest mode for each of these vibrations in order to conservatively define the operating envelope of the colony. Operating the colony in such a manner that any cyclic load has a frequency approaching the structure's natural frequency would be extremely dangerous. Such operation could lead to an unstable growth in the amplitude of vibrations causing catastrophic failure of the hull. A further reason for investigating the vibration modes of the hull is that the alternating stresses produced by vibration are a major driving force in the propagation of fatigue cracks in the hull. Minimizing hull vibrations would have the effect of slowing crack growth and increasing the safe life of the hull. Finally, a determination of the vibratiohal frequencies and amplitudes is necessary in order to ensure the physical and psychological well-being of the inhabitants of the colony. It is not clear what vibration levels are tolerable for humans on a continuous basis for long periods of time. Thus, the effect of vibrations ought to be reduced to a minimum. VII.B.3: TORSION In general the following equations govern the determination of the torsional vibration frequency: e = H re = -T By combining the above two equations, the homogenous dynamic equation can be written as: re + Gie
RkJQdWJsaXNoZXIy MTU5NjU0Mg==