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This is Fig. 24 from the 2013 GENOPT paper1. (before revision of the STAGS model) from the 2012 GENOPT paper2. Shown here is the STAGS finite element model of the optimized long propellant tank with two sets of struts, aft (Lower) and forward (Upper), with 4 pairs of struts at each axial location. The struts are pinned to the aft and forward propellant tank support rings and to rigid “ground”. The STAGS “410” finite element is used in the model of the propellant tank shell wall. In the STAGS model the external tapered doublers with maximum thickness = 0.886 inch are modeled as doublers of constant average thickness = 0.443 inch. This modification of the GENOPT/BIGBOSOR4 model has little effect on the vibration frequencies and mode shapes but has a huge effect on the maximum stresses predicted at the tips of the stringers in the internal orthogrid "layer" of the propellant tank shell wall.
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