formulations are discussed further, nor are any of their final formulas 



included here because they involve certain parameters which are not too 



easily determined without having recourse to their original references. 



INTERMEDIATE DEEP FRAMES TO INCREASE 

 GENERAL-INSTABILITY STRENGTH 



One of the more important geometric parameters which, influences 

 general-instability strength of ring- stiffened cylindrical pressure hulls is 

 the overall length L^^, which, in actuality, is the distance between rigid 

 holding bulkheads in submarine construction. Certain designs, and this is 

 becoming more common, particularly for deep- submergence vehicles, pre- 

 clude the use of rigid internal bulkheads to break up the overall length of 

 long hull compartments. The requirements may, for example, stem from 

 internal arrangements and other space considerations. In such cases, the 

 most efficient manner in which the general-instability strength of long 

 cylindrical compartments can be increased without increasing overall 

 shell thickness and/or cross-sectional properties of all the ring frames, 

 with their concomitant prohibitive weight increase, is the use of inter- 

 mediate heavy frames or mixed-framing arrangements. Such stiffening 

 systems can provide large increases in general-instability strength by 

 effectively "breaking up" these long hull compartments. In order to 

 efficiently design for maximum possible instability strength of such 

 structures within certain specified weight limitations, it is necessary to 

 have adequate theory which, when verified by experiment, can then be 

 converted to design criteria. 



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