Non-linear material three degree of freedom analysis of submarine drydock blocking systems

Abstract

U.S. Naval shipyards where submarines are dry-docked are located in regions of the United States where significant earthquakes are known to occur. The graving dry-docks at these shipyards are currently designed to withstand earthquake accelerations up to 0.26 g's. This thesis develops a nonlinear material model for wood drydock block caps which more closely represents its actual behavior than linear elastic material models used previously. Using this non-linear model, it is determined that submarine drydock blocking systems would fail at even lower earthquake accelerations than that predicted by linear material models. This confirms that submarine drydock blocking systems would fail at accelerations which are significantly lower than the Navy's 0.2 g survival requirement. New blocking materials are then analyzed using non-linear models developed in this thesis in order to determine their potential for increasing system survivability. The materials analyzed are natural rubber and dynamic isolators. It is determined that when these materials are incorporated in the blocking systems, significant increases in survivability occur; however, all the systems still fall well below the required 0.2 g level. This thesis makes it clear that the current submarine drydock blocking systems provide inadequate protection of the submarines from accelerations caused by highly probable earthquakes, but the use of new blocking materials can reduce the risk of blocking failure. (KT/AW)