FULL-SCALE FINITE ELEMENT ANALYSIS OF A PASSIVE SONOBUOY

Sonobuoys are relatively small, expandable sonar systems those are dropped or ejected from aircraft or ships, floating on the sea and serving as anti-submarine agents. Sonobuoys are subjected to high temperature differences in the storage conditions as well as vibration and/or shock loading during mission flights. Probably the most extreme case occurs when Sonobuoy hits the sea surface as it is dropped from an aircraft. In order to ensure the structural integrity and functionality of Sonobuoys, all these conditions should be considered carefully in design phase. The pressure-activated buoy mechanism should also be guaranteed to work properly, which would otherwise result in the failure of whole system. In this work, the finite element analyses of a full-scale Sonobuoy model with more than 2 million degrees of freedom were accomplished. Having managed to build a proper finite element model of the Sonobuoy, some modal analyses were run. The modal analyses were followed by random vibration analysis. For shock loading, some transient analyses were carried using implicit time integration. The input parameters for random vibration and shock analyses were determined according to the test parameters as specified in MIL-STD-810F, which is the standard for “Environmental Engineering Considerations and Laboratory Tests”. Sonobuoy was also hold at two extreme storage temperatures; +60 oC and -20 oC respectively and resulting thermal expansions and stress fields were revealed . The strike of Sonobuoy as it gets into the sea water was also simulated including the fluid-structure interaction. Lastly, the analysis of pressure-activated buoy mechanism was carried in submodel scale. This highly nonlinear problem was solved explicitly as well as implicitly and results were compared.