Nonlinear Finite Element Analysis of Composite Flextensional Transducer Shell

Presented here is the result of a Finite Element Analysis (FEA) and its correlation with test data for a Class IV flextensional underwater acoustic transducer. The thick, elliptical fiberglass/epoxy shell of the transducer Finite Element Model (FEM) was modeled with 20-node solid elements using effective engineering properties derived from a micromechanics theory. Unidirectional gap elements were used to model the clearance between the end curves of the shell and the two D-shaped aluminum inserts. The D-inserts were placed along the major axis of the shell to transmit the driving power of the piezoelectric ceramic stack in order to excite shell's flaxural modes for an efficient acoustic radiation. The model also featured large deformation. The predicted global displacements of the shell, as well as the local strain values at several critical locations in the shell, correlated very well with the test data obtained from the stack preload and hydrostatic pressure tests. Gapping between the end curve of the shell and the D-insert, which was detected during the pressure test, was also predicted in the analysis. Gapping has been shown to be detrimental to the structural, as well as the acoustic performance of the shell. The success of this pilot model, in accurately predicting the structural behavior of the transducer shell under simulated loading conditions, has lead to a series of FEA studies to determine the sensitivities of the shell's structural performance to thickness variation and to nonuniform material property distribution in the shell. Nonuniform material property distribution arise from the variation in parameters, such as moduli of the constituents, fiber volume fraction, and ply arrangement of the laminates. ... Active surveillance (reverberation), Data processing, Passive acoustic surveillance