ANALYTICAL AND EXPERIMENTAL INVESTIGATION ON THE FREE VIBRATION OF SUBMERGED STIFFENED STEEL PLATE

The approach developed in this paper applies to vibration analysis of rectangular stiffened plate coupled with fluid. It is obvious that the natural frequencies of a submerged structure are less than those of in vacuum and these are due to the effect of added mass of water to the structure. This paper focuses on the experimental, analytical and numerical solution of natural frequencies of submerged stiffened plate. The analytical solution based on the deflection equation of submerged orthotropic plate, Laplace’s equation and Rayleigh's method in vibration analysis. By used the FEM software the numerical results for natural frequencies are derived. The natural frequencies of the stiffened plate are obtained practically by using Fast Fourier Transformation functions (FFT) in experimental analysis. Experimental results demonstrate the validity of analytical and numerical solution and results.

Control Oriented Maneuver Model of Prismatic Planing Hull

Roll yaw coupled dynamics are not well characterized and existing low cost models are limited in range of applicability. We utilize an interpolation based approach to address a wider range of conditions with reduced computational requirements. By interpolating test data to estimate hydrodynamic forces and empirically modeling roll damping and added mass, we establish a 4DOF maneuvering model for prismatic planing hulls in calm water. It is validated against relevant tests and show significant computational resource savings in comparison with potential flow based methods. Simulation of an extreme turning maneuver and an asymmetrical loading case demonstrates its potential for use in initial design, control and evaluation.

Bio-inspired aquatic propulsion using piezoelectric effect

Underwater propulsion of fishes have inspired many biomimetic structures. Generally, the bio-inspired structures mimics the flapping behaviour of various control surfaces/fins in fishes. The present study mimics the flapping behaviour using a piezoelectric structure. The system is analyzed as a fluid structure interaction problem. The dynamic behaviour of a cantilever beam surrounded by a bounded fluid domain open at top is analyzed. The structure is modeled as a Euler-Bernoulli beam and the fluid is modeled using potential flow theory. The influence of domain size on the wet natural frequencies of the system was analyzed. The dimensions of the fluid domain wherein the variation in wet natural frequencies becomes insensitive were determined. The influence of added mass on the wet natural frequency was parametrized based on Non-dimensional Added Mass Increment (NAVMI) factor. The NAVMI factors were observed to be relatively higher for lower wet modes of the structure. Therefore, the peizo-beam was analyzed by exciting the lower wet modes. The thrust generated at different excitation frequencies were determined using tip velocity of the cantilever beam following Lighthill’s analogy. The results from the study indicated that higher propulsive thrust was produced for lower modes of excitation of the structure.