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Abstract:
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The study envisaged herein contains the numerical investigations on Perforated Plate
(PP) as well as numerical and experimental investigations on Perforated Plate with Lining
(PPL) which has a variety of applications in underwater engineering especially related to
defence applications. Finite element method has been adopted as the tool for analysis of
PP and PPL. The commercial software ANSYS has been used for static and free
vibration response evaluation, whereas ANSYS LS-DYNA has been used for shock
analysis. SHELL63, SHELL93, SOLID45, SOLSH190, BEAM188 and FLUID30 finite
elements available in the ANSYS library as well as SHELL193 and SOLID194 available
in the ANSYS LS-DYNA library have been made use of. Unit cell of the PP and PPL
which is a miniature of the original plate with 16 perforations have been used. Based
upon the convergence characteristics, the utility of SHELL63 element for the analysis of
PP and PPL, and the required mesh density are brought out. The effect of perforation,
geometry and orientation of perforation, boundary conditions and lining plate are
investigated for various configurations. Stress concentration and deflection factor are
also studied. Based on these investigations, stadium geometry perforation with horizontal
orientation is recommended for further analysis.Linear and nonlinear static analysis of PP and PPL subjected to unit normal pressure has
been carried out besides the free vibration analysis. Shock analysis has also been carried
out on these structural components. The analytical model measures 0.9m x 0.9m with
stiffener of 0.3m interval. The influence of finite element, boundary conditions, and lining plate on linear static response has been estimated and presented. Comparison of
behavior of PP and PPL in the nonlinear strain regime has been made using geometric
nonlinear analysis. Free vibration analysis of the PP and PPL has been carried out ‘in
vacuum’ condition and in water backed condition, and the influence of water backed
condition and effect of perforation on natural frequency have been investigated.Based upon the studies on the vibration characteristics of NPP, PP and PPL in water
backed condition and ‘in vacuum’ condition, the reduction in the natural frequency of the
plate in immersed condition has been rightly brought out. The necessity to introduce the
effect of water medium in the analysis of water backed underwater structure has been
highlighted.Shock analysis of PP and PPL for three explosives viz., PEK, TNT and C4 has been
carried out and deflection and stresses on plate as well as free field pressure have been
estimated using ANSYS LS-DYNA. The effect of perforations and the effect of lining
plate have been predicted. Experimental investigations of the measurement of free field
pressure using PPL have been conducted in a shock tank. Free field pressure has been
measured and has been validated with finite element analysis results. Besides, an
experiment has been carried out on PPL, for the comparison of the static deflection
predicted by finite element analysis.The distribution of the free field pressure and the estimation of differential pressure from
experimentation and the provision for treating the differential pressure as the resistance,
as a part of the design load for PPL, has been brought out. |