Study on free vibration response of a liquid retaining composite structure considering fluid-wall interaction

Free vibration response of composite side walls of liquid retaining tank is carried out in the present study using direct coupling method. Graphite-epoxy side walls are modelled using eight noded isoparametric element with five degrees of freedom per node. The fluid inside the reservoir is modelled with sixteen noded brick element. First-order shear deformation theory (FSDT) is employed to obtain the strain terms of the thin plate with proper shear correction factor. Plate and fluid are modelled separately in Matlab environment and then coupled in a direct way to obtain the vibration response of the side walls considering the effect of fluid–structure interaction (FSI). Influence of parametric variations in terms of ply angle, ply layers (number and thickness), stacking sequence, tank geometry and boundary conditions are considered and respective responses are presented graphically with several numerical examples. Convective wave propagation is more predominant in the second frequency of the fluid; hence, the first three natural frequencies are studied in depth to represent the actual free vibration response. Outcome of the present study shows that frequency values increase with increase in ply angle though symmetric 45° 2 layered lamination shows peak values among all the cross-ply or angle-ply variations. Height of the tank wall is also a guiding factor for frequency as it increases up to a ratio (height/length) of 0.5. Variation in boundary conditions reveals that tank with all edges simply supported for both the side walls has maximum frequency. Effect of convective wave response is also observed with the results associated with second frequency values. Mode shapes of the plate under different boundary conditions are also presented at the end.