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The free wet vibration characteristics of an idealized low-aspect-ratio cantilever wing are studied semi-analytically, numerically, and experimentally. The wing is modeled as a tapered, hollow Kirchhoff’s plate, with the chord-wise section as a symmetrical NACA0018 aerofoil. The chord length tapers from root to tip, over the span. The main aim is to set up a suitable radiation boundary problem for the vibrating cantilever wing, in order to semi-analytically generate the wet frequencies. The efficacy of the semi-analytical wet vibration approach is studied by comparing it with the other two approaches. The difficulties encountered are due to the hollow two-way tapered shape of the wing and the free edge boundary conditions on its three sides. The semi-analytical approach is based on Galerkin’s method, which includes the modal superposition of two orthogonal beam modeshapes (Free-Free beam in chord-wise and cantilever in span-wise directions). The plate modeshapes thus generated are further used in the 3D source distribution technique to calculate the fluid inertia, leading to a consistent drop in the natural frequencies. The cantilever wing has been fabricated and tested in-house. The underwater impact hammer test generates the wet natural frequencies. The free vibration frequencies are also verified numerically using ANSYS, and compared with experimental studies.

The free vibration of a rudder is studied here by theoretical, numerical, and experimental means. The rudder is modeled as a Kirchhoff’s plate, with chord-wise sections as symmetrical aerofoils of NACA0018 section. The free vibration is also studied numerically. The results have been compared with experimental studies. A model scale rudder has been constructed from a 3 mm thick metal sheet, with a length-scale ratio of 1:10. Impact hammer test has been down to excite all the natural frequencies, which have been picked up by two accelerometers into an FFT analyzer. Comparative studies have been done among the three methods.

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The free vibration of a low-aspect cantilever wing is studied by semianalytical, numerical, and experimental means. The wing is modeled as a two-way tapered, hollow Kirchhoff's plate, with the chord-wise section as symmetrical NACA0018 aerofoil. The chord length and the thickness taper from root to tip, over the span. The semianalytical approach is based on Galerkin's method, which includes the modal superposition of two orthogonal beam modeshapes (free-free beam in chord-wise direction and cantilever beam in span-wise direction). The free vibration is also studied numerically using ANSYS. The results have been compared with an experimental study, performing the dry impact hammer test. A model scale wing has been constructed from a 3-mm-thick metal sheet, with a length-scale ratio of 1:10. Comparative studies have been done among the three methods. The feasibility of modeling a low-aspect-ratio wing as a plate has been investigated. 1. Introduction Lifting surfaces commonly occur in engineering structures: fans, steam and gas turbine blades, impeller blades, wind turbine blades, helicopter fans, airplane wings, marine propeller blades, marine rudders and skegs, and other control surfaces like hydrofoils and wings in high-speed marine crafts. The lifting surface is typically a cantilever, with one edge welded to the main structure (root), and the other end free (tip). The span-wise geometry is tapered, for greater strength at the root and lighter weight at the tip. The chord-wise cross section is an aerofoil, which acts as a lifting surface to the incoming flow at varying angles of attack. The aspect ratio of the lifting surface, i.e., the ratio of the span length to the mean chord length, may vary from 0.4 to 0.6 in a turbine blade to 12 to 15 in an airplane wing/wind turbine. This work focuses on a low-aspect-ratio lifting surface, whose usual span-to-chord ratio is 1.5–2.