COMPARISON OF WAVE-INDUCED LOADS ON A NEAR SURFACE SLENDER BODY FROM INVISCID FLOW LINEAR SOLUTION AND AN EXPERIMENTAL MODEL TEST

摘要

The wave-induced loads experienced by a fully-submerged vehicle, but operating near the surface, play an important role in the design and operation of the vehicle. For an inviscid fluid with a monochromatic wave field, the first-order loads on a slender body of revolution can be solved for analytically using the method of singularities. The solution involves an integral expression dependent on the cross-sectional geometry of the body. For the canonical shape of a circular cylinder with hemispheric end caps, the integrals can be directly evaluated piecewise and a closed-form solution determined. This allows the rapid and easy calculation of wave-induced loads in any simple wave environment and at any operating depth. However, the use of potential flow ignores any viscous effects and effects due to changes to the wave as it passes over the vehicle. These effects may be important for smaller man-portable unmanned underwater vehicles. To determine the usefulness of this closed-form solution for small diameter bodies, an experimental model test was conducted to measure the loads where both potential and viscous effects are present. Experiments were performed for various wavelengths, at two model depths, and for one wave height while measuring the drag and vertical force along with the pitch moment on a 4.5 inch diameter model. These experimental loads are then compared to predicted loads from the analytic solution to assess their accuracy. This allows the determination of the importance of viscous effects and passing wave modification for wave-induced loads of small diameter underwater vehicles.