Free Surface Effect on the Hydrodynamics of an Underwater Vehicle Hullform, the Darpa Suboff

Abstract

This paper presents the numerical study on the hydrodynamic coefficients of the submarine hull form “DARPA SUBOFF” when deeply submerged and near the free surface when travelling straight ahead and at a range of drift angles. The Computational Fluid Dynamics (CFD)-based numerical model was validated with experimental data existing in the public domain for the SUBOFF, travelling over a range of drift angles when deeply submerged at a constant speed and in a straight line near the free surface over a range of speeds. The free surface effect on the hydrodynamic behaviour of the SUBOFF was then investigated throughout a range of speeds, drift angles and submergence depths. Results show that the effects of the free surface diminish rapidly with submergence and the near free surface hydrodynamic behaviour of the SUBOFF is highly Froude number dependent.

Hydrodynamic performance and wake study of an UUV sailing near the free surface

“…Due to the operational environment and tactical limitations, conventional powered UUVs sailing near the free surface often need to complete tactical actions such as near surface ventilation, power generation, rescue, missile launch, and periscope depth observation. Compared to deep water diving, UUVs sailing near the surface are affected by the Venturi effect, and their hydrodynamic forces show significant changes with depth and speed (Wang et al, 2019;Ling et al, 2022a;Ling et al, 2022b;Li et al, 2021;Dong et al, 2022;Huang et al, 2022). This requires UUVs to have good stealth technology.…”

Effects of Length-to-Diameter Ratio on a Near Free Surface Underwater Vehicle

“…This paper adopts the methodology from several publications (Ling et al, 2022a;Ling et al, 2022b;Ling et al, 2022c) as a common baseline but extends upon the previous by presenting a pseudo-timestep study, which investigates the effects of pseudo-timestep on force oscillations and free surface elevations, as well as an iterative convergence study by showing the computational residuals, forces, and moments. The methodology section presents the underwater vehicle hulls used in this study, the computational domain, the simulation setup, a mesh independence study, and experimental validation.…”

“…The computational domain used throughout this study is based on the David Taylor Model Basin of the Naval Surface Warfare Center Carderock Division (formerly known as the David Taylor Research Centre) with the dimensions and test parameters listed in Table 3. The domain was sized to coincide with a set of experimental data involving the SUBOFF undergoing steady drift angle tests by Roddy (1990) which was used for validation (Ling et al, 2022a;Ling et al, 2022b;Ling et al, 2022c). For reference, in terms of the L/D = 8.6 SUBOFF length, the numerical domain is sized as such from the centre of buoyancy as the origin: the inlet is 3 body lengths, L away, the outlet is 5 L away, the sides are 1.8 L away.…”

“…The Kelvin wake of a submarine moving at a constant velocity and submergence depth can be considered as a superposition of two dominant wake patterns with origins at the bow and aft shoulder. Ling et al (2022a) showed that the heave force induced by the interaction can evolve from a suction at lower Froude numbers to a repulsion at higher Froude numbers. The induced surge force and pitch moment had a more complex variation with respect to Froude number.…”

CFD Study on the Hydrodynamics of a Submarine Model Operating Near a Free-Surface

“…They have tested different geometries under several scenarios to understand the behaviour of squad submarines and to determine the optimal body geometry. Ling et al [7] conducted a numerical study to examine the hydrodynamics of the DARPA suboff under free surface effect. Ling et al [8] used CFD to investigate the effect of length-to-diameter ratio on the performance of a submarine operating near the free surface.…”