George D. Watt

A fully interactive dynamic simulation of a semi-submersible towing a large towfish

ISER and DREA are collaborating on the development of SIMRNIS, a fully interactive nonlinear submersible/cable/towfish six degree-of-freedom (DOF) time domain simulation. This capability is not found in standard tow system codes. SIMRMS is a meshing of the DREA Submersible Simulation Program (DSSP) and the DYNTOCABS tow cable/towfish simulator. DSSP is a nonlinear 6 DOF vehicle simulator that models control, propulsion, and ballasting. DYNTOCABS provides a three-dimensional, nonlinear, 3 DOF, finite segment simulation of the cable and includes a nonlinear 6 DOF model of an active towfish. The two programs have been merged so that the equations of motion for all system components are simultaneously integrated in time. New features and capabilities have also been developed. SIMRMS is used as a test bed to minimize technical risk for further development of a remote minehunting system. This paper discusses, and presents full scale sea trials data validating, the programs capabilities.

A Critical Review of Classical Force Estimation Methods for Streamlined Underwater Vehicles Using Experimental and CFD Data

Classical hydrodynamic force estimation methods are widely used by industrial designers of underwater vehicles for whom captive model experiments and CFD based simulations are uneconomical. They are also used in the preliminary design of submarines and when real time submarine simulations are required. These methods poorly estimate the contribution of the hull to the forces, especially at moderate to high incidence angles. This paper critically reviews the classical hull force estimation methods developed by Munk, Allen, Perkins and Jorgensen, and Sarpkaya. It compares the methods with experimentally validated CFD predictions of a streamlined body at incidence angles up to 30 degrees and for Reynolds numbers from 2.3 to 230 million. The comparison shows that inadequately modeled flow separation and leeside body vortices explain the poor force and moment predictions. This is partly due, at least, to the lack of a streamlined tail on the truncated missile shapes for which the estimation methods were developed.Copyright

Examination of the Flow Separation Characteristics Around a Streamlined Axisymmetric Shape

Using computational fluid dynamics (CFD), a study was conducted to predict the hydrodynamic forces and moments on an axisymmetric body over a range of yaw angles and Reynolds numbers. Computational results for hydrodynamic forces and moments show good agreement with experimental data, being within the experimental uncertainty range at most yaw angles. Deviations outside of the uncertainty range occurred for the lateral (Y) force values at yaw angles greater than 15 degrees. The development of the after-body vortex shows good agreement with experimental observation. Primary and secondary separation points and shear stress streamline behaviour are also compared with experiment data at a yaw angle of 24 degrees. Results are discussed with a view to identifying flow features critical to the development of new force estimation methods. The after-body vortex, at increasing yaw angles, influences the overall force and moment predictions through a complex interaction between the transport of after-body vorticity and the detachment/reattachment locations of the boundary layer. Adequate modeling of this after-body region is increasingly important at high yaw angles. One of the most important features that influences the overall forces and moments is the circumferential position of shear layer detachment and reattachment, which have a direct impact on the pressure distribution along the body.Copyright

A Concept for Docking a UUV With a Slowly Moving Submarine Under Waves

Docking an unmanned underwater vehicle (UUV) with a submerged submarine in littoral waters in high sea states requires more dexterity than either the submarine or streamlined UUV possess. The proposed solution uses an automated active dock to correct for transverse relative motion between the vehicles. Acoustic, electromagnetic, and optical sensors provide position sensing redundancy in unpredictable conditions. The concept is being evaluated by building and testing individual components to characterize their performance, errors, and limitations, and then simulating the system to establish its viability at low cost.

Hydrodynamic Forces and Moments on Slender Axisymmetric Bodies with Decks in Translation

A Computational Fluid Dynamics study of the DRDC STR hull with a custom deck in translation at various incidence and orientation angles was completed to obtain an increased understanding of how the deck geometry affects the hydrodynamic forces. Over one hundred simulations were performed on the specified geometry at a Reynolds numbers of 26 × 10. The total hull forces and moments, surface streamlines and wake topologies were extracted. A mesh sensitivity study was performed to check the accuracy of the simulations. Results of the flow field at symmetric orientations show similarities to the results of simulations with no deck. However, asymmetric deck orientations exhibit a much more complicated flow field and, in some cases, significant variations from the results of the total forces and moments of the no-deck geometry were identified.