The hydrodynamics models used in current controller algorithms and design of underwater vehicles do not account for the effects of viscosity, nonlinearity, and surface waves properly on the vehicle dynamics. The need to improve the reliability and efficiency of the underwater vehicles require better hydrodynamics and dynamics models, particularly for shallow water operations. Motivated by this need to improve the performance of the vehicles in shallow waters, we have investigated nonlinear, coupled fluid-body dynamics of underwater vehicles.

The fluid forces acting on the vehicle are computed using numerical methods based on boundary-integral and finite-difference formulations. Specifically, a boundary-integral method based on the mixed Eulerian-Lagrangian formulation of Longuet-Higgins and Cokelet (1976) is developed to analyze nonlinear inviscid wave-AUV interactions. Finite-difference method based on the projection method of Chorin (1967) and implemented using boundary-fitted coordinates is used to investigate the nonlinear viscous wave-AUV interactions. Linear frequency-domain results are also obtained using a boundary-integral formualtion based on simple-source distribution (Yeung, 1974). Results obtained by these various methods are compared to quantify and model the effects of viscosity and free-surface nonlinearity.

The motion response of the vehicle is determined by time-integrating the nonlinear equations of motion formulated in the body-fixed coordinate system. Accurate algorithms are under development to determine vehicle stability and maneuverability in shallow waters under the action of surface waves. Using the algorithms and the simulated results, ocean engineers can determine the viability of a mission in a given sea state and also improve the design of AUVs for special ops in coastal waters.

Participants (1998-2005)

Principal Investigator: P. Ananthakrishnan
Post-Doctoral Researchers / Engineers: Pierre-Emmanuel Guillerm, Sophie Decron
Graduate Students: Keqin Zhang, Christophe Puaut, Vimal Vinayan, Olivier Saout
UG Students : Laura J. Martel, Jim Lasswell, Tannen S. VanZwieten, Hannuman Bull
Interns: Sandrine B. Vantouraux, Eric Larnicol, Sophie Decron, Benoit Imbert, Nicolas Faisant

References

V. Vinayan, ``Boundary-Integral Analysis of Nonlinear Diffraction Forces on a Submerged Body,'' MS Thesis , Department of Ocean Engineering, Florida Atlantic University, 2003.

O. Saout, ``Computation of Hydrodynamic Coefficients and Determination of Dynamic Stability Characteristics of an Underwater Vehicle including Free Surface Effects,'' MS Thesis , Department of Ocean Engineering, Florida Atlantic University, 2002.

C. Puaut, ``Hydrodynamic Analysis of an Underwater Vehicle Including Free-Surface Effects'', MS Thesis , Department of Ocean Engineering, Florida Atlantic University, 2001.

P. Ananthakrishnan and S. Decron, ``Dynamics of Small- and Mini-Autonomous Underwater Vehicles: Part I. Analysis and Simulation for Midwater Applications'', Technical Report , 63p, Department of Ocean Engineering, Florida Atlantic University, July 2000

P. Ananthakrishnan and L. Martel, ``Simulation of AUV motion in shallow water,'' Proceedings of the Oceans Community Conference'98, Baltimore, 1998.

P. Ananthakrishnan, S. Vantouroux, K-Q. Zhang and S. M. Smith, ``Nonlinear dynamics and hydrodynamics considerations in the design of an autunomous underwater vehicle,'' Proceedings of the Oceanology International'98 Conference, vol. 3, pp. 119--128, Brighton, UK, 1998.

P. Ananthakrishnan and K. Zhang, ``AUV motion in a wave field,'' Proceedings of the IEEE OCEANS'98 Conference, Nice, France, 1998.