SOFTWARE SOLUTIONS BY DEJAN MATIC, BILL CLARK, GANESH VENKATESAN, CD-ADAPCOSubmarine Manuevering SimulationsThe numerical simulation of submarine maneuvering is a challenging problem that has only recently been addressed by advances in Computational Fluid Dynamics (CFD) software. In this article, we demonstrate how CD-adapco’s that, until recently, have challenged the state-of-the- integrates the computed shear stresses and pressure simulation technology can be applied to accurately art in computational resources. distribution on the surface of the body, providing the predict how a submarine’s motion is driven by hydro- The submarine in question is propelled by a three- hydrodynamic forces and moments acting on it. The dynamic forces, and compare numerical results with bladed rotating propeller. Maneuvers were executed equations of motion are then solved in order to obtain experimental data. through the application of rudder and stern planes, instantaneous displacements and rotations.The physics-based simulation of a full-scale subma- and controlled by varying the position of these control This information is used to update the computational rine performing maneuvers is an expensive proposi- surfaces in response to the submarine motion predict- mesh which is rotated and translated as a rigid body tion relative to many CFD applications. This is prin- ed by the simulation. with respect to an inertial frame of reference.cipally due to the wide range of length and timescales The integration and rigid body mesh movement are that must be resolved in order to predict accurately Numerical method performed automatically using CD-adapco’s Dynamic the ? ow around the submarine hull. An additional During the course of a maneuver, the submarine Fluid-Body Interaction (DFBI) model at each itera-challenge involves representing the full geometric changes its position and orientation continuously in tion. By converging this iteration process at each time complexity of an appended submarine and propul- time in response to the pressure ? eld generated by step, the trajectory of the body is obtained. The im-sion unit. The length scales range from the very thin application of the control surfaces. The simulation plicit nature of the method (in which equations of mo-boundary layer to the full length of the submarine. of a maneuver requires the coupled solution of equa- tion are calculated simultaneously with the ? ow ? eld) The time scales range from a fraction of the propel- tions of motion of the rigid body (in six degrees of is important to ensure the overall stability of the simu-ler blade passing period to the total duration of a ma- freedom) with unsteady Reynolds-averaged Navier- lation without using an impractically small time step.neuver - more if several maneuvers are combined in Stokes equations (URANS). The URANS solver uses a single simulation. These disparities in scale lead to a fully-implicit iterative time-integration scheme. Computational meshvery large computational meshes and simulation times It computes the ? ow ? eld around the body ? rst and The discretized domain consisted of 3 million com-putational cells, including layers of prismatic cells next to the walls, which was prescribed in order to capture the near wall boundary layer. The mesh was automatically constructed using CD-adapco’s auto-matic hexahedral meshing methodology: a simple background hexahedral mesh was created within the boundaries of the computational domain, overlapping the geometry of the submarine. Any hexahedral cells that were located completely inside the body or the extruded layer were deleted, while those that intersect this layer were trimmed so that any overlaps were re-moved. Finally, the mesh was locally re? ned in re-gions where large ? ow variations were expected.The propeller was enclosed inside the cylindrical Mesh resolution on propeller and control surfaces.18 Maritime Reporter & Engineering News • JANUARY 2014MR #1 (18-25).indd 18 1/7/2014 10:21:32 AM