The problem of ship manoeuvrability has reached nowadays a significant consideration, both for merchant ships, with the adoption of IMO standards, and naval ships, with the production of various documents by NATO Specialist Teams. In literature many works regarding manoeuvrability of single screw slow/medium speed ships are present, while a lack of information about twin screw ships (cruise ships, RoRo ferries, megayachts, naval vessels) exists. These ships are usually characterised by different hull forms and more complex stern configuration due to the presence of appendages like skegs, shaft lines and brackets, which can strongly affect manoeuvrability behaviour. In this work various prediction methods, namely statistical regressions, system identification and RANSE, have been investigated in order to evaluate twin screw naval vessels manoeuvrability behaviour. From this analysis stern appendages influence (including also non linear effects resulting from hull-appendages interactions) resulted one of the peculiar characteristics of this type of ships, clearly affecting their manoeuvring capabilities

This paper discusses the early phase of the ignition transient of the VEGA Launcher's third stage solid rocket motor, Zefiro 9A. During the first two firing tests of the Z9A SRM (QM2 and VT1) a peculiar unexpected negative force peak and a significant pressure unbalance in the motor chamber were measured during the very first phase of the ignition transient. In order to fix the unexpected negative force, out of the system specifications, a modification of the igniter re-design was decided for the Z9A SRM and a third static firing test was successfully carried out (VT2), with a reduction of the negative differential pressure of at least around a factor 3, followed by a reduction of the negative thrust by around the same factor. This paper wants to analyze the scenario outlined by the VT2 static firing test by means of three dimensional unsteady multi-component numerical simulations of the SRM pre-ignition transient. © 2011 IEEE.

The results of accurate compressible Navier-Stokes simulations of aerodynamic heating of the Vega launcher are presented. Three selected steady conditions of the Vega mission profile are considered: the first corresponding to the altitude of 18 km, the second to 25 km and the last to 33 km. The numerical code is based on the mathematical model described by the Favre-Average-Navier-Stokes equations; the turbulent model chosen for closure is the one-equation model by Spalart-Allmaras. The equations are discretized by a finite volume approach, that can handle block-structured meshes with partial overlap ("Chimera" grid-overlapping technique). The isothermal boundary condition has been applied to the lancher wall. Particular care was devoted to the construction of the discrete model; as a matter of facts, the launcher is equipped with many protrusions and geometrical peculiarities (as antennas, raceways, inter-stage connection flanges and retrorockets) that are expected to affect considerably the local thermal flow-field and the level of heat fluxes, because the flow have to undergo strong variation in space; consequently, special attention was devoted to the definition of a tailored mesh, capable of catching local details of the aerothermal flow field (shocks, expansion fans, boundary layer, etc..). The computed results are reported together with uncertainty and actual convergence order, that were estimated by the standard procedures suggested by AIAA.

In this work the numerical simulations of a submarine in straight ahead motion with the appendages at several prescribed deflection angles are performed. Due to the complex geometry involved (the presence of moving appendages), these simulations are rather demanding form the point of view of both grid generation and accuracy of the numerical method. In order to analyze these aspects, the numerical solutions are computed by means of an unsteady Reynolds averaged Navier-Stokes equations solver, which is particularly effective because of the high order discretization schemes adopted. From the point of view of mesh construction, a dynamic overset grid technique is used, where each geometrical element of the whole geometry is discretized with a set of block-structured body-conformal mesh with partial overlapping (Chimera approach). In the present paper, the details of the method and numerical results for several deflection angles of the bow and stern planes are presented.