Propulsion Plant Simulation for Fast Military Vessels

Design and optimization of the propulsion system is a crucial task of the ship design. In fact the behaviour of the propulsion system is a key aspect of the global behaviour of a ship, mainly if the ship is a naval vessel. Simulation techniques can be very effective to predict the propulsion plant behaviour during normal working conditions as well as during critical situations. Numerical simulation gives the possibility to foresee, at design stage, the behaviour of the ship propulsion plant during manoeuvres and gives the designer the possibility to optimise the choice of the system parameters (choice of a suitable pitch/r.p.m. combination law, engine governor calibration, scantling of the shaft line) in order to prevent engine and mechanical overloads or faults. Moreover by simulation it is possible to study and optimise the machinery control system. The paper presents a comprehensive approach to simulate the propulsion system behaviour during transients and off design conditions to be used for the control system setting and overall ship propulsion plants study. The presented approach was successfully used for the design of the new high speed Italian Frigates FREMM class. This ships class has a new propulsion plant concept: the COmbined Diesel eLectric And Gas (CODLAG) type, with single gear and two shaft lines. The application presented in this paper concerns the design of the propulsion control system with a detailed simulation of the Gas Turbine Control System (TCS) and of the controllable pitch propeller system. A comparison between simulation transients results and reference data is reported in the paper.