Design and optimization of the propulsion system is a crucial task of the ship design\ud process. The behaviour of the propulsion system, in transient conditions as well as in steady\ud state, is greatly affected by the capability of the control system to manage the available power\ud and to achieve the desired performance in the shortest time.\ud The selection of a proper control scheme is a trade-off between different and conflicting\ud needs. Two of the opposites are: increasing the ship operability by adding more functions and\ud more controls; and reducing the control system development and installation time and cost.\ud In this paper, the rapid prototyping and testing procedure for the development of the\ud propulsion controller of the new Italian aircraft carrier Cavour is presented, using real-time\ud hardware-in-the-loop (RT-HIL) simulation. The procedure is based on a wide use of simulation\ud technology. First, a complete dynamical model of the ship propulsion plant was developed.\ud Then, batch simulation was used to develop the best possible control scheme. Finally, RT-HIL\ud simulation was used to debug the real controller software and to tune the controller parameters\ud before sea trials.\ud The application of the procedure led to a significant reduction in the development phase of\ud the controller design. Furthermore, the adoption of the RT-HIL technology greatly reduced the\ud time spent to tune the control system during the ship delivery phase

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Abstract:The paper presents the main results of a research project directed to the development of mathematical models for the design and simulation of combined Gas Turbine-Steam or Diesel-Steam plants for marine applications. The goal is to increase the energy conversion efficiency of both gas turbines and diesel engines, adopted in ship propulsion systems, by recovering part of the thermal energy contained in the exhaust gases through Waste Heat Recovery (WHR) dedicated installations. The developed models are used to identify the best configuration of the combined plants in order to optimize, for the different applications, the steam plant layout and the performance of WHR plant components. This research activity has allowed to obtain significant improvements in terms of energy conversion efficiency, but also on other important issues: dimensions and weights of the installations, ship load capacity, environmental compatibility, investment and operating costs. In particular, the main results of the present study can be summarized as follows: (a) the quantitative assessment of the advantages (and limits) deriving by the application of a Combined Gas And Steam (COGAS) propulsion system to a large container ship, in substitution of the traditional two-stroke diesel engine; (b) the proposal of optimized WHR propulsion and power systems for an oil tanker, for which a quantitative evaluation is given of the attainable advantages, in terms of fuel consumption and emissions reduction, in comparison with more traditional solutions.

This article focuses on the mathematical model of the pitch control mechanism for a marine controllable pitch propeller, with the aim of describing the dynamic behaviour of this kind of system and its influence on ship performance. Too great a load on the blades can result in high pressures in the actuating system, response delays and control system problems, which are ultimately responsible for most mechanism failures. The behaviour of the controllable pitch propeller actuating mechanism is considered in terms of blade position, oil pressures inside the controllable pitch propeller hub and magnitudes of the forces acting on the blades. In the proposed mathematical model, the forces acting on the propeller blade are evaluated taking into account the yaw motion of the ship, the propeller speed (including shaft accelerations and decelerations) and the turning of the blade during the pitch change. On the basis of the introduced procedure, a controllable pitch propeller numerical model as part of an overall propulsion and manoeuvrability simulator representing the dynamic behaviour of a twin-screw fast vessel is developed. The aim of this work is to represent the ship propulsion dynamics through time-domain simulation, based on which the designers can develop and test several design options, in order to avoid possible machinery overloads with their consequent failures and to obtain the best possible ship performances. In this aspect, the controllable pitch propeller model is an essential design tool.

A turbocharged diesel engine numerical model, suitable for real-time ship manoeuvre simulation, is presented in this paper. While some engine components (mainly the turbocharger, intercooler and manifolds) are modelled by a filling and emptying approach, the cylinder simulation is based on a set of five-dimensional numerical matrices (each matrix is generated by means of a more traditional thermodynamic model based on in-cylinder actual cycle). The new cylinder calculation approach strongly reduces the engine transient computation time, making it possible to transform the simulation model into a real-time executable application. As a case study, the simulation methodology is applied to a high speed four stroke turbocharged marine diesel engine, whose design and off design running data are available from the technical sheet. In order to verify the suitability of the proposed model in real-time simulation applications, a yacht propulsion plant simulator is developed. Numerical results in ship acceleration and deceleration manoeuvres are shown, reducing the simulation running time of 99% in comparison with the corresponding in-cylinder actual cycle engine model.

The article shows the performance comparison between two marine engines, fuelled by diesel oil and natural gas respectively. Two different simulation codes, each for engine type, have been developed to extend the comparison to the whole working area of the examined engines. Although the maximum continuous power is very similar (about 2 MW at the same rotational speed), some differences exist in size, efficiency and pollutant emissions. The reasons are investigated through a specific thermodynamic analysis, by comparing the respective real cycles at several power and revolution values. In detail, the two combustion modes are analysed to explain the main differences that are found mostly in nitrogen oxides emissions

This work presents the main steps for the development of a multi-physic simulation platform, able to represent the dynamics of a twin screw ship in six degrees of freedom, taking into account the complete propulsion system including automation effects. The simulation platform has to be used in the preliminary design phase in order to study and design the propulsion plant and its control system. The ship motion model has been developed including roll motion, in order to capture the ship heel angles during tight turning circles, which may be significant for a fast naval vessel. Moreover, the simulation model includes a simplified representation of the asymmetric behaviour of the two propeller shafts during manoeuvres, which cannot be neglected when dealing with the propulsion plant behaviour. Several sub-models have been developed and calibrated by means of a set of experimental tests, in model and full scale. The sea trials campaign is finally used to validate and tune the developed simulator, thus the final version may be adopted as an optimization tool for other future designs (or sister ships) and for training purposes. Although the presented case study has been validated on a specific ship, most of the discussed models have a general application

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