Massimo Figari

Real-time simulation of a COGAG naval ship propulsion system

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

Machine learning approaches for improving condition-based maintenance of naval propulsion plants

Availability, reliability and economic sustainability of naval propulsion plants are key elements to cope with because maintenance costs represent a large slice of total operational expenses. Depending on the adopted strategy, impact of maintenance on overall expenses can remarkably vary; for example, letting an asset running up until breakdown can lead to unaffordable costs. As a matter of fact, a desideratum is to progress maintenance technology of ship propulsion systems from breakdown or preventive maintenance up to more effective condition-based maintenance approaches. The central idea in condition-based maintenance is to monitor the propulsion equipment by exploiting heterogeneous sensors, enabling diagnosis and, most of all, prognosis of the propulsion system’s components and of their potential future failures. The success of condition-based maintenance clearly hinges on the capability of developing effective predictive models; for this purpose, effective use of machine learning methods is proposed in this article. In particular, authors take into consideration an application of condition-based maintenance to gas turbines used for vessel propulsion, where the performance and advantages of exploiting machine learning methods in modeling the degradation of the propulsion plant over time are tested. Experiments, conducted on data generated from a sophisticated simulator of a gas turbine, mounted on a Frigate characterized by a COmbined Diesel eLectric And Gas propulsion plant type, will allow to show the effectiveness of the proposed machine learning approaches and to benchmark them in a realistic maritime application.

Controllable pitch propeller actuating mechanism, modelling and simulation

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.

Numerical modelling of propulsion, control and ship motions in 6 degrees of freedom

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 6 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 trial 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 training purposes. Although the presented case study has been validated on a specific ship, most of the discussed models have a general application.

Dynamic behaviour and stability of marine propulsion systems

The paper describes an approach used to study the dynamic behaviour of marine propulsion systems. The method consists of three main steps: analytical modelling of the ship propulsion system, stability analysis of the system, and dynamic behaviour of the propulsion plant. The model is based on non-linear first-order differential equations. The concepts of ‘geometric non-linear dynamics’ are used to highlight some important properties of the model. One of the main advantages of the method is that it enables some important dynamic properties of the propulsion system to be highlighted without solving the differential equations of motion. In particular circumstances an analytical solution of the proposed model is possible; the solution includes the steady state behaviour of the system, which is useful for the engine-propulsion matching.

Performance Decay Analysis of a Marine Gas Turbine Propulsion System

Marine propulsion plants are designed to be more and more efficient to minimize fuel consumption and pollution emissions. However, during the ship operating life, propulsion components and hull are characterized by a certain performance decay, responsible for a worse behavior of the overall propulsion plant. For this reason, the several propulsion components are periodically subjected to expensive maintenance works to restore, as far as possible, their original design characteristics. In the present study, the propulsive performance variation of a naval vessel, powered by a gas turbine as part of an innovative CODLAG system, is simulated and analyzed by means of a detailed and validated numerical code. A sensitivity analysis regarding the influence of the main components deterioration (gas turbine, propellers, and ship hull) on the overall behavior of the propulsion plant is carried out. Several speed profiles of the vessel have been analyzed in terms of the usual performance parameters (ship speed, engine power, and fuel consumption) as well as the pollution emissions of the gas turbine. The main aim of the work is to get useful information for the ship management and maintenance scheduling (condition-based maintenance).

Numerical investigation on ship energy efficiency by Monte Carlo simulation

In this article, the authors present a procedure to predict the energy efficiency operational indicator by Monte Carlo simulations, estimating the total ship fuel consumption as a function of displacement and speed considered as random variables. To characterize the probability density function of displacement and speed, a complete series of operating data concerning 2 years of navigation, of a RoPax engaged in a commercial trade in the Mediterranean Sea, were collected and used.

Propulsion retrofitting of the tall ship Amerigo Vespucci: Automation design by simulation

The paper is focused on the most important aspects of the electric propulsion retrofitting of the tall ship Amerigo Vespucci, decided by the Italian Navy in 2010 to improve performance, flexibility and reliability of the propulsion system. The automation design is based on a simulation study, aimed at the ship performance prediction in both sailing and motor propulsion conditions. In particular, an original control logic is investigated by numerical simulation, in order to drive the propeller to the “zero-thrust” condition during sailing propulsion: by this way, it could be possible to avoid the negative effect of the trailing propeller on the transmission efficiency and safety, as well as on the vessel speed.

Dimensionless Numerical Approaches for the Performance Prediction of Marine Waterjet Propulsion Units

One of the key issues at early design stage of a high-speed craft is the selection and the performance prediction of the propulsion system because at this stage only few information about the vessel are available. The objective of this work is precisely to provide the designer, in the case of waterjet propelled craft, with a simple and reliable calculation tool, able to predict the waterjet working points in design and off-design conditions, allowing to investigate several propulsive options during the ship design process. In the paper two original dimensionless numerical procedures, one referred to jet units for naval applications and the other more suitable for planing boats, are presented. The first procedure is based on a generalized performance map for mixed flow pumps, derived from the analysis of several waterjet pumps by applying similitude principles of the hydraulic machines. The second approach, validated by some comparisons with current waterjet installations, is based on a complete physical approach, from which a set of non-dimensional waterjet characteristics has been drawn by the authors. The presented application examples show the validity and the degree of accuracy of the proposed methodologies for the performance evaluation of waterjet propulsion systems.

LNG fueled barge for cold ironing: Feasibility study for the emission abatement in the Port of Genoa

The current scientific analysis aims at studying some maritime technical solutions for electric energy generation and delivery to ships moored in port by means of LNG fueled generators installed onboard a floating unit. Two different scenarios regarding the LNG supply chain are proposed and some options for producing cleaner electric energy are then investigated. The reference area considered in this study is the old port of Genoa where traffic of both passenger and cargo ships takes place. The paper presents an analysis concerning the main technical features of the considered solutions for an actual port calls scenario. The results regard the dimensions and weights of the proposed floating units and the most significant characteristics of the generation equipment, as far as average load factor, fuel consumption and cost are considered.