Gerasimos Theotokatos

On the cycle mean value modelling of a large two-stroke marine diesel engine

Owing to their simplicity and their ability to represent the engine behaviour sufficiently well, cycle mean value models have been used for investigations of the transient response of marine diesel engines as well as the development of engine control schemes. In the present paper, two cycle mean value approaches of different complexities applied to the modelling of a large two-stroke marine diesel engine are described. The first modelling approach is less detailed since only two differential equations are used to represent the engine crankshaft and turbocharger shaft dynamics, whereas the other engine operating parameters are calculated after the solution of a non-linear algebraic system. In the second approach, more comprehensive modelling is obtained by using four additional differential equations, so that the dynamics of engine scavenging and exhaust receivers are captured. Using both modelling approaches, cases of the engine transient operation are simulated and the derived results are presented. Then, by comparing the simulation results with previously published data, the advantages and drawbacks of each approach are discussed.

Techno-economical analysis of single pressure exhaust gas waste heat recovery systems in marine propulsion plants

In this article, the waste heat recovery (WHR) installations used for the production of saturated steam and electric power for the cases of a two-stroke and a four-stroke engine propulsion plant of a typical merchant ship are investigated. The examined WHR system is considered to be of the single steam pressure type with an external heat exchanger for the heating of feed water entering into the boiler drum. The option of using the engine air cooler for heating the feed water was also examined. The WHR installation was modeled under steady-state conditions, and the derived WHR installation parameters for various engine loads are presented and analyzed. Furthermore, using the simulation results, the improvement of Energy Efficiency Design Index (EEDI) of the examined ship is calculated, and the impact of the WHR on the ship EEDI is discussed. In addition, following the technical evaluation of the alternative options for the ship propulsion plant, an economic study was performed for a typical ship voyage. The derived results were presented and discussed leading to conclusions for the most techno-economical propulsion system configuration.

A Computational Study on the Performance and Emission Parameters Mapping of a Ship Propulsion System

In this article, the mapping of the performance and emission parameters of a merchant vessel propulsion system over the ship operating envelope was carried out by using a model capable of representing the ship propulsion system behaviour. The model was developed based on a modular approach and was implemented in the MATLAB/Simulink environment. The various parts of the propulsion engine as well as the shafting system, the propeller and ship hull were represented by separate submodels having the appropriate interface for exchanging the required variables to each other. The output of the model includes the performance and emission parameters of the engine as well as the operating parameters of the propeller and ship. Initially, the propulsion engine operation under steady-state conditions was simulated and the predicted engine performance parameters results were validated. Then, simulations of the ship propulsion system operating points at various resistance curves were performed. Based on the derived results, the mapping of the ship propulsion system performance and emission parameters was presented and their variation throughout the ship operating envelope was discussed. Finally, an example of using the derived results in order to minimise the fuel consumption and CO2 emissions for a typical ship route is presented and discussed.

Investigation of a Large High- Speed Diesel Engine Transient Behavior Including Compressor Surging and Emergency Shutdown

The operation of a large high-speed engine under transient loading conditions was investigated, using a detailed simulation code in conjunction with a model capable of predicting compressor surging. Engine loadings were applied, which were considered dangerous for initiating compressor surging and cases where compressor surging could occur were identified. A means of avoiding compressor surging by opening a bypass valve connected between the compressor outlet and turbine inlet was examined. Finally, the case of engine abrupt stopping by rapidly closing the engine emergency shutdown valve, located downstream of the compressor, was also investigated.

A decision support system for the development of voyage and maintenance plans for ships

The waterborne sector faces nowadays significant challenges due to several environmental, financial and other concerns. Such challenges may be addressed, among others, by optimising voyage plans, and diagnosing as early as possible engine failures that may lead to performance degradation. These two issues are addressed by the decision support system (DSS) presented herein, which focuses on the operation of merchant ships. For the development of voyage plans, a multicriteria decision problem is developed and handled with the PROMETHE method, while a multivariable control chart is used for the fault diagnosis problem. A MATLAB-based software implementation of the DSS has been developed adopting a modular architecture, while, in order to provide a generic software solution, the required input data are retrieved from dedicated web-services, following specific communication and data exchange protocols.

Improved Transient Control of a Two-Stroke Marine Diesel Engine With Variable Geometry Turbine

In this work, the cycle-mean-value approach to marine engine process simulation is considered. At first, a basic principles model is employed where the engine crankshaft and turbocharger shaft speeds are obtained by integration of the angular momentum conservation differential equations. Any other engine variable can then be obtained by solving a set of nonlinearly-coupled, algebraic equations, corresponding to energy and mass conservation through the engine. Nonlinear data analysis is then performed on this process model. By approximating the torque maps, generated by the thermodynamic basic principles model, with neural nets, explicit functional relationships are obtained. Identification of the power-plant operating regimes through linearization and decomposition is finally performed. In effect, a supervisory power-plant controller structure, applicable to real-time control and diagnostics, is proposed, incorporating the nonlinear state-space description of the plant.

Investigating an SVM-driven, one-class approach to estimating ship systems condition

ABSTRACT Maintenance is a major point that can affect vessel operation sustainability and profitability. Recent literature has shown that condition monitoring of ship systems shows great potential, albeit at significant data requirement costs. In this respect, this paper presents a novel methodology for intelligent, system-level engine performance monitoring, utilising noon-report data with minimal data assumptions. The proposed methodology is based on the training of a one-class Support Vector Machine, which models a diesel generator’s normal behaviour. Unseen data are then input into the model, where its output reflects a gauge of their normality, compared to the training dataset. This aids the dynamic detection of ship machinery incipient faults, contributing to the minimisation of ship downtime. A case study presenting applications of this modelling approach on ship machinery raw data is included, complemented by a sensitivity analysis. This demonstrates the applicability of the developed methodology in identifying deviant, abnormal ship machinery conditions.

Vulnerabilities and safety assurance methods in Cyber-Physical Systems: A comprehensive review

Abstract As Cyber-Physical Systems (CPSs) are a class of systems advancing in a number of safety-critical application areas, it is crucial to ensure that they operate without causing any harm to people, environment and assets. The complexity of CPSs though, render them vulnerable and accident-prone. In this study, the sources of complexity are meticulously examined and the state-of-the-art and novel methods that are used for the safety assurance of CPSs are reviewed. Furthermore, the identified safety assurance methods are assessed for their compatibility with the technical processes during the system design phase and the methods effectiveness on addressing the different CPSs sources of complexity is investigated. Advantages and disadvantages of the different safety assurance methods are also presented. Based on the results of this review, directions for the safety enhancement of CPSs and topics for future research in the area of CPSs safety are provided.

An intelligent system for vessels structural reliability evaluation

An intelligent system is proposed within INCASS (Inspection Capabilities for Enhanced Ship Safety) project for evaluating ship structural reliability and assisting in fatigue damage and structure response assessment. The system combines hydrodynamic, finite element and structural reliability models.. The hydrodynamic analysis model is not discussed in this paper. The finite element model input is a mesh for the mid-ship part of the vessel. Finally, the in-house structural reliability model input is the calculated output of the previous model as well as models for estimating crack development and propagation, corrosion growth and fatigue loading. The output includes the probability of failure for all the investigated components versus time which can be used to assess safe operation through the developed decision support software. The database can receive information from various sources including inspection and robotic systems data. The case study of a capsize bulk carrier the presents structural evaluation process.

Accurate instantaneous engine speed recording by employing an optical measurement system-application to a typical low power industrial engine

The presented work concerns the development of a novel measurement system for determining the instantaneous rotational speed of an engine with high accuracy. The developed system is mainly based on a commercially available optical sensor and appropriate data acquisition / post-processing procedure. The accuracy of the system is high; speed recording with a resolution of one degree of crank angle has been succeeded when measuring the speed of a one cylinder four stroke S.I. motored engine. The deduced experimental results were compared with the corresponding theoretical ones obtained by appropriate simulations, validating the proper functionality of the developed system. Furthermore, the system was also integrated into a typical four cylinder low power industrial engine successfully. Key-features of the proposed measurement configuration are accuracy, simplicity and low-cost suggesting numerous potential applications.