George G. Dimopoulos

Effect of reliability considerations on the optimal synthesis, design and operation of a cogeneration system

In most of the publications on optimization of energy systems, it is considered that the equipment is available for operation at any instant of time (i.e. it is not subject to failure) except, perhaps, of pre-determined periods of maintenance. Thus, it is left to the designer to decide empirically how to provide the system with redundancy, which is necessary in case of equipment failure. However, in this way, the final configuration may not be optimal. In the present work, reliability and availability are introduced in the thermoeconomic model of the system, so that redundancy is embedded in the optimal solution; in addition, more realistic values are obtained for the cost and profit, if any. The state-space method (SSM) of reliability analysis is used. The optimization problem is formulated at two levels: (A) synthesis and design, (B) operation under time-varying conditions. For the solution of the problem at level A and also at level B with no failure, a genetic algorithm coupled with a deterministic one is used. In case of partial failure, the optimization problem is solved by the Intelligent Functional Approach (IFA). The use of IFA combined with SSM is proved to be very efficient for decision making regarding systems under partial failure. It turned out that reliability aspects have a direct and significant impact on the optimal result at each one of the three levels: synthesis, design and operation.

Simulation of Marine Diesel Engine Propulsion System Dynamics During Extreme Maneuvering

The dynamic behavior of a typical four-stroke, medium-speed, marine diesel engine driving a Controllable Pitch Propeller (CPP) is investigated during ship maneuvering including fast propeller pitch changes. A modular model has been developed in Simulink/Matlab for the simulation of the dynamics of ship propulsion. The developed model considers the ship propulsion system as a set of three main modules: the engine, the propeller and the ship hull. The developed ship propulsion dynamics model has been validated with a wide range of experimental data from a 500 kW test engine (MAN B&W 5L16/24), coupled to a four quadrant electric brake (AEG), installed at the test-bed of the Laboratory of Marine Engineering of the National Technical University of Athens (NTUA/LME). The model was then used for the investigation of marine diesel engine behavior during load changing including some extreme maneuvering case scenarios such as Crash Stop, Full Astern and Full Ahead maneuvers. The resulting ship propulsion model is a reduced order model, which can easily be used for detailed studies such as engine-control during fast transient loadings, with accuracy and small computational cost.Copyright