Dynamic optimization of synthesis, design and operation of marine energy systems

Abstract

In order to cover the overall energy demands of a vessel (e.g. mechanical, electrical and thermal), energy systems onboard ships are required to produce energy of several forms while at the same time being completely autonomous and cost effective. Optimization of the ship’s energy system, as a whole, in terms of synthesis, design and operation, is nowadays an unavoidable aspect of the marine industry. Furthermore, once time dependencies (e.g. time-varying loads and weather conditions) are introduced, the optimization problem is imperatively characterized as dynamic and its complexity increases dramatically. This study is focused on the dynamic optimization of synthesis, design and operation of a marine energy system. The general method, based on differential-algebraic equation formalism combined with mixed-integer nonlinear programming, along with solution procedures is presented first. The three optimization levels (synthesis, design and operation) are tackled simultaneously, with no decomposition. The superconfiguration approach is followed for the synthesis optimization, while time-varying operational requirements with respect to weather conditions and loads are considered. The presentation of the general theory is followed by application examples. A nominal case as described by a particular weather profile and values of parameters is considered, and the optimization problem with minimization of the present worth cost as an objective function is stated and solved. The effect of crucial parameters such as fuel and capital costs on the optimum solution is studied. Also, the problem is solved with a different weather profile, thus revealing the effect of weather on the optimum solution.