This paper investigates the effect of waves on the propulsion system of a ship. In order to study the propulsion in different wave conditions, a procedure for wake estimation in waves has been implemented. A clear drop in the propulsion performance was observed in waves when engine propeller dynamics, wake variation and thrust and torque losses were taken into account. This can explain the drop in vessel performance often experienced in presence of waves in addition to the effect of added resistance. Therefore, performance prediction of ships in rough weather can be improved if the effects of waves on the propulsion system are considered. Specific problems causing drop in performance have also been identified. System response in case of extreme events like propeller emergence has been simulated for analyzing the performance and safety of the propulsion system. The framework of enginepropeller coupling demonstrated in this paper can also be used to analyze different components of propulsion system (e.g. propeller shaft, control system) in higher detail with realistic inputs. This paper is a step towards optimizing the propulsion of ships for realistic operating conditions rather than calm water condition for energy efficient and economic ships.

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Recent developments in marine power systems, energy storage devices (ESDs) technology, and modification to rules and regulations increase the opportunities to improve efficiency and reduce emissions. One particular application is the strategic loading, where the ESD is charged and discharged cyclically, altering the instantaneous fuel consumption, thus aiming to reduce the average fuel consumption. Due to the ESD switching behavior, a hybrid simulation framework is an appropriate dynamic modeling tool. The hybrid simulation model is important in proper design and verification of control strategies for hybrid power plants. A hybrid model was derived, modeling transients as continuous-time events and modeling instantaneous behavior changes as discrete events. Due to the complexity of the system and its hybrid nature (continuous and discrete times), it is important to validate the derived model, such that are known its accuracy and limitations. The developed hybrid model was validated using experiments at the Hybrid Machinery Laboratory, Norwegian University of Science and Technology. The analyzed effects are the steady state, transient behavior, and losses. The transient behaviors include Generator-set (genset) dynamics and load ramps. The losses include the production losses, transmission losses, and ESD losses. The non-modeled effects include the load fluctuation, genset speed variation about the given set-point, and thermal effects on the genset and on the ESD. The results show good correlation between the hybrid model and the experiments. The fuel consumption estimation error stayed below 3% for all 15 analyzed cases, as well as having less than 9% deviation for the NO x gas emissions estimation. The model is considered as a good approximation for the real operation, enabling its use for design and research purposes.INDEX TERMS Analytic approximations, engine management systems, energy storage, hybrid model, hybrid vehicles, marine systems. NOTATIONThroughout this paper, the following notation will be used:• The subscript ''0'' refers to the system initial states.• The subscript ''B'' refers to the ESD system.• The subscript ''C'' refers to the system while charging the Energy Storage Device (ESD).• The subscript ''D'' refers to the system while discharging the ESD.

Modern marine electric propulsion vessels have many systems. These interactions and integration aspects are essential when studying a system and subsystem behavior. This is especially important when considering fault scenarios, harsh weather, and complex marine operations. However, many simulators, including a selection presented here, study the positioning system and the power system separately. This paper proposes a simulator combining the two systems, as an extension to the marine systems simulator MATLAB/Simulink library. The intended use cases and the according design choices are presented. New subsystem models include a power-based electrical bus model and a simplified diesel engine model. Both are validated through the simulation against established models. In addition, established models for generators, electrical storage devices, thrusters, and a mean-value diesel engine model are summarized with rich references. Three case studies illustrate the multi-domain use of the simulator: 1) a semi-submersible drilling rig performing station keeping under environmental disturbances; 2) the same vessel subject to an electrical bus reconfiguration; and 3) a supply vessel with a hybrid power plant.INDEX TERMS Marine technology, marine vehicles, power system simulation, dynamic positioning.

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