Eirik Mathiesen

Marine Vessel and Power Plant System Simulator

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,s 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.

Dynamic Positioning System as Dynamic Energy Storage on Diesel-Electric Ships

A dynamic positioning (DP) system on a diesel-electric ship applies electric power to keep the positioning and heading of the ship subject to dynamic disturbances due to the winds, waves and other external forces using electric thrusters. Vice versa, position and heading errors can be allowed in order to implement energy storage in the kinetic and potential energy of the ship motion using the DP control system to convert between mechanical and electrical power. New simple formulas are derived in order to relate the dynamic energy storage capacity to the maximum allowed ship position deviation, as a function of the frequency of the requested dynamic energy storage. The benefits of DP dynamic energy storage are found to be reduced diesel-generator maintenance need, reduced fuel consumption and emissions, reduced risk for blackout, and increased operational flexibility allowing power-consuming operations such as drilling and lifting to be safely prioritized over DP for short periods of time.

REAL-TIME MARINE VESSEL AND POWER PLANT SIMULATION

In this paper, we present a system simulator of a marine vessel and power plant which contains the mechanical system with diesel engines, propellers, steering gear, and thrusters; the electrical system with generators, switchboards, breakers, and motors; and the plant level controllers with dynamic positioning controller, thrust control, and power management system. Interconnections are possible to simulate by using a multi domain simulator. This is important when evaluating system performance and fault handling. The simulator is implemented in Simulink and is modular, configurable and scalable. It can be extended to run on National Instruments’ cRIO embedded control and acquisition system, for real-time simulation.Copyright

Unit Commitment of Generator Sets During Dynamic Positioning Operation Based on Consequence Simulation

Abstract For vessels with dynamic positioning system, diesel-electric propulsion is often used. At all time the vessel should be able to withstand any single point failure without loss of position. This paper studies the use of simulation of worst-case failure to decide which configurations of the power plant are sufficient for the current operation. The loss of position due to reduced power to the thrusters is simulated and compared with the safety requirements. This method gives both a practical approach to implement the safety requirement and information which can be used as a decision support system or for automatic start and stop of generator sets. The operational cost is also optimized by using the results from the simulations.

Thrust Allocation With Dynamic Power Consumption Modulation for Diesel-Electric Ships

Modern ships and offshore units built for dynamic positioning (DP) are often powered by an electric power plant consisting of two or more diesel-electric generators. Actuation in any desired direction is achieved by placing electrical thrusters at suitable points on the hull. Usually, such ships also have other large electrical loads. Operations in the naturally unpredictable marine environment often necessitate large variations in power consumption, both by the thrusters and by the other consumers. This wears down the power plant and increases the fuel consumption and pollution. This paper introduces a thrust allocation algorithm that facilitates more stable loading on the power plant. This algorithm modulates the power consumption by coordinating the thrusters to introduce load variations that counteract the load variations from the other consumers on the ship. To reduce load variations without increasing the overall power consumption, it is necessary to deviate from the thrust command given by the DP system. The resulting deviations in the position and velocity of the vessel are tightly controlled, and the results show that small deviations are sufficient to fulfill the objective of reducing the load variations. The effectiveness of the proposed algorithm has been demonstrated on a simulated vessel with a diesel-electric power plant. A model for the simulation of a marine power plant for control design purposes has been developed.

Reducing power transients in diesel-electric dynamically positioned ships using re-positioning

A thrust allocation method with a functionality to assist power management systems by using the hull of the ship as a store of potential energy in the field of environmental forces has been recently proposed and demonstrated to work in simulation. This functionality allows the thrust allocation algorithm to decrease the power consumption in the thrusters when a sharp increase in power consumption is demanded elsewhere on the ship. This way, the high-frequency part of the load variations on the power plant can be reduced, at the expense of minor (typically less than 1 meter) variations in the position of the vessel. The advantages from reduced variations in load include reduced wear-and-tear of the power plant, more stable frequency on the electric grid, reduced risk of blackout due to underfrequency, and more reliable synchronization when connecting additional generators or connecting bus segments. In the present work, this functionality is improved further by continuously monitoring the environmental forces and modifying the setpoint of the dynamic positioning algorithm to place the vessel a short distance (e.g. 20 cm) in the direction of steepest increase of the environmental force potential, thus maximizing the available potential energy. The increased potential energy creates additional capacity for assisting the power plant, which is shown in simulation to be significant.