Rolls-Royce (Norway)

The aim of this work is to find the maximum torque density limit of a surface cooled SPM machine. In this paper, an analytical and a FEM-based model are developed under some theoretical conditions. Both models consist of a magnetic and a thermal part, where they are used to calculate the torque and the temperature distribution, respectively. Each model is then combined with an optimization process in order to maximize the torque density. The analytical model utilizes the GlobalSearch algorithm (GSA), while the FEM-based one uses the Pattern-Search (PS) approach. A case configuration is selected, and the results between the two models are presented and compared. It is shown that it is possible to determine a maximum limit for the torque density of a machine and the configuration used to get it. A parametric sensitivity analysis is carried out to analyze the influence of some typical parameters on the maximum torque density. Finally, this maximum limit is compared against typical SPMs.

The electric load demand on marine vessels is constantly changing during some operational modes, such as in harsh weather or complex operations. Therefore, diesel engines are typically used to handle these variations. Gas engines reduce the CO2 due to lower carbon content in LNG compared with diesel oil. However, they may not be able to handle the load variations of a marine power plant. There are multiple other energy sources with strict rate constraints, such as slow speed diesel engines and fuel cells. In such cases, a battery may be used to take care of the variations, while the generator set produces a slowly varying power. In this paper, a common power flow controller for the battery and the generator set is proposed. It utilizes the rotating inertia in the generator set as energy storage, in addition to a battery. This is done by allowing a small excursion in the speed of the generator set; the speed change will change the kinetic energy of the generator set and this is used analogously to energy storage. The controller is compared with a baseline controller based on virtual inertia and speed droop. A simulation study is included to demonstrate the performance of the control methods. The simulation study shows that the gas engine (with strict constraints) is not able to handle the given load series. Nonetheless, it can be used in combination with a battery to handle the variations. The power plant can handle a measured load series from an offshore vessel when either speed-droop control or model predictive control is used. However, the study indicates that by using MPC, the aging of the batteries and fuel rate variations can be reduced.

This paper presents an extensive analysis of the integral line-of-sight (ILOS) guidance method for path-following tasks of underactuated marine vehicles, operating on and below the sea surface. It is shown that due to the embedded integral action, the guidance law makes the vessels follow straight lines by compensating for the drift effect of environmental disturbances, such as currents, wind, and waves. The ILOS guidance is first applied to a 2-D model of surface vessels that includes the underactauted sway dynamics of the vehicle as well as disturbances in the form of constant irrotational ocean currents and constant dynamic, attitude dependent, and forces. The actuated dynamics are not considered at this point. A Lyapunov closed-loop analysis yields explicit bounds on the guidance law gains to guarantee uniform global asymptotic stability (UGAS) and uniform local exponential stability (ULES). The complete kinematic and dynamic closed-loop system of the 3-D ILOS guidance law is analyzed in the following and hence extending the analysis to underactuated autonomous underwater vehicles (AUVs) for the 3-D straight-line path-following applications in the presence of constant irrotational ocean currents. The actuated surge, pitch, and yaw dynamics are included in the analysis where the closed-loop system forms a cascade, and the properties of UGAS and ULES are shown. The 3-D ILOS control system is a generalization of the 2-D ILOS guidance. Finally, results from simulations and experiments are presented to validate and illustrate the theoretical results, where the 2-D ILOS guidance is applied to the cooperative autonomous robotics towing system vehicle and light AUV.

This paper presents a study of the influence from ice strengthening on the crashworthiness with regards to placement of LNG fuel tanks. First a brief introduction to the ship collision research as well as an assessment of the state of the art regarding nonlinear finite element analysis for use in ship collision analysis are given. Secondly the implications from the introduction of LNG fuel tanks on ships in context of collision safety are discussed. Thirdly how to quantify and compare energy absorption for different ship designs is discussed. This is followed by the presentation of a study regarding the horizontal placement of LNG fuel tanks. The study starts with presenting the variables chosen and the models made for the analysis. Energy versus indentation curves are presented for three different designs, where a standard cargo carrier is compared with two different design solutions where the cargo carrier is equipped with either vertical or longitudinal ice strengthening. It is concluded that in this case the benefit in terms of reduction of the minimum distance from the outer skin to the LNG fuel tank, as given in the current rules, is around 39%.

The influence of the welding process during the manufacturing of small slotless permanent-magnet synchronous machines (PMSMs) is studied in this paper. The focus lies on the change of the magnetic properties in high-quality silicon-iron (SiFe) and nickel-iron (NiFe) electrical steel sheets with thicknesses of 0.1 and 0.2 mm. It is shown that the welding process changes the magnetic material properties significantly and increases the specific iron losses. Experimental results are provided for magnetic flux densities up to 1.5 T and frequencies from quasi-static to 200 Hz. The obtained measurement data is afterward used in finite-element method (FEM) simulations to investigate the influence of the magnetic property changes on the motor performance, particularly with regard to stator core losses.

Free-piston diesel engines are characterized by freely moving pistons without any rigid crankshaft or camshaft connected to the pistons. This allows a highly compact and efficient engine design, but requires automatic control of the piston motion. This paper present a dynamic mathematical model of a free-piston diesel engine, a control oriented dynamic analysis, and a novel computer-based piston motion control system. Experimental evaluation of the results on a full scale diesel test cylinder show feasibility of the suggested control approach.