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The reported project aimed at examining properties and purposefulness of use of modern electromagnetic bearings for a screw propeller in a prototype version of a synchronous ring motor with rare earths magnets. Bearings of this type generate electromagnetic forces which keep the rotor in a state of levitation. The rotating machine with magnetic bearings can work in any environment which reveals diamagnetic properties (air, vacuum, water, liquid gases, etc.). However, a basic quality of the magnetic bearings is elimination of cooling installation and lubrication, which is necessary for proper operation of rotating machines with rolling and slide bearings, undergoing wear with time. Therefore the lifetime of the machine supported on magnetic bearings is incomparable with others. Also torque losses on this bearing are the smallest, compared to all known types of bearings. Ring thrusters can be used as the main drive for relatively small sea-going and inland vessels, and as manoeuvring drive for ships of arbitrary size, especially for AES (All Electric Ship) type vessels. This type of propeller is extremely useful for any types of abyssal vessels, autonomous and remotely controlled, and on submarines. It can also be used as effective generator of electric current for charging batteries in towing trains, barges for instance. The project consisted of three research tasks: 1. Designing, manufacturing and examination of a magnetic bearing on-line controlled by a digital controller, 2. Manufacturing a model of a ring thruster and examination of characteristics of a propeller mounted in the ring, 3. Examining the ferrofluid seal.A concept of the new thruster is a consequence of investigations carried out in Poland upon propellers and magnetic bearings in years 2001-2005
In the article a mathematical model of radial passive magnetic bearings applicable to ocean engineering units has been presented. The application of the bearings in ship thrusters should increase durability of propulsion systems and give lower maintenance costs. The rotor of thruster’s electric motor is suspended in magnetic field generated by radial passive magnetic bearings. However the maintaining of axial direction of the rotor must be controlled with electromagnets equipped with a high-dynamic controller. The risk of application of the magnetic bearings results from very low stiffness of the unit in comparison with rolling bearings. Also construction of the bearing should be different due to gyroscope effect and high forces generated during ship manoeuvring. The physical model performs correctly if electromagnets are controlled properly; and, technological problem with sealing system seems more significant than power supply to electromagnets winding. The equations presented in the article are necessary to build algorithms of a digital controller intended for on-line controlling magnetic bearing in axial direction
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