US-Egypt Cooperative Research: Experimental Investigation and Control of an Integrated JB/AMB rotor bearing

James Madison University, Harrisonburg VA

Investigators

Abstract

This project supports a cooperative research effort by Dr. Eric Maslen of James Madison University with Dr. Aly El-Shafei of Cairo University in Cairo, Egypt. They plan to study "The Design and Control Development of an Integrated JB/AMB". Most large turbomachinery use fluid film journal bearings (JBs) to support the rotor, limit vibrations, and to control potential instabilities. More recently, an alternate bearing technology has come into commercial use: active magnetic bearings (AMBs). These bearings offer a number of advantages, particularly because they can provide very favorable dynamic properties, useful in managing rotor stability. The goal of the project is to integrate the superior load capacity of journal bearings with the controllability characteristics of active magnetic bearings which can counteract the instability associated with fluid film journal bearings. To capitalize on the advantages of both bearing designs, the PIs will explore the combination of both bearings into a single integrated bearing design. The core hypothesis of the research is that it is possible to physically co-locate a fluid film and a magnetic bearing and construct a controller to a) ensure stability of the rotor/bearing system at all speeds of interest, b) satisfy a loadsharing objective that minimizes competition between the two bearing mechanisms, c) minimize a weighted combination of bearing-transmitted forces and rotor vibration to significantly reduce rotor vibration or pedestal force transmission for a given level of rotor unbalance. This research will develop the concept of a hybrid bearing,integrating a fluid film and magnetic bearing into a single component. One merit of this approach is that the two devices can operate in a complementary fashion with the fluid film component providing the bulk of load capacity and fault tolerance, while the magnetic component enhances the stability. It is expected that the combination can offer substantially higher stability margins than are currently afforded by tilt-pad fluid film bearings. The second merit of this approach is that a hybrid bearing can allow for performance optimization to a particular application as it is less dependent on hardware to control its operation. By incorporating bearing control through a choice of algorithms, the hybrid bearing design can adapt with system changes or upgrades to prolong the useful life of the bearing. A set of conventional controllers for addressing common system dynamics and an option for allowing in-situ tunability could also be provided. The results could have an immediate benefit for large stationary rotor systems (e.g., gas turbines, turbo expanders, megawatt scale motors). By building a strong collaboration between researchers in the United States and in Egypt, the project will promote exchange of scientific and engineering ideas as well as cultural exchange. Both the US and the Egyptian teams include junior scientists who will make multiple trips in both directions. The US activity will be conducted at James Madison University, a primarily undergraduate institution and will integrate undergraduate students from both the School of Engineering and from the Department of Integrated Science and Technology. Further, the results of this research will provide educational benefit for two engineering courses as a case study providing an example of design and analysis. Third, the research will potentially have direct impact on the welfare of the public at large, as high-speed rotating machinery pervades the technical base of modern societies. This resarch has significant potential to improve the efficiency of such machinery, especially in the energy sector. Advances in bearing technology will improve the overall performance and viability of the dependent technology sectors, which in turn provides benefits to the societies. This project is funded through the US-Egypt Joint Science and Technology Fund program. Support for the U.S. side of these cooperative projects is provided to the National Science Foundation by the U.S. Department of State. The Egyptian Government provides support for the Egyptian side of the collaboration.