This paper investigates numerically and experimentally the rotor drop dynamics when unexpected Active Magnetic Bearings (AMBs) shut down occurs.In such an event, the rotor behaviour drops on two touchdown bearings (TDBs) composed of a ball bearing and a ribbon damper providing stiffness and damping to the overall system. The aim of this paper is to establish and to validate the rotor-drop system model. A first experimental set up is used to identify the dynamic characteristics of the corrugated ribbon damper and to test the Kelvin-Voigt model and the generalized Dahl model. Then, three TDB models are proposed including either the first or the second ribbon damper models. The second experimental set-up is devoted to the rotor drop response of an industrial scale rotor-AMB system equipped with two TDBs. Rotor drop simulations in the time domain are carried out by using the Finite Element method and the three TDB models. Predicted and measured rotor drop responses are compared regarding the displacements as well as transmitted loads and permits evaluating the model efficiency.

The aim of this study was to develop and implement a new control approach dedicated to turbomachinery. The new, fuzzy based controller utilizes inputs expressed in polar coordinates. Its originality is that it manages two significant physical quantities, namely, tangential and radial velocities, associated with steady-state and transient behaviors, respectively. Three controllers are compared for the control of a flexible rotor supported by active magnetic bearings (AMBs): proportional-integral-derivative (PID), single-input and single-output (SISO) fuzzy and the new controller. The assessment was performed using an academic test rig and the results obtained with the new controller show that performances were enhanced with equivalent levels of stability and robustness.

The stability of rotating machinery is a major challenge for the floating production storage and offloading (FPSO) units such as steam turbines or centrifugal compressors. The use of active magnetic bearings (AMBs) in turbomachines enables high operating speeds, active mechatronic system for the diagnostics, and the control and enables downsizing of the whole installation footprint. In case of strong base motions, the rotor can contact its touchdown bearings (TDBs) which are used as emergency and landing bearings. The aim of this study is to assess the stability of a rotating machine supported on AMBs during severe foundation excitation. The combined effect of unbalance forces, base motion excitation, and contact non-linearity on a rotor–AMB system response is analyzed focusing on the capacity of an augmented proportional-integral-derivative controller to maintain the system stable. An academic scale test rig was used for the experimental investigations. The controller was efficient and able to maintain the system stable during and after the application of the excitation, but the dynamic capacity of the AMBs was largely oversized with respect to the studied system. In order to check the capacity of the AMBs, when they are designed as a function of the rotor weight and expected excitation, numerical simulations were carried out (downsized). A finite element (FE) model was developed to model the on-board rotor–AMB system. Predicted and measured responses due to impulse excitation applied on the foundations were compared. The capacity of the controller to maintain the system stability is then discussed.

The aim of this study is to assess the possibility to apply a new control approach dedicated to turbomachinery. The controller is fuzzy based using inputs expressed in polar coordinates. The advantage is that it manages two significant physical quantities, namely tangential and radial velocities that are related to steady state and transient behaviors, respectively. A synchronous filter is associated to the controller in order to enhance the ratio command force/bearing dynamic capacity. The approach was previously applied experimentally with success for the control of an academic test rig. It is adapted here for the control of an industrial compressor whose flexible rotor is supported by active magnetic bearings (AMB). At this stage, only numerical investigations are performed. The controller has to satisfy the standards and the end users requirements. In addition, it should be easy to implement. The behavior of the machine studied is assessed for several configurations of unbalances. A test that corresponds to usual industrial excitations (subsynchronous excitations at nominal speed) is also carried out. Results obtained are satisfactory and give insight into the potential of the approach. In addition, and as the fuzzy controller parameters are independent from the rotor design, the approach is a first step for the standardization of magnetic bearing controller synthesis.

In the last 10 years, major centrifugal compressor manufacturers have been investing in developing technologies to improve their products. Following the increasing demand in terms of performance, efficiency and compactness, the current trend in the compressor industry is to increase the “power density”. One big challenge of this “power density” approach is the increase of the rotational speed which may be related to rotordynamic concerns (e.g. crossing of higher rotor modes, stability). Commonly used in the aircraft gas turbines [16], the squeeze film dampers represent an efficient solution to deal with high vibrations and to ensure stable operation for supercritical rotors. In the Oil & Gas Centrifugal Compressors world, SFDs are not so often utilized by the manufacturers but sometimes chosen by the end users as a retrofit solution when high level of synchronous/sub-synchronous vibrations are experienced in the field. The experimental activities described in this paper represent the authors’ Company effort to validate the behavior of a special, integrated SFD type in order to add this component in the available technology portfolio of a centrifugal compressor using it since the design phase. To accomplish this target, the SFD testing was performed originally at the component level and finally at a system level on a “dummy rotor”, specifically designed to mimic the rotordynamic behavior of a real rotor (e.g. running across both the two first rigid modes and the first bending mode). The main objectives of the testing activity were: to check the benefit of using SFDs in order to increase the rotor system damping, to check the SFD overall operational performances, and finally to validate the rotordynamic predictability of this new rotor system. The system level testing program was performed in a high speed balancing bunker where the rotor was equipped with a magnetic exciter able to deliver sub-synchronous excitation. The main test results which will be described in details in the paper are anticipated here. SFDs showed a significant increase in the damping of rigid modes compared to a baseline configuration (rotor running on traditional journal bearings); the SFDs behavior was fully assessed both from rotordynamic viewpoint (rotor and damper housing vibrations) and from operational viewpoint (oil temperature and pressures directly measured in the damper land); finally the rotor modal damping identification techniques are applied to this highly damped rotor system in order to compare the experiment with the relevant predictions. As a conclusion the testing activity provided the authors’ Company with confidence in the use of this integrated SFD technology and enabled a new option for centrifugal compressor design.