Abstract: Various solutions for the design of oil-free bearings are discussed in the literature. Adding hydrodynamic preload to the foil bearings by profiling the inner bore of the bearing is one of the most frequently investigated methods for improving the bearing stability and damping character of the entire system. However, this approach leads to a reduced load capacity and thus to an increased lift-off speed of the foil bearings. Observations of this kind lead to the presentation of various solutions for active bearing contour adjustment, which benefits from different profiles of the lubricant film. Most of these concepts use piezoelectric stack actuators to generate the required alternating force, although the influence of the stiffness of adaptive elements on bearing performance is not fully discussed in the literature. The focus of this study is on the investigation of structural conformity, i.e., the harmonization of stiffness with respect to the requirements for shape control and load capacity of an adaptive air foil bearing (AAFB). The result may be a basis for the consideration of additional degrees of freedom in any concept with shape control as the main design framework in interaction between the lubricant and compliant structure in an air foil bearing from both static and dynamic points of view.

Hossein Sadri, A. Kyriasis, Henning Schlums, Michael Sinapius, IOPScience Smart Materials andStructures, Accepted: Juni.2020

Abstract: Aerodynamic foil bearings are used in various industrial applications, e.g. in cooling turbines, small gas turbines or exhaust gas turbochargers, to support light, high-speed rotors under extreme operating conditions. Air (or another gas) is used as a lubricant in these bearings. In addition, the possible thermal deformations and production errors can be compensated by a flexible foil structure between the lubricant film and the bearing housing in air foil bearings. Since many static and dynamic properties of the lubricant are strongly dependent on the inner contour of the bearing, the idea of an adaptive air foil bearing (AAFB) is developed to optimize the performance of the bearing at different operating points. This paper focuses on a semi-analytical approach based on plate theory and the Ritz method for approximating the static shape control of a piezoelectrically actuatable AAFB. The main objective of this study is to consider adaptive bearing shells in calculating the behavior of an AAFB, as they provide additional degrees of freedom to a passive air foil bearing without adaptivity. Before the final step is taken, the model presented in this analysis is used for the shape optimization of the adaptive frame of AAFB in order to achieve the most efficient shape adaption with regard to target shapes.

Johannes Michael Sinapius, ISBN: 978-3-662-55883-6

Introduction: Adaptronik ist eine vergleichsweise junge Disziplin der Ingenieurwissenschaften, die sich durch ausgeprägte Interdisziplinarität auszeichnet. Das vorliegende Buch bietet daher eine interdisziplinäre Betrachtung von adaptronischen Systemen. Ausgehend von den grundlegenden Prinzipien und Varianten adaptronischer Systeme sowie der Funktionswerkstoffe werden dem Leser die verschiedenen Funktionselemente erläutert. Anschließend werden die gewonnen Kenntnisse in der aktiven Formkontrolle, der aktiven Vibrationskontrolle und der aktiven Vibroakustik angewendet und vertieft. Hierbei wird ein Fokus auf aktuelle Beispiele aus der Forschung gelegt.

unter Mitautorschaft von Dr. Hossein Sadri.

Hossein Sadri, Henning Schlums, Michael Sinapius, ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition

Abstract: Aerodynamic foil bearings are suitable to support light, high-speed rotors under extreme operating conditions such as very low or very high temperatures, e.g. in cooling turbines, small gas turbines or exhaust gas turbochargers. The required bearing load capacity is generated by an aerodynamic pressure build-up in the corresponding lubrication gap. Due to the high dependence of the bearing performance on the bore geometry, the rotordynamic behavior (e.g. bearing stability) and static properties (e.g. load capacity) as a function of radial clearance and hydrodynamic preload are one of the main points of interest in recent studies. The outcome of both the experimental and the numerical investigations show the advantages and disadvantages of the various configurations of the bearing bore in different operating conditions. These observations lead to the basic idea of an adaptive air foil bearing (AAFB) in which, depending on the operating conditions, the bearing bore contour is changed by means of piezoelectric actuators applied to the compliant supporting shell. Similar to other shape morphing approaches, optimization with regard to various components of the mechanism is the next step in the design process after targeting the design pattern. This paper concentrates on an AAFB as an efficient approach to actively shape the contour of the bore clearance in a 3-pad bearing. Numerous FEM analyses of a functional model for an AAFB in addition to the experimental efforts reveal the main concerns of the design. Finally, the result of this study is a working graph for the AAFB under various loading conditions while operating with different input voltages of the actuators.

Hossein Sadri, A. Kiryasis, Henning Schlums, Michael Sinapius, ASME 2018 Conference on Smart Materials, Adaptive Structures and Intelligent Systems

Abstract: The aerodynamic foil bearing is a special type of air bearing in which the flexible foil structure between rotor and rigid housing supports the rotor bearing system with a greater robustness against thermal distortion and production misalignments. In such bearings, the generation of an aerodynamic pressure in the lubricating film after reaching the lift-off speed prevents the solid contact between rotor and foil structure. Since many static and dynamic properties of air foil bearings strongly depend on the inner contour of the bearing, the idea of an adaptive air foil bearing (AAFB) is developed to optimize the bearing’s performance at different operating points. This paper concentrates on a semi-analytical model based on plate theory using Ritz method for simulating the static shape control of piezoelectrically actuatable supporting segments for an AAFB under different loading conditions. The elastic suspension of the supporting segments and symmetries of the bearing are considered in the modeling. After validation by means of FEM analyses and experimental tests the influence of geometry and material is examined in a parametric study. Later on, the model is used for parameter optimization in order to achieve the most effective shape morphing.

Daniel Schmidt, Hossein Sadri, Artur Szewieczek, Michael Sinapius,Proc. SPIE 8695, Health Monitoring of Structural and Biological Systems 2013, 869503 (17 April 2013)

Abstract: Structural Health Monitoring (SHM) based on Lamb waves, a type of ultrasonic guided waves, is a promising technique for in-service inspection of composite structures. This study investigates the attenuation mechanisms of Lamb wave propagation fields. The attenuation of an anisotropic plate is experimental measured with air-coupled ultrasonic scanning techniques and analytical modeled using higher order plate theory. Based on the experimental and analytical data the various attenuation mechanisms are characterized for the fundamental Lamb wave modes.