High-Speed Rotor With Air Bearings Mounted on Flexible Supports: Test Bench and Experimental Results

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
G. Belforte ◽  
F. Colombo ◽  
T. Raparelli ◽  
V. Viktorov
Keyword(s):  
High Speed ◽  
Test Bench ◽  
Dynamic Stiffness ◽  
Experimental Results ◽  
Air Bearings ◽  
Stability Threshold ◽  
Air Turbine ◽  
Flexible Supports ◽  
The Stability ◽  
Rotational Response

A test bench for rotors supported by air bearings floating on O-rings is designed in order to study the whirl phenomenon and characterize the stability threshold with damping elements mounted on bearings. The work includes a description of the test bench and some preliminary experimental results. A rotor of 1kg mass and 37mm diameter is rotated up to 75,000rpm by an air turbine machined on the rotor. Capacitance probes, placed in two radial planes, allow orbit scanning of both the rotor and the bushing at different rotating speeds and suitable load devices permit measurement of the static and dynamic stiffness of the rotor-bearing system. Curves of rotational response using rubber O-rings of three different materials are shown and compared. Also presented are the Fourier spectra of the signals for rotor displacement. The phenomenon of whirl instability is shown in terms of whirl frequency and orbit amplitudes of the rotor and bearings. The effects of both supply pressure and angular velocity on the stability threshold are shown.

An Experimental Study on a High-Speed Rotor Supported by Air Bearings Mounted on O-Rings

2006 ◽  
Author(s):  
G. Belforte ◽  
T. Raparelli ◽  
V. Viktorov ◽  
F. Colombo
Keyword(s):  
High Speed ◽  
Test Bench ◽  
Dynamic Stiffness ◽  
Air Bearings ◽  
Stability Threshold ◽  
Supply Pressure ◽  
Air Turbine ◽  
Fourier Spectra ◽  
The Stability ◽  
Bearing System

A test bench on rotors supported on air bearings floating on O-rings has been designed in order to study the whirling phenomenon and individuate the stability threshold with the presence of damping elements mounted on the bearings. The work contains description of the test bench and the first experimental results. A rotor of 1 kg mass and 37 mm diameter is rotated up to 75000 rpm by an air turbine manufactured on the rotor. Capacitance probes, placed in two radial planes, allow to scan the orbits of both the rotor and the bushing at different rotating speeds and proper load devices make it possible to measure the static and dynamic stiffness of the rotor-bearing system. Diagrams on the rotating response using different kinds of rubber O-rings are presented and compared, with also indications on the Fourier spectra of the signals relative to the rotor displacement. The phenomenon of whirling instability is showed, with considerations on the whirling frequency and on the orbit amplitudes of the rotor and the bearings. The effect of both supply pressure and angular velocity on the stability threshold is showed.

Research and Design of Dynamic Stiffness Testing System for Actuator

2013 ◽  
Vol 753-755 ◽  
pp. 1731-1735
Author(s):  
Jian Chu ◽  
Feng Zhang
Keyword(s):  
Control System ◽  
Test Bench ◽  
Dynamic Stiffness ◽  
Testing System ◽  
Programmable Logic ◽  
Important Indicator ◽  
Actuator System ◽  
The Stability ◽  
Definition Of ◽  
Research And Design

Actuator is widely used in the control system. Among all characteristics of an actuator, dynamic stiffness is an important indicator; it must satisfy the requirement to inhibit the control surface’s flutter. This article described the definition of dynamic stiffness of actuator, introduced the importance of the research of dynamic stiffness of actuator, designed a test bench for dynamic stiffness testing and putted forward a method which based on Programmable Logic Controller to simulate a signal generator which generated sinusoidal signal load to test the dynamic stiffness of actuator, found out a worst point of the actuator’s dynamic stiffness, improved the stability of the actuator system and avoided the occurrence of flutter at the frequency.

An experimental study of high-speed rotor supported by air bearings: test RIG and first experimental results

2006 ◽  
Vol 39 (8) ◽  
pp. 839-845 ◽  
Author(s):  
Guido Belforte ◽  
Terenziano Raparelli ◽  
Vladimir Viktorov ◽  
Andrea Trivella ◽  
Federico Colombo
Keyword(s):  
Experimental Study ◽  
High Speed ◽  
Experimental Results ◽  
Air Bearings ◽  
Test Rig

scholarly journals Nonlinear Analysis of a Quasi-Zero Stiffness Air Suspension Based on the Cell-Mapping Method

2021 ◽  
Vol 26 (2) ◽  
pp. 148-160
Author(s):  
Long Chen ◽  
Jun Wang ◽  
Xing Xu ◽  
Xinwei Jiang ◽  
Feng Wang
Keyword(s):  
High Speed ◽  
Dynamic Stiffness ◽  
Mapping Method ◽  
Suspension System ◽  
Vehicle Speed ◽  
Cell Mapping ◽  
Air Suspension ◽  
Stable Conditions ◽  
Attractive Region ◽  
The Stability

The quasi-zero stiffness system has the characteristics of low dynamic stiffness and high static stiffness, which can bring a better driving experience and lower road dynamic load at high speed on irregular roads. This paper studies a type of interconnected quasi-zero stiffness air suspension system, which has two states, namely, the non-interconnected quasi-zero stiffness air suspension and the interconnected quasi-zero stiffness air suspension, to meet the performance requirements under different loads and vehicle speed. First, the mathematical model of the nonlinear system is established based on the basic principles of fluid mechanics and thermodynamics. Then, the stability of the equilibrium point is analyzed using the Lyapunov first method, where the quantitative analysis of the attractive region of the system is conducted through the bifurcation diagram and phase diagram. By using the Taylor series expansion, cell-mapping theory and domain map of attraction, the attractive region of the system is quantitatively analyzed to obtain the parametric feasible domain under stable conditions. Finally, the performance of the quasi-zero stiffness suspension system with the selected parameters under the stability constraint is verified by simulation analysis and experiment. The results show that the system represented in this paper provides higher suspension comfort and stability.

The Subsynchronous Dynamic Behavior of Tilting-Pad Journal Bearings

1992 ◽  
Vol 114 (1) ◽  
pp. 167-173 ◽  
Author(s):  
M. F. White ◽  
S. H. Chan
Keyword(s):  
High Speed ◽  
Dynamic Stiffness ◽  
Journal Bearings ◽  
Frequency Effect ◽  
Tilting Pad ◽  
Dimensional Finite Element ◽  
The Stability ◽  
Element Technique ◽  
Tilting Pad Journal Bearing ◽  
Tilting Pad Journal Bearings

Tilting-pad journal bearings are being increasingly used to avoid bearing instability problems. This paper describes the theory and results from a design program which has been developed for tilting-pad journal bearing calculations. The present approach is based on the numerical solution of the Reynolds equation using a one-dimensional finite element technique which considers temperature and viscosity changes and can also take into account the effect of turbulent flow. Computed results of dynamic stiffness and damping coefficients show very good agreement with data from the literature. The effects of various factors which may influence the bearing dynamic characteristics are discussed. For bearings with small preloads and operating at high Sommerfeld numbers, the effective damping at subsynchronous frequencies is considerably lower than that predicted for synchronous vibration. The stiffness is also affected by frequency. This frequency effect is attenuated by increased bearing preloads and offsets. Such factors have important consequences on the stability of high speed turbomachinery supported by tilting-pad journal bearings.

Dynamic Characterization of Tilting Pad Journal Bearings From Component and System Level Testing

2012 ◽  
Author(s):  
Adolfo Delgado ◽  
Mirko Librashi ◽  
Giuseppe Vannini
Keyword(s):  
Stability Analysis ◽  
High Speed ◽  
Dynamic Stiffness ◽  
Operating Conditions ◽  
Logarithmic Decrement ◽  
Experimental Results ◽  
System Level ◽  
Component Level ◽  
Force Coefficients ◽  
Tilting Pad

The dynamic response of a direct lube, 5-pad, rocker-back pivot tilting pad bearing is characterized in a controlled motion (component level) test rig, and in a spin bunker (full system level) using a dummy rotor mounted on two identical bearings. In the component level test, the force coefficients (stiffness, damping, mass) are identified from pseudorandom excitations using a 2-DOF model. N-DOF system including the pad motions has been shown to yield frequency dependent coefficients that warrant the use of asynchronous coefficients for stability analysis in centrifugal compressors. However, experimental results showed that the real part of the dynamic stiffness is well represented as a constant stiffness and mass coefficients while the imaginary part yields a constant damping coefficient (i.e. frequency independent). In the system level test, a dedicated dummy rotor (representative of a high speed centrifugal compressor rotor) is excited by a magnetic shaker throughout a frequency range covering the rotor modes of interest while spinning at constant speed. From the rotor harmonic response the damping of each mode is extracted using a curve-fitting method based on a 1-DOF model for a given set of speeds. The dummy rotor test provides reference values for system logarithmic decrement and further validates the component level test results. The logarithmic decrement prediction using identified bearing force coefficients are in good agreement with the experimental results. In addition, using for prediction identified coefficients in a classical K-C-M or synchronous K-C form yields similar results (within 15%). This indicates that for the given bearing geometry (clearance, offset and size) and operating conditions, synchronously reduced force coefficients are adequate for stability analysis. Comparison of the identified force coefficients with results from commercially available code yielded reasonable agreement on direct coefficients while some discrepancies are highlighted on the cross-coupled coefficients.

Static and Dynamic Characteristics of Oil Lubricated Beveled-Step Herringbone-Grooved Journal Bearings

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
M. M. Nemat-Alla ◽  
A. M. Gad ◽  
A. A. Khalil ◽  
A. M. Nasr
Keyword(s):  
Dynamic Characteristics ◽  
High Speed ◽  
Hydrodynamic Lubrication ◽  
Journal Bearings ◽  
Friction Torque ◽  
Experimental Results ◽  
Static And Dynamic Characteristics ◽  
Thrust Bearings ◽  
Rectangular Profile ◽  
The Stability

Recently, herringbone-grooved journal bearings (HGJBs) have important applications in high-speed rotating machinery. The groove action in pumping the lubricating fluid inward generates supporting stiffness and improves the stability of the bearing when operating concentrically. Several researchers have investigated the static and dynamic characteristics of HGJBs and grooved thrust bearings. Most of these investigations were theoretical and concentrated on HGJBs with rectangular-profile grooves. In the present work, the static and dynamic characteristics of the beveled-step HGJBs are experimentally investigated. The bearing attitude angle, pressure distribution, and bearing friction torque were measured on a hydrodynamic lubrication unit, and then the static and dynamic characteristics were determined. The obtained experimental results are compared to the obtained experimental results for plain journal bearing. The merits as well as the demerits of the groove profile were discussed through comparisons with plain journal bearings.

Influence of Multiphysical Effects on the Dynamics of the High Speed Mini Rotors—Part II: Results

2010 ◽  
Vol 132 (3) ◽  
Author(s):  
Emre Dikmen ◽  
Peter J. M. van der Hoogt ◽  
André de Boer ◽  
Ronald G. K. M. Aarts
Keyword(s):  
Modal Analysis ◽  
Dynamic Behavior ◽  
High Speed ◽  
Structural Model ◽  
Natural Frequencies ◽  
Experimental Setup ◽  
Flexible Supports ◽  
The Stability ◽  
Surrounding Fluid ◽  
Theoretical Results

In Part I of this work, a theoretical analysis showed that the surrounding air in the closed confinement between rotor and casing has a significant effect on the dynamic behavior of high speed minirotors. In order to validate the developed theoretical model, an experimental setup is designed and the dynamic behavior of the rotor with medium gap confinement is studied. The experimental setup has flexible supports, which consist of beams with adjustable length. The support stiffness is changed by altering the beam length. Modal analysis of the rotor is done in free-free conditions in order to test the capability of the rotordynamic model without the supports and multiphysical effects. The experimental and simulation results agree well with a difference of 1%. Then modal analysis of the whole structure is done at standstill and during operation in the absence of the casing. In this way, multiphysical effects are eliminated and only support effects on the dynamics of the structure are observed. The supports appear to have significant effect on the natural frequencies of the flexural modes of the system. Different support modeling techniques are studied and adequate equivalent models are obtained. These models are then implemented into the structural model of the rotor. Finally, multiphysical effects are tested at different speeds with different support stiffnesses. Experiments are performed with and without the casing for determining the change in the natural frequencies and onset of instability. The surrounding fluid has a significant effect on the stability of the system while the natural frequencies do not change significantly. The experimental and theoretical results are in fair agreement for predicting the natural frequencies and the onset of instability.

Research on Structure and Kinematics of Hexapod Robot Based on the Pneumatic Flexible Joint

2013 ◽  
Vol 401-403 ◽  
pp. 267-271
Author(s):  
De Xu Geng ◽  
He Peng ◽  
Jin Tao Zhang ◽  
Yun Wei Zhao ◽  
Guang Bin Wu
Keyword(s):  
High Speed ◽  
Test Bench ◽  
Control Method ◽  
Hexapod Robot ◽  
Gravity Center ◽  
Pneumatic Control ◽  
Translational Displacement ◽  
New Type ◽  
Set Up ◽  
The Stability

This paper developed a new type of hexapod robot using self-developed flexible space bending joints which can not only move from side to side or back and forth but also rotate. Then the principle of the movement and the gait of the hexapod robot were investigated, the kinematics model on translational displacement and velocity was followed. Furthermore, the test bench and pneumatic control system were set up, and the displacement, velocity and acceleration of the center of were acquired by high-speed camera shooting means. Finally, the stability of the gravity center and the control method of the hexapod robot were studied. The research of this paper provides a theoretical and practical basis for the application of bionic hexapod robot.

Finite Element Modeling of a High Speed Optical Depth Scanner

1999 ◽  
Author(s):  
J. Szydlo ◽  
R. Lehmann ◽  
T. Lassen ◽  
H. Bleuler
Keyword(s):  
High Speed ◽  
Critical Speed ◽  
Mechanical Deformation ◽  
Fe Modeling ◽  
Optical Performance ◽  
Air Bearings ◽  
Low Coherence ◽  
Air Turbine ◽  
Scan Rate ◽  
Bk7 Glass

Abstract A rotational high-speed depth scanner for an optical low-coherence reflectometer used for 3-D retina scanning has been developed and analyzed. A rotational speed of 427’000 rpm (in the range between the 4th and 5th critical speed) has been reached for the 5 × 5 × 2 mm3 BK7 glass cube, resulting in a record scan rate for this kind of instrument. This paper reports on our experimental results as well as the FE-modeling of the rotor and the internal-reflection glass cube under centrifugal stress, and on the interplay of mechanical deformation and optical performance. The scanner is mounted on air bearings and driven by an air turbine.

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