Nonlinear stability analysis and numerical continuation of bifurcations of a rotor supported by floating ring bearings

2021 ◽  
pp. 095440622110263
Author(s):  
Amira Amamou
Keyword(s):  
High Speed ◽  
Nonlinear Behavior ◽  
Cost Effective ◽  
Numerical Continuation ◽  
Physical Parameters ◽  
Nonlinear Phenomena ◽  
Nonlinear Stability Analysis ◽  
Damping Behavior ◽  
Fold Bifurcation ◽  
Oil Films

Floating ring bearings have been widely used, over the last decades, in rotors of automotive turbochargers because of their improved damping behavior and their good emergency-operating capabilities. They also offer a cost-effective design and have good assembly properties. Nevertheless, rotors with floating ring bearings show vibration effects of nonlinear nature induced by self-excited oscillations originating from the bearing oil films (oil whirl/whip phenomena) and may exhibit various nonlinear vibration effects which may cause damage to the rotor. In order to investigate these dynamic phenomena, this paper has developed a nonlinear model of a perfectly balanced rigid rotor supported by two identical floating ring bearings with consideration of their vibration behavior mainly governed by fluid dynamics. The dimensionless hydrodynamic forces of floating ring bearings have been derived based on the short bearing theory and the half Sommerfeld solution. Using the numerical continuation approach, different bifurcations are detected when a control parameter, the journal speed, is varied. Depending on the system’s physical parameters, the rotor can show stable or unstable limit cycles which themselves may collapse beyond a certain rotor speed to exhibit a fold bifurcation. Bifurcation analysis is performed to investigate the occurring instabilities and nonlinear phenomena. Such results explain the instabilities characteristics of the floating ring bearing in high-speed applications. It has also been found that the selection of the bearing modulus plays an important role in the characterization of the rotor stability threshold speed and bifurcation sequences. An understanding of the system’s nonlinear behavior serves as the basis for new and rational criteria for the design and the safe operation of rotating machines.

Nonlinear electroelastic resonators

2016 ◽  
Author(s):  
◽  
Christopher R. Kirkendall
Keyword(s):  
Numerical Methods ◽  
Global Bifurcation ◽  
Nonlinear Behavior ◽  
Quantitative Model ◽  
Numerical Continuation ◽  
Continuation Methods ◽  
Nonlinear Phenomena ◽  
Driving Frequency ◽  
Modal Interactions ◽  
Liquid Environment

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] In broad terms, this dissertation concerns the physics of electroelastic continua and its application to piezoelectric plate resonators, with a specific emphasis on nonlinear phenomena. The gradual reduction of device size, coupled with higher driving amplitudes, have revealed the need for a general framework to predict nonlinear behavior in resonant piezoelectric devices. Not only must a suitable theoretical model exist, but it should be amenable to analytical and numerical methods that give physical insight into the underlying nonlinear interactions. This work addresses the need for such a framework by extending existing theory and applying analytical and numerical methods in new ways. In the first chapter linear piezoelectric device physics is reviewed and a method for improving the quality factor of mass sensors in a liquid environment is presented. However, the limitations of this preliminary work motivate the focus on nonlinear behavior in the following chapters. After a brief review of electroelastic continua in chapter 2, the following chapter details the use of nonlinear Duffing behavior in a quartz resonator to improve mass sensitivity. A 1-DOF model is used but coupling with other modes is observed at higher driving amplitudes, showing the limits of the model. Thus, in chapter 4 a quantitative model is developed to predict the effect of modal interactions in nonlinear piezoelectric crystals. Perturbation analysis and numerical continuation methods are applied to reveal previously unwitnessed multistable behavior, which is then experimentally verified. As a result, the global bifurcation structure of quartz plates is mapped out in terms of the driving frequency and amplitude. The final chapter derives approximate nonlinear plate equations for electroelastic crystals, using both power series and trigonometric expansions. A very general reduced-order model of the governing PDEs is derived and used to quantify the effect of coupling to lateral eigenmodes on the Duffing behavior of the frequency response.

The Radio Probe™: A New Measurement Tool for High Speed Integrated Circuits

2005 ◽  
Author(s):  
Mark Kimball
Keyword(s):  
Integrated Circuits ◽  
Integrated Circuit ◽  
High Speed ◽  
Attenuation Factor ◽  
Cost Effective ◽  
Frequency Measurement ◽  
Single Frequency ◽  
Measurement Tool ◽  
Probe Design ◽  
Differential Measurement

Abstract This article presents a novel tool designed to allow circuit node measurements in a radio frequency (RF) integrated circuit. The discussion covers RF circuit problems; provides details on the Radio Probe design, which achieves an input impedance of 50Kohms and an overall attenuation factor of 0 dB; and describes signal to noise issues in the output signal, along with their improvement techniques. This cost-effective solution incorporates features that make it well suited to the task of differential measurement of circuit nodes within an RF IC. The Radio Probe concept offers a number of advantages compared to active probes. It is a single frequency measurement tool, so it complements, rather than replaces, active probes.

scholarly journals 2D-3D integration of hexagonal boron nitride and a high-κ dielectric for ultrafast graphene-based electro-absorption modulators

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Hitesh Agarwal ◽  
Bernat Terrés ◽  
Lorenzo Orsini ◽  
Alberto Montanaro ◽  
Vito Sorianello ◽  
...  
Keyword(s):  
Boron Nitride ◽  
Hafnium Oxide ◽  
High Speed ◽  
Hexagonal Boron Nitride ◽  
Temperature Stability ◽  
Cost Effective ◽  
Fold Increase ◽  
Building Blocks ◽  
High Quality ◽  
New Device

AbstractElectro-absorption (EA) waveguide-coupled modulators are essential building blocks for on-chip optical communications. Compared to state-of-the-art silicon (Si) devices, graphene-based EA modulators promise smaller footprints, larger temperature stability, cost-effective integration and high speeds. However, combining high speed and large modulation efficiencies in a single graphene-based device has remained elusive so far. In this work, we overcome this fundamental trade-off by demonstrating the 2D-3D dielectric integration in a high-quality encapsulated graphene device. We integrated hafnium oxide (HfO2) and two-dimensional hexagonal boron nitride (hBN) within the insulating section of a double-layer (DL) graphene EA modulator. This combination of materials allows for a high-quality modulator device with high performances: a ~39 GHz bandwidth (BW) with a three-fold increase in modulation efficiency compared to previously reported high-speed modulators. This 2D-3D dielectric integration paves the way to a plethora of electronic and opto-electronic devices with enhanced performance and stability, while expanding the freedom for new device designs.

scholarly journals Scale-Up Preparation of Crocins I and II from Gardeniajasminoides by a Two-Step Chromatographic Approach and Their Inhibitory Activity Against ATP Citrate Lyase

Molecules ◽  
2021 ◽  
Vol 26 (11) ◽  
pp. 3137
Author(s):  
Shuguang Guan ◽  
Qiaoli Pu ◽  
Yinan Liu ◽  
Honghong Wu ◽  
Wenbo Yu ◽  
...  
Keyword(s):  
Inhibitory Activity ◽  
High Speed ◽  
Scale Up ◽  
Cost Effective ◽  
Atp Citrate Lyase ◽  
Gardenia Jasminoides ◽  
Citrate Lyase ◽  
Human Disorders ◽  
Ic50 Values ◽  
Counter Current

Crocins are highly valuable natural compounds for treating human disorders, and they are also high-end spices and colorants in the food industry. Due to the limitation of obtaining this type of highly polar compound, the commercial prices of crocins I and II are expensive. In this study, macroporous resin column chromatography combined with high-speed counter-current chromatography (HSCCC) was used to purify crocins I and II from natural sources. With only two chromatographic steps, both compounds were simultaneously isolated from the dry fruit of Gardenia jasminoides, which is a cheap herbal medicine distributed in a number of countries. In an effort to shorten the isolation time and reduce solvent usage, forward and reverse rotations were successively utilized in the HSCCC isolation procedure. Crocins I and II were simultaneously obtained from a herbal resource with high recoveries of 0.5% and 0.1%, respectively, and high purities of 98.7% and 99.1%, respectively, by HPLC analysis. The optimized preparation method was proven to be highly efficient, convenient, and cost-effective. Crocins I and II exhibited inhibitory activity against ATP citrate lyase, and their IC50 values were determined to be 36.3 ± 6.24 and 29.7 ± 7.41 μM, respectively.

Narrowing longitudinally coupled prefabricated slab track maintenance duration with field data analysis of slab deformation under high temperature

2021 ◽  
pp. 095440972098626
Author(s):  
Zai-Wei Li ◽  
Xiao-Zhou Liu ◽  
Hong-Yao Lu ◽  
Yue-Lei He
Keyword(s):  
High Temperature ◽  
High Speed ◽  
Ride Comfort ◽  
Cost Effective ◽  
Periodic Variation ◽  
Longitudinal Force ◽  
Distribution Analysis ◽  
High Speed Rail ◽  
Track Maintenance ◽  
Slab Track

The deformation of longitudinally coupled prefabricated slab track (LCPST) due to high temperature may lead to a reduction in ride comfort and safety in high-speed rail (HSR) operation. It is thus critical to understand and track the development of such defects. This study develops an online monitoring system to analyze LCPST deformation at different slab depths under various temperatures. The trackside system, powered by solar energy with STM8L core that is ultra-low in energy consumption, is used to collect data of LCPST deformation and temperature level uninterruptedly. With canonical correlation analysis, it is found that LCPST deformation presents similar periodic variation to yearly temperature fluctuation and large longitudinal force may be generated as heat accumulates in summer, thereby causing track defects. Then the distribution of temperature and deformation data is categorized based on fuzzy c-means clustering. Through the distribution analysis, it is suggested that slab inspection can be shortened to 6 hours, i.e. from 10:00 am to 4:00 pm, reducing 14.3% track inspection workload from the current practice. The price of workload reduction is only a 2% chance of missed detection of slab deformation. The finding of this research can be used to enhance LCPST monitoring efficiency and reduce interruption to HSR operation, which is an essential step in promoting reliable and cost-effective track service.

VERTICAL SCALING OF TYPE I InP HBT WITH FT > 500 GHZ

2004 ◽  
Vol 14 (03) ◽  
pp. 625-631 ◽  
Author(s):  
J. W. LAI ◽  
W. HAFEZ ◽  
M. FENG
Keyword(s):  
Heterojunction Bipolar Transistors ◽  
High Speed ◽  
Impact Ionization ◽  
Cutoff Frequency ◽  
Current Gain ◽  
Vertical Scaling ◽  
Physical Parameters ◽  
Type I ◽  
Peak Current Density ◽  
Rf Performance

We have fabricated the high-speed InP/InGaAs -based single heterojunction bipolar transistors (SHBTs) with current gain cutoff frequency, fT from 166GHz to over 500GHz by the approach of vertical scaling. Collector thickness is reduced from 3000Å to 750Å and the peak current density is increased up to 1300kA/cm2. In this paper, device rf performance has been compared with respect to materials with different vertical dimensions. The scaling limitation is also studied by analytical approach. The extracted physical parameters suggest that the parasitic emitter resistance is the major limit on further enhancing ultra-scaled HBT intrinsic speed due to the associated RECBC delay. The cut-off frequency of a 500Å collector SHBT has been measured and the results indicate a dramatic drop on fT, supporting the conclusion projected by model analysis. It is also commented that for deeply downscaled HBTs, impact ionization could be another degrading mechanism limits device bandwidth.

Nonlinear Dynamics of an Imperfect Microbeam Under an Axial Load and Electric Excitation

2011 ◽  
Author(s):  
Laura Ruzziconi ◽  
Mohammad I. Younis ◽  
Stefano Lenci
Keyword(s):  
Nonlinear Dynamics ◽  
Microelectromechanical Systems ◽  
Complex Dynamics ◽  
Nonlinear Behavior ◽  
Single Mode ◽  
Phase Portraits ◽  
Nonlinear Phenomena ◽  
Theoretical Point ◽  
Initial Shape ◽  
Electric Excitation

This study is motivated by the growing attention, both from a practical and a theoretical point of view, toward the nonlinear behavior of microelectromechanical systems (MEMS). We analyze the nonlinear dynamics of an imperfect microbeam under an axial force and electric excitation. The imperfection of the microbeam, typically due to microfabrication processes, is simulated assuming the microbeam to be of a shallow arched initial shape. The device has a bistable static behavior. The aim is that of illustrating the nonlinear phenomena, which arise due to the coupling of mechanical and electrical nonlinearities, and discussing their usefulness for the engineering design of the microstructure. We derive a single-mode-reduced-order model by combining the classical Galerkin technique and the Pade´ approximation. Despite its apparent simplicity, this model is able to capture the main features of the complex dynamics of the device. Extensive numerical simulations are performed using frequency response diagrams, attractor-basins phase portraits, and frequency-dynamic voltage behavior charts. We investigate the overall scenario, up to the inevitable escape, obtaining the theoretical boundaries of appearance and disappearance of the main attractors. The main features of the nonlinear dynamics are discussed, stressing their existence and their practical relevance. We focus on the coexistence of robust attractors, which leads to a considerable versatility of behavior. This is a very attractive feature in MEMS applications. The ranges of coexistence are analyzed in detail, remarkably at high values of the dynamic excitation, where the penetration of the escape (dynamic pull-in) inside the double well may prevent the safe jump between the attractors.

Adaptive Network Coded Clouds: High Speed Downloads and Cost-Effective Version Control

2019 ◽  
Vol 7 (1) ◽  
pp. 19-33 ◽  
Author(s):  
Marton Sipos ◽  
Janus Heide ◽  
Daniel E. Lucani ◽  
Morten V. Pedersen ◽  
Frank H.P. Fitzek ◽  
...  
Keyword(s):  
High Speed ◽  
Cost Effective ◽  
Version Control ◽  
Adaptive Network ◽  
Effective Version

scholarly journals A gradient field defeats the inherent repulsion between magnetic nanorods

2014 ◽  
Vol 1 (2) ◽  
pp. 140271 ◽  
Author(s):  
Yu Gu ◽  
Ruslan Burtovyy ◽  
John Custer ◽  
Igor Luzinov ◽  
Konstantin G. Kornev
Keyword(s):  
Phase Portrait ◽  
High Speed ◽  
Uniform Magnetic Field ◽  
Gradient Field ◽  
Physical Parameters ◽  
Uniform Field ◽  
Experimental Conditions ◽  
Magnetic Nanorods ◽  
Field Gradients ◽  
And Control

When controlling the assembly of magnetic nanorods and chains of magnetic nanoparticles, it is extremely challenging to bring them together side by side while keeping a desired spacing between their axes. We show that this challenge can be successfully resolved by using a non-uniform magnetic field that defeats an inherent repulsion between nanorods. Nickel nanorods were suspended in a viscous film and a non-uniform field was used to control their placement. The in-plane movement of nanorods was tracked with a high-speed camera and a detailed image analysis was conducted to quantitatively characterize the behaviour of the nanorods. The analysis focused on the behaviour of a pair of neighbour nanorods, and a corresponding dynamic model was formulated and investigated. The complex two-dimensional dynamics of a nanorod pair was analysed analytically and numerically, and a phase portrait was constructed. Using this phase portrait, we classified the nanorod behaviour and revealed the experimental conditions in which nanorods could be placed side by side. Dependence of the distance between a pair of neighbour nanorods on physical parameters was analysed. With the aid of the proposed theory, one can build different lattices and control their spacing by applying different field gradients.

Control of a lamination process

2005 ◽  
Vol 219 (1) ◽  
pp. 69-81 ◽  
Author(s):  
R Whalley ◽  
M Ebrahimi
Keyword(s):  
High Speed ◽  
Closed Loop ◽  
Cost Effective ◽  
Closed Loop System ◽  
Design Validation ◽  
Control Effort ◽  
Speed Of Response ◽  
Feedback Compensation ◽  
Lamination Process ◽  
Compensation Design

A high-speed laminating machine for a fabric coating and conversion process is considered. Following analysis procedures, state-space and the admittance transfer function descriptions for the system are derived. Regulation of the fabric tension owing to heat shrinkage and environmental and coating variations is necessary. An optimum, minimum control effort strategy is proposed, enabling simple cost effective regulation, without the use of active elements. The speed of response of the system is improved by the use of feedback compensation. Design validation, via simulation, obtaining the open- and closed-loop system responses is employed, demonstrating the achievement of smooth, almost monotonic variations in tension following reference changes, as specified.

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