Nonlinear Behavior Analysis of a Rotor Supported on Fluid-Film Bearings

2005 ◽  
Vol 128 (1) ◽  
pp. 35-40 ◽  
Author(s):  
Guangyan Shen ◽  
Zhonghui Xiao ◽  
Wen Zhang ◽  
Tiesheng Zheng
Keyword(s):  
Behavior Analysis ◽  
Dynamical Behavior ◽  
Nonlinear Behavior ◽  
Fluid Film ◽  
Diagnostic Tools ◽  
Nonlinear Phenomena ◽  
Frequency Spectra ◽  
Nonlinear Dynamical ◽  
Synchronous Motion ◽  
Period Motion

A fast and accurate model to calculate the fluid-film forces of a fluid-film bearing with the Reynolds boundary condition is presented in the paper by using the free boundary theory and the variational method. The model is applied to the nonlinear dynamical behavior analysis of a rigid rotor in the elliptical bearing support. Both balanced and unbalanced rotors are taken into consideration. Numerical simulations show that the balanced rotor undergoes a supercritical Hopf bifurcation as the rotor spin speed increases. The investigation of the unbalanced rotor indicates that the motion can be a synchronous motion, subharmonic motion, quasi-period motion, or chaotic motion at different rotor spin speeds. These nonlinear phenomena are investigated in detail. Poincaré maps, bifurcation diagram and frequency spectra are utilized as diagnostic tools.

Stable and Unstable Quasiperiodic Oscillations in Robot Dynamics

1993 ◽  
Author(s):  
G. Stépán ◽  
G. Haller
Keyword(s):  
Nonlinear Dynamical Systems ◽  
Dynamical Behavior ◽  
Time Lag ◽  
Nonlinear Behavior ◽  
Degree Of Freedom ◽  
Robot Dynamics ◽  
Robot Arm ◽  
Delayed Systems ◽  
Nonlinear Dynamical ◽  
Quasiperiodic Oscillations

Abstract Delays in robot control may result in unexpectedly sophisticated nonlinear dynamical behavior. Experiments on force controlled robots frequently show periodic and quasiperiodic oscillations which cannot be explained without including the time lag and/or the sampling time of the system in our models. Delayed systems, even of low degree of freedom, can produce phenomena which are already well understood in the theory of nonlinear dynamical systems but hardly ever occur in simple mechanical models. To illustrate this, we analyze the delayed positioning of a single degree of freedom robot arm. The analytical results show typical nonlinear behavior in the system which may go through a codimension two Hopf bifurcation for an infinite set of parameter values, leading to the creation of two-tori in the phase space. These results give a qualitative explanation for the existence of self-excited quasiperiodic oscillations in the dynamics of force controlled robots.

Detection of Reinforced Concrete Thermal Damage by Nonlinear Ultrasonic Spectroscopy

2019 ◽  
Vol 296 ◽  
pp. 143-148
Author(s):  
Michal Matysík ◽  
Iveta Plšková ◽  
Zdeněk Chobola
Keyword(s):  
Reinforced Concrete ◽  
Nonlinear Behavior ◽  
Nonlinear Effects ◽  
Reinforced Concrete Beams ◽  
Nonlinear Phenomena ◽  
Ultrasonic Spectroscopy ◽  
Frequency Spectra ◽  
Ultrasound Waves ◽  
Nonlinear Ultrasonic ◽  
Pass Through

Nonlinear Ultrasonic Spectroscopy (NUS) methods investigates nonlinear phenomena that occur when the sound or ultrasound waves pass through the material. This paper focuses on the use of these methods for nondestructive testing of reinforced concrete damaged by high temperature. For this research, reinforced concrete beams with one steel rod were made and the NUS measuring equipment was assembled. An appropriate nonlinear parameter was selected to assess the damage. The nonlinear behavior of thermally damaged reinforced concrete was manifested by the deformation of ultrasound waves passing through the measured samples, resulting in nonlinear effects in the frequency spectra of the recorded signal.

SPATIOTEMPORAL STRUCTURES IN UNDOPED PHOTOEXCITED SEMICONDUCTOR SUPERLATTICES

2001 ◽  
Vol 11 (11) ◽  
pp. 2817-2822 ◽  
Author(s):  
A. PERALES ◽  
L. L. BONILLA ◽  
M. MOSCOSO ◽  
J. GALÁN
Keyword(s):  
Degrees Of Freedom ◽  
Dynamical Behavior ◽  
Nonlinear Dynamical System ◽  
Nonlinear Behavior ◽  
Numerical Continuation ◽  
Continuation Methods ◽  
Semiconductor Superlattices ◽  
Nonlinear Dynamical ◽  
Strongly Nonlinear ◽  
Parameter Ranges

Semiconductor superlattices are a very interesting example of a nonlinear dynamical system with a large number of degrees of freedom. They show a strongly nonlinear behavior and they are well suited for the observation of current instabilities. In the present work, the dynamical behavior of undoped photoexcited superlattices has been analyzed by numerical continuation methods and bifurcation theory within the framework of a simple drift-diffusion model. The control parameters are the applied dc voltage and the carrier density, which are related to the laser power. We compile our results in a phase diagram and locate the lines where the system undergoes qualitative changes of behavior. The oscillatory regions are related to the appearance and disappearance of Hopf tongue crossings, for which oscillations appear as sub- or supercritical bifurcations. This implies the existence of voltage windows of current oscillations and hysteresis in appropriate parameter ranges, which agrees with recent experimental observations.

scholarly journals Dynamical visualization of anisotropic electromagnetic re-emissions from a single metal micro-helix at THz frequencies

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
T. Notake ◽  
T. Iyoda ◽  
T. Arikawa ◽  
K. Tanaka ◽  
C. Otani ◽  
...  
Keyword(s):  
Real Time ◽  
Electromagnetic Waves ◽  
Electromagnetic Compatibility ◽  
Smart Antenna ◽  
Dynamical Behavior ◽  
Measurement Techniques ◽  
Spatial Evolution ◽  
Frequency Spectra ◽  
3D Objects ◽  
Current Oscillations

AbstractThe capability for actual measurements—not just simulations—of the dynamical behavior of THz electromagnetic waves, including interactions with prevalent 3D objects, has become increasingly important not only for developments of various THz devices, but also for reliable evaluation of electromagnetic compatibility. We have obtained real-time visualizations of the spatial evolution of THz electromagnetic waves interacting with a single metal micro-helix. After the micro-helix is stimulated by a broadband pico-second pulse of THz electromagnetic waves, two types of anisotropic re-emissions can occur following overall inductive current oscillations in the micro-helix. They propagate in orthogonally crossed directions with different THz frequency spectra. This unique radiative feature can be very useful for the development of a smart antenna with broadband multiplexing/demultiplexing ability and directional adaptivity. In this way, we have demonstrated that our advanced measurement techniques can lead to the development of novel functional THz devices.

scholarly journals Bistable dynamics beyond rotating wave approximation

2014 ◽  
Vol 23 (02) ◽  
pp. 1450019 ◽  
Author(s):  
Y. A. Sharaby ◽  
S. Lynch ◽  
A. Joshi ◽  
S. S. Hassan
Keyword(s):  
Ring Cavity ◽  
Dynamical Behavior ◽  
Single Mode ◽  
Unstable State ◽  
Nonlinear Dynamical ◽  
Rotating Wave Approximation ◽  
Wave Approximation ◽  
Atomic Medium ◽  
Bistable Dynamics ◽  
Rotating Wave

In this paper, we investigate the nonlinear dynamical behavior of dispersive optical bistability (OB) for a homogeneously broadened two-level atomic medium interacting with a single mode of the ring cavity without invoking the rotating wave approximation (RWA). The periodic oscillations (self-pulsing) and chaos of the unstable state of the OB curve is affected by the counter rotating terms through the appearance of spikes during its periods. Further, the bifurcation with atomic detuning, within and outside the RWA, shows that the OB system can be converted from a chaotic system to self-pulsing system and vice-versa.

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.

The Motion of Floating Systems: Nonlinear Dynamics in Periodic and Random Waves

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Katrin Ellermann
Keyword(s):  
Dynamical Behavior ◽  
Nonlinear Behavior ◽  
Operating Conditions ◽  
Random Waves ◽  
Multiple Components ◽  
Random Disturbances ◽  
Restoring Forces ◽  
Steady State Responses ◽  
External Forces ◽  
Floating Systems

Floating systems, such as ships, barges, or semisubmersibles, show a dynamical behavior, which is determined by their internal structure and the operating conditions caused by external forces e.g., due to waves and wind. Due to the complexity of the system, which commonly includes coupling of multiple components or nonlinear restoring forces, the response can exhibit inherently nonlinear characteristics. In this paper different models of floating systems are considered. For the idealized case of purely harmonic forcing they all show nonlinear behavior such as subharmonic motion or different steady-state responses at constant operating conditions. The introduction of random disturbances leads to deviations from the idealized case, which may change the overall response significantly. Advantages and limitations of the different mathematical models and the applied numerical techniques are discussed.

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