Subharmonic response of lipid-coated monodisperse microbubbles

2017 ◽  
Vol 141 (5) ◽  
pp. 3952-3952 ◽  
Author(s):  
Qian Li ◽  
Tyrone M. Porter
Keyword(s):  
Subharmonic Response

Bifurcation Analysis of Self-Acting Gas Journal Bearings

2001 ◽  
Vol 123 (4) ◽  
pp. 755-767 ◽  
Author(s):  
Cheng-Chi Wang ◽  
Cha’o-Ku`ang Chen
Keyword(s):  
Dynamic Behavior ◽  
Reynolds Equation ◽  
Rotational Velocity ◽  
Power Spectra ◽  
Journal Bearings ◽  
Operating Conditions ◽  
Finite Differences Method ◽  
Subharmonic Response ◽  
Rotor Center ◽  
Rotor Mass

This paper studies the bifurcation of a rigid rotor supported by a gas film bearing. A time-dependent mathematical model for gas journal bearings is presented. The finite differences method and the Successive Over Relation (S.O.R) method are employed to solve the Reynolds’ equation. The system state trajectory, Poincare´ maps, power spectra, and bifurcation diagrams are used to analyze the dynamic behavior of the rotor center in the horizontal and vertical directions under different operating conditions. The analysis shows how the existence of a complex dynamic behavior comprising periodic and subharmonic response of the rotor center. This paper shows how the dynamic behavior of this type of system varies with changes in rotor mass and rotational velocity. The results of this study contribute to a further understanding of the nonlinear dynamics of gas film rotor-bearing systems.

Some Observations of Chaotic Vibration Phenomena in High-Speed Rotordynamics

1991 ◽  
Vol 113 (1) ◽  
pp. 50-57 ◽  
Author(s):  
F. F. Ehrich
Keyword(s):  
Numerical Model ◽  
High Speed ◽  
Chaotic Behavior ◽  
Narrow Region ◽  
System A ◽  
Vibratory Response ◽  
Local Contact ◽  
Jeffcott Rotor ◽  
Subharmonic Response ◽  
Static Part

Subharmonic response in rotordynamics may be encountered when a rotor is operated with its rotational centerline eccentric to that of a close clearance static part, so that local contact can take place during each orbit when the rotor is excited by residual unbalance. The rotor will tend to bounce at or near its fundamental frequency when the rotor is operated at or near a speed which is a whole number [n] times that frequency. Using a simple numerical model of a Jeffcott rotor mounted on a nonlinear spring, it is found that the vibratory response in the transition zone midway between adjacent zones of subharmonic response has all the characteristics of chaotic behavior. The transition from subharmonic to chaotic response has a complex substructure which involves a sequence of bifurcations of the orbit with variations in speed. This class of rotordynamic behavior was confirmed and illustrated by experimental observations of the vibratory response of a high-speed turbomachine, operating at a speed between 8 and 9 times its fundamental rotor frequency when in local contact across a clearance in the support system. A narrow region between zones of 8th order and 9th order subharmonic response was identified where the response had all the characteristics of the chaotic motion identified in the numerical model.

scholarly journals Recent Experiences and Advances in Contrast-Enhanced Subharmonic Ultrasound

2015 ◽  
Vol 2015 ◽  
pp. 1-6 ◽  
Author(s):  
John R. Eisenbrey ◽  
Anush Sridharan ◽  
Ji-Bin Liu ◽  
Flemming Forsberg
Keyword(s):  
Contrast Agents ◽  
Tumor Imaging ◽  
Three Dimensional ◽  
Ultrasound Contrast Agents ◽  
Surrounding Tissue ◽  
Contrast Enhanced Ultrasound ◽  
Ultrasound Contrast ◽  
Contrast Enhanced ◽  
Subharmonic Response

Nonlinear contrast-enhanced ultrasound imaging schemes strive to suppress tissue signals in order to better visualize nonlinear signals from blood-pooling ultrasound contrast agents. Because tissue does not generate a subharmonic response (i.e., signal at half the transmit frequency), subharmonic imaging has been proposed as a method for isolating ultrasound microbubble signals while suppressing surrounding tissue signals. In this paper, we summarize recent advances in the use of subharmonic imagingin vivo. These advances include the implementation of subharmonic imaging on linear and curvilinear arrays, intravascular probes, and three-dimensional probes for breast, renal, liver, plaque, and tumor imaging.

Subharmonic response of ultrasonically driven liquid helium

1978 ◽  
Vol 64 (S1) ◽  
pp. S33-S33
Author(s):  
R. F. Carey ◽  
J. A. Rooney ◽  
C. W. Smith
Keyword(s):  
Liquid Helium ◽  
Subharmonic Response

Noninvasive estimation of dynamic pressures in vitro and in vivo using the subharmonic response from microbubbles

2011 ◽  
Author(s):  
Jaydev K. Dave ◽  
Valgerdur G. Halldorsdottir ◽  
John R. Eisenbrey ◽  
Ji-Bin Liu ◽  
Maureen E. McDonald ◽  
...  
Keyword(s):  
Noninvasive Estimation ◽  
Subharmonic Response

scholarly journals Pattern formation in weakly damped parametric surface waves driven by two frequency components

1997 ◽  
Vol 341 ◽  
pp. 225-244 ◽  
Author(s):  
WENBIN ZHANG ◽  
JORGE VIÑALS
Keyword(s):  
Pattern Formation ◽  
Surface Waves ◽  
Frequency Ratio ◽  
Navier Stokes ◽  
Parametric Surface ◽  
Navier Stokes Equation ◽  
Low Viscosity ◽  
Frequency Components ◽  
Subharmonic Response ◽  
Arbitrary Frequency

A quasi-potential approximation to the Navier–Stokes equation for low-viscosity fluids is developed to study pattern formation in parametric surface waves driven by a force that has two frequency components. A bicritical line separating regions of instability to either of the driving frequencies is explicitly obtained, and compared with experiments involving a frequency ratio of 1/2. The procedure for deriving standing wave amplitude equations valid near onset is outlined for an arbitrary frequency ratio following a multiscale asymptotic expansion of the quasi-potential equations. Explicit results are presented for subharmonic response to a driving force of frequency ratio 1/2, and used to study pattern selection. Even though quadratic terms are prohibited in this case, hexagonal or triangular patterns are found to be stable in a relatively large parameter region, in qualitative agreement with experimental results.

A New Class of Asynchronous Rotordynamic Response in High-Speed Rotors

2007 ◽  
Author(s):  
Fredric F. Ehrich
Keyword(s):  
High Speed ◽  
Critical Frequency ◽  
Piecewise Linear ◽  
Dominant Frequency ◽  
Data Points ◽  
Subharmonic Response ◽  
Single Mass ◽  
Similar Appearance ◽  
The Individual ◽  
Representative Points

Virtually all of the nonlinear rotordynamic phenomena studied in the past result in excitation of rotor response at a dominant frequency at or near the critical frequency at rotational speeds other than the critical speed. In experimental work on a “macro-rig” of a micro-rotor in development some years ago at the Gas Turbine Laboratory of MIT, an unforeseen array of asynchronous response frequencies at other than the critical were noted when the rotor was operated at both subcritical and supercritical speeds. However, those responses were not explored in detail at the time. The patterned responses were apparently related to subharmonic and ultra-subharmonic response, but at frequencies lower than the critical frequency. More recently, the author noted a similar pattern of rotordynamic response in the course of operation at subcritical of an experimental turbomachinery component which was experiencing a local rub between the rotor and stator of an interstage seal. Data from that incident revealed a pattern of asynchronous response that had a very similar appearance to the earlier observation. Using a simple numerical model of a rotor employing a single mass mounted on a massless shaft and a piecewise linear (that is, a bilinear) bearing support stiffness to represent the system, it was possible to replicate the response at individual representative points over a range of sub-, trans-, and supercritical high-speed rotor operation. A generalized expression was derived inductively to represent the individual data points. The resultant pattern of data replicated the patterns of data from the two test vehicles which originally inspired the investigation and suggested the means of their suppression where their presence might be undesirable.

scholarly journals Self-demodulation effect on subharmonic response of ultrasound contrast agent

2012 ◽  
Author(s):  
V. Daeichin ◽  
T. Faez ◽  
A. Needles ◽  
G. Renaud ◽  
J. G. Bosch ◽  
...  
Keyword(s):  
Contrast Agent ◽  
Ultrasound Contrast Agent ◽  
Ultrasound Contrast ◽  
Subharmonic Response
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