Two Way Coupled Fields Multi-Physics Modeling Is Investigated as an Additional Approach to Address Fluid Elastic Instability

2021 ◽  
Author(s):  
Michael Breach
Keyword(s):  
Time Delay ◽  
Relative Phase ◽  
Phase Lag ◽  
Elastic Instability ◽  
Coupled Fields ◽  
Flow Perturbation ◽  
Future Paper ◽  
Out Of Plane ◽  
Physics Modeling ◽  
Additional Approach

Abstract Two way coupled fields multi-physics modeling is investigated as an additional approach to address out-of-plane FEI. It is established in the literature that to model the damping-controlled fluid elastic instability, a finite time delay between tube vibration and fluid perturbation must be realized. The phase lag between tube vibration and flow perturbation due to damping must be adequately captured by the model. The effects of tube frequency, turbulence level, location, and mean gap velocity on the relative phase values must also be captured. This approach will allow the time delay between tube vibration and flow perturbation due to damping, as well as turbulence, and stiffness to be intrinsically modeled. We will introduce the applicability of the method to in-plane FEI in a future paper once we have based lined it against out of plane FEI empirical results.

An Experimental Study of the Phase Lag Causing Fluidelastic Instability in Tube Bundles

2011 ◽  
Author(s):  
Ahmed Khalifa ◽  
David Weaver ◽  
Samir Ziada
Keyword(s):  
Time Delay ◽  
Phase Lag ◽  
Interstitial Flow ◽  
Flow Perturbation ◽  
Pressure Transducers ◽  
Fluid Forces ◽  
Fluidelastic Instability ◽  
Pitch Ratio ◽  
Downstream Flow ◽  
Lift And Drag

The phenomenon of fluidelastic instability forms a major limitation on the performance of tube and shell heat exchangers. It is believed that fluidelastic instability is attributed to two main mechanisms; the first is called the “Damping Mechanism”, while the second is called the “Stiffness Mechanism”. It is established in the literature that in order to model the damping controlled fluidelastic instability, a finite time delay between tube vibration and fluid response has to be introduced. Experimental investigation of the time delay between structural motion and the induced fluid forces is detailed in the present study. A parallel triangular tube array consisting of seven rows and six columns of aluminum tubes is built with a pitch ratio of 1.54. Hot-wire measurements of the interstitial flow perturbations are recorded while monitoring the tube vibrations in the lift and drag directions. Pressure transducers are installed inside the instrumented tubes to monitor the fluid forces. The phase lag between tube vibration and flow perturbation is obtained at different locations in the array. The effect of tube frequency, turbulence level, location of measurements, and mean gap velocity on the relative phase values is investigated. It is found that there are two well-defined regions of phase trends along the flow channel. It is concluded from this study that the time delay between tube vibration and downstream flow perturbation is associated with the vorticity convection downstream, while the time delay for upstream perturbations is associated with the effect of flow separation and vorticity generation which is propagated upstream from the vibrating tube.

Effect of Spray-Wall Interaction On Thermoacoustic Instability Prediction by Flame Transfer Function and the Convective Time Delay Method

2021 ◽  
Author(s):  
Sheng Meng ◽  
Man Zhang
Keyword(s):  
Time Delay ◽  
Transfer Function ◽  
Numerical Models ◽  
Time Lag ◽  
Interaction Model ◽  
Phase Lag ◽  
Thermoacoustic Instability ◽  
Spray Flame ◽  
Wall Interaction ◽  
Definition Of

Abstract This study numerically investigates the effect of spray-wall interactions on thermoacoustic instability prediction. The LES-based flame transfer function (FTF) and the convective time delay methods are used by combining the Helmholtz acoustic solver to predict a single spray flame under the so-called slip and film spray-wall conditions. It is found that considering more realistic film liquid and a wall surface interaction model achieves a more accurate phase lag in both of the time lag evaluations compared to the experimental results. Additionally, the results show that a new time delay exists between the liquid film fluctuation and the unsteady heat release, which explains the larger phase value in the film spray-wall condition than in the slip condition. Moreover, the prediction capability of the FTF framework and the convective time delay methodology in the linear regime are also presented. In general, the instability frequency differences predicted using the FTF framework under the film condition are less than 10 Hz compared with the experimental data. However, an underestimation of the numerical gain value leads to requiring a change in the forcing position and an improvement in the numerical models. Due to the ambiguous definition of the gain value in the convective time delay method, this approach leads to arbitrary and uncertain thermoacoustic instability predictions.

Fluid-Elastic Instability of Rotated Square Array U-Tubes in Air-Water Flow

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
In-Cheol Chu ◽  
Heung June Chung ◽  
Chang Hee Lee
Keyword(s):  
Tube Bundle ◽  
Damping Ratio ◽  
Elastic Instability ◽  
Two Phase ◽  
Instability Constant ◽  
Out Of Plane ◽  
Vibration Responses ◽  
Mode Vibration ◽  
Square Array ◽  
Side Flow

Fluid-elastic instability characteristics of a U-tube bundle were experimentally investigated in air-water two-phase flow. A total of 39 U-tubes were arranged in a rotated square array with a pitch-to-diameter ratio of 1.633. Vibration responses of four U-tubes were measured with three-axis accelerometers. Two sets of experiments were performed to investigate the onset of fluid-elastic instability, and the damping and hydrodynamic mass of the U-tube. The experiments were performed for a void fraction of 70–95%. Fluid-elastic instability was clearly observed in an out-of-plane mode vibration. The effect of a primary side flow on the vibration of U-tube was investigated separately. The damping ratio of the present U-tube was higher than the damping ratio of the cantilever tubes in the literature. The hydrodynamic mass of the U-tube was generally in accordance with the hydrodynamic mass of the cantilever tubes in the literature. The instability constant (K) of the Connors equation was assessed with a simplified effective gap velocity, and the fluid-elastic instability constant was 8.5.

Smooth Pursuit of a Partially Occluded Object

Perception ◽  
1996 ◽  
Vol 25 (1_suppl) ◽  
pp. 150-150 ◽  
Author(s):  
L S Stone ◽  
J Lorenceau ◽  
B R Beutter
Keyword(s):  
Relative Phase ◽  
Object Motion ◽  
Image Motion ◽  
Visual Signal ◽  
Phase Lag ◽  
Motion Signal ◽  
Retinal Image Motion ◽  
The Mean ◽  
Partially Occluded ◽  
Retinal Information

There has long been qualitative evidence that humans can pursue an object defined only by the motion of its parts (eg Steinbach, 1976 Vision Research16 1371 – 1375). We explored this quantitatively using an occluded diamond stimulus (Lorenceau and Shiffrar, 1992 Vision Research32 263 – 275). Four subjects (one naive) tracked a line-figure diamond moving along an elliptical path (0.9 Hz) either clockwise (CW) or counterclockwise (CCW) behind either an X-shaped aperture (CROSS) or two vertical rectangular apertures (BARS), which obscured the corners. Although the stimulus consisted of only four line segments (108 cd m−2), moving within a visible aperture (0.2 cd m−2) behind a foreground (38 cd m−2), it is largely perceived as a coherently moving diamond. The intersaccadic portions of eye-position traces were fitted with sinusoids. All subjects tracked object motion with considerable temporal accuracy. The mean phase lag was 5°/6° (CROSS/BARS) and the mean relative phase between the horizontal and vertical components was +95°/+92° (CW) and −85°/−75° (CCW), which is close to perfect. Furthermore, a \chi2 analysis showed that 56% of BARS trials were consistent with tracking the correct elliptical shape ( p<0.05), although segment motion was purely vertical. These data disprove the main tenet of most models of pursuit: that it is a system that seeks to minimise retinal image motion through negative feedback. Rather, the main drive must be a visual signal which has already integrated spatiotemporal retinal information into an object-motion signal.

scholarly journals Accurate relative-phase and time-delay maps all over the emission cone of hyperentangled photon source

2016 ◽  
Author(s):  
Salem F. Hegazy ◽  
Jala El-Azab ◽  
Yehia A. Badr ◽  
Salah S. A. Obayya
Keyword(s):  
Time Delay ◽  
Relative Phase ◽  
Photon Source

A Simultaneous Phase Shift Interferometry Used to Pulse Laser Pump-Probe Approach

2011 ◽  
Vol 346 ◽  
pp. 670-674 ◽  
Author(s):  
Hai Ying Song ◽  
Xue Peng He ◽  
Shi Bing Liu ◽  
Tao Chen
Keyword(s):  
Time Delay ◽  
Phase Shift ◽  
Pulse Laser ◽  
Laser Wavelength ◽  
Interference Channels ◽  
Phase Lag ◽  
Pump Probe ◽  
Laser Pump ◽  
Light Interference ◽  
Theoretical Results

A simultaneous phase shift interferometry was proposed to determine the time delay accurately in the pulse laser pump-probe detecting. The relevant optical system formed by four light interference channels was designed and optimized based on Jones theory. The light intensity distribution of interference pattern associated with the phase lag from these four light interference channels was derived by Jones matrix. The possible errors that exist in the applications were calculated. The theoretical results show that the minimum resolution of the time delay can be achieved to attosecond level for 800nm laser wavelength.

Impact of Device Variability and Circuit Phase Shift in Synchronized Spin Torque Oscillators

2007 ◽  
Vol 998 ◽  
Author(s):  
Johan Persson ◽  
Yan Zhou ◽  
Johan Akerman
Keyword(s):  
Phase Diagram ◽  
Time Delay ◽  
Process Variations ◽  
Small Time ◽  
Spin Transfer Torque ◽  
Spin Torque ◽  
Plane Anisotropy ◽  
Out Of Plane ◽  
The Impact ◽  
Spin Torque Oscillators

ABSTRACTCurrent-induced magnetization dynamics in a system composed of two electrically coupled spin torque oscillators (STOs) is examined. The dynamics of the STOs is modeled by the Landau–Lifshitz–Gilbert equations modified with a Slonczewski spin-transfer torque term. To study the impact of realistic process variations on STO synchronization we let the two STOs have different in-plane anisotropy fields (Hk). The simulation also provides for a time delay τ. We construct a phase diagram of the STO synchronization as a function of Hk and direct current (Idc) at different τ. The phase diagram turns out to be quite rich with different types of synchronized precession modes. While the synchronized state is originally very sensitive to STO process variations and can only sustain up to 4% Hk variation, the addition of a small time delay dramatically improves its robustness and allows as much as 145% Hk variation in the entire out-of-plane precession regime. It is also shown that the two STOs can not only be locked in frequency, but also in phase at a given τ and the phase difference between the two STOs can be tuned by varying the dc current.

scholarly journals Relative-phase and time-delay maps all over the emission cone of hyperentangled photon source

2017 ◽  
Vol 56 (2) ◽  
pp. 026114 ◽  
Author(s):  
Salem F. Hegazy ◽  
Yahia A. Badr ◽  
Salah S. A. Obayya
Keyword(s):  
Time Delay ◽  
Relative Phase ◽  
Photon Source
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