scholarly journals A Computational Study on the Damping-Amplitude Dependence and Estimation of the Limit Cycle Oscillations for Normal Triangular Arrays with One Tube Undergoing Fluidelastic Instability

Proceedings ◽  
2018 ◽  
Vol 2 (23) ◽  
pp. 1498
Author(s):  
Beatriz de Pedro ◽  
Guillermo Laine ◽  
Luis Tufiño ◽  
Jorge Parrondo
Keyword(s):  
Flow Velocity ◽  
Limit Cycle ◽  
Vibration Amplitude ◽  
Computational Study ◽  
Experimental Studies ◽  
Amplitude Dependence ◽  
Limit Cycle Oscillations ◽  
Cfd Model ◽  
Time Step ◽  
Fluidelastic Instability

While the estimation of the critical velocity for fluidelastic instability of tube arrays has received considerable attention for decades, the studies intended to analyze the post-stable behavior have been scarce. However, the behavior of the system under instability, is also interesting in order to characterize the amount of energy transferred from fluid to structure. A computational study has been carried out for the case of one tube vibrating in a normal triangular array by means of a CFD model previously developed with Fluent by the authors. This model incorporates the motion of the vibrating tube by means of user defined functions for both forced and free oscillations, so that the tube position can be updated and the mesh rebuilt at every time step. First, predictions of limit-cycle oscillations (zero net damping) were obtained for pitch ratios P/d = 1.25 and 1.375, so that the experimental response curves (amplitude against flow velocity) measured in other experimental studies could be used for contrast purposes. After validation, the CFD model was used to investigate how the net damping of the fluid-structure system depends on the vibration amplitude for a given flow velocity, which shows the non-linear nature of the tube response. Finally, special simulation series were conducted to explore the effects of pitch ratio, Reynolds number and structural damping on the net damping of the system for constant vibration amplitude.

Simulation of aircraft-pilot coupling as limit-cycle oscillations

1998 ◽  
Author(s):  
Guofeng Lin ◽  
Edward Lan ◽  
Jay Brandon
Keyword(s):  
Limit Cycle ◽  
Limit Cycle Oscillations

Sensitivity analysis of limit cycle oscillations

2012 ◽  
Vol 231 (8) ◽  
pp. 3228-3245 ◽  
Author(s):  
Joshua A. Krakos ◽  
Qiqi Wang ◽  
Steven R. Hall ◽  
David L. Darmofal
Keyword(s):  
Sensitivity Analysis ◽  
Limit Cycle ◽  
Limit Cycle Oscillations

Multi-Head Spatio-Temporal Attention Mechanism for Urban Anomaly Event Prediction

2021 ◽  
Vol 5 (3) ◽  
pp. 1-21
Author(s):  
Huiqun Huang ◽  
Xi Yang ◽  
Suining He
Keyword(s):  
New York ◽  
Experimental Studies ◽  
Attention Mechanism ◽  
City Management ◽  
Temporal Attention ◽  
Spatial Correlations ◽  
Time Step ◽  
Event Prediction ◽  
Spatio Temporal ◽  
Prediction Approach

Timely forecasting the urban anomaly events in advance is of great importance to the city management and planning. However, anomaly event prediction is highly challenging due to the sparseness of data, geographic heterogeneity (e.g., complex spatial correlation, skewed spatial distribution of anomaly events and crowd flows), and the dynamic temporal dependencies. In this study, we propose M-STAP, a novel Multi-head Spatio-Temporal Attention Prediction approach to address the problem of multi-region urban anomaly event prediction. Specifically, M-STAP considers the problem from three main aspects: (1) extracting the spatial characteristics of the anomaly events in different regions, and the spatial correlations between anomaly events and crowd flows; (2) modeling the impacts of crowd flow dynamic of the most relevant regions in each time step on the anomaly events; and (3) employing attention mechanism to analyze the varying impacts of the historical anomaly events on the predicted data. We have conducted extensive experimental studies on the crowd flows and anomaly events data of New York City, Melbourne and Chicago. Our proposed model shows higher accuracy (41.91% improvement on average) in predicting multi-region anomaly events compared with the state-of-the-arts.

Study on Vibration Reduction of Finishing Lapping Machine for Bearing Race

2011 ◽  
Vol 199-200 ◽  
pp. 1496-1500
Author(s):  
Jia Man ◽  
Lian Hong Zhang ◽  
Yong Liang Chen
Keyword(s):  
Vibration Amplitude ◽  
Vibration Reduction ◽  
Experimental Studies ◽  
Machining Efficiency ◽  
Bearing Race ◽  
Excitation Force ◽  
Lapping Machine ◽  
Light Material ◽  
Vibration Performance

It is key to improve the machining efficiency of finishing lapping machine to restrain the vibration that raise with work speed. The vibration amplitude is influenced by the excitation force of unbalanced crank-rocker mechanism and the anti-vibration performance of guide. Following improving schemes as adding counterweight to crank-rocker mechanism, adopting the light material motion components and enhancing the anti-vibration performance of guide are proposed based on theoretical and experimental studies. The improving schemes are verified by the experiment.

An Analysis of In-Flow Fluidelastic Instability Based on a Physical Insight

2014 ◽  
Author(s):  
Tomomichi Nakamura
Keyword(s):  
Flow Velocity ◽  
Flow Instability ◽  
Pressure Sensors ◽  
Measured Data ◽  
Critical Flow ◽  
Nonlinear Phenomenon ◽  
Critical Flow Velocity ◽  
Fluid Force ◽  
Tube Arrays ◽  
Fluidelastic Instability

Fluidelastic vibration of tube arrays caused by cross-flow has recently been highlighted by a practical event. There have been many studies on fluidelastic instability, but almost all works have been devoted to the tube-vibration in the transverse direction to the flow. For this reason, there are few data on the fluidelastic forces for the in-flow movement of the tubes, although the measured data on the stability boundary has gradually increased. The most popular method to estimate the fluidelastic force is to measure the force acting on tubes due to the flow, combined with the movement of the tubes. However, this method does not give the physical explanation of the root-cause of fluidelastic instability. In the work reported here, the in-flow instability is assumed to be a nonlinear phenomenon with a retarded or delayed action between adjacent tubes. The fluid force acting on tubes are estimated, based on the measured data in another paper for the fixed cylinders with distributed pressure sensors on the surface of the cylinders. The fluid force acting on the downstream-cylinder is assumed in this paper to have a delayed time basically based on the distance between the separation point of the upstream-cylinder to the re-attachment point, where the fluid flows with a certain flow velocity. Two models are considered: a two-cylinder and three–cylinder models, based on the same dimensions as our experimental data to check the critical flow velocity. Both models show the same order of the critical flow velocity and a similar trend for the effect of the pitch-to-diameter ratio of the tube arrays, which indicates this analysis has a potential to explain the in-flow instability if an adequate fluid force is used.

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