scholarly journals Prograde and retrograde precession of a fluid-filled cylinder

2021 ◽  
Author(s):  
Federico Pizzi ◽  
Andre Giesecke ◽  
Jan Simkanin ◽  
Frank Stefani
Keyword(s):  
Optimal Parameter ◽  
Axisymmetric Flow ◽  
Smooth Transition ◽  
Flow State ◽  
Dynamo Action ◽  
Retrograde Motion ◽  
Nutation Angle ◽  
Centrifugal Instability ◽  
Flow Components ◽  
Flow States

Abstract We numerically study precession driven flows in a cylindrical container whose nutation angle varies between 60 and 90 degrees for prograde and retrograde precession. For prograde precession we observe sharp transitions between a laminar and a turbulent flow state with low and high geostrophic axisymmetric flow components related with a centrifugal instability, while for retrograde precession a rather smooth transition between a low state and a high state occurs. At the same time prograde and perpendicular precession shows an abrupt breakdown of the flow directly excited by the forcing mechanism, which is not the case for retrograde motion. We characterize the corresponding flow states in terms of the directly driven, non-axisymmetric Kelvin mode, the axisymmetric geostrophic mode, and an axisymmetric poloidal flow which is promising for precession-driven dynamo action. The latter issue is discussed with particular view on an optimal parameter choice for the DRESDYN dynamo project.

scholarly journals A Deep Learning Approach of Vehicle Multitarget Detection from Traffic Video

2018 ◽  
Vol 2018 ◽  
pp. 1-11 ◽  
Author(s):  
Xun Li ◽  
Yao Liu ◽  
Zhengfan Zhao ◽  
Yue Zhang ◽  
Li He
Keyword(s):  
Detection Rate ◽  
Detection Method ◽  
Training Model ◽  
Learning Approach ◽  
Flow State ◽  
False Detection Rate ◽  
False Detection ◽  
Road Vehicles ◽  
Traffic Video ◽  
Flow States

Vehicle detection is expected to be robust and efficient in various scenes. We propose a multivehicle detection method, which consists of YOLO under the Darknet framework. We also improve the YOLO-voc structure according to the change of the target scene and traffic flow. The classification training model is obtained based on ImageNet and the parameters are fine-tuned according to the training results and the vehicle characteristics. Finally, we obtain an effective YOLO-vocRV network for road vehicles detection. In order to verify the performance of our method, the experiment is carried out on different vehicle flow states and compared with the classical YOLO-voc, YOLO 9000, and YOLO v3. The experimental results show that our method achieves the detection rate of 98.6% in free flow state, 97.8% in synchronous flow state, and 96.3% in blocking flow state, respectively. In addition, our proposed method has less false detection rate than previous works and shows good robustness.

scholarly journals EFFECTS OF FLOW STATES ON ELITE ATHLETES IN INVASION TEAM SPORTS: SYSTEMATIC REVIEW PROTOCOL

2021 ◽  
Author(s):  
Luis Eugênio Martiny ◽  
◽  
Larissa Zanetti Theil ◽  
Eloy Maciel Neto ◽  
Gonçalo Dias ◽  
...  
Keyword(s):  
Systematic Review ◽  
Elite Athletes ◽  
Team Sports ◽  
Flow State ◽  
Systematic Review Protocol ◽  
Review Protocol ◽  
Review Question ◽  
Flow States

Review question / Objective: How does the flow state occur in invasion team sports (e.g., prevents; disrupts; restores; triggers; facilitates; hampers) and how does it influence the Elite athletes performance? Rationale: The flow state has been configured as an important flooring condition in the search for the best performance. However, there is an absence of systematizations about the flow state specifically in invasive team sports and its impact on performance. Therefore, it is relevant to qualify the types of studies conducted, their main correlations and causalities, as well as their main evidence and limitations. Condition being studied: The flow in invasion team sports and its impact on the Elite athletes performance.

scholarly journals The Potential Interaction Between Time Perception and Gaming: A Narrative Review

2019 ◽  
Vol 18 (5) ◽  
pp. 1226-1246 ◽  
Author(s):  
Filip M. Nuyens ◽  
Daria J. Kuss ◽  
Olatz Lopez-Fernandez ◽  
Mark D. Griffiths
Keyword(s):  
Emotion Regulation ◽  
Time Perception ◽  
Emotional Reactivity ◽  
Attentional Focus ◽  
Potential Interaction ◽  
Narrative Review ◽  
Flow State ◽  
Attentional Resources ◽  
Time Control ◽  
Flow States

Abstract Compromised time control is a variable of interest among disordered gamers because time spent on videogames can directly affect individuals’ lives. Although time perception appears to be closely associated with this phenomenon, previous studies have not systematically found a relationship between time perception and gaming. Therefore, the purpose of this narrative review is to explore how gaming disorder may be associated with time perception. It has been found that gamers exhibit a stronger attentional focus as well as an improved working memory compared with non-gamers. However, gamers (and especially disordered gamers) exhibit a stronger reaction to gaming cues which—coupled with an altered emotion regulation observed among disordered gamers—could directly affect their time perception. Finally, “'flow states”' direct most of the attentional resources to the ongoing activity, leading to a lack of resources allocated to the time perception. Therefore, entering a flow state will result in an altered time perception, most likely an underestimation of duration. The paper concludes that the time loss effect observed among disordered gamers can be explained via enhanced emotional reactivity (facilitated by impaired emotion regulation).

Simulation and Intelligent Control of Stratified Flow Control Sink

2014 ◽  
Vol 644-650 ◽  
pp. 171-174
Author(s):  
Lei Rao ◽  
Wei Wei Tao
Keyword(s):  
Flow Control ◽  
Flow Velocity ◽  
Intelligent Control ◽  
Effective Range ◽  
Flow State ◽  
Simulation Data ◽  
Interactive Interface ◽  
Control Of Flow ◽  
Set Up ◽  
Flow States

This article proposes a sink which is multi-circulating stratified control of flow velocity. We research the different effective range of one certain flow state with changing velocity of each layer of the sink and obtain several typical flow states with changing velocity combination There are some changes of effective range between different velocities through studying the different flow states. We can get expected flow states in different combinations. Then we use neutral network and the simulation data to realize the intelligent control and set up a friendly interactive interface.

Laboratory and numerical studies of baroclinic waves in an internally heated rotating fluid annulus: a case of wave/vortex duality?

1997 ◽  
Vol 337 ◽  
pp. 155-191 ◽  
Author(s):  
P. L. READ ◽  
S. R. LEWIS ◽  
R. HIDE
Keyword(s):  
Numerical Simulations ◽  
Potential Vorticity ◽  
Axisymmetric Flow ◽  
Zonal Flow ◽  
Chaotic Advection ◽  
Rotating Fluid ◽  
Mean Flow ◽  
Baroclinic Waves ◽  
Vortex Merging ◽  
Flow Components

The structure, transport properties and regimes of flow exhibited in a rotating fluid annulus, subject to internal heating and sidewall cooling, are studied both in the laboratory and in numerical simulations. The performance of the numerical model is verified quantitatively to within a few per cent in several cases by direct comparison with measurements in the laboratory of temperature and horizontal velocity fields in the axisymmetric and regular wave regimes. The basic azimuthal mean flow produced by this distribution of heat sources and sinks leads to strips of potential vorticity in which the radial gradient of potential vorticity changes sign in both the vertical and horizontal directions. From diagnosis of the energy budget of numerical simulations, the principal instability of the flow is shown to be predominantly baroclinic in nature, though with a non-negligible contribution towards the maintenance of the non-axisymmetric flow components from the barotropic wave–zonal flow interaction. The structure of the regime diagram for the internally heated baroclinic waves is shown to have some aspects in common with conventional wall-heated annulus waves, but the former shows no evidence for time-dependence in the form of ‘amplitude vacillation’. Internally heated flows instead evidently prefer to make transitions between wavenumbers in the regular regime via a form of vortex merging and/or splitting, indicating a mixed vortex/wave character to the non-axisymmetric flows in this system. The transition towards irregular flow occurs via a form of wavenumber vacillation, also involving vortex splitting and merging events. Baroclinic eddies are shown to develop from an initial axisymmetric flow via a mixed sinuous/varicose instability, leading to the formation of detached vortices of the same sign as the ambient axisymmetric potential vorticity at that level, in a manner which resembles recent simulations of atmospheric baroclinic frontal instability and varicose barotropic instabilities. Dye tracer experiments confirm the mixed wave/vortex character of the equilibrated instabilities, and exhibit chaotic advection in time-dependent flows.

Detecting Students’ Flow States and Their Construct Through Electroencephalogram: Reflective Flow Experiences, Balance of Challenge and Skill, and Sense of Control

2020 ◽  
Vol 58 (8) ◽  
pp. 1515-1540
Author(s):  
Shu-Fen Wu ◽  
Yu-Ling Lu ◽  
Chi-Jui Lien
Keyword(s):  
Test Performance ◽  
Sense Of Control ◽  
Flow State ◽  
Time Data ◽  
Chi Square ◽  
Time Flow ◽  
E Learning ◽  
Flow Experiences ◽  
High Skill ◽  
Flow States

Previous studies measured flow states using students’ self-reported experiences, resulting in issues regarding nonobjective and nonreal-time data. Thus, this study used an electroencephalogram (EEG) to measure the EEG-detected real-time flow states (EEG-Fs) of 30 students from the 4th and 5th grades. Their EEG measurements, self-reported reflective flow experiences (SR-Fs), grade levels (GLs), balance of challenge and skill (BCS), and sense of control, represented by their overall test performance (OA-tp) and momentary test performance (MOM-tp), were analyzed to establish their EEG-F’s construct. Based on the results of a chi-square test, the EEG-F correlates significantly with SR-F, BCS, OA-tp, and MOM-tp. A J48 decision tree analysis and logistic regression further revealed that in-flow experiences (in-EEG-F) were detected when students had high SR-Fs, where the BCS contributed to flow states. In particular, students with a low-challenge/high-skill BCS demonstrated an in-EEG-F state upon having a high OA-tp. For high-challenge/high-skill, the in-EEG-F state was determined through their MOM-tp. Through the EEG and flow state construct, this study revealed a whole-part association between students’ momentary and overall reflective flow experiences and identified viable paths for inducing students’ EEG-Fs, which can contribute to future e-learning development when integrated with a brain-computer interface for e-learning or e-evaluation systems.

scholarly journals On the value of water quality data and informative flow states in karst modelling

2017 ◽  
Vol 21 (12) ◽  
pp. 5971-5985 ◽  
Author(s):  
Andreas Hartmann ◽  
Juan Antonio Barberá ◽  
Bartolomé Andreo
Keyword(s):  
Water Quality ◽  
Water Resource ◽  
Quality Data ◽  
Model Parameters ◽  
Flow State ◽  
Saturated Flow ◽  
Water Quality Data ◽  
Model Parameter ◽  
Time Period ◽  
Flow States

Abstract. If properly applied, karst hydrological models are a valuable tool for karst water resource management. If they are able to reproduce the relevant flow and storage processes of a karst system, they can be used for prediction of water resource availability when climate or land use are expected to change. A common challenge to apply karst simulation models is the limited availability of observations to identify their model parameters. In this study, we quantify the value of information when water quality data (NO3− and SO42−) is used in addition to discharge observations to estimate the parameters of a process-based karst simulation model at a test site in southern Spain. We use a three-step procedure to (1) confine an initial sample of 500 000 model parameter sets by discharge and water quality observations, (2) identify alterations of model parameter distributions through the confinement, and (3) quantify the strength of the confinement for the model parameters. We repeat this procedure for flow states, for which the system discharge is controlled by the unsaturated zone, the saturated zone, and the entire time period including times when the spring is influenced by a nearby river. Our results indicate that NO3− provides the most information to identify the model parameters controlling soil and epikarst dynamics during the unsaturated flow state. During the saturated flow state, SO42− and discharge observations provide the best information to identify the model parameters related to groundwater processes. We found reduced parameter identifiability when the entire time period is used as the river influence disturbs parameter estimation. We finally show that most reliable simulations are obtained when a combination of discharge and water quality date is used for the combined unsaturated and saturated flow states.

scholarly journals Performance of high-speed hydrodynamic sliding bearings with lubricating oils combining laminar and turbulent flows

2020 ◽  
Vol 12 (6) ◽  
pp. 168781402093338
Author(s):  
Yingjia Wang ◽  
Minshan Liu ◽  
Dongchen Qin ◽  
Zhenwei Yan
Keyword(s):  
Turbulent Flows ◽  
Working Conditions ◽  
High Speed ◽  
Flow State ◽  
Mixed Flow ◽  
Sliding Bearings ◽  
Oil Film ◽  
Flow Changes ◽  
Laminar And Turbulent Flows ◽  
Flow States

High-speed hydrodynamic sliding bearings use lubricating oil that can have laminar and turbulent flow states, yet turbulent states remain relatively unstudied. This study combines theoretical analysis, numerical modeling, and experiments to analyze lubrication fluids in such bearings. It considers Reynolds equations, energy equations, and temperature-viscosity relationships under laminar and turbulent flows. The governing equations are solved by the finite difference method. Two-dimensional distributions of Reynolds number, pressure, and temperature in the bearing film, as well as the lubrication characteristics like bearing capacity and frictional force under working conditions, are analyzed. Single and mixed flow states are compared, which demonstrates the coexistence states of laminar and turbulent flows in an oil film under specific working conditions. Oil film flow distributions differ significantly according to rotational speed and eccentric conditions. Flow changes under high eccentricity are complex. The characteristics of oil films in a single flow state deviate significantly from those in mixed flow. Changes in flow state and heat should not be ignored during analysis of the lubrication performance of high-speed bearings.

The instability nature of the Vogel–Escudier flow

2015 ◽  
Vol 766 ◽  
pp. 590-610 ◽  
Author(s):  
Miguel A. Herrada ◽  
Vladimir N. Shtern ◽  
M. M. Torregrosa
Keyword(s):  
Shear Layer ◽  
Axial Velocity ◽  
Inflection Point ◽  
Critical Reynolds Number ◽  
Axisymmetric Flow ◽  
Rotating Disk ◽  
Base Flow ◽  
Cylinder Length ◽  
Centrifugal Instability ◽  
Circulatory Flow

AbstractThe instability of the steady axisymmetric flow in a sealed elongated cylinder, driven by a rotating end disk, is studied with the help of numerical simulations. It is argued that this instability is of the shear-layer type, being caused by the presence of an inflection point in the radial distribution of axial velocity of the base circulatory flow. The disturbance kinetic energy is localized in both the radial and axial directions, reaching its peak near the rotating disk, where the magnitude of base-flow axial velocity is close to its maximum. The critical Reynolds number, $\mathit{Re}_{cr}$, is found to be nearly $h$-independent for $h>5$; $h$ is the cylinder length-to-radius ratio. It is shown that the sidewall co-rotation suppresses the instability. As the co-rotation increases, the centrifugal instability becomes the most dangerous, i.e. determines $\mathit{Re}_{cr}$. Physical explanations are given for the stabilizing effect of the co-rotation, which is stronger (weaker) for the shear-layer (centrifugal) instability.

Sign in / Sign up

Export Citation Format

Share Document