• Title/Summary/Keyword: Flow Frequency

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Evaluation of Flow Experience by using Psychophysiological Visual Feedbacks

  • Kim, Jung Yong;Min, Seung Nam;Park, Yong Duck
    • Journal of the Ergonomics Society of Korea
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    • v.32 no.6
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    • pp.481-487
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    • 2013
  • Objective: The present study aims to evaluate the visual reactions of users when they are playing games of different flow levels, and to explore the visual variables that can sensitively reflect the different flow levels. Background: The flow is defined as a psychological state where interface users feel their actions in a virtual setting identical to those in real environment. To measure the flow states of users, the questionnaire-based FSS(Flow State Scale) has mostly been used. However, this method is a qualitative test that has limits in terms of the accuracy of users' flow experiences. Therefore, more accurate methods to measure users' flow experiences are required. Method: Ten subjects participated in the experiment, where the independent variables were three games with different flow levels(puzzle games, dot drawing and coloring) and the time frame(the first and last 10 seconds in game playing), whereas the dependent variables included the pupil size and the frequency and duration of eye blinking. This study was a within-subject design. Each participant performed three types of games with different flow levels 3 times for each for 10 minutes, and their visual reactions to each game were measured. Results: The higher the flow cause the bigger pupil size(p<0.01) and the lower eye blinking frequency(p<0.1), indicating that different types of games lead to different flow levels. The pupil size during the last 10 seconds when the flow level was higher was bigger by 2.1% compared with that during the first 10 seconds in game playing(p<0.1), and the eye blinking frequency decreased by 12%(p<0.01). Conclusion: It was found out that the pupil size and the frequency and duration of eye blinking were psychophysiological indices for evaluating users' flow experiences, which could quantify the flow states users go through. The psychophysiological variables capable of measuring diverse aspects of the flow need diversifying to be applicable to precise measurement of the flow. Application: These studies are warranted for both quantitative analysis of flow levels and qualitative improvement of cyber leisure in line with development of healthy games.

Regional Low Flow Frequency Analysis Using Bayesian Multiple Regression (Bayesian 다중회귀분석을 이용한 저수량(Low flow) 지역 빈도분석)

  • Kim, Sang-Ug;Lee, Kil-Seong
    • Journal of Korea Water Resources Association
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    • v.41 no.3
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    • pp.325-340
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    • 2008
  • This study employs Bayesian multiple regression analysis using the ordinary least squares method for regional low flow frequency analysis. The parameter estimates using the Bayesian multiple regression analysis were compared to conventional analysis using the t-distribution. In these comparisons, the mean values from the t-distribution and the Bayesian analysis at each return period are not significantly different. However, the difference between upper and lower limits is remarkably reduced using the Bayesian multiple regression. Therefore, from the point of view of uncertainty analysis, Bayesian multiple regression analysis is more attractive than the conventional method based on a t-distribution because the low flow sample size at the site of interest is typically insufficient to perform low flow frequency analysis. Also, we performed low flow prediction, including confidence interval, at two ungauged catchments in the Nakdong River basin using the developed Bayesian multiple regression model. The Bayesian prediction proves effective to infer the low flow characteristic at the ungauged catchment.

The Characteristics of Pulsating Flow in a Hydraulic Pipe (유압관로에서 맥동유동 특성에 관한 연구)

  • 모양우;유영태;김지화
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.13 no.7
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    • pp.653-665
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    • 2001
  • The characteristics of the pulsating flow in a hydraulic pipe have been investigated. It is necessary to study the power control of the power transmission system in the landing gear system of aircraft and the design of robots. In this system, the power transmission pipeline is composed of a hydraulic system, and the operating flow is unsteady flow. The wave equation varying with frequency is analyzed in order to investigate the characteristics of unsteady flow in such a pipe. This wave equation involves the propagation coefficient in terns of frequency and viscosity. The theoretical result of this wave equation are compared with experimental result. Each wave equation, varying with the propagation coefficient, is analyzed theoretically. then, a sinusoidal wave generator is built in order to make better sinusoidal waves, and a rectifier is built to eliminate the noise from the hydraulic pump. The theoretical results of the wave equation in the flow of viscous fluid agree well with experimental results.

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Mechanism of Electrohydrodynamic Flow in AC Electrowetting (AC 전기습윤 중 전기수력학 유동의 메카니즘)

  • Lee, Ho-Rim;Ko, Sung-Hee;Yun, Sung-Chan;Kang, Kwan-Hyoung
    • Proceedings of the KSME Conference
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    • 2008.11b
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    • pp.2648-2651
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    • 2008
  • In AC electrowetting, it has been reported that there is a flow inside droplets. The flow characteristics such as flow rate, direction and the pattern of streamline are altered according to the frequency range of applied voltage. However, the mechanism of the flow has not been explained yet. This work is concentrated on investigation of the flow mechanism when high-frequency voltage is applied to droplets. We propose that this phenomenon arises from the electro-thermal flow. A numerical analysis is performed for the needle-electrode-plane geometry in which the Coulombic force term is included in the Navier-Stokes equation. According to our analysis, electrical charge is generated due to conductivity gradient which is originated from the nonuniform Joule heating of fluid medium. The result of the analysis is compared with experimental result.

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Flow Control and Heat Transfer Enhancement from a Heated Block by an Inflow Pulsation (I) Flow Field Computation (입구 유동 가진에 의한 사각 발열체 주위의 유동제어 및 열전달촉진 (I) 유동장 수치해석)

  • 리광훈;김서영;성형진
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.14 no.7
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    • pp.592-598
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    • 2002
  • The characteristics of a pulsating flow field from a heated block representing heat-dissipating electronic component in a channel have been numerically investigated. At the channel inlet a pulsating sinusoidal flow is imposed. The Reynolds number based on the channel height (H) is fixed at Re=500, and the forcing frequency is varied in the range of $0\leqSt\leq2$. Numerical results on the time-dependent flow field are obtained and averaged over a cycle of pulsation. The effect of the important governing parameters such as the Strouhal number is investigated in detail. The results indicate that the recirculating flow behind the block is substantially affected by the pulsation frequency. To characterize the periodic vortex shedding due to the inflow pulsation, numerical flow visualizations are carried out.

Correlation analysis of the wind of a cable-stayed bridge based on field monitoring

  • Li, Hui;Laima, Shujin;Li, Na;Ou, Jinping;Duan, Zhondong
    • Wind and Structures
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    • v.13 no.6
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    • pp.529-556
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    • 2010
  • This paper investigates the correlation of wind characteristics monitored on a cable-stayed bridge. Total five anemoscopes are implemented into the bridge. Two out of 5 anemoscopes in inflow and two out of 5 anemoscopes in wake-flow along the longitudinal direction of the bridge are installed. Four anemoscopes are respectively distributed at two cross-sections. Another anemoscope is installed at the top of the tower. The correlation of mean wind speed and direction, power spectral density, the turbulent intensity and integral length of wind in flow at two cross-sections are investigated. In addition, considering the non-stationary characteristics of wind, the spatial correlation in time-frequency is analyzed using wavelet transform and different phenomenon from those obtained through FFT is observed. The time-frequency analysis further indicates that intermittence, coherence structures and self-similar structures are distinctly observed from fluctuant wind. The flow characteristics around the bridge deck at two positions are also investigated using the field measurement. The results indicate that the mean wind speed decrease when the flow passing through the deck, but the turbulence intensity become much larger and the turbulence integral lengths become much smaller compared with those of inflow. The relationship of RMS (root mean square) of wake-flow and the mean wind speed of inflow is approximately linear. The special structures of wake-flow in time-frequency domain are also analyzed using wavelet transform, which aids to reveal the forming process of wake-flow.

Combustion Stability and the Properties of Methane/Air Mixture Subjected to Unsteady Flow Fluctuations (비정상 유동의 메탄/공기 혼합기 반응안정성 효과 연구)

  • Lee, Eui-Ju;Oh, Chang-Bo
    • Journal of the Korean Society of Safety
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    • v.26 no.5
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    • pp.1-6
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    • 2011
  • Flame extinction and the chemistry of stoichiometric methane/air mixture were investigated numerically in the PSR(perfectly stirred reactor). For the study, PSR code was modified to be possible to unsteady calculation, and the sinusoidal fluctuation was subjected to the residence time. In the region of residence time far from the extinction limit, combustion mode was strongly dependent on the frequency. The low frequency excitation provided the quasi-steady behavior on the temperature and the concentrations of related species, but small variation of temperature was observed under high frequency. In the region of residence time near the extinction limit, the mixture subjected above 1 KHz was still reacting even though extinction had to be occurred under quasi-steady concept. The attenuation of extinction limit resulted from that chemical time was comparable to the flow time. The mean mole fractions of both NO and CO were almost same regardless of imposed frequency. However, the average mole fraction of $C_2H_2$ was decreased as increasing frequency, which implies that soot yield might be reduced at the higher frequency of flow excitation. The result provides the basic concept for flame stabilization, and it will be used to design a mild combustor.

At-site Low Flow Frequency Analysis Using Bayesian MCMC: I. Theoretical Background and Construction of Prior Distribution (Bayesian MCMC를 이용한 저수량 점 빈도분석: I. 이론적 배경과 사전분포의 구축)

  • Kim, Sang-Ug;Lee, Kil-Seong
    • Journal of Korea Water Resources Association
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    • v.41 no.1
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    • pp.35-47
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    • 2008
  • The low flow analysis is an important part in water resources engineering. Also, the results of low flow frequency analysis can be used for design of reservoir storage, water supply planning and design, waste-load allocation, and maintenance of quantity and quality of water for irrigation and wild life conservation. Especially, for identification of the uncertainty in frequency analysis, the Bayesian approach is applied and compared with conventional methodologies in at-site low flow frequency analysis. In the first manuscript, the theoretical background for the Bayesian MCMC (Bayesian Markov Chain Monte Carlo) method and Metropolis-Hasting algorithm are studied. Two types of the prior distribution, a non-data- based and a data-based prior distributions are developed and compared to perform the Bayesian MCMC method. It can be suggested that the results of a data-based prior distribution is more effective than those of a non-data-based prior distribution. The acceptance rate of the algorithm is computed to assess the effectiveness of the developed algorithm. In the second manuscript, the Bayesian MCMC method using a data-based prior distribution and MLE(Maximum Likelihood Estimation) using a quadratic approximation are performed for the at-site low flow frequency analysis.

Frequency Response of Turbulent Flow to Momentum Forcing in a Channel with Wall Blowing (질량분사가 있는 채널 내부 난류 유동의 외부교란에 대한 주파수 특성)

  • Na, Yang;Lee, Chang-Jin
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.38 no.1
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    • pp.64-72
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    • 2010
  • Due to the interaction between main oxidizer flow and the wall injected flow resulting from the regression process, a specific time characteristics identified in the frequency spectrum of streamwise velocity is generated in the hybrid rocket motor. In order to understand the response of the turbulent flow to two different types of external momentum forcing, LES analysis was conducted without considering the combustion. It turns out that both concentrated and distributed forcings do not lead to the disastrous resonance phenomenon. Energy contents are enhanced due to the added momentum but the peak frequency was not modified in the turbulent flow near the end of the rocket motor. Natural frequency of the flow system should be taken into account to further pursue the instability issue by using external forcing.

Research for the Pulsating Pressure Characteristics by a Damper and an Accumulator in the High Frequency Hydraulic System (고주파 유압시스템에서 감치장치와 축압기에 의한 맥동 충격파 감쇄특성에 대한 연구)

  • Kim, Yang-Soo;Kim, Jae-Soo;Rho, Hyung-Woon
    • 유체기계공업학회:학술대회논문집
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    • 2004.12a
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    • pp.641-647
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    • 2004
  • Characteristics of the high frequency pulsatile flow have been investigated experimentally to understand the flow phenomena in the hydraulic system. The accumulator in high frequency hydraulic system but that is not effective all frequency zone. Therefore, a hydraulic damper used with accumulator is suggested to reduce the high frequency pulsatile where the accumulator is not effective. The pulsating pressure obtained by Pressure measurement system are analyzed to power spectral density distribution. According to the variations of pump input pressure and actuator acceleration frequency, the pressure is measured with or without an accumulator or pulsatile damper The amplitude of pressure with damper is very lower than those without accumulator or damper due to absorbing function of damper. As the frequency of actuator acceleration is increased, the effect of damper becomes very important to decrease the amplitude of pulsatile Pressure waveform with high frequencies.

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