• 한국물환경학회지
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• 제34권1호
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• pp.10-25
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• 2018

This study was conducted to estimate the habitat suitability of 17 benthic macroinvertebrate taxa in the Hwayang stream. Habitat Suitability Index (HSI) of benthic macroinvertebrates from the Hwayang stream was developed based on three physical habitat factors which include current velocity, water depth, and the substrate. The Weibull model was used as a probability density function to analyze the distribution of individual abundance by physical factors. The number of species and the total individual abundance increased along with the increase in current velocity. By means of Canonical Correspondence Analysis (CCA), the relative importance of each factor was determined in the following order: current velocity, water depth, and the mean diameter. The results depicted that, the most influential factor in the growth of benthic macroinvertebrates in the Hwavang system was current velocity. After comparing the analyzed results from the Hwayang stream with the resukts from the Gapyeong stream, the integrated HSI was drawn. The results indicated that current velocity and substrate had similar distributions of HSI in the two streams. This was due to the addition of unmeasured data from previous surveys, or the fact that benthic macroinvertebrates adapted to deeper waters in the Hwayang Stream. Most taxa showed a clear preference for a fast current velocity, deep water depth and coarse substrate except Baetiella, Epeorus, (mayflies), and Hydropsyche (caddisfly).

• 한국물환경학회지
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• 제33권5호
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• pp.587-599
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• 2017

Physical environmental factors (water depth, current velocity and substrate) and fish community were surveyed in the Gapyeong stream, Korea. The fish group of Gapyeong Stream was divided into three types. Lithophilic fish, Koreocobitis rotundicaudata and Pseudopungtungia tenuicorpa preferred shallow depth, low-velocity current, and coarse bed condition, whereas Coreoleuciscus splendidus and Microphysogobio longidorsalis were adapted to high-velocity current and bed materials. Nektonic fish, Zacco koreanus and Zacco platypus appeared in a wide range of physical conditions. Intermediate fish, Hemibarbus longirostris, Pungtungia herzi and Coreoperca herzi adapted to moderate water depths and current velocities. Among them, H. longirostris and C. herzi were adapt to various bed materials. C. splendidus, M. longidorsalis and P. herzi showed high niche overlap for current velocity, water depth and substrate with Z. koreanus and Z. platypus. The occurrence of M. longidorsalis in a relatively low-velocity current compared to Z. koreanus and Z. platypus suggests that the current velocity act as a isolation factor for these species. The competition, isolation and character displacement among these species investigated detail in the future. Based on canonical correspondence analysis, the relative importance of each environmental factor was determined as substrate > water depth > current velocity.

• 한국환경과학회지
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• 제4권2호
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• pp.245-251
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• 1995

Generally, It is Introduced to well-known other models without considering tidal current of the field. The paper presents field measurements and numerical model solving velocity field of Cheonsu Bay by two-dimensional tidal model. It was proved that this scheme is easy to handle complex topography. Computed results is represented characteristics of tidal current for Cheonsu Bay. The results of the study can be summarized as follows ; 1. Tide form number has 0.21 value. Tidal range estimated 630.3 cm on spring, 454.1 cm on mean and 277.9 cm on neap, respectively 2. Tidal current has semi-diurnal form. Distance of traveling observed 16.6 km on flood and 15.5 km on ebb. 3. Tidal velocity showed reversing current. It was found that tidal velocity above 100 cm/sec is about 20 %. 4. Computed results are in good agreement with the observed data. Applying the algorithm to Cheonsu Bay, velocity fields and dry bank phenomena are simulated well in spite of complex topography. 5. An advanced study on the effects of open boundary conditions should be continuously performed.

• The Journal of Korean Physical Therapy
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• 제11권2호
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• pp.37-42
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• 1999

The purpose of this study was to determine whether percutaneous interferential current stimulation on thoracic sympathetic ganglia with amplitude modulated frequency (AMF) $90\~100$ bps and subthreshold of muscle contraction for 10 minutes on peripheral blood flow velocity in healthy subjects. Thirty-seven healthy volunteers were assigned randomly into an experimental group (n=25) and a control group (n=12). the experimental group received interferential current stimulation with subthreshold of the muscle contraction of current at AMF $90\~100$ bps on $1st\~5th$ thoracic sympathetic ganglial region for 10 minutes. The control group received same handling and electode placement, but no current was applied. Using a Doppler blood flow meter, the radial arterial blood flow velocities and the pulse raters were determined for two-way analysis of variance for repeated measures on time and group. There were no significant difference between the two groups with respect to the changes in arterial blood flow velocity and pulse rate over the four measurement times. Interferential current stimulation did not change in mean blood flow velocity and pulse rate. We conclude that interferential current stimulation on the thoracic sympathetic ganglia, as used in this study, did not dilate peripheral artery. This results suggests that interferential current stimulation dose not alter the activtiy of sympathetic nerve.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1951-1956
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• 2004

The transient nature and complex flow geometries of two-phase gas-liquid flows cause fundamental difficulties when measuring flow velocity using an electromagnetic flowmeter. Recently, a current-sensing flowmeter was introduced to obtain measurements with high temporal resolution (Ahn et $al.^{(1)}$). In this study, current-sensing flowmeter theory was applied to measure the fast velocity transients in slug flows. To do this, the velocity fields of axisymmetric gas-liquid slug flow in a vertical pipe were obtained using Volume-of-Fluid (VOF) method and the virtual potential distributions for the electrodes of finite size were also computed using the finite volume method for the simulated slug flow. The output signal prediction for slug flow was carried out from the velocity and virtual potential (or weight function) fields. The flowmeter was numerically calibrated to obtain the cross-sectional liquid mean velocity at an electrode plane from the predicted output signal. Two calibration parameters are required for this procedure: a flow pattern coefficient and a localization parameter. The flow pattern coefficient was defined by the ratio of the liquid resistance between the electrodes for two-phase flow with respect to that for single-phase flow, and the localization parameter was introduced to avoid errors in the flowmeter readings caused by liquid acceleration or deceleration around the electrodes. These parameters were also calculated from the computed velocity and virtual potential fields. The results can be used to obtain the liquid mean velocity from the slug flow signal measured by a current-sensing flowmeter.

• The Journal of Korean Physical Therapy
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• 제27권5호
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• pp.351-355
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• 2015

Purpose: This study was conducted to determine how stimulation using Russian current changes isokinetic exercise performance of quadriceps muscle and its antagonist muscles. Methods: Subjects were 20 20-year-old healthy adults who were instructed in the flexion to extension of knees in angular velocity $60^{\circ}/sec$ and $180^{\circ}/sec$ using a Biodex (Biodex system 3). We measured the difference in muscle performance between the Russian current stimulated at the same time during the flexion to extension of knees and not stimulated. Results: The results showed that when Russian current stimulation was applied at the angular velocity $60^{\circ}/sec$, the flexed and extended muscles and the angular velocity $180^{\circ}/sec$ increased significantly, but the peak torque of flexing muscles at the angular velocity $180^{\circ}/sec$ did not increase. Conclusion: These findings suggest that Russian current stimulation with isokinetic exercise of the knee joint could affect the quadriceps muscle and its antagonist muscle performance of muscle strength and endurance.

• 한국정보통신학회논문지
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• 제21권9호
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• pp.1818-1825
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• 2017

ADCP(Acoustic Doppler Current Profiler) 는 초음파의 도플러 효과를 이용하여 수중에서 유속의 측정 및 교란 정도를 분석한다. 따라서 수신되는 각 공간 영역에 대한 속도 정보를 추출하기 위하여 수신 펄스 신호에 대한 자기 상관 함수나 FFT(Fast Fourier Transform) 스펙트럼을 추정한다. 그러나 자기 상관 함수 추정은 수신되는 반사 신호가 가우시안 형태의 대칭적인 도플러 스펙트럼을 가진다는 가정이 필요하며 이러한 조건이 만족 되지 않는 경우 추정치에서의 큰 편향오차가 발생할 수 있다. 또한 유속의 변화가 빠르게 나타나는 경우 신호 획득시간이 짧아 유속을 측정하기 위한 자기 상관 함수 나 FFT 스펙트럼의 정확한 추정이 어렵다. 따라서 본 논문에서는 반사 신호가 대칭형 또는 비대칭형 가우시안 형태의 스펙트럼을 보이면서 상대적으로 짧은 반사 획득 신호인 경우에도 정확한 유속 추정이 가능한 AR(Autoregressive) 스펙트럼 첨두치 추정 방법을 제안하였다. 이러한 방법을 이용하면 기존 방법에 비하여 그 정확도를 개선할 수 있음을 보였다. 제안된 방법의 평가를 위하여 다양한 환경에서의 모의 신호들을 구현하였으며 그 결과들을 비교하고 분석하였다.

• 대한기계학회논문집B
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• 제29권6호
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• pp.671-686
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• 2005

The transient nature and complex geometries of two-phase gas-liquid flows cause fundamental difficulties when measuring flow velocity using an electromagnetic flowmeter. Recently, a current-sensing flowmeter was introduced to obtain measurements with high temporal resolution (Ahn et al.). In this study, current-sensing flowmeter theory was applied to measure the fast velocity transients in slug flows. The velocity fields of axisymmetric gas-liquid slug flow in a vertical pipe were obtained using Volume-of-Fluid (VOF) method, and the virtual potential distributions for the electrodes of finite size were also computed using the finite volume method for simulating slug flow. The output signal prediction for slug flow was carried out from the velocity and virtual potential (or weight function) fields. The flowmeter was numerically calibrated to obtain the cross-sectional liquid mean velocity at an electrode plane from the predicted output signal. Two calibration parameters are proposed for this procedure: a flow pattern coefficient and a localization parameter. The flow pattern coefficient was defined by the ratio of the liquid resistance between the electrodes for two-phase flow with respect to that for single-phase flow, and the localization parameter was introduced to avoid errors in the flowmeter readings caused by liquid acceleration or deceleration around the electrodes. These parameters were also calculated from the computed velocity and virtual potential fields. The results can be used to obtain the liquid mean velocity from the slug flow signal measured by a current-sensing flowmeter.

• 수산해양기술연구
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• 제46권2호
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• pp.165-172
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• 2010

This study was performed to estimate the swimming velocity of Pacific saury (Cololabis saira) migrated offshore Funka Bay of Hokkaido using an acoustic Doppler current profiler (OceanSurveyor, RDI, 153.6kHz) established in T/S Ushio-maru of Hokkaido University, in September 27, 2003. The ADCP's doppler shift revealed as the raw data that the maximum swimming velocity was measured 163.0cm/s, and its horizontal swimming speed and direction were $72.4{\pm}24.1\;cm/s$, $160.1^{\circ}{\pm}22.3^{\circ}$ while the surrounding current speed and direction were $19.6{\pm}8.4\;cm/s$, $328.1^{\circ}{\pm}45.3^{\circ}$. To calculate the actual swimming speed of Pacific saury in each bins, comparisons for each stratified bins must be made between the mean surrounding current velocity vectors, measured for each stratified bin, and its mean swimming velocity vectors, assumed by reference (threshold > -70dB) and 5dB margin among four beams of ADCP. As a result, the actual averaged swimming velocity was 88.6cm/s and the averaged 3-D swimming velocity was 91.3cm/s using the 3-D velocity vector, respectively.

• Ocean and Polar Research
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• 제33권3호
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• pp.309-319
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• 2011

This is a preliminary study of the feasibility of obtaining reliable tidal current harmonic constants, using one month of current observations, to verify the accuracy of a tidal model. An inference method is commonly used to separate out the tidal harmonic constituents when the available data spans less than a synodic period. In contrast to tidal constituents, studies of the separation of tidal-current harmonics are rare, basically due to a dearth of the long-term observation data needed for such experiments. We conducted concurrent and monthly harmonic analyses for tidal current velocities and heights, using 2 years (2006 and 2007) of current and sea-level records obtained from the Tidal Current Signal Station located in the narrow waterway in front of Incheon Lock, Korea. Firstly, the l-year harmonic analyses showed that, with the exception of $M_2$ and $S_2$ semidiurnal constituents, the major constituents were different for the tidal currents and heights. $K_1$, for instance, was found to be the 4th major tidal constituent but not an important tidal current constituent. Secondly, we examined monthly variation in the amplitudes and phase-lags of the $S_2$ and $K_1$ current-velocity and tide constituents over a 23-month period. The resultant patterns of variation in the amplitudes and phase-lags of the $S_2$ tidal currents and tides were similar, exhibiting a sine curve form with a 6-month period. Similarly, variation in the $K_1$ tidal constant and tidal current-velocity phase lags showed a sine curve pattern with a 6-month period. However, that of the $K_1$ tidal current-velocity amplitude showed a somewhat irregular sine curve pattern. Lastly, we investigated and tested the inference methods available for separating the $K_2$ and $S_2$ current-velocity constituents via monthly harmonic analysis. We compared the effects of reduction in monthly variability in tidal harmonic constants of the $S_2$ current-velocity constituent using three different inference methods and that of Schureman (1976). Specifically, to separate out the two constituents ($S_2$ and $K_2$), we used three different inference parameter (i.e. amplitude ratio and phase-lag diggerence) values derived from the 1-year harmonic analyses of current-velocities and tidal heights at (near) the short-term observation station and from tidal potential (TP), together with Schureman's (1976) inference (SI). Results from these four different methods reveal that TP and SI are satisfactorily applicable where results of long-term harmonic analysis are not available. We also discussed how to further reduce the monthly variability in $S_2$ tidal current-velocity constants.