• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2002년도 유체기계 연구개발 발표회 논문집
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• pp.370-377
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• 2002

Generally, the system of calculation for the multi-path ultrasonic flow meters can be divided into two methods by how to get the mean velocity, namely, weighting and direct method. Weighting-method derive the mean velocity through modeling in theoretical velocity profile. Direct-method derive the mean velocity though actual flow distribution. The system of calculation varies with maker's transducer configuration and integration method. Each system has merits and demerits. This paper describes the system of integration that calculates line velocity over cross-section of the circular pipe. Flow rate mr discussed in this paper is a difference between theoretical flow rate and integrated flow rate according to values of Reynolds number in symmetric flow field or theoretical flow rate and integrated flow rate according to rotated model in asymmetric flow field.

• 한국환경과학회지
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• 제28권6호
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• pp.535-544
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• 2019

We computed parameters that affect velocity distribution by applying Chiu's two-dimensional velocity distribution equation based on the theory of entropy probability and acoustic doppler current profiler (ADCP) of Jungmun-stream, Akgeun-stream, and Yeonoe-stream among the nine streams in Jeju Province between July 2011 and June 2015. In addition, velocity and flow were calculated using a surface image velocimeter to evaluate the parameters estimated in the velocity observation section of the streams. The mean error rate of flow based on ADCP velocity data was 16.01% with flow calculated using the conventional depth-averaged velocity conversion factor (0.85), 6.02% with flow calculated using the surface velocity and mean velocity regression factor, and 4.58% with flow calculated using Chiu's two-dimensional velocity distribution equation. If surface velocity by a non-contact velocimeter is calculated as mean velocity, the error rate increases for large streams in the inland areas of Korea. Therefore, flow can be calculated precisely by utilizing the velocity distribution equation that accounts for stream flow characteristics and velocity distribution, instead of the conventional depth-averaged conversion factor (0.85).

• 한국환경과학회지
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• 제20권1호
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• pp.107-118
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• 2011

While the assessment of mean flow field is very important to characterize the hydrodynamic aspect of the flow regime in river, the conventional methodologies have required very time-consuming efforts and cost to obtain the mean flow field. The paper provides an efficient technique to quickly assess mean flow field by developing and applying spatial averaging method utilizing repeatedly surveyed acoustic Doppler current profiler(ADCP)'s cross-sectional measurements. ADCP has been widely used in measuring the detailed velocity and discharge in the last two decades. In order to validate the proposed spatial averaging method, the averaged velocity filed using the spatial averaging was compared with the bench-mark data computed by the time-averaging of the consistent fix-point ADCP measurement, which has been known as a valid but a bit inefficient way to obtain mean velocity field. The comparison showed a good agreement between two methods, which indicates that the spatial averaging method is able to be used as a surrogate way to assess the mean flow field. Bed shear stress distribution, which is a derived hydrodynamic quantity from the mean velocity field, was additionally computed by using both spatial and time-averaging methods, and they were compared each other so as to validate the spatial averaging method. This comparison also gave a good agreement. Therefore, such comparisons proved the validity of the spatial averaging to quickly assess mean flow field. The mean velocity field and its derived riverine quantities can be actively used for characterizing the flow dynamics as well as potentially applicable for validating numerical simulations.

• 설비공학논문집
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• 제10권1호
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• pp.108-117
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• 1998

This study was performed to analyze the fluid flow characteristics and the temperature distribution of the aquarium for fish breeding. In this study, the finite volume method and turbulence k-$\varepsilon$ model with the SIMPLE computational algorithm are used to study the water flow in the aquarium. The calculation parameters are the circulating flow rate and the basin depth, and the experiments were carried out for the water flow visualization This numerical analysis gives reasonable velocity distributions in good agreement with the experimental data. As the results of the three dimmentional simulations, the sectional mean velocity increased as the sectional mean temperature increases for constant basin depth, and the mean velocity increased more rapidly for small basin depth than that of large basin depth, The mean velocity and temperature can be expressed as the function of the circulating flow rates and the basin depth.

• 대한기계학회논문집B
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• 제24권7호
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• pp.924-929
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• 2000

This paper addresses a new technique of measuring the mean flow velocity over the cross sectional area of the pipe using sound field reconstruction. When fluid flows in the pipe and two plane waves propagate oppositely through the medium, the flow velocity causes the change of wave number of the plane waves. The wave number of the positive going plane wave decreases and that of negative going one increases in comparison to static medium in the pipe. Theoretical backgrounds of this method are introduced in detail and the measurement of mean flow velocity using the sound field reconstruction is not affected by velocity profile upstream of microphones.

• 한국전산유체공학회지
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• 제16권4호
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• pp.28-38
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• 2011

Large eddy simulation(LES) of fully developed turbulent pipe flow has been performed to investigate the effect of Reynolds number on the flow field at $Re_{\tau}$=180, 395, 590 based on friction velocity and pipe radius. A dynamic subgrid-scale model for the turbulent subgrid-scale stresses was employed to close the governing equations. The mean flow properties, mean velocity profiles and turbulent intensities obtained from the present LES are in good agreement with the previous numerical and experimental results currently available. The Reynolds number effects were observed in the mean velocity profile, root-mean-square of velocity fluctuations, Reynolds shear stress and turbulent viscosity.

• 대한기계학회논문집
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• 제18권3호
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• pp.793-804
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• 1994

Turbulence intensity caused by piston movement was almost as same tendency as the piston speed. The turbulence intensity was increased from 0.39m/s to 0.79m/s when mean piston speed increased from 2.33m/s to 4.67m/s. In this case the maximum turbulence intensity caused by piston speed was decreased about 82 percent near the top dead center at the end of compression stroke. The maximum turbulence intensity was created from 12m/s to 22m/s when inlet flow velocity was increased from 22m/s to 45m/s. Also turbulence intensity caused by inlet flow velocity was linearly increased from 0.97m/s at top dead center at the end of compression stroke. The ratio of turbulence intensity and mean inlet flow velocity was about 3 percent for inlet flow velocity.

• 대한물리의학회지
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• 제10권1호
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• pp.115-120
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• 2015

PURPOSE: Vertebrobasilar insufficiency (VBI) should be carefully assessed in patient for whom manipulation of the cervical spine is to be undertaken. The purpose of this study was to investigate the changes in posterior cerebral artery blood flow velocity following head and body positioning by transcranial doppler ultrasonography (TCD) in healthy subjects. METHODS: Twenty two healthy female (mean age $20.77{\pm}1.30yrs.$) participants volunteered to participate in the study. None of the participants had a history of neck pain or headache within the last 6 months. To evaluate the cerebral blood flow, we measured the mean flow velocity of the posterior cerebral artery unilaterally (right side). The blood flow velocity was measured under 3 different head positions (in a neutral head position, ipsilateral head rotation and contralateral head rotation position) and 2 different body conditions (supine position and sitting position). RESULTS: The mean blood flow velocity of posterior cerebral artery was decreased in body positioning from supine to sitting (p<.05), but the decreased rate of blood flow velocity in posterior cerebral artery did not change significantly between ipsilateral head rotation and contralateral head rotation (p>.05). CONCLUSION: These result of our study show that body positioning (sitting and supine) affect the blood flow velocity in posterior cerebral artery.

• 동력기계공학회지
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• 제4권4호
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• pp.25-31
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• 2000

This paper represents the vector fields and three dimensional mean velocities in the X-Y plane of cone type swirl gas burner measured by using X-probe from the hot-wire anemometer system. This experiment is carried out at flowrate 350 and $450{\ell}/min$ respectively in the test section of subsonic wind tunnel. The vector plot shows that the maximum axial mean velocity component is focused in the narrow slits distributed radially on the edge of a cone type swirl burner, for that reason, there is some entrainment of ambient air in the outer region of the burner and the rotational flow can be shown in the inner region of the burner because mean velocity W is distributed about twice as large as mean velocity V due to inclined flow velocity ejecting from the swirl vanes of a cone type baffle plate of burner. Moreover, the mean velocities are largely distributed near the outer region of burner within $X/R{\fallingdotseq}1.5$, hence, the turbulent characteristics are anticipated to be distributed largely in the center of this region due to the large inclination of mean velocity and swirl effect.

• 대한의생명과학회지
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• 제11권4호
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• pp.435-439
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• 2005

To determine the appropriate concentration of papaverine hydrochloride(PPV) for therapeutic intraarterial infusion against cerebral vasospasm and to measure the mean blood flow velocity of the middle cerebral artery in rabbits. Vasospasm was induced in the experimental groups (3 days after infusion; group 1, n=3, 7 days after infusion; group 2, n=3) and a control group (n=l) by placing a blood clot in the subarachnoid space around the top of the internal carotid siphon. PPV (5 mg/kg) was infused into the internal carotid artery. The vascular diameters of the internal carotid artery (ICA) and middle cerebral artery (MCA) were measured on angiograms before and after infusion. The mean blood flow velocity in the MCA was measured on transcranial doppler sonograms before and 24 hours after infusion. After fixation, the MCA was dissected out, stained, and examined microscopically. After PPV infusion in both groups, vascular dilatation of about $20\%$ was seen. The mean increase in blood flow velocity in the group $1(30\%)$ was smaller than in the group $2(70\%)$. The mean blood flow velocity in the MCA decreased by about $30\%$ in both groups, but increased again after 24 hours nearly to the level before PPV infusion. PPV infusion may be more effective in early stages of vasospasm when vascular walls have fewer histologic changes.