• The Journal of the Korea Contents Association
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• v.15 no.2
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• pp.499-506
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• 2015

The friction velocity is a quantity with the dimensions of velocity defined by the friction stress and density of a wall surface at near wall of flow condition. Also, the friction velocity is the hydraulic parameter describing shear force at the bottom flow. Moreover, it is a very important factor in designing open channel and essential to determine the mixing coefficient in the main flow direction. The estimation of the friction velocity are such as methods using channel slope, linear law of the mean velocity at viscous sub-layer and direct measurement of wall shear stress, etc. In the present study, we propose a friction velocity equation that has been optimized by combining the concept of entropy, which is used in stochastic method, and to verify the proposed equation, the experimental data measured by Song was used. The R squared for friction velocities between proposed equation and friction velocity formula analyzed 0.999 to 1.000 in a very good agreement with each equation.

• The Journal of the Korea Contents Association
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• v.16 no.4
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• pp.614-623
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• 2016

Grid(pipe network) design is an important element of Smart Water Grid, which essential to estimate hydraulic parameters such as the pressure, friction factor, friction velocity, head loss and energy slope. Especially, friction velocity in a grid is an important factor in conjunction with energy gradient, friction coefficient, pressure and head loss. However, accurate estimation friction head loss, friction velocity and friction factor are very difficult. The empirical friction factor is still estimated by using theory and equation which were developed one hundred years ago. Therefore, in this paper, new equation from maximum velocity and friction velocity is developed by using integration relationship between Darcy-Weisbach's friction head loss equation and Schlichting equation and regression analysis. To prove the developed equation, smooth pipe data areis used. Proposed equation shows high accuracy compared to observed data. Study results are expected to be used in stability improvements and design in a grid.

• Proceedings of the Korea Water Resources Association Conference
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• 2004.05b
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• pp.429-433
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• 2004

According to researchers, the influential factors of scouring are generally divided into three factors: the flow conditions, the type and position of structures, and the characteristics of bed materials. In addition, scouring is affected by the 3-dimensional turbulent boundaries, the unsteady flow, the movement of sediment in the scour-hole area, the approach flow velocity and depth, the width of bridge foundation/pier, and the particle size of bed materials. However, it is difficult to estimate the scour depth near bridge piers when all conditions are factored in at once. Therefore, for reasonably accurate estimates of scour depth, it is essential to consider sufficiently the flow force and resisting force for scour. That is, to determine the shear stress concerning the bed material distribution is needed. In this study, the experiments were performed under the condition of a steady state of flow. As a result, scouring occurred at velocity ratios of 0.476,$(V/V_c=0.476)$, and the scour depth was increased linearly as the velocity ratio increased. in addition, the average values of shear stress ratio at zero scouring depth in both rectangular and circular piers were approximately 7$(\tau_c/\tau_{approach})$ and in the case for same size bed particle material. The results of this study can be used for the fundamental material for estimating the scour depth of bed materials.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05b
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• pp.29-35
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• 1996

For the Reactor Coolant System(RCS) flow rate measurement by the secondary calorimetric heat balance method, the coolant temperature of the hot leg is needed. Several Resistance Temperature Detectors(RTD) are installed in the hot leg to measure the temperature, but the average value of RTDs does not correctly represent the energy-averaged(bulk) temperature because of the thermal stratification phenomenon. Therefore some correction is introduced to predict the bulk temperature, but the correction inevitably contains uncertainty because the stratification is not defined well quantitatively yet. Therefore a large uncertainty for the correction has been used for the conservative estimation. But unrealistically large uncertainty causes degradation of the measurement method and yields difficulty to meet the acceptance criterion in start-up flow measurement test. In this paper, an analytical estimation is made on the correction and the related uncertainty using the measured hot leg velocity profile of System 80 reactor flow model test and the measured temperatures of YGN 3&4 and PVNGS 1&2 start-up tests. The results reveal that the magnitude of the correction uncertainty is much smaller than that used in the previous design. Therefore, the confidence on the flow rate measurement method can be improved and the difficulty in start-up flow measurement test can be lessened if the smaller correction uncertainty obtained through this estimation is applied.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.2
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• pp.1533-1540
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• 2015

In order to demonstrate the flow properties of the river bed and the design of hydraulic structures, the estimation of friction velocity is essentially required. However, existing friction velocity equations such as Log method and Power law have trouble to estimate the friction velocity because a boundary condition and various hydraulic properties are changed constantly in near the wall. In the present study, therefore, a new friction velocity equation that can minimize the parameters and reduce an error was suggested. To verify accuracy and reliability for the proposed equation, Clauser method, $\sqrt{gRI}$ method, reynolds stress method by Dr. Song were compared with the proposed method by estimated entropy parameter M for each channel. Consequently, the results show that uniform flow condition as well as non-uniform flow condition with highly accuracy nearly matched in case of accelerating non-uniform condition of $R^2=0.9621$, Decelerating Non Uniform condition of $R^2=0.9274$, Uniform condition of $R^2=0.8865$.

• Nuclear Engineering and Technology
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• v.55 no.12
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• pp.4561-4569
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• 2023

A correct understanding of vibration-based degradation is crucial from the standpoint of maintenance for Steam Generators (SG) as crucial mechanical equipment in nuclear power plants. This study has established a novel approach to developing a model for investigating tube bundle degradation according to crack growth caused by two-phase Flow-Induced Vibration (FIV). An important step in the approach is to calculate the two-phase flow field parameters between the SG tube bundles in various zones using the porous media model to determine the velocity and vapor volume fraction. Afterward, to determine the vibration properties of the tube bundles, the Fluid-Solid Interaction (FSI) analysis is performed in eighteen thermal-hydraulic zones. Tube bundle degradation based on crack growth using the sixteen most probable initial cracks and within each SG thermal-hydraulic zone is performed to calculate useful lifetime. Large Eddy Simulation (LES) model, Paris law, and Wiener process model are considered to model the turbulent crossflow around the tube bundles, simulation of elliptical crack growth due to the vibration characteristics, and estimation of SG tube bundles degradation, respectively. The analysis shows that the tube deforms most noticeably in the zone with the highest velocity. As a result, cracks propagate more quickly in the tube with a higher height. In all simulations based on different initial crack sizes, it was observed that zone 16 experiences the greatest deformation and, subsequently, the fastest degradation, with a velocity and vapor volume fraction of 0.5 m/s and 0.4, respectively.

• Magazine of the Korean Society of Agricultural Engineers
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• v.37 no.3_4
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• pp.82-89
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• 1995

The efforts of formulation have been reviewed and the results of existing laboratory experiments are investigated in order to describe the contracted flow which occurs at the final closure of sea dike construction. The regional characteristics of contracted flow is analyzed by checking the drawdown curve, and Chezy's mean velocity equation is employed to estimate the discharge rate at the closure. Weir-type discharge equations are reviewed, which are derived from Bernoulli equation, and the problems of the equations are discussed. Chezy's mean velocity equation is considered to be widely and generally applicable, and the empirical factor introduced in Chezy's equation is named 'form drag factor' since it is primarily dependent on the form drag caused by the contraction of discharge area. Laboratory experiments were conducted mainly in order to investigate the variation of form drag factor against various parameters, and an empirical equation is developed for the estimation of form drag factor.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.7
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• pp.853-858
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• 2003

The suitable estimation of the filter width in the dynamic eddy viscosity model were investigated in high Reynolds number channel flow. In this study, the improvement on matters by optimizing the test filter shape was attempted through the numerical experiment. The way that select optimum test filter width is recommended. Some test filters, one is based on a discrete representation of the top-hat filter and another are based on a high-order filtering operation, are evaluated in simulations of the turbulent channel flow at Reynolds number 1020, based on friction velocity and channel half width. It appears that the estimation of test filter width practically can decrease the dissipative nature of dynamic eddy viscosity model with explicit test filter. It shows that the value of the filter width ratio used in the dynamic procedure must match the properties of the test filter actually used in the calculation.

• The Journal of Korean Medicine
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• v.17 no.1 s.31
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• pp.345-360
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• 1996

Background and Purpose: To evaluate the blood flow velocity using doppler ultrasound of the carotid artery, vertebral artery, and basilar artery in stroke patients Material and Methods: To evaluate the blood flow, I measured the peak systolic velocity and mean velocity of the common carotid artery(CCA), internal carotid artery(ICA), external carotid artery (ECA). vertebral artery(VA), and basilar artery(BA) in 44 stroke patients and 15 healthy adults. To investigate the difference between ischemic stroke patients and normal healthy adults, I selected 44 ischemic stroke patients diagnosed by brain CT and brain MRI, and 15 healthy adults who did not have any symptoms of stroke, hypertension, heart disease, and diabetes melitus. Results: Peak velocity in normal adults was 50.6${\pm}$1.6cm/sec in the CCA, 67.2${\pm}$1.7cm/sec in the ICA, 62.5${\pm}$2.4cm/see in the ECA, 45.5${\pm}$1.9cm/sec VA. and 50.5${\pm}$3.5cm/sec in the BA. Mean velocity in normal adults was 26.9${\pm}$1.1cm/sec in the CCA, 43.7${\pm}$1.4cm/sec in the ICA, 26.7${\pm}$1.3cm/sec in the ECA. 31.6${\pm}$1.9cm/sec in the VA and 33.0${\pm}$2.6cm/sec in the BA. In this study, there was a significant increase in the velocity of ICA, ECA, and VA of ischemic stroke patients in comparison with normal healthy adults. And the blood flow velocity of this study in the CCA and ECA was different from other reported foreign values and the other known values in my country. Conclusion: There was a significant difference in the blood flow velocity between ischemic stroke patients and normal healthy adults. And the blood flow velocity of this study was different from other reported foreign values and the other known values in my country. Therefore, it needs more detailed studies about old aged Korean and ischemic stroke patients than previous studies.

• Journal of the Korean Institute of Telematics and Electronics B
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• v.31B no.9
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• pp.150-158
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• 1994

In this paepr, Fuzzy Constraint Line Clustering (FCLC) method for optical flow estimation is proposed. FCLC represents the spatical and temporal gradients as fuzzy sets. Based on these sets, several constraint lines with different membership values are generated for the poxed whose velocity is to be estimated. We describe the process for obtaining the membership values of the spatial and temporal gradients and that of the corresponding constraint line. We also show the process for deciding the tightest cluster of point formalated by intersection between constraint lines. For the synthetic and real images, the results of FCLC are compared with of CLC.