• Journal of the korean Society of Automotive Engineers
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• v.14 no.6
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• pp.48-59
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• 1992

This study is on the performance of the perforated tube muffler when it operates as an exhaust silencer with through-flow, steady or pulsating. Theoretical estimation of the insertion loss was made by means of transfer matrix and by using the impedance equation for the perforated tube obtained for the case of low-speed steady through-flow. Experiment was performed for the measurement of the insertion loss at two flow conditions. The one is a steady flow from the exhaust pipe of an idling diesel engine. The effect of the through-flow velocity and steadiness on the muffler performance was obtained. By comparing the theoretical prediction with the experimental result, the validity of the impedance equation in the theoretical model was discussed. It has been found that steadiness as well as magnitude of the through-flow has a significant effect on the performance of the perforated tube muffler. Especially, the self-noise due to the pulsating flow in the engine exhaust system must be taken into account for the prediction of the muffler performance.

• Ocean and Polar Research
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• v.30 no.3
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• pp.239-247
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• 2008

Spatial distribution of water flow generated by tidal current was investigated within a Zostera marina(seagrass) bed in Wonpo Bay. Water flow and elevation were observed during the seagrass growing season. The spatial distribution of water flow was numerically estimated using roughness coefficient. Water flow inside the seagrass meadow was compared with the observed values. Velocity in Zostera marina vegetated areas was approximately $25{\sim}84%$ lower than that of unvegetated areas. However, flow direction was the same. Intensity of the flood tide diminished appreciably within the seagrass bed, while its pattern was also affected. It is therefore concluded that water flow is influenced by Zostera marina meadows.

• Journal of Environmental Impact Assessment
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• v.18 no.5
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• pp.271-280
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• 2009

The objective of this study is to develop a reliable flow forecasting model based on neural network algorithm in order to provide flow rate at stream sections without flow measurement in Nakdong river. Stream flow rate measured at 8-days interval by Nakdong river environment research center, daily upper dam discharge and precipitation data connecting upstream stage gauge were used in this development. Back propagation neural network and multi-layer with hidden layer that exists between input and output layer are used in model learning and constructing, respectively. Model calibration and verification is conducted based on observed data from 3 station in Nakdong river.

• 연구논문집
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• s.29
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• pp.123-130
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• 1999

Flow divider valve, a kind of hydraulic control valve to divide the flow from one input line to two output line uniformly, should be able to keep the constant flow to output lines despite of the change load or supply pressure. Having 5-10% flow diving error in commercial hydraulic products is one of main source of the accumulated error caused hydraulic system problem and demands the development of flow divider valve to control flow more accurately, In this paper, the dynamic characteristics of flow divider valve are investigated by the numerical estimation of the spool motion considered the external supply force. The optimum design of flow divider valve are proposed to reduce the flow diving error. For the dynamic characteristics analysis, the change of sectional area of fixed and variable orifice, and spool are studied when the input signal is accepted to a constant load.

• Journal of Advanced Marine Engineering and Technology
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• v.24 no.3
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• pp.79-87
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• 2000

This paper describes experimental investigations of helium-air exchange flow through openings with vertical partitions. Such exchange flows may occur following rupture accident of stand pipe in high temperature gas cooled reactor. Exchange flow rates are investigated experimentally by using partitioned opening and opening with extended partition to assess fluids interference of the exchange flow at the stand pipe rupture accident. A tests vessel with the two types of opening on top of test cylinder is used in the experiments. An estimation method of mass increment is developed and applied to measure the exchange flow rate. A technique of flow visualization by Mach-Zehnder interferometer is provided to recognize the exchange flows. Amplitude and progress of interference fringes of the flows are observed and used as a support in comparison with the exchange flow rates. Flow passages of upward flow of the helium and downward flow of the air for both two types of the opening are separated by inserted partition within the opening, but in the case of partitioned opening, unseparated flow is formed at the opening entrance and the two flows interface. The exchange flow rate for the partitioned opening is not greater than that of the opening with extended partition because of the fluids interference at the entrance of opening. Finally, the fluids interference at the opening entrance is found to be one of important factors on the helium-air exchange flow rate.

• Journal of Korean Society of Transportation
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• v.35 no.1
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• pp.63-78
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• 2017

The purpose of this study is to determine the optimal aggregation interval to increase the reliability when estimating representative value of individual vehicle travel time collected by DSRC equipment in interrupted traffic flow section in National Highway. For this, we use the bimodal asymmetric distribution data, which is the distribution of the most representative individual vehicle travel time collected in the interrupted traffic flow section, and estimate the MSE(Mean Square Error) according to the variation of the aggregation interval of individual vehicle travel time, and determine the optimal aggregation interval. The estimation equation for the MSE estimation utilizes the maximum estimation error equation of t-distribution that can be used in asymmetric distribution. For the analysis of optimal aggregation interval size, the aggregation interval size of individual vehicle travel time was only 3 minutes or more apart from the aggregation interval size of 1-2 minutes in which the collection of data was normally lost due to the signal stop in the interrupted traffic flow section. The aggregation interval that causes the missing part in the data collection causes another error in the missing data correction process and is excluded. As a result, the optimal aggregation interval for the minimum MSE was 3~5 minutes. Considering both the efficiency of the system operation and the improvement of the reliability of calculation of the travel time, it is effective to operate the basic aggregation interval as 5 minutes as usual and to reduce the aggregation interval to 3 minutes in case of congestion.

• Journal of information and communication convergence engineering
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• v.9 no.3
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• pp.319-324
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• 2011

In computing the optical flow. Horn and Schunck's method which is a representative algorithm is based on differentiation. But it is difficult to estimate the velocity for a large displacement by this algorithm. To cope with this problem multigrid method has been proposed. In this paper, we have proposed a scaled multigrid algorithm which the initial flow for a level is calculated by the summation of the optimally scaled flow and error flow. The optimally scaled flow is the scaled expanded flow of the previous level, which can generate an estimated second image having the least RMS error with respect to the original second image, and the error flow is the flow between the estimated second image (generated by the optimally scaled flow) and the original second image. The flow for this level is then estimated using the original first and second images and the initial flow for that level. From among the various coarsest starting levels of the multigrid algorithm, we select the one that finally gives the best estimated flow. Better results were achieved using our proposed method compared with Horn and Schunck's method and a conventional multigrid algorithm.

• Journal of Korean Society on Water Environment
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• v.25 no.3
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• pp.432-440
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• 2009

The effect of selecting hydrologic item for calculating objective function on calibration of stream flow was evaluated by Hydrologic Simulation Porgram-Fortran (HSPF) linked with Model Independent Parameter Optimizer (PEST). Daily and monthly stream flow and flow duration were used to calculate objective function. Automated calibration focused on monthly stream was proper to analyze seasonal or yearly water budget but not proper to predict daily stream flow or percent chance flow exceeded. Calibration result focused on flow duration is proper to predict precent chance flow exceeded but not proper to analyze water budget or predict peak flow. These results indicate that hydrologic item calculated for objective function on calibration procedure could influence calibration results and watershed modeler should select carefully hydrologic item for the purpose of model application. Current, the criteria of stream flow of Korean TMDL is generated based on percent chance flow exceeded, so flow duration should be included to calculate objective function on calibration procedure for the estimation of criteria of stream flow using hydrologic model.

• Journal of Korea Water Resources Association
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• v.40 no.2 s.175
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• pp.113-124
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• 2007

Low flow is a minimum flow discharging during a dry season in a unregulated stream which can be shared by nature and human being. It is also a standard flow that determines a diversion requirement by evaluating water supply ability of streamflow in the aspect of water use. Low flow indices are used as average low flow and 1-day 10-year low flow in Korea and Japan and as 7-day 10-year low flow in the United States of America and the United Kingdom. In this research, these three indices were compared by the data observed and generated. Although daily records are needed to calculate the low flow, gauging stations are limited and records of the dry season are insufficient in Korea. Drainage-area ratio method is mainly used in Korea to estimate the low flow. This research shows the guideline when the drainage-area ratio method, the regional regression method, and the baseflow correlation method to calculate the low flow of ungauged basins are applied and recommends low flow estimation method suitable to Korea.

• Journal of Korea Water Resources Association
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• v.40 no.10
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• pp.801-810
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• 2007

In this study, validity and limitation of the estimation of roughness coefficient using the measured field data are investigated and the errors of the calculated roughness coefficient are analyzed. The assumption of uniform flow led to much difference of the computed results in low flow, and this is due to change of the cross-section informations such as flow area and hydraulic radius rather than the difference of velocity head. From the comparison between the estimations of average roughness coefficient in the reach which is relatively long, the calculation using the modified Newton-Raphson method is very efficient and accurate. In the measured roughness coefficient, the errors of measured flow and stage are included and the lower flow is, the larger the magnitude of error of measured roughness coefficient is. But the error of depth and velocity associated with uncertainty of roughness coefficient is less than about 5% in the both of low and high flow, and it shows the validity of measured roughness coefficient.